Multi-machine parallel zero sequence current control method and device, electronic equipment and medium

Abstract

This disclosure provides a method, device, electronic equipment, and medium for controlling zero-sequence current in a multi-unit parallel system, relating to the technical fields of power electronics. The specific implementation scheme is as follows: The total number of parallel modules in a multi-unit parallel energy storage converter system, the local modulation status information, and the positive and negative DC bus voltages of the local converter are obtained; based on the total number of parallel modules, a derating factor for the number of parallel units is calculated; based on the local modulation status information, the available modulation margin is calculated in real time, and the available modulation margin is mapped to a zero-sequence current limiting factor; based on the positive and negative DC bus voltages of the local converter, the local neutral point potential offset is calculated, and a neutral point potential correction factor is calculated based on the local neutral point potential offset; based on the parallel unit derating factor, the zero-sequence current limiting factor, and the neutral point potential correction factor, a preset reference limiting value is dynamically adjusted, and the local zero-sequence current dynamic limiting value is obtained and sent to the zero-sequence current controller.

Description

Technical Field

[0001] This disclosure belongs to the field of power electronic control technology, specifically relating to a method and device for controlling zero-sequence current in parallel multi-machine systems, electronic equipment, and computer-readable storage medium. Background Technology

[0002] With the increasing demand for grid connection of new energy sources, parallel operation of multiple energy storage converters has become the mainstream solution to improve system capacity. However, multi-unit parallel systems face two major technical challenges: one is the problem of zero-sequence circulating current. The parallel structure with a common AC / DC bus provides a path for circulating current, which can cause waveform distortion, additional device losses, and in severe cases, system instability. The other is the problem of midpoint potential fluctuation. For three-level topologies, midpoint potential fluctuation and zero-sequence circulating current are strongly coupled, and single-target control cannot take both into account.

[0003] In existing technologies, the control of the zero-sequence current loop generally adopts a proportional-integral regulator and sets a fixed limit value to prevent controller saturation. This approach has poor adaptability to single-machine operating conditions: under light loads, the limit is too strict, wasting voltage equalization capacity; under heavy loads, the limit is too loose, easily leading to modulation oversaturation and current distortion; when multiple stages are connected in parallel, the limit of each module is set independently, and there is no information exchange between them; the voltage equalization loops of each module may cross-influence each other, and the zero-sequence current commands cancel each other out or superimpose, causing oscillations at a specific frequency. Summary of the Invention

[0004] This disclosure provides a method and apparatus for controlling zero-sequence current in parallel multi-machine systems, an electronic device, and a computer-readable storage medium.

[0005] According to the first aspect, a method for controlling zero-sequence current in a multi-unit parallel system is provided, applicable to any converter module in a system of multiple energy storage converters in parallel. The method includes: acquiring the total number of parallel modules in the system, the local modulation status information, and the positive and negative DC bus voltages of the local converter; calculating a derating factor based on the total number of parallel modules; calculating the available modulation margin in real time based on the local modulation status information, and mapping the available modulation margin to a zero-sequence current limiting factor; calculating the local neutral point potential offset based on the local DC bus voltages, and calculating a neutral point potential correction factor based on the local neutral point potential offset; dynamically adjusting a preset reference limiting value based on the parallel module derating factor, the zero-sequence current limiting factor, and the neutral point potential correction factor, and obtaining and sending the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

[0006] Based on the second aspect, another method for controlling zero-sequence current in a multi-machine parallel system is provided, applicable to any converter module in a system of multiple energy storage converters in parallel. This method includes: acquiring the local zero-sequence current command, the zero-sequence voltage at the common coupling point, and the local zero-sequence current limit value; determining whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold; when the absolute value of the zero-sequence voltage is greater than the interference threshold, determining that there is mutual interference between the multi-machine voltage equalization rings, and superimposing the local zero-sequence current command, which is then low-pass filtered, with the zero-sequence voltage used as a positive feedforward to form the final zero-sequence current command; and inputting the final zero-sequence current command to the zero-sequence voltage... The zero-sequence current controller output is fed into a limiter, which sets the current limit value to the current zero-sequence current limit. When the output of the zero-sequence current controller reaches the limit, the integral accumulation of the zero-sequence current controller is stopped, and the limiting error is filtered by a first-order low-pass filter. The filtered error is then fed back to the controller input for smoothing. When the output of the zero-sequence current controller deviates from the limit, the integral accumulation of the zero-sequence current controller is resumed based on the filtered error to obtain the zero-sequence control quantity. Based on the zero-sequence control quantity and the given voltage signal output by the current loop, a three-phase modulated wave is obtained and sent to the power device.

[0007] According to a third aspect, a multi-unit parallel zero-sequence current control device is provided, applied to any converter module in a multi-unit parallel energy storage converter system. The device includes: a parameter acquisition unit configured to acquire the total number of parallel modules in the multi-unit parallel energy storage converter system, local modulation status information, and local DC-side positive and negative bus voltages; a derating calculation unit configured to calculate a derating factor based on the total number of parallel modules; a coefficient calculation unit configured to calculate the available modulation margin in real time based on the local modulation status information and map the available modulation margin to a zero-sequence current limiting factor; an offset calculation unit configured to calculate the local midpoint potential offset based on the local DC-side positive and negative bus voltages and calculate a midpoint potential correction factor based on the local midpoint potential offset; and a limiting calculation unit configured to dynamically adjust a preset reference limiting value based on the parallel derating factor, the zero-sequence current limiting factor, and the midpoint potential correction factor, and obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

[0008] According to the fourth aspect, a multi-machine parallel zero-sequence current control device is provided, applied to any converter module in a multi-energy storage converter parallel system. The device includes: a value acquisition unit configured to acquire the local zero-sequence current command, the zero-sequence voltage at the common coupling point, and the local current zero-sequence current limit value; a judgment unit configured to judge whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold; a command generation unit configured to, when the absolute value of the zero-sequence voltage is greater than the interference threshold, determine that there is mutual interference between the multi-machine voltage equalization rings, and superimpose the local zero-sequence current command, after low-pass filtering, with the zero-sequence voltage as a positive feedforward, to form the final zero-sequence current command; and a limit processing unit configured to output the final zero-sequence current command... The signal is fed into a zero-sequence current controller, and the output of the zero-sequence current controller is sent to a limiter. The limiter's limit is the current zero-sequence current limit value. The smoothing unit is configured to stop the integral accumulation of the zero-sequence current controller when the output of the zero-sequence current controller reaches the limit value, and to obtain the filtering error by passing the limit error through a first-order low-pass filter. The filtering error is then fed back to the controller input for smoothing. The recovery unit is configured to restore the integral accumulation of the zero-sequence current controller based on the filtering error when the output of the zero-sequence current controller deviates from the limit value, and to obtain the zero-sequence control quantity. The transmitting unit is configured to obtain and transmit a three-phase modulated wave to the power device based on the zero-sequence control quantity and the given voltage signal output by the current loop.

[0009] According to a fifth aspect, an electronic device is provided, comprising: at least one processor; and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform a method as described in any implementation of the first or second aspect.

[0010] According to a sixth aspect, a non-transitory computer-readable storage medium is provided that stores computer instructions for causing a computer to perform the method described in any implementation of the first or second aspect.

[0011] The multi-unit parallel zero-sequence current control method and apparatus provided in the embodiments of this disclosure are applied to any converter module in a multi-unit parallel energy storage converter system. First, the total number of parallel modules in the multi-unit parallel energy storage converter system, the local modulation status information, and the positive and negative DC bus voltages of the local converter are obtained. Second, based on the total number of parallel modules, the derating factor for the number of parallel modules is calculated. Third, based on the local modulation status information, the available modulation margin is calculated in real time and mapped to the zero-sequence current limiting factor. Then, based on the positive and negative DC bus voltages of the local converter, the local midpoint potential offset is calculated, and the midpoint potential correction factor is calculated according to the local midpoint potential offset. Finally, based on the parallel module derating factor, the zero-sequence current limiting factor, and the midpoint potential correction factor, a preset reference limiting value is dynamically adjusted to obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller. Therefore, by reducing the total number of parallel modules, the overall loop current loss control is prevented due to the superposition of multiple machines; the midpoint potential offset is included in the limiting calculation to achieve a dual-objective synergistic mechanism of midpoint balance and zero-sequence circulating current suppression; the fundamental and harmonic modulation in real time is calculated, the remaining available modulation margin is extracted, and it is mapped to the zero-sequence current limiting coefficient. By dynamically adjusting the reference limiting value through the zero-sequence current limiting coefficient and the midpoint potential correction coefficient, the limiting value can be automatically reduced when the margin is small under heavy load, avoiding over-modulation; when the margin is large under light load, the limiting is relaxed, making full use of the voltage equalization capability of the converter.

[0012] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become readily apparent from the following description. Attached Figure Description

[0013] The accompanying drawings are provided to better understand this solution and do not constitute a limitation of this disclosure. Wherein:

[0014] Figure 1 This is a flowchart of an embodiment of the multi-machine parallel zero-sequence current control method according to the present disclosure; Figure 2 This is a schematic diagram of a system with multiple energy storage converters connected in parallel, as disclosed in this publication. Figure 3 This is a flowchart of another embodiment of the multi-machine parallel zero-sequence current control method according to the present disclosure; Figure 4 The zero-sequence circulating current is obtained by using the multi-stage parallel zero-sequence current control method disclosed in this paper; Figure 5 The output power is the result of using the multi-stage parallel zero-sequence current control method disclosed herein. Figure 6 This is a schematic diagram of a structure of an embodiment of the multi-machine parallel zero-sequence current control device according to the present disclosure; Figure 7 This is a schematic diagram of another embodiment of the multi-machine parallel zero-sequence current control device according to the present disclosure; Figure 8 This is a block diagram of an electronic device used to implement the multi-machine parallel zero-sequence current control method of the embodiments of this disclosure. Detailed Implementation

[0015] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0016] The technical solutions of this disclosure are illustrated below through specific embodiments. It should be understood that one or more steps mentioned in this disclosure do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not to limit the order of each method or to limit the scope of implementation of this disclosure. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of implementation of this disclosure.

[0017] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0018] In traditional technologies, the control of the zero-sequence current loop generally uses a proportional-integral regulator and sets a fixed limit value to prevent controller saturation. This method has the following drawbacks: the limit is too strict under light load, wasting voltage equalization capacity; the limit is too loose under heavy load, which can easily lead to modulation oversaturation and current distortion; the limit of each converter module is set independently, and there is no information exchange between them; the midpoint potential coupling is not considered, and the midpoint potential deviation will affect the effective range of the zero-sequence circulating current control.

[0019] To address the technical problems of poor adaptability to operating conditions, mutual interference among multiple machines, and midpoint potential coupling caused by fixed amplitude limiting in existing technologies, this disclosure provides a method for controlling zero-sequence current in parallel operation of multiple machines. Figure 1 The flowchart 100 illustrates an embodiment of the multi-machine parallel zero-sequence current control method according to the present disclosure. The multi-machine parallel zero-sequence current control method is applied to any converter module in a system of multiple energy storage converters connected in parallel. The method specifically includes the following steps: Step 101: Obtain the total number of parallel modules in the parallel system of multiple energy storage converters, the local modulation status information, and the positive and negative bus voltages on the DC side of the local converter.

[0020] In this embodiment, the local modulation status information includes real-time operating data that characterizes the current voltage utilization of the inverter, such as the d-axis modulation degree, q-axis modulation degree, zero-sequence modulation degree, and harmonic modulation degree currently output by the local unit.

[0021] In this embodiment, each converter module forms a parallel system of multiple energy storage converters via a CAN bus or RS485 communication network. Each converter module includes an energy storage converter and a controller. The controller periodically broadcasts query commands. Upon receiving an address matching request, each slave node encapsulates its own (the current converter module) operating status into a standard data frame and transmits it back. Specifically, as follows... Figure 2 As shown, a parallel system of multiple energy storage converters has three parallel modules, each of which is a converter module. When any converter module is used as the local unit, the local controller can collect the total number of parallel modules, the local unit's modulation status information, and the local unit's DC-side positive and negative bus voltages. Specifically, in a specific register address of the communication data frame, the local unit reports the total number of parallel modules (representing the number of converter modules currently operating in parallel), the local unit's modulation status information, and the local unit's DC-side positive and negative bus voltages. The controller (such as...) Figure 2 (As shown) After parsing the messages of each node, the module current sharing control and fault diagnosis are realized by comparing the status words. At the same time, the bus voltage balancing and protective shutdown strategies are executed based on the DC side voltage data to ensure the coordinated and stable operation of the multi-machine parallel system.

[0022] Optionally, step 101 above includes: injecting a small characteristic harmonic current of a specific frequency into the point of common coupling (PCC), detecting the PCC voltage response at that frequency band, and calculating the current equivalent grid impedance. Since the more parallel modules connected, the smaller the system's equivalent grid impedance, the controller can implicitly estimate the total number of parallel modules currently in operation by looking up a table or using a preset impedance-number inversion algorithm. The controller can directly obtain its own modulation state information at the underlying hardware time domain. Specifically, the controller directly reads the maximum and minimum values ​​of the actual duty cycle of the three-phase bridge arms during the current PWM switching cycle.

[0023] Step 102: Calculate the derating factor for the number of parallel modules based on the total number of parallel modules.

[0024] In this embodiment, the derating factor for the number of parallel converters is a dynamically generated attenuation multiplier based on the parallel converter modules in a multi-converter parallel system. As the number of parallel converters increases, the risk of zero-sequence circulating current and high-frequency resonance in the multi-converter system amplifies nonlinearly. This derating factor is used to actively and adaptively tighten (reduce) the allowable limit of zero-sequence current when the number of parallel converters is large, sacrificing some of the individual converter's regulation capability in exchange for the global stability of the entire multi-converter parallel system.

[0025] In this embodiment, the derating factor for the number of parallel modules can be obtained by offline table lookup. Specifically, a derating mapping table is pre-stored in the controller. This derating mapping table is used to represent the correspondence between the total number of parallel modules and the derating factor for the number of parallel modules. This implementation method can avoid the execution cycle delay caused by calculation while sacrificing minimal control accuracy.

[0026] Optionally, the derating factor for the number of parallel units can also be calculated using an exponential decay function. Specifically, step 102 above further includes: the derating factor can be calculated using an exponential decay function, i.e. (Where k is the preset decay time constant). Compared to the inverse proportional function, the exponential model has a smoother derating as the initial number of parallel units increases, and can ensure that the derating coefficient converges to a non-zero safety bottom line when the number of units is extremely large, preventing the zero-sequence control dead zone.

[0027] Step 103: Based on the local modulation state information, calculate the available modulation margin in real time and map the available modulation margin to the zero-sequence current limiting coefficient.

[0028] In this embodiment, the available modulation margin refers to the difference between the maximum allowable modulation index and the current actual total modulation index of the inverter under the current operating conditions; the zero-sequence current limiting coefficient is a scaling factor between 0 and 1 obtained by mapping the available modulation margin through a preset function. The inverter's DC voltage utilization rate has an upper limit. If a large regulation limit is still applied to the zero-sequence circulating current under heavy load conditions (when active / reactive current already occupies a large portion of the modulation amplitude), it will lead to PWM modulation oversaturation and cause severe current distortion. This zero-sequence current limiting coefficient implements an adaptive anti-saturation mechanism that allows for more regulation under light loads (loose limiting) and less regulation under heavy loads (strict limiting).

[0029] In this embodiment, step 103 includes: mapping the reference voltage vector and DC bus voltage state of the local unit in the local unit modulation state information to a two-phase stationary coordinate system to obtain the current reference voltage vector, and calculating its amplitude and the current vector phase angle; determining the hexagonal boundary of the spatial vector diagram based on the current total DC side voltage of the local unit. Based on the sector where the current vector phase angle is located (a total of 6 sectors, each sector is 60 degrees), the maximum dynamic voltage vector amplitude that does not overmodulate under this specific phase angle is calculated using equation (1).

[0030] (1) In equation (1), The local electrical angle of the current reference voltage vector within the current sector (range 0°~60°). This represents the dynamic maximum voltage vector magnitude.

[0031] The available modulation margin between the current reference voltage vector endpoint and the modulation boundary is calculated in real time using equation (2). : (2) The calculated available modulation margin and its rate of change (differential term) are used as the two inputs to the fuzzy controller. Through a preset fuzzy rule base (e.g., "if the margin is small and still decreasing rapidly, then the limiting coefficient should be reduced significantly"), the zero-sequence current limiting coefficient is output after defuzzification. This method can effectively address the dynamic overshoot problem under sudden load changes.

[0032] Alternatively, after calculating the available modulation margin, it can also be mapped to a limiting coefficient using a nonlinear activation function (such as a Sigmoid variant or a piecewise function).

[0033] Step 104: Calculate the neutral point potential offset of the machine based on the positive and negative bus voltages on the DC side of the machine, and calculate the neutral point potential correction coefficient based on the neutral point potential offset of the machine.

[0034] In this embodiment, the local midpoint potential offset is the absolute value of the difference between the DC-side positive half-bus voltage and the negative half-bus voltage in a three-level topology; the midpoint potential correction coefficient is a penalty factor calculated based on the local midpoint potential offset. In a three-level converter, the injection of zero-sequence circulating current directly affects the midpoint potential. When a severe midpoint potential offset is detected, the midpoint potential correction coefficient is reduced, thereby actively limiting the adjustment range of the zero-sequence current and preventing strong coupling oscillation between zero-sequence current control and voltage equalization control.

[0035] In this embodiment, to avoid system chattering caused by frequent changes in the limiting value during small steady-state fluctuations, the calculation of the midpoint potential correction coefficient can incorporate a quadratic penalty function with a dead zone. Specifically, a safe voltage dead zone (e.g., 5V) is set. When the midpoint potential offset is within the dead zone, the midpoint potential correction coefficient is determined to be always 1 (i.e., no intervention). When the offset exceeds the dead zone, the correction coefficient is rapidly reduced proportionally to the square of the excess. This nonlinear design achieves excellent control performance of "insensitive to small deviations and strongly suppressing large deviations."

[0036] Step 105: Based on the derating factor of the number of parallel units, the zero-sequence current limiting factor, and the midpoint potential correction factor, dynamically adjust the preset reference limiting value, obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

[0037] In this embodiment, step 105 first obtains the local zero-sequence current dynamic limit value, and then sends the local zero-sequence current dynamic limit value to the zero-sequence current controller. Step 105 specifically includes: multiplying the baseline limit value by the parallel unit derating factor, the zero-sequence current limit factor, and the midpoint potential correction factor to obtain three independent candidate limit values; then, taking the minimum value among these three candidate limit values ​​as the final local zero-sequence current dynamic limit value. This method avoids the problem of multiple coefficients being multiplied together when they are all around 0.8, resulting in an excessively small final limit value, thus ensuring that the system's regulation capability is maximized under multiple constraints.

[0038] Optionally, step 105 may include: weighting and summing the derating factor for the number of parallel units, the zero-sequence current limiting factor, and the midpoint potential correction factor, where the sum of the weighting factors W1, W2, and W3 is 1, and is dynamically configured by the upper-level power grid dispatch instructions. For example, when the power grid requires strong reactive power support, the weight W2 of the zero-sequence current limiting factor is increased; in a weak power grid with high risk of multi-machine parallel resonance, the weight W1 of the derating factor for the number of parallel units is increased, which gives the system a very strong multi-scenario adaptive capability.

[0039] The multi-unit parallel zero-sequence current control method provided in the embodiments of this disclosure firstly acquires the total number of parallel modules in the parallel system of multiple energy storage converters, the local modulation status information, and the positive and negative DC bus voltages of the local converter; secondly, based on the total number of parallel modules, a derating factor for the number of parallel units is calculated; thirdly, based on the local modulation status information, the available modulation margin is calculated in real time, and the available modulation margin is mapped to a zero-sequence current limiting factor; then, based on the positive and negative DC bus voltages of the local converter, the local neutral point potential offset is calculated, and a neutral point potential correction factor is calculated based on the local neutral point potential offset; finally, based on the parallel unit derating factor, the zero-sequence current limiting factor, and the neutral point potential correction factor, a preset reference limiting value is dynamically adjusted to obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller. Therefore, by reducing the total number of parallel modules, the overall loop current loss control is prevented due to the superposition of multiple machines; the midpoint potential offset is included in the limiting calculation to achieve a dual-objective synergistic mechanism of midpoint balance and zero-sequence circulating current suppression; the fundamental and harmonic modulation in real time is calculated, the remaining available modulation margin is extracted, and it is mapped to the zero-sequence current limiting coefficient. By dynamically adjusting the reference limiting value through the zero-sequence current limiting coefficient and the midpoint potential correction coefficient, the limiting value can be automatically reduced when the margin is small under heavy load, avoiding over-modulation; when the margin is large under light load, the limiting is relaxed, making full use of the voltage equalization capability of the converter.

[0040] In one optional implementation of this disclosure, the above calculation of the parallel unit derating factor based on the total number of parallel modules includes: subtracting one from the total number of parallel modules to obtain a first intermediate value; adding one to the product of the parallel attenuation factor and the first intermediate value to obtain a second intermediate value; and dividing one by the second intermediate value to obtain the parallel unit derating factor.

[0041] Specifically, see equation (3) for the calculation formula of the derating factor for the number of parallel units: α(N)= (3) In equation (3), α(N) represents the derating factor for the number of parallel units, and λ is the parallel attenuation factor, with a value range of 0.03 to 0.1. N is the total number of parallel modules. When N = 1, α(N) = 1; when N = 10, α(N) = 0.5 to 0.7.

[0042] In multi-machine parallel systems, inconsistent parameters among modules, such as saturation voltage drop of switching transistors, on-resistance, and asymmetrical circuit layout, can lead to uneven current distribution, which is not a simple summation. When the total number of parallel modules N changes, the value of λ should be determined based on the current value of the module with the highest current and the junction temperature of the module with the highest temperature. In practical applications, the derating factor range for the number of parallel units is determined based on batch testing of the modules.

[0043] In one optional implementation of this disclosure, the above-mentioned calculation of the available modulation margin in real time based on the local modulation state information and mapping the available modulation margin to the zero-sequence current limiting coefficient includes: calculating the current overall modulation degree based on the local modulation state information; subtracting the current overall modulation degree from the maximum allowable modulation degree to obtain the available modulation margin; and mapping the available modulation margin to the zero-sequence current limiting coefficient.

[0044] In this optional implementation method, the current general dispatch system is estimated in real time using equation (4). : (4) In equation (4) , For fundamental frequency modulation, Harmonic modulation; The available modulation margin is calculated using equation (5): (5) In equation (5), The maximum permissible modulation index ranges from 0.9 to 1.0. The modulation margin is mapped to the zero-sequence current limiting coefficient β using equation (6): β = (6) In equation (6), the value of β ranges from 0.1 to 1.0.

[0045] Optionally, the above calculation of the current overall modulation scheme based on the local modulation state information includes: extracting the fundamental modulation scheme component and harmonic modulation scheme component of the local instrument, wherein the fundamental modulation scheme component includes d-axis modulation scheme, q-axis modulation scheme and zero-sequence modulation scheme; obtaining the comprehensive fundamental modulation scheme based on the square root of the sum of the squares of the d-axis modulation scheme, q-axis modulation scheme and zero-sequence modulation scheme; and adding the comprehensive fundamental modulation scheme to the harmonic modulation scheme component to obtain the current overall modulation scheme.

[0046] Optionally, after subtracting the current total modulation index from the maximum allowable modulation index to obtain the available modulation margin, the method further includes: determining whether the available modulation margin is greater than zero; if so, using a linear or nonlinear positive correlation mapping function to map the available modulation margin to a zero-sequence current limiting coefficient with a value between 0.1 and 1.0; if not, determining that the system is in an overmodulation risk state and forcibly setting the zero-sequence current limiting coefficient to a preset lower limit safety value.

[0047] In one optional implementation of this disclosure, the above-mentioned calculation of the neutral point potential offset based on the positive and negative DC bus voltages of the machine, and the calculation of the neutral point potential correction coefficient based on the neutral point potential offset, includes: taking the absolute value of the difference between the positive and negative DC bus voltages of the machine as the neutral point potential offset; subtracting the neutral point potential offset from the rated DC voltage, multiplying by the rated correction coefficient, to obtain the neutral point potential correction coefficient.

[0048] In this optional implementation, Vdc+ and Vdc- represent the positive and negative bus voltages on the DC side of the machine, and ΔVdc represents the neutral point potential offset of the machine. The neutral point potential offset ΔVdc = |Vdc+ - Vdc-| is detected, and the neutral point potential correction coefficient is calculated using equation (7). : = 1 - (7) In equation (7), This is a correction factor, ranging from 0.2 to 0.5, when the midpoint potential is balanced. ≈1; when the midpoint potential shift is severe, Reduce the amplitude limit value to prevent excessive adjustment of the equalizing ring from causing coupled oscillation.

[0049] Optionally, the value range of the above-mentioned rated correction coefficient is 0.2 to 0.5; after subtracting the midpoint potential offset of the machine from one, dividing by the rated DC voltage, and multiplying by the rated correction coefficient to obtain the midpoint potential correction coefficient, the above-mentioned multi-machine parallel zero-sequence current control method further includes: when the midpoint potential offset of the machine approaches zero, the midpoint potential correction coefficient approaches one, maintaining the control range of the zero-sequence current; when the midpoint potential offset of the machine increases, causing the midpoint potential correction coefficient to decrease, the dynamic limit value of the zero-sequence current of the machine is actively reduced through the midpoint potential correction coefficient to suppress the coupling oscillation between the equalizing ring and the zero-sequence ring.

[0050] In one optional implementation of this disclosure, the above-mentioned dynamic adjustment of the preset reference limit value based on the parallel number of units derating factor, zero-sequence current limiting factor, and midpoint potential correction factor to obtain and send the local zero-sequence current dynamic limit value to the zero-sequence current controller includes: multiplying the preset reference limit value by the parallel number of units derating factor, then by the zero-sequence current limiting factor, and then by the midpoint potential correction factor to obtain the local zero-sequence current dynamic limit value; and sending the local zero-sequence current dynamic limit value to the zero-sequence current controller.

[0051] In this optional implementation, equation (8) is used to calculate the dynamic limit value of the zero-sequence current of the machine. : α(N) β( ) (ΔVdc)(8) In equation (8), This is the baseline limit value, which is determined based on the converter module capacity.

[0052] The limiting dynamic adjustment of zero-sequence current is related to three factors: parallel attenuation factor, modulation margin mapping coefficient, and midpoint potential offset correction coefficient. Equation (3) mainly reflects these three factors.

[0053] To achieve multi-machine coordinated commissioning of a multi-machine parallel system of energy storage converters, this disclosure provides another method for zero-sequence current control in a multi-machine parallel system. Figure 3 The flowchart 300 illustrates another embodiment of the multi-machine parallel zero-sequence current control method according to the present disclosure. This method is applied to any converter module in a system of multiple energy storage converters connected in parallel. The multi-machine parallel zero-sequence current control method includes the following steps: Step 301: Obtain the local zero-sequence current command, the zero-sequence voltage at the common coupling point, and the local current zero-sequence current limit value.

[0054] In this embodiment, the generation of zero-sequence current command, the acquisition of zero-sequence voltage at the point of common coupling (PCC), and the dynamic management of zero-sequence current limit value are realized through the signal acquisition and processing unit of any converter module deployed in a parallel system of multiple energy storage converters.

[0055] In this embodiment, firstly, a voltage sensor connected to the common coupling point is used to collect three-phase voltage signals in real time. After analog-to-digital conversion, the signals are transformed to a rotating coordinate system through Clark and Park transformations, and the zero-sequence voltage component U0 is extracted as a voltage feedforward signal. Simultaneously, the control system generates a zero-sequence current command value based on the upper-level power dispatch command or voltage imbalance compensation requirements. This zero-sequence current command value is compared with the maximum allowed zero-sequence current limit value i0max of the inverter. After being processed by the limiting circuit, the actual zero-sequence current reference value i0ref is obtained—where the limit value i0max is dynamically determined by the rated capacity of the inverter power devices, heat dissipation conditions, and real-time temperature monitoring data. Finally, the limited zero-sequence current reference value i0ref and the zero-sequence voltage U0 of the common coupling point are input to the zero-sequence current control loop. A modulation wave signal is generated by a proportional-integral (PI) regulator and superimposed on the three-phase PWM modulation command to achieve closed-loop control of the inverter's zero-sequence current. This enables the grid zero-sequence voltage imbalance compensation or specific zero-sequence power injection function to be completed while meeting equipment safety constraints.

[0056] Step 302: Determine whether the absolute value of the zero-sequence voltage is greater than the preset interference threshold.

[0057] In this embodiment, the preset interference threshold is not a fixed constant, but an adaptive threshold calculated in real time based on the background harmonics of the power grid. Specifically, the controller collects the total harmonic distortion (THD) of the power grid voltage in real time. When the THD indicates that the background noise of the power grid is increasing, the interference threshold is dynamically raised to avoid the multi-machine cooperative mechanism being falsely triggered by the original noise of the power grid.

[0058] Step 303: When the absolute value of the zero-sequence voltage is greater than the preset interference threshold, it is determined that there is mutual interference between the multi-machine voltage equalization ring. The zero-sequence current command of the machine is filtered by low-pass filter and then superimposed with the zero-sequence voltage as a positive feedforward to form the final zero-sequence current command.

[0059] In this embodiment, mutual interference in the multi-machine voltage equalization ring refers to a system state in which the absolute value of the zero-sequence voltage at the common coupling point exceeds a preset interference threshold. This indicates that the local control strategies of multiple converters are in conflict (e.g., commands cancel each other out or superimpose), resulting in the accumulation of zero-sequence energy at a specific frequency (e.g., 5kHz) in the system.

[0060] In this embodiment, a moving average filter synchronized with the inverter's switching frequency can be used to low-pass filter the local zero-sequence current command. Compared to traditional infinite impulse response low-pass filters, the moving average filter can achieve absolute zeroing (complete filtering) of specific high-frequency switching ripple within a complete switching cycle, eliminating high-frequency interference without introducing significant phase lag. Subsequently, this phase-shift-free low-pass command is directly superimposed with the extracted zero-sequence voltage, significantly improving the dynamic response speed of the feedforward compensation.

[0061] In this embodiment, when the absolute value of the zero-sequence voltage is greater than the preset interference threshold, anti-integral saturation is performed: the integral accumulation of the PI controller is paused, and the integral term remains unchanged; Step 304: Input the final zero-sequence current command to the zero-sequence current controller, and send the output of the zero-sequence current controller to the limiter.

[0062] In this embodiment, the limiting limit of the limiter is the current zero-sequence current limiting value.

[0063] In this embodiment, to avoid output waveform truncation and high-order harmonic injection caused by sudden command changes in traditional hard clipping, a nonlinear soft limiter based on the sigmoid function or hyperbolic tangent function (Tanh) is used. Specifically, as the output of the zero-sequence current controller gradually approaches the current zero-sequence current limit value, the soft limiter smoothly and asymptotically compresses the output to the limiting boundary through nonlinear gain. This alternative implementation ensures that the system does not experience overcurrent while maintaining the continuity of the derivatives of the control variables, greatly improving the grid-connected power quality of the converter under critical disturbance conditions.

[0064] Step 305: When the output of the zero-sequence current controller reaches the limiting limit, stop the integral accumulation of the zero-sequence current controller, and obtain the filtering error by passing the limiting error through a first-order low-pass filter. Feed the filtering error back to the controller input for smoothing.

[0065] In this embodiment, the limiting error is smoothed using a first-order low-pass filter, specifically a variable-parameter exponential moving average (EMA) digital filter. Unlike a fixed-parameter RC equivalent filter, the smoothing factor of this EMA filter is dynamically adjusted according to the derivative of the limiting error: when the limiting error changes drastically, the smoothing factor is decreased to enhance the filtering effect; when the error changes gradually, the smoothing factor is increased to reduce delay. Simultaneously, the smoothing is fed back to the controller input. Instead of simply subtracting the error from the given command, the filtered error is multiplied by a dynamic proportional coefficient and added as a penalty term to the proportional adjustment channel of the zero-sequence current controller. This stops the integral accumulation while actively suppressing overshoot by utilizing the fast response characteristics of the proportional channel.

[0066] Optionally, step 305 further includes: obtaining the original output value of the zero-sequence current controller and calculating the sign function value of the original output value; multiplying the sign function value by the limiting limit to obtain the actual limiting output value; subtracting the actual limiting output value from the original output value to obtain the limiting error; inputting the limiting error to a first-order low-pass filter to obtain the filtering error; and when the absolute value of the original output value begins to be less than the limiting limit, smoothly restoring the integral accumulation operation of the zero-sequence current controller according to the decay trend of the filtering error to avoid step shocks during the de-limiting process.

[0067] Step 306: When the output of the zero-sequence current controller deviates from the limit, the integral accumulation of the zero-sequence current controller is restored according to the filtering error to obtain the zero-sequence control quantity.

[0068] In this embodiment, to completely eliminate system chattering that may be caused by the moment of delimiting, a step-by-step recovery strategy based on grid phase zero-crossing synchronization is adopted, according to the integral accumulation of filter error recovery. Specifically, when the output of the zero-sequence current controller is detected to have deviated from the limiting limit, the controller does not immediately fully recover the integral action, but waits for the phase-locked loop to detect the next natural zero-crossing of the common coupling point voltage. At the zero-crossing moment, an initial integral value is calculated based on the current amplitude of the filter error and assigned to the integrator. The integral gain is then gradually restored to the rated value in the subsequent operating cycles in a discrete step-by-step manner. This scheme utilizes the physical characteristic of the AC system having the minimum energy at the zero-crossing point, achieving truly "disturbance-free" delimiting.

[0069] In this embodiment, the limited entry and exit process is smooth and gradually recovers, avoiding step impact.

[0070] Step 307: Based on the zero-sequence control quantity and the given voltage signal output by the current loop, obtain and send a three-phase modulated wave to the power device.

[0071] In this embodiment, the three-phase modulated wave is not obtained by directly superimposing zero-sequence voltage components onto the three-phase sinusoidal reference voltage. Instead, it is achieved by redistributing the zero-vector duration at the underlying Space Vector Pulse Width Modulation (SVPWM) layer. Specifically, after receiving the zero-sequence control quantity, the controller keeps the duration of the effective voltage vectors (V1-V6) unchanged to maintain active and reactive power output. Instead, it breaks the principle of equal distribution of the durations of the two zero vectors (V0 and V7) in traditional SVPWM, and asymmetrically extends the duration of V0 or V7 according to the polarity and magnitude of the zero-sequence control quantity. This alternative scheme based on underlying vector duty cycle scheduling does not require changing the waveform of the given voltage signal in the current loop, avoids the reduction of the linear modulation region, and has higher DC voltage utilization under low-voltage ride-through or heavy-load conditions.

[0072] The multi-machine parallel zero-sequence current control method provided in this disclosure first obtains the zero-sequence current command of the local machine, the zero-sequence voltage at the common coupling point, and the current zero-sequence current limit value of the local machine; secondly, it determines whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold; if so, it determines that there is mutual interference between the multi-machine voltage equalization rings, and after low-pass filtering, the local zero-sequence current command is superimposed with the zero-sequence voltage as a positive feedforward to form the final zero-sequence current command; thirdly, the final zero-sequence current command is input to the zero-sequence current controller, and the output of the zero-sequence current controller is sent to the limit value. The amplitude limiter is set to the current zero-sequence current limit value. Then, when the output of the zero-sequence current controller reaches the limit, the integral accumulation of the zero-sequence current controller stops, and the limiting error is fed back to the controller input as a filtering error through a first-order low-pass filter for smoothing. Next, when the output of the zero-sequence current controller deviates from the limit, the integral accumulation of the zero-sequence current controller resumes based on the filtering error to obtain the zero-sequence control quantity. Finally, based on the zero-sequence control quantity and the given voltage signal output by the current loop, a three-phase modulated wave is obtained and sent to the power device. Thus, through the derating factor of the number of parallel units and the zero-sequence voltage coordination mechanism at the common coupling point, the mutual interference of zero-sequence circulating currents in multi-unit parallel operation is effectively suppressed, and specific frequency oscillations are eliminated.

[0073] In some embodiments of this disclosure, when it is determined that there is mutual interference between the multi-machine equalization rings, the above-mentioned multi-machine parallel zero-sequence current control method further includes: obtaining a pre-calculated derating coefficient for the number of parallel units; multiplying a preset coordination attenuation factor by the derating coefficient for the number of parallel units to obtain an updated derating coefficient, so as to control the current zero-sequence current limit value through the updated derating coefficient.

[0074] In this optional implementation, all parallel modules synchronously reduce the derating factor α(N) of the number of parallel units, and the updated derating factor... (N)=α(N) µ, where µ is the coordination attenuation factor, can be 0.6 to 0.8. The coordination attenuation factor is adjusted according to the threshold to indicate that there is mutual interference. The coordination factor is reduced to 60%-80% as an empirical value.

[0075] Optionally, the above-mentioned multi-machine parallel zero-sequence current control method further includes: when it is determined that there is mutual interference in the multi-machine voltage equalization ring, a synchronization coordination command is sent to all converter modules through a high-speed communication network; after receiving the synchronization coordination command, each converter module synchronously multiplies a preset coordination attenuation factor by a pre-calculated derating factor for the number of parallel units to obtain an updated derating factor; wherein, the value range of the coordination attenuation factor is 0.6 to 0.8; and the updated derating factor is used to dynamically compress the current zero-sequence current limit value.

[0076] Further reference Figure 6 As an implementation of the methods shown in the above figures, this disclosure provides an embodiment of a multi-machine parallel zero-sequence current control device, which is similar to... Figure 1 Corresponding to the method embodiments shown, the device can be specifically applied to terminal devices.

[0077] like Figure 6 As shown, the multi-unit parallel zero-sequence current control device 600 provided in this embodiment includes: a parameter acquisition unit 601, a derating calculation unit 602, a coefficient calculation unit 603, an offset calculation unit 604, and a limiting calculation unit 605. The parameter acquisition unit 601 can be configured to acquire the total number of parallel modules in the multi-unit parallel energy storage converter system, the local modulation status information, and the local DC-side positive and negative bus voltages. The derating calculation unit 602 can be configured to calculate the derating coefficient based on the total number of parallel modules. The coefficient calculation unit 603 can be configured to calculate the available modulation margin in real time based on the local modulation status information and map the available modulation margin to a zero-sequence current limiting coefficient. The offset calculation unit 604 can be configured to calculate the local midpoint potential offset based on the local DC-side positive and negative bus voltages and calculate the midpoint potential correction coefficient based on the local midpoint potential offset. The aforementioned limiting calculation unit 605 can be configured to dynamically adjust the preset reference limiting value based on the parallel unit derating factor, the zero-sequence current limiting factor, and the midpoint potential correction factor, and obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

[0078] In this embodiment, the specific processing of the parameter acquisition unit 601, derating calculation unit 602, coefficient calculation unit 603, offset calculation unit 604, and limiting calculation unit 605 in the multi-machine parallel zero-sequence current control device 600, and the resulting technical effects, can be found in the following references: Figure 1The relevant descriptions of steps 101, 102, 103, 104, and 105 in the corresponding embodiments will not be repeated here.

[0079] In some embodiments of this disclosure, the derating calculation unit 602 is configured to: subtract one from the total number of parallel modules to obtain a first intermediate value; add one to the product of the parallel attenuation factor and the first intermediate value to obtain a second intermediate value; and divide one by the second intermediate value to obtain the derating coefficient for the number of parallel modules.

[0080] In some embodiments of this disclosure, the coefficient calculation unit 603 is configured to: calculate the current overall modulation degree based on the local modulation state information; subtract the current overall modulation degree from the maximum allowable modulation degree to obtain the available modulation margin; and map the available modulation margin to the zero-sequence current limiting coefficient.

[0081] In some embodiments of this disclosure, the offset calculation unit 604 is configured to: take the absolute value of the difference between the positive and negative bus voltages on the DC side of the machine as the machine's midpoint potential offset; subtract the machine's midpoint potential offset from the rated DC voltage, multiply by the rated correction factor, and obtain the midpoint potential correction factor.

[0082] In some embodiments of this disclosure, the above-mentioned limiting calculation unit 605 is configured to: multiply a preset reference limiting value by a derating factor for the number of parallel units, then by a zero-sequence current limiting factor, and then by a midpoint potential correction factor to obtain a local zero-sequence current dynamic limiting value; and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

[0083] The multi-unit parallel zero-sequence current control device provided in this embodiment firstly acquires the total number of parallel modules in the parallel system of multiple energy storage converters, the local modulation status information, and the positive and negative DC bus voltages of the local converter. Secondly, the derating calculation unit 602 calculates the derating coefficient based on the total number of parallel modules. Thirdly, the coefficient calculation unit 603 calculates the available modulation margin in real time based on the local modulation status information and maps the available modulation margin to the zero-sequence current limiting coefficient. Then, the offset calculation unit 604 calculates the local midpoint potential offset based on the local DC bus voltages and calculates the midpoint potential correction coefficient based on the local midpoint potential offset. Finally, the limiting calculation unit 605 dynamically adjusts the preset reference limiting value based on the parallel derating coefficient, the zero-sequence current limiting coefficient, and the midpoint potential correction coefficient, and obtains and sends the local zero-sequence current dynamic limiting value to the zero-sequence current controller. Therefore, by reducing the total number of parallel modules, the overall loop current loss control is prevented due to the superposition of multiple machines; the midpoint potential offset is included in the limiting calculation to achieve a dual-objective synergistic mechanism of midpoint balance and zero-sequence circulating current suppression; the fundamental and harmonic modulation in real time is calculated, the remaining available modulation margin is extracted, and it is mapped to the zero-sequence current limiting coefficient. By dynamically adjusting the reference limiting value through the zero-sequence current limiting coefficient and the midpoint potential correction coefficient, the limiting value can be automatically reduced when the margin is small under heavy load, avoiding over-modulation; when the margin is large under light load, the limiting is relaxed, making full use of the voltage equalization capability of the converter.

[0084] Further reference Figure 7 As an implementation of the methods shown in the above figures, this disclosure also provides another embodiment of a multi-machine parallel zero-sequence current control device, which is similar to... Figure 3 Corresponding to the method embodiment shown, the device can be specifically applied to any converter module in a system of multiple energy storage converters connected in parallel.

[0085] like Figure 7As shown, the multi-machine parallel zero-sequence current control device 700 provided in this embodiment includes: a value acquisition unit 701, a judgment unit 702, an instruction generation unit 703, a limiting processing unit 704, a smoothing processing unit 705, a recovery unit 706, and a sending unit 707. The value acquisition unit 701 can be configured to acquire the local zero-sequence current instruction, the zero-sequence voltage at the common coupling point, and the current zero-sequence current limiting value of the local machine. The judgment unit 702 can be configured to determine whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold. The instruction generation unit 703, when the absolute value of the zero-sequence voltage is greater than the interference threshold, determines that there is mutual interference between the multi-machine voltage equalization rings, and after low-pass filtering, superimposes the local zero-sequence current instruction with the zero-sequence voltage as a positive feedforward to form the final zero-sequence current instruction. The limiting processing unit 704 can be configured to input the final zero-sequence current instruction to the zero-sequence current controller and send the output of the zero-sequence current controller to the limiting unit. The limiter's limit is the current zero-sequence current limit value; the smoothing processing unit 705 can be configured to stop the integral accumulation of the zero-sequence current controller when the output of the zero-sequence current controller reaches the limit, and obtain the filtering error by passing the limit error through a first-order low-pass filter, and feed the filtering error back to the controller input for smoothing processing; the recovery unit 706 can be configured to restore the integral accumulation of the zero-sequence current controller according to the filtering error when the output of the zero-sequence current controller deviates from the limit, and obtain the zero-sequence control quantity; the transmitting unit 707 can be configured to obtain and transmit a three-phase modulated wave to the power device based on the zero-sequence control quantity and the given voltage signal output by the current loop.

[0086] In this embodiment, the specific processing of the multi-machine parallel zero-sequence current control device 700, including the value acquisition unit 701, the judgment unit 702, the instruction generation unit 703, the limiting processing unit 704, the smoothing processing unit 705, the recovery unit 706, and the sending unit 707, and their resulting technical effects, can be found in the following references: Figure 3 The relevant descriptions of steps 301, 302, 303, 304, 305, 306, and 307 in the corresponding embodiments will not be repeated here.

[0087] In one embodiment of this disclosure, the multi-machine parallel zero-sequence current control device 700 further includes an update unit (not shown in the figure), which is configured to: obtain a pre-calculated derating factor for the number of parallel units; multiply the derating factor for the number of parallel units by a preset coordination attenuation factor to obtain an updated derating factor, so as to control the current zero-sequence current limit value through the updated derating factor.

[0088] The multi-machine parallel zero-sequence current control device provided in this embodiment firstly acquires the zero-sequence current command of the local machine, the zero-sequence voltage of the common coupling point, and the current zero-sequence current limit value of the local machine; secondly, the judgment unit 702 judges whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold; the command generation unit 703 determines that there is mutual interference between the multi-machine voltage equalization ring, and after low-pass filtering, the local zero-sequence current command is superimposed with the zero-sequence voltage as a positive feedforward to form the final zero-sequence current command; thirdly, the limit processing unit 704 inputs the final zero-sequence current command to the zero-sequence current controller, and converts the zero-sequence current controller's input... The input is a limiter, whose limit is the current zero-sequence current limit value. Then, when the output of the zero-sequence current controller reaches the limit, the smoothing unit 705 stops the integral accumulation of the zero-sequence current controller and feeds back the filtering error obtained by passing the limit error through a first-order low-pass filter to the controller input for smoothing. Next, when the output of the zero-sequence current controller deviates from the limit, the recovery unit 706 restores the integral accumulation of the zero-sequence current controller based on the filtering error to obtain the zero-sequence control quantity. Finally, the sending unit 707 obtains and sends a three-phase modulated wave based on the zero-sequence control quantity and the given voltage signal output by the current loop. Thus, through the derating factor of the number of parallel units and the zero-sequence voltage coordination mechanism at the common coupling point, the mutual interference of zero-sequence circulating currents when multiple units are connected in parallel is effectively suppressed, and specific frequency oscillations are eliminated.

[0089] The collection, storage, use, processing, transmission, provision, and disclosure of user personal information involved in the technical solution disclosed herein comply with the provisions of relevant laws and regulations and do not violate public order and good morals.

[0090] According to embodiments of this disclosure, this disclosure also provides an electronic device, a readable storage medium, and a computer program product.

[0091] Figure 8 A schematic block diagram of an example electronic device 800 that can be used to implement embodiments of the present disclosure is shown. The electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device may also represent various forms of mobile devices, such as personal digital processors, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their patterns are merely examples and are not intended to limit the implementation of the present disclosure described and / or claimed herein.

[0092] like Figure 8As shown, the electronic device 800 includes a computing unit 801, which can perform various appropriate actions and processes according to a computer program stored in a read-only memory (ROM) 802 or a computer program loaded from a storage unit 808 into a random access memory (RAM) 803. The RAM 803 may also store various programs and data required for the operation of the electronic device 800. The computing unit 801, ROM 802, and RAM 803 are interconnected via a bus 804. An input / output (I / O) interface 805 is also connected to the bus 804.

[0093] Multiple components in electronic device 800 are connected to I / O interface 805, including: input unit 806, such as keyboard, mouse, etc.; output unit 807, such as various types of displays, speakers, etc.; storage unit 808, such as disk, optical disk, etc.; and communication unit 809, such as network card, modem, wireless transceiver, etc. Communication unit 809 allows electronic device 800 to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0094] The computing unit 801 can be a variety of general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the computing unit 801 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various special-purpose artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, a digital signal processor (DSP), and any suitable processor, controller, microcontroller, etc. The computing unit 801 performs the various methods and processes described above, such as the multi-machine parallel zero-sequence current control method. For example, in some embodiments, the multi-machine parallel zero-sequence current control method can be implemented as a computer software program, which is tangibly contained in a machine-readable medium, such as storage unit 808. In some embodiments, part or all of the computer program can be loaded and / or installed on the electronic device 800 via ROM 802 and / or communication unit 809. When the computer program is loaded into RAM 803 and executed by the computing unit 801, one or more steps of the multi-machine parallel zero-sequence current control method described above can be performed. Alternatively, in other embodiments, the computing unit 801 may be configured to perform a multi-machine parallel zero-sequence current control method by any other suitable means (e.g., by means of firmware).

[0095] Various embodiments of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SoCs), payload-programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include implementations in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a dedicated or general-purpose programmable processor, capable of receiving data and instructions from a storage system, at least one input device, and at least one output device, and transmitting data and instructions to the storage system, the at least one input device, and the at least one output device.

[0096] The program code used to implement the methods of this disclosure may be written in any combination of one or more programming languages. This program code may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable multi-machine parallel zero-sequence current control device, such that when executed by the processor or controller, the program code causes the patterns / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on a machine, partially on a machine, as a standalone software package partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0097] In the context of this disclosure, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0098] To provide interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device for displaying information to the user (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor); and a keyboard and pointing device (e.g., a mouse or trackball) through which the user provides input to the computer. Other types of devices can also be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including sound input, voice input, or tactile input).

[0099] The systems and technologies described herein can be implemented in computing systems that include backend components (e.g., as a data server), or computing systems that include middleware components (e.g., an application server), or computing systems that include frontend components (e.g., a user computer with a graphical user interface or web browser through which a user can interact with implementations of the systems and technologies described herein), or any combination of such backend, middleware, or frontend components. The components of the system can be interconnected via digital data communication of any form or medium (e.g., a communication network). Examples of communication networks include local area networks (LANs), wide area networks (WANs), and the Internet.

[0100] It should be understood that the various forms of processes shown above can be used to rearrange, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved, and this is not limited herein.

[0101] The foregoing description of specific exemplary embodiments of this disclosure is for illustrative and explanatory purposes. These descriptions are not intended to limit this disclosure to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of this disclosure and their practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of this disclosure, as well as various different choices and variations. The scope of this disclosure is intended to be defined by the claims and their equivalents.

Claims

1. A method for controlling zero sequence current in a plurality of parallel connected machines, characterized by, The method, applicable to any converter module in a parallel system of multiple energy storage converters, includes: Obtain the total number of parallel modules in the parallel system of multiple energy storage converters, the local modulation status information, and the positive and negative bus voltages on the DC side of the local converter; Calculate the derating factor for the number of parallel modules based on the total number of parallel modules; Based on the local modulation state information, the available modulation margin is calculated in real time, and the available modulation margin is mapped to the zero-sequence current limiting coefficient. Based on the DC side positive and negative bus voltages of the machine, calculate the midpoint potential offset of the machine, and calculate the midpoint potential correction coefficient based on the midpoint potential offset of the machine. Based on the derating factor of the number of parallel units, the zero-sequence current limiting factor, and the midpoint potential correction factor, the preset reference limiting value is dynamically adjusted to obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

2. The method of claim 1, wherein, The calculation of the derating factor for the number of parallel units based on the total number of parallel modules includes: Subtract one from the total number of parallel modules to obtain the first intermediate value; Add the product of the parallel attenuation factor and the first intermediate value to obtain the second intermediate value; Divide one by the second intermediate value to obtain the derating factor for the number of parallel units.

3. The method of claim 1, wherein, The step of calculating the available modulation margin in real time based on the local modulation state information and mapping the available modulation margin to a zero-sequence current limiting coefficient includes: Based on the local modulation state information, calculate the current overall modulation index; Subtracting the current total modulation index from the maximum permissible modulation index yields the available modulation margin; The available modulation margin is mapped to a zero-sequence current limiting factor.

4. The method of claim 1, wherein, The calculation of the neutral point potential offset based on the DC side positive and negative bus voltages of the machine, and the calculation of the neutral point potential correction coefficient based on the neutral point potential offset, includes: The absolute value of the difference between the positive and negative bus voltages on the DC side of the machine is taken as the midpoint potential offset of the machine. The midpoint potential correction factor is obtained by subtracting the midpoint potential offset of the machine from the rated DC voltage and multiplying it by the rated correction factor.

5. The method according to any one of claims 1 to 4, characterized in that, The step of dynamically adjusting the preset reference limit value based on the derating factor of the number of parallel units, the zero-sequence current limiting factor, and the midpoint potential correction factor, and obtaining and sending the local zero-sequence current dynamic limiting value to the zero-sequence current controller includes: Multiply the preset baseline limit value by the derating factor of the number of parallel units, then by the zero-sequence current limit factor, and then by the midpoint potential correction factor to obtain the dynamic limit value of the zero-sequence current of the machine. Send the local zero-sequence current dynamic limit value to the zero-sequence current controller.

6. A method for controlling zero sequence current in a plurality of machines connected in parallel, characterized by, The method, applicable to any converter module in a parallel system of multiple energy storage converters, includes: Obtain the local zero-sequence current command, the zero-sequence voltage at the common coupling point, and the local current zero-sequence current limit value; Determine whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold; When the absolute value of the zero-sequence voltage is greater than the interference threshold, it is determined that there is mutual interference between the multi-machine voltage equalization ring. The zero-sequence current command of the machine is low-pass filtered and then superimposed with the zero-sequence voltage as a positive feedforward to form the final zero-sequence current command. The final zero-sequence current command is input to the zero-sequence current controller, and the output of the zero-sequence current controller is sent to the limiter, the limit of which is the current zero-sequence current limit value. When the output of the zero-sequence current controller reaches the limiting limit, the integral accumulation of the zero-sequence current controller is stopped, and the limiting error is filtered by a first-order low-pass filter. The filtered error is then fed back to the controller input for smoothing. When the output of the zero-sequence current controller deviates from the limiting limit, the integral accumulation of the zero-sequence current controller is restored according to the filtering error to obtain the zero-sequence control quantity; Based on the given voltage signal output from the zero-sequence control quantity and the current loop, a three-phase modulated wave is obtained and sent to the power device.

7. The method of claim 6, wherein, When determining that there is mutual interference among the multi-machine equalizing rings, the method further includes: Obtain the pre-calculated derating factor for the number of parallel units; The updated derating factor is obtained by multiplying the preset coordination attenuation factor by the derating factor of the number of parallel units, and the updated derating factor is used to control the current zero-sequence current limit value.

8. A multi-machine parallel zero sequence current control device, characterized by, The device is applicable to any converter module in a parallel system of multiple energy storage converters, and includes: The parameter acquisition unit is configured to acquire the total number of parallel modules in the parallel system of the multiple energy storage converters, the local modulation status information, and the positive and negative bus voltages on the DC side of the local unit. The derating calculation unit is configured to calculate the derating coefficient for the number of parallel modules based on the total number of parallel modules; The coefficient calculation unit is configured to calculate the available modulation margin in real time based on the local modulation state information, and map the available modulation margin to a zero-sequence current limiting coefficient. The offset calculation unit is configured to calculate the neutral point potential offset of the machine based on the positive and negative bus voltages of the machine's DC side, and to calculate the neutral point potential correction coefficient based on the neutral point potential offset of the machine. The limiting calculation unit is configured to dynamically adjust the preset reference limiting value based on the derating factor of the number of parallel units, the zero-sequence current limiting factor, and the midpoint potential correction factor, and obtain and send the local zero-sequence current dynamic limiting value to the zero-sequence current controller.

9. A multi-machine parallel zero sequence current control device, characterized by, The device is applicable to any converter module in a parallel system of multiple energy storage converters, and includes: The numerical acquisition unit is configured to acquire the local zero-sequence current command, the zero-sequence voltage at the common coupling point, and the local current zero-sequence current limit value. The judgment unit is configured to determine whether the absolute value of the zero-sequence voltage is greater than a preset interference threshold. The instruction generation unit is configured to determine that there is mutual interference between the multi-machine voltage equalization ring when the absolute value of the zero-sequence voltage is greater than the interference threshold, and to superimpose the local zero-sequence current instruction with the zero-sequence voltage as a positive feedforward to form the final zero-sequence current instruction after low-pass filtering. The limiting processing unit is configured to input the final zero-sequence current command to the zero-sequence current controller and send the output of the zero-sequence current controller to the limiter, wherein the limiting limit of the limiter is the current zero-sequence current limiting value; The smoothing unit is configured to stop the integral accumulation of the zero-sequence current controller when the output of the zero-sequence current controller reaches the limiting limit, and to obtain the filtering error by passing the limiting error through a first-order low-pass filter, and to feed the filtering error back to the controller input for smoothing. The recovery unit is configured to recover the integral accumulation of the zero-sequence current controller based on the filtering error when the output of the zero-sequence current controller deviates from the limiting limit, thereby obtaining the zero-sequence control quantity. The transmitting unit is configured to obtain and transmit a three-phase modulated wave to the power device based on the given voltage signal output by the zero-sequence control quantity and the current loop.

10. An electronic device, comprising: include: At least one processor; and a memory communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the method of any one of claims 1-7.

11. A non-transitory computer-readable storage medium having stored thereon computer instructions, wherein, The computer instructions are used to cause the computer to perform the method according to any one of claims 1-7.

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