MULTI-AXIS BLDC MOTOR CONTROLLER

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.