What is an Electrical Drive?
An electrical drive is a type of system used to control the motion of an electrical machine. In simple terms, a drive that uses an electric motor is called an electrical drive. The primary power source for an electrical drive can come from various prime movers, including:
- Diesel or gasoline engines,
- Gas or steam turbines,
- Steam turbines,
- Hydraulic turbines, and
- Electrical generators
- Wind turbines.
This primary mover supplies the drive with the necessary mechanical energy to control the motion.
The primary mover provides the required mechanical energy to control the motion. Each source is selected based on the specific application and energy requirements.
How do electrical drives operate?
The drive is positioned between the electrical supply and the motor, where it receives power and regulates the energy delivered to the motor. This setup allows the drive system to control various motor parameters, including speed, direction, acceleration, deceleration, and torque. It can also manage the motor shaft’s position in advanced systems and ensure precise operation. Additionally, modern drives may provide energy efficiency, fault diagnostics, and system integration capabilities, which optimize drive performance in industrial and commercial applications.
Block Diagram of an Electrical Drive
The figure below shows a typical block diagram representation of an electric drive system:
Components of Electrical Drive
An electric drive has the following components.
- Power supply
- Power electronic converter
- Motor
- Load
- Control unit
- Sensing unit
Image: siemens.com
1. Power Source
The power Source is responsible for providing the energy the system requires to perform its intended operation. It supplies electrical power to the drive, which is converted and regulated as needed. The power source can vary depending on the application and may include AC mains, batteries, solar panels, or generators.
2. Power Electronic Converter
This device converts the supplied electrical energy into a form suitable for driving the motor, typically transforming it into mechanical energy. Depending on the application, the converter may perform AC to DC, DC to AC, AC to AC, or DC to DC conversion. It regulates voltage, current, and frequency to control the motor’s speed, torque, and direction.
The power controller regulates the amount of power supplied to the motor to ensure it operates within its capacity. This regulation is essential because the power flowing through the system directly influences the torque-speed characteristics needed to meet the load’s requirements.
During transient events like starting, braking, and similar actions, this device limits the current to specific levels to prevent voltage overloads or dips in the system.
3. Control and Sensing Units
Under closed-loop operation, this unit controls the power converter by processing the input command and the feedback signal from the load. This feedback-driven control ensures that the system maintains optimal operating conditions. To achieve this, the control unit works seamlessly with the sensor unit to monitor critical parameters like voltage, current, or speed and provides real-time feedback.
The sensing unit monitors the motor’s current or speed while ensuring system protection. It is an integral part of the closed-loop system and provides accurate feedback and stable performance.
The sensor unit serves an important dual role within the system. It detects and measures key parameters such as the motor’s current, speed, or voltage and ensures precise monitoring of operating conditions. By consistently providing precise feedback to the control unit, the sensing mechanism ensures efficient system operation and sustained stability within a closed-loop configuration. This real-time feedback enables the system to adapt dynamically to changes in load or operating conditions.
4. Electric Motor
The primary function of the motor is to convert input energy into mechanical motion. In electric drive systems, most DC motors are configured as series, shunt, or compound types, while AC motors use squirrel cage and slip ring induction designs. These motors are chosen for their efficiency and suitability in various applications. Additionally, stepper motors and brushless DC motors are commonly utilized in specialized applications where precise control, higher efficiency, and reliability are critical.
5. Load
The load is a system component defined by the torque-speed characteristics required for its operation, such as:
- Pumps,
- Machines, and so on.
The electric motor and load are designed to be compatible with each other in terms of their torque-speed characteristics.
Types of Electrical Drives
Electric drives are classified based on several factors. The primary classification is based on the power supply, which generally divides electric drives into two categories:
- AC Drives and
- DC Drives
Electrical drives are classified into three categories:
- Group drive,
- Individual drive, and
- Multi-motor drive.
Additionally, these drives can be further classified based on the various factors listed below:
Electrical drives are categorized into two types based on their operating speed:
- constant speed drives and
- Variable speed drives.
Electrical drives are classified into two categories according to the number of motors:
- Single motor drives and
- Multi-motor drives.
Electrical drives are categorized into two types based on the control parameter:
- Constant torque drives and
- Constant power drives
1). AC Drives
An alternating current (AC) drive is a device that controls the speed of an electric motor to:
- Enhance process control
- Minimize energy consumption and improve energy efficiency
- Reduce mechanical stress in motor control applications
- Optimize the performance of various electric motor-powered systems
Drives can also be employed to convert energy from natural and renewable sources, such as solar, wind, and tidal power, and transfer it to the electrical grid or use it for domestic applications. AC drives are integrated into hybrid technologies, which combine traditional energy sources with energy storage systems to create total energy management solutions.
The operation of AC drives depends on the type of AC power input they receive. Compared to DC drives, AC drives are generally lighter and more compact. There are two types of AC drives.
- Induction motor drives and
- Synchronous motor drives
AC drives are also called variable frequency drives (VFDs), adjustable speed drives (ASDs), variable speed drives (VSDs), frequency converters, inverters, and power converters.
2). DC Drives
A direct current (DC) drive, commonly known as a DC drive, is a system used to control the speed of DC motors. It operates by converting the input alternating current (AC) supply into direct current (DC) using a converter circuit that employs rectifiers such as diodes and thyristors. In the past, DC generators were used to produce variable DC voltage, which was then utilized to regulate the speed of DC motors.
DC drives are systems where the motive force that powers the system is in the form of direct current (DC). Their primary applications include:
- Variable(Adjustable) Speed Drives and
- Position Control.
DC drive uses power electronic converters to regulate and control the motor’s speed and torque,
3). Group Drive
The term “group drive” refers to a system where multiple machines are mounted on a single shaft and powered by a single large motor. The large motor often called the main motor, drives a common shaft in the group drive setup, which is also known as a line shaft drive. Using multi-step pulleys, several smaller machines are connected to the central shaft of the larger motor, which operates in sync with the main motor.
4). Individual Drive
An individual drive refers to a system in which a single electric motor is used to drive or provide energy for the operation of a single machine. When an individual drive is employed, the specific function being carried out is typically more secure, as the motor’s operation is completely dedicated to that machine, which reduces the complexity and potential risks associated with shared or multiple motor systems.
Individual drives can be used in situations where a constant speed is necessary, such as in
Individual drives are suitable for applications where constant speed is essential, such as in conveyor systems, pumps, fans, and compressors. These drives ensure stable and precise motor performance for the following processes which require consistent speed for optimal operation.
- Paper mills and
- Textile sector.
This drive is also employed in single spindle drilling machines, as well as numerous varieties of electrical hand tools and some metal-working machine tools.
This drive is also used in single-spindle drilling machines, a variety of electrical hand tools, and certain types of metal-working machine tools. It provides precise and consistent motor control for driving large machinery that requires stable speed and efficient operation.
The following machines require the use of individual drives, as they are the only available option for ensuring proper operation:
- Cranes,
- Lifts,
- Lathes
- Conveyor system
In a wide range of individual drive applications, the electric motor is an essential component of the machine, It provides the necessary power and control for its drive operation.
5). Single-Motor Drive
A single motor is used to power multiple equipment through a line shaft or belt system. However, this setup is inflexible and inefficient because it can not change the speed of each load. The single motor is shared by all the connected equipment, which can lead to challenges in adjusting the speed for different loads. On the other hand, the single motor, single load drive is the most common type of drive system, where each load has its dedicated motor that operates continuously.
6). Multi-Motor Drive
A multi-motor electric drive is a system that utilizes multiple motors to operate different components or parts of the same machine. This setup allows more precise control and efficient operation, as each motor can be run to meet the speed torque requirement of the specific component.
Multi-motor drives are used in complex machinery or systems where different parts need to operate independently, such as conveyor belts, industrial robots, and automated manufacturing equipment. Additionally, multi-motor drives provide the flexibility to adjust the speed or torque of individual components, and therefore, it is used for applications that require varied operational conditions.
7). Constant Speed Drive
A constant speed drive (CSD), also known as a constant speed generator, is a form of transmission that takes power from an input shaft that rotates at a wide – range of speeds and delivers it to an output shaft that rotates at a constant speed, despite the fluctuating input. They are used to power mechanisms that require a steady input speed, such as electrical generators.
A constant speed drive (CSD), also called a constant speed generator, is a type of transmission system that receives power from an input shaft rotating at variable speeds and transfers it to an output shaft that maintains a constant speed, regardless of fluctuations in the input. They are used for driving mechanisms that require a steady input speed. CSDs are commonly used in power generation and other systems that require constant speed under varying load conditions.
8). Variable Speed Drive
Variable speed drives (VSD), also known as variable frequency drives (VFD), are used to control motor speed and optimize energy savings. The major components of the VSD system are,
- A three-phase AC induction motor and
- A variable frequency power source
The variable frequency power supply generates a pulse-width modulated current that changes the power and frequency provided to the motor. This allows for precise control of the motor speed across a wide range. VSDs are used in pump and fan applications to alter the pump or fan speed based on demand, frequently resulting in significant energy savings.
The variable frequency drive generates a pulse-width modulated current that adjusts the power and frequency supplied to the motor. The precise control of frequency controls the motor speed over a broad range. VSDs are commonly used in pump and fan applications. They adjust the speed based on demand, resulting in significant energy savings.
9). Constant Torque Drive
When the torque produced by the motor equals the torque produced by the load, the motor-load system is at equilibrium speed, known as the steady torque drive. The drive will continue to operate in a steady state at this speed as long as it remains the speed at which stable equilibrium can be maintained.
10). Constant Power Drive
A constant power drive refers to the ability of an electric power system to return to a state of operating equilibrium after being subjected to physical or electrical disturbances. The system variables are controlled to ensure that the entire power system remains intact. This stability is measured relative to the initial operating condition of the electric power system.
Why are electrical drives required?
Electrical drives allow the use of power in a broad range, from milliwatts to megawatts for speed regulation and reducing the overall system operational costs.
- To make motor stopping and reversing faster and more accurate.
- To control the starting current
- To provide protection
- To enable advanced control for variables like temperature, pressure, and level
Advancements in power electronics, microprocessors, and digital technology have led to modern electric drives that are smaller, more efficient, affordable, and higher-performing than traditional electric drives, which rely on large, rigid, and costly multi-machine systems for variable speed.
Why do motors use drives?
A drive controls the motor’s speed, torque, direction, and power.DC drives are used to manage shunt-wound DC motors, which have unique armature and field windings. Similarly, AC drives regulate speed, torque, and power in AC induction motors. AC drives are widely used in industrial applications to optimize energy usage and enhance overall system performance.
Advantages of Electrical Drive
- Electric drives are environmentally friendly as they do not produce smoke, fumes, or ash, making them a clean and sustainable choice. This feature makes electric drives highly suitable for use in underground railways, tube railways, and other enclosed environments where air quality and safety are critical.
- Electric drives are highly flexible, and their performance can be effectively controlled using electronic devices like SCRs, IGBTs, and microcontrollers.
- They are available in a wide range of torque, speed, and power options, and can be used for diverse applications and performance requirements.
- Electric drives are compact and occupy less space, making them ideal for applications where space is limited.
- They do not require any warm-up time and can be started immediately.
- Electric drives can be operated remotely.
- They provide a reliable power source, ensuring consistent and dependable performance for various applications.
- They are powered by electrical energy which offers several advantages over other forms of energy, such as higher efficiency, better control, and reduced environmental impact.
- Electric drives are adaptable to a wide range of operating conditions, including environments where they may be submerged in liquids, exposed to explosive chemicals, used in mining, or operated in radioactive settings.
- Electric drives offer high schedule speeds and the ability to handle heavy traffic, all while requiring less terminal space.
- They reduce maintenance costs and time, making them cost-effective.
Disadvantages of Electrical Drive
- The initial capital cost of setting up an electric drive can be high.
- Electric drives are generally suitable only for electrified railways.
- Electric drives require additional control circuitry for proper functioning.
- Electric drives may produce some noise pollution during operation.
- Electric drives can have a weaker dynamic response compared to other drive systems.
- A power outage can completely disrupt the operation of an electric power train.
- The output power of an electric drive may be lower compared to other systems.
Applications of Electrical Drive
Electric drives are commonly used in various applications, including:
- Pumps
- Fans
- Motors
- Transportation systems
- Turbines
- Engines
- Air conditioning and refrigeration systems
- Conveyor belts
- Elevators and lifts
- Industrial robots
- Compressors
- Home appliances (e.g., washing machines, dishwashers)
- Power tools
- HVAC systems
- Electric vehicles (EVs)
- Renewable energy systems (e.g., wind turbines, solar power generation)
- Pumps,
- Fans,
- Motors,
- Transportation systems,
- Turbines,
- Engines, and
- Other industrial and home applications
- Trolleys
- Solar-powered vehicles.
- Lathe machines,
- Shears,
- Frequency converters,
- Refrigeration and
- Air conditioning,
