CN114069658B - Control method for off-grid time of micro-grid - Google Patents
Control method for off-grid time of micro-grid Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/48—Controlling the sharing of the in-phase component
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/50—Controlling the sharing of the out-of-phase component
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks
Abstract
A control method for off-grid time of a micro-grid comprises the following steps: step 1, initializing, namely calibrating the internal load of a micro-grid, a power generation unit and the attribute and the parameter of an off-grid energy storage system; step 2, based on the analysis of the micro-grid at off-grid moment during grid connection, the measurement and control system regulates and controls the power and controllable load of the off-grid energy storage system and the power generation unit; step 3, when the micro-grid is continuously off-grid, passing through the power factor alpha of each load point in the micro-grid beari And a voltage u beari Sequencing the products or the ratio values, and measuring the quality and the quality synchronous control of each load point; step 4, load shedding occurs when the micro grid is off-grid, so that three-phase unbalance of the line is caused, and the voltage sequencing sort (U as ,U bs ,U cs ) Screening out high, medium and low voltages, and performing comparison analysis for control; and 5, analyzing the grid-connected time of the micro-grid during off-grid, and regulating and controlling the controllable equipment by the measurement and control system.
Description
Technical Field
The invention relates to a control method for off-grid time of a micro-grid.
Background
The 15 departments of the building and urban and rural construction department, the science and technology department, the industry and informatization department, the ecological environment department, the country plain office and the like release opinion about strengthening green low-carbon construction in county and county, and require the vigorous development of green buildings and building energy conservation. The renewable energy sources suitable for local resource endowment and demand are greatly developed, geothermal energy, biomass energy, an air source, a water source heat pump and the like are developed and utilized according to local conditions, clean heat supply of an area and clean heating of northern county are promoted, and the proportion of traditional fossil energy sources in building energy is reduced by improving the roof photovoltaic proportion of newly built plants, public buildings and the like and implementing the modes of photovoltaic building integrated development and the like. According to the notification requirements, the future renewable energy sources should enter a large-area popularization and rapid development period, and a large number of micro-grids are distributed in the power grid in order to ensure the stability of the power grid. However, in combination with the rapid development of renewable energy power generation technology, energy storage technology and load control technology in recent years, a large number of power electronic equipment such as distributed renewable energy power generation is connected to a 400V low-voltage power distribution network, the power flow of the power grid is changed at any time, and the load structure tends to be complicated. A large number of capacitive, inductive and resistive loads are connected into the low-voltage distribution network, the characteristics of the power grid are changed at any time due to the randomness of electricity consumption, and the large influence is caused on the quality of the power grid, and the large influence is mainly reflected in the fact that the upper limit and the lower limit of unbalance of voltage, frequency and three phases exceed the standard, the power factor is reduced, the line loss is increased and the like. Especially when the upper-level power grid fails, the independent-networking micro-power grid is impacted greatly, and the quality of the power grid is seriously reduced. Therefore, it is very important and urgent to ensure the quality of the power grid and improve the reliability of the important load power supply.
Traditional micro-grid parallel/off-grid switching is performed according to grid frequency and voltage upper and lower limit thresholds. When the micro-grid is connected and disconnected, the current load and the state of the power generation unit are analyzed in real time, the system is separated from the main grid clamp, the load is supported independently to operate, the balance state of the original system is broken due to the fact that the micro-grid is instantaneously disconnected, the micro-grid is in an unstable state, the instability of the power supply voltage and the frequency in the micro-grid area can damage electric equipment, and meanwhile power failure accidents possibly caused by independent networking failure can be caused.
Disclosure of Invention
The invention aims to overcome the defects that the change of the power supply environment and the power flow of a micro-grid at the off-grid moment, the change of the voltage, the power, the frequency, the power factor and the three-phase voltage balance of the power grid caused by the change of the balance of the power grid, and the quality of the micro-grid are seriously influenced, and provides a control method for the off-grid moment of the micro-grid, so that the micro-grid at the off-grid moment has no disturbance, reliably and stably operates, the quality of the power grid is ensured, and the requirements of the micro-grid are met.
The micro-grid system consists of a transformer in a platform region, a measurement and control system, an off-grid energy storage system, n power generation units, n main loads, n non-main controllable loads and the like. The grid-connected and off-grid energy storage system is arranged at the position of the micro-grid close to the transformer in the transformer area; the n power generation units, the n main loads and the n non-main controllable loads are distributed on the micro-grid and have the data communication function, and n is an integer. The measurement and control system is positioned at the transformer of the transformer station area and has a wired and wireless communication mode, and can receive the upper-level fault signal and the scheduling instruction upwards and monitor the power parameters of the transformer station area and the equipment data in the micro-grid network downwards. The wired or wireless communication modes comprise optical fibers, ethernet, carrier waves, 4G, 5G, loRa and the like. All the measured and controlled objects have the functions of control and data transmission. The parallel-off-grid energy storage system consists of three independent phase bidirectional converters and three-phase common energy storage, and each phase bidirectional converter has independent control capability. And when grid connection is performed, the grid-connected and off-grid energy storage system outputs in a current source mode, and the quality of the micro-grid is treated by absorbing or releasing power. When the micro-grid is off-grid, the off-grid energy storage system is used for networking, and the voltage source mode output is used for providing voltage, current and frequency for the load and the power generation unit.
The control method of the micro-grid off-grid moment comprises the following steps:
step 1, initializing
All controllable equipment of the district micro-grid comprises: in a related data input measurement and control system of a main controllable load, a power generation unit, an off-grid energy storage system and a non-main controllable load, performing attribute calibration and parameter setting, and determining the relative distance and position of each device by taking a transformer in a transformer area as an origin;
the relevant data of all controllable devices of the district micro-grid of the measurement and control system are input, and the relevant data comprise: the power of the load, the capacity and the power of the power generation unit, the input and output power of the off-grid energy storage system, and the upper limit and the lower limit of the capacity of the off-grid energy storage system and the residual capacity thereof.
Calibrating the relative distance, position and line model of main load, non-main load, wind power, photovoltaic and other power generation units and the transformer in the transformer area by taking the transformer in the transformer area as an origin;
and the measurement and control system receives the fault signal and the scheduling instruction of the upper stage in real time, and downwardly reads the electric power parameters of the micro-grid and all equipment information. When the upper grid connection or fault information is received, the measurement and control system controls the quality of the power grid of each device according to the historical data of the previous moment and combining the power grid characteristics of each device of the current micro-grid.
Step 2, the measurement and control system reads all controllable equipment data of the platform in real time, calculates and analyzes the power of the micro-grid at off-grid time and off-grid energy storage system and power generation unit, and regulates and controls the power of the off-grid energy storage system and the power generation unit, and the method comprises the following steps:
(1) The measurement and control system reads all controllable equipment data of the platform area in real time, and the method comprises the following steps: and the off-grid energy storage system absorbs or releases power p zes A residual electric quantity soc; output voltage u of each power generation unit pow1 ,u pow2 …u pown Power p pow1 ,p pow2 ……p pown The method comprises the steps of carrying out a first treatment on the surface of the Power P of each non-main load point nbear1 ,P nbear2 ,……,P nbearn The method comprises the steps of carrying out a first treatment on the surface of the Power factor alpha of main load mbear1 ,α mbear2 ,……,α mbearn Voltage u mbear1 ,u mbear2 ,……,u mbearn And power P mbear1 ,P mbear2 ,……,P mbearn The method comprises the steps of carrying out a first treatment on the surface of the Transformer power P in transformer area B Current I B Sum voltage U B . Calculating the total power of all power generation units and the total power of all non-main loads:
total power of the power generation unit:
total power of non-main controllable load:
when the measurement and control system monitors the measuring current I of the transformer in the transformer area B The power flow direction is more than 0, the power grid supplies power to the micro-grid, and the voltage distribution is output to the tail end of the power grid by the transformer in the transformer area, so that the micro-grid is formedThe characteristic is from high to low; when the transformer in the monitoring station area of the measurement and control system measures the current I B The power flow direction is less than 0, the micro-grid supplies power to the power grid, the voltage distribution is output to the tail end of the power grid by the transformer in the transformer area, and the characteristics from low to high are presented; transformer measuring current I B =0, power and load balancing within the microgrid.
Wherein P is nbear Total power for non-primary controllable loads; p (P) bear The total power of the controllable load; p (P) main Total power for the primary load; p is p inbear Power for the i-th non-primary controllable load; p (P) nbear1 ,P nbear2 ,……,P nbearn Power of non-primary controllable loads of 1 st to nth stations, respectively; p is p zpow Is the total power of the power generation unit; p is p ipow I e (1, 2., n) for the i-th power generation unit power; u (u) pow1 ,u pow2 …u pown Output voltages of the 1 st to nth power generation units, respectively; p is p pow1 ,p pow2 ……p pown Output powers of the 1 st to nth power generation units, respectively; i B The low-voltage side current of the transformer in the transformer area is obtained; p (P) B The power of the low-voltage side of the transformer in the transformer area is calculated; u (U) B The low-voltage side voltage of the transformer in the transformer area is obtained; the soc is the residual capacity of the energy storage battery of the off-grid energy storage system; alpha mbear1 ,α mbear2 ,……,α mbearn Power factors of the 1 st to nth main loads respectively; u (u) mbear1 ,u mbear2 ,……,u mbearn The voltages of the 1 st to nth main loads respectively; p (P) mbear1 ,P mbear2 ,……,P mbearn The power of the main loads from the 1 st to the nth; n is an integer not less than 1.
(2) When the micro-grid is connected, the measurement and control system calculates and separates the power of the energy storage system and the power generation unit so as to control related equipment when the micro-grid is separated from the grid, and the method specifically comprises the following steps:
2.1 at grid-connected time, when the transformer low-voltage side current I of the transformer area B When the power flow direction is less than 0, the micro-grid supplies power to the power grid, and the measurement and control system generates the total power p through all the power generation units zpow And releasing or absorbing power p by off-grid energy storage system zes And transformer low-side power P B Calculating the power consumption P of all loads all Load demand power P in micro-grid at future off-grid moment bear Finally, the future micro-grid support power P is obtained fzes 。
2.1.1 when the micro grid support Power P is in the future fzes When < 0, the total output power p of all the power generation units is described zpow Greater than the load demand power P bear Whereby future micro-grid support power P when off-grid occurs in the future fzes And absorbing or reducing the redundant power of the power generation unit through the off-grid energy storage system.
The measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.1.1.1 when the soc of the off-grid energy storage system is less than the soc u In the time, the measurement and control system predicts the future micro-grid support power P at off-grid time fzes And when off-grid occurs, sending a power absorption instruction to the micro-grid to the off-grid energy storage system.
2.1.1.2 when the soc of the grid-connected and off-grid energy storage system is more than or equal to the soc u When the system is in operation, the non-main controllable load is not reduced, and the measurement and control system is used for measuring and controlling the power P at the low-voltage side of the transformer in the network station B Total power p of all power generation units zpow Calculating the distribution coefficient mu of the power of each power generation unit zes By the power distribution coefficient mu of each generating unit zes And the output power P of each power generation unit powi Calculating to obtain the load shedding power P of each power generation unit zesi . When the future off-grid occurs, the measurement and control system is used for measuring and controlling the load shedding power P of each power generation unit zesi And sending out a power output reducing instruction to each power generation unit.
2.2 Low-side Current I of transformer in transformer area at grid-connected time B When the temperature is more than or equal to 0;
the power flow direction is supplied to the micro-grid by the power grid, which indicates that the power generation units in the micro-grid and the parallel-off-grid energy storage system can not meet the load power demand, and the measurement and control system at the moment is based on the output power P of the transformer in the transformer area B Total power p of all power generating units zpow And the off-grid energy storage system absorbs or releases power p zes Calculating all load consumption powers P respectively all Load demand power P at future off-grid time baer Finally obtaining the future micro-grid support power P of the predicted off-grid moment fzes 。
2.2.1 when the micro grid support Power P is in the future fzes When the temperature is more than or equal to 0,
description of the output Power p of the Power generating Unit zpow Less than the load demand power P baer The grid-connected and off-grid energy storage system is required to release power, and the power released by the grid-connected and off-grid energy storage system to the micro grid is the future micro grid support power P fzes 。
The measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.2.1.1 when the soc of the off-grid energy storage system is greater than or equal to the soc l In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes When off-grid occurs, the off-grid energy storage system is sent out to release power instruction codes for the micro-grid, so that the off-grid energy storage system releases power P for the micro-grid fzes 。
2.2.1.2 when the soc of the off-grid energy storage system is less than the soc l And when the micro-grid is in a power failure state, starting a protection program by the off-grid energy storage system.
2.2.2 when the micro grid support Power P is in the future fzes When less than 0;
description of total output Power p of all Power generating units after load shedding due to non-Primary controllable zpow Greater than the load demand power P baer Whereby the micro-grid supports power P in the future fzes And absorbing or reducing redundant power of the power generation unit for the off-grid moment and the off-grid energy storage system in the future. At the moment, the measurement and control system reads the residual capacity soc of the off-grid energy storage system, analyzes the absorbed or released power of the off-grid energy storage system under different residual capacities, and distributes the power generated by the power generation unit:
2.2.2.1 when the soc of the off-grid energy storage system is less than the soc u When off-grid occurs, the measurement and control system predicts future micro-grid support power P at off-grid time according to the measurement and control system fzes The parallel-to-off-grid energy storage system sends out a power absorption instruction to the micro-grid to enable the parallel-to-off-grid energy storageSystem absorbing power P to micro grid fzes 。
2.2.2.2 when the soc of the off-grid energy storage system is greater than or equal to the soc u When the measurement and control system selects part of non-main controllable load equipment, the sum of the load power of the non-main controllable load equipment is smaller than or equal to the absolute value |P of the future micro-grid support power fzes Ban subtract cut.
Wherein, the soc u The upper limit value of the residual capacity of the energy storage is the off-grid energy storage; soc l The lower limit value of the residual capacity of the grid-connected and off-grid energy storage system; the soc is the residual capacity of the off-grid energy storage system; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi The reduced output power value for each power generation unit; p (P) powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; i is 1,2,3 … … n, n is more than or equal to 1 and is an integer;
step 3, treating method after off-grid of micro-grid
When the micro-grid continuously runs off-grid, the micro-grid changes from grid connection to off-grid, the non-main load is reduced, the output power of the power generation unit is adjusted, and the like, so that the active power and the reactive power of the micro-grid are changed, and the power factor alpha at a certain load point is especially beari Less than or equal to the lower limit value alpha of the power factor l I.e. alpha beari ≤α l When accompanied by a voltage u beari And the power grid quality is seriously in an out-of-standard state when the power grid is out of limit up and down. When the measurement and control system reads a certain load point voltage u beari Less than or equal to the lower voltage limit U lgb (1+β%), i.e. u beari ≤U lgb When (1+beta%) is reached, the measurement and control system calculates the power factor alpha of each point in the micro-grid beari And the voltage u corresponding to the point beari When alpha is beari ·u beari The smaller the product value of (2) is, the relatively poorer the network quality at the point is, so that alpha is passed beari ·u beari The product size can directly measure the quality of each load point in the micro-grid;
similarly, when the measurement and control system reads a certain load point voltage u beari Greater than equal toAt the upper voltage limit U ugb (1-beta%), i.e. u beari ≥U ugb When (1-beta%), calculating the power factor alpha of each point in the micro-grid beari And the voltage u corresponding to the point beari Ratio of whenThe smaller the product value of (2) the worse the network quality at that point, so that by +.>The quality of each load point in the micro-grid is directly measured according to the ratio and the load power factor alpha of the adjacent load points beari Calculating the compensation reactive power Q beari The power and reactive power output is changed through the power generation unit or the grid-connected and off-grid energy storage system absorbs the utility ratio of the micro-grid to compensate.
Wherein U is lgb Is the lower voltage standard value; u (U) ugb Is the upper voltage standard value; alpha l Is the lower limit value of the power factor; beta.epsilon.1, 2,3 … … 10; alpha bear1 ,α bear2 ……α bearn The power factors of the corresponding controllable load points 1 to n are respectively; u (u) bear1 ,u bear2 ,……,u bearn The voltage is the voltage corresponding to the controllable load points 1-n; u (u) beari Is the i-th point load voltage; q (Q) beari Is reactive power; u (u) pow1 ,u pow2 …u pown Output voltages corresponding to the power generation units 1 to n; i.epsilon.1, 2,3 … … n; n is more than or equal to 1.
Step 4, three-phase imbalance treatment method
Because a large number of single-phase loads and partial power generation units exist in the micro-grid line, the load of each line and the synchronous rate of the power generation units are different, and particularly, when the micro-grid is off-grid, the load is not reduced by the main controllable load, and three-phase unbalance of the line is easily caused. According to the initialized positioning, the measurement and control system respectively finds out the relative terminal equipment of the three-phase power grid, reads the related data and analyzes each single-phase voltage U as 、U bs 、U cs For each phase voltage, sort by high, medium, low(U as ,U bs ,U cs ) Calculating the difference between the high voltage and the low voltage, and converting the voltage difference DeltaU m And a voltage difference allowable threshold U mδ And comparing, and performing corresponding control according to different comparison results. The purpose is to analyze the phase line voltage, when the phase line voltage is high, the load is light or the power supply power of the power generation unit is large, and when the phase line voltage is low, the load is heavy or the power supply power of the power generation unit is small. Thus, the capacity of independent control of each phase of the grid-connected and off-grid energy storage system is utilized, and the line voltage is reduced by increasing the load through absorbing power with high phase line voltage. The power supply capacity of the line is improved by releasing low power to the line circuit, and the line voltage is improved. And 5, when the micro-grid is off-grid, the measurement and control system regulates and controls the power of the grid-connected and off-grid energy storage system and the power generation unit at the moment of grid connection of the micro-grid and inputs the power into the grid-connected and off-grid energy storage system and the power generation unit under non-main load operation, and the method comprises the following steps of:
The measurement and control system receives the upper-level dispatching instruction, monitors the state of the large power grid in real time, starts and leaves the grid energy storage system to carry out grid synchronization adjustment when the micro power grid is allowed to be connected, and simultaneously carries out grid connection work flow according to the current micro power grid off-grid state:
(1) After the synchronous closing of the power grid is successful, converting the off-grid energy storage system into a current source mode from a voltage source mode, and performing self-adaptive charge and discharge control on the off-grid energy storage system according to the current state of the residual electric quantity soc;
(2) In order to prevent the quality mutation of the micro-grid, the non-main load is recovered in sequence from small to large according to the condition of reducing and cutting the non-main load when the micro-grid is off-grid;
(3) In order to prevent the quality mutation of the micro-grid, the power generation units are sequentially and time-sharing recovered to generate power normally according to the current power generation situation of the power generation units when the micro-grid is off-grid.
Further, 2.1 of the step 2 is implemented when the low-voltage side current I of the transformer in the transformer area is at the grid-connected time B When the power flow direction is less than 0, the micro-grid supplies power to the power grid, and the measurement and control system supplies the total power p of all power generation units zpow Releasing or absorbing power p with and from an energy storage system zes Summing and calculating the low-side power P of the transformer in the transformer area B To obtain all negative differencesPower consumption P of charge all I.e. P all ＝P zpow +P zes -P B . Because the main load work is ensured during off-grid operation, the energy output of the micro-grid is reduced by the load-reducing non-main controllable load, and the load demand power P in the micro-grid at the future off-grid moment is obtained by subtracting the non-main controllable load from the power consumption of all loads bear ＝P all -P nbear . Due to load demand power P at a future off-grid time bear Power is supplied by the power generation unit and the parallel off-grid energy storage system, and the future micro-grid supports power P fzes To predict load demand power P in micro-grid at off-grid time bear Total power p generated by all power generation units zpow The difference and the parallel-to-off-grid energy storage system absorb or release power P zes And, P fzes ＝P bear -P zpow +P zes 。
Further, 2.1.1 of the step 2, when the micro grid supports the power P in the future fzes When less than 0, the total output power p of all the power generation units is described zpow Greater than the load demand power P bear Whereby the future microgrid support power P when a future off-grid occurs fzes And absorbing or reducing redundant power of the power generation unit for the micro-grid to pass through and leave the grid energy storage system.
Therefore, considering the residual capacity soc condition of the off-grid energy storage system, the measurement and control system analyzes the off-grid energy storage residual capacity soc as follows:
2.1.1.1 when the residual capacity soc of the off-grid energy storage system is less than the upper limit value soc of the residual energy storage capacity u I.e. soc < soc u In the time, the measurement and control system predicts the future micro-grid support power P at off-grid time fzes And when off-grid occurs, sending a power absorption instruction to the micro-grid to the off-grid energy storage system.
2.1.1.2 when the residual capacity soc of the parallel-to-off-grid energy storage system is greater than or equal to the upper limit value soc of the residual energy storage capacity u I.e. soc is greater than or equal to soc u When the load is not reduced, the load is not mainly controlled, and the measurement and control system is used for measuring and controlling the power P at the low-voltage side of the transformer in the network station B Total power p generated by all power generation units zpow The ratio of each power generation sheet is obtainedMeta-power P powi Distribution coefficient mu zes I.e.And then the power distribution coefficient mu of each power generation unit zes With the output power P of each power generation unit powi Multiplying to obtain the load-shedding power P of each power generation unit zesi I.e. P zesi ＝μ zes ·P powi The measurement and control system is used for measuring and controlling the load shedding power P of each power generation unit when the off-grid occurs in the future zesi And sending out a power output reducing instruction to each power generation unit.
Wherein P is bear The power is required for the load in the micro-grid at the future off-grid moment; p (P) all Power is consumed to obtain all loads; p is p zpow Generating total power for all the power generation units; p (P) zes Releasing or absorbing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; p (P) B The power of the low-voltage side of the transformer in the transformer area is calculated; i B The low-voltage side current of the transformer in the transformer area is obtained; u (U) B The low-voltage side voltage of the transformer in the transformer area is obtained; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi Load shedding power for each power generation unit; p (P) powi Outputting power for each power generation unit; the soc is the residual capacity of the off-grid energy storage system; soc u The upper limit residual capacity of the grid-connected and off-grid energy storage system; i is 1,2,3 … … n, n is more than or equal to 1, and is an integer;
further, 2.2 of the step 2, when the grid connection is performed, the low-voltage side current I of the transformer in the transformer area B When the load flow direction is not less than 0, the power grid supplies power to the micro-grid, so that the power generation units in the micro-grid and the parallel-off-grid energy storage system cannot meet the load power consumption requirement, and the measurement and control system measures and controls the output power P of the transformer in the transformer area B Total power p to all power generation units zpow Absorbing or releasing power p with and from an on-grid energy storage system zes Summing, calculating to obtain all load consumption power P all I.e. P all ＝P B +P zpow +P zes Since the micro-grid ensures the main load work during off-grid operation, the non-main controllable load P is reduced nbear Reducing the energy output of the micro-grid, so that the total load power P all Subtracting the non-main controllable load to obtain the load demand power P at the future off-grid moment baer ，P baer ＝P all -P nbear . Due to load demand power P at a future off-grid time baer The power is supplied by the power generation unit and the parallel off-grid energy storage system, so that the load demand power P at the future off-grid moment is reduced baer And the total power p of the power generation unit zpow Calculating the difference value, and absorbing or releasing power P by the difference value and the off-grid energy storage system zes Summing to obtain the future micro-grid support power P of the predicted off-grid moment fzes I.e. P fzes ＝P baer -P zpow +P zes 。
2.2.1 when the micro grid support Power P is in the future fzes When not less than 0, the total output power p of all the power generation units is described zpow Less than the load demand power P baer The grid-connected and off-grid energy storage system is required to release power, so that the micro-grid support power P in the future fzes For power released to the microgrid by the off-grid energy storage system when off-grid occurs. Meanwhile, the measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.2.1.1 when the residual capacity soc of the off-grid energy storage system is greater than or equal to the lower limit value soc of the off-grid energy storage residual capacity l I.e. soc is greater than or equal to soc l In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes And when off-grid occurs, a power release instruction for the micro-grid is sent to the off-grid energy storage system.
2.2.1.2 when the residual capacity soc of the off-grid energy storage system is smaller than the lower limit value soc of the off-grid energy storage residual capacity l I.e. soc < soc l And when the micro-grid is in a power failure state, starting a protection program by the off-grid energy storage system.
Further, 2.2.2 of the step 2, when the micro grid supports the power P in the future fzes < 0, indicating the total output power p of all power generation units due to load shedding of non-primary controllable loads zpow Greater than the load demand power P baer Whereby the micro-grid supports power P in the future fzes And absorbing or reducing the redundant power of the power generation unit for the future off-grid moment and the off-grid energy storage system. At the moment, the measurement and control system reads the residual capacity soc of the off-grid energy storage system, analyzes the absorbed or released power of the off-grid energy storage system under different residual capacities, and distributes the power generated by the power generation unit:
2.2.2.1 when the residual capacity soc of the off-grid energy storage system is smaller than the upper limit value soc of the off-grid energy storage residual capacity u I.e. soc < soc u In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes And when off-grid occurs, sending a power absorption instruction to the micro-grid to the off-grid energy storage system.
2.2.2.2 when the residual capacity soc of the off-grid energy storage system is greater than or equal to the upper limit value soc of the off-grid energy storage residual capacity u I.e. soc is greater than or equal to soc u At this time, the measurement and control system selects a part of non-main controllable load equipment, and the sum of the load power of the non-main controllable load equipment is smaller than or equal to the absolute value |P of the future micro-grid support power fzes Ban from decreasing, i.e. non-primary controllable load P nbear ≤|P fzes |。
Wherein, the soc u The upper limit value of the residual capacity of the energy storage is the off-grid energy storage; soc l The lower limit value of the residual capacity of the grid-connected and off-grid energy storage system; the soc is the residual capacity of the off-grid energy storage system; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi The reduced output power value for each power generation unit; p (P) powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; i is 1,2,3 … … n, n is more than or equal to 1, and is an integer.
Further, in the step 3, the measurement and control system reads the output voltage u of each power generation unit in real time pow1 ,u pow2 …u pown Power p pow1 ,p pow2 ……p pown And the power factor alpha of each controllable load point bear1 ,α bear2 ……α bearn Voltage u bear1 ,u bear2 ,……,u bearn . And calculates the power factor alpha beari And the voltage u corresponding to the point beari The product, or the power factor alpha, is calculated beari And the voltage u corresponding to the point beari The ratio is sorted from small to large by a sorting function sort, and the lower limit value alpha of the relative power factor is screened out l The voltage is greater than or equal to the upper limit U beari ≥U ugb (1-beta%) or less of the lower limit U beari ≤U lgb (1+β%) load point, where β e (1, 2,3 … … 10), namely:
sort([α bear1 ·u bear1 ,α bear2 ·u bear2 ,……,α bearn ·u bearn ])
or (b)
The measurement and control system determines the priority control sequence and positioning of the load according to the sequence, and the method is the smallest, next smallest, third smallest and so on, and simultaneously determines the positioning of the power generation unit with the nearest relative distance according to the controlled load positioning.
The measurement and control system sequentially reads the output power P of the corresponding power generation units according to the priority control sequence and positioning of the load points powi And is matched with rated lower limit output power P of the power generation unit lpow Comparison, treatment was performed by the following steps:
(1) When judging a certain power generation unit P powi ≥P lpow When the load point load power factor alpha is measured and controlled by the measurement and control system according to the load point load power factor alpha adjacent to the measurement and control system beari Calculate the compensation reactive power Q beari ，U when the load point voltage beari ≤U lgb (1+beta%) and the measurement and control system is based on reactive power Q beari And the power generation units corresponding to the load priority control sequence and the positioning control in sequence send out a command for compensating reactive power output.
When the load point voltage U beari ≥U ugb When (1-beta%), the measurement and control system is based on reactive power Q beari Generating units corresponding to the load priority control sequence and the positioning control in turn send out compensationReactive output and instructions to reduce active output.
(2) When only one group of power generation units exist in the load point lines with 2 or more than 2 load points, the measurement and control system reads the load power factor value which is closest to the power generation units in relative distance, and controls the power generation units to output compensation reactive power.
(3) When judging a certain power generation unit P powi ＜P lpow When the power generation unit cannot provide reactive power output, the measurement and control system selects the power which is closest to the power generation unit and has the output power of more than or equal to P powi Rated lower limit output power P lpow Or by compensating reactive power output by a grid-connected energy storage system in dependence on the power factor of the load location that is relatively closest to it.
Wherein U is lgb Is the lower voltage standard value; u (U) ugb Is the upper voltage standard value; alpha l Is the lower limit value of the power factor; beta.epsilon.1, 2,3 … … 10; alpha bear1 ,α bear2 ……α bearn The power factor is the power factor corresponding to 1-n controllable load points; u (u) bear1 ,u bear2 ,……,u bearn The voltage is corresponding to 1-n controllable load points; u (u) beari Is the i-th point load voltage; q (Q) beari Is reactive power; p (P) powi Outputting power for each generating unit, i epsilon 1,2,3 … … n; u (u) pow1 ,u pow2 …u pown Outputting voltages for the corresponding 1-n power generation units; p is p pow1 ,p pow2 ……p pown Output power of the corresponding 1-n power generation units; p (P) lpow Is rated lower limit output power; n is more than or equal to 1.
Further, in the step 4, in the three-phase imbalance treatment method,
at the same time of controlling the micro-grid, the measurement and control system performs voltage sequencing on the sort (U as ,U bs ,U cs ) Respectively screen out the highest voltage U max Minimum voltage U min And the next highest voltage U med And will have the highest voltage U max And the lowest voltage U min Performing difference calculation to obtain a high-low voltage difference delta U m ＝U max -U min And the difference delta U between the high voltage and the low voltage m Allowable threshold value U of voltage difference mδ Comparison is performed:
(1) When the measurement and control system judges the difference delta U between the high voltage and the low voltage m Greater than or equal to the voltage difference allowable threshold U mδ I.e. DeltaU m ≥U mδ When the highest voltage U is obtained max And the lowest voltage U min Average voltage U of (2) aver I.e.And will average voltage U aver And the next highest voltage U med Performing difference calculation, i.e. DeltaU med ＝U avre -U med 。
1.1 when the measurement and control system judges the average voltage U aver And the next highest voltage U med The difference is greater than zero DeltaU med When > 0, it is the highest voltage U max The deviation is large. The measurement and control system outputs the highest voltage U max And the next highest voltage U med Performing difference calculation to obtain a high-medium-low voltage difference delta U abcδ ＝U max -U med . Because each phase of the parallel-to-off-grid energy storage system has the capability of independent control, the measurement and control system releases or absorbs the power P to the highest-voltage phase line according to the current parallel-to-off-grid energy storage system zes And the highest voltage U max And a difference DeltaU between high, medium and low voltages abcδ The ratio of (2) is subjected to product calculation,obtaining the power value delta P absorbed by the parallel-off-grid energy storage system on the basis of the original power of the highest voltage phase line zes Whereby the measurement and control system is based on the absorbed power value DeltaP zes And sending out an absorbed power instruction to the off-grid energy storage system.
1.2 when the measurement and control system judges the average voltage U aver And the next highest voltage U med The difference is less than zero DeltaU med When less than 0, the voltage is the minimum voltage U min The deviation is large. The measurement and control system calculates the next highest voltage U med And the lowest voltage U min To obtain the difference delta U of high, medium and low voltages abcδ ＝U med -U min . Due to the grid-connected and off-grid energy storage system Each phase of the system has independent control capability, and the measurement and control system releases or absorbs power P to the lowest voltage phase line according to the current off-grid energy storage system zes And the lowest pressure U min And a difference DeltaU between high, medium and low voltages abcδ The ratio of (2) is subjected to product calculation,obtaining the release power value delta P increased by the off-grid energy storage system on the lowest voltage phase line zes Whereby the measurement and control system is based on the increased release power value ΔP zes And sending a released power instruction to the off-grid energy storage system.
2.2 when the measurement and control system judges the difference delta U between the high voltage and the low voltage m Less than the voltage difference allowable threshold U mδ And when the micro-grid is in a state of being out of the grid, the measurement and control system maintains the current power value absorbed or released, and sends an absorbed or released power instruction to the parallel-to-off-grid energy storage system, so that the three-phase balance of the micro-grid is ensured.
Wherein: u (U) as Outputting voltage for phase A of the opposite end equipment of the three-phase power grid; u (U) bs Outputting voltage for B phase of opposite terminal equipment of the three-phase power grid; u (U) cs Outputting voltage for C phase of the opposite end equipment of the three-phase power grid; u (U) aver The average voltage of the highest voltage and the lowest voltage of the three-phase power grid relative to the terminal equipment; deltaU m Is the difference between the high voltage and the low voltage; u (U) mδ A voltage difference enable threshold; u (U) max The highest voltage of the three-phase power grid relative to the terminal equipment; u (U) min The lowest voltage of the three-phase power grid relative to the end equipment; u (U) med The next highest voltage for the opposite end device of the three-phase network; deltaU abcδ Is the difference value of high, medium and low voltages; ΔP zes Adding an absorbed or released power value for the measurement and control system; sort is the ranking function.
Drawings
FIG. 1 is a topological structure diagram of a microgrid;
FIG. 2 is a flow chart of a control method of the present invention in FIG. 1;
FIG. 3 shows transformer data of the transformer in the grid-connected time zone as I in step 2 of the control method of the present invention B A < 0 flow chart;
FIG. 4 shows the present inventionIn the control method step 2, transformer data of a transformer in a grid-connected time zone is regarded as I B And (5) when the flow is more than or equal to 0, the flow chart is formed.
Detailed Description
The invention is further described below with reference to the drawings and detailed description.
As shown in fig. 1, the micro-grid system applied by the control method for the off-grid moment of the micro-grid of the present invention is composed of a transformer in a transformer area, a measurement and control system, an off-grid energy storage system, a power generation unit 1, … …, a power generation unit n, a main load 1, … …, a main load n, a non-main controllable load 1, … …, a non-main controllable load n, etc. The grid-connected and off-grid energy storage system is arranged at the position of the micro-grid close to the transformer in the transformer area; the power generation units 1 and … …, the power generation units n, the main loads 1 and … …, the main loads n and the non-main controllable loads 1 and … … are distributed on the micro-grid, and all have a data communication function, wherein n is an integer. The measurement and control system is positioned at the transformer of the transformer area and is provided with a wired and wireless communication mode, the upper-level fault signal and the scheduling instruction are received upwards, and the power parameters at the transformer of the transformer area and the equipment in the micro-grid network are monitored downwards. Wired or wireless communication means include fiber optics, ethernet, carrier waves, 4G, 5G, loRa, etc.
All the measured and controlled objects have the functions of control and data transmission. The parallel-off-grid energy storage system consists of three independent phase bidirectional converters and three-phase common energy storage, and each phase bidirectional converter has independent control capability. And outputting the power by the grid-connected and off-grid energy storage system in a current source mode when the power is connected, and controlling the quality of the micro-grid for absorbing or releasing the power. When the micro-grid is off-grid, the off-grid energy storage system is used for networking and outputting in a voltage source mode, and voltage, current and frequency are provided for the load and the power generation unit.
The steps of the method for controlling the off-grid time of the micro-grid are shown in figure 2.
Step 1, initializing
All controllable equipment of the district micro-grid comprises: and (3) inputting the main controllable load, the non-main controllable load, the power generation unit, the off-grid energy storage system and other related data into a measurement and control system, performing attribute calibration and parameter setting, and determining the relative distance and position of each device by taking the transformer in the transformer area as an origin.
The following related data of all controllable devices of the district micro-grid of the measurement and control system are input, wherein the data comprise: the power of the load, the capacity and the power of the power generation unit, the input and output power of the off-grid energy storage system, and the upper limit and the lower limit of the capacity of the off-grid energy storage system and the residual capacity thereof.
The transformer in the transformer area is used as an origin, and the main load, the non-main load, the wind power, the photovoltaic and other power generation units, the relative distance between the transformer in the transformer area, the position and the line model are calibrated;
and the measurement and control system receives the fault signal and the scheduling instruction of the upper stage in real time, and downwardly reads the electric power parameters of the micro-grid and all equipment information. When the upper grid connection or fault information is received, according to the data of the previous time of history, the power grid characteristics of each device of the current micro-grid are combined, and the power grid quality of each device is controlled and guaranteed.
Step 2, predicting and analyzing the power of the off-grid energy storage system and the power generation unit by the micro-grid at the off-grid moment, and reading all controllable equipment data of the platform area in real time by the measurement and control system, and calculating and controlling the power of the off-grid energy storage system and the power generation unit by the measurement and control system, wherein the method comprises the following steps of:
(1) The measurement and control system reads all controllable equipment data of the platform area in real time, and the method comprises the following steps: and the off-grid energy storage system absorbs or releases power p zes A residual electric quantity soc; output voltage u of each power generation unit pow1 ,u pow2 …u pown Power p pow1 ,p pow2 ……p pown The method comprises the steps of carrying out a first treatment on the surface of the Power P of each non-main load point nbear1 ,P nbear2 ,……,P nbearn The method comprises the steps of carrying out a first treatment on the surface of the Power factor alpha of main load mbear1 ,α mbear2 ,……,α mbearn Voltage u mbear1 ,u mbear2 ,……,u mbearn And power P mbear1 ,P mbear2 ,……,P mbearn The method comprises the steps of carrying out a first treatment on the surface of the Transformer power P in transformer area B Current I B Sum voltage U B . And for calculating the total power of all power generation units and the total power of all non-main loads:
Total power of the power generation unit:
total power of non-main controllable load:
when the transformer in the monitoring station area of the measurement and control system measures the current I B The power flow direction is more than 0, the power grid supplies power to the micro-grid, and the voltage distribution is output to the tail end of the power grid by the transformer in the transformer area and shows the characteristic of high to low; i B The direction of the < 0 tide is that the micro-grid supplies power to the power grid, and the voltage distribution is output to the tail end of the power grid by the transformer in the transformer area and shows the characteristic of low to high; i B =0 is power supply and load balance within the microgrid;
wherein P is nbear Total power for non-primary controllable loads; p (P) bear Total power for total controllable load; p (P) main Total power for the primary load; p is p inbear The power of the non-primary controllable load of the ith station; p (P) nbear1 ,P nbear2 ,……,P nbearn Non-primary controllable load powers of the 1 st to nth stations respectively; p is p zpow Is the total power of the power generation unit; p is p ipow I e (1, 2., n) for the i-th power generation unit power; u (u) pow1 ,u pow2 …u pown Output voltages of the 1 st to nth power generation units; p is p pow1 ,p pow2 ……p pown Output powers of the 1 st to nth power generation units, respectively; i B The low-voltage side current of the transformer in the transformer area is obtained; p (P) B The power of the low-voltage side of the transformer in the transformer area is calculated; u (U) B The low-voltage side voltage of the transformer in the transformer area is obtained; p is p zes Absorbing or releasing power for the grid-connected and off-grid energy storage system, wherein the soc is the residual capacity of an energy storage battery of the grid-connected and off-grid energy storage system; alpha mbear1 ,α mbear2 ,……,α mbearn Power factors of the 1 st to nth main loads respectively; u (u) mbear1 ,u mbear2 ,……,u mbearn The voltages of the 1 st to nth main loads respectively; p (P) mbear1 ,P mbear2 ,……,P mbearn Respectively 1 st to nth main stationsThe power of the load; n is an integer not less than 1.
(2) When the micro-grid is connected, the measurement and control system calculates and separates the power of the energy storage system and the power generation unit so as to control related equipment when the micro-grid is separated from the grid, and the method specifically comprises the following steps:
2.1 at grid-connected time, when the transformer low-voltage side current I of the transformer area B When less than 0;
the tide direction is the power supply of the micro-grid to the power grid, and the measurement and control system generates the total power p through all the power generation units zpow And releasing or absorbing power p by off-grid energy storage system zes And transformer low-side power P B Respectively calculating the power consumption P of all loads all Load demand power P in micro-grid at future off-grid moment bear Finally, the future micro-grid support power P is obtained fzes 。
2.1.1 when the micro grid support Power P is in the future fzes When the number of the groups is less than 0,
description of total output Power p of all generating units zpow Greater than the load demand power P bear Whereby the future microgrid support power P when a future off-grid occurs fzes And absorbing or reducing redundant power of the power generation unit for the micro-grid to pass through and leave the grid energy storage system.
The measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.1.1.1 when the soc of the off-grid energy storage system is less than the soc u In the time, the measurement and control system predicts the future micro-grid support power P at off-grid time fzes When off-grid occurs, the off-grid energy storage system is sent out to absorb power instructions to the micro-grid, and the off-grid energy storage system absorbs power P to the micro-grid fzes 。
2.1.1.2 when the soc of the grid-connected and off-grid energy storage system is more than or equal to the soc u When the load is not reduced, the load is not mainly controlled, and the measurement and control system is used for measuring and controlling the power P at the low-voltage side of the transformer in the network station B Total power p of all power generation units zpow Calculating the distribution coefficient mu of the power of each power generation unit zes And through the power distribution coefficient mu of each generating unit zes And the output power P of each power generation unit powi Calculating to obtain the load shedding power P of each power generation unit zesi . When the future off-grid occurs, the measurement and control system is used for measuring and controlling the load shedding power P of each power generation unit zesi And sending out a power output reducing instruction to each power generation unit.
2.2 Low-side Current I of transformer in transformer area at grid-connected time B When the temperature is more than or equal to 0;
the power flow direction is supplied to the micro-grid by the power grid, which indicates that the power generation units in the micro-grid and the parallel-off-grid energy storage system can not meet the load power demand, and the measurement and control system at the moment is based on the output power P of the transformer in the transformer area B Total power p of all power generating units zpow And the off-grid energy storage system absorbs or releases power p zes Respectively calculating to obtain all load consumption power P all Load demand power P at future off-grid time baer Finally obtaining the future micro-grid support power P of the predicted off-grid moment fzes 。
2.2.1 when the micro grid support Power P is in the future fzes When the temperature is more than or equal to 0,
description of the output Power p of the Power generating Unit zpow Less than the load demand power P baer The grid-connected and off-grid energy storage system is required to release power, and the power released by the grid-connected and off-grid energy storage system to the micro grid is the future micro grid support power P fzes 。
The measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.2.1.1 when the soc of the off-grid energy storage system is greater than or equal to the soc l In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes When off-grid occurs, the off-grid energy storage system is sent out to release power instruction codes for the micro-grid, and the off-grid energy storage system releases power P for the micro-grid fzes 。
2.2.1.2 when the soc of the off-grid energy storage system is less than the soc l And when the micro-grid is in a power failure state, starting a protection program by the off-grid energy storage system.
2.2.2 when the micro grid support Power P is in the future fzes When less than 0;
description of all Power generating units after load shedding due to non-primary controllable loadsIs set to the total output power p zpow Greater than the load demand power P baer Whereby the micro-grid supports power P in the future fzes And absorbing or reducing redundant power of the power generation unit for the off-grid moment and the off-grid energy storage system in the future. At the moment, the measurement and control system reads the residual capacity soc of the off-grid energy storage system, analyzes the absorbed or released power of the off-grid energy storage system under different residual capacities, and distributes the power generated by the power generation unit:
2.2.2.1 when the soc of the off-grid energy storage system is less than the soc u When off-grid occurs, the measurement and control system predicts future micro-grid support power P at off-grid moment according to the prediction fzes The power P is absorbed by the off-grid energy storage system by sending a power absorption instruction to the micro-grid to the off-grid energy storage system fzes 。
2.2.2.2 when the soc of the off-grid energy storage system is greater than or equal to the soc u When the measurement and control system selects part of non-main controllable load equipment, the sum of the load power of the non-main controllable load equipment is smaller than or equal to the absolute value |P of the future micro-grid support power fzes Ban subtract cut.
Wherein, the soc u The upper limit value of the residual capacity of the energy storage is the off-grid energy storage; soc l The lower limit value of the residual capacity of the grid-connected and off-grid energy storage system; the soc is the residual capacity of the off-grid energy storage system; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi The reduced output power value for each power generation unit; p (P) powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; i is 1,2,3 … … n, n is more than or equal to 1 and is an integer;
step 3, treating method after off-grid of micro-grid
When the micro-grid continuously runs off-grid, the micro-grid changes from grid connection to off-grid, load shedding of non-main load, adjustment of output power of a power generation unit and the like, so that active power and reactive power of the micro-grid are changed, and especially, the power factor alpha at a certain load point beari Sum voltage u beari And when the load point micro-grid quality is smaller than or equal to the corresponding upper limit and lower limit, the load point micro-grid quality is changed and exceeds the standard. The invention has a voltage u at a certain load point beari Lower limit U or less lgb (1+beta%) and using power factor alpha of every load point in micro-grid beari And corresponds to the load point voltage u beari Is ordered by product size, when alpha beari ·u beari The smaller the product value of (c), the poorer the grid quality at that point.
Also, at a certain load point, the voltage is equal to or higher than the upper limit U ugb (1-beta%) by the power factor alpha at each point in the microgrid beari And the voltage u corresponding to the point beari Calculating the ratio whenThe smaller the product value of the (C) is, the worse the power grid quality is, thus measuring the relative quality of each load point in the micro-grid, and according to the load power factor alpha of the adjacent load points beari Calculating the compensation reactive power Q beari And compensating by a power generation unit or an off-grid energy storage system.
Step 4, three-phase imbalance treatment method
Because a large number of single-phase loads and partial power generation units exist in the micro-grid line, the load of each line and the synchronous rate of the power generation units are different, and particularly, when the micro-grid is off-grid, the load is not reduced by the main controllable load, and three-phase unbalance of the line is easily caused. According to the initialized positioning, the measurement and control system respectively finds out the relative terminal equipment of the three-phase power grid, reads the related data and analyzes each single-phase voltage U as 、U bs 、U cs For each phase voltage, sort the sort (U) by high, medium and low as ,U bs ,U cs ) Calculating the difference between the high voltage and the low voltage, and converting the voltage difference DeltaU m And a voltage difference allowable threshold U mδ Comparing, and performing corresponding control according to different comparison results;
the purpose is to analyze the phase line voltage, when the phase line voltage is high, the load is light or the power supply power of the power generation unit is large, and when the phase line voltage is low, the load is heavy or the power supply power of the power generation unit is small. Thus, the capacity of independent control of each phase of the grid-connected and off-grid energy storage system is utilized, and the line voltage is reduced by increasing the load through absorbing power with high phase line voltage. The power supply capacity of the line is improved by releasing low power to the line circuit, and the line voltage is improved.
And 5, when the micro-grid is off-grid, the measurement and control system regulates and controls the power of the grid-connected and off-grid energy storage system and the power generation unit at the moment of grid connection of the micro-grid and inputs the power into the grid-connected and off-grid energy storage system and the power generation unit under non-main load operation, and the method comprises the following steps of:
the measurement and control system receives the upper-level dispatching instruction, monitors the state of the large power grid in real time, starts and leaves the grid energy storage system to carry out grid synchronization adjustment when the micro power grid is allowed to be connected, and simultaneously carries out grid connection work flow according to the current off-grid state of the micro power grid.
1) After the synchronous closing of the power grid is successful, converting the off-grid energy storage system into a current source mode from a voltage source mode, and performing self-adaptive charge and discharge control on the off-grid energy storage system according to the current state of the residual electric quantity soc;
2) In order to prevent the quality mutation of the micro-grid, the non-main load is restored to the working mode from small to large in sequence according to the condition of reducing and cutting the non-main load during off-grid;
3) In order to prevent the quality mutation of the micro-grid, the normal power generation mode of the power generation unit is recovered in a time-sharing mode in sequence according to the current power generation state of the power generation unit when the micro-grid is off-grid.
Further, based on the analysis, the control method for the off-grid time of the micro-grid specifically comprises the following steps:
in step 2, (2) when the power grid is connected, calculating and off-grid power of the energy storage system and the power generation unit so that when the micro-grid is off-grid, the measurement and control system controls related equipment, wherein the method comprises the following steps of:
2.1 As shown in FIG. 3, when the transformer is low-side current I B When < 0:
the tide direction is the power supply of the micro-grid to the power grid, and the measurement and control system is used for supplying power to the power grid through the total power p of all power generation units zpow Releasing or absorbing power p with and from an energy storage system zes Summing and combining with low-voltage side power P of transformer in transformer area B And the difference value is calculated to obtain the power consumption P of all loads all I.e. P all ＝P zpow +P zes -P B . Because the main load work is ensured during off-grid operation, the energy output of the micro-grid is reduced by the load-reducing non-main controllable load, and the load demand power P in the micro-grid at the future off-grid moment is obtained by subtracting the non-main controllable load from the power consumption of all loads bear ＝P all -P nbear . Due to load demand power P at a future off-grid time bear Powered by the power generation unit and the off-grid energy storage system, whereby the future micro-grid supports power P fzes To predict load demand power P in micro-grid at off-grid time bear Total power p generated by all power generation units zpow And then absorb or release power P with the grid-connected or off-grid energy storage system zes Summation calculations of (i.e. P) fzes ＝P bear -P zpow +P zes 。
For example, the total power p generated by all power generating units zpow =600 kW and the grid-connected and off-grid energy storage system charge absorption power p zes Summing up = -20KW and feeding power P with the low voltage side of the district transformer B Calculation of the difference value and the = -100kW, obtaining all load consumption power, namely:
P all ＝P zpow +P zes -P B =600 kW-20kW-100 kw=480 kW. Since the main load work is ensured during off-grid operation, the off-load non-main controllable load is reduced to reduce the energy output of the micro-grid, and all load consumption power is subtracted by the non-main controllable load P nbear 200kW, obtaining load demand power P in micro-grid at future off-grid moment bear ＝P all -P nbear =480 kW-200 kw=280 kW. Due to load demand power P at a future off-grid time bear =280 kW is supplied by the power generation unit and the off-grid energy storage system, whereby the future microgrid support power P fzes For the load demand power P in the micro-grid at the future off-grid moment bear Total power p generated by all power generation units zpow Is used for absorbing or releasing power P by a parallel-to-grid energy storage system zes And calculating, namely:
P fzes ＝P bear -P zpow +P zes ＝280kW-600kW-20kW＝-340kW。
2.1.1 when micro-grid is in futureSupport power P fzes ＜0，
Description of total output Power P of all generating units zpow =600 kW greater than the load demand power P bear The load is mainly supplied by the power generation unit, so that when off-grid occurs in the future, the micro-grid absorbs or reduces the redundant output power P of the power generation unit through the off-grid energy storage system to ensure the stability of the grid voltage and reduce the energy loss fzes = -340kW. When the residual capacity soc condition of the off-grid energy storage system is considered, the measurement and control system analyzes the residual capacity soc of the energy storage system:
2.1.1.1 if the residual capacity soc=60% of the off-grid energy storage system is smaller than the upper limit value soc of the residual capacity u =90%, i.e. soc < soc u In the future, the measurement and control system supports the power P according to the micro-grid fzes And when off-grid occurs, sending out a code for absorbing power instructions to the micro-grid to the off-grid energy storage system.
2.1.1.2 when the residual capacity soc=90% of the parallel and off-grid energy storage system is greater than or equal to the upper limit value soc of the residual energy storage capacity u =90%, i.e. soc is greater than or equal to soc u When the load is not reduced, the non-main controllable load is not reduced, and the measurement and control system is used for measuring and controlling the power P of the low-voltage side of the transformer of the network station according to the measurement and control system B Total power p of all power generation units zpow The ratio of the power P of each power generation unit is obtained powi Distribution coefficient mu zes ，
I.e.
If the power generation unit 1 is P pow1 =100 kW, e.g. power generation unit 2P pow2 =200 kW, e.g. power generation unit 3P pow3 =150 kW, e.g. power generation unit 4P pow4 =150 kW. Power distribution coefficient mu of each power generation unit zes With the output power P of each power generation unit powi To obtain the load-shedding power P of each power generation unit zesi Namely, the load shedding power of the 1 st power generation unit is as follows:
P zes1 ＝μ zes ·P pow1 ＝-0.166×100kW＝-16.6kW；
the load shedding power of the 2 nd generating unit is P zes2 ＝μ zes ·P pow2 ＝-0.166×200kW＝-33.2kW；
The load shedding power of the 3 rd generating unit is P zes3 ＝μ zes ·P pow3 ＝-0.166×150kW＝-25kW；
The load shedding power of the 4 th power generation unit is P zes4 ＝μ zes ·P pow4 The method comprises the steps that = -0.166 multiplied by 150kW = -25kW, and when off-grid occurs in the future, the measurement and control system respectively depends on the load shedding power P of the 1 st power generation unit zes1 The method comprises the steps of (1) sending out instruction codes for reducing power output to a 1 st power generation unit by using = -16.6 kW; load shedding power P according to the 2 nd generation unit zes2 The method comprises the steps of (1) sending out instruction codes for reducing power output to a 2 nd power generation unit by using = -32.2 kW; load shedding power P according to 3 rd generating unit zes3 The method comprises the steps of (1) sending out a power output reducing instruction code to a 3 rd power generation unit by using = -25 kW; load shedding power P according to 4 th power generation unit zes4 And the power output reducing instruction code is sent to the 4 th power generation unit by the= -25 kW.
Wherein P is bear The power is required for the load in the micro-grid at the future off-grid moment; p (P) nbear Power is demanded for non-primary loads; p (P) all Power is consumed to obtain all loads; p is p zpow The total power generated by all power generation units; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi Load shedding power for each power generation unit; p (P) powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system at a future off-grid moment; p (P) fzes Supporting power for future micro-grids; the soc is the residual capacity of the off-grid energy storage system; soc u The upper limit residual capacity of the grid-connected and off-grid energy storage system; soc l The lower limit residual capacity of the grid-connected and off-grid energy storage system; i.epsilon.1, 2,3 … … n; p (P) B The power of the low-voltage side of the transformer in the transformer area is calculated; i B The low-voltage side current of the transformer in the transformer area is obtained; u (U) B The low-voltage side voltage of the transformer in the transformer area is obtained;
2.2 As shown in FIG. 4, at the time of grid connection, the measurement and control system reads the transformer data of the transformer in the transformer area, when I B When not less than 0：
The power flow direction is supplied to the micro-grid by the power grid, which indicates that the power generation units in the micro-grid and the parallel-off-grid energy storage system can not meet the load power demand, and the measurement and control system measures and controls the output power P of the transformer in the transformer area B And the total power generation unit power p zpow And the off-grid energy storage system absorbs or releases power p zes Summing up to obtain all load consumption power P all I.e. P all ＝P B +P zpow +P zes Since the micro-grid ensures the main load work during off-grid operation, the load-shedding non-main controllable load is reduced to reduce the energy output of the micro-grid, so the total load power P all Subtracting the non-main controllable load to obtain the load demand power P at the future off-grid moment bear ＝P all -P nbear . Due to load demand power P at a future off-grid time baer The power is supplied by the power generation unit and the parallel off-grid energy storage system, so that the load demand power P at the future off-grid moment is reduced baer And the total power p of the power generation unit zpow Calculating the difference value and absorbing or releasing power P with the parallel-to-off-grid energy storage system zes To obtain the future micro-grid support power P of the predicted off-grid moment fzes I.e. P fzes ＝P baer -P zpow +P zes 。
Such as the output power P of the low-voltage side of the transformer in the transformer area B =400 kW and total power p of all power generation units zpow =100 kW, and off-grid energy storage system charging absorption power p zes Summing up = -20KW to obtain all load power consumption, i.e. P all ＝P B +P zes +P zpow =400 kW-20 kw+100kw=480 kW. Since the main load work is ensured during off-grid operation, the off-load non-main controllable load is reduced to reduce the energy output of the micro-grid, and all load consumption power is subtracted by the non-main controllable load P nbear 200kW, obtaining load demand power P in micro-grid at future off-grid moment bear ＝P all -P nbear =480 kW-200 kw=280 kW. Due to load demand power P at a future off-grid time bear =280 kW is supplied by the power generation unit and the off-grid energy storage system, whereby the future microgridSupport power P fzes The power P is required for the load at the future off-grid moment bear Total power p generated by all power generation units zpow Is used for absorbing or releasing power P by a parallel-to-grid energy storage system zes And, namely:
P fzes ＝P bear -P zpow +P zes ＝280kW-100kW-20kW＝160kW。
2.2.1 future microgrid support Power P at this time fzes ≥0，
Illustrating the total output power p of the power generation unit zpow =100 kW less than the load demand power P baer =280 kW, the grid-connected and off-grid energy storage system is required to release power, whereby the future microgrid support power P fzes And 160kW is the power value released by the off-grid energy storage system to the micro-grid at the future off-grid moment.
Meanwhile, considering the residual energy storage capacity soc of the measurement and control system and the off-grid energy storage system, and analyzing the residual energy storage capacity soc:
2.2.1.1 when the residual capacity soc=60% of the off-grid energy storage system is greater than the lower limit value soc of the off-grid energy storage residual capacity l =30%, i.e. soc is greater than or equal to soc l In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes And the power instruction code for the micro-grid release is sent out to the grid-connected and grid-disconnected energy storage system when the grid disconnection occurs, wherein the power instruction code is 160 kW.
2.2.1.2 when the residual capacity soc=30% of the off-grid energy storage system is less than or equal to the lower limit value soc of the off-grid energy storage residual capacity l =30%, i.e. soc < soc l And when the micro-grid is in a power failure state, starting a protection program by the off-grid energy storage system.
2.2.2 total power of all power generating units zpow =300 kW, load demand power P baer =280 kW and the parallel-off-grid energy storage system charging absorption power p zes When the power consumption is within the range of-20 KW,
P fzes ＝P bear -P zpow +P zes =280 kW-300kW-20 kw= -40kW, at which time the future microgrid support power P fzes < 0, indicating the total output power p of the power generation unit due to load shedding of non-primary controllable load zpow =300 kW greater than the load demand power P baer =280 kW, whereby the future microgrid support power P fzes The = -40kW is the future off-grid moment and the off-grid energy storage system absorbs or removes excess power from the power generation unit.
At the moment, the measurement and control system reads the residual capacity soc of the off-grid energy storage system and analyzes the absorbed or released power of the off-grid energy storage system and the distribution of the generated power of the generating unit under different residual capacities:
2.2.2.1 when the residual capacity soc=70% of the off-grid energy storage system is smaller than the upper limit value soc of the off-grid energy storage residual capacity u =90%, i.e. soc < soc u In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes And (3) when off-grid occurs, the energy storage system which is connected with the grid in parallel sends out a power absorption instruction to the micro-grid.
2.2.2.2 when the residual capacity soc=90% of the off-grid energy storage system is greater than or equal to the upper limit value soc of the off-grid energy storage residual capacity u =90%, i.e. soc is greater than or equal to soc u At this time, the measurement and control system selects a part of non-main controllable load equipment, and the sum of the load power of the non-main controllable load equipment is smaller than or equal to the absolute value |P of the future micro-grid support power fzes Ban from decreasing, i.e. non-primary controllable load P nbear ≤|P fzes |＝40kW。
Wherein P is powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system at a future off-grid moment; p (P) fzes Supporting power for future micro-grids; the soc is the residual capacity of the off-grid energy storage system; soc u The upper limit residual capacity of the grid-connected and off-grid energy storage system; soc l The lower limit residual capacity of the grid-connected and off-grid energy storage system; i.epsilon.1, 2,3 … … n.
Claims (4)
1. The control method for the off-grid moment of the micro-grid is characterized by comprising the following steps of:
step 1, initializing
All controllable equipment of the district micro-grid comprises: in a related data input measurement and control system of a main controllable load, a non-main controllable load, a power generation unit and an off-grid energy storage system, performing attribute calibration and parameter setting, and determining the relative distance and position of each device by taking a transformer in a transformer area as an origin;
relevant data of all controllable devices of a district micro-grid of a measurement and control system are input, and the method comprises the following steps: the power of the load, the capacity and the power of the power generation unit, the input power and the output power of the off-grid energy storage system, and the upper limit and the lower limit of the capacity of the off-grid energy storage system and the residual capacity thereof;
calibrating the relative distance, position and line model of main load, non-main load, wind power, photovoltaic and other power generation units and the transformer in the transformer area by taking the transformer in the transformer area as an origin;
The measurement and control system receives the fault signal and the scheduling instruction of the upper level in real time, and downwardly reads the electric power parameters of the micro-grid and all equipment information; when the upper grid connection or fault information is received, according to the historical data of the previous moment, combining the power grid characteristics of each device of the current micro-grid, and controlling and guaranteeing the power grid quality of each device;
step 2, the measurement and control system reads all controllable equipment data of the platform in real time, calculates and analyzes the power of the micro-grid at off-grid time and off-grid energy storage system and power generation unit, and regulates and controls the power of the off-grid energy storage system and the power generation unit, and the method comprises the following steps:
(1) The measurement and control system reads all controllable equipment data of the platform area in real time, and the method comprises the following steps: and the off-grid energy storage system absorbs or releases power p zes A residual electric quantity soc; output voltage u of each power generation unit pow1 ,u pow2 …u pown Power p pow1 ,p pow2 ……p pown The method comprises the steps of carrying out a first treatment on the surface of the Power P of each non-main load point nbear1 ,P nbear2 ,……,P nbearn The method comprises the steps of carrying out a first treatment on the surface of the Power factor alpha of main load mbear1 ,α mbear2 ,……,α mbearn Voltage u mbear1 ,u mbear2 ,……,u mbearn And power P mbear1 ,P mbear2 ,……,P mbearn The method comprises the steps of carrying out a first treatment on the surface of the Transformer power P in transformer area B Current I B Sum voltage U B The method comprises the steps of carrying out a first treatment on the surface of the For calculating total power of all power generation units and all non-primaryTotal power of load:
total power of the power generation unit:
total power of non-main controllable load:
wherein P is nbear Total power for non-primary controllable loads; p (P) bear Total power for total controllable load; p (P) main Total power for the primary load; p is p inbear The power of the non-primary controllable load of the ith station; p (P) nbear1 ,P nbear2 ,……,P nbearn Non-primary controllable load powers of the 1 st to nth stations respectively; p is p zpow Is the total power of the power generation unit; p is p ipow I e (1, 2., n) for the i-th power generation unit power; u (u) pow1 ,u pow2 …u pown Output voltages of the power generation units of the 1 st to the n th stages respectively; p is p pow1 ,p pow2 ……p pown Output powers of the 1 st to nth power generation units, respectively; i B The low-voltage side current of the transformer in the transformer area is obtained; p (P) B The power of the low-voltage side of the transformer in the transformer area is calculated; u (U) B The low-voltage side voltage of the transformer in the transformer area is obtained; the soc is the residual capacity of the energy storage battery of the off-grid energy storage system; alpha mbear1 ,α mbear2 ,……,α mbearn Power factors of the 1 st to nth main loads respectively; u (u) mbear1 ,u mbear2 ,……,u mbearn The voltages of the 1 st to nth main loads respectively; p (P) mbear1 ,P mbear2 ,……,P mbearn The power of the main loads from the 1 st to the nth; an integer n is greater than or equal to 1;
(2) When the micro-grid is connected, the measurement and control system calculates and separates the power of the energy storage system and the power generation unit so as to control related equipment when the micro-grid is separated from the grid, and the method specifically comprises the following steps:
2.1 at grid-connected time, when the transformer low-voltage side current I of the transformer area B When less than 0; the flow direction is that the micro-grid supplies power to the grid, and the measurement and control system is communicatedTotal power p generated by all power generation units zpow And releasing or absorbing power p by off-grid energy storage system zes And transformer low-side power P B Calculating the power consumption P of all loads all Load demand power P in micro-grid at future off-grid moment bear Finally, the future micro-grid support power P is obtained fzes ；
2.1.1 when the micro grid support Power P is in the future fzes When the number of the groups is less than 0,
description of total output Power p of all generating units zpow Greater than the load demand power P bear Whereby future micro-grid support power P when off-grid occurs in the future fzes Absorbing or reducing redundant power of the power generation unit for the micro-grid to pass through and leave the grid energy storage system;
the measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.1.1.1 when the soc of the off-grid energy storage system is less than the soc u In the time, the measurement and control system predicts the future micro-grid support power P at off-grid time fzes When off-grid occurs, a power absorption instruction for the micro-grid is sent to the off-grid energy storage system;
2.1.1.2 when the soc of the grid-connected and off-grid energy storage system is more than or equal to the soc u When the system is in operation, the non-main controllable load is not reduced, and the measurement and control system is used for measuring and controlling the power P of the low-voltage side of the transformer in the network station B Total power p generated by all power generation units zpow Calculating the distribution coefficient mu of the power of each power generation unit zes By the power distribution coefficient mu of each generating unit zes And the output power P of each power generation unit powi Calculating to obtain the load shedding power P of each power generation unit zesi The method comprises the steps of carrying out a first treatment on the surface of the When the future off-grid occurs, the measurement and control system is used for measuring and controlling the load shedding power P of each power generation unit zesi Sending out a power output reducing instruction to each power generation unit;
2.2 Low-side Current I of transformer in transformer area at grid-connected time B When the temperature is more than or equal to 0;
the power grid supplies power to the micro-grid in the tide direction, so that the power generation units in the micro-grid and the parallel off-grid energy storage system cannot meet the load power consumption requirement, and the measurement and control system is based on the platformOutput power P of zone transformer B Total power p of all power generating units zpow And the off-grid energy storage system absorbs or releases power p zes Calculating all load consumption powers P respectively all Load demand power P at future off-grid time baer Finally obtaining the future micro-grid support power P of the predicted off-grid moment fzes ；
2.2.1 when the micro grid support Power P is in the future fzes When the temperature is more than or equal to 0,
description of the output Power p of the Power generating Unit zpow Less than the load demand power P baer The grid-connected and off-grid energy storage system is required to release power, and the power released by the grid-connected and off-grid energy storage system to the micro grid is the future micro grid support power P fzes ；
The measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.2.1.1 when the soc of the off-grid energy storage system is greater than or equal to the soc l In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes When off-grid occurs, the off-grid energy storage system is sent out to release power instruction codes for the micro-grid, so that the off-grid energy storage system releases power P for the micro-grid fzes ；
2.2.1.2 when the soc of the off-grid energy storage system is less than the soc l When the micro-grid is in a power failure state, the off-grid energy storage system starts a protection program;
2.2.2 when the micro grid support Power P is in the future fzes When less than 0;
description of total output Power p of all Power generating units after load shedding due to non-Primary controllable zpow Greater than the load demand power P baer Whereby the micro-grid supports power P in the future fzes Absorbing or reducing redundant power of the power generation unit for the off-grid time and the off-grid energy storage system in the future; at the moment, the measurement and control system reads the residual capacity soc of the off-grid energy storage system, analyzes the absorbed or released power of the off-grid energy storage system under different residual capacities, and distributes the power generated by the power generation unit:
2.2.2.1 when the soc of the off-grid energy storage system is less than the soc u When off-grid occurs, the measurement and control system predicts the future off-grid moment according to the predictionMicro grid support power P fzes The parallel-to-off-grid energy storage system sends out a power absorption instruction to the micro-grid, so that the parallel-to-off-grid energy storage system absorbs power P to the micro-grid fzes ；
2.2.2.2 when the soc of the off-grid energy storage system is greater than or equal to the soc u When the measurement and control system selects part of non-main controllable load equipment, the sum of the load power of the non-main controllable load equipment is smaller than or equal to the absolute value |P of the future micro-grid support power fzes Ban subtract cut;
wherein, the soc u The upper limit value of the residual capacity of the energy storage is the off-grid energy storage; soc l The lower limit value of the residual capacity of the grid-connected and off-grid energy storage system; the soc is the residual capacity of the off-grid energy storage system; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi The reduced output power value for each power generation unit; p (P) powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; i is 1,2,3 … … n, n is more than or equal to 1 and is an integer;
step 3, governance after off-grid of the micro-grid occurs, and the method is as follows:
when the micro-grid continuously runs off-grid, the micro-grid is changed from grid connection to off-grid, the non-main load is reduced, the output power of the power generation unit is adjusted, the active power and the reactive power of the micro-grid are changed, and the power factor alpha at a certain load point beari Less than or equal to the lower limit value alpha of the power factor l I.e. alpha beari ≤α l When accompanied by a voltage u beari The power grid quality is seriously in an out-of-standard state when the power grid is out of limit up and down; when the measurement and control system reads a certain load point voltage u beari Less than or equal to the lower voltage limit U lgb (1+β%), i.e. u beari ≤U lgb When (1+beta%) the measurement and control system passes through the power factor alpha of every point in the micro-grid beari And the voltage u corresponding to the point beari Product calculation, when alpha beari ·u beari The smaller the product value of (2) is, the relatively poorer the network quality at the point is, so that alpha is passed beari ·u beari The product can directly measure the quality of each load point in the micro-gridInferior;
similarly, when the measurement and control system reads a certain load point voltage u beari Greater than or equal to the upper voltage limit U ugb (1-beta%), i.e. u beari ≥U ugb (1-beta%) by the power factor alpha at each point in the microgrid beari And the voltage u corresponding to the point beari Calculating the ratio whenThe smaller the product value of (2) the worse the network quality at that point, so that by +.>The quality of each load point in the micro-grid is directly measured according to the ratio and the load power factor alpha of the adjacent load points beari Calculating the compensation reactive power Q beari The power and reactive power output is changed through the power generation unit or the power is absorbed by the off-grid energy storage system to compensate the utility ratio of the micro-grid;
wherein U is lgb Is the lower voltage standard value; u (U) ugb Is the upper voltage standard value; alpha l Is the lower limit value of the power factor; beta.epsilon.1, 2,3 … … 10; alpha bear1 ,α bear2 ……α bearn The power factor is the power factor corresponding to the controllable load points 1-n; u (u) bear1 ,u bear2 ,……,u bearn The voltage is the voltage corresponding to the controllable load points 1-n; u (u) beari Is the i-th point load voltage; q (Q) beari Is reactive power; u (u) pow1 ,u pow2 …u pown Output voltages corresponding to the power generation units 1 to n; i.epsilon.1, 2,3 … … n; n is more than or equal to 1;
step 4, three-phase unbalance treatment method comprises the following steps of
Because a large number of single-phase loads and partial power generation units exist in the micro-grid lines, the load of each line and the synchronous rate of the power generation units are different, and when the micro-grid is off-grid, the load is not reduced by the main controllable load, so that the three-phase unbalance of the lines is easily caused; according to the initialized positioning, the measurement and control system respectively finds out the relative terminal equipment of the three-phase power grid, reads the related data and analyzes each single-phase powerPressure U as 、U bs 、U cs For each phase voltage, sort the sort (U) by high, medium and low as ,U bs ,U cs ) Calculating the difference between the high voltage and the low voltage, and converting the voltage difference DeltaU m And a voltage difference allowable threshold U mδ Comparing, and performing corresponding control according to different comparison results;
and 5, when the micro-grid is off-grid, the measurement and control system regulates and controls the power of the grid-connected and off-grid energy storage system and the power generation unit at the moment of grid connection of the micro-grid and inputs the power into the grid-connected and off-grid energy storage system and the power generation unit under non-main load operation, and the method comprises the following steps of:
the measurement and control system receives the superior dispatching instruction and monitors the state of the large power grid in real time, when the micro power grid is allowed to be connected, the measurement and control system is started and is separated from the grid energy storage system to conduct grid synchronous regulation and control, and meanwhile, the measurement and control system carries out grid connection work flow according to the current micro power grid off-grid state:
(1) After the synchronous closing of the power grid is successful, converting the off-grid energy storage system into a current source mode from a voltage source mode, and performing self-adaptive charge and discharge control on the off-grid energy storage system according to the current state of the residual electric quantity soc;
(2) In order to prevent the quality mutation of the micro-grid, the non-main load is recovered in sequence from small to large according to the off-grid load shedding non-main load condition;
(3) In order to prevent the quality mutation of the micro-grid, the power generation units are sequentially and time-sharing recovered to generate power normally according to the power generation current condition of the power generation units during off-grid.
2. The method for controlling the off-grid time of the micro-grid according to claim 1, wherein in the step 2, (2) the power of the off-grid energy storage system and the power generation unit is calculated and off-grid when the micro-grid is connected, so that the measurement and control system controls the related equipment when the micro-grid is off-grid, specifically as follows:
2.1 when the transformer is in the transformer area, the low-voltage side current I B When < 0:
the tide direction is the power supply of the micro-grid to the power grid, and the measurement and control system generates the total power p through all the power generation units zpow Releasing or absorbing power p with and from an energy storage system zes Summing and transforming with the transformer areaLow side power P of the device B And the difference value is calculated to obtain the power consumption P of all loads all I.e. P all ＝P zpow +P zes -P B The method comprises the steps of carrying out a first treatment on the surface of the Because the main load work is ensured during off-grid operation, the energy output of the micro-grid is reduced by the load-reducing non-main controllable load, and the load demand power P in the micro-grid at the future off-grid moment is obtained by subtracting the non-main controllable load from the power consumption of all loads bear ＝P all -P nbear The method comprises the steps of carrying out a first treatment on the surface of the Due to load demand power P at a future off-grid time bear Power is supplied by the power generation unit and the parallel off-grid energy storage system, and the future micro-grid supports power P fzes To predict load demand power P in micro-grid at off-grid time bear Total power p generated by all power generation units zpow The difference and the parallel-to-off-grid energy storage system absorb or release power P zes And, P fzes ＝P bear -P zpow +P zes ；
2.1.1 when the micro grid support Power P is in the future fzes When less than 0, the total power p output by all the power generation units is described zpow Greater than the load demand power P bear Whereby the future microgrid support power P when a future off-grid occurs fzes Absorbing or reducing redundant power of the power generation unit for the micro-grid to pass through and leave the grid energy storage system;
therefore, considering the residual capacity soc condition of the off-grid energy storage system, the measurement and control system analyzes the off-grid energy storage residual capacity soc as follows:
2.1.1.1 when the residual capacity soc of the off-grid energy storage system is less than the upper limit value soc of the residual energy storage capacity u I.e. soc < soc u In the time, the measurement and control system predicts the future micro-grid support power P at off-grid time fzes When off-grid occurs, a power absorption instruction for the micro-grid is sent to the off-grid energy storage system;
2.1.1.2 when the residual capacity soc of the parallel-to-off-grid energy storage system is greater than or equal to the upper limit value soc of the residual energy storage capacity u I.e. soc is greater than or equal to soc u When the load is not reduced, the load is not mainly controlled, and the measurement and control system is used for measuring and controlling the power P at the low-voltage side of the transformer in the network station B Total power p generated by all power generation units zpow The ratio of the components is that,obtaining the power P of each power generation unit powi Distribution coefficient mu zes I.e.And then the power distribution coefficient mu of each power generation unit zes With the output power P of each power generation unit powi To obtain the load-shedding power P of each power generation unit zesi I.e. P zesi ＝μ zes ·P powi The measurement and control system is used for measuring and controlling the load shedding power P of each power generation unit when the off-grid occurs in the future zesi Sending out a power output reducing instruction to each power generation unit;
wherein P is bear The power is required for the load in the micro-grid at the future off-grid moment; p (P) all Power is consumed to obtain all loads; p is p zpow Generating total power for all the power generation units; p (P) zes Releasing or absorbing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; p (P) B The power of the low-voltage side of the transformer in the transformer area is calculated; i B The low-voltage side current of the transformer in the transformer area is obtained; u (U) B The low-voltage side voltage of the transformer in the transformer area is obtained; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi Load shedding power for each power generation unit; p (P) powi Outputting power for each power generation unit; the soc is the residual capacity of the off-grid energy storage system; soc u The upper limit residual capacity of the grid-connected and off-grid energy storage system; i is an integer of 1,2,3 and … … n, n is more than or equal to 1;
2.2 Low-side Current I of transformer in transformer area at grid-connected time B And (3) when the temperature is equal to or higher than 0:
the power flow direction is supplied to the micro-grid by the power grid, which indicates that the power generation units in the micro-grid and the parallel-off-grid energy storage system can not meet the load power demand, and the measurement and control system measures and controls the output power P of the transformer in the transformer area B Total power p to all power generation units zpow Absorbing or releasing power p with and from an on-grid energy storage system zes Summing, calculating to obtain all load consumption power P all I.e. P all ＝P B +P zpow +P zes Since the micro-grid ensures the main load work during off-grid operation, the non-main controllable load P is reduced nbear Reducing the energy output of the micro-grid, so that the total load power P all Subtracting the non-main controllable load to obtain the load demand power P at the future off-grid moment baer ，P bear ＝P all -P nbear The method comprises the steps of carrying out a first treatment on the surface of the Due to load demand power P at a future off-grid time baer The power is supplied by the power generation unit and the parallel off-grid energy storage system, so that the load demand power P at the future off-grid moment is reduced baer And the total power p of the power generation unit zpow Calculating the difference value, and absorbing or releasing power P by the difference value and the off-grid energy storage system zes Summing to obtain the future micro-grid support power P of the predicted off-grid moment fzes I.e. P fzes ＝P baer -P zpow +P zes ；
2.2.1 when the micro grid support Power P is in the future fzes ≥0
Description of total output power p of all generating units zpow Less than the load demand power P baer The grid-connected and off-grid energy storage system is required to release power, so that the micro-grid support power P in the future fzes The power released by the off-grid energy storage system to the micro-grid when off-grid occurs; meanwhile, the measurement and control system analyzes the residual energy storage capacity soc of the off-grid energy storage system:
2.2.1.1 when the residual capacity soc of the off-grid energy storage system is greater than or equal to the lower limit value soc of the off-grid energy storage residual capacity l I.e. soc is greater than or equal to soc l In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes When off-grid occurs, a power release instruction for the micro-grid is sent to the off-grid energy storage system;
2.2.1.2 when the residual capacity soc of the off-grid energy storage system is smaller than the lower limit value soc of the off-grid energy storage residual capacity l I.e. soc < soc l When the micro-grid is in a power failure state, the off-grid energy storage system starts a protection program;
2.2.2 when the micro grid support Power P is in the future fzes < 0, indicating that after the load is relieved due to non-main controllable load, the total power p is output by all power generation units zpow Greater than the load demand power P baer Whereby the micro-grid supports power P in the future fzes Absorbing or reducing redundant power of the power generation unit for the off-grid time and the off-grid energy storage system in the future;
at the moment, the measurement and control system reads the residual capacity soc of the off-grid energy storage system, analyzes the absorbed or released power of the off-grid energy storage system under different residual capacities, and distributes the power generated by the power generation unit:
2.2.2.1 when the residual capacity soc of the off-grid energy storage system is smaller than the upper limit value soc of the off-grid energy storage residual capacity u I.e. soc < soc u In the time, the measurement and control system predicts future micro-grid support power P at off-grid moment fzes When off-grid occurs, a power absorption instruction for the micro-grid is sent to the off-grid energy storage system;
2.2.2.2 when the residual capacity soc of the off-grid energy storage system is greater than or equal to the upper limit value soc of the off-grid energy storage residual capacity u I.e. soc is greater than or equal to soc u At this time, the measurement and control system selects a part of non-main controllable load equipment, and the sum of the load power of the non-main controllable load equipment is smaller than or equal to the absolute value |P of the future micro-grid support power fzes Ban from decreasing, i.e. non-primary controllable load P nbear ≤|P fzes |；
Wherein, the soc u The upper limit value of the residual capacity of the energy storage is the off-grid energy storage; soc l The lower limit value of the residual capacity of the grid-connected and off-grid energy storage system; the soc is the residual capacity of the off-grid energy storage system; mu (mu) zes Distributing coefficients for the power of each power generation unit; p (P) zesi The reduced output power value for each power generation unit; p (P) powi Outputting power for each power generation unit; p (P) zes Absorbing or releasing power for the off-grid energy storage system; p (P) fzes Supporting power for future micro-grids; i is 1,2,3 … … n, n is more than or equal to 1 and is an integer.
3. The specific method for controlling the off-grid time of the micro-grid according to claim 1, wherein the step 3 is characterized in that the method for controlling the off-grid micro-grid comprises the following steps:
the measurement and control system reads the output voltage u of each power generation unit in real time pow1 ,u pow2 …u pown Power p pow1 ,p pow2 ……p pown And each ofPower factor alpha of controllable load point bear1 ,α bear2 ……α bearn Voltage u bear1 ,u bear2 ,……,u bearn The method comprises the steps of carrying out a first treatment on the surface of the And calculates the power factor alpha beari And the voltage u corresponding to the point beari The product, or the power factor alpha, is calculated beari And the voltage u corresponding to the point beari The ratio is sorted from small to large by a sorting function sort, and the lower limit value alpha of the relative power factor is screened out l The voltage is greater than or equal to the upper limit U beari ≥U ugb (1-beta%) or less of the lower limit U beari ≤U lgb (1+β%) load point, where β e (1, 2,3 … … 10), namely:
sort([α bear1 ·u bear1 ,α bear2 ·u bear2 ,……,α bearn ·u bearn ])
or (b)The measurement and control system determines the priority control sequence and positioning of the load according to the sequence, and the method comprises the steps of determining the positioning of the power generation unit with the nearest relative distance according to the controlled load positioning by the smallest, next smallest and third smallest and so on;
The measurement and control system sequentially reads the output power P of the corresponding power generation units according to the priority control sequence and positioning of the load points powi And is matched with rated lower limit output power P of the power generation unit lpow Comparison, treatment was performed by the following steps:
(1) When judging a certain power generation unit P powi ≥P lpow When the load point load power factor alpha is measured and controlled by the measurement and control system according to the load point load power factor alpha adjacent to the measurement and control system beari Calculate the compensation reactive power Q beari ，U when the load point voltage beari ≤U lgb (1+beta%) and the measurement and control system is based on reactive power Q beari The power generation units corresponding to the load priority control sequence and the positioning control in turn send out a command for compensating reactive power output;
when the load point voltageU beari ≥U ugb When (1-beta%), the measurement and control system is based on reactive power Q beari The power generation units corresponding to the load priority control sequence and the positioning control in turn send out instructions for compensating reactive power output and reducing active power output;
(2) When only one group of power generation units exist in 2 or more load point lines, the measurement and control system reads the load power factor value which is closest to the power generation units in relative distance, and controls the power generation units to output compensation reactive power;
(3) When judging a certain power generation unit P powi ＜P lpow When the power generation unit cannot provide reactive power output, the measurement and control system selects the power which is closest to the power generation unit and has the output power of more than or equal to P powi Rated lower limit output power P lpow The reactive power output is compensated by the power factor of the load position which is closest to the grid energy storage system;
wherein U is lgb Is the lower voltage standard value; u (U) ugb Is the upper voltage standard value; alpha l Is the lower limit value of the power factor; beta.epsilon.1, 2,3 … … 10; alpha bear1 ,α bear2 ……α bearn The power factor is the power factor corresponding to 1-n controllable load points; u (u) bear1 ,u bear2 ,……,u bearn The voltage is corresponding to 1-n controllable load points; u (u) beari Is the i-th point load voltage; q (Q) beari Is reactive power; p (P) powi Outputting power for each generating unit, i epsilon 1,2,3 … … n; u (u) pow1 ,u pow2 …u pown Outputting voltages for the corresponding 1-n power generation units; p is p pow1 ,p pow2 ……p pown Output power of the corresponding 1-n power generation units; p (P) lpow Is rated lower limit output power; n is more than or equal to 1.
4. The method for controlling the off-grid time of the micro-grid according to claim 1, wherein in the step 4, the three-phase imbalance treatment method is as follows:
while managing the micro-grid, the measurement and control system performs measurement and control by voltage sequencing sort (U as ,U bs ,U cs ) Separate screenSelect the highest voltage U max Minimum voltage U min And the next highest voltage U med And will have the highest voltage U max And the lowest voltage U min Performing difference calculation to obtain a high-low voltage difference delta U m ＝U max -U min And the difference delta U between the high voltage and the low voltage m Allowable threshold value U of voltage difference mδ Comparison is performed:
(1) When the measurement and control system judges the difference delta U between the high voltage and the low voltage m Greater than or equal to the voltage difference allowable threshold U mδ I.e. DeltaU m ≥U mδ When the highest voltage U is obtained max And the lowest voltage U min Averaging voltage U aver I.e.And will average voltage U aver And the next highest voltage U med Performing difference calculation, i.e. DeltaU med ＝U avre -U med ；
1.1 when the measurement and control system judges the average voltage U aver And the next highest voltage U med The difference is greater than zero DeltaU med When > 0, it is the highest voltage U max The deviation is large; the measurement and control system outputs the highest voltage U max And the next highest voltage U med Calculating the difference value to obtain a difference value delta U of high, medium and low voltages abcδ ＝U max -U med The method comprises the steps of carrying out a first treatment on the surface of the Because each phase of the parallel-to-off-grid energy storage system has the capability of independent control, the measurement and control system releases or absorbs the power P to the highest-voltage phase line according to the current parallel-to-off-grid energy storage system zes And the highest voltage U max And a difference DeltaU between high, medium and low voltages abcδ The ratio of (2) is subjected to product calculation,obtaining the power value delta P absorbed by the parallel-off-grid energy storage system on the basis of the original power of the highest voltage phase line zes Whereby the measurement and control system is based on the absorbed power value DeltaP zes Sending an absorbed power instruction to the off-grid energy storage system;
1.2 when the measurement and control system judges the average voltage U aver And the next highest voltage U med The difference is smallAt zero DeltaU med When less than 0, the voltage is the minimum voltage U min The deviation is large; the measurement and control system calculates the next highest voltage U med And the lowest voltage U min To obtain the difference delta U of high, medium and low voltages abcδ ＝U med -U min The method comprises the steps of carrying out a first treatment on the surface of the Because each phase of the parallel-to-off-grid energy storage system has the capability of independent control, the measurement and control system releases or absorbs the power P to the lowest voltage phase line according to the current parallel-to-off-grid energy storage system zes And the lowest pressure U min And a difference DeltaU between high, medium and low voltages abcδ The ratio of (2) is subjected to product calculation,obtaining the release power value delta P increased by the off-grid energy storage system on the lowest voltage phase line zes Whereby the measurement and control system is based on the increased release power value ΔP zes Sending a released power instruction to the off-grid energy storage system;
2.2 when the measurement and control system judges the difference delta U between the high voltage and the low voltage m Less than the voltage difference allowable threshold U mδ When the micro-grid power control system is used, the measurement and control system maintains the current power value absorbed or released, and sends an absorbed or released power instruction to the off-grid energy storage system, so that the three-phase balance of the micro-grid is ensured;
wherein: u (U) as Outputting voltage for phase A of the opposite end equipment of the three-phase power grid; u (U) bs Outputting voltage for B phase of opposite terminal equipment of the three-phase power grid; u (U) cs Outputting voltage for C phase of the opposite end equipment of the three-phase power grid; u (U) aver The average voltage of the highest voltage and the lowest voltage of the three-phase power grid relative to the terminal equipment; deltaU m Is the difference between the high voltage and the low voltage; u (U) mδ A voltage difference enable threshold; u (U) max The highest voltage of the three-phase power grid relative to the terminal equipment; u (U) min The lowest voltage of the three-phase power grid relative to the end equipment; u (U) med The next highest voltage for the opposite end device of the three-phase network; deltaU abcδ Is the difference value of high, medium and low voltages; ΔP zes Adding an absorbed or released power value for the measurement and control system; sort is the ranking function.
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