Wind power generation system broadband impedance online active measurement device, method and application

Abstract

The invention discloses an online active measurement device and method for broadband impedance of a wind power generation system and its application, comprising an energy dissipation device, which realizes an active impedance measurement function while realizing a fault ride-through function; by injecting a controlled broadband small signal current into the system, the response of the wind farm side or the system side is measured, thereby realizing online measurement of broadband impedance of the wind farm and the power grid side; the invention realizes real-time measurement of power grid impedance of the wind farm and the power transmission system, cooperates with an inverse linear frequency modulation (RC-PWM) control strategy, obtains RC-PWM signals by forming a function and locking an inverse function, realizes fast and high-precision broadband impedance measurement, and the proposed signal generation device and method avoid frequency band gaps caused by spectrum shifting caused by an industrial frequency carrier.

Description

Technical Field

[0001] The invention relates to a measuring device, and in particular to an online active measuring device, method and application of broadband impedance of a wind power generation system. Background Art

[0002] In the past decade, wind power generation systems have developed rapidly with their advantages of cleanliness and low cost, and have made great contributions to solving the energy crisis. A large number of literatures point out that the surge in the number of wind farms has greatly changed the dynamic operation of the power system, causing various oscillation problems including subsynchronous and supersynchronous oscillations, medium-frequency oscillations, and broadband oscillations. An effective solution is to improve the control loop of power electronic devices according to the corresponding system impedance, such as adding active damping control. The resonance point can usually be obtained using the system impedance, and this can be used as a guide for the optimization of control parameters and applied to the control loop of power electronic devices, which can greatly reduce system instability and ensure the safe and stable operation of wind power generation systems.

[0003] In practical applications, due to confidentiality requirements, it is difficult to obtain specific parameters such as the control loop and topology of the wind turbine, which makes it difficult to verify the accuracy of computational modeling. Therefore, impedance measurement technology is often used to obtain real-time system impedance. The literature points out that the external perturbation method is more reliable. Since the measurement method based on the sinusoidal wave scanning frequency method takes a long time, broadband impedance measurement technology has received widespread attention. This method can obtain the broadband characteristics of the system within a shorter signal injection time. Common broadband impedance measurement technologies include random pulse width modulation signals, which are characterized by uncontrollable excitation frequency bands; pseudo-random binary sequences, which can be applied to the control loop of the grid-connected converter, but the spectral resolution is fractional, which can easily cause spectrum leakage in the Fourier transform; Chrip pulse modulation signals, which are characterized by the need for additional perturbation circuits, and the gaps in the injection frequency band limit their application.

[0004] Prior art, such as Chinese patent application, application number: CN201811357313.7, publication number: CN109738703A discloses a high-voltage broadband impedance measurement device and its control method, the high-voltage broadband impedance measurement device mainly includes a high-voltage broadband voltage disturbance injection device, a voltage and current signal processing unit, and a broadband impedance calculation and monitoring system. The high-voltage broadband voltage disturbance injection device adopts a two-stage transformer mode of industrial frequency step-down transformer + multi-winding phase-shifting transformer to take power from the high-voltage side, and each winding on the secondary side of the multi-winding phase-shifting transformer is connected to an AC / DC / AC power unit; the AC / DC / AC power unit is composed of a three-phase controllable full bridge, a DC side capacitor and a single-phase H bridge; the disturbance injection device is connected in series to the high-voltage side line of the new energy power generation equipment to be tested through a broadband step-up transformer, and the three-phase controllable full bridge of the voltage disturbance injection device adopts rectification / feedback control, and its output adopts open-loop control considering the DC side voltage fluctuation. The present invention can meet the demand for online measurement of broadband output impedance characteristics of power electronic equipment such as photovoltaic, wind power, and reactive power compensation.

[0005] The Chinese patent application, with application number: CN202010975113.9 and publication number: CN112260263A, discloses a method and device for measuring the impedance of an onshore doubly-fed wind farm through a traditional DC transmission system, which relates to the technical field of renewable energy power generation and transmission systems, and is used to achieve impedance measurement of an onshore doubly-fed wind farm through a traditional DC transmission system, providing a reliable and accurate data basis for stability analysis. The scheme is as follows: obtain the structural parameters of the doubly-fed wind farm subsystem; based on the structural parameters, control parameters and related steady-state values ​​of the given doubly-fed wind farm subsystem, calculate the wind farm impedance value Z at a specific frequency f wf (s). Obtain the output active power P of the traditional DC transmission subsystem and the output reactive power Q of the traditional DC transmission subsystem. Calculate the impedance value Z of the traditional DC transmission subsystem at a specific frequency f. LCC (s); Z wf (s) and Z LCC (s) Perform impedance cascade and obtain the total impedance value of the entire onshore double-fed wind farm through the traditional DC transmission system at a specific frequency f.

[0006] However, the above-mentioned prior art relies on complex rectification, inversion and corresponding energy storage and voltage stabilization equipment. The power frequency voltage carrier in the system will cause frequency shift to produce a band gap, which cannot achieve low-cost and high-precision measurement of impedance compared to the present invention. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention discloses an online active measurement device, method and application of broadband impedance of a wind power generation system, and the technical solution thereof is as follows:

[0008] A wind power generation system broadband impedance online active measurement device comprises a module 1 for realizing energy consumption, a module 2 for realizing broadband impedance measurement function, a module 3 for realizing voltage level conversion, and a module 4; the characteristics are as follows:

[0009] The module 1 is a set of anti-parallel thyristors and energy-consuming resistors: when the wind power generation system generates power surplus due to a fault, the thyristors are turned on and the energy-consuming resistors are put into use to consume the surplus energy and realize fault ride-through, and are in standby mode under normal circumstances;

[0010] The module 2 is connected in series with the module 1, and includes an energy-consuming resistor and a bidirectional switch in parallel: the bidirectional switch is composed of a set of anti-series power electronic switches and corresponding freewheeling diodes, and the power electronic switch is used to receive a control signal generated by a microprocessor to generate a disturbance current for measuring impedance;

[0011] The module 3 includes a transformer, which reduces the wind power system voltage at the access point of the energy-consuming functional module to the working voltage of the device, so as to reduce the requirements on the rated voltage level, heat dissipation and insulation level of the modules 1 and 2;

[0012] Module 4 includes a current transformer CT, a voltage transformer PT and a microprocessor: the current transformer CT is installed on the wind farm side of the device grid-connected point to measure the disturbance current injection situation on the wind power system side; the voltage transformer PT is placed at the grid-connected point of the energy consumption device to measure the voltage signal at that point.

[0013] The present invention also discloses an online active measurement method of broadband impedance, comprising the online active measurement device of broadband impedance of a wind power generation system according to any one of claims 1 to 2, characterized in that it comprises the following steps:

[0014] Step 1: Obtain the broadband impedance applicable to the wind farm through an online active measurement device for broadband impedance of a wind power generation system;

[0015] Step 2: Use an inverse linear frequency modulation PWM (RC-PWM) signal to control the AC chopper;

[0016] Step 3: Analyze the working state of the anti-series IGBT to obtain the interference current and response voltage; obtain the disturbance current i generated by the bridge arm under the control of the positive and negative cycle RC-PWM signal of the voltage respectively. d (t);

[0017] Step 4: Use fast Fourier transform to obtain the impedance value without the influence of band gap.

[0018] The invention also discloses an online measurement method for broadband impedance applied to a wind power generation system of a wind farm.

[0019] Beneficial Effects

[0020] 1) The disturbance signal generating device does not require complicated rectification, inversion and corresponding energy storage and voltage stabilization equipment, and can be realized by simply modifying the inherent energy consumption devices of the wind farm, thereby reducing the cost.

[0021] 2) The proposed RC-PWM control signal makes the disturbance current evenly distributed within the wide frequency band required for testing, avoiding the frequency band gap caused by the frequency shift caused by the power frequency voltage carrier.

[0022] 3) Modular transformation can flexibly adjust the switching groups according to the actual response and control the amplitude of the injected signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the wind power system of the present invention;

[0024] Figure 2 (a) is a typical AC chopper topology of the present invention; Figure 2 (b) Improved AC chopper with active impedance measurement (single-phase view); Figure 2 (c) is a schematic diagram of the bridge arm connected in Δ connection or Y connection.

[0025] Figure 3 Interference current and amplitude-frequency characteristics under RC-PWM signal and CPWM signal control:

[0026] (a) Chirp signal and CPWM signal;

[0027] (b) RC-PWM signal; amplitude-frequency characteristics;

[0028] (c) CPWM signal;

[0029] (d) Disturbance current generated by CPWM signal;

[0030] (e) RC-PWM signal;

[0031] (f) Disturbance current generated by RC-PWM signal;

[0032] Figure 4 (a) In the first stage, the system voltage is in a positive cycle, and the IGBT receives a turn-on command; (b) In the second stage, the system voltage is in a positive cycle, and the IGBT receives a turn-off command; (c) In the third stage, the system voltage is in a negative cycle, and the IGBT receives a turn-on command; (d) In the fourth stage, the system voltage is in a negative cycle, and the IGBT receives a turn-off command;

[0033] Figure 5 (a) Background voltage U m0 Waveform; (b) U m0 Spectrum; (c) Background current I m0 Waveform (d) I m0 Spectrum;

[0034] Figure 6 (a) Disturbance current i d Waveform; (b)i d Spectrum; (c) Response voltage U r Waveform; (d) U r Spectrum. DETAILED DESCRIPTION

[0035] A device for online active measurement of broadband impedance of a wind power generation system comprises a module 1 for realizing energy consumption, a module 2 for realizing broadband impedance measurement function, and modules 3 and 4 for realizing voltage level conversion. Figure 2 The impedance measurement and energy consumption functions are Figure 2 (b) Module A on the right is completed. In practical applications, it can be used as a bridge arm to connect to the wind power generation system in a Δ connection or a Y connection. Since the wind power generation system is three-phase symmetrical, the three-phase system can be analyzed as three single-phase systems respectively. The present invention uses the single-phase device view as an example for explanation. Module A is composed of module 1 for realizing energy consumption, module 2 for realizing broadband impedance measurement function, and module 3 for realizing voltage level conversion to reduce costs. Module 1 is a group of anti-parallel thyristors and energy-consuming resistors. When the wind power generation system generates power surplus due to faults such as short circuits, the thyristors are turned on and the energy-consuming resistors are put into use to consume surplus energy and realize fault crossing. Under normal circumstances, it is cold standby. Module 2 is composed of an energy-consuming resistor and a bidirectional switch in parallel, and then connected in series with module 1. The bidirectional switch is composed of a group of high-performance power electronic switches (such as IGBT) connected in anti-series and corresponding freewheeling diodes. The high-performance power electronic switch is used to receive the control signal generated by the microprocessor to generate a disturbance current for measuring impedance. Module 3 is composed of a transformer, which reduces the wind power system voltage at the access point of the energy consumption device to the working voltage of the device to reduce the requirements for the rated voltage level, heat dissipation and insulation of modules 1 and 2. Module 4 is composed of a current transformer CT, a voltage transformer PT and a high-performance microprocessor. The current transformer CT is installed on the wind farm side of the device grid connection point to measure the disturbance current injection on the wind power system side. If the grid side impedance needs to be measured, a current transformer can be added on the grid side of the grid connection point. The voltage transformer PT is placed at the grid connection point of the transformed energy consumption device to measure the voltage signal at that point. The measurement signals are all transmitted to the local microprocessor. When the voltage amplitude continues to rise and exceeds the threshold, the microprocessor triggers module 1 to start the energy consumption function. The microprocessor is also used to generate a control signal for impedance measurement, and generates a corresponding disturbance signal through module 2. In addition, after the disturbance signal is injected into the wind power system, the CT and PT transformers in module 3 are used to obtain the disturbance signal and response signal information on the wind farm side. After the microprocessor performs frequency domain analysis and response calculation, the broadband impedance information on the wind power system side (if necessary, the grid side) can be obtained.

[0036] On the basis of the above, the present invention discloses an online measurement method of broadband impedance, which is characterized by:

[0037] The steps include:

[0038] Step 1: Obtain the broadband impedance applicable to the wind farm through the broadband impedance online active measurement device of the wind power generation system:

[0039] Figure 1 This is a topology diagram of a conventional wind power system, in which wind turbines collect energy and then send it out through a centralized booster station. In order to solve the low-voltage ride-through problem caused by short-circuit faults, a grid-connected energy-consuming device is often configured in the wind power system. The energy-consuming device is located between the booster transformer and the grid side to consume surplus energy in the event of a fault.

[0040] The structure of energy consumption device in wind power generation system is as follows Figure 2 As shown in (a), these choppers are grouped and connected in parallel on the bus. When a short circuit occurs, they are put into use in groups in turn to consume surplus energy. However, under normal operating conditions, energy-consuming devices are idle most of the time, which is not conducive to improving the utilization rate of power grid assets. Therefore, the present invention transforms the structure of the chopper group, integrates the active impedance measurement function while realizing the fault crossing function of the energy-consuming device. By injecting a controlled broadband small signal current into the system and measuring the response on the wind power system side or the system side, broadband impedance modeling of the wind power system side and the power grid side can be achieved.

[0041] The impedance measurement and energy consumption functions are completed by module A on the right. In practical applications, it can be used as a bridge arm to connect to the wind power generation system in Δ connection or Y connection. Since the wind power generation system is three-phase symmetrical, the three-phase system can be analyzed as three single-phase systems respectively. The present invention uses the single-phase device view as an example for explanation. Module A is composed of module 1 for realizing energy consumption, module 2 for realizing broadband impedance measurement function, and module 3 for realizing voltage level conversion to reduce costs. Module 1 is a group of anti-parallel thyristors and energy-consuming resistors. When the wind power generation system generates power surplus due to faults such as short circuit, the thyristors are turned on and the energy-consuming resistors are put into use to consume surplus energy and realize fault crossing. Under normal circumstances, it is cold standby. Module 2 is composed of energy-consuming resistors and bidirectional switches in parallel, and then connected in series with module 1. The bidirectional switch is composed of a group of high-performance power electronic switches (such as IGBT) connected in reverse series and corresponding freewheeling diodes. The high-performance power electronic switch is used to receive the control signal generated by the microprocessor to generate a disturbance current for measuring impedance. Module 3 is composed of a transformer, which reduces the wind power system voltage at the access point of the energy consumption device to the working voltage of the device to reduce the requirements for the rated voltage level, heat dissipation and insulation of modules 1 and 2. Module 4 is composed of a current transformer CT, a voltage transformer PT and a high-performance microprocessor. The current transformer CT is installed on the wind farm side of the device grid connection point to measure the disturbance current injection on the wind power system side. If the grid side impedance needs to be measured, a current transformer can be added on the grid side of the grid connection point. The voltage transformer PT is placed at the grid connection point of the modified energy consumption device to measure the voltage signal at that point. The measurement signals are all transmitted to the local microprocessor. When the voltage amplitude continues to rise and exceeds the threshold, the microprocessor triggers module 1 to start the energy consumption function. The microprocessor is also used to generate a control signal for impedance measurement, and generates a corresponding disturbance signal through module 2. In addition, after the disturbance signal is injected into the wind power system, the CT and PT transformers in module 3 are used to obtain the disturbance signal and response signal information on the wind farm side. After the microprocessor performs frequency domain analysis and response calculation, the broadband impedance information on the wind power system side (if necessary, the grid side) can be obtained.

[0042] Step 2: Control the AC chopper using an inverted linear frequency modulated PWM (RC-PWM) signal

[0043] The impedance of wind power system is generally measured using CPWM as the disturbance signal, which is a variable frequency pulse width modulation (chirp-PWM, CPWM) based on variable frequency sinusoidal signal. The harmonic components of CPWM signal are mostly distributed in 10-50Hz. The harmonic components outside the set frequency band are relatively large compared with the variable signal, and the harmonic energy distribution is not concentrated enough; the uniformity of harmonic amplitude distribution is poor, so when injecting broadband current interference, it is easy to appear the frequency band gap caused by the shift of the power frequency voltage carrier spectrum. Use CPWM signal to carry out disturbance current measurement test in the frequency band of 1500-3000Hz. Figure 3 (d) shows the CPWM signal and its corresponding interference current. It can be seen that when CPWM is used as the disturbance signal, a large number of frequency band gaps will appear.

[0044] To avoid this situation, an RC-PWM signal is needed to control the AC chopper. This signal is based on a linear chirp wave with a linear time-varying frequency, and the frequency can be expressed as:

[0045] g chirp =sin(2πf min t+π(f max -f min )t / T) (1)

[0046] Among them, g chirp is the signal frequency; f min is the minimum system frequency; f max is the maximum system frequency; T is the disturbance injection time. The CPWM signal is obtained by the shaping function. The shaping function is chirp If it is greater than 0, it is converted to 1, otherwise it is converted to 0:

[0047]

[0048] Furthermore, the RC-PWM signal can be obtained through the phase-locked inversion function, and the "0-1" inversion is achieved when the positive and negative poles of the input voltage are switched:

[0049]

[0050] or

[0051]

[0052] Figure 3 (ab) show the spread spectrum of the RC-PWM signal generated by the improved AC chopper and its corresponding interference current. When the positive and negative poles of the input voltage are switched, the former will increase g chirp Converted to 1, otherwise to 0. The latter realizes "0-1" inversion when the positive and negative polarity of the input voltage switches. Figure 3 Comparison between (c) and (f) shows that compared with the CPWM control method, the RC-PWM control signal is used to transfer the spectrum shift to the control signal, thereby avoiding the band gap caused by the spectrum shift effect of the power frequency voltage on the control signal, avoiding the secondary measurement caused by the band gap, and realizing full-band disturbance injection of all resolvable frequencies in the controllable disturbance band.

[0053] Step 3: Analyze the working state of the anti-series IGBT to obtain the interference current and response voltage

[0054] exist Figure 4 In the first topological stage shown in (a), the system is in the positive voltage cycle, the IGBT receives the opening command, T4, R1, IGBT2, and T2 are connected to the operating circuit, and the response current i generated by module 2 in the positive voltage cycle can be measured by the current transformer. d , at this time the device outputs a positive disturbance current. In this case, the disturbance current can be expressed as:

[0055]

[0056] Among them, i d (t) is the disturbance current, u(t) is the system voltage signal, g(t) is the signal for controlling the IGBT, and represents the amplitude of the injected current affected by R1 and R2. r It can be measured directly by a voltage transformer.

[0057] exist Figure 4 In the second topological stage shown in (b), the system is in a positive voltage cycle, the IGBT receives a shutdown command, T4, R1, and R2 are connected to the operating circuit, and no disturbance current is input to the system. d =0.

[0058] exist Figure 4 In the third topological stage shown in (c), the system is in a negative voltage cycle, the IGBT receives the turn-on command, T3, R1, T1, and IGBT2 are connected to the operating circuit, and the measuring device outputs a negative disturbance current. In this case, the disturbance current can be expressed as:

[0059]

[0060] exist Figure 4 In the third topological stage shown in (d), the system is in a negative voltage cycle, the IGBT receives the turn-on command, T3, R1, and R2 are connected to the operating circuit, and no disturbance current is input to the system. d =0.

[0061] Step 4: Use fast Fourier transform technology to obtain the impedance value without the influence of band gap

[0062] In actual operation, the harmonic components of various frequencies contained in the original power transmission system will affect the accuracy of the measurement results. On the one hand, accurate impedance measurement results can be obtained by increasing the amplitude of the disturbance signal to improve the signal-to-noise ratio;

[0063] First, the voltage transformer PT and the current transformer CT in the device module 4 can be used to measure the background signal U of the normal operation of the system. m0 ,I m0 Without interfering.

[0064] Secondly, when the microprocessor injects the disturbance signal RC-PWM into the impedance measurement device, the disturbance current I can be measured by the voltage transformer PT and the current transformer CT. d And the response voltage U r .

[0065] After obtaining the background noise, response voltage and disturbance current, the fast Fourier transform technology can be used to quickly calculate the impedance value and obtain the measured impedance. Its transfer function is:

[0066]

[0067] Among them U m0 (jω),I m0 (jω) is the system background noise; U r (jω) is the inverter response voltage; I d (jω) is the interference current generated by the bridge arm controlled by the RC-PWM signal.

[0068] The present invention proposes an online active measurement device and method for broadband impedance of a wind power generation system. By transforming the energy consumption device of the wind power system, real-time measurement of the grid impedance of the wind power system and the transmission system is achieved. In combination with an RC-PWM control strategy, an RC-PWM signal is obtained by forming a function and locking an inverse function, thereby achieving fast and high-precision broadband impedance measurement.

[0069] The present invention modulates the energy-consuming resistor switch to generate chopping current by modifying the energy-consuming device of the wind power system, and injects the required broadband interference signal into the system, and obtains the impedance characteristics of the system by measuring the interference current injected into the system and its corresponding voltage. The real-time impedance measurement of the wind power system side and the power grid side is realized; fast and high-precision broadband impedance measurement is realized, and the proposed signal generation device and method avoid the frequency band gap caused by the spectrum shift caused by the power frequency carrier.

[0070] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. An online active measurement method of a broadband impedance online active measurement device for a wind power generation system, the online active measurement device comprising a module 1 for realizing energy consumption, a module 2 for realizing broadband impedance measurement function, a module 3 for realizing voltage level conversion, and a module 4; The module 1 is a set of anti-parallel thyristors and energy-consuming resistors: when the wind power generation system generates power surplus due to a fault, the thyristors are turned on and the energy-consuming resistors are put into use to consume the surplus energy and realize fault ride-through, and are in standby mode under normal circumstances; The module 2 is connected in series with the module 1, and includes an energy-consuming resistor and a bidirectional switch in parallel: the bidirectional switch is composed of a set of anti-series power electronic switches and corresponding freewheeling diodes, and the power electronic switch is used to receive a control signal generated by a microprocessor to generate a disturbance current for measuring impedance; The module 3 includes a transformer, which reduces the wind power system voltage at the access point of the energy-consuming functional module to the working voltage of the online active measurement device, so as to reduce the requirements on the rated voltage level, heat dissipation and insulation level of the modules 1 and 2; Module 4 includes a current transformer CT, a voltage transformer PT and a microprocessor: the current transformer CT is installed at the wind farm side of the device grid connection point to measure the disturbance current injection situation on the wind power system side; the voltage transformer PT is placed at the energy consumption device grid connection point to measure the voltage signal at the energy consumption device grid connection point; The voltage signals at the grid connection point of the energy consumption device are all transmitted to the local microprocessor. When the voltage amplitude continues to rise and exceeds the threshold, the microprocessor triggers module 1 to start the energy consumption function. The microprocessor is also used to generate a control signal for impedance measurement, and generates a corresponding disturbance signal through module 2. In addition, after the disturbance signal is injected into the wind power system, the current transformer CT and the voltage transformer PT in module 4 are used to obtain the disturbance signal and response signal information on the wind farm side. After the microprocessor performs frequency domain analysis and response calculation, the broadband impedance information on the wind power system side can be obtained, which is characterized by: The steps include: Step 1: Obtain the broadband impedance applicable to the wind farm through an online active measurement device for broadband impedance of a wind power generation system; Step 2: Use the inverted linear frequency modulation RC-PWM signal to control the AC chopper; Step 3: Analyze the working state of the anti-series IGBT to obtain the interference current and response voltage; obtain the disturbance current generated by the bridge arm under the control of the positive and negative cycle RC-PWM signal of the voltage respectively. ; Step 4: Use fast Fourier transform to obtain the impedance value without the influence of band gap; The step 2 further includes the following contents: The AC chopper is controlled by an RC-PWM signal, which is based on a linear chirp wave with a linear time-varying frequency. The frequency can be expressed as: ； in, is the signal frequency; is the minimum system frequency; is the maximum system frequency; is the disturbance injection time; the CPWM signal is obtained by the shaping function, which is If it is greater than 0, it is converted to 1, otherwise it is converted to 0: ； The RC-PWM signal is obtained by the phase-locked inversion function, and the "0-1" inversion is achieved when the positive and negative poles of the input voltage are switched: or 。 2. The online active measurement method of the broadband impedance online active measurement device of a wind power generation system according to claim 1 is characterized by: The step 4 further includes the following contents: firstly, the voltage transformer PT and the current transformer CT of the module 4 in the online active measurement device are used to measure the background signal of the normal operation of the system. , without interfering; Secondly, when the microprocessor injects the disturbance signal RC-PWM into the impedance measurement device, the disturbance current at this time is measured using the voltage transformer PT and the current transformer CT. And the response voltage ; Thirdly, after obtaining the background noise, response voltage and disturbance current, the fast Fourier transform technology is used to quickly calculate the impedance value, and the measured impedance can be obtained. Its transfer function is: ； in is the system background noise; is the inverter response voltage; It is the interference current generated by the RC-PWM signal controlling the bridge arm.

3. The wind power generation system of the wind farm is characterized by: An online active measurement method comprising the online active measurement device for broadband impedance of a wind power generation system as described in any one of claims 1-2.

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