An active filter control method, device, equipment and medium
By controlling the voltage signal through the difference between the nth harmonic reference current and the feedback current, the output voltage and current phase of the SVG are adjusted, which solves the problem of poor harmonic control in high-voltage DC converter stations and achieves more efficient harmonic suppression and system stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- STATE GRID CHONGQING ELECTRIC POWER CO ELECTRIC POWER RES INST
- Filing Date
- 2025-04-14
- Publication Date
- 2026-07-17
Smart Images
Figure CN120262451B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of filtering, and in particular to an active filtering control method, apparatus, device, and medium. Background Technology
[0002] In traditional harmonic mitigation schemes, the 12 / 24 dual-coordinated passive filter bank installed in the converter station can only mitigate the characteristic subharmonics 12k±1 (k=1, 2, 3, ...) of the converter station, failing to mitigate non-characteristic background harmonics and potentially amplifying low-frequency background harmonics. Meanwhile, the traditional capacitive active filter control method, R-APF (Active Power Filter), while capable of mitigating non-characteristic harmonics, remains effective in high-voltage environments where the SVG (Static Var Generator) connection point has a high inductance. Particularly in HVDC converter stations, the combination of SVG and step-up transformers further complicates harmonic mitigation. Because the inductive reactance of the series-connected step-up transformer at harmonic frequencies is typically much greater than the virtual impedance of the SVG, it often fails to achieve the desired harmonic suppression effect. Summary of the Invention
[0003] The purpose of this invention is to provide an active filter control method, apparatus, device, and medium that can control the filtered current to continuously approach the phase of the voltage leading the nth harmonic by using the difference between the nth harmonic reference current and the feedback current. The nth harmonic reference current effectively suppresses harmonic amplification and improves harmonic mitigation. The specific scheme is as follows:
[0004] In a first aspect, this application discloses an active filter control method applied to SVG, comprising:
[0005] The current error is obtained by subtracting the nth harmonic reference current from the feedback current; wherein, the nth harmonic is a non-characteristic harmonic, and the phase of both the nth harmonic reference current and the feedback current leads the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage that leads the nth harmonic voltage. The current;
[0006] A voltage control signal is generated based on the current error;
[0007] The duty cycle of the control delay is adjusted based on the voltage control signal to control the output voltage;
[0008] Filtering is performed based on the output voltage and the voltage at the control point of the SVG to obtain a phase that leads the nth harmonic voltage. The current.
[0009] Optionally, before subtracting the nth harmonic reference current from the feedback current to obtain the current error, the method further includes:
[0010] Obtain the voltage of the control point of the SVG; wherein, the control point is the common point where the SVG and the low-voltage side of the step-up transformer are connected;
[0011] The voltage at the control point is filtered to obtain the nth harmonic voltage;
[0012] The ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG is used as the magnitude of the nth harmonic reference current.
[0013] The phase of the nth harmonic reference current is controlled to lead the phase of the nth harmonic voltage. .
[0014] Optionally, before using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current, the method further includes:
[0015] Obtain the virtual impedance of the SVG;
[0016] The voltage filtering at the control point is achieved by a second-order generalized integrator. The transfer function of the second-order generalized integrator is determined based on the resonant gain and natural angular frequency of the nth harmonic, as shown in the following formula:
[0017] ;
[0018] in, Let be the transfer function of the second-order generalized integrator. The resonant gain of the nth harmonic is... Let be the natural angular frequency of the nth harmonic, and s be a complex variable;
[0019] The voltage control signal generated based on the current error is implemented by a current loop controller. The transfer function of the current loop controller is determined based on the channel gain, the resonant gain of the nth harmonic, the passband width of the nth harmonic, and the natural angular frequency of the nth harmonic. The specific formula is as follows:
[0020] ;
[0021] in, Let be the transfer function of the current loop controller. The channel gain is [value]. The resonant gain of the nth harmonic is... Let n be the natural angular frequency of the nth harmonic. The passband width of the nth harmonic;
[0022] The transfer function of the control delay is determined based on the signal modulation ratio and the sampling period, and the specific formula is as follows:
[0023] ;
[0024] in, Let be the transfer function of the control delay. The signal modulation ratio is... The sampling period is the period in question.
[0025] The open-loop transfer function of the current loop controller is determined based on the transfer function of the current loop controller and the transfer function of the control delay unit, as shown in the following formula:
[0026] ;
[0027] in, Let be the open-loop transfer function of the current loop controller. Let be the transfer function of the current loop controller. Let L be the transfer function of the control delay, L be the equivalent reactance of the SVG, and R be the equivalent resistance of the SVG.
[0028] Optionally, after filtering based on the output voltage and the voltage of the control point of the SVG, the method further includes:
[0029] The equivalent virtual harmonic impedance of the SVG is determined based on the virtual impedance, the transfer function of the second-order generalized integrator, the transfer function of the current loop controller, and the open-loop transfer function of the current loop controller, as shown in the following formula:
[0030] ;
[0031] in, The equivalent virtual harmonic impedance of the SVG is... The voltage at the control point. The phase of the voltage leading the nth harmonic is The current, The virtual impedance, Let be the transfer function of the second-order generalized integrator. Let be the open-loop transfer function of the current loop controller.
[0032] Optionally, the virtual impedance is a fixed value, or the virtual impedance is adaptively adjusted based on the capacity of the SVG.
[0033] Optionally, the current loop controller employs proportional-resonant control.
[0034] Optionally, after filtering based on the output voltage and the voltage of the control point of the SVG, the method further includes:
[0035] The HAR of the SVG is calculated using the following formula:
[0036] ;
[0037] in, Let lg be the HAR of the SVG, and lg be the common logarithm. The equivalent impedance of the passive filter bank, The inductive reactance of the step-up transformer, The equivalent virtual harmonic impedance of the SVG is... The equivalent impedance of the AC system, For frequency.
[0038] Secondly, this application discloses an active filter control device applied to an SVG, comprising:
[0039] The calculation module is used to subtract the nth harmonic reference current from the feedback current to obtain the current error; wherein the nth harmonic is a non-characteristic harmonic, and the phase of both the nth harmonic reference current and the feedback current leads the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage that leads the nth harmonic voltage. The current;
[0040] The generation module is used to generate a voltage control signal based on the current error;
[0041] The control module is used to adjust the duty cycle of the control delay based on the voltage control signal in order to control the output voltage;
[0042] The filtering module is used to filter the output voltage and the voltage of the control point of the SVG to obtain a phase that leads the nth harmonic voltage. The current.
[0043] Thirdly, this application discloses an electronic device, including:
[0044] Memory, used to store computer programs;
[0045] A processor is used to execute the computer program to implement the active filter control method described above.
[0046] Fourthly, this application discloses a computer-readable storage medium for storing a computer program, wherein the computer program, when executed by a processor, implements the active filtering control method as described above.
[0047] This application provides an active filter control method, apparatus, device, and medium applied to SVG, comprising: subtracting the nth harmonic reference current from the feedback current to obtain the current error; wherein the nth harmonic is a non-characteristic harmonic, and the phases of both the nth harmonic reference current and the feedback current lead the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage that leads the nth harmonic. The current is measured; a voltage control signal is generated based on the current error; the duty cycle of the control delay is adjusted based on the voltage control signal to control the output voltage; the output voltage and the voltage at the control point of the SVG are filtered to obtain the phase of the voltage leading the nth harmonic. The current. It can be seen that this application controls the filtered current to continuously approach the phase of the voltage leading the nth harmonic by using the difference between the nth harmonic reference current and the feedback current. The nth harmonic reference current effectively suppresses harmonic amplification and improves the harmonic control effect. Attached Figure Description
[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments 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.
[0049] Figure 1 This is a flowchart of an active filter control method disclosed in this invention;
[0050] Figure 2 This is a schematic diagram of the structure of an LCC-HVDC converter station system disclosed in this invention;
[0051] Figure 3 This invention discloses a harmonic equivalent circuit diagram of an LCC-HVDC converter station system.
[0052] Figure 4 This invention discloses a harmonic impedance model of SVG under resistive active filter control;
[0053] Figure 5 This is a Bode plot of a dual-coordinated filter disclosed in this invention;
[0054] Figure 6 This invention discloses a harmonic impedance model of SVG under capacitive active filter control;
[0055] Figure 7 This is a control structure diagram of a capacitive active filter control disclosed in this invention;
[0056] Figure 8 The HAR curve of a passive filter bank disclosed in this invention;
[0057] Figure 9 This invention discloses a HAR curve under capacitive active filter control.
[0058] Figure 10 This is a schematic diagram of the structure of an active filter control device disclosed in this invention;
[0059] Figure 11 This is a structural diagram of an electronic device disclosed in this invention. Detailed Implementation
[0060] The core of this invention is to provide an active filter control method, device, equipment, and medium, which can control the filtered current to continuously approach the phase of the voltage leading the nth harmonic by using the difference between the nth harmonic reference current and the feedback current. The nth harmonic reference current effectively suppresses harmonic amplification and improves the harmonic control effect.
[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0062] As a device based on power electronics technology, SVG (Static Var Generator) is widely used in reactive power compensation and dynamic voltage regulation. Furthermore, SVG also possesses active filtering capabilities, effectively suppressing high-order harmonics generated by power electronic equipment (such as converters and frequency converters). SVG can dynamically adjust the output voltage and current waveforms according to the actual operating conditions of the power grid, providing virtual impedance to actively regulate harmonic currents. Therefore, SVG not only improves the power quality of the power grid but also, to some extent, supplements the shortcomings of passive filters in traditional harmonic mitigation schemes, playing a particularly important role in complex power grids such as high-voltage DC converter stations.
[0063] In high-voltage power grids, the inductance of the SVG and the inductive reactance of the step-up transformer affect the reactive power compensation and harmonic mitigation effects. SVG typically provides rapid reactive power regulation through power electronic devices; however, when the inductance at the SVG connection point is large, the inductive reactance of the step-up transformer creates a low-pass filtering effect, affecting the SVG's dynamic response and reactive power compensation. This limits the SVG's harmonic compensation capability, especially when the inductive reactance of the step-up transformer is large, where traditional R-APF control often fails to effectively suppress high-order harmonics in converter stations. Therefore, this invention provides an active power filter control method.
[0064] For details, please see Figure 1 As shown, Figure 1 This is a flowchart of an active filter control method disclosed in this invention.
[0065] This active filtering control method, applied to SVG, includes:
[0066] S11. Subtract the nth harmonic reference current from the feedback current to obtain the current error; where the nth harmonic is a non-characteristic harmonic, and the phases of both the nth harmonic reference current and the feedback current lead the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage leading the nth harmonic. The current.
[0067] In this embodiment, before subtracting the nth harmonic reference current from the feedback current to obtain the current error, the method may further include: acquiring the voltage of the control point of the SVG; filtering the voltage of the control point to obtain the nth harmonic voltage; using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current; and controlling the phase of the nth harmonic reference current to lead the phase of the nth harmonic voltage. The control point is the common point connecting the SVG and the low-voltage side of the step-up transformer. The feedback current is the current in the branch where the SNG is located. The voltage at the control point is filtered, and the phase of the nth harmonic reference current is controlled to lead the phase of the nth harmonic voltage. All are implemented using a second-order generalized integrator.
[0068] The current error is obtained by performing a differential calculation between the nth harmonic reference current and the actual feedback current. This current error reflects the deviation between the current in the branch where the SNG is located and the target current. To improve control accuracy, the converter station system can use moving average filtering or Kalman filtering to preprocess the current error, thereby eliminating the effects of high-frequency noise and sampling jitter.
[0069] S12. Generate voltage control signal based on current error.
[0070] In this embodiment, the voltage control signal generated based on the current error can be implemented by a current loop controller. The current loop controller can adopt proportional-resonant (PR) control. Proportional-resonant control has high gain at a specific frequency (such as the nth harmonic frequency), which can achieve zero steady-state error tracking of harmonic current and improve compensation accuracy.
[0071] S13. Adjust the duty cycle of the control delay based on the voltage control signal to control the output voltage.
[0072] In this embodiment, the generated voltage control signal is sent to a control delay unit, and the output voltage is precisely controlled by adjusting the duty cycle of the control delay unit. This step can employ SVM (Space Vector Modulation) technology to optimize the turn-on timing of the switching devices. This ensures both the waveform quality of the output voltage and improves the energy conversion efficiency of the converter station system.
[0073] S14. Filter the output voltage and the voltage at the control point of the SVG to obtain the phase of the voltage leading the nth harmonic. The current.
[0074] In this embodiment, the inverter output filter performs filtering based on the output voltage and the voltage at the control point of the SVG, so as to control the filtered current to continuously approach the phase of the nth harmonic voltage. The nth harmonic reference current effectively suppresses harmonic amplification and improves the harmonic control effect.
[0075] This active filtering control method can effectively suppress harmonics in LCC-HVDC (Line Commutated Converter Based High Voltage Direct Current) converter station systems. A schematic diagram of a typical LCC-HVDC converter station system can be found here. Figure 2 As shown. Among them, The equivalent resistance of the AC side system. The equivalent reactance of the AC side system, For the current of the AC side system, The voltage of PCC (Point of Common Coupling). This is the current after filtering by the passive filter bank. This represents the current in the branch where the SVG is located. The gray area represents the inductive reactance of the step-up transformer, while the gray area represents the specific topology of the passive filter bank, including the topology of the dual-coordinated passive filter and the capacitor bank. During operation, the converter needs to absorb a large amount of reactive power and generate characteristic harmonics of order 12k±1 (k=1, 2, 3, ...). To meet the reactive power requirements of the converter station system and reduce the impact of harmonics on the power grid, a passive filter bank and an SVG (Static Var Generator) are connected in parallel on the converter station bus. The passive filter bank includes six sets of 12 / 24 dual-coordinated passive filters and two sets of capacitors. The capacitor bank is mainly used for emergency reactive power support and is usually not used during normal operation of the converter station system. The SVG is connected to the PCC (Power Control Center) through the step-up transformer for dynamic reactive power regulation. Its voltage and current sensors are located on the low-voltage side of the step-up transformer and are defined as the SVG's POC (Point of Control). The POC facilitates voltage acquisition and control of the SVG.
[0076] It should be noted that the harmonic equivalent circuit of the LCC-HVDC converter station system can be found in [reference needed]. Figure 3 As shown, where, The equivalent impedance of the AC system, This represents the equivalent impedance of a passive filter bank. The equivalent inductive reactance of the transformer connected to the SVG. For the virtual impedance of SVG, This represents the equivalent background harmonic voltage of an AC system. It is the equivalent harmonic current after the grid connection point.
[0077] Furthermore, for the harmonic impedance model of SVG under R-APF control, please refer to [link to relevant documentation]. Figure 4 As shown, where, For harmonic resistors, The total impedance of the SVG is given. The R-APF (Resonant-Actuated Power Filter) controls the SVG to behave as a harmonic resistance within the harmonic frequency range, providing damping for the converter station system to alleviate resonance problems. The R-APF control strategy is effective in low-voltage, small-capacity scenarios; however, in high-voltage scenarios (such as high-voltage converter stations), the SVG is typically connected to the converter station system in series with a step-up transformer to reduce the voltage level of the equipment. In this case, the monitoring and control point of the SVG is located at the POC (Point of Control) rather than the PCC (Pressure Point of Control). Because the inductive reactance of the step-up transformer at harmonic frequencies is usually much larger than the virtual impedance of the SVG, the harmonic suppression effect of the SVG is poor.
[0078] Specifically, according to Figure 2 The impedance Bode plot of the dual-coordinated filter topology can be obtained; please refer to [link to relevant documentation]. Figure 5As shown in the diagram, the horizontal axis represents frequency, and the vertical axis represents phase / amplitude. The dual-coordinated filter exhibits capacitive behavior in the low-frequency range up to 600Hz (12th harmonic). Resonance may occur when the capacitive impedance approaches the inductive impedance of the converter station system. It should be noted that although the SVG processed by this active filter control method also exhibits capacitive characteristics—that is, the active filter control method controls the SVG to act as a virtual harmonic capacitor—the SVG offers higher controllability than the passive filter impedance, allowing for more flexible adjustment of the virtual harmonic capacitor to avoid resonance. Since the SVG is controlled to act as a virtual harmonic capacitor through an active filter control method, this virtual harmonic capacitor can change the resonance conditions of the converter station system, prevent harmonic amplification, and effectively eliminate the influence of the step-up transformer connected to the SVG on harmonic suppression. Therefore, this active filter control method is also called capacitive active filter control, i.e., C-APF control. For the harmonic impedance model under C-APF control, please refer to [link to relevant documentation]. Figure 6 As shown, where, For the inductive reactance of the step-up transformer, Let j be the inductance of the step-up transformer, and j be the imaginary unit.
[0079] In practical applications, C-APF control regulates harmonic components in the system by controlling virtual harmonic capacitors. Although virtual harmonic capacitors are not actual capacitors, they can adjust harmonic energy by changing the phase relationship between current and voltage, much like traditional capacitors. This regulation method effectively reduces the impact of harmonics, prevents harmonic amplification, and reduces interference to the converter station system. Furthermore, unlike passive filters, virtual harmonic capacitors do not exist as actual physical components and therefore do not generate additional active power losses. This means that virtual capacitors can effectively reduce energy losses in the converter station system, improve the overall efficiency of the system, and maintain good harmonic suppression. The advantage of this method is that it improves the flexibility and effectiveness of harmonic suppression without additional hardware investment, while dynamically responding to the system's reactive power demand, thereby improving overall operating efficiency and stability.
[0080] As can be seen, this application controls the filtered current to continuously approach the phase of the voltage leading the nth harmonic by using the difference between the nth harmonic reference current and the feedback current. The nth harmonic reference current effectively suppresses harmonic amplification and improves the harmonic control effect.
[0081] Based on the above embodiments:
[0082] As an optional embodiment, before using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current, the method further includes:
[0083] Obtain the virtual impedance of the SVG;
[0084] The voltage filtering at the control point is achieved using a second-order generalized integrator. The transfer function of the second-order generalized integrator is determined based on the resonant gain and natural angular frequency of the nth harmonic, as shown in the following formula:
[0085] ;
[0086] in, Let be the transfer function of the second-order generalized integrator. The resonant gain of the nth harmonic. Let be the natural angular frequency of the nth harmonic, and s be a complex variable;
[0087] The voltage control signal generated based on the current error is implemented by a current loop controller. The transfer function of the current loop controller is determined based on the channel gain, the resonant gain of the nth harmonic, the passband width of the nth harmonic, and the natural angular frequency of the nth harmonic. The specific formula is as follows:
[0088] ;
[0089] in, This is the transfer function of the current loop controller. For channel gain, The resonant gain of the nth harmonic. The natural angular frequency of the nth harmonic. The passband width of the nth harmonic;
[0090] The transfer function of the control delay is determined based on the signal modulation ratio and sampling period, and the specific formula is as follows:
[0091] ;
[0092] in, The transfer function for controlling the delay, The signal modulation ratio, The sampling period;
[0093] The open-loop transfer function of the current loop controller is determined based on the transfer function of the current loop controller and the transfer function of the control delay unit. The specific formula is as follows:
[0094] ;
[0095] in, Let be the open-loop transfer function of the current loop controller. This is the transfer function of the current loop controller. To control the transfer function of the delay unit, L is the equivalent reactance of the SVG, and R is the equivalent resistance of the SVG.
[0096] Capacitive active filter control can be summarized into two stages: a reference current generation stage and an output current control stage. The reference current generation stage includes a second-order generalized integrator and a divider. The output current control stage tracks the nth harmonic reference current and includes a first adder, a second adder, a current loop controller, a control delay, and an inverter output filter. For details, please refer to [link to relevant documentation]. Figure 7 As shown, Figure 7 This is a control structure diagram of a capacitive active filter control disclosed in this invention, wherein, For the voltage at the control point, It is a second-order generalized integrator. For the nth harmonic voltage, For division, The reference current for the nth harmonic is... For current loop controller, To control the delay, For inverter output filter, The phase of the voltage leading the nth harmonic. The current.
[0097] In practical applications, a second-order generalized integrator is used to filter the voltage at the control point to obtain the nth harmonic voltage. This nth harmonic voltage serves as the input to a divider, which outputs an nth harmonic reference current. Simultaneously, the second-order generalized integrator controls the phase of the nth harmonic reference current to lead the phase of the nth harmonic voltage. The feedback current is negative feedback. The nth harmonic reference current and the feedback current serve as inputs to the first adder. The first adder outputs the difference between the nth harmonic reference current and the feedback current, which is the current error. The current loop controller generates a voltage control signal based on the current error and outputs it to the control delay unit. The control delay unit adjusts its duty cycle based on the voltage control signal to control the output voltage. The output voltage and the feedforward voltage serve as inputs to the second adder. The second adder outputs the difference between the output voltage and the feedforward voltage. The inverter output filter filters based on this difference to obtain the phase of the voltage leading the nth harmonic. The current. Obtain the phase of the voltage leading the nth harmonic. The current is the harmonic current of this branch, which will affect the harmonic distribution of the entire converter station system, such as grid-side harmonic current and harmonic voltage at the point of common coupling.
[0098] In this context, the feedforward voltage refers to the voltage at the control point of the SVG. Voltage feedforward is a strategy that optimizes control by acquiring information about grid voltage changes in advance. Voltage feedforward can predict and adjust the output of the converter station system before grid voltage changes occur, thereby avoiding interference caused by grid voltage fluctuations. In this way, the converter station system can respond to grid voltage changes more quickly, reducing delays and instabilities, and improving the speed and accuracy of regulation.
[0099] It should be noted that the virtual impedance can be a fixed value or adaptively adjusted based on the remaining capacity of the SVG. A larger remaining capacity of the SVG will result in a smaller virtual impedance, and vice versa. The current loop controller uses proportional-resonant control.
[0100] As can be seen, in this embodiment, before using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current, the transfer functions of the second-order generalized integrator, the current loop controller, the control delay unit, and the open-loop transfer function of the current loop controller are first determined so that the equivalent virtual harmonic impedance of the SVG can be calculated subsequently.
[0101] As an optional embodiment, after filtering based on the output voltage and the voltage of the control point of the SVG, the method further includes:
[0102] The equivalent virtual harmonic impedance of the SVG is determined based on the virtual impedance, the transfer function of the second-order generalized integrator, the transfer function of the current loop controller, and the open-loop transfer function of the current loop controller. The specific formula is as follows:
[0103] ;
[0104] in, The equivalent virtual harmonic impedance of the SVG. For the voltage at the control point, The phase of the voltage leading the nth harmonic. The current, For virtual impedance, Let be the transfer function of the second-order generalized integrator. This is the open-loop transfer function of the current loop controller.
[0105] Specifically, when using R-APF control, It exhibits resistive characteristics; however, when using C-APF control, It exhibits capacitive impedance. The capacitive impedance of the SVG can cancel out the inductive impedance of the step-up transformer, thereby changing the resonance conditions of the converter station system, preventing harmonic amplification, and effectively eliminating the influence of the step-up transformer connected to the SVG on harmonic suppression.
[0106] When using traditional harmonic mitigation schemes, the number of dual-coordinated filters deployed is adjusted according to operating conditions. The number of deployed dual-coordinated filters alters the impedance characteristics of the passive filter bank, causing varying degrees of harmonic amplification. To measure the impact of the passive filter bank on converter station system resonance, the HAR (Harmonic Amplification Ratio) of the passive filter is defined, with the following formula:
[0107] ;
[0108] in, Let be the harmonic amplification ratio of the passive filter, and lg be the commonly used logarithm. This represents the harmonic voltage at PCC when no passive filter is connected. This represents the harmonic voltage at PCC after the passive filter bank is connected. The equivalent impedance of the passive filter bank, For the inductive reactance of the step-up transformer, For frequency.
[0109] When HAR is less than 0, the passive filter bank can effectively suppress specific harmonic currents; when HAR is greater than 0, the harmonic current injection caused by the passive filter bank exceeds the original value, indicating an amplification effect on specific harmonics. The HAR values under different conditions were calculated by changing the number of passive filters in operation. The results are as follows... Figure 8 As shown, with the increase in the number of passive filters, the harmonic gain curve shifts to the left along the horizontal axis. Here, the horizontal axis represents frequency, and the vertical axis represents... h5 represents the 5th harmonic, and N is the number of passive filters used. When four sets of passive filters are used, the 5th harmonic... Reaching the peak value indicates that the harmonic amplification effect is most significant at this point. The region greater than 0 is the magnified region. Regions with values less than 0 are suppression regions.
[0110] right Figure 8 Analysis shows that by controlling the activation or deactivation of the passive filter bank, the resonant point can be adjusted, thereby reducing the target frequency to some extent. However, this method may affect the harmonic suppression effect and reactive power compensation capability at other frequencies. The C-APF control proposed in this application can effectively prevent harmonic amplification and reduce the harmonic distortion at the target frequency. At the same time, it does not affect the harmonic suppression effect and reactive power compensation capability at other frequencies.
[0111] In this embodiment, after filtering based on the output voltage and the voltage of the SVG control point, the method may further include: calculating the HAR of the SVG, with the specific formula as follows:
[0112] ;
[0113] in, Here, lg represents the harmonic amplification ratio of the SVG, and lg is the commonly used logarithm. The equivalent impedance of the passive filter bank, For the inductive reactance of the step-up transformer, The equivalent virtual harmonic impedance of the SVG. The equivalent impedance of the AC system, For frequency.
[0114] When using C-APF control with different step-up transformer inductances, Please refer to the curve. Figure 9 As shown, four sets of passive filters are currently in use. The horizontal axis represents Frequency, and the vertical axis represents... h5 represents the 5th harmonic. The equivalent virtual harmonic impedance of the SVG. For the inductive reactance of the step-up transformer, Here, j represents the inductance of the step-up transformer, and j is the imaginary unit. The region greater than 0 is the magnified region. The region less than 0 is the suppression region, when When the inductance is 0 (i.e., there is no series transformer inductance), the total impedance of the SVG is equal to the virtual reactance under C-APF control. In this case, similar to R-APF control, C-APF control can break the resonance condition of the converter station system and effectively suppress harmonic amplification. Moreover, by adjusting the size of the virtual harmonic capacitor through C-APF control, different harmonic suppression effects can be achieved. When the SVG is connected to the converter station system through a step-up transformer, C-APF control can still maintain good suppression performance and will not fail due to the increase of the inductance of the step-up transformer. It has strong adaptability and robustness and can achieve effective harmonic suppression even in high-voltage scenarios.
[0115] As can be seen, C-APF control controls the equivalent virtual harmonic impedance of the SVG to appear as a capacitive impedance. The capacitive impedance cancels out the inductive impedance of the step-up transformer. This changes the resonance conditions of the converter station system, prevents harmonic amplification, and effectively eliminates the influence of the step-up transformer connected to the SVG on harmonic suppression.
[0116] Accordingly, see Figure 10 As shown, Figure 10This is a schematic diagram of an active filter control device disclosed in this invention. An embodiment of this invention also provides an active filter control device applied to an SVG, which may include:
[0117] Calculation module 11 is used to subtract the nth harmonic reference current from the feedback current to obtain the current error; wherein, the nth harmonic is a non-characteristic harmonic, and the phase of both the nth harmonic reference current and the feedback current leads the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage that leads the nth harmonic voltage. The current;
[0118] Generation module 12 is used to generate a voltage control signal based on the current error;
[0119] Control module 13 is used to adjust the duty cycle of the control delay based on the voltage control signal to control the output voltage;
[0120] Filtering module 14 is used to filter based on the output voltage and the voltage of the control point of the SVG to obtain a phase that leads the nth harmonic voltage. The current.
[0121] As can be seen, this application controls the filtered current to continuously approach the phase of the voltage leading the nth harmonic by using the difference between the nth harmonic reference current and the feedback current. The nth harmonic reference current effectively suppresses harmonic amplification and improves the harmonic control effect.
[0122] In some specific embodiments, the active filter control device may further include:
[0123] A voltage acquisition unit is used to acquire the voltage of the control point of the SVG; wherein, the control point is the common point where the SVG and the low-voltage side of the step-up transformer are connected;
[0124] A filtering unit is used to filter the voltage at the control point to obtain the nth harmonic voltage;
[0125] The nth harmonic reference current calculation unit is used to take the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current.
[0126] The control unit is used to control the phase of the nth harmonic reference current to lead the phase of the nth harmonic voltage. .
[0127] In some specific embodiments, the active filter control device may further include:
[0128] A virtual impedance acquisition unit is used to acquire the virtual impedance of the SVG;
[0129] The first transfer function determination unit, used to filter the voltage at the control point, is implemented by a second-order generalized integrator. The transfer function of the second-order generalized integrator is determined based on the resonant gain and natural angular frequency of the nth harmonic, as shown in the following formula:
[0130] ;
[0131] in, Let be the transfer function of the second-order generalized integrator. The resonant gain of the nth harmonic is... Let be the natural angular frequency of the nth harmonic;
[0132] The second transfer function determination unit is used to generate the voltage control signal based on the current error, which is implemented by the current loop controller. It determines the transfer function of the current loop controller based on the channel gain, the resonant gain of the nth harmonic, the passband width of the nth harmonic, and the natural angular frequency of the nth harmonic. The specific formula is as follows:
[0133] ;
[0134] in, Let be the transfer function of the current loop controller. The channel gain is [value]. The resonant gain of the nth harmonic is... Let n be the natural angular frequency of the nth harmonic. The passband width of the nth harmonic;
[0135] The third transfer function determination unit is used to determine the transfer function of the control delay based on the signal modulation ratio and the sampling period, as shown in the following formula:
[0136] ;
[0137] in, Let be the transfer function of the control delay. The signal modulation ratio is... The sampling period is the period in question.
[0138] The open-loop transfer function determination unit is used to determine the open-loop transfer function of the current loop controller based on the transfer function of the current loop controller and the transfer function of the control delay unit. The specific formula is as follows:
[0139] ;
[0140] in, Let be the open-loop transfer function of the current loop controller. Let be the transfer function of the current loop controller. Let L be the transfer function of the control delay, L be the equivalent reactance of the SVG, and R be the equivalent resistance of the SVG.
[0141] In some specific embodiments, the active filter control device may further include:
[0142] The equivalent virtual harmonic impedance determination unit is used to determine the equivalent virtual harmonic impedance of the SVG based on the virtual impedance, the transfer function of the second-order generalized integrator, the transfer function of the current loop controller, and the open-loop transfer function of the current loop controller. The specific formula is as follows:
[0143] ;
[0144] in, The equivalent virtual harmonic impedance of the SVG is... The voltage at the control point. The phase of the voltage leading the nth harmonic is The current, The virtual impedance, Let be the transfer function of the second-order generalized integrator. Let be the open-loop transfer function of the current loop controller.
[0145] In some specific implementations, the virtual impedance is a fixed value, or the virtual impedance is adaptively adjusted based on the capacity of the SVG.
[0146] In some specific implementations, the current loop controller employs proportional-resonant control.
[0147] In some specific embodiments, the active filter control device may further include:
[0148] The HAR calculation unit is used to calculate the HAR of the SVG, and the specific formula is as follows:
[0149] ;
[0150] in, Let lg be the harmonic amplification ratio of the SVG, and lg be the common logarithm. The equivalent impedance of the passive filter bank, The inductive reactance of the step-up transformer, The equivalent virtual harmonic impedance of the SVG is... The equivalent impedance of the AC system, For frequency.
[0151] Furthermore, embodiments of this application also disclose an electronic device, Figure 11 This is a structural diagram of an electronic device disclosed in this invention. The content of the diagram should not be construed as limiting the scope of this application. The electronic device 20 may specifically include: at least one processor 21, at least one memory 22, a power supply 23, a communication interface 24, an input / output interface 25, and a communication bus 26. The memory 22 stores a computer program, which is loaded and executed by the processor 21 to implement the relevant steps in the active filter control method disclosed in any of the foregoing embodiments. Furthermore, the electronic device 20 in this embodiment may specifically be an electronic computer.
[0152] In this embodiment, the power supply 23 is used to provide operating voltage for each hardware device on the electronic device 20; the communication interface 24 can create a data transmission channel between the electronic device 20 and external devices, and the communication protocol it follows can be any communication protocol applicable to the technical solution of this application, and is not specifically limited here; the input / output interface 25 is used to acquire external input data or output data to the outside world, and its specific interface type can be selected according to specific application needs, and is not specifically limited here.
[0153] In addition, the memory 22, as a carrier for resource storage, can be a read-only memory, random access memory, disk, or optical disk, etc. The resources stored thereon can include an operating system 221, computer programs 222, etc., and the storage method can be temporary storage or permanent storage.
[0154] The operating system 221 is used to manage and control the various hardware devices on the electronic device 20 and the computer program 222, which may be Windows Server, Netware, Unix, Linux, etc. In addition to including a computer program capable of performing the active filter control method executed by the electronic device 20 as disclosed in any of the foregoing embodiments, the computer program 222 may further include a computer program capable of performing other specific tasks.
[0155] Furthermore, this application also discloses a computer-readable storage medium for storing a computer program; wherein, when the computer program is executed by a processor, it implements the DC voltage control of the aforementioned disclosed inverter. Specific steps of this method can be found in the corresponding content disclosed in the foregoing embodiments, and will not be repeated here.
[0156] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.
[0157] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0158] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. An active filter control method, characterized in that, Applied to SVG, including: The current error is obtained by subtracting the nth harmonic reference current from the feedback current; wherein, the nth harmonic is a non-characteristic harmonic, and the phase of both the nth harmonic reference current and the feedback current leads the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage that leads the nth harmonic voltage. The current; A voltage control signal is generated based on the current error; The duty cycle of the control delay is adjusted based on the voltage control signal to control the output voltage; Filtering is performed based on the output voltage and the voltage at the control point of the SVG to obtain a phase that leads the nth harmonic voltage. The current; Before subtracting the nth harmonic reference current from the feedback current to obtain the current error, the process also includes: Obtain the voltage of the control point of the SVG; wherein, the control point is the common point where the SVG and the low-voltage side of the step-up transformer are connected; The voltage at the control point is filtered to obtain the nth harmonic voltage; The ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG is used as the magnitude of the nth harmonic reference current. The phase of the nth harmonic reference current is controlled to lead the phase of the nth harmonic voltage. ; Before using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current, the method further includes: Obtain the virtual impedance of the SVG; The voltage filtering at the control point is achieved by a second-order generalized integrator. The transfer function of the second-order generalized integrator is determined based on the resonant gain and natural angular frequency of the nth harmonic, as shown in the following formula: ； in, Let be the transfer function of the second-order generalized integrator. The resonant gain of the nth harmonic is... Let be the natural angular frequency of the nth harmonic, and s be a complex variable; The voltage control signal generated based on the current error is implemented by a current loop controller. The transfer function of the current loop controller is determined based on the channel gain, the resonant gain of the nth harmonic, the passband width of the nth harmonic, and the natural angular frequency of the nth harmonic. The specific formula is as follows: ； in, Let be the transfer function of the current loop controller. The channel gain is [value]. The resonant gain of the nth harmonic is... Let n be the natural angular frequency of the nth harmonic. The passband width of the nth harmonic; The transfer function of the control delay is determined based on the signal modulation ratio and the sampling period, as shown in the following formula: ； in, Let be the transfer function of the control delay. The signal modulation ratio is... The sampling period is the period in question. The open-loop transfer function of the current loop controller is determined based on the transfer function of the current loop controller and the transfer function of the control delay unit, as shown in the following formula: ； in, Let be the open-loop transfer function of the current loop controller. Let be the transfer function of the current loop controller. Let L be the transfer function of the control delay, L be the equivalent reactance of the SVG, and R be the equivalent resistance of the SVG.
2. The active filter control method as described in claim 1, characterized in that, After filtering based on the output voltage and the voltage of the control point of the SVG, the process further includes: The equivalent virtual harmonic impedance of the SVG is determined based on the virtual impedance, the transfer function of the second-order generalized integrator, the transfer function of the current loop controller, and the open-loop transfer function of the current loop controller, as shown in the following formula: ； in, The equivalent virtual harmonic impedance of the SVG is... The voltage at the control point. The phase of the voltage leading the nth harmonic is The current, The virtual impedance, Let be the transfer function of the second-order generalized integrator. Let be the open-loop transfer function of the current loop controller.
3. The active filter control method as described in claim 1, characterized in that, The virtual impedance is a fixed value, or the virtual impedance is adaptively adjusted based on the capacity of the SVG.
4. The active filter control method as described in claim 1, characterized in that, The current loop controller employs proportional-resonant control.
5. The active filter control method according to any one of claims 1 to 4, characterized in that, After filtering based on the output voltage and the voltage of the control point of the SVG, the process further includes: The HAR of the SVG is calculated using the following formula: ； in, Let lg be the harmonic amplification ratio of the SVG, and lg be the common logarithm. The equivalent impedance of the passive filter bank, The inductive reactance of the step-up transformer, The equivalent virtual harmonic impedance of the SVG is... The equivalent impedance of the AC system, For frequency.
6. An active filter control device, characterized in that, Applied to SVG, including: The calculation module is used to subtract the nth harmonic reference current from the feedback current to obtain the current error; wherein the nth harmonic is a non-characteristic harmonic, and the phase of both the nth harmonic reference current and the feedback current leads the phase of the nth harmonic voltage. The feedback current is the phase of the filtered voltage that leads the nth harmonic voltage. The process includes, before subtracting the nth harmonic reference current from the feedback current to obtain the current error, further comprising: acquiring the voltage of the control point of the SVG; wherein the control point is the common point connecting the SVG and the low-voltage side of the step-up transformer; filtering the voltage of the control point to obtain the nth harmonic voltage; using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current; and controlling the phase of the nth harmonic reference current to lead the phase of the nth harmonic voltage. Before using the ratio of the nth harmonic voltage to the equivalent virtual harmonic impedance of the SVG as the magnitude of the nth harmonic reference current, the method further includes: obtaining the virtual impedance of the SVG; filtering the voltage at the control point using a second-order generalized integrator, and determining the transfer function of the second-order generalized integrator based on the resonant gain and natural angular frequency of the nth harmonic, as shown in the following formula: ;in, Let be the transfer function of the second-order generalized integrator. The resonant gain of the nth harmonic is... Let be the natural angular frequency of the nth harmonic, and s be a complex variable. The voltage control signal generated based on the current error is implemented by a current loop controller. The transfer function of the current loop controller is determined based on the channel gain, the resonant gain of the nth harmonic, the passband width of the nth harmonic, and the natural angular frequency of the nth harmonic. The specific formula is as follows: ;in, Let be the transfer function of the current loop controller. The channel gain is [value]. The resonant gain of the nth harmonic is... Let n be the natural angular frequency of the nth harmonic. Let be the passband width of the nth harmonic; the transfer function of the control delay is determined based on the signal modulation ratio and sampling period, and the specific formula is as follows: ;in, Let be the transfer function of the control delay. The signal modulation ratio is... The sampling period is given; the open-loop transfer function of the current loop controller is determined based on the transfer function of the current loop controller and the transfer function of the control delay unit, as shown in the following formula: ;in, Let be the open-loop transfer function of the current loop controller. Let be the transfer function of the current loop controller. Let L be the transfer function of the control delay, L be the equivalent reactance of the SVG, and R be the equivalent resistance of the SVG. The generation module is used to generate a voltage control signal based on the current error; The control module is used to adjust the duty cycle of the control delay based on the voltage control signal in order to control the output voltage; The filtering module is used to filter the output voltage and the voltage of the control point of the SVG to obtain a phase that leads the nth harmonic voltage. The current.
7. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the active filter control method as described in any one of claims 1 to 5.
8. A computer-readable storage medium, characterized in that, Used to store a computer program, wherein the computer program, when executed by a processor, implements the active filter control method as described in any one of claims 1 to 5.