A method and system for reactive power distribution in a heterogeneous parallel converter

Abstract

The application relates to the technical field of power electronics and micro-grid control, in particular to a reactive power distribution method and system for heterogeneous parallel converters. The method obtains operation control data of droop control type and virtual synchronous generator control type converters, and constructs a reactive power distribution model; the output reactive power of each converter, the system average reactive power and the reactive current component are calculated; an adaptive virtual impedance adjustment amount is generated based on the model, and is fused with a constant virtual impedance to form a total virtual impedance, which is used for correcting the voltage control amount of each converter; further, a voltage compensation amount is generated according to the voltage deviation of the point of common coupling, and the voltage reference value is adjusted in combination with the voltage control amount, so that the coordinated distribution and optimized control of the reactive power among the converters are realized. The application realizes the adaptive and balanced distribution and the current loop suppression of the reactive power of the heterogeneous parallel converters, and improves the system operation stability, the voltage support capability and the power quality.

Description

Technical Field

[0001] This application relates to the fields of power electronics technology and microgrid control technology, and in particular to a method and system for reactive power distribution in heterogeneous parallel converters. Background Technology

[0002] In related technologies, with the increasing penetration rate of distributed energy and the rapid development of microgrid technology, multi-converter parallel systems with voltage source converters as the core are widely used in islanded operation and weak grid scenarios. These systems typically consist of multiple converters with different control strategies, connected in parallel to a common AC bus (PCC) to provide active and reactive power support to the load and achieve stable control of system voltage and frequency. Among these, the rational allocation of reactive power is crucial for maintaining bus voltage quality, reducing line losses, and ensuring stable system operation.

[0003] However, in practical engineering applications, converter control strategies are increasingly exhibiting heterogeneous characteristics. For example, droop-controlled converters and virtual synchronous generator (VSG) controlled converters coexist in the same system. Droop control achieves power distribution without communication through reactive power-voltage characteristics, while VSG control enhances the system's dynamic response by introducing rotor motion equations to simulate the inertia and damping characteristics of a synchronous generator. Due to the fundamental differences between these control strategies in terms of equivalent output impedance characteristics, dynamic response speed, and voltage regulation mechanisms, reactive power distribution deviations and inter-machine circulating current problems are easily caused in parallel systems.

[0004] On the other hand, existing reactive power sharing methods mostly rely on fixed droop coefficient adjustments or fixed virtual impedance compensation strategies. However, these methods typically depend on accurate modeling of system parameters such as line impedance. When system parameters are uncertain or operating conditions change, their control performance deteriorates significantly. Furthermore, fixed parameter strategies struggle to adapt to the dynamic coupling effects of coexisting heterogeneous control strategies, easily leading to problems such as bus voltage dips or insufficient circulating current suppression. In addition, traditional methods often fail to effectively combine global reactive power deviation with local circulating current information for joint adjustment, making it difficult to balance reactive power distribution accuracy and system stability.

[0005] In summary, the technical problems existing in the relevant technologies need to be improved. Summary of the Invention

[0006] The main objective of this application is to propose a reactive power distribution method and system for heterogeneous parallel converters, which can achieve adaptive balanced distribution of reactive power in heterogeneous parallel converters, effectively suppress reactive circulating currents and improve system voltage stability and dynamic response capability, thereby improving the stability and power quality of parallel system operation.

[0007] To achieve the above objectives, one aspect of this application proposes a reactive power allocation method for heterogeneous parallel converters, the method comprising the following steps: Acquire the operation control data of the heterogeneous parallel converter system; the heterogeneous parallel converter system includes a droop-controlled converter and a virtual synchronous generator controlled converter; Based on the aforementioned operation control data, a reactive power allocation model is constructed; Based on the aforementioned operation control data, calculate the output reactive power of each converter, the system average reactive power, and the reactive circulating current component; Based on the reactive power allocation model, the output reactive power, the system average reactive power, and the reactive circulating current component, an adaptive virtual impedance adjustment is generated. Based on the adaptive virtual impedance adjustment and the constant virtual impedance, the total virtual impedance is determined, and the voltage control quantity of each converter is corrected based on the total virtual impedance. The voltage compensation amount is generated based on the voltage deviation at the point of common coupling, and the output voltage reference value of each converter is adjusted in conjunction with the voltage control amount to obtain the reactive power distribution result.

[0008] In some embodiments, the operation control data includes the output reactive power information, output current information, point of common coupling voltage information, and system circulating current information of each converter, as well as the corresponding control parameter information; the control parameter information includes droop control parameters, virtual synchronous generator control parameters, and virtual impedance parameters.

[0009] In some embodiments, constructing a reactive power allocation model based on the operational control data includes: Based on the aforementioned operation control data, extract the control type information and corresponding control parameter information for each converter; Based on the control type information and control parameter information, a functional mapping relationship between the reactive power of each converter and the reference value of the output voltage is established. Based on the aforementioned function mapping relationship, the reactive power regulation characteristics of converters with different control types are equivalently characterized to form a reactive power expression form. Based on the aforementioned reactive power expression, a reactive power allocation model for a heterogeneous parallel converter system is constructed.

[0010] In some embodiments, calculating the output reactive power of each converter, the system average reactive power, and the reactive circulating current component based on the operating control data includes: Based on the output voltage and output current information of each converter in the operation control data, the reactive power output of each converter is calculated in the synchronous rotating coordinate system. The reactive power output of each converter is averaged to obtain the system average reactive power. Based on the deviation between the output reactive power of each converter and the average reactive power of the system, the reactive power deviation of each converter is determined. Based on the correlation between the output voltage difference information and the output current information of each converter, the voltage coupling component between converters is extracted, and the reactive circulating current component is determined.

[0011] In some embodiments, generating an adaptive virtual impedance adjustment based on the reactive power allocation model, the output reactive power, the system average reactive power, and the reactive circulating current component includes: Based on the reactive power allocation model, the output reactive power and the system average reactive power are mapped by the model to obtain the reactive power allocation deviation. The reactive circulating current component is modeled equivalently to obtain the circulating current compensation amount; The reactive power distribution deviation and the circulating current compensation are combined to obtain the comprehensive adjustment amount; Based on the comprehensive adjustment amount, and using a proportional-integral control algorithm for adaptive adjustment, an adaptive virtual impedance adjustment amount is generated.

[0012] In some embodiments, the formula for calculating the adaptive virtual impedance adjustment is as follows: ; in, This indicates the amount of adaptive virtual impedance adjustment; Represents constant virtual inductive impedance; Indicates adaptive virtual sensing impedance; and These represent the reactive power proportional coefficient and integral coefficient of the adaptive virtual reactance, respectively. and These represent the circulation proportionality coefficient and integral coefficient, respectively; This represents the average reactive power of the inverter; Indicates the first The actual output reactive power of the converter; s represents the Laplace operator; This represents the average value of the reactive circulating current component along the q-axis of the converter. Indicates the first The q-axis reactive circulating current component of the converter.

[0013] In some embodiments, determining the total virtual impedance based on the adaptive virtual impedance adjustment and the constant virtual impedance, and correcting the voltage control quantity of each converter based on the total virtual impedance, includes: The adaptive virtual impedance adjustment is superimposed on the constant virtual impedance to obtain the total virtual impedance value; Based on the total virtual impedance value, it is directly applied to the converter voltage control feedforward link to construct an equivalent output impedance adjustment amount; The converter voltage reference value is mapped and corrected based on the equivalent output impedance adjustment to generate a voltage control correction value.

[0014] In some embodiments, the step of generating a voltage compensation amount based on the common coupling point voltage deviation and adjusting the output voltage reference value of each converter in conjunction with the voltage control amount to obtain the reactive power distribution result includes: Obtain the actual voltage value and voltage reference value at the point of common coupling; The voltage deviation at the point of common coupling is determined based on the deviation between the actual voltage value and the reference voltage value. Based on the voltage deviation at the common connection point, a voltage compensation amount is generated through a voltage secondary control algorithm. The voltage compensation amount is sent to each converter and superimposed with the voltage control amount of each converter to obtain the output voltage reference value of each converter. The output voltage of each converter is adjusted based on the output voltage reference value to obtain the reactive power distribution result.

[0015] In some embodiments, the voltage compensation amount is calculated using the following formula: ; ; in, Indicates the first Voltage compensation amount of the distributed generation unit; Indicates the voltage compensation amount at the point of common coupling; This represents the bus voltage control coefficient; This indicates the actual voltage measured at the point of common coupling; and These represent the proportional and integral coefficients of the voltage secondary control, respectively; s represents the Laplace operator; n represents the total number of converters in the parallel system; j represents the number of converters connected to the second-order converter. Any other unit that interacts with the platform for information exchange Unit number; Indicates the first Voltage compensation amount of the unit.

[0016] To achieve the above objectives, another aspect of this application proposes a reactive power distribution system for heterogeneous parallel converters, the system comprising: The data acquisition module is used to acquire the operation and control data of the heterogeneous parallel converter system; the heterogeneous parallel converter system includes a droop-controlled converter and a virtual synchronous generator controlled converter. The model building module is used to build a reactive power allocation model based on the operation control data. The calculation module is used to calculate the output reactive power of each converter, the average reactive power of the system, and the reactive circulating current component based on the operation control data. The impedance adjustment module is used to generate an adaptive virtual impedance adjustment amount based on the reactive power distribution model, the output reactive power, the system average reactive power, and the reactive circulating current component. The voltage control module is used to determine the total virtual impedance based on the adaptive virtual impedance adjustment and the constant virtual impedance, and to correct the voltage control amount of each converter based on the total virtual impedance. The result output module is used to generate a voltage compensation amount based on the voltage deviation at the point of common coupling, and adjust the output voltage reference value of each converter in combination with the voltage control amount to obtain the reactive power distribution result.

[0017] To achieve the above objectives, another aspect of this application provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the above-described method.

[0018] To achieve the above objectives, another aspect of the embodiments of this application proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0019] To achieve the above objectives, another aspect of this application provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0020] The embodiments of this application include at least the following beneficial effects: This application provides a reactive power allocation method and system for heterogeneous parallel converters. This scheme acquires the operation control data of the heterogeneous parallel converter system and constructs a reactive power allocation model to achieve unified modeling and coordinated control of droop-controlled converters and virtual synchronous generator-controlled converters. Compared with the prior art, this invention can achieve adaptive and precise allocation of reactive power among heterogeneous converters. By introducing an adaptive virtual impedance adjustment mechanism based on the system average reactive power and reactive circulating current components, it effectively suppresses circulating current within the parallel system, reduces power coupling and imbalance problems between converters with different control strategies, and improves the accuracy and dynamic stability of reactive power allocation. Simultaneously, it corrects the voltage control quantity through the total virtual impedance and generates a voltage compensation quantity in conjunction with the voltage deviation at the point of common coupling, achieving secondary adjustment of the output voltage reference value and enhancing the voltage support capability and voltage recovery speed at the point of common coupling. Furthermore, this method reduces reliance on manual parameter tuning, enhances the system's adaptability and robustness to changes in operating conditions and parameter disturbances, improves dynamic response performance and convergence characteristics, and enhances the engineering applicability and operational reliability of heterogeneous parallel systems. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a method for reactive power allocation in a heterogeneous parallel converter provided in an embodiment of this application. Figure 2 This is a single-phase equivalent circuit diagram of two inverters operating in parallel, provided in an embodiment of this application. Figure 3 This is a circuit diagram of the circulating current model of multiple inverters operating in parallel provided in the embodiments of this application; Figure 4 This is a schematic diagram of a dq coordinate dual closed-loop control structure based on virtual impedance provided in an embodiment of this application; Figure 5 This is a schematic diagram of the heterogeneous parallel converter voltage secondary control and virtual impedance collaborative control structure provided in the embodiments of this application; Figure 6 This is a waveform diagram of the active power output of the inverter under droop control in the simulation provided in the embodiments of this application; Figure 7 This is a waveform diagram of the reactive power output of the inverter under droop control in the simulation provided in the embodiments of this application; Figure 8 This is a simulation of the inverter phase A output current waveform under droop control and its partial magnified view provided in the embodiments of this application; Figure 9 This is a waveform diagram of the active power output of the inverter under VSG control in the simulation provided in the embodiments of this application; Figure 10This is a waveform diagram of the reactive power output of the inverter under VSG control in the simulation provided in the embodiments of this application; Figure 11 This is a simulation of the inverter's A-phase output current waveform under VSG control and its partial magnified view provided in the embodiments of this application; Figure 12 This is a waveform diagram of the output reactive power of the inverter in a heterogeneous parallel converter system provided in the embodiments of this application; Figure 13 This is a voltage waveform diagram of the PCC point of a heterogeneous parallel converter system in a simulation provided in this application embodiment; Figure 14 This is a simulation of the inverter phase A output current waveform and its partial magnification in a heterogeneous parallel converter system provided in this application embodiment; Figure 15 This is a transient frequency response diagram of a heterogeneous parallel converter system in a simulation provided in the embodiments of this application; Figure 16 This is a schematic diagram of a heterogeneous parallel converter reactive power distribution system provided in an embodiment of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0023] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0024] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0026] Before providing a detailed description of the embodiments of this application, some of the nouns and terms used in the embodiments of this application will be explained first. The nouns and terms used in the embodiments of this application shall be interpreted as follows: Heterogeneous parallel converters refer to a parallel operation structure consisting of converters with different control strategies in the same power parallel system, such as a system in which a droop control type converter and a virtual synchronous generator control type converter are connected to a common AC bus. A droop-controlled converter is a voltage source converter that automatically adjusts the output voltage reference value to achieve power distribution based on the reactive power-voltage droop characteristic (QU Droop Control). A Virtual Synchronous Generator (VSG) is a control converter that incorporates the rotor motion equations, inertia, and damping characteristics of a synchronous generator to enable the converter to exhibit dynamic response characteristics similar to those of a synchronous generator. The point of common coupling (PCC) is a common electrical connection node where multiple converters or distributed power sources are connected to the power grid or microgrid, used for unified voltage reference and power interaction; Reactive power refers to the power component in a power system that is used to establish and maintain the electromagnetic field but does not directly perform work; it is used to characterize the voltage support capability of an AC system. The reactive circulating current component refers to the non-load reactive power circulating component caused by voltage amplitude differences or inconsistent control parameters between converters operating in parallel. The dq rotating coordinate system refers to an analysis method that maps three-phase AC quantities to a synchronous rotating coordinate system through coordinate transformation. It is used to convert AC quantities into DC quantities to simplify control and calculation. Secondary voltage control refers to a control strategy that, based on primary voltage control, achieves voltage recovery and optimization at the point of common coupling through centralized or distributed regulation at the system level. DG unit refers to Distributed Generation Unit, which is a small power generation device or unit that is connected to the power system or microgrid and can generate and output electricity locally. Examples include photovoltaic power generation unit, wind power generation unit, and energy storage inverter power generation unit. It is used to realize the access and coordinated operation of distributed energy. PWM stands for Pulse Width Modulation, a control method that controls output quantities such as voltage or current by adjusting the duty cycle of a switching signal. It is widely used in power electronic converters to achieve precise control of the inverter's output voltage amplitude, frequency, and waveform.

[0027] This application provides a method and system for reactive power allocation in heterogeneous parallel converters. This scheme acquires the operating control data of the heterogeneous parallel converter system and constructs a reactive power allocation model, achieving unified modeling and coordinated control of droop-controlled converters and virtual synchronous generator-controlled converters. Compared to existing technologies, this invention can achieve adaptive and precise reactive power allocation among heterogeneous converters. By introducing an adaptive virtual impedance adjustment mechanism based on the system's average reactive power and reactive circulating current components, it effectively suppresses circulating current within the parallel system, reduces power coupling and imbalance problems between converters with different control strategies, and improves the accuracy and dynamic stability of reactive power allocation. Simultaneously, it corrects the voltage control quantity through the total virtual impedance and generates a voltage compensation quantity based on the voltage deviation at the point of common coupling (PCC), achieving secondary adjustment of the output voltage reference value and enhancing the PCC voltage support capability and voltage recovery speed. Furthermore, this method reduces reliance on manual parameter tuning, improves the system's adaptability and robustness to changes in operating conditions and parameter disturbances, enhances dynamic response performance and convergence characteristics, and improves the engineering applicability and operational reliability of heterogeneous parallel systems.

[0028] This application provides a reactive power allocation method for heterogeneous parallel converters, relating to the fields of power electronics and microgrid control technology. This method can be applied to terminals, servers, or software running on either. In some embodiments, the terminal can be a smartphone, tablet, laptop, desktop computer, smart speaker, smartwatch, or vehicle terminal, but is not limited thereto. The server can be configured as an independent physical server, a server cluster or distributed system composed of multiple physical servers, or a cloud server providing basic cloud computing services such as cloud services, cloud databases, cloud computing, cloud functions, cloud storage, network services, cloud communication, middleware services, domain name services, security services, CDN, and big data and artificial intelligence platforms. The server can also be a node server in a blockchain network. The software can be an application implementing a reactive power allocation method for heterogeneous parallel converters, but is not limited to the above forms.

[0029] This application can be used in a wide variety of general-purpose or special-purpose computer system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable consumer electronics devices, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices. This application can be described in the general context of computer-executable instructions executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform specific tasks or implement specific abstract data types. This application can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0030] Figure 1 This is an optional flowchart of a reactive power allocation method for heterogeneous parallel converters provided in an embodiment of this application. Figure 1 The method may include, but is not limited to, steps S1 to S6: S1: Obtain the operation control data of the heterogeneous parallel converter system; the heterogeneous parallel converter system includes droop control type converters and virtual synchronous generator control type converters; the operation control data includes the output reactive power information, output current information, point of common coupling voltage information, system circulating current information, and corresponding control parameter information of each converter; the control parameter information includes droop control parameters, virtual synchronous generator control parameters, and virtual impedance parameters.

[0031] In this embodiment, the central controller provides unified operational status awareness for the heterogeneous parallel system composed of droop-controlled converters and virtual synchronous generator (VSG) controlled converters. Each converter collects its own operational data in real time through its local controller and periodically uploads it to the central controller according to a preset communication protocol. The sampling period can be set to within the range of 1ms to 10ms based on the system's dynamic characteristics. The central controller synchronously receives the data from each converter and eliminates sampling deviations caused by communication delays through a timestamp alignment mechanism, ensuring that the operational data from different converters have a unified time reference.

[0032] In terms of data composition, the operation control data includes reactive power output information, output current information, point of common coupling voltage information, system circulating current information, and corresponding control parameter information for each converter. Specifically, the reactive power output information characterizes the reactive power distribution status of each converter; the output current information reflects the power exchange relationship between each converter and the common bus; the point of common coupling voltage information characterizes the bus voltage deviation; and the system circulating current information characterizes the non-load current circulation state between converters. The control parameter information includes the droop control coefficient, the virtual inertia and damping parameters of the virtual synchronous generator, and the initial value of the virtual impedance, used to characterize the differences in control strategies for each converter.

[0033] Furthermore, the central controller performs basic preprocessing on the acquired operational control data, including anomaly removal and sliding filtering to reduce the impact of measurement noise. It also performs unified structured encapsulation of data from different types of converters to form standardized operational state vectors. This standardized data is stored in a real-time computing cache for subsequent reactive power allocation model construction and circulating current calculation input, thereby ensuring the real-time performance and consistency of the model calculations.

[0034] S2: Construct a reactive power distribution model based on the operation control data; Based on operational control data, a reactive power allocation model is constructed, including: Based on the operation control data, extract the control type information and corresponding control parameter information of each converter; Based on control type information and control parameter information, a functional mapping relationship between reactive power and output voltage reference value of each converter is established. Based on the function mapping relationship, the reactive power regulation characteristics of converters with different control types are equivalently characterized to form a reactive power expression form; Based on the reactive power expression form, a reactive power allocation model for heterogeneous parallel converter systems is constructed.

[0035] In this embodiment, after acquiring the operational control data, the control attributes of each converter are first parsed to extract control type information, which is used to distinguish between droop-controlled converters and virtual synchronous generator-controlled converters. Simultaneously, the corresponding control parameter information for each converter is extracted, including reactive power droop coefficient, virtual inertia parameter, damping parameter, and virtual impedance setpoint, to characterize the dynamic response characteristics and regulation capabilities of the converters under different control strategies. This unified aggregation of information provides fundamental data support for subsequent model construction.

[0036] In further implementation, a mapping relationship between reactive power and output voltage reference values ​​is established for converters with different control types. For droop control converters, reactive power changes are mapped to the adjustment process of the output voltage reference value through a preset voltage droop mechanism, which describes their static regulation characteristics. For virtual synchronous generator control converters, based on their equivalent synchronous machine control structure, reactive power changes are modeled in correspondence with the virtual voltage regulation process to reflect the influence of their inertia and damping characteristics on the dynamic process of voltage regulation, thus forming a unified response description method under different control strategies.

[0037] Based on this, the reactive power regulation characteristics of converters with different control types are equivalently unified and transformed into a unified expression of reactive power and voltage reference values. This allows the dynamic behavior under different control strategies to be compared and described within the same analytical framework. Finally, a reactive power allocation model for a heterogeneous parallel converter system is constructed based on this equivalent expression. This model can simultaneously characterize differences in control types, parameter differences, and system coupling effects, providing a unified mathematical foundation and analytical basis for subsequent adaptive virtual impedance regulation and circulating current suppression.

[0038] Specifically, the droop-controlled converter adopts the reactive-voltage (QU) droop characteristic, the expression of which is: ; In the formula: U is the reference value of the inverter output voltage; This represents the amplitude of the inverter's no-load output voltage. This is the inverter reactive power droop factor. These are the nominal values ​​of the active and reactive power of the converter; The VSG-controlled converter introduces rotor motion equations to simulate the inertia and damping characteristics of a synchronous generator based on droop control. The rotor motion equations are as follows: ; In the formula: Let VSG be the moment of inertia. The damping coefficient; P and P represent the active reference command and actual active output of VSG, respectively; and These represent the actual and nominal values ​​of the inverter's output angular frequency, respectively.

[0039] This embodiment simplifies the study of reactive power allocation errors by constructing a reactive power allocation model, focusing on... Figure 2 The equivalent model shown consists of two voltage source inverters, and it is assumed that their line parameters and control parameters are exactly the same. Figure 2 middle U 1∠ θ 1 andU 2∠ θ 2 indicates the output voltage of the grid-connected inverter; Z 1∠ δ 1 and Z 2∠ δ 2 represents the equivalent line impedance of the system; i o1 and i o2 This indicates the current flowing through the circuit.

[0040] The output current of an inverter can be expressed in terms of power and voltage: ; In the formula, Indicates the first The output current of a distributed generation (DG / inverter) is represented by a complex number. Indicates the first The converter outputs active power; Indicates the first The converter outputs reactive power.

[0041] Near the steady-state operating point, the voltage drop across each line impedance can be approximated by the following equation: ; In the formula, Indicates the first The voltage drop caused by the line impedance of the converter; Indicates the first The equivalent line resistance from the converter to the point of common coupling (PCC); Indicates the first The equivalent line reactance from the converter to the PCC.

[0042] The output port voltage amplitudes of the two distributed generation units (DG units) were obtained: ; ; In the formula, and This indicates the output voltage amplitude of the two DG converters; Indicates the voltage at the point of common coupling (PCC); and This represents the equivalent line reactance from the first and second converters to the PCC. and This represents the equivalent line resistance from the first and second converters to the PCC. and This indicates the active power output of the two converters; and This indicates the reactive power output of the two converters.

[0043] Both DG units employ droop control; assuming their reactive power-voltage droop coefficient... same: ; Define reactive power error for: ; Similarly: ; Further considering that the active power under steady-state conditions has been proportionally distributed according to the active power droop factor, i.e., P1=P2=P, in order to obtain a first-order approximate analytical expression for the reactive power sharing error, a linearized approximation of reactive power Q1≈Q2≈Q can be taken under the premise that the error is small: ; The reactive power distribution error can be approximated as: ; The above formula shows that the reactive power distribution accuracy is not only related to the reactive power droop factor, but also affected by the equivalent interconnect impedance of each inverter. Assuming Z1 > Z2, ΔQ is less than 0, and the reactive power output of DG1 is less than that of DG2, indicating that the unit with the larger line impedance will provide less reactive power and have a larger voltage drop. Furthermore, the ratio of reactive power output by each inverter is: ; Only when the connection impedance is proportional to the reactive power droop factor can the actual output reactive power be distributed according to the rated power. In this case: ; At this time, the output of different DGs is unresponsive. and The combined impact, among which, It is inversely proportional to the rated reactive power. Ignoring line resistance, we investigate the impact of feeder reactance mismatch on reactive power distribution error.

[0044] S3: Based on the operation control data, calculate the output reactive power of each converter, the average reactive power of the system, and the reactive circulating current component; Based on the operation control data, the output reactive power of each converter, the system average reactive power, and the reactive circulating current component are calculated, including: Based on the output voltage and output current information of each converter in the operation control data, the output reactive power of each converter is calculated in the synchronous rotating coordinate system. The reactive power output of each converter is averaged to obtain the system average reactive power. Based on the deviation between the output reactive power of each converter and the average reactive power of the system, the reactive power deviation of each converter is determined. Based on the correlation between the output voltage difference information and the output current information of each converter, the voltage coupling component between converters is extracted, and the reactive circulating current component is determined.

[0045] In this embodiment, the electrical quantities of each converter in the synchronous rotating coordinate system are first analyzed based on the output voltage and output current information in the operation control data. A coordinate transformation mechanism is used to convert the three-phase AC quantities into a unified dq coordinate expression form, enabling decoupled analysis of voltage and current quantities in a unified reference system. Based on this decoupling result, the reactive power characterization of each converter is extracted, thereby obtaining the real-time calculation results of the output reactive power of each converter.

[0046] Based on this, the reactive power output of each converter is aggregated and processed. By averaging the reactive power data of all converters, the system average reactive power is obtained, which serves as a benchmark to characterize the overall reactive power distribution of the system. This average value reflects the overall reactive power supply status of the current system under the heterogeneous control strategy and provides a unified reference for subsequent deviation analysis.

[0047] Furthermore, by comparing and analyzing the differences between the reactive power output of each converter and the system average reactive power, the reactive power deviation of each converter is determined, which characterizes the degree of imbalance in the reactive power distribution process of each unit. Simultaneously, by combining the correlation between the output voltage difference information and output current information of each converter, the voltage coupling effect between converters is extracted and analyzed, identifying the power circulation path caused by voltage differences, thereby determining the reactive circulating current component in the system and providing crucial feedback for subsequent virtual impedance adjustment.

[0048] Specifically, the reactive power circulating current component extraction mechanism is as follows: The output voltage difference of parallel inverters generates inter-inverter circulating current. Circulating current is defined as the current flowing between multiple inverters through the PCC point but not through the load. A typical circulating current structure between n three-phase parallel inverters is as follows: Figure 3 As shown, where For the output current vector, For circulation vectors, Let be the circulating current vector between the m-th and i-th inverters, where i = 1, 2, …n, and i ≠ m. The circulating current does not participate in external power supply, but it increases the current stress and losses of power electronic devices, and in severe cases, it may trigger overcurrent protection and disrupt the stability of the parallel system.

[0049] According to Kirchhoff's laws: ; ; In the formula, Indicates the first The inverter output voltage phasor; Indicates the first The equivalent line impedance from the inverter to the point of common coupling (PCC); Indicates the first Taiwan inverter output current phasor; Indicates the first The inverter output current; Indicates the total output current of the system; This represents the equivalent impedance of the load.

[0050] Assuming the inverters have the same equivalent interconnect impedance, Zo1 = Zo2 = ... = Zon, the output current of each inverter can be obtained as follows: ; In the formula: Indicates the first Taiwan and the The output voltage difference of the inverter This represents the sum of voltage differences between the m-th inverter and the other n-1 inverters.

[0051] The expression for the circulating current between the m-th and i-th inverters is defined as follows: ; In the formula, Indicates the first The equivalent output impedance of the inverter.

[0052] It can be seen that the circulating current amplitude is inversely proportional to the equivalent interconnect impedance, and increases with the increase of the voltage vector difference at the terminals of the parallel inverters. When the equivalent interconnect impedance of n parallel inverters is purely inductive, it can be simplified to: ; In the formula, n represents the number of inverters connected in parallel; and Indicates the first Taiwan and the The output voltage amplitude of the inverter; and This indicates the phase angle of the corresponding inverter output voltage; This represents the equivalent output line impedance.

[0053] If the voltage amplitudes at the terminals of each inverter are the same, i.e., U1 = U2 = …= Un, then the imaginary part of the circulating current approaches zero. At this time, the circulating current is mainly composed of the active component caused by the phase difference of the inverter output voltage.

[0054] S4: Generate an adaptive virtual impedance adjustment based on the reactive power distribution model, output reactive power, system average reactive power, and reactive circulating current component; Specifically, based on the reactive power allocation model, output reactive power, system average reactive power, and reactive circulating current component, an adaptive virtual impedance adjustment is generated, including: Based on the reactive power allocation model, the model mapping calculation is performed on the output reactive power and the system average reactive power to obtain the reactive power allocation deviation. The reactive circulating current component is modeled equivalently to obtain the circulating current compensation amount; The reactive power distribution deviation and the circulating current compensation are combined to obtain the comprehensive adjustment amount. Based on the comprehensive adjustment amount, and using the proportional-integral control algorithm for adaptive adjustment, an adaptive virtual impedance adjustment amount is generated.

[0055] In this embodiment, after obtaining the reactive power allocation model, output reactive power, system average reactive power, and reactive circulating current component, the operating status of each converter is first mapped and analyzed based on the reactive power allocation model. The current reactive power output of each converter is correlated with the system average level to form a unified model mapping space, which is used to characterize the relative reactive power allocation position of each converter in the system.

[0056] Based on this, the reactive power distribution deviation is obtained by calculating the difference between the reactive power output of each converter and the average reactive power of the system. This deviation is used to characterize the degree of reactive power distribution imbalance of each converter under the current operating condition. This deviation can reflect the power distribution offset caused by differences in control strategies and inconsistent line impedances.

[0057] Furthermore, the reactive circulating current component is modeled equivalently, transforming its original current circulation characteristics into a circulating current influence quantity that can be used for control regulation. By analyzing the interaction between the output voltage difference and current between converters, the circulating current is converted into an equivalent disturbance affecting the stability of the system's reactive power distribution, thereby obtaining the circulating current compensation quantity for subsequent control correction.

[0058] Finally, the reactive power distribution deviation and the circulating current compensation are fused together to form a comprehensive adjustment quantity. Based on this comprehensive adjustment quantity, a proportional-integral control algorithm is used for adaptive adjustment. By tracking and cumulatively correcting the deviation change trend in real time, an adaptive virtual impedance adjustment quantity is generated, providing a control basis for subsequent dynamic updates of the virtual impedance.

[0059] Specifically, the formula for calculating the adaptive virtual impedance adjustment is as follows: ; in, This indicates the amount of adaptive virtual impedance adjustment; Represents constant virtual inductive impedance; Indicates adaptive virtual sensing impedance; and These represent the reactive power proportional coefficient and integral coefficient of the adaptive virtual reactance, respectively. and These represent the circulation proportionality coefficient and integral coefficient, respectively; This represents the average reactive power of the inverter; Indicates the first The actual output reactive power of the converter; s represents the Laplace operator; This represents the average value of the reactive circulating current component along the q-axis of the converter. Indicates the first The q-axis reactive circulating current component of the converter.

[0060] S5: Determine the total virtual impedance based on the adaptive virtual impedance adjustment and the constant virtual impedance, and correct the voltage control quantity of each converter based on the total virtual impedance; Specifically, the total virtual impedance is determined based on the adaptive virtual impedance adjustment and the constant virtual impedance, and the voltage control quantities of each converter are corrected based on the total virtual impedance, including: The total virtual impedance value is obtained by superimposing the adaptive virtual impedance adjustment amount with the constant virtual impedance. Based on the total virtual impedance value directly acting on the converter voltage control feedforward link, an equivalent output impedance regulation is constructed. The converter voltage reference value is mapped and corrected based on the equivalent output impedance adjustment to generate a voltage control correction value.

[0061] In this embodiment, after obtaining the adaptive virtual impedance adjustment and the constant virtual impedance, both are first processed to unify their dimensions and data structures, so that they are both input to the control module in the same impedance representation form. Then, the two types of impedance are superimposed to obtain the total virtual impedance value corresponding to each converter, which is used to uniformly represent its equivalent output impedance characteristics, thereby providing basic parameters for subsequent voltage control correction.

[0062] Based on this, the total virtual impedance value is directly applied to the voltage control feedforward link of the converter, and the original voltage control link is processed by equivalent impedance embedding. By introducing the total virtual impedance into the feedforward path, the converter exhibits adjustable equivalent output impedance characteristics at the control level, thereby changing its power exchange characteristics with the point of common coupling and realizing indirect control of reactive power distribution behavior.

[0063] Furthermore, based on the equivalent output impedance adjustment after introducing the total virtual impedance, the converter voltage reference value is mapped and corrected. This transforms the voltage deviation caused by impedance changes into a voltage control correction, enabling the voltage reference value of each converter to adaptively adjust according to the system's operating state. Through this correction mechanism, converters with different control types operate under a unified voltage reference, thereby achieving reactive power distribution according to the target, reducing circulating current and voltage deviations caused by impedance differences, and improving the overall system stability and power quality.

[0064] refer to Figure 4 As shown, Figure 4 This is a schematic diagram of the dq coordinate dual closed-loop control structure based on virtual impedance in this invention, used to illustrate the control process of achieving equivalent output impedance reshaping and reactive power distribution optimization through the synergistic effect of the voltage outer loop, current inner loop and virtual impedance link in a heterogeneous parallel converter system.

[0065] In the outer voltage loop, the controller calculates the deviations between the d-axis and q-axis voltage reference values ​​and the actual voltages, and processes these deviations through a proportional-integral regulator to generate corresponding current reference values. This process achieves decoupled control of active and reactive components in a synchronous rotating coordinate system, enabling the converter to independently adjust the power demand along different axes, thereby improving the accuracy and response speed of reactive power regulation.

[0066] In the virtual impedance effect, an equivalent virtual impedance is introduced. The d-axis and q-axis voltage reference signals are corrected so that the voltage command is dynamically adjusted before entering the current control loop, thereby changing the equivalent output impedance characteristics of the converter. Simultaneously, Figure 4 middle Used to compensate for the effects of capacitive coupling. This is used to compensate for the effects of inductive coupling, thereby reducing cross-coupling between the d and q axes and improving the system's decoupling control capability. In the inner current loop, the reference current and the actual current are tracked and controlled by a current regulator, and the result is output to the PWM modulation module to achieve precise driving of the power switching devices. This ensures that the system still has a stable dynamic response and good reactive power distribution performance after the introduction of virtual impedance.

[0067] S6: Generate voltage compensation based on the voltage deviation at the point of common coupling, and adjust the output voltage reference value of each converter in conjunction with the voltage control quantity to obtain the reactive power distribution result.

[0068] Specifically, a voltage compensation amount is generated based on the voltage deviation at the point of common coupling, and the output voltage reference value of each converter is adjusted in conjunction with the voltage control amount to obtain the reactive power distribution result, including: Obtain the actual voltage value and voltage reference value at the point of common coupling; The voltage deviation at the point of common coupling is determined based on the deviation between the actual voltage value and the voltage reference value. Based on the voltage deviation at the point of common coupling, a voltage compensation amount is generated through a voltage secondary control algorithm. The voltage compensation amount is sent to each converter and superimposed and corrected with the voltage control amount of each converter to obtain the output voltage reference value of each converter. The reactive power distribution result is obtained by adjusting the output voltage of each converter based on the output voltage reference value.

[0069] In this embodiment, the actual value of the point of common coupling (PCC) voltage is first obtained, and a preset voltage reference value is simultaneously obtained to characterize the expected bus voltage level of the system. By comparing and analyzing the actual value and the reference value in real time, a PCC voltage deviation is formed. This deviation reflects the overall voltage stability of the system and the bus voltage fluctuation caused by uneven reactive power distribution.

[0070] Based on this, the voltage deviation at the point of common coupling is input into the secondary voltage control algorithm for processing. The secondary voltage control algorithm operates based on a centralized control framework, and through proportional-integral adjustment of the voltage deviation, it achieves dynamic correction of the system's long-term voltage offset, thereby generating a voltage compensation amount used to restore bus voltage stability.

[0071] Furthermore, the voltage compensation amount is transmitted to each parallel converter via the communication network and superimposed with the local voltage control amount of each converter for correction, thereby uniformly adjusting the output voltage reference value of each converter. This process enables voltage-level consistency and coordination among converters with different control types, reducing voltage inconsistencies caused by differences in control strategies.

[0072] Finally, based on the corrected output voltage reference value, each converter adjusts its output voltage under the action of its local controller, allowing the system to re-enter a stable operating state. During this process, the voltage compensation mechanism and virtual impedance control work together to maintain stable bus voltage while simultaneously distributing reactive power according to the target ratio, thus obtaining the final reactive power distribution result and effectively suppressing circulating current and voltage dips.

[0073] refer to Figure 5 As shown, Figure 5 This is a schematic diagram of the voltage secondary control and virtual impedance collaborative control structure of heterogeneous parallel converters in an embodiment of the present invention. It is used to illustrate the overall control process of achieving voltage stability at the point of common coupling and balanced distribution of reactive power through a hierarchical control structure under the condition of parallel operation of droop control type and virtual synchronous generator (VSG) control type converters.

[0074] In the system architecture layer, Figure 5It contains three converter units operating in parallel, each with its own independent control loop. Each converter internally includes a voltage secondary control module, a virtual impedance loop, an inner loop controller, and a PWM drive and power conversion unit. The voltage secondary control module, located in the upper-level control structure, receives the voltage deviation signal at the point of common coupling and generates a corresponding voltage compensation. This compensation is then distributed to each converter via a communication network, achieving multi-node consistent voltage correction.

[0075] In the local control layer, each converter superimposes and corrects the compensation from the secondary voltage control module with the local voltage control quantity to form a new voltage reference value. After this reference value enters the grid control structure, it undergoes equivalent output impedance adjustment through a virtual impedance stage, thereby unifying the equivalent electrical characteristics of converters with different control types. This reduces the problem of uneven reactive power distribution caused by differences in line impedance and control strategies.

[0076] In the power conversion and feedback layer, the corrected voltage command is processed by the inner-loop current controller and then enters the PWM module to drive the inverter power switching devices to achieve energy conversion. Simultaneously, the output current and power information of each converter are fed back to the point of common coupling and controller in real time to calculate reactive power and circulating current status, and to support secondary voltage control and dynamic adjustment of virtual impedance. Through this multi-layered collaborative control, the control objectives of voltage stability, precise reactive power distribution, and effective circulating current suppression in the heterogeneous parallel system are achieved.

[0077] Specifically, the formula for calculating the voltage compensation amount is as follows: ; ; in, Indicates the first Voltage compensation amount of the distributed generation unit; Indicates the voltage compensation amount at the point of common coupling; This represents the bus voltage control coefficient; This indicates the actual voltage measured at the point of common coupling; and These represent the proportional and integral coefficients of the voltage secondary control, respectively; s represents the Laplace operator; n represents the total number of converters in the parallel system; j represents the number of converters connected to the second-order converter. Any other unit that interacts with the platform for information exchange Unit number; Indicates the first Voltage compensation amount of the unit.

[0078] In this embodiment, an islanded microgrid model with three inverters connected in parallel was built in the MATLAB / Simulink simulation environment to verify the effectiveness of the proposed strategy. The system parameters are shown in Table 1.

[0079] Table 1: Simulation parameters of a three-inverter parallel system;

[0080] The line impedance ratio of the three inverters is set to 0.6:0.75:0.85 to simulate different distances from the PCC point. The initial load is 6kW + 6kvar. The adaptive virtual impedance control proposed in this invention is applied at 0.4s, and an additional 3kW + 3kvar load is applied at 1.2s.

[0081] Specifically, the simulation of all droop controls is performed as follows: When using traditional droop control from 0 to 0.4 seconds, the reactive power distribution error of the three inverters is relatively large due to differences in line impedance. After implementing the proposed strategy at 0.4 seconds, the reactive power distribution error is reduced to within ±0.2%. Figure 7 , Figure 8 The results show that after the strategy is implemented, the three-phase output current waveforms almost completely overlap, and the circulating current is effectively suppressed.

[0082] Since the frequency of each inverter is the same in steady state Figure 6 It can be seen that under the traditional droop control strategy, the output active power of all three inverters remains at the nominal value of 2kW. After a sudden load increase of 1.2s, the active power output of the inverters increases simultaneously, and the system can always achieve good active power distribution. However, due to the difference in line impedance, Figure 7 It can be seen that the reactive power distribution error among the inverters is relatively large, making it impossible to distribute it evenly according to capacity. In the 0~1.2s time period, the calculated relative reactive power errors are 51.69%, 6.19%, The reactive power relative errors after a 1.2s load increase are 51.52%, -6.74%, and -44.78%, respectively, indicating that the reactive power distribution patterns under the two steady-state conditions are almost identical.

[0083] When the proposed adaptive virtual impedance control strategy is adopted, the inverter's output power waveform is as follows: Figure 6 , Figure 7 As shown. After the virtual impedance is applied at t=0.4s, the active power oscillates and quickly recovers to the rated value. When the load increases at t=1.2s, the three machines synchronously step to a new steady-state value with very small overshoot.

[0084] After switching from the traditional control strategy to the proposed virtual impedance control at t=0.4s, the reactive power output of the three inverters quickly converged to a new steady state, reaching 1907var, 1912var, and 1913var respectively. The reactive power distribution errors were -0.192%, 0.070%, and 0.122%, respectively, with the maximum distribution error decreasing by two orders of magnitude, a significant improvement compared to the 0~0.4s range. At t=1.2s, with an additional 3kW + 3kvar load, the active power output of the inverters was still reasonably evenly distributed, with reactive power outputs of 2782var, 2789var, and 2789var respectively. The reactive power distribution errors were -0.167%, 0.084%, and 0.084%, respectively, all far less than 1%, demonstrating the robustness of the proposed distribution strategy under disturbances.

[0085] Next, the circulating current characteristics between inverters are analyzed. Figure 8 The waveforms and partial magnification of the A-phase output current of each inverter under the proposed reactive power distribution strategy are presented. During the 0-0.4s period, when using traditional droop control, the output current of the inverters exhibits significant amplitude and phase differences due to variations in the line impedance from each inverter to the PCC, with a maximum reactive circulating current peak of 1.98A. After switching to the proposed control strategy at 0.4s, the output A-phase current curves of the three inverters essentially overlap. While the current amplitude increases after load changes, the circulating current remains approximately zero. This demonstrates that the proposed adaptive virtual impedance strategy effectively reduces system circulating current and improves power quality.

[0086] Specifically, the simulation of all VSG controls is performed as follows: Simulations were performed on a homogeneous system using VSG control in islanded mode, with identical control parameters matched to the droop control parameters. During the 0~1.2s period, the load power setpoint was 6kW+6kvar; during the 1.2s~2s period, the load power increased to 9kW+9kvar. Figure 9 It can be seen that, since the virtual moment of inertia and virtual damping coefficient are equal in steady state, the active power output of the GFM remains consistent.

[0087] When adaptive virtual impedance is not enabled, Figure 10 The maximum reactive power error shown is 50%. After the virtual impedance is applied at 0.4s, the inverter's output reactive power is 1907var, 1913var, and 1912var, with reactive power distribution errors of 0.192%, -0.070%, and -0.122%, respectively. After the load increases at 1.2s, the inverter's output reactive power is 2783var, 2790var, and 2789var, with reactive power distribution errors of 0.155%, -0.096%, and -0.060%, respectively. The reactive power distribution characteristics are improved, indicating that the proposed reactive power distribution strategy is also applicable to VSG control.

[0088] Figure 11 The A-phase current curves of the three inverters using VSG control are shown. During the 0-0.4s interval without virtual impedance, due to the non-negligible difference in equivalent impedance between the lines, the inverter output current phasors deviate, and the maximum circulating current remains at 1.98A. After the proposed control strategy is applied at 0.4s, the A-phase current waveforms of each inverter essentially overlap. The proposed control strategy suppresses the circulating current between parallel inverters, ensuring that the distributed units operate at rated power.

[0089] Specifically, the simulation of the heterogeneous parallel converter system (including two droop-controlled converters and one VSG-controlled converter) is as follows: To analyze the interaction characteristics between inverters operating in parallel with different control strategies under actual conditions, a three-unit heterogeneous operating condition is simulated. GFM1 and GFM2 employ droop control with the same coefficients, while GFM3 employs VSG control with corresponding parameters. The three inverters are operated in parallel, and the output power response and current waveforms are observed. The adaptive virtual impedance is engaged at t=0.4s, load 2 is added at t=1s, and the proposed voltage secondary control strategy is engaged at t=1.6s. The inverter's output reactive power waveform is as follows: Figure 12 As shown, during the period from 0.4s to 1s, the steady-state reactive power was 1924var, 1928var, and 1930var, respectively, and the calculated power distribution errors were 0.173%, -0.035%, and -0.138%, respectively. The situation was similar during the load increase phase.

[0090] To verify the effectiveness of the proposed secondary voltage control in a heterogeneous parallel converter system and its impact on reactive power distribution performance, the proposed secondary voltage control was activated at t=1.6s, and the voltage change at the PCC point and the output reactive power change were observed. Figure 13 It can be seen that with the implementation of the virtual impedance, the voltage at point PCC dropped from 220.5V to 217.4V, and then further dropped to 214.8V when the load increased after 1.2s. After implementing the proposed secondary voltage control, by compensating for the voltage deviation between adjacent units, the bus voltage recovered to 219V, and the deviation of the PCC voltage from its steady-state value was reduced by 73.68%. At this point... Figure 12 The steady-state reactive power of the three generators is 2930var, 2935var, and 2936var, respectively, and the power distribution errors are 0.125%, -0.045%, and -0.08%, respectively. This indicates that accurate reactive power distribution can still be achieved between the DG units after voltage compensation is added.

[0091] Figure 14The circulating current waveforms among the inverters in a heterogeneous parallel converter system are shown. From 0 to 0.4 s, the maximum circulating current among the inverters is 1.97 A. After the proposed control strategy is applied at 0.4 s, the phases of the output A-phase currents are basically the same, and the amplitude ratio is approximately 1:1:1. This demonstrates that the virtual impedance control strategy proposed in this paper is also applicable to heterogeneous parallel converter systems, ensuring high-precision reactive power distribution among the converters.

[0092] Figure 15 The transient frequency characteristics of the heterogeneous system were demonstrated. Compared with the homogeneous system, the heterogeneous parallel converter system exhibited smaller frequency oscillation amplitudes and faster decay, indicating that connecting converters with different dynamic characteristics can improve the transient stability of isolated microgrids. From the perspective of frequency recovery time, the transient settling times of the homogeneous droop control, homogeneous VSG, and heterogeneous systems were 0.302s, 0.401s, and 0.325s, respectively. This is because the VSG unit provides virtual inertia and damping, reducing the system's frequency change rate, while the droop control provides rapid primary regulation. The parallel connection of these two forms a "fast-slow complementarity," achieving a balance between peak frequency deviation and steady-state time response.

[0093] The above embodiments demonstrate that the strategy proposed in this invention can effectively solve the reactive power distribution and circulating current problems of heterogeneous parallel converter systems, and improve system voltage quality and transient performance.

[0094] Please see Figure 16 This application also provides a reactive power distribution system for heterogeneous parallel converters, the system comprising: The data acquisition module is used to acquire the operation and control data of the heterogeneous parallel converter system, which includes a droop-controlled converter and a virtual synchronous generator controlled converter. The model building module is used to build a reactive power allocation model based on the operation control data; The calculation module is used to calculate the output reactive power of each converter, the average reactive power of the system, and the reactive circulating current component based on the operation control data. The impedance adjustment module is used to generate an adaptive virtual impedance adjustment amount based on the reactive power distribution model, output reactive power, system average reactive power, and reactive circulating current component. The voltage control module is used to determine the total virtual impedance based on the adaptive virtual impedance adjustment and the constant virtual impedance, and to correct the voltage control quantity of each converter based on the total virtual impedance. The result output module is used to generate voltage compensation based on the voltage deviation at the point of common coupling, and adjust the output voltage reference value of each converter in combination with the voltage control quantity to obtain the reactive power distribution result.

[0095] It is understood that the content of the above method embodiments is applicable to this system embodiment. The specific functions implemented in this system embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0096] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the above-described method. This electronic device can be any smart terminal, including tablet computers, in-vehicle computers, etc.

[0097] It is understood that the content of the above method embodiments is applicable to this device embodiment. The specific functions implemented by this device embodiment are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0098] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0099] It is understood that the content of the above method embodiments is applicable to this storage medium embodiment. The specific functions implemented in this storage medium embodiment are the same as those in the above method embodiments, and the beneficial effects achieved are also the same as those achieved in the above method embodiments.

[0100] This application also provides a computer program product, including a computer program that, when executed by a processor, implements the above-described method.

[0101] It is understood that the content of the above method embodiments is applicable to the embodiments of this program product. The specific functions implemented by the embodiments of this program product are the same as those of the above method embodiments, and the beneficial effects achieved are also the same as those achieved by the above method embodiments.

[0102] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0103] This application provides a method and system for reactive power allocation in heterogeneous parallel converters. This scheme acquires the operating control data of the heterogeneous parallel converter system and constructs a reactive power allocation model, achieving unified modeling and coordinated control of droop-controlled converters and virtual synchronous generator-controlled converters. Compared to existing technologies, this invention can achieve adaptive and precise reactive power allocation among heterogeneous converters. By introducing an adaptive virtual impedance adjustment mechanism based on the system's average reactive power and reactive circulating current components, it effectively suppresses circulating current within the parallel system, reduces power coupling and imbalance problems between converters with different control strategies, and improves the accuracy and dynamic stability of reactive power allocation. Simultaneously, it corrects the voltage control quantity through the total virtual impedance and generates a voltage compensation quantity based on the voltage deviation at the point of common coupling (PCC), achieving secondary adjustment of the output voltage reference value and enhancing the PCC voltage support capability and voltage recovery speed. Furthermore, this method reduces reliance on manual parameter tuning, improves the system's adaptability and robustness to changes in operating conditions and parameter disturbances, enhances dynamic response performance and convergence characteristics, and improves the engineering applicability and operational reliability of heterogeneous parallel systems.

[0104] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0105] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0106] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0107] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0108] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A method for reactive power distribution in heterogeneous parallel converters, characterized in that, The method includes the following steps: Acquire the operation control data of the heterogeneous parallel converter system; the heterogeneous parallel converter system includes a droop-controlled converter and a virtual synchronous generator controlled converter; Based on the aforementioned operation control data, a reactive power allocation model is constructed; Based on the aforementioned operation control data, calculate the output reactive power of each converter, the system average reactive power, and the reactive circulating current component; Based on the reactive power allocation model, the output reactive power, the system average reactive power, and the reactive circulating current component, an adaptive virtual impedance adjustment is generated. Based on the adaptive virtual impedance adjustment and the constant virtual impedance, the total virtual impedance is determined, and the voltage control quantity of each converter is corrected based on the total virtual impedance. The voltage compensation amount is generated based on the voltage deviation at the point of common coupling, and the output voltage reference value of each converter is adjusted in conjunction with the voltage control amount to obtain the reactive power distribution result.

2. The method according to claim 1, characterized in that, The operation control data includes the output reactive power information, output current information, point of common coupling voltage information, and system circulating current information of each converter, as well as the corresponding control parameter information; the control parameter information includes droop control parameters, virtual synchronous generator control parameters, and virtual impedance parameters.

3. The method according to claim 1, characterized in that, The step of constructing a reactive power allocation model based on the operational control data includes: Based on the aforementioned operation control data, extract the control type information and corresponding control parameter information for each converter; Based on the control type information and control parameter information, a functional mapping relationship between the reactive power of each converter and the reference value of the output voltage is established. Based on the aforementioned function mapping relationship, the reactive power regulation characteristics of converters with different control types are equivalently characterized to form a reactive power expression form. Based on the aforementioned reactive power expression, a reactive power allocation model for a heterogeneous parallel converter system is constructed.

4. The method according to claim 1, characterized in that, The calculation of the output reactive power of each converter, the system average reactive power, and the reactive circulating current component based on the operation control data includes: Based on the output voltage and output current information of each converter in the operation control data, the reactive power output of each converter is calculated in the synchronous rotating coordinate system. The reactive power output of each converter is averaged to obtain the system average reactive power. Based on the deviation between the output reactive power of each converter and the average reactive power of the system, the reactive power deviation of each converter is determined. Based on the correlation between the output voltage difference information and the output current information of each converter, the voltage coupling component between converters is extracted, and the reactive circulating current component is determined.

5. The method according to claim 1, characterized in that, The step of generating an adaptive virtual impedance adjustment based on the reactive power allocation model, the output reactive power, the system average reactive power, and the reactive circulating current component includes: Based on the reactive power allocation model, the output reactive power and the system average reactive power are mapped by the model to obtain the reactive power allocation deviation. The reactive circulating current component is modeled equivalently to obtain the circulating current compensation amount; The reactive power distribution deviation and the circulating current compensation are combined to obtain the comprehensive adjustment amount; Based on the comprehensive adjustment amount, and using a proportional-integral control algorithm for adaptive adjustment, an adaptive virtual impedance adjustment amount is generated.

6. The method according to claim 5, characterized in that, The formula for calculating the adaptive virtual impedance adjustment is as follows: ； in, This indicates the amount of adaptive virtual impedance adjustment; Represents constant virtual inductive impedance; Indicates adaptive virtual sensing impedance; and These represent the reactive power proportional coefficient and integral coefficient of the adaptive virtual reactance, respectively. and These represent the circulation proportionality coefficient and integral coefficient, respectively; This represents the average reactive power of the inverter. Indicates the first The actual output reactive power of the converter; s represents the Laplace operator; This represents the average value of the reactive circulating current component along the q-axis of the converter. Indicates the first The q-axis reactive circulating current component of the converter.

7. The method according to claim 1, characterized in that, The step of determining the total virtual impedance based on the adaptive virtual impedance adjustment and the constant virtual impedance, and correcting the voltage control quantity of each converter based on the total virtual impedance, includes: The adaptive virtual impedance adjustment is superimposed on the constant virtual impedance to obtain the total virtual impedance value; Based on the total virtual impedance value, it is directly applied to the converter voltage control feedforward link to construct an equivalent output impedance adjustment amount; The converter voltage reference value is mapped and corrected based on the equivalent output impedance adjustment to generate a voltage control correction value.

8. The method according to claim 1, characterized in that, The process of generating a voltage compensation amount based on the voltage deviation at the point of common coupling, and adjusting the output voltage reference values ​​of each converter in conjunction with the voltage control amount to obtain the reactive power distribution result includes: Obtain the actual voltage value and voltage reference value at the point of common coupling; The voltage deviation at the point of common coupling is determined based on the deviation between the actual voltage value and the reference voltage value. Based on the voltage deviation at the common connection point, a voltage compensation amount is generated through a voltage secondary control algorithm. The voltage compensation amount is sent to each converter and superimposed with the voltage control amount of each converter to obtain the output voltage reference value of each converter. The output voltage of each converter is adjusted based on the output voltage reference value to obtain the reactive power distribution result.

9. The method according to claim 8, characterized in that, The formula for calculating the voltage compensation amount is as follows: ； ； in, Indicates the first Voltage compensation amount of the distributed generation unit; Indicates the voltage compensation amount at the point of common coupling; This represents the bus voltage control coefficient; This indicates the actual voltage measured at the point of common coupling; and These represent the proportional and integral coefficients of the voltage secondary control, respectively; s represents the Laplace operator; n represents the total number of converters in the parallel system; j represents the number of converters connected to the second-order converter. Any other unit that interacts with the platform for information exchange Unit number; Indicates the first Voltage compensation amount of the unit.

10. A reactive power distribution system for heterogeneous parallel converters, characterized in that, The system includes: The data acquisition module is used to acquire the operation and control data of the heterogeneous parallel converter system; the heterogeneous parallel converter system includes a droop-controlled converter and a virtual synchronous generator controlled converter. The model building module is used to build a reactive power allocation model based on the operation control data. The calculation module is used to calculate the output reactive power of each converter, the average reactive power of the system, and the reactive circulating current component based on the operation control data. The impedance adjustment module is used to generate an adaptive virtual impedance adjustment amount based on the reactive power distribution model, the output reactive power, the system average reactive power, and the reactive circulating current component. The voltage control module is used to determine the total virtual impedance based on the adaptive virtual impedance adjustment and the constant virtual impedance, and to correct the voltage control amount of each converter based on the total virtual impedance. The result output module is used to generate a voltage compensation amount based on the voltage deviation at the point of common coupling, and adjust the output voltage reference value of each converter in combination with the voltage control amount to obtain the reactive power distribution result.

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