General testing device and method for weak grid adaptability of power electronic grid-connected equipment

Abstract

This invention discloses a general testing device and method for the weak grid adaptability of power electronic grid-connected equipment, including a converter module, a main control module, an input transformer, and an output transformer. The converter module includes a rectifier circuit unit and its filter circuit, and an inverter circuit unit and its filter circuit. The main control module controls the converter module and includes a rectifier control unit, an inverter control unit, and a host computer that are communicatively connected to each other. The rectifier control unit is connected to the rectifier circuit unit, and the inverter control unit is connected to the inverter circuit unit. The rectifier control unit and the inverter control unit receive and execute input commands from the host computer to adjust the operating state of the converter module. The inverter control unit is based on the equivalent grid impedance transfer function of a generalized second-order integrator. Using this invention, a wide-frequency domain simulation of AC grid impedance can be achieved, greatly improving the test accuracy.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to a general testing device and method for the weak grid adaptability of power electronic grid-connected equipment. Background Technology

[0002] In recent years, with the increasing penetration rate of new energy sources, the power system stability problems caused by the interaction between new energy grid-connected equipment and the power grid have become increasingly serious. Specifically, new energy power generation systems, mainly photovoltaic and wind power, are mostly distributed in a decentralized manner, and are often located in remote areas such as deserts and islands. They are usually connected to the grid through long-distance transmission and distribution lines. In this case, the system line impedance often changes the impedance characteristics of the power grid, causing the power grid to exhibit wide-frequency domain weak grid characteristics, affecting the operating performance of grid-connected equipment, and thus causing stability problems such as system oscillations. Therefore, wide-frequency domain high-precision simulation devices are urgently needed for grid adaptability testing of new energy grid-connected equipment before it is put into operation.

[0003] For example, Chinese patent document CN116223948A discloses a functional testing system for low-voltage photovoltaic grid-connected equipment. By simulating the photovoltaic grid-connection process, it effectively evaluates functions such as islanding protection and grid-connection management on the generation side during the photovoltaic grid-connection process, thereby achieving the goal of improving the reliability of grid-connected operation.

[0004] Chinese patent document CN114977283A discloses a method, system and equipment for testing the ultimate short-circuit ratio of grid-connected new energy power generation equipment. Based on a simulation model, voltage disturbance simulation tests are conducted to obtain the minimum line impedance value under voltage disturbance and the corresponding power value, making the obtained minimum line impedance value more accurate and better applicable to scenarios where new energy is connected to a weak power grid.

[0005] However, existing power grid simulation techniques often oversimplify the power grid, treating it as an infinitely strong grid and ignoring the influence of grid impedance. Summary of the Invention

[0006] This invention provides a general testing device and method for the weak grid adaptability of power electronic grid-connected equipment. By using a generalized second-order integrator to simulate the AC grid impedance in a wide frequency domain, it can greatly improve the test frequency domain and test accuracy.

[0007] A general testing device for the weak grid adaptability of power electronic grid-connected equipment includes a converter module, a main control module, an input transformer, and an output transformer; the input transformer is connected to the AC grid, and the output transformer is connected to the device under test; The converter module includes a rectifier circuit unit and its filter circuit, and an inverter circuit unit and its filter circuit. The main control module is used to control the converter module, including a rectifier control unit, an inverter control unit, and a host computer that are interconnected; the rectifier control unit is connected to the rectifier circuit unit, and the inverter control unit is connected to the inverter circuit unit; The rectifier control unit and the inverter control unit receive and execute input commands from the host computer to adjust the operating state of the converter module; the inverter control unit is based on the equivalent grid impedance transfer function of the generalized second-order integrator.

[0008] Furthermore, the host computer is configured as follows: Receives the user-defined raw reference voltage value and mains impedance parameters, where the mains impedance parameters include the equivalent inductance. and equivalent resistance ; The grid impedance parameters are output to the inverter control unit. Real-time display of impedance simulation frequency domain response characteristics.

[0009] Furthermore, the inverter control unit is further configured as follows: Collect the current value at the PCC point The PCC point is located between the output transformer and the device under test. Based on PCC point current value Equivalent power grid impedance transfer function Calculate the dynamic voltage compensation component ; Based on the original reference voltage value and dynamic voltage compensation component Generate PCC point reference voltage ; Based on PCC point reference voltage Measured voltage at PCC point The capacitor current of the filter circuit is used to generate the final modulated signal of the inverter unit; A PWM modulation signal is generated by comparing the final modulation signal of the inverter unit with the carrier signal.

[0010] Furthermore, the equivalent grid impedance transfer function Specifically: ; ; in, For equivalent inductance, Equivalent resistance; For the complex frequency variable in the Laplace transform, The transfer function of the generalized second-order integrator. It is the resonant angular frequency; It is the cutoff angular frequency.

[0011] Furthermore, the dynamic voltage compensation component is calculated. The formula is: ; in, is the complex frequency variable in the Laplace transform.

[0012] Furthermore, the reference voltage at point PCC The formula is: ; in, is the complex frequency variable in the Laplace transform.

[0013] Furthermore, based on the PCC point reference voltage Measured voltage at PCC point The capacitor current of the filter circuit is used to generate the final modulated signal of the inverter unit. The specific process is as follows: Calculate the reference voltage at PCC point Compared with the measured voltage The difference between them; The difference is input to the voltage controller to generate a preliminary modulation signal; Introducing capacitor current feedforward compensation in the filter circuit: The final modulation signal is generated by multiplying the initial modulation signal by the capacitor current value of the filter circuit corresponding to the inverter circuit unit by a proportional coefficient and then subtracting the result.

[0014] A general test method for the weak grid adaptability of power electronic grid-connected equipment, using the aforementioned general test device for the weak grid adaptability of power electronic grid-connected equipment, includes the following steps: (1) No-load normal operation: With the device under test disconnected from the test device, set the original reference voltage value through the host computer and record the actual voltage value of the PCC point output by the test device; (2) Normal operation under load: During the test, the original reference voltage setting should be consistent with the normal no-load operation. The device under test should be set to unity power factor control for a duration of not less than 30 minutes. Record the measured voltage value at the PCC point of the test device output and the measured current value at the PCC point of the device under test. If the device under test is disconnected from the grid during the test, record the test duration and the disconnection time of the device under test. (3) No-load test operation: With the device under test disconnected from the test device, the original reference voltage value, grid impedance parameters and generalized second-order integrator parameters are set through the host computer, and the measured voltage value of the PCC point output by the test device is recorded. (4) Load test operation: During the test, the original reference voltage value, grid impedance parameters and generalized second-order integrator parameters should be consistent with the no-load test operation. The device under test is set to unity power factor control. The resonant angular frequency of the generalized second-order integrator is adjusted from the no-load test operation value and gradually increased in 10% increments. Each increment should last at least 20s. The measured voltage value at the PCC point of the test device output and the measured current value at the PCC point of the device under test are recorded. If the device under test is disconnected from the grid during the test, the test duration and the disconnection time of the device under test are recorded.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The universal testing device and method for weak grid adaptability of power electronic grid-connected equipment based on a second-order generalized integrator (SOGI) proposed in this invention can effectively simulate grid impedance without explicit differentiation operations, thus avoiding the bandwidth-limited first-order low-pass filter (LPF) used in existing methods. Comparative analysis shows that the impedance simulation method based on SOGI can not only achieve accurate impedance simulation, but also reflect weak grid characteristics over a wider frequency range than the traditional LPF method. This method is simple to implement and is more suitable for engineering applications than methods based on transmission line models. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is an overall framework diagram of the universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to the present invention.

[0018] Figure 2 This is a schematic diagram of the operation of the inverter control unit in an embodiment of the present invention.

[0019] Figure 3 The simulation results show a comparison between the traditional method and the method of this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that, unless otherwise specified, the features in the following embodiments and implementation methods can be combined with each other.

[0022] like Figure 1 As shown, a general testing device for the weak grid adaptability of power electronic grid-connected equipment includes a converter module, a main control module, an input transformer, an output transformer, and the device under test.

[0023] The converter module includes a rectifier circuit unit and its filter circuit, and an inverter circuit unit and its filter circuit. The main control module controls the converter module and includes a rectifier control unit, an inverter control unit, and a host computer. The rectifier control unit is connected to the rectifier circuit unit, and the inverter control unit is connected to the inverter circuit unit. The host computer is communicatively connected to both the rectifier control unit and the inverter control unit, and the rectifier control unit is also communicatively connected to the inverter control unit. The rectifier control unit and the inverter control unit receive and execute input commands from the host computer to adjust the operating state of the converter module.

[0024] The host computer is configured to: receive the user-set raw reference input (raw reference voltage value) and grid impedance parameters; output the grid impedance parameters to the inverter control unit; and display the impedance analog frequency domain response characteristics in real time.

[0025] In this invention, the inverter control unit is based on the equivalent grid impedance transfer function of the generalized second-order integrator, such as... Figure 2 As shown, the inverter control unit is further configured as follows: S1, Collect the current value at PCC point The PCC point is located between the output transformer and the device under test.

[0026] S2, based on the PCC point current value Equivalent power grid impedance transfer function Calculate the dynamic voltage compensation component .

[0027] Equivalent power grid impedance transfer function Specifically: ; ; in, For equivalent inductance, Equivalent resistance; For the complex frequency variable in the Laplace transform, The transfer function of the generalized second-order integrator. It is the resonant angular frequency; It is the cutoff angular frequency.

[0028] S3, based on the original reference voltage value and dynamic voltage compensation component Generate PCC point reference voltage .

[0029] Calculate dynamic voltage compensation components The formula is: ; in, is the complex frequency variable in the Laplace transform.

[0030] PCC point reference voltage The formula is: ; in, is the complex frequency variable in the Laplace transform.

[0031] S4, based on PCC point reference voltage Measured voltage at PCC point The capacitor current of the filter circuit, together with the current of the capacitor, generates the final modulated signal of the inverter unit. The specific process is as follows: Calculate the reference voltage at PCC point Compared with the measured voltage The difference between them; The difference is input to the voltage controller to generate a preliminary modulation signal; Introducing capacitor current feedforward compensation in the filter circuit: The final modulation signal is generated by multiplying the initial modulation signal by the capacitor current value of the filter circuit corresponding to the inverter circuit unit by a proportional coefficient and then subtracting the result.

[0032] S5 generates a PWM modulation signal based on the comparison between the final modulation signal of the inverter unit and the carrier signal.

[0033] A general test method for the weak grid adaptability of power electronic grid-connected equipment, using the aforementioned general test device for the weak grid adaptability of power electronic grid-connected equipment, includes the following steps: (1) No-load normal operation: With the device under test disconnected from the test device, set the original reference voltage value through the host computer and record the actual voltage value of the PCC point output by the test device; (2) Normal operation under load: During the test, the original reference voltage setting should be consistent with the normal no-load operation. The device under test should be set to unity power factor control for a duration of not less than 30 minutes. Record the measured voltage value at the PCC point of the test device output and the measured current value at the PCC point of the device under test. If the device under test is disconnected from the grid during the test, record the test duration and the disconnection time of the device under test. (3) No-load test operation: With the device under test disconnected from the test device, the original reference voltage value, grid impedance parameters and generalized second-order integrator parameters are set through the host computer, and the measured voltage value of the PCC point output by the test device is recorded. (4) Load test operation: During the test, the original reference voltage value, grid impedance parameters and generalized second-order integrator parameters should be consistent with the no-load test operation. The device under test is set to unity power factor control. The resonant angular frequency of the generalized second-order integrator is adjusted from the no-load test operation value and gradually increased in 10% increments. Each increment should last at least 20s. The measured voltage value at the PCC point of the test device output and the measured current value at the PCC point of the device under test are recorded. If the device under test is disconnected from the grid during the test, the test duration and the disconnection time of the device under test are recorded.

[0034] like Figure 3 As shown in the figure, (a) presents the experimentally measured PCC voltage waveform and its FFT results using the conventional method; Figure (b) presents the PCC voltage and its FFT analysis results obtained using the method of this invention. It can be seen that the time-domain waveform obtained using the conventional method shows no significant harmonic distortion at high frequencies, while the PCC voltage obtained using the method of this invention exhibits slight resonance at 1850Hz. This proves that the simulation bandwidth achievable by this method is at least 1850Hz. Therefore, compared with the conventional method, the method of this invention can accurately simulate the power grid impedance characteristics over a wider frequency range.

[0035] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A universal testing device for the adaptability of power electronic grid-connected equipment to weak power grids, characterized in that, It includes a converter module, a main control module, an input transformer, and an output transformer; the input transformer is connected to the AC power grid, and the output transformer is connected to the device under test; The converter module includes a rectifier circuit unit and its filter circuit, and an inverter circuit unit and its filter circuit. The main control module is used to control the converter module, including a rectifier control unit, an inverter control unit, and a host computer that are interconnected; the rectifier control unit is connected to the rectifier circuit unit, and the inverter control unit is connected to the inverter circuit unit; The rectifier control unit and the inverter control unit receive and execute input commands from the host computer to adjust the operating state of the converter module; the inverter control unit is based on the equivalent grid impedance transfer function of the generalized second-order integrator.

2. The universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to claim 1, characterized in that, The host computer is configured as follows: Receives the user-defined raw reference voltage value and mains impedance parameters, where the mains impedance parameters include the equivalent inductance. and equivalent resistance ; The grid impedance parameters are output to the inverter control unit. Real-time display of impedance simulation frequency domain response characteristics.

3. The universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to claim 2, characterized in that, The inverter control unit is further configured to: Collect the current value at the PCC point The PCC point is located between the output transformer and the device under test. Based on PCC point current value Equivalent power grid impedance transfer function Calculate the dynamic voltage compensation component ; Based on the original reference voltage value and dynamic voltage compensation component Generate PCC point reference voltage ; Based on PCC point reference voltage Measured voltage at PCC point The capacitor current of the filter circuit is used to generate the final modulated signal of the inverter unit; A PWM modulation signal is generated by comparing the final modulation signal of the inverter unit with the carrier signal.

4. The universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to claim 3, characterized in that, Equivalent power grid impedance transfer function Specifically: ； ； in, For equivalent inductance, Equivalent resistance; For the complex frequency variable in the Laplace transform, The transfer function of the generalized second-order integrator. It is the resonant angular frequency; It is the cutoff angular frequency.

5. The universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to claim 3, characterized in that, Calculate dynamic voltage compensation components The formula is: ； in, is the complex frequency variable in the Laplace transform.

6. The universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to claim 3, characterized in that, PCC point reference voltage The formula is: ； in, is the complex frequency variable in the Laplace transform.

7. The universal testing device for the weak grid adaptability of power electronic grid-connected equipment according to claim 3, characterized in that, Based on PCC point reference voltage Measured voltage at PCC point The capacitor current of the filter circuit is used to generate the final modulated signal of the inverter unit. The specific process is as follows: Calculate the reference voltage at PCC point Compared with the measured voltage The difference between them; The difference is input to the voltage controller to generate a preliminary modulation signal; Introducing capacitor current feedforward compensation in the filter circuit: The final modulation signal is generated by multiplying the initial modulation signal by the capacitor current value of the filter circuit corresponding to the inverter circuit unit by a proportional coefficient and then subtracting the result.

8. A general test method for the adaptability of power electronic grid-connected equipment to weak power grids, characterized in that, The general testing device for weak grid adaptability of power electronic grid-connected equipment according to any one of claims 1 to 7 includes the following steps: (1) No-load normal operation: With the device under test disconnected from the test device, set the original reference voltage value through the host computer and record the actual voltage value of the PCC point output by the test device; (2) Normal operation under load: During the test, the original reference voltage setting should be consistent with the normal no-load operation. The device under test should be set to unity power factor control for a duration of not less than 30 minutes. Record the measured voltage value at the PCC point of the test device output and the measured current value at the PCC point of the device under test. If the device under test is disconnected from the grid during the test, record the test duration and the disconnection time of the device under test. (3) No-load test operation: With the device under test disconnected from the test device, the original reference voltage value, grid impedance parameters and generalized second-order integrator parameters are set through the host computer, and the measured voltage value of the PCC point output by the test device is recorded. (4) Load test operation: During the test, the original reference voltage value, grid impedance parameters and generalized second-order integrator parameters should be consistent with the no-load test operation. The device under test is set to unity power factor control. The resonant angular frequency of the generalized second-order integrator is adjusted from the no-load test operation value and gradually increased in 10% increments. Each increment should last at least 20s. The measured voltage value at the PCC point of the test device output and the measured current value at the PCC point of the device under test are recorded. If the device under test is disconnected from the grid during the test, the test duration and the disconnection time of the device under test are recorded.

Images