Control method and device of energy storage converter, energy storage converter and system

Abstract

This invention provides a control method, apparatus, energy storage converter, and system for an energy storage converter, relating to the field of power electronics technology. The method includes: acquiring the three-phase bridge-side current of any energy storage converter in an AC-DC parallel configuration; determining a zero-sequence voltage compensation amount based on the three-phase bridge-side current of any energy storage converter; using the zero-sequence voltage compensation amount to suppress the low-frequency zero-sequence circulating current generated by the energy storage converter; superimposing the zero-sequence voltage compensation amount onto the three-phase modulation wave output from the internal current loop of any energy storage converter to obtain a superimposed three-phase modulation wave; and modulating a pulse drive signal based on the superimposed three-phase modulation wave to control any energy storage converter. This invention can suppress the zero-sequence circulating current existing between energy storage converters in an AC-DC parallel configuration.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a control method, device, energy storage converter, and system for an energy storage converter. Background Technology

[0002] A power conversion system (PCS) connects a battery system to the power grid to achieve bidirectional energy conversion and is a crucial piece of equipment supporting the power system. As battery system capacity continues to increase, the capacity and performance requirements for PCS also rise accordingly. To meet the demands of large-capacity battery systems, PCS design must fully consider issues such as thermal management under high current and high voltage, electrical stress, and system reliability.

[0003] Traditional technologies typically employ single-unit large-capacity PCS to meet the power requirements of large-capacity battery systems. However, single-unit large-capacity PCS suffers from drawbacks such as difficulties in heat dissipation at high power, challenges in selecting power devices and supporting electrical components, a sharp increase in manufacturing costs, and excessive parallel connection of DC-side battery clusters.

[0004] To overcome the shortcomings of single-unit large-capacity PCS, a parallel AC / DC energy storage converter scheme has been proposed. This scheme involves connecting multiple small-capacity single-unit PCS in parallel with their AC and DC sides, and then connecting them together between the power grid and the battery system. However, since each PCS has independent control circuits, sampling circuits, and control loops, differences inevitably exist between their hardware parameters and software control timing. These differences lead to the formation of zero-sequence circulating currents among the parallel AC / DC energy storage converters. These zero-sequence circulating currents increase system losses and temperature rise, reduce the overall system efficiency, cause voltage instability, and affect the stability of the power system. Summary of the Invention

[0005] This invention provides a control method, device, energy storage converter, and system for energy storage converters to suppress zero-sequence circulating currents between energy storage converters connected in parallel with AC / DC converters.

[0006] In a first aspect, embodiments of the present invention provide a control method for an energy storage converter, comprising: For each energy storage converter connected in parallel with AC and DC, the three-phase bridge-side current of any energy storage converter is obtained; the DC terminals of each energy storage converter connected in parallel are connected to the battery system, and the AC terminals of each energy storage converter connected in parallel are connected to the power grid. Based on the three-phase bridge-side current of any of the energy storage converters, the zero-sequence voltage compensation amount is determined; the zero-sequence voltage compensation amount is used to suppress the low-frequency zero-sequence circulating current generated by the energy storage converter. The zero-sequence voltage compensation is superimposed on the three-phase modulated wave output from the internal current loop of any of the energy storage converters to obtain the superimposed three-phase modulated wave. Based on the superimposed three-phase modulated wave, a pulse drive signal is modulated to control any one of the energy storage converters.

[0007] In one possible implementation, determining the zero-sequence voltage compensation based on the three-phase bridge-side current of any of the energy storage converters includes: Based on the three-phase bridge-side current of any of the energy storage converters, determine the zero-sequence current of the energy storage converter. The difference between the zero-sequence current and the set value is calculated, and the difference is controlled by PI to obtain the zero-sequence voltage compensation amount; the difference between the set value and zero is within the set error range.

[0008] In one possible implementation, the AC-DC parallel energy storage converters include: a master energy storage converter and at least one slave energy storage converter; the master energy storage converter and each slave energy storage converter communicate with each other. If any of the energy storage converters is a slave energy storage converter, then the step of modulating and determining the pulse drive signal based on the superimposed three-phase modulation wave includes: The updated triangular carrier is obtained by performing a triangular carrier zeroing operation; the triangular carrier zeroing operation is triggered by a carrier synchronization signal; the carrier synchronization signal is sent by the host energy storage converter at a set time before its own triangular carrier crosses zero. Based on the comparison results between the superimposed three-phase modulated wave and the updated triangular carrier wave, the pulse drive signal is modulated and determined.

[0009] In one possible implementation, the energy storage converter adopts a three-level inverter topology; The three-phase modulated wave output from the internal current loop of any of the energy storage converters is superimposed with the zero-sequence voltage compensation to obtain the superimposed three-phase modulated wave, which includes: For any of the energy storage converters, obtain the DC upper capacitor voltage value and the DC lower capacitor voltage value in the three-level inverter topology of the energy storage converter; Based on the DC upper capacitor voltage value and the DC lower capacitor voltage value, determine the voltage balance compensation amount; The injection direction of the voltage balance compensation is determined based on the three-phase bridge side current; the injection direction is used to reflect the positive and negative polarities of the voltage balance compensation. According to the injection direction, the voltage balance compensation is injected into the three-phase modulated wave output by the internal current loop of the energy storage converter, and the zero-sequence voltage compensation is superimposed to obtain the superimposed three-phase modulated wave.

[0010] In one possible implementation, determining the injection direction of the voltage balance compensation amount based on the three-phase bridge-side current includes: The three-phase bridge-side current is transformed to obtain positive-sequence active current and positive-sequence reactive current. Determine the characteristic value of the positive sequence current based on the positive sequence active current and the positive sequence reactive current; The injection direction of the voltage balance compensation is determined based on the positive sequence current characteristic value.

[0011] In one possible implementation, determining the positive-sequence current characteristic value based on the positive-sequence active current and the positive-sequence reactive current includes: When the positive sequence active current and the positive sequence reactive current are in the same direction, the sum of the positive sequence active current and the positive sequence reactive current is determined as the characteristic value of the positive sequence current. When the positive sequence active current and the positive sequence reactive current are in opposite directions, it is detected whether the amplitude of the positive sequence active current is greater than the first amplitude threshold. If the amplitude of the positive sequence active current is greater than the first amplitude threshold, then the positive sequence active current is determined as the characteristic value of the positive sequence current. If the amplitude of the positive sequence active current is less than or equal to the first amplitude threshold, then it is detected whether the amplitude of the positive sequence reactive current is greater than the second amplitude threshold. If the amplitude of the positive sequence reactive current is greater than the second amplitude threshold, then the positive sequence reactive current is determined as the characteristic value of the positive sequence current. If the amplitude of the positive sequence reactive current is less than or equal to the second amplitude threshold, then the sum of the positive sequence active current and the positive sequence reactive current is determined as the characteristic value of the positive sequence current.

[0012] In one possible implementation, determining the injection direction of the voltage balance compensation amount based on the positive sequence current characteristic value includes: If the positive sequence current characteristic value is greater than a preset first characteristic value, then the injection direction of the voltage balance compensation is determined to be negative injection; the first characteristic value is greater than 0. If the positive sequence current characteristic value is less than the preset second characteristic value, then the injection direction of the voltage balance compensation is determined to be positive injection; the second characteristic value is less than 0.

[0013] In a second aspect, embodiments of the present invention provide an energy storage converter device, comprising: The acquisition module is used to acquire the three-phase bridge-side current of any one of the energy storage converters in the AC-DC parallel connection; the DC terminals of each of the energy storage converters in the AC-DC parallel connection are connected in parallel to the battery system, and the AC terminals of each of the energy storage converters in the AC-DC parallel connection are connected in parallel to the power grid. The compensation module is used to determine the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any of the energy storage converters; the zero-sequence voltage compensation amount is used to suppress the low-frequency zero-sequence circulating current generated by the energy storage converters. The control module is used for: The zero-sequence voltage compensation is superimposed on the three-phase modulated wave output from the internal current loop of any of the energy storage converters to obtain the superimposed three-phase modulated wave. Based on the superimposed three-phase modulated wave, a pulse drive signal is modulated to control any one of the energy storage converters.

[0014] Thirdly, embodiments of the present invention provide an energy storage converter, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation of the first aspect.

[0015] Fourthly, embodiments of the present invention provide a system comprising a plurality of energy storage converters as described in the third aspect, wherein the DC terminals of each energy storage converter are connected in parallel to a battery system, and the AC terminals of each energy storage converter are connected in parallel to a power grid.

[0016] Fifthly, embodiments of the present invention provide a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method described in the first aspect or any possible implementation thereof.

[0017] In a sixth aspect, embodiments of the present invention provide a computer program product, including a computer program that, when executed by a processor, implements the method described in the first aspect or any possible implementation thereof.

[0018] In this embodiment, the zero-sequence voltage compensation amount is determined by the three-phase bridge-side current of any energy storage converter in the AC-DC parallel configuration. This zero-sequence voltage compensation amount is then superimposed on the three-phase modulation wave output by the internal current loop to determine the pulse drive signal, which can effectively suppress the low-frequency zero-sequence circulating current generated by the energy storage converter itself.

[0019] Furthermore, since the DC and AC terminals of each energy storage converter are connected in parallel, forming a low-impedance electrical coupling path, when the low-frequency zero-sequence circulating current of any energy storage converter is effectively suppressed, the zero-sequence voltage at its AC terminal is forced to be clamped near zero potential, thereby simultaneously blocking the zero-sequence circulating current paths of other energy storage converters connected in parallel. Therefore, this embodiment does not require independent zero-sequence circulating current closed-loop control for each energy storage converter to achieve low-frequency zero-sequence circulating current suppression for the entire system, significantly reducing the complexity and computational cost of the control system.

[0020] Furthermore, when multiple energy storage converters simultaneously perform independent zero-sequence circulating current suppression, low-frequency oscillations in the system can easily occur due to differences in their control parameters and sampling delays. This embodiment, however, controls only one energy storage converter, thereby fundamentally avoiding coupling competition between them and effectively preventing low-frequency oscillations, significantly improving the operational stability and reliability of the parallel energy storage system. Attached Figure Description

[0021] Figure 1 This is an application scenario diagram of the control method for an energy storage converter provided in an embodiment of the present invention; Figure 2 This is a flowchart illustrating the implementation of a control method for an energy storage converter according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a three-level NPC topology provided in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the implementation of a control method for an energy storage converter according to another embodiment of the present invention; Figure 5 This is a timing diagram of the main unit energy storage converter transmitting a carrier synchronization signal according to an embodiment of the present invention; Figure 6 This is a schematic diagram of a triangular carrier synchronization process provided in an embodiment of the present invention; Figure 7 This is a flowchart illustrating the implementation of a control method for an energy storage converter according to another embodiment of the present invention; Figure 8 This is a schematic flowchart of determining the characteristic value of positive sequence current according to an embodiment of the present invention; Figure 9 This is a schematic diagram of the control device for the energy storage converter provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of the energy storage converter provided in an embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] Traditional technologies typically employ a single-unit, high-capacity PCS solution to meet the power requirements of large battery systems. However, this approach faces several technical bottlenecks in practical engineering applications: First, the increased power level of the single unit leads to significant heat dissipation issues for power devices (such as IGBTs), limiting the improvement of system power density. Second, constrained by the voltage levels, current specifications, switching characteristics, and costs of existing power semiconductor devices, further increases in single-unit capacity lead to a sharp rise in the difficulty of selecting AC / DC side switching devices and related electrical equipment, as well as manufacturing costs. Furthermore, high-capacity single-unit solutions often require direct parallel connection of numerous battery clusters on the DC side, making it difficult to effectively address the resulting circulating currents and capacity imbalances between battery clusters. To overcome these shortcomings, see [link to relevant documentation]. Figure 1 A proposed AC / DC parallel energy storage converter scheme involves connecting multiple small-capacity PCS units in parallel on both the AC and DC sides, and then connecting them together between the power grid and the battery system. This scheme effectively reduces the design complexity of individual units and improves the flexibility and redundancy of system configuration through modular parallel expansion. However, since each parallel PCS has independent control circuits, sampling circuits, and software control algorithms, differences inevitably exist between its hardware parameters and software control timing, leading to the induction of zero-sequence circulating current in the parallel system. Zero-sequence circulating current generates additional losses in power devices and line impedance, resulting in decreased system efficiency and increased device temperature rise. Simultaneously, zero-sequence circulating current interferes with the waveform quality of the grid-connected current, causing voltage fluctuations at the point of common coupling, posing a serious threat to the safe and stable operation of the power system.

[0024] To effectively suppress zero-sequence circulating current among the parallel AC / DC power storage converters (PCSs), this embodiment determines the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any one of the parallel AC / DC power storage converters. This zero-sequence voltage compensation amount is then superimposed on the three-phase modulation wave output from its internal current loop to generate a pulse drive signal, thereby suppressing the low-frequency zero-sequence circulating current generated by the power storage converter itself. Furthermore, since the DC and AC terminals of each parallel AC / DC power storage converter are connected in parallel, when the low-frequency zero-sequence circulating current of any power storage converter is effectively suppressed, the zero-sequence voltage at its AC terminal is forced to be clamped near zero potential, thus simultaneously blocking the zero-sequence circulating current path of other power storage converters connected in parallel. Therefore, this embodiment achieves low-frequency zero-sequence circulating current suppression for the entire system by implementing closed-loop control of the zero-sequence circulating current of only one power storage converter.

[0025] Furthermore, the applicant's research has found that when multiple energy storage converters simultaneously perform independent zero-sequence circulating current suppression, low-frequency oscillations in the system are easily triggered due to differences in their respective control parameters and sampling delays. This embodiment, however, controls only one of the energy storage converters, effectively preventing the generation of low-frequency oscillations and significantly improving the operational stability and reliability of the parallel energy storage system.

[0026] See Figure 2 The flowchart illustrating the implementation of the control method for the energy storage converter provided in this embodiment of the invention is described in detail below: Step 201: For each energy storage converter connected in AC-DC parallel configuration, obtain the three-phase bridge-side current of any energy storage converter.

[0027] See Figure 1 The DC terminals of each energy storage converter in the AC-DC parallel configuration are connected in parallel to the battery system, and the AC terminals of each energy storage converter are connected in parallel to the power grid. For multiple energy storage converters in the AC-DC parallel configuration, this embodiment can obtain the three-phase bridge-side current of any one of the energy storage converters for closed-loop control to suppress the low-frequency zero-sequence circulating current generated by the energy storage converter itself. In this embodiment, "multiple" refers to two or more.

[0028] Energy storage converters commonly employ a three-level inverter topology, such as a three-level NPC topology or a three-level ANPC topology. In a three-level inverter topology, the three-phase bridge-side current refers to the current flowing through the AC output terminals of the power switching devices on the bridge arms of the converter, i.e., the three-phase currents flowing out from the midpoints of the three bridge arms. See also... Figure 3 Taking a three-level NPC topology as an example, the three-phase bridge-side current refers to the three-phase line current flowing out from the midpoint of the NPC bridge arm, denoted as _____. , and .

[0029] As an optional implementation, each energy storage converter in the AC-DC parallel system can be internally equipped with a current sampling circuit, an analog-to-digital converter (AD) chip, a field-programmable gate array (FPGA) chip, and a digital signal processor (DSP) chip. The current sampling circuit (i.e., the three-phase bridge-side current acquisition circuit) is used to acquire the bridge-side current signal of each phase. The three-phase bridge-side current acquisition circuit can be electrically connected to the FPGA chip via an external AD chip. The FPGA chip controls the AD chip to complete the analog-to-digital conversion of the three-phase bridge-side current signal and sends the converted digital current signal to the DSP chip via parallel communication. After receiving the three-phase bridge-side current digital signal, the DSP chip can perform subsequent steps such as zero-sequence current calculation, PI control, and modulation wave superposition.

[0030] Step 202: Determine the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any energy storage converter. The zero-sequence voltage compensation amount is used to suppress the low-frequency zero-sequence circulating current generated by the energy storage converter.

[0031] The applicant has discovered through research that low-frequency zero-sequence circulating current is mainly caused by the formation of a closed loop of zero-sequence current between various energy storage converters connected in parallel with AC / DC converters. Accordingly, low-frequency zero-sequence circulating current can be suppressed by suppressing the zero-sequence current.

[0032] In some embodiments, the zero-sequence current of any energy storage converter can be determined based on the three-phase bridge-side current of the energy storage converter; then, the difference between the zero-sequence current and the set value is calculated, and the difference is PI controlled to obtain the zero-sequence voltage compensation amount.

[0033] Here, the difference between the given value and zero is set to be within a set error range. For example, the given value can be set to 0.

[0034] Zero-sequence current It can be represented as: .

[0035] Based on the determination of the zero-sequence current, this embodiment can determine the zero-sequence current. The zero-sequence voltage compensation output by the PI controller is obtained by sending the feedback value and the setpoint to the PI controller. Here, the PI controller is used to perform proportional-integral regulation on the difference between the setpoint and the feedback value.

[0036] This embodiment sets the given value to 0, which is equivalent to taking 0 as the target value, and drives the zero-sequence current to approach zero, thereby achieving the purpose of suppressing the zero-sequence current and thus suppressing the low-frequency zero-sequence circulating current.

[0037] Step 203: For any three-phase modulated wave output from the internal current loop of the energy storage converter, the zero-sequence voltage compensation is superimposed to obtain the superimposed three-phase modulated wave.

[0038] Energy storage converters typically have a current loop inside. This current loop obtains the three-phase bridge-side current and the target current value of the energy storage converter to output a three-phase voltage signal (i.e., a three-phase modulated wave), which is used to control the output current of the energy storage converter and thus track the target current value.

[0039] In related technologies, the pulse drive signal is typically determined directly based on the three-phase modulation wave output from the current loop to control the switching of power switching devices, thereby controlling the energy storage converter. However, this embodiment superimposes the zero-sequence voltage compensation onto the three-phase modulation wave output from the current loop, and determines the pulse drive signal based on the superimposed three-phase modulation wave. This allows the pulse drive signal to simultaneously contain the target current value and low-frequency zero-sequence circulating current suppression information, enabling the energy storage converter to actively suppress its own low-frequency zero-sequence circulating current while tracking the target current value.

[0040] In this embodiment, the process of superimposing the zero-sequence voltage compensation amount onto the three-phase modulation wave is an algebraic superposition process. By superimposing the zero-sequence voltage compensation amount onto each phase voltage signal output by the current loop, the superimposed three-phase voltage signal can be obtained, which is the superimposed three-phase modulation wave.

[0041] It should be noted that the zero-sequence voltage compensation is a common-mode component with the same direction and amplitude in the three-phase modulation wave. This superposition operation does not change the line voltage difference between the three-phase modulation waves. Therefore, the above superposition operation will not affect the normal power output of the energy storage converter, but only corrects the common-mode component of the three-phase modulation wave, thereby achieving the technical effect of not affecting the main power transmission and only suppressing the low-frequency zero-sequence circulating current.

[0042] Step 204: Based on the superimposed three-phase modulation wave, modulate and determine the pulse drive signal to control any energy storage converter.

[0043] In this embodiment, a modulation strategy can be used to modulate the superimposed three-phase modulation wave to obtain a pulse drive signal. This pulse drive signal is used to control the on / off switching of the power switching devices inside the energy storage current device, so as to achieve the purpose of controlling the energy storage converter.

[0044] For example, the above modulation strategy can be sinusoidal pulse width modulation (SPWM) or space vector pulse width modulation (SVPWM), and this embodiment does not specifically limit it.

[0045] For example, the DSP chip in the energy storage converter is used to calculate the zero-sequence current compensation amount and superimpose it onto the three-phase modulation wave to obtain the superimposed three-phase modulation wave. The superimposed three-phase modulation wave is written to the FPGA chip through the DSP parallel port communication. The FPGA chip obtains the SVPWM modulated pulse drive signal according to the superimposed three-phase modulation wave.

[0046] In this embodiment, the zero-sequence voltage compensation amount is determined by the three-phase bridge-side current of any energy storage converter in the AC-DC parallel configuration. This zero-sequence voltage compensation amount is then superimposed on the three-phase modulation wave output by the internal current loop to determine the pulse drive signal, which can effectively suppress the low-frequency zero-sequence circulating current generated by the energy storage converter itself.

[0047] Furthermore, since the DC and AC terminals of each energy storage converter are connected in parallel, forming a low-impedance electrical coupling path, when the low-frequency zero-sequence circulating current of any energy storage converter is effectively suppressed, the zero-sequence voltage at its AC terminal is forced to be clamped near zero potential, thereby simultaneously blocking the zero-sequence circulating current paths of other energy storage converters connected in parallel. Therefore, this embodiment does not require independent zero-sequence circulating current closed-loop control for each energy storage converter to achieve low-frequency zero-sequence circulating current suppression for the entire system, significantly reducing the complexity and computational cost of the control system.

[0048] Furthermore, when multiple energy storage converters simultaneously perform independent zero-sequence circulating current suppression, low-frequency oscillations in the system can easily occur due to differences in their control parameters and sampling delays. This embodiment, however, controls only one energy storage converter, thereby fundamentally avoiding coupling competition between them and effectively preventing low-frequency oscillations, significantly improving the operational stability and reliability of the parallel energy storage system.

[0049] The above embodiments primarily target the suppression of low-frequency zero-sequence circulating current. It should be noted that not only low-frequency zero-sequence circulating current exists between the parallel AC / DC energy storage converters, but also high-frequency zero-sequence circulating current. To further suppress high-frequency zero-sequence circulating current, this embodiment also provides a new control method for energy storage converters. In this method, each parallel AC / DC energy storage converter includes: one master energy storage converter and at least one slave energy storage converter. The master energy storage converter and each slave energy storage converter communicate with each other via optical fiber. The division between the master and slave energy storage converters can be set according to actual conditions; this embodiment does not impose specific limitations on this.

[0050] See Figure 4 The method includes: Step 401: For each energy storage converter connected in AC-DC parallel configuration, obtain the three-phase bridge-side current of any one of the energy storage converters. It should be emphasized that "any one of the energy storage converters" here can be any slave energy storage converter.

[0051] Step 402: Determine the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any energy storage converter.

[0052] Step 403: For the three-phase modulated wave output from the internal current loop of any energy storage converter, the zero-sequence voltage compensation is superimposed to obtain the superimposed three-phase modulated wave.

[0053] For detailed implementation methods of steps 401 and 403 above, please refer to [link to relevant documentation]. Figure 2 The corresponding implementation examples will not be described in detail here.

[0054] Step 404: Obtain the updated triangular carrier wave.

[0055] Here, the updated triangular carrier is obtained by performing a triangular carrier zeroing operation. The triangular carrier zeroing operation is triggered by a carrier synchronization signal. The carrier synchronization signal is sent by the host energy storage converter at a set time before its own triangular carrier crosses zero.

[0056] Here, each energy storage converter in the AC-DC parallel configuration can generate a periodic triangular carrier wave within itself (e.g., an FPGA chip within it). This triangular carrier wave is used to generate a pulse drive signal in conjunction with the superimposed three-phase modulated wave.

[0057] The applicant has discovered that high-frequency zero-sequence circulating current is mainly caused by the instantaneous common-mode voltage difference resulting from the asynchrony of the triangular carrier waves between parallel energy storage converters. To suppress high-frequency zero-sequence circulating current, in each carrier cycle, this embodiment can send a carrier synchronization signal from the master energy storage converter to the slave energy storage converter. The slave energy storage converter updates its own triangular carrier wave according to the received carrier synchronization signal (e.g., by performing a triangular carrier wave zeroing operation), thereby achieving synchronization of the master and slave carrier cycles. This ensures that each energy storage converter outputs the same common-mode voltage at the same time, blocking the generation path of high-frequency zero-sequence circulating current at its source.

[0058] In some embodiments, the master energy storage converter can send a carrier synchronization signal to the slave at the zero-crossing moment. However, considering that the slave energy storage converter has a fixed processing delay for the carrier synchronization signal and that the hardware circuit has a transmission delay, in this embodiment, the master energy storage converter can send a carrier synchronization signal to each slave energy storage converter at a set time before its own triangular carrier crosses zero.

[0059] It is understandable that the time difference between the set time and the zero-crossing time can be determined based on the processing delay of the slave energy storage converter on the carrier synchronization signal and the transmission delay of the hardware circuit.

[0060] This embodiment uses a compensation mechanism that sends the signal in advance so that when the slave energy storage converter receives the carrier synchronization signal and completes the zeroing operation, its triangular carrier arrives at the zero-crossing point at the same time as the master's triangular carrier, thereby achieving complete periodic synchronization between the master and slave carriers.

[0061] Considering the critical commutation process near the zero-crossing point of the modulation wave in a three-level inverter topology, performing a carrier zero-crossing operation at this moment may lead to increased stress on the switching transistors or PWM pulse disturbances. Therefore, this embodiment can mark the counting direction of the triangular carrier. For example, flag=0 indicates that the triangular carrier counts incrementally from zero to the carrier peak, and flag=1 indicates that the triangular carrier counts incrementally from the carrier peak to the zero-crossing point. See [link to documentation] Figure 5The FPGA chip inside the energy storage converter can generate a triangular carrier wave with a period of 2T. When the carrier period increases from 0 to T and then decreases from T to 0, one carrier period is completed. The master energy storage converter only sends a carrier synchronization signal to the slave device when flag=1 (i.e., the triangular carrier wave is in the self-decreasing direction), thereby avoiding the synchronization action from being performed within the safe range after the modulation wave crosses zero.

[0062] In some embodiments, the carrier synchronization signal can be a pulse signal with a preset pulse width (e.g., 5 microseconds). After receiving the signal, the slave energy storage converter can also determine whether the pulse width of the received signal meets the preset pulse width condition. If it does, a triangular carrier zeroing operation is performed; if it does not, the signal is ignored. By determining the pulse width, false triggering caused by electromagnetic interference can be effectively prevented, thus improving the reliability of carrier synchronization.

[0063] like Figure 6 As shown, the host energy storage converter counts the triangular carrier value in real time and detects whether the triangular carrier counting direction is in the decrement direction. When it is determined that the triangular carrier direction is in the decrement direction (i.e., flag=1), it further detects whether the triangular carrier value is less than a set value (e.g., 33) to determine whether the set time before the zero crossing has been reached. If it is determined that the triangular carrier value is less than the set value, a square wave signal with a preset pulse width (e.g., 5 microseconds) is generated as a carrier synchronization signal, and this carrier synchronization signal is sent to the slave energy storage converter via optical fiber.

[0064] The slave energy storage converter detects whether the pulse width of the received carrier synchronization signal is within a preset width (e.g., 5 microseconds). If the pulse width is within the preset width, the slave energy storage converter performs a carrier zeroing operation, resetting the current triangular carrier count to zero and obtaining an updated triangular carrier, thereby achieving carrier period synchronization with the master. If the pulse width is not within the preset width, the current signal is deemed invalid, and the zeroing operation is not performed. Furthermore, if the slave energy storage converter fails to receive a valid carrier synchronization signal within a preset timeout period, a carrier synchronization fault timeout is determined, indicating a fault in slave carrier synchronization. The system controller can then report the fault status or take preset protection actions (e.g., shutdown or switching to independent operation mode).

[0065] Step 405: Based on the comparison results of the superimposed three-phase modulated wave and the updated triangular carrier wave, the modulated pulse drive signal is determined.

[0066] This embodiment can execute a modulation strategy (e.g., SVPWM) based on the superimposed three-phase modulated wave and the updated triangular carrier. SVPWM uses the superimposed three-phase modulated wave as the voltage reference vector and the updated triangular carrier as the modulation carrier. By comparing the three-phase modulated wave with the triangular carrier, the switching time of each phase arm is determined; that is, when the instantaneous value of the modulated wave is greater than the instantaneous value of the triangular carrier, a high level is output; when the instantaneous value of the modulated wave is less than the instantaneous value of the triangular carrier, a low level is output. This generates a series of high-frequency pulse sequences (i.e., pulse drive signals) whose width varies with the amplitude of the modulated wave, used to control the on and off of the power switching devices.

[0067] It should be noted that the above method only describes the carrier synchronization method for any slave energy storage converter performing low-frequency zero-sequence circulating current closed-loop control when suppressing high-frequency zero-sequence circulating current. For the other slave energy storage converters in the AC-DC parallel system, the same carrier synchronization method can be used to suppress their own high-frequency zero-sequence circulating current. However, it should be noted that the other slave energy storage converters do not need to perform low-frequency zero-sequence circulating current closed-loop control. Low-frequency zero-sequence circulating current closed-loop control only needs to be performed by one energy storage converter (master or slave) in the AC-DC parallel system to avoid control coupling and system oscillation caused by multiple converters simultaneously performing low-frequency circulating current suppression.

[0068] In some embodiments, if the "any energy storage converter" performing the aforementioned low-frequency zero-sequence circulating current control is the master energy storage converter, then the master energy storage converter itself does not need to perform a triangular carrier zeroing operation (because it is itself the source of the carrier synchronization signal). Instead, it only needs to send a carrier synchronization signal to each slave energy storage converter at a set time before its own triangular carrier crosses zero, so that each slave energy storage converter can update its triangular carrier. At this time, the triangular carrier of the master energy storage converter maintains its original period, and each slave energy storage converter achieves carrier period synchronization with the master energy storage converter by receiving the carrier synchronization signal and performing a triangular carrier zeroing operation.

[0069] Regardless of whether the low-frequency zero-sequence circulating current closed-loop control task is undertaken by the master or slave, the carrier synchronization mechanism for high-frequency zero-sequence circulating current suppression remains unchanged: the master acts as the source of the carrier synchronization signal, sending synchronization signals to each slave in each carrier cycle; each slave acts as the receiver of the carrier synchronization signal, performing a triangular carrier zeroing operation based on the received synchronization signal, thereby achieving carrier cycle synchronization between the master and slave. The execution entity of the aforementioned low-frequency zero-sequence circulating current closed-loop control and the carrier synchronization mechanism for high-frequency zero-sequence circulating current suppression are independent of each other and do not interfere with each other.

[0070] The above embodiments primarily suppress low-frequency and high-frequency zero-sequence circulating currents. However, in energy storage converters operating in parallel AC / DC configurations, a three-level inverter topology is typically used, such as a three-level NPC topology or a three-level ANPC topology. Figure 3 Taking the three-level NPC topology shown as an example, this type of topology can lead to an imbalance at the midpoint of the upper and lower DC capacitors (i.e., the voltage values ​​of the upper DC capacitor C2 and the lower DC capacitor C1 are not equal), which in turn causes system oscillation, decreased efficiency, increased output voltage harmonics, asymmetrical stress on switching devices, some devices bearing higher voltages, and decreased reliability.

[0071] The applicant's research revealed that different switching states caused shifts and fluctuations in the inflow and outflow of the DC midpoint current, and that the magnitude and direction of the active and reactive currents were the root cause of the DC midpoint potential problem. To solve the problem of the imbalance at the midpoint of the upper and lower capacitors on the DC side, see [reference needed]. Figure 7 This embodiment provides a new control method for an energy storage converter, including: Step 701: For each energy storage converter connected in AC-DC parallel configuration, obtain the three-phase bridge-side current of any energy storage converter.

[0072] Step 702: Determine the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any energy storage converter.

[0073] For detailed implementation methods of steps 701 to 702 above, please refer to [link to relevant documentation]. Figure 2 The corresponding implementation examples will not be described in detail here.

[0074] Step 703: For any energy storage converter, obtain the DC upper capacitor voltage value and DC lower capacitor voltage value in the three-level inverter topology of the energy storage converter.

[0075] See Figure 3 The DC upper capacitor voltage value and the DC lower capacitor voltage value are the same as the voltage values ​​of the DC upper capacitor C2 and the DC lower capacitor C1. In this embodiment, each energy storage converter can be equipped with a voltage acquisition circuit to collect the DC upper capacitor voltage value of the energy storage converter. and DC capacitor voltage value The sampling signal is acquired by the FPGA's external AD converter and then sent to the DSP via parallel communication for DC upper and lower capacitor voltage equalization control.

[0076] Step 704: Determine the voltage balance compensation amount based on the DC upper capacitor voltage value and the DC lower capacitor voltage value.

[0077] In this embodiment, the difference between the DC upper capacitor voltage value and the DC lower capacitor voltage value can be calculated first: Next, the above difference The voltage balance compensation amount is obtained after being fed into a PI controller and adjusted by proportional-integral control. : 。

[0078] Step 705: Determine the injection direction of the voltage balance compensation amount based on the three-phase bridge side current; the injection direction is used to reflect the positive and negative polarities of the voltage balance compensation amount.

[0079] In this embodiment, the three-phase bridge-side current can be transformed to obtain positive-sequence active current and positive-sequence reactive current; then, based on the positive-sequence active current and positive-sequence reactive current, the characteristic value of the positive-sequence current is determined; finally, based on the characteristic value of the positive-sequence current, the injection direction of the voltage balance compensation is determined.

[0080] Specifically, the Clark transformation is first used to transform the three-phase bridge-side current from the three-phase stationary coordinate system (abc coordinate system) to the two-phase stationary coordinate system. (coordinate system), to obtain Axial components and Axial components : Next, the two-phase stationary coordinate system is transformed to the dq coordinate system, which rotates synchronously with the positive-sequence voltage of the grid, through the positive-sequence Park transformation, to obtain the positive-sequence active current. and positive sequence reactive current : in, This represents the phase angle of the grid voltage output by the phase-locked loop.

[0081] Simultaneously, negative-sequence active current is extracted through negative-sequence Park transform. and negative sequence reactive current : When there are imbalances or harmonics in the power grid The coordinate system current includes a positive sequence component ( and ), and negative order components ( and ): ; In the formula, This indicates that the positive sequence current is stationary in both phases. Orthogonal components in a coordinate system This indicates that the negative sequence current is at rest in both phases. Orthogonal components in a coordinate system. This indicates that the positive sequence current is stationary in both phases. Orthogonal components in the coordinate system This indicates that the negative sequence current is at rest in both phases. Orthogonal components in a coordinate system.

[0082] After the positive-order Park transform, the negative-order component ( and The positive-sequence component will appear on the dq axis at a frequency of 2 times the harmonic frequency, causing interference to the positive-sequence component; after the negative-sequence Park transform, the positive-sequence component ( and It will also appear on the dq axis at twice the frequency, forming cross-coupling.

[0083] To eliminate the aforementioned cross-coupling, the positive-sequence and negative-sequence components need to be decoupled. The basic principle of decoupling is to subtract the second harmonic interference term generated by the negative-sequence component from the original positive-sequence component. Mathematically, the decoupling of the positive-sequence component can be expressed as: In the formula, This represents the positive-sequence active current after decoupling. This represents the positive-sequence active current before decoupling. This represents the positive-sequence reactive current after decoupling. This represents the positive-sequence reactive current before decoupling.

[0084] Negative-order decoupling is symmetrical to positive-order decoupling, but the signs of the coupling terms are opposite (because the negative-order rotations are in the opposite direction). Negative-order component decoupling can be expressed as: In the formula, This represents the negative-sequence active current after decoupling. This represents the negative-sequence active current before decoupling. This represents the negative sequence reactive current after decoupling. This represents the negative sequence reactive current before decoupling.

[0085] Here, for , , , By employing a first-order low-pass filter, for example, with a cutoff frequency of 15Hz, negative sequence components and harmonics above the second harmonic, as well as interference noise, can be effectively filtered out, resulting in... , , , .

[0086] In this embodiment, the decoupled positive-sequence active current and positive-sequence reactive current are used as the final positive-sequence active current and positive-sequence reactive current to determine the characteristic value of the positive-sequence current, and then determine the injection direction of the voltage balance compensation.

[0087] Specifically, the process for determining the characteristic value of the positive sequence current is as follows: When the positive sequence active current and positive sequence reactive current When in the same direction, the positive sequence active current will be... and positive sequence reactive current The sum of these values ​​is determined as the characteristic value of the positive sequence current. See also Figure 8 ,like and All are greater than 0, or and If all are less than 0, then .

[0088] When the positive-sequence active current and the positive-sequence reactive current are in opposite directions, it is detected whether the amplitude of the positive-sequence active current is greater than the first amplitude threshold. If the amplitude of the positive-sequence active current is greater than the first amplitude threshold, the positive-sequence active current is determined as the positive-sequence current characteristic value. If the amplitude of the positive-sequence active current is less than or equal to the first amplitude threshold, it is detected whether the amplitude of the positive-sequence reactive current is greater than the second amplitude threshold. If the amplitude of the positive-sequence reactive current is greater than the second amplitude threshold, the positive-sequence reactive current is determined as the positive-sequence current characteristic value. If the amplitude of the positive-sequence reactive current is less than or equal to the second amplitude threshold, the sum of the positive-sequence active current and the positive-sequence reactive current is determined as the positive-sequence current characteristic value.

[0089] See Figure 8 When the positive-sequence active current and the positive-sequence reactive current are in opposite directions, the following two situations exist: when At that time, detection Whether it holds true (for example, the first amplitude threshold can be 10); if ,but .like Then detect Does it hold true (for example, the second amplitude threshold can be 10); if it holds true, then If not, then .

[0090] when At that time, detection Whether it holds true (for example, the first amplitude threshold can be 10); if ,but .like Then detect Does it hold true (for example, the second amplitude threshold can be 10); if it holds true, then If not, then .

[0091] Determining the characteristic value of positive sequence current Based on this, if the positive sequence current characteristic value is greater than the preset first characteristic value, then the injection direction of the voltage balance compensation is determined to be negative injection. If the positive sequence current characteristic value is less than the preset second characteristic value, then the injection direction of the voltage balance compensation is determined to be positive injection.

[0092] Here, the first eigenvalue is greater than 0, and the second eigenvalue is less than 0. For example, the first eigenvalue can be 10. The second eigenvalue can be -10.

[0093] If the positive sequence current characteristic value is less than or equal to a preset first characteristic value (e.g., 10) and greater than or equal to a preset second characteristic value (e.g., -10), then the voltage balance compensation amount will not be injected into the three-phase modulation wave.

[0094] Step 706: According to the injection direction, the voltage balance compensation is injected into the three-phase modulation wave output by the internal current loop of the energy storage converter, and the zero-sequence voltage compensation is superimposed to obtain the superimposed three-phase modulation wave.

[0095] Here, if the injection direction is forward injection, the voltage balance compensation amount will be taken as a positive value (i.e., The superimposed voltage is applied to the three-phase modulation wave, and normalization and limiting are performed. Then, the zero-sequence voltage compensation is further superimposed to obtain the superimposed three-phase modulation wave.

[0096] If the injection direction is negative, then the voltage balance compensation amount will be negative (i.e., The superimposed voltage is applied to the three-phase modulation wave, and normalization and limiting are performed. Then, the zero-sequence voltage compensation is further superimposed to obtain the superimposed three-phase modulation wave.

[0097] Step 707: Obtain the updated triangular carrier wave.

[0098] Step 708: Based on the comparison results of the superimposed three-phase modulated wave and the updated triangular carrier wave, the modulated pulse drive signal is determined.

[0099] For detailed implementation methods of steps 707-708 above, please refer to [link to relevant documentation]. Figure 4 The corresponding implementation examples will not be described in detail here.

[0100] The above method only introduces the control method for any energy storage converter performing low-frequency zero-sequence circulating current closed-loop control, used to suppress low-frequency and high-frequency zero-sequence circulating current and ensure the balance of the midpoint potential of the upper and lower capacitors on the DC side. It should be noted that for the other energy storage converters in the AC-DC parallel system (e.g., slave energy storage converters not undertaking low-frequency zero-sequence circulating current control, and master energy storage converters), their corresponding voltage balance compensation can also be injected into the corresponding three-phase modulation wave to generate pulse drive signals, thereby ensuring the balance of their respective DC side midpoint potentials. However, the other energy storage converters do not need to further superimpose zero-sequence voltage compensation on top of the injected voltage balance compensation, to avoid control coupling and system oscillation caused by multiple converters simultaneously performing low-frequency zero-sequence circulating current control.

[0101] In other words, in an AC-DC parallel system, only one energy storage converter (master or slave) needs to undertake the closed-loop control task of low-frequency zero-sequence circulating current. The voltage balance compensation and zero-sequence voltage compensation are superimposed on the three-phase modulation wave output by the current loop. The other energy storage converters only need to superimpose their own voltage balance compensation to achieve their own midpoint potential balance while passively suppressing the low-frequency zero-sequence circulating current through the clamping effect of the master on the common-mode voltage.

[0102] In this way, this embodiment not only ensures the independent balance of the DC side midpoint potential of each parallel energy storage converter, but also avoids the regulation conflict and system oscillation that may be caused by multiple converters performing low-frequency zero-sequence circulating current control at the same time, thus significantly improving the stability and reliability of the system.

[0103] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0104] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0105] Figure 9 A schematic diagram of the control device for an energy storage converter provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 9 As shown, the control device of the energy storage converter includes: acquisition module 91, compensation module 92 and control module 93.

[0106] The acquisition module 91 is used to acquire the three-phase bridge-side current of any energy storage converter in the AC-DC parallel configuration; the DC terminals of each energy storage converter in the AC-DC parallel configuration are connected in parallel to the battery system, and the AC terminals of each energy storage converter in the AC-DC parallel configuration are connected in parallel to the power grid. Compensation module 92 is used to determine the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any energy storage converter; the zero-sequence voltage compensation amount is used to suppress the low-frequency zero-sequence circulating current generated by the energy storage converter. Control module 93 is used for: The three-phase modulated wave output from the internal current loop of any energy storage converter is superimposed with the zero-sequence voltage compensation to obtain the superimposed three-phase modulated wave. Based on the superimposed three-phase modulated waves, a pulse drive signal is modulated to control any energy storage converter.

[0107] Optional, compensation module 92, specifically used for: Determine the zero-sequence current of any energy storage converter based on the three-phase bridge-side current of that energy storage converter. Calculate the difference between the zero-sequence current and the setpoint, and apply PI control to the difference to obtain the zero-sequence voltage compensation; the difference between the setpoint and zero is within the set error range.

[0108] Optionally, each energy storage converter in the AC-DC parallel configuration includes: a master energy storage converter and at least one slave energy storage converter; the master energy storage converter and each slave energy storage converter communicate with each other. If any energy storage converter is a slave energy storage converter, then control module 93 is specifically used for: The updated triangular carrier is obtained by performing a triangular carrier zeroing operation. The triangular carrier zeroing operation is triggered by a carrier synchronization signal. The carrier synchronization signal is sent by the host energy storage converter at a set time before its own triangular carrier crosses zero. Based on the comparison results between the superimposed three-phase modulated wave and the updated triangular carrier wave, the modulation determines the pulse drive signal.

[0109] Optionally, the energy storage converter adopts a three-level inverter topology; Control module 93 is specifically used for: For any energy storage converter, obtain the DC upper capacitor voltage value and the DC lower capacitor voltage value in the three-level inverter topology of the energy storage converter. The voltage balance compensation amount is determined based on the DC upper capacitor voltage value and the DC lower capacitor voltage value. The injection direction of the voltage balance compensation is determined based on the three-phase bridge side current; the injection direction is used to reflect the positive and negative polarities of the voltage balance compensation. According to the injection direction, the voltage balance compensation is injected into the three-phase modulated wave output by the internal current loop of the energy storage converter, and the zero-sequence voltage compensation is superimposed to obtain the superimposed three-phase modulated wave.

[0110] Optional, control module 93, specifically used for: The three-phase bridge side current is transformed to obtain the positive sequence active current and the positive sequence reactive current. Determine the characteristic value of the positive sequence current based on the positive sequence active current and the positive sequence reactive current; The injection direction of the voltage balance compensation is determined based on the characteristic value of the positive sequence current.

[0111] Optional, control module 93, specifically used for: When the positive sequence active current and the positive sequence reactive current are in the same direction, the sum of the positive sequence active current and the positive sequence reactive current is determined as the characteristic value of the positive sequence current. When the positive sequence active current and the positive sequence reactive current are in opposite directions, it is detected whether the amplitude of the positive sequence active current is greater than the first amplitude threshold. If the amplitude of the positive sequence active current is greater than the first amplitude threshold, then the positive sequence active current is determined as the characteristic value of the positive sequence current. If the amplitude of the positive sequence active current is less than or equal to the first amplitude threshold, then it is detected whether the amplitude of the positive sequence reactive current is greater than the second amplitude threshold. If the amplitude of the positive sequence reactive current is greater than the second amplitude threshold, then the positive sequence reactive current is determined as the characteristic value of the positive sequence current. If the amplitude of the positive sequence reactive current is less than or equal to the second amplitude threshold, then the sum of the positive sequence active current and the positive sequence reactive current is determined as the characteristic value of the positive sequence current.

[0112] Optional, control module 93, specifically used for: If the positive sequence current characteristic value is greater than the preset first characteristic value, then the injection direction of the voltage balance compensation is determined to be negative injection; the first characteristic value is greater than 0. If the positive sequence current characteristic value is less than the preset second characteristic value, then the injection direction of the voltage balance compensation is determined to be positive injection; the second characteristic value is less than 0.

[0113] This device embodiment is used in the above method embodiment, and its technical effects and implementation principles are the same as those of the above method embodiment, so they will not be repeated here.

[0114] Figure 10 This is a schematic diagram of the energy storage converter provided in an embodiment of the present invention. Figure 10 As shown, the energy storage converter 10 of this embodiment includes a processor 100 and a memory 101. The memory 101 stores a computer program 102. When the processor 100 executes the computer program 102, it implements the steps in the various method embodiments described above. Alternatively, when the processor 100 executes the computer program 102, it implements the functions of each module / unit in the various device embodiments described above.

[0115] For example, computer program 102 can be divided into one or more modules / units, which are stored in memory 101 and executed by processor 100 to complete the present invention. The one or more modules / units can be a series of computer program instruction segments capable of performing specific functions, which describe the execution process of computer program 102 in energy storage converter 10.

[0116] The energy storage converter 10 may include, but is not limited to, a processor 100 and a memory 101. Those skilled in the art will understand that... Figure 10 This is merely an example of the energy storage converter 10 and does not constitute a limitation on the energy storage converter 10. It may include more or fewer components than shown, or combine certain components, or different components. For example, the energy storage converter 10 may also include input / output devices, network access devices, buses, etc.

[0117] The processor 100 can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0118] The memory 101 can be an internal storage unit of the energy storage converter 10, such as a hard disk or RAM of the energy storage converter 10. The memory 101 can also be an external storage device of the energy storage converter 10, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the energy storage converter 10. Furthermore, the memory 101 can include both internal storage units and external storage devices of the energy storage converter 10. The memory 101 is used to store the computer program 102 and other programs and data required by the energy storage converter 10. The memory 101 can also be used to temporarily store data that has been output or will be output.

[0119] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0120] This invention also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, it implements the methods described in the above-described method embodiments.

[0121] This invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the methods described in the above-described method embodiments.

[0122] Computer programs include computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. Computer-readable media can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0123] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0124] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A control method of an energy storage converter, characterized by, include: For each energy storage converter connected in parallel with AC and DC, the three-phase bridge-side current of any energy storage converter is obtained; the DC terminals of each energy storage converter connected in parallel are connected to the battery system, and the AC terminals of each energy storage converter connected in parallel are connected to the power grid. Based on the three-phase bridge-side current of any of the energy storage converters, the zero-sequence voltage compensation amount is determined; the zero-sequence voltage compensation amount is used to suppress the low-frequency zero-sequence circulating current generated by the energy storage converter. The zero-sequence voltage compensation is superimposed on the three-phase modulated wave output from the internal current loop of any of the energy storage converters to obtain the superimposed three-phase modulated wave. Based on the superimposed three-phase modulated wave, a pulse drive signal is modulated to control any one of the energy storage converters.

2. The control method for the energy storage converter according to claim 1, characterized in that, The determination of the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any of the energy storage converters includes: Based on the three-phase bridge-side current of any of the energy storage converters, determine the zero-sequence current of the energy storage converter. The difference between the zero-sequence current and the set value is calculated, and the difference is controlled by PI to obtain the zero-sequence voltage compensation amount; the difference between the set value and zero is within the set error range.

3. The control method for the energy storage converter according to claim 1, characterized in that, Each of the AC-DC parallel energy storage converters includes: a master energy storage converter and at least one slave energy storage converter; the master energy storage converter and each slave energy storage converter communicate with each other. If any of the energy storage converters is a slave energy storage converter, then the step of modulating and determining the pulse drive signal based on the superimposed three-phase modulation wave includes: The updated triangular carrier is obtained by performing a triangular carrier zeroing operation; the triangular carrier zeroing operation is triggered by a carrier synchronization signal; the carrier synchronization signal is sent by the host energy storage converter at a set time before its own triangular carrier crosses zero. Based on the comparison results between the superimposed three-phase modulated wave and the updated triangular carrier wave, the pulse drive signal is modulated and determined.

4. The control method for the energy storage converter according to any one of claims 1-3, characterized in that, The energy storage converter adopts a three-level inverter topology. The three-phase modulated wave output from the internal current loop of any of the energy storage converters is superimposed with the zero-sequence voltage compensation to obtain the superimposed three-phase modulated wave, which includes: For any of the energy storage converters, obtain the DC upper capacitor voltage value and the DC lower capacitor voltage value in the three-level inverter topology of the energy storage converter; Based on the DC upper capacitor voltage value and the DC lower capacitor voltage value, determine the voltage balance compensation amount; The injection direction of the voltage balance compensation is determined based on the three-phase bridge side current; the injection direction is used to reflect the positive and negative polarities of the voltage balance compensation. According to the injection direction, the voltage balance compensation is injected into the three-phase modulated wave output by the internal current loop of the energy storage converter, and the zero-sequence voltage compensation is superimposed to obtain the superimposed three-phase modulated wave.

5. The control method for the energy storage converter according to claim 4, characterized in that, The step of determining the injection direction of the voltage balance compensation amount based on the three-phase bridge side current includes: The three-phase bridge-side current is transformed to obtain positive-sequence active current and positive-sequence reactive current. Determine the characteristic value of the positive sequence current based on the positive sequence active current and the positive sequence reactive current; The injection direction of the voltage balance compensation is determined based on the positive sequence current characteristic value.

6. The control method for the energy storage converter according to claim 5, characterized in that, The step of determining the positive-sequence current characteristic value based on the positive-sequence active current and the positive-sequence reactive current includes: When the positive sequence active current and the positive sequence reactive current are in the same direction, the sum of the positive sequence active current and the positive sequence reactive current is determined as the characteristic value of the positive sequence current. When the positive sequence active current and the positive sequence reactive current are in opposite directions, it is detected whether the amplitude of the positive sequence active current is greater than the first amplitude threshold. If the amplitude of the positive sequence active current is greater than the first amplitude threshold, then the positive sequence active current is determined as the characteristic value of the positive sequence current. If the amplitude of the positive sequence active current is less than or equal to the first amplitude threshold, then it is detected whether the amplitude of the positive sequence reactive current is greater than the second amplitude threshold. If the amplitude of the positive sequence reactive current is greater than the second amplitude threshold, then the positive sequence reactive current is determined as the characteristic value of the positive sequence current. If the amplitude of the positive sequence reactive current is less than or equal to the second amplitude threshold, then the sum of the positive sequence active current and the positive sequence reactive current is determined as the characteristic value of the positive sequence current.

7. The control method for the energy storage converter according to claim 5, characterized in that, Determining the injection direction of the voltage balance compensation amount based on the positive sequence current characteristic value includes: If the positive sequence current characteristic value is greater than a preset first characteristic value, then the injection direction of the voltage balance compensation is determined to be negative injection; the first characteristic value is greater than 0. If the positive sequence current characteristic value is less than the preset second characteristic value, then the injection direction of the voltage balance compensation is determined to be positive injection; the second characteristic value is less than 0.

8. A control device for an energy storage converter, characterized in that, include: The acquisition module is used to acquire the three-phase bridge-side current of any one of the energy storage converters in the AC-DC parallel connection; the DC terminals of each of the energy storage converters in the AC-DC parallel connection are connected in parallel to the battery system, and the AC terminals of each of the energy storage converters in the AC-DC parallel connection are connected in parallel to the power grid. The compensation module is used to determine the zero-sequence voltage compensation amount based on the three-phase bridge-side current of any of the energy storage converters; the zero-sequence voltage compensation amount is used to suppress the low-frequency zero-sequence circulating current generated by the energy storage converters. The control module is used for: The zero-sequence voltage compensation is superimposed on the three-phase modulated wave output from the internal current loop of any of the energy storage converters to obtain the superimposed three-phase modulated wave. Based on the superimposed three-phase modulated wave, a pulse drive signal is modulated to control any one of the energy storage converters.

9. An energy storage converter, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the method as described in any one of claims 1 to 7.

10. A system, characterized in that, It includes multiple energy storage converters as described in claim 9, with the DC terminals of each energy storage converter connected in parallel to the battery system and the AC terminals of each energy storage converter connected in parallel to the power grid.

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