04-05-2012, 02:50 PM
Optimal PID Speed Control of Brushless DC Motors Using LQR Approach
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Introduction
The most common type of actuator that converts
electrical energy into mechanical motion is the electric
motor. The speed of permanent magnet DC motors is easy
to be controlled for the torque-speed curve being almost
hear 111. Brushless DC (BLDC) motors develop from
permanent magnet DC motors. BLDC motors have the
advantages like permanent magnet DC motors, such as
good response and easy control. In addition, BLDC
motors use Hall effect sensors in place of mechanical
commutations and brushes. Therefore, BLDC motors
possess other benefits that permanent magnet DC motors
lack for, such as low noise, no mechanical loss, and etc.
BLDC motors have been widely applied in many control
systems--the spindle motor in compact disc drives with
the goal of a low moment of inertia for example.
Brushless DC motors
Permanent magnet DC motors use mechanical
commutators and brushes to achieve the commutation.
However, BLDC motors adopt Hall effect sensors in place
of mechanical commutators and brushes [9]. The stators
of BLDC motors are the coils, and the rotors are the
permanent magnets.
Conclusions
This paper has presented a novel tuning formula that
uses the LQR methodology to seek the optimal PID
parameters. The main merits of the proposed scheme
include (I) there is no need for the ohseiver design (2)
there is no constraint in the PID parameters (3) the
weighting functions could be determined through poles
assignment. The existence conditions of the optimal PID
controller for desired response are also ubmitted. The
whole design idea has been successfully implemented on
the speed control of a BLDC motor. Computer
simulations and experimental results demonstrate that the
excellent performance of the optimal PID controller.