Direct Active and Reactive Power Control of Three-Phase Inverter for AC Motor Drives With Small DC-Link Capacitors Fed by Single-Phase Diode Rectifier

This paper proposes a power controller used for three-phase inverters with small dc-link capacitors fed by a single-phase diode rectifier. The effect of the reactive power was investigated based on a power flow analysis between a dc-link and three-phase inverter. These results enable the development of a direct active/reactive power controller in discrete time instead of adopting a classical proportional-integral (PI)-type current regulator, which directly leverages the total power flow of the system. A suitable reactive power selection method was presented to improve the overall system efficiency. The command voltage vector at each discrete time step can be simply and intuitively determined by an inverter power without requiring motor current-regulating PI gains and additional control functions. The proposed controller regulates an average motor velocity/airgap torque while simultaneously shaping a grid-side current with a high power factor and low harmonics to meet IEC61000-3-2 requirements. The proposed structure can be applied to three-phase inverters for a broad family of ac motors, such as induction and permanent magnet synchronous motors.