Multi-unit series high power inverter power supply circuit diagram design

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Overview:
1 Introduction Since the early 1990s, multi-level inverters have become more and more widely used in the field of high voltage and high power. Multilevel converters have three basic topologies: diode-clamped, flying-span capacitors, and multi-cell series. In comparison, multi-cell tandem models have several major advantages:
1) The inverter structure is based on a traditional two-level inverter unit, so the main circuit topology is very simple.
2) The power unit adopts a modular structure, so all power units can be interchanged, maintenance is very convenient, and there are not a large number of clamp diodes or voltage balance capacitors in the circuit.
3) Each inverter bridge is powered by independent DC voltage sources, and there is no neutral point voltage imbalance.
In this paper, the high-power inverter power supply adopts multi-cell series technology, which combines the dual power control technology of single power unit with the horizontal phase shift PWM technology, which not only reduces the voltage level requirements of the switching device, but also satisfies the system's output voltage and The output power requirement has obtained a higher equivalent switching frequency than the simple multi-cell series technology, which greatly reduces the switching loss, further improves the output waveform, and reduces the harmonic distortion rate of the output voltage. Moreover, the power unit is The grid voltage is supplied by the phase-shifting transformer with multiple secondary sides, which has less harmonic pollution to the power grid and high input power factor. It is not necessary to use input harmonic filter and power factor compensation device.

2 Multi-unit series high-power inverter power supply control principle Multi-unit series three-phase high-power inverter power supply block diagram shown in Figure 1, according to the output power requirements, each phase uses three units in series, three phases have nine groups identical Power unit. The carriers of the three power units per phase differ from each other by 120°, the output phase voltage is 7 levels, and the line voltage is 12 levels. Each power unit is subjected to full output current, but only provides 1/3 of the phase voltage and 1/9 of the output power. Compared with a large-capacity inverter directly connected in series with a high-voltage device, since the entire power unit is connected in series, the highest voltage that the device can withstand is the DC bus voltage of the power unit, and the low-voltage power device can be directly used, the device does not have to be connected in series, and there is no device. The voltage equalization problem caused by the series. The low-voltage IGBT power module used in the power unit has a simple driving circuit and mature and reliable technology. By varying the number of series of power units per phase or the output voltage level of the power unit, high voltage outputs of different voltage levels can be achieved.

Figure 1 Block diagram of multi-cell series high-power inverter power supply

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