Electric Drive System – Definition and Functional Blocks
Electric drive system is an essential part of modern industrial and transportation applications. It is used to control the motion of electrical machines efficiently. The electric drive system consists of five main functional blocks, namely:
- Source
- Power Modulator
- Motor
- Load
- Control and Sensing Unit
The block diagram of an electrical drive shows how each of these components work together to convert electrical energy into controlled mechanical motion.
Functional Blocks of Electric Drive System
1. Source
The power source provides the required energy to the electric drive system. It can be either an AC or DC source. The converter acts as an interface between the source and the motor, providing adjustable voltage, current, and frequency as required by the motor.
2. Power Modulator
Power modulators are devices that alter the nature, frequency, and intensity of power to control electrical drives. They ensure that the motor receives appropriate power as per load conditions and performance requirements.
Power modulators can be classified into three main types:
- Converters
- Variable Impedance Circuits
- Switching Circuits
Converters
Converters are used to change electrical power from one form to another, depending on the motor and source requirements. The main types of converters used in electrical drives are:
- 1. AC to DC Converter (Rectifier): Used when the source is AC and the motor is DC. For example, rectifiers are used to run DC motors from AC supply.
- 2. AC Regulator: Commonly used for AC motors to control speed. Example – a TRIAC-based voltage regulator is used in fan speed control.
- 3. DC to DC Converter (Chopper): Used when DC supply is constant but variable DC is needed. Commonly used for speed control of DC motors below base speed using armature voltage control.
- 4. DC to AC Converter (Inverter): Converts DC to AC power, used to drive AC motors such as in electric vehicles or traction applications.
- 5. Cycloconverter: Converts AC power at one frequency to AC power at another frequency. Used for speed control of induction or synchronous motors by varying supply frequency. As it requires many thyristors, it is typically used in high-power drives.
Variable Impedance Circuits and Switching Circuits
Variable impedance circuits are used for speed control by changing the resistance or impedance of the circuit. This method is simple and cost-effective but less efficient, hence used in low-cost DC and AC drives.
3. Control Unit
The control unit governs the overall operation of the power modulator and drive system. It decides the speed, torque, and direction of the motor by processing input signals and feedback.
The control unit varies based on the type of power modulator used. For instance, when semiconductor converters are used, the control unit consists of firing circuits that include linear devices and microprocessors for precise control.
4. Sensing Unit
The sensing unit monitors important parameters such as motor current, voltage, and speed. These signals are fed back to the control unit to maintain stable operation and desired performance of the drive system.
5. Load
The load is the mechanical system that requires motion, such as a conveyor belt, pump, or fan. The type of load determines the torque-speed characteristics needed from the motor and thus influences the choice of the entire drive system.
Conclusion
The electric drive system is a combination of electrical and mechanical components working together to achieve controlled motion. Each block — source, power modulator, motor, control, sensing, and load — plays a crucial role in ensuring efficiency, precision, and reliability of the overall system.
FAQs on Electric Drive System
Q1. What are the main components of an electric drive system?
Answer: The main components are Source, Power Modulator, Motor, Load, Control Unit, and Sensing Unit.
Q2. What is the function of a power modulator?
Answer: The power modulator regulates the voltage, current, and frequency supplied to the motor to control speed and torque efficiently.
Q3. What is the use of a cycloconverter in electrical drives?
Answer: A cycloconverter changes the frequency of AC power and is mainly used for speed control of large AC motors like induction or synchronous motors.
Q4. What is the role of the control unit in electric drives?
Answer: The control unit sends signals to the power modulator based on desired performance and feedback from sensors to maintain smooth operation.
Q5. Which converter is used in DC motor drives?
Answer: AC to DC converter (Rectifier) or DC-DC converter (Chopper) is commonly used in DC motor drives depending on the power source type.