Decoupled control of a 4-leg inverter via a new 4/spl times/4 transformation matrix

Abstract

Four-leg (3-phase 4-wire) inverters are developed to power unbalanced/nonlinear three-phase loads. A unique 4/spl times/4 decoupling transformation matrix is used that enables direct transformation between the four degree-of-freedom (DOF) leg-modulation space of the inverter and its corresponding 3-DOF output-voltage v space. This is analogous to the well-known 3/spl times/3 "abc-qd" transformation developed for the 3-leg inverter. Details of this new 4/spl times/4 "Quad" transform are provided, along with a depiction of the voltage-vectors produced. Advanced synchronous-frame control techniques are applied with this 4-to-3 "abcn-qdo" transform to create a UPS-style inverter with sinewave output. Experimental results for an 8.6 kV a prototype inverter are presented.