Conventional pulse-frequency-modulated (PFM) series resonant high-voltage
(HV) direct-current (DC) power supplies have the limitations of poor controllability
at light load, high conduction loss, large output voltage ripple, slow transient
response and high current stress on circuit components at low switching frequencies.
This thesis proposes four novel topologies of HV DC-DC converters, namely, ZCSSR
(zero current switching - series resonant) inverter-fed, ZCS-SR inverter-fed
voltage multiplier (VM) based, ZCS-DSR (zero current switching - double series
resonant) inverter-fed and ZCS-DSR inverter-fed VM based. First and second
topologies are controlled by using digital tuning of tank capacitance and variable
pulse frequency with dual-mode operation. Third and fourth topologies are controlled
by PFM with dual-mode operation. The effectiveness of all the proposed power
converter topologies and corresponding control scheme are verified by simulation
and experimental results. First and second converters have superior performances
compared to the conventional PFM converter in terms of their wider range of output
voltage controllability, lower percent ripple, lower current stress on circuit
components and higher efficiency. The main features of third and fourth proposed
converters are that they are highly efficient and have very simple circuit operations.
Among all the proposed converters, the ZCS-SR inverter-fed VM based HV DC-DC
converter is the best choice for X-ray systems with the power range from 100W to
350W. The measured efficiency at 100W is 87% and 92% at 350W
