Off-grid inversion control method of energy storage system

Abstract

The invention discloses an off-grid inversion control method for an energy storage system, and the method employs an off-grid control system which is composed of a first collection circuit, a second collection circuit, a power calculation module, a droop control circuit, a voltage synthesis module, a voltage and current double-loop control circuit, a third collection module, a modulation circuit, and a virtual impedance circuit. The voltage and current double-loop control circuit is composed of a current inner loop circuit and a voltage outer loop circuit, and the structure solves the problems that the response speed of a control system is relatively slow and the precision of the control system is not high enough.

Description

Technical Field

[0001] The present invention relates to the technical field of power control, and in particular to an off-grid inverter control method for an energy storage system. Background Art

[0002] Energy storage system, also known as energy storage system, is a device or system that can store excess heat, kinetic energy, electrical energy, potential energy, chemical energy and other energies and release them when needed. Its working principle is to convert energy into different physical forms for storage so that it can be converted back into energy supply when needed. Energy storage systems are widely used in many fields such as power systems, renewable energy, industry and civil buildings. Among them, the off-grid inverter control method refers to how the inverter controls the output voltage, current and power to meet the needs of the load without the support of the large power grid. The main control goal of the off-grid inverter is to output stable voltage and current that meet the load operating conditions. Since the system does not have the voltage and frequency support of the large power grid, the inverter needs to independently adjust the amplitude, frequency and phase of the output voltage, as well as the size and phase of the output current to ensure that the load can work normally.

[0003] For example, the Chinese patent "A Grid-connected and Off-grid Switching Device for Energy Storage System" with announcement number CN220139245U includes a battery module, an energy storage converter and a static transfer switch. The positive and negative electrodes of the battery module are connected to the positive and negative electrodes of the energy storage converter respectively. The three phases of the AC output end of the energy storage converter are connected to the three phases of the input end of the static transfer switch and the three phases of the load respectively. The three phases of the output end of the static transfer switch are connected to the three phases of the load and the three phases of the grid respectively. A DC circuit breaker is provided between the battery module and the energy storage converter. The DC circuit breaker is closed under normal circumstances. When the current flowing through exceeds the capacity of the energy storage inverter, it is disconnected. A first AC circuit breaker is arranged between the connection lines between the three phases of the AC output end of the energy storage inverter and the three phases of the load. The first AC circuit breaker is three-phase and is respectively connected to each connected wiring line. A second AC circuit breaker is arranged on the connection line between the three phases of the output end of the static conversion switch and the three phases of the load. The second AC circuit breaker is three-phase and is respectively connected to each connected wiring line. The static conversion switch adopts thyristor as a switching device, and the energy storage inverter adopts a DC / AC bidirectional converter that changes the output and input power according to the load.

[0004] Although the above-mentioned existing technology can realize off-grid inverter control of the inverter, in actual use, on the one hand, the control system response speed is relatively slow, and it may not be able to respond in time to the rapidly changing load, resulting in fluctuations in the output voltage and frequency. On the other hand, the accuracy of the control system is not high enough. Usually, the performance of droop control is greatly affected by parameters such as the droop coefficient. If the parameters such as the droop coefficient change, the control performance will be reduced. Therefore, it does not meet the existing needs. In this regard, we propose an off-grid inverter control method for an energy storage system. Summary of the invention

[0005] The object of the present invention is to provide an off-grid inverter control method for an energy storage system to solve the problems of relatively slow response speed of the control system and insufficient precision of the control system proposed in the above background technology.

[0006] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: an off-grid inverter control method for an energy storage system, comprising an off-grid control system, wherein the off-grid control system is composed of a first acquisition circuit, a second acquisition circuit, a power calculation module, a droop control circuit, a voltage synthesis module, a voltage-current dual-loop control circuit, a third acquisition module, a modulation circuit and a virtual impedance circuit, and the voltage-current dual-loop control circuit is composed of a current inner loop circuit and a voltage outer loop circuit.

[0007] Preferably, the current inner loop circuit is composed of a current regulator, a modulation circuit, a switch circuit and a current feedback circuit.

[0008] Preferably, the voltage outer loop circuit consists of a voltage regulator and a voltage feedback circuit.

[0009] Preferably, the expression of the droop control circuit is:

[0010]

[0011] Among them, m is the active frequency droop characteristic coefficient, n is the reactive voltage droop characteristic coefficient, F n is the rated frequency of the power grid, P n is the output active power of the micro power source at the rated frequency, U0 is the voltage amplitude when the output reactive power of the micro power source is zero, and P and Q are the measured values ​​of the active and reactive power output of the inverter power source, respectively.

[0012] Preferably, the expression of the virtual impedance circuit is:

[0013]

[0014] Among them, U refd , U refq All are command voltage, L v is the virtual inductance, w is the virtual characteristic coefficient, ioq 、i od Both are inverter output currents.

[0015] Preferably, the input ends of the first acquisition circuit and the second acquisition circuit are electrically connected to the inverter, the output ends of the first acquisition circuit and the second acquisition circuit are connected to the power calculation module, and the other output end of the second acquisition circuit is electrically connected to the input and output ends of the virtual impedance circuit, the output end of the power calculation module is electrically connected to the input end of the droop control circuit, and the output end of the droop control circuit is electrically connected to the input end of the voltage synthesis module.

[0016] Preferably, the input end of the voltage-current dual-loop control circuit is electrically connected to the output end of the voltage synthesis module, the output end of the voltage-current dual-loop control circuit is electrically connected to the input end of the third acquisition module, and the output end of the third acquisition module is electrically connected to the input end of the modulation circuit.

[0017] Preferably, the output end of the virtual impedance circuit is electrically connected to another input end of the voltage synthesis module.

[0018] Preferably, the output end of the voltage regulator is electrically connected to the input end of the current regulator, the output end of the current regulator is electrically connected to the input end of the modulation circuit, the output end of the modulation circuit is electrically connected to the input end of the switching circuit, the output end of the switching circuit is electrically connected to the input end of the current feedback circuit, and the output end of the current feedback circuit is electrically connected to another input end of the current regulator.

[0019] Preferably, another output terminal of the switch circuit is electrically connected to an input terminal of a voltage feedback circuit, and an output terminal of the voltage feedback circuit is electrically connected to another input terminal of a voltage regulator.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention can improve the response speed of the off-grid control system by providing a voltage and current dual-loop control circuit. The voltage and current dual-loop control circuit is composed of a current inner loop circuit and a voltage outer loop circuit. The two loops are independent of each other but interact with each other to jointly realize stable control of the circuit. The voltage outer loop circuit is responsible for measuring and controlling the magnitude of the power supply output voltage to maintain a stable output voltage. It usually includes a comparator and a voltage feedback circuit. The comparator compares the output voltage signal with the reference voltage signal and outputs a control signal. The voltage feedback circuit sends the control signal back to the output port of the power supply to adjust the output voltage; the current inner loop circuit is responsible for measuring the magnitude of the power supply output current, and realizes closed-loop control of the output current according to the current feedback loop flowing through the load. It samples the current output by the power supply and compares it with the set current to calculate the error signal, and then inputs the error signal into the current controller for processing to generate a control signal to control the current output by the power supply. When the output voltage deviates from the reference voltage, the voltage comparator will detect this deviation and generate an error signal. This error signal is sent to the voltage controller, and after processing, a control signal is generated. The control signal acts on the output end of the power supply to adjust the output voltage of the power supply to make it close to the reference voltage until the output voltage stabilizes near the reference voltage. The current inner loop circuit also obtains the current error signal by sampling the current output by the power supply and comparing it with the set current. The current error signal is sent to the current controller for processing to generate a corresponding control signal. This control signal acts directly on the output end of the power supply to control the output current of the power supply to keep it near the set current value. The dual-loop control has a fast response speed to the circuit load change, and can quickly adjust the output voltage and current when the load changes to maintain the stable operation of the circuit.

[0022] 2. The present invention can improve the control accuracy of the off-grid control system by providing a virtual impedance circuit. The virtual impedance circuit first converts the digital signal into an analog signal by digital signal processing, applies the effect of virtual impedance during the processing, and then uses an algorithm to simulate the impedance characteristics of components such as resistors, inductors, and capacitors. The impedance size, phase, and frequency response parameters are adjusted as needed to achieve precise control of the circuit behavior, thereby improving the control accuracy of the off-grid control circuit.

[0023] 3. In the present invention, the virtual impedance circuit and the voltage-current dual-loop control circuit are regulated by the droop control circuit. The droop control circuit first detects the output power of the inverter, including active power and reactive power. Then, through decoupling control, the droop control circuit adjusts the output frequency according to the change of active power, and adjusts the amplitude of the output voltage according to the change of reactive power. According to the droop characteristic curve and the real-time power measurement value, the droop control calculates the reference value of the inverter output voltage and frequency. Finally, the reference value is used as the input of the voltage-current dual-loop control circuit to guide the output voltage and current regulation of the inverter. The value of the virtual impedance is adjusted as needed to optimize the power distribution and voltage and current regulation, so that the overall off-grid control system operates stably, thereby improving the control effect of the off-grid control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The overall structural principle diagram of the control system of the present invention;

[0025] Figure 2 It is a schematic diagram of the dual-loop control circuit structure of the present invention;

[0026] Figure 3 It is a structural diagram of the droop circuit of the present invention;

[0027] Figure 4 It is a structural diagram of the dual-loop control circuit of the present invention;

[0028] Figure 5 This is a structural diagram of the virtual impedance circuit of the present invention.

[0029] In the figure: 1. off-grid control system; 2. first acquisition circuit; 3. second acquisition circuit; 4. power calculation module; 5. droop control circuit; 6. voltage synthesis module; 7. voltage and current dual-loop control circuit; 701. current inner loop circuit; 7011. current regulator; 7012. modulation circuit; 7013. switch circuit; 7014. current feedback circuit; 702. voltage outer loop circuit; 7021. voltage regulator; 7022. voltage feedback circuit; 8. third acquisition module; 9. modulation circuit; 10. virtual impedance circuit. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] See also Figure 1-5An embodiment of the present invention is as follows: an off-grid inverter control method for an energy storage system, comprising an off-grid control system 1, the off-grid control system 1 being composed of a first acquisition circuit 2, a second acquisition circuit 3, a power calculation module 4, a droop control circuit 5, a voltage synthesis module 6, a voltage-current dual-loop control circuit 7, a third acquisition module 8, a modulation circuit 9 and a virtual impedance circuit 10, the voltage-current dual-loop control circuit 7 being composed of a current inner loop circuit 701 and a voltage outer loop circuit 702.

[0032] When the output voltage deviates from the reference voltage, the voltage comparator will detect this deviation and generate an error signal. This error signal is sent to the voltage controller, and after processing, a control signal is generated. The control signal acts on the output end of the power supply to adjust the output voltage of the power supply to make it close to the reference voltage until the output voltage stabilizes near the reference voltage. The current loop also obtains a current error signal by sampling the current output by the power supply and comparing it with the set current. The current error signal is sent to the current controller for processing to generate a corresponding control signal. This control signal acts directly on the output end of the power supply to control the output current of the power supply to keep it near the set current value.

[0033] See also Figure 1 and Figure 4 The current inner loop circuit 701 is composed of a current regulator 7011, a modulation circuit 7012, a switch circuit 7013 and a current feedback circuit 7014, so as to control the output current through the current inner loop circuit 701.

[0034] See also Figure 1 and Figure 4 The voltage outer loop circuit 702 is composed of a voltage regulator 7021 and a voltage feedback circuit 7022, so that the output voltage can be controlled through the voltage outer loop circuit 702.

[0035] See also Figure 1 and Figure 3 , the expression of droop control circuit 5 is:

[0036]

[0037] Among them, m is the active frequency droop characteristic coefficient, n is the reactive voltage droop characteristic coefficient, F n is the rated frequency of the power grid, P n is the output active power of the micro power supply at the rated frequency, U0 is the voltage amplitude when the output reactive power of the micro power supply is zero, P and Q are the measured values ​​of the active and reactive power output of the inverter power supply, respectively, which facilitates the preliminary control of the control system through the droop control circuit 5.

[0038] See also Figure 1 and Figure 5, the expression of the virtual impedance circuit 10 is:

[0039]

[0040] Among them, U refd , U refq All are command voltage, L v is the virtual inductance, w is the virtual characteristic coefficient, i oq 、i od Both are inverter output currents, which facilitates improving the control accuracy of the control system through the virtual impedance circuit 10.

[0041] See also Figure 1 The input ends of the first acquisition circuit 2 and the second acquisition circuit 3 are both electrically connected to the inverter, the output ends of the first acquisition circuit 2 and the second acquisition circuit 3 are connected to the power calculation module 4, and the other output end of the second acquisition circuit 3 is electrically connected to the input end of the virtual impedance circuit 10, the output end of the power calculation module 4 is electrically connected to the input end of the droop control circuit 5, and the output end of the droop control circuit 5 is electrically connected to the input end of the voltage synthesis module 6, so that the active voltage or the reactive voltage can be distinguished through the first acquisition circuit 2 and the second acquisition circuit 3.

[0042] See also Figure 1 The input end of the voltage-current dual-loop control circuit 7 is electrically connected to the output end of the voltage synthesis module 6, the output end of the voltage-current dual-loop control circuit 7 is electrically connected to the input end of the third acquisition module 8, and the output end of the third acquisition module 8 is electrically connected to the input end of the modulation circuit 9, so that the voltage processed by the voltage-current dual-loop control circuit 7 is transmitted to the modulation circuit 9 through the third acquisition module 8.

[0043] See also Figure 1 The output end of the virtual impedance circuit 10 is electrically connected to the other input end of the voltage synthesis module 6, so that the virtual impedance circuit 10 can transmit the processed voltage to the voltage synthesis module 6.

[0044] See also Figure 2 and Figure 4 The output end of the voltage regulator 7021 is electrically connected to the input end of the current regulator 7011, the output end of the current regulator 7011 is electrically connected to the input end of the modulation circuit 7012, the output end of the modulation circuit 7012 is electrically connected to the input end of the switch circuit 7013, the output end of the switch circuit 7013 is electrically connected to the input end of the current feedback circuit 7014, and the output end of the current feedback circuit 7014 is electrically connected to the other input end of the current regulator 7011, so as to facilitate the transmission of the current signal to the current regulator 7011 through the current feedback circuit 7014.

[0045] See also Figure 2 and Figure 4 The other output end of the switch circuit 7013 is electrically connected to the input end of the voltage feedback circuit 7022, and the output end of the voltage feedback circuit 7022 is electrically connected to the other input end of the voltage regulator 7021, so as to facilitate the transmission of the voltage signal to the voltage regulator 7021 through the voltage feedback circuit 7022.

[0046] Working principle: The virtual impedance circuit 10 first converts the digital signal into an analog signal by digital signal processing, applies the effect of virtual impedance in the processing process, and then uses the algorithm to simulate the impedance characteristics of components such as resistors, inductors, capacitors, etc. The impedance size, phase and frequency response parameters are adjusted as needed to achieve precise control of the circuit behavior. The droop control circuit 5 first detects the output power of the inverter, including active power and reactive power. Then, through decoupling control, the droop control circuit 5 adjusts the output frequency according to the change of active power and the amplitude of the output voltage according to the change of reactive power. According to the droop characteristic curve and the real-time power measurement value, the droop control calculates the reference value of the inverter output voltage and frequency. Finally, the reference value is used as the input of the voltage and current dual-loop control circuit 7 to guide the output voltage and current regulation of the inverter; the value of the virtual impedance is adjusted as needed to optimize power distribution and voltage and current regulation.

[0047] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. An off-grid inverter control method for an energy storage system, comprising an off-grid control system (1), characterized in that: The off-grid control system (1) is composed of a first acquisition circuit (2), a second acquisition circuit (3), a power calculation module (4), a droop control circuit (5), a voltage synthesis module (6), a voltage-current dual-loop control circuit (7), a third acquisition module (8), a modulation circuit (9) and a virtual impedance circuit (10); the voltage-current dual-loop control circuit (7) is composed of a current inner loop circuit (701) and a voltage outer loop circuit (702).

2. The off-grid inverter control method of an energy storage system according to claim 1, characterized in that: The current inner loop circuit (701) is composed of a current regulator (7011), a modulation circuit (7012), a switch circuit (7013) and a current feedback circuit (7014).

3. The off-grid inverter control method of an energy storage system according to claim 2, characterized in that: The voltage outer loop circuit (702) is composed of a voltage regulator (7021) and a voltage feedback circuit (7022).

4. The off-grid inverter control method of an energy storage system according to claim 3, characterized in that: The expression of the droop control circuit (5) is: Among them, m is the active frequency droop characteristic coefficient, n is the reactive voltage droop characteristic coefficient, F n is the rated frequency of the power grid, P n is the output active power of the micro power source at the rated frequency, U0 is the voltage amplitude when the output reactive power of the micro power source is zero, and P and Q are the measured values ​​of the active and reactive power output of the inverter power source, respectively.

5. The off-grid inverter control method of an energy storage system according to claim 4, characterized in that: The expression of the virtual impedance circuit (10) is: Among them, U refd , U refq All are command voltage, L v is the virtual inductance, w is the virtual characteristic coefficient, i oq 、i od Both are inverter output currents.

6. The off-grid inverter control method of an energy storage system according to claim 5, characterized in that: The input ends of the first acquisition circuit (2) and the second acquisition circuit (3) are both electrically connected to the inverter, the output ends of the first acquisition circuit (2) and the second acquisition circuit (3) are connected to the power calculation module (4), and the other output end of the second acquisition circuit (3) is electrically connected to the input and output ends of the virtual impedance circuit (10), the output end of the power calculation module (4) is electrically connected to the input end of the droop control circuit (5), and the output end of the droop control circuit (5) is electrically connected to the input end of the voltage synthesis module (6).

7. The off-grid inverter control method of an energy storage system according to claim 6, characterized in that: The input end of the voltage-current dual-loop control circuit (7) is electrically connected to the output end of the voltage synthesis module (6), the output end of the voltage-current dual-loop control circuit (7) is electrically connected to the input end of the third acquisition module (8), and the output end of the third acquisition module (8) is electrically connected to the input end of the modulation circuit (9).

8. The off-grid inverter control method of an energy storage system according to claim 7, characterized in that: The output end of the virtual impedance circuit (10) is electrically connected to another input end of the voltage synthesis module (6).

9. The off-grid inverter control method of an energy storage system according to claim 8, characterized in that: The output end of the voltage regulator (7021) is electrically connected to the input end of the current regulator (7011), the output end of the current regulator (7011) is electrically connected to the input end of the modulation circuit (7012), the output end of the modulation circuit (7012) is electrically connected to the input end of the switch circuit (7013), the output end of the switch circuit (7013) is electrically connected to the input end of the current feedback circuit (7014), and the output end of the current feedback circuit (7014) is electrically connected to another input end of the current regulator (7011).

10. The off-grid inverter control method of an energy storage system according to claim 9, characterized in that: The other output end of the switch circuit (7013) is electrically connected to the input end of the voltage feedback circuit (7022), and the output end of the voltage feedback circuit (7022) is electrically connected to the other input and output end of the voltage regulator (7021).

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