Analysis of the Soft-Start Circuit of the High Voltage Power Supply Based on PSM Technology

The power supply based on pulse step modulation technology has been widely used as the high-voltage power supply (HVPS) for additional heating systems. The topology contains numbers of converters and multisecondary transformers. For the magnetizing inrush of the transformer and charging current of the converters connecting with the secondary windings of transformer, the power up of the power supply system is quite complex. There are resistor branches series with the transformer and each converter is used to limit the inrush current. A lot of resister branches and parallel contactors in the converter modules are required, and as a result the dissipation and electromagnetic interference inside the module are serious. In this paper, the soft-start circuit is simplified to only one resistor branch. The precharge circuits of the converters, which are connected to the secondary, are diverted from the inside of the modules to the primary winding of transformer. Since the multisecondary transformer powers up at the same time as converters, the capacitors in all converters will limit the ramp up rate of the transformer voltage, and the magnetic inrush current can be ignored. To analyze the characters of the precharge branches, all converters can be equaled as parallel during the soft-start process. The equivalent circuit, a series RLC circuit, is proposed in this paper. A 1.2-kV power supply, contains 12 converters, with soft start has been built up in laboratory. Simulation and experiment results are shown to verify the theoretical analysis. A new soft-start circuit of 100-kV HVPS system was designed.