Error function based power allocation strategy for energy storage systems

Abstract

The application discloses an energy storage system power distribution strategy based on an error function, mainly comprising an event-triggered dynamic consistency algorithm module, an error function-based SOC equalization algorithm module, a virtual voltage drop module, a voltage compensation module and a voltage and current double-loop control module. The event-triggered dynamic consistency algorithm module is added, so that the system changes from "timed communication" to "on-demand communication", while reducing the communication burden, the error function-based SOC equalization algorithm module can dynamically divide the output current of each energy storage unit according to the real-time deviation of the state of charge of each energy storage unit and the average state of charge of the energy storage system, thereby improving the accuracy of the equal division of the output current between energy storage units with different capacities. In addition, the virtual voltage drop module and the voltage compensation module ensure that the voltage is stable within the rated range.

Description

Power allocation strategy for energy storage systems based on error function Technical Field

[0001] This invention relates to the field of distributed energy storage systems in DC microgrids, and in particular to a power allocation strategy for energy storage systems based on an error function. Background Technology

[0002] With the increasing proportion of renewable energy and increasingly stringent power quality requirements for power systems, DC microgrids have attracted widespread attention and are rapidly expanding in scale due to their reliability, scalability, and high efficiency. To meet the power level requirements of DC microgrids, multiple energy storage units are often connected in parallel to form a distributed energy storage system. To avoid imbalances in the State of Charge (SOC) of the energy storage units, leading to overcharging or over-discharging and affecting the lifespan of the energy storage units and the stability of the DC microgrid, coordinated control of the output current and SOC of each energy storage unit is necessary to ensure precise distribution of the output current according to capacity ratio and balanced SOC. Summary of the Invention

[0003] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0004] 1) In the event-triggered dynamic consistency algorithm module, the state of charge of each energy storage unit is... and virtual pressure drop As input, the output obtained after passing through the event-triggered dynamic consistency algorithm module is the average state of charge of the energy storage system. and virtual voltage drop average The specific expression for the event-triggered dynamic consistency algorithm module is as follows:

[0005] (1)

[0006] In equation (1), each energy storage unit is considered as a node. , They are nodes In the sequence The untriggered state of the next iteration For nodes A preset constant, For nodes The set of neighboring nodes, For nodes and nodes The weighting constants between them , The first sequence Node at the next iteration and nodes The cumulative difference between the estimated values , They are nodes and nodes In the The triggering state of the next iteration. For nodes In the The triggering state of the next iteration. For nodes In the The trigger threshold for the next iteration;

[0007] 2) In the SOC equalization algorithm module based on the error function, the state of charge of the energy storage unit is... and the average state of charge of the energy storage system As input, the output obtained after passing through the SOC equalization algorithm module based on the error function is the adjusted droop coefficient. The specific expression for the SOC equalization algorithm module based on the error function is as follows:

[0008] (2)

[0009] In equation (2), This is the initial droop coefficient. For the balance adjustment coefficient, Used for defining the error function. It is the inductor current;

[0010] 3) In the virtual voltage drop module, adjust the droop coefficient. Energy storage unit output current The average virtual pressure drop of the energy storage system and bus voltage reference value As input, the virtual voltage drop module outputs a virtual voltage drop reference value. The specific expression for the virtual voltage drop module is as follows:

[0011] (3)

[0012] In equation (3), For the virtual voltage drop of the energy storage unit, This is a compensation amount for current distribution accuracy. and All are virtual voltage drop module PI controllers;

[0013] 4) In the voltage compensation module, the bus voltage of the energy storage system is... Bus voltage reference value DC voltage of energy storage unit and virtual voltage drop reference value As the input, the voltage compensation module outputs a capacitor voltage reference value. The specific expression for the voltage compensation module is as follows:

[0014] (4)

[0015] In equation (4), This is the voltage compensation amount. and All are voltage compensation module PI controllers;

[0016] 5) In the voltage and current dual-loop control module, set the capacitor voltage reference value. As the input, the voltage and current dual-loop control module outputs the drive voltage. driving voltage The modulated signal is then obtained by comparing it with the triangular carrier wave.

[0017] Compared with existing technologies, the principles and advantages of this solution are as follows:

[0018] This invention discloses a power allocation strategy for an energy storage system based on an error function, mainly including an event-triggered dynamic consistency algorithm module, an error function-based SOC balancing algorithm module, a virtual voltage drop module, a voltage compensation module, and a voltage-current dual-loop control module. By adding the event-triggered dynamic consistency algorithm module, the system changes from "timed communication" to "on-demand communication," reducing the communication burden. Meanwhile, the error function-based SOC balancing algorithm module can dynamically distribute the output current of each energy storage unit based on the real-time deviation between the state of charge of each energy storage unit and the average state of charge of the energy storage system, improving the accuracy of current distribution among energy storage units of different capacities. Furthermore, the virtual voltage drop module and the voltage compensation module ensure that the voltage remains stable within the rated range. Attached Figure Description

[0019] Figure 1 is a main circuit diagram of the energy storage system in an embodiment of the present invention;

[0020] Figure 2 is a control block diagram of the power allocation strategy of the energy storage system based on the error function in an embodiment of the present invention;

[0021] Figure 3 is a control structure diagram of the virtual voltage drop module in an embodiment of the present invention;

[0022] Figure 4 is a control structure diagram of the voltage compensation module in an embodiment of the present invention;

[0023] Figure 5 shows the SOC waveform of the traditional control strategy in an embodiment of the present invention;

[0024] Figure 6 shows the SOC waveform of the improved control strategy in an embodiment of the present invention;

[0025] Figure 7 shows the output current waveform of the conventional control strategy in an embodiment of the present invention.

[0026] Figure 8 shows the output current waveform of the improved control strategy in an embodiment of the present invention.

[0027] Figure 9 is a bus voltage waveform diagram of the conventional control strategy in an embodiment of the present invention;

[0028] Figure 10 is a bus voltage waveform diagram of the improved control strategy in an embodiment of the present invention. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments:

[0030] Figure 1 shows the main circuit diagram of the energy storage system. The energy storage system consists of i energy storage units connected in parallel via a DC-DC converter. For any energy storage unit, For filtering inductors, For inductor current, The DC voltage of the energy storage unit. Output current to the energy storage unit. The corresponding line impedance. For load resistance, This is the bus voltage of the energy storage system.

[0031] Figure 2 shows the control block diagram of the power allocation strategy of the energy storage system based on the error function; Figure 3 shows the control structure diagram of the virtual voltage drop module; and Figure 4 shows the control structure diagram of the voltage compensation module, including the following steps:

[0032] In the event-triggered dynamic consistency algorithm module, the state of charge of each energy storage unit is... and virtual pressure drop As input, the output obtained after passing through the event-triggered dynamic consistency algorithm module is the average state of charge of the energy storage system. and virtual voltage drop average The specific expression for the event-triggered dynamic consistency algorithm module is as follows:

[0033] (5)

[0034] In equation (5), each energy storage unit is considered as a node. , They are nodes In the sequence The untriggered state of the next iteration For nodes A preset constant, For nodes The set of neighboring nodes, For nodes and nodes The weighting constants between them , The first sequence Node at the next iteration and nodes The cumulative difference between the estimated values , They are nodes and nodes In the The triggering state of the next iteration. For nodes In the The triggering state of the next iteration. For nodes In the The trigger threshold for the next iteration;

[0035] In the SOC equalization algorithm module based on the error function, the state of charge of the energy storage unit is... and the average state of charge of the energy storage system As input, the output obtained after passing through the SOC equalization algorithm module based on the error function is the adjusted droop coefficient. The specific expression for the SOC equalization algorithm module based on the error function is as follows:

[0036] (6)

[0037] In equation (6), This is the initial droop coefficient. For the balance adjustment coefficient, Used for defining the error function. It is the inductor current;

[0038] In the virtual voltage drop module, the adjusted droop coefficient will be... Energy storage unit output current The average virtual pressure drop of the energy storage system and bus voltage reference value As input, the virtual voltage drop module outputs a virtual voltage drop reference value. The specific expression for the virtual voltage drop module is as follows:

[0039] (7)

[0040] In equation (7), For the virtual voltage drop of the energy storage unit, This is a compensation amount for current distribution accuracy. and All are virtual voltage drop module PI controllers;

[0041] In the voltage compensation module, the bus voltage of the energy storage system is... Bus voltage reference value DC voltage of energy storage unit and virtual voltage drop reference value As the input, the voltage compensation module outputs a capacitor voltage reference value. The specific expression for the voltage compensation module is as follows:

[0042] (8)

[0043] In equation (8), This is the voltage compensation amount. and All are voltage compensation module PI controllers;

[0044] In the voltage and current dual-loop control module, the capacitor voltage reference value is... As the input, the voltage and current dual-loop control module outputs the drive voltage. driving voltage The modulated signal is then obtained by comparing it with the triangular carrier wave.

[0045] Figures 5 and 6 show the SOC waveforms for the traditional control strategy and the improved control strategy, respectively. The energy storage system consists of four energy storage units with different capacities, and the capacity ratio is [value missing]. The initial droop factor of the four energy storage units is set proportionally based on the reciprocal of their capacity. Therefore, the initial droop factor of the four energy storage units is... satisfy The actual values ​​were 1 / 3, 1 / 3, 0.5, and 0.5, respectively. The initial SOCs were 90%, 86%, 84%, and 82%, respectively. The line impedances of the four energy storage units were 0.50Ω, 0.60Ω, 0.54Ω, and 0.40Ω, respectively. The reference value for the bus voltage was... Balance adjustment coefficient Under the traditional control strategy, the State of Charge (SOC) difference among energy storage units with the same capacity and initial droop coefficient gradually decreases, but the SOC of the four energy storage units does not reach uniformity at the end of the simulation. Under the improved control strategy, the SOC of energy storage units with larger initial SOC values ​​decreases faster, while the SOC of energy storage units with smaller initial SOC values ​​decreases slower. The SOC of the four energy storage units reaches equality at 2.4 seconds of simulation time, and thereafter decreases at the same rate, reaching dynamic equilibrium.

[0046] Figures 7 and 8 show the output current waveforms of the traditional and improved control strategies, respectively. Under the traditional control strategy, the difference in output current among the four energy storage units gradually decreases. However, at the end of the simulation, the output currents of the four energy storage units are 4.46A, 3.75A, 5.86A, and 5.19A, respectively, which does not meet the requirement of proportional distribution of output current according to the capacity of the four energy storage units. Under the improved droop control strategy, the larger the capacity of the energy storage unit, the larger its output current. As the discharge time increases, the output currents of energy storage units with the same capacity and the same initial droop coefficient gradually approach each other and reach equilibrium at 2.4 seconds. At this time, the output currents of the four energy storage units are 9.6A, 9.6A, 6.4A, and 6.4A, respectively, satisfying the ratio 1.5:1.5:1:1. Furthermore, as the simulation progresses, the output currents of each energy storage unit remain at equilibrium.

[0047] Figures 9 and 10 show the bus voltage waveforms under the traditional and improved control strategies, respectively. Under the traditional control strategy, the bus voltage is only 389V, resulting in a 7V drop compared to the reference bus voltage value. Under the improved droop control strategy, the bus voltage is 400V, thanks to the introduction of a voltage compensation module that eliminates the bus voltage drop.

[0048] The above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Therefore, any changes made in accordance with the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A power allocation strategy for an energy storage system based on an error function, characterized in that, Includes the following steps: 1) In the event-triggered dynamic consistency algorithm module, the state of charge of each energy storage unit is... and virtual pressure drop As input, the output obtained after passing through the event-triggered dynamic consistency algorithm module is the average state of charge of the energy storage system. and virtual voltage drop average The specific expression for the event-triggered dynamic consistency algorithm module is as follows: In equation (1), each energy storage unit is considered as a node. 、 They are nodes In the sequence The untriggered state of the next iteration For nodes A preset constant, For nodes The set of neighboring nodes, For nodes and nodes The weighting constants between them 、 The first sequence Node at the next iteration and nodes The cumulative difference between the estimated values 、 They are nodes and nodes In the The triggering state of the next iteration. For nodes In the The triggering state of the next iteration. For nodes In the The trigger threshold for the next iteration; 2) In the SOC equalization algorithm module based on the error function, the state of charge of the energy storage unit is determined. and the average state of charge of the energy storage system As input, the output obtained after passing through the SOC equalization algorithm module based on the error function is the adjusted droop coefficient. The specific expression for the SOC equalization algorithm module based on the error function is as follows: In equation (2), This is the initial droop coefficient. For the balance adjustment coefficient, Used for defining the error function. For inductor current; 3) In the virtual voltage drop module, the adjusted droop coefficient Energy storage unit output current The average virtual pressure drop of the energy storage system and bus voltage reference value As input, the virtual voltage drop module outputs a virtual voltage drop reference value. The specific expression for the virtual voltage drop module is as follows: In equation (3), For the virtual voltage drop of the energy storage unit, This is the compensation amount for current distribution accuracy. and All are virtual voltage drop module PI controllers; 4) In the voltage compensation module, the bus voltage of the energy storage system is... Bus voltage reference value DC voltage of energy storage unit and virtual voltage drop reference value As the input, the voltage compensation module outputs a capacitor voltage reference value. The specific expression for the voltage compensation module is as follows: In equation (4), This is the voltage compensation amount. and All are voltage compensation module PI controllers; 5) In the voltage and current dual-loop control module, the capacitor voltage reference value is... As the input, the voltage and current dual-loop control module outputs the drive voltage. driving voltage The modulated signal is then obtained by comparing it with the triangular carrier wave.

2. The power allocation strategy for an energy storage system based on an error function according to claim 1, characterized in that, In step 1), the weighting constant The range of values ​​is 。

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