CN116632806B - SOC (system on chip) quick equalization strategy without sagging control of direct-current micro-grid energy storage system - Google Patents

Abstract

The invention discloses a SOC fast balancing strategy without droop control for a DC microgrid energy storage system, which mainly includes a communication module, a current sharing module, a voltage compensation module, an SOC balancing module and a voltage and current double closed-loop module. In the communication module, each energy storage unit only communicates point-to-point with adjacent nodes, and the average value of the SOC and virtual state variables of the energy storage system can be obtained without a central controller; in the current sharing module, by introducing a transition factor, The output current is accurately distributed in proportion to the capacity of the energy storage unit; in the voltage compensation module, the drop in bus voltage is effectively compensated and the bus voltage is controlled near the rated value; in the SOC balancing module, the energy storage unit is directly affected by SOC Current closed-loop control further dynamically changes the output current to achieve rapid SOC balancing.

Description

SOC fast equalization strategy without droop control for DC microgrid energy storage system

Technical field

The invention relates to the field of DC microgrid energy storage systems, in particular to a SOC rapid equalization strategy without droop control for DC microgrid energy storage systems.

Background technique

With the rapid development of renewable energy, microgrid technology has received widespread attention. Compared with AC microgrids, DC microgrids do not need to consider issues such as phase synchronization, reactive power compensation, and harmonic suppression, and can be compatible with DC power sources such as photovoltaics and fuel cells. Due to the randomness and volatility of renewable energy power generation units in DC microgrids, energy storage systems are mainly relied on to smooth system power fluctuations and improve system stability. In order to avoid failure of the entire energy storage system due to a single point failure in the power grid, multiple energy storage units need to be connected in parallel to form a distributed energy storage system. When multiple energy storage units are used in parallel, the state-of-charge (SOC) ) will cause over-discharge or deep charging of some energy storage units, shortening the service life of distributed energy storage units. At the same time, droop control, as a commonly used current sharing method in DC microgrids, cannot take into account power accuracy at the same time due to its own characteristics. Distribution and bus voltage drop defects, so it is necessary to adjust the output current of the energy storage unit through its own capacity and SOC to ensure that the output current of the energy storage unit is accurately distributed in proportion to the capacity, SOC balance and bus voltage drop are within the allowable range.

Contents of the invention

In order to achieve the above objects, the technical solutions provided by the present invention are:

1) The two energy storage units are connected in parallel to the DC bus through the corresponding converter and the line impedance R _linei , and jointly supply power to the load R _load . At the starting point of each sampling period, the inductor current i _Li , the output current i _oi , The output voltage u _oi and the state of charge SOC _i of the energy storage unit are sampled respectively;

2) In the communication module, each energy storage unit only needs to exchange information with adjacent energy storage units, and the state of charge SOC _i and virtual state variable y of each energy storage unit in the energy storage system can be obtained without a central controller. Global information of _i , and then use the dynamic consistency algorithm to obtain the average state of charge SOC _avg and the average virtual state variable y _avg of the energy storage system;

3) In the current sharing module, divide the output current i _oi by the maximum rated current i _max of the energy storage unit, and then divide it by the energy storage unit capacity coefficient k _i to get the intermediate coefficient n _i , and then subtract the intermediate coefficient from the coefficient 1 n _i gets the transition factor m _i ;

4) In the voltage compensation module, multiply the transition factor m _i by the output voltage u _oi to obtain the virtual state variable y _i , then use the dynamic consistency algorithm to obtain the virtual state variable average value y _avg , and then use the virtual state variable average value y _avg Divide the process voltage u _zi by the transition factor m _i , and then subtract the process voltage u _zi from the reference voltage u _ref through an integrator to obtain the voltage compensation amount Δu _i ;

5) In the SOC balancing module and voltage and current double closed-loop module, the voltage compensation amount Δu _i obtained in the voltage compensation module is directly added to the reference voltage u _ref , and then the output voltage u _oi of the energy storage unit is subtracted, and then through the voltage external The loop PI controller G _V (s) obtains the current inner loop reference current I _ai , then adds I _ai to the SOC balance current I _bi and subtracts the inductor current i _Li , and the result is passed through the current inner loop PI controller G _I (s), the driving voltage u _si is obtained, and then the driving voltage u _si is compared with the triangular carrier wave to obtain the PWM modulation signal. The specific calculation process of the SOC balance current I _bi is as follows:

Subtract the local energy storage unit state of charge SOC _i from the energy storage system state of charge average SOC _avg obtained in the communication module, and then multiply by Obtain the balance coefficient q _i , where ρ is the acceleration factor and ε is the accuracy factor. Then multiply the balance coefficient q _i by the absolute value of the current inner loop reference current |I _ai | to obtain the SOC balance current I _bi and the SOC balance current I _bi The expression is:

Compared with the existing technology, the principles and advantages of this solution are as follows:

The invention discloses a SOC fast balancing strategy without droop control for a DC microgrid energy storage system, which mainly includes a communication module, a current sharing module, a voltage compensation module, an SOC balancing module and a voltage and current double closed-loop module. In the communication module, each energy storage unit only communicates point-to-point with adjacent nodes, and the average value of the SOC and virtual state variables of the energy storage system can be obtained without a central controller; in the current sharing module, by introducing a transition factor, The output current is accurately distributed in proportion to the capacity of the energy storage unit; in the voltage compensation module, the drop in bus voltage is effectively compensated and the bus voltage is controlled near the rated value; in the SOC balancing module, the energy storage unit is directly affected by SOC Current closed-loop control further dynamically changes the output current to achieve rapid SOC balancing.

Description of the drawings

Figure 1 is the main circuit diagram of the DC microgrid energy storage system in the embodiment of the present invention;

Figure 2 is a control block diagram of the SOC fast equalization strategy without droop control for the DC microgrid energy storage system in the embodiment of the present invention;

Figure 3 is a SOC waveform diagram of the energy storage unit in the embodiment of the present invention;

Figure 4 is a DC side output current waveform diagram of the energy storage unit in the embodiment of the present invention;

Figure 5 is a bus voltage waveform diagram of the energy storage system in the embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific examples:

Figure 1 is the main circuit diagram of the DC microgrid energy storage system. The energy storage system consists of two energy storage units connected in parallel through a DC-DC converter. DESU ₁ is the first energy storage unit, and u _o1 is the first energy storage unit. DC side output voltage, i _o1 is the DC side output current of the first energy storage unit, R _line1 is the line impedance corresponding to the first energy storage unit, the line impedances of the two energy storage units are 0.4Ω and 0.5Ω respectively, R _load is the load resistance.

Figure 2 is the control block diagram of the SOC fast equalization strategy without droop control for the DC microgrid energy storage system, which includes the following steps:

1) The two energy storage units are connected in parallel to the DC bus through the corresponding converter and the line impedance R _linei , and jointly supply power to the load R _load . At the starting point of each sampling period, the inductor current i _Li , the output current i _oi , The output voltage u _oi and the state of charge SOC _i of the energy storage unit are sampled respectively;

2) In the communication module, each energy storage unit only needs to exchange information with adjacent energy storage units, and the state of charge SOC _i and virtual state variable y of each energy storage unit in the energy storage system can be obtained without a central controller. Global information of _i , and then use the dynamic consistency algorithm to obtain the average state of charge SOC _avg and the average virtual state variable y _avg of the energy storage system;

3) In the current sharing module, divide the output current i _oi by the maximum rated current i _max of the energy storage unit, and then divide it by the energy storage unit capacity coefficient k _i to get the intermediate coefficient n _i , and then subtract the intermediate coefficient from the coefficient 1 n _i gets the transition factor m _i ;

4) In the voltage compensation module, multiply the transition factor m _i by the output voltage u _oi to obtain the virtual state variable y _i , then use the dynamic consistency algorithm to obtain the virtual state variable average value y _avg , and then use the virtual state variable average value y _avg Divide the process voltage u _zi by the transition factor m _i , and then subtract the process voltage u _zi from the reference voltage u _ref through an integrator to obtain the voltage compensation amount Δu _i ;

5) In the SOC balancing module and voltage and current double closed-loop module, the voltage compensation amount Δu _i obtained in the voltage compensation module is directly added to the reference voltage u _ref , and then the output voltage u _oi of the energy storage unit is subtracted, and then through the voltage external The loop PI controller G _V (s) obtains the current inner loop reference current I _ai , then adds I _ai to the SOC balance current I _bi and subtracts the inductor current i _Li , and the result is passed through the current inner loop PI controller G _I (s), the driving voltage u _si is obtained, and then the driving voltage u _si is compared with the triangular carrier wave to obtain the PWM modulation signal. The specific calculation process of the SOC balance current I _bi is as follows:

Subtract the local energy storage unit state of charge SOC _i from the energy storage system state of charge average SOC _avg obtained in the communication module, and then multiply by Obtain the balance coefficient q _i , where ρ is the acceleration factor and ε is the accuracy factor. Then multiply the balance coefficient q _i by the absolute value of the current inner loop reference current |I _ai | to obtain the SOC balance current I _bi and the SOC balance current I _bi The expression is:

Figure 3 shows the SOC waveform of the energy storage unit. The distributed energy storage system works in the discharge mode. The initial SOC ₁ and SOC ₂ are 90% and 87% respectively. When the SOC is higher than the average value, the SOC equilibrium current I _bi >0, the DC side output current i _oi becomes larger, and the energy storage unit discharges faster. The larger the SOC of the energy storage unit, the faster its SOC decreases; when the SOC is lower than the average, vice versa; finally in 1.04 seconds Achieve SOC balance at the same time.

Figure 4 is the DC side output current waveform of the energy storage unit. Since the capacity ratio of the two energy storage units is 3:2, the capacity coefficients are selected as k ₁ =3 and k ₂ =2 respectively. In the discharge mode, because With the existence of the capacity coefficient k _i , after the SOC of the two energy storage units is balanced, the output currents of the two energy storage units are 12A and 8A respectively, achieving the purpose of accurate distribution in proportion to the capacity of the energy storage unit.

Figure 5 shows the bus voltage waveform of the energy storage system. Due to the existence of the voltage compensation module, it can ensure that the bus voltage is controlled near the reference value of 400V when the system is stable. Although the bus voltage does not reach near 400V before SOC equalization, the SOC is within 1.04 seconds. Balance can be achieved when SOC is balanced, so this is acceptable; the bus voltage fluctuation caused by SOC balancing is also within the allowable range.

The implementation examples described above are only preferred embodiments of the present invention and do not limit the scope of the present invention. Therefore, any changes made based on the shape and principle of the present invention should be covered by the protection scope of the present invention.

Claims (2)

1. The SOC rapid balancing strategy without droop control for DC microgrid energy storage system is characterized by including the following steps: 1) The two energy storage units are connected in parallel to the DC bus through the corresponding converter and the line impedance R _linei , and jointly supply power to the load R _load . At the starting point of each sampling period, the inductor current i _Li , the output current i _oi , The output voltage u _oi and the state of charge SOC _i of the energy storage unit are sampled respectively; 2) In the communication module, each energy storage unit only needs to exchange information with adjacent energy storage units, and the state of charge SOC _i and virtual state variable y of each energy storage unit in the energy storage system can be obtained without a central controller. Global information of _i , and then use the dynamic consistency algorithm to obtain the average state of charge SOC _avg and the average virtual state variable y _avg of the energy storage system; 3) In the current sharing module, divide the output current i _oi by the maximum rated current i _max of the energy storage unit, and then divide it by the energy storage unit capacity coefficient k _i to get the intermediate coefficient n _i , and then subtract the intermediate coefficient from the coefficient 1 n _i gets the transition factor m _i ; 4) In the voltage compensation module, multiply the transition factor m _i by the output voltage u _oi to obtain the virtual state variable y _i , then use the dynamic consistency algorithm to obtain the virtual state variable average value y _avg , and then use the virtual state variable average value y _avg Divide the process voltage u _zi by the transition factor m _i , and then subtract the process voltage u _zi from the reference voltage u _ref through an integrator to obtain the voltage compensation amount Δu _i ; 5) In the SOC balancing module and voltage and current double closed-loop module, the voltage compensation amount Δu _i obtained in the voltage compensation module is directly added to the reference voltage u _ref , and then the output voltage u _oi of the energy storage unit is subtracted, and then through the voltage external The loop PI controller G _V (s) obtains the current inner loop reference current I _ai , then adds I _ai to the SOC balance current I _bi and subtracts the inductor current i _Li , and the result is passed through the current inner loop PI controller G _I (s), the driving voltage u _si is obtained, and then the driving voltage u _si is compared with the triangular carrier wave to obtain the PWM modulation signal. The specific calculation process of the SOC balance current I _bi is as follows: Subtract the local energy storage unit state of charge SOC _i from the energy storage system state of charge average SOC _avg obtained in the communication module, and then multiply by Obtain the balance coefficient q _i , where ρ is the acceleration factor and ε is the accuracy factor. Then multiply the balance coefficient q _i by the absolute value of the current inner loop reference current |I _ai | to obtain the SOC balance current I _bi and the SOC balance current I _bi The expression is: 2. The SOC fast equalization strategy without droop control for the DC microgrid energy storage system according to claim 1, characterized in that the value range of step 5) acceleration factor ρ is 0.6<ρ<1.2, and the equalization accuracy factor ε is The value range is 0.001<ε<0.01.