Inverter control method and system based on virtual synchronous generator control

Abstract

The invention provides an inverter control method and system based on virtual synchronous generator control, relates to the technical field of power grids, and aims to enable an inverter to provide voltage and frequency support in a weak power grid scene and improve the robustness and stability of a power system. The inverter is a three-phase four-bridge-arm T-type three-level inverter. The method comprises the following steps of: calculating actual values of active power and reactive power by sampling three-phase voltage and current of a network side; and adjusting the virtual angular frequency and the voltage phase angle of the inverter through a VSG control strategy by using the actual value of the active power. And generating an electromotive force amplitude of the inverter by using the actual value of the reactive power through a VSG control strategy. And modulating the three-phase reference voltage generated based on the values through a double-closed-loop control strategy to obtain a modulated two-phase reference voltage. And inversely transforming the modulated two-phase reference voltage back to the three-phase static coordinate system to generate a three-phase inversion voltage, and generating a switching signal of the inverter according to the voltage to drive a switching device of the inverter.

Description

Technical Field

[0001] The present application relates to the field of power grid technology, and in particular to a control method and system for an inverter based on virtual synchronous generator control. Background Art

[0002] Currently, the volatility and uncertainty of renewable energy integration into the power system pose challenges to grid operations. As renewable energy sources become increasingly prevalent in the grid, power fluctuations can lead to unstable voltage and frequency, and even grid collapse.

[0003] In traditional power systems, grid stability relies primarily on the mechanical inertia generated by large rotating turbines or synchronous generators in fossil fuel power plants. This mechanical inertia protects against grid speed fluctuations and helps regulate grid voltage and frequency, thereby maintaining grid stability. However, with the integration of high-proportion renewable energy sources such as photovoltaics and wind power, synchronous generators are no longer able to provide inertial support for the grid, resulting in reduced grid stability after the loss of mechanical inertia. In the context of renewable energy integration, the most widely used inverters are based on a phase-locked loop (PLL) grid-following control strategy, which outputs a predetermined current waveform by detecting the grid voltage phase.

[0004] The grid-following inverter has a simple structure and is easy to implement. It is suitable for scenarios where the grid is stable and has small fluctuations. However, it is highly dependent on the grid, lacks the ability to support voltage and frequency, and is difficult to cope with complex operating conditions such as island operation and weak grid disturbances. Summary of the Invention

[0005] The present application provides a control method and system for an inverter based on virtual synchronous generator control, which enables the inverter to provide voltage and frequency support in weak power grid scenarios, thereby improving the robustness and stability of the power system.

[0006] In a first aspect, a control method for an inverter based on virtual synchronous generator control is provided, wherein the inverter is a three-phase four-leg T-type three-level inverter, and the method includes: Determine the actual value of active power and reactive power based on the three-phase voltage and three-phase current sampled on the grid side. The grid side refers to the side where the inverter is connected to the grid. According to the actual value of active power, the virtual angular frequency of the inverter and the generated voltage phase angle are adjusted through the active frequency loop of the virtual synchronous generator control strategy; According to the actual value of reactive power, the electromotive force amplitude of the inverter is generated through the reactive voltage loop of the virtual synchronous generator control strategy; Generate a three-phase reference voltage in a three-phase stationary coordinate system according to the voltage phase angle and the electromotive force amplitude; Perform coordinate transformation on the three-phase reference voltage to obtain a two-phase reference voltage in a two-phase rotating coordinate system; The two-phase reference voltage is modulated by dual closed-loop decoupling control of the voltage outer loop and the current inner loop to obtain a modulated two-phase reference voltage; The modulated two-phase reference voltage is inversely transformed into a three-phase stationary coordinate system to generate a three-phase inverter voltage; generating a switching signal of an inverter according to the three-phase inverter voltage; The switching devices of the inverter are driven according to the switching signals.

[0007] In a feasible design, generating a switching signal of an inverter according to the three-phase inverter voltage includes: Determine the midpoint voltage adjustment amount that is in opposite phase to the three-phase inverter voltage according to the voltage extreme value of the three-phase bridge arm to the midpoint of the inverter; The midpoint voltage regulation amount is added to the three-phase inverter voltage Phase voltage, Phase voltage and Phase voltage, to achieve compensation for the three-phase inverter voltage; The switching signal of the inverter is generated according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount.

[0008] In a feasible design, the midpoint voltage regulation amount is determined according to the voltage extreme value of the three-phase bridge arm of the inverter to the midpoint; the midpoint voltage regulation amount is added to the three-phase inverter voltage. Phase voltage, Phase voltage and Phase voltage, using the following formula: ; ; ; ; in, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the midpoint voltage regulation amount, express 、 and The maximum value of express 、 and The minimum value of Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage.

[0009] In a feasible design, generating a switching signal of the inverter according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount includes: Compare the compensated three-phase inverter voltage with the triangle carrier to generate the inverter Phase bridge arm, Phase bridge arm and Switching signal of the phase bridge arm; The midpoint voltage regulation amount is compared with the triangular carrier to generate a switching signal for the fourth bridge arm of the inverter.

[0010] In a feasible design, the two-phase reference voltage is modulated by dual closed-loop decoupling control of the voltage outer loop and the current inner loop to obtain the modulated two-phase reference voltage, including: Perform coordinate transformation on the three-phase voltage to obtain the voltage sampling value in the two-phase rotating coordinate system; Perform coordinate transformation on the three-phase current to obtain the current sampling value in the two-phase rotating coordinate system; The error between the two-phase reference voltage and the voltage sampling value is input into the proportional-integral controller of the voltage outer loop to obtain the current reference value; The error between the current reference value and the current sampling value is input into the proportional-integral controller of the current inner loop, and after decoupling processing, the modulated two-phase reference voltage is obtained.

[0011] In a feasible design, the virtual angular frequency of the inverter is adjusted according to the actual value of the active power through the active frequency loop of the virtual synchronous generator control strategy, including: According to the actual value of active power and the reference value of active power, the virtual angular frequency of the inverter is dynamically adjusted in combination with the equivalent virtual inertia and the damping coefficient.

[0012] In one possible design, the method includes: The equivalent virtual inertia is determined according to the system capacity corresponding to the inverter.

[0013] In one possible design, the method includes: The damping coefficient is determined according to the sensitivity of power disturbance to frequency and the equivalent virtual inertia.

[0014] In a second aspect, a control system for an inverter based on virtual synchronous generator control is provided. The inverter is a three-phase four-leg T-type three-level inverter. The system includes: Active power and reactive power determination module, used to determine the actual value of active power and reactive power based on the three-phase voltage and three-phase current sampled from the grid side, where the grid side refers to the side where the inverter is connected to the grid; The virtual angular frequency adjustment module is used to adjust the virtual angular frequency of the inverter and generate the voltage phase angle according to the actual value of the active power through the active frequency loop of the virtual synchronous generator control strategy: A voltage regulation module is used to generate the electromotive force amplitude of the inverter through the reactive voltage loop of the virtual synchronous generator control strategy according to the actual value of reactive power; The voltage regulation module is further used to generate a three-phase reference voltage in a three-phase stationary coordinate system according to the voltage phase angle and the electromotive force amplitude; The voltage regulation module is also used to perform coordinate transformation on the three-phase reference voltage to obtain a two-phase reference voltage in a two-phase rotating coordinate system; The voltage regulation module is further used to modulate the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop to obtain a modulated two-phase reference voltage; The voltage regulation module is also used to inversely transform the modulated two-phase reference voltage into a three-phase stationary coordinate system to generate a three-phase inverter voltage; A switching signal generating module, used for generating a switching signal of an inverter according to a three-phase inverter voltage; The switching device driving module is used to drive the switching device of the inverter according to the switching signal.

[0015] The embodiments of the present application are designed based on the principle of a virtual synchronous generator. By simulating the inertia and damping characteristics of a traditional synchronous generator, the three-phase four-bridge-leg T-type three-level inverter is able to independently construct the voltage and frequency of the power grid. This fully utilizes the advantages of high efficiency and high power quality of the three-phase four-bridge-leg T-type three-level inverter, enhances the inverter's adaptability in complex power systems, and enables the inverter to play an important role in power grid operation.

[0016] Specifically, by treating the inverter as a synchronous generator, the active frequency loop of the virtual synchronous generator control strategy adjusts the inverter's virtual angular frequency based on the actual active power value, thereby achieving frequency support. This frequency support function enables the inverter to provide effective frequency support in weak grid scenarios, thereby improving the robustness and stability of the entire power system. In this way, the inverter can not only cope with various fluctuations and disturbances in the grid, but also alleviate the vulnerability of the grid to a certain extent, ensuring the continuity and reliability of power supply. The reactive voltage loop of the virtual synchronous generator control strategy dynamically generates the electromotive force amplitude based on the actual reactive power value to maintain the stability of the output voltage amplitude and ensure voltage quality. After generating a three-phase reference voltage in a three-phase stationary coordinate system based on the voltage phase angle and electromotive force amplitude, a coordinate transformation is performed to obtain a two-phase reference voltage in a two-phase rotating coordinate system. Modulating the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop achieves stable control of the voltage amplitude and phase, effectively suppressing fluctuations caused by internal system disturbances and external loads, and further improving the robustness and dynamic response of the power system. The modulated two-phase reference voltage is inversely transformed into a three-phase stationary coordinate system to generate a three-phase inverter voltage. The switching signal of the inverter is generated according to the three-phase inverter voltage. The switching device of the inverter is driven according to the switching signal, thereby controlling the inverter to stably output a voltage signal, so that the power system to which the inverter belongs has the ability to self-regulate and support voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 This is a schematic flow chart of a control method for an inverter based on virtual synchronous generator control provided by an exemplary embodiment of the present application; Figure 2 This is a circuit topology diagram of a three-phase four-leg T-type three-level inverter provided by an exemplary embodiment of the present application; Figure 3 This is a schematic diagram of an active frequency loop provided by an exemplary embodiment of the present application; Figure 4 This is a schematic diagram of a reactive voltage loop provided by an exemplary embodiment of the present application; Figure 5 This is a schematic diagram of an exemplary embodiment of the present application providing an example of a triangular carrier modulating the on-off of a switching device; Figure 6This is a schematic diagram of active power output of a three-phase four-leg T-type three-level inverter network strategy provided by an exemplary embodiment of the present application; Figure 7 This is a schematic diagram of reactive power output of a three-phase four-leg T-type three-level inverter network strategy provided by an exemplary embodiment of the present application; Figure 8 This is a diagram showing a voltage pre-synchronization result of a three-phase four-leg T-type three-level inverter network strategy provided by an exemplary embodiment of the present application. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0020] At present, when connecting to renewable energy, the power grid system faces the challenges of frequency fluctuations, insufficient inertia and reduced stability. As a key device, the inverter lacks the inherent inertia characteristics of the synchronous generator if it adopts grid-type control technology, which will pose a threat to the stable operation of the power grid. Therefore, this application proposes an innovative solution, which is to integrate the virtual synchronous generator (VSG) technology into the three-phase four-leg T-type three-level inverter to simulate the inertia, damping and frequency response characteristics of the synchronous generator. The introduction of this technology aims to give the inverter the ability of adaptive adjustment and rapid response, thereby enhancing its adaptability to complex disturbances in the power grid and significantly improving the frequency support capability of the power grid and the dynamic stability of the voltage.

[0021] like Figure 1 As shown, the present application provides a control method for an inverter based on virtual synchronous generator control, wherein the inverter is a three-phase four-leg T-type three-level inverter, and the method includes: S110 , determining an actual value of active power and an actual value of reactive power according to the three-phase voltage and three-phase current obtained by sampling the grid side.

[0022] The grid side refers to the side where the inverter is connected to the grid.

[0023] like Figure 2As shown in the figure, this application provides a circuit topology diagram of a three-phase four-bridge-leg T-type three-level inverter, which includes three parts: DC side power conversion, AC filtering and grid-connected interface. It can support the virtual synchronous generator control strategy to achieve DC to three-phase AC power conversion and grid-connected operation. The typical characteristics of the three-phase four-bridge-leg inverter are 、 、 A neutral line bridge arm is added to the three bridge arms With smoothing inductor The fourth bridge arm provides a stable midpoint for the system, providing a path for zero-sequence current while also meeting the neutral line requirements of electrical equipment.

[0024] Specifically, Figure 2 The T-type three-level bridge arm includes Phase bridge arm, Phase bridge arm, Phase bridge arm and the fourth bridge arm (i.e. bridge arm). Among them, The phase bridge arm consists of 4 switching tubes ( )constitute, The phase bridge arm consists of 4 switching tubes ( )constitute, The phase bridge arm consists of 4 switching tubes ( )constitute, The bridge arm consists of 4 switch tubes ( ) is composed of. The DC bus capacitor includes the positive bus capacitor and negative bus capacitor , the positive bus capacitor is connected in series with the negative bus capacitor to provide a neutral point (N) and suppress the DC side voltage ripple. The voltage of the positive bus capacitor is , the voltage of the negative bus capacitor is The DC bus voltage is . Point is the positive pole of the DC bus. Point is the negative pole of the DC bus. Point is the neutral point of the three-level inverter. 、 、 、 There are four connection points. 、 、 are the filter inductors, 、 、 They are filter capacitors respectively. 、 、 、 are the inverter current, 、 、 are the capacitor current, 、 、 are the load currents respectively.

[0025] Based on the three-phase voltage and three-phase current, the actual value of active power and the actual value of reactive power can be calculated according to the instantaneous power theory. First, by collecting the instantaneous values of the three-phase voltage and three-phase current, they are converted into a two-phase stationary or rotating coordinate system using Clarke transform or Park transform. In the two-phase coordinate system, the actual value of active power can be obtained by multiplying the d-axis component of the voltage and current, while the actual value of reactive power can be obtained by multiplying the q-axis component of the voltage and current. This method can reflect the power status of the system in real time and accurately, providing basic data for subsequent power control strategies. It can also be implemented in other ways, which are not limited in this application.

[0026] S120 , according to the actual value of the active power, adjusting the virtual angular frequency of the inverter and generating the voltage phase angle through the active frequency loop of the virtual synchronous generator control strategy.

[0027] In a feasible design, the virtual angular frequency of the inverter is adjusted according to the actual value of the active power through the active frequency loop of the virtual synchronous generator control strategy in the following way: According to the actual value of active power and the reference value of active power, the virtual angular frequency of the inverter is dynamically adjusted in combination with the equivalent virtual inertia and the damping coefficient.

[0028] For example, according to the actual value of active power and the reference value of active power, combined with the equivalent virtual inertia and the damping coefficient, the virtual angular frequency of the inverter is dynamically adjusted, which is achieved by the following formulas (1), (2), (3) and (4), where the active frequency loop is as follows: Figure 3 shown.

[0029] , formula (1); , formula (2); , formula (3); , formula (4); in, represents the expected output active power, Indicates the output active power reference value, Indicates the active loop proportional coefficient, Indicates the output frequency reference value, represents the virtual angular frequency of the inverter output, Indicates the actual value of active power (i.e. the actual active power output by the inverter). represents the damping coefficient, represents the equivalent virtual moment of inertia, Indicates time, Indicates the frequency deviation, Indicates the virtual angular frequency of the output after adjustment. Usually, empirical values are selected and obtained through experimental debugging, which can ensure that the system has good transient response, small static error and stability.

[0030] in, Figure 3 in for and The product of Represents the integral part of the transfer function. Figure 3 In the system, the system first compares the output frequency reference value and the virtual angular frequency of the inverter output , and get the frequency deviation The frequency deviation is proportional to the amplified, converted to power increments, and summed at the node with Superposition to form the expected output active power Expected output active power The actual value of active power Compare and After the link processing, through the mechanical rotation equation (by The inertial effect of the synchronous generator rotor is simulated (implemented in this step), slowing down the frequency mutation rate and providing the system with short-term energy buffering. The product of the damping coefficient and the frequency deviation is introduced as negative feedback into the mechanical rotation equation, introducing the mechanical damping effect into the control loop, rapidly dissipating the frequency oscillation energy and suppressing overshoot. Superimpose the final Get the adjusted virtual angular frequency Through the synergistic effect of the equivalent virtual moment of inertia and the damping coefficient, the active power loop retains the inertial response characteristics of the traditional synchronous machine and achieves high-precision frequency tracking through closed-loop feedback. When a disturbance occurs, the virtual inertia slows down the frequency change rate, providing "inertial support" for the system; the damping term accelerates the oscillation attenuation to avoid continuous instability; the dynamic correction of the power error further ensures that the steady-state frequency has no static error. These designs give the system both strong anti-interference capabilities and high dynamic performance, effectively supporting the frequency stability of weak power grids or isolated island microgrids.

[0031] For example, the voltage phase angle is generated using the following formula (5): , formula (5); in, It represents the voltage phase angle obtained by integrating the inverter output angular frequency.

[0032] The above example is based on the mechanical rotation equation. By introducing equivalent virtual inertia and damping coefficient, the inertial response and damping characteristics of the traditional synchronous generator are simulated, thereby achieving the output angular frequency of the inverter. Dynamic adjustment can enhance the frequency stability and anti-disturbance capability of the system. In the specific implementation, formula (1) is calculated by the active loop proportional coefficient Fast response frequency deviation ( ), dynamically correct the expected output active power , forming a preliminary frequency support; Formula (2) further converts the power deviation ( ) is related to the rate of change of frequency, where the equivalent virtual inertia is given by ( ) reflects the inertial buffering effect of the system on frequency fluctuations, slowing down the frequency mutation speed, while the damping coefficient suppresses frequency oscillation ( ) accelerates energy dissipation and avoids sustained fluctuations. The synergistic effect of these two factors enables the system to maintain short-term power balance through virtual inertia during sudden load changes or grid disturbances, while also enabling rapid convergence to a steady-state frequency with the help of the damping term, significantly improving both dynamic response speed and steady-state accuracy during transients. This model exhibits both high robustness and low error under complex operating conditions, effectively addressing frequency instability caused by a lack of physical inertia during renewable energy grid integration and providing autonomous frequency regulation capabilities for microgrids or weak grids.

[0033] The equivalent virtual moment of inertia reflects the virtual motor's ability to resist frequency disturbances. Larger values result in slower system frequency response to power fluctuations, exhibiting stronger inertia but also exhibiting response lag. Smaller values result in greater sensitivity to frequency changes and faster response, but are also prone to oscillation. To optimize the equivalent virtual moment of inertia, one feasible design determines the equivalent virtual inertia based on the inverter's corresponding system capacity.

[0034] For example, the following formula (6) is used to determine the equivalent virtual inertia according to the system capacity corresponding to the inverter: , formula (6); in, represents the inertia constant, Indicates the system capacity, Indicates the rated angular frequency.

[0035] The above formula (6) determines the equivalent virtual inertia, which can ensure that when the system capacity increases, the inertial support capability increases proportionally, avoiding excessive deterioration of the response lag caused by simply increasing J. When the system capacity decreases, the inertial support capability decreases proportionally, avoiding a significant increase in the oscillation risk caused by simply reducing J.

[0036] The inverter's system capacity directly determines the physical limits of its inertial response. In the example above, a larger capacity increases the configurable upper limit of the equivalent virtual inertia. This allows the inverter to release more power to mitigate sudden frequency fluctuations when the grid frequency fluctuates, significantly shortening the response time.

[0037] Similar to mechanical damping, it is used to reduce frequency oscillations in synchronous machines. A damping power is provided to smooth the frequency response of the system and prevent power angle oscillation. Mathematically, it is reflected as the damping term of the system's first-order low-pass filter. In order to optimize the damping coefficient, in a feasible design, the damping coefficient is determined based on the sensitivity of the power disturbance to frequency and the equivalent virtual inertia.

[0038] Exemplarily, the following formula (7) is used to determine the damping coefficient according to the sensitivity of the power disturbance to the frequency.

[0039] , formula (7); in, Indicates the typical damping ratio, which is generally between 0.7 and 1.0. It represents the sensitivity of power disturbance to frequency, and is usually a constant obtained through experience or simulation fitting.

[0040] In the above example, by comprehensively considering the sensitivity of power disturbance to system frequency and the effect of equivalent virtual inertia, the damping coefficient can be accurately calculated. This design strategy aims to set the system's damping coefficient to or slightly above critical damping, ensuring a stable frequency response and avoiding oscillations in the face of power disturbances. This design approach significantly improves the system's dynamic performance and ensures stable operation of the power system.

[0041] Furthermore, the above The determination method limits the value range of the equivalent virtual inertia, avoids power angle instability, and can balance the technical contradiction between response speed and stability.

[0042] S130 , generating an electromotive force amplitude of the inverter through a reactive voltage loop of a virtual synchronous generator control strategy according to the actual value of the reactive power.

[0043] For example, according to the actual value of reactive power, the reactive voltage loop of the virtual synchronous generator control strategy generates the electromotive force amplitude of the inverter, which is implemented by the following formulas (8) and (9), where the reactive voltage loop is as follows: Figure 4 shown.

[0044] , formula (8); , formula (9); in, represents the expected output reactive power, Indicates the output reactive power reference value, Represents the reactive loop proportional coefficient, Indicates the rated voltage reference value, Indicates the voltage sampling value, represents the integral coefficient, Indicates the actual value of reactive power (i.e. output reactive power sampling value), represents the electromotive force amplitude, Indicates the inverter electromotive force reference value.

[0045] in, and It can ensure that the system has good transient response, small static error and stability, and Usually, empirical values are selected and obtained through experimental debugging.

[0046] exist Figure 4 In the system, the voltage deviation ( )through Amplification directly reflects the degree of voltage deviation. The amplified voltage deviation is added to the output reactive power reference value. The expected output reactive power is obtained Expected output reactive power and output reactive power sampling value The difference is converted into the adjustment value of the inverter electromotive force reference value through the proportional integral link, and the inverter electromotive force amplitude is obtained by adding the adjustment value to the inverter electromotive force reference value. for and The product of Indicates the integration link.

[0047] The virtual synchronous generator control strategy proposed in the above example achieves the goal of adjusting the inverter output voltage amplitude in real time according to the power error through the dynamic adjustment mechanism of the reactive voltage loop, thereby effectively ensuring the steady-state accuracy and anti-disturbance capability of the system. Specifically, the voltage deviation ( ) and output reactive power reference value Combined to generate the desired output reactive power , providing a dynamic correction benchmark for the reactive voltage loop; Formula (9) further uses the integral link ( ) Convert the reactive power tracking error into the adjustment value of the inverter electromotive force reference value, use the adjustment value to adjust the inverter electromotive force reference value and then output the inverter electromotive force amplitude. Among them, the proportional coefficient Quickly respond to voltage fluctuations to suppress transient deviations, integral coefficient The steady-state error is gradually eliminated. The two work together to ensure that the system can quickly converge to a stable state when the load changes suddenly or the grid is disturbed, while maintaining high-precision voltage amplitude control.

[0048] S140 , generating a three-phase reference voltage in a three-phase stationary coordinate system according to the voltage phase angle and the electromotive force amplitude.

[0049] For example, the three-phase reference voltage in the three-phase stationary coordinate system is generated according to the voltage phase angle and the electromotive force amplitude, and is implemented using the following formulas (10), (11), and (12): , formula (10); , formula (11); , formula (12); in, Indicates the three-phase stationary coordinate system Phase reference voltage, Indicates the three-phase stationary coordinate system Phase reference voltage, Indicates the three-phase stationary coordinate system Phase reference voltage.

[0050] S150 , performing coordinate transformation on the three-phase reference voltage to obtain a two-phase reference voltage in a two-phase rotating coordinate system.

[0051] Specifically, the three-phase reference voltage is transformed into a two-phase rotating coordinate system. The reference quantity on the axis is shown in the following formula (13): , formula (13); in, Indicates the two-phase rotating coordinate system Axis reference voltage, Indicates the two-phase rotating coordinate system Axis reference voltage, Indicates the two-phase rotating coordinate system Axis reference voltage.

[0052] visible The shaft reference voltage is the inverter electromotive force amplitude, and Axis reference voltage and The axis reference voltage is all 0.

[0053] S160 , modulating the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop to obtain a modulated two-phase reference voltage.

[0054] In a feasible design, the following method is used to modulate the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop to obtain the modulated two-phase reference voltage: Perform coordinate transformation on the three-phase voltage to obtain the voltage sampling value in the two-phase rotating coordinate system; Perform coordinate transformation on the three-phase current to obtain the current sampling value in the two-phase rotating coordinate system; The error between the two-phase reference voltage and the voltage sampling value is input into the proportional-integral controller of the voltage outer loop to obtain the current reference value; The error between the current reference value and the current sampling value is input into the proportional-integral controller of the current inner loop, and after decoupling processing, the modulated two-phase reference voltage is obtained.

[0055] by Figure 2 As an example of the circuit topology shown in the figure, the grid-side A phase voltage obtained by sampling , B phase voltage , C phase voltage , respectively, perform coordinate transformation to obtain the voltage sampling value in the two-phase rotating coordinate system 、 The grid-side A phase current obtained by sampling , B phase current , C phase current , respectively, perform coordinate transformation to obtain the current sampling value in the two-phase rotating coordinate system 、 Among them, the inverter Phase is connected to the grid side A phase, the inverter Phase is connected to the grid side B phase, the inverter Phase is connected to the grid side C phase. The value of the axis reference voltage and voltage sampling value The error in the two-phase reference voltage The axis reference voltage value 0 and the voltage sampling value The errors are input to the proportional integral controller of the voltage outer loop to obtain the current reference value and . Set the current reference value and current sampling value The error and current reference value and current sampling value The error is input to the proportional integral controller of the current inner loop, and after decoupling processing, the modulated two-phase reference voltage is obtained. and .

[0056] This embodiment achieves precise and stable control of voltage amplitude and phase through a cascaded decoupling control architecture consisting of an outer voltage loop and an inner current loop. Specifically, the outer voltage loop transforms the three-phase voltage into voltage samples in a two-phase rotating coordinate system. After comparing these values with the reference voltage, the outer current loop generates a current reference value through a proportional-integral controller. This process eliminates steady-state errors through the integral element, accurately locking the voltage amplitude target. The inner current loop then inputs the deviation between the current reference value and the transformed two-phase current sample values into a proportional-integral controller. Combined with decoupling compensation, it dynamically eliminates current oscillations caused by fluctuations in inductance and capacitance parameters and sudden load changes, thereby rapidly correcting voltage phase offset and achieving precise phase tracking. With the dual loops working together, the outer loop prioritizes voltage amplitude tracking and load disturbance resistance in the low-frequency band, while the inner loop ensures rapid current response and harmonic suppression in the high-frequency band. This allows the inverter system to effectively suppress internal system disturbances and fluctuations caused by external loads, maintaining high-precision voltage amplitude control under complex operating conditions and improving the robustness and dynamic performance of the control system.

[0057] S170 , inversely transforming the modulated two-phase reference voltage into a three-phase stationary coordinate system to generate a three-phase inverter voltage.

[0058] Continue with Figure 2 As an example of the circuit topology shown in the figure, the modulated two-phase reference voltage and Inverse transformation to the three-phase stationary coordinate system generates the three-phase inverter voltage Phase voltage , Phase voltage and Phase voltage .

[0059] S180 , generating a switching signal for the inverter according to the three-phase inverter voltage.

[0060] In a feasible design, the switching signal of the inverter is generated according to the three-phase inverter voltage in the following manner: Determine the midpoint voltage adjustment amount that is in opposite phase to the three-phase inverter voltage according to the voltage extreme value of the three-phase bridge arm to the midpoint of the inverter; The midpoint voltage regulation amount is added to the three-phase inverter voltage Phase voltage, Phase voltage and Phase voltage, to achieve compensation for the three-phase inverter voltage; The switching signal of the inverter is generated according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount.

[0061] Continue with Figure 2 As an example of the circuit topology shown in the figure, according to the three-phase bridge arm of the inverter (i.e. Phase bridge arm, Phase bridge arm and The voltage extreme value of the phase bridge arm to the midpoint O determines the midpoint voltage regulation amount that is opposite to the three-phase inverter voltage . Adjust the midpoint voltage Superimposed on the three-phase inverter voltage Phase voltage 、 Phase voltage and Phase voltage , after compensation Phase voltage , after compensation Phase voltage and after compensation Phase voltage The switching signal of the inverter is generated according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount.

[0062] The above example, based on the introduction of a fourth bridge arm structure, generates a midpoint voltage adjustment variable in real time based on the maximum and minimum values of the three-phase voltages, which is in phase with the three-phase inverter voltage, forcing adjustments to the output voltages of each phase. Because the midpoint voltage adjustment variable can reflect the degree of imbalance in the three-phase voltages in real time, when the voltage of a phase is high (or low), the midpoint voltage adjustment variable acts as a negative compensation voltage to offset the offset of the midpoint potential, thereby achieving dynamic regulation and stable control of the midpoint voltage, effectively preventing midpoint drift and improving the long-term reliability of the system.

[0063] In a feasible design, the midpoint voltage regulation amount is determined according to the voltage extreme value of the three-phase bridge arm of the inverter to the midpoint; the midpoint voltage regulation amount is added to the three-phase inverter voltage. Phase voltage, Phase voltage and Phase voltage, using the following formula (14), formula (15), formula (16) and formula (17): , formula (14); , formula (15); , formula (16); , formula (17); in, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the midpoint voltage regulation amount, express 、 and The maximum value of express 、 and The minimum value of Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage.

[0064] The above example calculates the maximum value of the three-phase bridge arm voltage in real time and minimum value , characterizes the degree of three-phase load imbalance; the reverse compensation voltage is generated by formula (17) , to offset the influence of the three-phase voltage extreme value difference on the midpoint potential; Superimposed on the voltage of each phase bridge arm, forcing the inverter to output three-phase voltage 、 and The midpoint potential approaches the DC bus midpoint O, realizing dynamic regulation and stable control of the midpoint voltage.

[0065] In a feasible design, the switching signal of the inverter is generated according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount in the following manner: Compare the compensated three-phase inverter voltage with the triangle carrier to generate the inverter Phase bridge arm, Phase bridge arm and Switching signal of the phase bridge arm; The midpoint voltage regulation amount is compared with the triangular carrier to generate a switching signal for the fourth bridge arm of the inverter.

[0066] The switching signal is used to define the conduction duty cycle and frequency of the switching device.

[0067] For example Figure 5 As shown (where the vertical axis represents the level, the horizontal axis represents the represents the phase angle), with modulation For example, four switching devices Voltage signal and triangular carrier Real-time comparison, when When the level is higher than the triangular carrier, it generates or A high-level signal (i.e. or On the contrary, it generates or A low-level signal (i.e. or The disconnect signal is: and complementary (i.e. one turns on when the other turns off), and Complementary. It can be seen that the switch signal includes an on signal and an off signal.

[0068] 、 and The way to modulate the switching device is The method of modulating the switching device is similar and will not be repeated here.

[0069] The above example generates the three-phase inverter voltage by independently comparing the compensated three-phase inverter voltage with the triangular carrier. Phase bridge arm, Phase bridge arm and The switching signals of the first three bridge arms are modulated independently using the midpoint voltage adjustment amount. This, combined with the triangular carrier modulation of the first three bridge arms, creates a multi-level modulation strategy that significantly improves the output voltage quality. Specifically, the switching signal of the fourth bridge arm is independently modulated using the midpoint voltage adjustment amount. This, combined with the triangular carrier modulation of the first three bridge arms, results in more voltage steps in the inverter output waveform, significantly reducing the voltage jump amplitude and high-frequency harmonic components, significantly improving the voltage waveform quality and stabilizing voltage control.

[0070] S190 , driving the switching device of the inverter according to the switching signal.

[0071] For example, when the switching signal is high, the driver circuit applies a positive bias voltage (+15V) to the switching device (such as the gate of an IGBT), causing it to saturate and conduct, allowing current to flow through the device. When the switching signal is low, the driver circuit applies a negative bias voltage (-5V) or zero voltage, rapidly removing gate charge, forcing the device to shut down and blocking the current path.

[0072] In order to verify the effect of the embodiment of the present application, the present application conducted a simulation and generated the following Figure 6 The active power output of the three-phase four-leg T-type three-level inverter network strategy is shown in FIG. Figure 7The reactive power output of the three-phase four-leg T-type three-level inverter network construction strategy shown in FIG, and Figure 8 The voltage pre-synchronization results of the three-phase four-leg T-type three-level inverter network construction strategy are shown.

[0073] exist Figure 6 In the equation, the vertical axis is active power and the horizontal axis is time (in seconds). Figure 7 In the equation, the vertical axis is reactive power and the horizontal axis is time (in seconds). Figure 6 0~1.5s is the pre-synchronization process, 1.5s~3s is the setting For 10kW, set it to 3s~10s is 15kW. Figure 7 0~1.5s is the pre-synchronization process, 1.5s~5s is the setting 0var, 5s~10s setting 2kvar. Figure 6 and Figure 7 It can be seen that the control strategy based on the three-phase four-leg T-type three-level inverter provided by the present application has an excellent output power tracking effect, which means that in the case of a sudden change in the grid voltage or phase, the present application solution can perform active power compensation and reactive power compensation through active power and reactive power, thereby stabilizing the grid voltage and phase, and ensuring that the inverter can operate continuously and stably.

[0074] In addition, if Figure 8 As shown (where the horizontal axis is time (in seconds) and the vertical axis is voltage), during the pre-synchronization process, the output voltage of the inverter using the control method of this application gradually matches the grid voltage within 0 to 1.5 seconds, ensuring smooth grid integration. After pre-synchronization, the inverter achieves seamless on-grid and off-grid switching. Smooth on-grid and off-grid switching reduces inrush current and thus the impact on the grid, helping to maintain grid stability.

[0075] In summary, the control method for the inverter based on virtual synchronous generator control provided in this application has excellent output power tracking effect and voltage pre-synchronization performance, is applicable to various power systems, and provides strong support for the stable operation of the power system.

[0076] The embodiments of the present application are designed based on the principle of a virtual synchronous generator. By simulating the inertia and damping characteristics of a traditional synchronous generator, the three-phase four-bridge-leg T-type three-level inverter is able to independently construct the voltage and frequency of the power grid. This fully utilizes the advantages of high efficiency and high power quality of the three-phase four-bridge-leg T-type three-level inverter, enhances the inverter's adaptability in complex power systems, and enables the inverter to play an important role in power grid operation.

[0077] Specifically, by treating the inverter as a synchronous generator, the active frequency loop of the virtual synchronous generator control strategy adjusts the inverter's virtual angular frequency based on the actual active power value, thereby achieving frequency support. This frequency support function enables the inverter to provide effective frequency support in weak grid scenarios, thereby improving the robustness and stability of the entire power system. In this way, the inverter can not only cope with various fluctuations and disturbances in the grid, but also alleviate the vulnerability of the grid to a certain extent, ensuring the continuity and reliability of power supply. The reactive voltage loop of the virtual synchronous generator control strategy dynamically generates the electromotive force amplitude based on the actual reactive power value to maintain the stability of the output voltage amplitude and ensure voltage quality. After generating a three-phase reference voltage in a three-phase stationary coordinate system based on the voltage phase angle and electromotive force amplitude, a coordinate transformation is performed to obtain a two-phase reference voltage in a two-phase rotating coordinate system. Modulating the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop achieves stable control of the voltage amplitude and phase, effectively suppressing fluctuations caused by internal system disturbances and external loads, and further improving the robustness and dynamic response of the power system. The modulated two-phase reference voltage is inversely transformed into a three-phase stationary coordinate system to generate a three-phase inverter voltage. The switching signal of the inverter is generated according to the three-phase inverter voltage. The switching device of the inverter is driven according to the switching signal, thereby controlling the inverter to stably output a voltage signal, so that the power system to which the inverter belongs has the ability to self-regulate and support voltage.

[0078] Since the control method provided in this application enables the inverter to have fast dynamic response capabilities and good adaptability, the inverter using this control method is suitable for various application scenarios such as microgrids and distributed power sources. Specifically, when the inverter using this control method works as a distributed power source, it supports black start, can independently establish voltage and frequency, achieve island operation and can quickly respond to load changes. When connected to the microgrid, faced with more complex grid impedance and short-circuit current changes, the inverter using this control method can take into account the grid connection quality and frequency and voltage support capabilities, and can adapt to different grid strengths. In addition, the inverter using this control method can achieve seamless on-grid and off-grid switching, and the grid connection process is smooth, effectively avoiding grid disturbances.

[0079] In addition, the control method provided by this application has a wide range of engineering applications. For example, sudden load changes may cause frequency and voltage fluctuations. The inverter using this control method has the ability to quickly and dynamically adjust to cope with adverse fluctuations. For another example, changes in grid conditions such as short-circuit capacity, faults, and fluctuations also have a direct impact on inverter operation. The control method of this application uses the inverter to enable the power system to quickly identify and adjust the supporting grid.

[0080] In summary, this application coordinates the design of the virtual synchronous generator control logic with the multi-arm structure of the three-phase, four-arm T-type three-level inverter to form a highly adaptable control system. This not only maintains the network construction capability and grid support performance, but also fully utilizes the advantages of the multi-level topology in output quality and loss, enabling the power system to which the inverter belongs to operate stably under weak grid or island conditions. Furthermore, because the inverter using this control method can operate independently and adapt to the island mode, it has greater robustness and collaborative control potential, and is suitable for future power systems with high penetration of new energy and weakened grids.

[0081] The present application also provides a control system for an inverter based on virtual synchronous generator control, wherein the inverter is a three-phase four-leg T-type three-level inverter, and the system includes: Active power and reactive power determination module, used to determine the actual value of active power and reactive power based on the three-phase voltage and three-phase current sampled from the grid side, where the grid side refers to the side where the inverter is connected to the grid; The virtual angular frequency adjustment module is used to adjust the virtual angular frequency of the inverter and generate the voltage phase angle according to the actual value of the active power through the active frequency loop of the virtual synchronous generator control strategy: A voltage regulation module is used to generate the electromotive force amplitude of the inverter through the reactive voltage loop of the virtual synchronous generator control strategy according to the actual value of reactive power; The voltage regulation module is further used to generate a three-phase reference voltage in a three-phase stationary coordinate system according to the voltage phase angle and the electromotive force amplitude; The voltage regulation module is also used to perform coordinate transformation on the three-phase reference voltage to obtain a two-phase reference voltage in a two-phase rotating coordinate system; The voltage regulation module is further used to modulate the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop to obtain a modulated two-phase reference voltage; The voltage regulation module is also used to inversely transform the modulated two-phase reference voltage into a three-phase stationary coordinate system to generate a three-phase inverter voltage; A switching signal generating module, used for generating a switching signal of an inverter according to a three-phase inverter voltage; The switching device driving module is used to drive the switching device of the inverter according to the switching signal.

[0082] In a feasible design, the switching signal generation module generates the switching signal of the inverter according to the three-phase inverter voltage in the following manner: Determine the midpoint voltage adjustment amount that is in opposite phase to the three-phase inverter voltage according to the voltage extreme value of the three-phase bridge arm to the midpoint of the inverter; The midpoint voltage regulation amount is added to the three-phase inverter voltage Phase voltage, Phase voltage and Phase voltage, to achieve compensation for the three-phase inverter voltage; The switching signal of the inverter is generated according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount.

[0083] In a feasible design, the switch signal generation module determines the midpoint voltage adjustment amount according to the voltage extreme value of the three-phase bridge arm of the inverter to the midpoint through the following formula; the midpoint voltage adjustment amount is added to the three-phase inverter voltage respectively. Phase voltage, Phase voltage and Phase voltage: ; ; ; ; in, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the midpoint voltage regulation amount, express 、 and The maximum value of express 、 and The minimum value of Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage.

[0084] In a feasible design, the switching signal generation module generates the switching signal of the inverter according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount in the following manner: Compare the compensated three-phase inverter voltage with the triangle carrier to generate the inverter Phase bridge arm, Phase bridge arm and Switching signal of the phase bridge arm; The midpoint voltage regulation amount is compared with the triangular carrier to generate a switching signal for the fourth bridge arm of the inverter.

[0085] In a feasible design, the voltage regulation module modulates the two-phase reference voltage through dual closed-loop decoupling control of the voltage outer loop and the current inner loop in the following manner to obtain the modulated two-phase reference voltage: Perform coordinate transformation on the three-phase voltage to obtain the voltage sampling value in the two-phase rotating coordinate system; Perform coordinate transformation on the three-phase current to obtain the current sampling value in the two-phase rotating coordinate system; The error between the two-phase reference voltage and the voltage sampling value is input into the proportional-integral controller of the voltage outer loop to obtain the current reference value; The error between the current reference value and the current sampling value is input into the proportional-integral controller of the current inner loop, and after decoupling processing, the modulated two-phase reference voltage is obtained.

[0086] In a feasible design, the virtual angular frequency regulation module adjusts the virtual angular frequency of the inverter according to the actual value of the active power through the active frequency loop of the virtual synchronous generator control strategy in the following manner: According to the actual value of active power and the reference value of active power, the virtual angular frequency of the inverter is dynamically adjusted in combination with the equivalent virtual inertia and the damping coefficient.

[0087] In a feasible design, the virtual angular frequency adjustment module is further used to determine the equivalent virtual inertia according to the system capacity corresponding to the inverter.

[0088] In a feasible design, the virtual angular frequency adjustment module is further configured to determine a damping coefficient according to the sensitivity of the power disturbance to the frequency and the equivalent virtual inertia.

[0089] For other implementations and effects of the above system, please refer to the description in the embodiment of the control method for an inverter based on virtual synchronous generator control, which will not be repeated here.

[0090] The basic principles of the present application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, and effects mentioned in this application are merely illustrative and not restrictive, and it should not be assumed that these advantages, strengths, and effects are required of each embodiment of this application. In addition, the specific details disclosed above are merely illustrative and facilitating understanding, and are not restrictive. The above details do not limit this application to necessarily being implemented using the above specific details.

[0091] It should be understood that although the steps in the flowcharts of the accompanying drawings are shown in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the flowcharts of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0092] The block diagrams of the devices, devices, equipment, and systems involved in this application are intended only as illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As will be appreciated by those skilled in the art, these devices, devices, equipment, and systems can be connected, arranged, or configured in any manner. Words such as "include," "comprise," "have," and the like are open-ended words, meaning "including but not limited to," and can be used interchangeably therewith. The words "or" and "and" used herein refer to the words "and / or" and can be used interchangeably therewith, unless the context clearly indicates otherwise. The word "such as" used herein refers to the phrase "such as but not limited to," and can be used interchangeably therewith.

[0093] It should also be noted that in the apparatus, device, and method of the present application, each component or each step can be decomposed and / or recombined, and such decomposition and / or recombination should be regarded as equivalent solutions of the present application.

[0094] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects without departing from the scope of the present application. Therefore, the present application is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0095] The above description has been provided for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although a number of example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A control method for an inverter based on virtual synchronous generator control, characterized in that: The inverter is a three-phase four-bridge-arm T-type three-level inverter, and the method includes: determining an actual value of active power and an actual value of reactive power based on the three-phase voltage and three-phase current sampled on the grid side, where the grid side refers to a side where the inverter is connected to the grid; According to the actual value of the active power, the virtual angular frequency of the inverter is adjusted and the voltage phase angle is generated through the active frequency loop of the virtual synchronous generator control strategy; generating an electromotive force amplitude of the inverter through a reactive voltage loop of a virtual synchronous generator control strategy according to the actual value of the reactive power; generating a three-phase reference voltage in a three-phase stationary coordinate system according to the voltage phase angle and the electromotive force amplitude; Performing coordinate transformation on the three-phase reference voltage to obtain a two-phase reference voltage in a two-phase rotating coordinate system; Modulating the two-phase reference voltage through dual closed-loop decoupling control of a voltage outer loop and a current inner loop to obtain a modulated two-phase reference voltage; The modulated two-phase reference voltage is inversely transformed into a three-phase stationary coordinate system to generate a three-phase inverter voltage; generating a switching signal of the inverter according to the three-phase inverter voltage; The switching device of the inverter is driven according to the switching signal.

2. The method according to claim 1, characterized in that Generating a switching signal of the inverter according to the three-phase inverter voltage includes: Determining a midpoint voltage adjustment amount that is in opposite phase to the three-phase inverter voltage according to the voltage extreme value of the three-phase bridge arm of the inverter to the midpoint; The midpoint voltage adjustment amount is respectively added to the midpoint voltage of the three-phase inverter voltage. Phase voltage, Phase voltage and Phase voltage, to achieve compensation for the three-phase inverter voltage; A switching signal of the inverter is generated according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount.

3. The method according to claim 2, characterized in that Determine the midpoint voltage adjustment amount according to the voltage extreme value of the three-phase bridge arm of the inverter to the midpoint; add the midpoint voltage adjustment amount to the midpoint voltage of the three-phase inverter voltage respectively. Phase voltage, Phase voltage and Phase voltage, using the following formula: ； ； ； ； in, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, Indicates the three-phase inverter voltage Phase voltage, represents the midpoint voltage adjustment amount, express 、 and The maximum value of express 、 and The minimum value of Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage, Indicates the voltage after compensation of midpoint voltage regulation Phase voltage.

4. The method according to claim 2 or 3, characterized in that Generating a switching signal of the inverter according to the compensated three-phase inverter voltage and the midpoint voltage adjustment amount includes: Compare the compensated three-phase inverter voltage with the triangular carrier to generate the inverter Phase bridge arm, Phase bridge arm and Switching signal of the phase bridge arm; The midpoint voltage adjustment amount is compared with a triangular carrier to generate a switching signal for the fourth bridge arm of the inverter.

5. The method according to any one of claims 1 to 3, characterized in that The two-phase reference voltage is modulated by dual closed-loop decoupling control of a voltage outer loop and a current inner loop to obtain a modulated two-phase reference voltage, including: Performing coordinate transformation on the three-phase voltage to obtain voltage sampling values in a two-phase rotating coordinate system; Performing coordinate transformation on the three-phase current to obtain current sampling values in a two-phase rotating coordinate system; Inputting the error between the two-phase reference voltage value and the voltage sampling value into the proportional-integral controller of the voltage outer loop to obtain a current reference value; The error between the current reference value and the current sampling value is input into a proportional-integral controller of a current inner loop, and after decoupling processing, a modulated two-phase reference voltage is obtained.

6. The method according to any one of claims 1 to 3, characterized in that The adjusting the virtual angular frequency of the inverter by the active frequency loop of the virtual synchronous generator control strategy according to the actual value of the active power includes: The virtual angular frequency of the inverter is dynamically adjusted according to the actual value of the active power and the reference value of the active power in combination with the equivalent virtual inertia and the damping coefficient.

7. The method according to claim 6, characterized in that The method comprises: The equivalent virtual inertia is determined according to a system capacity corresponding to the inverter.

8. The method according to claim 6, characterized in that The method comprises: The damping coefficient is determined according to the sensitivity of the power disturbance to the frequency and the equivalent virtual inertia.

9. A control system for an inverter based on virtual synchronous generator control, characterized in that: The inverter is a three-phase four-bridge-arm T-type three-level inverter, and the system includes: an active power and reactive power determination module, configured to determine an actual value of active power and an actual value of reactive power based on three-phase voltage and three-phase current sampled from a grid side, where the grid side refers to a side where the inverter is connected to a grid; A virtual angular frequency adjustment module is used to adjust the virtual angular frequency of the inverter and generate a voltage phase angle through the active frequency loop of the virtual synchronous generator control strategy according to the actual value of the active power: a voltage regulation module, configured to generate an electromotive force amplitude of the inverter through a reactive voltage loop of a virtual synchronous generator control strategy according to the actual value of the reactive power; The voltage regulation module is further configured to generate a three-phase reference voltage in a three-phase stationary coordinate system according to the voltage phase angle and the electromotive force amplitude; The voltage regulation module is further configured to perform coordinate transformation on the three-phase reference voltage to obtain a two-phase reference voltage in a two-phase rotating coordinate system; The voltage regulation module is further configured to modulate the two-phase reference voltage through a dual closed-loop decoupling control of a voltage outer loop and a current inner loop to obtain a modulated two-phase reference voltage; The voltage regulation module is further used to inversely transform the modulated two-phase reference voltage into a three-phase stationary coordinate system to generate a three-phase inverter voltage; a switching signal generating module, configured to generate a switching signal for the inverter according to the three-phase inverter voltage; A switching device driving module is used to drive the switching device of the inverter according to the switching signal.

Images