Modes of Operation of Three-Phase Inverters

Three-phase inverters have different modes of operation, while the load power factor angle varies over a 3600 range. A method of analysis is described which makes it possible to find these modes of operation. The method is based on the use of Park vectors. These vectors-generally used in the analysis of three-phase ac machines-are composed of the instantaneous values of a three-phase system. Voltage and current vectors of a three-phase inverter are used to find the current distribution of the inverter. An analysis is given of all the possible conditions of an inverter connected to an active load that can produce any load power factor from zero leading to zero lagging. Some special modes of operation are discussed in detail. Ranges of load power factor angles having different types of commutations are obtained. A control method is shown which makes it possible to obtain effective voltage regulation at the full range of load power factor at a reduced commutation frequency.