A Scalar Resonant-Filter-Bank-Based Output-Voltage Control Method and a Scalar Minimum-Switching-Loss Discontinuous PWM Method for the Four-Leg-Inverter-Based Three-Phase Four-Wire Power Supply

An all-scalar-control and pulsewidth-modulation (PWM) approach for the four-leg-inverter (FLI)-based three-phase transformerless four-wire power supply (PS) is proposed. The output voltage of each phase is controlled independently, and its controller is formed by a stationary-frame resonant-filter bank accompanied with proportional-control and output-capacitor current-based active-damping loops. The simple and easy to implement scalar-control method exhibits superior overall steady state and dynamic performance in the PS applications involving loads with high crest factor and/or significant load imbalance. Utilizing the inverter zero-state partitioning, a generalized form of scalar PWM for the FLI is developed. A novel minimum loss discontinuous PWM method, which provides minimum switching losses under all loading conditions (including load imbalance), is derived. This simple scalar method provides superior performance, and unlike the vector methods, it is easy to implement. The controller and modulator design and implementation details for the system are given. Linear and nonlinear loads for balanced and imbalanced load operating conditions are considered. The scalar-control and PWM methods are proven by means of theory, simulations, and thorough laboratory experiments of a 5-kVA PS.