Patent ID: 6108225
Filing Date: 2000-08-22
Classification: H02M

Abstract:
A power device for providing to a load circuit an AC voltage synchronized with an AC power source, the device comprising a first series circuit of first and second switching elements connected to be coincident in their forward direction with each other and respectively having an inverse directional current passing element connected in parallel to the switching element, a second series circuit of third and fourth switching elements connected to be coincident in their forward direction and respectively having an inverse directional current passing element connected in parallel to each switching element, a third series circuit of two rectifying elements in the same direction as the inverse directional current passing elements, a smoothing capacitor to which the first, second and third series circuits are connected in parallel, a first inductor connected through the AC power source between a node of the switching elements of the first series circuit and a node of the two rectifying elements in the third series circuit, and a second inductor connected through the load circuit between the node of the switching elements in the first series circuit and a node of the switching elements in the second series circuit, wherein the device further comprises a boost converter connected to the AC power source and including at least part of the switching elements and first inductor, a buck converter connected to the smoothing capacitor and including at least part of the respective switching elements and the second inductor, a control circuit for controlling the operation of the respective switching elements to have at least one of the switching elements used in common in the boost and buck converters and to provide a period in which currents flowing through the commonly used switching element upon operation of the boost converter and upon operation of the buck converter in directions cancelling each other, and means for detecting the state of the load circuit, the control circuit receiving an output from the load state detecting means to have the operation of the switching elements varied in accordance with a lowering in a load resistance of the load circuit.