Single Phase Induction Motor Speed Control

Introduction Single Phase Induction Motor Speed Control  Induction motors are widely used in many residential, industrial, commercial, and utility applications. Single-phase induction motors are widely used in home and industrial appliances. This project is designed to control the speed of a single-phase induction motor using an easy operating knob, which is commonly used in home automation application. The main advantage of these motors is their ability to operate from a single-phase power supply.

Single Phase Induction Motor Speed Control Block Diagram

Single Phase Induction Motor Speed Control Hardware Requirements  Op-amp  Opto-isolators  SCRs  Voltage Regulator  Transformer  Diodes  LED  Resistors  Capacitors  Lamp

Single Phase Induction Motor Speed Control Types of Single Phase Induction Motor  Split phase induction motor,  Capacitor start inductor motor,  Capacitor start capacitor run induction motor,  Shaded pole induction motor.

Single Phase Induction Motor Speed Control Power Supply

Single Phase Induction Motor Speed Control About Power Supply  The 230V AC supply is first stepped down to 12V AC using a step down transformer.  This is then converted to DC using bridge rectifier.  The AC ripples is filtered out by using a capacitor and given to the input pin of voltage regulator  At output pin of this regulator we get a constant 12V DC which is used for different ICs in this project.

Single Phase Induction Motor Speed Control Induction Motor

Single Phase Induction Motor Speed Control Induction Motor  The single-phase induction machine is the most frequently used motor for refrigerators, washing machines, clocks, drills, compressors, pumps, and so forth.  The single-phase motor stator has a laminated iron core with two windings arranged perpendicularly.  One is the main winding And  The other is the auxiliary winding or starting winding.

Single Phase Induction Motor Speed Control  This “single-phase” motors are truly two-phase machines.  The motor uses a squirrel cage rotor, which has a laminated iron core with slots.  Aluminium bars are moulded on the slots and short-circuited at both ends with a ring. Induction Motor

Single Phase Induction Motor Speed Control Soft Starter  A soft starter is another form of reduced voltage starter for A.C. induction motors.  The soft starter is similar to a primary resistance or primary reactance starter in that it is in series with the supply to the motor.  The current into the starter equals the current out.  The soft starter employs solid state devices to control the current flow and therefore the voltage applied to the motor.

Single Phase Induction Motor Speed Control Soft Starter  Soft starters are connected in series with the line voltage applied to the motor, or can be connected inside the delta loop of a delta connected motor, controlling the voltage applied to each winding.  Voltage control is achieved by means of solid state A.C. switches in series with one or more phases. These switches comprise either: a. Triac b. Diode & SCR c. Two SCRs

Single Phase Induction Motor Speed Control SCR - Silicon Controlled Rectifier  A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow.  An SCR can be seen as a conventional rectifier controlled by a gate signal.  It is a 4-layered 3-terminal device.  When the gate to cathode voltage exceeds a certain threshold, the device turns 'on' and conducts current.

Single Phase Induction Motor Speed Control  The operation of a SCR can be understood in terms of a pair of tightly coupled Bipolar Junction Transistors.  SCR has Three States: Reverse blocking mode, Forward blocking mode, and Forward conducting mode. SCR - Silicon Controlled Rectifier

Single Phase Induction Motor Speed Control Comparator  Op amps & comparators look very similar.  But a comparator gives a logic output indicating the relative potentials on its two inputs.  An op amp amplifies the differential voltage between its two inputs – and is designed always to be used in closed-loop applications.  Potential dividers are connected to the inverting and non inverting inputs of the op-amp to give some voltage at these terminals.

Single Phase Induction Motor Speed Control  Supply voltage is given to +V and –V is connected to ground.  The output of this comparator will be logic high (i.e., supply voltage) if the non-inverting terminal input is greater than the inverting terminal input of the comparator.  If the inverting terminal input is greater than the non-inverting terminal input then the output of the comparator will be logic low (i.e., gnd). Comparator

Single Phase Induction Motor Speed Control Working Principle  To start the motor with low current, two anti-parallel SCRs connected in series with an induction motor to the utility supply. When the project is in operation, the firing angle is adjusted according to the requirement, which leads to changed intensity of a lamp or speed control of an induction motor. An op-amp operates in comparator mode that compares with zero voltage pulses to develop a saw-tooth voltage.firing angle is adjusted  This saw tooth waveform is further compared against a varying voltage by a potentiometer for the level comparator to develop delayed pulses for triggering the SCRs. A lamp is provided in this project in place of an induction motor for demonstration purpose.

Single Phase Induction Motor Speed Control Advantages  Single phase motor is that it requires a two wire supply  Single-phase motors are less expensive to manufacture than other motors.  Capacitor-start motors are good general purpose motors and they are ideal for most occasions.  The single phase motors are simple in construction, cheap in cost, reliable and easy to repair and maintain.

Single Phase Induction Motor Speed Control Disadvantages  Single phase motor are that their power is limited.  They do not have good starting torque and they have a complex starting switch in some cases.  Speed control of induction motors are difficult.  At low loads, the power factor drops to very low values

Single Phase Induction Motor Speed Control Applications  Single phase motor finds its application in  Vacuum Cleaner  Fans  Washing machine  Centrifugal pump  Blowers  Small toys

Single Phase Induction Motor Speed Control Further Enhancement  The project can be enhanced by using six SCRs, two connected in back to back for each phase for a three phase load and the same project can also be enhanced to run motor in both the directions.

Single Phase Induction Motor Speed Control Conclusion  Single phase power system is widely used in domestic purpose, commercial purpose and to some extent in industrial purpose. As the single phase system is more economical and the power requirement in most of the houses, shops, offices are small, which can be easily met by single phase system. The single phase Induction motors are simple in construction, cheap in cost, reliable and easy to repair and maintain.single phase Induction motors