Development of main traction inverter and its test device for subway vehicles

1 Overview

The AC03 electric trains of Shanghai Metro Line 3 were introduced in the early 21st century and are AC transmission vehicles manufactured by the French company ALSTOM. Their main traction inverters are composed of 1 200 A/3 300 V IGBT modules, and the main circuit structure is shown in Figure 1. The circuit structure of the AC03 electric vehicle main traction inverter is basically similar to that of other imported AC transmission vehicles, but the difference is that a low-inductance dry metal film filter capacitor is installed between OV and ground, and the capacitance parameter is 6.8 μF/640 V to reduce the electromagnetic interference (EMI) of high-frequency radiation.

PIM1 in Figure 1 is a three-phase IGBT inverter module of the traction inverter, model ONIX 1500 IGBT, and its appearance structure is shown in Figure 2. The upper part is the filter capacitor, and the filter inductor is installed in the inverter box; the middle part is the control circuit and drive circuit; the lower part is the IGBT module and the base heat sink.

PIM2 in Figure 1 is a brake chopper module, which is used to consume the braking energy in the brake resistor through PIM2 when the energy cannot be fed back to the grid in the electric braking state. The brake chopper module is similar to the inverter module in structure, but is assembled separately from the inverter module. The switching frequency of the chopper is 650 Hz. As shown in Figure 1, the chopper module consists of 4 IGBTs, two of which are connected in parallel as choppers, and the other two IGBTs are used as freewheeling tubes of the brake resistor.

The AC03 electric train has been in operation for nearly 10 years. During operation, the IGBT module of the main traction inverter often fails, so it is necessary to equip it with appropriate testing equipment to detect it and find the corresponding problems so as to overhaul and maintain the main traction inverter.

2 Traction inverter module structure and working principle

2.1 Traction inverter module structure and circuit analysis

The main circuit and control circuit block diagram of the traction inverter IGBT module are shown in Figure 3.

According to Figure 3, the traction inverter module structure can be divided into the following parts.

1) The upper main circuit consists of 6 IGBT modules forming a three-phase inverter circuit, namely VVVF. In addition, there are 4 IGBT modules forming a brake chopper circuit, which is separate from the three-phase inverter circuit (see PIM2 in Figure 1).

2) The middle driver circuit board has a gate drive circuit for each IGBT. Each circuit also has its own status feedback signal and fault information. These feedback information must be fed back to the computer (AGAT) for processing and judgment. In addition, each LV interface connector is responsible for two drive circuits of one phase bridge arm, such as LV1 is responsible for the drive circuits 1 and 4 of the upper tube T1 and lower tube T4 of the PH1 phase.

3) The AC square wave power supply at the bottom has a DC voltage of 48 V and outputs a 35 kHz, 24 V AC square wave power supply to power the driver circuit board. It is used to generate two drive power supplies that are electrically isolated from the control circuit of the input signal. When it is turned on, the DC voltage is 15 V, and when it is turned off, the DC voltage is -12 V. In addition, there are also fault and protection information on the power supply circuit board, which is also fed back to the computer for processing and judgment. The interface connector of the power supply is LV5.

In addition, as can be seen from Figure 3, the interfaces between the three-phase inverter module and the external connection are: in the main circuit, there are P, N, PH1-3 (output three-phase AC end) and ground wire; in the control circuit, it is realized through LV1, 2, 3, 5 connectors.

Because the circuit structure of the brake chopper module is similar to that of the inverter module and is connected to the control circuit through the LV4 connector, it will not be introduced here.

2.2 Control circuit analysis

2.2.1 AC square wave power supply board

The AC square wave power board is used to power the driver circuit board. When the power board is normal, when a DC voltage of 48 V is input to the input end, an oscilloscope is used to test the output end, and a 35 kHz, 24 V AC square wave power supply should be measured, as shown in Figure 4.

2.2.2 Driver circuit board

When the driver circuit board is working normally, after applying the 35 kHz, 24 V AC square wave power supply to the input end of the high-frequency transformer of the driver circuit board, its two secondary windings are rectified and stabilized to obtain two electrically isolated drive power supplies, namely, the forward conduction voltage DC 15 V and the reverse bias voltage DC -12 V when turned off. At this time, when the drive signal is not input, the gate voltage applied to the IGBT is the reverse bias voltage, which is about DC -12 V; when the drive signal is added, the voltage signal VGE for driving the IGBT will be obtained at the output end.

3 Traction Inverter IGBT Module Test Device

3.1 Test device structure analysis

The structure and system block diagram of the developed inverter test device are shown in Figure 5. The strong power part mainly consists of high-voltage DC power supply, LEM sensor, simulated load and test object; the console is the core of test and control, mainly composed of data acquisition card, computer, conditioning circuit and other components; by writing the measurement and control professional software LabVIEW8.5, the measured data and waveform can be analyzed in real time and saved or printed, and the test process can be completed manually.

This inverter test device has complete testing functions and can test one IGBT module, one phase (i.e. one bridge arm) or three phases separately; it can not only realize high voltage testing, but also low voltage testing, i.e. non-destructive testing. Generally, for faulty IGBT modules, non-destructive testing is first performed, and high voltage testing is then implemented after the problem is found and repaired.

3.2 Test steps and test analysis

A portable tester can be used to perform a low voltage test first.

1) Test the AC square wave power board. Test whether the output terminal is a 24 V, 35 kHz square wave voltage after adding DC 48 V.

2) Test the driver circuit board. Input the drive signal. The drive signal of the IGBT traction inverter on the AC03 electric train is a square wave voltage signal of 10 to 15 V, as shown in Figure 6. The zero line width on the waveform corresponds to the dead time of the upper and lower tubes of a bridge arm, which is adjustable (this figure is enlarged for clarity, but it is actually very small). The same voltage waveform VGE is obtained at the output end of the driver circuit board, but the reverse voltage amplitude is -12 V.

3) Test the power module. As shown in Figure 7, the inverter bridge of one phase (such as PH1 phase) is connected to form a half-bridge inverter circuit. In the figure, T1 is the upper tube, T4 is the lower tube, R is a pure resistance load (about 100 Ω), and E1 and E2 are DC power supplies, which are approximately between DC 15 and 24 V.

(1) Only the upper tube T1 is turned on. The driving signal of the inverter bridge of one phase of the traction inverter (composed of the upper tube and the lower tube) is input by the pins (5, 6) of the corresponding interface connector LV, and the driving signals of the two driving circuit boards corresponding to the upper and lower tubes should be mutually inverted, which ensures that only one of the upper and lower tubes can be turned on. At the same time, the input driving signal must also ensure that there is a dead time between the upper and lower tubes. If the driving signal of 500 Hz and 10 V square wave voltage is input to pins 5 and 6, the upper tube T1 is turned on, and the waveform on the load resistor R is tested with an oscilloscope. VR is a square wave voltage with the same pulse width (duty cycle of about 50%) and amplitude of E1. The measured waveform is shown in Figure 8; at this time, the T4 tube is turned off, that is, cut off.

(2) Only the lower tube T4 is turned on. If the input signals on pins 5 and 6 are reversed, that is, originally 5 is "+" and 6 is "0", and now 6 is "+" and 5 is "0", then T1 is turned off and T4 is turned on. Use an oscilloscope to observe the waveform on the resistor R. VR will be a reverse square wave voltage waveform with an amplitude of E2.

(3) Alternating conduction of the upper and lower tubes Only when the corresponding driving circuit functions of the upper and lower tubes are confirmed to be normal, the test of alternating conduction of the upper and lower tubes can be carried out. Input a 500 Hz, 10 V AC square wave voltage drive signal to LV pins 5 and 6. It is required that when changing from +10 V to -10 V, it must pass through the "0" level, and the maintenance time of the "0" level must be at least greater than the dead time, so that the upper and lower tubes will be alternately turned on. The voltage waveform on the load resistor R measured by the oscilloscope, VR, becomes an AC square wave voltage waveform with the same frequency and width as +E1 and -E2, as shown in Figure 9. The "0" level segment in the figure corresponds to the "0" level segment of the input signal, that is, the dead time of the upper and lower tubes.

By testing the electrical performance of the faulty module and comparing it with the test results of the normal module, we can determine and analyze the problem and repair it. After the repair, we can test and check again. If everything is normal, it means that the traction inverter IGBT module function has returned to normal.

If there is any doubt about the IGBT on the faulty module, it can be further tested with high voltage. During the high voltage test, as shown in Figure 5, connect the main traction inverter IBGT module to the "test object" link, and then perform the test operation on the console. The required voltage and current waveforms are displayed on the display, and can be recorded or printed and saved when necessary. The format of performing high voltage testing on the console and printing and saving the test waveform is shown in Figure 10. The upper part of the figure is 1 to 4 from left to right, and the lower part is 5 to 8. Among them, 1 to 3 are three-phase current waveforms. Since the main circuit is connected as a half-bridge inverter circuit, the phase currents of 1 and 3 are equal and opposite, and the middle phase 2 does not flow current, so it is zero. 4 and 5 are line voltages and are equal. 6 and 7 are the DC voltage of the intermediate circuit and the current of the intermediate circuit. 8 shows a waveform, indicating that the console is working normally.

4 Conclusion

应用所研制的测试装置，可以对AC03 型电动列车用的主牵引逆变器IGBT 模块电路进行测试与分析。因测试装置测试功能齐全，又有便携式测试仪，所以运营维护部门应用相当方便，而且显著地提高了检修和维护的效率。