Transformerless Hybrid Topology for Medium-Voltage Reactive-Power Compensation

In this paper, natural sinusoidal hybrid converter is presented for medium-voltage reactive-power control applications. Main high-voltage inverter that produces fundamental reactive current is a square-wave inverter. Several single-phase full-bridge converters are connected in series with this square inverter to eliminate harmonic voltages from the net output voltage of this hybrid converter. DC bus voltages of these cells are naturally controlled. Two different switching strategies are proposed for these series cells in this paper-one is pulse width modulation (PWM) type and the other is non-PWM type. Dc bus voltage of main high-voltage inverter is varied to have variable reactive power. Finally, experimental results are produced here to validate this hybrid topology and its proposed control strategies from a scale-down proto model.