DESIGN AND IMPLEMENTATION OF BLDC MOTOR DRIVE CONTROLLER FOR ELECTRIC VEHICLE APPLICATION

Abstract

The renewed global interest and international efforts to reduce dependency on exhaustible fossil fuels have provided the necessary impetus to the electric vehicle (EV) related research areas including battery systems, motors, drive controllers and different driving mechanisms for automotive applications. The major technological challenges faced by the earlier EV systems were heavy electric batteries, inadequate performance of electric motors, lack of electronic control systems and cost issues. Over the years all these areas of concern have been adequately addressed by the existing research works and technological advancements for wider acceptance of EVs. Permanent magnet motors (PMMs) are among the most prominent type of electric motors used in EV applications. Brushless DC (BLDC) motors and permanent magnet synchronous motors (PMSM) are the widely used PMMs in EV applications. Their inherent advantages such as fast response, compact size, light weight, high efficiency, brushless configuration, and good dynamic performance have given the major impetus to the wider application scope in EVs and automation industry applications. The development of BLDC motor drives with high performance characteristics coincided with the availability of dedicated motor controllers, high performance microcontrollers and inverters with power switching devices like power metal oxide-semiconductor field-effect transistors (MOSFETs) due to advancements in VLSI techniques. This has led to their increased deployment in EV applications. BLDC motors equipped with hall effect sensors (HESs) for feedback are a preferred solution where continuous tracking of rotor position is not required and discrete known positions at fixed angular interval are sufficient for the application. It is a commonly used arrangement in several types of EVs, home appliances, and automation applications. BLDC motor drives offer inherent advantages of increased power density, low maintenance requirements and precise control system mechanisms. The motor operation requires deployment of electronic commutation methods and control mechanisms that are implemented through a dedicated controller. Essential drive parameters such as phase currents, phase voltages, duty cycle of inverter switching signals, their synchronization and commutation sequence are all controlled and monitored by this controller. The control of motor torque and speed according to the application requirements is maintained by deploying appropriate software in the controller for implementing state machine logic and computational algorithms. Besides control of motor operation, provision for fault tolerant control (FTC) methods and diagnostic software routines are also essential in the motor controller design. Thus, controller vi design is one of the most important aspects of a BLDC motor drive system. This research work focuses on the design and development of the motor controller for sensored BLDC motor drives with three HESs. The simulation model of the 3-phase BLDC motor drive with trapezoidal BEMF profile is developed in MATLAB software platform for simulation and analysis. The hardware test bench set up for the research work includes 32bit ARM microcontroller based controller circuit with inverter and driver sections. The software development is carried out using the IAR IDE platform for ARM controllers. The overall operation of drive control mechanism and associated application in BLDC motor drives with HESs is dependent on the integrity of the signals obtained from three HESs and, their synchronization with the motor back electromotive force (BEMF) profile. These HESs are mounted inside the BLDC motor in majority of the applications. Any error in HES signals directly affects the operation of the drive. The issues of mistiming in HES signals and delayed signal at the controller input terminals are reported in mass scale produced motors for applications like electric rickshaw and three wheeler EVs. HES signal issues arise mainly due to incorrect sensor positioning owing to mechanical, mounting, or production problems. Other factors like ageing, degradation, and filter circuit component failure in the controller circuit also contribute to the HES signal mistiming. The inaccurately timed HES signals result in mistimed switching of the inverter switches in the controller. This causes deviations in the commutation instants. This can further cause increased current and torque ripples, noise and jerks along with inaccurate position control in the drive. Besides, there are other issues of unwanted glitches in the HES signals that need to be addressed by the controller without allowing disturbance in the control scheme. These types of errors have a more pronounced effect on drives employing small sized BLDC motors with higher numbers of poles. Furthermore, the FTC schemes need to be developed in such a way that one type of fault control operation does not hinder the implementation of other FTC schemes in controller. The integrity of the original state machine model, startup routines and control system stability must remain intact by implementation of the FTCs and correction schemes in the controller. The presented research work includes analysis and mitigation of the faults related to HES signal timings. The mapping of unbalanced HES signals with corresponding HESs is investigated for mitigating the effects of this type of fault in a better and efficient way. Furthermore, the investigation and estimation of commutation delay angles by establishing a direct approximation relation with DC link current profile is presented. This is especially advantageous for applications relying only on DC link current measurement without phase current or BEMF estimation schemes. The possibility of actual implementation of the FTC schemes in motor controller is an important aspect from a practical application viewpoint. The vii FTC schemes corresponding to HES signal timing issues, commutation delay and glitches in HES signals are proposed in the research work. These FTC schemes can be incorporated in the controller without requiring any modifications to the circuit, control algorithm, state machine model, or application guidelines. Other FTC techniques can be applied in accordance with the control algorithm. The design and development of the motor controller is carried out by implimenting HES based BLDC drive control mechanism that is used in several EV applications. The controller is developed around a 32-bit STM32 ARM microcontroller for integration with 1 kW BLDC motor commonly used in electric autorickshaws. The hardware test bench setup is developed for motor controller integration and, for experimental verification of the proposed algorithms. In EV applications such as electric rickshaws, manual harness connectors are used to connect HESs and phase wiring connections of the motor and controller. Automatic phase sequence detection is required in these applications. Hence, the auto phase sequence detection method is also implemented and validated in the controller. This is required in EV applications particularly like electric rickshaws wherein the phase and HES terminals of motor and controller set are joined manually by harness connectors. Experimental validation of all proposed schemes is carried out in the developed motor controller hardware test bench setup for demonstrating controller operation and efficacy of the proposed solutions. Further study and analysis of the effect of the HES signal faults and improvements due to FTC scheme implementation on the motor performance such as phase voltage, phase current, DC link current profile and speed are carried out in the research work.