A method, apparatus and device for improving robustness of an inverter under weak grid

Abstract

The application discloses a method, device and equipment for improving robustness of an inverter under a weak network. The method comprises the following steps: obtaining an inverter-side current signal, and processing the inverter-side current signal by using a first-order high-pass filter to obtain an active damping feedback signal; obtaining a grid-connected point voltage signal, and processing the grid-connected point voltage signal by using an adjustable weighting coefficient to obtain a weighted feedforward signal; superimposing an output signal of a current controller, the active damping feedback signal and the weighted feedforward signal to generate a modulation wave signal; and controlling the inverter based on the modulation wave signal to adjust output impedance of the inverter. The application can improve robustness and stability of the inverter under the weak network without increasing hardware cost.

Description

Technical Field

[0001] This invention relates to the field of power electronic control technology, and specifically to a method, apparatus, and equipment for improving the robustness of inverters under weak grid conditions. Background Technology

[0002] As the interface device between renewable energy power generation systems and the power grid, the control performance of grid-connected inverters directly affects the system's stability and power quality. LCL filters are widely used due to their excellent attenuation capability for high-frequency harmonics, but LCL filters have inherent resonant spikes, requiring damping control to ensure system stability.

[0003] In existing technologies, improving inverter robustness typically involves full grid voltage feedforward and active damping via capacitor current feedback. The former reshapes the output impedance, while the latter introduces a virtual resistor to increase the output impedance and reduce the impedance ratio, thus achieving the Nyquist stability criterion. The wider the range of grid impedances under which stability is achieved, the better the inverter's robustness.

[0004] However, introducing full feedforward of grid voltage can lead to positive feedback loops, which can worsen the stability of weak grids and introduce high-frequency grid noise. The former is particularly problematic, as this positive feedback effectively reduces the inverter's output impedance, causing the originally stable system to oscillate or even become unstable after being connected to an inductive grid. Simply put, the feedforward, originally intended to suppress grid disturbances, becomes the root cause of system instability.

[0005] Introducing active damping with capacitive current feedback has the drawback that the feedback capacitive current and other signals are susceptible to high-frequency noise interference. Improving the signal-to-noise ratio often requires adding hardware filters or using high-precision sensors, which increases costs. Furthermore, the equivalent virtual impedance of traditional active damping with capacitive current feedback is affected by digital control delays. When the grid impedance changes, the delay may cause the virtual resistance to become "negative" in a specific frequency band, thus inducing oscillations. Although there are delay compensation schemes, this undoubtedly increases the design complexity.

[0006] In general, under weak grid conditions, the grid impedance varies widely with load and operating conditions, causing the LCL resonant point to shift. Traditional fixed-parameter active damping and fixed-coefficient feedforward control struggle to maintain robust system stability across the entire operating range. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a method, apparatus and device for improving the robustness of inverters under weak grid conditions.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for improving the robustness of an inverter under weak grid conditions, comprising: The inverter-side current signal is acquired and processed using a first-order high-pass filter to obtain an active damping feedback signal. The grid connection point voltage signal is acquired, and the grid connection point voltage signal is processed using adjustable weighting coefficients to obtain a weighted feedforward signal; The output signal of the current controller, the active damping feedback signal, and the weighted feedforward signal are superimposed to generate a modulated wave signal; The inverter is controlled based on the modulated wave signal to adjust the output impedance of the inverter.

[0009] Furthermore, the cutoff frequency of the first-order high-pass filter is determined based on the resonant frequency of the LCL filter of the inverter.

[0010] Furthermore, the cutoff frequency of the first-order high-pass filter is equal to the resonant frequency of the LCL filter.

[0011] Furthermore, the adjustable weighting coefficient is the ratio of the first adjustable parameter to the pulse width modulation equivalent gain; The grid connection point voltage signal is processed using adjustable weighting coefficients to obtain a weighted feedforward signal, including: The adjustable weighting coefficients are used as weighting factors to weight the grid connection point voltage signal to obtain the weighted feedforward signal.

[0012] Furthermore, the method also includes: Monitor the arm current of the inverter, and in response to the arm current exceeding a preset current threshold, record the arm current to obtain the recorded current waveform; Frequency analysis is performed on the recorded current waveform to locate the overcurrent frequency; The cutoff frequency of the first-order high-pass filter is adjusted based on the overcurrent frequency.

[0013] Furthermore, the method also includes: The distortion rate of the grid connection point voltage is determined based on the grid connection point voltage signal; In response to the change in the distortion rate exceeding a first preset threshold within a half-cycle time, the adjustable weighting coefficient is adjusted by a preset step value. Monitor the change in distortion rate after adjusting the adjustable weighting coefficient, and selectively repeat the adjustment of the adjustable weighting coefficient according to the change result until the fluctuation range of the distortion rate meets the second preset threshold.

[0014] Furthermore, adjusting the adjustable weighting coefficients according to preset step values ​​includes: The adjustable weighting coefficient is adjusted along the first direction by a preset step value. If the fluctuation range of the distortion rate still does not meet the second preset threshold after adjusting to the upper limit of the value, the adjustable weighting coefficient is adjusted along the second direction opposite to the first direction.

[0015] Furthermore, the current controller is a proportional resonant controller with phase compensation.

[0016] A second aspect of the present invention provides an apparatus for improving the robustness of an inverter under weak grid conditions, comprising: The first processing module is used to acquire the inverter-side current signal and process the inverter-side current signal using a first-order high-pass filter to obtain an active damping feedback signal. The second processing module is used to acquire the grid connection point voltage signal and process the grid connection point voltage signal using adjustable weighting coefficients to obtain a weighted feedforward signal. The superposition module is used to superimpose the output signal of the current controller, the active damping feedback signal, and the weighted feedforward signal to generate a modulated wave signal. The control module is used to control the inverter based on the modulated wave signal to adjust the output impedance of the inverter.

[0017] Furthermore, the cutoff frequency of the first-order high-pass filter is determined based on the resonant frequency of the LCL filter of the inverter.

[0018] Furthermore, the cutoff frequency of the first-order high-pass filter is equal to the resonant frequency of the LCL filter.

[0019] Furthermore, the adjustable weighting coefficient is the ratio of the first adjustable parameter to the pulse width modulation equivalent gain; when the second processing module processes the grid connection point voltage signal using the adjustable weighting coefficient to obtain the weighted feedforward signal, it is specifically used to: use the adjustable weighting coefficient as a weighting factor to weight the grid connection point voltage signal to obtain the weighted feedforward signal.

[0020] Furthermore, the first processing module is also used to: monitor the arm current of the inverter; in response to the arm current exceeding a preset current threshold, record the arm current to obtain a recorded current waveform; perform frequency analysis on the recorded current waveform to locate the overcurrent frequency; and adjust the cutoff frequency of the first-order high-pass filter based on the overcurrent frequency.

[0021] Furthermore, the second processing module is also used to: determine the distortion rate of the grid connection point voltage based on the grid connection point voltage signal; adjust the adjustable weighting coefficient by a preset step value in response to the change in the distortion rate within half a cycle time exceeding a first preset threshold; monitor the change result of the distortion rate after the adjustment of the adjustable weighting coefficient, and selectively repeat the adjustment of the adjustable weighting coefficient according to the change result until the fluctuation range of the distortion rate meets the second preset threshold.

[0022] Furthermore, when the second processing module adjusts the adjustable weighting coefficient according to a preset step value, it is specifically used to: adjust the adjustable weighting coefficient along a first direction according to a preset step value; if the fluctuation range of the distortion rate still does not meet the second preset threshold after adjusting to the upper limit of the value, then adjust the adjustable weighting coefficient along a second direction opposite to the first direction.

[0023] Furthermore, the current controller is a proportional resonant controller with phase compensation.

[0024] A third aspect of the present invention provides an electronic device, including a memory and a processor, wherein the memory stores a computer program that, when executed by the processor, implements the method described in the first aspect.

[0025] A fourth aspect of the present invention provides a computer-readable storage medium having program instructions stored thereon, which, when executed, implement the method described in the first aspect.

[0026] The advantages and beneficial effects of this invention are as follows: By changing the feedback sampling point from capacitor current to inverter-side current, and introducing a first-order high-pass filter in the feedback path to generate an active damping feedback signal, the grid connection point voltage is simultaneously acquired and a weighted feedforward signal is generated using adjustable weighting coefficients. Finally, the current controller output, the active damping feedback signal, and the weighted feedforward signal are superimposed to generate a modulated wave, thereby regulating the inverter output impedance. Since the inverter-side current sampling can reuse existing overcurrent protection sensors, no additional hardware is required, reducing system implementation costs. The first-order high-pass filter has extremely low gain at the fundamental frequency, which does not affect normal grid-connected current control, while providing effective damping near the LCL resonant frequency, significantly suppressing resonance spikes. Furthermore, the introduction of adjustable weighted feedforward coefficients allows the system to flexibly adjust the feedforward strength according to the actual grid impedance, improving the phase-frequency characteristics of the inverter output impedance across the entire frequency band, compensating for phase lag, and thus enhancing the inverter's impedance ratio under weak grid conditions. In summary, this invention can improve the robustness and stability of the inverter under weak grid conditions without increasing hardware costs. Attached Figure Description

[0027] Figure 1This is a control structure diagram of an LCL grid-connected inverter that uses active damping with capacitor current feedback in the existing technology. Figure 2 It is a Bode plot of the power grid impedance variation using existing technical solutions; Figure 3 This is a flowchart of the method for improving the robustness of inverters under weak grid conditions according to the present invention; Figure 4 This is a schematic diagram of the control structure of the present invention to improve the robustness of inverters under weak grid conditions; Figure 5 This is a Bode plot of the scheme of the present invention when the power grid impedance changes; Figure 6 It is a Bode plot of the inverter output impedance without feedforward. Figure 7 It is a Bode plot of the inverter output impedance under full feedforward conditions; Figure 8 This is the Bode plot of the inverter output impedance under weighted feedforward conditions; Figure 9 This is a schematic diagram of the device structure for improving the robustness of inverters under weak grid conditions according to the present invention; Figure 10 This is a schematic diagram of the structure of the electronic device of the present invention. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0029] Figure 1 This is a control structure diagram of an LCL grid-connected inverter using capacitor current feedback active damping in existing technology. It should be noted that... Figure 1 and Figure 4 The structure shown is a control block diagram built based on the system transfer function and mathematical model. It is used to illustrate the mathematical relationships between signals and does not represent the actual hardware structure of the inverter. The signal superposition nodes (addition points) in the block diagram represent algebraic summation operations of the signals and do not necessarily represent the physical adder hardware.

[0030] Figure 1 Reference current It is the desired grid-connected current setpoint of the inverter output, the reference current. With grid-side current The error signal is obtained by comparing the feedback value, and the error signal is then processed by the current controller. It then enters the modulated wave adder. Simultaneously, the capacitor current... via feedback pathway ( The transfer function of the feedback path is then connected to the modulated wave adder in the form of negative feedback to form active damping. In the existing scheme, the transfer function on the feedback path... It is typically represented by a proportional gain coefficient, which is used to equivalently introduce virtual resistance to suppress LCL resonance.

[0031] The modulated wave signal passes through the delay stage in sequence. Equivalent gain of inverter Then, the inverter output voltage is generated, and then the grid-side current is output through an LCL filter. To the grid connection point, where the LCL filter is connected to the inverter-side inductor. Filter capacitor , grid-side inductor constitute.

[0032] In this existing scheme, the open-loop transfer function of the system can be expressed as: in: This is the transfer function of the current controller; The transfer function for the system delay element; This represents the equivalent gain of the inverter's SPWM. Here is the transfer function on the feedback path (in this case, the proportionality constant); This refers to the inductance value on the inverter side. This refers to the grid-side inductance value. This is the value of the filter capacitor; For the Laplace operator.

[0033] In one exemplary existing solution, the LCL filter parameters are: inverter-side inductance... Grid-side inductor Filter capacitor The DC-side voltage is 750V, using bipolar SPWM modulation, and the inverter's equivalent gain is... The current controller uses a proportional-integral (PI) controller, designed with an open-loop cutoff frequency of 1000Hz and a corner frequency of 100Hz. The corresponding proportional gain is... Integral coefficient The digital control delay is equivalent to 1.5 sampling periods, with a sampling frequency of 20kHz.

[0034] The existing solution operates under ideal power grid conditions (i.e., power grid impedance). This can effectively dampen the resonant spikes of the LCL filter. However, under weak grid conditions, the grid impedance... It is not negligible and varies with the load. When the equivalent grid impedance exist When the frequency fluctuates within a certain range, the actual resonant frequency of the system will shift towards lower frequencies. Bode plot analysis shows that as... As the value increases, the system phase margin decreases significantly; when When this reaches a certain level, the closed-loop poles will enter the right half-plane of the complex plane, leading to system instability. Furthermore, the capacitor current... The signal itself contains a large amount of switching ripple and high-frequency noise, resulting in a low signal-to-noise ratio. This often requires additional hardware filtering circuits or high-precision sensors, increasing system costs. Digital control delays may also cause the equivalent virtual resistance to exhibit negative resistance characteristics in specific frequency bands, further deteriorating the system's stability under weak network conditions.

[0035] Figure 2 The Bode plot of the existing technology solution is shown under varying grid impedance. From... Figure 2 It can be seen that, with the increase of grid impedance As the frequency increases, the system's resonant peak shifts to lower frequencies, and the phase margin decreases significantly. When When a certain point is reached, the phase curve crosses the -180° line, and the system loses stability.

[0036] Figure 3 This is a flowchart of the method for improving the robustness of inverters under weak grid conditions according to the present invention. Figure 4 This is a schematic diagram of the control structure of the present invention to improve the robustness of the inverter under weak grid conditions. The following is a combination of... Figure 3 , Figure 4 This invention introduces a method for improving the robustness of inverters under weak grid conditions. For example... Figure 3 As shown, the method includes the following steps: S101. Obtain the inverter-side current signal and process it using a first-order high-pass filter to obtain an active damping feedback signal.

[0037] This invention embodiment changes the feedback sampling point from the capacitor current of the prior art. Change to inverter-side current. Inverter-side current can be drawn from the inverter-side inductor. The current sensor is directly sampled at the output terminal. This current sensor is usually used for the overcurrent protection function of the inverter, so there is no need to add an additional hardware sensor, which can reduce the system cost.

[0038] In this embodiment of the invention, a first-order high-pass filter is introduced, and the transfer function of the feedback path is... Represented as: in, This represents the gain coefficient of the high-pass filter. This is the cutoff angular frequency of the high-pass filter. The signal after this high-pass filtering is the active damped feedback signal. The gain of the first-order high-pass filter is close to zero near the fundamental frequency, therefore it does not affect the control of the fundamental current; the gain is close to zero near the resonant frequency. This provides sufficient damping signal.

[0039] S102. Obtain the grid connection point voltage signal and process the grid connection point voltage signal using adjustable weighting coefficients to obtain a weighted feedforward signal.

[0040] Grid connection point voltage signal The voltage signal can be obtained by sampling at the common connection point between the inverter and the grid using a voltage sensor. The weighted feedforward branch processes the grid connection point voltage signal with adjustable weighting coefficients and then feeds it into the modulated wave adder in a positive feedforward manner.

[0041] S103. The output signal of the current controller, the active damping feedback signal, and the weighted feedforward signal are superimposed to generate a modulated wave signal.

[0042] Among them, the current controller The output signal is the control quantity obtained by processing the error signal between the reference current and the feedback value of the inverter output current through the current controller. The three signals are superimposed by an adder, where the active damped feedback signal is negative feedback and the weighted feedforward signal is positive feedforward. The resulting modulated wave signal is then sequentially processed by a delay circuit. Equivalent gain of pulse width modulation This generates the inverter output voltage command.

[0043] S104. Control the inverter based on the modulation wave signal to adjust the output impedance of the inverter.

[0044] The modulated wave signal controls the switching of the inverter's power switching transistors through modulation methods such as SPWM or SVPWM to generate the inverter's output voltage. This voltage is then filtered by an LCL filter to output the grid-connected current. Through the synergistic effect of the above-mentioned active damped feedback and weighted feedforward, the output impedance phase frequency characteristics of the inverter under weak grid conditions are improved, and the system robustness is enhanced.

[0045] In the scheme of this invention, the transfer function from the modulated wave to the inverter-side current can be expressed as: As can be seen from the above equation, the damping term in the denominator includes the factor. This is precisely the zero-point polynomial of the system. This means that the damping effect is maximized at the resonant frequency, thereby effectively suppressing the LCL resonant spike.

[0046] Figure 5 The Bode plot of the present invention is shown under varying grid impedance. From... Figure 5 It can be seen that even under large fluctuations in grid impedance (e.g., 0~9mH), the system's resonant spikes are effectively suppressed, and both the amplitude margin and phase margin remain at sufficient levels, significantly improving the system's robustness.

[0047] This invention replaces the feedback sampling point with the inverter-side current instead of the capacitor current, and introduces a first-order high-pass filter in the feedback path to generate an active damping feedback signal. Simultaneously, it acquires the grid-connected voltage and uses adjustable weighting coefficients to generate a weighted feedforward signal. Finally, the current controller output, the active damping feedback signal, and the weighted feedforward signal are superimposed to generate a modulated wave, thereby regulating the inverter's output impedance. Since the inverter-side current sampling can reuse existing overcurrent protection sensors, no additional hardware is required, reducing system implementation costs. The first-order high-pass filter has extremely low gain at the fundamental frequency, not affecting normal grid-connected current control, while providing effective damping near the LCL resonant frequency, significantly suppressing resonance spikes. Furthermore, the introduction of adjustable weighted feedforward coefficients allows the system to flexibly adjust the feedforward strength according to the actual grid impedance, improving the phase-frequency characteristics of the inverter's output impedance across the entire frequency band, compensating for phase lag, and thus enhancing the inverter's impedance ratio under weak grid conditions. In summary, this invention can improve the robustness and stability of the inverter under weak grid conditions without increasing hardware costs.

[0048] In order to maximize the suppression effect of active damping at the resonant frequency and avoid adverse effects on the fundamental frequency control, a preferred embodiment of the present invention is that the cutoff frequency of the first-order high-pass filter is determined based on the resonant frequency of the LCL filter of the inverter.

[0049] In one embodiment, the cutoff frequency of the first-order high-pass filter is equal to the resonant frequency of the LCL filter.

[0050] LCL filter resonant frequency It can be calculated using the following formula: The transfer function from the modulated wave to the inverter-side current shows that it includes a damping term. , It is exactly the zero point of the system, indicating that the damping term has the strongest effect at the zero point. This means that when the cutoff frequency of the high-pass filter is set to be equal to the resonant frequency of the LCL, the zero factor approaches zero at that resonant frequency, making the damping term the dominant term in the denominator of the transfer function, thereby producing the maximum damping effect at the resonant frequency and effectively suppressing the LCL resonant peak.

[0051] To achieve a damping effect at the resonant frequency, a first-order high-pass filter is designed. Its corner frequency is equal to the system's resonant frequency. Assume the high-pass filter gain coefficient... With a value of 0.05, the open-loop transfer function can be expressed as: See the Bode plot of the open-loop transfer function. Figure 5 It can be observed that the resonant spikes of the LCL filter are effectively suppressed. Even under varying grid impedance, the system maintains sufficient gain and phase margins, significantly improving robustness.

[0052] In order to further improve the phase tracking accuracy of the grid-connected current and achieve better output impedance phase compensation effect in conjunction with the weighted feedforward, the preferred embodiment of the present invention is that the current controller is a proportional resonant controller with phase compensation.

[0053] The proportional resonant controller can provide high gain at specific frequencies, achieving zero steady-state error tracking. Adding a phase compensation stage further improves the phase margin of the control loop. When the phase-compensated proportional resonant controller works in conjunction with the aforementioned weighted grid voltage feedforward, the phase-frequency characteristics of the inverter output impedance are further improved, and robust stability under weak grid conditions is significantly enhanced.

[0054] In order to normalize the feedforward quantity to the modulation wave voltage level and facilitate parameter tuning and adaptive adjustment in the digital controller, a preferred embodiment of the present invention is that the adjustable weighting coefficient is the ratio of the first adjustable parameter to the pulse width modulation equivalent gain; the grid connection point voltage signal is processed using the adjustable weighting coefficient to obtain a weighted feedforward signal, including: using the adjustable weighting coefficient as a weighting factor to weight the grid connection point voltage signal to obtain the weighted feedforward signal.

[0055] The formula for calculating the weighted feedforward signal is: Among them, the first adjustable parameter These are the original weighting coefficients, and their values ​​typically range from 1 to 2. to Between these values, the range of the normalized adjustable weighting coefficients is: to Pulse width modulation equivalent gain It is usually a proportionality coefficient determined by the DC bus voltage and the modulation method.

[0056] The introduction of the weighted feedforward signal alters the inverter's output admittance. The expression for the inverter's output admittance is: As can be seen from the above formula, where The item is subject to the first adjustable parameter The impact. When (i.e., without feedforward) the output admittance has a severe phase lag at high frequencies. Figure 6 It shows no feedforward ( Bode plot of inverter output impedance under the condition of ). From Figure 6 It can be seen that in the frequency band around 6.4kHz, the phase frequency characteristics of the output impedance do not meet the Nyquist impedance stability criterion (i.e., the phase difference exceeds the range of -90° to 90°), and the system is at risk of instability.

[0057] when In the case of full feedforward, the introduction of a positive feedback term into the molecule causes excessive phase lead in the low-frequency range, which in turn reduces stability. Figure 7 Full feedforward (shown) Bode plot of inverter output impedance under the condition of ). From Figure 7 It can be seen that full feedforward severely degrades the phase frequency characteristics in the low-frequency band, and the impedance stability criterion is not met in almost the entire frequency band. In fact, feedforward has a counterproductive effect on the system.

[0058] By Take as a middle and An appropriate value between (e.g., taking) ,and The normalization coefficient is approximately It can achieve good phase frequency characteristics across the entire frequency band, enabling the system to meet the Nyquist impedance stability criterion when the power grid impedance changes. Figure 8 The weighted feedforward (e.g.) is shown Bode plot of inverter output impedance with a normalization factor of approximately 0.0133. Compare... Figure 6 and Figure 7 It can be seen that the weighted feedforward achieves good phase-frequency characteristics across the entire frequency band, with only minor issues in a few frequency bands. Furthermore, the amplitude-frequency characteristics in the low-frequency band are significantly improved, and the phase margin at the amplitude crossover frequency is increased, resulting in a significant improvement in robustness. If a proportional resonant controller with phase compensation is further employed, the phase improvement effect will be even more pronounced.

[0059] In the actual operation of weak power grids, the grid impedance The actual resonant frequency of the LCL filter deviates from its nominal design value due to changes in load and operating conditions. When the resonant frequency shifts, the cutoff frequency of the high-pass filter, originally designed to be equal to the nominal resonant frequency, no longer matches the actual resonant point, resulting in a decrease in active damping effect and potentially triggering resonant overcurrent. To address this issue, a preferred embodiment of the present invention further includes: monitoring the arm current of the inverter; recording the arm current in response to the arm current exceeding a preset current threshold to obtain a recorded current waveform; performing frequency analysis on the recorded current waveform to locate the overcurrent frequency; and adjusting the cutoff frequency of the first-order high-pass filter based on the overcurrent frequency.

[0060] During inverter operation, the instantaneous value of the arm current is continuously monitored. The arm current can be obtained through current sensors on the inverter arms, which are typically used for overcurrent protection. When the detected arm current amplitude exceeds a preset current threshold (e.g., 1.2 times the rated capacity), the waveform recording function is automatically triggered to record the arm current waveform before and after the alarm time at a high sampling frequency (e.g., 20kHz and above). After waveform recording is completed, frequency analysis is performed on the recorded current waveform to locate the overcurrent frequency.

[0061] For example, the frequency analysis process is as follows: First, determine whether there is an overcurrent exceeding a preset current threshold. If an overcurrent exists, increase the cutoff frequency of the high-pass filter used for analysis by 1kHz and monitor the current amplitude after filtering again. If the current amplitude is less than the overcurrent threshold, it indicates that the overcurrent frequency is approximately near the current cutoff frequency, and the current cutoff frequency is then identified as the overcurrent frequency. If the current amplitude is still greater than the overcurrent threshold, continue to increase the cutoff frequency in 1kHz increments, repeating the above operation until the overcurrent frequency is located. If no overcurrent exists, decrease the cutoff frequency by 1kHz and monitor whether the filtered current amplitude exceeds the overcurrent threshold. If it does, the overcurrent frequency is located. If it still does not exceed the limit, then continue to adjust downwards.

[0062] Locate the overcurrent frequency Then, the first-order high-pass filter in the inverter-side current feedback channel is... The cutoff frequency is updated to , that is to say If the overcurrent alarm still triggers after the update and startup, then it will be triggered in 100Hz increments. Fine-tune the cutoff frequency upwards and downwards until the overcurrent phenomenon disappears. Using this method, the active damping parameters can be automatically adjusted when changes in grid impedance cause resonant frequency drift, ensuring the system remains in an optimal damping state.

[0063] This invention can automatically locate the actual overcurrent frequency and adjust the high-pass filter cutoff frequency to match it when the resonant point shifts under weak power grid conditions, thereby restoring the maximum damping effect. The selection of the weighted feedforward coefficients also affects the stability of the system under weak grid conditions. When the grid impedance changes, the previously optimal weighting coefficients may no longer be applicable, leading to an increase in the voltage distortion rate at the grid connection point. To address this issue, the method further includes: determining the distortion rate of the grid connection point voltage based on the grid connection point voltage signal; adjusting the adjustable weighting coefficients by a preset step value in response to the change in the distortion rate exceeding a first preset threshold within a half-cycle time; monitoring the change in the distortion rate after the adjustment of the adjustable weighting coefficients; and selectively repeating the adjustment of the adjustable weighting coefficients based on the change results until the fluctuation range of the distortion rate meets a second preset threshold.

[0064] During inverter operation, the voltage distortion rate (Total Harmonic Distortion, THD) is calculated in real time based on the acquired grid connection point voltage signal. To improve response speed, simplified algorithms such as sliding window RMS calculation can be used to perform short-time fluctuation monitoring at a rate of 20kHz, which has higher sensitivity than the traditional DFT algorithm. When a sudden upward change in voltage distortion rate is detected within half a cycle (0.01s for a 50Hz grid), and the magnitude of the change exceeds a first preset threshold (e.g., 10%), it is determined that the current grid impedance has changed significantly, and the system is becoming unstable. At this time, the inverter automatically alarms and shuts down for protection.

[0065] To further improve the reliability of adaptive adjustment and ensure that the optimal coefficient is found, a preferred embodiment of the present invention is to adjust the adjustable weighting coefficient according to a preset step value, including: adjusting the adjustable weighting coefficient along a first direction according to a preset step value; if the fluctuation range of the distortion rate still does not meet the second preset threshold after adjusting to the upper limit of the value, then adjusting the adjustable weighting coefficient along a second direction opposite to the first direction.

[0066] For example, first adjust the weighting coefficients upwards (increasing direction) in increments of 0.2. After each adjustment, the system is restarted and the voltage distortion rate is monitored. If the distortion rate fluctuation range is stable within the second preset threshold (e.g., 5%), the adjustment stops and the current weighting coefficient is locked. If the distortion rate still does not meet the requirements after the weighting coefficient has reached the upper limit of 1 (corresponding to full feedforward), the weighting coefficient is adjusted downward (in decreasing direction) in steps of 0.2 until the distortion rate fluctuation meets the requirements or reaches the lower limit of 0. Through this bidirectional step search strategy, the optimal weighting coefficient that adapts to the current grid impedance can be found across the entire coefficient range.

[0067] In another optional implementation, the search direction can be dynamically adjusted according to the trend of distortion rate changes, without strictly waiting to reach the upper limit. That is, to avoid ineffective adjustments, if the distortion rate fluctuation range is detected to continuously deviate from the second preset threshold during the adjustment along the first direction, the adjustment in the first direction can be terminated in advance, even if the upper limit has not been reached, and the adjustment can be switched to the second direction. For example, when the adjustable weighting coefficient is gradually adjusted along the first direction according to a preset step value, and the distortion rate increases after multiple consecutive adjustments, and the fluctuation range of the distortion rate completely deviates from the value direction of the second preset threshold, indicating that the distortion rate is deteriorating, then the adjustment is made along the second direction, which is opposite to the first direction.

[0068] The embodiments of the present invention can automatically search for the optimal feedforward weighting coefficients based on the distortion state of the grid connection point voltage, so that the system can remain stable and have small voltage distortion under different grid impedance conditions.

[0069] This invention also provides a device for improving the robustness of inverters under weak grid conditions, such as... Figure 9 As shown, the device includes: The first processing module 901 is used to acquire the inverter-side current signal and process the inverter-side current signal using a first-order high-pass filter to obtain an active damping feedback signal. The second processing module 902 is used to acquire the grid connection point voltage signal and process the grid connection point voltage signal using adjustable weighting coefficients to obtain a weighted feedforward signal. The superposition module 903 is used to superimpose the output signal of the current controller, the active damping feedback signal, and the weighted feedforward signal to generate a modulated wave signal. The control module 904 is used to control the inverter based on the modulation wave signal to adjust the output impedance of the inverter.

[0070] In one implementation, the cutoff frequency of the first-order high-pass filter is determined based on the resonant frequency of the LCL filter of the inverter.

[0071] In one embodiment, the cutoff frequency of the first-order high-pass filter is equal to the resonant frequency of the LCL filter.

[0072] In one embodiment, the adjustable weighting coefficient is the ratio of the first adjustable parameter to the pulse width modulation equivalent gain; when the second processing module 902 processes the grid connection point voltage signal using the adjustable weighting coefficient to obtain the weighted feedforward signal, it is specifically used to: use the adjustable weighting coefficient as a weighting factor to weight the grid connection point voltage signal to obtain the weighted feedforward signal.

[0073] In one embodiment, the first processing module 901 is further configured to: monitor the arm current of the inverter; in response to the arm current exceeding a preset current threshold, record the arm current to obtain a recorded current waveform; perform frequency analysis on the recorded current waveform to locate the overcurrent frequency; and adjust the cutoff frequency of the first-order high-pass filter based on the overcurrent frequency.

[0074] In one embodiment, the second processing module 902 is further configured to: determine the distortion rate of the grid connection point voltage based on the grid connection point voltage signal; adjust the adjustable weighting coefficient by a preset step value in response to the change in the distortion rate within a half-cycle time exceeding a first preset threshold; monitor the change result of the distortion rate after the adjustment of the adjustable weighting coefficient, and selectively repeat the adjustment of the adjustable weighting coefficient based on the change result until the fluctuation range of the distortion rate meets the second preset threshold.

[0075] In one embodiment, when the second processing module 902 adjusts the adjustable weighting coefficient according to a preset step value, it is specifically used to: adjust the adjustable weighting coefficient along a first direction according to a preset step value; if the fluctuation range of the distortion rate still does not meet the second preset threshold after adjusting to the upper limit of the value, then adjust the adjustable weighting coefficient along a second direction opposite to the first direction.

[0076] In one embodiment, the current controller is a proportional resonant controller with phase compensation.

[0077] Figure 9 The device for improving the robustness of the inverter under weak grid conditions in the illustrated embodiment can be used to implement the technical solution of the above method embodiment. Its implementation principle and technical effect are similar, and will not be described again here.

[0078] Figure 10 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. The electronic device provided in this embodiment can execute the processing flow provided in the method embodiment for improving the robustness of inverters under weak grid conditions, such as... Figure 5 As shown, the electronic device 1100 includes: a memory 1101, a processor 1102, a computer program, and a communication interface 1103; wherein the computer program is stored in the memory 1101 and is configured to be executed by the processor 1102 as described above to improve the robustness of the inverter under weak grid conditions.

[0079] In addition, embodiments of the present invention also provide a computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor to implement the method for improving the robustness of inverters under weak grid conditions as described in the above embodiments.

[0080] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the robustness of inverters under weak grid conditions, characterized in that, include: The inverter-side current signal is acquired and processed using a first-order high-pass filter to obtain an active damping feedback signal. The grid connection point voltage signal is acquired, and the grid connection point voltage signal is processed using adjustable weighting coefficients to obtain a weighted feedforward signal; The output signal of the current controller, the active damping feedback signal, and the weighted feedforward signal are superimposed to generate a modulated wave signal; The inverter is controlled based on the modulated wave signal to adjust the output impedance of the inverter.

2. The method according to claim 1, characterized in that, The cutoff frequency of the first-order high-pass filter is determined based on the resonant frequency of the LCL filter of the inverter.

3. The method according to claim 2, characterized in that, The cutoff frequency of the first-order high-pass filter is equal to the resonant frequency of the LCL filter.

4. The method according to claim 1, characterized in that, The adjustable weighting coefficient is the ratio of the first adjustable parameter to the pulse width modulation equivalent gain; The grid connection point voltage signal is processed using adjustable weighting coefficients to obtain a weighted feedforward signal, including: The adjustable weighting coefficients are used as weighting factors to weight the grid connection point voltage signal to obtain the weighted feedforward signal.

5. The method according to claim 1, characterized in that, The method further includes: Monitor the arm current of the inverter, and in response to the arm current exceeding a preset current threshold, record the arm current to obtain the recorded current waveform; Frequency analysis is performed on the recorded current waveform to locate the overcurrent frequency; The cutoff frequency of the first-order high-pass filter is adjusted based on the overcurrent frequency.

6. The method according to claim 1, characterized in that, The method further includes: The distortion rate of the grid connection point voltage is determined based on the grid connection point voltage signal; In response to the change in the distortion rate exceeding a first preset threshold within a half-cycle time, the adjustable weighting coefficient is adjusted by a preset step value. Monitor the change in distortion rate after adjusting the adjustable weighting coefficient, and selectively repeat the adjustment of the adjustable weighting coefficient according to the change result until the fluctuation range of the distortion rate meets the second preset threshold.

7. The method according to claim 6, characterized in that, Adjusting the adjustable weighting coefficients according to preset step values ​​includes: The adjustable weighting coefficient is adjusted along the first direction by a preset step value. If the fluctuation range of the distortion rate still does not meet the second preset threshold after adjusting to the upper limit of the value, the adjustable weighting coefficient is adjusted along the second direction opposite to the first direction.

8. The method according to claim 1, characterized in that, The current controller is a proportional resonant controller with phase compensation.

9. A device for improving the robustness of an inverter under weak grid conditions, characterized in that, include: The first processing module is used to acquire the inverter-side current signal and process the inverter-side current signal using a first-order high-pass filter to obtain an active damping feedback signal. The second processing module is used to acquire the grid connection point voltage signal and process the grid connection point voltage signal using adjustable weighting coefficients to obtain a weighted feedforward signal. The superposition module is used to superimpose the output signal of the current controller, the active damping feedback signal, and the weighted feedforward signal to generate a modulated wave signal. The control module is used to control the inverter based on the modulated wave signal to adjust the output impedance of the inverter.

10. An electronic device, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program that, when executed by the processor, implements the method as described in any one of claims 1-8.

Images