Sliding mode observer and controller for Performance improvement of Brushless DC Motor

Abstract

Abstract-The present paper proposes a control scheme comprising of a new sliding mode controller (SMC) with sliding mode observer (SMO) for improved performance of a Brushless DC (BLDC) motor. The SMO is used to estimate rotor speed and rotor position using terminal voltages and currents of the BLDC motor. The error between actual and estimated currents taken as the sliding surface from which the back emf is estimated which is further used to estimate rotor position and speed. The SMC consists of both speed control and current control loops where the reference to the currents is derived from speed error using PI controller. The speed error and current error together comprises the sliding surface. The proposed SMC is an alternative to second order SMC and it eliminates the derivative of the sliding variable for speed control thus eliminating complexity while preserving the benefits. The simulation results of the proposed scheme are compared with those of the conventional scheme to prove its effectiveness.Keyword-BLDC Motor, Sliding mode controller, Sliding mode observer I. INTRODUCTION There has been a tremendous interest in permanent magnet drives in recent years due to their excellent characteristics like low power requirement, high energy savings and ease of control. Majority of the BLDC motor advantages attributed to its construction in which its armature winding placed in stator and field is provided withthe permanent magnets placed in rotor. This makes the cooling arrangement is easier for BLDC motor as compared to the conventional dc motor. Due to the permanent magnet rotor, the commutation process is not possible from the rotor side like a DC motor [1]. So an electronic commutation is used in which the supply to the motor will be controlled through inverter. In order to make a phase to conduct, we need to find the exact location of the rotor poles and the commutation sequence must be ensured such that a phase difference of 90o must be maintained between stator flux and rotor flux to get maximum torque [2].To attain information regarding the position of rotor, transducers like hall sensors are used. The hall sensor transmits logic high or logic low signal based on the proximity of a pole as the magnetic field of a pole induces emf in it. For a three phase BLDC motor, three sensors are aligned with 1200 phase shift to get complete information regarding back emf voltages in all phases and this hall sensor circuit is placed on the non-rotating part of motor [3].The position sensor circuit requires a special arrangement to be mounted on the motor and need dedicated electronic circuitry. If the motor is far away from the control center, then we need a separate cabling system for signal transmission. All these requirements increase the cost and reduce the reliability of the drive [4]. Hence sensor control schemes cannot be utilized in situations where high reliability is needed and the motor has to operate in harsh environments. One of the solutions is to estimate the position of the rotor using voltage and curr...

Critical Review on Torque Ripple Sources and Mitigation Control Strategies of BLDC Motors in Electric Vehicle Applications

“…Similar to this, SMC operates senselessly and employs a higher order sliding mode observer (HOSMO), mostly for speed and position estimates. It is suitable for electric vehicle (EV) applications because it produces consistent results with low estimation error, improved speed tracking efficiency, and minimal torque ripples [233,237]. In addition, Hysteresis controller and SMC work together to improve motor current control, it can track the reference signal with a reasonable response time even when the motor's parameters are changed, and SMC does not need any additional sensors for current measurement [234].…”