A multi-battery energy storage system power equalization control method

Abstract

The application discloses a kind of multi-cell energy storage system power equalization control method.The application controls energy storage converter output power by obtaining the SOP of energy storage unit connected with each energy storage converter, and considers the requirements of power charging and discharging and battery consistency;Each energy storage converter only needs to consider the information of corresponding DC side energy storage unit, and meets the characteristics of droop control;When there is temperature difference difference condition in each energy storage battery, the application reasonably allocates the output power of each energy storage converter by calling the SOP information of corresponding energy storage battery;At the same time, when the temperature, capacity and aging degree of energy storage battery are different, SOC reaches consistency and then inconsistency condition appears again, SOP comprehensively considers SOC, voltage, capacity, temperature and other constraints, which can better meet the requirement of battery consistency.

Description

Technical Field

[0001] This invention relates to the field of energy storage battery balancing technology, and specifically to a power balancing control method for multi-battery energy storage systems. Background Technology

[0002] In grid-side energy storage applications, energy storage systems typically have high capacity configurations and utilize a large number of lithium iron phosphate (LFP) batteries. However, due to limitations in lithium-ion battery manufacturing processes, inconsistencies exist between individual lithium batteries. During use, these differences are amplified by factors such as operating temperature, discharge efficiency, and the impact of protection circuits on the battery pack. This inconsistency causes circulating current losses and a bottleneck effect, particularly jeopardizing the system's safety and reliability, and leading to a reduction in the effective capacity and cycle life of the entire battery cluster. Besides controlling these inconsistencies in the manufacturing process, another effective method to address the inconsistency issue in lithium battery packs is to implement balanced battery management.

[0003] Patent publication CN113193245A proposes a State of Health (SOH) balancing method for microgrid distributed battery energy storage systems. This method eliminates inconsistencies by introducing a State of Health (SOH) variable into traditional droop control. However, SOH represents the degradation state, measuring the degree of battery aging (the ratio of current capacity to factory rated capacity). SOH balancing inevitably means sacrificing the capacity of some batteries with good health to match the degradation level of the worst-healthy batteries. While this achieves uniform capacity across all batteries, it shortens the lifespan of batteries with better health, at the cost of reducing the usable capacity of batteries with high SOH. Patent publication CN113507151A proposes a State of Charge (SOC) collaborative control method for multiple energy storage units. This method adds a State of Charge (SOC) variable to traditional droop control, achieving a near-uniform charge level among all energy storage batteries and eliminating battery inconsistencies. However, each energy storage module needs to obtain the SOC information of all energy storage batteries, resulting in information exchange between systems and negating the advantage of droop control without communication. Furthermore, when the temperature difference, capacity, and aging degree of each energy storage battery differ, power distribution is achieved after SOC balancing, but inconsistencies will arise again at the next moment. The system does not consider the maximum output power capability of each energy storage battery, leading to some batteries experiencing excessively low output power due to temperature differences, resulting in over-discharge and battery damage. Summary of the Invention

[0004] To address the shortcomings of the above technologies, this invention provides a power balancing control method for multi-battery energy storage systems. This method not only possesses the advantages of droop control without communication, but also enables power distribution of the energy storage converter under extreme conditions, preventing over-discharge of any particular battery.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A power balancing control method for a multi-battery energy storage system, applied to a microgrid with multiple energy storage converters operating in parallel, wherein the DC side of each energy storage converter is connected to an energy storage battery; includes the following steps:

[0007] Step 1: Obtain the DC side voltage and current of each energy storage converter, calculate the peak power SOP of each energy storage battery in real time through the battery management system, and send the obtained data back to the control system of each energy storage converter.

[0008] Step 2: Obtain the AC grid-side output voltage and output current of each energy storage converter, and calculate the output active power and reactive power of the corresponding energy storage converter based on the AC grid-side voltage and current.

[0009] Step 3: Based on the active power, reactive power, and peak power, an improved droop control is adopted to determine the regulation frequency and regulation voltage value of each energy storage converter. The peak power is taken into account in the improved droop control.

[0010] Step 4: Based on the regulation frequency and regulation voltage value of each energy storage converter, the output power of the energy storage converter is adjusted accordingly through dual-loop regulation of voltage and current.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] This invention controls the output power of the energy storage converter by acquiring the SOP (State of Operation) of the energy storage unit connected to each energy storage converter, thus balancing the requirements of power charging / discharging and battery consistency. In previous technologies, SOC (State of Charge) equalization required each energy storage converter to acquire information from all energy storage units, resulting in information exchange between converters and negating the advantage of droop control without communication. This invention only needs to consider the information of the corresponding DC-side energy storage unit for each energy storage converter, satisfying the characteristics of droop control. When there are temperature differences among the energy storage batteries, previous power allocation methods did not consider the maximum output power capacity of the energy storage batteries, leading to over-discharge when a battery's SOP is too low due to temperature differences, damaging the battery. This invention rationally allocates the output power of each energy storage converter by calling the corresponding energy storage battery's SOP information. Furthermore, when energy storage batteries have different temperatures, capacities, and aging levels, inconsistencies may reappear after the SOC reaches consistency. The SOP comprehensively considers constraints such as SOC, voltage, capacity, and temperature, better meeting the requirements of battery consistency. Attached Figure Description

[0013] Figure 1 This is a system schematic diagram of the present invention;

[0014] Figure 2This is a control block diagram of power balancing control technology for multi-battery energy storage systems. Detailed Implementation

[0015] The present invention will now be described in detail with reference to specific examples and accompanying drawings.

[0016] The multi-battery energy storage system of the present invention, as described above Figure 1 As shown, several energy storage converters are connected in parallel on their AC sides to the AC power grid or load; each energy storage converter is connected to an energy storage battery on its DC side, and the energy storage battery is composed of multiple battery cells connected in series and parallel; wherein u DC i DC These represent the output voltage and current of the energy storage battery, u and u, respectively. abc i abc Z represents the three-phase output voltage and current of the energy storage converter, and Z represents the line impedance of the energy storage converter.

[0017] This embodiment uses one of the battery energy storage systems as an example, such as Figure 2 As shown, a power balancing control method for a multi-battery energy storage system includes the following steps:

[0018] Step 1: Obtain the output voltage u of each energy storage battery DC Output current i DC The battery management system (BMS) calculates the current remaining available capacity Ci and peak power SOP of each energy storage unit in real time and sends the acquired data back to each PCS control system.

[0019] Step 2: Obtain the AC grid-side output voltage u of each energy storage converter. abc Output current i abc The output active power P of the corresponding energy storage converter is calculated based on the AC grid voltage and current. i and reactive power Q i .

[0020] Optionally, based on the grid-side output voltage and output current, the active power and reactive power of each of the parallel energy storage converters are calculated, specifically including:

[0021] The three-phase output voltage on the grid side is transformed to obtain the d-axis voltage component and the q-axis voltage component.

[0022] The three-phase output current on the grid side is transformed to obtain the d-axis current component and the q-axis current component.

[0023] The active power and reactive power of each energy storage converter are calculated based on the d-axis voltage component, q-axis voltage component, d-axis current component, and q-axis current component.

[0024] Step 3: Based on the active power, reactive power, and SOP, calculate the regulation frequency and regulation voltage amplitude of each energy storage converter:

[0025]

[0026] Where i represents the number of energy storage converters, i = 1, 2, 3...n; f i f represents the regulation frequency of the i-th energy storage converter; n Indicates the rated frequency; P i SOP represents the active power of the i-th energy storage converter; i K represents the peak power that the DC-side energy storage unit of the i-th energy storage converter can output; SOP U represents the power regulation coefficient; i U represents the regulating voltage amplitude of the i-th energy storage converter; n Indicates the rated voltage amplitude; Q i K represents the reactive power output of the i-th energy storage converter; P K represents the droop factor of active power. Q The droop factor represents the reactive power.

[0027] Step 4: Based on the regulation frequency f and regulation voltage amplitude U of each energy storage converter, the output power of the energy storage converter is adjusted accordingly through dual-loop voltage and current control, specifically including:

[0028] S1: Obtain the three-phase output voltage of each energy storage converter, and transform it according to the adjustment frequency to obtain the d-axis voltage component and the q-axis voltage component;

[0029] S2: Subtract the amplitude of the adjusted voltage from the d-axis voltage component and the q-axis voltage component respectively to obtain the first d-axis adjustment component and the first q-axis adjustment component after passing through the PI controller;

[0030] S3: Obtain the three-phase inductor current of each energy storage converter, and transform it according to the adjustment frequency to obtain the d-axis inductor current component and the q-axis inductor current component.

[0031] S4: The difference between the first adjustment component of the d-axis and the inductor current component of the d-axis is obtained by passing the difference through the PI controller to obtain the second adjustment component of the d-axis; the difference between the first adjustment component of the q-axis and the inductor current component of the q-axis is obtained by passing the difference through the PI controller to obtain the second adjustment component of the q-axis.

[0032] S5: Based on the adjustment frequency, perform inverse transformation processing on the second adjustment components of the d-axis and q-axis to obtain the three-phase adjustment voltage of each of the parallel energy storage converters;

[0033] S6: Based on the three-phase regulated voltage of each energy storage converter, its operation is controlled by pulse width modulation, and the output power of the energy storage converter is adjusted accordingly to achieve reasonable power distribution. This ensures that the energy storage converter with a higher SOP (State of Operation) outputs more power, and the energy storage converter with a lower SOP outputs less power. In other words, batteries with higher SOPs discharge more, and batteries with lower SOPs discharge less, ultimately achieving SOP balance at a certain point and achieving power equalization, eliminating inconsistencies.

[0034] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A power balancing control method for a multi-battery energy storage system, applied to a microgrid with multiple energy storage converters operating in parallel, wherein the DC side of each energy storage converter is connected to an energy storage battery, characterized in that... Includes the following steps: Step 1: Obtain the DC side voltage and current of each energy storage converter; The peak power of each energy storage battery is calculated in real time by the battery management system, and the acquired data is sent back to the control system of each energy storage converter. Step 2: Obtain the AC grid-side output voltage and output current of each energy storage converter; Based on the AC grid-side output voltage and output current, calculate the corresponding energy storage converter's output active power and reactive power. Step 3: Based on the active power, reactive power, and peak power, an improved droop control is adopted to determine the regulation frequency and regulation voltage value of each energy storage converter. The peak power is taken into account in the improved droop control. Step 4: Based on the adjustment frequency and adjustment voltage value of each energy storage converter, the output power of the energy storage converter is adjusted through dual-loop control of voltage and current, so that the energy storage converter with higher peak power of energy storage unit has higher output power, and the energy storage converter with lower peak power of energy storage unit has lower output power. The improved droop control is characterized by the following formula: Where i represents the number of energy storage converters, i = 1, 2, 3...n; This represents the regulation frequency of the i-th energy storage converter; Indicates the rated frequency; This represents the active power of the i-th energy storage converter; This represents the peak power that the DC-side energy storage unit of the i-th energy storage converter can output; Indicates the power regulation coefficient; This represents the regulating voltage amplitude of the i-th energy storage converter; Indicates the rated voltage amplitude; This represents the reactive power output of the i-th energy storage converter; The droop factor represents the active power. The droop factor represents the reactive power.

2. The power equalization control method for a multi-battery energy storage system according to claim 1, characterized in that: Based on the grid-side output voltage and output current, the corresponding active and reactive power outputs of the energy storage converter are calculated, specifically including: The three-phase output voltage on the grid side is transformed to obtain the d-axis voltage component and the q-axis voltage component; The three-phase output current on the grid side is transformed to obtain the d-axis current component and the q-axis current component. The active power and reactive power of each energy storage converter are calculated based on the d-axis voltage component, q-axis voltage component, d-axis current component, and q-axis current component.

3. The power equalization control method for a multi-battery energy storage system according to claim 1, characterized in that: Step four specifically involves: S1: Obtain the three-phase output voltage of each energy storage converter, transform and process it according to the adjustment frequency to obtain the d-axis voltage component and the q-axis voltage component; S2: Subtract the adjusted voltage amplitude from the d-axis voltage component and the q-axis voltage component respectively to obtain the first d-axis adjustment component and the first q-axis adjustment component after passing through the PI controller; S3: Obtain the three-phase inductor current of each energy storage converter, transform and process it according to the adjustment frequency to obtain the d-axis inductor current component and the q-axis inductor current component; S4: The difference between the first adjustment component of the d-axis and the inductor current component of the d-axis is obtained by passing the difference through a PI controller to obtain the second adjustment component of the d-axis; the difference between the first adjustment component of the q-axis and the inductor current component of the q-axis is obtained by passing the difference through a PI controller to obtain the second adjustment component of the q-axis. S5: Based on the adjustment frequency, the second adjustment components of the d-axis and q-axis are subjected to inverse transformation to obtain the three-phase adjustment voltage of each parallel energy storage converter; S6: Control the operation of each energy storage converter by pulse width modulation based on the three-phase regulation voltage of each energy storage converter, and adjust the output power of the energy storage converter accordingly.

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