Electrical Drive: What is it?

What is Electrical Drive?

An electrical drive is a system that is used to control the motion of an electrical machine. In other words, electrical drive refers to the drive that employs an electric motor.

As a primary source of energy, the electrical drive employs any of the prime movers such as 

1. Diesel or gasoline engine,
2. Gas or steam turbines,
3. Steam engines,
4. Hydraulic motors, and
5. Electrical motors.

This prime mover provides mechanical energy to the drive, allowing it to control motion.

Block Diagram of Electrical Drive

The image below shows the electrical drive’s block diagram.

The electrical motor is used to power electrical loads such as

1. Fans,
2. Pumps,
3. Trains, and so on.

The speed and torque requirements of an electrical load are determined. The load drive motor is selected based on the load’s capabilities.

Electric Drive Components

The power modulator, motor, controlling unit,& sensing units are the main components of electrical drives.

1. Power Source
2. Power Modulator 
3. Control Unit 
4. Sensing Unit  
5. Electric Motor and
6. Load

Their components are described in detail below.

1). Power Source

The power source (supply) in the above diagram provides the system with the necessary energy.

The converter and the motor interact to one another, and the power source controls the motor’s voltage, frequency, and current.

2). Power Modulator 

The power modulator controls the source’s output power. It directs power from the source to the motor in such a way that the motor transmits the load’s required speed-torque characteristic.

During transient operations such as

• Starting,
• Braking, and
• Speed reversal,

the excessive current drawn from the source is reversed.

The excessive current drawn from the source may cause it to overload or cause a voltage drop.

As a result, the power modulator limits the source and motor current.

The power modulator converts energy based on the needs of the motor, for example, if the source is DC and an induction motor is used, the power modulator converts DC to AC.

It also selects the motor’s mode of operation, either motoring or braking.

3). Control Unit 

The power modulator, which operates at low voltage and power levels, is controlled by the control unit.

The power modulator is also controlled by the control unit. For the protection of the power modulator and the motor, it generates command signals.

An input command signal from an input to the control unit that adjusts the operating point of the drive.

4). Sensing Unit  

It detects specific drive parameters such as motor current and speed. It is primarily required for either protection or closed loop operation.

5). Electric Motor

This primarily converts applied energy (source) into mechanical motion. The significant proportion of DC motors used in electric drive systems are in

• Series,
• Shunt, and 
• Compound form,

whereas AC motors are slip ring induction motors. In some cases, stepper motors or brushless DC motors are used.

6). Load

The system load is specified based on the torque/speed characteristics of the system, such as pumps, machines, and so on.

In terms of torque-speed characteristics, the electric motor and load are compatible.

What is the operation of an electric drive?

Electric drives necessarily require a three-phase alternating current supply.

The incoming fixed frequency AC (alternating current) supply is rectified to produce a DC signal, which is then smoothed and circuitry provides input and output stage decoupling.

The output stage switches and provides a variable frequency three phase AC supply to the motor using software controlled Insulated Gate Bi-junction Transistors (IGBTs). 

The IGBTs are represented in the circuit by the switches 1 through 6; a centre tap of every column of switches is connected to an individual phase of the motor windings.

Switches 5 and 4 are closed, allowing current to flow through the W and V phases. Switches 5 and 4 may open and 3 and 2 may close in the next mode of operation, passing current through the V and U phases.

The software controls the sequential opening and closing of the switches as well as the duration of each step, resulting in pulse width modulation.

The varying pulse width effectively simulates an alternating current waveform as seen by the load on the motor windings.

Types of Electrical Drives

There are many various considerations that can be used to classify electric drives.

In addition, these drives are further classified according to the specifications described below.

Based on Supply

In this category, there are two types.

They are

1. AC Motor drives and
2. DC Motor drives

1). AC Motor Drives

AC drives are 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 known as Variable Frequency Drive (VFD) or Variable Speed Drive (VSD) (VSD).

2). DC motor Drives

It is essentially a speed control system for a DC electrical motor that supplies voltage to the motor in order for it to operate at the desired speed.

There are two types of DC drives:

• Analogue DC drives and
• Digital DC drives.

Precision control is possible with digital DC drives.

Based on Number of Motors

In this category, there are three types. They are

1). Individual Drive

Each component of a machine will have its own drive motor.

Ex: Lathe machine

2). Multi Motor Drive

Different parts of a machine are actuated by separate motors.

Ex: Cranes

3). Group Drive

A group drive employs a single motor to power two or more machines.

A single shaft connects the motor to the other machines, which are connected to the shaft via belts and pulleys.

The most cost-effective mode of transportation is group driving.

Based on Speed

In this category, there are two types. They are

1). Constant Speed Drive

Machine tools need to have more (or) less constant speed drives, and they also use squirrel cage induction motors and manual controls.

2). Variable Speed Drive

The variable speed drive’s primary function is to regulate the machine’s speed, in addition to its acceleration, deceleration, torque, and ultimately its direction of travel.

They are utilised in order to lessen the amount of power that is consumed.

Based on Control Parameters

In this category, there are three options. They have

1). Vector Control Drive

Vector control is the most accurate type of variable frequency drive (VFD).

Torque and speed are controlled in this mode by an inverter using pulse width modulation (PWM).

These are used for alternating current synchronous and induction motors.

2). Constant Power Drive

Constant power drive occurs when a motor, while carrying rated current in its armature, provides constant power at all speeds in a specific range of speed control.

3). Constant Torque Drive

When communicating with fixed volumes, the constant torque load type drive needs to handled.

Ex: screw compressors, feeders, and conveyors.

How to choose an electric motor?

The drive should be capable of supplying and controlling the motor, which will be connected to the application’s requirements.

The motor voltage, power rating, and full-load current must all be matched; any over-load requirements, such as higher torque for start-up, must also be considered.

The feedback mechanism, as well as any input/output (I/O) requirements, must be considered.

Communication protocols such as

• CAN-Open,
• Profibus, and
• Operating temperature 

should be considered, and so should the need for any ventilation (or) forced cooling.

Advantages of the Electric Drive

• Electric drives are environmentally friendly because they emit no smoke, fumes, or ash. As a result, electric drives are best suited for subway and tube railways.
• Electric drives are versatile because their performance can be effectively controlled by electronic devices such as SCRs, IGBTs, and microcontrollers.
• There is a wide range of torque, speed, and power available.
• Electric drives are smaller and take up less space.
• They do not require any warm-up time and can be used immediately.
• Electric drives can be controlled remotely.
• A consistent source of drive.
• Powered by electrical energy, which has several advantages over other energy sources.
• Adaptable to a variety of operating conditions, including submersion in liquid, explosive chemical or mining environments, radioactive environments, and so on.
• Electric drives have a high schedule speed and traffic handling capacity, requiring less terminal space.
• Less maintenance is required, as well as less maintenance time. Electric drives are cost effective.

Disadvantages of the Electric Drive

• Installing an electric drive has a high capital cost.
• Electric drives are only appropriate for electrified tracks.
• Additional control circuitry is required for electric drives.
• Electric drives can occasionally cause noise pollution.
• The dynamic response of electric drives is poor.
• A power outage can render an electric drive completely inoperable.
• The output power of an electric drive is limited.

Applications of the Electric Drive

• This drive’s primary application is electric traction, which is the transportation of materials from one location to another. Electric tractions include electric trains, trams, buses, trolleys, and solar-powered vehicles with built-in batteries.
• Electrical drives are widely used in a wide range of domestic and industrial applications, including motors, transportation systems, factories, textile mills, pumps, fans, robots, and so on.
• These are used as primary movers in gasoline or diesel engines, turbines (gas or steam), and hydraulic and electric motors.