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A 3D PWM control, H-bridge tri-level inverter for power quality compensation in three-phase four-wired systems

A three-dimensional pulse width modulation (3D PWM) control, H-bridge tri-level inverter, acts as a power quality compensator for three-phase four-wired systems, is proposed. Such compensator is an alternative of diode-clamped inverter based one, which generally suffers from the DC-link voltage unbalance problem and possesses low expandability in very high-voltage and high-power applications. This paper based on the concepts of switching function and state-variable formulation to deduce the mathematical model of H-bridge tri-level inverter, with also an enhanced switching table that balances the average switching frequency of the switches. The compensation is accomplished through a sign cubical hysteresis control strategy, which controls the total 27 space vectors in 3D aspect to inject the nearest negative amplitude of harmonics into the load currents to compensate both the harmonic an in-phase currents into the systems to reduce the peak-load power supply from the generator. System-level simulation results demonstrate the feasibility of such compensator.