A Novel Generalized Low-Order Harmonic Current Suppression Method for Multiphase Open-End Winding Motors

Medium-voltage multi-phase open-end winding motors and three level multi-phase H-bridge large-capacity inverters are the preferred solutions for large ship propulsion systems. However, open-end winding motor systems exhibit high-amplitude 3<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>rd</i></sup>, 5<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>th</i></sup>, and 7<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>th</i></sup> order harmonics (abbreviation “low-order harmonics”) current due to H-bridge inverter PWM modulation dead zone and the motor’s non-ideal magnetic field. Limited by the current loop bandwidth of inverter with low switching frequency, it is difficult to suppress low-order harmonic currents with conventional methods. Firstly, this paper gives twelve-phase open-end winding induction motor mathematical model and its closed-loop control strategy. Secondly, combined with the phase characteristics of motor windings, a novel generalized low-order harmonic currents transformation matrix and its suppression method are proposed. The new method converts low-order harmonics into DC components by two sets of three-phase winding currents with a 30-degree phase difference and cooperates with a simple proportional-integral regulator to achieve closed-loop control. Moreover, the controller parameters for the proposed method are designed. Finally, the experiments are conducted to verify the proposed method under steady-state and dynamic conditions. The results show 3<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>rd</i></sup>, 5<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>th</i></sup>, and 7<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>th</i></sup> order current harmonics of the twelve-phase motor system are reduced by over 70%. The proposed method is simple to implement and can be extended to other multi-phase motor systems.