IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE) e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 11, Issue 1 Ver. IV (Jan. – Feb. 2016), PP 19-25 www.iosrjournals.org DOI: 10.9790/1676-11141925 www.iosrjournals.org 19 | Page Sensorless Control of Brushless DC motors and H ∞ Control Theory Applications - A Literature Review K Vinida 1 , Mariamma Chacko 2 1 (Department of Ship Technology, Cochin University of Science & Technology, India) 2 (Department of Ship Technology, Cochin University of Science & Technology, India) Abstract : This paper reviews the recent developments in the field of sensorless control of Brushless Direct Current motors. Moreover a survey of application of H ∞ control theory for robust control, considering the uncertainties like modeling errors and external disturbances in various motors and systems has been carried out. This provides a deeper insight into the recent developments and future scope in the robust control of sensorless BLDC motors to mitigate the effects of parametric uncertainties and unmodeled dynamics. Keywords - BLDC motor, Disturbance, H ∞ control, Robust, Sensorless control. I. Introduction Brushless Direct Current motors (BLDCM) exhibit tremendous advantages such as elimination of sparking, better speed verses torque characteristics, noiseless operation, higher speed ranges, better service life, rugged construction, etc. This finds applications in day to day life such as household products, military, aerospace, industrial automation and so on. A lot of research work is being carried out in proper commutation of windings, improvement in speed variation, reduction of torque ripples and response time and stability of the motor under disturbances as well as uncertainties. When the stator phases in a BLDCM are energised, a flux is generated in the stator which interacts with the rotor magnetic flux. Maximum torque is produced when the angle between stator and rotor flux is 90 degrees. Therefore, it is important to know the position of rotor in order to ensure alignment of stator flux close to 90 degrees. There are two ways of rotor position sensing in a BLDCM, which are by use of sensors [1] and by sensorless methods. Position sensorless control technology attracts increasing research interest because it saves cost, space, maintenance, etc. and has become one of the most promising trends of BLDCM control system. Rotor position sensing by various sensorless techniques has been proposed in the literature which include inductance and flux measurement method, back emf detection, estimation and observer based models. Usually, there exist nonlinearities and perturbations in mechanical control objects. The modelling of these parameters for control design is difficult. Even though they are modelled, control system design and adjustment of parameters with a conventional controller like PID are difficult and tuning requires more work and consumes time. Robust control is concerned with the problem of designing control systems when there is uncertainty about the model of the system to be controlled or when there are external disturbances influencing the behaviour of the system. The modern approach to design controllers which are robust against model uncertainties is provided by the H ∞ control theory. This paper presents the research efforts carried out by various researchers in this field starting from the year 1991 which is being basically categorised based on sensorless BLDC motor control and various applications of H ∞ control theory. II. Research Efforts On Rotor Position Sensing By Sensorless Techniques Obtaining rotor position information from electrical measurements without any position sensor is the technique used in a permanent magnet brushless sensorless drive. Various existing technologies that are being adopted in the sensorless control of BLDC motors are shown in Fig. 1. The control methods of BLDC motor which include types of PWM techniques used, various methods for rotor position detection, initial rotor position detection, recent advances in the position sensorless control of BLDC motors and the expected future research works to provide insight in sensorless drive techniques along with their benefits have been reviewed in the literature [2]-[5]. The research efforts carried out on the three basic types of sensorless control schemes that are found in the literature are described below. 2.1 Research Efforts on Position Estimation Using Inductance And Flux Measurements The inductance of a phase which includes both self and mutual inductances and hence the flux linkage, varies with the rotor position. The flux linkage is calculated using measured voltages and currents as per equations (1)