Soft Switching Of Three Phase Induction Motor
Induction motor is the workhorse of an industry. It has its applications in a wide power range, from fractional watt to megawatts. But its high switching current poses a serious problem to the system. As we start an induction motor, the high switching current flows through the windings of the motor.
2025-06-28 16:29:35 - Adil Khan
Soft Switching Of Three Phase Induction Motor
Project Area of Specialization Electrical/Electronic EngineeringProject SummaryInduction motor is the workhorse of an industry. It has its applications in a wide power range, from fractional watt to megawatts. But its high switching current poses a serious problem to the system. As we start an induction motor, the high switching current flows through the windings of the motor. This current causes a dip in the voltage of that line and may damage the equipment connected on the line. Moreover motor starts with a jerk which causes mechanical wear and tear. In order to cope with this problem we have to reduce the switching current so that our equipment is being protected from any damage and motor starts smoothly without any jerk. Many methods are in practice in the industry. These methods include addition of a resistor with the windings so that the switching current can be lowered, star-delta conversion technique, DOL method etc. These methods are not efficient because the inrush current cannot be smoothed by these methods. In other words transients are always there, which can cause damage.
Therefore to tackle these problems, we use soft switching. In soft switching applied voltages are controlled. By controlling the voltages, the switching current and switching torque will be controlled, hence the motor will run smoothly without having any transients.
Project ObjectivesThe objective of this project is to switch a three phase induction motor smoothly without any mechanical jerk, to limit the high switching current within acceptable limits and to overcome the problems caused by these high inrush current.
A soft switching ramps up the voltage applied to the motor from the initial voltage to the full voltage. The voltage is initially kept low to avoid sudden jerks during the start. The voltage and torque increases gradually so that the induction motor starts to accelerate. This ramp up voltage provides sufficient torque for the load to accelerate gradually, and hence mechanical and electrical shocks are minimized from the system.
The main requirement is to develop a robust front-end system that can softly switch a three phase induction motor, and limit its switching current within limitations.
To design models and simulate direct online switching and two solid state soft switching (MOSFET) for three phase induction motor in a closed loop system using Proteus software.
- To carry out the performance evaluation of the DOL with MOSFET based soft starter.
- To compare using the parameters observed during simulation, the operation of the direct online switching (DOL) with MOSFET soft switching for the three phase induction motor.
The mechanical shock delivered to the rotor or to couplings or to any intermediate gearing and the driven load by a high switching current is most severe when the motor is started direct on line. Even reduced voltage switching devices like the star delta starter or Auto transformer switching still impose shock loads because of the very current peaks which cause severe transient torques at the moments of intermediate switching.
The effect of such repeated shocks is to decrease the life of the motor and increase the cost of maintenance.
Project Implementation MethodAs there are several techniques for soft switching and industries are using it from several years till date, but we had thought something different for our project. We would be using VFD (variable frequency drive) method. Soft switching of three phase induction motor using VFD method. Because a variable frequency drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage of its power supply. The VFD also has the capacity to control ramp-up and ramp-down of the motor during start or stop, respectively.
Even though the drive controls the frequency and voltage of power supplied to the motor, we often refer to this as speed control, since the result is an adjustment of motor speed.
There are many reasons why we may want to adjust this motor speed.
For example, to
- Save energy and improve system efficiency
- Convert power in hybridization applications
- Match the speed of the drive to the process requirements
- Match the torque or power of a drive to the process requirements
Improve the working environment
Lower noise levels, for example from fans and pumps - Reduce mechanical stress on machines to extend their lifetime
Shave peak consumption to avoid peak-demand prices and reduce the motor size required
In addition, today’s drives integrate networking and diagnostic capabilities to better control performance and increase productivity. So, energy savings, intelligent motor control and reduction of peak-current drawn are three great reasons to choose a VFD as the controller in every motor-driven system.
The most common uses of a VFD are for control of fans, pumps and compressors, and these applications account for 75% of all drives operating globally.
Soft starters and across-the-line contactors are other, less sophisticated types of motor controllers. A soft starter is a solid-state device and provides a gentle ramp-up to full speed during startup of an electric motor.
An across-the-line contactor is a type of motor controller that applies the full line voltage to an electric motor.
Benefits of the ProjectThe soft switching used in three phase induction motor eliminates high inrush current and high mechanical torque on startup. It reduces cable and switch-gear rating in power supply network. It prevents any dip in line voltage. The soft starter has desirable features of soft, step-less acceleration & deceleration.
A soft switching helps to limit transient voltages, while also protecting against sudden surges of power that accompany both normal operation, and power outages. Reduce risk to personnel and limit personal harm. Major equipment can be very dangerous, and there's always a risk involved with using it.
Reduce risk of wear and damage. Making operations switches smoothly and in a controlled manner reduces overall wear, making conveyor systems, cranes, major tools, and pump systems last longer and need less service overall.
Reduce the risks of power surges or surges during operation. A soft switching helps to limit transient voltages, while also protecting against sudden surges of power that accompany both normal operation, and power outages.
Reduce risk to personnel and limit personal harm. Major equipment can be very dangerous, and there’s always a risk involved with using it. That’s why including a motor starter, one that polices electrical charges and makes operation smoother and more predictable, is an excellent way to reduce the risks of personal harm in the workplace
Technical Details of Final DeliverableWhile designing this circuit, a choice had to be made between the two main types of switches used in power electronics. One is the power MOSFET, which is much like a standard MOSFET, but designed to handle relatively large voltages and currents. The other is the insulated gate bipolar transistor, or IGBT. Each has its advantages, and there is a high degree of overlap in the specifications of the two. IGBTs tend to be used in very high voltage applications, nearly above generally above 600V. They do not have the high frequency switching capability of MOSFETs, and tend to be used at frequencies lower than 29 kHz. They can handle high currents, are able to output greater than 5kW, and have very good thermal operating ability, being able to operate properly above 100 Celsius. One of the major disadvantages of IGBTs is their unavoidable current tail when they turn on. IGBTs have high voltage drop as compared to the MOSFETs. These specifications make power MOSFETs the ideal choice for us. If our system was a larger, commercial application with a high power output, IGBTs would be the choice.
Final Deliverable of the Project Hardware SystemCore Industry Energy Other Industries Others Core Technology Internet of Things (IoT)Other Technologies OthersSustainable Development Goals Industry, Innovation and InfrastructureRequired Resources| Item Name | Type | No. of Units | Per Unit Cost (in Rs) | Total (in Rs) |
|---|---|---|---|---|
| Total in (Rs) | 47000 | |||
| LCD | Equipment | 1 | 600 | 600 |
| Arduino UNO | Equipment | 2 | 1500 | 3000 |
| Opto coupler | Equipment | 8 | 50 | 400 |
| MOSFETs IR740 | Equipment | 12 | 75 | 900 |
| Gate Drivers IR2101 | Equipment | 6 | 200 | 1200 |
| PCB Sheet single state | Equipment | 1 | 1200 | 1200 |
| Heat Sinks | Equipment | 1 | 500 | 500 |
| Transformer | Equipment | 1 | 500 | 500 |
| Three Phase Motor | Equipment | 1 | 15000 | 15000 |
| DC Voltmeter | Equipment | 1 | 2000 | 2000 |
| Solder/Solder Frame | Equipment | 1 | 2000 | 2000 |
| Solder Wire | Equipment | 1 | 400 | 400 |
| Wire | Equipment | 3 | 500 | 1500 |
| Steel Frame | Equipment | 1 | 7000 | 7000 |
| Paint | Equipment | 1 | 1500 | 1500 |
| Acrylic | Equipment | 1 | 3000 | 3000 |
| White Board | Equipment | 1 | 600 | 600 |
| Resistor | Equipment | 50 | 5 | 250 |
| Capacitor 16v 470uF | Equipment | 1 | 20 | 20 |
| Capacitor 450v 100uF | Equipment | 1 | 200 | 200 |
| Capacitor 5v 2.2uF | Equipment | 3 | 10 | 30 |
| Diodes | Equipment | 10 | 10 | 100 |
| Bulb Holder | Equipment | 1 | 50 | 50 |
| Bulb | Equipment | 1 | 350 | 350 |
| Pen | Miscellaneous | 10 | 100 | 1000 |
| Pencil | Miscellaneous | 10 | 100 | 1000 |
| Glue gun | Miscellaneous | 1 | 800 | 800 |
| Glue gun tubes | Miscellaneous | 2 | 50 | 100 |
| Black Board Marker | Miscellaneous | 2 | 50 | 100 |
| Scale | Miscellaneous | 2 | 75 | 150 |
| Rubber/sharpener | Miscellaneous | 2 | 25 | 50 |
| Printing Paper sheets(A4) | Miscellaneous | 1 | 400 | 400 |
| Cutter | Miscellaneous | 1 | 150 | 150 |
| Wire Cutter tool | Miscellaneous | 1 | 250 | 250 |
| Printing | Miscellaneous | 1 | 700 | 700 |