A method and system for stable control of multi-machine parallel connection of network-forming converters

Abstract

The application provides a kind of network type converter multi-machine parallel stable control method and system, comprising: obtaining the d-axis current component and q-axis current component at grid-connected point, and virtual impedance link generates d-axis virtual voltage component and q-axis virtual voltage component;D-axis virtual voltage component and q-axis virtual voltage component are input into AC voltage loop controller, and the d-axis current component and q-axis current component of voltage loop output are generated;Feedforward damping compensation link processes the d-axis current component and q-axis current component of voltage loop output, obtains d-axis output voltage and q-axis output voltage;Through AC current loop controller, d-axis output modulation voltage and q-axis output modulation voltage are generated;D-axis output voltage and q-axis output voltage are superimposed to d-axis output modulation voltage and q-axis output modulation voltage respectively, and d-axis output synthesis modulation voltage and q-axis output synthesis modulation voltage are obtained, and dynamic adjustment is carried out.The application effectively improves the oscillation stability of network type converter multi-machine parallel system.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, specifically to a stable control method and system for multiple grid-connected converters in parallel. Background Technology

[0002] Driven by the "dual-carbon" strategy, the proportion of new energy power generation such as wind power and photovoltaic power continues to rise, propelling the power system towards a "dual-high" form with a high proportion of renewable energy and a high proportion of power electronic equipment. Grid-type converters, with their autonomous voltage building and active grid support characteristics, have become core equipment for building new power systems.

[0003] In the prior art, patent CN110190734A discloses a control method and device for a power electronic converter, which adopts a dual closed-loop control of an outer loop and a current inner loop. The current inner loop includes a d-axis current inner loop and a q-axis current inner loop; it also includes a current command cross-decoupling control link: the d-axis current command value is superimposed on the output value of the q-axis current inner loop after passing through a first proportional adjustment coefficient; the q-axis current command value is superimposed on the output value of the d-axis current inner loop after passing through a second proportional adjustment coefficient. Although decoupling can be achieved, it does not consider the problem that power disturbances generated in the scenario of multiple machines connected in parallel and grid-connected can easily cause power oscillations.

[0004] However, with the large-scale deployment of grid-connected converters in strong power grid scenarios, low-frequency oscillation problems have gradually emerged. Studies have shown that the negative damping effect caused by the interaction between converter units and between the converter and the grid in grid-connected multi-machine parallel systems is the core cause of oscillations. Existing technologies have key shortcomings in addressing the low-frequency oscillation problem in grid-connected multi-machine parallel systems: First, existing suppression strategies are mostly developed based on single-machine systems, making it difficult to simultaneously address both machine-grid interaction oscillations under strong power grids and machine-machine interaction oscillations under weak power grids; second, existing strategies do not adequately consider the adaptability to non-ideal operating conditions commonly found in multi-machine systems, such as differences in control parameters between units and uneven power output.

[0005] Therefore, it is urgent to propose targeted low-frequency oscillation suppression schemes based on the stability mechanism analysis considering the interaction effects of multiple machines, so as to improve the stable operation capability of multi-machine parallel grid converter systems. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of this application is to provide a stable control method and system for multiple parallel grid-connected converters.

[0007] The first aspect of this application provides a stable control method for multiple parallel grid-connected converters. Obtain the d-axis current component and q-axis current component at the grid connection point, and generate the d-axis virtual voltage component and q-axis virtual voltage component through the virtual impedance link in the additional damping control module; The d-axis virtual voltage component and the q-axis virtual voltage component are input into the AC voltage loop controller in the inner loop control module to generate the d-axis current component and the q-axis current component output by the voltage loop. The d-axis current component and q-axis current component of the voltage loop output are processed by the feedforward damping compensation stage in the additional damping control module to obtain the d-axis output voltage and q-axis output voltage; at the same time, the d-axis output modulation voltage and q-axis output modulation voltage are generated by the AC current loop controller in the inner loop control module. The d-axis output voltage and q-axis output voltage are superimposed on the d-axis output modulation voltage and q-axis output modulation voltage, respectively, to obtain the d-axis output composite modulation voltage and q-axis output composite modulation voltage, which are then dynamically adjusted.

[0008] Optionally, the feedforward damping compensation stage includes a high-pass filter stage and a gain stage; The feedforward damping compensation stage processes the d-axis current component and the q-axis current component sequentially through the high-pass filter stage and the gain stage to generate the d-axis output voltage and the q-axis output voltage. The d-axis output voltage and q-axis output voltage are respectively superimposed on the d-axis output modulation voltage and the q-axis output modulation voltage to generate the d-axis output composite modulation voltage and the q-axis output composite modulation voltage, and the d-axis output modulation voltage and the q-axis output modulation voltage are dynamically adjusted.

[0009] Optionally, the expressions for the d-axis output synthesized modulation voltage and the q-axis output synthesized modulation voltage are respectively: ; ; In the formula, V dref The output modulation voltage is for the d-axis. V fdd This represents the d-axis output voltage of the feedforward damping circuit. V mdref The output is a synthesized modulation voltage for the d-axis; V qref This is the q-axis output modulation voltage. V fdq This is the q-axis output voltage of the feedforward damping circuit. V mqref The output is a synthesized modulation voltage for the q-axis; The d-axis output voltage of the feedforward damping element Vfdd and q-axis output voltage V fdq They are respectively: ; ; In the formula, T fd The time constant of the high-pass filter. K fd This represents the gain coefficient of the gain element in the feedforward damping compensation stage. s For complex variables in the transfer function; i fdd , i fdq These are the d-axis and q-axis current components output by the AC voltage loop controller, respectively.

[0010] Optionally, the high-pass filter stage in the feedforward damping compensation stage H fd ( s This is used to filter out DC components from the input signal, and its expression is: H fd ( s ) = T fd · s / ( T fd · s + 1); In the formula, T fd It is a time constant; s For complex variables in the transfer function; Wherein, the time constant of the high-pass filter T fd The frequency range of the low-frequency oscillation is determined, and it satisfies the following: T fd ≥ 1 / (2π· f c_min ); In the formula, f c_min This is the minimum low-frequency oscillation frequency that a grid-connected converter can generate under strong or weak power grid conditions, and the low-frequency oscillation frequency is 1 to 2 Hz.

[0011] Optionally, the gain coefficient of the gain element in the feedforward damping compensation stage. K fd The gain coefficient is determined based on the actual compensated system phase margin, and the value range of the gain coefficient is 1 to 10.

[0012] Optionally, the step of obtaining the d-axis current component and q-axis current component at the grid connection point and generating the d-axis virtual voltage component and q-axis virtual voltage component through the virtual impedance link in the additional damping control module is as follows: the virtual voltage component is generated by the voltage drop of the d-axis current component and q-axis current component at the grid connection point through the virtual impedance in a negative feedback manner. The generation of the virtual voltage component includes: converting the d-axis current component at the grid connection point... i d The resistance value through the virtual impedance link R v Then, the inductive reactance of the q-axis current component at the grid connection point through the virtual impedance link is - oh 0 L v The values ​​are then superimposed to obtain the virtual d-axis voltage component. V vd ; The q-axis current component at the grid connection point i q The resistance value through the virtual impedance element R v Then, the inductive reactance of the d-axis current component at the grid connection point through the virtual impedance element. oh 0 L v The values ​​are then superimposed to obtain the virtual q-axis voltage component. V vq .

[0013] Optionally, when the voltage loop controller outputs the d-axis current component and the q-axis current component, it uses the virtual d-axis voltage component. V vd The virtual q-axis voltage distribution V vq Combined with d-axis reference voltage q-axis reference voltage and the measured d-axis voltage at the grid connection point V sd q-axis electrical measurement value at grid connection point V sq The difference between them is controlled by PI. H v ( s After that, the q-axis current component and the q-axis current component are output respectively; The voltage loop controller includes a cross-decoupling mechanism, which uses the d-axis voltage measurement value at the grid connection point. V sd The q-axis electrical measurement value of the grid connection point V sq go through oh 0 C f ( oh 0 is the rated angular frequency. C f After passing through the filter capacitor, the current is cross-input to the q-axis and d-axis respectively, and combined with the d-axis current component, the q-axis current component, and the d-axis current component at the grid connection point. i d and the q-axis current component at the grid connection point i q Output the reference value of the AC current loop controller. i cdref and i cqref .

[0014] A second aspect of this application provides a stable control system for multiple parallel grid-connected converters, implemented based on any one of the stable control methods for multiple parallel grid-connected converters described in this application. Includes: a basic control module and an additional damping control module; The additional damping control module is connected to the inner loop control module in the basic control module. The additional damping control module is equipped with a virtual impedance link and a feedforward damping compensation link to suppress low-frequency oscillations in the multi-machine parallel system of the grid-type converter. The inner loop control module includes an AC voltage loop controller for outputting the d-axis current component and the q-axis current component. The virtual impedance link is used to generate a virtual voltage component by negative feedback of the voltage drop generated by the current at the grid connection point through the virtual impedance, and input it to the AC voltage loop controller. The feedforward damping compensation circuit processes the d-axis current component and the q-axis current component respectively to obtain the d-axis output voltage and the q-axis output voltage, and applies the d-axis output voltage and the q-axis output voltage to the d-axis output modulation voltage and the q-axis output modulation voltage respectively for dynamic adjustment.

[0015] Optionally, the inner loop controller has a voltage and current dual closed-loop structure; The inner loop control also includes an AC current loop controller, a voltage feedforward circuit, and a current feedforward circuit. The current feedforward circuit is set in the AC voltage loop controller to form AC voltage closed-loop control. The voltage feedforward circuit is set in the AC current loop controller to form AC current closed-loop control. The AC current loop controller outputs the d-axis modulation voltage and the q-axis modulation voltage.

[0016] Optionally, the stability control system further includes an outer loop control module, which is connected to the AC voltage loop controller and is used to control the active power and reactive power of the grid-type converter and generate a synchronous phase angle. The outer loop control module includes an active power synchronization link controlled by VSG and a reactive power-voltage control link. The d-axis voltage reference value and the q-axis voltage reference value are generated through the reactive power-voltage control loop.

[0017] This application provides a stable control method for a multi-unit parallel grid-connected converter. It employs techniques such as adding a virtual impedance element and a feedforward damping compensation element during the control process. The virtual impedance reshapes the system output impedance to provide basic damping, while the feedforward compensation branch injects adaptive damping for the oscillation frequency band. This effectively enhances the low-frequency oscillation stability of the multi-unit parallel grid-connected converter system under both strong and weak grid conditions. It not only effectively suppresses low-frequency oscillations but also possesses excellent dynamic performance. It can be used in grid-connected power electronic equipment such as photovoltaic power generation units, direct-drive wind turbines, and energy storage systems, enabling the multi-unit system to maintain stable operation across a wide grid short-circuit ratio range.

[0018] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0019] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a structural diagram illustrating a stable control system for a grid-type converter with multiple units connected in parallel, according to an exemplary embodiment.

[0020] Figure 2 The diagram shows the output power waveforms at the grid connection point of the system before and after implementing the proposed stability control method under strong and weak power grids, according to an exemplary embodiment.

[0021] Figure 3 This is a flowchart illustrating a stable control method for multiple parallel grid-connected converters according to an exemplary embodiment. Detailed Implementation

[0022] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0023] In the description of the embodiments of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0024] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0025] In the description of the embodiments in this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0026] The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or devices.

[0027] In existing technologies, most suppression strategies are developed based on single-machine systems, making it difficult to simultaneously address both machine-grid interactive oscillations under strong power grids and machine-machine interactive oscillations under weak power grids. To address these issues, this application provides a stability control method for multiple parallel grid-connected converters to solve the aforementioned problems.

[0028] Reference Figure 3 As shown in one embodiment of this application, a stability control method for a grid-connected converter with multiple units in parallel includes: S100: Obtain the d-axis current component and q-axis current component at the grid connection point, and generate the d-axis virtual voltage component and q-axis virtual voltage component through the virtual impedance link in the additional damping control module. S200: Input the d-axis virtual voltage component and the q-axis virtual voltage component into the AC voltage loop controller in the inner loop control module to generate the d-axis current component and the q-axis current component of the voltage loop output. S300 processes the d-axis current component and q-axis current component of the voltage loop output through the feedforward damping compensation stage in the additional damping control module to obtain the d-axis output voltage and q-axis output voltage; at the same time, the AC current loop controller in the inner loop control module generates the d-axis output modulation voltage and q-axis output modulation voltage. S400: The d-axis output voltage and q-axis output voltage are superimposed on the d-axis output modulation voltage and q-axis output modulation voltage, respectively, to obtain the d-axis output composite modulation voltage and q-axis output composite modulation voltage, and then dynamically adjusted.

[0029] Specifically, firstly, the d-axis and q-axis current components at the grid connection point are acquired; secondly, the virtual impedance link introduces the voltage drop generated by the current at the grid connection point through the virtual impedance into the voltage loop reference value in a negative feedback manner; next, the d-axis and q-axis current components, as well as the d-axis and q-axis output modulation voltages, output from the AC voltage loop controller are acquired; then, the d-axis current component is processed by the feedforward damping compensation link and applied to the d-axis output modulation voltage to generate the d-axis output composite modulation voltage; simultaneously, the q-axis current component is processed by the feedforward damping compensation link and applied to the q-axis output modulation voltage to generate the q-axis output composite modulation voltage; finally, based on the d-axis and q-axis output composite modulation voltages, the output modulation voltages of the d-axis and q-axis are dynamically adjusted to suppress low-frequency oscillations that occur in multiple grid-connected converters under strong or weak grid conditions.

[0030] In the embodiments described above, by acquiring the relevant current and output modulation voltage of the AC voltage loop controller, a virtual impedance link is used to introduce the voltage drop generated by the current at the grid connection point through the virtual impedance into the voltage loop reference value in a negative feedback manner; the feedforward damping compensation link processes the q-axis current component and the d-axis current component respectively, and generates the d-axis output composite modulation voltage and the q-axis output composite modulation voltage based on the processing results, which effectively improves the oscillation stability of the grid-connected multi-machine parallel system, so that the multi-machine system can maintain stable operation within a wide grid short-circuit ratio range and has good dynamic performance.

[0031] In some specific embodiments of this application, the feedforward damping compensation stage of the additional damping control module includes a high-pass filter stage and a gain stage.

[0032] The feedforward damping compensation stage processes the d-axis current component and the q-axis current component sequentially through a high-pass filter stage and a gain stage to generate the d-axis output voltage and the q-axis output voltage. The d-axis output voltage and the q-axis output voltage are then superimposed onto the d-axis output modulation voltage and the q-axis output modulation voltage, respectively, to generate the d-axis output composite modulation voltage and the q-axis output composite modulation voltage. The d-axis output modulation voltage and the q-axis output modulation voltage are then dynamically adjusted.

[0033] Specifically, refer to Figure 1 As shown, AC voltage loop controller H v ( s The d-axis current component of the output is applied to the d-axis output modulation voltage after passing through a high-pass filter (to extract high-frequency components) and a gain stage (to adjust the amplitude). V dref The summation yields the d-axis output synthesized modulation voltage. V mdref At the same time, the AC voltage loop controller H v ( s The output q-axis current component is passed through a high-pass filter. H d ( s and gain coefficient K d Apply it to the q-axis output modulation voltage V qref The q-axis output synthesized modulation voltage is obtained. V mqref .

[0034] The high-pass filter allows only high-frequency signals to pass through while attenuating low-frequency components. By introducing the high-frequency component of the current into the output modulation voltage, the voltage output is quickly adjusted to suppress disturbances during dynamic processes (when the high frequency changes). In steady state (low-frequency or DC components), the output of the high-pass filter is close to zero, avoiding static effects on the output modulation voltage, thereby achieving low-frequency suppression.

[0035] In the embodiments described above, the high-frequency dynamic components of the current are extracted by a high-pass filter, and the voltage reference value is dynamically corrected after gaining. This effectively suppresses the impact of low-frequency disturbances on system stability, while ensuring control accuracy in steady state. The high-pass filter isolates low-frequency signals and avoids static errors, while the gain stage improves the dynamic response speed.

[0036] Furthermore, the expressions for the d-axis output synthesized modulation voltage and the q-axis output synthesized modulation voltage are as follows: ; ; In the formula,V dref The output modulation voltage is for the d-axis. V fdd This represents the d-axis output voltage of the feedforward damping circuit. V mdref The output is a synthesized modulation voltage for the d-axis; V qref This is the q-axis output modulation voltage. V fdq This is the q-axis output voltage of the feedforward damping circuit. V mqref The output is a synthesized modulation voltage for the q-axis.

[0037] Among them, the d-axis output voltage of the feedforward damping element V fdd and q-axis output voltage V fdq They are respectively: ; ; In the formula, T fd The time constant of the high-pass filter. K fd This represents the gain coefficient of the gain element in the feedforward damping compensation stage. s For complex variables in the transfer function; i fdd , i fdq These are the d-axis and q-axis current components output by the AC voltage loop controller, respectively.

[0038] Furthermore, AC voltage loop controller H v ( s The expression for ) is, H v ( s ) = k p-v + k i-v / s ; In the formula, k p-v and k i-v These are the proportional and integral coefficients of the PI control in the AC voltage loop controller. s These are complex variables in the transfer function.

[0039] In some specific embodiments of this application, the high-pass filter stage in the feedforward damping compensation stage H fd (s This is used to filter out DC components from the input signal, and its expression is: H fd ( s ) = T fd · s / ( T fd · s + 1); In the formula, T fd It is a time constant; s These are complex variables in the transfer function.

[0040] Among them, the time constant of the high-pass filter T fd It is determined by the frequency range of the low-frequency oscillation and satisfies the following conditions; T fd ≥ 1 / (2π· f c_min ); In the formula, f c_min This refers to the minimum low-frequency oscillation frequency generated by a grid-connected converter under strong or weak power grid conditions, and the... f c_min The value ranges from 1 to 2 Hz.

[0041] For example, refer to Figure 2 As shown, the time constant of the high-pass filter is set to 0.159 s.

[0042] Furthermore, the gain coefficient of the gain element in the feedforward damping compensation stage. K fd The gain coefficient is determined based on the actual compensated system phase margin, and its value ranges from 1 to 10.

[0043] In some specific embodiments of this application, the d-axis current component and q-axis current component at the grid connection point are obtained, and the d-axis virtual voltage component and q-axis virtual voltage component are generated by the virtual impedance link in the additional damping control module as follows: the d-axis current component and q-axis current component at the grid connection point are generated by the voltage drop generated by the virtual impedance through the virtual impedance in the form of negative feedback to generate virtual voltage components.

[0044] Generating virtual voltage components includes: converting the d-axis current components at the grid connection point. i d The resistance value through the virtual impedance link R v Then, the inductive reactance of the q-axis current component at the grid connection point through the virtual impedance link is... oh0 L v The values ​​are then superimposed to obtain the virtual d-axis voltage component. V vd .

[0045] The q-axis current component at the grid connection point i q The resistance value through the virtual impedance element R v Then, the inductive reactance of the d-axis current component at the grid connection point through the virtual impedance link. oh 0 L v The values ​​are then superimposed to obtain the virtual q-axis voltage component. V vq .

[0046] Specifically, in some embodiments of this application, the virtual impedance element is based on the d-axis component of the current at the grid connection point. i d and q-axis components i q As input, the voltage drop generated by the current through the virtual impedance is used to generate a virtual voltage component via negative feedback; the d-axis current component i at the grid connection point is... d The virtual resistance value through the virtual impedance element R v This generates a resistive voltage drop component and simultaneously generates the q-axis current component at the grid connection point. i q Virtual inductive reactance through virtual impedance circuit oh 0 L v The inductive voltage drop component is generated, and the virtual d-axis voltage component is obtained by superimposing the two types of components. V vd Simultaneously, the q-axis current component at the grid connection point... i q The virtual resistance value through the virtual impedance element R v Generate a resistive voltage drop component, and convert the d-axis current component i at the grid connection point. d Virtual inductive reactance through virtual impedance circuit oh 0 L v The inductive voltage drop component is generated, and the virtual q-axis voltage component is obtained by superimposing the two types of components. V vq .

[0047] In the embodiments described above, the virtual impedance construction method eliminates the need for additional hardware impedance components. It effectively constructs an inverter output impedance with both resistive and inductive characteristics in the dq synchronous rotating coordinate system. The resistive voltage drop component introduces active damping into the system, effectively suppressing the circulating current and LC filter resonance risks during multi-unit parallel operation. Simultaneously, the cross-inductive voltage drop component decouples the d-axis and q-axis control channels, eliminating coupling interference between current components and offsetting the impact of actual line impedance differences on power distribution accuracy. This improves the inverter's stability, dynamic response performance, and multi-unit parallel adaptability under various operating modes, including grid-connected and islanded modes.

[0048] The formula for introducing the voltage drop generated by the current at the grid connection point into the d-axis voltage loop reference value via negative feedback in the virtual impedance loop is as follows: ; In the formula, i d and i q These are the d-axis and q-axis current components at the grid connection point, respectively. R v and L v These are the resistance and inductance values ​​of the virtual impedance link, respectively; oh 0 is the rated angular frequency; V vd This represents the virtual d-axis voltage component.

[0049] Furthermore, the formula for introducing the voltage drop generated by the current at the grid connection point into the q-axis voltage loop reference value through negative feedback in the form of virtual impedance is as follows: ; In the formula, V vq This represents the virtual q-axis voltage component.

[0050] Among them, the resistance value of the virtual impedance element R v The value ranges from 0.08 to 0.78 pu, and the inductance value... L v The value range is 0.06 ~ 2.45 pu.

[0051] In some specific embodiments of this application, the voltage loop controller outputs the d-axis current component and the q-axis current component through a virtual d-axis voltage component. V vd Virtual q-axis voltage V vq Combined with d-axis reference voltage q-axis reference voltage and the measured d-axis voltage at the grid connection point V sd q-axis electrical measurement value at grid connection point V sq The difference between them is controlled by PI. H v ( s After that, the q-axis current component and the q-axis current component are output respectively.

[0052] The voltage loop controller includes a cross-decoupling element, which uses the d-axis voltage measurement value at the grid connection point. V sd q-axis electrical measurement value at grid connection point V sq go through oh 0 C f ( oh 0 is the rated angular frequency. C f After passing through the filter capacitor, the current is cross-input to the q-axis and d-axis respectively, and then combined with the d-axis current component, the q-axis current component, and the d-axis current component at the grid connection point. i d and the q-axis current component at the grid connection point i q Reference value of output AC current loop controller i cdref and i cqref .

[0053] Specifically, when generating current loop reference commands, the voltage loop controller first bases them on the d-axis reference voltage. q-axis reference voltage Combined with virtual d-axis voltage components V vd Virtual q-axis voltage component V vq The measured value of the d-axis voltage at the grid connection point V sd , q-axis voltage measurement value V at grid connection point sq The difference between them yields the d-axis and q-axis voltage control deviation signals, which are then input to the voltage loop PI controller H. v(s) The output includes d-axis and q-axis current control components; the voltage loop controller incorporates a cross-decoupling mechanism to convert the measured d-axis voltage V at the grid connection point into a single unit. sd , q-axis voltage measurement value V at grid connection point sq respectively oh 0 C f After calculation, the data is cross-input to the q-axis and d-axis control channels, and then combined with the aforementioned d-axis and q-axis current control components and the d-axis current component i at the grid connection point. d q-axis current component i qFinally, the d-axis current reference value of the AC current loop controller is generated. i cdref and q-axis current reference value i cqref .

[0054] In the embodiments described above, the reference voltage is corrected using virtual voltage components through the coordinated setting of the voltage loop control and cross-decoupling stages. This effectively constructs a virtual output impedance for the inverter at the control level, optimizing power distribution accuracy and circulating current suppression in multi-unit parallel scenarios without additional hardware components. Simultaneously, through closed-loop feedback of the grid connection point voltage, zero steady-state error tracking of the d-axis and q-axis reference voltages is achieved, improving the amplitude and phase control accuracy of the inverter output voltage. oh 0 C f The cross-coupling stage eliminates the cross-coupling effect of the LC filter capacitor voltage in the dq synchronous rotating coordinate system, making the d and q axis voltage control channels independent of each other, which greatly improves the dynamic response speed and control stability of the voltage loop and avoids the resonance spike of the LC filter. In addition, based on the voltage loop output combined with the cross-coupling signal, a precise current loop reference command is generated, which improves the inverter's anti-interference capability and operational stability in multiple operating modes such as grid-connected and islanded.

[0055] Where, the d-axis is - V vd - V sd The difference is used by a PI controller to obtain the d-axis current component, and the q-axis is obtained similarly. The virtual voltage component is superimposed using negative feedback. oh 0 C f In oh 0 is the rated angular frequency. C f This is a filter capacitor. By cross-feeding the d-axis and q-axis voltage measurements into each other's channels, decoupling of the d-axis and q-axis voltage control is achieved, eliminating the cross-coupling effect caused by the LC filter.

[0056] Based on the same inventive concept, a second aspect of this application provides a stable control system for a grid-connected converter with multiple units in parallel, implemented based on any of the stable control methods for a grid-connected converter with multiple units in parallel, comprising: a basic control module and an additional damping control module.

[0057] The additional damping control module is connected to the inner loop control module in the basic control module. The additional damping control module is equipped with a virtual impedance link and a feedforward damping compensation link to suppress low-frequency oscillations in the multi-machine parallel system of the grid-type converter.

[0058] The inner loop control module includes an AC voltage loop controller for outputting d-axis and q-axis current components; a virtual impedance circuit for generating a virtual voltage component by negative feedback of the voltage drop generated by the current at the grid connection point through the virtual impedance, and inputting it to the AC voltage loop controller; and a feedforward damping compensation circuit for processing the d-axis and q-axis current components to obtain the d-axis output voltage and q-axis output voltage, and applying the d-axis output voltage and q-axis output voltage to the d-axis output modulation voltage and q-axis output modulation voltage respectively for dynamic adjustment.

[0059] Specifically, the inner loop control module controls the AC side voltage and current of the grid-connected converter and generates the modulation voltage. The virtual impedance circuit generates a virtual voltage component by negative feedback of the voltage drop generated by the current at the grid connection point through the virtual impedance, and inputs it to the AC voltage loop controller. The feedforward damping compensation circuit processes the d-axis current component and q-axis current component output by the AC voltage loop controller to obtain the d-axis output voltage and q-axis output voltage, and applies the d-axis output voltage to the d-axis output modulation voltage and the q-axis output voltage to the q-axis output modulation voltage to dynamically adjust the output modulation voltage of the d-axis and q-axis.

[0060] The embodiments described above in this application effectively improve the oscillation stability of a multi-machine parallel system of a grid-type converter by adding virtual impedance and feedforward damping compensation links to the basic control module of the grid-type converter. This enables the multi-machine system to maintain stable operation over a wide range of grid short-circuit ratios and has good dynamic performance.

[0061] The virtual impedance circuit processes the grid-connected point current through virtual resistance and virtual inductance to generate a virtual voltage component, which is then negatively fed back to the voltage loop reference value input. This component works in conjunction with the given reference voltage and the actual measured value, and after being regulated by the voltage loop PI, outputs the d-axis and q-axis current components. This achieves equivalent reshaping of the converter output impedance at the control level, and by introducing positive damping, it suppresses low-frequency oscillations and improves the stability of multi-machine parallel operation.

[0062] In some specific embodiments of this application, the inner loop controller is a voltage and current dual closed-loop structure.

[0063] The inner loop control also includes an AC current loop controller, a voltage feedforward circuit, and a current feedforward circuit.

[0064] The current feedforward element is set in the AC voltage loop controller to form AC voltage closed-loop control; the voltage feedforward element is set in the AC current loop controller to form AC current closed-loop control.

[0065] The AC current loop controller outputs modulation voltage on the d-axis and modulation voltage on the q-axis.

[0066] Specifically, in AC current loop control, the AC current loop controller monitors and regulates the AC current in real time. Simultaneously, a voltage feedforward loop is introduced to detect voltage changes in advance and quickly feed them back to the current control loop. This assists the AC current loop controller in adjusting its control strategy promptly to respond quickly to the impact of voltage changes on the current, thus forming AC current closed-loop control. In AC voltage loop control, the AC voltage loop controller monitors and regulates the AC voltage, while the current feedforward loop acquires current change information in real time and feeds it back to the voltage control loop. This helps the AC voltage loop controller quickly respond to the impact of current changes on the voltage, thus forming AC voltage closed-loop control. These two loops work together to form a dual closed-loop structure of voltage and current, achieving precise control of the system voltage and current.

[0067] Among them, such as Figure 1 As shown, the voltage loop control and current loop control are cascaded, controlling the voltage and current feedback signals of the main circuit, respectively. Specifically, in the voltage loop control, the voltage feedback signal... V sd、q The difference between the input and the reference value is used as the input to the voltage loop controller; in the current loop control, the current feedback signal... i cd、q The difference between the voltage loop and the reference value is used as the input to the current loop controller. Therefore, both the voltage loop and the current loop are "closed-loop" controls.

[0068] The current feedforward element is a component of the voltage loop control, and the voltage feedforward element is a component of the current loop control.

[0069] It should be noted that the inner loop control module is used to control the AC side voltage and current of the grid-type converter and generate the modulation voltage; the additional damping compensation module is used to improve the oscillation stability of the multi-machine parallel system of the grid-type converter, so that the multi-machine system can maintain stable operation within a wide range of grid short-circuit ratios and has good dynamic performance.

[0070] Secondly, the input to the feedforward damping compensation stage in this application is the current signal output by the "voltage loop controller," which refers to a PI controller. H v ( s The current signal output by the "voltage loop control" is the input reference signal for the "current loop control".

[0071] The embodiments described above in this application achieve independent and coordinated control of AC current and AC voltage by setting up an AC current loop controller, an AC voltage loop controller, a voltage feedforward link, and a current feedforward link to form a voltage and current dual closed-loop structure. The voltage feedforward link in the AC current loop control and the current feedforward link in the AC voltage loop control can improve the system's response speed and anti-interference capability, enabling rapid and accurate output adjustment in the face of external interference and load changes, ensuring the stability of AC current and voltage, improving the overall system's control accuracy and stability, and enhancing the system's adaptability to different operating conditions.

[0072] In some specific embodiments of this application, the stability control system further includes an outer loop control module, which is connected to the AC voltage loop controller and is used to control the active and reactive power of the grid-type converter and generate the synchronous phase angle.

[0073] The outer loop control module includes the active power synchronization link controlled by VSG and the reactive power-voltage control link.

[0074] The d-axis voltage reference value and the q-axis voltage reference value are generated through the reactive power-voltage control loop.

[0075] It should be noted that the outer loop control module is used to simulate the inertial characteristics, damping characteristics, and primary frequency and voltage regulation characteristics of a synchronous generator, control the active and reactive power of the grid-type converter, and generate the synchronous phase angle. Specifically, refer to Figure 1 As shown, in the synchronization circuit, the active power reference value... P ref With actual power P Do the difference, after 1 / oh The change obtained after 0 is equivalent to the change in torque. After passing through the virtual moment of inertia and damping element, the angular frequency is obtained. Then, after integration, the output phase angle value is obtained.

[0076] In the reactive power-voltage control loop, the reactive power reference value Q ref With feedback value Q The deviation, and then compared with the reference value of the output voltage amplitude. V tref and measured values V sd After subtraction, a reactive voltage droop factor is applied. D q The difference between the output and the input is given by a gain of 1 / K The integrator is used to obtain the d-axis voltage reference value. .

[0077] The inner loop control module includes AC voltage loop control and AC current loop control. The AC voltage loop control includes a current feedforward component; the AC current loop control includes a voltage feedforward component.

[0078] In AC voltage loop control, a reference value for q-axis AC voltage loop control is set. = 0, so that the voltage measurement value at the grid connection point is 0. V sd and V sq Follow each and The output signal of the AC voltage loop control also serves as the reference value for the AC current loop control. i cdref and i cqref These are respectively related to the current at the converter output. i cd and i cq After subtraction, the d and q components of the output modulation voltage are obtained through the PI control loop. Based on the frequency, phase and voltage amplitude output by the outer loop control module, a three-phase modulation wave can be formed. After PWM modulation, the switching signals of the converter power devices are obtained.

[0079] This application improves the oscillation stability of a multi-machine parallel system of a grid-type converter by adding virtual impedance and feedforward damping compensation links to the basic control module of the grid-type converter. This enables the multi-machine system to maintain stable operation over a wide range of grid short-circuit ratios and has good dynamic performance.

[0080] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0081] The following examples and comparative examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.

[0082] Application Example 1: Taking a multi-machine parallel system of a grid-connected converter as an example, referring to the grid-connected converter parameters in Table 1 below, the system exhibits "machine-grid" interactive oscillation under strong grid conditions and "machine-machine" interactive oscillation under weak grid conditions. The time constant of the high-pass filter in the feedforward damping compensation stage is set. T fd = 0.159 s, gain coefficient K fd= 5; The resistance value in the virtual impedance circuit is set to 0.28 pu, and the inductance value is set to 0.06 pu. Under strong grid conditions, the proposed control method is applied when the system reaches the 5th second of operation, and the output power at the grid connection point converges rapidly, effectively suppressing the "machine-grid" interactive oscillation. Under weak grid conditions, the proposed control method is applied when the system reaches the 23rd second of operation, and the output power at the grid connection point also converges rapidly, successfully suppressing the "machine-machine" interactive oscillation.

[0083] Table 1 Parameters of Network Converter

[0084] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A stable control method for multiple parallel grid-connected converters, characterized in that... ,include: Obtain the d-axis current component and q-axis current component at the grid connection point, and generate the d-axis virtual voltage component and q-axis virtual voltage component through the virtual impedance link in the additional damping control module; The d-axis virtual voltage component and the q-axis virtual voltage component are input into the AC voltage loop controller in the inner loop control module to generate the d-axis current component and the q-axis current component output by the voltage loop. The d-axis current component and q-axis current component of the voltage loop output are processed by the feedforward damping compensation stage in the additional damping control module to obtain the d-axis output voltage and q-axis output voltage; at the same time, the d-axis output modulation voltage and q-axis output modulation voltage are generated by the AC current loop controller in the inner loop control module. The d-axis output voltage and q-axis output voltage are superimposed on the d-axis output modulation voltage and q-axis output modulation voltage, respectively, to obtain the d-axis output composite modulation voltage and q-axis output composite modulation voltage, which are then dynamically adjusted.

2. The stable control method for multiple parallel grid-connected converters according to claim 1, characterized in that, The feedforward damping compensation stage includes a high-pass filter stage and a gain stage. The feedforward damping compensation stage processes the d-axis current component and the q-axis current component sequentially through the high-pass filter stage and the gain stage to generate the d-axis output voltage and the q-axis output voltage. The d-axis output voltage and q-axis output voltage are respectively superimposed on the d-axis output modulation voltage and the q-axis output modulation voltage to generate the d-axis output composite modulation voltage and the q-axis output composite modulation voltage, and the d-axis output modulation voltage and the q-axis output modulation voltage are dynamically adjusted.

3. The stability control method for multiple parallel grid-connected converters according to claim 2, characterized in that, The expressions for the d-axis output synthesized modulation voltage and the q-axis output synthesized modulation voltage are as follows: ； ； In the formula, V dref The output modulation voltage is for the d-axis. V fdd This represents the d-axis output voltage of the feedforward damping circuit. V mdref The output is a synthesized modulation voltage for the d-axis; V qref This is the q-axis output modulation voltage. V fdq This is the q-axis output voltage of the feedforward damping circuit. V mqref The output is a synthesized modulation voltage for the q-axis; The d-axis output voltage of the feedforward damping element V fdd and q-axis output voltage V fdq They are respectively: ； ； In the formula, T fd The time constant of the high-pass filter. K fd This represents the gain coefficient of the gain element in the feedforward damping compensation stage. s For complex variables in the transfer function; i fdd , i fdq These are the d-axis and q-axis current components output by the AC voltage loop controller, respectively.

4. The stable control method for multiple parallel grid-connected converters according to claim 3, characterized in that, The high-pass filter stage in the feedforward damping compensation circuit H fd ( s This is used to filter out DC components from the input signal, and its expression is: H fd ( s ) = T fd · s / ( T fd · s + 1)； In the formula, T fd It is a time constant; s For complex variables in the transfer function; Wherein, the time constant of the high-pass filter T fd The frequency range of the low-frequency oscillation is determined, and it satisfies the following: T fd ≥ 1 / (2π· f c_min )； In the formula, f c_min This refers to the minimum low-frequency oscillation frequency generated by the grid-type converter under strong or weak power grid conditions, and the low-frequency oscillation frequency is 1 to 2 Hz.

5. The stability control method for multiple parallel grid-connected converters according to claim 4, characterized in that, The gain coefficient of the gain element in the feedforward damping compensation stage K fd The gain coefficient is determined based on the actual compensated system phase margin, and the value range of the gain coefficient is 1 to 10.

6. The stability control method for multiple parallel grid-connected converters according to claim 1, characterized in that, The process of obtaining the d-axis current component and q-axis current component at the grid connection point and generating the d-axis virtual voltage component and q-axis virtual voltage component through the virtual impedance link in the additional damping control module is as follows: the virtual voltage component is generated by the voltage drop of the d-axis current component and q-axis current component at the grid connection point through the virtual impedance in a negative feedback manner. The generation of virtual voltage components includes: converting the d-axis current component at the grid connection point... i d The resistance value through the virtual impedance link R v Then, the inductive reactance of the q-axis current component at the grid connection point through the virtual impedance link is - ω 0 L v The values ​​are then superimposed to obtain the virtual d-axis voltage component. V vd ; The q-axis current component at the grid connection point i q The resistance value through the virtual impedance element R v Then, the inductive reactance of the d-axis current component at the grid connection point through the virtual impedance element. ω 0 L v The values ​​are then superimposed to obtain the virtual q-axis voltage component. V vq .

7. The stability control method for multiple parallel grid-connected converters according to claim 6, characterized in that, When the voltage loop controller outputs the d-axis current component and the q-axis current component, it uses the virtual d-axis voltage component. V vd The virtual q-axis voltage distribution V vq Combined with d-axis reference voltage q-axis reference voltage and the measured d-axis voltage at the grid connection point V sd q-axis electrical measurement value at grid connection point V sq The difference between them is controlled by PI. H v ( s After that, the q-axis current component and the q-axis current component are output respectively; The voltage loop controller includes a cross-decoupling mechanism, which uses the d-axis voltage measurement value at the grid connection point. V sd The q-axis electrical measurement value of the grid connection point V sq go through ω 0 C f The current is then cross-input to the q-axis and d-axis respectively, and combined with the d-axis current component, the q-axis current component, and the d-axis current component at the grid connection point. i d and the q-axis current component at the grid connection point i q Output the reference value of the AC current loop controller. i cdref and i cqref .

8. A stable control system for a grid-connected converter with multiple units in parallel, characterized in that, The method for stable control of multiple parallel grid-connected converters according to any one of claims 1-7 includes: a basic control module and an additional damping control module. The additional damping control module is connected to the inner loop control module in the basic control module. The additional damping control module is equipped with a virtual impedance link and a feedforward damping compensation link to suppress low-frequency oscillations in the multi-machine parallel system of the grid-type converter. The inner loop control module includes an AC voltage loop controller for outputting the d-axis current component and the q-axis current component. The virtual impedance link is used to generate a virtual voltage component by negative feedback of the voltage drop generated by the current at the grid connection point through the virtual impedance, and input it to the AC voltage loop controller. The feedforward damping compensation circuit processes the d-axis current component and the q-axis current component respectively to obtain the d-axis output voltage and the q-axis output voltage, and applies the d-axis output voltage and the q-axis output voltage to the d-axis output modulation voltage and the q-axis output modulation voltage respectively for dynamic adjustment.

9. The stable control system for multi-machine parallel grid-connected converters according to claim 8, characterized in that, The inner loop controller has a voltage and current dual closed-loop structure. The inner loop control also includes an AC current loop controller, a voltage feedforward circuit, and a current feedforward circuit. The current feedforward circuit is set in the AC voltage loop controller to form AC voltage closed-loop control. The voltage feedforward circuit is set in the AC current loop controller to form AC current closed-loop control. The AC current loop controller outputs the d-axis modulation voltage and the q-axis modulation voltage.

10. The stable control system for multi-machine parallel grid-connected converters according to claim 8, characterized in that, The stability control system also includes an outer loop control module, which is connected to the AC voltage loop controller and is used to control the active and reactive power of the grid-type converter and generate a synchronous phase angle. The outer loop control module includes an active power synchronization link controlled by VSG and a reactive power-voltage control link. The d-axis voltage reference value and the q-axis voltage reference value are generated by the reactive power-voltage control loop.

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