Electrical Drives: Introduction, classification
What is meant by Electrical Drives?
- Systems employed for motion control are called as Drives.
- It may employ any of the prime movers (Diesel engines, steam turbines and electric motors) for supplying mechanical energy for motion control.
- Drives employing electric motors are called as Electrical Drives.
- In other words,
A Drive is a combination of various systems combined together for the purpose of motion control.
Basic Components of Electric Drive System:
The electric drive system has five main functional blocks namely a power source, Power Modulator(Converter), a motor, a mechanical load and a Controller(which incorporates sensing unit and control unit).
- The power source provides the required energy to the electric drive system. The converter interfaces the motor with the power source and provides the motor with adjustable voltage, current and frequency.
- The controller monitors the operation of the entire system and ensure the overall system performance and stability. The ratings of mechanical load and type of power source is not in our decision.
- The mechanical loads are determined by the nature of the industrial operation and the power source is determined by what is available at the site. But we can select the other components like electric motor, converter and controller.
- The function of converters is to convert the electric waveform of the power source to a waveform that the motor can use. For example the available power source is AC and the motor is DC series motor, then the converter converts ac into dc. In other words a rectifier circuit is placed in the system.
- The motor for the particular application is selected by considering various factors like cost, meeting the power level and performance required by the load during steady state and dynamic operations.
Advantages of Electrical Drives:
- Do not pollute the environment.
- Unlike other prime movers there is no need to refuel or warm-up the motor.
- They are available with wide range of torque, speed and power.
- Electric braking can be employed. Therefore they are having flexible control characteristics.
- In the past, Induction and synchronous motors were employed mainly in constant speed drives.Variable speed drives uses dc motor.
- Now a days AC motors also used in variable speed drives due to development of semiconductor converters.
- The reason is due to the presence of commutator and brushes, DC motors have number of disadvantages.
Application (Traction motors):
One of the major application of electric drives is Electric Traction. ie to transport men and materials from one place to another. Various types of Electric Traction are
(i) Electric trains
(ii) Electric buses
(iii) Trams(tramways) & trolleys
(iii)Battery driven solar-powered vehicles
In India, 25kV, 50Hz single phase supply is used for traction.
Classification of Electrical Drives:
Generally electrical drives are classified as follows:
 Group drive
 Individual Drive
 Multi motor drive
In addition to this drives are further classified,
Based on supply:
AC drives and DC drives
Based on running speed:
Constant speed(single speed) Drives and Variable speed drives
Based on number of motors:
Single motor drives and Multi motor drives
Based on control Parameter:
Constant torque drives and Constant power drives