Minimization of Capacitor Voltage Difference for Four-leg Inverter Dual-parallel IM System

In the situations where multiple motors operate at the same speed, this paper designs a dual-parallel induction motor (IM) system supplied by three-phase four-leg inverter (FLI) for cost reduction and fault tolerance of normal system. The dc offset and ac fluctuation of capacitor voltages exist in this system due to the motor phases connected to bus capacitors' mid-point. It seriously affects voltage utilization and stable operational range. A novel synchronous control scheme with the ability of ac voltage fluctuation minimization (AVFM) and dc voltage offset elimination (DVOE) is proposed. The unified model of dual IMs is used to design the speed regulator, and the model predictive flux control (MPFC) method is combined with space vector modulation (SVM) to realize torque and flux control of dual IMs. AVFM is realized by controlling the electrical angle difference of dual IMs as, which is first presented in this scheme. An angle regulator is proposed to control the electrical angle by adjusting stator flux amplitude. DVOE is realized by injecting a compensatory voltage vector, which is simplified in this scheme to avoid the voltage filter or additional coordinate transformation in conventional method. Experiment results verify the effectiveness of proposed scheme.