Start-stop control method for impedance test power supply of grid-connected converter of new energy

Abstract

The application discloses a start-stop control method of a new energy grid-connected converter impedance test power supply, and belongs to the technical field of power electronic testing. The method is designed in view of the safety problems such as overvoltage and impact current that are easily generated in the switching process of the impedance test power supply based on the open-winding structure of a wide-frequency coupling transformer, and detailed start logic and switching-out logic are designed. The control method avoids the safety hazards such as high voltage and impact current generated in the start and switching-out processes of the test power supply by coordinating the action time sequence of the low-voltage switch K 1, short-circuit switch K 2, relay K 3 and combining the freewheeling resistor R and zero vector buffering technology; meanwhile, a quasi-proportional resonant (QPR) control algorithm is adopted to guarantee the accuracy of wide-frequency impedance measurement. The application makes up for the core defects of the lack of switching safety control in the prior art, realizes high safety and reliability in the test process, and is suitable for impedance characteristic tests of various new energy grid-connected converters.

Description

Technical Field

[0001] This invention belongs to the field of power electronics testing technology, specifically relating to a start-stop control method for a power supply for impedance testing of a new energy grid-connected converter. It is used to solve the safety control problem when the test power supply is connected / disconnected from the grid and the converter under test during the impedance characteristic testing of new energy grid-connected converters, thereby achieving high safety and reliability in the testing process while ensuring the accuracy of impedance measurement. Background Technology

[0002] Power electronic converters, serving as grid-connected interfaces for new energy power generation units, are increasingly being used in power systems, leading to a growing problem of broadband oscillations. Impedance characteristics are a core parameter for analyzing the dynamic interaction stability between the grid-connected converter and the power grid. Accurately measuring the broadband impedance characteristics of the grid-connected converter is crucial for assessing the stability of the grid-connected system and preventing oscillation problems.

[0003] Existing impedance measurement methods, such as the disturbance injection method and frequency scanning method based on linear transformers, mainly focus on the generation of disturbance signals, frequency coverage, or measurement accuracy optimization, but generally neglect the safety control issues of the switching process of the test power supply and grid-connected circuit.

[0004] The paper "Measurement Method of Frequency Coupling Characteristics of Wideband Grid-Connected Inverters Using Multi-Sinusoidal Signal Injection," published by Nian Heng, Li Meng, Chen Liang, et al. in the November 20, 2020 issue of the *Proceedings of the Chinese Society for Electrical Engineering* (Vol. 40, No. 22), proposes an impedance measurement method based on model predictive control and multi-sinusoidal signal injection. However, the paper lacks a systematic safety logic design for the switching process of the test power supply and lacks a protection mechanism against the risks of inrush current or open-circuit overvoltage that may occur during transformer coupling injection.

[0005] The patent "Impedance Measurement Method for Adaptive Control of Disturbance Frequency and Disturbance Amplitude" (Announcement No.: CN110456161B), authorized by Li Fei, Huang Yao, Liu Yang, and others on June 1, 2021, proposes an impedance measurement method that adapts to changes in the system operating point by adjusting the frequency and amplitude of the disturbance signal in real time. However, this patent only focuses on the adaptive optimization of the disturbance signal and does not involve the safety logic of the test power supply switching process, lacking a detailed protection mechanism against the risks of inrush current or open-circuit overvoltage.

[0006] In summary, the existing technology has the following problems: (1) In actual testing scenarios, the test power supply needs to be connected in series with the grid-connected converter of the new energy under test and the power grid through a wideband coupling transformer. Since the wideband coupling transformer has an open winding structure, if there is a lack of systematic switching logic, instantaneous overvoltage is very likely to occur when the test power supply is connected or disconnected. The voltage amplitude can soar from tens of volts during normal operation to thousands of volts, leading to safety accidents such as transformer winding breakdown, damage to the converter under test, and even personal injury.

[0007] (2) Existing impedance measurement technologies rarely have start-stop control methods and switching logic methods specifically for the test power supply of impedance characteristics of grid-connected converters for new energy sources. This cannot solve the above-mentioned safety hazards and restricts the engineering application of the test technology. Summary of the Invention

[0008] To overcome the shortcomings of the existing technology, this invention proposes a start-stop control method for impedance test power supply of new energy grid-connected converters. It proposes a start-stop control logic based on zero vector, and achieves safe and reliable connection and disconnection of test power supply and grid-connected circuit by optimizing the switching sequence, so as to ensure the safety of equipment and personnel. At the same time, the quasi-proportional resonance (QPR) control algorithm ensures the accuracy of impedance measurement, and the control is simple and easy to implement in engineering.

[0009] The technical solution of the present invention is as follows.

[0010] A start-stop control method for an impedance test power supply of a new energy grid-connected converter, the method involving a circuit system including a test power supply, a wideband coupling transformer, and a loop A consisting of the new energy grid-connected converter and the power grid connected in series; the wideband coupling transformer is composed of three single-phase wideband coupling transformers; the test power supply consists of a DC power supply, a PWM rectifier, and a bridge arm-side LCL filter connected in series, with a relay installed at the other end of the filter. K 3. The test power supply passes through this relay. K 3. Connect / disconnect to the primary side of the broadband coupling transformer; a low-voltage switch is installed at the output terminal of the secondary side of the broadband coupling transformer. K 1. The wideband coupling transformer passes through this low-voltage switch. K 1. Enables connection / disconnection of circuit A; a current-limiting resistor is connected in parallel across both ends of each phase winding on the primary side of the broadband coupling transformer. R Current limiting resistor R With short circuit switch K 2 Parallel connection, short-circuit switch K 2 Control current limiting resistor R The input and output; Includes the following steps: Step 1: Check the initial state of the circuit system to ensure the low-voltage switch... K1. Short-circuit switch K 2 and relays K All three are in the open state, then the short-circuit switch is closed. K 2. Put the circuit system into an initial standby state; Step 2: According to the set startup logic, connect the test power supply in series with circuit A through a wideband coupling transformer, and then perform impedance characteristic test on the new energy grid-connected converter according to Step 3. Step 3: Following the established disturbance test method, control the test power supply to output disturbance voltage and simultaneously acquire the port voltage of the new energy grid-connected converter. u a , u b , u c and the secondary current flowing through the broadband coupling transformer i a , i b , i c For the collected u a , u b , u c and i a , i b , i c The impedance characteristics of the new energy grid-connected converter are calculated by performing a Fourier transform. Step 4: According to the set cut-out logic, disconnect the test power supply, wideband coupling transformer and circuit A to complete the power-off cut-out of the test power supply.

[0011] Preferably, the startup logic set in step 2 specifically includes the following steps: Step 2.1: Perform a power supply operation on the grid side to put the circuit system into a pre-powered state; Step 2.2: Close the low-voltage switch on the secondary side of the broadband coupling transformer. K 1; Step 2.3: Start the new energy grid-connected converter to bring it into working condition; Step 2.4: Power on the DC power supply of the test power supply to put the test power supply into the output standby state; Step 2.5, close the relay. K 3. After a delay of Y1, control the PWM rectifier to emit a zero vector; Step 2.6, disconnect the short-circuit switch. K2. After a delay of Y2, the PWM rectifier is controlled to output the disturbance voltage waveform required for normal testing in a soft-start mode, thus completing the power-on of the test power supply.

[0012] Preferably, the disturbance test method set in step 3 specifically includes the following steps: Step 3.1, determine the disturbance frequency range F, where F is [ f min , f max ],in f min For minimum disturbance frequency, f max The maximum disturbance frequency is defined; N frequency test points d are set in frequency segments within the disturbance frequency range F. n n is the frequency test point d n The sequence numbers, n=1,2,...,N; Step 3.2: Control the test power supply and sequentially test at frequency test point d. n The output sinusoidal voltage disturbance is recorded, and the frequency of the sinusoidal voltage disturbance is denoted as the disturbance frequency. f n ; Step 3.3: Collect the port voltage of the new energy grid-connected converter. u a , u b , u c and the secondary current flowing through the broadband coupling transformer i a , i b , i c ; Step 3.4, process the collected data. u a , u b , u c and i a , i b , i c Performing a Fourier transform yields the result at the perturbation frequency. f n Below, the voltage amplitude per phase at the port of the grid-connected converter for new energy sources. U n and phase Current amplitude per phase I n and phase The amplitude of the impedance of the grid-connected converter for new energy sources was calculated. and phase The calculation formula is: ; Step 3.5: Following steps 3.2 to 3.4, traverse all frequency test points d. n N perturbation frequencies are obtained. f n The magnitudes of N impedances and phase Then with perturbation frequency f n The x-axis represents the amplitude. and phase Using the vertical axis as the ordinate, the impedance characteristic curve of the new energy grid-connected converter is plotted in a plane coordinate system, and the impedance characteristic of the new energy grid-connected converter in a wide frequency band is evaluated through the impedance characteristic curve.

[0013] Preferably, the method for controlling the output disturbance voltage of the test power supply in step 3 is as follows: Set the setpoint for the phase voltage on the secondary side of the wideband coupling transformer. u a_ref , u b_ref , u c_ref And sample the corresponding actual phase voltage on the secondary side in real time. u a0 , u a0 , u a0 As a voltage feedback value; The error signal between the voltage setpoint and the voltage feedback value of each phase on the secondary side of the broadband coupled transformer is processed by a quasi-proportional resonant control algorithm to obtain the output signal. m a , m b , m c Output signal m a , m b , m c The PWM rectifier of the test power supply is driven to make the feedback value track the given value, and after stabilization, the voltage feedback value is output as the voltage response at the grid connection point. The transfer function G(s) of the quasi-proportional resonance control algorithm is:

[0014] in, K p This is the proportionality coefficient.K r The resonance coefficient, ω c The cutoff frequency, s For the Laplace operator, ω n It is the resonant angular frequency. ω n =2π f n ; By adjusting the resonant angular frequency ω n To adjust the frequency of the sinusoidal voltage disturbance f n .

[0015] Preferably, the cut-out logic set in step 4 specifically includes the following steps: Step 4.1: Control the PWM rectifier to gradually reduce the modulation to zero, and control the DC power supply voltage of the test power supply to drop to 0. Step 4.2, close the short-circuit switch K 2. To create a current loop in the primary winding of the broadband coupling transformer; Step 4.3: After a delay of Y3, block the PWM wave; Step 4.4: Disconnect the relay after a delay of Y4. K 3; Step 4.5: Turn off the grid-connected converter for new energy sources and disconnect the low-voltage switch. K 1 and short circuit switch K 2. Perform a power outage operation on the grid side.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. A detailed start-stop control method for the series wideband coupling transformer structure was designed, which effectively avoids the danger of open circuit of the wideband coupling transformer during operation and ensures the safety of equipment and personnel.

[0017] 2. By adopting the QPR control strategy, high-precision, low-distortion tracking and output of sinusoidal disturbance voltage at various frequency points can be achieved over a wide frequency band, laying the foundation for obtaining an accurate impedance model.

[0018] 3. The designed input and output method has good adaptability and is also applicable to other methods for measuring the impedance characteristics of new energy converters, so as to ensure the safety of equipment and personnel. Attached Figure Description

[0019] Figure 1 This is a topology diagram of the circuit system involved in this invention.

[0020] Figure 2 This is the overall flowchart of the present invention.

[0021] Figure 3 The startup logic designed for this invention.

[0022] Figure 4 The cut-out logic designed for this invention.

[0023] Figure 5 This is a block diagram of the power supply control principle of the present invention (taking phase a as an example).

[0024] Figure 6 This is a waveform diagram of the secondary side of the wideband coupling transformer when the test power is switched on, as shown in this invention.

[0025] Figure 7 This is a waveform diagram of the secondary side of the wideband coupling transformer when the test power supply is switched off, as shown in the present invention.

[0026] Figure 8 This is a curve showing the wideband impedance characteristics of a new energy grid-connected converter obtained from actual testing. Detailed Implementation

[0027] The embodiments of the present invention will now be described with reference to the accompanying drawings and specific examples.

[0028] Figure 1 The diagram shown is a topology of the circuit system involved in this invention. Figure 1 As can be seen, the circuit system involved in the measurement method includes a test power supply, a wideband coupling transformer, and a loop A consisting of the grid-connected converter of the new energy source under test and the power grid connected in series. The wideband coupling transformer is composed of three single-phase wideband coupling transformers. The test power supply consists of a DC power supply, a PWM rectifier, and a bridge arm-side LCL filter connected in series. A relay is installed at the other end of the filter. K 3. The test power supply passes through this relay. K 3. Connect / disconnect to the primary side of the broadband coupling transformer; a low-voltage switch is installed at the output terminal of the secondary side of the broadband coupling transformer. K 1. The wideband coupling transformer passes through this low-voltage switch. K 1. Enables connection / disconnection of circuit A; a current-limiting resistor is connected in parallel across both ends of each phase winding on the primary side of the broadband coupling transformer. R Current limiting resistor R With short circuit switch K 2 Parallel connection, short-circuit switch K 2 Control current limiting resistor R The input and output.

[0029] exist Figure 1In the above diagram, T1, T2, and T3 represent three single-phase wideband coupling transformers, R represents three current-limiting resistors, L1 and L2 are filter inductors, C is a filter capacitor, and U... dc R is the voltage of the DC power supply. g L is the line resistance. g This refers to the line inductance.

[0030] Figure 2 This is a flowchart of the method of the present invention. Figure 3 The startup logic designed for this invention, Figure 4 The cutout logic designed for this invention, Figure 5 This is the control diagram of the test power supply in this invention, by Figure 2 , Figure 3 , Figure 4 and Figure 5 As can be seen, the start-stop control method of the impedance test power supply for a new energy grid-connected converter of the present invention includes the following steps: Step 1: Check the initial state of the circuit system to ensure the low-voltage switch... K 1. Short-circuit switch K 2 and relays K All three are in the open state, then the short-circuit switch is closed. K 2. Put the circuit system into an initial standby state.

[0031] Step 2: According to the set startup logic, connect the test power supply in series with circuit A through a wideband coupling transformer, and then perform impedance characteristic test on the new energy grid-connected converter according to Step 3.

[0032] In this embodiment, the set startup logic specifically includes the following steps: Step 2.1: Perform a power supply operation on the grid side to put the circuit system into a pre-powered state; Step 2.2: Close the low-voltage switch on the secondary side of the broadband coupling transformer. K 1; Step 2.3: Start the new energy grid-connected converter to bring it into working condition; Step 2.4: Power on the DC power supply of the test power supply to put the test power supply into the output standby state; Step 2.5, close the relay. K 3. After a delay of Y1, control the PWM rectifier to emit a zero vector; Step 2.6, disconnect the short-circuit switch. K 2. After a delay of Y2, the PWM rectifier is controlled to output the disturbance voltage waveform required for normal testing in a soft-start mode, thus completing the power-on of the test power supply.

[0033] In this embodiment, Y1 is set to 1 second and Y2 is set to 30 seconds.

[0034] Step 3: Following the established disturbance test method, control the test power supply to output disturbance voltage and simultaneously acquire the port voltage of the new energy grid-connected converter. u a , u b , u c and the secondary current flowing through the broadband coupling transformer i a , i b , i c For the collected u a , u b , u c and i a , i b , i c The impedance characteristics of the new energy grid-connected converter are calculated by performing a Fourier transform.

[0035] In this embodiment, the disturbance test method set in step 3 specifically includes the following steps: Step 3.1, determine the disturbance frequency range F, where F is [ f min , f max ],in f min For minimum disturbance frequency, f max The maximum disturbance frequency is defined; N frequency test points d are set in frequency segments within the disturbance frequency range F. n n is the frequency test point d n The sequence numbers, n=1,2,...,N; Step 3.2: Control the test power supply and sequentially test at frequency test point d. n The output sinusoidal voltage disturbance is recorded, and the frequency of the sinusoidal voltage disturbance is denoted as the disturbance frequency. f n ; Step 3.3: Collect the port voltage of the new energy grid-connected converter. u a , u b , u c and the secondary current flowing through the broadband coupling transformer i a , i b ,i c ; Step 3.4, process the collected data. u a , u b , u c and i a , i b , i c Performing a Fourier transform yields the result at the perturbation frequency. f n Below, the voltage amplitude per phase at the port of the grid-connected converter for new energy sources. U n and phase Current amplitude per phase I n and phase The amplitude of the impedance of the grid-connected converter for new energy sources was calculated. and phase The calculation formula is: ; Step 3.5: Following steps 3.2 to 3.4, traverse all frequency test points d. n N perturbation frequencies are obtained. f n The magnitudes of N impedances and phase Then with perturbation frequency f n The x-axis represents the amplitude. and phase Using the vertical axis as the ordinate, the impedance characteristic curve of the new energy grid-connected converter is plotted in a plane coordinate system, and the impedance characteristic of the new energy grid-connected converter in a wide frequency band is evaluated through the impedance characteristic curve.

[0036] In this embodiment, the method for controlling the output disturbance voltage of the test power supply in step 3 is as follows: Set the setpoint for the phase voltage on the secondary side of the wideband coupling transformer. u a_ref , u b_ref , u c_ref And sample the corresponding actual phase voltage on the secondary side in real time. u a0 , u a0 , u a0 As a voltage feedback value; The error signal between the voltage setpoint and the voltage feedback value of each phase on the secondary side of the broadband coupled transformer is processed by a quasi-proportional resonant control algorithm to obtain the output signal. m a , m b , m c Output signal m a , m b , m c The PWM rectifier of the test power supply is driven to make the feedback value track the given value, and after stabilization, the voltage feedback value is output as the voltage response at the grid connection point. The transfer function G(s) of the quasi-proportional resonance control algorithm is:

[0037] in, K p This is the proportionality coefficient. K r The resonance coefficient, ω c The cutoff frequency, s For the Laplace operator, ω n It is the resonant angular frequency. ω n =2π f n ; By adjusting the resonant angular frequency ω n To adjust the frequency of the sinusoidal voltage disturbance f n .

[0038] In this embodiment, the minimum perturbation frequency f min =1Hz, maximum disturbance frequency f max =2kHz.

[0039] In this embodiment, the N frequency test points d n The settings are as follows: We set N=46, meaning we set 46 frequency test points in the disturbance frequency range F, as follows: In the [1Hz-10Hz] frequency band, 10 frequency test points are set at equal intervals of 1Hz, namely: 1Hz, 2Hz, 3Hz, 4Hz, 5Hz, 6Hz, 7Hz, 8Hz, 9Hz, and 10Hz. In the [10Hz-100Hz] frequency band, except for the fundamental frequency which is blank, 8 frequency test points are set at equal intervals of 10Hz, namely: 20Hz, 30Hz, 40Hz, 60Hz, 70Hz, 80Hz, 90Hz, and 100Hz. In the [100Hz-1000Hz] frequency band, 18 frequency test points are set at equal intervals of 50Hz, namely: 150Hz, 200Hz, 250Hz, 300Hz, 350Hz, 400Hz, 450Hz, 500Hz, 550Hz, 600Hz, 650Hz, 700Hz, 750Hz, 800Hz, 850Hz, 900Hz, 950Hz, and 1000Hz. In the [1000Hz-2000Hz] frequency band, 10 frequency test points are set at equal intervals of 100Hz, namely: 1100Hz, 1200Hz, 1300Hz, 1400Hz, 1500Hz, 1600Hz, 1700Hz, 1800Hz, 1900Hz, and 2000Hz.

[0040] Step 4: According to the set cut-out logic, disconnect the test power supply, wideband coupling transformer and circuit A to complete the power-off cut-out of the test power supply.

[0041] In this embodiment, the cut-out logic set in step 4 specifically includes the following steps: Step 4.1: Control the PWM rectifier to gradually reduce the modulation to zero, and control the DC power supply voltage of the test power supply to drop to 0. Step 4.2, close the short-circuit switch K 2. To create a current loop in the primary winding of the broadband coupling transformer; Step 4.3: After a delay of Y3, block the PWM wave; Step 4.4: Disconnect the relay after a delay of Y4. K 3; Step 4.5: Turn off the grid-connected converter for new energy sources and disconnect the low-voltage switch. K 1 and short circuit switch K 2. Perform a power outage operation on the grid side.

[0042] In this embodiment, Y3 is set to 1 second and Y4 is set to 2 seconds. Figure 6 This is a waveform diagram of the secondary side of the broadband coupling transformer when the test power is switched on, according to the present invention. Figure 7 This is a waveform diagram of the secondary side of the broadband coupling transformer when the test power supply is switched off, as per the present invention. Figure 6 , Figure 7 It can be seen that the connection and disconnection of the test power supply device are relatively smooth, which proves the effectiveness of the proposed connection and disconnection control method.

[0043] Figure 8 The selected frequency band is [10Hz-1000Hz], which is a part of the broadband impedance characteristic curve obtained by the method in step 3.

Claims

1. A start-stop control method for an impedance test power supply for a new energy grid-connected converter, the circuit system involved in the method including a test power supply, a wideband coupling transformer, and a loop A consisting of the new energy grid-connected converter and the power grid connected in series; the wideband coupling transformer is composed of three single-phase wideband coupling transformers; the test power supply consists of a DC power supply, a PWM rectifier, and a bridge arm-side LCL filter connected in series, and a relay is installed at the other end of the filter. K 3. The test power supply passes through this relay. K 3. Connect / disconnect to the primary side of the broadband coupling transformer; a low-voltage switch is installed at the output terminal of the secondary side of the broadband coupling transformer. K 1. The wideband coupling transformer passes through this low-voltage switch. K 1. Enables connection / disconnection of circuit A; a current-limiting resistor is connected in parallel across both ends of each phase winding on the primary side of the broadband coupling transformer. R Current limiting resistor R With short circuit switch K 2 Parallel connection, short-circuit switch K 2 Control current limiting resistor R The input and output; Its features are, The start / stop control method includes the following steps: Step 1: Check the initial state of the circuit system to ensure the low-voltage switch... K 1. Short-circuit switch K 2 and relays K All three are in the open state, then the short-circuit switch is closed. K 2. Put the circuit system into an initial standby state; Step 2: According to the set startup logic, connect the test power supply in series with circuit A through a wideband coupling transformer, and then perform impedance characteristic test on the new energy grid-connected converter according to Step 3. Step 3: Following the established disturbance test method, control the test power supply to output disturbance voltage and simultaneously acquire the port voltage of the new energy grid-connected converter. u a , u b , u c and the secondary current flowing through the broadband coupling transformer i a , i b , i c For the collected u a , u b , u c and i a , i b , i c The impedance characteristics of the new energy grid-connected converter are calculated by performing a Fourier transform. Step 4: According to the set cut-out logic, disconnect the test power supply, wideband coupling transformer and circuit A to complete the power-off cut-out of the test power supply.

2. The start-stop control method for an impedance test power supply of a new energy grid-connected converter according to claim 1, characterized in that, The startup logic set in step 2 specifically includes the following steps: Step 2.1: Perform a power supply operation on the grid side to put the circuit system into a pre-powered state; Step 2.2: Close the low-voltage switch on the secondary side of the broadband coupling transformer. K 1; Step 2.3: Start the new energy grid-connected converter to bring it into working condition; Step 2.4: Power on the DC power supply of the test power supply to put the test power supply into the output standby state; Step 2.5, close the relay. K 3. After a delay of Y1, control the PWM rectifier to emit a zero vector; Step 2.6, disconnect the short-circuit switch. K 2. After a delay of Y2, the PWM rectifier is controlled to output the disturbance voltage waveform required for normal testing in a soft-start mode, thus completing the power-on of the test power supply.

3. The start-stop control method for an impedance test power supply for a new energy grid-connected converter according to claim 1, characterized in that, The disturbance test method set in step 3 specifically includes the following steps: Step 3.1, determine the disturbance frequency range F, where F is [ f min , f max ],in f min For minimum disturbance frequency, f max The maximum disturbance frequency is defined; N frequency test points d are set in frequency segments within the disturbance frequency range F. n n is the frequency test point d n The sequence numbers, n=1,2,...,N; Step 3.2: Control the test power supply and sequentially test at frequency test point d. n The output sinusoidal voltage disturbance is recorded, and the frequency of the sinusoidal voltage disturbance is denoted as the disturbance frequency. f n ; Step 3.3: Collect the port voltage of the new energy grid-connected converter. u a , u b , u c and the secondary current flowing through the broadband coupling transformer i a , i b , i c ; Step 3.4, process the collected data. u a , u b , u c and i a , i b , i c Performing a Fourier transform yields the result at the perturbation frequency. f n Below, the voltage amplitude per phase at the port of the grid-connected converter for new energy sources. U n and phase Current amplitude per phase I n and phase The amplitude of the impedance of the grid-connected converter for new energy sources was calculated. and phase The calculation formula is: ； Step 3.5: Following steps 3.2 to 3.4, traverse all frequency test points d. n N perturbation frequencies are obtained. f n The magnitudes of N impedances and phase Then with perturbation frequency f n The x-axis represents the amplitude. and phase Using the vertical axis as the ordinate, the impedance characteristic curve of the new energy grid-connected converter is plotted in a plane coordinate system, and the impedance characteristic of the new energy grid-connected converter in a wide frequency band is evaluated through the impedance characteristic curve.

4. The start-stop control method for an impedance test power supply of a new energy grid-connected converter according to claim 3, characterized in that, The method for controlling the output disturbance voltage of the test power supply in step 3 is as follows: Set the setpoint for the phase voltage on the secondary side of the wideband coupling transformer. u a_ref , u b_ref , u c_ref And sample the corresponding actual phase voltage on the secondary side in real time. u a0 , u a0 , u a0 As a voltage feedback value; The error signal between the voltage setpoint and the voltage feedback value of each phase on the secondary side of the broadband coupled transformer is processed by a quasi-proportional resonant control algorithm to obtain the output signal. m a , m b , m c Output signal m a , m b , m c The PWM rectifier of the test power supply is driven to make the feedback value track the given value, and after stabilization, the voltage feedback value is output as the voltage response at the grid connection point. The transfer function G(s) of the quasi-proportional resonance control algorithm is: in, K p This is the proportionality coefficient. K r The resonance coefficient, ω c The cutoff frequency, s For the Laplace operator, ω n It is the resonant angular frequency. ω n =2π f n ; By adjusting the resonant angular frequency ω n To adjust the frequency of the sinusoidal voltage disturbance f n .

5. The start-stop control method for an impedance test power supply for a new energy grid-connected converter according to claim 2, characterized in that, The cut-out logic set in step 4 specifically includes the following steps: Step 4.1: Control the PWM rectifier to gradually reduce the modulation to zero, and control the DC power supply voltage of the test power supply to drop to 0. Step 4.2, close the short-circuit switch K 2. To create a current loop in the primary winding of the broadband coupling transformer; Step 4.3: After a delay of Y3, block the PWM wave; Step 4.4: Disconnect the relay after a delay of Y4. K 3; Step 4.5: Turn off the grid-connected converter for new energy sources and disconnect the low-voltage switch. K 1 and short circuit switch K 2. Perform a power outage operation on the grid side.

Images