DC distributed energy storage unit droop control method based on battery state
By acquiring the SOC information of the distributed energy storage unit and constructing the droop control coefficient, the impact of battery state changes on SOC balance in the DC system was resolved, achieving stable and reliable operation of the distributed energy storage unit and ensuring the stability and reliability of the system.
Patent Information
- Application Number
- CN202510860456.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-25
- Publication Date
- 2025-11-07
AI Technical Summary
The existing SOC equalization control strategy for distributed energy storage units in DC systems fails to effectively consider changes in battery state, resulting in a reduction in the actual effective capacity of the battery and affecting system stability and reliability.
By acquiring the SOC information of distributed energy storage units, their operating ranges are divided, and droop control coefficients are constructed based on battery state. Droop control equations are then built to control the operation of distributed energy storage units, ensuring SOC balance and system stability.
It achieves SOC balancing of each distributed energy storage unit, ensuring the stable and reliable operation of the DC distributed energy storage system, avoiding battery overcharging or over-discharging caused by SOC imbalance, and improving the stability and reliability of the system.
Smart Images
Figure CN120914732A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to a DC system droop control method, in particular to a DC distributed energy storage unit droop control method based on battery state. BACKGROUND
[0002] DC systems of clean energy generation such as photovoltaic have been widely concerned, in order to suppress the power fluctuation caused by the randomness of clean energy and improve the power supply reliability, distributed energy storage units (ESU) are usually installed in the system.
[0003] The control strategy of the existing DC system distributed ESU mainly considers the SOC of the ESU battery to form a droop control to realize the power distribution and voltage control of the distributed ESU, and remarkable achievements have been made in the SOC balancing of the distributed ESU. However, in the long-term operation of the battery, its actual effective capacity gradually decreases, and if the SOC is still determined according to the rated capacity, it will have a great influence on the droop control formed by the SOC, thereby affecting the stable operation of the DC system.
[0004] Therefore, in order to solve the above technical problems, it is necessary to put forward a new technical means. SUMMARY
[0005] Therefore, the purpose of the present application is to provide a DC distributed energy storage unit droop control method based on battery state, by distributing the SOC information of the distributed energy storage unit battery and dividing the charging and discharging capacity of the distributed energy storage unit into operation intervals, and constructing the droop control coefficient based on the SOC information of the battery to control the operation of the distributed energy storage unit, fully considering the influence of the battery state of the distributed energy storage unit on the operation of the distributed energy storage unit, thereby realizing the SOC balancing of each distributed energy storage unit and ensuring the stable and reliable operation of the DC distributed energy storage system.
[0006] The present application provides a DC distributed energy storage unit droop control method based on battery state, comprising the following steps:
[0007] S1. Obtain the SOC information of each distributed energy storage unit in the DC system;
[0008] S2. Determine the SOC operation interval of the distributed energy storage unit;
[0009] S3. Determine the droop control coefficient of the distributed energy storage unit in the charging mode and the discharging mode based on the SOC information of the distributed energy storage unit and the SOC operation interval;
[0010] S4. Constructing a droop control equation of the distributed energy storage unit, inputting the droop control coefficient into the droop control equation to determine a voltage reference value of the distributed energy storage unit, and controlling the distributed energy storage unit to work by using the voltage reference value.
[0011] Further, the SOC operation interval of the distributed energy storage unit specifically comprises:
[0012] determining a lower limit value SOC α and an upper limit value SOC β of the SOC interval division of the distributed energy storage unit.
[0013] taking (0, SOC α ) as a discharging limit interval of the distributed energy storage unit.
[0014] taking (SOC α , SOC β ) as an optimal operation interval of the distributed energy storage unit.
[0015] taking (SOC β , 1) as a charging limit interval of the distributed energy storage unit.
[0016] Further, the droop control coefficient determination process of the distributed energy storage unit in the discharging mode is as follows:
[0017]
[0018] wherein:
[0019] R di_dis (SOC) represents the droop control coefficient of the i-th distributed energy storage unit in the discharging mode, R0 represents an initial droop coefficient of the distributed energy storage unit, SOC i represents the SOC value of the i-th distributed energy storage unit, SOC ave represents the average value of the SOC of all distributed energy storage units in the DC system, and k, n and m are all adjustment factors.
[0020] Further, the droop control coefficient determination process of the distributed energy storage unit in the charging mode is as follows:
[0021]
[0022] wherein: R di_cha (SOC) represents the droop control coefficient of the i-th distributed energy storage unit in the discharging mode, R0 represents an initial droop coefficient of the distributed energy storage unit, SOC i represents the SOC value of the i-th distributed energy storage unit, SOC ave represents the average value of the SOC of all distributed energy storage units in the DC system, and k, n and m are all adjustment factors.
[0023] Further, the droop control equation of the distributed energy storage unit is specifically:
[0024]
[0025] Wherein: R di (SOC) represents the droop control coefficient of the distributed energy storage unit, when the charging mode is adopted R di_cha (SOC), when the discharging mode is adopted R di_dis (SOC), u refi represents the given voltage of the i th distributed energy storage unit, is the reference voltage of the i th distributed energy storage unit, i bi represents the output current of the i th distributed energy storage unit.
[0026] The beneficial effects of the present application: through the present application, through the SOC information of the distributed energy storage unit battery and the division of the charging and discharging capacity of the distributed energy storage unit, the droop control coefficient is determined based on the SOC information of the battery and the distributed energy storage unit is controlled by the droop control coefficient, the influence of the battery state of the distributed energy storage unit on the operation of the distributed energy storage unit is fully considered, so as to realize the SOC balance of each distributed energy storage unit and ensure the stable and reliable work of the direct current distributed energy storage system. BRIEF DESCRIPTION OF DRAWINGS
[0027] The present application will be further described below in conjunction with the drawings and examples:
[0028] Figure 1 The flowchart of the present application.
[0029] Figure 2 The circuit topology of the distributed energy storage unit.
[0030] Figure 3 The battery SOC operation interval division.
[0031] Figure 4 The discharging mode SOC balance droop control operation curve.
[0032] Figure 5 The SOC balance segmented droop control system based on battery state estimation.
[0033] Figure 6 The same capacity battery discharging working condition curve.
[0034] Figure 7 The battery charging working condition curve considering capacity attenuation. DETAILED DESCRIPTION
[0035] The present application will be further described below in conjunction with the drawings and examples:
[0036] As shown in Figure 2 , Figure 2 is the topology of the distributed energy storage unit, wherein C b1 is the battery side voltage stabilizing capacitor; C b2 is the DC system side capacitor; L b is the transformer circuit inductance; U b is the battery side output voltage; i L is the current on the inductor; g1 and g2 are the driving signals of the switch tube; u b and i b are the DC system side voltage and current, respectively; S1 and S2 are the switch tubes.
[0037] The transformer of the ESU usually adopts voltage / current double closed loop control, and the voltage reference value in the double loop control can be provided by the droop control.
[0038] The expression of the battery SOC of the distributed energy storage unit is:
[0039]
[0040] In the formula, SOC0 is the initial value of the battery SOC, Q act is the actual effective capacity of the battery, t is the charging and discharging time, and i b (t) is the battery charging and discharging current.
[0041] Derive the SOC expression on both sides:
[0042]
[0043] In the formula, SOC' is the battery SOC change rate.
[0044] Taking two parallel running ESUs adopting droop control as an example:
[0045]
[0046] In the formula, R di is the droop control coefficient, and i=1, 2.
[0047] According to the theoretical derivation, the SOC change rate is related to the product of the actual capacity of the battery and the set droop coefficient; therefore, the technical scheme of the present application is proposed, specifically as shown in Figure 1 :
[0048] The present application provides a DC distributed energy storage unit droop control method based on the battery state, which comprises the following steps:
[0049] S1. Obtain the SOC information of each distributed energy storage unit in the DC system;
[0050] S2. determining the SOC operating interval of the distributed energy storage unit;
[0051] S3. determining the droop control coefficient of the distributed energy storage unit in the charging mode and the discharging mode based on the SOC information of the distributed energy storage unit and the SOC operating interval;
[0052] S4. constructing a droop control equation of the distributed energy storage unit, inputting the droop control coefficient into the droop control equation to determine the voltage reference value of the distributed energy storage unit, and controlling the distributed energy storage unit to work with the voltage reference value. Through the above method, the SOC information of the distributed energy storage unit battery and the charging and discharging capacity of the distributed energy storage unit are divided into operating intervals, and the droop control coefficient is determined based on the SOC information of the battery, and the distributed energy storage unit is controlled to operate with the droop control coefficient. The influence of the battery state of the distributed energy storage unit on the operation of the distributed energy storage unit is fully considered, so as to realize the SOC balance of each distributed energy storage unit and ensure the stable and reliable operation of the direct-current distributed energy storage system.
[0053] In this embodiment, the SOC operating interval of the distributed energy storage unit specifically includes:
[0054] determining the lower limit value SOC α and the upper limit value SOC β of the SOC interval of the distributed energy storage unit;
[0055] taking (0, SOC α ) as the discharging limit interval of the distributed energy storage unit;
[0056] taking (SOC α , SOC β ) as the optimal operating interval of the distributed energy storage unit;
[0057] taking (SOC β , 1) as the charging limit interval of the distributed energy storage unit. Specifically as shown in Figure 3 SOC α and SOC β Divide the battery SOC into three operating intervals. When the ESU battery SOC is in region 2, i.e. the optimal operating interval, the corresponding charging and discharging capacity is higher, at this time it is hoped that the battery will charge and discharge at a faster speed; when the SOC of the ESU battery is in region 1 or region 3, i.e. the charging and discharging limit interval, the battery charging and discharging capacity is lower, at this time it is hoped to slow down the battery charging and discharging speed, and as far as possible to make the battery away from the operating boundary, avoid the battery SOC close to the boundary to cause the ESU to exit operation, and reduce the reliability of the distributed ESU.
[0058] In this embodiment, the process of determining the droop control coefficient of the distributed energy storage unit in the discharging mode is:
[0059]
[0060] wherein:
[0061] R di_dis (SOC) represents the droop control coefficient of the i-th distributed energy storage unit in discharging mode, R0 represents the initial droop coefficient of the distributed energy storage unit, SOC i represents the SOC value of the i-th distributed energy storage unit, SOC ave represents the average SOC value of all distributed energy storage units in the DC system, and k, n and m are all adjustment factors.
[0062] The process for determining the droop control coefficient of the distributed energy storage unit in charging mode is as follows:
[0063]
[0064] wherein: R di_cha (SOC) represents the droop control coefficient of the i-th distributed energy storage unit in discharging mode, R0 represents the initial droop coefficient of the distributed energy storage unit, SOC i represents the SOC value of the i-th distributed energy storage unit, SOC ave represents the average SOC value of all distributed energy storage units in the DC system, and k, n and m are all adjustment factors.
[0065] The droop control equation of the distributed energy storage unit is as follows:
[0066]
[0067] wherein: R di (SOC) represents the droop control coefficient of the distributed energy storage unit, R di_cha (SOC) is used in charging mode, R di_dis (SOC) is used in discharging mode, u refi represents the given voltage of the i-th distributed energy storage unit, is the reference voltage of the i-th distributed energy storage unit, i bi represents the output current of the i-th distributed energy storage unit.
[0068] Taking the discharging mode as an example, it is assumed that the SOC of each ESU > SOC α , and the SOC equalization droop control curve is as shown in Figure 4 When the SOC value of the ESU is greater than SOC ave , the term in the droop coefficient is greater than 0, then is greater than 1, and by analogy, the SOC value is less than SOC aveESU exp The term is less than 1, so the droop coefficient of the ESU with a large SOC value is less than the ESU with a small SOC value. The slope of the droop curve represents the droop coefficient, and the droop curve with a large droop coefficient has a large slope, so the droop curve corresponding to the ESU with a large SOC value has a small slope, as shown by the green line in the figure. At the same voltage, the output current of the droop curve with a small slope is large, that is, the ESU with a large SOC value can output a larger current, and the ESU with a small SOC value can output a smaller current, so that the SOC of each unit gradually tends to be consistent. When the SOC of all ESUs is equal, The term is equal to 0, so the exponential term is equal to 1, and at this time the droop coefficient becomes the initial droop coefficient R0. Similarly, the droop control in the charging mode can also achieve the effect of reasonably distributing the current among the ESUs and ultimately achieving SOC balancing.
[0069] The SOC balancing segmented droop control system based on battery state estimation is as shown in Figure 5 The SOC i , inductance current, output voltage and current and other operating information of the ESU are obtained, and the voltage reference value is provided for the voltage / current double-loop control through the control link, and further a PWM control signal is output for the ESU. Among them, in order to fully consider the influence of the actual state of the battery on the operation control of the ESU, the SOC information determined based on the battery state estimation is introduced into the droop control; based on the relationship between the SOC state and the charging and discharging capacity, the battery operating interval is divided and the corresponding SOC balancing segmented droop control is designed.
[0070] In this embodiment Figure 6 , the output current of the ESU, the battery SOC and the DC bus voltage curve under the same capacity battery discharge working condition are shown. It can be seen that the initial SOC of the three ESUs is 0.65, 0.625 and 0.6 respectively, the actual capacity of the battery is 2Ah, and the three ESUs are in the discharge mode.
[0071] From Figure 6 (a) and (b), it can be seen that the droop coefficient can be dynamically adjusted according to the SOC of the ESU. In the initial stage, the currents of the three ESUs are distributed according to the initial SOC, so the ESU1 with a larger initial SOC outputs the largest current, about 7.43A at 5s, and the ESU3 with a smaller initial SOC outputs the smallest current, about 5.96A at 5s. With the continuous discharge of the battery, the current can be dynamically adjusted according to the SOC, and at the 75s moment, the output currents of the three ESUs tend to be consistent, about 6.68A, and at this time the SOC of each ESU battery also reaches the balanced state. At 100s, the SOC of each ESU is 0.310. From Figure 6(c) The DC bus voltage is approximately 385.4V, which deviates from the set value by 14.6V. The proposed control can keep the DC bus voltage within 5% of the set value.
[0072] When battery capacities are equal, the control method proposed in this invention can dynamically adjust the droop coefficient according to the SOC of each ESU, and rationally distribute the load current according to the SOC. Under discharge conditions, ESUs with larger SOCs are allocated more load current, and ESUs with smaller SOCs are allocated less load current, ultimately achieving SOC balance and avoiding overcharging or over-discharging of ESUs due to SOC imbalance, thereby improving the lifespan of energy storage.
[0073] In this embodiment Figure 7 The output current, battery SOC, and DC bus voltage curves of the ESU under battery charging conditions that take capacity degradation into account are shown. The initial SOCs of the three ESUs are 0.4, 0.375, and 0.35, respectively, and the actual battery capacities during the simulation period are 2Ah, 1.8Ah, and 1.6Ah, respectively.
[0074] The initial SOCs of the three ESU batteries, determined based on their actual effective capacity, are 0.4, 0.417, and 0.43, respectively. Figure 7 As shown in (a) and (b), each ESU can fully consider the actual state of the battery. The three ESUs dynamically adjust their current according to their actual SOC. ESU1, with the lowest actual SOC, has a larger charging current, approximately -4.4A at 9s, while ESU3, with the highest actual SOC, has a smaller charging current, approximately -3.5A at 9s. At 100s, the output current of the three ESUs becomes basically consistent, approximately -3.97A. At this point, the battery SOC of each ESU also reaches a relatively balanced state, approximately 0.68. Figure 7 In (c), the DC bus voltage is approximately 409V, which deviates from the set value by 9V. The DC bus voltage remains stable and within 5% of the set value.
[0075] The control method proposed in this invention can adaptively adjust the current magnitude according to the SOC operating status. When the SOC is in the extreme operating range, the current magnitude can be dynamically adjusted according to the difference between the SOC and the operating range boundary, so as to reasonably allocate the ESU output and make the battery operate in the optimal range as much as possible, thereby improving the stability of the energy storage system.
[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A battery state based DC distributed energy storage unit droop control method, characterized in that: The method comprises the following steps: S1. obtaining SOC information of each distributed energy storage unit in a direct current system; S2. determining an SOC operation interval of the distributed energy storage unit; S3. determining a droop control coefficient of the distributed energy storage unit in a charging mode and a discharging mode based on the SOC information of the distributed energy storage unit and the SOC operation interval; S4. constructing a droop control equation of the distributed energy storage unit, inputting the droop control coefficient into the droop control equation to determine a voltage reference value of the distributed energy storage unit, and controlling the distributed energy storage unit to work by using the voltage reference value.
2. The droop control method for DC distributed energy storage units based on battery state according to claim 1, characterized in that: The SOC operation interval of the distributed energy storage unit comprises: determining a lower limit value SOC of the SOC interval division of the distributed energy storage unit α and an upper limit value SOC β ; (0, SOC) α This serves as the discharge limit range for distributed energy storage units. The (SOC α , SOC β ) is the optimal operation interval of the distributed energy storage unit. (SOC β ,1) as a charging limit interval for the distributed energy storage unit.
3. The droop control method for DC distributed energy storage units based on battery state according to claim 2, characterized in that: The droop control coefficient determination process of the distributed energy storage unit in the discharging mode is: wherein: R di_dis Ri represents the droop control coefficient of the i-th distributed energy storage unit in discharge mode, R0 represents the initial droop coefficient of the distributed energy storage unit, SOC i represents the SOC value of the i-th distributed energy storage unit, SOC ave represents the average value of the SOC of all distributed energy storage units in the DC system, and k, n and m are all adjustment factors.
4. The method of claim 2, wherein: The droop control coefficient determination process of the distributed energy storage unit in the charging mode is: wherein: R di_cha (SOC) represents the droop control coefficient of the i-th distributed energy storage unit in discharging mode, R0represents the initial droop coefficient of the distributed energy storage unit, SOC i represents the SOC value of the i-th distributed energy storage unit, SOC ave represents the average SOC of all distributed energy storage units in the DC system, and k, n and m are all adjustment factors.
5. The battery state based DC distributed energy storage unit droop control method of claim 3 or 4, wherein: The droop control equation of the distributed energy storage unit is: wherein: R di (SOC) represents the droop control coefficient of the distributed energy storage unit, when the charging mode is adopted R di_cha (SOC), when the discharging mode is adopted R di_dis (SOC), u refi represents the given voltage of the i-th distributed energy storage unit, is the reference voltage of the i-th distributed energy storage unit, i bi represents the output current of the i-th distributed energy storage unit.