A capacitor-charging power supply using a series-resonant three-level inverter topology

In this paper we present a capacitor charging power supply (CCPS) using a series-resonant three-level inverter topology to improve voltage regulation and use semiconductor switches having low blocking voltage capability such as MOSFETs. This inverter can be operated with two modes, full power mode (FPM) and half power mode (HPM). In FPM inverter supplies the high frequency step up transformer with full DC-link voltage(V/sub DC/) and in HPM with half DC-link voltage(V/sub DC//2). HPM switching method will be adopted when CCPS output voltage reaches the preset target value and operates in refresh mode-charge is maintained on the capacitor. In this topology each semiconductor devices blocks a half of the DC-link voltage, for example we can use the 250 V semiconductor switch when designing 500 V DC-link voltage inverter system without considering the margin. A 15 kW, 30 kV CCPS has been built and tested for an electric precipitator application. The CCPS operates from an input voltage of 500 VDC and has a variable output voltage between 10 to 30 kV and 1 kHz repetition rate at 44 nF capacitive load. A resonant frequency of 67.9 kHz was selected and a voltage regulation of 0.83% has been achieved through the use of half power mode without using the forced cut off the switch current. The theory of operation, circuit topology and test results are given.