A method, system and device for voltage control of a grid-forming converter

Abstract

This application discloses a voltage control method, system, and device for grid-connected converters, belonging to the field of power electronic converter control technology. This method addresses the problem of insufficient voltage support capability at the common coupling point in existing grid-connected converters based on voltage and current dual closed-loop control due to virtual impedance and line impedance voltage drop. By adding a compensation term to its reactive power-voltage droop control loop to compensate for the impedance voltage drop, the method ultimately improves the voltage support capability of the grid-connected control converter and enhances the voltage stability of the power system.

Description

Technical Field

[0001] This application belongs to the field of converter control technology, and relates to a voltage control method, system and equipment for a grid-type converter. Background Technology

[0002] Building a new power system with an increasing proportion of renewable energy is the main implementation path in the power sector. However, with the continuous increase in the penetration rate of renewable energy, the new power system faces the challenge of insufficient active support capabilities. Grid-type converters can provide active support for the grid inertia, frequency, and voltage, and are considered an effective way to solve the above challenges.

[0003] Typical grid-connected converter control mainly consists of two parts: active power-frequency control and reactive power-voltage control. The active power-frequency control section primarily provides inertia and frequency support to the grid. Typical control methods include droop control, power synchronization control, and virtual synchronous generator control. The reactive power-voltage control section is responsible for injecting reactive power into the grid to provide voltage support. Typical control schemes include dual-loop voltage and current control, single-loop reactive power control, and RMS voltage control. Among these, dual-loop voltage and current control has advantages such as low harmonics, embedded current limiting, and strong compatibility with grid-connected control. Single-loop reactive power control and RMS voltage control are characterized by simple control structures and strong robustness and stability. Both types of reactive power-voltage control have been applied to some extent in current grid-connected converter products.

[0004] To improve the voltage support performance of grid-connected converters and enhance power system voltage stability, scholars have conducted extensive research. Currently, research on voltage support for grid-connected converters mainly focuses on large grid disturbance conditions (such as grid voltage dips and short-circuit faults), with proposed control strategies centered on low-voltage ride-through technology, including grid mode switching control, virtual impedance control, and dynamic adjustment of voltage / power reference values. Research on voltage support for grid-connected converters under small disturbance conditions is relatively limited, mainly involving variable reactive power droop control and active and reactive power coordination control; however, the former is prone to causing system dynamic instability, while the latter suffers from high algorithm complexity and significant engineering implementation difficulties.

[0005] Existing single-loop reactive power control and RMS voltage control can directly establish the droop relationship between reactive power and the RMS voltage by sampling the common coupling point (CCP) voltage or introducing a CCP voltage estimation stage, unaffected by virtual impedance and line impedance voltage drops. However, existing dual-loop voltage and current control establishes the droop relationship between reactive power and induced electromotive force (EMF). Because of the line impedance between the filter capacitor and the CCP voltage, the resulting voltage drop affects the voltage support effect; furthermore, the induced EMF is not directly equivalent to the filter capacitor voltage, but rather controls the filter capacitor voltage through a virtual impedance stage, and the voltage drop across this impedance also affects the voltage support effect. These two voltage drops together result in the existing dual-loop voltage and current control having a lower voltage support capability than existing single-loop reactive power control and RMS voltage control. Summary of the Invention

[0006] This application aims to improve the voltage support capability of existing voltage and current dual closed-loop control systems, providing technical support for improving the voltage stability of new power systems. This application provides a voltage control method, system, and device for grid-connected converters, solving the technical problem that existing grid-connected converters based on voltage and current dual closed-loop control have insufficient voltage support capability at the point of common coupling due to virtual impedance and line impedance voltage drop.

[0007] To achieve the above objectives, this application employs the following technical means: In a first aspect, this application provides a voltage control method for a grid-type converter, comprising: adding a voltage or reactive power compensation term in the reactive power-voltage droop control loop of the grid-type converter based on voltage and current dual closed-loop control, wherein the compensation term is used to compensate for the voltage drop caused by the virtual impedance of the grid-type converter and the line impedance between the filter capacitor and the common coupling point, thereby enhancing the support capability for the voltage at the common coupling point.

[0008] As a further improvement to this application, when the compensation term is a voltage compensation term, the voltage compensation term is... ,in This is the true value of the induced electromotive force. The voltage at the common coupling point is used; the voltage compensation term is superimposed on the induced electromotive force reference value.

[0009] As a further improvement to this application, the compensation term is a reactive power compensation term. ,in, This is the reactive power droop factor. This is the true value of the induced electromotive force. The common coupling point voltage; the reactive power compensation term is superimposed on the reactive power reference value.

[0010] As a further improvement to this application, the common coupling point voltage is obtained in any of the following ways: (a) Directly sample the voltage at the common coupling point; (b) Estimate based on filter capacitor voltage, output current and line impedance parameters.

[0011] As a further improvement to this application, the common coupling point voltage estimation method is as follows: calculate the difference between the voltage phasor of the filter capacitor and the voltage phasor generated by the output current on the line impedance.

[0012] As a further improvement to this application, the true value of the induced electromotive force The estimation method is as follows: calculate the sum of the voltage phasor of the filter capacitor and the voltage phasor generated by the output current on the virtual impedance.

[0013] As a further improvement to this application, the compensation term can be low-pass filtered before being superimposed on the reference value: When the compensation term is voltage compensation, the voltage compensation term is filtered by a low-pass filter and then superimposed on the induced electromotive force reference value; When the compensation term is reactive power compensation, the reactive power compensation term is superimposed on the reactive power reference value after passing through a low-pass filter.

[0014] As a further improvement to this application, the common coupling point voltage The estimation is based on the following model: ; The true value of the induced electromotive force One specific estimation method is as follows: ; in, and These are virtual resistance and virtual inductance, respectively; , For the voltage of the filter capacitor dq or αβ Axial components, , For the output current dq or αβ Axial components; , For line resistance and inductance, This is the virtual angular frequency.

[0015] Secondly, this application provides a grid-type converter voltage control system, comprising: The voltage and current dual closed-loop control module is used to realize the basic voltage control of the grid-type converter; The compensation module is used to execute the grid-type converter voltage control method described above.

[0016] Thirdly, this application provides a grid-type converter device, including the aforementioned voltage control system.

[0017] Compared with the prior art, this application has the following advantages: This application compensates for the voltage drop caused by virtual impedance and line impedance by adding a compensation term, effectively establishing a direct droop relationship between reactive power and the voltage at the point of common coupling (PCC), thereby significantly improving the voltage support effect of grid-connected converters at PCC. This method effectively overcomes the shortcomings of existing voltage and current dual-loop control in voltage support capability compared to other grid-connected control strategies (such as single reactive power loop control and RMS voltage control). It has a simple structure, is easy to modify and integrate into existing engineering projects, and is particularly helpful in enhancing the voltage support capability of grid-connected converters, providing effective technical support for improving the voltage stability of new power systems. Attached Figure Description

[0018] Figure 1 The control block diagram of an existing grid-type converter based on voltage and current dual closed-loop control is shown. Figure 2 The equivalent circuit diagram of an existing grid-type converter based on voltage and current dual closed-loop control is shown. Figure 3 A schematic diagram of the reactive power-voltage droop curve for a grid-type converter; Figure 4 The overall block diagram of voltage support enhancement control for grid-connected converters is shown; where (a) is based on voltage V comp (a) Compensation; (b) Based on reactive power Q comp compensate; Figure 5 A block diagram of the reactive power-voltage droop control loop for voltage support enhancement control of a grid-type converter; wherein, (a) is based on voltage V comp (a) Compensation; (b) Based on reactive power Q comp compensate; Figure 6 Block diagram of the common coupling point voltage estimation method; Figure 7 The true value of the induced electromotive force E Estimation method flowchart; Figure 8 A comparison of the voltage response at the point of common coupling under the condition of a grid voltage drop of 0.1 pu and SCR=2; Figure 9 A comparison of the voltage response at the point of common coupling under the condition of a grid voltage drop of 0.1 pu and SCR=10; Figure 10This is a comparison diagram of the voltage response at the common coupling point under the condition of a sudden increase in reactive power of the load. Detailed Implementation

[0019] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] Existing single-loop reactive power control and RMS voltage control can establish a droop relationship between reactive power and the point of common coupling (PCC) voltage, while existing dual-loop voltage-current control can only establish a droop relationship between reactive power and induced electromotive force (EMF). Because of the voltage drop between the induced EMF and the PCC voltage caused by the virtual impedance and the line impedance from the filter capacitor to the PCC, the voltage support capability of existing dual-loop voltage-current control is inferior to that of existing single-loop reactive power control and RMS voltage control. Therefore, this application aims to propose a voltage support enhancement control method. By adding a reactive power compensation term to the existing dual-loop voltage-current control, it compensates for the voltage drop caused by the virtual impedance of the converter and the line impedance from the filter capacitor to the PCC, thereby enhancing the support effect of the grid-type converter on the PCC voltage.

[0021] The existing control block diagram of a grid-type converter based on dual closed-loop voltage and current control is as follows: Figure 1 As shown, it establishes reactive power. With reference value of induced electromotive force The droop relationship between the two is used by the grid-type converter to support the common coupling point voltage during disturbances. . Figure 1 The corresponding equivalent circuit diagram is as follows: Figure 2 As shown, the grid-type converter is equivalent to a converter with an amplitude of Voltage source string virtual impedance The true value of induced electromotive force in steady state Equal to the reference value of induced electromotive force .

[0022] Depend on Figure 2 Knowing the true value of the induced electromotive force voltage at common coupling point There exists a virtual impedance With line impedance The resulting impedance voltage drop This means that when a grid-type converter provides voltage support at the common coupling point, it must first compensate for the impedance voltage drop. This severely weakens the voltage support capability of the grid-type converter. Therefore, it is necessary to compensate for this impedance voltage drop in the grid-type converter control algorithm to enhance the voltage support effect of the grid-type converter.

[0023] In existing grid-connected converter voltage and current dual closed-loop control, the induced electromotive force (EMF) reference value and reactive power are related through a drooping link. However, there is a voltage drop between the induced EMF and the actual point-of-compatibility (POC) voltage, caused by the converter's virtual impedance and the line impedance from the filter capacitor to the POC. This voltage drop prevents the converter's output reactive power from effectively and directly supporting the POC voltage, weakening its voltage regulation capability under grid disturbances.

[0024] The first objective of this application is to provide a voltage support enhancement control method for a grid-type converter, applied to a grid-type converter based on voltage and current dual closed-loop control, comprising the following steps: In the existing reactive power-voltage droop control loop of the grid-type converter based on voltage and current dual closed-loop control, a compensation term is added. The compensation term is used to compensate for the voltage drop caused by the virtual impedance of the converter and the line impedance between the filter capacitor and the common coupling point, so as to enhance the support capability for the voltage of the common coupling point.

[0025] The implementation of this method can be referred to Figure 4 The overall control block diagram is shown. Specifically, based on the conventional voltage outer loop and current inner loop control structure, and in the reactive power-voltage droop stage, a compensation calculation unit is added. This unit calculates the sum of the virtual impedance voltage drop and the line impedance voltage drop in real time and converts it into a corresponding compensation signal. For example, in a specific embodiment, this compensation term can be based on the real value of the induced electromotive force E acquired or estimated in real time and the voltage at the common coupling point. The difference is used for calculation. The controller's sampling frequency can be selected as 10kHz to ensure rapid compensation for voltage drop. This compensation calculation function can be implemented through the software algorithm module in the converter's main control chip. In practical applications, other models of this main control chip can also be selected.

[0026] Its working principle lies in introducing a compensation factor related to the impedance voltage drop to compensate for the impedance voltage drop between the induced electromotive force and the common coupling point voltage. This allows the reactive power output of the converter to respond more directly to changes in the common coupling point voltage, rather than being consumed or distorted by the intermediate impedance voltage drop. From the perspective of the equivalent circuit, this method is equivalent to shifting the reactive power-voltage droop characteristic curve from the induced electromotive force terminal to the common coupling point.

[0027] By adopting this implementation method, the adverse effects of virtual impedance and line impedance are effectively offset, making the grid-type converter's support for the common coupling point voltage more direct and robust, and improving the converter's voltage stability capability at the common coupling point voltage.

[0028] This application proposes a voltage control method for grid-type converters. The method involves adding a reactive power compensation term to the classic reactive power-voltage droop control loop of a grid-type converter. By compensating for the voltage drop caused by the virtual impedance of the converter and the line impedance between the filter capacitor and the common coupling point, the voltage fluctuation at the common coupling point is effectively suppressed, thereby improving the voltage support capability of the grid-type control converter and enhancing the voltage stability of the power system.

[0029] Figure 3 This is a schematic diagram of the reactive power-voltage droop curve of a grid-connected converter, with reference values ​​for the induced electromotive force. voltage at common coupling point The reactive power deviation corresponding to the pressure difference in steady state is: Since reactive power deviation is linearly related to impedance voltage drop, impedance voltage drop can also be compensated by compensating for reactive power deviation.

[0030] In existing voltage and current dual closed-loop control, the droop relationship is established based on and Between; due to and There is an impedance voltage drop between them, which leads to The actual support effect is weakened; by compensating for the reactive power deviation corresponding to this voltage drop, the system can be made to operate equivalently at... - On the curve, thereby improving voltage support capability.

[0031] Based on this, this application proposes two voltage support enhancement control methods for grid-type converters. The specific implementation methods are as follows: In the existing reactive power droop link of grid-type control based on voltage and current dual loops, 1) a voltage compensation term is added. ;2) Add reactive power compensation item Its corresponding overall block diagram is as follows: Figure 4 As shown, (a) is based on voltage (a) Compensation; (b) Based on reactive power compensate; Figure 4 In the middle: the main circuit includes: mains voltage Grid impedance Common coupling point, grid-type converter (including filter capacitors, virtual impedance, etc.); control section includes: active power-frequency control loop; reactive power-voltage control loop (including voltage and current dual closed loop); added compensation module.

[0032] As a further improvement to this application, when calculating the compensation term, if the resistance component in the line impedance is... Much smaller than the inductive component The effect of the resistance component is ignored. A simplified formula is used to calculate the voltage at the common coupling point. or induced electromotive force An estimate is performed. For the aforementioned compensation item... or A dynamic limiting mechanism is applied, with the limiting value dynamically adjusted based on the rate of change of reactive power output from the grid-connected converter. When the rate of change exceeds a preset threshold, the limiting value is reduced. Introducing dynamic limiting prevents excessive compensation during transient processes from causing system oscillations or instability. Linking the rate of change to the limiting mechanism improves the robustness and safety of the method.

[0033] Specifically, there are two compensation methods: voltage compensation ( Figure 4 (a): Compensation signal ; directly superimposed on the induced electromotive force reference value Above. Reactive power compensation ( Figure 4 (b) ): Compensation signal It is directly superimposed on the reactive power reference value. During the control process, the system detects or estimates... and Calculate the compensation amount and inject it into the corresponding control loop; thereby offsetting the voltage drop caused by the virtual impedance and line impedance, and achieving [the desired effect]. Direct support.

[0034] The compensation item is the voltage compensation item. ,in This is the true value of the induced electromotive force. This is the voltage at the common coupling point; the voltage compensation term is superimposed on the induced electromotive force reference value. This specific implementation corresponds to... Figure 5 (a) shows the control block diagram. The actual value of the induced electromotive force. E pass Figure 7 The estimation module shown provides the results.

[0035] Common coupling point voltage This can be obtained directly by measuring at the common coupling point using a voltage sensor. The calculated difference ( As an additional voltage compensation signal It is directly added to the initial reference value of the induced electromotive force output from the drooping element. In practical applications, other models of this voltage sensor can also be selected.

[0036] Its working principle is to directly use the impedance voltage drop as a correction factor for the voltage command. When the voltage at the point of common coupling... When the load increases, the compensation item decreases. The value of ) will increase, thereby raising the final induced electromotive force reference value. This drives the converter to output a higher voltage to compensate for the voltage drop and maintain... Stability.

[0037] This implementation method, through direct voltage feedforward compensation, can quickly respond to voltage changes, and the dynamic adjustment process is intuitive, which helps to improve the response speed and control accuracy of the voltage control loop.

[0038] Add voltage Compensation or reactive power See the block diagram of the compensated reactive power-droop control. Figure 5 Among them, (a) is based on voltage. (a) Compensation; (b) Based on reactive power compensate. Figure 5 middle: (Rated voltage) (Reactive power reference value) (Measured reactive power) , ; Sag coefficient , (Reference value of induced electromotive force).

[0039] The control process is as follows: the compensation term directly participates in the droop calculation; thus, the droop characteristic changes from... - Turn to - The structure is simple, requiring only the addition of a subtractor and an adder to the existing control system.

[0040] Figure 5 In The voltage at the common coupling point can be obtained directly by sampling. If direct sampling is not possible, it can be estimated by combining the line impedance information. The corresponding block diagram is shown below. Figure 6 . Figure 6 middle, v outd and v outq Capacitor voltagesV out exist dq coordinate system dq Quantity, i outd and i outq Output current i out exist dq coordinate system dq Quantity, R line and L line These are the line resistance and the line inductance, respectively. ω m This is the virtual angular frequency.

[0041] (a) Voltage compensation method: In Add to the generation process ; (b) Reactive power compensation method: In Add to the generation process .

[0042] Figure 6 In: Input signal (in) (in coordinate system): Filter capacitor voltage: Output current: Line parameters: Virtual angular frequency: Output: Estimated ; As one specific embodiment of this application, the common coupling point voltage The following model can be used for estimation: ; The parameters are defined as described above.

[0043] Similarly, the true value of the induced electromotive force One specific estimation method is as follows: ; in, and These are virtual resistance and virtual inductance, respectively.

[0044] The control process is as follows: This formula is based on the line impedance voltage drop model. The line voltage drop is subtracted from the capacitor voltage to obtain the common coupling point voltage. It is suitable for scenarios where a common coupling point voltage sensor cannot be directly installed. It provides the necessary compensation control. Signal.

[0045] Figure 5The true value of induced electromotive force in The same method can be used to estimate impedance by combining virtual impedance information; the corresponding block diagram is shown below. Figure 7 . Figure 7 middle, R v This is a virtual resistor.

[0046] The compensation item is the reactive power compensation item. ,in This is the reactive power droop factor; the reactive power compensation term is superimposed on the reactive power reference value. This specific implementation corresponds to... Figure 5 (b) shows the control block diagram. Reactive power droop factor. This is a preset control parameter whose value is related to the rated capacity of the converter and the allowable voltage regulation range; for example, it can be set to 0.05 pu. The calculated reactive power compensation term... As an additional reactive power command, it is input into the existing reactive power control loop. In practical applications, the droop factor... The specific value can be set according to the power grid dispatch requirements or the results of on-site commissioning.

[0047] Its working principle is to compensate at the power level. The impedance voltage drop is converted into an additional reactive power demand signal. When a voltage drop exists, this compensation term will dynamically adjust the reactive power output, causing the induced electromotive force generated by the converter to overcome this impedance voltage drop, and ultimately stabilize the voltage at the point of common coupling.

[0048] This implementation transforms the voltage support problem into a power regulation problem, making it easier to integrate with existing power control frameworks, achieving smooth power command adjustments, and having a more moderate impact on system power balance.

[0049] Common coupling point voltage The voltage can be obtained through one of the following methods: direct sampling of the common coupling point voltage; or estimation based on the filter capacitor voltage, output current, line impedance parameters, and virtual angular frequency. In the first direct sampling method, a three-phase voltage transformer or voltage sensor needs to be installed at the common coupling point. In the second estimation method, when it is inconvenient to directly install a sensor at the common coupling point, an estimation method is used... Figure 6 The estimation model is shown. This method utilizes the filter capacitor voltage, which can be directly measured at the converter outlet. V out and output current i out and known line parameters (resistance) R line and inductor L line The voltage at the point of common coupling is inferred by calculating the voltage drop across the line impedance. Virtual angular frequency. ωm It is generated by the internal control loop of the converter and is usually close to the grid synchronization angular frequency.

[0050] Its working principle is to calculate the voltage state at the remote common coupling point by measuring the local electrical quantities of the converter, combining them with known network topology parameters, and applying Kirchhoff's voltage law in circuit theory. This avoids the need to install additional sensors, reducing system cost and complexity.

[0051] Employing estimation as a backup or primary method enhances the practicality and robustness of the control strategy. Even in scenarios where the voltage at the common coupling point cannot be directly measured, this method remains effective, expanding its application scope.

[0052] Common coupling point voltage The following formula is used to calculate it: Figure 6 The flowchart describes the specific mathematical expression of the estimation method. v outd and v outq The voltage of the filter capacitor is rotating synchronously. dq The direct and quadrature components in the coordinate system can be obtained by measuring the three-phase capacitor voltage and performing coordinate transformation. outd and i outq i outd and i outq It is the component of the converter output current in the same coordinate system. R line and L line These are the line resistance and inductance values ​​connecting the filter capacitor and the common coupling point; these are inherent parameters of the system. ω m This is the virtual angular velocity generated by the internal control of the converter. During the calculation, first calculate... dq The voltage components after subtracting the voltage drop due to line impedance on the axis are then analyzed, and the magnitude of their combined vector is calculated to obtain the result. The estimated value.

[0053] Its working principle is based on dq Impedance voltage drop model in coordinate system. This formula accurately describes the voltage drop caused by alternating current along the line from the converter outlet to the point of common coupling (PCC). The PCC voltage can be obtained by subtracting this voltage drop from the local voltage.

[0054] This specific calculation formula provides a clear and programmable implementation path with moderate computational load, making it suitable for real-time operation in digital signal processors and ensuring the accuracy and real-time performance of voltage estimation.

[0055] True value of induced electromotive force EEstimate using the formula, which is Figure 7 The flowchart describes the specific mathematical expression of the estimation method. Among them, R v and L v These are the virtual resistance and virtual inductance values ​​set in the control algorithm. They are key parameters for grid control and are used to simulate the impedance characteristics of a synchronous generator. v outd , v outq , i outd , i outq as well as ω m The definition and acquisition method are the same as before. The meaning of the formula is to superimpose the voltage drop across the virtual impedance (considering the resistance and inductance effects) onto the voltage of the filter capacitor, thereby obtaining the amplitude of the equivalent voltage source (i.e., induced electromotive force) inside the converter.

[0056] Its working principle is to solve for the voltage before the virtual impedance in reverse. In the control algorithm, the induced electromotive force command... E ref The capacitor voltage command is generated only after passing through the virtual impedance stage. The estimation formula then uses the actually measured capacitor voltage and output current to calculate the true value of the induced electromotive force acting on the "front end" of the virtual impedance. E .

[0057] This estimation method allows for the real-time acquisition of key state variables within the control loop without requiring additional hardware. E This provides the necessary input for the accurate calculation of the compensation item and is one of the key steps in realizing this application.

[0058] The above-mentioned method for estimating the voltage and induced electromotive force at the common coupling point is used in synchronous rotation. dq This can be implemented using a coordinate system as an example; similarly, it can also be implemented in... αβ Implemented in a coordinate system. The compensation term is introduced during the stage where the induced electromotive force reference value or reactive power reference value is generated in the reactive-voltage outer loop.

[0059] Its working principle is to utilize dq The coordinate system transforms the control of AC quantities into the control of DC quantities, simplifying the design of the PI regulator and achieving decoupled control of active and reactive power. The dual closed-loop structure of voltage and current ensures the waveform quality of the output voltage and the rapid tracking and current-limiting protection of the current.

[0060] Adopt mature dqThe coordinate system and dual closed-loop control framework ensure that the proposed solution is compatible with most existing converter control platforms, facilitating engineering implementation and promotion, while retaining the dynamic performance and stability advantages of the original control structure.

[0061] The proposed method enhances the voltage support capability of grid-connected converters. The control strategy of this application primarily targets scenarios where the grid voltage amplitude changes by a small magnitude and at a slow rate (e.g., within ±10%), or where the reactive power demand of the local load undergoes a step or gradual change. Particularly in weak grid environments with low short-circuit ratios and high grid impedance, the impact of line impedance voltage drop is more significant, and the compensation effect of this application is more pronounced. In implementation, the controller parameters (such as the gain of the compensation stage) can be tuned according to the typical grid strength (SCR range) of the target application scenario to optimize dynamic response and stability.

[0062] Its working principle is to improve voltage control performance by compensating for the voltage drop across the linear impedance.

[0063] This implementation method clarifies the advantageous application scenarios of this application, making it clearly valuable and targeted in improving the voltage stability of weak power grids with a high proportion of new energy access, and avoiding confusion with large disturbance control strategies used for fault ride-through.

[0064] The voltage support enhancement control for grid-type converters proposed in this application compensates for the voltage drop caused by the virtual impedance and line impedance of the grid-type converter, which is equivalent to establishing reactive power. voltage at common coupling point The droop relationship between reactive power and voltage achieves the same effect as the reactive power-voltage droop relationship constructed by existing single reactive power loop control and voltage RMS control, ultimately enhancing the voltage support capability of grid-type converters.

[0065] The voltage enhancement control method for grid-type converters proposed in this application significantly improves the voltage support effect of grid-type converters at the common coupling point by adding an additional voltage or reactive power compensation link on the basis of the existing voltage and current dual-loop control structure. Moreover, the compensation link has a simple structure and is easy to implement in engineering.

[0066] The voltage control method for grid-type converters proposed in this application compensates for the voltage drop caused by the virtual impedance of the grid-type converter and the line impedance between the filter capacitor and the common coupling point. This is equivalent to establishing a droop relationship between reactive power and the voltage at the common coupling point, thereby improving the voltage support capability of existing grid-type converters based on voltage and current dual closed-loop control.

[0067] Example: This application, through the... Figure 4 China grid voltage Applying a step command to simulate the voltage support effect of a grid converter by changing... Figure 4 China grid impedance The magnitude is used to simulate the change in the short-circuit ratio (SCR).

[0068] Figures 8-10 The simulation results compare the voltage support enhancement control method for grid-type converters proposed in this application with existing voltage-current dual-loop control. Among them, Figure 8 The grid voltage under the condition of SCR=2 (weak grid) The voltage response waveform at the point of common coupling when the voltage drops by 0.1 pu. Figure 9 The grid voltage under SCR=10 (strong power grid) operating condition The voltage response waveform at the point of common coupling when the voltage drops by 0.1 pu. Figure 10 This is the voltage response waveform at the common coupling point when the reactive power of the load suddenly increases under off-grid conditions.

[0069] Figure 8-10 The comparison results show that, compared with the existing voltage and current dual closed-loop control, the voltage support enhancement control method for grid-type converters proposed in this application not only improves the voltage at the common coupling point in steady state, but also suppresses the change in the voltage at the common coupling point during the transient process of grid voltage drop. This indicates that the voltage support enhancement control method for grid-type converters proposed in this application improves the voltage support effect at the common coupling point.

[0070] The second objective of this application is to provide a voltage support enhancement control system for a grid-type converter, comprising: an existing voltage and current dual closed-loop control module for implementing basic control of the grid-type converter; and a compensation enhancement module for calculating the compensation terms as described above. The hardware carrier of this system is the converter controller, which typically includes a digital signal processor, analog signal acquisition circuitry, pulse drive circuitry, etc. The voltage and current dual closed-loop control module is a standard software module for existing grid-type converter controllers. The compensation enhancement module is a software functional module whose inputs include data from sensors. V bus Signals (or estimates) and those derived from internal calculations E The value is output as the compensation amount. V comp or Q comp The droop control module is also a software module. It receives voltage reference values, reactive power feedback values, and compensation amounts, and then... Figure 5 The logic shown performs droop calculations and outputs a corrected reference value. These modules execute sequentially within the same control interrupt of the DSP, for example, at an interrupt frequency of 10kHz.

[0071] Its working principle is that all modules of the system work together. In each control cycle, the compensation enhancement module calculates the required compensation amount based on the real-time electrical state, the droop control module incorporates this compensation amount into the reference value calculation, and the voltage and current dual closed-loop control module performs fast closed-loop adjustment based on the corrected reference value to drive the power device to generate the desired voltage output.

[0072] The third objective of this application is to provide a grid-connected converter device, including the voltage support enhancement control system described above. This device refers to a complete grid-connected converter product, whose main power circuit includes a three-phase full-bridge converter composed of IGBTs or SiC MOSFETs, LC or LCL filters, contactors, etc. The control system, as the core control unit of this device, is integrated within the converter's control cabinet. The control system is connected to the drive board and sensors in the power cabinet via optical fiber or cable. The entire device is installed in a new energy power station (such as a photovoltaic power station or wind farm) or energy storage power station, and its AC side is connected to a common coupling point via a circuit breaker, thereby connecting to the power grid.

[0073] Its working principle is that the device operates as an active voltage support node in the power grid. When its built-in control system executes the enhanced control method of this application, the device can more effectively inject or absorb reactive power into the power grid to smooth voltage fluctuations at the point of common coupling.

[0074] This implementation extends the scope of protection to specific physical devices (products) that include the control system of this application, realizing a complete intellectual property protection chain from control method to final product, which helps to enhance the market competitiveness of the product.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation methods of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A voltage control method for a grid-type converter, characterized in that, include: In the reactive power-voltage droop control loop of the grid-type converter based on voltage and current dual closed-loop control, a voltage or reactive power compensation term is added. The compensation term is used to compensate for the voltage drop caused by the virtual impedance of the grid-type converter and the line impedance between the filter capacitor and the common coupling point, thereby enhancing the support capability for the voltage of the common coupling point.

2. The voltage control method for a grid-type converter according to claim 1, characterized in that, When the compensation term is a voltage compensation term, the voltage compensation term is ,in This is the true value of the induced electromotive force. The voltage at the common coupling point is used; the voltage compensation term is superimposed on the induced electromotive force reference value.

3. The voltage control method for a grid-type converter according to claim 1, characterized in that, When the compensation term is a reactive power compensation term, the reactive power compensation term is wherein is a reactive droop coefficient, is a real value of induced electromotive force, is a point of common coupling voltage; the reactive power compensation term is superimposed on a reactive power reference value.

4. The meshed voltage control method of a power converter according to claim 2 or 3, characterized by, The common coupling point voltage is obtained in any of the following ways: (a) Directly sample the voltage at the common coupling point; (b) Estimate based on filter capacitor voltage, output current and line impedance parameters.

5. The network-forming converter voltage control method of claim 4, wherein, The method for estimating the voltage at the common coupling point is as follows: calculate the difference between the voltage phasor of the filter capacitor and the voltage phasor generated by the output current on the line impedance.

6. The network-configured voltage controller method of claim 2 or 3, wherein, The real value of the induced electromotive force The estimation method is to calculate the sum of the filtered capacitor voltage phasor and the voltage phasor generated by the output current on the virtual impedance. 7.The network configuration type converter voltage control method according to claim 1, wherein The compensation term is low-pass filtered and then superimposed on the reference value, wherein: When the compensation term is voltage compensation, the voltage compensation term is filtered by a low-pass filter and then superimposed on the induced electromotive force reference value; When the compensation term is reactive power compensation, the reactive power compensation term is superimposed on the reactive power reference value after passing through a low-pass filter.

8. The voltage control method for a grid-type converter according to claim 2, characterized in that, The common coupling point voltage Estimates were made in accordance with the following model: ； The true value of the induced electromotive force One specific estimation method is as follows: ； in, and These are virtual resistance and virtual inductance, respectively; , For the voltage of the filter capacitor dq or αβ Axial components, , For the output current dq or αβ Axial components; , For line resistance and inductance, This is the virtual angular frequency.

9. A meshed voltage control system of a power converter, characterized by, include: The voltage and current dual closed-loop control module is used to realize the basic voltage control of the grid-type converter; A compensation module is used to execute the grid-type converter voltage control method according to any one of claims 1 to 8.

10. A meshed network of power converter devices, characterized in that, Includes the voltage control system as described in claim 9.

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