Nonlinear Torque Control of BLAC Motor Karel Jezernik, Robert Horvat, Milan Čurkovič University of Maribor, Faculty of Electrical Engineering and Computer Science, Maribor, Slovenia (e-mail: karel.jezernik@ini-mb.si, robert.horvat@uni-mb.si, milan.curkovic@uni-mb.si)} Abstract: This study presents the implementation of a hybrid control strategy applied to a brushless AC (BLAC) motor drive. Hybrid control is a general approach for control of a switching-based Hybrid Systems (HS). This class of HS includes a continuous process controlled by a discrete controller with a finite number of states. The overall stability of the system is shown using Lyapunov technique. The Lyapunov functions used contain a term penalizing incremental energy of control error, torque and stator current, enhancing the stability. The closed-loop system with the proposed control low provides good transient response and good regulation the BLAC motor control. A new logical FPGA torque controller based on Lyapunov theory are developed, analyzed and experimentally verified. Keywords: Brushless motors, Discrete-event systems, Lyapunov methods, Motor control, Stability analysis 1. INTRODUCTION The Brushless AC (BLAC) motor is now widely used industrial drive applications due to its many advantages such as high power factor, high torque density, high efficiency, small size, and weight. A position sensor is required to enable high quality control and performance of a BLAC motor. The nonlinear and complex dynamic interactions of AC machine, coupled with the fact that some important qualities are not measurable, cause considerable difficulties in designing high performance AC drive control. Additionally, the uncertainties arising from imperfect knowledge of system inputs and inaccuracies in the mathematical modeling itself, contribute to performance degradation of the feedback control system. Over the years it has been generally accepted that field orientation, in one of its many forms, is the most promising control method for a high dynamic performance AC drive. The direct torque control (DTC) is basically an advanced scalar control method and has found acceptance in replacement of conventional volts/Hz control (Boldea at al.). In spite of AC drives widespread popularity no rigorous stability proof for field oriented control or DTC control was available in the literature. In this paper we provide some answers to these questions (Buja at al.). This paper introduces recently developed hybrid based approach for modelling of discrete event systems in the field of power electronics and motion control. Power electronic circuits are hybrid dynamic systems. Because of the ON and OFF switching of power electronic devices, the operation of power electronic circuits can be described by a set of discrete states with associated continuous dynamics. A hybrid structure arises when a logical control unit governs such a system by using logic decision (Buisson at al.). In this paper a hybrid control law based on Lyapunov stability theory, without linearization, is proposed that strictly quarantines a sufficient stability region in the state space for the system against large-signal disturbances. In this approach, Lyapunov direct method which is the most important tool for nonlinear control system design is used. Lyapunov theory has for long time been an important tool in linear as well as nonlinear control. However, its use within nonlinear control has been changed by the difficulties to find the Lyapunov function for a given system. If one can be found, the system is known to be stable, but the task of finding such a function has often been left to the imagination and experience of the designer (Branicky at al.). In using the direct method, the idea is to construct a scalar- energy-like function (Lyapunov function) for the system and to examine the function's time variation. The closed-loop system with the proposed control law not only guarantees a sufficient stability region, but also provides good transient response and good regulation. The aim of this paper is the design of a control law for a BLACM to achieve good torque control in steady state and transient operating conditions. The feedback system is globally asymptotically stable in the sense of the Lyapunov stability theory. Therefore we are interested in an extension of the Lyapunov function concept. This concept used such a scalar function which contains a logical discontinuous input switching function penalizing the torque, i.e. current control error, enhancing the stability. 2. BLAC MOTOR CONTROL The BLAC motor combines many of the advantages of the permanent excited AC motor and the synchronous motor. The BLAC motor needs low reactive current, so similar to the DC motor, the current is proportional to the torque. The shaft torque is therefore easy to estimate by detecting three- phase current of BLAC motor. The BLAC motor is the combination of a permanent excited synchronous motor and a 5th IFAC Symposium on Mechatronic Systems Marriott Boston Cambridge Cambridge, MA, USA, Sept 13-15, 2010 978-3-902661-76-0/10/$20.00 © 2010 IFAC 453 10.3182/20100913-3-US-2015.00006