Current source rectifiers in discontinuous conduction modes of operation

While operation of the three phase Current Source Rectifier (CSR) for ac-to-dc conversion using phase control or low frequency pulse control is well established in a wide variety of applications, CSR realization using high frequency Pulse-Width-Modulation (PWM) control is being studied recently as a potentially competitive alternative to a Voltage Source Rectifier (VSR). In the CSR reverse blocking gate turn-off switches are realized using series connected diodes, which prevent any reversal of the dc link current. A significant consequence of this limitation occurs at light load conditions. The dc link inductor current enters discontinuous mode of operation and leads to loss of control of output voltage and highly distorted input current, which compromises the potential advantages of the approach. This paper characterizes the CSR while operating in discontinuous conduction mode and proposes a modulation strategy which restores control of output voltage and ensures nearly sinusoidal current at light loads. Simulation and hardware results are provided for a 3kW laboratory scale prototype system.