CN115208195A - Control method for improving power grid stability of hybrid energy storage system - Google Patents

Control method for improving power grid stability of hybrid energy storage system Download PDF

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CN115208195A
CN115208195A CN202210729062.0A CN202210729062A CN115208195A CN 115208195 A CN115208195 A CN 115208195A CN 202210729062 A CN202210729062 A CN 202210729062A CN 115208195 A CN115208195 A CN 115208195A
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power
value
voltage
energy storage
current
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丁宝苍
姚旭
张开碧
苏本吉
陈瑞芳
蒋文芹
毛诗玉
熊广
杜凯
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Chongqing University of Post and Telecommunications
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • 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

Abstract

The invention discloses a control method for improving the stability of a power grid by a hybrid energy storage system, which comprises the following steps: an outer ring voltage control based on droop characteristics and an inner ring power control based on improved Model Predictive Control (MPC) are adopted to form a double closed-loop control structure, the energy storage converter is controlled, the outer ring is a voltage ring, an inner ring power reference value is generated through the outer ring by utilizing the droop characteristics of the system, and the trend of preventing the change of direct-current voltage is achieved; the inner ring is a power ring and is used for tracking a power reference value generated by the outer ring, a prediction value is calculated through a prediction model, and a switching state corresponding to the prediction value closest to the prediction value is selected to act on the energy storage converter; and designing power prediction models in Buck and Boost modes, constructing a target function according to the relation between the power prediction value and the power reference value, and designing the inner loop control.

Description

Control method for improving power grid stability of hybrid energy storage system
Technical Field
The invention belongs to the technical field of power grid control, and particularly relates to a method for stabilizing power fluctuation of a power grid by utilizing predictive control and a hybrid energy storage system.
Background
With the increase of the power demand, the conventional thermal power generation has been unable to meet the power demand. Meanwhile, the problems of severe shortage of coal and petroleum resources, global greenhouse effect and the like are caused. Compared with the traditional energy, the new energy power generation mode has the advantages of less pollution, large reserve and the like, plays a vital role in solving the problems of resource exhaustion and energy pollution at present, and is particularly important to develop a new power generation mode to replace or supplement the traditional power generation mode. The novel power generation modes of wind energy, solar energy and the like become important green energy in the century, and all countries in the world are researching new energy power generation and are rapidly developed. Therefore, the influence of the new energy power generation after grid connection on the safe and stable operation of the power grid is worthy of deep research.
In order to solve the coordination problem of renewable energy and a large power grid, micro-grid technology is proposed by students. The micro-grid consists of a distributed power supply, an energy conversion device, a load, an energy storage device and the like. The micro-grid is an independent system, electric energy is generated through a power generation device in the micro-grid and is distributed to each power utilization unit through a bus, self control and self management can be achieved, and internal power conversion is mainly completed through power electronic devices such as DC/DC and DC/AC. The micro-grid can also be operated in parallel with the large power grid, so that the power consumption requirement of a user is met, the renewable energy is well buffered when being connected into the large power grid, and the coordination problem of the renewable energy and the large power grid can be solved through self-regulation in the micro-grid system.
The energy storage system is used as an essential ring in the microgrid and is matched with the distributed power supply, so that the effect of 'peak clipping and valley filling' can be achieved in the microgrid, and the energy storage system plays an important role in the aspects of improving the electric energy quality of the microgrid, improving the stability of the system and the like. Due to the strong instability of renewable energy sources, for example, the power generation amount of wind power generation varies with the change of seasons in one year, the situation that no wind exists or the wind power is too small to start a fan and therefore no power output exists often occurs, and the change of the generated power is severe. Similarly, solar power generation varies greatly with day and night. Therefore, the power generated by the power generation unit may not be matched with the load terminal at all times, when the power generated by the power generation terminal is too much, the energy is wasted, and when the power is too little, the demand of the load cannot be met. The energy storage system can solve the problem satisfactorily, when the electric quantity generated by the power generation unit is excessive, the energy storage system stores the redundant electric quantity, and when the electric quantity generated by the power generation unit is insufficient, the energy storage system releases the stored electric energy to maintain the power balance of the system. Meanwhile, the distributed power supply and the load have strong fluctuation, so that the voltage of a micro-grid bus can generate large fluctuation, and the quality of electric energy supplied to the load is difficult to ensure. The reasonable energy storage system control strategy is designed, the power output value of the energy storage element is adjusted constantly, the fluctuation of the bus voltage can be effectively inhibited, and the stability of the power system is improved. Therefore, the research of the energy storage operation control technology has important long-term significance and practical significance for the development of the power industry.
Application publication number CN105515209B, a micro-grid hybrid energy storage system and a control method thereof, include: the micro-grid public alternating current bus is connected with the first branch bus and the second branch bus through a micro-grid energy management system, and is also connected with the first branch bus through a transformer TM 4; the micro-grid public alternating current bus is also connected with the first branch circuit bus through a transformer TM 5; the first branch bus is respectively connected with the lithium battery energy storage module, the super capacitor energy storage module and the lead-acid battery energy storage module; and the second branch circuit bus is connected with the load module. According to the method, the internal energy storage system and the load of the microgrid are predicted, and in the processes of grid-connected operation, isolated network operation and state switching of the microgrid, the internal energy storage device and the load are optimally controlled according to the characteristics of the energy storage power supply and the load, and the system output is smoothed, so that the intermittence and the volatility of renewable energy sources are effectively inhibited.
The invention does not solve the problem of low dynamic response speed of the system, adopts MPC to replace the traditional PI control, optimizes the double closed-loop control strategy, improves the dynamic response speed of the system, solves the problem of prediction deviation caused by large disturbance or modeling error of the system, ensures the optimal selected output state of the system in a control period, and further improves the stability of the system after new energy is connected to the grid.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. A control method for improving the stability of a power grid by a hybrid energy storage system is provided. The technical scheme of the invention is as follows:
a control method for improving the stability of a power grid by a hybrid energy storage system comprises the following steps:
an outer ring voltage control based on droop characteristics and an inner ring power control based on improved Model Predictive Control (MPC) are adopted to form a double closed-loop control structure, the energy storage converter is controlled, the outer ring is a voltage ring, an inner ring power reference value is generated through the outer ring by utilizing the droop characteristics of the system, and the trend of preventing the change of direct-current voltage is achieved; the inner ring is a power ring and is used for tracking a power reference value generated by the outer ring, a prediction value is calculated through a prediction model, and a switching state corresponding to the prediction value closest to the prediction value is selected to act on the energy storage converter;
and designing power prediction models in Buck and Boost modes, constructing a target function according to the relation between the power prediction value and the power reference value, and designing the inner loop control.
Further, the outer ring is a voltage ring, and the inner ring is generated through the outer ring by utilizing the droop characteristic of the systemThe loop power reference value specifically includes: the method comprises the following steps of sampling the voltage value of a direct current bus in real time, comparing the voltage value with a rated voltage value, calculating a droop coefficient, obtaining a reference current value of input current at a direct current side, namely an input value of inner ring control, wherein the droop control is to calculate the droop coefficient according to a U-I characteristic curve to control output current, and then charging and discharging an energy storage element according to the calculated output current value to keep the voltage of the direct current bus stable, wherein the relation of the U-I characteristic curve is as follows: u shape ref ＝U set -kI dc ，
Wherein U is ref Is a reference voltage, U set To output a voltage, I dc To output a current.
The droop control coefficient was calculated as:
Figure BDA0003712143430000031
U L is the voltage when the converter is fully loaded, I max The current is the current when the converter is fully loaded.
The obtained voltage U of the direct current bus end dc-sto And reference value of DC bus terminal voltage
Figure BDA0003712143430000032
The reference power value P of the required direct current side input power is finally obtained through comparison and calculation of the droop coefficient * This power value is an input reference value for the inner loop model predictive control.
Further, the current prediction model and the voltage prediction model in the Boost mode are further simplified and arranged to obtain:
Figure BDA0003712143430000041
Figure BDA0003712143430000042
U sto is the voltage value of the energy storage system side, i sto As electricity of energy storage unitsCurrent, i.e. current through inductor L of the converter, R L Is an inductive resistance, T s For a sampling period, L is the energy storage inductor of the circuit, U dc-sto (k) Is the voltage value of the DC bus side, U d The voltage at the freewheeling diode is R is a resistor, and C is a filter capacitor.
And S represents the on-off state of T2, the S belongs to {0,1}, wherein 1 represents conduction, 0 represents off, the inductive current at the moment k, the voltage value of the direct current bus side, the voltage value of the energy storage side and the switch state are read according to the prediction model, and the inductive current at the moment k +1 and the voltage value of the direct current bus side are obtained through the current prediction model and the voltage prediction model.
Further, the current prediction model and the voltage prediction model established in the Buck mode are further simplified and arranged to obtain:
Figure BDA0003712143430000043
Figure BDA0003712143430000044
similarly, S represents the on-off state of T, and belongs to the field of {0,1}, wherein 1 represents on, and 0 represents off;
and obtaining power prediction models corresponding to all switch states. Calculating the predicted power value at the moment k +1 as follows:
P(k+1|k)＝i sto (k+1)×U dc-sto (k+1) (21)
the formula for calculating the predicted value of the power at the k +1 moment after feedback correction is as follows:
P(k+1)＝P(k+1|k)+[P(k)-P(k|k-1)] (22)。
further, the difference between the predicted power and the expected power value is used to form the objective function. The construction of the target function requires a power predicted value and a power reference value, the power predicted value is obtained through the constructed power prediction model, and the power reference value is an outer ring output value;
according to the multi-step prediction method, the predicted value of the k +2 moment is required to be calculated according to the switch state of the k moment, an objective function is established according to the predicted value of the k +2 moment, and then the objective function is minimized. The switching state combination M (k) at the k moment corresponding to the minimum value of the objective function enables the system performance to be optimal, the M (k) acts on the system at the k moment, and the objective function established by taking the power as a control target is as follows:
J＝|P(k+2)-P * | (23)
and obtaining power values at the k +1 moment and the k +2 moment through calculation of a prediction model, and obtaining an optimal switching state to control the bidirectional DC/DC by taking the power value at the k +2 moment and a power reference value as the input of a target optimization function so as to control the energy storage device.
The invention has the following advantages and beneficial effects:
aiming at the problem that the response speed of the traditional double closed-loop control strategy based on PI control is low, the invention provides a double closed-loop control strategy by changing MPC. And a double closed-loop control structure is formed by adopting outer-loop voltage control based on droop characteristics and inner-loop power control based on improved MPC, so that the energy storage converter is controlled, and the dynamic response speed of the system is improved. Firstly, according to the basic structure and the operation mode of the direct-current microgrid, comparing several common forms of accessing HESS into the direct-current microgrid, selecting a storage battery and a super capacitor to be connected in parallel, and respectively accessing the storage battery and the super capacitor into the topological structure of the direct-current microgrid through a bidirectional DC/DC converter. Next, the HESS dual closed-loop control strategy is optimized.
The invention provides a control strategy of a double closed-loop structure, wherein an outer ring is a voltage ring, and an inner ring power reference value is generated through the outer ring by utilizing the droop characteristic of a system, so that the trend of preventing the change of direct-current voltage is realized; the inner ring is a power ring and is used for tracking a power reference value generated by the outer ring, a prediction value is calculated through a prediction model, and a switching state corresponding to the prediction value closest to the desired value is selected to act on the energy storage converter, so that the dynamic response speed of the system is improved, and the capability of stabilizing the power fluctuation of the direct current micro-grid is enhanced. Designing power prediction models in Buck and Boost modes, constructing a target function according to the relation between a power prediction value and a power reference value, and designing inner loop control. The dynamic response speed of the hybrid energy storage system under the condition of power fluctuation is improved, and the voltage recovery time when the voltage of the direct current bus suddenly changes is greatly reduced.
The invention has the innovation points that the problem of non-ideal dynamic performance of the traditional double closed-loop control is considered, the MPC control adopting multi-step prediction is adopted for the hybrid energy storage system, the predicted values at the next two moments are calculated, the system output state corresponding to the optimal solution acts on the current moment, the problem of prediction deviation caused by large disturbance or modeling error of the system is solved, the optimal selected output state of the system in a control period is ensured, the dynamic response speed of the system is improved, and the stability of the system after new energy grid connection is further improved.
Drawings
FIG. 1 is a preferred embodiment U-I characteristic control regulation curve provided by the present invention
FIG. 2: an outer loop voltage control flow chart;
FIG. 3: a schematic diagram of a bidirectional DC/DC converter;
FIG. 4: boost mode schematic diagram;
FIG. 5: a schematic diagram when T2 is turned off in a Boost mode;
FIG. 6: a schematic diagram when T2 is conducted in a Boost mode;
FIG. 7 is a schematic view of: t2 is an equivalent model diagram when being turned off;
FIG. 8: t2 is an equivalent model diagram when being conducted;
FIG. 9: a Buck mode schematic diagram;
FIG. 10: a schematic diagram when T1 is turned off in a Buck mode;
FIG. 11: a schematic diagram of T1 conduction time in a Buck mode;
FIG. 12: t1 is an equivalent model diagram when being conducted;
FIG. 13 is a schematic view of: and (4) an equivalent model diagram when T1 is turned off.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail and clearly with reference to the accompanying drawings. The described embodiments are only some of the embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
first, in the control strategy of the hybrid energy storage system, the outer loop employs voltage control based on droop characteristics. The reference current value of the input current at the direct current side, namely the input value of the inner ring control can be obtained by sampling the voltage value of the direct current bus in real time, comparing the voltage value with the rated voltage value and calculating the droop coefficient. The droop control is to calculate the droop coefficient according to the U-I characteristic curve to control the output current. And then, charging and discharging the energy storage element according to the calculated output current value so as to keep the voltage of the direct current bus stable. The principle of the U-I characteristic control regulation curve is shown in figure 1.
The relation of the U-I characteristic curve is as follows: u shape ref ＝U set -kI dc ，
Wherein U is ref Is a reference voltage, U set To output a voltage, I dc To output a current.
The droop control coefficient was calculated as:
Figure BDA0003712143430000071
droop control can regulate the active and reactive power output by the microgrid. Droop control has the advantage of being very simple and reliable. Fig. 2 shows an outer loop voltage control flow chart. The obtained voltage U of the direct current bus end dc-sto And reference value of DC bus terminal voltage
Figure BDA0003712143430000072
The reference power value P of the required direct current side input power is finally obtained through comparison and calculation of the droop coefficient * . This power value is the input reference value for the inner loop model predictive control.
In a microgrid system, the dc bus voltage tends to be unstable due to randomness and variability of distributed generation or sudden changes in load. At this time, the energy storage system must compensate for the shortage or surplus of the microgrid dc bus by generating or absorbing electric energy to maintain the electric energy quality and reliable operation of the microgrid. A bi-directional DC/DC converter is typically used to convert and regulate voltage to charge and discharge the energy storage unit. Fig. 3 shows a schematic diagram of a bidirectional DC/DC converter. As shown, T1 and T2 are two MOSFET tubes. The on/off state of the MOSFET transistor is determined by the hybrid energy storage controller. When the hybrid energy storage controller issues a turn-on or turn-off command, the MOSFET transistor turns on or off accordingly. L is the energy storage inductance of the circuit, and C is the filter capacitor. D1 and D2 are two freewheeling diodes connected in parallel with the MOSFET to prevent the switching tube from being burnt by overlarge reverse voltage at the moment of switching on or switching off.
There are two modes of operation of bidirectional DC/DC: boost mode (fig. 4) and Buck mode (fig. 7). When the circuit works in a Boost mode, current flows from left to right, and the energy storage element discharges.
When T2 is in the off period (fig. 5), the branch at T2 acts as an open circuit, so that current flows through the freewheeling diode D1 to U2, and the energy stored in the inductor L is discharged from the anti-parallel freewheeling diode D1 of T1 to U2. When T2 is turned on (fig. 6), current returns to U1 through T2, and the entire circuit charges the inductor by U1.
And establishing a bidirectional DC/DC prediction model in a Boost working mode according to the working principle and characteristics of the bidirectional DC/DC. Under the Boost working mode of bidirectional DC/DC, the freewheeling diode D1 and the MOSFET T2 work. According to the switching state of T2, two models are established, namely a prediction model when T2 is switched on and off.
When the MOSFET T2 is turned off, the equivalent model is shown in fig. 7:
the hybrid energy storage system consists of a lithium battery or a super capacitor, and U is sto Is the voltage value of the energy storage system side, i sto The current of the energy storage unit, i.e. the current flowing through the inductor L of the converter. R L Is an inductive resistance. The inductor resistance cannot be neglected for accuracy of the modeling. Therefore, the invention also considers the inductance resistance R in the process of creating the equivalent circuit diagram L And U d 。U d Is the forward voltage drop, U, of the diode when it is conducting in the forward direction dc-sto Is the voltage value on the dc bus side.
During the off period of the MOSFET T2, the electric energy stored in the inductor L is released to the dc bus side through the freewheeling diode D1, and the relationship can be obtained according to the equivalent circuit diagram of fig. 7:
Figure BDA0003712143430000081
Figure BDA0003712143430000091
discretizing the formula by using an Euler method, and simplifying and sorting to obtain:
Figure BDA0003712143430000092
Figure BDA0003712143430000093
U sto (k) For the voltage across the energy storage unit at time k, i sto (k) For the energy-storage unit current at time k, U dc-sto (k) Is the DC bus voltage at time k, T s Is the sampling period. i.e. i sto (k + 1) is the current of the energy storage unit at the moment of k +1, U dc-sto And (k + 1) is the voltage of two ends of the direct current bus at the moment of k + 1.
Equations (3) and (4) are prediction models established when the MOSFET tube T2 is turned off in the Boost mode. The inductive current, the direct current bus side voltage value and the energy storage side voltage value at the moment k can be read, and the inductive current value and the direct current bus side voltage value at the moment k +1 can be obtained through the established prediction model.
When the MOSFET T2 is turned on, the equivalent model is shown in fig. 8, and the relationship is obtained:
Figure BDA0003712143430000094
Figure BDA0003712143430000095
discretizing by using an Euler method, and simplifying and sorting to obtain:
Figure BDA0003712143430000096
Figure BDA0003712143430000097
equations (7) and (8) are prediction models established when the MOSFET tube T2 is conducted in the Boost mode. As in the case of turn-off, the inductor current, the voltage value on the dc bus side, and the voltage value on the energy storage side may be read from time k. And obtaining the inductance current value and the direct current bus side voltage value at the k +1 moment through the established prediction model.
According to the formulas (3), (4), (7) and (8), a current prediction model and a voltage prediction model in a Boost mode can be obtained, and the current prediction model and the voltage prediction model are further simplified and arranged:
Figure BDA0003712143430000101
Figure BDA0003712143430000102
s represents the on-off state of T2, and S is equal to {0,1}, wherein 1 represents on and 0 represents off. And reading the inductive current, the direct current bus side voltage value, the energy storage side voltage value and the switch state at the moment k according to the prediction model, and obtaining the inductive current and the direct current bus side voltage value at the moment k +1 through the current prediction model and the voltage prediction model.
When the circuit works in the Buck mode, the current direction is from right to left, and the energy storage element is in a charging state at the moment.
Fig. 10 is a schematic diagram of T1 when turned off. At this time, the branch of T1 is equivalent to an open circuit, and the current flows to the U1 inductor L through the freewheeling diode D2, and the electromagnetic waves stored in the U1 inductor L are released to U1 through the anti-parallel freewheeling diode D2 of T2. When T1 is in the on period, the schematic diagram is as shown in fig. 11. Current flows from U2 to U1 through T1. The entire circuit is charged from U2 to U1.
And establishing a bidirectional DC/DC prediction model in the Buck working mode according to the working principle and characteristics of the bidirectional DC/DC. The free-wheeling diode D2 and the MOSFET tube T1 work in a Buck working mode of bidirectional DC/DC. And establishing two models according to the switching state of the T1, namely a prediction model when the T1 is switched on and a prediction model when the T1 is switched off.
When the MOSFET T1 is turned on, the equivalent model diagram is shown in fig. 12. During the conduction period of the MOSFET T1, the current passes through T1 from U dc-sto Flow direction U sto And the whole circuit charges the energy storage element from the bus side. The relation can be obtained according to the equivalent circuit diagram:
Figure BDA0003712143430000103
Figure BDA0003712143430000104
discretizing by using an Euler method, and simplifying and sorting to obtain:
Figure BDA0003712143430000111
Figure BDA0003712143430000112
when the MOSFET T1 is turned off, the equivalent model is shown in fig. 13, and the relationship:
Figure BDA0003712143430000113
Figure BDA0003712143430000114
discretizing by using an Euler method, and simplifying and sorting to obtain:
Figure BDA0003712143430000115
Figure BDA0003712143430000116
according to the formulas (13), (14), (17) and (18), a current prediction model and a voltage prediction model which are established in the Buck mode can be obtained, and the current prediction model and the voltage prediction model are further simplified and arranged to obtain:
Figure BDA0003712143430000117
Figure BDA0003712143430000118
similarly, S represents the on-off state of T, and S is equal to {0,1}, wherein 1 represents on and 0 represents off.
And (3) substituting the expressions (9), (10), (19) and (20) for the expression (21) to obtain power prediction models corresponding to all the switch states. Calculating the predicted power value at the moment k +1 as follows:
P(k+1|k)＝i sto (k+1)×U dc-sto (k+1) (21)
the calculation formula of the predicted power value at the k +1 moment after feedback correction is as follows:
P(k+1)＝P(k+1|k)+[P(k)-P(k|k-1)] (22)
the bidirectional DC/DC converter is used for controlling the charging and discharging of the energy storage element, so that the bidirectional flow of energy from the micro-grid to the energy storage system and from the energy storage system to the micro-grid is realized, and the shortage of the power of the direct current bus is compensated. Thus, the present invention chooses to construct the objective function with the difference between the predicted power and the expected power value. The construction of the objective function requires a power prediction value and a power reference value, the power prediction value is obtained through the constructed power prediction model, and the power reference value is an outer ring output value.
According to the multi-step prediction method, the predicted value of k +2 moment is required to be calculated according to the switching state of k moment, an objective function is established according to the predicted value of k +2 moment, and then the objective function is minimized. And the switching state combination M (k) at the moment k corresponding to the minimum value of the objective function enables the system performance to be optimal, and the M (k) acts on the system at the moment k. The objective function established with power as the control target is:
J＝|P(k+2)-P * | (23)
and calculating by a prediction model to obtain power values at the k +1 moment and the k +2 moment. And taking the power value at the k +2 moment and the power reference value as the input of a target optimization function to obtain an optimal switching state to control the bidirectional DC/DC, further controlling the energy storage device, and realizing the functions of flexible energy management and restraining the power fluctuation of the power generation unit or the load. The control method of the hybrid energy storage system can enable the super capacitor and the lithium battery to respond quickly when the bus power fluctuates, and the aim of stabilizing the power fluctuation of the micro-grid is fulfilled by absorbing or releasing the power, so that the bus voltage is kept stable.
The systems, devices, modules or units illustrated in the above embodiments may be implemented by a computer chip or an entity, or by a product with certain functions. One typical implementation device is a computer. In particular, the computer may be, for example, a personal computer, a laptop computer, a cellular telephone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising a … …" does not exclude the presence of another identical element in a process, method, article, or apparatus that comprises the element.
The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.

Claims (5)

1. A control method for improving the stability of a power grid by a hybrid energy storage system is characterized by comprising the following steps:
the droop characteristic-based outer ring voltage control and the improved model predictive control MPC-based inner ring power control are adopted to form a double closed-loop control structure, the energy storage converter is controlled, the outer ring is a voltage ring, an inner ring power reference value is generated through the outer ring by utilizing the droop characteristic of the system, and the trend of preventing the change of direct-current voltage is achieved; the inner ring is a power ring and is used for tracking a power reference value generated by the outer ring, calculating a predicted value through a prediction model, and selecting a switching state corresponding to the predicted value closest to the expected value to act on the energy storage converter;
and designing power prediction models in Buck and Boost modes, constructing a target function according to the relation between the power prediction value and the power reference value, and designing the inner loop control.
2. The control method for improving grid stability of the hybrid energy storage system according to claim 1, wherein the outer ring is a voltage ring, and an inner ring power reference value is generated by the outer ring by using a droop characteristic of the system, specifically comprising: the method comprises the following steps of sampling the voltage value of a direct current bus in real time, comparing the voltage value with a rated voltage value, calculating a droop coefficient, obtaining a reference current value of input current at a direct current side, namely an input value of inner ring control, wherein the droop control is to calculate the droop coefficient according to a U-I characteristic curve to control output current, and then charging and discharging an energy storage element according to the calculated output current value to keep the voltage of the direct current bus stable, wherein the relation of the U-I characteristic curve is as follows: u shape ref ＝U set -kI dc ，
Wherein U is ref Is a reference voltage, U set To output a voltage, I dc To output a current.
The droop control coefficient was calculated as:
Figure FDA0003712143420000011
U L is the voltage I of the converter under full load max The current is the current when the converter is fully loaded.
The obtained voltage U of the direct current bus end dc-sto And reference value of DC bus terminal voltage
Figure FDA0003712143420000012
The reference power value P of the required direct current side input power is finally obtained through comparison and calculation of the droop coefficient * This power value is an input reference value for the inner loop model predictive control.
3. The control method for improving the power grid stability of the hybrid energy storage system according to claim 1, wherein the current prediction model and the voltage prediction model in the Boost mode are further simplified and arranged to obtain:
Figure FDA0003712143420000021
Figure FDA0003712143420000022
U sto is the voltage value of the energy storage system side, i sto For the current of the energy storage unit, i.e. the current through the inductor L of the converter, R L Is an inductive resistance, T s For a sampling period, L is the energy storage inductor of the circuit, U dc-sto (k) Is the voltage value of the DC bus side, U d The voltage at the freewheeling diode is R is a resistor, and C is a filter capacitor.
And S represents the on-off state of T2, the S belongs to {0,1}, wherein 1 represents conduction, 0 represents off, the inductive current at the moment k, the voltage value of the direct current bus side, the voltage value of the energy storage side and the switch state are read according to the prediction model, and the inductive current at the moment k +1 and the voltage value of the direct current bus side are obtained through the current prediction model and the voltage prediction model.
4. The control method for improving the grid stability of the hybrid energy storage system according to claim 3, wherein the current prediction model and the voltage prediction model established in the Buck mode are further simplified and collated to obtain:
Figure FDA0003712143420000023
Figure FDA0003712143420000024
similarly, S represents the on-off state of T, and belongs to the field of {0,1}, wherein 1 represents on, and 0 represents off;
and obtaining power prediction models corresponding to all the switch states. Calculating the predicted power value at the moment k +1 as follows:
P(k+1|k)＝i sto (k+1)×U dc-sto (k+1) (21)
the formula for calculating the predicted value of the power at the k +1 moment after feedback correction is as follows:
P(k+1)＝P(k+1|k)+[P(k)-P(k|k-1)] (22)。
5. the control method for improving grid stability of the hybrid energy storage system according to claim 4, wherein the objective function is formed by a difference between the predicted power and the expected power. The construction of the target function requires a power predicted value and a power reference value, the power predicted value is obtained through the constructed power prediction model, and the power reference value is an outer ring output value;
according to the multi-step prediction method, the predicted value of k +2 moment is required to be calculated according to the switching state of k moment, an objective function is established according to the predicted value of k +2 moment, and then the objective function is minimized. The switching state combination M (k) at the k moment corresponding to the minimum value of the objective function enables the system performance to be optimal, the M (k) acts on the system at the k moment, and the objective function established by taking the power as a control target is as follows:
J＝|P(k+2)-P * | (23)
and obtaining power values at the k +1 moment and the k +2 moment through calculation of a prediction model, and obtaining an optimal switching state to control the bidirectional DC/DC by taking the power value at the k +2 moment and a power reference value as the input of a target optimization function so as to control the energy storage device.
CN202210729062.0A 2022-06-24 2022-06-24 Control method for improving power grid stability of hybrid energy storage system Pending CN115208195A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117239711A (en) * 2023-11-13 2023-12-15 四川大学 Energy storage control method and device for improving power supply quality of well group of oil pumping unit

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117239711A (en) * 2023-11-13 2023-12-15 四川大学 Energy storage control method and device for improving power supply quality of well group of oil pumping unit
CN117239711B (en) * 2023-11-13 2024-02-02 四川大学 Energy storage control method and device for improving power supply quality of well group of oil pumping unit

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