03-05-2011, 03:32 PM
Abstract
This paper introduces a sensorless nonlinear control
scheme for controlling the speed of a permanent magnet
synchronous motor (PMSM) driving an unknown load torque.
The states of the motor and disturbance torque are estimated via
an extended nonlinear observer avoiding the use of mechanical
sensors. The control strategy is an exact feedback linearization
law, with trajectory tracking evaluated on estimated values
of the PMSM states and the disturbance torque. The system
performance is evaluated by simulations.
I. INTRODUCTION
ELECTRICAL drives using permanent magnet synchronous
motors (PMSM’s) are often used in many
applications. The performance of adjustable speed drives
containing PMSM’s can be improved implementing nonlinear
control strategies. Among others, feedback linearization has
emerged as a very useful control law for electrical drives [1],
[2]. It consists in exactly linearizing the PMSM by feedback
and transformation, so that well-known linear control strategies
can be used on the whole state space. The implementation of
feedback linearization, as well as the other strategies, requires
an optical/mechanical sensor to obtain position and speed as
part of the state to be fed back. However, mechanical sensors
can be avoided when sensorless control strategies are designed.
In such cases rotor position and speed must be estimated and
these estimated values used to compute the control law.
State observers can be used to estimate the rotor position and
speed of PMSM’s. Several approaches to obtain PMSM state
observers have been proposed, nonlinear full order observers
based on linearization, extended Kalman filter (EKF), viz. nonlinear
observers, nonlinear reduced order observers (see [3] and
references therein). In [4], [5] and [6] observer-based speed controllers
have been proposed. In these papers certain assumptions
have to be introduced to design the observer-based con-
Manuscript received September 3, 1998; revised March 16, 1999. This work
was supported by the National University of La Plata (UNLP), Secretaría de
Ciencia y Técnica (SECYT), National Research Council (CONICET), and
Statal Research Council (CICPBA).
J. Solsona is with the Universidad Nacional del Comahue and CONICET
Grupo de Control Automático y Sistemas (GCAyS), Facultad de Ingeniería,
U.N.Co Buenos Aires 1400, 8300 Neuquén, Argentina.
M. I. Valla is with the Universidad Nacional de La Plata and CONICET Laboratorio
de Electrónica Industrial, Control e Instrumentación (LEICI), Facultad
de Ingeniería, U.N.L.P. CC 91, 1900 La Plata, Argentina.
C. Muravchik is with the Universidad Nacional de La Plata and CICPBA Laboratorio
de Electrónica Industrial, Control e Instrumentación (LEICI), Facultad
de Ingeniería, U.N.L.P. CC 91, 1900 La Plata, Argentina.
Publisher Item Identifier S 0885-8969(00)04517-4.
troller. In [5], a known load torque has been considered, while
in [6] the value of inductance is assumed to be zero to design the
controller. In [4], the authors assume that machine speed is approximately
constant during a short time interval. Nevertheless,
when higher performance is required the mismatches caused
by an unknown load torque, a nonzero inductance and variable
speed have to be compensated. In this paper we use the extended
nonlinear observer presented in [7] to estimate the PMSM state
vector and the disturbance torque. Then, we construct a sensorless
speed control strategy capable of tracking speed references
when the PMSM drives unknown load torques.
The paper is organized as follows. In section II the equations
describing the PMSM model are reviewed. In section III
feedback linearization applied to PMSM is obtained. The nonlinear
extended observer used to estimate PMSM’s states and
unknown load torque is briefly described in section IV. The proposed
sensorless nonlinear speed control is introduced in section
V. System performance is evaluated in section VI. Finally, conclusions
are drawn in section VII.
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