Modeling of multileg sine-wave inverters: A geometric approach

Three fundamental sine-wave inverter topologies are analyzed: two-leg tone- phase, two-wire); three-leg (three-phase, three-wire); and four-leg (three- phase, four-wire). The topologies are "full-bridge" voltage-source inverter s with LC filters suitable for producing sinusoidal output voltages. The sw itching states and corresponding output voltage vectors produced by each in verter are identified and presented along with an analysis of the geometric arrangement of these voltage vectors. A pattern of characteristics is esta blished whereby the "qd" modeling forms commonly used with three-leg invert ers are extended to address the expanded capabilities of the four-leg inver ter. A unique 4x4 decoupling transformation matrix is presented for the fou r-leg inverter that enables direct transformation between the four-degree-o f-freedom (DOF) leg-modulation space of the inverter and its corresponding 3-DOF output-voltage space. This is shown to be directly analogous to the w ell-known "abc-qd" transformation developed for the three-leg inverter, Ful ly decoupled models for each inverter are presented.