Research On Zero Sequence Current Suppression For Open Winding PMSM With Common Dc Bus

With the development of rare earth permanent magnet material, power electrical devices, pulse width modulation technology and motor control technology, permanent magnet synchronous motor (PMSM) has been developed rapidly in recent years. And PMSM has been widely used in wind power generation field, AC servo field, etc. for its merits of high power density, high torque inertia ratio, high efficiency flexible structure, and so on. To meet the needs in high voltage and high power occasion, a novel topology of PMSM by reforming the traditional structure is proposed where the motor winding is open both sides and is fed by two converters which is named open windng (OW) PMSM. In this paper, the OW-PMSM with common DC bus especially the equivalent circuit of zero axis and the suppression of zero sequence current is studied from theoretical analysis, mathematical model, simulation analysis and experiment verification.The mathematical model of OW-PMSM under rotating coordinate system (d-g-0system) is deduced in this paper. The equivalent circuits of zero axis with isolated DC bus and with common DC bus are analyzed, and the zero sequence current is exiting in the latter structure which is produced by the the common voltage generated of two converters and the triple frequency harmonic component of back EMF and might deteriorate the efficiency and operation stability. To solve this problem, three zero sequence current suppression strategies are proposed in this paper:1) A closed loop control strategy of zero sequence current is researched in this paper to control the conmon voltage of the two converters for compensating the triple frequency harmonic conponent of back EMF to suppress the zero sequence current. And a zero sequence current suppression strategy based on compensating the common mode voltage of resistance and zero sequanece induction in the equivalent circuits of zero axis is proposed. In addition, the modulation of common mode voltage based on SPWM and SVPWM, and the influence on DC voltage utilization of common mode.voltage are analyzed. But several lower pass filters and proportional integral controllers are needed in this strategy, which makes a complex system.2) To simplify the control system, a zero sequence current suppression strategy based on proportional resonant controller (PR) is proposed because the back EMF and the zero sequence current are mainly made of the triple frequency harmonic components. And the impact produced by motor parameter variation, PR parameter variation, speed variation and the harmonics of the back EMF is analyzed. But PR controller could only control one frequency component.3) To solve the problem in the occasion where the zero sequence component of back EMF contains several harmonics such as3rd,9th,15th, and so on, a zero sequence suppression stretage based on repetitive controller (RC) is proposed. The design method and the stability analysis of the control system are introduced.Finally, the simulation model and the1kW experiment system of OW-PMSM with common DC bus are built to validate the availability of three proposed strategies.