Approaching the Ideal BLDC Motor: A Novel Electronic Speed Controller System for a Generator-Converted BLDC Motor with Field Weakening Feature

Abstract

The concept of an ideal Brushless DC (BLDC) motor which has adjustable rotor magnetic field offers an opportunity for wider BLDC area of implementation as a very versatile electric powerhouse especially in variable load areas such as on electric vehicle or other people movers. Characterized by its high-efficiency level, low maintenance and long service duration, the lack of physical commutation brush like in regular DC motor dictates the requirement of an electronic control system to regulates its commutation. An electronic control system equipped with rotor field control capability in a collaboration with an ideal BLDC motor, is believed to offers wider implementation opportunity. Unlike a normal BLDC motor which has a standard power curved characterized with maximum power is only achievable in one specific speed, if properly controlled will have an adjustable maximum power in a wide range of rotational speed. This study proposes a novel approach to an ideal BLDC implementation through novel electronic speed controller with rotor field control in addition to normal standard motor power control. As there is no such thing as an ideal BLDC motor at the current moment, an automotive generator which has an electromagnetic rotor is converted to become a BLDC motor as an effort to approach the ideal BLDC motor concept. Field weakening, the term used for adjusting rotor magnetic field in induction motor control, is adopted as the term for adjusting the BLDC rotor field in operation. Further, a novel an electronic control system is developed which special features to also control the rotor magnetic field. The converted generator has been found to able to function like an ideal BLDC motor, by adjusting the electromagnetic rotor in its operation. It has been found to be able to provides maximum motor power within a wide range of rotational speed. Through rotor field adjustment, the converted generator provides a real-time versatile capability of allocating its power to either the high torque at low motor speed or to a very high speed at minimum torque. 39% to 81% operational efficiency levels have been achieved during the experiment, rendering the performance level of the converted generator and controller way above brushed DC motor and in par with most of standard BLDC motor. The Field Weakening control has also been found to be useable for speed control. Further, a Proportional – Integral close-loop speed regulation has also been developed for both motor and rotor control and was found to be able to works subsequently with seamless transition between each other.