Mine inverter based on isolation and transformation of power electronic transformer

At present, the mine inverter and the power frequency transformer are placed separately, which occupies too much underground working space. And the inverter output voltage has high harmonic content and poor waveform quality. In order to solve the above problems, the theoretical relationship between transformer operating frequency and volume is analyzed. It is concluded that under the same transmission power, the high-frequency transformer has a more streamlined size, smaller volume and higher power density compared with the operating frequency transformer. The intermediate filter capacitor in the common topology is replaced by power electronic transformer (DC-DC converter containing high frequency transformer). The paper proposes a composite mine inverter topology based on power electronic transformer isolation and transformation. The number of fully controlled switching devices IGBT in this topology is only half of the total number of power devices, which makes the inverter structure more compact and smaller, reduces the inverter switching losses, reduces hardware complexity and production costs, and improves efficiency and reliability. The control strategies of the three-phase rectifier input stage, the intermediate isolation transformer transmission stage and the three-phase variable frequency output stage in this topology are given. The fast space vector pulse width modulation (SVPWM) algorithm in 120° coordinate system is used to control the output stage to output the ideal variable frequency three-phase symmetric sinusoidal AC voltage. The steady-state and dynamic characteristics of the inverter at all levels are analyzed through simulation and experiment. The results show that the inverter can realize the secondary conversion of the inverter output and voltage level, and the output voltage regulation range is more flexible. The fast SVPWM algorithm in 120° coordinate system reduces the output voltage harmonic content, and the output three-phase voltage waveform is good.