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General overview of motor drivesGeneral overview of motor drivesMechanical relay based motor drivesMechanical relay based motor drivesSemiconductor based motor drivesSemiconductor based motor drivesSpeed Control IssuesSpeed Control IssuesProtection IssuesProtection Issues Interfacing IssuesInterfacing Issues
General OverviewGeneral Overview
What is a DC Motor?What is a DC Motor? A machine that converts electrical to mechanical A machine that converts electrical to mechanical
energy.energy.
What to control in a DC motor?What to control in a DC motor? SpeedSpeed DirectionDirection Start/StopStart/Stop Positional?Positional?
General Overview – Speed General Overview – Speed ControlControl
Speed ControlSpeed ControlCan be achieved by controlling voltage or Can be achieved by controlling voltage or
current.current.The most simplest method of control is by The most simplest method of control is by
inserting a resistor (high power resistor – inserting a resistor (high power resistor – aka cement resistor) in series with the DC aka cement resistor) in series with the DC motor.motor.This method is simple but not efficient due to This method is simple but not efficient due to
high power loss (heat) at the resistor.high power loss (heat) at the resistor.
General Overview – Speed General Overview – Speed ControlControl
Variable voltage approachVariable voltage approachBy reducing/increasing the supply voltage By reducing/increasing the supply voltage
of the DC motor will decrease/increase the of the DC motor will decrease/increase the DC motor speed.DC motor speed.
The most practical method to control The most practical method to control voltage is via the PWM method.voltage is via the PWM method.
General Overview – General Overview – DirectionDirection
Basic conceptBasic conceptThe only way to control direction is change The only way to control direction is change
the ‘polarity’ of the DC motor.the ‘polarity’ of the DC motor.The ‘polarity’ of the DC motor will The ‘polarity’ of the DC motor will
determine the direction of current flow determine the direction of current flow hence will determine the direction of hence will determine the direction of rotation of the DC motor.rotation of the DC motor.
General Overview - StartGeneral Overview - Start
Starting a DC motorStarting a DC motor The most easiest way to start a DC motor is by The most easiest way to start a DC motor is by
switching in the power supply.switching in the power supply. However, it would introduce high current spikes However, it would introduce high current spikes
into the motor circuit due to the motor inertia, into the motor circuit due to the motor inertia, Inductive characteristics and also start with load Inductive characteristics and also start with load condition.condition. Consequences: ‘fried’ controller, mosfets, stripboards, Consequences: ‘fried’ controller, mosfets, stripboards,
break down of insulation and also ‘fried’ circuits!break down of insulation and also ‘fried’ circuits!
General Overview - StartGeneral Overview - Start
SolutionSolutionBy reducing the supply voltage during By reducing the supply voltage during
starting (ramp start).starting (ramp start). Introducing high resistance during starting.Introducing high resistance during starting.All this can be achieved by using a All this can be achieved by using a
controller – atmel, PIC, OOPic, etc etc.controller – atmel, PIC, OOPic, etc etc.
General Overview - StopGeneral Overview - Stop
Stopping a DC motorStopping a DC motorSimplest method is by switching off the Simplest method is by switching off the
power supply.power supply.However, if the motor has inertia, However, if the motor has inertia,
instantaneous stop is not possible.instantaneous stop is not possible.
General Overview - StopGeneral Overview - Stop
SolutionSolutionSudden reversal of polaritySudden reversal of polarityRegenerative braking / Electronic BrakingRegenerative braking / Electronic BrakingThese solution would require the use of a These solution would require the use of a
controller.controller.
General Overview - General Overview - PositionalPositional
Is positional possible?Is positional possible? Yes – Servo motor / Stepper Motor.Yes – Servo motor / Stepper Motor. Servo motor – position is based upon the pulse Servo motor – position is based upon the pulse
width of PWM signal going into the servo.width of PWM signal going into the servo. Stepper motor – position is possible by counting Stepper motor – position is possible by counting
the number of pulse sequence given to the the number of pulse sequence given to the stepper.stepper.
All this is possible by incorporating controller.All this is possible by incorporating controller.
H bridge DC Motor Drive H bridge DC Motor Drive CircuitCircuit
Shaped like the letter ‘H’Shaped like the letter ‘H’Advantage – ability to control direction, Advantage – ability to control direction,
speed, start and stop.speed, start and stop.Disadvantage will be dependent upon the Disadvantage will be dependent upon the
component used.component used.
H Bridge ComponentsH Bridge Components
RelayRelay Mechanical switchMechanical switch Very robustVery robust Types of relay – 5V, 9V, 12V.. Etc etcTypes of relay – 5V, 9V, 12V.. Etc etc Relay types will be dependent upon supply Relay types will be dependent upon supply
voltage and the voltage at which pulse is given voltage and the voltage at which pulse is given to the relay contacts.to the relay contacts.
Speed control is not possible.Speed control is not possible. Safety – interface to relay must be protected, Safety – interface to relay must be protected,
free wheeling diode must be installed to protect free wheeling diode must be installed to protect from the ‘inductive’ kick.from the ‘inductive’ kick.
H Bridge ComponentsH Bridge Components
MosfetMosfetSemiconductor relaySemiconductor relayCapable of withstanding high current flowCapable of withstanding high current flowEg: IRF, IRFZ seriesEg: IRF, IRFZ seriesFor optimized H bridge configuration, must For optimized H bridge configuration, must
have ‘p’ and ‘n’ channel mosfets.have ‘p’ and ‘n’ channel mosfets.Disadvantage, gate is sensitive to high Disadvantage, gate is sensitive to high
currents.currents.
H Bridge Example circuitH Bridge Example circuit
M
Vcc
Control Signal
Control Signal
Control Signal
Control Signal
Relay Relay
Relay Relay
H Bridge example circuitH Bridge example circuit
M
Vcc
Control Signal/ULN2003 output
Free Wheeling
diode Free Wheeling
diode
Control Signal/ULN2003 output
Vcc
Relay Relay
MosFet Driver circuit – Totem MosFet Driver circuit – Totem Pole DriverPole Driver
ULN
2003microcontroller
Vg Vs
R1 R
MosFet Driver circuit – Totem MosFet Driver circuit – Totem Pole Driver with optoisolatorPole Driver with optoisolator
microcontroller
Vg Vs
R1 R
Optoisolator
Speed Control IssuesSpeed Control Issues
All relay driverAll relay driverSpeed control is not possibleSpeed control is not possible
All relay driver with MosfetAll relay driver with MosfetSpeed control is possibleSpeed control is possible
Semiconductor based driverSemiconductor based driverSpeed control is possibleSpeed control is possible
Speed Control IssuesSpeed Control Issues Speed control can be achieved by giving a PWM Speed control can be achieved by giving a PWM
pulse train to the semiconductor swtich.pulse train to the semiconductor swtich. This will determine the duration at which the This will determine the duration at which the
motor receives voltage.motor receives voltage. If the switching is done fast enough, the average If the switching is done fast enough, the average
voltage received by the motor may be controlled.voltage received by the motor may be controlled. Therefore, the average voltage received by the Therefore, the average voltage received by the
motor will be dependent upon the ‘duty ratio’ motor will be dependent upon the ‘duty ratio’ (time ratio at which the switch is ‘on’) of the (time ratio at which the switch is ‘on’) of the switch.switch.
Protection IssuesProtection Issues
MotorMotor If the motor only turns in one direction, free If the motor only turns in one direction, free
wheeling diode is recommended to discharge wheeling diode is recommended to discharge any remaining voltage stored in the motor when any remaining voltage stored in the motor when the motor is not rotating.the motor is not rotating.
MosfetMosfet A free wheeling diode is also recommended to A free wheeling diode is also recommended to
discharge the internal capacitance in the Mosfet discharge the internal capacitance in the Mosfet during turn off and turn on.during turn off and turn on.
Protection IssuesProtection Issues
FuseFuse It is also recommended to put a fuse to generally It is also recommended to put a fuse to generally
protect the circuit in the event of a current surge. protect the circuit in the event of a current surge. Remember, fuse is cheap, mosfets and relays Remember, fuse is cheap, mosfets and relays are expensive!.are expensive!.
ConnectionsConnections All connections to the motor must be ‘wired’, DO All connections to the motor must be ‘wired’, DO
NOT use the copper stripboard as the NOT use the copper stripboard as the connectors to motors. Copper stripboard do not connectors to motors. Copper stripboard do not have current capacity.have current capacity.
Interfacing IssuesInterfacing IssuesMicroC via ULN 2003 vs MicroC via MicroC via ULN 2003 vs MicroC via
Optoisolators?Optoisolators? Using ULN2003 is simple but it has a disadvantage Using ULN2003 is simple but it has a disadvantage
of a common ground for both MicroC and Motor of a common ground for both MicroC and Motor circuit.circuit. In the event of a current surge during start, stop, direction In the event of a current surge during start, stop, direction
change, excess current will go to ground and could ‘fry’ the change, excess current will go to ground and could ‘fry’ the microcontroller.microcontroller.
Solution is by using an optoisolator (4n25) to separate the Solution is by using an optoisolator (4n25) to separate the ground for both MicroC and Motor circuit.ground for both MicroC and Motor circuit.
Cost wise, optoisolator would cost about RM1 each while a Cost wise, optoisolator would cost about RM1 each while a MicroC would cost a lot!!.MicroC would cost a lot!!.