AC load power supply system and method

Abstract

The present disclosure provides an AC load power supply system and method, the system comprising: a power supply device and a DC / AC converter; the AC side of the DC / AC converter is coupled to an AC power grid and an AC load via an AC bus; the power supply device outputs DC power and is coupled to the DC side of the DC / AC converter via a DC bus; wherein the power supply device comprises an energy storage module and a controller; the energy storage module comprises at least a first energy storage unit and a second energy storage unit, the controller is configured to control the conversion operation of the first energy storage unit to output a low-frequency component to the DC bus, and the controller is further configured to control the conversion operation of the second energy storage unit to output a high-frequency power to the DC bus.

Description

Technical Field

[0001] The present disclosure relates to the field of power supply and distribution, and in particular to an AC load power supply system and method. Background Art

[0002] In order to ease the pressure on power supply, DC microgrid systems consisting of photovoltaic, wind power generation, and energy storage devices have gradually attracted attention. Considering the randomness of load fluctuations and the intermittent and distributed characteristics of renewable energy such as photovoltaic and wind power generation, the stability of DC microgrids has brought great challenges, and energy storage devices play an important role in ensuring energy balance, power quality, and stable operation of the system.

[0003] High-power AC loads, such as electric vehicle charging stations and AC asynchronous motors, require electric energy that is divided into long-term steady-state electric energy and instantaneous dynamic electric energy. A single energy storage device that handles both high-frequency sudden load demands and low-frequency long-term load demands will sacrifice battery performance and increase battery costs.

[0004] When the grid capacity is limited or the grid fails, high-power AC loads require seamless switching of power supply. However, the current external uninterruptible power supply (UPS) cannot achieve seamless switching, resulting in power outages for the loads. Summary of the invention

[0005] The embodiments of the present disclosure provide an AC load power supply system and method, thereby overcoming one or more problems caused by limitations and defects of the prior art at least to a certain extent.

[0006] Other features and advantages of the present disclosure will become apparent from the following detailed description, or may be learned in part by the practice of the present disclosure.

[0007] According to a first aspect of an embodiment of the present disclosure, an AC load power supply system is proposed, the system comprising: a power supply device and a DC / AC converter; the AC side of the DC / AC converter is coupled to an AC power grid and an AC load via an AC bus; the power supply device outputs DC power and is coupled to the DC side of the DC / AC converter via a DC bus; wherein the power supply device comprises an energy storage module and a controller; the energy storage module comprises at least a first energy storage unit and a second energy storage unit, the controller being configured to control a conversion operation of the first energy storage unit to output a low-frequency component to the DC bus, and the controller being further configured to control a conversion operation of the second energy storage unit to output a high-frequency power to the DC bus.

[0008] In an exemplary embodiment of the present disclosure, the controller is configured to control the first energy storage unit to operate in a current source mode to output the low-frequency component; the controller is also configured to control the second energy storage unit to operate in a voltage source mode to output the high-frequency power.

[0009] In an exemplary embodiment of the present disclosure, the first energy storage unit includes a low power density energy storage element and a first DC / DC converter, and the controller is configured to control an output current of the first DC / DC converter.

[0010] In an exemplary embodiment of the present disclosure, the second energy storage unit includes a high power density energy storage element and a second DC / DC converter, and the controller is configured to control an output voltage of the second DC / DC converter.

[0011] In an exemplary embodiment of the present disclosure, the first energy storage unit or the second energy storage unit includes a flywheel energy storage device and an AC / DC converter, and the controller is configured to control an output current or an output voltage of the AC / DC converter.

[0012] In an exemplary embodiment of the present disclosure, the energy storage module has an output port coupled to the DC bus, the energy storage module includes a plurality of energy storage units, the output ends of the plurality of energy storage units are connected in parallel and coupled to the output port, and the total converted electrical energy of the energy storage module is transmitted to the DC bus through the output port.

[0013] In an exemplary embodiment of the present disclosure, the power supply device is a DC microgrid system, and the DC microgrid system further includes one or more of a photovoltaic power generation module, a wind power generation module and a diesel generator.

[0014] In an exemplary embodiment of the present disclosure, the controller includes: a calculation unit, which is used to calculate the output power of the energy storage module based on the voltage signal of the DC bus and the current signal of the energy storage module; a power extraction unit, coupled to the calculation unit, which extracts the low-frequency component in the output power; a current source control unit, coupled to the power extraction unit, which is used to adjust the output power of the first energy storage unit according to the low-frequency component; a voltage source control unit, which is used to adjust the output voltage of the second energy storage unit according to the voltage reference value of the DC bus to stabilize the voltage of the DC bus, and the second energy storage unit automatically outputs the high-frequency power.

[0015] In an exemplary embodiment of the present disclosure, the first energy storage unit includes a low power density battery, the second energy storage unit includes a high power density battery, and the calculation unit is also used to calculate a first state of charge of the high power density battery; and a second state of charge of the low power density battery.

[0016] In an exemplary embodiment of the present disclosure, the power extraction unit includes: a first calculation module, used to calculate the average power change rate based on the output power; and a filtering module, used to filter the output power when the average power change rate is greater than a power fluctuation threshold to obtain the low-frequency component in the output power.

[0017] In an exemplary embodiment of the present disclosure, the power extraction unit also includes: a second calculation module, used to calculate the first charge-discharge balance and the second charge-discharge balance according to the first state of charge and the second state of charge, respectively; a first adjustment module, used to determine the window function according to the second charge-discharge balance, the output power and the average power change rate and send it to the filtering module, so as to adjust the window width and window shape of the filtering module according to the window function; a second adjustment module, used to adjust the cutoff frequency of the filtering module according to the first charge-discharge balance, calculate the response function of the cutoff frequency in the time domain and send it to the filtering module.

[0018] In an exemplary embodiment of the present disclosure, the filtering module calculates a filtering function according to the window function, the response function and the output power, so as to extract the low-frequency component according to the filtering function.

[0019] In an exemplary embodiment of the present disclosure, when the average power change rate is less than or equal to a power fluctuation threshold, the output power is the low-frequency component, which is output to the current source control unit.

[0020] In an exemplary embodiment of the present disclosure, the AC load is an AC asynchronous motor, the second energy storage unit is used to provide power when the AC asynchronous motor is started, and the first energy storage unit is used to provide power when the AC asynchronous motor is running stably.

[0021] In an exemplary embodiment of the present disclosure, the AC load is an electric vehicle charging station.

[0022] According to a second aspect of an embodiment of the present disclosure, an AC load power supply method is proposed, which is used in an AC load power supply system. The AC load power supply system includes a power supply device and a DC / AC converter, wherein the AC side of the DC / AC converter is coupled to an AC power grid and an AC load via an AC bus; the power supply device outputs DC power and is coupled to the DC side of the DC / AC converter via a DC bus; wherein the power supply device includes an energy storage module and a controller; the energy storage module includes at least a first energy storage unit and a second energy storage unit, and the controller is configured to control the conversion operation of the first energy storage unit to output a low-frequency component to the DC bus, and the controller is further configured to control the conversion operation of the second energy storage unit to output a high-frequency power to the DC bus, wherein the power supply method includes:

[0023] Step 1, collecting the voltage of the DC bus and the output current of the energy storage module to calculate the output power of the energy storage module;

[0024] Step 2, extracting the output power to obtain a low-frequency component;

[0025] Step 3, adjusting the output power of the first energy storage unit according to the low-frequency component so that it outputs the low-frequency component required by the AC load;

[0026] Step 4: adjusting the output voltage of the second energy storage unit according to the voltage reference value of the DC bus to stabilize the voltage of the DC bus so as to output the high-frequency power required by the AC load.

[0027] In an exemplary embodiment of the present disclosure, the method further includes: calculating a first state of charge of a second energy storage unit in the high-power energy storage device; and calculating a second state of charge of a low-power energy storage device in the first energy storage unit.

[0028] In an exemplary embodiment of the present disclosure, step 2 includes:

[0029] Step 21, calculating the average power change rate according to the output power;

[0030] When the average power change rate is greater than the power fluctuation threshold, the output power is filtered to obtain a low-frequency component in the output power; when the average power change rate is less than or equal to the power fluctuation threshold, the output power is the low-frequency component.

[0031] In an exemplary embodiment of the present disclosure, step 2 further includes:

[0032] Step 22, calculating a first charge-discharge balance degree and a second charge-discharge balance degree according to the first state of charge and the second state of charge respectively;

[0033] Step 23, determining a window function according to the second charge-discharge balance degree, the output power and the power change rate, so as to adjust the window width and window shape of the filter module according to the window function;

[0034] Step 24, adjusting the preset cutoff frequency according to the first charge-discharge balance degree to obtain a final cutoff frequency, and calculating a response function of the final cutoff frequency in the time domain;

[0035] Step 25, calculating a filter function according to the window function, the response function and the output power.

[0036] The AC load power supply system and method provided by the present disclosure adopts a frequency division control mechanism. For example, a low power density energy storage unit operates in a current source mode to provide low frequency power; a high power density energy storage unit operates in a voltage source mode to automatically provide high frequency power, that is, automatically provide a power difference. The power supply system can operate in a grid-connected mode to supply power to the grid and the AC load at the same time. At this time, the DC / AC converter can operate in an AC current source or a virtual synchronous machine; the power supply system can also serve as a backup power supply and operate in an off-grid mode to supply power to the AC load alone. At this time, the DC / AC converter can operate in an AC voltage source or a virtual synchronous machine. The AC load power supply system of the present disclosure can achieve seamless switching between grid connection and off-grid connection. When the AC load is a charging station, the AC load power supply system of the present disclosure can realize grid-connected and off-grid power supply to the charging station without changing the existing charging station structure.

[0037] In some embodiments, the output power of the energy storage module is determined based on the voltage of the DC bus and the output current thereof, and the power signals of other nodes and AC loads of the power supply system can be obtained without relying on communication.

[0038] In some embodiments, the parameters of the filter module are adaptively adjusted according to the charge state of the high power density energy storage element, the charge state of the low power density energy storage element and the output power of the energy storage module, so that the low-frequency component that the hybrid energy storage module needs to output can be detected in a timely and accurate manner, ensuring that the hybrid energy storage module works as long as possible while satisfying the control effect, and avoiding system shutdown due to overcharging or over-discharging of the battery.

[0039] It is to be understood that the foregoing general description and the following detailed description are exemplary only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. The drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other drawings can also be obtained based on these drawings without creative work.

[0041] Figure 1 A schematic diagram of an AC load power supply system according to an exemplary embodiment of the present invention is shown.

[0042] Figure 2 A schematic diagram of an AC load power supply system according to another exemplary embodiment of the present invention is shown.

[0043] Figure 3A and Figure 3B Schematic diagrams of an AC load power supply system according to yet another exemplary embodiment of the present disclosure are respectively shown.

[0044] Figure 4 Show Figure 1 Circuit diagram of the AC load power supply system in .

[0045] Figure 5 Show Figure 4 1123 in FIG.

[0046] Figure 6 Show Figure 4 1124 in FIG.

[0047] Figure 7 is a schematic diagram of a power extraction unit according to an example embodiment of the present disclosure.

[0048] Figure 8 A schematic diagram showing an example embodiment of the present invention in which the AC load is an electric vehicle charging station.

[0049] Fig. 9 A schematic diagram showing an AC load according to an exemplary embodiment of the present invention is an AC asynchronous motor.

[0050] Fig.10 A flow chart of an AC load power supply method according to an exemplary embodiment of the present invention is shown.

[0051] Fig.11 Show according to Fig.10 Flowchart of step 2 in an example implementation. DETAILED DESCRIPTION

[0052] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present invention will be comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0053] The described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present invention. However, those skilled in the art will appreciate that the technical solution of the present invention may be practiced while omitting one or more of the specific details, or other systems, components, methods, steps, etc. may be adopted. In other cases, known systems, methods, implementations or operations are not shown or described in detail to avoid blurring various aspects of the present invention.

[0054] The accompanying drawings are only schematic illustrations of the present invention, and the same reference numerals in the drawings represent the same or similar parts, so their repeated description will be omitted. Some block diagrams shown in the accompanying drawings do not necessarily correspond to physically or logically independent entities. These functional entities can be implemented in software form, or in one or more hardware modules or integrated circuits, or in different networks and / or processor methods and / or microcontroller methods.

[0055] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and steps, nor must they be executed in the order described. For example, some steps can be decomposed, and some steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0056] Figure 1 FIG. 2 is a schematic diagram of an AC load power supply system according to an exemplary embodiment of the present invention. Figure 1 As shown, the AC load power supply system 1 includes: a power supply device 11 and a DC / AC converter 12. The AC side of the DC / AC converter 12 is coupled to the AC grid 9 and the AC load 10 through the AC bus 8; the power supply device 11 outputs DC power and is coupled to the DC side of the DC / AC converter 12 via the DC bus 13. The power supply device 11 includes an energy storage module 111 and a controller 112, wherein the energy storage module 111 includes at least a first energy storage unit 1111 and a second energy storage unit 1112. The controller 112 is configured to control the conversion operation of the first energy storage unit 1111 to output low-frequency power to the DC bus 13; the controller 112 is also configured to control the conversion operation of the second energy storage unit 1112 to output high-frequency power to the DC bus 13.

[0057] The power required by the AC load 10 includes high-frequency power and low-frequency power. The controller 112 can decompose the power signal of the AC load, extract the low-frequency component, and control the first energy storage unit 1111 to provide low-frequency power based on the low-frequency component, and control the output voltage of the second energy storage unit 1112 so that the second energy storage unit automatically provides the required high-frequency power.

[0058] The AC load power supply system disclosed in the present invention is connected to the AC power grid and the AC load at the same time through the AC bus. When the AC power grid fails and trips the grid or receives a dispatch command to switch to island operation, the power supply system 1 can achieve seamless switching and continue to supply power to the AC load. When the AC power grid capacity is insufficient and cannot meet the power supply demand of the AC load, the power supply system 1 outputs energy to the AC power grid; or because the power grid is limited by the switch capacity of the AC power grid, the power grid cannot meet the power supply demand of the AC load, and the power supply system 1 cooperates with the AC power grid to supply power to the load. Therefore, only the backup power supply system 1 needs to be added, without changing the structure and configuration of the original power grid, to achieve off-grid and grid-connected power supply, and at the same time, it can effectively respond to changes in the power supply demand of the AC load.

[0059] The DC / AC converter 12 receives the DC power output by the power supply device and converts it into AC power to feed the AC power grid or AC load. Preferably, the DC / AC converter 12 is a bidirectional DC / AC converter to realize bidirectional energy flow. It can feed the power output by the power supply device to the power grid, and can also convert the excess power in the power grid to store it in the energy storage module. In some embodiments, the DC / AC converter 12 is a central power conditioner (PCS) that performs power conversion and adjusts the power quality. The central PCS can adopt a variety of control strategies. For example, when connected to the grid, the high-power PCS can operate in the AC current source mode or perform virtual synchronous machine control on the PCS; when off the grid, the high-power PCS can operate in the AC voltage source mode or perform virtual synchronous machine control on the PCS. The energy storage module and the power conditioner in the present disclosure can also be integrated into a complete energy storage system, which has the characteristics of high reliability, high power output and fast response, and can play the functions of load transfer, peak power regulation and demand regulation in the power grid.

[0060] Furthermore, a transformer is provided between the DC / AC converter and the AC grid; similarly, a transformer is provided between the DC / AC converter and the AC load. A protective device such as an AC circuit breaker is also provided on the AC bus 8, which will not be described in detail here.

[0061] The controller 112 is configured to control the first energy storage unit 1111 to operate in a current source mode to output the required low-frequency power. Specifically, the controller 112 calculates the output power P of the energy storage module. ESS And extract the low-frequency component P in the output power L , the low frequency component PL As the command value, the controller 112 L The output current of the first energy storage unit 1111 is adjusted to provide the required low-frequency power. The controller 112 is also configured to control the second energy storage unit 1112 to operate in the voltage source mode to output the required high-frequency power. Specifically, the controller 112 obtains the voltage reference value U of the DC bus 13. ref As the command value, according to U ref Adjust the output voltage U of the second energy storage unit 1112 dc , to stabilize the voltage of the DC bus 13 and automatically output the required high-frequency power.

[0062] The first energy storage unit 1111 includes a low power density energy storage element and a first DC / DC converter, and the controller 112 is configured to control the output current of the first DC / DC converter. The second energy storage unit 1112 includes a high power density energy storage element and a second DC / DC converter, and the controller 112 is configured to control the output voltage of the second DC / DC converter. Preferably, the first DC / DC converter and the second DC / DC converter are bidirectional DC / DC converters.

[0063] Energy storage elements can be divided into two categories according to their output characteristics: high power density and low power density. Low power density energy storage elements have high energy density, but low power density and long response time, and are suitable for low-frequency output; high power density energy storage elements have high power density, short response time, but low energy density, and are suitable for high-frequency output. In order to cope with AC load power fluctuations and stabilize the DC bus voltage, the energy storage module needs to frequently absorb or emit large power. Frequent high-power charging and discharging will seriously affect the battery life, and a single energy storage device is difficult to meet both power and energy requirements. In this case, the first energy storage unit 1111 is a low power density energy storage unit, which uses low power density energy storage elements, and the second energy storage unit 1112 is a high power density energy storage unit, which uses high power density energy storage elements to form a hybrid energy storage module 111. The low power density energy storage elements and high power density energy storage elements cooperate in output, complementing each other's advantages, which not only meets the load power scheduling curve, but also improves the dynamic performance of the hybrid energy storage module 111 and extends the service life of each energy storage element.

[0064] In the hybrid energy storage module of this embodiment, the first energy storage unit operates in the current source mode to provide low-frequency power, and the second energy storage unit operates in the voltage source mode to stabilize the voltage on the DC bus 13, while automatically providing the power shortfall. Compared with the solution in which both the first energy storage unit and the second energy storage unit operate in the current source mode, the DC bus voltage fluctuation can be suppressed more quickly, the DC bus voltage can be ensured to be stable, the dynamic response is good, and the service life of the energy storage element is extended. The first energy storage unit operates in the current source mode, and the second energy storage unit operates in the voltage source mode. The first energy storage unit provides the required low-frequency power, and the second energy storage unit automatically provides the power difference and outputs the required high-frequency power. Therefore, the power given by the two does not need to be obtained by frequency division, and the tracking performance of the high-frequency power is better.

[0065] like Figure 1 As shown, the energy storage module 111 also has an output port 1113, which is coupled to the DC bus 13. The output ends of the first energy storage unit 1111 and the second energy storage unit 1112 are connected in parallel and coupled to the output port 1113. The total output electrical energy of the energy storage module 111 is transmitted to the DC bus 13 through the output port 1113.

[0066] In other embodiments, the energy storage module 111 includes multiple energy storage units, wherein a portion of the multiple energy storage units include low power density energy storage elements, and another portion of the multiple energy storage units include high power density energy storage elements. Further, the energy storage units including low power density energy storage elements provide low frequency power, and these energy storage units are first energy storage units. Similarly, the energy storage units including high power density energy storage elements provide high frequency power, and these energy storage units are second energy storage units. The controller 112 collects the voltage U of the DC bus. dc and the current I at the output port 1113 of the hybrid energy storage module dc , calculate the output power P of the hybrid energy storage module ESS , which is the power required by the AC load. Generally speaking, the distance between the power supply device and the AC load is far, and the controller relies on the communication system to obtain the power signal required by the AC load, resulting in poor tracking performance of high-frequency power. In this case, the controller collects the DC voltage and DC current at the output port 1113, calculates the output power of the energy storage module, that is, the power required by the AC load, and the controller does not rely on communication and directly obtains the power signal of the AC load.

[0067] Figure 2 FIG. 2 is a schematic diagram of an AC load power supply system according to another exemplary embodiment of the present invention. Figure 1The power supply system 1 shown is similar, and the same component numbers represent the same components, structures and functions, which will not be repeated here. In this embodiment, the AC load power supply system 2 includes a power supply device 21 and a DC / AC converter 22. The AC side of the DC / AC converter 22 is coupled to the AC power grid 9 and the AC load 10 through the AC bus 8; the power supply device 21 outputs DC power and is coupled to the DC side of the DC / AC converter via the DC bus 23. The power supply device 21 includes an energy storage module 211 and a controller 212, wherein the energy storage module 211 includes at least a first energy storage unit 2111 and a second energy storage unit 2112. The first energy storage unit 2111 includes a low power density energy storage element, and the second energy storage unit 2112 includes a high power density energy storage element. The difference from the power supply system 1 in the first embodiment is that either the first energy storage unit 2111 or the second energy storage unit 2112 includes a flywheel energy storage device and an AC / DC converter. The flywheel energy storage device is connected to the AC side of the AC / DC converter, and the DC side of the AC / DC converter is coupled to the output port 2113 .

[0068] Flywheel energy storage is an emerging electric energy storage technology. Flywheel energy storage devices have the characteristics of high energy storage density, high power density, long life, wide operating temperature range, low loss, environmental protection and low maintenance cost. They have great advantages in improving power quality and adapting to load changes. Flywheel energy storage devices can be used as low power density energy storage elements or high power density energy storage elements. Figure 2 As shown, the energy storage module 211 uses a flywheel energy storage device as a high power density energy storage element and a battery as a low power density energy storage element, and the battery and the flywheel energy storage cooperate with each other to form a hybrid energy storage module 211. The battery provides low frequency power, and the flywheel energy storage provides high frequency power while maintaining the DC bus voltage stable.

[0069] Figure 3A and Figure 3B Schematic diagrams of an AC load power supply system according to another exemplary embodiment of the present disclosure are shown respectively. Figure 3A As shown, the AC load power supply system 3 includes: a power supply device 31A and a DC / AC converter 32. The power supply device includes an energy storage module 311, a controller 312 and a photovoltaic power generation module 313, wherein the energy storage module 311 includes at least a first energy storage unit 3111 and a second energy storage unit 3112. In this embodiment, the output power P calculated by the controller ESS is the total power of the photovoltaic power generation module and the AC load. Figure 3B As shown, the power supply device 31B includes a photovoltaic power generation module, a gas turbine power generation module, and an energy storage module, which transmits energy to the outside through a DC bus to form a DC microgrid system, wherein the electric energy generated by the gas turbine is converted into DC electric energy through an AC / DC converter and transmitted to the DC bus.

[0070] In some embodiments, the power supply device is a DC microgrid, and the power supply in the DC microgrid has various forms, such as but not limited to: photovoltaic power generation module, wind power generation module, hybrid energy storage module, micro gas turbine or diesel generator, etc. The DC microgrid and the central PCS form an AC load power supply system, which can operate in two modes: grid-connected and islanded. When the AC power grid fails, the AC load power supply system quickly disconnects from the AC power grid and independently supplies power to the AC load; when the AC power grid fails and returns to normal, the AC load power supply system is reconnected to the AC power grid through grid-connected control and re-enters grid-connected operation. Coordinated control between the micro sources in the DC microgrid maintains the power balance of the power supply system and stabilizes the DC bus voltage.

[0071] Figure 4 Show Figure 1 The circuit diagram of the AC load power supply system in FIG. Figure 4 As shown, the first energy storage unit 1111 includes a low power density energy storage element and a first DC / DC converter, and the second energy storage unit 1112 includes a high power density energy storage element and a second DC / DC converter. The controller 112 includes a calculation unit 1121, a power extraction unit 1122, a current source control unit 1123, and a voltage source control unit 1124.

[0072] The calculation unit 1121 is used to calculate the voltage signal U of the DC bus 13 according to the voltage signal U dc and the current signal I of the energy storage module output port 1113 dc Calculate the output power P of the energy storage module 111 ESS ; Power extraction unit 1122, coupled to the calculation unit 1121, extracts the output power P ESS The low frequency component P L The current source control unit 1123 is coupled to the power extraction unit 1122 and is used according to the low frequency component P L Regulate the output power of the first energy storage unit; the voltage source control unit 1124 adjusts the output voltage of the second energy storage unit according to the voltage reference value of the DC bus 13 to stabilize the voltage U of the DC bus 13 dc At the same time, the second energy storage unit 1112 automatically outputs high-frequency power to provide the power shortage.

[0073] In this embodiment, when the AC load power supply system 4 independently supplies power to the AC load, the output power of the energy storage module 111 is the power required by the load, and the power signal of the AC load 10 can be obtained without relying on communication. In some embodiments, the power supply device 11 also includes a photovoltaic power generation module. When the AC load power supply system 4 independently supplies power to the AC load 10, the output power of the energy storage module 111 is the total power of the photovoltaic power generation module and the AC load 10. There is no need to collect the power signal of the photovoltaic power generation module and the power signal of the AC load separately, and the power signal of the AC load is directly obtained without relying on communication. In other embodiments, the AC load power supply system 4 includes multiple power generation modules, and the total power of the power generation module and the AC load 10 is directly obtained by calculating the output power of the energy storage module.

[0074] According to an example embodiment of the present invention, the first energy storage unit 1111 includes a low power density battery, the second energy storage unit 1112 includes a high power density battery, and the calculation unit 1121 is further used to calculate the state of charge of the high power density battery, recorded as the first state of charge SOC1; and the state of charge of the low power density battery, recorded as the second state of charge SOC2.

[0075] According to an exemplary embodiment of the present invention, the current source control unit 1123 is configured to receive the low-frequency component P output by the power extraction unit 1122. L , the charging and discharging current I1 of the low power density energy storage element and the DC bus voltage U dc , outputs a switching signal to control the switching device of the first DC / DC converter. The voltage source control unit 1124 is used to receive the voltage reference value U of the DC bus 13. ref , DC bus voltage U dc The charging and discharging current I2 of the high power density energy storage element is used to output a switching signal to control the switching device of the second DC / DC converter.

[0076] Figure 5 Show Figure 4 FIG. 1 is a control block diagram of the current source control unit 1123. Figure 5 As shown, the first DC / DC converter controls the charge and discharge current of the low power density energy storage element, thereby adjusting the output power of the first energy storage unit. Specifically, the current source control unit 1123 receives the low frequency component P L As its power command, divided by the DC bus voltage U dc Get the reference value I of the charge and discharge current 1r , the actual charge and discharge current I1 and the reference value I 1rAfter comparison, a control signal is generated by a PI regulator, and a drive signal is output after PWM modulation to drive the switching device of the first DC / DC converter to realize the charge and discharge control of the low power density energy storage element, thereby adjusting the output power of the first energy storage unit to provide the required low-frequency power.

[0077] Figure 6 Show Figure 4 FIG. 1 is a control block diagram of the voltage source control unit 1124. Figure 6 As shown, the charging and discharging current of the high power density energy storage element is controlled by the second DC / DC converter, thereby adjusting the output voltage of the second energy storage unit to stabilize the DC bus voltage and automatically provide high frequency power. The voltage source control unit 1124 receives the DC bus 13 voltage reference value U ref As voltage command, the actual bus voltage U dc With reference value U ref After comparison, the PI regulator generates the reference value I of the charge and discharge current 2r , the actual charge and discharge current I2 and the reference value I 2r After comparison, a control signal is generated by the PI regulator, and a drive signal is output after PWM modulation to drive the switching device of the second DC / DC converter, thereby realizing the charge and discharge control of the high power density energy storage element to stabilize the DC bus voltage and automatically provide power shortage.

[0078] Figure 7 is a schematic diagram of a power extraction unit according to an exemplary embodiment of the present disclosure. Figure 7 As shown, the power extraction unit includes a first calculation module for receiving the output power P ESS , and according to the output power P ESS Calculate the average power change rate F within the time period t t ; Filter module, used when the average power change rate F t When the power fluctuation threshold is greater than the receiving output power P ESS Filter to obtain the output power P ESS The low frequency component P L , start the frequency division control mechanism. In this embodiment, the power fluctuation threshold is 1. Among them, the average power change rate F t The calculation formula is as follows:

[0079]

[0080] Where ΔP t It represents the power change in time period t, that is, the maximum power minus the minimum power in time period t, and t takes a smaller value; P n Indicates rated power.

[0081] The filter module uses the FIR filter algorithm to filter the output power PESS Filter to obtain the output power P ESS The low frequency component P L .

[0082] According to an exemplary embodiment of the present invention, the power extraction unit further includes a second calculation module for calculating and obtaining a first charge-discharge balance degree R according to the first state of charge SOC1 and the second state of charge SOC2. H and the second charge-discharge balance R L ; A first adjustment module is used to adjust the charge and discharge balance according to the second L , output power P ESS and the average power change rate F t The window function G(n) is determined and sent to the filter module to adjust the window width and window shape of the filter module according to the window function G(n); the second adjustment module is used to adjust the window width and window shape of the filter module according to the first charge-discharge balance R H Adjust the preset cutoff frequency ω0 of the filter module to obtain the final cutoff frequency ω c , calculate the final cutoff frequency ω c The response function H in the time domain f (n) and sent to the filtering module. The second calculation module calculates the first charge-discharge balance R by the following formula: H :

[0083]

[0084] The second charge-discharge balance R L The calculation method and the first charge-discharge balance R H Similarly. According to formula (2), the range of charge-discharge balance is: [-1,1]. The closer the charge-discharge balance is to 0, the moderate the charge-discharge capacity is; the closer the charge-discharge balance is to -1, the stronger the charge capacity is and the weaker the discharge capacity is; the closer the charge-discharge balance is to 1, the stronger the discharge capacity is and the weaker the charge capacity is. Therefore, the expected value of charge-discharge balance is 0.

[0085] The first adjustment module adjusts the charge and discharge balance according to the second charge and discharge balance R L Determine whether the low power density energy storage element is close to overcharge or overdischarge, and if so, increase the window width of the window function G(n) in the filter module. Further, the first adjustment module can adjust the window width N(t) of the window function G(n) according to the following formula:

[0086]

[0087] Among them, N0 is the preset minimum sample width; F0 is the preset target power fluctuation rate; R(t-1) is the charge-discharge balance at time t-1. In the case of weak charging capacity or weak discharging capacity, the output of the hybrid energy storage system will be limited when smoothing fluctuations, so the filtering effect needs to be weakened; when the power fluctuation is large, the filtering effect needs to be strengthened.

[0088] Furthermore, the weight adjustment method of the filter module is shown in the following formula:

[0089]

[0090] Among them, k is a weight factor, which is selected according to the sample data; the larger the k, the more importance is attached to the recent output power, and the smaller the impact of the earlier output power.

[0091] Furthermore, according to the output power P ESS Adjust the weight α(n), as shown in the following formula:

[0092]

[0093] Among them, P N is the set value, the discrete sequence of output power P ESS (n) and P ESS The difference of (n-1) is large, indicating that the output power changes suddenly and greatly. By reducing the weight α(n) of this shot data, the filtered data is made smoother.

[0094] The first adjustment module determines the expression of the window function G(n), as shown below:

[0095]

[0096] The second adjustment module adjusts the cutoff frequency ω of the filter module according to the following formula: c :

[0097]

[0098] Among them, ω0 is the preset cutoff frequency, D B The distance between the current charge and discharge balance degree and ±1 when the cut-off frequency adaptive adjustment needs to be started; ω H is the base frequency for superposition.

[0099] When the first charge-discharge balance R H The absolute value of is greater than 1-D B When the first charge-discharge balance degree R H The absolute value of D BWhen , it indicates that the high power density energy storage element has a moderate state of charge, and it is necessary to start the cutoff frequency reduction calculation to enhance the filtering effect and increase the output of the high power energy storage element; when the first charge and discharge balance R H The absolute value of D B <|R H |≤(1-D B ), the preset cut-off frequency ω0 is maintained.

[0100] The second adjustment module obtains the response function H according to the following formula f (n):

[0101]

[0102] According to an exemplary embodiment of the present invention, the filtering module is based on the window function G(n), the response function H f (n) and output power P ESS , calculate the filter function. The calculation method of the filter function is as follows:

[0103]

[0104] According to an exemplary embodiment of the present invention, when the average power change rate F t When the power fluctuation threshold is less than or equal to the output power P ESS That is the low frequency component P L At this time, there is no need to start the frequency division control mechanism, the output power P ESS It is low-frequency power, which is input into the current source control unit to control the charging and discharging operation of the low-power density energy storage element.

[0105] The filtering method in the above embodiment adopts an open-loop control strategy, and the low-frequency component obtained by the filtering module is input to the current source control unit. The filtering method of the present invention can also adopt a closed-loop control strategy, and the low-frequency component P obtained by the filtering module is input to the current source control unit. L , calculate P L If the power fluctuation rate is greater than the set value, adjust the filter parameters, for example, according to P L The power fluctuation rate is used to adjust the filtering parameters, and PL is input into the filtering module for filtering to obtain a new low-frequency release until the low-frequency component obtained after filtering is less than the set value.

[0106] In the related art, the filter usually uses a first-order or second-order digital low-pass filter to filter the signal to achieve frequency division processing, which has the following disadvantages: the power signal is divided based on the communication interaction; it is difficult to take into account the filtering delay and filtering attenuation ratio, resulting in the coupling of high-frequency and low-frequency components, making the frequency division effect very poor, affecting the operation of the energy storage module; and the charge state of the energy storage element is not reasonably introduced into the frequency division method, resulting in a short operation time of the energy storage module and an insufficiently optimized working mode. The AC load power supply system of the disclosed embodiment is based on the FIR (Finite Impulse Response) filter frequency division method that introduces the charge state of the energy storage element, which can timely and accurately detect the low-frequency power that the hybrid energy storage system needs to output, control the low-power density energy storage unit to work, and the high-frequency power will be automatically processed by the high-power density energy storage unit. The variables such as the charge state of the hybrid energy storage system, the fluctuation size of the output power, and the recent output power are introduced into the parameter design of the filter, and the filter parameters are adjusted adaptively in real time to optimize the configuration, so that the hybrid energy storage module can work as long as possible under the premise of satisfying the control effect, and avoid the power supply system from stopping due to overcharging or over-discharging of the battery.

[0107] Figure 8 FIG. 4 is a schematic diagram showing an example embodiment of an AC load as an electric vehicle charging station according to the present invention. In this embodiment, the AC load power supply system 4 and Figure 1 The power supply system 1 shown is similar, and the same component numbers represent the same components, structures and functions, which will not be repeated here. In this embodiment, the AC load power supply system 4 includes a power supply device 41 and a DC / AC converter 42. The AC side of the DC / AC converter 42 is coupled to the AC grid 9 and the AC load 10 through the AC bus 8; the power supply device 41 outputs DC power and is coupled to the DC side of the DC / AC converter via the DC bus 43. The power supply device 41 includes a photovoltaic power generation module, an energy storage module 411 and a controller 412, wherein the energy storage module 411 includes at least a first energy storage unit 4111 and a second energy storage unit 4112. The first energy storage unit 4111 includes a low power density energy storage element, and the second energy storage unit 412 includes a high power density energy storage element. In a specific embodiment, any one of the first energy storage unit 4111 or the second energy storage unit 4112 may also include a flywheel energy storage device and an AC / DC converter. In this embodiment, the AC load 10 includes electric vehicle charging stations 1 to n.

[0108] Generally speaking, electric vehicle charging stations include daily average stable traffic flow and fluctuating traffic flow. Therefore, affected by the number of charging vehicles, the electric energy required by electric vehicle charging stations is divided into long-term steady-state energy and instantaneous dynamic energy. When the power supply system 4 supplies power to the electric vehicle charging station, the power that the energy storage module needs to provide is the sum of the photovoltaic power generation module and the AC load power, which includes low-frequency components and high-frequency components. Among them, the high-frequency component is provided by a high-power density energy storage unit, and the high-power density energy storage unit operates in a voltage source mode, and the low-frequency component is provided by a low-power density energy storage unit, and the low-power density energy storage unit operates in a current source mode. The AC power supply system 4 is hung on the power grid through a high-power central PCS and an AC bus. It can be used as a backup power supply to power the electric vehicle charging station when the AC power grid fails, and it can also constitute an energy regulation system, for example, when the power grid capacity is limited, it cooperates with the power grid to power the electric vehicle charging station. The power supply system of the present invention realizes the grid-connected or off-grid power supply to the charging station without changing the existing charging station structure, and realizes seamless switching between grid-connected and off-grid through a DC / AC converter 42.

[0109] According to an exemplary embodiment of the present invention, the AC load may also be an AC asynchronous motor, such as Fig. 9 As shown, the AC load 10 is an AC asynchronous motor. In the load application scenario of a high-power asynchronous motor, a large starting current is required when the high-power AC asynchronous motor starts, which is often 6 to 7 times the rated current. Power supply from the power grid is limited by the circuit breaker capacity and transformer capacity, and the existing distribution network capacity cannot provide it. The AC load power supply system of this embodiment can provide a starting current when the high-power asynchronous motor starts. For example, the power for starting the AC asynchronous motor is provided by a high-power density energy storage unit, and the power for stable operation of the AC asynchronous motor is provided by a low-power density energy storage unit.

[0110] In some embodiments, the power supply device is a DC microgrid, and the power supply in the DC microgrid has various forms, such as but not limited to: photovoltaic power generation module, wind power generation module, hybrid energy storage module, micro gas turbine or diesel generator, etc. The DC microgrid and the central PCS form an AC load power supply system. When connected to the grid, it can run on an AC current source or a virtual synchronous machine to supply power to the grid and charging station, or to supply power to an AC asynchronous motor; when disconnected from the grid, it can run on an AC voltage source or a virtual synchronous machine to supply power to a charging station or an AC asynchronous motor. The AC load power supply system is connected to the grid through a circuit breaker. Once the grid fails and jumps to the grid or receives a dispatch command to switch to island operation, it can seamlessly switch to continuously supply power to the load.

[0111] In the power supply system of the present invention, the power that the energy storage module needs to provide is the sum of the power of the power generation module (such as a photovoltaic power generation module, a wind power generation module, etc.) and the AC load, that is, the energy storage module has a power scheduling curve, and the hybrid energy storage module outputs power according to the power scheduling curve. Generally speaking, the power scheduling curve includes high-frequency power and low-frequency power, wherein the low-frequency power corresponds to the low-frequency long-term load demand, and the high-frequency power corresponds to the high-frequency sudden load demand. For example, the high-frequency power corresponds to the power required when the AC asynchronous motor is started, the power demand generated when a large number of charging vehicles are connected to the AC charging station for a short time, or the fluctuating traffic volume in the electric vehicle charging station; the low-frequency power corresponds to the power of the AC asynchronous motor when it is running stably or the long-term steady-state electric energy required by the electric vehicle charging station is determined by the average stable traffic volume in the electric vehicle charging station every day. The controller adjusts the output voltage of the high-power density energy storage unit to automatically provide the required high-frequency power. The controller adjusts the output power of the low-power density energy storage unit to provide the required low-frequency power.

[0112] The controller includes a power extraction unit for extracting the output power P ESS The frequency division method adopts the FIR filter which introduces the state of charge to realize the low-frequency components in the circuit. It has the advantages of large filtering attenuation ratio and small phase delay near the cutoff frequency. The low-frequency components after filtering can be ideally decoupled from the high-frequency components. The charging and discharging can be balanced according to the state of charge, which can extend the operation time of the hybrid energy storage module and avoid overcharging or over-discharging of the energy storage elements.

[0113] The AC load power supply system adopts a frequency division control mechanism. The controller controls the low power density energy storage unit to operate in the current source mode to provide low frequency power. The controller controls the high power density energy storage unit to operate in the voltage source mode to automatically provide high frequency power, that is, automatically provide the power difference. When the power supply device only includes the energy storage module, the output power of the energy storage module is equal to the power required by the AC load; when the power supply device includes the energy storage module and the power generation module, the output power of the energy storage module is equal to the sum of the power of the AC load and the power generation module.

[0114] The power supply device and the DC / AC converter form an AC load power supply system to be coupled to the AC bus. When connected to the grid, the DC / AC converter can operate as an AC current source or a virtual synchronous machine, and the power supply system supplies power to the grid and the AC load; when off-grid, the DC / AC converter can operate as an AC voltage source or a virtual synchronous machine, and the power supply system supplies power to the AC load. When the AC load is a charging station, the AC load power supply system disclosed in the present invention can realize grid-connected and off-grid power supply to the charging station without changing the existing charging station structure.

[0115] In some implementations, the output power of the hybrid energy storage system is determined based on the voltage of the DC bus and the output current of the hybrid energy storage system, and the power signals of other nodes and AC loads of the DC microgrid can be obtained without relying on communication.

[0116] In some implementations, the parameters of the filter module are adaptively adjusted according to the charge state of the high-power-density energy storage element, the charge state of the low-power-density energy storage element, and the output power of the hybrid energy storage module, so that the low-frequency component that the hybrid energy storage module needs to output can be detected in a timely and accurate manner, ensuring that the hybrid energy storage module has the longest possible working time while satisfying the control effect, and avoiding system shutdown due to battery overcharging or over-discharging.

[0117] Fig.10 FIG. 2 is a flow chart showing a method for supplying power to an AC load according to an exemplary embodiment of the present invention. Fig.10 As shown, the AC load power supply method is used Figure 1 or Figure 4 or Figure 8 or Fig. 9 The AC load power supply system shown in the figure, the AC load power supply method at least includes steps 1 to 4.

[0118] Step 1: Calculate the output power P of the energy storage module based on the voltage of the DC bus and the output current of the energy storage module. ESS .

[0119] Step 2: Extract output power P ESS The low frequency component P L .

[0120] Step 3, adjusting the output power of the first energy storage unit so that it outputs a low-frequency component.

[0121] Step 4: adjust the output voltage of the second energy storage unit so that it actively outputs the power shortfall in the output power.

[0122] Among them, the output power P is obtained through the FIR filter ESS The low frequency component P L , corresponding to the low-frequency output that the energy storage module needs to provide; the power deficit refers to the power component remaining after filtering out the low-frequency component in the output power, which corresponds to the high-frequency output that the energy storage module needs to provide.

[0123] According to an example embodiment of the present invention, the first energy storage unit includes a low power density battery, the second energy storage unit includes a high power density battery, and the AC load power supply method further includes: calculating the state of charge of the high power density battery, recorded as a first state of charge SOC1; calculating the state of charge of the low power density battery, recorded as a second state of charge SOC2.

[0124] Fig.11 Show according to Fig.10 FIG. 2 is a flow chart of step 2 in an example implementation. Fig.11 As shown, the above step 2 further includes steps 21 to 25.

[0125] Step 21, according to the output power P ESS Calculate the average power change rate F within the time period t t The average power change rate F can be calculated according to formula (1): t When the average power change rate F t When the power fluctuation threshold is greater than the output power P ESS Filter to obtain the output power P ESS The low frequency component P L , output to the first energy storage unit as the power instruction of the first energy storage unit; when the average power change rate F t When the power fluctuation threshold is less than or equal to the output power P ESS Only low-frequency power fluctuations are included, and no output power P ESS The power command is filtered and directly output to the first energy storage unit as the power command of the first energy storage unit.

[0126] Step 22, respectively calculating a first charge-discharge balance R according to the first state of charge SOC1 and the second state of charge SOC2 H and the second charge-discharge balance R L The charge-discharge balance can be calculated according to formula (2).

[0127] Step 23, according to the second charge-discharge balance R L , output power P ESS and power change rate F t The window function G(n) is determined to adjust the window width and window shape of the filter module according to the window function G(n). The window width can be adjusted according to formula (3), and the weight value can be adjusted according to formula (4) and formula (5) to adjust the window shape. The expression of the window function can be calculated according to formula (6).

[0128] Step 24: according to the first charge-discharge balance R H Adjust the preset cutoff frequency ω0 to obtain the final cutoff frequency ω c , calculate the final cutoff frequency ω c The response function H in the time domain f (n). The cutoff frequency ω can be calculated according to formula (7): c , calculate the response function H according to formula (8) f (n).

[0129] Step 25: According to the window function G(n) and the response function H f(n) and output power P ESS , calculate the filter function, and extract the low-frequency component according to the filter function. The filter function can be calculated according to formula (9).

[0130] Those skilled in the art will appreciate that all or part of the steps for implementing the above embodiments are implemented as a computer program executed by a central processing unit (CPU). When the computer program is executed by the central processing unit (CPU), the above functions defined by the above system provided by the present disclosure are executed. The program may be stored in a computer-readable storage medium, which may be a read-only memory, a disk or an optical disk, etc.

[0131] In addition, it should be noted that the above figures are only schematic illustrations of the processes included in the system according to the exemplary embodiments of the present disclosure, and are not intended to be limiting. It is easy to understand that the processes shown in the above figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0132] Those skilled in the art will appreciate that the above modules can be distributed in the method according to the description of the embodiment, or can be changed accordingly to be only different from one or more methods of the embodiment. The modules of the above embodiments can be combined into one module, or can be further divided into multiple sub-modules.

[0133] Through the description of the above embodiments, it is easy for those skilled in the art to understand that the example embodiments described here can be implemented by software, or by software combined with necessary hardware. Therefore, the technical solution according to the embodiment of the present disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.) or on a network, and includes several instructions to enable a computing device (which can be a personal computer, a server, a mobile terminal, or a network device, etc.) to execute the system according to the embodiment of the present disclosure.

[0134] The exemplary embodiments of the present disclosure are specifically shown and described above. It should be understood that the present disclosure is not limited to the detailed structures, configurations or implementation systems described herein; on the contrary, the present disclosure is intended to cover various modifications and equivalent configurations included in the spirit and scope of the appended claims.

Claims

1. An AC load power supply system, characterized in that: include: Power supply and DC / AC converter; The AC side of the DC / AC converter is coupled to the AC grid and the AC load via an AC bus; The power supply device outputs direct current power, which is coupled to the direct current side of the DC / AC converter via a direct current bus; Wherein, the power supply device includes an energy storage module and a controller; The energy storage module includes a first energy storage unit and a second energy storage unit, the controller is configured to control the conversion operation of the first energy storage unit to output low-frequency power to the DC bus, and the controller is further configured to control the conversion operation of the second energy storage unit to output high-frequency power to the DC bus; The controller comprises: A calculation unit, used to calculate the output power of the energy storage module according to the voltage signal of the DC bus and the current signal of the energy storage module; A power extraction unit, coupled to the calculation unit, extracting a low-frequency component from the output power; a current source control unit, coupled to the power extraction unit, and configured to adjust the output power of the first energy storage unit according to the low-frequency component; A voltage source control unit is used to adjust the output voltage of the second energy storage unit according to the voltage reference value of the DC bus, and the second energy storage unit automatically outputs the high-frequency power.

2. The AC load power supply system according to claim 1, characterized in that: The controller is configured to control the first energy storage unit to operate in a current source mode to output the low-frequency power; the controller is also configured to control the second energy storage unit to operate in a voltage source mode to output the high-frequency power.

3. The AC load power supply system according to any one of claims 1 to 2, characterized in that: The first energy storage unit includes a low power density energy storage element and a first DC / DC converter, and the controller is configured to control an output current of the first DC / DC converter.

4. The AC load power supply system according to any one of claims 1 to 2, characterized in that: The second energy storage unit includes a high power density energy storage element and a second DC / DC converter, and the controller is configured to control an output voltage of the second DC / DC converter.

5. The AC load power supply system according to any one of claims 1 to 2, characterized in that: The first energy storage unit or the second energy storage unit includes a flywheel energy storage device and an AC / DC converter, and the controller is configured to control an output current or an output voltage of the AC / DC converter.

6. The AC load power supply system according to any one of claims 1 to 2, characterized in that: The energy storage module has an output port coupled to the DC bus. The energy storage module includes a plurality of energy storage units. The output ends of the plurality of energy storage units are connected in parallel and coupled to the output port. The total output electrical energy of the energy storage module is transmitted to the DC bus through the output port.

7. The AC load power supply system according to any one of claims 1 to 2, characterized in that: The power supply device is a DC microgrid system, and the DC microgrid system also includes one or more of a photovoltaic power generation module, a wind power generation module and a diesel generator.

8. The AC load power supply system according to any one of claims 1 to 2, characterized in that: The first energy storage unit includes a low power density battery, the second energy storage unit includes a high power density battery, and the calculation unit is further used to calculate a first state of charge and a second state of charge.

9. The AC load power supply system according to claim 8, characterized in that: The power extraction unit comprises: A first calculation module, configured to calculate an average power change rate within a time period according to the output power; The filtering module is used to filter the output power when the average power change rate is greater than a power fluctuation threshold to obtain the low-frequency component in the output power.

10. The AC load power supply system according to claim 9, characterized in that: The power extraction unit also includes: a second calculation module, configured to calculate a first charge-discharge balance degree and a second charge-discharge balance degree according to the first state of charge and the second state of charge; a first adjustment module, configured to determine a window function according to the second charge-discharge balance degree, the output power, and the average power change rate, and send the window function to the filtering module, so as to adjust a window width and a window shape of the filtering module according to the window function; The second adjustment module is used to adjust the cutoff frequency of the filter module according to the first charge-discharge balance degree, calculate the response function of the cutoff frequency in the time domain and send it to the filter module.

11. The power supply system according to claim 10, characterized in that: The filtering module calculates a filtering function according to the window function, the response function and the output power, and extracts the low-frequency component according to the filtering function.

12. The power supply system according to claim 11, characterized in that: When the average power change rate is less than or equal to the power fluctuation threshold, the output power is the low-frequency component, which is output to the current source control unit.

13. The power supply system according to any one of claims 1 to 2, characterized in that: The AC load is an AC asynchronous motor, the second energy storage unit is used to provide power when the AC asynchronous motor is started, and the first energy storage unit is used to provide power when the AC asynchronous motor is running stably.

14. The power supply system according to any one of claims 1 to 2, characterized in that: The AC load is an electric vehicle charging station.

15. An AC load power supply method, used in an AC load power supply system, the AC load power supply system comprising a power supply device and a DC / AC converter, the AC side of the DC / AC converter is coupled to an AC grid and an AC load via an AC bus; the power supply device outputs DC power, which is coupled to the DC side of the DC / AC converter via a DC bus; wherein, The power supply device includes an energy storage module and a controller; The energy storage module includes a first energy storage unit and a second energy storage unit; the controller includes: a calculation unit, a power extraction unit, a current source control unit, and a voltage source control unit; characterized in that the power supply method includes: Step 1, calculating the output power of the energy storage module according to the voltage of the DC bus and the output current of the energy storage module; Step 2, extracting the low-frequency component in the output power; Step 3, adjusting the output power of the first energy storage unit according to the low-frequency component so that it outputs the low-frequency component; Step 4: adjusting the output voltage of the second energy storage unit according to the voltage reference value of the DC bus, and enabling it to automatically output high-frequency power.

16. The AC load power supply method according to claim 15, characterized in that: The first energy storage unit includes a low power density battery, the second energy storage unit includes a high power density battery, and the power supply method further includes: A first state of charge and a second state of charge are calculated.

17. The AC load power supply method according to claim 16, characterized in that: The step 2 comprises: Step 21, calculating an average power change rate within a time period according to the output power; When the average power change rate is greater than the power fluctuation threshold, the output power is filtered to obtain the low-frequency component in the output power and output it to the current source control unit; when the average power change rate is less than or equal to the power fluctuation threshold, the output power is the low-frequency component output to the current source control unit.

18. The AC load power supply method according to claim 17, characterized in that: The step 2 also includes: Step 22, calculating a first charge-discharge balance degree and a second charge-discharge balance degree according to the first state of charge and the second state of charge respectively; Step 23, determining a window function according to the second charge-discharge balance degree, the output power and the power change rate, so as to adjust a window width and a window shape of a filter module according to the window function; Step 24, adjusting the preset cutoff frequency according to the first charge-discharge balance degree to obtain a final cutoff frequency, and calculating a response function of the final cutoff frequency in the time domain; Step 25, calculating a filter function according to the window function, the response function and the output power; Wherein, the power extraction unit includes: the filtering module.

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