Vienna rectifier system based on fft harmonic detection and harmonic suppression method thereof

Abstract

The application discloses a Vienna rectifier system based on FFT harmonic detection and a harmonic suppression method thereof, the system comprising a Vienna rectifier main circuit and a control module, and the harmonic suppression method comprising that a fundamental current loop adopts PI control under a synchronous rotating coordinate system to ensure fundamental tracking performance. On this basis, a sliding window FFT is used to perform real-time spectrum analysis on actual grid-side current to obtain harmonic content of each preset characteristic harmonic, and an adaptive parameter regulator dynamically adjusts the resonance gain or the enable state of a corresponding harmonic QPR controller according to the content: when the content is high, the suppression is enhanced, and when the content is extremely low, the controller is turned off. The harmonic QPR controller takes a stationary coordinate system current error as input and outputs a harmonic compensation voltage to be superposed on a fundamental control voltage. Through use of the application, total harmonic distortion of input current of the Vienna rectifier under all working conditions is effectively reduced. The application can be widely applied to the technical field of electric energy conversion.

Description

Technical Field

[0001] This invention relates to the field of power conversion technology, and in particular to a Vienna rectifier system based on FFT harmonic detection and its harmonic suppression method. Background Technology

[0002] Vienna rectifiers, as a three-level, three-phase power factor correction topology, are widely used in electric vehicle charging, communication power supplies, and industrial drives due to their advantages such as low power switching voltage stress, no bridge arm shoot-through risk, and high efficiency. To meet increasingly stringent current harmonic standards, Vienna rectifiers typically employ a dual closed-loop control structure with an outer voltage loop and an inner current loop. The control performance of the inner current loop directly determines the harmonic content of the grid-side current.

[0003] Traditional current inner loops often employ PI control in a synchronous rotating coordinate system, but their ability to suppress low-order harmonics is limited, resulting in a high total harmonic distortion (THD) of the input current. Proportional resonant control can provide high gain at specific frequencies, achieving zero steady-state error tracking for specific harmonics, but it is sensitive to grid frequency fluctuations. Quasi-proportional resonant control improves frequency robustness by increasing the resonant bandwidth, but the parameters of existing QPR controllers remain fixed after tuning.

[0004] In practical applications, changes in grid background harmonics and load conditions cause dynamic changes in the main harmonic components and their content in the Vienna rectifier input current. Fixed QPR parameters are difficult to achieve optimal harmonic suppression under all operating conditions: under certain operating conditions, the suppression is insufficient when the content of a specific harmonic is significantly increased; under other operating conditions, when the content of that harmonic is extremely low, a fixed high gain may introduce additional noise and even affect system stability.

[0005] Therefore, how to make the QPR controller adaptively match the actual harmonic distribution has become a technical problem that urgently needs to be solved. Summary of the Invention

[0006] In view of this, in order to solve the problems of dynamic changes in input current harmonics and poor adaptability of traditional fixed-parameter QPR control in existing Vienna rectifiers under complex operating conditions, firstly, this invention proposes a Vienna rectifier system based on FFT harmonic detection. This system includes a Vienna rectifier main circuit and a control module, wherein: The control module includes: a voltage outer loop controller, which generates an active current reference value based on the deviation between the voltage command and the feedback; a fundamental current control unit, including a coordinate transformation module and a PI current regulator, used for PI control in a synchronous rotating coordinate system and inverse transformation to a two-phase stationary coordinate system to output the fundamental control voltage; an FFT harmonic online detection module, which extracts the characteristic subharmonic content in the grid-side current online based on sliding window FFT; an adaptive parameter regulator, which determines the gain coefficient and enable signal of each QPR based on the harmonic content; a harmonic QPR controller, which outputs the corresponding compensation voltage; and a superposition and modulation unit.

[0007] The main circuit of the Vienna rectifier includes a three-phase AC power supply, a three-phase input filter inductor L, a Vienna rectifier bridge arm, and a first and second output capacitor on the DC side. Each phase of the Vienna rectifier bridge arm includes a bidirectional switch and six freewheeling diodes, and the load is connected in parallel on the DC side.

[0008] Applied to the Vienna rectifier system described above, this invention also provides a harmonic suppression method, which includes the following steps: First, the three-phase current and voltage on the grid side are acquired. The actual fundamental current in the synchronous rotating coordinate system and the actual current in the two-phase stationary coordinate system are obtained through Clark / Park transformation. An outer-loop voltage controller generates an active current reference based on the DC bus input. This reference, along with the reactive current reference, is compared with the actual current in the synchronous rotating coordinate system. The resulting output, via PI regulation, is the fundamental voltage in the synchronous rotating coordinate system, which is then inversely transformed back to the two-phase stationary coordinate system to obtain the fundamental control voltage. Simultaneously, the actual current in the two-phase stationary coordinate system is decomposed in real-time using a sliding-window FFT to extract the characteristic subharmonic amplitude. This is used to dynamically adjust the gain coefficient and activation state of each harmonic QPR controller. Subsequently, the deviation between the fundamental current reference and the actual value in the two-phase stationary coordinate system is fed into these QPR controllers to generate harmonic compensation voltage. Finally, the fundamental control voltage, harmonic compensation voltage, and DC voltage equalization regulation are superimposed to form a modulation wave, driving the Vienna rectifier switch to operate, thereby suppressing input current harmonics.

[0009] Based on the above scheme, this invention provides a Vienna rectifier system and its harmonic suppression method based on FFT harmonic detection. The fundamental current loop adopts mature synchronous rotating coordinate system PI control, which is simple in structure, has fast dynamic response, and no steady-state error. On this basis, the main harmonic components and their content in the input current are detected in real time and accurately using FFT, and the gain of the corresponding harmonic QPR controller is adjusted online accordingly to dynamically match the harmonic suppression capability with the actual harmonic distribution. When the content of a specific harmonic increases, the resonant gain of the corresponding QPR is automatically increased to enhance suppression; when the content of that harmonic is extremely low, the gain is automatically reduced or the controller is turned off to avoid additional noise amplification and interference to the fundamental control loop. This scheme decouples the fundamental control and harmonic compensation, significantly improving the current quality, robustness, and efficiency of the Vienna rectifier under all operating conditions, and is easy to implement on DSP or FPGA. Attached Figure Description

[0010] Figure 1 This is a structural block diagram of a Vienna rectifier system based on FFT harmonic detection according to the present invention; Figure 2 This is a flowchart of the harmonic suppression method of the present invention; Figure 3 This is the Bode plot of a quasi-proportional resonant controller; Figure 4 This is a diagram of harmonic content in Maltab simulation before using this method; Figure 5 This is a diagram of harmonic content after using this method in Maltab simulation; Figure 6 This is a diagram of the harmonic content on a 15KW experimental platform before using this method; Figure 7 This is a diagram showing the harmonic content of a 15KW experimental platform after using this method. Detailed Implementation

[0011] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0012] It should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0013] It should be understood that the terms "system," "apparatus," "unit," and / or "module" used in this application are a method of distinguishing different components, elements, parts, sections, or assemblies at different levels. However, if other terms can achieve the same purpose, they may be replaced by other expressions.

[0014] Unless the context explicitly indicates an exception, words such as "a," "an," "a kind," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list; a method or apparatus may also include other steps or elements. An element defined by the phrase "comprising a..." does not exclude the presence of other identical elements in the process, method, product, or apparatus that includes the element.

[0015] In the description of the embodiments of this application, "a plurality of" refers to two or more. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

[0016] Furthermore, flowcharts are used in this application to illustrate the operations performed by the system according to embodiments of this application. It should be understood that the preceding or following operations are not necessarily performed precisely in sequence. Instead, the steps can be processed in reverse order or simultaneously. Additionally, other operations can be added to these processes, or one or more steps can be removed from them.

[0017] Reference Figure 1 This is a structural block diagram of an optional example of the Vienna rectifier system based on FFT harmonic detection proposed in this invention. The Vienna rectifier system may include, but is not limited to, the Vienna rectifier main circuit and control module, wherein: The main circuit of the Vienna rectifier includes: a three-phase AC power supply, a three-phase input filter inductor L, Vienna rectifier bridge arms, and DC-side output capacitors C1 and C2. Each phase of the Vienna rectifier bridge arm consists of a bidirectional switch and two freewheeling diodes. The load is connected in parallel on the DC side.

[0018] The three-phase AC power supply's A, B, and C phase outputs are connected to the AC input of the Vienna rectifier bridge arm via three filter inductors L. The DC side includes an upper capacitor C1 and a lower capacitor C2 connected in series. The positive terminal of C1 is the positive terminal P of the DC bus, and the negative terminal of C2 is the negative terminal N of the DC bus. The series connection point of C1 and C2 is the DC midpoint O. The load is connected in parallel between the positive terminal P and the negative terminal N of the DC bus.

[0019] Each phase of the Vienna rectifier bridge arm has the same structure. Taking phase A as an example, the bridge arm consists of two fast recovery diodes D1 and D2 connected in series, forming the upper and lower half-arms. The connection point of the two diodes is the AC input terminal of this phase. A bidirectional switch S1 is connected between the AC input terminal and the midpoint O of the DC side capacitor. The bidirectional switch S1 can be composed of two common-emitter or common-collector IGBT / MOSFETs connected in series, or a single bidirectional switching device can be used.

[0020] The control system mainly includes a sampling circuit, a phase-locked loop, an outer voltage loop, a fundamental PI current loop, a harmonic QPR compensation loop, and a space vector pulse width modulation.

[0021] The input terminal of the outer voltage loop controller receives the total DC voltage setpoint. and DC side total voltage feedback value Its output terminal is connected to the current setpoint input terminal of the fundamental current control unit to provide an active current reference. ; The sampling circuit acquires the three-phase grid voltage and three-phase input current, and its output is connected to the coordinate transformation module of the phase-locked loop and the fundamental current control unit, respectively.

[0022] Phase-locked loop output grid voltage phase angle To the coordinate transformation module.

[0023] The fundamental current control unit includes a coordinate transformation module and a PI current regulator. The coordinate transformation module receives the three-phase current and phase angle. Output the actual fundamental current in the synchronous rotating coordinate system. and the actual current in a two-phase stationary coordinate system .

[0024] The input terminal of the PI current regulator receives the current error ( Its output is connected to the inverse transformation module, and it also receives the phase angle. Output fundamental control voltage in two-phase stationary coordinate system And sent to the superposition and modulation unit.

[0025] The input of the FFT harmonic online detection module is connected to the two-phase stationary coordinate system actual current signal output by the fundamental current control unit. (or one of them), perform sliding window FFT analysis on it. The output of the online harmonic detection module is connected to the input of the adaptive parameter regulator, which will output the amplitude values ​​of each characteristic harmonic detected in real time. Sent out.

[0026] The output of the adaptive parameter regulator is connected to the gain control terminal of each harmonic QPR controller, providing their respective resonant gain. Or enable signal.

[0027] The signal input terminals of each harmonic QPR controller are connected in parallel to obtain the MQPR, which receives the current error in a two-phase stationary coordinate system. (Based on fundamental current reference) With actual current (Obtained by subtraction). The output terminals of each harmonic QPR controller output harmonic compensation voltages corresponding to the order of harmonics. The total harmonic compensation voltage is then summed and superimposed. It is sent to the superposition and modulation unit.

[0028] The input of the superposition and modulation unit collects the fundamental control voltage, total harmonic compensation voltage, and equalization adjustment amount, and the output generates a PWM drive signal, which is connected to each bidirectional switch of the Vienna rectifier main circuit to control its on and off.

[0029] Figure 1 In this context, SVPWM stands for Space Vector Pulse Width Modulation, and MQPR stands for Harmonic QPR Compensator.

[0030] The harmonic suppression method applied to the above Vienna rectifier system is referred to Figure 2 This includes the following steps: To facilitate the description of the control method of this invention, a simplified mathematical model of the Vienna rectifier in a two-phase stationary coordinate system (αβ) is first given. Ignoring the switching frequency ripple and AC side resistance, the AC side voltage equation of the Vienna rectifier can be expressed as: In the formula, This represents the component of the grid-side voltage along the αβ axis; This represents the component of the grid-side current along the αβ axis; Let α be the component of the AC-side modulation voltage of the rectifier along the αβ axis. This model shows that by controlling the modulation voltage... This allows for direct control of the grid-side current.

[0031] Through the Park transformation, the fundamental mathematical model in the synchronous rotating coordinate system (dq) can be further obtained: in, This represents the grid-side voltage component along the dq axis; This represents the component of the grid-side current along the dq axis; For the components of the modulation voltage on the dq axis; This is the grid angular frequency. Through feedforward decoupling, it is possible to achieve... The PI regulator enables independent control of the DC quantity and achieves zero steady-state error tracking of the DC quantity. This invention utilizes this characteristic to construct a fundamental current loop, while assigning the harmonic suppression task to a QPR controller based on the αβ coordinate system.

[0032] Step S1: Collect the three-phase input current and three-phase grid voltage on the grid side, and obtain the actual fundamental current in the synchronous rotating coordinate system and the actual current in the two-phase stationary coordinate system through Clark transformation and Park transformation; Sample three-phase grid voltage and three-phase input current Phase-locked loop (PLL) is used to obtain the grid voltage phase angle. The actual current in a two-phase stationary coordinate system is obtained by Clark transformation of the three-phase current. Simultaneously, the actual fundamental current in the synchronous rotating coordinate system is obtained through Park transformation. .

[0033] Step S2: Generate an active current reference based on the output of the outer loop of the DC side total voltage; DC side total voltage With a given value Comparison, the active current reference output by the PI regulator .

[0034] To achieve unity power factor, reactive current reference .

[0035] Step S3: Combining the active current and reactive current references, compare them with the actual fundamental current in the synchronous rotating coordinate system to generate the fundamental control voltage in the synchronous rotating coordinate system. respectively with The fundamental current error is obtained by subtraction and fed into a PI current regulator, whose transfer function is: And add a feedforward decoupling term. and Output fundamental control voltage in synchronous rotating coordinate system ; Step S4: Perform Park inverse transformation on the fundamental control voltage in the rotating coordinate system to obtain the fundamental control voltage in the two-phase stationary coordinate system. The fundamental control voltage in the two-phase stationary coordinate system is obtained by inverse Park transform. .

[0036] Step S5: Perform online spectrum analysis of the actual current in the two-phase stationary coordinate system using sliding window FFT, and extract the harmonic content of the preset characteristic subharmonics in real time; according to The fundamental current reference in the two-phase stationary coordinate system is obtained by inverse Park transform. Calculate the current error in the stationary coordinate system This serves as the input to each harmonic QPR controller. Here, since the PI current loop already ensures fundamental frequency tracking, the error signal mainly contains harmonic components.

[0037] Actual grid-side current (or Enter the FFT harmonic online detection module and use sliding window FFT.

[0038] Step S6: Based on the harmonic content of each characteristic subharmonic, adaptively adjust the gain coefficient and enable state of the harmonic QPR controller corresponding to that characteristic subharmonic. Let the sampling frequency be The number of sampling points in one power frequency cycle is The sampling sequence within the data window is The real-time amplitude of the h-th harmonic. Calculated by the following formula: Each time the sampling window slides one point, the oldest data is removed. And add the latest data The calculation is then repeated to obtain the amplitudes of the 5th, 7th, 11th, and 13th characteristic harmonics in real time. These amplitudes are then output as harmonic content to the adaptive parameter regulator.

[0039] The adaptive parameter regulator independently generates the resonant gain coefficients of each harmonic QPR controller based on the content of each harmonic. For the h-th harmonic, its resonant gain... The regulation law is described by the following piecewise function: in, To preset the maximum gain, and These are the upper and lower threshold values, respectively. This function ensures that the gain changes continuously and linearly with the harmonic content between the high and low thresholds, and directly shuts down the corresponding controller when the harmonic content is below the lower threshold.

[0040] Step S7: The difference between the fundamental current reference signal in the two-phase stationary coordinate system and the actual current in the two-phase stationary coordinate system is taken as the current error and sent to each harmonic QPR controller to obtain the harmonic compensation voltage. Each harmonic QPR controller uses current error As input, the resonant frequencies of its transfer function are respectively set at... And the resonant gain Updated in real time by an adaptive parameter regulator. For example, the transfer function of the 5th harmonic QPR controller is: Output harmonic compensation voltage components The total harmonic compensation voltage is obtained by superimposing the outputs of all harmonic QPRs. .

[0041] Step S8: Superimpose the fundamental control voltage, the harmonic compensation voltage, and the DC voltage equalization adjustment to generate a modulation wave signal; fundamental frequency control voltage Total Harmonic Compensation Voltage And the voltage equalization regulation amount obtained by PI regulation of the voltage difference between the upper and lower DC capacitors. The three factors are combined to form the final modulation voltage: The equalization adjustment can be generated using conventional midpoint potential balance control methods, such as those based on voltage difference. It is obtained by combining the PI regulator with the current polarity.

[0042] Step S9: Drive the power switch of the Vienna rectifier based on the modulation wave signal to suppress the input current harmonics.

[0043] According to the Vienna rectifier mathematical model, the modulation voltage directly determines the rate of change of AC side current. Therefore, after the superimposed voltage is modulated by space vector pulse width modulation, a drive signal is generated, which can control each power switch of the Vienna rectifier, realizing the decoupled control of fundamental current tracking and harmonic current suppression.

[0044] Through the above process, the system maintains good fundamental frequency tracking performance with the fundamental frequency PI control while simultaneously sensing the magnitude of each harmonic in the input current and dynamically matching the QPR control strength. When a harmonic increases sharply due to background harmonics in the power grid or load changes, the FFT quickly detects it, and the adaptive parameter regulator immediately increases the corresponding resonant gain to enhance suppression capability. When the system operates under a light-load, clean power grid where the harmonic is almost non-existent, the gain drops to zero, avoiding noise amplification by the resonant controller and not affecting the stability margin of the fundamental frequency PI loop.

[0045] The Vienna rectifier and its harmonic suppression method proposed in the above embodiments are simulated and verified.

[0046] Table 1 shows the detailed parameters of the VIENNA rectifier.

[0047] Under full-load steady-state conditions, the harmonic spectrum of the grid-side current was compared between the cases without harmonic suppression (using only fundamental PI control) and with the addition of the adaptive QPR harmonic suppression of this invention. Figure 3The Bode plot results of the quasi-proportional resonant controller can be shown, which produce extremely large amplitudes at 250Hz, 350Hz, 550Hz, and 650Hz (i.e., the 5th, 7th, 11th, and 13th harmonics) to suppress harmonics. Figure 4 This is a spectrum analysis of the A-phase input current when there is no harmonic suppression for a 15kW power supply. Figure 5 This is a spectrum analysis of the A-phase input current when a 15kW power supply with harmonic suppression is applied. Figure 4 and Figure 5 FFT analysis results for both cases are presented. Without harmonic suppression, the current THD is 6.2%, with the 5th harmonic amplitude at 2.73A, the 7th harmonic amplitude at 1.008A, and a significant component of the 11th harmonic. After incorporating the adaptive QPR harmonic suppression of this invention, the characteristic harmonics are significantly attenuated, with the 5th harmonic reduced to 0.164A, the 7th harmonic reduced to 0.047A, and the 11th harmonic approaching the noise floor, resulting in a THD of 2.12%.

[0048] Figure 6 This is the spectrum of the three-phase input current (A, B, and C) at 6kW without adaptive harmonic suppression. Figure 7 This is the spectrum of the three-phase input current (A, B, and C) when adaptive harmonic suppression is applied to a 6kW power supply. Figure 6 and Figure 7 FFT analysis results for two scenarios under the experimental platform are presented. Without harmonic suppression, the current THD is approximately 15%, with the 5th harmonic amplitude at 1.26 A and the 7th harmonic amplitude at 0.444 A. After incorporating the adaptive QPR harmonic suppression of this invention, all characteristic harmonics are significantly attenuated, with the 5th harmonic reduced to 0.107 A and the 7th harmonic reduced to 0.051 A, resulting in a THD reduction to 8%.

[0049] The spectral comparison clearly shows that the adaptive QPR control of the present invention can accurately lock and effectively suppress the main low-order harmonics, and due to the gain adaptive mechanism, it does not introduce additional high-frequency noise while ensuring the harmonic suppression effect.

[0050] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A Vienna rectifier system based on FFT harmonic detection, comprising a Vienna rectifier main circuit and a control module, characterized in that, The control module includes: The voltage outer loop controller is used to generate an active current reference based on the DC total voltage command and feedback; The fundamental current control unit, including a coordinate transformation module and a PI current regulator, is used to perform closed-loop control of the fundamental current in a synchronous rotating coordinate system and output the fundamental control voltage in a two-phase stationary coordinate system. The FFT harmonic online detection module is used to perform sliding window FFT analysis on the actual grid-side current in a two-phase stationary coordinate system and output the harmonic content of characteristic subharmonics. An adaptive parameter regulator is used to receive the harmonic content of the characteristic subharmonic and output the QPR gain coefficient and enable signal corresponding to each harmonic. Harmonic QPR controller, used to output harmonic compensation voltage; The superposition and modulation unit is used to superimpose the fundamental control voltage, the harmonic compensation voltage and the DC equalization adjustment amount to generate a modulation wave, and output a PWM drive signal to the Vienna rectifier main circuit.

2. The Vienna rectifier system based on FFT harmonic detection according to claim 1, characterized in that, The Vienna rectifier main circuit includes a three-phase AC power supply, a three-phase input filter inductor L, Vienna rectifier bridge arms, and a first DC-side output capacitor and a second DC-side output capacitor, wherein: Each phase of the Vienna rectifier bridge arm includes a bidirectional switch and six freewheeling diodes; The load is connected in parallel on the DC side; The three-phase output terminals of the three-phase AC power supply are connected to the AC input terminals of the Vienna rectifier bridge arm through three-phase input filter inductors. The positive terminal of the first output capacitor on the DC side is the positive terminal of the DC bus; The negative terminal of the second output capacitor on the DC side is the negative terminal of the DC bus; The connection point of the series connection between the first output capacitor on the DC side and the second output capacitor on the DC side is the DC midpoint; The load is connected in parallel between the positive terminal of the DC bus and the negative terminal of the DC bus.

3. A harmonic suppression method applied to the Vienna rectifier system as described in claim 1, characterized in that, Includes the following steps: The three-phase input current and three-phase grid voltage on the grid side are collected, and the actual fundamental current in the synchronous rotating coordinate system and the actual current in the two-phase stationary coordinate system are obtained by Clark transformation and Park transformation. The active current reference is generated based on the output of the outer loop of the DC side total voltage. By combining the active current and reactive current references, and comparing them with the actual fundamental current in a synchronous rotating coordinate system, a fundamental control voltage in a synchronous rotating coordinate system is generated. Perform an inverse Park transform on the fundamental control voltage in the step rotating coordinate system to obtain the fundamental control voltage in the two-phase stationary coordinate system. The actual current in the two-phase stationary coordinate system is subjected to online spectrum analysis using sliding window FFT to extract the harmonic content of preset characteristic subharmonics in real time. Based on the harmonic content of each characteristic subharmonic, the gain coefficient and enable state of the harmonic QPR controller corresponding to that characteristic subharmonic are adaptively adjusted. The difference between the fundamental current reference signal in the two-phase stationary coordinate system and the actual current in the two-phase stationary coordinate system is taken as the current error and sent to each harmonic QPR controller to obtain the harmonic compensation voltage. The fundamental control voltage, the harmonic compensation voltage, and the DC voltage equalization adjustment are superimposed to generate a modulation wave signal; The power switch of the Vienna rectifier is driven by the modulated wave signal to suppress the input current harmonics.

4. The harmonic suppression method according to claim 3, characterized in that, The adaptive adjustment method of the gain coefficient of the harmonic QPR controller includes: For any harmonic, if its harmonic content is higher than the preset upper limit threshold, the resonant gain of the corresponding harmonic QPR controller will be set to the preset maximum gain. If the harmonic content is lower than the preset lower threshold, the resonant gain is set to zero and the harmonic QPR controller is disabled; If the harmonic content is between the preset upper limit threshold and the preset lower limit threshold, the corresponding resonant gain value is calculated based on the harmonic content.

5. The harmonic suppression method according to claim 3, characterized in that, The transfer function of the harmonic QPR controller is as follows: in, For harmonic order, The fundamental angular frequency, For the first The resonant gain corresponding to the subharmonic. For the corresponding bandwidth coefficient, This represents the Laplace operator.

6. The harmonic suppression method according to claim 3, characterized in that, The adjustment law of the resonant gain is described by the following piecewise function: in, To preset the maximum gain, and These are the upper and lower threshold values, respectively. Indicates the first Real-time amplitude of the subharmonic.

7. The harmonic suppression method according to claim 3, characterized in that, The sliding window FFT online spectrum analysis specifically includes: A fixed sampling frequency is used, and sampling points of one fundamental period are selected to form a sliding data window; When a new sampling point is acquired, the earliest sampling point in the sliding data window is removed and the FFT is recalculated. The amplitude of each characteristic subharmonic is output in real time as the harmonic content.

8. The harmonic suppression method according to claim 3, characterized in that, The preset number of the characteristic subharmonics includes at least the 5th, 7th, 11th, and 13th harmonics.

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