An Optimal Excitation Control Technique for Brushless Induction Excited Synchronous Motor (BINSYM)

The popularity of electrified transportation is increasing exponentially day by day. Researchers are recently looking for a brushless and permanent magnet (PM)-less solution for electric vehicle motors. Wound-field synchronous motor (WFSM) is a suitable alternative to PM-based machines. The brushless induction excited synchronous motor (BINSYM) is a WFSM where the exciter, an induction machine (IM), is embedded inside a synchronous machine (SM) frame. The SM and IM are wound for different numbers of poles to achieve magnetic decoupling. The purpose of IM is to control the field current of SM. The IM is controlled in deep-plugging mode at a constant slip frequency over the entire speed range to minimize its reactive power demand. The SM is designed to operate at an extended speed range with a maximum speed-to-base speed ratio of 4.4. Since the rotor is of wound field type, the SM has the flexibility of reducing the field current. An efficiency maximization algorithm is proposed that sets the right magnitude of field current in SM. Simulation of BINSYM-based system has been carried out in MATLAB/Simulink to validate the control strategies. Experimental findings from the laboratory prototype machine closely match the simulation results.

I. Introduction

The focus on transportation electrification has increased exponentially in the last decade due to increasing environmental issues. Electric motors and their control form the heart of electric vehicles (EVs). Researchers look for several aspects like high power and torque density, high efficiency, cost, ease of control, high constant power speed range (CPSR), etc., while choosing the motors [1]. Till now permanent magnet (PM)-based motors have been widely used because of their merits of high torque and power density, efficiency compared with induction motor (IM), wound-field synchronous motor (WFSM), and switched reluctance motor (SRM) [1], [2]. However, rare-earth material (REM) is susceptible to temperature variations, costly, and not uniformly available worldwide [3], [4]. PM-based motors suffer from other issues like demagnetization of PM under extended speed range and reduced fault tolerance [5]. These drawbacks motivate researchers to find alternatives to PM-based motors. The DC-excited vernier reluctance machine (DC-VRM) has been found to be a viable alternative to PM machines for low-speed high-torque applications [6], [7], [8]. However, these machines have issues of low power factor and satisfactory performance is achieved only by the right choice of slot/pole combination and stator winding layout. Brushless WFSM is an alternative to the PM-based motors as it has superior field weakening capability, enhanced safety by directly removing the field excitation under faulty conditions [9]. WFSM has already been used in Renault Zoe EV and BMW iX3 e-Drive model [10].