Step-up DC-DC converter for megawatt size applications

This study describes a novel DC-DC converter concept which is capable of achieving very high step-up gains with megawatt (MW) level power transfers. The converter is based on two four-switch bridges around a LC circuit and does not utilise iron core transformers. The converter topology is simple and utilises thyristors as switches, with potentially soft switching operation. The high-voltage circuit does not suffer from excessive switch stresses or reverse recovery problems. The analytical modelling indicates that loading, and not the voltage gain, determines the converter size and the control input magnitude. For a given converter, the gain and either loading or operating frequency can be arbitrary selected. The converter shows good controllability with a linear characteristic if the operating frequency is used as the control input. The detailed digital simulation on PSCAD platform confirms conclusions from theoretical analysis on a 5 MW test system, which connects 4 kV source to 80 kV high voltage DC grid. The simulation studies of loses, with realistic internal resistances, indicate that efficiencies of around 95% could be expected.