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Voltage Synthesis Using Dual Virtual Quadrature Sources—A New Concept in AC Power Conversion

Controlling an ac voltage often involves changing the amplitude, phase, and/or harmonic content of the voltage. This can require the addition of voltage at or around the zero crossing of the available ac voltage. Synthesis of this additional voltage normally requires an ac or dc source (or energy storage element) from which the desired voltage can be synthesized using pulsewidth modulation techniques. This paper proposes a novel concept wherein dual virtual quadrature sources are used to synthesize the required additional voltage. This is seen to result in simple low-cost ac converters that are robust, have minimal component count, and can realize phase shift and/or harmonic control without requiring multiple sources or energy-storage elements. The approach is seen to have simple implementation and can realize potentially useful devices such as controllable transformers and inverter-less active filters.