Hybrid amplitude control method and system applied to grid-following type converter, storage medium and grid-following type converter

Abstract

According to the hybrid amplitude control method and system applied to the grid-following type converter, the storage medium and the grid-following type converter, double closed-loop control of the voltage outer loop and the current inner loop is adopted for the d-axis voltage component, voltage stable control and current accurate adjustment are combined, the stable amplitude of the output voltage of the converter can be guaranteed, and the stability of the output voltage of the converter is improved. The current change can be quickly responded to suppress disturbance; and direct current closed-loop control is adopted for the q-axis current component, so that reactive power output can be accurately controlled, and the converter can still maintain good power factor and reactive support capability in a weak network environment. The d-axis voltage closed loop and q-axis current closed loop mixed control architecture not only retains the grid-connected stability advantage of the following grid type control under the strong grid, but also enhances the endurance capacity to the voltage fluctuation of the power grid by introducing the d-axis voltage outer loop, and effectively reduces the sensitivity of the converter to the impedance of the power grid.

Description

Technical Field

[0001] This application relates to the technical field, and in particular to a hybrid amplitude control method, system, storage medium, and grid-connected converter applied to a grid-connected converter. Background Technology

[0002] With the increasing scale of grid-connected renewable energy, the short-circuit ratio of the power system is decreasing, and the inertia and damping levels are insufficient. The basic assumptions of grid-connected control strategies are no longer suitable, leading to problems such as reduced voltage stability, reduced synchronization stability, and poor stability under large disturbances. When grid-connected converters are connected to weak grids, instability may occur due to the difference in synchronization between their control strategies and the external grid, especially under high grid connection intensity. Therefore, improving the instability of grid-connected converters in weak grid environments is an important research direction in modern power systems. To address these issues, researchers have proposed various methods to improve the stability of grid-connected converters in weak grid environments. Existing solutions mainly revolve around two core aspects: reducing sensitivity to grid impedance and enhancing system damping. These solutions involve improving synchronization mechanisms (such as adaptive PLLs or power synchronization loops), adding virtual or active damping, reshaping output impedance, and even switching to grid-connected control strategies. Combined with parameter adaptation and hardware-assisted measures, these multi-level solutions aim to maintain stable operation under weak grid conditions.

[0003] In recent years, research has gradually shifted towards the organic integration of grid-based and grid-following control concepts. Hybrid control enables inverters to adaptively switch modes or achieve continuous transitions under different operating conditions. For example, grid-following control is used under strong grid conditions to ensure grid-connected stability, while grid-based control is switched to under weak grid or islanded operation to achieve active voltage and frequency support. Hybrid inverter control is considered one of the important development directions for new power systems. Future research will focus more on the adaptability and robustness of control strategies, deep integration with grid operating status awareness, and engineering feasibility and standardization. Overall, hybrid inverter control provides a new technical path for achieving high-proportion renewable energy integration and safe and stable power system operation, possessing significant research value and broad application prospects.

[0004] Current research on hybrid control primarily focuses on improving converter performance through hybrid synchronization control. For example, combining phase-locked loops (PLLs) with droop control utilizes a hysteresis loop-like mechanism to achieve hybrid synchronization control. Some literature proposes a "universal controller" framework, introducing PLLs into power synchronization control to achieve hybrid synchronization control. Other literature proposes hybrid amplitude control methods based on grid-connected converters, effectively improving the strong grid instability of grid-connected converters. However, for grid-connected converters, existing technologies lack methods to improve their performance from the perspective of hybrid amplitude control. Summary of the Invention

[0005] The purpose of this application is to at least address one of the aforementioned technical deficiencies, particularly the lack of technical deficiencies in the prior art that improve the performance of grid-type converters from the perspective of hybrid amplitude control.

[0006] This application provides a hybrid amplitude control method for a grid-connected converter, wherein the grid-connected converter is synchronized with the power grid via a phase-locked loop, and the control method includes:

[0007] Obtain the voltage and current signals on the AC side of the grid-connected converter;

[0008] Based on the synchronous phase output of the phase-locked loop, the voltage signal and the current signal are transformed into a synchronous rotating coordinate system to obtain the d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component;

[0009] Closed-loop control is performed on the d-axis voltage component to generate d-axis voltage control commands;

[0010] Closed-loop control is performed on the q-axis current component to generate q-axis voltage control commands;

[0011] Based on the d-axis voltage control command and the q-axis voltage control command, drive signals are generated to control the power switching transistors of the grid-connected converter.

[0012] Optionally, the step of performing closed-loop control on the d-axis voltage component to generate d-axis voltage control commands includes:

[0013] The d-axis voltage component is compared with a d-axis voltage reference value to obtain a first error signal;

[0014] Perform a first proportional-integral adjustment on the first error signal to output the inner loop reference value of the d-axis current;

[0015] The reference value of the inner loop of the d-axis current is compared with the d-axis current component to obtain the second error signal;

[0016] The second error signal is subjected to a second proportional-integral adjustment, and a d-axis voltage control command is output.

[0017] Optionally, the d-axis voltage reference value is a constant value or a value dynamically adjusted according to the power grid operating status.

[0018] Optionally, the step of performing closed-loop control on the q-axis current component to generate a q-axis voltage control command includes:

[0019] The q-axis current component is compared with a q-axis current reference value to obtain a third error signal;

[0020] The third error signal is subjected to a third proportional-integral adjustment to output a q-axis voltage control command.

[0021] Optionally, the q-axis current reference value is a constant value, zero, or a value dynamically generated according to the reactive power command.

[0022] Optionally, the step of generating drive signals for controlling the power switching transistors of the grid-connected converter based on the d-axis voltage control command and the q-axis voltage control command includes:

[0023] The d-axis voltage control command and the q-axis voltage control command are inversely transformed based on the synchronous phase output of the phase-locked loop to obtain the modulated wave signal in the three-phase stationary coordinate system.

[0024] The modulated wave signal is compared with the carrier signal to generate a pulse width modulation signal, and the pulse width modulation signal is used as the drive signal to control the power switching transistors of the grid-connected converter.

[0025] This application also provides a grid-connected converter control system, wherein the grid-connected converter is synchronized with the power grid via a phase-locked loop, and the system includes:

[0026] The signal acquisition module is used to acquire the voltage and current signals on the AC side of the grid-connected converter;

[0027] The signal conversion module is used to convert the voltage signal and the current signal to a synchronous rotating coordinate system based on the synchronous phase output of the phase-locked loop, so as to obtain the d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component;

[0028] The first instruction generation module is used to perform closed-loop control on the d-axis voltage component to generate d-axis voltage control instructions.

[0029] The second instruction generation module is used to perform closed-loop control on the q-axis current component to generate q-axis voltage control instructions.

[0030] The drive signal generation module is used to generate drive signals for controlling the power switching transistors of the grid-connected converter based on the d-axis voltage control command and the q-axis voltage control command.

[0031] Optionally, the drive signal generation module includes:

[0032] The inverse transformation module is used to inversely transform the d-axis voltage control command and the q-axis voltage control command based on the synchronous phase output of the phase-locked loop to obtain the modulation wave signal in the three-phase stationary coordinate system.

[0033] The signal comparison and generation module is used to compare the modulated wave signal with the carrier signal, generate a pulse width modulation signal, and use the pulse width modulation signal as a drive signal to control the power switching transistors of the grid-connected converter.

[0034] This application also provides a computer-readable storage medium storing computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the hybrid amplitude control method applied to a grid converter as described in any of the above embodiments.

[0035] This application also provides a grid-connected converter, including a power conversion main circuit and a grid-connected converter control system as described in the above embodiments, wherein the grid-connected converter control system is used to control the power conversion main circuit.

[0036] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0037] This application provides a hybrid amplitude control method, system, storage medium, and grid-connected converter for use in grid-connected converters. The grid-connected converter is synchronized with the power grid via a phase-locked loop (PLL). After acquiring the voltage and current signals from the AC side of the grid-connected converter, the method transforms these signals to a synchronous rotating coordinate system based on the synchronization phase output from the PLL, obtaining d-axis voltage components, q-axis voltage components, d-axis current components, and q-axis current components. Then, closed-loop control is performed on the d-axis voltage components to generate d-axis voltage control commands; closed-loop control is also performed on the q-axis current components to generate q-axis voltage control commands; finally, based on the d-axis and q-axis voltage control commands, drive signals for controlling the power switching transistors of the grid-connected converter are generated. In this process, this application employs a dual closed-loop control of the d-axis voltage component using an outer voltage loop and an inner current loop, combining voltage stabilization control with precise current regulation. This ensures both the stable amplitude of the converter's output voltage and a rapid response to current changes to suppress disturbances. Meanwhile, direct current closed-loop control of the q-axis current component precisely controls reactive power output, enabling the converter to maintain a good power factor and reactive power support capability even in weak grid environments. This hybrid control architecture, combining d-axis voltage and q-axis current closed loops, retains the grid-connected stability advantages of grid-connected control under strong grid conditions while enhancing tolerance to grid voltage fluctuations through the introduction of the d-axis voltage outer loop, effectively reducing the converter's sensitivity to grid impedance. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart illustrating a hybrid amplitude control method applied to a grid-connected converter, provided in an embodiment of this application;

[0040] Figure 2 This is a schematic diagram of the control process for closed-loop control of the d-axis voltage component provided in an embodiment of this application;

[0041] Figure 3 A schematic diagram of a grid-connected converter control system provided in this application embodiment;

[0042] Figure 4 This application provides an overall structural diagram of a grid-connected converter hybrid amplitude control system.

[0043] Figure 5This is a schematic diagram of the internal structure of the hybrid amplitude control of the structure-grid system provided in the embodiments of this application;

[0044] Figure 6 A schematic diagram illustrating the specific control effect of the grid-connected converter in the single-machine grid-connected system simulation model under MATLAB / Simulink provided for the embodiments of this application.

[0045] Figure 7 A waveform comparison diagram of the hybrid amplitude control method provided in the embodiments of this application under the same parameter conditions. Detailed Implementation

[0046] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] In one embodiment, such as Figure 1 As shown, Figure 1 This application provides a flowchart illustrating a hybrid amplitude control method for a grid-connected converter, as illustrated in an embodiment of the present application. The application provides a hybrid amplitude control method for a grid-connected converter, wherein the grid-connected converter is synchronized with the power grid via a phase-locked loop, and the control method may include:

[0048] S110: Acquire the voltage and current signals on the AC side of the grid-connected converter.

[0049] In this step, when performing mixed amplitude control on the grid-connected converter, the three-phase voltage and current signals at the connection point between the converter's AC side and the grid are first acquired using voltage and current sensors, respectively. These sensors need to have high precision and a wide dynamic range to ensure accurate capture of signal changes under different operating conditions (such as grid voltage fluctuations and load abrupt changes), providing reliable raw data for subsequent control stages. The acquired analog signals can be filtered and amplified by signal conditioning circuits before being converted into digital signals and input to the control chip for coordinate transformation and closed-loop control calculations.

[0050] S120: Based on the synchronous phase output of the phase-locked loop, the voltage and current signals are transformed to a synchronous rotating coordinate system to obtain the d-axis voltage component, q-axis voltage component, d-axis current component, and q-axis current component.

[0051] In this step, after obtaining the voltage and current signals of the AC side of the grid-connected converter through S110, this application can transform the voltage and current signals to a synchronous rotating coordinate system based on the synchronous phase output of the phase-locked loop, thereby obtaining the d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component.

[0052] Understandably, a phase-locked loop (PLL) tracks the phase and frequency of the grid voltage and outputs a rotating coordinate system phase angle θ synchronized with the grid. This application substitutes the acquired voltage signals (ua, ub, uc) and current signals (ia, ib, ic) in the three-phase stationary coordinate system into the Parker transform formula to obtain the components in the synchronous rotating coordinate system (dq coordinate system): d-axis voltage component ud, q-axis voltage component uq, d-axis current component id, and q-axis current component iq. The core of the Parker transform is to convert three-phase AC quantities into DC components through an orthogonal transformation matrix, facilitating subsequent closed-loop control design. Through this transformation, the AC signal, which originally varies sinusoidally with time, is converted into a DC signal, enabling the control algorithm to more simply and accurately regulate voltage and current.

[0053] S130: Perform closed-loop control on the d-axis voltage component to generate d-axis voltage control commands.

[0054] In this step, after obtaining the d-axis voltage component ud through S120, this application can perform closed-loop control on it to generate d-axis voltage control commands.

[0055] Specifically, this closed-loop control can adopt a dual closed-loop structure of voltage outer loop and current inner loop: First, the d-axis voltage component ud is compared with the preset d-axis voltage reference value ud_ref to obtain the first error signal e_ud = ud_ref -ud; e_ud is then subjected to a first proportional-integral (PI) regulation to output the d-axis current inner loop reference value id_ref. The transfer function of the first PI regulator is G_ud(s) = Kp_ud + Ki_ud / s, where Kp_ud is the proportional coefficient and Ki_ud ​​is the integral coefficient. Through parameter tuning, rapid elimination of voltage error and zero steady-state error tracking can be achieved; Next, id_ref is compared with the actual d-axis current component id to obtain the second error signal e_id = id_ref - id; e_id is then subjected to a second PI regulation to output the d-axis voltage control command ud_cmd. The transfer function of the second PI regulator is G_id(s) = Kp_id + Ki_id / s, and its function is to quickly track the current reference value, suppress current disturbances, and improve the dynamic response speed of the system. For example, when the grid voltage suddenly drops, ud will decrease instantaneously, the first error signal e_ud will increase, the first PI regulator will output a larger id_ref, the inner loop of the drive current will rapidly increase id, thereby increasing the output voltage through the power regulation of the converter and keeping ud stable near the reference value.

[0056] S140: Perform closed-loop control on the q-axis current component to generate q-axis voltage control commands.

[0057] In this step, after obtaining the q-axis current component iq through S120, this application can perform closed-loop control on it to generate q-axis voltage control commands.

[0058] Specifically, this application compares the q-axis current component iq with a preset q-axis current reference value iq_ref to obtain a third error signal e_iq = iq_ref - iq; performs a third PI regulation on e_iq to output a q-axis voltage control command uq_cmd, and the transfer function of the third PI regulator is G_iq(s) = Kp_iq + Ki_iq / s. The q-axis current is typically related to reactive power. When iq_ref is set to zero, the converter outputs zero reactive power and operates in unity power factor mode. If iq_ref is dynamically generated based on the reactive power command Q_ref (e.g., iq_ref = Q_ref / (1.5U_dc), where U_dc is the DC bus voltage), precise control of reactive power can be achieved. For example, when the power grid needs to absorb reactive power, iq_ref is set to a positive value. The third PI regulator changes the output voltage phase of the converter by adjusting uq_cmd, so that iq tracks the reference value, thereby injecting the specified reactive power into the power grid and supporting the stability of the power grid voltage.

[0059] S150: Based on the d-axis voltage control command and the q-axis voltage control command, generate drive signals for controlling the power switching transistors of the grid-connected converter.

[0060] In this step, after obtaining the d-axis voltage control command ud_cmd and the q-axis voltage control command uq_cmd through S130 and S140 respectively, this application can perform Parker inverse transformation on these two commands based on the synchronous phase θ output by the phase-locked loop to obtain the modulation wave signal (u_a_mod, u_b_mod, u_c_mod) in the three-phase stationary coordinate system.

[0061] Subsequently, this application compares the modulated wave signal with a high-frequency carrier signal (such as a triangular wave) to generate a pulse width modulation (PWM) signal. When the amplitude of the modulated wave signal is greater than that of the carrier signal, the PWM signal outputs a high level; otherwise, it outputs a low level. These PWM signals are directly sent to the drive circuit of the converter's power switching transistors (such as IGBTs and MOSFETs) to control the switching transistors' on and off states, thereby regulating the converter's output voltage and current to achieve power transmission or absorption from the grid. For example, if the frequency of the modulated wave signal is the grid frequency (50Hz or 60Hz) and the frequency of the carrier signal is 10kHz, then the switching frequency of the switching transistors is 10kHz. Rapid switching enables precise modulation of the output voltage, ensuring stable operation of the converter under various grid conditions.

[0062] In the above embodiments, this application employs a dual closed-loop control of the d-axis voltage component using an outer voltage loop and an inner current loop. This combines voltage stabilization control with precise current regulation, ensuring both the stable amplitude of the converter's output voltage and rapid response to current changes to suppress disturbances. Meanwhile, direct current closed-loop control of the q-axis current component allows for precise control of reactive power output, enabling the converter to maintain a good power factor and reactive power support capability even in weak grid environments. This hybrid control architecture, combining d-axis voltage and q-axis current loops, retains the grid-connected stability advantages of grid-based control under strong grid conditions while enhancing tolerance to grid voltage fluctuations through the introduction of the d-axis voltage outer loop, effectively reducing the converter's sensitivity to grid impedance.

[0063] In one embodiment, such as Figure 2 As shown, Figure 2 This is a schematic diagram of the control process for closed-loop control of the d-axis voltage component provided in an embodiment of this application; S130, performing closed-loop control on the d-axis voltage component to generate a d-axis voltage control command, may include:

[0064] S131: Compare the d-axis voltage component with a d-axis voltage reference value to obtain the first error signal.

[0065] S132: Perform first proportional-integral adjustment on the first error signal and output the inner loop reference value of the d-axis current.

[0066] S133: Compare the inner loop reference value of the d-axis current with the d-axis current component to obtain the second error signal.

[0067] S134: Perform a second proportional-integral adjustment on the second error signal and output a d-axis voltage control command.

[0068] In this embodiment, when performing closed-loop control on the d-axis voltage component, the output voltage amplitude can be stably controlled first through the outer voltage loop, and the current can be rapidly adjusted through the inner current loop. The two work together to cope with the dynamic changes of the power grid and the load.

[0069] Specifically, the core function of the outer voltage loop is to eliminate steady-state voltage error and ensure that the converter output voltage is stable near the preset d-axis voltage reference value. For example, when the load suddenly increases, causing the converter output current to increase, the d-axis voltage component ud may decrease slightly due to power loss. At this time, the first error signal e_ud (ud_ref - ud) will immediately increase. The first PI regulator will gradually accumulate the regulation amount through integral action and output a larger d-axis current inner loop reference value id_ref, driving the current inner loop to respond quickly.

[0070] The inner current loop tracks id_ref, and its dynamic response is much faster than the outer voltage loop. It can adjust the d-axis current component id within microseconds, compensating for voltage changes by altering the converter's output power. For example, when id_ref increases, the second error signal e_id (id_ref - id) triggers the second PI regulator to output a higher d-axis voltage control command ud_cmd, causing the power switch to increase its on-time and boosting the converter's output voltage amplitude, thus quickly pulling ud back to the reference value.

[0071] It should be noted that when performing first proportional-integral (PI) regulation on the first error signal and second PI regulation on the second error signal, the parameters of the PI controller can be tuned according to the system performance requirements. For example, the proportional coefficient Kp_ud of the voltage outer loop needs to balance regulation speed and stability. If Kp_ud is too large, it may lead to voltage overshoot or even oscillation; if it is too small, the response speed will be slow and voltage fluctuations cannot be suppressed in time. It can usually be determined through a step response experiment: input a step reference signal to the voltage outer loop, observe the dynamic process of the output voltage, and gradually adjust Kp_ud and the integral coefficient Ki_ud ​​to make the system achieve a response characteristic with no overshoot and fast convergence. The parameter tuning of the current inner loop focuses more on the dynamic response speed. Since the time constant of the current inner loop is much smaller than that of the voltage outer loop, Kp_id can be appropriately increased to improve the current tracking speed, while adjusting Ki_id can eliminate the current steady-state error.

[0072] For example, during load changes, the inner current loop needs to complete current regulation within 1-2 switching cycles. Therefore, the value of Kp_id must ensure that the inner loop bandwidth is high enough to quickly compensate for current deviations caused by load changes. Furthermore, to further improve the system's anti-interference capability, a feedforward compensation stage can be introduced into the PI regulator, such as feeding the grid voltage forward to the inner current loop to preemptively offset the impact of grid voltage fluctuations on the current, making current regulation more precise and faster. Through reasonable parameter tuning, the dual-loop control structure can achieve rapid current tracking while ensuring voltage stability, providing strong support for the reliable operation of the converter.

[0073] In one embodiment, the d-axis voltage reference value is a constant value or a value dynamically adjusted according to the power grid operating status.

[0074] In this embodiment, the setting of the d-axis voltage reference value directly affects the operating characteristics of the grid-connected converter. It can be flexibly configured as a constant value or a dynamically adjusted value according to the actual application scenario. When set to a constant value, it usually corresponds to the rated output voltage amplitude of the converter and is suitable for operating conditions where the grid voltage is stable and the load fluctuation is small. For example, in a distributed generation system under a standard grid environment, the converter needs to maintain a stable output voltage to ensure the grid-connected power quality. At this time, fixing the d-axis voltage reference value to the rated value (such as setting it to 311V in a 380V system) can ensure that the output voltage is not affected by load changes and always remains at the rated level through dual closed-loop control.

[0075] In weak grid environments or microgrid scenarios where grid voltage fluctuates frequently, the d-axis voltage reference value needs to be dynamically adjusted according to the grid operating status. For example, by monitoring the voltage amplitude at the grid point of common coupling (PCC) in real time, if a grid voltage drop is detected (such as a drop to 80% of the rated value), the d-axis voltage reference value can be appropriately reduced according to a preset voltage support strategy (such as based on the low voltage ride-through standard) to match the grid voltage changes and prevent the converter from disconnecting from the grid due to overcurrent or overvoltage protection. If the grid voltage is within the normal range but there are small fluctuations, the d-axis voltage reference value can be adjusted to "measured grid voltage + preset compensation amount" by introducing a feedforward signal of the grid voltage, so that the converter output voltage is coordinated with the grid voltage, reducing reactive power exchange and improving system operating efficiency.

[0076] Furthermore, dynamic adjustment can also be combined with the operating status of the converter. For example, when the DC bus voltage fluctuates, the d-axis voltage reference value can be adjusted through voltage droop control logic to achieve power balance between the DC and AC sides. For instance, when the DC bus voltage rises, the d-axis voltage reference value can be appropriately reduced to decrease the active power output of the converter, thereby suppressing further rises in the DC bus voltage. Conversely, when the DC bus voltage falls, the d-axis voltage reference value can be increased to increase the active power output and support the stability of the DC bus voltage.

[0077] Through this dynamic adjustment mechanism, the converter can better adapt to complex and ever-changing power grid conditions, improving the robustness and adaptability of the system.

[0078] In one embodiment, the closed-loop control of the q-axis current component in S140 to generate a q-axis voltage control command may include:

[0079] S141: Compare the q-axis current component with a q-axis current reference value to obtain a third error signal.

[0080] S142: Perform third proportional-integral adjustment on the third error signal and output q-axis voltage control command.

[0081] In this embodiment, the closed-loop control of the q-axis current component focuses on the precise adjustment of reactive power. Its core logic is to achieve flexible output or absorption of reactive power by the converter by tracking a preset q-axis current reference value. Specifically, the generation of the q-axis current reference value is directly related to the reactive power demand of the system: when the grid needs reactive power support, the q-axis current reference value can be dynamically calculated based on the voltage deviation at the point of common coupling (PCC). For example, if the PCC voltage is lower than 90% of the rated value, a positive iq_ref is generated according to the voltage-reactive power droop characteristic (e.g., an increase of 0.05 pu of reactive current for every 1% decrease in voltage), driving the converter to inject reactive power into the grid to raise the voltage; if the PCC voltage is higher than the rated value, a negative iq_ref is generated, causing the converter to absorb reactive power from the grid to suppress excessive voltage.

[0082] In closed-loop control, the processing of the third error signal e_iq (iq_ref - iq) needs to balance response speed and stability. Since the adjustment of the q-axis current directly affects the reactive power balance of the power grid, the parameter tuning of the third PI regulator needs to match the dynamic characteristics of the power grid: the proportional coefficient Kp_iq determines the reactive current tracking speed. If Kp_iq is too large, it may cause q-axis current overshoot, leading to grid voltage fluctuations; if it is too small, it cannot respond to reactive power demand in a timely manner. For example, in islanded microgrid operation, sudden changes in inductive or capacitive loads can rapidly alter reactive power demand. In this case, Kp_iq needs to be appropriately increased to ensure that the third PI regulator completes tracking of iq_ref within 10ms, maintaining microgrid voltage stability. The integral coefficient Ki_iq is used to eliminate the steady-state error of the reactive current. After the system enters steady state, Ki_iq gradually adjusts the output through accumulated error, making the actual q-axis current component iq completely consistent with the reference value, avoiding reactive power deviation during long-term operation.

[0083] Furthermore, to enhance the anti-interference capability of q-axis current control, this application can also introduce grid voltage feedforward compensation in the third PI regulator: the q-axis voltage component uq in the synchronous rotating coordinate system is fed forward to the regulator's output, thus preemptively offsetting the impact of grid voltage fluctuations on the q-axis current. For example, when a sudden drop in grid voltage causes uq to decrease instantaneously, the feedforward compensation signal directly increases the amplitude of the q-axis voltage control command uq_cmd, prompting the power switch to quickly adjust the phase of the output voltage, preventing iq from deviating from the reference value due to grid voltage changes. Through this control method combining feedforward and feedback, the q-axis current closed-loop control can achieve precise and rapid reactive power adjustment under complex grid operating conditions, providing reliable reactive power support for the stable operation of grid-connected converters.

[0084] In one embodiment, the q-axis current reference value is a constant value, zero, or a value dynamically generated according to the reactive power command.

[0085] In this embodiment, different settings of the q-axis current reference value correspond to different reactive power operation modes of the converter, which can be flexibly selected according to the actual grid demand. When the q-axis current reference value is set to a constant value, it is usually used in scenarios where the converter needs to maintain a fixed reactive power output for a long time. For example, in a distributed generation system, in order to compensate for the inductive losses of the line, iq_ref can be set to a fixed positive value, so that the converter continuously injects reactive power into the grid, reduces the line voltage drop, and improves the voltage quality of the end users.

[0086] If the q-axis current reference value is set to zero, the converter operates in unity power factor mode. At this time, the output reactive power is zero, and all output power is active power. This is suitable for situations where the power grid has no special requirements for reactive power and only needs to transmit active power. For example, in a photovoltaic grid-connected power generation system, when the grid voltage is stable, setting iq_ref=0 can achieve the maximum efficiency of active power transmission and avoid line losses caused by reactive power transmission.

[0087] The mode of dynamically generating the q-axis current reference value based on reactive power commands is suitable for scenarios requiring real-time response to the grid's reactive power demand. Its generation logic is typically based on the mathematical relationship between reactive power and q-axis current: In a three-phase system, the relationship between reactive power Q and q-axis current iq is Q = 1.5U_dc * iq (where U_dc is the DC bus voltage). Therefore, iq_ref can be directly calculated from the reactive power command Q_ref using iq_ref = Q_ref / (1.5U_dc). For example, when the grid dispatch center issues a reactive power absorption command of Q_ref=100kVar, the system can quickly calculate the corresponding iq_ref as a negative value (assuming U_dc=800V, then iq_ref= -100000 / (1.5*800) ≈ -83.3A). The third PI regulator then drives the q-axis current to track this reference value, enabling the converter to absorb the specified reactive power from the grid and assisting the grid in maintaining voltage stability. This dynamic generation mode endows the converter with the ability to participate in the reactive power dispatch of the power grid, enabling it to flexibly adjust reactive power output according to the real-time status of the power grid, which has important application value in smart grids and microgrids.

[0088] In one embodiment, generating drive signals for controlling the power switching transistors of the grid-connected converter based on the d-axis voltage control command and the q-axis voltage control command in S150 may include:

[0089] S151: The d-axis voltage control command and the q-axis voltage control command are inversely transformed based on the synchronous phase output of the phase-locked loop to obtain the modulation wave signal in the three-phase stationary coordinate system.

[0090] S152: Compare the modulated wave signal with the carrier signal to generate a pulse width modulation signal, and use the pulse width modulation signal as a drive signal to control the power switching transistor of the grid-connected converter.

[0091] In this embodiment, the inverse transformation stage is the key bridge connecting the synchronous rotating coordinate system and the three-phase stationary coordinate system. Its core is to use the synchronous phase θ output by the phase-locked loop to convert the voltage control commands (ud_cmd, uq_cmd) under the dq axis into modulation wave signals (ua_mod, ub_mod, uc_mod) under the abc three-phase stationary coordinate system.

[0092] Specifically, the mathematical model of the inverse transform is based on a combination of the Clark transform and the inverse Park transform: First, the dq-axis components are converted into α-β components in a two-phase stationary coordinate system using the inverse Park transform, and then extended into three-phase components using the inverse Clark transform. For example, when ud_cmd = 311V, uq_cmd = 0V, and the synchronous phase θ = ωt (ω is the grid angular frequency), the inverse Park transform yields the α-axis voltage component uα = ud_cmd*cosθ - uq_cmd*sinθ = 311cosωt, and the β-axis voltage component uβ = ud_cmd*sinθ + uq_cmd*cosθ = 311sinωt. Subsequently, the inverse Clark transform converts uα and uβ into three-phase modulated wave signals, ultimately obtaining a sinusoidal modulated wave synchronized with the grid, providing a foundation for subsequent pulse width modulation.

[0093] The pulse width modulation (PWM) stage is responsible for converting the continuous modulated wave signal into discrete power switch drive signals. A commonly used modulation method is sinusoidal pulse width modulation (SPWM), which works by comparing the three-phase modulated wave signal with a high-frequency triangular carrier signal: when the modulated wave amplitude is higher than the carrier amplitude, a high-level drive signal is output, turning on the corresponding power switch; when the modulated wave amplitude is lower than the carrier amplitude, a low-level drive signal is output, turning off the switch. For example, if the carrier frequency is set to 10kHz (period 100μs), the switch will complete one turn-on or turn-off action every 100μs based on the comparison result between the modulated wave and the carrier. By adjusting the amplitude and phase of the modulated wave, the on-time ratio of the switch can be precisely controlled, thereby changing the amplitude and frequency of the converter output voltage. Furthermore, to avoid a short circuit on the DC bus caused by simultaneous conduction of the upper and lower switches on the same bridge arm, a dead time (usually 1-5μs) needs to be introduced into the drive signal to ensure that the lower switch only turns on after the upper switch turns off, and vice versa.

[0094] It should be noted that the synchronization phase accuracy of the inverse transformation directly affects the synchronization between the modulated wave and the power grid. If there is a phase deviation in the output phase of the phase-locked loop (PLL), it will cause a phase difference between the modulated wave and the grid voltage, thus affecting the power factor and grid-connected stability of the converter. Therefore, in practical applications, it is necessary to optimize the dynamic response characteristics of the PLL (such as by adding a phase compensation stage) to ensure the real-time performance and accuracy of the synchronization phase. Meanwhile, the carrier frequency of the pulse width modulation (PWM) needs to be reasonably selected according to the power rating of the converter and the characteristics of the switching transistors: for medium-to-high power converters (e.g., above 100kW), the carrier frequency is usually set to 5-10kHz to balance switching losses and output power quality; for low-power converters (e.g., below 10kW), the carrier frequency can be appropriately increased to 20kHz to reduce the harmonic content of the output voltage.

[0095] Through the coordinated operation of inverse transformation and pulse width modulation, the converter can transform the voltage command generated by the dq axis closed-loop control into actual power switching actions, ultimately achieving precise regulation of output voltage and reactive power.

[0096] The grid-connected converter control system provided in the embodiments of this application is described below. The grid-connected converter control system described below can be referred to in correspondence with the hybrid amplitude control method applied to the grid-connected converter described above.

[0097] In one embodiment, such as Figure 3 As shown, Figure 3 This application provides a schematic diagram of a grid-connected converter control system according to an embodiment of the present application. The present application also provides a grid-connected converter control system, wherein the grid-connected converter is synchronized with the power grid via a phase-locked loop. The system may include a signal acquisition module 210, a signal conversion module 220, a first instruction generation module 230, a second instruction generation module 240, and a drive signal generation module 250, specifically including the following:

[0098] The signal acquisition module 210 is used to acquire the voltage and current signals on the AC side of the grid-connected converter.

[0099] The signal conversion module 220 is used to convert the voltage signal and the current signal to a synchronous rotating coordinate system based on the synchronous phase output of the phase-locked loop, so as to obtain the d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component.

[0100] The first instruction generation module 230 is used to perform closed-loop control on the d-axis voltage component to generate d-axis voltage control instructions.

[0101] The second instruction generation module 240 is used to perform closed-loop control on the q-axis current component to generate q-axis voltage control instructions.

[0102] The drive signal generation module 250 is used to generate drive signals for controlling the power switching transistors of the grid-connected converter based on the d-axis voltage control command and the q-axis voltage control command.

[0103] In the above embodiments, this application employs a dual closed-loop control of the d-axis voltage component using an outer voltage loop and an inner current loop. This combines voltage stabilization control with precise current regulation, ensuring both the stable amplitude of the converter's output voltage and rapid response to current changes to suppress disturbances. Meanwhile, direct current closed-loop control of the q-axis current component allows for precise control of reactive power output, enabling the converter to maintain a good power factor and reactive power support capability even in weak grid environments. This hybrid control architecture, combining d-axis voltage and q-axis current loops, retains the grid-connected stability advantages of grid-based control under strong grid conditions while enhancing tolerance to grid voltage fluctuations through the introduction of the d-axis voltage outer loop, effectively reducing the converter's sensitivity to grid impedance.

[0104] In one embodiment, the drive signal generation module 250 may include:

[0105] The inverse transformation module is used to inversely transform the d-axis voltage control command and the q-axis voltage control command based on the synchronous phase output of the phase-locked loop to obtain the modulated wave signal in the three-phase stationary coordinate system.

[0106] The signal comparison and generation module is used to compare the modulated wave signal with the carrier signal, generate a pulse width modulation signal, and use the pulse width modulation signal as a drive signal to control the power switching transistors of the grid-connected converter.

[0107] In one embodiment, this application also provides a computer-readable storage medium storing computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the hybrid amplitude control method applied to a grid converter as described in any of the above embodiments.

[0108] In one embodiment, this application also provides a grid-connected converter, including a power conversion main circuit and a grid-connected converter control system as described in the above embodiments, wherein the grid-connected converter control system is used to control the power conversion main circuit.

[0109] In a specific implementation, such as Figure 4 , 5 As shown, Figure 4 This is a schematic diagram of the overall structure of the hybrid amplitude control system for grid-connected converters provided in an embodiment of this application. Figure 5 This is a schematic diagram of the internal structure of the hybrid amplitude control of the structure-grid system provided in the embodiments of this application; Figure 4 , Figure 5 middle, The three-phase voltage output by the inverter (abc coordinate system) This refers to the inverter-side inductor current (three-phase). This is the inverter-side filter inductor (the first segment of the LCL filter). This is the equivalent series resistance of the inverter-side inductor. This refers to the filter capacitor in an LCL filter. The three-phase voltage across the filter capacitor is [value]. This refers to the grid-connected current (the current injected into the grid in three phases). This is the grid-side inductor (the third segment of the LCL filter). The equivalent resistance on the grid side (line resistance + grid impedance) is used. The abc-dq coordinate transformation refers to abc→dq / dq→abc, the Park transformation and inverse transformation, used to convert three-phase AC quantities in the abc coordinate system into DC quantities in the synchronous rotating coordinate system (dq coordinate system). Let be the component of the inverter-side inductor current in the dq coordinate system. Let be the components of the grid-connected current in the dq coordinate system. Let be the components of the filter capacitor voltage in the dq coordinate system. The rotation angle in the dq coordinate system is output by the PLL. The PLL (phase-locked loop) is used to detect and lock the grid phase and frequency, synchronizing the dq coordinate system with the grid voltage, given the grid angular frequency. This is the reference value for the d-axis capacitor voltage. This is the reference value for the q-axis inductor current. The current inner loop reference value is used. PWM (Pulse Width Modulation) generates inverter switching signals based on the voltage command output by the controller. The voltage component along the d-axis is the result of transformation through the dq coordinate system. This represents the q-axis voltage component after transformation through the dq coordinate system. This is a voltage error signal. This is the current error signal.

[0110] This application has been approved. Figure 4 , Figure 5The circuit structure implements hierarchical control logic for d-axis voltage and q-axis current: the d-axis component of the filter capacitor voltage is calculated by the outer voltage loop PI regulator to generate a d-axis reference value for the inverter-side inductor current. The difference between this reference value and the actual d-axis inductor current enters the inner current loop PI regulator, ultimately outputting a d-axis voltage control command. Meanwhile, the q-axis inductor current reference value is directly compared with the actual q-axis inductor current, and the inner current loop PI regulator generates a q-axis voltage control command. This hierarchical control architecture ensures the stability of the capacitor voltage amplitude (through the d-axis voltage outer loop) and achieves accurate reactive current tracking (through the q-axis current inner loop). Simultaneously, the three-segment structure of the LCL filter effectively suppresses high-frequency harmonics in the grid-connected current, making the output current waveform closer to a sine wave, thus meeting the stringent power quality requirements of the power grid.

[0111] Indicatively, such as Figure 6 , 7 As shown, Figure 6 This is a schematic diagram illustrating the specific control effect of the grid-connected converter in the single-machine grid-connected system simulation model under MATLAB / Simulink provided in the embodiments of this application. Figure 7 Waveform comparison diagram of the hybrid amplitude control method provided in the embodiments of this application under the same parameter conditions; Figure 6 In the middle, at 1.5s, the system impedance Zg rises from 0.2pu to 2pu (equivalent to a decrease in grid strength), which shows that the grid type is unstable under traditional single-loop current control and oscillations occur. Figure 7 Under the same parameter conditions, the system impedance Zg increases from 0.2 pu to 2 pu in 1.5s, which proves that the hybrid amplitude control method of this application can achieve stability and effectively improve the unstable characteristics of the grid-type converter in weak grids.

[0112] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0113] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0114] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hybrid amplitude control method applied to a grid-connected converter, characterized in that, The grid-connected converter is synchronized with the power grid via a phase-locked loop, and the control method includes: Obtain the voltage and current signals on the AC side of the grid-connected converter; Based on the synchronous phase output of the phase-locked loop, the voltage signal and the current signal are transformed into a synchronous rotating coordinate system to obtain the d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component; Closed-loop control is performed on the d-axis voltage component to generate d-axis voltage control commands; Closed-loop control is performed on the q-axis current component to generate q-axis voltage control commands; Based on the d-axis voltage control command and the q-axis voltage control command, drive signals are generated to control the power switching transistors of the grid-connected converter.

2. The hybrid amplitude control method according to claim 1, characterized in that, The closed-loop control of the d-axis voltage component to generate d-axis voltage control commands includes: The d-axis voltage component is compared with a d-axis voltage reference value to obtain a first error signal; Perform a first proportional-integral adjustment on the first error signal to output the inner loop reference value of the d-axis current; The reference value of the inner loop of the d-axis current is compared with the d-axis current component to obtain the second error signal; The second error signal is subjected to a second proportional-integral adjustment, and a d-axis voltage control command is output.

3. The hybrid amplitude control method according to claim 2, characterized in that, The d-axis voltage reference value is a constant value or a value dynamically adjusted according to the power grid operating status.

4. The hybrid amplitude control method according to claim 1, characterized in that, The closed-loop control of the q-axis current component to generate a q-axis voltage control command includes: The q-axis current component is compared with a q-axis current reference value to obtain a third error signal; The third error signal is subjected to a third proportional-integral adjustment to output a q-axis voltage control command.

5. The hybrid amplitude control method according to claim 4, characterized in that, The q-axis current reference value is a constant value, zero, or a value dynamically generated according to the reactive power command.

6. The hybrid amplitude control method according to any one of claims 1-5, characterized in that, The generation of drive signals for controlling the power switching transistors of the grid-connected converter based on the d-axis voltage control command and the q-axis voltage control command includes: The d-axis voltage control command and the q-axis voltage control command are inversely transformed based on the synchronous phase output of the phase-locked loop to obtain the modulated wave signal in the three-phase stationary coordinate system. The modulated wave signal is compared with the carrier signal to generate a pulse width modulation signal, and the pulse width modulation signal is used as the drive signal to control the power switching transistors of the grid-connected converter.

7. A grid-connected converter control system, characterized in that, The grid-connected converter is synchronized with the power grid via a phase-locked loop, and the system includes: The signal acquisition module is used to acquire the voltage and current signals on the AC side of the grid-connected converter; The signal conversion module is used to convert the voltage signal and the current signal to a synchronous rotating coordinate system based on the synchronous phase output of the phase-locked loop, so as to obtain the d-axis voltage component, q-axis voltage component, d-axis current component and q-axis current component; The first instruction generation module is used to perform closed-loop control on the d-axis voltage component to generate d-axis voltage control instructions. The second instruction generation module is used to perform closed-loop control on the q-axis current component to generate q-axis voltage control instructions. The drive signal generation module is used to generate drive signals for controlling the power switching transistors of the grid-connected converter based on the d-axis voltage control command and the q-axis voltage control command.

8. The grid-connected converter control system according to claim 7, characterized in that, The drive signal generation module includes: The inverse transformation module is used to inversely transform the d-axis voltage control command and the q-axis voltage control command based on the synchronous phase output of the phase-locked loop to obtain the modulation wave signal in the three-phase stationary coordinate system. The signal comparison and generation module is used to compare the modulated wave signal with the carrier signal, generate a pulse width modulation signal, and use the pulse width modulation signal as a drive signal to control the power switching transistors of the grid-connected converter.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the hybrid amplitude control method for a grid-connected converter as described in any one of claims 1 to 6.

10. A grid-connected converter, characterized in that, It includes a power conversion main circuit and a grid-connected converter control system as described in claim 7 or 8, wherein the grid-connected converter control is used to control the power conversion main circuit.

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