CN110460052B - Photovoltaic inversion control method capable of improving power quality of power distribution network - Google Patents
Photovoltaic inversion control method capable of improving power quality of power distribution network 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
- H02J3/01—Arrangements for reducing harmonics or ripples
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- 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
- Y02E40/40—Arrangements for reducing harmonics
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E70/00—Other energy conversion or management systems reducing GHG emissions
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Abstract
The invention relates to a photovoltaic inversion control method capable of improving the power quality of a power distribution network, which is technically characterized by comprising the following steps of: the method comprises the following steps: step 1, a first control state of independent filtering control: when a nonlinear load is started on the user side, a load side sensor detects voltage and current, and THD is calculated in real time through an instantaneous reactive power method u Harmonic current, when the load side THD u When the voltage is higher than the limit value and lasts for N power frequency periods, calculating compensation current according to the residual capacity of the photovoltaic grid-connected inverter, and filtering harmonic waves; step 2, a second control state of multi-inverter linkage filtering control: when the load side sensor detects THD u When the power frequency is lower than the limit value and N power frequency periods are continued, the inverter stops the first control state, after the energy storage module is charged, the inverter can enter the second control state, and the inverters are linked to compensate the power grid harmonic waves. The invention can reduce the cost of improving the electric energy quality and ensure the user benefit.
Description
Technical Field
The invention belongs to the technical field, relates to an intelligent soft switching voltage control method of an active power distribution network, and particularly relates to a photovoltaic inversion control method capable of improving the power quality of the power distribution network.
Background
With the continuous development of photovoltaic power generation technology, the cost of photovoltaic power generation is gradually reduced. The new energy grid-connected subsidy policy is continuously perfected, so that the development of the whole industry is further promoted. At present, distributed photovoltaic power generation is already carried into thousands of households, and a user can install a set of solar power generation system on the roof of the household, so that benefits are obtained through selling electricity. However, with the use of a large number of power electronics by the user, a large number of harmonic injections may result, which not only reduces the power factor, but may also be subject to fines when the harmonic distortion rate exceeds a limit.
The general photovoltaic grid-connected inverter is provided with a passive filter device, but when a user uses a large amount of nonlinear loads, the filter effect is difficult to meet the requirement, and harmonic waves are caused to enter a power grid to pollute the power grid. The harmonic wave of the power grid can affect the misoperation of a protective element, a relay and an automatic system device in an electric circuit, and an electric measuring instrument is inaccurate and even can cause serious electric accidents. The harm of the power harmonic wave is reflected on the aspects of our life, and the power harmonic wave affects the power transmission system, the power protection device, the household appliances and the communication equipment, and the harmonic wave has serious influence on our life. Passive filters cannot dynamically compensate for harmonic currents, and active filters can compensate for harmonics that vary in size and frequency, but are expensive.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a photovoltaic inversion control method capable of improving the power quality of a power distribution network, solves the technical problem of insufficient harmonic compensation capability of a single inverter, can fully utilize the residual capacity of each photovoltaic grid-connected inverter through linkage control of a plurality of inverters, reduces the cost for improving the power quality, and ensures the benefit of users.
The invention solves the practical problems by adopting the following technical scheme:
a photovoltaic inversion control method capable of improving the power quality of a power distribution network comprises a first control state and a second control state, and specifically comprises the following steps:
The specific method of the step 1 is as follows:
the load side sensor detects voltage and current in real time and is realized by an instantaneous reactive power methodTime of day THD calculation u THD when user enables nonlinear load u Ascending; when the load side THD u Above the limit and for N power frequency cycles, the sensor sends harmonic current and THD to the inverter u Simultaneously delivering THD to a solar controller u And stopping charging the energy storage module, and verifying THD by the inverter u If the current is higher than the limit value, entering a first control state if the current exceeds the limit value, calculating the residual capacity by the inverter, adding load harmonic current into the instruction current according to the residual capacity, and filtering out harmonic waves.
The specific method of the step 2 is as follows: when the load side sensor detects THD u After being lower than the limit value and lasting N power frequency periods, THD is respectively sent to the inverter, the solar controller and the TTU u Information;
the inverter receives THD u After the information, THD is checked u Whether the first control state is overrun or not, and stopping the first control state if the first control state is not overrun;
the solar controller receives THD u After information, the solar controller detects the state of the photovoltaic panel, when the generated energy of the photovoltaic panel is larger than grid-connected power, the energy storage module is charged, when the voltage of the battery rises to a certain degree, or the sensor transmits THD to the solar controller u When the voltage is larger than the limit value, namely the inverter enters a first control state, stopping charging; after the charging is finished, the solar controller transmits a control signal to the TTU, and the TTU simultaneously receives the THD of the load side u After the information and the solar controller instruction, TTU judges THD u If the total power consumption is smaller than the limit value, calculating the THD of the power grid side u When the grid side THD u When the power frequency exceeds the limit and lasts for N power frequency periods, the TTU inquires the corresponding inverter, the inverter enters a second control state, the inverter transmits residual capacity to the TTU, the TTU data acquisition and processing module acquires data on the power distribution network side, the data acquisition and processing module acquires harmonic current of the power grid and compensation coefficients of the inverters after analysis and processing, the harmonic current and the compensation coefficients of the inverters are transmitted to the corresponding inverter through the transmitter, then the inverters are linked to compensate harmonic waves on the power grid side, and when the load side sensor detects THD u When the power frequency exceeds the limit value and lasts for N power frequency periods, the corresponding inverter exits the second control state and enters the first control stateAnd (3) rejecting TTU access.
Moreover, THD of the step 1 u The calculation formula of (2) is as follows:
U n effective values of all harmonic voltages not greater than a certain order H, U 1 As the effective value of the fundamental wave voltage component, the harmonic wave voltage can be obtained by an instantaneous reactive power ip-iq method;
the remaining capacity of the photovoltaic grid-connected inverter in the step 1 can be obtained according to the rated power and the grid-connected power of the inverter:
P ri ＝(P i -P ei )*95％
in the above, P ri For the remaining capacity of the ith inverter, P i Rated power of the ith inverter, P ei The grid-connected power of the ith inverter;
and is obtainable according to the formula:
I ri ＝(I i -I ei )*95％
in the above, I i To calculate the maximum allowable current according to the rated capacity of the ith inverter, I ei Is the grid-connected current of the ith inverter, I ri And compensating the current for the permission of the ith inverter.
When the load side THD u Above the limit and for N power frequency cycles, the sensor sends a harmonic current I to the inverter refi To prevent the compensation current from exceeding the limit, the cut-off current is processed according to the following steps:
The proportion calculation method of the inverter compensation harmonic current in the step 2 is as follows:
harmonic power of the power grid is P s ，P r total For the total remaining capacity of the inverter operating in the second control state, P rj For the remaining capacity of the jth inverter operating in the second control state, when P r total ≥P s When (1):
when P r total ＜P s When (1):
the compensation ratio obtained by the method is K j Compensation current of each inverter:
I ref is the harmonic current of the power grid side, I rj For the maximum allowable compensation current of each inverter entering the second control state,
the current is compensated for harmonics of each inverter in the second control state.
When PV (photovoltaic) j+1 When receiving the instruction for entering the second control state, the TTU controller recalculates the compensation proportion K j+1 After finishing the setting, the TTU controller sends new compensation commands to all inverters, and j+1 machines compensate according to the new setting proportion.
The invention has the advantages and beneficial effects that:
1. the invention preferentially meets the requirements of the user side, and the harmonic wave generated by the user side is preferentially compensated by utilizing the residual capacity of the photovoltaic grid-connected inverter, so that the safe use of the electric appliance is ensured; when the user side energy storage module is full, the voltage harmonic distortion rate of the power grid side is judged, and the scale factors are distributed according to the residual capacity of different inverters, so that the electric energy quality of the power grid is treated, and the method has huge social benefits. When the photovoltaic panel does not work at night, the inverter is powered by the energy storage module, and the inverter can still work in the first working state and the second working state. The system is close to a sensor network of a user, the acquired data is more accurate, the TTU monitors the operation condition of the distribution transformer in real time, the acquired information can be transmitted to a main station and each photovoltaic grid-connected inverter, and the data required by the operation control and management of the distribution system are provided. The TTU has the functions of data acquisition and control, and also has a powerful communication function, the TTU can communicate with the power distribution substation or the main station on the pair, report real-time information acquired by the terminal, simultaneously receive various control commands issued by the substation/main station, and can communicate with intelligent devices such as a nearby sensor, an inverter and the like on the pair, and the requirements of an automatic system of the distribution network can be met no matter the communication mode, the communication protocol and the communication interface. The effective communication and sensor distribution ensure the electricity quality of users, and the harmonic wave of the power grid is compensated by fully utilizing a plurality of inverter networks, so that the social benefit is remarkable and the future development prospect is wide.
2. The invention requires a key parameter detection for inverter control, and the harmonic current and harmonic voltage are calculated compensation current and THD u The harmonic current and harmonic voltage are obtained by an instantaneous reactive power ip-iq method. The invention does not need to calculate the power, only needs to carry out coordinate transformation processing on the current signal, directly obtains the corresponding harmonic current signal, reduces the signal acquisition amount and the data calculation amount, has simple realization, small delay and good real-time performance, and is widely used for real-time monitoring of the harmonic wave.
3. According to the invention, the residual capacity of the photovoltaic grid-connected inverter is utilized, and when a user uses a nonlinear load to generate a large number of harmonic waves, the harmonic waves generated by the user are filtered out in a full-power manner; when the voltage harmonic distortion rate at the user side is lower than the limit value, the distributed sensor, the TTU and the solar controller are used for controlling the voltage harmonic distortion rate at the user side together, the inverters are used for compensating the harmonic current of the power grid in a linkage mode, and the control method can obtain huge social benefits as the photovoltaic power generation goes into thousands of households.
Drawings
FIG. 1 is a logic control diagram of the present invention;
FIG. 2 is a system block diagram of the photovoltaic power generation of the present invention;
FIG. 3 is a schematic diagram of the instantaneous reactive power ip-iq of the present invention;
FIG. 4 is a block diagram of a harmonic current compensation system according to the present invention;
FIG. 5 is a block diagram of a multiple inverter coordinated control of the present invention;
FIG. 6 is a block diagram of a modular design of a sensor node of the present invention;
fig. 7 is a block diagram of a TTU communication module of the present invention.
Detailed Description
Embodiments of the invention are described in further detail below with reference to the attached drawing figures:
a photovoltaic inversion control method capable of improving the power quality of a power distribution network, as shown in figure 1, comprises a first control state and a second control state, and specifically comprises the following steps:
in this embodiment, the specific method of the first control state of the independent filtering control in step 1 is: the load side sensor detects voltage and current in real time, and THD is calculated in real time through an instantaneous reactive power method u (Voltage harmonic distortion Rate), THD when nonlinear load is enabled on user side u Ascending toThe method comprises the steps of carrying out a first treatment on the surface of the THD at 380V nominal grid voltage according to the specification of national standard GB/T14549-1993 u Less than 5% when the load side THD u Above the limit and for N power frequency cycles, the sensor sends harmonic current and THD to the inverter u Simultaneously delivering THD to a solar controller u (stopping charging of the energy storage module), the inverter verifies THD u If the harmonic current is higher than the limit value, the inverter enters a first working state if the harmonic current exceeds the limit value, the inverter calculates the residual capacity, load harmonic current is added into the command current according to the residual capacity, and under the condition that the inverter is ensured to be normally connected with the grid, harmonic waves are filtered out, so that impact of a nonlinear load on a power grid is reduced.
In this embodiment, the specific method for the second control state of the multi-inverter linkage filtering control in step 2 is as follows: when the load side sensor detects THD u After the (voltage harmonic distortion rate) is lower than the limit value and lasts for N power frequency periods, THD is respectively sent to the inverter, the solar controller and the TTU u Information, THD is received by the inverter u After the information, THD is checked u Whether the first control state is overrun or not, and stopping the first control state if the first control state is not overrun; the solar controller receives THD u After information, the solar controller detects the state of the photovoltaic panel, when the generated energy of the photovoltaic panel is larger than grid-connected power, the energy storage module is charged, when the voltage of the battery rises to a certain degree, or the sensor transmits THD to the solar controller u When the voltage is larger than the limit value, namely the inverter enters a first control state, stopping charging; after the charging is finished, the solar controller transmits a control signal to the TTU, and the TTU simultaneously receives the THD of the load side u After information and a solar controller instruction (ensuring the charging of an energy storage module), TTU judges THD u If the total power consumption is smaller than the limit value, calculating the THD of the power grid side u When the grid side THD u When the power frequency exceeds the limit and lasts for N power frequency periods, the TTU inquires the corresponding inverter, the inverter enters a second control state, the inverter transmits residual capacity to the TTU, the TTU data acquisition and processing module acquires data on the power distribution network side, the data are analyzed and processed to obtain the harmonic current of the power grid and the coefficient of each inverter for compensating the harmonic current, the coefficient is transmitted to the corresponding inverter through the transmitter, then the inverters are linked to compensate the harmonic wave on the power grid side, and when the THD is detected by the load side sensor u When the limit value is exceeded and N power frequency periods are continued, the corresponding inverter exits the second control state and enters the first control state, and TTU access is refused.
In the present embodiment, both the first control state and the second control state require THD calculation u (sensor calculates load side THD u TTU calculates grid side THD u ) And the remaining capacity P of the inverter r The second control state requires calculating the proportion of the compensation harmonic wave of each inverter, and the specific method is as follows:
THD according to the circuit principle u Is calculated according to the formula:
U n effective values of all harmonic voltages not greater than a certain order H, U 1 As the effective value of the fundamental wave voltage component, the harmonic wave voltage can be obtained by an instantaneous reactive power ip-iq method;
the residual power of the photovoltaic grid-connected inverter can be obtained according to the rated power and the grid-connected power of the inverter:
P ri ＝(P i -P ei )*95％ (2)
P ri for the remaining capacity of the ith inverter, P i Rated power of the ith inverter, P ei And reserving five percent of power margin for the grid-connected power of the ith inverter to prevent the overload operation of the inverter, and protecting the inverter.
From equation (2):
I ri ＝(I i -I ei )*95％ (3)
I i to calculate the maximum allowable current according to the rated capacity of the ith inverter, I ei Is the grid-connected current of the ith inverter, I ri And compensating the current for the permission of the ith inverter.
When the load side THD u Above the limit and for N power frequency cycles, the sensor sends a harmonic current I to the inverter refi To prevent the compensation current from exceeding the limit, the cut-off current is processed according to the following steps:
The second control state is calculated according to the compensation ratio of each inverter as follows:
harmonic power of the power grid is P s ，P r total For the total remaining capacity of the inverter operating in the second control state, P rj For the remaining capacity of the jth inverter operating in the second control state, when P r total ≥P s When (1):
when P r total ＜P s When (1):
P r total ≥P s In the time-course of which the first and second contact surfaces,
therefore, the residual capacity of each inverter can be fully utilized to filter out harmonic waves, but the harmonic waves of the power grid cannot be comprehensively treated; p (P) r total ＜P s When the residual capacity of each inverter is not fully utilized, the compensation current is distributed in each inverter in proportion, the purpose of more compensation of the inverter with more residual capacity and less compensation of the inverter with less residual capacity can be achieved, and simultaneously under the coordination control of an upper-layer controller, the THD (total heat transfer) of the actual load side and the power grid side can be realized u The working state is automatically converted, the requirement of compensating harmonic wave of a user is preferably met, the control of the harmonic wave of the power grid is assisted as much as possible, and huge social benefit is achieved.
The compensation ratio obtained by the formulas (6) and (7) is K j Compensation current of each inverter:
I ref is the harmonic current of the power grid side, I rj For the maximum allowable compensation current of each inverter entering the second control state,
the current is compensated for harmonics of each inverter in the second control state.
When PV (photovoltaic) j+1 When the (j+1th inverter) receives the instruction for entering the second control state, the TTU controller recalculates the compensation proportion K j+1 After finishing setting, TTU controller sends new compensation command to all inverters, j+1 simultaneously (synchronous signal can be u) a The next cycle zero crossing point) is compensated according to the new set proportion.
In this embodiment, the second control state, i.e., the multi-inverter linkage control, is not limited to the linkage compensation of the harmonic wave on the grid side, but may be linked to the user who compensates the harmonic wave seriously and is not enough to compensate the harmonic wave depending on the remaining capacity of the own inverter. Under the condition that the grid-connected inverter is not provided with an energy storage module, the grid-connected inverter can still work under the first and second controlAnd in a state, the grid-connected inverter does not work at night. And under the condition that the grid-connected inverter is provided with an energy storage module, when the photovoltaic panel does not work at night, the energy storage module serves as an energy source of the photovoltaic grid-connected inverter, and the inverter works according to the first working state and the second working state. When the load side THD u When the current is greater than the limit value, the sensor sends harmonic current and THD to the inverter u Simultaneously delivering THD to a solar controller u Inverter verification THD u If the power supply is higher than the limit value, the power supply enters a first working state, and the energy storage module supplies power to the inverter to filter harmonic current. When the load side sensor detects THD u After being lower than the limit value and lasting N power frequency periods, the THD is sent to the inverter, the solar controller and the TTU u Information, THD is received by the inverter u After the information, THD is checked u If the first control state is exceeded, stopping the first control state if the first control state is not exceeded, and receiving THD by the solar controller u After the information, the solar controller detects the state of the photovoltaic panel, and when the photovoltaic panel does not work, the solar controller transmits a control signal to the TTU, and the TTU simultaneously receives the THD at the load side u After the information and the solar controller instruction, TTU judges THD u If the total power consumption is smaller than the limit value, calculating the THD of the power grid side u When the grid side THD u And when the power frequency exceeds the limit and lasts for N power frequency periods, entering a second control state, wherein grid-connected power of the first control state and the second control state is zero, and harmonic compensation current is obtained according to (4) and (8).
The distributed sensor realizes ad hoc network according to user distribution, TTU is used as a 'sink node' to carry out two-way communication with the sensor, the solar controller and the inverter, the load side sensor and the corresponding photovoltaic grid-connected inverter are connected to a monitoring platform through the TTU, the monitoring platform is a background monitoring server, and the load of a user is heating equipment, refrigerating equipment or energy storage equipment; when the inverter is in a second control state, namely multi-inverter linkage filtering control, the photovoltaic grid-connected inverter, the sensor and the TTU respectively carry out real-time load side THD on the current power state u THD of voltage and current information and power grid side u Information such as voltage and current is provided to a monitoring platform through communication, and the monitoring platform is based on the data and the userThe load characteristics and the service condition data are subjected to remote big data analysis, so that the photovoltaic energy is absorbed, the electricity quality and grid-connected income of a user are fully ensured, and meanwhile, the active power grid harmonic compensation has great social benefit.
The logic control diagram of the inverter for filtering is shown in fig. 1, the inverter utilizes the residual capacity to filter out the harmonic waves of the user side and the power grid side, and when the harmonic distortion rate of the user side and the power grid side is lower than the limit value, the inverter is fed in a grid-connected mode. The first and second control states require detection of harmonic currents, the first control state being defined by the load side THD u The second control state is determined by the load side THD u Grid-side THD u And solar controller instructions. The charge and discharge states and the normal grid-connected states of the energy storage module related in the control process are not important in the invention, so that the description is omitted here.
As shown in fig. 2, which is a block diagram of a photovoltaic power generation system, the inverter filters harmonics on the user side and the grid side by using the residual capacity, and when the harmonic distortion rate on the user side and the grid side is lower than a limit value, the inverter is fed in a grid-connected mode. The load side sensor detects current and voltage data in real time and calculates voltage harmonic distortion rate and harmonic compensation current, and as shown in fig. 3, an instantaneous reactive power ip-iq schematic diagram is shown. The ip 'and iq' obtain three-phase current fundamental wave components through inverse transformation, the fundamental wave signals obtained through filtering are subtracted from the sampled total current signals, and harmonic current signals can be obtained, and the current can be used as harmonic compensation current. And (3) evaluating the line impedance and the load impedance of the power grid by adopting a current disturbance monitoring method, and calculating the voltage harmonic distortion rate according to a formula (1).
The load side current compensation system block diagram is shown in FIG. 4, when the load side THD u Above the limit and for N power frequency cycles, the sensor calculates harmonic current and THD u And send harmonic current and THD to the photovoltaic grid-connected inverter u Simultaneously delivering THD to a solar controller u (stopped state of charge), inverter verifies THD u If it is higher than the limit value, if it exceeds the limit value, then it can be fed intoIn the first working state, the inverter calculates the compensation current according to the formula (4), adds the load harmonic compensation current into the instruction current, and filters the load side harmonic.
When the load side sensor detects THD u After (voltage harmonic distortion rate) is lower than the limit value and lasts for N power frequency periods, THD is sent to an inverter, a solar controller and a TTU u Information, THD is received by the inverter u After the information, THD is checked u If the first control state is exceeded, stopping the first control state if the first control state is not exceeded, and receiving THD by the solar controller u After the information, the solar controller detects whether the generated energy of the photovoltaic panel is larger than a grid-connected power instruction, when the generated energy of the photovoltaic panel is larger than the grid-connected power, the energy storage module is charged, when the battery voltage rises to a certain degree, or the solar controller receives THD at the load side u And when the voltage is larger than the limit value, namely, the inverter enters the first control state, the charging is stopped. After the charging is finished, the solar controller transmits a charging finishing signal to the TTU, and the TTU receives the THD of the load side at the same time u After the information and the solar controller instruction, TTU judges THD of the load side u If the total power consumption is smaller than the limit value, calculating the THD of the power grid side u When the grid side THD u And when the power frequency exceeds the limit and lasts for N power frequency periods, the TTU inquires the corresponding inverter, the inverter enters a second control state, and harmonic compensation current of each working inverter and the inverter in the second control state can be obtained according to the harmonic current of the power grid and the residual capacity of the inverter by the formula (8). When PV (photovoltaic) j+1 When the (j+1th inverter) receives the instruction for entering the second control state, the TTU controller recalculates the compensation proportion K i After finishing setting, TTU controller sends new compensation command to all inverters, j+1 simultaneously (synchronous signal can be u) a The next cycle zero crossing point) is compensated according to the new set proportion.
When the load side sensor detects THD u When the limit value is exceeded and N power frequency periods are continued, the sensor sends harmonic current data and THD to the corresponding inverter u Inverter verification THD u If the control state is higher than the limit value, the second control state is exited and the first control state is entered when the control state is exceeded.
The control block diagram is shown in fig. 5, where m inverters are operated in a first control state and n-m inverters are operated in a second control state. When the harmonic distortion rate exceeds the standard due to the nonlinear load used by the user side, the sensor initiates communication to the inverter, a sensor node modularized design structure diagram is shown in fig. 6, the core of the sensor is a control module, and the control module is responsible for completing the processing, storage and receiving and transmitting work of acquired data and managing the power supply module.
The TTU communication module block diagram is shown in fig. 7, the transceiver receives information from the inverter, the solar controller and the sensor, after filtering and amplifying, the instruction is sent to the controller after demodulation, and then the controller sends the main station command to the data acquisition and processing module through the serial port. The data acquisition and processing module acquires the data of the distribution transformer according to the received main station command, and after analysis processing, the data information and the control command are sent to the controller of the communication module through the serial port, modulated and finally sent to the inverter through the transceiver. The TTU also has a fault wave recording function, and when the power grid fails, the TTU quickly and timely transmits a large amount of fault data to the master station, and the master station analyzes the fault type according to the user load service condition and the electrical data when the fault occurs and provides data support for fault prediction. The effective communication and sensor distribution ensure the electricity quality of users, and the harmonic wave of the power grid is compensated by fully utilizing a plurality of inverter networks, so that the social benefit is remarkable and the development prospect is wide.
The working principle of the invention is as follows:
the invention, based on the similarity between the topological structure of the inverter and the active filter, plays the role of compensating the load harmonic wave by the residual capacity of the grid-connected inverter, not only ensures the grid-connected income of users, but also improves the power factor and prevents the load harmonic wave from polluting the power grid. The multi-grid-connected inverter linkage compensation power grid harmonic wave can fully utilize the residual capacity of the inverter, reduce a series of hazards generated by the power grid harmonic wave, and have huge social benefits. In view of the above, the present invention provides a photovoltaic inverter control method capable of improving power quality of a power distribution network, including a first control state and a second control state: the first control state is independent filtering control, and is based on the data transmitted from the load side sensorNonlinear load switching occurs when the load side THD u When the voltage harmonic distortion rate exceeds the limit and lasts for N power frequency periods, the photovoltaic grid-connected inverter adds harmonic current at the load side into the instruction current according to the residual capacity, so as to play a role in filtering the load harmonic current, and avoid the condition that the load harmonic affects the power quality of the power grid; the second control state is multi-inverter linkage filtering control, and each unit is composed of a photovoltaic grid-connected inverter, a load side sensor and a solar controller by taking a user as a unit, wherein the load side THD is calculated by the load side sensor u When the power frequency is lower than the limit value and the power frequency lasts for N power frequency periods, the photovoltaic panel charges the energy storage module, after the charging is finished, the solar controller transmits a control instruction to a TTU (distribution transformer monitoring terminal), and the TTU calculates THD at the power grid side u When the grid side THD u And when the power frequency exceeds the limit and lasts for N power frequency periods, entering a second control state, and controlling the multiple inverters to compensate the harmonic current of the power grid in a linkage way by using the TTU to calculate the filtering proportion according to the residual capacity of the multiple inverters. The method has the advantages that harmonic damage of nonlinear loads at a user side is reduced when the nonlinear loads are used, meanwhile, the plurality of inverters are used for compensating power grid harmonic waves, the problem that the single inverter is insufficient in harmonic compensation capacity is solved, the residual capacity of each photovoltaic grid-connected inverter can be fully utilized through linkage control of the plurality of inverters, the cost for improving the power quality is reduced, and meanwhile, the user benefit is guaranteed.
It should be emphasized that the embodiments described herein are illustrative rather than limiting, and that this invention encompasses other embodiments which may be made by those skilled in the art based on the teachings herein and which fall within the scope of this invention.
Claims (5)
1. A photovoltaic inversion control method capable of improving the power quality of a power distribution network is characterized by comprising the following steps of: the method comprises a first control state and a second control state, and comprises the following specific steps:
step 1, a first control state of independent filtering control: when the user side starts the nonlinear load, the load side sensor detects the voltage and current through the instantaneous reactive powerMethod for calculating THD in real time u Harmonic current, when the load side THD u When the sensor is higher than the limit value and lasts for N power frequency periods, the sensor sends THD at the load side to the inverter u The harmonic current information is used for calculating compensation current according to the residual capacity of the photovoltaic grid-connected inverter, and harmonic waves are filtered under the condition that the photovoltaic inverter is ensured to be normally grid-connected;
step 2, a second control state of multi-inverter linkage filtering control: when the load side sensor detects THD u When the power frequency is lower than the limit value and N power frequency periods are continued, the inverter stops the first control state, after the energy storage module is charged, the inverter can enter the second control state, the inverters are linked to compensate the power grid harmonic wave, and the compensation coefficient is adjusted in real time along with the addition and the withdrawal of the inverter;
the specific method of the step 2 is as follows: when the load side sensor detects THD u After being lower than the limit value and lasting N power frequency periods, THD is respectively sent to the inverter, the solar controller and the TTU u Information;
the inverter receives THD u After the information, THD is checked u Whether the first control state is overrun or not, and stopping the first control state if the first control state is not overrun;
the solar controller receives THD u After information, the solar controller detects the state of the photovoltaic panel, when the generated energy of the photovoltaic panel is larger than grid-connected power, the energy storage module is charged, when the voltage of the battery rises to a certain degree, or the sensor transmits THD to the solar controller u When the voltage is larger than the limit value, namely the inverter enters a first control state, stopping charging; after the charging is finished, the solar controller transmits a control signal to the TTU, and the TTU simultaneously receives the THD of the load side u After the information and the solar controller instruction, TTU judges THD u If the total power consumption is smaller than the limit value, calculating the THD of the power grid side u When the grid side THD u When the power frequency exceeds the limit and lasts for N power frequency periods, the TTU inquires the corresponding inverter, the inverter enters a second control state, the inverter transmits residual capacity to the TTU, the TTU data acquisition and processing module acquires data on the power distribution network side, harmonic current of the power grid and compensation coefficients of the inverters are obtained after analysis and processing, and then the data are transmitted to the corresponding inverter through the transmitterThen the inverters are linked to compensate the harmonic wave at the side of the power grid, when the sensor at the load side detects THD u When the limit value is exceeded and N power frequency periods are continued, the corresponding inverter exits the second control state and enters the first control state, and TTU access is refused.
2. The photovoltaic inversion control method capable of improving the power quality of a power distribution network according to claim 1, wherein the method comprises the following steps: the specific method of the step 1 is as follows:
the load side sensor detects voltage and current in real time, and THD is calculated in real time through an instantaneous reactive power method u THD when user enables nonlinear load u Ascending; when the load side THD u Above the limit and for N power frequency cycles, the sensor sends harmonic current and THD to the inverter u Simultaneously delivering THD to a solar controller u And stopping charging the energy storage module, and verifying THD by the inverter u If the current is higher than the limit value, entering a first control state if the current exceeds the limit value, calculating the residual capacity by the inverter, adding load harmonic current into the instruction current according to the residual capacity, and filtering out harmonic waves.
3. The photovoltaic inversion control method capable of improving the power quality of a power distribution network according to claim 1 or 2, wherein the method comprises the following steps: THD of said step 1 u The calculation formula of (2) is as follows:
in U n Effective values of all harmonic voltages not greater than a certain order H, U 1 For the effective value of the fundamental voltage component, the harmonic voltage can be obtained by an instantaneous reactive power ip-iq method.
4. The photovoltaic inversion control method capable of improving the power quality of a power distribution network according to claim 1 or 2, wherein the method comprises the following steps: the residual capacity of the photovoltaic grid-connected inverter in the step 1 can be obtained according to the rated power and the grid-connected power of the inverter:
P ri ＝(P i -P ei )*95％
in the above, P ri For the remaining capacity of the ith inverter, P i Rated power of the ith inverter, P ei The grid-connected power of the ith inverter;
and is obtainable according to the formula:
I ri ＝(I i -I ei )*95％
in the above, I i To calculate the maximum allowable current according to the rated capacity of the ith inverter, I ei Is the grid-connected current of the ith inverter, I ri The allowable compensation current for the ith inverter;
when the load side THD u Above the limit and for N power frequency cycles, the sensor sends a harmonic current I to the inverter refi To prevent the compensation current from exceeding the limit, the cut-off current is processed according to the following steps:
5. The photovoltaic inversion control method capable of improving the power quality of a power distribution network according to claim 1, wherein the method comprises the following steps: the proportion calculation method of the inverter compensation harmonic current in the step 2 is as follows:
harmonic power of the power grid is P s ，P r total For the total remaining capacity of the inverter operating in the second control state，P rj For the remaining capacity of the jth inverter operating in the second control state, when P r total ≥P s When (1):
when P r total ＜P s When (1):
the compensation ratio obtained by the method is K j Compensation current of each inverter:
I ref is the harmonic current of the power grid side, I rj For the maximum allowable compensation current of each inverter entering the second control state,
compensating the current for harmonics of each inverter in the second control state;
when PV (photovoltaic) j+1 When receiving the instruction for entering the second control state, the TTU controller recalculates the compensation proportion K j+1 After finishing the setting, the TTU controller sends new compensation commands to all inverters, and j+1 machines compensate according to the new setting proportion.
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