Principles of Operation of Three-level Phase Shift Controlled Converter

One of requirements for the next generation of power supplies in constant voltage source mode is to achieve high power density with high efficiency. In nowadays, at power level 5 – 10 kW and at input voltage level 1 kV, the DC/DC converters are usually implemented with a halfbridge or with full-bridge topologies using IGBT devices. One of the drawbacks that these converters present is to maintain ZVS for a wide load range, an additional resonant inductance must be included. This in turns increases the circulating energy, which increases the conduction losses in the converter. One of the disadvantages of this topology presents in high-voltage applications is that each switch in the full-bridge DC/DC converter is subjected to the full bus voltage. In this voltage range, MOSFET devices with a high RDSon may be used. This approach increases the conduction losses of the DC/DC converter. Another option for this power range is to use IGBT devices, but these devices are not suitable for high switching frequency due to their bipolar structure. One of perspective solutions of this problem is using topology, which reduces the voltage stress across the power switches. If the secondary voltage level is low, (up to 100V) then is possible to use Schottky diodes, with excellent static and dynamic parameters. In this case all power semiconductor devices have unipolar structure, appropriate for high switching frequencies.