Speed Control of BLDC Motor

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Speed Control of BLDC Motor

Introduction

The aim of the project is to control the speed of a BLDC motor using a microcontroller with the help of SVPWM-Technique. A Brushless DC (BLDC) motor drive is characterized by higher efficiency, lower maintenance and higher cost. Therefore it is necessary That to have a lower cost but effective BLDC motor controller. Based on the principle of PWM speed of the motor can be controlled.

 Blog Diagram


Required Hardware Components
                                             
ü 1234 series microcontroller
ü LCD
ü Transformer
ü Regulated Power supply 5volts
ü Capacitors
ü Resistors
ü Diodes
ü BLDC fan
ü EEPROM
ü  
Software components
ü Keil Compiler
ü Language’s-Embedded C or Assembly
Microcontroller
o  The AT89C51 is a low-power high performance CMOS 8 bit microcomputer with 8 kilobytes of flash programmable and erasable read only memory (PEROM).
o  The on chip flash allows to programmer to reprogram the microcontroller as per requirement.

Features
o  8K Bytes of in-system reprogrammable flash memory.
o  Endurance - 1000 Wrights/Erase cycles.
o  Fully static operation - 0Hz to 24MHz.
o  Three level Program memory lock.
o  256 X 8-bit internal RAM.
BLDC Motor
The BLDC motor is a AC synchronous motor with permanent magnet on the rotor and winding on stator.
Permanent magnet Creates rotor flux and induce rotor flux and energized stator windings and creates electromagnetic poles.
The rotor is attracted by the energized stator phase.
By using the appropriate sequence to supply the stator phases, a rotating field on the stator is created and maintained.
The lead between the rotor and the rotating field must be controlled to produce torque and this synchronization implies knowledge of the rotor position.
Principle of BLDC Motor

o  Frequency inverter used as commutator.
o  Commutation depends on rotor position.
o  Speed control by motor voltage.
o  Angle between mmfs of a stator and rotor is fixed to 90 degree.
o  motor behaves like a DC motor.
o  No commutation occurs on spinning shaft.

Circuit Operation

The operation of the circuit can be explained in three parts.
o  Control circuit
o  motor driver and gate driving circuit
o  Converter circuit

Control Circuit

o  Control circuit gives out the switching signals to the converter bridge.
o  A microcontroller is dedicated to generate these witching pulses.
o  The microcontroller is programmed to give out pulse according to SVPWMM technique.program is compiled in keil software.
o  The Hex code generated is loaded into the microcontroller.
o  The controller used is AT89C52.
o  The controller is operated at 11.059MHz Frequency.

Motor Driver and Gate Driving Circuit

o   instead of using an inverter and a regulator we have used a motor driver HW3A which acts as inverter to supply the voltage for the motor.
o  HW3A is an inbuilt inverter which is having inverter circuit as well as MOSFET Driver circuit.
o  we are using this type of technique because of on using general inverter.
o  we are facing the difficulties like large heat dissipation so that this heat would cause a heat sinking problem which in turn results in the failure of the inverter.
o  By using this motor driver the circuit complexity, is reduced and the heat dissipation problem is also reduced.

Converter Circuit

o  The converter circuit is provided the motor driver.
o  The D.C supply is fed through a bridge rectifier.
o  The switches in the motor driver are turned ON and OFF as per the program.
o  The rectifier circuit is made of diodes.
o  The component used is IN4007 which is capable of' locking a reverse voltage of 1000v DC and can carry a current of 10A continuous.
o  all these components are placed on general PCB.
o  Control circuit and gate driving circuit components are soldered directly on the PCB.

o  Whereas the power components as connected with suitable connectors as they carry larger currents.

working
o  The basic construction of a brushless dc consists of a fan blade attached to a permanent magnet rotor that surrounds the electromagnetic coils of the stator and associated control electronics.
o  A typical biphasic brushless fan motor is made from a permanent magnet rotor assembly that surrounds for electromagnetic coils.
o  The coils work in pairs with coils & and C forming one phase and coils B and D the other phase.
o  A Halle effect sensor monitors rotor position providing feedback to the embedded MCG for commutation, speed regulation, and fault detection.
o  Commutation between the two phase windings in the dc fan takes place electronically by alternately applying power to L1 and L2.
o  Dead zones between the power pulses limit current for speed control and helps minimize a cogging effect when the rotor magnets align with the stator coils.
o  The on and off power of the commutation period resembles the output from a pulse width modulator.
o  The MCG uses a PWM to control the period of the motor drivers and, thus set fan speed.
o  affaced back from the all sensor monitors actual fan rpm and indicate when communication should take place.

o   The MCU continuously monitors motor speed by measuring the output period of the hall effect sensor.
o  A period that run shorter than the target length indicates motor speed is too fast.


Speed Control Of  BLDC Motor
o  pulse width modulation is a commonly used technique for controlling power to an electrical device.
o  The PWM switching frequency has to be much faster than what would affect the load.
o  Typically switching have to be done several times a minute in an electric stove, 120Hz in a lamp dimmer, from few kilo hertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kin audio amplifiers and computer power supplies.    
o  The term duty cycle describes the proportion of on time to the regular interval or period of time.
o  A low duty cycle corresponds to low power, because the power is of for most of the time.
o  Duty cycle is expressed in percent 100% being fully on.
o   The main advantage of PWM is that power loss in the switching devices is very low.
o  when a switch is off there is practically no current  and when it is on, there is almost no voltage drop across the switch.
o  power loss, being the product of voltage and current, is thus in both cases close to zero.
o  The desired speed can be obtained, changing the duty cycle.
o  The PWM in microcontroller is used to control the duty cycle of DC motor.



Applications

o  BLDC motors fulfill man, functions originally performed by brushed DC motors.

o  Cost and control complex it, prevents BLDC motors from replacing brushed motors completely in lowest cost areas.

o  High power BLDC motors are found in electric Vehicles and hybrid vehicles.


Advantages

o  voltage and current rating is high.
o  High speed can be achieved.
o  As there is no brushes it requires no servicing.
o  There is no sparking, less electrical noise.

Conclusion

The hardware for closed loop control of BLDC motor using microcontroller is designed. By using the PWM technique speed of the BLDC motor was controlled and it was made to run at exactly entered speed. in future this hardware will be implemented and the speed control will be observed.

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