Fault ride-through control method and device of grid-connected converter, controller and grid-connected converter

Abstract

The invention provides a fault ride-through control method and device of a grid-connected converter, a controller and the grid-connected converter. The method comprises the steps that when it is detected that the grid-connected converter enters a fault ride-through quit stage, a given value of a current loop is set to be zero and kept for a first preset duration; and after the first preset duration, controlling the given value of the current loop to recover to the value before the fault ride-through state, and compensating the output phase of the phase-locked loop based on the power grid voltage. According to the technical scheme, the transition time for stably quitting the current limiting state is provided for the grid-connected converter through the current loop zero-setting buffer, and adjustment impact caused by sudden change of the current given value from the current limiting level to the normal level is prevented; and then, when the given value of the current loop is recovered, phase-locked loop phase compensation is synchronously carried out, so that possible abrupt change of the voltage phase of the power grid during fault clearing is avoided, and the accuracy of coordinate transformation is ensured. And through the synergistic effect of the two, the output current waveform is kept smooth and stable while the active power is quickly recovered.

Description

Technical Field

[0001] This invention relates to the field of low voltage ride-through control technology, and in particular to a fault ride-through control method, device, controller, and grid-connected converter for a grid-connected converter. Background Technology

[0002] With the increasing proportion of renewable energy sources such as wind power and photovoltaics in the power system, power electronic converters, as the core interface connecting to the grid, play a decisive role in the stable operation of the grid due to their dynamic control performance. Especially in areas with relatively weak grid structures, high grid impedance, and insufficient voltage support capacity, converters not only need to complete energy transmission but are also required to maintain grid connection stability and actively support grid voltage under extreme conditions such as grid faults. Their control robustness and dynamic performance have become a key link in ensuring the safe and stable operation of the new power system.

[0003] Low-voltage ride-through (LVR) is one of the core technical requirements of grid-connected converters. When the grid voltage drops, the converter needs to limit its output current to prevent device damage and maintain stable terminal voltage through reactive power support. During the grid fault clearing and LVR recovery phase, the converter needs to quickly restore its active power to the pre-fault level to meet the recovery time requirements of relevant standards. However, existing LVR recovery control strategies often exhibit oscillations in the converter's output current waveform. This oscillation can affect power quality and may even cause resonance between the converter and the grid, threatening the stable operation of the grid-connected system. Summary of the Invention

[0004] This invention provides a fault ride-through control method, device, controller, and grid-connected converter for grid-connected converters, in order to solve the problem of output current waveform oscillation during the low-voltage ride-through recovery phase of grid-connected converters.

[0005] In a first aspect, embodiments of the present invention provide a fault ride-through control method for a grid-connected converter, comprising: Detect whether the grid-connected converter has entered the fault ride-through exit phase; If the grid-connected converter enters the fault ride-through exit phase, the current loop setpoint is set to zero and maintained for a first preset duration. After the first preset time period, the current loop setpoint is restored to the value before the fault ride-through state, and the output phase of the phase-locked loop is compensated based on the grid voltage.

[0006] Secondly, embodiments of the present invention provide a fault ride-through control device for a grid-connected converter, comprising: The fault crossing exit detection module is used to detect whether the grid-connected converter has entered the fault crossing exit phase; The current loop zeroing module is used to set the current loop setpoint to zero and maintain it for a first preset time if the grid-connected converter enters the fault ride-through exit phase. The phase compensation module is used to control the current loop setpoint to return to the value before the fault ride-through state after the first preset time period, and to compensate the output phase of the phase-locked loop based on the grid voltage.

[0007] Thirdly, embodiments of the present invention provide a controller, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the fault ride-through control method for a grid-connected converter as described in any possible implementation of the first aspect above.

[0008] Fourthly, embodiments of the present invention provide a grid-connected converter, including the controller described in the third aspect above.

[0009] This invention provides a fault ride-through control method, device, controller, and grid-connected converter for a grid-connected converter. When the grid-connected converter detects that it has entered the fault ride-through exit phase, the method sets the current loop setpoint to zero and maintains it for a first preset time. After the first preset time, the current loop setpoint is restored to its value before the fault ride-through state, and the output phase of the phase-locked loop (PLL) is compensated based on the grid voltage. This technical solution provides a smooth transition time for the grid-connected converter to exit the current-limiting state by buffering the current loop to zero, preventing adjustment shocks caused by sudden changes in the current setpoint from the current-limiting level to the normal level. Subsequently, when the current setpoint is restored, PLL phase compensation is performed synchronously to avoid sudden changes in the grid voltage phase during fault clearing, ensuring the accuracy of coordinate transformation. The two work together to ensure that while active power recovers rapidly, the output current waveform remains smooth and stable, significantly improving the system's transient stability and power quality. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of the present invention, 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 This is an application scenario diagram of the fault ride-through control method for grid-connected converters provided in the embodiments of the present invention; Figure 2 This is a flowchart illustrating the implementation of the fault ride-through control method for grid-connected converters provided in this embodiment of the invention. Figure 3This is a schematic diagram of the fault ride-through control device for a grid-connected converter provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the controller provided in an embodiment of the present invention. Detailed Implementation

[0012] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0013] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described below in conjunction with the accompanying drawings.

[0014] Figure 1 This diagram illustrates an application scenario of the fault ride-through control method for grid-connected converters provided in this embodiment of the invention. Figure 1 As shown, taking a photovoltaic grid-connected system as an example, the photovoltaic device is connected to the grid through a grid-connected converter. Under normal circumstances, the fault ride-through control loop of the grid-connected converter includes a decision loop, a current loop, and a voltage loop. In the decision loop, the grid voltage value is obtained, and then the corresponding current setpoint is determined based on the grid voltage value. In the current loop, the current loop output value is calculated based on the current setpoint and the actual value of the grid-connected converter's output current. Then, the current loop output value is used as the voltage loop setpoint. Based on the difference between the voltage loop setpoint and the grid voltage, the target control quantity is calculated. Finally, the target control quantity is used to generate a PWM (Pulse Width Modulation) signal to control the grid-connected converter. The grid-connected converter can be a grid-connected inverter or an energy storage converter connected to an energy storage system; no restriction is placed here.

[0015] To ensure uninterrupted operation during grid faults, grid-connected converters must possess high and low voltage ride-through capabilities. Existing technologies can effectively address stability and support issues during voltage dips. However, during the grid fault clearing and fault ride-through exit phases, grid-connected converters commonly exhibit severe oscillations in their output current waveform when restoring active power output, seriously threatening power quality and system stability.

[0016] Research revealed that the current oscillation during low-voltage breakdown stems from a complex coupling process. The primary cause lies in the abrupt change in the grid voltage phase. When a grid fault is instantaneously cleared, the voltage amplitude recovers, but its phase often undergoes a step change. At this time, the dynamic response of the grid-connected converter's phase-locked loop (PLL) cannot instantaneously track this abrupt change, resulting in a deviation between its output synchronous phase and the actual grid phase. This phase error causes the rotating coordinate system used for current control to become out of sync with the grid voltage vector. Current regulation and pulse width modulation performed in this misaligned coordinate system directly generate negative sequence and harmonic components, manifesting as severe oscillations in the output current.

[0017] Secondly, the abrupt change in control commands is another key contributing factor. To meet the grid connection standards' requirement for rapid active power recovery, control strategies often jump the control current loop setpoint directly from the limit or zero value during the high-low voltage recovery period to a higher value before the fault after voltage recovery. This abrupt change in the setpoint far exceeds the instantaneous tracking capability of the current loop, easily leading to regulator saturation and output overshoot, thereby triggering system oscillations. Furthermore, these two factors are coupled and mutually reinforcing. Phase deviation leads to distortion in power calculation and control, while the drastic current change affects the generator terminal voltage through grid impedance feedback, further disturbing the phase-locked loop and forming a positive feedback oscillation loop. This problem is particularly prominent in weak grid environments with high grid impedance.

[0018] To avoid the aforementioned problems, this application provides a fault ride-through control method for grid-connected converters. The execution entity of this method is the fault ride-through controller of the grid-connected converter. See [link to relevant documentation]. Figure 2 The flowchart illustrating the implementation of the fault ride-through control method for grid-connected converters provided in this embodiment of the invention is described in detail below: S101: Detect whether the grid-connected converter has entered the fault ride-through exit stage.

[0019] In this embodiment, the fault ride-through exit phase is the transition phase when the grid-connected converter is in the fault ride-through state and the grid voltage recovers, during which the grid-connected converter follows the grid voltage to return from the fault ride-through state to the normal operating state before the fault.

[0020] This embodiment can determine whether a grid-connected converter has entered the fault ride-through exit phase based on the grid voltage value. Specifically, during low-voltage ride-through, the controller determines that the grid-connected converter has entered the fault ride-through exit phase after detecting that the grid voltage value is greater than a first preset voltage threshold for a set duration. The first preset voltage threshold can be 80% to 90% of the grid rated voltage, and the set duration can be 2 ms. During high-voltage ride-through, the controller determines that the grid-connected converter has entered the fault ride-through exit phase after detecting that the grid voltage value is less than a second preset voltage threshold for a set duration. The second preset voltage threshold can be 115% to 130% of the grid rated voltage.

[0021] S102: If the grid-connected converter enters the fault ride-through exit stage, the current loop setpoint is set to zero and maintained for a first preset duration.

[0022] In this embodiment, during the fault ride-through phase, the grid-connected converter first determines the total current limit value of the current loop.

[0023] Specifically, first, the maximum allowable peak current of the device is obtained. Then, based on the depth of grid voltage anomaly, this maximum peak current is reduced to obtain the current loop current limiting value. The greater the depth of grid voltage anomaly, the greater the grid short-circuit current, and the larger the reduction in the maximum peak current, thus reducing device stress. The depth of grid voltage anomaly includes voltage sag depth and voltage overvoltage depth. If the grid-connected converter is in a low-voltage ride-through state, the lower limit of the grid voltage reference is subtracted from the actual grid voltage value to obtain the voltage difference. Then, the voltage difference is divided by the grid rated voltage to obtain the voltage sag depth. If the grid-connected converter is in a high-voltage ride-through state, the actual grid voltage value is subtracted from the upper limit of the grid voltage reference to obtain the voltage difference. Then, the voltage difference is divided by the grid rated voltage to obtain the voltage overvoltage depth.

[0024] Then, determine the reactive current setpoint and the active current setpoint.

[0025] Specifically, during low-voltage ride-through, the grid voltage value is acquired in real time, and then the positive-sequence voltage amplitude of the grid voltage is input into the formula. The reactive current given value is obtained; under high voltage ride-through condition, the positive sequence voltage amplitude of the grid voltage is input into the formula. .in, This represents the reactive current setpoint. Indicates the gain coefficient. Indicates the lower limit of the grid voltage reference value. Indicates the upper limit of the grid voltage reference value. This represents the positive-sequence voltage amplitude of the power grid. I n This indicates the rated current of the grid-connected converter.

[0026] Then based on the formula The active current setpoint is obtained. .

[0027] As can be seen, during fault ride-through, the current loop setpoint changes with the depth of the voltage anomaly. Throughout the fault ride-through phase, the current loop setpoint is in a current-limited state (d-axis active current setpoint drops to 20%-30% of the rated value during low-voltage ride-through, and even lower during high-voltage ride-through). During the exit phase, the current loop setpoint needs to be restored to its pre-fault value; for example, the d-axis current setpoint is typically 100% of the rated current, while the q-axis current setpoint is typically 20% of the rated current. If the current loop setpoint is directly switched abruptly from the current-limited value to the rated value, the current loop regulator will experience integral saturation due to the sudden change in the input signal. The PWM control signal output by the regulator will instantly reach its maximum value, causing the actual output current to far exceed the rated value, resulting in significant overshoot oscillation.

[0028] Therefore, in this embodiment, the current loop setpoint is cleared to zero and maintained for a first preset duration, increasing the zero-value transition zone. During the clearing period, the current loop first smoothly exits the current limiting regulation state, and the actual current gradually decreases to a low level as the current loop setpoint returns to zero. The regulator's integral term is naturally released, avoiding integral saturation. Subsequently, it slowly recovers from zero, and the input signal changes smoothly, allowing the regulator to accurately track and completely eliminate the risk of overshoot.

[0029] Specifically, the first preset duration can be 15~25ms. This value can be determined based on the depth of the power grid anomaly. That is, the deeper the power grid anomaly, the longer the first preset duration. This is because under a minor fault, the power grid recovers quickly, the phase deviation of the phase-locked loop is small, and the buffer required for the current loop to exit the current-limiting state is short. However, under a severe fault, the transient fluctuations during power grid recovery are large, the phase deviation of the phase-locked loop is large, and a longer time is needed to calibrate the phase and release the integral saturation of the current loop. At this time, the first preset duration needs to be increased to avoid insufficient buffering leading to recovery oscillation.

[0030] S103: After the first preset time, the current loop setpoint is restored to the value before the fault ride-through state, and the output phase of the phase-locked loop is compensated based on the grid voltage.

[0031] In this embodiment, when the controller detects that the grid-connected converter has entered the fault ride-through state, it latches the current loop setpoint value at the moment before the grid-connected converter entered the fault ride-through state. After clearing the current loop setpoint value to zero for a first preset time, the current loop setpoint value is restored to the value at the moment before the fault ride-through state.

[0032] Furthermore, to avoid sudden current changes, this embodiment can gradually increase the current loop setpoint from zero to the value before the fault crossover state after a first preset time period.

[0033] On the other hand, during fault ride-through, whether it's a high-voltage or low-voltage ride-through fault, the grid voltage fluctuates drastically. To prevent the phase-locked loop (PLL) from losing lock, its loop bandwidth is reduced and the filter coefficient is increased to ensure control stability. However, after the fault is cleared, the grid phase quickly returns to positive, and due to the adjustment lag, the estimated phase output of the PLL deviates from the actual phase of the grid.

[0034] Secondly, during the fault ride-through exit phase, the grid-connected converter needs to restore the current setpoint, and current regulation relies on the phase-locked loop (PLL) to perform dq transformation. If a phase deviation exists, it will cause the current loop to misjudge the feedback current, leading to overshoot oscillation; on the other hand, it will generate second harmonics in the current, distorting the waveform and even resonating with the grid impedance, which will exacerbate voltage fluctuations. At this time, if the PLL recovers on its own, it will take a long time, far exceeding the exit phase buffer period, during which time current oscillation will have already occurred.

[0035] To avoid current oscillation, this embodiment, in addition to clearing the current loop setpoint to zero, also requires phase compensation of the phase-locked loop output phase to directly correct transient deviations, quickly synchronize the phase, thereby avoiding the above-mentioned problems and ensuring smooth current recovery.

[0036] Specifically, the implementation process of a phase-locked loop includes: For grid voltage U g The voltage is transformed to the dq axis to obtain the q-axis voltage component Uq. Then, the q-axis voltage component Uq is filtered. The filtered q-axis voltage component Uq is subtracted from the q-axis voltage setpoint to obtain the q-axis voltage difference. The q-axis voltage difference is input to the PI controller to obtain the frequency setpoint. The frequency setpoint is subtracted from the frequency feedback value to obtain the frequency difference. The frequency difference is then integrated to obtain the output phase of the phase-locked loop. The output phase of the phase-locked loop is then compensated based on the grid voltage. Finally, the compensated output phase angle is used for voltage / current coordinate transformation.

[0037] Furthermore, the compensation amount for the output phase of the phase-locked loop can be determined based on the difference between the actual phase of the grid voltage and the output phase of the phase-locked loop under the current operating cycle, and this compensation amount can be used to compensate the output phase of the phase-locked loop.

[0038] As can be seen from the above embodiments, the above technical solution provides a smooth transition time for the grid-connected converter to exit the current-limiting state through a current loop zero buffer, preventing regulation shocks caused by sudden changes in the current setpoint from the current-limiting level to the normal level. Subsequently, phase-locked loop phase compensation is performed simultaneously when the current setpoint recovers, avoiding possible sudden changes in the grid voltage phase during fault clearing and ensuring the accuracy of coordinate transformation. The two work together to ensure that while active power recovers rapidly, the output current waveform remains smooth and stable, significantly improving the system's transient stability and power quality.

[0039] In one possible implementation, after detecting that the grid-connected converter has entered the fault ride-through exit phase, the method provided in this embodiment further includes: Within the first preset time period, increase the grid voltage U g The feedforward filter coefficients.

[0040] In this embodiment, within the first preset time period after entering the fault ride-through exit phase, the feedforward filtering coefficient of the grid voltage is increased to accelerate the voltage feedforward tracking speed and help maintain voltage stability.

[0041] Specifically, the grid voltage feedforward filter coefficient is a parameter used in voltage feedforward control to filter high-frequency noise in the grid voltage and adjust the feedforward response speed. The larger the feedforward filter coefficient, the faster the feedforward tracking speed; the smaller the feedforward filter coefficient, the better the filtering effect.

[0042] As can be seen from the above embodiments, at the moment of fault ride-through recovery, the grid voltage often contains a large number of harmonics and noise. Although the standard feedforward filter coefficient can ensure steady-state accuracy, it will delay the feedforward action, resulting in control lag. By temporarily increasing the feedforward filter coefficient, the response speed is accelerated during the transient process, allowing the voltage feedforward channel to reflect changes in grid voltage more quickly, thereby generating compensation earlier. This effectively offsets part of the impact of grid voltage disturbances on the current loop, reduces the control burden of the current loop, complements the current loop zero-set strategy, and together creates a more stable internal condition for the smooth recovery of subsequent power.

[0043] In one possible implementation, the specific process of increasing the feedforward filter coefficient of the grid voltage within the first preset time period includes: The first filter coefficient is determined based on the grid short-circuit ratio; Within the first preset time period, the feedforward filter coefficient of the grid voltage is increased to the first filter coefficient.

[0044] Specifically, the short circuit ratio (SCR) represents the ratio of the short circuit capacity at the grid connection point to the rated capacity of the grid-connected converter. It is a core indicator for measuring grid strength. The larger the SCR value, the stronger the grid; the smaller the SCR value, the weaker the grid.

[0045] The first filter coefficient is the target feedforward filter coefficient calculated based on the grid short-circuit ratio, and it is the set value of the feedforward filter coefficient within the first preset time period.

[0046] Specifically, to improve computational efficiency, this embodiment classifies the power grid into weak, medium-intensity, and strong grids based on the short-circuit ratio (SCR) value. A weak grid is defined as an SCR value less than a first value; a medium-intensity grid is defined as an SCR value greater than or equal to the first value but less than a second value; and a strong grid is defined as an SCR value greater than or equal to the second value. The first value is less than the second value. For example, the first value can be 2, and the second value can be 3. The controller can determine the current grid type based on its SCR value and then determine the corresponding first filter coefficient. A larger SCR value corresponds to a smaller first filter coefficient, ensuring effective signal filtering when grid voltage fluctuations are minimal; conversely, a smaller SCR value corresponds to a larger first filter coefficient, improving control response speed under weak grid conditions.

[0047] As can be seen from the above embodiments, the grid short-circuit ratio is a key indicator for measuring the strength of the power grid. Under weak grid conditions (low short-circuit ratio), the grid impedance is high, and the voltage is more prone to fluctuation, requiring a faster feedforward response; therefore, a larger filter coefficient should be set. Conversely, under strong grid conditions, a smaller coefficient can be selected to avoid introducing excessive noise. By establishing a mapping relationship between the filter coefficient and the grid short-circuit ratio, the control parameters can be automatically optimized according to the grid operating conditions, thereby achieving the best feedforward compensation effect under different grid intensities and improving the universality and effectiveness of the control method in different application scenarios.

[0048] In one possible implementation, another step of increasing the feedforward filter coefficient of the grid voltage within the first preset time period includes: The first filter coefficient is determined based on the degree of fluctuation of the grid voltage; Within the first preset time period, the feedforward filter coefficient of the grid voltage is increased to the first filter coefficient.

[0049] Specifically, when the grid-connected converter is in fault ride-through state, the controller can determine the degree of voltage fluctuation based on the difference between the grid voltage at the moment the grid-connected converter enters the fault ride-through exit stage and the grid voltage at the previous moment. Then, based on the degree of voltage fluctuation, the controller determines the first filter coefficient. The degree of voltage fluctuation is positively correlated with the first filter coefficient, that is, the greater the degree of voltage fluctuation, the larger the first filter coefficient, thereby accelerating the response speed of the grid voltage.

[0050] Specifically, when performing feedforward filtering on the grid voltage, the first filter coefficient can be used for both the q-axis and d-axis components of the grid voltage.

[0051] In one possible implementation, another process for increasing the feedforward filter coefficient of the grid voltage within the first preset time period includes: Multiplying the grid voltage by a first weighting factor yields the first grid voltage component; The first grid voltage component is filtered using the feedforward filter coefficients to obtain a first voltage value; Subtracting the first grid voltage component from the grid voltage yields the second grid voltage component; The voltage feedback value is obtained by adding the first voltage value to the second grid voltage component.

[0052] Specifically, the first weighting coefficient is a proportional coefficient used to split the grid voltage, determining the proportion of voltage components participating in the filtering. The value range of the first weighting coefficient is... When the power grid fluctuation is small, k A value of 1 can be set to filter the entire grid voltage to improve the robustness of system control. When the grid-connected system enters the fault ride-through exit phase, This is to achieve a balance between response speed and control stability.

[0053] As can be seen from the above embodiments, this embodiment, through a differentiated filtering design that partially filters and partially passes through the grid voltage, can overcome the inherent limitations of full filtering. It achieves the stability of the first grid voltage component through dynamic filtering coefficients, and ensures the real-time control through the passing through of the second grid voltage component. The voltage feedback value obtained by superimposing the two components has the advantages of both stability and fast response, making the control performance of the grid-connected converter more stable under complex operating conditions of weak grids.

[0054] In one possible implementation, the specific implementation process of compensating the output phase of the phase-locked loop based on the grid voltage in S103 includes: The phase compensation value is determined based on the difference between the actual phase of the grid voltage and the output phase of the phase-locked loop; During the first operating cycle of the grid-connected converter after the first preset time, the output phase of the phase-locked loop is compensated using the phase compensation value; In multiple operating cycles following the first operating cycle, the phase compensation value is controlled to decrease linearly, and the decreased phase compensation value is used to compensate the output phase of the phase-locked loop in the corresponding cycle until the phase compensation value decreases to zero.

[0055] In this embodiment, the operating cycle is the core control cycle of the grid-connected converter, which is usually the switching cycle of the grid-connected converter and serves as the time reference for phase compensation.

[0056] Specifically, the controller first calculates the difference between the actual phase of the grid voltage and the phase-locked loop output phase. The difference is used as the initial value for phase compensation. In the first operating cycle after the first preset time, this initial value is... Superimposed on the output phase of the phase-locked loop The compensated phase-locked loop output phase is obtained. Then, the compensated phase-locked loop is used to output the phase. The coordinate transformation of the grid voltage and the output current of the grid-connected converter is performed. Then, the phase compensation value is linearly decreased in each operating cycle, and reduced to zero within a preset number of operating cycles. The preset number can be 5 to 15.

[0057] As can be seen from the above embodiments, this embodiment first determines the initial phase compensation value based on the difference between the actual phase of the grid voltage and the phase-locked loop output phase, ensuring the accuracy and relevance of the phase compensation and accurately offsetting the phase jump caused by fault clearing. Secondly, by linearly decreasing the phase compensation value to zero over multiple operating cycles, rather than compensating in one step or instantly canceling it, a gradual phase correction is achieved. This allows the phase-locked loop itself to have a smooth transition process to gradually track and take over the compensated phase, ultimately achieving disturbance-free synchronization. If the phase compensation value is suddenly removed, it will be equivalent to a new phase step, triggering secondary oscillations. Therefore, the linear decreasing phase compensation strategy provided in this embodiment is the core guarantee for ensuring the smoothness of the entire phase recovery process and suppressing current oscillations caused by phase asynchrony.

[0058] In one possible implementation, the specific implementation process of controlling the current loop setpoint to be restored to the value before the fault ride-through state in S103 includes: The current loop setpoint is controlled to linearly recover from zero to the value before the fault ride-through state within a second preset time period.

[0059] This embodiment further optimizes the recovery process of the current loop setpoint, limiting the recovery action to a linear recovery from zero within a second preset time period. This soft-start logic avoids abrupt changes in power command. If the current setpoint jumps directly from zero to a larger value before the fault, it will cause a huge step command to the current loop, leading to current regulator saturation, output overshoot, and continuous oscillation. By linearly soft-starting the current loop setpoint, a large step is decomposed into a series of small incremental steps, enabling the current loop to output current smoothly, thereby softening the power recovery process. This not only suppresses current waveform oscillations but also reduces stress on the DC bus voltage and power devices, balancing recovery speed and system safety.

[0060] Specifically, the second preset duration can be 10~20ms.

[0061] In one possible implementation, the specific implementation process of controlling the current loop setpoint to linearly recover from zero to its value before the fault ride-through state within a second preset time period includes: Within a first time period of a second preset duration, the current loop setpoint is increased from zero using a first preset slope. Then, within a second time period, the current loop setpoint is linearly increased using a second preset slope until it reaches the value prior to the fault-crossing state. The first time period begins at the start of the second preset duration, and the second time period follows the first time period. The first preset slope is less than the second preset slope.

[0062] Specifically, when the current loop recovery is just starting, the current loop has just exited the zero-buffer state, the integral term of the regulator (such as a PI controller) has not yet fully stabilized, and the actual current is still at a low level. At the same time, the phase-locked loop may still be fine-tuning its phase, and the grid voltage may also have slight fluctuations. If the current loop setpoint is increased rapidly with a large slope at this time, the deviation between the current loop setpoint and the actual value will increase instantaneously, causing the regulator's integral to saturate, and thus resulting in current overshoot oscillation. A small slope allows the current loop setpoint to increase slowly, giving the current loop enough time to track and the regulator to start smoothly, avoiding the initial shock.

[0063] After a small slope transition, the current loop has entered a stable tracking state, and the actual current rises steadily with the current loop setpoint, with no risk of saturation in the regulator's integral term. The phase-locked loop phase has also synchronized, and the grid voltage tends to stabilize. At this point, there is no need to limit the slope. Using a large slope to quickly increase the current loop setpoint can complete the recovery from zero to the pre-fault setpoint within the second preset time of the total duration, ensuring a rapid return of active power, meeting the grid connection standard requirements for high-voltage and low-voltage recovery time, and avoiding power deficits that could affect grid stability due to slow recovery.

[0064] In one possible implementation, the fault ride-through exit phase includes a low-voltage ride-through exit phase; the specific implementation process of S101 includes: When the grid-connected converter is in a low voltage ride-through state, obtain the output current value of the grid-connected converter; The output current value is transformed by dq to obtain the actual value of the d-axis current. Subtract the actual value of the d-axis current from the given value of the d-axis current to obtain the d-axis current difference; If the d-axis current difference is greater than a preset difference threshold, the grid-connected converter is determined to have entered the low-voltage ride-through exit phase.

[0065] In this embodiment, when the grid-connected converter is in the low voltage ride-through state, if the difference between the given value of the d-axis current and the actual value of the d-axis current is greater than the preset difference threshold, it indicates that the grid voltage is recovering. The given value of the d-axis current calculated based on the grid voltage increases instantaneously, while the actual value of the d-axis current has not yet kept up with the change. Therefore, the difference in d-axis current will suddenly increase. Based on this phenomenon, it can be determined that the grid-connected converter has entered the low voltage ride-through exit stage.

[0066] When a grid-connected converter is in high-voltage ride-through mode, if the difference between the given d-axis current and the actual d-axis current is less than the second difference threshold, it indicates that the grid voltage is recovering. The given d-axis current calculated based on the grid voltage decreases instantaneously, while the actual d-axis current has not yet kept up with the change. Therefore, the d-axis current difference (negative value) will suddenly decrease. This phenomenon can be used to determine that the grid-connected converter has entered the high-voltage ride-through exit phase. The second difference threshold is less than zero.

[0067] As can be seen from the above embodiments, this embodiment can sensitively and reliably capture the moment when the grid voltage begins to recover by calculating the difference between the given value and the actual value of the d-axis current in real time.

[0068] In one possible implementation, the specific implementation process of S101 above includes: The grid voltage is obtained. In the low voltage ride-through state, if the grid voltage is greater than the lower limit of the grid voltage reference, it is determined that the fault ride-through exit stage has been entered. In the high voltage ride-through state, if the grid voltage is less than the upper limit of the grid voltage reference, it is determined that the fault ride-through exit stage has been entered.

[0069] In one possible implementation, the specific implementation process of setting the current loop setpoint to zero and maintaining it for a first preset duration in S102 includes: Set both the d-axis current loop setpoint and the q-axis current loop setpoint to zero and maintain them for the first preset duration.

[0070] As can be seen from the above embodiments, during the fault ride-through phase, sudden changes in the given values ​​of both the d-axis current (representing active power) and the q-axis current (representing reactive power) can trigger oscillations. Setting both to zero simultaneously completely halts the active and reactive power output commands of the converter, bringing it into a unified and deterministic zero state. This avoids the control coupling complexity and potential dynamic imbalance problems caused by setting one axis to zero while keeping the other non-zero, simplifies the control logic, and ensures that the system's behavior is controllable and predictable when exiting this state.

[0071] In one possible implementation, if the grid-connected converter enters the fault ride-through exit phase, the method provided in this embodiment further includes: After obtaining the grid voltage, the negative sequence component in the grid voltage is removed.

[0072] In this embodiment, after low-pass filtering the grid voltage, the three-phase grid voltage is transformed from the abc coordinate system to... coordinate system, to obtain ,based on Coordinate system voltage The negative-order components are calculated using a negative-order rotation matrix. The calculation formula can be... ;in, express negative order components of the axis, express Negative order components, The angular frequency of the power grid. The characteristic corresponding to twice the fundamental frequency of the negative sequence component.

[0073] The separated negative order components ( , After reversing, superimpose to The original shaft voltage signal is used to obtain the grid voltage signal after removing the negative sequence component. , The formula is: .in, Indicates purified shaft voltage signal, Indicates purified Shaft voltage signal.

[0074] Finally, the grid voltage signal after removing the negative sequence component is used for subsequent calculations. During the fault ride-through exit phase, the negative sequence component causes misalignment of the dq coordinate transformation, leading to misjudgment of the feedback current by the current loop and triggering overshoot oscillations. After removing the negative sequence component, the voltage feedforward signal accurately reflects the actual grid state, the current loop regulation has no spurious deviations, and the current overshoot during the recovery phase can be significantly reduced, avoiding frequent oscillations.

[0075] 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 the present invention.

[0076] The following are device embodiments of the present invention. For details not described in detail, please refer to the corresponding method embodiments described above.

[0077] Figure 3 A schematic diagram of the low-voltage ride-through control device provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 3 As shown, the fault ride-through control device 100 for the grid-connected converter includes: The fault crossing exit detection module 110 is used to detect whether the grid-connected converter has entered the fault crossing exit stage. The current loop zeroing module 120 is used to set the current loop setpoint to zero and maintain it for a first preset time if the grid-connected converter enters the fault ride-through exit stage. The phase compensation module 130 is used to control the current loop setpoint to return to the value before the fault ride-through state after the first preset time period, and to compensate the output phase of the phase-locked loop based on the grid voltage.

[0078] In one possible implementation, the fault ride-through control device 100 of the grid-connected converter further includes: a filter coefficient adjustment module, used to increase the feedforward filter coefficient of the grid voltage within the first preset time period after the grid-connected converter is detected to have entered the fault ride-through exit stage.

[0079] In one possible implementation, the filter coefficient adjustment module is specifically used for: The first filter coefficient is determined based on the grid short-circuit ratio; Within the first preset time period, the feedforward filter coefficient of the grid voltage is increased to the first filter coefficient.

[0080] In one possible implementation, the phase compensation module 130 is specifically used for: The phase compensation value is determined based on the difference between the actual phase of the grid voltage and the output phase of the phase-locked loop; During the first operating cycle of the grid-connected converter after the first preset time, the output phase of the phase-locked loop is compensated using the phase compensation value; In multiple operating cycles following the first operating cycle, the phase compensation value is controlled to decrease linearly, and the decreased phase compensation value is used to compensate the output phase of the phase-locked loop in the corresponding cycle until the phase compensation value decreases to zero.

[0081] In one possible implementation, the phase compensation module 130 is further configured to: The current loop setpoint is controlled to linearly recover from zero to the value before the fault ride-through state within a second preset time period.

[0082] In one possible implementation, the fault ride-through exit phase includes a low-voltage ride-through exit phase; the ride-through exit detection module 110 includes: When the grid-connected converter is in a low voltage ride-through state, obtain the output current value of the grid-connected converter; The output current value is transformed by dq to obtain the actual value of the d-axis current. Subtract the actual value of the d-axis current from the given value of the d-axis current to obtain the d-axis current difference; If the d-axis current difference is greater than a preset difference threshold, the grid-connected converter is determined to have entered the low-voltage ride-through exit phase.

[0083] In one possible implementation, the current loop zeroing module 120 is specifically used for: Set both the d-axis current loop setpoint and the q-axis current loop setpoint to zero and maintain them for the first preset duration.

[0084] Figure 4 This is a schematic diagram of the controller provided in an embodiment of the present invention. Figure 4 As shown, the controller 4 in this embodiment includes a processor 40, a memory 41, and a computer program 42 stored in the memory 41 and executable on the processor 40. When the processor 40 executes the computer program 42, it implements the steps in the above embodiments of the fault ride-through control method for various grid-connected converters, for example... Figure 2 Steps S101 to S103 are shown. Alternatively, when the processor 40 executes the computer program 42, it implements the functions of each module / unit in the above-described device embodiments.

[0085] For example, the computer program 42 may be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to complete the present invention. 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 the computer program 42 in the controller 4.

[0086] The controller 4 can be a computing device such as a desktop computer, laptop, handheld computer, or cloud server. The controller 4 may include, but is not limited to, a processor 40 and a memory 41. Those skilled in the art will understand that... Figure 4 This is merely an example of controller 4 and does not constitute a limitation on controller 4. It may include more or fewer components than shown, or combine certain components, or different components. For example, the controller may also include input / output devices, network access devices, buses, etc.

[0087] The processor 40 may 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. A general-purpose processor may be a microprocessor or any conventional processor.

[0088] The memory 41 can be an internal storage unit of the controller 4, such as a hard disk or memory of the controller 4. The memory 41 can also be an external storage device of the controller 4, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card equipped on the controller 4. Furthermore, the memory 41 can include both internal storage units and external storage devices of the controller 4. The memory 41 is used to store the computer program and other programs and data required by the controller. The memory 41 can also be used to temporarily store data that has been output or will be output.

[0089] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0090] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0091] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0092] In the embodiments provided by this invention, it should be understood that the disclosed devices / controllers and methods can be implemented in other ways. For example, the device / controller embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0093] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0094] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0095] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the fault ride-through control method embodiments of the various grid-connected converters described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[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 of fault ride-through control for a grid-connected converter, characterized in that, The method comprises: detecting whether the grid-connected converter enters a fault ride-through exit phase; if the grid-connected converter enters the fault ride-through exit phase, setting a current loop given value to zero and maintaining for a first preset time length; after the first preset time length, controlling the current loop given value to return to a value before a fault ride-through state, and compensating an output phase of a phase-locked loop based on a grid voltage.

2. The fault ride-through control method of a grid-connected converter according to claim 1, characterized in that, After detecting that the grid-connected converter enters the fault ride-through exit phase, the method further comprises: within the first preset time length, increasing a feedforward filter coefficient of the grid voltage.

3. The fault ride-through control method of a grid-connected converter according to claim 2, characterized in that, The increasing the feedforward filter coefficient of the grid voltage within the first preset time length comprises: determining a first filter coefficient according to a grid short-circuit ratio; within the first preset time length, increasing the feedforward filter coefficient of the grid voltage to the first filter coefficient.

4. The fault ride-through control method of a grid-connected converter according to claim 1, characterized in that, The compensating the output phase of the phase-locked loop based on the grid voltage comprises: determining a phase compensation value based on a difference between an actual phase of the grid voltage and the output phase of the phase-locked loop; within a first operation cycle of the grid-connected converter after the first preset time length, compensating the output phase of the phase-locked loop by using the phase compensation value; within multiple operation cycles after the first operation cycle, controlling the phase compensation value to decrease linearly, and compensating the output phase of the phase-locked loop of a corresponding operation cycle by using the decreased phase compensation value until the phase compensation value decreases to zero.

5. The method of fault ride-through control of a grid-connected converter according to claim 1, wherein, The controlling the current loop given value to return to the value before the fault ride-through state comprises: controlling the current loop given value to linearly return to the value before the fault ride-through state from zero within a second preset time length.

6. The method of fault ride-through control of a grid-connected converter according to claim 1, characterized in that, The fault ride-through exit phase comprises a low-voltage ride-through exit phase. The detecting whether the grid-connected converter enters the fault ride-through exit phase comprises: when the grid-connected converter is in a low-voltage ride-through state, obtaining an output current value of the grid-connected converter; performing dq transformation on the output current value to obtain a d-axis current actual value; subtracting the d-axis current actual value from a d-axis current given value to obtain a d-axis current difference value; if the d-axis current difference value is greater than a preset difference threshold value, determining that the grid-connected converter enters the low-voltage ride-through exit phase.

7. The method of fault ride-through control of a grid-connected converter according to claim 1, wherein, The setting the current loop given value to zero and maintaining for the first preset time length comprises: setting both a d-axis current loop given value and a q-axis current loop given value to zero and maintaining for the first preset time length.

8. A fault ride-through control device for a grid-connected converter, characterized in that, The method comprises: a ride-through exit detection module configured to detect whether the grid-connected converter enters a fault ride-through exit phase; a current loop zero setting module configured to, if the grid-connected converter enters the fault ride-through exit phase, set a current loop given value to zero and maintain for a first preset time length; a phase compensation module configured to, after the first preset time length, control the current loop given value to return to a value before a fault ride-through state, and compensate an output phase of a phase-locked loop based on a grid voltage.

9. A controller comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, The processor, when executing the computer program, implements the steps of the fault ride-through control method of the grid-connected converter according to any one of claims 1 to 7.

10. A grid-tie converter, characterized by, The controller comprises: the controller according to claim 9.

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