An electrical drive is defined as an electronic device designed to control certain parameters of the motor for controlling the electrical energy into mechanical power in a precise controllable way.
Electrical power systems employed for motion control are called “Electrical Drives”.
It consists of a sophisticated electronic system or a combination of different systems for the purpose of motion control.
Motion is provided with the help of prime movers.
Example of prime movers are Petrol engines, Diesel engines, gas or steam turbines, steam engines, hydraulic motors, and electric motors.
Drives power systems employing electric motors are known as electric drives.
A modern electrical drive capable of variable controlled speed is made of some important parts as shown in the below block diagram.
Source: Source can be DC or AC source.
Power converter: AC to DC, AC to AC, DC to DC, DC to AC converters.
Motor: Converts electrical energy in to mechanical energy, it is the heart of the electrical system.
Commonly used motors are
Load: It can be a machine to accomplish a given task. Example is Pump, Fan, Machine tools.
Controller: The power required for the motor is supplied by the controller.
Sensor: Depending upon the type of control required, various inputs from sensors are taken. An example is a speed, current.
There are two types available in this category. They are
AC drive is a device used to control the speed of an electric motor such as a three-phase induction motor by changing the frequency of the electrical supply to the motor.
AC drive is also called Variable Frequency Drive (VFD) or Variable Speed Drive (VSD).
It is basically speed control system of a DC electrical motor that supplies voltage to the motor to operate at desired speed.
DC drives are classified as analog DC drives and digital DC drives.
Digital DC drive can offer precision control.
There are three types available in this category. They are
There will be a separate drive motor for various parts of a machine.
Example: Lathe machine.
Separate motors are provided for actuating different parts of a machine.
Example: Cranes.
In a group drive, one motor is used as a drive for two or several machines.
The motor is connected by a single shaft, other machines are connected to the shaft by belts and pulleys.
Group drive is most economical.
There are two types available in this category. They are
Machine tools require more or less constant speed drives, squirrel cage induction motor along with the manual controls are used.
The main purpose of variable speed drive is to control speed along with acceleration, deceleration, torque and finally the direction of machine.
They are used to reduce power consumption.
There are three types available in this category. They are
Vector control is most accurate than any other kind of variable frequency drive (VFD).
In this control mode, torque and speed controlled using pulse width modulation (PWM) techniques in an inverter.
These are used for AC synchronous and induction motors.
When a motor while carrying rated current in its armature provides constant power at all speeds in a certain range of speed control it is known as constant power drive in that range of speed control.
Constant torque load type drive is distinctive when fixed volumes are being handled.
Examples are screw compressors, feeders, and conveyors.
Extensively used in
References:
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