The electric drive system consists of five main functional blocks namely as
- source
- Power Modulator,
- Motor,
- Load,
- The control unit and the sensing unit.
The block diagram showed the components of the electrical drive-
1.SOURCE
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.
2.POWER MODULATOR
Power Modulators are the devices which alter the nature or frequency as well as changes the intensity of power to control electrical drives.
power modulators can be classified into three types,
- Converters,
- Variable impedance circuits and Switching Circuits.
Converters
As the name suggests, converters are used to convert currents from one type to other type. Depending on the type of function, converters can be divided into 5 types -
1.AC to DC converters(Rectifier) –
When the source is available in form of AC and we need to drive DC motor then that case AC-DC converter is required.
2. AC regulators-
Generally, AC regulator is used in case of AC motor for speed control. For example TRIAC is used as voltage regulator for speed control of fan.
3.Choppers or DC-DC converters-
When supply is fixed DC and drive need variable DC then that condition Chopper is used.
Generally, this type of drive is used for controlling the speed of DC motor less than base speed by armature voltage control.
4.Inverters -
When the source is available in form of DC and we need to drive AC motor then that case DC-AC converter is required.
This type of drive also used for traction.
5.Cycloconverters-
Cycloconverters is used for changing the frequency of AC power to the desired value. This drive is used generally in AC motor such as induction motor or, the synchronous motor for speed controlling by increased or decreased the frequency. Since Cycloconverters required a lot of thyristors, therefore, it is used for high power rating drive.
Variable impedance circuits and Switching circuits-
Variable Impedance circuits are used for controlling speed by varying the resistance or impedance of the circuit. These controlling methods are used for low-cost DC and ac drives.
3. CONTROL UNIT-
Control unit depends upon the type of power modulator which is to be used. These are of many kinds.
For example-when semiconductor converters are used, then the control unit consists of firing circuits, which employ linear devices and microprocessors.