Converter load test device based on PI regulator and control method thereof

Abstract

The invention belongs to the technical field of current transformer load test, and particularly relates to a current transformer load test device based on a PI regulator and a control method thereof, and the device comprises a DC power supply module, a PWM inversion module, an LCL voltage stabilization filtering module and a PWM rectification feedback module. An energy closed-loop path is constructed through a PWM rectification feedback module, a three-phase full-control MOSFET bridge and a unit power factor control strategy (setting q-axis modulation voltage Vgq = 0) are adopted, and a PI regulator with a proportionality coefficient Kp1 = 1.0 and an integral coefficient Ki1 = 0.8 is matched to accurately regulate grid-side d-axis current igd, so that rectification-side current and voltage are in the same phase, and the synchronous rectification efficiency is greatly improved; meanwhile, feedback energy is buffered through a direct-current bus capacitor Cdc, impact of energy fluctuation on a direct-current bus is avoided, and finally electric energy originally dissipated in a load test is efficiently fed back to the direct-current power supply module.

Description

Technical Field

[0001] This invention belongs to the field of converter load testing technology, specifically relating to a converter load testing device and its control method based on a PI regulator. Background Technology

[0002] With the rapid development of power electronics technology, the performance and reliability testing of converters, as the core devices for power conversion, is of paramount importance. Load testing is a necessary step in evaluating key indicators such as the load-carrying capacity, output waveform quality, dynamic response, and efficiency of converters. Traditional converter load testing devices often use resistive or electronic loads to consume electrical energy, which dissipates as heat during the test. This not only causes serious energy waste but also requires a high-power cooling system, leading to increased device size and operating costs. These drawbacks are particularly pronounced in high-power, long-term testing scenarios.

[0003] To address energy consumption issues, some technologies have attempted to introduce energy feedback functionality. However, existing feedback devices have significant shortcomings: on the one hand, they mostly employ uncontrolled rectification or simple PWM rectification topologies, resulting in low feedback efficiency and high harmonic content in grid-side current, which can easily interfere with the power grid or DC bus; on the other hand, they lack suitable filtering and isolation designs, which cannot effectively filter out high-frequency harmonics from the converter output to ensure test accuracy, nor can they achieve voltage matching and electrical isolation under different test conditions, posing potential test safety hazards. Summary of the Invention

[0004] To address the aforementioned shortcomings of the prior art, this invention provides a converter load testing device and its control method based on a PI regulator.

[0005] In a first aspect, the present invention provides a converter load testing device based on a PI regulator, comprising: DC power supply module, used to provide controllable DC bus voltage; The PWM inverter module, whose DC side is connected in parallel with the DC power supply module, is used to convert DC power into three-phase AC power. The LCL voltage regulator and filter module has its input terminal connected to the AC side of the PWM inverter module to filter out high-frequency harmonics. The isolation transformer module has its primary side connected to the output of the LCL voltage regulator and filter module to achieve electrical isolation and voltage matching. The load and measurement module, whose input terminal is connected to the secondary side of the isolation transformer module, is used to simulate a variable load and acquire voltage and current signals; The sampling module is used to collect the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module in real time. The PWM rectifier feedback module has its AC side connected in parallel with the secondary side of the isolation transformer module, and its DC side connected in parallel with the positive and negative buses of the DC power supply module. It is used to synchronously rectify AC energy and feed it back to the DC bus. The digital control unit has its input connected to the sampling module and its output connected to the drive terminals of the PWM inverter module and the PWM rectifier feedback module, respectively. It is used to execute the dual closed-loop PI control algorithm and generate SVPWM drive signals.

[0006] Further improvements to this technical solution include the following: the PWM rectification feedback module includes: The three-phase fully controlled MOSFET bridge has its AC side terminals a, b, and c connected in parallel with the secondary side terminals of the isolation transformer module. The DC bus capacitor Cdc has its positive terminal connected to the positive bus of the DC power module and its negative terminal connected to the negative bus of the DC power module, and is used to buffer the feedback energy. The PI controller, with a proportional coefficient Kp1=1.0 and an integral coefficient Ki1=0.8, is used to control the grid-side d-axis current igd relative to the setpoint igd. ref The error is adjusted and the d-axis feedback modulation voltage Vgd is output; The SVPWM modulator is used to generate six PWM signals by performing an inverse Park transformation on Vgd and the q-axis feedback modulation voltage Vgq=0, so as to drive the three-phase fully controlled MOSFET bridge to achieve unity power factor synchronous rectification and efficiently feed the load test energy back to the DC bus.

[0007] Further improvements to this technical solution include a sampling module that includes: A voltage Hall sensor, whose input terminal is connected in parallel with the three-phase output terminals of the load and measurement module, is used to isolate and attenuate the three-phase voltage Uabc in a 100:1 ratio; The current Hall sensor, which is perforated and connected to the three-phase output cable of the load and measurement module, is used to convert the three-phase current Iabc into a voltage signal at a ratio of 50mV / A. A 14-bit synchronous ADC, whose input is connected to the output of a voltage Hall sensor and a current Hall sensor, is used to synchronously digitize Uabc and Iabc at a sampling rate of 16 kHz and provide real-time feedback data to the digital control unit.

[0008] In a second aspect, the present invention provides a control method for the converter load testing device based on a PI regulator as described in any one of the above claims, comprising: S1. Start the device and complete the initialization preparation, set the output voltage of the DC power module and the initial load parameters of the load and measurement module; S2. The digital control unit obtains the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module through the sampling module, executes the dual closed-loop PI control algorithm to generate SVPWM drive signal, drives the PWM inverter module to convert DC power into three-phase AC power, and after the LCL voltage stabilization and filtering module filters out high-frequency harmonics, it transmits the power to the load and measurement module through the isolation transformer module. S3. The digital control unit performs synchronous rectification control on the PWM rectification feedback module. Based on the electrical signal collected by the sampling module, it adjusts the working state of the PWM rectification feedback module and rectifies the AC energy consumed by the load and measurement module into DC power and feeds it back to the DC bus of the DC power supply module. S4, the load and measurement module simulates dynamic load changes according to the set parameters, and simultaneously collects voltage and current data during the test to realize the monitoring and data recording of the converter load test.

[0009] Further improvements to this technical solution include step S1, which includes: S101. Start the DC power supply module, set its output voltage to 50V DC voltage, and provide a stable and controllable DC bus voltage. S102. Initialize the load and measurement module, set the initial load parameters to a variable resistor with a resistance range of 0 to 10Ω, to simulate dynamic load changes from 0 to 2A, and to calibrate the sampling accuracy of the voltage and current sensors. S103. Set the initial parameters of the system through the digital control unit, including PI controller parameters, switching frequency of 8kHz, sampling frequency of 16kHz, and complete the self-test and synchronization preparation of each module.

[0010] Further improvements to this technical solution include step S2, which includes: S201, The sampling module collects the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module in real time; S202. Perform Clark transformation on the collected three-phase current Iabc to convert it into current components in the stationary coordinate system α-β. and ; S203. Perform a Park transform on the current component after the Clark transform to decouple it into a DC component in the rotating coordinate system dq. and ; S204. The error between Ud and the given voltage value Ud_ref is adjusted by the voltage outer loop PI controller. The proportional coefficient Kp2=0.61 and integral coefficient Ki2=0.89 of the voltage outer loop PI controller, and the output is the d-axis current command id_ref as the current inner loop. S205, via the current inner loop PI controller Error with id_ref and The error with iq_ref is adjusted. The proportional coefficient Kp3=1.602 and integral coefficient Ki3=1.498 of the current inner loop PI controller, and the modulation voltages Vd' and Vq' in the dq coordinate system are output. S206. Perform inverse Park transform and inverse Clark transform on Vd' and Vq' to generate a three-phase modulated signal; S207. The modulation signal is compared with the triangular carrier at a switching frequency of 8kHz by the SVPWM modulator to generate 6 PWM drive signals to drive the MOSFET switching devices of the PWM inverter module. S208: The inverter output is filtered by the LCL voltage regulator and filter module to remove high-frequency harmonics, and then transmitted to the load and measurement module after electrical isolation and voltage matching are achieved through the isolation transformer module.

[0011] Further improvements to this technical solution include the Clark transform, expressed by the formula: ; in, , The current component in the stationary coordinate system α-β is expressed in amperes. , , The instantaneous current values ​​for phases A, B, and C are respectively, in amperes; The Park transformation can be expressed by the following formula: ; in, , The current is expressed in amperes in the rotating coordinate system dq. The rotation angle is generated by the phase-locked loop synchronizing the grid voltage phase, in radians.

[0012] Further improvements to this technical solution include the inverse Park transform being expressed by the following formula: ; The inverse Clark transform is expressed by the formula: ; in, , , The generated three-phase modulated voltage is expressed in volts.

[0013] Further improvements to this technical solution include step S3, which includes: S301, The sampling module collects the three-phase AC current signal ig_abc from the rectifier side in real time; S302. Perform Clark and Park transformations on ig_abc to convert it into DC quantities igd and igq in the rotating coordinate system dq. S303. The error between igd and the given current value igd_ref is adjusted by a PI regulator. The proportional coefficient Kp1=1.0 and the integral coefficient Ki1=0.8 of the PI regulator. The output d-axis feedback modulation voltage Vgd is set, and the q-axis modulation voltage Vgq=0 is set to achieve unity power factor control. S304. Perform inverse Park transform and inverse Clark transform on Vgd and Vgq to generate a three-phase feedback modulation signal; S305 generates 6 PWM signals through the SVPWM modulator to drive the three-phase fully controlled MOSFET bridge of the PWM rectification feedback module to achieve synchronous rectification, rectifying the AC energy consumed by the load and measurement module into DC power, and feeding it back to the DC bus of the DC power supply module.

[0014] Further improvements to this technical solution include step S4, which includes: S401, the load and measurement module simulates dynamic load changes according to the set parameters. The resistance value of the variable resistor is adjusted in the range of 0 to 10Ω to simulate the step or continuous change of the load current from 0 to 2A. S402. Real-time acquisition of three-phase voltage Uabc and three-phase current Iabc during the test process. Data is acquired through voltage and current sensors at a sampling frequency of 10kHz, and waveform, RMS value, frequency and harmonic content are recorded. The S403 digital control unit processes and analyzes the collected data, including calculating total harmonic distortion, dynamic response time, and energy feedback efficiency, and realizes data storage and visualization monitoring through the MATLAB / Simulink platform. S404. Adjust control parameters based on monitoring results.

[0015] The beneficial effects of this invention are as follows: This invention constructs an energy closed-loop path through a PWM rectification feedback module, employing a three-phase fully controlled MOSFET bridge and a unity power factor control strategy (assuming the q-axis modulation voltage Vgq=0). Combined with a PI regulator with a proportional coefficient Kp1=1.0 and an integral coefficient Ki1=0.8, it precisely adjusts the grid-side d-axis current igd, ensuring that the rectifier-side current and voltage are in phase, significantly improving synchronous rectification efficiency. Simultaneously, the DC bus capacitor Cdc buffers the feedback energy, preventing energy fluctuations from impacting the DC bus. Ultimately, the electrical energy originally dissipated during load testing is efficiently fed back to the DC power supply module, completely solving the drawbacks of traditional resistive / electronic loads' "heat dissipation." This reduces operating energy consumption while decreasing the need for high-power cooling systems, shrinking the device size, and lowering operating costs, making it particularly suitable for high-power, long-duration converter testing scenarios.

[0016] On the one hand, the present invention sets up an LCL voltage regulation and filtering module, which can effectively filter out high-frequency harmonics output by the PWM inverter module, avoiding the influence of harmonic interference on the test data. On the other hand, the digital control unit adopts a dual closed-loop PI control architecture of "voltage outer loop + current inner loop". It achieves precise current decoupling through Clark transformation (decoupling the three-phase current Iabc into α-β stationary coordinate system components) and Park transformation (converting it into dq rotating coordinate system DC quantity). Combined with parameter optimization of the voltage outer loop PI and the current inner loop PI, as well as SVPWM modulation with an 8kHz switching frequency, it ensures the stability of the amplitude and frequency of the three-phase AC output by the PWM inverter module, and significantly reduces the total harmonic distortion. In addition, the sampling module uses voltage Hall sensors, current Hall sensors and a 14-bit synchronous ADC to provide high-precision, real-time voltage / current feedback data for dual closed-loop control, further ensuring the accuracy and repeatability of the test results.

[0017] This invention incorporates an isolation transformer module between the LCL voltage regulation and filtering module and the load and measurement module. Electrical isolation is achieved through a linear transformer model, avoiding interference and safety hazards between the high and low voltage sides during testing. Simultaneously, the isolation transformer can adjust its turns ratio according to different converter testing requirements, achieving voltage matching between the primary side (adapting to inverter output) and the secondary side (adapting to load input), meeting testing requirements under multiple operating conditions, and solving the problems of existing feedback devices lacking isolation design and having poor voltage adaptability.

[0018] The load and measurement module simulates dynamic load changes (step or continuous changes) of 0-2A using a variable resistor (0-10Ω resistance range), accurately reproducing load fluctuation scenarios in actual converter operation. Simultaneously, this module collects test data in real time (voltage / current waveforms, RMS values, frequency, harmonic content). The digital control unit, combined with the MATLAB / Simulink platform, calculates and stores key indicators such as total harmonic distortion, dynamic response time, and energy feedback efficiency, and supports visual monitoring, facilitating intuitive evaluation of converter performance by testers. Furthermore, based on the monitoring results, the PI controller parameters can be dynamically adjusted to further optimize system control and enhance the flexibility and comprehensiveness of testing. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic block diagram of the simulation system corresponding to the converter load test device.

[0021] Figure 2 This is a block diagram of a DC-AC closed-loop control.

[0022] Figure 3 This is a block diagram of an AC-DC closed-loop control.

[0023] Figure 4 The waveforms of the three-phase voltage and three-phase current after inversion are shown.

[0024] Figure 5 The waveforms of the three-phase voltage and three-phase current before rectification are shown.

[0025] Figure 6 This is a schematic flowchart of the control method. Detailed Implementation

[0026] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the specific embodiments. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0028] like Figure 1 As shown, the present invention provides a converter load testing device based on a PI regulator, comprising: DC power supply module, used to provide controllable DC bus voltage; The PWM inverter module, whose DC side is connected in parallel with the DC power supply module, is used to convert DC power into three-phase AC power. The LCL voltage regulator and filter module has its input terminal connected to the AC side of the PWM inverter module to filter out high-frequency harmonics. The isolation transformer module has its primary side connected to the output of the LCL voltage regulator and filter module to achieve electrical isolation and voltage matching. The load and measurement module, whose input terminal is connected to the secondary side of the isolation transformer module, is used to simulate a variable load and acquire voltage and current signals; The sampling module is used to collect the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module in real time. The PWM rectifier feedback module has its AC side connected in parallel with the secondary side of the isolation transformer module, and its DC side connected in parallel with the positive and negative buses of the DC power supply module. It is used to synchronously rectify AC energy and feed it back to the DC bus. The digital control unit has its input connected to the sampling module and its output connected to the drive terminals of the PWM inverter module and the PWM rectifier feedback module, respectively. It is used to execute the dual closed-loop PI control algorithm and generate SVPWM drive signals.

[0029] Specifically, the PWM rectification feedback module includes: The three-phase fully controlled MOSFET bridge has its AC side terminals a, b, and c connected in parallel with the secondary side terminals of the isolation transformer module. The DC bus capacitor Cdc has its positive terminal connected to the positive bus of the DC power module and its negative terminal connected to the negative bus of the DC power module, and is used to buffer the feedback energy. The PI controller, with a proportional coefficient Kp1=1.0 and an integral coefficient Ki1=0.8, is used to control the grid-side d-axis current igd relative to the setpoint igd. ref The error is adjusted and the d-axis feedback modulation voltage Vgd is output; The SVPWM modulator is used to generate six PWM signals by performing an inverse Park transformation on Vgd and the q-axis feedback modulation voltage Vgq=0, so as to drive the three-phase fully controlled MOSFET bridge to achieve unity power factor synchronous rectification and efficiently feed the load test energy back to the DC bus.

[0030] In addition, the sampling module includes: A voltage Hall sensor, whose input terminal is connected in parallel with the three-phase output terminals of the load and measurement module, is used to isolate and attenuate the three-phase voltage Uabc in a 100:1 ratio; The current Hall sensor, which is perforated and connected to the three-phase output cable of the load and measurement module, is used to convert the three-phase current Iabc into a voltage signal at a ratio of 50mV / A. A 14-bit synchronous ADC, whose input is connected to the output of a voltage Hall sensor and a current Hall sensor, is used to synchronously digitize Uabc and Iabc at a sampling rate of 16 kHz and provide real-time feedback data to the digital control unit.

[0031] The overall simulation system architecture of the energy feedback converter load test device of the present invention is as follows: Figure 1 As shown, the system mainly consists of a DC power supply module, a PWM inverter module, an LCL voltage regulator and filter module, an isolation transformer module, a load and measurement module, a sampling module, a PWM rectification feedback module, and a digital control unit.

[0032] In practical implementation, the DC power supply module uses a 50V DC voltage source to provide a stable and controllable DC bus voltage for the system. The PWM inverter module adopts a three-phase full-bridge topology, using MOSFETs as switching devices, and its DC side is connected in parallel with the DC power supply module. The LCL voltage regulator and filter module is configured with an inductance of 1mH and a capacitance of 4.7μF. Its input is connected to the AC side of the PWM inverter module to filter out high-frequency harmonics. The isolation transformer module adopts a linear transformer model with a turns ratio of 1:1. Its primary side is connected to the output of the LCL voltage regulator and filter module to achieve electrical isolation and voltage matching. The load and measurement module uses variable resistors with a resistance range of 0-10Ω to simulate dynamic load changes of 0-2A and integrates voltage and current sensors. The sampling module includes a voltage Hall sensor (isolated and attenuated at a 100:1 ratio) and a current Hall sensor (converted at a 50mV / A ratio), which, together with a 14-bit synchronous ADC, acquires the three-phase voltage Uabc and three-phase current Iabc in real time at a sampling rate of 16kHz. The AC side of the PWM rectifier feedback module is connected in parallel with the secondary side of the isolation transformer module, and the DC side is connected in parallel with the positive and negative buses of the DC power supply module, forming an energy feedback path. The digital control unit uses a DSP processor with a built-in dual closed-loop PI control algorithm to generate SVPWM drive signals.

[0033] Closed-loop control strategy for DC-AC inverter circuits, such as Figure 2 As shown, the specific implementation steps are as follows: Signal acquisition and transformation: The sampling module acquires the three-phase voltage Uabc and three-phase current Iabc on the load side in real time; the three-phase current is converted into components in the stationary coordinate system α-β through Clark transformation; Park Transform Decoupling: The Park transform converts the α-β coordinate system components into DC components in the rotating coordinate system dq. Dual closed-loop PI control: The voltage outer loop PI controller (parameters Kp2=0.61, Ki2=0.89) adjusts the error between Ud and the given value Ud_ref (corresponding to the 32V line voltage), and outputs the d-axis current command id_ref. The current inner loop PI controller (parameters Kp1=1.602, Ki1=1.498) adjusts the error between id and id_ref, and the error between iq and iq_ref (assuming iq_ref=0), and outputs the modulation voltages Vd' and Vq'. Inverse transformation and SVPWM modulation: Inverse Park transformation and inverse Clark transformation are performed on Vd' and Vq' to generate three-phase modulation signals. Then, 6 PWM waves are generated by the SVPWM modulator at a switching frequency of 8kHz to drive the inverter bridge MOSFETs.

[0034] Closed-loop control of AC-DC rectifier feedback circuit, such as Figure 3 As shown, the specific implementation steps are as follows: Current signal acquisition: The sampling module acquires the three-phase current ig_abc on the rectifier side, and then converts it into DC quantities igd and igq in the dq coordinate system through Clark and Park transformations.

[0035] PI regulation and unity power factor control: The PI regulator (parameters Kp1=1.0, Ki1=0.8) adjusts the error between igd and the given value Igd_ref, outputs the d-axis modulated voltage Vgd, and sets the q-axis voltage Vgq=0 to ensure that the grid-side current and voltage are in phase.

[0036] Energy feedback is achieved by generating a PWM signal through inverse transformation and SVPWM modulation, which drives a three-phase fully controlled MOSFET bridge to feed AC energy back to the DC bus. The feedback path and the DC bus capacitor Cdc provide a buffering effect.

[0037] Using the control algorithm described above, the system output waveform is as follows: Figure 4 and Figure 5 As shown. Figure 4 The waveforms of the three-phase voltage and three-phase current after inversion are shown. It can be seen that the voltage is stable at 32V line voltage, the current has high sinusoidal degree, and the harmonic distortion is less than 3%. Figure 5 The three-phase voltage and current waveforms before rectification are displayed, verifying the effectiveness of unity power factor control, with a feedback efficiency of over 95%.

[0038] The simulation parameters were set according to the system design requirements (as shown in Table 1), and multi-condition tests were conducted using the above algorithm model. The simulation results verified that the dual closed-loop control and synchronous rectification algorithm can ensure that the system outputs a high-quality sine wave under rated load, fully demonstrating the accuracy, stability, and efficiency of the control strategy of this invention.

[0039] Table 1 shows the simulation parameters.

[0040] The load test simulation and program algorithm for an energy feedback converter based on dual closed-loop control and synchronous rectification include: Design a DC-AC-DC converter circuit: The overall simulation model consists of three parts: LCL voltage regulator module, load and measurement module, DC power supply module, PWM inverter module, LCL voltage regulator module, load and measurement module, sampling module and rectification module.

[0041] The DC-AC inverter circuit, through a three-phase full-bridge topology and SVPWM modulation, precisely converts DC power into three-phase AC power with controllable amplitude and frequency. Its dual closed-loop voltage and current control, combined with LCL filtering, achieves high-precision voltage regulation, low THD, and fast dynamic response, providing the core energy conversion foundation for the system. The DC-AC-DC energy feedback circuit, through the PWM rectification of converter 2, efficiently feeds the inverter output AC power back to the DC bus, using the voltage potential difference to drive energy reverse flow. Combined with unity power factor control and dead-time optimization, it significantly reduces DC power output.

[0042] The AC voltage signal sampled by the inverter is converted into a DC signal through Clark and Park transformations and compared with the given voltage. Then, it is precisely tracked by PI control and then SPWM modulation is performed to drive the signal output.

[0043] The AC current signal sampled by the rectifier section is converted into a DC signal through Clark and Park transformations and compared with the given current. Then, it is converted into a three-phase AC current through PI control and compared with a triangular wave to output a PWM wave to regulate the output current.

[0044] The DC-AC-DC energy feedback converter circuit described in this invention plays a crucial role in practical industrial and scientific research applications. Its core value lies in achieving efficient and controllable bidirectional flow of electrical energy. This circuit topology and control method are widely used in scenarios such as new energy vehicle motor-to-tow test platforms, aviation / ship power grid ground power supplies, high-power AC servo drive aging test systems, and photovoltaic / energy storage converter grid-connected test devices. In these applications, the device can simulate various loads under real-world operating conditions and efficiently and cleanly feed the electrical energy that would otherwise be consumed by the load resistance during the test back to the DC bus or grid, rather than dissipating it as heat.

[0045] Its significant advantages lie in its superior energy-saving performance. Through synchronous rectification technology, kinetic or electrical energy is fed back, significantly reducing operating costs and heat dissipation requirements, aligning with the green and low-carbon development concept. Secondly, it provides a high-precision testing environment. Based on PI regulator closed-loop control, it can stably output AC power with highly controllable amplitude, frequency, and waveform quality, achieving rapid dynamic response and ensuring the accuracy and repeatability of test results. Finally, it achieves multi-functionality; a single device can perform both inverter output testing and energy recovery, exhibiting high integration and reducing actual equipment investment and floor space. Therefore, this invention not only solves the inherent drawbacks of traditional energy-consuming load testing devices but also provides a highly efficient, accurate, and reliable advanced testing solution.

[0046] Closed-loop control of DC-AC inverter circuit based on PI regulator: In one exemplary embodiment, a voltage loop based on a PI regulator is used for closed-loop control of the DC-AC inverter circuit. The three-phase AC power is converted into a DC signal by Clark and Park transformations, compared with a given voltage, passed through a PI regulator, and then subjected to inverse Clark and Park transformations to generate a PWM wave. When the regulated voltage is higher than the voltage of the modulated triangular wave, the output is high; when the regulated voltage is lower than the voltage of the modulated triangular wave, the output is low.

[0047] The Clark transform is expressed by the following formula: ; The Park transformation is expressed by the following formula: ; in, , , These are the currents for phases A, B, and C, respectively. and Decompose the three-phase current into a stationary coordinate system The current, and Decompose the three-phase current into a rotating coordinate system The current.

[0048] Closed-loop control of AC-DC rectifier energy feedback circuit based on PI regulator: In this embodiment, a current loop based on a PI regulator is used to perform closed-loop control of the AC-DC rectifier circuit. The AC current signal sampled by the rectifier section is converted into a DC signal through Clark transformation and Park transformation and compared with the given current. Then, through PI control, it is converted into three-phase AC current and compared with a triangular wave to output a PWM wave to regulate the output current.

[0049] like Figure 6 As shown, the present invention provides a control method for a converter load testing device based on a PI regulator as described in any one of the above claims, comprising: S1. Start the device and complete the initialization preparation, set the output voltage of the DC power module and the initial load parameters of the load and measurement module; S2. The digital control unit obtains the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module through the sampling module, executes the dual closed-loop PI control algorithm to generate SVPWM drive signal, drives the PWM inverter module to convert DC power into three-phase AC power, and after the LCL voltage stabilization and filtering module filters out high-frequency harmonics, it transmits the power to the load and measurement module through the isolation transformer module. S3. The digital control unit performs synchronous rectification control on the PWM rectification feedback module. Based on the electrical signal collected by the sampling module, it adjusts the working state of the PWM rectification feedback module and rectifies the AC energy consumed by the load and measurement module into DC power and feeds it back to the DC bus of the DC power supply module. S4, the load and measurement module simulates dynamic load changes according to the set parameters, and simultaneously collects voltage and current data during the test to realize the monitoring and data recording of the converter load test.

[0050] First, step S1 includes: S101. Start the DC power supply module, set its output voltage to 50V DC voltage, and provide a stable and controllable DC bus voltage. S102. Initialize the load and measurement module, set the initial load parameters to a variable resistor with a resistance range of 0 to 10Ω, to simulate dynamic load changes from 0 to 2A, and to calibrate the sampling accuracy of the voltage and current sensors. S103. Set the initial parameters of the system through the digital control unit, including PI controller parameters, switching frequency of 8kHz, sampling frequency of 16kHz, and complete the self-test and synchronization preparation of each module.

[0051] Secondly, step S2 includes: S201, The sampling module collects the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module in real time; S202. Perform Clark transformation on the collected three-phase current Iabc to convert it into current components in the stationary coordinate system α-β. and ; S203. Perform a Park transform on the current component after the Clark transform to decouple it into a DC component in the rotating coordinate system dq. and ; S204. The error between Ud and the given voltage value Ud_ref is adjusted by the voltage outer loop PI controller. The proportional coefficient Kp2=0.61 and integral coefficient Ki2=0.89 of the voltage outer loop PI controller, and the output is the d-axis current command id_ref as the current inner loop. S205, via the current inner loop PI controller Error with id_ref and The error with iq_ref is adjusted. The proportional coefficient Kp3=1.602 and integral coefficient Ki3=1.498 of the current inner loop PI controller, and the modulation voltages Vd' and Vq' in the dq coordinate system are output. S206. Perform inverse Park transform and inverse Clark transform on Vd' and Vq' to generate a three-phase modulated signal; S207. The modulation signal is compared with the triangular carrier at a switching frequency of 8kHz by the SVPWM modulator to generate 6 PWM drive signals to drive the MOSFET switching devices of the PWM inverter module. S208: The inverter output is filtered by the LCL voltage regulator and filter module to remove high-frequency harmonics, and then transmitted to the load and measurement module after electrical isolation and voltage matching are achieved through the isolation transformer module.

[0052] Furthermore, the Clark transform can be expressed by the following formula: ; in, , The current component in the stationary coordinate system α-β is expressed in amperes. , , The instantaneous current values ​​for phases A, B, and C are respectively, in amperes; The Park transformation can be expressed by the following formula: ; in, , The current is expressed in amperes in the rotating coordinate system dq. The rotation angle is generated by the phase-locked loop synchronizing the grid voltage phase, in radians.

[0053] Furthermore, the inverse Park transform can be expressed by the following formula: ; The inverse Clark transform is expressed by the formula: ; in, , , The generated three-phase modulated voltage is expressed in volts.

[0054] Next, step S3 includes: S301, The sampling module collects the three-phase AC current signal ig_abc from the rectifier side in real time; S302. Perform Clark and Park transformations on ig_abc to convert it into DC signals igd and igq in the rotating coordinate system dq. The Clark and Park transformation formulas are the same as S202 and S203 in claim 3, except that the current signal is replaced by ig_abc. S303. The error between igd and the given current value igd_ref is adjusted by a PI regulator. The proportional coefficient Kp1=1.0 and the integral coefficient Ki1=0.8 of the PI regulator. The output d-axis feedback modulation voltage Vgd is set, and the q-axis modulation voltage Vgq=0 is set to achieve unity power factor control. S304. Perform inverse Park transform and inverse Clark transform on Vgd and Vgq to generate a three-phase feedback modulation signal; the inverse transform formula is the same as S206 in claim 3. S305 generates 6 PWM signals through the SVPWM modulator to drive the three-phase fully controlled MOSFET bridge of the PWM rectification feedback module to achieve synchronous rectification, rectifying the AC energy consumed by the load and measurement module into DC power, and feeding it back to the DC bus of the DC power supply module.

[0055] Additionally, step S4 includes: S401, the load and measurement module simulates dynamic load changes according to the set parameters. The resistance value of the variable resistor is adjusted in the range of 0 to 10Ω to simulate the step or continuous change of the load current from 0 to 2A. S402. Real-time acquisition of three-phase voltage Uabc and three-phase current Iabc during the test process. Data is acquired through voltage and current sensors at a sampling frequency of 10kHz, and waveform, RMS value, frequency and harmonic content are recorded. The S403 digital control unit processes and analyzes the collected data, including calculating total harmonic distortion, dynamic response time, and energy feedback efficiency, and realizes data storage and visualization monitoring through the MATLAB / Simulink platform. S404. Adjust control parameters based on monitoring results.

[0056] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A PI regulator-based inverter load testing device, characterized by, The application relates to a PWM synchronous rectifier test system, which comprises the following parts: a direct-current power module for providing a controllable direct-current bus voltage; a PWM inverter module connected in parallel with the direct-current power module at the direct-current side and used for converting direct current into three-phase alternating current; an LCL voltage stabilizing filter module connected with the alternating current side of the PWM inverter module at the input end and used for filtering high-frequency harmonics; an isolation transformer module connected with the output end of the LCL voltage stabilizing filter module at the primary side and used for realizing electrical isolation and voltage matching; a load and measurement module connected with the secondary side of the isolation transformer module at the input end and used for simulating a variable load and collecting voltage and current signals; a sampling module used for collecting three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module in real time; a PWM rectifier feedback module connected in parallel with the secondary side of the isolation transformer module at the alternating current side and connected in parallel with the positive and negative buses of the direct-current power module at the direct-current side, and used for synchronously rectifying alternating current energy and feeding back the alternating current energy to the direct-current bus; a digital control unit connected with the sampling module at the input end and connected with the driving ends of the PWM inverter module and the PWM rectifier feedback module at the output end, and used for executing a double-closed-loop PI control algorithm and generating SVPWM driving signals.

2. The PI regulator based variable current load test device of claim 1, wherein, The PWM rectifier feedback module comprises: a three-phase fully-controlled MOSFET bridge connected in parallel with the secondary side of the isolation transformer module at the sub-ends a, b and c of the alternating current side; a direct-current bus capacitor Cdc connected with the positive bus of the direct-current power module at the positive pole and connected with the negative bus of the direct-current power module at the negative pole, and used for buffering feedback energy; A PI regulator with a proportional coefficient Kp1 = 1.0 and an integral coefficient Ki1 = 0.8 is used to regulate the error between the grid-side d-axis current igd and a given value igd ref and output a d-axis feedback modulation voltage Vgd; an SVPWM modulator used for generating six PWM signals by inversely Park transforming Vgd and q-axis feedback modulation voltage Vgq=0, so as to drive the three-phase fully-controlled MOSFET bridge to realize unit power factor synchronous rectification and efficiently feed back load test energy to the direct-current bus.

3. The PI regulator based variable current load test device of claim 1, wherein, The sampling module comprises: a voltage Hall sensor connected in parallel with the three-phase output terminals of the load and measurement module at the input end, and used for isolating and attenuating three-phase voltage Uabc by 100:1; a current Hall sensor sleeved on the three-phase output cable of the load and measurement module, and used for converting three-phase current Iabc into voltage signals by 50mV / A; a 14-bit synchronous ADC connected with the output ends of the voltage Hall sensor and the current Hall sensor at the input end, and used for synchronously digitizing Uabc and Iabc at a 16kHz sampling rate and providing real-time feedback data to the digital control unit.

4. A control method of the PI regulator-based converter load test device according to any one of claims 1 to 3, characterized by, The application further relates to a PWM synchronous rectifier test method, which comprises the following steps: S1, starting the starting device and completing initialization preparation, setting the output voltage of the direct-current power module and the initial load parameters of the load and measurement module; S2, the digital control unit acquires three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module through the sampling module, executes a double-closed-loop PI control algorithm to generate SVPWM driving signals, drives the PWM inverter module to convert direct current into three-phase alternating current, transmits the alternating current to the load and measurement module through the LCL voltage stabilizing filter module and the isolation transformer module after filtering high-frequency harmonics, and realizes unit power factor synchronous rectification. S3, the digital control unit performs synchronous rectification control for the PWM rectification feedback module, adjusts the working state of the PWM rectification feedback module based on the electrical signals collected by the sampling module, and rectifies the alternating current energy consumed by the load and measurement module into direct current and then feeds it back to the direct current bus of the direct current power supply module; S4, the load and measurement module simulates dynamic load changes according to the set parameters, and collects voltage and current data during the test process to realize monitoring and data recording of the converter load test.

5. The control method according to claim 4, characterized by Step S1 includes: S101, start the direct current power supply module, set its output voltage to 50V direct current voltage, and provide a stable controllable direct current bus voltage; S102, initialize the load and measurement module, set the initial load parameter to a variable resistor resistance range of 0 to 10Ω, which is used to simulate dynamic load changes of 0 to 2A, and calibrate the sampling accuracy of the voltage and current sensors; S103, set the initial parameters of the system through the digital control unit, including the PI controller parameters, the switching frequency of 8kHz, the sampling frequency of 16kHz, and complete the self-checking and synchronization preparation of each module.

6. The control method according to claim 4, characterized by Step S2 includes: S201, the sampling module collects the three-phase voltage Uabc and three-phase current Iabc output by the load and measurement module in real time; S202. Perform Clark transformation on the collected three-phase current Iabc to convert into current component in stationary coordinate system α-β and ; S203, performing Park transformation on the current component after the Clark transformation to decouple into a direct current component in a rotating coordinate system d-q and ; S204, adjust the error of Ud and the given voltage value Ud_ref through the voltage outer loop PI controller, the proportional coefficient Kp2 of the voltage outer loop PI controller is 0.61, the integral coefficient Ki2 is 0.89, and the output is used as the d-axis current instruction id_ref of the current inner loop; S205, via the current inner loop PI controller Error with id_ref and The error with iq_ref is adjusted, and the proportional coefficient Kp3=1.602 and integral coefficient Ki3=1.498 of the current inner loop PI controller are used to output the modulation voltages Vd' and Vq' in the dq coordinate system. S206, perform inverse Park transformation and inverse Clark transformation on Vd' and Vq' to generate three-phase modulation signals; S207, compare the modulation signals with the triangular carrier through the SVPWM modulator at a switching frequency of 8kHz to generate 6-way PWM drive signals to drive the MOSFET switching devices of the PWM inverter module; S208, the inverter output is filtered by the LCL voltage stabilization filter module to filter out high-frequency harmonics, and then transmitted to the load and measurement module after electrical isolation and voltage matching through the isolation transformer module.

7. The control method according to claim 6, characterized by, The Clark transformation is represented by the formula: ； wherein, , is the current component in the stationary coordinate system α-β in amperes; , , are the current instantaneous values of the A-phase, B-phase and C-phase, respectively, in amperes; The Park transformation is represented by the formula: ； wherein, , is the direct current component in the d-q rotating coordinate system, in amperes; is the rotation angle, generated from the phase-locked loop of the grid voltage phase, in radians.

8. The control method according to claim 7, characterized by, The inverse Park transformation is represented by the formula: ； The inverse Clark transformation is represented by the formula: ； wherein, , , is the generated three-phase modulation voltage in volts.

9. The control method according to claim 4, characterized by, Step S3 includes: S301, the sampling module collects the three-phase alternating current signal ig_abc on the rectification side in real time; S302, perform Clark transformation and Park transformation on ig_abc to convert it into direct current igd and igq in the rotating coordinate system d-q; S303, adjust the error of igd and the given current value igd_ref through the PI regulator, the proportional coefficient Kp1 of the PI regulator is 1.0, the integral coefficient Ki1 is 0.8, the output d-axis feedback modulation voltage Vgd, and the q-axis modulation voltage Vgq is set to 0 to realize unit power factor control; S304, perform inverse Park transformation and inverse Clark transformation on Vgd and Vgq to generate three-phase feedback modulation signals; S305, generating 6-way PWM signals through the SVPWM modulator to drive the three-phase full-controlled MOSFET bridge of the PWM rectification feedback module, realizing synchronous rectification, and rectifying the AC energy consumed by the load and measurement module into DC power to be fed back to the DC bus of the DC power module.

10. The control method according to claim 4, characterized by Step S4 comprises: S401, the load and measurement module simulates dynamic load changes according to the set parameters, adjusts the resistance value in the range of 0 to 10Ω through the variable resistor, and simulates 0 to 2A load current step or continuous change; S402, real-time acquisition of three-phase voltage Uabc and three-phase current Iabc during the test process, data acquisition through voltage and current sensors at a sampling frequency of 10 kHz, and recording of waveforms, effective values, frequencies and harmonic contents; S403, the digital control unit processes and analyzes the collected data, including calculation of total harmonic distortion, dynamic response time and energy feedback efficiency, and realization of data storage and visual monitoring through the MATLAB / Simulink platform; S404, adjusting the control parameters based on the monitoring results.

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