Research on Hysteresis Control of Switch Transformer Soft Starter

When starting high-voltage and large-capacity motors, it is necessary to reduce the starting impulse current and the grid voltage drop through the soft starting device. At the secondary side of the transformer, the use of switch-transformer type soft starter control can not only effectively avoid the series connection of valve groups, but also reduce the technical difficulty, which is suitable for fan and pump loads. According to the working principle of switch transformer type soft starter and the waveform characteristics of each part, select the appropriate sampling position of synchronous signal. By analyzing the phase shift angle difference between the synchronous source and the valve group voltage at different starting stages, the adjustment range of the valve group trigger angle is deduced. According to the characteristics of soft start, a hysteresis control method with feedforward is proposed. This method has small current overshoot, strong system robustness, and improves the system response speed at fixed switching frequency. The negative feedback effect of synchronous signal phase shift on current control is analyzed by stator voltage rationality of the proposed control strategy.