A modular converter power unit testing method

Abstract

The present invention discloses a method for testing a power unit of a modular converter. The experimental process of the test method mainly involves simulating the test environment of the power unit under test in a digital real-time simulator, providing the real voltage and current to the power unit under test through a power amplifier, and collecting the port signal of the power unit under test and sending it back to the real-time simulator to achieve circuit interconnection. At the same time, the digital real-time simulator collects the state of the power module under test and executes control of the power module under test. The present invention does not require the design of additional hardware circuits and control algorithms, and can flexibly simulate the voltage and current waveforms of the power unit under various complex working conditions, fully test the performance of the power unit, and can be applied to different modular converters. The present invention can significantly shorten the test cycle of modular converters and accelerate the speed of equipment development.

Description

Technical Field

[0001] The invention relates to a modular converter power unit testing method. Background Art

[0002] For converters with complex structures, especially modular converters that contain a large number of power units and work at high voltage and high current, such as modular multilevel converters (MMC), before building the entire converter, the thermal characteristics, switching characteristics and other performance of the power unit must be tested, and the circuit design of its control unit, auxiliary power supply, capacitor voltage sampling, communication link, etc. must be verified. Therefore, it is necessary to simulate the voltage and current waveforms of the power unit when it is working, so that the power unit can operate like in actual applications, so as to test its performance.

[0003] The most direct method for testing MMC involves generating a sinusoidal current to the power unit through a resonant circuit. However, it cannot provide the DC component and even harmonics in the bridge arm current when the MMC is running, and the power unit is basically in open-loop operation, and control algorithms such as capacitor voltage balance cannot be applied and tested. Another type of test method is to design a special current source that can accurately provide the bridge arm current waveform of the MMC, but it requires additional time and economic costs, and a current source control method needs to be designed, and it must be controlled synchronously with the power unit. At the same time, the current test method cannot flexibly simulate the voltage and current waveforms under various working conditions, such as fault short circuits, power flow reversals, etc. For other modular converters, such as cascaded H-bridge converters and staggered parallel converters, there is currently no universal power unit test method. Summary of the invention

[0004] In view of the problem that the current modular converter power unit test method is complex and inflexible, the present invention provides a modular converter power unit test method. The present invention does not need to design additional hardware circuits and control algorithms, can universally and flexibly test the power units of various modular converters, and can simulate a variety of complex working conditions to test the thermal characteristics, switching characteristics, etc. of the power unit under various working conditions.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A modular converter power unit testing method comprises the following steps:

[0007] Step 1: The digital real-time simulator simulates the main power circuit of the modular converter except the power unit under test and the power grid, load or other equipment interconnected with the modular converter, and generates a voltage signal of the port of the power unit under test. The voltage signal is connected to multiple power amplifiers through the communication module. The power amplifiers amplify the voltage signal and connect to the power unit under test to provide real voltage and current for the power unit under test with a single or multiple ports.

[0008] Step 2: The voltage and current signals of the port of the power unit under test are collected to the digital real-time simulator through analog-to-digital conversion. The digital real-time simulator performs delay compensation and high-frequency noise filtering on the received voltage and current signals to realize the interaction between the power unit under test and the main power circuit;

[0009] Step 3: The digital real-time simulator controls the main power circuit and the power unit under test, and executes the upper control strategy to generate a voltage reference signal for the modular converter. The voltage reference signal is modulated and balanced between modules to obtain a PWM signal for each power unit. The PWM signal corresponding to the power unit under test is transmitted to the power unit under test through the communication module.

[0010] Step 4: The voltage, current and temperature signals of the power unit under test required for execution control are collected to the digital real-time simulator through the communication module, and the required main power circuit state can be directly obtained in the digital real-time simulator.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. The present invention does not require the design of additional hardware circuits and control algorithms, can flexibly simulate the voltage and current waveforms of the power unit under various complex working conditions, fully test the performance of the power unit, and can be applied to different modular converters.

[0013] 2. The present invention can significantly shorten the test cycle of modular converters and accelerate the speed of equipment development. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structure of the modular converter power unit test platform;

[0015] Figure 2 It is a schematic diagram of the structure of a modular multi-level converter power unit test platform;

[0016] Figure 3 It is an example waveform of the modular multilevel converter power unit test platform under steady-state operation;

[0017] Figure 4It is an example waveform of the modular multi-level converter power unit test platform simulating the transient process of AC side voltage drop;

[0018] Figure 5 It is an example waveform of the modular multi-level converter power unit test platform simulating the power reversal transient process;

[0019] Figure 6 It is a structural diagram of a test platform for a DC transformer power unit with series input and parallel output. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0021] The present invention provides a modular converter power unit test platform, the structure of which is as follows: Figure 1 As shown, it is mainly composed of five parts: a host computer, a digital real-time simulator, a power amplifier, a power unit under test, and a communication module. The host computer is connected to the digital real-time simulator through the communication module, and the digital real-time simulator is connected to the power unit under test via the communication module and the power amplifier. The power unit under test includes power semiconductor devices, drive circuits, capacitors, inductors, and voltage, current, and temperature sampling circuits. The experimental process of the test method is mainly to simulate the test environment of the power unit under test in the digital real-time simulator, provide the real voltage and current to the power unit under test through the power amplifier, and collect the port signal of the power unit under test and send it back to the real-time simulator to realize circuit interconnection. At the same time, the digital real-time simulator collects the state of the power module under test and executes control of the power module under test. The specific test steps are as follows:

[0022] Step 1: The digital real-time simulator simulates the main power circuit of the modular converter except the power unit under test and the power grid, load or other equipment interconnected with the modular converter, and generates a voltage signal of the port of the power unit under test. The voltage signal is connected to multiple power amplifiers through the communication module. The power amplifiers amplify the voltage signal and connect to the power unit under test to provide real voltage and current for the power unit under test with a single or multiple ports.

[0023] Step 2: The voltage and current signals of the port of the power unit under test are collected to the digital real-time simulator through analog-to-digital conversion. The digital real-time simulator performs delay compensation and high-frequency noise filtering on the received voltage and current signals to realize the interaction between the power unit under test and the main power circuit;

[0024] Step 3: The digital real-time simulator controls the main power circuit and the power unit under test, and executes the upper control strategy to generate a voltage reference signal for the modular converter. The voltage reference signal is modulated and balanced between modules to obtain a PWM signal for each power unit. The PWM signal corresponding to the power unit under test is transmitted to the power unit under test through the communication module.

[0025] Step 4: The voltage, current and temperature signals of the power unit under test required for execution control are collected to the digital real-time simulator through the communication module, and the required main power circuit state can be directly obtained in the digital real-time simulator.

[0026] In the present invention, the digital real-time simulator not only simulates the steady-state operating conditions of the modular converter, but also simulates complex conditions such as short-circuit faults and power reversal, tests the thermal characteristics, switching characteristics, stress, etc. of the power unit under test under various conditions, and verifies the correctness of the driving, sampling, communication and other circuits of the power unit under test.

[0027] In the present invention, the upper-level control strategy executed in the digital real-time simulator includes an outer control loop strategy and an inner control loop strategy. The outer control loop strategy includes power flow control, DC bus voltage control, overall energy control, energy balance control strategy between phases and bridge arms, etc. The inner control loop strategy includes DC current and AC side current control strategy.

[0028] In the present invention, the proposed power unit testing method is applicable to a variety of modular converters.

[0029] Figure 2 The specific implementation method of the modular multilevel converter (MMC) power unit test platform is given. The power unit under test is a standard submodule, including switch devices, capacitors, capacitor voltage and temperature sampling circuits, and drive circuits. The host computer is connected to the digital real-time simulator through the LAN interface, sends control instructions to it, and detects the model status in the digital real-time simulator. The digital real-time simulator simulates the main power circuit of the MMC except the power unit under test and the DC grid connected to the DC side of the MMC ( u DC Indicates), the AC grid or AC load connected to the AC side, generating the voltage signal of the power unit port under test u V. The voltage signal is connected to the power amplifier through the electrical signal interface. The power amplifier amplifies the voltage signal and connects it to the power unit under test to provide real voltage and current for the power unit under test. The current signal of the port of the power unit under test is collected to the digital real-time simulator through analog-to-digital conversion. The digital real-time simulator performs delay compensation and high-frequency noise filtering on the received current signal to realize the interaction between the power unit under test and the main power circuit. The digital real-time simulator executes the control of the simulated main power circuit and the power unit under test. It executes the upper-level control strategy and generates the voltage reference signal of the modular converter. The voltage reference signal is modulated by carrier phase shift and balanced by sub-modules to obtain the PWM signal of each power unit. The PWM signal corresponding to the power unit under test is transmitted to the power unit under test through the optical fiber interface. The voltage, current and temperature signals of the power unit under test required for execution control are collected to the digital real-time simulator through the optical fiber communication interface, and the required main power circuit state can be directly obtained in the digital real-time simulator.

[0030] Figure 3 , Figure 4 , Figure 5 Respectively in Figure 2 The following are example waveforms of the MMC steady-state operation, AC voltage drop transient process, and power reversal transient process simulated on the test platform. Figure 3~Figure 5 It can be seen that the capacitor voltage of the power unit under test can always remain stable, indicating that the digital real-time simulator effectively controls the power unit under test. Using this test platform, the main power circuit state of the MMC under different working conditions can be flexibly simulated (such as Figure 3~Figure 5 The AC and DC side voltages and currents in the power unit are measured), and the port current under different working conditions is provided to the power unit under test. The changes in capacitor voltage under different working conditions are observed. The thermal characteristics, switching characteristics, stress, etc. of the power unit under test are tested under various working conditions, and the correctness of the driving, sampling, communication and other circuits of the power unit are verified.

[0031] Figure 6 The specific implementation method of the input series output parallel DC transformer (ISOP SST) power unit test platform is given. The power unit under test includes switch devices, capacitors, transformers, capacitor voltage, current and temperature sampling circuits, and drive circuits. The host computer is connected to the digital real-time simulator through the LAN interface, sends control instructions to it, and detects the model status in the digital real-time simulator. The digital real-time simulator simulates the main power circuit of the ISOP SST except the power unit under test and the high-voltage DC grid connected to the high-voltage side of the ISOP SST ( u HV Indicates), medium voltage DC voltage connected to the low voltage side ( u MV, generating a voltage signal at the port of the power unit under test. The voltage signal is connected to two power amplifiers through an electrical signal interface. The power amplifier amplifies the voltage signal and connects it to the power unit under test, providing real voltage and current for the two ports of the power unit under test. The current signal at the port of the power unit under test is collected to the digital real-time simulator through analog-to-digital conversion. The digital real-time simulator performs delay compensation and high-frequency noise filtering on the received current signal to realize the interaction between the power unit under test and the main power circuit. The digital real-time simulator executes the control of the simulated main power circuit and the power unit under test. It executes the upper-level control strategy and generates a voltage reference signal for the modular converter. The voltage reference signal is modulated by carrier phase shift and balanced between modules to obtain the PWM signal of each power unit. The PWM signal corresponding to the power unit under test is transmitted to the power unit under test through the optical fiber interface. The voltage, current and temperature signals of the power unit under test required for execution control are collected to the digital real-time simulator through the optical fiber communication interface, and the required main power circuit state can be directly obtained in the digital real-time simulator.

Claims

1. A modular converter power unit testing method, characterized in that The method comprises the following steps: Step 1: The digital real-time simulator simulates the main power circuit of the modular converter except the power unit under test and the power grid, load or other equipment interconnected with the modular converter, and generates a voltage signal of the port of the power unit under test. The voltage signal is connected to multiple power amplifiers through the communication module. The power amplifiers amplify the voltage signal and connect to the power unit under test to provide real voltage and current for the power unit under test with a single or multiple ports. Step 2: The voltage and current signals of the port of the power unit under test are collected to the digital real-time simulator through analog-to-digital conversion. The digital real-time simulator performs delay compensation and high-frequency noise filtering on the received voltage and current signals to realize the interaction between the power unit under test and the main power circuit; Step 3: The digital real-time simulator controls the main power circuit and the power unit under test, and executes the upper control strategy to generate a voltage reference signal for the modular converter. The voltage reference signal is modulated and balanced between modules to obtain a PWM signal for each power unit. The PWM signal corresponding to the power unit under test is transmitted to the power unit under test through the communication module. Step 4: The voltage, current and temperature signals of the power unit under test required for execution control are collected to the digital real-time simulator through the communication module, and the required main power circuit state can be directly obtained in the digital real-time simulator.

2. The modular converter power unit testing method according to claim 1, characterized in that In the step one, the digital real-time simulator simulates the steady-state operating conditions of the modular converter, simulates short-circuit faults, and complex conditions of power reversal, tests the thermal characteristics, switching characteristics, and stress of the power unit under test under various conditions, and verifies the correctness of the driving, sampling, and communication circuits of the power unit under test.

3. The modular converter power unit testing method according to claim 1, characterized in that In the step three, the upper-level control strategy executed in the digital real-time simulation machine includes an outer-loop control loop strategy and an inner-loop control loop strategy. The outer-loop control loop strategy includes power flow control, DC bus voltage control, overall energy control, and energy balance control strategy between phases and bridge arms. The inner-loop control loop strategy includes DC current and AC side current control strategy.

4. The modular converter power unit testing method according to claim 1, characterized in that The power unit under test includes a power semiconductor device, a driving circuit, a capacitor, an inductor, a voltage sampling circuit, a current sampling circuit and a temperature sampling circuit.

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