A UNIFIED MODULATION ALGORITHM FOR VOLTAGE AND CURRENT SOURCE INVERTERS BASED ON AC-AC MATRIX CONVERTER THEORY

A unified pulse width modulation (PWM) algorithm is presented that is derived from ac-ac matrix converter theory. The algorithm can be used to implement either a voltage source or a current source inverter, using only conventional bridge topologies. The resultant modulation strategy produces minimal low-order ac harmonics, yet it is readily capable of being computed on line in a single switching cycle by a low-cost microprocessor at switching frequencies of up to several kilohertz. The unified algorithm also has the desirable feature of independent control of the output waveform magnitude and frequency and provides for a wide range of operation without changing the switching frequency. Furthermore, the strategy guarantees dc source current continuity for the current source inverter topology while still allowing the ac output current to step change to a new value within one switching cycle. The paper presents theory, simulation results, and experimental results showing the unified algorithm in operation.