Partial resonant AC link converter: A highly reliable variable frequency drive

In this paper a soft switched ac link ac-ac converter is employed as a variable frequency drive (VFD). The proposed configuration is a reliable, efficient, and compact converter with unity power factor at the input side. It is, in fact, a partial resonant converter i.e. only a small time interval is allocated to resonance in each cycle. Hence, while the resonance facilitates zero voltage turn on of the switches and soft turn-off, the LC link has low reactive ratings and low power dissipation. Due to the soft switching of the switches, the switching frequency can be increased and the high frequency of the link minimizes the size of the passive components. Both buck and boost operations in forward and reverse directions are feasible through this converter. Moreover, this converter is capable of increasing and decreasing the frequency over a wide range. Other than regulating the output current pulses to control the speed of motor the control algorithm also controls the input power factor and therefore no external power factor correction circuitry is required. In this paper field-oriented control scheme is applied to the proposed VFD for controlling the speed of the motor. Both simulation and experimental results are included in this paper to verify the performance of the proposed VFD.