A SOC balancing control method for multiple parallel energy storage devices

Abstract

The present invention discloses a method for SOC balancing control of multiple parallel energy storage devices. First, the central controller obtains the average SOC value of x energy storage devices, and the adaptive active power droop coefficient K is obtained by a real-time correction droop coefficient method. P , and introduced into the active power-voltage droop control, then the output voltage amplitude reference is generated by introducing the voltage deviation integral method, and the output voltage command is synthesized with the output voltage frequency reference, and the output capacitor voltage inductor current double closed-loop control is performed. The control method proposed by the present invention combines the real-time correction of the droop coefficient method and the introduction of the voltage deviation integral method to achieve SOC balance under inconsistent SOC, and eliminates the influence of line impedance by introducing the voltage deviation integral method, further solving the influence of different output power on SOC balance, and finally achieving SOC balance between parallel energy storage devices under inconsistent SOC and different line impedance.

Description

Technical Field

[0001] The present invention belongs to the technical field of distributed energy storage in a microgrid island mode, and specifically relates to a SOC balancing control method for multiple parallel energy storage devices. Background Art

[0002] Environmental pollution and energy crisis are becoming increasingly serious. With the development and application of new energy generation technologies such as photovoltaic, hydropower and wind power, and in order to coordinate the contradiction between large power grids and distributed power sources, microgrid applications have emerged. Since distributed power generation in microgrids is intermittent and volatile, multiple parallel energy storage devices are required to maintain the reliability and stability of microgrid operation. The energy storage device consists of energy storage battery packs and energy storage converters.

[0003] Due to the differences in production materials and manufacturing processes of energy storage battery packs in the microgrid system, the initial SOC values ​​of the energy storage battery packs in the energy storage device are inconsistent. When the energy storage device is connected to the microgrid AC bus with inconsistent lengths, the line impedance is different, which makes the output power of each energy storage device different. These will cause the SOC of multiple parallel energy storage devices to be unbalanced during the charging and discharging process. SOC imbalance causes some energy storage devices to over-charge and discharge, reaching the charge and discharge limit, thereby shortening the service life of the energy storage device, so that a certain energy storage device will be out of operation prematurely. When the capacity of the remaining energy storage devices is insufficient to meet the load demand, some loads will be out of operation, and in more serious cases, the system will crash. Therefore, it is of great research significance to adjust the output power of the energy storage device in real time to balance the SOC under the SOC imbalance of the energy storage device caused by various situations. Summary of the invention

[0004] The purpose of the present invention is to provide a method for SOC balancing control of multiple parallel energy storage devices, which solves the impact of different output powers on SOC balancing and achieves SOC balancing among energy storage devices.

[0005] The technical solution adopted by the present invention is a method for SOC balancing control of multiple parallel energy storage devices, comprising the following steps:

[0006] Step 1: Collect the output voltage u of the energy storage converter x o_x , output current i o_x and the inductor current i L_x , obtain the current SOC of each energy storage battery pack through the SOC estimation algorithm x Value, where x represents the number of the energy storage converter, and x∈[1,n], and n represents the number of energy storage converters, and n≥2;

[0007] Step 2: Calculate the average active power P of the energy storage converter x according to the average power calculation method. x and average reactive power Qx ;

[0008] Step 3: The average active power P x After SOC balancing control, the output voltage amplitude E of the energy storage converter x is obtained x ; The average reactive power Q x and reactive power droop coefficient K q Multiply them to get the frequency change Δf, and then multiply Δf by the no-load point frequency f * The output frequency reference f of the energy storage converter x is obtained by subtraction; finally, the output reference voltage u is synthesized ref_x ;

[0009] Step 4: Set the output voltage closed-loop instruction u ref_vir_x The output voltage u of the energy storage converter x o_x The difference is passed through the voltage regulator to obtain the inductor current command i of the energy storage converter x. L_ref_x ;

[0010] Step 5: Set the inductor current command i L_ref_x and the inductor current i of the energy storage converter x L_x The difference is passed through the current regulator to obtain the modulation signal u x ;

[0011] Step 6: Modulate the signal u x The driving and protection circuit drives the four power switch tubes S1-S4 of the H-bridge inverter circuit to be turned on and off, thereby achieving SOC balance among the energy storage devices.

[0012] The present invention is also characterized in that

[0013] In step 1, the SOC is estimated using the ampere-hour integration method, the open circuit voltage method or the Kalman filter method.

[0014] In step 2, the average power is calculated using the traditional product method, virtual orthogonal vector calculation method or integral averaging method.

[0015] The specific steps of step 3 are:

[0016] Step 3.1, construct the adaptive active droop coefficient K in the active-voltage droop control of the energy storage converter x through the SOC balancing method of real-time correction of the droop coefficient when the SOC is inconsistent p ;

[0017] Step 3.2: The average active power P of the energy storage converter x is x and active power droop coefficient K p Multiply them to get the voltage change ΔU x , ΔU x and the no-load voltage amplitude U *The voltage amplitude U is obtained by subtracting e_x ;

[0018] In step 3.2, ΔU x and the no-load voltage amplitude U * The voltage amplitude U is obtained by subtracting e_x The calculation formula is:

[0019] U e_x =U * -K P ·P x ;

[0020] Step 3.3, set the voltage amplitude U e_x As input, the output voltage amplitude reference E of the energy storage converter x is obtained through SOC balancing control of the voltage deviation integration method when the line impedance is different. x ;

[0021] In step 3.3, the voltage amplitude U e_x As input, the output voltage amplitude reference E of the energy storage converter x is obtained through SOC balancing control of the voltage deviation integration method when the line impedance is different. x The calculation formula is:

[0022]

[0023] Among them, U pcc is the bus voltage amplitude, k i is the integral adjustment coefficient;

[0024] Step 3.4: reference the output voltage amplitude of the energy storage converter x to E x The output voltage frequency reference f is synthesized into the output voltage reference u of converter x ref_x .

[0025] In step 3.1, the adaptive active droop coefficient K of the energy storage converter x is constructed according to the real-time modified droop coefficient method. p The method is:

[0026] A, collect the SOC of x energy storage battery packs x The central controller calculates the average SOC value SOC ave , the SOC average value calculation formula is:

[0027]

[0028] B, collect the energy storage battery SOC x Value and SOC average SOC ave The difference is obtained through the proportional integral regulator. The formula is as follows:

[0029]

[0030] in, is the equilibrium factor, k mp is the proportional adjustment coefficient, k mi is the integral adjustment coefficient;

[0031] C, in the discharge state, Subtract from 1 and add Multiply to get the adaptive active power droop coefficient K P ; In the charging state, and 1, and Multiply to get the adaptive active power droop coefficient K P , K P The calculation formula is as follows:

[0032]

[0033] in is the initial droop coefficient.

[0034] In step 4, the voltage regulator adopts a proportional-integral regulator, a deadbeat control regulator, a proportional resonant regulator or a repetitive control regulator.

[0035] In step 5, the current regulator adopts a deadbeat control regulator, a predictive current regulator or a proportional regulator.

[0036] The beneficial effects of the present invention are:

[0037] 1) The method of the present invention obtains the average value of the SOC of the energy storage battery group by means of communication, and then transmits the average value of the SOC to the local controller for processing. The deviation of the SOC between the energy storage devices is adjusted by the proportional integral controller, which can speed up the SOC balancing speed and can be extended to multiple energy storage devices;

[0038] 2) The existing SOC balancing control method considering mismatched line impedance adopts the method of adding a fixed virtual impedance to achieve impedance matching of the energy storage device, and then achieves SOC balancing through the SOC balancing stage. However, as the line impedance changes, new deviations will be formed between the SOCs in the energy storage device. The method proposed in the present invention combines the real-time correction of the droop coefficient method and the introduction of the voltage deviation integral method to achieve SOC balancing under inconsistent SOCs by real-time correction of the droop coefficient of the energy storage device, and eliminates the influence of line impedance by introducing the voltage deviation integral method, further solving the influence of different output power on SOC balancing, and finally achieving SOC balancing with strong adaptability.

[0039] 3) The method of the present invention does not require detection of converter line impedance, and is therefore applicable to microgrid systems of various structures and is simple to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of a circuit structure of multiple energy storage devices connected in parallel in an isolated island microgrid on which the method of the present invention relies;

[0041] Figure 2 The overall control block diagram of the energy storage device parallel system based on SOC balancing control of the method of the present invention;

[0042] Figure 3 It is a structural diagram of SOC balancing control combining the droop coefficient correction method when SOC is inconsistent and the voltage deviation integration method when line impedance is different in the method of the present invention;

[0043] a. When the SOC is inconsistent, the SOC balancing control process of the real-time correction droop coefficient method; b. When the line impedance is different, the SOC balancing control process of the voltage deviation integration method.

[0044] Figure 4 It is a simulation result diagram of the SOC waveform of the energy storage battery pack in the discharge state of the energy storage device when the SOC is inconsistent and the line impedance is different in the method of the present invention;

[0045] Figure 5 It is a simulation result diagram of the output power waveform of the energy storage device in the discharge state of the energy storage device when the SOC is inconsistent and the line impedance is different in the method of the present invention;

[0046] Figure 6 This is a simulation result diagram of the SOC waveform of the energy storage battery pack when the SOC is inconsistent and the line impedance is different in the method of the present invention, when the energy storage device is in a charging state.

[0047] Figure 7 This is a simulation result diagram of the output power waveform of the energy storage device in the charging state when the SOC is inconsistent and the line impedance is different in the method of the present invention. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] The method of the present invention is based on a multiple energy storage device parallel system that the SOC balancing control method combines with the real-time correction droop coefficient method and the introduction of the voltage deviation integral method, such as Figure 1 As shown, it includes multiple energy storage battery groups, each of which is connected to the public AC bus after passing through the energy storage converter, filter and line impedance, where L x , C x is the inductance and capacitance of the filter, Z lx is the line impedance, x = 1, 2, 3 ... n; then the common AC bus supplies power to the load, which can be resistive, inductive, capacitive or nonlinear;

[0050] The present invention provides a method for balancing the SOC of multiple parallel energy storage devices. Figure 2-3 As shown, the following steps are included:

[0051] Step 1: Collect the output voltage u of the energy storage converter x o_x , output current i o_x and the inductor current i L_x , obtain the current SOC of each energy storage battery pack through the SOC estimation algorithm x Value, where x represents the number of the energy storage converter, and x∈[1,n], and n represents the number of energy storage converters, and n≥2;

[0052] In step 1, the SOC is estimated using the ampere-hour integration method, the open circuit voltage method or the Kalman filter method.

[0053] Step 2: Calculate the average active power P of the energy storage converter x according to the average power calculation method. x and average reactive power Q x ;

[0054] In step 2, the average power is calculated using the traditional product method, virtual orthogonal vector calculation method or integral averaging method.

[0055] Step 3: The average active power P x After SOC balancing control, the output voltage amplitude E of the energy storage converter x is obtained x ; The average reactive power Q x and reactive power droop coefficient K q Multiply them to get the frequency change Δf, and then multiply Δf by the no-load point frequency f * The output frequency reference f of the energy storage converter x is obtained by subtraction; finally, the output reference voltage u is synthesized ref_x ;

[0056] The specific steps of step 3 are:

[0057] Step 3.1, construct the adaptive active droop coefficient K in the active-voltage droop control of the energy storage converter x through the SOC balancing method of real-time correction of the droop coefficient when the SOC is inconsistent p ;

[0058] In step 3.1, the adaptive active droop coefficient K of the energy storage converter x is constructed according to the real-time modified droop coefficient method. p The method is:

[0059] A, collect the SOC of x energy storage battery packs x The central controller calculates the average SOC value SOC ave , the SOC average value calculation formula is:

[0060]

[0061] B, collect the energy storage battery SOC x Value and SOC average SOC ave The difference is obtained through the proportional integral regulator. The formula is as follows:

[0062]

[0063] in, is the equilibrium factor, k mp is the proportional adjustment coefficient, k mi is the integral adjustment coefficient;

[0064] C, in the discharge state, Subtract from 1 and add Multiply to get the adaptive active power droop coefficient K P ; In the charging state, and 1, and Multiply to get the adaptive active power droop coefficient K P . K P The calculation formula is as follows:

[0065]

[0066] in is the initial droop coefficient;

[0067] Step 3.2: The average active power P of the energy storage converter x is x and active power droop coefficient K p Multiply them to get the voltage change ΔU x , ΔU x and the no-load voltage amplitude U * The voltage amplitude U is obtained by subtracting e_x ;

[0068] In step 3.2, ΔU x and the no-load voltage amplitude U * The voltage amplitude U is obtained by subtracting e_x The calculation formula is:

[0069] U e_x =U * -K P ·P x ;

[0070] Step 3.3, set the voltage amplitude U e_xAs input, the output voltage amplitude reference E of the energy storage converter x is obtained through SOC balancing control of the voltage deviation integration method when the line impedance is different. x ;

[0071] In step 3.3, the voltage amplitude U e_x As input, the output voltage amplitude reference E of the energy storage converter x is obtained through SOC balancing control of the voltage deviation integration method when the line impedance is different. x The calculation formula is:

[0072]

[0073] Among them, U pcc is the bus voltage amplitude, k i is the integral adjustment coefficient;

[0074] Step 3.4: reference the output voltage amplitude of the energy storage converter x to E x The output voltage frequency reference f is synthesized into the output voltage reference u of converter x ref_x ;

[0075] Step 4: Set the output voltage closed-loop instruction u ref_vir_x The output voltage u of the energy storage converter x o_x The difference is passed through the voltage regulator to obtain the inductor current command i of the energy storage converter x. L_ref_x ;

[0076] In step 4, the voltage regulator adopts a proportional-integral regulator, a deadbeat control regulator, a proportional resonant regulator or a repetitive control regulator.

[0077] Step 5: Set the inductor current command i L_ref_x and the inductor current i of the energy storage converter x L_x The difference is passed through the current regulator to obtain the modulation signal u x ;

[0078] In step 5, the current regulator adopts a deadbeat control regulator, a predictive current regulator or a proportional regulator.

[0079] Step 6: Modulate the signal u x The driving and protection circuit drives the four power switch tubes S1-S4 of the H-bridge inverter circuit to be turned on and off, thereby achieving SOC balance among the energy storage devices.

[0080] The present invention is based on the simulation results of a SOC balancing control method for multiple parallel energy storage devices, such as Figure 4-7 shown.

[0081] Figure 4-5This is the simulation result diagram of the three energy storage devices under discharge state when the SOC is inconsistent and the line impedance is different. The initial SOC values ​​of the three energy storage battery groups are 0.8, 0.75 and 0.7 respectively. It can be seen from the figure that at about 6s, the SOC of the three energy storage battery groups tends to be consistent, and the output power between the energy storage devices tends to be balanced.

[0082] Figure 6-7 This is a simulation result diagram of the charging state of the three energy storage devices when the SOC is inconsistent and the line impedance is different. The initial SOC values ​​of the three energy storage battery groups are 0.3, 0.35 and 0.4 respectively. It can be seen from the figure that at around 6s, the SOC of the three energy storage battery groups tends to be consistent, and the output power between the energy storage devices tends to be balanced.

[0083] The method of the present invention aims at the problem of SOC imbalance of each energy storage device caused by different SOCs of multiple parallel energy storage devices and different line impedances in low-voltage microgrids, and proposes a SOC balancing control method based on the combination of real-time correction of droop coefficient method and introduction of voltage deviation integral method. SOC balancing under inconsistent SOC is achieved by real-time correction of the droop coefficient of the energy storage device, and the influence of line impedance is eliminated by introducing the voltage deviation integral method, further solving the influence of different output power on SOC balancing, and finally achieving SOC balancing between energy storage devices.

Claims

1. A method for SOC balancing control of multiple parallel energy storage devices, characterized in that: The following steps are involved: Step 1: Collect the output voltage u of the energy storage converter x o_x , output current i o_x and the inductor current i L_x , obtain the current SOC of each energy storage battery pack through the SOC estimation algorithm x Value, where x represents the number of the energy storage converter, and x∈[1,n], and n represents the number of energy storage converters, and n≥2; Step 2: Calculate the average active power P of the energy storage converter x according to the average power calculation method. x and average reactive power Q x ; Step 3: The average active power P x After SOC balancing control, the output voltage amplitude E of the energy storage converter x is obtained x ; The average reactive power Q x and reactive power droop coefficient K q Multiply them to get the frequency change Δf, and then multiply Δf by the no-load point frequency f * The output frequency reference f of the energy storage converter x is obtained by subtraction; finally, the output reference voltage u is synthesized ref_x ; The specific steps of step 3 are: Step 3.1, construct the adaptive active droop coefficient K in the active-voltage droop control of the energy storage converter x through the SOC balancing method of real-time correction of the droop coefficient when the SOC is inconsistent p ; In step 3.1, the adaptive active droop coefficient K of the energy storage converter x is constructed according to the real-time modified droop coefficient method. p The method is: A, collect the SOC of x energy storage battery packs x The central controller calculates the average SOC value SOC ave , the SOC average value calculation formula is: B, collect the energy storage battery SOC x Value and SOC average SOC ave The difference is obtained through the proportional integral regulator. The formula is as follows: in, is the equilibrium factor, k mp is the proportional adjustment coefficient, k mi is the integral adjustment coefficient; C, in the discharge state, Subtract from 1 and add Multiply to get the adaptive active power droop coefficient K P ; In the charging state, and 1, and Multiply to get the adaptive active power droop coefficient K P , K P The calculation formula is as follows: in is the initial droop coefficient; Step 3.2: The average active power P of the energy storage converter x is x and active power droop coefficient K p Multiply them to get the voltage change ΔU x , ΔU x and the no-load voltage amplitude U * The voltage amplitude U is obtained by subtracting e_x ; In step 3.2, ΔU x and the no-load voltage amplitude U * The voltage amplitude U is obtained by subtracting e_x The calculation formula is: IN e_x =U * -K P ·P x ; Step 3.3, set the voltage amplitude U e_x As input, the output voltage amplitude reference E of the energy storage converter x is obtained through SOC balancing control of the voltage deviation integration method when the line impedance is different. x ; In step 3.3, the voltage amplitude U e_x As input, the output voltage amplitude reference E of the energy storage converter x is obtained through SOC balancing control of the voltage deviation integration method when the line impedance is different. x The calculation formula is: Among them, U pcc is the bus voltage amplitude, k i is the integral adjustment coefficient; Step 3.4: reference the output voltage amplitude of the energy storage converter x to E x The output voltage frequency reference f is synthesized into the output reference voltage u of converter x ref_x ; Step 4: Set the output voltage closed-loop instruction u ref_vir_x The output voltage u of the energy storage converter x o_x The difference is passed through the voltage regulator to obtain the inductor current command i of the energy storage converter x. L_ref_x ; Step 5: Set the inductor current command i L_ref_x and the inductor current i of the energy storage converter x L_x The difference is passed through the current regulator to obtain the modulation signal u x ; Step 6: Modulate the signal u x The driving and protection circuit drives the four power switch tubes S1-S4 of the H-bridge inverter circuit to be turned on and off, thereby achieving SOC balance among the energy storage devices.

2. A method for SOC balancing control of multiple parallel energy storage devices according to claim 1, characterized in that: In step 1, the SOC is estimated using the ampere-hour integration method, the open circuit voltage method or the Kalman filter method.

3. The SOC balancing control method for multiple parallel energy storage devices according to claim 1 is characterized in that: In step 2, the average power is calculated using the traditional product method, virtual orthogonal vector calculation method or integral averaging method.

4. The SOC balancing control method for multiple parallel energy storage devices according to claim 1 is characterized in that: In step 4, the voltage regulator adopts a proportional-integral regulator, a deadbeat control regulator, a proportional resonant regulator or a repetitive control regulator.

5. The SOC balancing control method for multiple parallel energy storage devices according to claim 1, characterized in that: In step 5, the current regulator adopts a deadbeat control regulator, a predictive current regulator or a proportional regulator.

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