A control method for interleaved parallel DC / DC converters for SOC balancing

Abstract

The present invention discloses a control method for staggered parallel DC / DC converters for SOC balancing, which mainly includes a consistency algorithm, phase-splitting adaptive droop control, virtual voltage drop balancing control, voltage feedforward control, voltage and current dual-loop control and phase shift control. Through the consistency algorithm, each staggered parallel DC / DC converter can obtain the system's SOC average value without a central controller. Through phase-splitting adaptive droop control and virtual voltage drop balancing control, the SOC balancing of energy storage units of different capacities and the precise distribution of output current according to the capacity of the energy storage unit are achieved. At the same time, the phase-splitting adaptive droop control is used to solve the problem of uneven current distribution per phase of the staggered parallel DC / DC converter, and voltage feedforward control is introduced to effectively avoid the deviation of the bus voltage. In addition, phase shift control is used to reduce current ripple. In summary, the present invention can achieve SOC balancing of energy storage units of different capacities and precise distribution of output current according to capacity, and maintain the bus voltage at the rated value to ensure stable operation of the system.

Description

Technical Field

[0001] The present application relates to the technical field of distributed energy storage systems, and in particular to a control method for staggered parallel DC / DC converters for SOC balancing. Background Art

[0002] As global climate issues become increasingly severe, distributed power generation has become a focus of attention. In order to reduce the impact of the uncertainty of distributed power output on the power grid and load, microgrids have been proposed as a solution. Since the output power of distributed power sources is random, it is necessary to configure a distributed energy storage system to ensure the power balance of the DC microgrid. Among them, the staggered parallel DC / DC converter, as a key component of the distributed energy storage system, significantly improves the overall performance and stability of the energy storage system through its efficient energy conversion and flexible control strategy. At present, distributed energy storage systems usually use droop control to achieve accurate distribution of the output current of distributed power sources. Droop control is simple, reliable, and independent of communication. However, due to the mismatch of line impedance and the different capacities of distributed energy storage units, the traditional droop control cannot simultaneously achieve bus voltage stability and accurate distribution of output current between energy storage units according to capacity. At the same time, in order to extend the service life of the energy storage unit and avoid excessive use of a certain energy storage unit, the state of charge (SOC) of each energy storage unit should be balanced to meet the output current distribution of each energy storage unit according to the rated capacity and SOC balance. On the other hand, due to the use of staggered parallel DC / DC converters, the inductor current of each phase in a single converter may be unevenly distributed, further resulting in excessive converter output current ripple. In summary, there are still many problems that have not been solved in the process of using staggered parallel DC / DC converters in distributed energy storage systems. Summary of the invention

[0003] In order to solve the above technical problems, the present application provides a control method of staggered parallel DC / DC converters for SOC balancing.

[0004] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0005] A control method for interleaved parallel DC / DC converters for SOC balancing is provided, which comprises the following steps:

[0006] Step 1: In the distributed energy storage system, the distributed energy storage unit is connected to the DC bus through the interleaved parallel DC / DC converter via the filter capacitor. At the starting point of each sampling cycle, the inductor current I of the i-th interleaved parallel DC / DC converter is iLn , DC output voltage V ci , DC bus voltage V bus And the state of charge SOC of the i-th energy storage uniti The samples are taken respectively, where i is the converter number, i=1,2,…,m, and n is the inductor number, n=1,2.

[0007] Step 2: In the consistency algorithm module, the state of charge SOC i and virtual voltage drop V dropi As input, after the consistency algorithm, the average state of charge SOC of the energy storage system is obtained avg And the virtual voltage drop average value V dropavg .

[0008] Step 3: In the voltage feedforward control module, set the voltage setting value V ref With DC bus voltage V bus Subtract and input the voltage feedforward PI controller G PI1 (s), the result and the voltage setting value V ref After adding, the output feedforward voltage V α .

[0009] Step 4: In the phase-separated adaptive droop control module, the average state of charge SOC of the energy storage system is calculated. avg and state of charge SOC i Input the adaptive droop coefficient module and output the adaptive droop coefficient R i In equivalent resistance compensation, the n-phase inductor current I iLn The average value of the inductor current I is calculated iLavg , inductor current I iLn Subtract the average inductor current I iLavg The result is multiplied by the adjustment coefficient k and then added to the droop coefficient R i The result is judged to be zero-crossing. If it is greater than zero, the phase droop coefficient R is output. iLn The actual value of the phase droop coefficient R is output if it is less than zero. iLn is zero, and the inductor current I iLn And the phase droop coefficient R iLn Multiply to get the inductor single-phase voltage drop V in , the feed-forward voltage V α Subtract the inductor single-phase voltage drop V in , get the inductor phase droop control voltage V βn .

[0010] Step 5: In the virtual voltage drop balance control module, the equivalent resistance R eq The expression is:

[0011]

[0012] Using the n-phase inductor current I iLn The total inductor current Ii , the equivalent resistance R eq Multiply the total inductor current I i As a virtual voltage drop V dropi , the virtual voltage drop V dropi The virtual voltage drop average value V dropavg The difference is input into the virtual voltage drop equalization PI controller G PI2 (s), the result is the same as the inductor phase droop control voltage V βn Add together to get the virtual voltage drop balance voltage V γn .

[0013] Step 6: In the voltage and current dual-loop control module, the virtual voltage drop equalization voltage V γn , DC output voltage V ci and the inductor current I iLn As input, after voltage and current dual loop control, the output duty cycle D n .

[0014] Step 7: In the phase shift control module, set the duty cycle D n The corresponding modulation wave period signal is generated as input, and the signal is delayed at the same time. The output result controls the insulated gate bipolar transistor IGBT in the staggered parallel DC / DC converter.

[0015] In the specific implementation process, the adaptive droop coefficient R in step 4 i The expression is:

[0016]

[0017] Where x is the equilibrium speed factor, R oi is the initial droop coefficient, the initial droop coefficient R oi The setting ratio is inversely proportional to the capacity of the energy storage system, and the adaptive droop coefficient has different forms under charging and discharging conditions.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention discloses a control method for staggered parallel DC / DC converters for SOC balancing, which mainly includes a consistency algorithm, phase-splitting adaptive droop control, virtual voltage drop balancing control, voltage feedforward control, voltage and current dual-loop control and phase shift control. Through the consistency algorithm, each staggered parallel DC / DC converter can obtain the system's SOC average value without a central controller. Through phase-splitting adaptive droop control and virtual voltage drop balancing control, the SOC balancing of staggered parallel DC / DC converters of different capacities and the precise distribution of output current according to converter capacity are achieved. At the same time, the phase-splitting adaptive droop control is used to solve the problem of uneven current distribution per phase of the staggered parallel DC / DC converter, and voltage feedforward control is introduced to effectively avoid the deviation of the bus voltage. In addition, phase shift control is used to reduce current ripple. In summary, the present invention can achieve SOC balancing of converters of different capacities and precise distribution of output current according to capacity, and maintain the bus voltage at the rated value to ensure stable operation of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a main circuit diagram of an energy storage system using staggered parallel DC / DC converters in an embodiment of the present invention;

[0021] Figure 2 1 is a general control block diagram of an interleaved parallel DC / DC converter in an embodiment of the present invention;

[0022] Figure 3 A control block diagram of voltage feedforward control in an embodiment of the present invention;

[0023] Figure 4 It is a control block diagram of the phase-splitting adaptive droop control in an embodiment of the present invention;

[0024] Figure 5 It is a control block diagram of virtual voltage drop balancing control in an embodiment of the present invention;

[0025] Figure 6 The state of charge SOC in the embodiment of the present invention i Waveform diagram of

[0026] Figure 7 is the DC bus voltage V in the embodiment of the present invention bus Waveform diagram of

[0027] Figure 8 is the output current I in the embodiment of the present invention i Waveform diagram of

[0028] Fig. 9 is the inductor current I in the embodiment of the present invention 1Ln Waveform diagram of . DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments:

[0030] Figure 1 The main circuit diagram of the energy storage system using staggered parallel DC / DC converters is shown. The energy storage system consists of four energy storage units connected in parallel through staggered parallel DC / DC converters, where i is the converter number, i=1,2,3,4, n is the inductor number, n=1,2,DESU i is the energy storage unit, I iLn is the inductor current, V ci is the DC output voltage, V bus is the DC bus voltage, R linei is the line impedance. The line impedances of the four energy storage units are 0.5Ω, 0.6Ω, 0.54Ω, and 0.4Ω respectively. load is the load resistance, and the capacities of the four energy storage units are 3F, 3F, 2F, and 2F. To simulate the actual situation where the inductance of each phase is different due to objective factors, the inductance of each converter No. 1 is set to 0.0018H, the inductance of No. 2 is set to 0.002H, and the DC bus voltage reference value V ref Set to 400V.

[0031] Figure 2 The figure shows the overall control block diagram of the interleaved parallel DC / DC converter. Figure 3 is a control block diagram of voltage feedforward control in an embodiment of the present invention, Figure 4 is a control block diagram of the phase-splitting adaptive droop control in an embodiment of the present invention, Figure 5 This is a control block diagram of virtual voltage drop balancing control in an embodiment of the present invention, and the specific contents are as follows:

[0032] At the beginning of each sampling period, the inductor current I of the i-th interleaved parallel DC / DC converter is iLn , DC output voltage V ci , DC bus voltage V bus And the state of charge SOC of the i-th energy storage unit i The samples are taken respectively, where i is the converter number, i=1,2,…,m, and n is the inductor number, n=1,2.

[0033] In the consistency algorithm module, the state of charge SOC i and virtual voltage drop V dropi As input, after the consistency algorithm, the average state of charge SOC of the energy storage system is obtained avg And the virtual voltage drop average value V dropavg .

[0034] exist Figure 3 In the voltage feedforward control module, the voltage setting value V ref With DC bus voltage Vbus Subtract and input the voltage feedforward PI controller G PI1 (s), the result and the voltage setting value V ref After adding, the output feedforward voltage V α .

[0035] exist Figure 4 In the phase-separated adaptive droop control module, the average state of charge SOC of the energy storage system is avg and state of charge SOC i Input the adaptive droop coefficient module and output the adaptive droop coefficient R i In equivalent resistance compensation, the n-phase inductor current I iLn The average value of the inductor current I is calculated iLavg , inductor current I iLn Subtract the average inductor current I iLavg The result is multiplied by the adjustment coefficient k and then added to the droop coefficient R i The result is judged to be zero-crossing. If it is greater than zero, the phase droop coefficient R is output. iLn The actual value of the phase droop coefficient R is output if it is less than zero. iLn is zero, and the inductor current I iLn And the phase droop coefficient R iLn Multiply to get the inductor single-phase voltage drop V in , the feed-forward voltage V α Subtract the inductor single-phase voltage drop V in , get the inductor phase droop control voltage V βn .

[0036] Adaptive droop coefficient R i The expression is:

[0037]

[0038] Where x is the equilibrium speed factor, R oi is the initial droop coefficient, the initial droop coefficient R oi The setting ratio is inversely proportional to the capacity of the energy storage system, and the adaptive droop coefficient has different forms under charging and discharging conditions.

[0039] exist Figure 5 In the virtual voltage drop balance control module, the equivalent resistance R eq The expression is:

[0040]

[0041] Using the n-phase inductor current I iLn The total inductor current I i , the equivalent resistance R eq Multiply the total inductor current Ii As a virtual voltage drop V dropi , the virtual voltage drop V dropi The virtual voltage drop average value V dropavg The difference is input into the virtual voltage drop equalization PI controller G PI2 (s), the result is the same as the inductor phase droop control voltage V βn Add together to get the virtual voltage drop balance voltage V γn .

[0042] In the voltage and current dual-loop control module, the virtual voltage drop equalization voltage V γn , DC output voltage V ci and the inductor current I iLn As input, after voltage and current dual loop control, the output duty cycle D n .

[0043] In the phase shift control module, the duty cycle D n The corresponding modulation wave period signal is generated as input, and the signal is delayed at the same time. The output result controls the insulated gate bipolar transistor IGBT in the staggered parallel DC / DC converter.

[0044] Figure 6 State of charge SOC i The waveform diagram shows that under normal working conditions, the four energy storage units can dynamically adjust the output power through the phase-separated adaptive droop control module of the present invention and complete SOC balance. It can be seen from the figure that the four SOC curves converge at a certain rate and complete balance around 3 seconds, which verifies that the control method proposed in the present invention can complete SOC balance by dynamically adjusting the adaptive droop coefficient.

[0045] Figure 7 is the DC bus voltage V bus The waveform diagram shows that under normal working conditions, the voltage feedforward control module can dynamically adjust the converter output voltage to balance the voltage drop caused by the droop control. As can be seen from the figure, the DC bus voltage curve fluctuates except during the early startup process. The DC bus voltage is stable at 400V for the rest of the time, that is, the DC bus voltage reference value V ref It is verified that the control method proposed in the present invention can maintain the bus voltage to the set value through voltage feedforward control.

[0046] Figure 8 is the output current I i The waveform diagram shows that under normal working conditions, the virtual voltage drop balancing module can reduce the impact of line impedance and complete the precise distribution of current. It can be seen from the figure that the output current is finally stabilized at 9A, 9A, 6A, and 6A, respectively, achieving the goal of the output current being inversely proportional to the capacity, verifying the feasibility of the virtual voltage drop module.

[0047] Fig. 9 is the inductor current I 1Ln The waveform diagram shows that under normal working conditions, the phase-separated adaptive droop control module makes the current of each phase tend to an equal value through virtual resistance compensation, which verifies that the control method proposed in the present invention can solve the problem of uneven current distribution of each phase when the phase inductance values ​​are different.

[0048] The embodiments described above are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, all changes made according to the shape and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for interleaved parallel DC / DC converters for SOC balancing, characterized in that: The following steps are involved: Step 1: In the distributed energy storage system, the distributed energy storage unit is connected to the DC bus through the interleaved parallel DC / DC converter via the filter capacitor. At the starting point of each sampling cycle, the inductor current I of the i-th interleaved parallel DC / DC converter is iLn , DC output voltage V ci , DC bus voltage V bus And the state of charge SOC of the i-th energy storage unit i Sampling is performed respectively, where i is the converter number, i=1,2,…,m, and n is the inductor number, n=1,2; Step 2: In the consistency algorithm module, the state of charge SOC i and virtual voltage drop V dropi As input, after the consistency algorithm, the average state of charge SOC of the energy storage system is obtained avg And the virtual voltage drop average value V dropavg ; Step 3: In the voltage feedforward control module, set the voltage setting value V ref With DC bus voltage V bus Subtract and input the voltage feedforward PI controller G PI1 (s), the result and the voltage setting value V ref After adding, the output feedforward voltage V α ; Step 4: In the phase-separated adaptive droop control module, the average state of charge SOC of the energy storage system is calculated. avg and state of charge SOC i Input the adaptive droop coefficient module and output the adaptive droop coefficient R i In equivalent resistance compensation, the n-phase inductor current I iLn The average value of the inductor current I is calculated iLavg , inductor current I iLn Subtract the average inductor current I iLavg The result is multiplied by the adjustment coefficient k and then added to the droop coefficient R i The result is judged to be zero-crossing. If it is greater than zero, the phase droop coefficient R is output. iLn The actual value of the phase droop coefficient R is output if it is less than zero. iLn is zero, and the inductor current I iLn And the phase droop coefficient R iLn Multiply to get the inductor single-phase voltage drop V in , the feed-forward voltage V α Subtract the inductor single-phase voltage drop V in , get the inductor phase droop control voltage V βn ; Step 5: In the virtual voltage drop balance control module, the equivalent resistance R eq The expression is: Using the n-phase inductor current I iLn The total inductor current I i , the equivalent resistance R eq Multiply the total inductor current I i As a virtual voltage drop V dropi , the virtual voltage drop V dropi The virtual voltage drop average value V dropavg The difference is input into the virtual voltage drop equalization PI controller G PI2 (s), the result is the same as the inductor phase droop control voltage V βn Add together to get the virtual voltage drop balance voltage V γn ; Step 6: In the voltage and current dual-loop control module, the virtual voltage drop equalization voltage V γn , DC output voltage V ci and the inductor current I iLn As input, after voltage and current dual loop control, the output duty cycle D n ; Step 7: In the phase shift control module, set the duty cycle D n The corresponding modulation wave period signal is generated as input, and the signal is delayed at the same time, and the output result controls the insulated gate bipolar transistor IGBT in the staggered parallel DC / DC converter.

2. The SOC balancing-oriented interleaved parallel DC / DC converter control method according to claim 1, characterized in that: Adaptive droop coefficient R in step 4 i The expression is: Where x is the equilibrium speed factor, R oi is the initial droop coefficient, the initial droop coefficient R oi The setting ratio is inversely proportional to the capacity of the energy storage system, and the adaptive droop coefficient has different forms under charging and discharging conditions.

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