Mohsin Khan | mohsinkhanmit26@gmail.com |, Sameer Gunjal | sameergunjal27@gmail.com |
NitishRaina | aston.villa050@gmail.com | and Prasheel V. Suryawanshi* (Project guide)
Abstract: In this brief, a multi-axis
controller is proposed for speed-position control of BLDC motor. The
construction of this controller will begin with the development of switching
circuit, which is the heart of power module. PIC controller will be used to
generate commutation sequence. Proteus(ISIS) is primarily used to analyze the
drive circuit virtually so that the circuit parameters such as components
specifications in terms of voltage and current can be predicted so that
component selection can be done.
The speed control is implemented using Proportional-Integral-Derivative (PID)
algorithm.
Keywords: Switching Circuit, PID
Algorithm, BLDC Motor
INTRODUCTION
The term "Multi-Axis Synchronization" refers
to the motion which requires coordination, and the techniques used to achieve
control of the motion. When two or more axes of motion are involved on a single
machine, that machine is employing multi-axis motion.The need for multi-axis
synchronization arises whenever the axes must move together and the
relationship between their respective motions is important. Brushless Direct
Current (BLDC) motors are one of the motor types rapidly gaining popularity. As
a name implies, BLDC motors do not uses brushes for commutation, instead they
are electronically commutated.
Motor commutation of BLDC motor is implemented by an
electronic controller and to determine the rotor position and to know when to
commutate, either hall sensor (Sensored commutation) or back EMF generated in
the stator winding of the motor (Sensorless commutation) are used. Hall sensor
based controller are simpler to implement compared to the sensorless control
and are used in application that require good starting torque. This paper
discusses a hall sensored commutation control that uses dsPIC33F256MC710
micro-controller as the motor controller.
Depending on the number of the stator, BLDC motors are
available in 1-phase, 2-phase and 3-phase configuration. This paper discusses
the 3-phase BLDC motor control in close loop control configuration.
Fig1. BLDC MOTOR TRANSVERSE SECTION
Fig1 shows a transverse section of a BLDCmotorwith a
rotor that has alternate N and S permanent magnets.Hall sensors are embedded
into the stationary partof the motor.Based on the physical position of the Hall
sensors,there are two versions of output. The Hall sensors maybe at 60° or 120°
phase shift to each other. Based on
this, the motor manufacturer defines the
commutationsequence, which should be followed when controllingthe motor. A
functional block diagram of our proposed system is depicted in Figure 2
Fig 2. System Block Diagram
The input reference speed is provided by
potentiometer. The dsPIC33F256MC710 implements the closed-loop control plus
3-phase motor commutation. A PID controller is used to implement the
closed-loop control that uses both the reference input speed and the actual
motor speed feedback to update the timer PWM duty cycle that in turn, controls
the motor-speed.
DSPIC33F
MOTION CONTROL
A typical multi-axis motion control system requires simultaneous and
synchronized speed and position control of more than one motor. Also,
exploiting PID algorithm for each of the speed and position control along
various axes of a plant requires a micro-controller with sufficiently large
number of peripherals suitable for motion control purpose, along with extensive
mathematical processing capability. dsPIC33F DSCs(Digital Signal
Controllers) with motor control,
peripherals offer the performance of a DSP with the simplicity of an
MCU(Microcontroller unit), with its 16-bit core designed to execute high
performance, precision motor control systems. The powerful array of
peripherals, render dsPIC33F devices suitable for control applications.
CONTROL
MECHANISM
Two control mechanisms have been implemented in
this project viz. open loop and the close loop.
A. OPEN LOOP
CONTROL
In open loop control system when an input
signal directs the control element to respond, an
output will be produced.
Fig3. Open Loop Control System
There is no any means for controller to make sure
the task was performed correctly and it often needs human intervention to
obtain accurate results. Examples of the open loop control systems include
washing machines, light switches, gas ovens, etc.
B. CLOSE LOOP CONTROL
Closed-loop controls are used in application that
require more accurate and adaptive control of the system. These control use
feedback to direct the output states of a dynamic system. Closed-loop system
overcome the drawbacks of open-loop control to provide compensation for
disturbances in the system, stability in unstable process and reduced
sensitivity to parameter variations (Dynamic load variation).
Fig4. Close Loop Control System
A PID controller is a closed-loop control implementation that is widely used and is
most commonly used as a feedback controller. This paper describes a PID
controller to provide closed-loop control for the 3-phase BLDC motor control.
HARDWARE DESIGN
3-PHASE POWER MODULE
The 3-phase power module is used to
drive the BLDC motor as specified by the control
signal provided by the controller to
the driver. This power module uses six transistors to control the current flow
in the motor windings. The transistors provided at the top and bottom turn on
and off repeatedly according to predetermined sequence, thereby controlling the
flow of current to the motor windings.
SOFTWARE
The software for the motion control has been developed
in embedded C using C30 compiler of Microchip in MPLAB IDE.
RESULT AND
ANALYSIS
Figure 6 shows experimental set-up of system and Figure 7
shows motor's speed received in computer through serial communication.
Fig. 6 Experimental Set-up
Fig. 7 Serial Communication
Figure 8 and Fig. 9 shows the LCD interfaced with controller in 4-bit
and 8-bit mode respectively.
Fig. 8 LCD Interfacing(4-bit)
Fig. 9 LCD Interfacing(8-bit)
six PWM generated by
the controller.
CONCLUSION
This paper describe the speed control of three
phase BLDC motor. Microchip’s
16-bit
dsPIC33F256MC710 micro-controller is used to
generate six PWM signals. The top and bottom transistors turn on and off,
according to predefined sequence. The 3-phase power module is used to boost the voltage to
drive motor at higher voltage level.
The PID controller reduces the error
between reference speed and actual speed. The duty cycle of PWM is modulated according to
the error between setpoint and actual value of speed.
