predefined speed control of bldc motor

ssssPredefined Speed Control of BLDC Motor

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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 to have a low-cost but effective BLDC motor controller. Based on the principle of PWM, speed of the motor can be controlled.

Predefined Speed Control of BLDC Motor

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Block Diagram







Hardware Components

8051 series Microcontroller LCD Transformer Voltage Regulator Capacitors Resistors Diodes BLDC Fan EEPROM







Software Components

Keil compiler

Languages: Embedded C or Assembly.







MICROCONTROLER

The AT89C52 is a low-power, high performance CMOS 8-bit microcomputer with 8Kbytes of Flash programmable and erasable read only memory (PEROM).

The on-chip Flash allows the program memory to be reprogrammed in system or by a conventional nonvolatile memory programmer.







Features

8K Bytes of In-System Reprogrammable Flash Memory

Endurance: 1,000 Write/Erase Cycles

Fully Static Operation: 0 Hz to 24 MHz

Three-level Program Memory Lock

256 x 8-bit Internal RAM







BLDC Motor

The BLDC motor is an AC synchronous motor with permanent magnets on the rotor (moving part) and windings on the stator (fix part).

Permanent magnets create the rotor flux and the energized stator windings create electromagnet 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.

BLDC Motor







Principle of BLDC Motor

Frequency inverter used as Commutator.

Commutation depends on rotor position.

Speed control by motor voltage.

Angle between mmfs of a stator and rotor is fixed to 90 degree.

Motor behaves like a DC Motor.

No commutation occurs on spinning shaft.







Circuit Operation

The operation of the circuit can be explained in three parts.

Control circuit

Motor driver and Gate driving circuit

Converter circuit







Control Circuit

Control circuit gives out the switching signals to the converter bridge.

A microcontroller is dedicated to generate the switching pulses.

The microcontroller is programmed to give out pulse according to SVPWMM technique.

Program is compiled in Keil software.







The HEX code generated is loaded into the Microcontroller.

The controller used is AT89C52.

The controller is operated at 11.059 MHz frequency.

Control Circuit







Instead of using an inverter and a regulator we have used a motor driver HW30A which acts as inverter to supply the voltage for the Motor.

HW30A is an inbuilt Inverter which is having Inverter circuit as well as MOSFET Driver circuit.

We are using this type of technique because of on using general inverter.

Motor Driver And Gate Driving Circuit







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.

By using this motor driver the circuit complexity is reduced and the heat dissipation problem, is also reduced.

Motor Driver And Gate Driving Circuit







Converter Circuit

The converter circuit is provided by the Motor driver.

The D.C supply is fed through a bridge rectifier.

The switches in the Motor driver are turned ON and OFF as per the program.

The rectifier circuit is made of diodes.

The component used is IN4007 which is capable of blocking a reverse voltage of 1000 V DC and can carry a current of 10A continuous.







All these components are placed on General PCB.

Control circuit and gate driving circuit components are soldered directly on the Pcb.

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

Converter circuit







Working

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.

A typical biphase brushless fan motor is made from a permanent magnet rotor assembly that surrounds four electromagnetic coils.

The coils work in pairs, with coils A and C forming one phase and coils B and D the other phase.







A Halleffect sensor monitors rotor position, providing feedback to the embedded MCU for commutation, speed regulation, and fault detection.

Commutation between the two phase windings in the dc fan takes place electronically by alternately applying power to L1 and L2.

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.

The on and off power of the commutation period resembles the output from a pulse width modulator.

Working Principle







The MCU uses a PWM to control the period of the motor drivers and, thus set fan speed.

Feedback from the Hall sensor monitors actual fan rpm and indicate when communication should take place.

The MCU continuously monitors motor speed by measuring the output period of the Hall effect sensor.

A period that run shorter than the target length indicates motor speed is too fast.

Working Principle







Speed Control Of BLDC Motor

Pulse width modulation is a commonly used technique for controlling power to an electrical device.

The PWM switching frequency has to be much faster than what would affect the load.

Typically switching’s have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies







The term duty cycle describes the proportion of on time to the regular interval or period of time.

A low duty cycle corresponds to low power, because the power is off for most of the time.

Duty cycle is expressed in percent, 100% being fully on.

The main advantage of PWM is that power loss in the switching devices is very low.








When a switch is off there is practically no current and when it is on, there is almost no voltage drop across the switch.

Power loss, being the product of voltage and current, is thus in both cases close to zero.

The desired speed can be obtained by changing the duty cycle.

The PWM in microcontroller is used to control the duty cycle of DC motor.

Average Voltage=D * Vin








SIMULATION RESULTS FOR VARIOUS PWM PULSES

The speed control technique employed here is pulse width modulation (PWM) technique.

The duty cycle determines the speed of the motor

Average voltage = D * Vin

The average voltage obtained for various duty cycles is also mentioned and as the duty cycle percentage decreases average voltage also decreases from the supply voltage.







Duty cycle is defined as the percentage of time the motor is ON.

Therefore, the duty cycle is given as

Duty Cycle = 100% x Pulse Width/Period

Where, Duty Cycle in (%) Pulse Width = Time the signal is in the ON or high state(sec)

Period = Time of one cycle (sec).


SIMULATION RESULTS FOR VARIOUS PWM PULSES






Applications

BLDC motors fulfill many functions originally performed by brushed DC motors.

Cost and control complexity prevents BLDC motors from replacing brushed motors completely in lowest cost areas.

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







Advantages

Voltage and current rating is high.

High speed can be achieved.

As there is no brushes it requires no servicing.

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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predefined speed control of bldc motor

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