Energy storage system and transient power control method thereof

Abstract

The present application relates to an energy storage system, comprising an external capacitor module, a feedforward control module and two or more energy storage converters. The external capacitor module actively discharges when the voltage of a DC bus drops, and then the feedforward control module collects the discharge current of the external capacitor module and outputs a feedforward control signal to each energy storage converter based on the discharge current. Each energy storage converter then adjusts the output current through its current control loop based on the feedforward control signal to restore the voltage of the DC bus to a stable state. This system externalizes the filter capacitor on the DC bus side of the energy storage converter, and can flexibly configure the size of the filter capacitor according to the ripple requirements of different energy storage systems, avoiding the maintenance inconvenience caused by the mismatch of the capacity when the capacitor is built into the energy storage converter. The feedforward control signal directly acts on the current control loop of the energy storage converter, thereby improving the response speed of the energy storage converter and reducing the risk of system collapse due to short-term power imbalance.

Description

Technical Field

[0001] The present application relates to the field of transient power control, and in particular to an energy storage system and a transient power control method thereof. Background Art

[0002] With the development of power technology and the application of distributed energy, the advantages of low-voltage DC power supply and distribution are gradually becoming apparent. In traditional DC power supply and distribution energy storage systems, capacitors are installed on the DC bus side of the energy storage converter. When a sudden increase in DC bus power causes a voltage drop, these capacitors are used to immediately discharge the capacitors to maintain normal system operation while the energy storage converter responds and stabilizes.

[0003] The above transient response process places high demands on the equivalent capacitance and response speed of the energy storage converter's DC bus. However, current energy storage converters already integrate filter capacitors internally. This can lead to redundant or insufficient capacitance for systems with varying response and ripple characteristics. If capacitance is insufficient, the energy storage converter's response speed will not meet power requirements within a short period of time, posing the risk of system failure. Summary of the Invention

[0004] Based on this, it is necessary to provide an energy storage system and a transient power control method thereof to address the issues of capacitor configuration and response speed of the above-mentioned energy storage converter.

[0005] An energy storage system comprises: an external capacitor module, a feedforward control module, and two or more energy storage converters, each of the energy storage converters is connected to an energy storage battery and a DC bus, the external capacitor module is connected in parallel between the positive and negative poles of the DC bus, and the feedforward control module is connected to the external capacitor module and each of the energy storage converters;

[0006] The external capacitor module is used to actively discharge when the voltage of the DC bus drops;

[0007] The feedforward control module is used to collect the discharge current of the external capacitor module and output a feedforward control signal to each of the energy storage converters according to the discharge current;

[0008] Each of the energy storage converters is used to adjust the output current through its current control loop according to the feedforward control signal, so as to improve the response speed of the energy storage converter and ultimately restore the voltage of the DC bus to a stable state.

[0009] In one embodiment, the voltage drop of the DC bus occurs when there is a power shortage in the DC bus.

[0010] In one embodiment, the feedforward control module includes a collection device and a signal generating device, the collection device is connected to the external capacitor module and the signal generating device, and the signal generating device is connected to each of the energy storage converters.

[0011] In one embodiment, the acquisition device is a current transformer.

[0012] In one embodiment, the signal generating device is a square wave generator.

[0013] In one embodiment, the external capacitor module is composed of two or more capacitors connected in parallel.

[0014] In one embodiment, the DC bus side of each energy storage converter has a single built-in capacitor, and the voltage across the built-in capacitor is used to input into the voltage control loop of each energy storage converter for control.

[0015] A transient power control method for an energy storage system is implemented based on any of the above energy storage systems, the method comprising:

[0016] The feedforward control module obtains the discharge current of the external capacitor module; wherein the external capacitor module actively discharges when the voltage of the DC bus drops;

[0017] The feedforward control module generates a feedforward control signal according to the discharge current, and outputs the feedforward control signal to each energy storage converter;

[0018] Each of the energy storage converters adjusts the output current through its current control loop according to the feedforward control signal, so as to improve the response speed of the energy storage converter and ultimately restore the voltage of the DC bus to a stable state.

[0019] In one embodiment, the magnitude of the discharge current and the depth of the voltage drop can be expressed by the following formula:

[0020]

[0021] Wherein, I is the discharge current, C is the equivalent capacitance of the external capacitor device, is the depth of the voltage drop.

[0022] In one embodiment, the feedforward control signal is a square wave signal, and the voltage drop of the DC bus is generated when there is a power shortage in the DC bus; each of the energy storage converters adjusts the output current through its current control loop according to the feedforward control signal to improve the response speed of the energy storage converter, and ultimately restores the voltage of the DC bus to a stable state, including:

[0023] Analyzing and generating a feedforward current according to the square wave signal;

[0024] Inputting the feedforward current into the current control loop of each energy storage converter to obtain a feedback signal;

[0025] According to the feedback signal, the output current is adjusted to improve the response speed of the energy storage converter, and ultimately reduce the power difference to within a threshold range; the power difference is the difference between the total output power of each of the energy storage converters and the load power of the DC bus.

[0026] The above-mentioned energy storage system and transient power control method thereof externalize the filter capacitor on the DC bus side of the energy storage converter, and can flexibly configure the size of the filter capacitor according to the ripple requirements of different energy storage systems, thereby avoiding the maintenance inconvenience caused by the mismatch of the capacity when the capacitor is built into the energy storage converter. Then, by adopting a feedforward control module to directly collect the DC current of the external capacitor device as a measure for judging the size of the power shortage, the output feedforward control signal directly acts on the current control loop of the energy storage converter, thereby improving the response speed of the energy storage converter, quickly restoring the voltage of the DC bus to a stable state, and reducing the risk of system collapse due to short-term power imbalance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a system block diagram of an energy storage system in one embodiment;

[0028] Figure 2 A control logic diagram of an energy storage converter in one embodiment;

[0029] Figure 3 is a flow chart of a transient power control method in one embodiment;

[0030] Figure 4 is a flow chart of a transient power control method according to another embodiment;

[0031] Figure 5 FIG. 4 is a transient power response control logic diagram of an energy storage system in one embodiment. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0034] It will be understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor without departing from the scope of this application. The first resistor and the second resistor are both resistors, but they are not the same resistor.

[0035] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if there is transmission of electrical signals or data between the connected circuits, modules, units, etc.

[0036] When used herein, the singular forms "a", "an", and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" and the like specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof.

[0037] Low-voltage DC power supply and distribution systems typically utilize a busbar structure, connected to the upstream AC grid via AC / DC converters. They also integrate distributed photovoltaic energy sources and energy storage batteries to power DC loads. Due to these advantages and the emergence of distributed energy resources, low-voltage DC power supply and distribution systems are gaining widespread adoption. In low-voltage DC power supply and distribution systems that incorporate intermittent energy sources such as wind and solar, energy storage systems—using energy storage batteries connected to energy storage converters to provide power to the DC bus—serve as system energy routing and are a crucial component of system transient power regulation.

[0038] Due to the limitations of the series-parallel connection method for energy storage batteries, energy storage systems typically utilize multiple, parallel-connected, small-capacity energy storage converters based on the battery capacity. To reduce light-load losses when powering the DC bus, the energy storage converters typically have an automatic sleep function. This means that when the load power connected to the DC bus is low, the power required from the energy storage system also decreases, causing some energy storage converters to enter a sleep state, with their switches inactive. Therefore, when the DC bus is unloaded or lightly loaded, a single energy storage converter can maintain the bus voltage. To reduce losses within the converter itself, the remaining energy storage converters are placed in a sleep state, with their switches inactive. Alternatively, energy storage converters can be placed in an unloaded state, where their switches are active but no power is output. However, when high-power equipment is connected to the DC bus or when other power supply failures occur, the lightly loaded or sleep energy storage converters are required to respond quickly, switching from standby to active mode and outputting the required power.

[0039] Energy storage converters typically have capacitors on the DC bus side. When a sudden power surge in the system causes the DC bus voltage to drop, the capacitors can then enter a discharge phase while the dormant energy storage converters wait for their response and enter the operating state, maintaining normal system operation. During the capacitor discharge process, the energy storage converter generates a DC voltage reference value based on the DC voltage reference generation loop. This is then passed through the voltage and current control loops, which utilize PI control, to output a PWM control signal. This controls the duty cycle of the switching transistors within the energy storage converter, switching the standby energy storage converter to the operating state. This increases the overall energy storage system's output power to the DC bus and fills the required power gap. This control process requires generating a voltage reference value, then outputting a current reference value through the outer loop of the voltage control loop, and then feeding a PWM control signal to the inner loop of the current control loop. This entire control process and strategy is overly lengthy, hindering the energy storage converter's ability to respond quickly.

[0040] In addition, the response speed of the energy storage converter in the above control process is related to the DC voltage value, the size of the capacitor, and the size of the power shortage. Among them, when there are certain response speed requirements for the energy storage converter, the size of the external equivalent capacitance of the energy storage system is the only most controllable. However, when configuring capacitors, the choice of capacity is related to the transient response characteristics and ripple characteristics of the system voltage. If the capacitor is too small, it may not meet the system transient performance and system ripple requirements; if the capacitor is too large, it will cause a waste of resources. For traditional energy storage converters, the filter capacitor is already integrated inside the converter. For different system requirements, it may cause capacitor redundancy or insufficient capacitance value, requiring additional parallel capacitors. Once the capacitance is insufficient, the energy storage converter will not meet the power requirements in a short period of time, and there will be a risk of system collapse.

[0041] Therefore, in order to solve the above problems, in order to make the no-load energy storage converter output power quickly, or to make the dormant energy storage converter output power quickly after switching to the working state, in one embodiment, an energy storage system is proposed, such as Figure 1 As shown, it includes: an external capacitor module 110, a feedforward control module 120 and more than two energy storage converters 130, each energy storage converter 130 is connected to an energy storage battery and a DC bus, the external capacitor module 110 is connected in parallel between the positive and negative poles of the DC bus, and the feedforward control module 120 is connected to the external capacitor module 110 and each energy storage converter 130; the external capacitor module 110 is used to actively discharge when the voltage of the DC bus drops; the feedforward control module 120 is used to collect the discharge current of the external capacitor module 110 and output a feedforward control signal to each energy storage converter 130 according to the discharge current; each energy storage converter 130 is used to adjust the output current through its current control loop according to the feedforward control signal to improve the response speed of the energy storage converter 130, and finally restore the voltage of the DC bus to a stable state.

[0042] There are more than two energy storage converters 130, and each energy storage converter 130 is connected to a corresponding energy storage battery and a DC bus, so as to transmit the power in the energy storage battery to the DC bus after voltage step-up / down, filtering, and rectification, and then supply power to the load connected to the DC bus through the DC bus. Figure 1 As shown, the energy storage system may include more than two energy storage batteries. The number of energy storage converters connected to each energy storage battery is not unique and can be configured according to the capacity of the energy storage battery. The connection relationship and principle of this power supply process can refer to the conventional settings in the field and will not be described in detail in the embodiments of this application.

[0043] The external capacitor module 110 is connected in parallel between the positive and negative poles of the DC bus and serves as a filter capacitor on the DC bus side of each energy storage converter 130. To meet the capacitance requirements, in one embodiment, the external capacitor module 110 is composed of two or more capacitors connected in parallel. Alternatively, the external capacitor module 110 can be directly composed of a single large capacitor.

[0044] It is understood that the size of the equivalent capacitance of the external capacitor module 110 is not unique and can be configured according to actual conditions such as the total capacity of each energy storage converter 130 and the ripple requirements of the energy storage system. Specifically, in the energy storage system, the control mode of the energy storage converter is generally constant voltage control (or droop control). Figure 2As shown, the DC voltage reference value Uref is obtained based on the DC voltage reference generation loop, and then the DC voltage reference value Uref and the collected DC voltage U0 are passed through the voltage control loop using PI control to obtain the DC current reference value Iref, and then the DC current reference value Iref is obtained by passing the collected inductor current IL through the current control loop using PI control to obtain the PWM control signal output to control the duty cycle of the switch tube inside the energy storage converter, thereby adjusting the output current of the energy storage converter. Therefore, it can be understood that the capacity of each energy storage converter is directly related to the maximum current allowed to be output by the energy storage converter. Taking the BUCK converter as an example, the voltage ripple calculation formula is as follows:

[0045]

[0046] It can be seen from the above formula that the voltage ripple size ΔV0 and the AC component size of the inductor current ΔI L , switching frequency T S It is related to the size of the DC side capacitor C. Among them, the AC component of the inductor current ΔI L In the BUCK circuit, the magnitude remains unchanged in continuous mode; when operating in discontinuous mode, the magnitude of the AC component of the inductor current ΔI L It is directly related to the average current, that is, the capacity configuration size. In the above ripple current formula, the controllable variable is the DC side equivalent capacitance value C. Based on the system ripple requirements, the equivalent capacitance size C, that is, the equivalent capacitance size of the external capacitor module 110, can be calculated.

[0047] The feedforward control module 120 is used to collect the current of the external capacitor module 110 and generate a feedforward control signal based on the current and output it to each energy storage converter 120, so that the energy storage converter 120 can adjust the output current of the energy storage converter according to the feedforward control signal. Figure 2 As shown, after the feedforward control module 120 outputs the feedforward control signal to the energy storage converter 120, the feedforward control signal is parsed into a feedforward current I* inside the energy storage converter 120. The feedforward current I* directly acts on the current control loop to obtain a PWM control signal output to control the duty cycle of the switch tube inside the energy storage converter, thereby achieving regulation of the output current of the energy storage converter.

[0048] Specifically, when a high-power device is suddenly connected to the DC bus or when another power supply fails, the DC bus will experience a voltage sag. This means that the voltage drop exceeds a sag threshold within a unit time. The unit time can be a very short unit time, and the sag threshold can be set based on actual system parameters. Accordingly, in one embodiment, a voltage sag on the DC bus occurs when there is a power deficit on the DC bus. It is understood that a power deficit refers to the difference between the actual load power of the DC bus and the output power of the energy storage converter. For example, the energy storage system is currently operating at no load, with all energy storage converters switched to sleep mode. Then, when a 5kW load is suddenly added, the energy storage converters in the energy storage system cannot respond quickly enough and switch from sleep mode to active mode, outputting 5kW of power to the load. The power deficit at this point is 5kW. It is understood that the response speed of the energy storage converter is the time required for the converter to switch from sleep mode to active mode. A shorter response time indicates a faster response speed, while a longer response time indicates a slower response speed.

[0049] Furthermore, when there is a power shortage, the external capacitor module 110 will actively release the energy stored therein into the DC bus based on the size of the power shortage and the depth of the voltage drop. The energy will flow into the DC bus. The voltage drop speed is proportional to the equivalent capacitance C of the external capacitor module 110. Then, the feedforward control module 120 connects to and collects the discharge current I of the external capacitor module 110, and outputs a feedforward control signal to each energy storage converter 130 based on the discharge current I. Then, within the energy storage converter 120, the feedforward control signal is parsed into a feedforward current I*. This feedforward current I* directly acts on the current control loop to obtain a PWM control signal output to control the duty cycle of the switch tube within the energy storage converter, thereby increasing the output current of the energy storage converter, so that the energy storage converter can receive the power shortage signal more quickly, improve the response speed, and increase the output power, so that the power difference is reduced to within the threshold range. The power difference is the difference between the total output power of each energy storage converter and the load power of the DC bus. The threshold range can be a small threshold close to zero, or it can be set to zero. When the power difference decreases to within the threshold range, it can be understood that the DC bus voltage has returned to a stable state.

[0050] The above-mentioned energy storage system externalizes the filter capacitor on the DC bus side of the energy storage converter, and can flexibly configure the size of the filter capacitor according to the ripple requirements of different energy storage systems, avoiding the maintenance inconvenience caused by the mismatch of the capacity when the capacitor is built into the energy storage converter. Then, by adopting the feedforward control module to directly collect the DC current of the external capacitor device as a measure of the power shortage size, the output feedforward control signal directly acts on the current control loop of the energy storage converter, thereby improving the response speed of the energy storage converter and reducing the risk of system collapse due to short-term power imbalance.

[0051] In one embodiment, Figure 1 As shown, the feedforward control module 120 includes a collection device and a signal generating device. The collection device is connected to the external capacitor module 110 and the signal generating device. The signal generating device is connected to each energy storage converter 130 .

[0052] Specifically, the acquisition device is used to collect the current of the external capacitor module 110 and output the current to the signal generating device. The signal generating device generates a feedforward control signal based on the received current and outputs it to each energy storage converter 120, so that the energy storage converter 120 can adjust the output current of the energy storage converter according to the feedforward control signal.

[0053] In one embodiment, the data acquisition device is a current transformer. The current transformer is connected in series to the circuit of the external capacitor module 110 to collect the discharge current of the external capacitor module 110 when the DC bus is about to experience a power shortage. When the DC bus experiences different degrees of power shortage, the discharge current of the external capacitor module 110 varies. By detecting the magnitude of the discharge current, the degree of the DC bus power shortage can be determined.

[0054] In one embodiment, the signal generating device is a square wave generator. After the current transformer collects the discharge current from the external capacitor module 110, it outputs the current to the square wave generator. The square wave generator converts the received discharge current into a high-frequency square wave signal through its control unit. The higher the received discharge current, the higher the frequency of the square wave signal, indicating a greater power deficit in the DC bus.

[0055] In one embodiment, the DC bus side of each energy storage converter 130 has a single built-in capacitor, and the voltage across the built-in capacitor is used to input the voltage control loop of each energy storage converter for control. Specifically, when an integral external capacitor module 110 is used to connect each energy storage converter as a filter capacitor on the DC bus side of the energy storage converter, a single built-in capacitor must be retained inside each energy storage converter 130 to achieve basic control functions. In this embodiment, only a single capacitor element needs to be retained inside each energy storage converter 130, and there is no need to expand the capacity in parallel internally, which can achieve the purpose of reducing the volume of the energy storage converter and improving the power density of the energy storage converter.

[0056] In one embodiment, Figure 3 As shown, a transient power control method for an energy storage system is provided, which is implemented based on any of the above energy storage systems, and the method includes:

[0057] Step 302: The feedforward control module obtains the discharge current of the external capacitor module; wherein the external capacitor module actively discharges when the voltage of the DC bus drops.

[0058] Specifically, when a high-power device is suddenly connected to the DC bus or when another power supply fails, the DC bus will experience a voltage sag. This means that the voltage drop exceeds a sag threshold within a unit time. The unit time can be a very short unit time, and the sag threshold can be set based on actual system parameters. Accordingly, in one embodiment, a voltage sag on the DC bus occurs when there is a power deficit on the DC bus. It will be understood that a power deficit refers to the change in power within a unit time. For example, the energy storage system is currently operating at no load, with all energy storage converters switched to sleep mode. Then, when a 5kW load is suddenly added, the energy storage converters in the energy storage system cannot respond quickly enough and switch from sleep mode to active mode, outputting 5kW of power to the load. The power deficit at this point is 5kW. It will be understood that the response speed of the energy storage converter is the time required for the converter to switch from sleep mode to active mode. A shorter response time indicates a faster response speed, while a longer response time indicates a slower response speed.

[0059] Furthermore, when there is a power shortage, the energy storage converters cannot immediately switch operating modes. Based on the power shortage and the depth of the voltage drop, the external capacitor module will actively release the stored energy into the DC bus. The voltage drop rate is proportional to the equivalent capacitance C of the external capacitor module. In one embodiment, the discharge current I and the depth of the voltage drop can be expressed by the following formula:

[0060]

[0061] Where I is the discharge current, C is the equivalent capacitance of the external capacitor device, is the depth of the voltage drop.

[0062] Step 304: The feedforward control module generates a feedforward control signal according to the discharge current, and outputs the feedforward control signal to each energy storage converter.

[0063] Specifically, the feedforward control module is used to collect the discharge current of the external capacitor module, and generate a feedforward control signal based on the current and output it to each energy storage converter, so that the energy storage converter can adjust the output current of the energy storage converter according to the feedforward control signal.

[0064] Step 306: Each energy storage converter adjusts its output current through its current control loop according to the feedforward control signal to improve the response speed of the energy storage converter and ultimately restore the voltage of the DC bus to a stable state.

[0065] Specifically, in the energy storage system, the control mode of the energy storage converter is generally constant voltage control (or droop control). Figure 2As shown, a DC voltage reference value Uref is obtained according to a DC voltage reference generation loop, and then the DC voltage reference value Uref and the collected DC voltage U0 are subjected to a voltage control loop using PI control to obtain a DC current reference value Iref, which is then subjected to a current control loop using PI control with the collected inductor current IL to obtain a PWM control signal output to control the duty cycle of the switch tube inside the energy storage converter, thereby achieving regulation of the output current of the energy storage converter.

[0066] Furthermore, after the energy storage converter receives the feedforward control signal sent by the feedforward control module, the feedforward control signal can be directly applied to the current control loop to obtain a PWM control signal output to increase the output current of the energy storage converter, so that the energy storage converter can receive the power shortage signal more quickly, improve the response speed, and increase the output power of the energy storage converter, so that the power difference is reduced to within the threshold range.

[0067] In one embodiment, the feedforward control signal is a square wave signal, and the voltage drop of the DC bus is generated when there is a power shortage in the DC bus; Figure 4 and Figure 5 As shown, step 306 includes:

[0068] Step 402: Analyze and generate a feedforward current according to the square wave signal.

[0069] Specifically, a current transformer is connected in series with the circuit of the external capacitor module. It collects the discharge current of the external capacitor module when the DC bus is about to generate a power shortage and outputs it to the square wave generator. The square wave generator converts the received discharge current into a high-frequency square wave signal through a control unit on the square wave generator and sends it to each energy storage converter. Furthermore, within the energy storage converter, the high-frequency square wave signal is analyzed into the feedforward current I*.

[0070] Step 404: Input the feedforward current into the current control loop of each energy storage converter to obtain a feedback signal.

[0071] Specifically, the feedforward current I* is directly applied to the current control loop of the internal control logic of the energy storage converter to obtain a feedback signal D, wherein the feedback signal D is a PWM control signal.

[0072] Step 406: According to the feedback signal, the output current is adjusted to improve the response speed of the energy storage converter, and finally the power difference is reduced to within the threshold range; the power difference is the difference between the total output power of each energy storage converter and the load power of the DC bus.

[0073] Specifically, the PWM control signal is output to control the duty cycle of the switch tube within the energy storage converter, thereby increasing the output current of the energy storage converter and the output power of the energy storage converter, so that the power difference is reduced to within a threshold range. The power difference is the difference between the total output power of each energy storage converter and the load power of the DC bus. The threshold range can be a small threshold close to zero or set to zero. When the power difference is reduced to within the threshold range, it can be understood that the voltage of the DC bus has returned to a stable state.

[0074] The implementation solution provided by the transient power control method of the energy storage system is similar to the implementation solution described in the above-mentioned energy storage system. Therefore, the specific limitations of one or more transient power control method embodiments provided above can be found in the above-mentioned limitations on the energy storage system and will not be repeated here.

[0075] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. An energy storage system, characterized in that: include: An external capacitor module, a feedforward control module, and two or more energy storage converters, each of the energy storage converters is connected to an energy storage battery and a DC bus, the external capacitor module is connected in parallel between the positive and negative poles of the DC bus, and the feedforward control module is connected to the external capacitor module and each of the energy storage converters; The external capacitor module is used to actively discharge when the voltage of the DC bus drops; The feedforward control module is used to collect the discharge current of the external capacitor module and output a feedforward control signal to each of the energy storage converters according to the discharge current; Each of the energy storage converters is used to adjust the output current through its current control loop according to the feedforward control signal, so as to improve the response speed of the energy storage converter and ultimately restore the voltage of the DC bus to a stable state; The feedforward control module includes an acquisition device and a signal generating device. The acquisition device is connected to the external capacitor module and the signal generating device. The signal generating device is connected to each of the energy storage converters. The acquisition device is a current transformer. The signal generating device is a square wave generator.

2. The energy storage system according to claim 1, characterized in that The voltage drop of the DC bus occurs when there is a power shortage in the DC bus.

3. The energy storage system according to claim 1, characterized in that The external capacitor module is composed of two or more capacitors connected in parallel.

4. The energy storage system according to claim 1, characterized in that The DC bus side of each energy storage converter has a single built-in capacitor, and the voltage across the built-in capacitor is used to input into the voltage control loop of each energy storage converter for control.

5. A transient power control method for an energy storage system, characterized in that: Based on the energy storage system according to any one of claims 1 to 4 above, the method includes: The feedforward control module obtains the discharge current of the external capacitor module; wherein the external capacitor module actively discharges when the voltage of the DC bus drops; The feedforward control module generates a feedforward control signal according to the discharge current, and outputs the feedforward control signal to each energy storage converter; the feedforward control signal is a square wave signal; Each of the energy storage converters adjusts the output current through its current control loop according to the feedforward control signal, so as to improve the response speed of the energy storage converter and ultimately restore the voltage of the DC bus to a stable state.

6. The transient power control method according to claim 5, characterized in that: The magnitude of the discharge current and the depth of the voltage drop are expressed by the following formula: in, I is the discharge current, C is the equivalent capacitance of the external capacitor module, is the depth of the voltage drop.

7. The transient power control method according to claim 5, wherein: The voltage drop of the DC bus is generated when there is a power shortage in the DC bus; each of the energy storage converters adjusts the output current through its current control loop according to the feedforward control signal to improve the response speed of the energy storage converter, and finally restores the voltage of the DC bus to a stable state, including: Analyzing and generating a feedforward current according to the square wave signal; Inputting the feedforward current into the current control loop of each energy storage converter to obtain a feedback signal; According to the feedback signal, the output current is adjusted to improve the response speed of the energy storage converter, and ultimately reduce the power difference to within a threshold range; the power difference is the difference between the total output power of each of the energy storage converters and the load power of the DC bus.

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