Download Digital Control Strategy for Four Quadrant Operation of Three Phase

DIGITAL CONTROL STRATEGY FOR FOUR
QUADRANT OPERATION OF THREE PHASE
BLDC MOTOR WITH LOAD VARIATIONS
C. Sheeba Joice, S. R. Paranjothi,and V.Jaeahar Seenthil Kumar
IEEE TRANSACTIONS ON INDUSTRIAL INFORMATICS, VOL. 9,NO. 2,MAY 2013
974~982
老師:王明賢
學生:方偉晋
Abstract
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Brushless DC (BLDC) motor drives are becoming more popular in industrial, traction application.
This paper deals with the digital control of three phase BLDC motor.
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The motor is controlled in all the four quadrants without any loss of power; in fact energy is
conserved during the regenerative period.
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The digital controller dsPIC30F4011, which is very advantageous over other controllers, as it
combines the calculation capability of Digital Signal Processor and controlling capability of PIC
microcontroller, to achieve control.
Outline
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Introduction
BLDC motor
Four Quadrant Operation
PI Controller
COMPLETE DRIVE SYSTEM
Introduction
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BLDC motor has a rotor with permanent magnets and a stator with windings. The Brushless DC
motor is driven by rectangular or trapezoidal voltage strokes coupled with the given rotor position.
BLDC motors often incorporate either internal or external position sensors to sense the actual rotor
position or its position can also be detected without sensors.
BLDC motor
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The numbers shown around the peripheral
of the motor diagram in Fig. 1 represent the
sensor position code.
Based on the combination of these three
Hall sensor signals , the exact sequence of
commutation can be determined.
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Fig. 1. BLDC Motor Star connected.
BLDC motor
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These signals are decoded by combinational
logic to provide the firing signals for 120
conduction on each of the three phases.
The rotor position decoder has six outputs
which control the upper and lower phase leg
MOSFETs of Fig. 2
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Fig. 2. Equivalent Circuit of power stage of
BLDC motor
Four Quadrant Operation
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There are four possible modes or quadrants
of operation using a Brushless DC Motor
which is depicted in Fig. 3.
Fig. 3.
Four Quadrant Operation
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When BLDC motor is operating in the first and third quadrant, the supplied voltage is greater than
the back emf which is forward motoring and reverse motoring modes respectively, but the direction
of current flow differs.
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When the motor operates in the second and fourth quadrant the value of the back emf generated by
the motor should be greater than the supplied voltage which are the forward braking and reverse
braking modes of operation respectively, here again the direction of current flow is reversed.
Four Quadrant Operation
Fig. 4. Operating Modes
PI Controller
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The regulation of speed is accomplished with PI Controller. By increasing the
proportional gain of the speed controller, the controller’s sensitivity is increased to
have faster reaction for small speed regulation errors.
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This increased sensitivity also reduces the speed overshooting. The armature
current reduces faster, once the desired speed is achieved.
PI Controller
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An increase of the integral gain will allow the motor speed to catch up with the
speed reference ramp a lot faster during sampling periods.
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This will indeed allow a faster reaction to small speed error integral terms that
occur when a signal is regulated following a ramp.
PI Controller
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The controller will react in order to diminish the speed error integral a lot faster by producing
a slightly higher accelerating torque when following an accelerating ramp.
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On the other hand, too high increase of the proportional and integral gains can cause
instability, and the controller becoming insensitive.
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Too high gains may also result in saturation. Tuning process is by trial and error method and
the Proportional Constant and Integral Constant are 0.1 and 0.03 respectively.
COMPLETE DRIVE SYSTEM
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The position signals obtained from the Hall sensors of the motor are read by the I/O lines of
the dsPIC controller.
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The Hall sensor inputs give the position of the rotor which is fed to the controller. The
controller compares it with the reference speed and generates an error signal.
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The required direction of rotation either clockwise or counter clockwise can also be fed to
the digital controller.
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The PWM module of the controller generates appropriate PWM signals, which are applied to
the three phase inverter.
COMPLETE DRIVE SYSTEM
Fig. 5. Closed Loop Drive.
COMPLETE DRIVE SYSTEM
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The Hall sensor signals and the phase
current (of one phase) of three phase
Brushless DC motor are shown in Fig. 6.
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The digital storage oscilloscope images
shown in Fig. 6 indicate the trapezoidal
voltage of phases RY and YB.
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Fig. 6. Hall Sensor signals and
Phase Current