Balance Control of Split Capacitor Potential for Magnetically Levitated Motor System Using Zero-Phase Current

Abstract

We have previously proposed a driving method for both a three-phase permanent magnet motor and one- degree-of-freedom controlled magnetic suspension using only a three-phase inverter. In this driving system, the suspension winding for magnetic suspension is connected between a neutral- point of the Y-connected three-phase motor winding and a middle point of two DC voltage sources. The current flowing in this part is denoted by the zero- phase current here. The suspension force is actively controlled by the zero- phase current in this system. This paper proposes a further simplified configuration, where the DC-link voltage is split by two capacitors using a DC voltage source. The split capacitor potential, however, is unbalanced by the DC component of the zero- phase current, owing to the offset detection error of the current sensor and the bias current of the magnetic suspension. This paper addresses the balance control of the split capacitor potential. We propose two balance control methods, including the voltage feedback control and the voltage sensorless control. The experimental results demonstrate the effectiveness of the proposed balance control.