Fault ride-through control method, system and inverter for grid-connected inverters

Abstract

The application provides a kind of grid-connected inverter fault ride-through control method, system and inverter, it is related to grid-connected control technical field.The method comprises: obtaining the grid voltage signal in the process of power grid fault recovery;The grid voltage signal is filtered, and the filtered grid voltage signal is obtained;According to the grid voltage signal and the filtered grid voltage signal, determine voltage feedforward quantity;The voltage feedforward quantity is superimposed with the voltage quantity output by current loop, and the target voltage control quantity is obtained;The target voltage control quantity is modulated, and the corresponding PWM driving signal is obtained, to control the output current of the inverter.The application makes the current output by inverter can be more quickly and accurately stable to reach standard requirements, and gives consideration to dynamic response performance and system operation stability of inverter control.

Description

Technical Field

[0001] This application relates to the field of grid-connected control technology, and in particular to a fault ride-through control method, system and inverter for a grid-connected inverter. Background Technology

[0002] During grid operation, faults such as voltage dips, surges, and three-phase voltage imbalances may occur. After the faults are cleared, a voltage recovery process begins. Active and reactive currents are the core electrical indicators that the inverter outputs to the grid. During fault ride-through recovery, industry standards require that the active and reactive currents output by the inverter be quickly and accurately adjusted from the fault values ​​to the normal values ​​after grid recovery within a specified time. Furthermore, the response time of current regulation (the time from the start of voltage recovery to the current reaching the standard value) and the response amount (i.e., the actual current value reached) must both meet the standard requirements to ensure the stable and compliant operation of the inverter and the grid.

[0003] In related technologies, the current control logic for inverters mainly involves first detecting the amplitude of grid voltage fluctuations, and then controlling the inverter to adjust its output active and reactive currents according to standard requirements, so that they reach the corresponding active and reactive current values ​​within a certain time. However, in actual control processes, the inverter's dynamic response capability is poor. For example, during grid fault recovery, problems such as long response times, insufficient response quantities, and overcurrent may occur when adjusting active and reactive currents, which can easily lead to inverter disconnection from the grid and affect the stable operation of the grid system. Summary of the Invention

[0004] This application provides a fault ride-through control method, system, and inverter for grid-connected inverters to address the problem of poor dynamic response capability of inverters in the prior art.

[0005] In a first aspect, embodiments of this application provide a fault ride-through control method for a grid-connected inverter, including: Acquire grid voltage signals during grid fault recovery; The grid voltage signal is filtered to obtain a filtered grid voltage signal; The voltage feedforward amount is determined based on the grid voltage signal and the filtered grid voltage signal; The voltage feedforward quantity is superimposed with the voltage output from the current loop to obtain the target voltage control quantity; The target voltage control quantity is subjected to three-level modulation processing to obtain a corresponding PWM drive signal, which is used to control the output current of the inverter.

[0006] In one possible implementation, determining the voltage feedforward amount based on the grid voltage signal and the filtered grid voltage signal includes: The grid voltage signal is subjected to coordinate transformation processing to obtain the instantaneous voltage feedforward of the d-axis and the instantaneous voltage feedforward of the q-axis; The filtered grid voltage signal is subjected to coordinate transformation to obtain the filtered voltage feedforward amount on the d-axis and the filtered voltage feedforward amount on the q-axis. The instantaneous voltage feedforward and filtered voltage feedforward of the d-axis and q-axis are weighted and summed respectively to obtain the voltage feedforward of the d-axis and the voltage feedforward of the q-axis.

[0007] In one possible implementation, the method further includes, before performing a weighted summation of the instantaneous voltage feedforward and the filtered voltage feedforward on the d-axis and q-axis, respectively: When the power grid is operating normally, the instantaneous feedforward weighting coefficients corresponding to the instantaneous voltage feedforward quantity and the filter feedforward weighting coefficients corresponding to the filter voltage feedforward quantity are obtained. Based on the real-time operating status of the inverter during the power grid fault recovery process, the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient are dynamically adjusted. Wherein, both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient are greater than or equal to 0, and the sum of the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient is equal to 1.

[0008] In one possible implementation, dynamically adjusting the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient based on the real-time operating status of the inverter during the grid fault recovery process includes: If the inverter is currently in an overcurrent sealing pulse state, then the instantaneous feedforward weighting coefficient is reduced and the filter feedforward weighting coefficient is increased; If the response time and / or response amount of the current inverter output current do not meet the preset requirements, then the instantaneous feedforward weighting coefficient is increased and the filter feedforward weighting coefficient is decreased.

[0009] In one possible implementation, the step of reducing the instantaneous feedforward weighting coefficient and increasing the filter feedforward weighting coefficient if the inverter is currently in an overcurrent sealing pulse state includes: The instantaneous feedforward weighting coefficient is reduced to a preset first value, and the filtered feedforward weighting coefficient is increased to a preset second value.

[0010] In one possible implementation, the step of increasing the instantaneous feedforward weighting coefficient and decreasing the filter feedforward weighting coefficient if the response time and / or response amount of the current inverter output current do not meet the preset requirements includes: The instantaneous feedforward weighting coefficient is gradually increased according to a preset step size, and the filter feedforward weighting coefficient is gradually decreased according to the preset step size, until the response time and response amount of the inverter output current meet the preset requirements.

[0011] In one possible implementation, the method further includes: Once the power grid fault is recovered, both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient are adjusted to the weighting coefficients corresponding to the normal operating state of the power grid.

[0012] In one possible implementation, the step of superimposing the voltage feedforward quantity with the voltage output from the current loop to obtain the target voltage control quantity includes: The voltage feedforward of the d-axis is superimposed with the voltage output of the id current loop to obtain the target voltage control quantity of the d-axis. The target voltage control quantity for the q-axis is obtained by superimposing the voltage output of the iq current loop with the voltage feedforward of the q-axis.

[0013] Secondly, embodiments of this application provide a fault ride-through control system for a grid-connected inverter, comprising: The signal acquisition module is used to acquire the grid voltage signal during the grid fault recovery process; The signal filtering module is used to filter the grid voltage signal to obtain the filtered grid voltage signal; The voltage calculation module is used to determine the voltage feedforward amount based on the grid voltage signal and the filtered grid voltage signal; The voltage calculation module is also used to superimpose the voltage feedforward quantity with the voltage output of the current loop to obtain the target voltage control quantity. The signal modulation module is used to perform three-level modulation processing on the target voltage control quantity to obtain a corresponding PWM drive signal, so as to control the output current of the inverter.

[0014] Thirdly, embodiments of this application provide an inverter, including the fault ride-through control system of the grid-connected inverter described in the second aspect above.

[0015] This application provides a fault ride-through control method for a grid-connected inverter. The method acquires the grid voltage signal during grid fault recovery; filters the grid voltage signal to obtain a filtered grid voltage signal; simultaneously uses both the original and filtered grid voltage signals to determine a voltage feedforward, and superimposes this voltage feedforward onto the voltage output of the current loop to form the final target voltage control quantity. The target voltage control quantity is then modulated to obtain a corresponding PWM drive signal to control the inverter's output current. Since the voltage feedforward is directly superimposed on the current loop output, it can compensate for the disturbance to the current caused by grid voltage fluctuations in advance, significantly improving the inverter's current dynamic response speed during grid fault recovery. Furthermore, it avoids feedback adjustment based on the current loop after current deviations occur, reducing the current loop's closed-loop adjustment burden, lowering current overshoot and oscillation, and enabling the inverter's output current (active / reactive) to reach the standard requirements more quickly and accurately. This improves the control accuracy and response speed throughout the fault ride-through process, solving the problems of slow response speed and insufficient response quantity in traditional control methods. Furthermore, by employing a voltage feedforward approach that combines the original voltage and the filtered voltage, the instantaneous change characteristics of the original voltage can be utilized to ensure the speed of control, while the filtered voltage can suppress the influence of grid harmonics, disturbances and noise on the control loop, thus balancing the dynamic response performance of inverter control with the stability of system operation.

[0016] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this specification. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, 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.

[0018] Figure 1 This is a schematic flowchart of a fault ride-through control method for a grid-connected inverter provided in an embodiment of this application; Figure 2 This is a schematic diagram of the control loop of a grid-connected inverter provided in one embodiment of this application; Figure 3 This is a flowchart illustrating a fault ride-through control method for a grid-connected inverter provided in another embodiment of this application; Figure 4 This is a schematic diagram of the control loop of a grid-connected inverter provided in another embodiment of this application; Figure 5This is a schematic diagram of the fault ride-through control system of a grid-connected inverter provided in one embodiment of this application; Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0019] The present application will be described more clearly below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the function of 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. These all fall within the protection scope of the present application.

[0020] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0021] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0022] In the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0024] Furthermore, the term "multiple" mentioned in the embodiments of this application should be interpreted as two or more.

[0025] In related technologies, when a grid fault occurs, such as a voltage drop, the inverter detects the fault and outputs active and reactive currents in the fault state according to standard requirements to support grid operation. After the grid fault is cleared, the voltage recovery phase begins. During this phase, the grid voltage gradually recovers from the fault value to the rated value. This phase is the critical link in fault ride-through. It requires adjusting the inverter's output active and reactive currents according to standard requirements based on grid voltage changes, ensuring they reach the corresponding active and reactive current values ​​within a certain time. However, in actual control, the inverter's dynamic response capability is poor; the response time and quantity of active and reactive currents do not meet standard requirements. For example, during grid fault recovery, problems such as long response times, insufficient response quantities, and overcurrent can occur, easily leading to inverter disconnection from the grid and affecting the stable operation of the grid system.

[0026] To address the aforementioned technical issues, this application proposes the following technical concept: Voltage signals are acquired during grid restoration, and filtered to obtain a filtered voltage signal. Since both the original and filtered voltage signals are three-phase voltage signals, coordinate transformation is required to obtain the instantaneous voltage feedforward (d-axis / q-axis) corresponding to the original voltage signal and the filtered voltage feedforward (d-axis / q-axis) corresponding to the filtered voltage signal. The instantaneous and filtered voltage feedforward are then weighted and fused according to appropriate proportions to obtain the final target voltage feedforward (d-axis / q-axis), which is superimposed on the current loop output. This proactively compensates for the disturbances caused by grid voltage fluctuations to the current. Simultaneously, the weighted fusion ratio of the instantaneous and filtered voltage feedforward is dynamically adjusted based on the actual operating conditions of the inverter, significantly improving the inverter's dynamic current response speed during grid fault restoration. This enables the inverter's output current (active / reactive) to reach the standard requirements more quickly and accurately, improving the control accuracy and response speed throughout the fault ride-through process and solving the problems of slow response speed and insufficient response quantity in traditional control methods. Furthermore, by employing a voltage feedforward method that combines the original voltage and the filtered voltage, the instantaneous change characteristics of the original voltage can be utilized to ensure the speed of control. At the same time, the filtered voltage can suppress the influence of grid harmonics, disturbances and noise on the control loop, enabling the inverter to smoothly track the grid voltage recovery without overcurrent or fluctuations. This balances the dynamic response performance of the inverter control with the stability of system operation.

[0027] The fault ride-through control method for a grid-connected inverter provided according to an exemplary embodiment of this application will now be described with reference to the accompanying drawings.

[0028] It should be noted that the execution subject of the method provided in this application embodiment can be a processor, a controller, or other devices with the same processing capabilities.

[0029] Figure 1This is a schematic flowchart of a fault ride-through control method for a grid-connected inverter provided in an embodiment of this application; like Figure 1 As shown, the method in this application embodiment may include the following steps: Step S101: Obtain the grid voltage signal during the grid fault recovery process.

[0030] In this step, after the power grid experiences a fault and enters the recovery process, the inverter can, but is not limited to, acquire the power grid voltage signal through hardware sampling circuits or software sampling methods. This power grid voltage signal is a three-phase AC voltage signal (Ua, Ub, Uc), which is the original disturbance signal during the power grid fault recovery process.

[0031] Step S102: Filter the grid voltage signal to obtain a filtered grid voltage signal.

[0032] In this step, during the grid fault recovery process, voltage imbalance, harmonic distortion, transient spikes, and other issues may occur. After acquiring the original grid voltage signal, a specific filtering algorithm is used to filter it to remove interference such as harmonics and transient spikes from the grid voltage, resulting in a filtered and clean three-phase grid voltage signal (Ua_f, Ub_f, Uc_f).

[0033] It is understandable that the filtering algorithm in this embodiment needs to be adapted to the grid fault ride-through condition. Since the filtered grid voltage signal also needs to participate in voltage feedforward regulation, the selection of the filtering algorithm needs to simultaneously satisfy the filtering effect and minimize the signal delay in order to ensure the balance between the filtering effect and the dynamic response. It is necessary to filter out interference while avoiding excessive signal delay caused by over-filtering (over-filtering will lead to poor dynamic performance of the filter feedforward and a decrease in the overall response capability after weighting).

[0034] It should be noted that the filtering method selected in this embodiment can be a second-order generalized integrator, a low-pass filter, or other filtering methods that can meet the above filtering and dynamic response requirements. This embodiment does not specifically limit which filtering algorithm to choose.

[0035] Step S103: Determine the voltage feedforward amount based on the grid voltage signal and the filtered grid voltage signal.

[0036] It should be noted that since the raw grid voltage signal can reflect grid fluctuations in real time, using the raw grid voltage for instantaneous voltage feedforward into the inverter's control loop can quickly compensate for the impact of grid fluctuations, thus improving the inverter's dynamic response performance. However, harmonics and transient spikes present in the raw grid voltage signal can also be introduced into the control loop, causing secondary disturbances to the grid due to inverter output current fluctuations. Filtered grid voltage eliminates harmonics and other interference components. Using filtered grid voltage for filtered voltage feedforward avoids current fluctuations and overcurrent risks caused by introducing interference signals into the current loop control loop, ensuring the stability of the inverter's current output. However, filtering inevitably introduces a slight signal delay, and using filtered voltage feedforward alone can affect the inverter's dynamic response performance. Based on this, this embodiment proposes to use the original grid voltage signal and the filtered grid voltage signal to jointly determine the voltage feedforward amount. This not only preserves the dynamic response performance of instantaneous voltage feedforward, but also reduces interference from the grid by using filtered voltage feedforward. The "fast response" of the original grid voltage and the "stable control" of the filtered grid voltage form complementary control, which solves the problem of "fast but unstable" or "stable but not fast" in a single feedforward method, and achieves a balance between the dynamic response speed and stability of the inverter current.

[0037] In this step, both the original and filtered grid voltage signals are three-phase AC voltages, requiring coordinate transformation to convert them into DC quantities along the d-axis and q-axis. For example, the original grid voltage signal is converted into DC quantities along the d-axis and q-axis using Clark transform (3 / 2 transform) + Park transform (2 / rotation transform), yielding the instantaneous voltage feedforward Ud_s along the d-axis and Uq_s along the q-axis. Similarly, the filtered grid voltage signal is converted into DC quantities along the d-axis and q-axis using Clark transform (3 / 2 transform) + Park transform (2 / rotation transform), yielding the filtered voltage feedforward Ud_f along the d-axis and Uq_f along the q-axis. Finally, the final voltage feedforward (Ud / Uq) is determined by combining the instantaneous voltage feedforward (d-axis / q-axis) and the filtered voltage feedforward (d-axis / q-axis).

[0038] Step S104: The voltage feedforward quantity is superimposed with the voltage output from the current loop to obtain the target voltage control quantity.

[0039] Step S105: Modulate the target voltage control quantity to obtain a corresponding PWM drive signal to control the output current of the inverter.

[0040] In steps S104 and S105, the inverter's voltage loop control includes d-axis current loop control (id current loop) and q-axis current loop control (iq current loop), refer to Figure 2The voltage feedforward quantity Ud of the d-axis is superimposed with the voltage output of the id current loop to obtain the target voltage control quantity of the d-axis; the voltage feedforward quantity Uq of the q-axis is superimposed with the voltage output of the iq current loop to obtain the target voltage control quantity of the q-axis. Finally, the target voltage control quantities of the d-axis and q-axis are pulse-width modulated (PWM) by the modulation module to output the corresponding PWM drive signal. The PWM drive signal drives the switching transistors of the inverter, thereby controlling the active and reactive current output by the inverter.

[0041] In this embodiment, since the voltage feedforward is directly superimposed on the current loop output, it can compensate for the disturbances caused by grid voltage fluctuations to the current in advance, significantly improving the inverter's dynamic current response speed during grid fault recovery. Furthermore, it avoids feedback adjustment based on the current loop after current deviations occur, reducing the burden of closed-loop regulation in the current loop, lowering current overshoot and oscillation, and enabling the inverter's output current (active / reactive) to reach standard requirements more quickly and accurately. This improves control accuracy and response speed throughout the fault ride-through process, solving the problems of slow response speed and insufficient response quantity in traditional control methods. Moreover, the voltage feedforward method combining the original voltage and the filtered voltage not only utilizes the instantaneous change characteristics of the original voltage to ensure control speed but also suppresses the influence of grid harmonics, disturbances, and noise on the control loop through the filtered voltage. This avoids introducing grid harmonics and other interference into the current loop control loop, preventing current fluctuations and overcurrent risks, ensuring the stability of the inverter's current output, and balancing the inverter's dynamic response performance with system operational stability.

[0042] Figure 3 This is a flowchart illustrating a fault ride-through control method for a grid-connected inverter provided in another embodiment of this application.

[0043] like Figure 3 As shown, the method in this application embodiment may include the following steps: Step S301: Obtain the grid voltage signal during the grid fault recovery process.

[0044] Step S302: Filter the grid voltage signal to obtain a filtered grid voltage signal.

[0045] It should be noted that the implementation of steps S301 and S302 in this embodiment can be referred to the explanation of the relevant steps in the above-mentioned method embodiments, and will not be repeated here.

[0046] Step S303: Perform coordinate transformation processing on the grid voltage signal to obtain the instantaneous voltage feedforward Ud_s on the d-axis and the instantaneous voltage feedforward Uq_s on the q-axis.

[0047] In this step, the original grid voltage signal is transformed into three-phase voltages Ua, Ub, and Uc using Clark transformation (3 / 2 transformation) to convert them into voltage components Uα and Uβ in a two-phase stationary α / β coordinate system. Then, it is transformed into two-phase stationary α / β components Uα and Uβ using Park transformation (2 / rotation transformation) to convert them into d-axis / q-axis components Ud_s and Uq_s (instantaneous voltage feedforward quantities of the d-axis / q-axis) that rotate synchronously with the grid fundamental wave.

[0048] It should be noted that the formulas for Clark transform (3 / 2 transform) and Park transform (2 / rotation transform) can be found in relevant technologies, and will not be explained in detail here.

[0049] Step S304: Perform coordinate transformation processing on the filtered grid voltage signal to obtain the filtered voltage feedforward amount Ud_f on the d-axis and the filtered voltage feedforward amount Uq_f on the q-axis.

[0050] In this step, the coordinate transformation process of the filtered grid voltage signal is the same as in step S303, and will not be explained again here.

[0051] Step S305: Obtain the instantaneous feedforward weighting coefficient corresponding to the instantaneous voltage feedforward quantity and the filter feedforward weighting coefficient corresponding to the filter voltage feedforward quantity when the power grid is operating normally.

[0052] In this step, when the power grid is operating normally, the instantaneous feedforward weighting coefficient k1 corresponding to the instantaneous voltage feedforward and the filter feedforward weighting coefficient k2 corresponding to the filter voltage feedforward can be used as basic weighting coefficients. Their specific values ​​can be determined through actual measurement based on the normal operation of the power grid, and an optimal combination of basic weighting coefficients can be obtained (e.g., k1=0.5, k2=0.5). Under the normal operation of the power grid, this optimal combination of basic weighting coefficients is used to perform a weighted summation of the instantaneous voltage feedforward and the filter voltage feedforward, thereby ensuring that the inverter output can quickly and smoothly adapt to the grid voltage and complete grid connection when the power grid is operating normally. When the power grid experiences a fault and enters the recovery process, the two weighting coefficients can be further adjusted based on this combination of weighting coefficients to meet the requirements of inverter output response speed and stability during the power grid fault recovery process.

[0053] Step S306: Based on the real-time operating status of the inverter during the power grid fault recovery process, dynamically adjust the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient.

[0054] Wherein, both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient are greater than or equal to 0, and the sum of the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient is equal to 1.

[0055] In one possible implementation, dynamically adjusting the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient based on the real-time operating status of the inverter during the grid fault recovery process includes: if the inverter is currently in an overcurrent blocking pulse state, then reducing the instantaneous feedforward weighting coefficient and increasing the filter feedforward weighting coefficient; if the response time and / or response amount of the inverter output current do not meet preset requirements, then increasing the instantaneous feedforward weighting coefficient and decreasing the filter feedforward weighting coefficient.

[0056] Understandably, instantaneous voltage feedforward and filtered voltage feedforward complement each other in terms of speed and stability. Instantaneous voltage feedforward (corresponding to weighting coefficient k1): no filtering, no signal delay, fast response, and strong dynamics, but it introduces grid harmonics and transient disturbances, easily causing current fluctuations and overcurrent problems. Filtered voltage feedforward (corresponding to weighting coefficient k2): after filtering, harmonic interference is removed, operation is stable, and overcurrent is prevented, but the signal delay introduced by filtering slows down the response speed and reduces the response quantity. Therefore, the essence of weighting coefficient adjustment is to dynamically balance the inverter's dynamic response speed, operational stability, and anti-interference capability based on the actual operating conditions of grid fault recovery, and the formulation of adjustment rules is completely in line with the core characteristic differences between instantaneous feedforward and filtered feedforward.

[0057] In this embodiment, the overcurrent blocking pulse is a hardware protection action of the inverter. It means that when the current exceeds the rated value, the controller immediately blocks the drive pulse of the power switch. Essentially, this is because too much grid interference (harmonics, transient spikes, etc.) is introduced into the control loop, causing the current loop regulation to become unstable and triggering a sudden increase in current. This indicates that the proportion of instantaneous voltage feedforward is too high. Stability is the primary issue to be addressed under this condition. Therefore, it is necessary to reduce the weighting coefficient of instantaneous feedforward and increase the weighting coefficient of filter feedforward (ensuring that the sum of the two weighting coefficients is 1). By increasing the weighting coefficient of filter voltage feedforward, the proportion of filter voltage feedforward that filters out harmonics / disturbances can be increased, thereby significantly reducing grid interference entering the current control loop. This can quickly eliminate the impact of grid transient disturbances on the current, avoid overshooting and overcurrent in the current loop due to disturbance regulation, make the current output more stable, eliminate overcurrent, avoid blocking pulses, and ensure that the inverter does not disconnect from the grid or get damaged during fault ride-through.

[0058] The inverter's output current response time and / or response amount failing to meet preset requirements (insufficient response amount) indicates a slow dynamic current response (i.e., the current reaches the standard value too slowly) and the actual current amplitude not meeting the standard. Essentially, this stems from the inverter's insufficient dynamic tracking capability for grid voltage recovery. However, the absence of overcurrent, current fluctuation, or other stability issues under these conditions suggests minimal impact from harmonics / interference in the current grid. Instead, the delay characteristics of the filter voltage feedforward become the primary limiting factor. The filtering process causes a lag in the voltage feedforward compensation signal, preventing timely support for the current loop to quickly track grid voltage recovery. Therefore, it is necessary to reduce the weighting coefficient k2 of the filter voltage feedforward while increasing the weighting coefficient k1 of the instantaneous voltage feedforward. This reduces the proportion of the delayed and slow-responding filter voltage feedforward and increases the proportion of the fast-responding instantaneous voltage feedforward. Timely compensation using the instantaneous voltage feedforward significantly improves the dynamic response of the current loop, resolving the technical problems of slow response and insufficient response amount.

[0059] It should be noted that there are two ways to adjust the weighting coefficients based on the actual operating status of the inverter. The first is a one-time adjustment, which involves conducting offline tests in advance, traversing all typical operating conditions of the inverter (such as normal operation, insufficient response, overcurrent sealing pulse, etc.), obtaining the optimal fixed weighting coefficient value for each condition, and pre-storing it in the controller. When the inverter is running online, it directly calls upon the corresponding operating condition and switches to the preset coefficient value in one step. The second is a gradual adjustment method, which involves gradually increasing or decreasing the weighting coefficients according to the actual operating status of the inverter until the inverter returns to normal. The following sections will explain these two weighting coefficient adjustment methods in conjunction with the two operating conditions.

[0060] In one possible implementation, the step of reducing the instantaneous feedforward weighting coefficient and increasing the filter feedforward weighting coefficient if the inverter is currently in an overcurrent sealing pulse state includes: reducing the instantaneous feedforward weighting coefficient to a preset first value and increasing the filter feedforward weighting coefficient to a preset second value.

[0061] In this embodiment, offline testing can be performed in advance for the overcurrent sealing pulse condition to obtain the optimal weighting coefficient combination. For example, during the overcurrent sealing pulse, the instantaneous feedforward weighting coefficient k1 = preset first value (e.g., 0.2), and the filter feedforward weighting coefficient k2 = preset second value (e.g., 0.8). The inverter detects its own operating status in real time and determines that it has entered the overcurrent sealing pulse condition. It directly assigns k1 and k2 to the preset coefficient values ​​corresponding to this condition to quickly complete the weighting coefficient adjustment.

[0062] In one possible implementation, the step of increasing the instantaneous feedforward weighting coefficient and decreasing the filter feedforward weighting coefficient if the response time and / or response amount of the current inverter output current do not meet the preset requirements includes: gradually increasing the instantaneous feedforward weighting coefficient according to a preset step size, and gradually decreasing the filter feedforward weighting coefficient according to the preset step size, until the response time and response amount of the inverter output current meet the preset requirements.

[0063] In this embodiment, the inverter monitors the output current's response time, response quantity, and overcurrent status in real time online. It then finely adjusts k1 and k2 step-by-step with a fixed preset step size (k1+k2=1 during adjustment). The indicators are verified after each adjustment step until the response time and response quantity meet the preset requirements, at which point the adjustment stops. This is an online closed-loop optimization process of simultaneous adjustment and testing. The preset step size can be set according to actual needs. For example, if the preset step size is set to 0.05, when the response time / response quantity is detected to be substandard, the value of k1 is gradually increased according to this fixed compensation (e.g., 0.05 / step), while the value of k2 is gradually decreased (k1+0.05, k2-0.05 per cycle) until the response time and response quantity meet the standard requirements.

[0064] In this embodiment, the one-time preset coefficient adjustment method offers fast adjustment speed and simple logic, making it suitable for transient emergency conditions such as overcurrent suppression pulses, quickly suppressing overcurrent and preventing the protection action from escalating. The gradual coefficient adjustment method does not rely on offline testing, adapting to complex operating conditions with different power grid sites, voltage dip depths, and equipment parameters. It allows for gradual fine-tuning to the standard requirements, finding the real-time optimal coefficient under the current operating condition, maximizing the balance between dynamic response and operational stability, significantly improving control accuracy. It is also more suitable for operating conditions where response time / response quantity does not meet standards, avoiding the problems of insufficient or excessive adjustment of the one-time preset coefficient value. Therefore, different weighted coefficient adjustment methods can be selected according to the actual operating conditions to leverage their respective advantages, ensuring both the dynamic response speed and output stability of the inverter output.

[0065] Step S307: The instantaneous voltage feedforward and the filtered voltage feedforward of the d-axis and q-axis are weighted and summed respectively to obtain the voltage feedforward of the d-axis and the voltage feedforward of the q-axis.

[0066] Step S308: The voltage feedforward quantity is superimposed with the voltage output from the current loop to obtain the target voltage control quantity.

[0067] In steps S307 and S308, after obtaining the corresponding weighting coefficients (instantaneous feedforward weighting coefficient k1 and filter feedforward weighting coefficient k2) for the two voltage feedforward quantities based on the current inverter operating state, refer to... Figure 4The instantaneous voltage feedforward Ud_s on the d-axis and the filtered voltage feedforward Ud_f on the d-axis are weighted and summed to obtain the voltage feedforward Ud on the d-axis (Ud = Ud_s*k1 + Ud_f*k2); the instantaneous voltage feedforward Uq_s on the q-axis and the filtered voltage feedforward Uq_f on the q-axis are weighted and summed to obtain the voltage feedforward Uq on the q-axis (Uq = Uq_s*k1 + Uq_f*k2). Then, the voltage feedforward Ud on the d-axis is superimposed with the voltage output from the id current loop to obtain the target voltage control quantity on the d-axis; the voltage feedforward Uq on the q-axis is superimposed with the voltage output from the iq current loop to obtain the target voltage control quantity on the q-axis.

[0068] Step S309: Modulate the target voltage control quantity to obtain a corresponding PWM drive signal to control the output current of the inverter.

[0069] In this step, the target voltage control values ​​for the d-axis and q-axis are restored to three-phase voltage reference values ​​through inverse Park and inverse Clark transformations, and then input into the modulation module. Figure 4 The modulation module generates a PWM drive signal with a corresponding duty cycle based on the three-phase voltage reference value using a pulse width modulation algorithm, which drives the inverter's power switches to turn on and off. According to the duty cycle of the PWM drive signal, the inverter's power switches turn on and off in a regular manner, outputting an actual three-phase voltage that matches the voltage reference value. By changing the voltage difference between the inverter and the grid, the inverter's output current (active and reactive) is ultimately adjusted to track the current loop setpoint, achieving dynamic response optimization.

[0070] In one possible implementation, the method further includes: after the power grid fault is recovered, adjusting both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient to the weighting coefficients corresponding to the normal operating state of the power grid.

[0071] In this embodiment, after the inverter completes grid fault ride-through, it enters normal operating state. At this time, the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient can be restored to the optimal basic weighting coefficient under normal state, so that when the grid is operating normally, the inverter output can also quickly and smoothly adapt to the grid voltage to complete grid connection.

[0072] In this embodiment, the advantages and disadvantages of the instantaneous grid voltage and the filtered voltage are complemented by weighted fusion. This retains the fast response advantage of instantaneous feedforward while filtering grid harmonic interference through filtered feedforward. This avoids the shortcomings of a single feedforward method, which is fast but prone to overcurrent or has strong anti-interference but slow response, thus achieving a balance between response speed and operational stability. Furthermore, the weighting coefficients are dynamically adjusted according to the inverter's operating conditions, enabling adaptive control of the inverter during grid fault ride-through. This improves the intelligence and accuracy of the control, ultimately ensuring that the inverter's active and reactive current indicators meet the standards during grid fault recovery. This not only ensures that the inverter itself meets the fault ride-through standards but also allows it to output current smoothly and accurately during grid recovery, guaranteeing the inverter's compliant grid connection. At the same time, it avoids secondary disturbances to the grid caused by inverter current fluctuations, improving the overall operational stability of the grid.

[0073] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0074] Figure 5 This is a schematic diagram of the fault ride-through control system of a grid-connected inverter provided in one embodiment of this application.

[0075] like Figure 5 As shown, the fault ride-through control system for the grid-connected inverter provided in this embodiment may include: a signal acquisition module 501, a signal filtering module 502, a coefficient adjustment module 503, a voltage calculation module 504, and a signal modulation module 505.

[0076] The system includes a signal acquisition module 501 for acquiring the grid voltage signal during grid fault recovery; a signal filtering module 502 for filtering the grid voltage signal to obtain a filtered grid voltage signal; a voltage calculation module 504 for determining the voltage feedforward amount based on the grid voltage signal and the filtered grid voltage signal; the voltage calculation module 504 is also used to superimpose the voltage feedforward amount with the voltage output from the current loop to obtain a target voltage control amount; and a signal modulation module 505 for performing three-level modulation processing on the target voltage control amount to obtain a corresponding PWM drive signal for controlling the output current of the inverter.

[0077] In one possible implementation, the voltage calculation module 504 is specifically used to: perform coordinate transformation processing on the grid voltage signal to obtain the instantaneous voltage feedforward quantity on the d-axis and the instantaneous voltage feedforward quantity on the q-axis; perform coordinate transformation processing on the filtered grid voltage signal to obtain the filtered voltage feedforward quantity on the d-axis and the filtered voltage feedforward quantity on the q-axis; and perform weighted summation on the instantaneous voltage feedforward quantity on the d-axis and the filtered voltage feedforward quantity on the q-axis, respectively, to obtain the voltage feedforward quantity on the d-axis and the voltage feedforward quantity on the q-axis.

[0078] In one possible implementation, the fault ride-through control system of the grid-connected inverter further includes: a coefficient adjustment module 503, used to acquire the instantaneous feedforward weighting coefficient corresponding to the instantaneous voltage feedforward and the filter feedforward weighting coefficient corresponding to the filter voltage feedforward when the grid is operating normally; and to dynamically adjust the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient according to the real-time operating status of the inverter during the grid fault recovery process; wherein the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient are both greater than or equal to 0, and the sum of the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient is equal to 1.

[0079] In one possible implementation, the coefficient adjustment module 503 is specifically used to reduce the instantaneous feedforward weighting coefficient and increase the filter feedforward weighting coefficient if the inverter is currently in an overcurrent sealing pulse state; and to increase the instantaneous feedforward weighting coefficient and reduce the filter feedforward weighting coefficient if the response time and / or response amount of the inverter output current do not meet the preset requirements.

[0080] In one possible implementation, the coefficient adjustment module 503 is specifically used to reduce the instantaneous feedforward weighting coefficient to a preset first value and increase the filter feedforward weighting coefficient to a preset second value when the inverter is currently in the state of overcurrent sealing pulse.

[0081] In one possible implementation, the coefficient adjustment module 503 is specifically used to gradually increase the instantaneous feedforward weighting coefficient according to a preset step size and gradually decrease the filter feedforward weighting coefficient according to the preset step size when the response time and / or response amount of the current inverter output current do not meet the preset requirements, until the response time and response amount of the inverter output current meet the preset requirements.

[0082] In one possible implementation, the coefficient adjustment module 503 is further configured to adjust both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient to the weighting coefficients corresponding to the normal operation state of the power grid after the power grid fault is restored.

[0083] In one possible implementation, the voltage calculation module 504 is further configured to superimpose the voltage feedforward of the d-axis with the voltage output of the id current loop to obtain the target voltage control quantity of the d-axis; and to superimpose the voltage feedforward of the q-axis with the voltage output of the iq current loop to obtain the target voltage control quantity of the q-axis.

[0084] It should be noted that the detailed implementation process of the above system embodiments can be found in the relevant method embodiments section, and will not be repeated here.

[0085] This application also provides an inverter, including the fault ride-through control system of the grid-connected inverter described in the above system embodiments.

[0086] Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. For example... Figure 6 As shown, the device 600 of this embodiment includes a processor 610 and a memory 620, wherein the memory 620 stores a computer program 621 that can run on the processor 610. When the processor 610 executes the computer program 621, it implements the steps in any of the above method embodiments. Alternatively, when the processor 610 executes the computer program 621, it implements the functions of each module / unit in the above device embodiments.

[0087] For example, computer program 621 may be divided into one or more modules / units, one or more of which are stored in memory 620 and executed by processor 610 to complete this application. The one or more modules / units may be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of computer program 621 in device 600.

[0088] Those skilled in the art will understand that Figure 6 This is merely an example of a device and does not constitute a limitation on the device. It may include more or fewer components than shown, or combinations of certain components, or different components, such as input / output devices, network access devices, buses, etc.

[0089] The processor 610 can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0090] The memory 620 can be an internal storage unit of the device, such as a hard disk or RAM, or an external storage device, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., provided in the electronic device. The memory 620 can also include both internal and external storage units of the electronic device. The memory 620 is used to store computer programs and other programs and data required by the electronic device. The memory 620 can also be used to temporarily store data that has been output or will be output.

[0091] For the sake of simplicity and clarity, only the above-described functional modules / units are used as examples. In practical applications, the functions described above can be assigned to different functional modules / units as needed. These modules / units can be implemented in hardware, software, or a combination of both.

[0092] An embodiment of this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the fault ride-through control method for grid-connected inverters in the above-described method embodiments.

[0093] This invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the fault ride-through control method for grid-connected inverters in the above-described method embodiments.

[0094] Computer programs include computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. Computer-readable media can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0095] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not detailed or described in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0096] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for fault ride-through control of a grid-connected inverter, characterized in that, include: Acquire grid voltage signals during grid fault recovery; The grid voltage signal is filtered to obtain a filtered grid voltage signal; The voltage feedforward amount is determined based on the grid voltage signal and the filtered grid voltage signal; The voltage feedforward quantity is superimposed with the voltage output from the current loop to obtain the target voltage control quantity; The target voltage control quantity is modulated to obtain a corresponding PWM drive signal, which is used to control the output current of the inverter.

2. The fault ride-through control method of a grid-connected inverter according to claim 1, characterized in that, The step of determining the voltage feedforward amount based on the grid voltage signal and the filtered grid voltage signal includes: The grid voltage signal is subjected to coordinate transformation processing to obtain the instantaneous voltage feedforward of the d-axis and the instantaneous voltage feedforward of the q-axis; The filtered grid voltage signal is subjected to coordinate transformation to obtain the filtered voltage feedforward amount on the d-axis and the filtered voltage feedforward amount on the q-axis. The instantaneous voltage feedforward and filtered voltage feedforward of the d-axis and q-axis are weighted and summed respectively to obtain the voltage feedforward of the d-axis and the voltage feedforward of the q-axis.

3. The fault ride-through control method of a grid-connected inverter according to claim 2, characterized in that, Before performing a weighted summation of the instantaneous voltage feedforward and the filtered voltage feedforward on the d-axis and q-axis respectively, the method further includes: When the power grid is operating normally, the instantaneous feedforward weighting coefficients corresponding to the instantaneous voltage feedforward quantity and the filter feedforward weighting coefficients corresponding to the filter voltage feedforward quantity are obtained. Based on the real-time operating status of the inverter during the power grid fault recovery process, the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient are dynamically adjusted. Wherein, both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient are greater than or equal to 0, and the sum of the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient is equal to 1.

4. The fault ride-through control method of a grid-connected inverter according to claim 3, characterized in that, The step of dynamically adjusting the instantaneous feedforward weighting coefficient and the filter feedforward weighting coefficient based on the real-time operating status of the inverter during the grid fault recovery process includes: If the inverter is currently in an overcurrent sealing pulse state, then the instantaneous feedforward weighting coefficient is reduced and the filter feedforward weighting coefficient is increased; If the response time and / or response amount of the current inverter output current do not meet the preset requirements, then the instantaneous feedforward weighting coefficient is increased and the filter feedforward weighting coefficient is decreased.

5. The fault ride-through control method of a grid-connected inverter according to claim 4, characterized in that, If the inverter is currently in an overcurrent sealing pulse state, then the instantaneous feedforward weighting coefficient is reduced and the filter feedforward weighting coefficient is increased, including: The instantaneous feedforward weighting coefficient is reduced to a preset first value, and the filtered feedforward weighting coefficient is increased to a preset second value.

6. The fault ride-through control method of a grid-connected inverter according to claim 4, wherein, If the response time and / or response amount of the current inverter output current do not meet the preset requirements, then the instantaneous feedforward weighting coefficient is increased and the filter feedforward weighting coefficient is decreased, including: The instantaneous feedforward weighting coefficient is gradually increased according to a preset step size, and the filter feedforward weighting coefficient is gradually decreased according to the preset step size, until the response time and response amount of the inverter output current meet the preset requirements.

7. The fault ride-through control method of a grid-connected inverter according to claim 3, wherein, The method further includes: Once the power grid fault is recovered, both the instantaneous feedforward weighting coefficient and the filtered feedforward weighting coefficient are adjusted to the weighting coefficients corresponding to the normal operating state of the power grid.

8. The fault ride-through control method of a grid-connected inverter according to any one of claims 2 to 7, characterized in that, The step of superimposing the voltage feedforward quantity with the voltage output from the current loop to obtain the target voltage control quantity includes: The voltage feedforward of the d-axis is superimposed with the voltage output of the id current loop to obtain the target voltage control quantity of the d-axis. The target voltage control quantity for the q-axis is obtained by superimposing the voltage output of the iq current loop with the voltage feedforward of the q-axis.

9. A fault ride-through control system for a grid-connected inverter, characterized in that, include: The signal acquisition module is used to acquire the grid voltage signal during the grid fault recovery process; The signal filtering module is used to filter the grid voltage signal to obtain the filtered grid voltage signal; The voltage calculation module is used to determine the voltage feedforward amount based on the grid voltage signal and the filtered grid voltage signal; The voltage calculation module is also used to superimpose the voltage feedforward quantity with the voltage output of the current loop to obtain the target voltage control quantity. The signal modulation module is used to modulate the target voltage control quantity to obtain a corresponding PWM drive signal to control the output current of the inverter.

10. An inverter, characterized by, include: The fault ride-through control system for a grid-connected inverter as described in claim 9.

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