A digitally tuned resonant capacitance control with narrow range frequency modulation for ZCS high voltage X-ray power supply

This paper presents the use of a digitally tuned resonant capacitance control with narrow range frequency modulation to regulate the output voltage of a zero current switching series resonant (ZCS-SR) inverter-fed transformer-linked DC-DC converter for X-ray power supply application. In this control scheme, the series resonant inverter consists of several capacitors which are switched into and out of resonant tank circuit by relays. The capacitance of the resonant tank is modulated digitally by controlling the closure of relays which causes the output voltage to increase or decrease in steps. The output voltage in between any two adjacent steps is adjusted by varying the switching frequency in a narrow range. By modulating both resonant tank capacitance and switching frequency, it is able to regulate the output voltage over a wide range. Furthermore, the switching losses of the proposed system are eliminated with all switches operating under soft switching conditions over the entire range of output voltage. Verification of the proposed system is done by computer simulation using Orcad PSPICE.