Electrical Drive and Motor Control

In regenerative braking of a 3-phase induction motor, the rotor speed of the motor must exceed the synchronous speed of the motor. The regenerative braking characteristic is the continuation ofthe motoring characteristic into the upper part of quadrants II/IV. The maximum regenerative braking torque is higher than the maximum motoring torque.
During plugging, the slip is close to 2 because the motor is rotating in the opposite direction to the rotating magnetic field. The slip is defined as the difference between the synchronous speed and the rotor speed.

In dynamic braking of d.c. series motor with self-excitation, the supply to the motori is switched off and then the armature circuit including the series field winding is connected across a resistor ensuring that the excitation is not reversed during the change over. The dynamic braking torque is
T = (IR + R_rRn_a)
where the flux ø is dependent on the armature current I_a. When braking is initiated, the current is high, thus, resulting in increased value of flux, and the torque is also high, being approximately proportional to square of the current. The speed torque characteristics for dynamic braking are in the second quadrant as shown below. To employ dynamic braking in d.c. series motors, the armature of the shunt is disconnected from the supply and is connected across a variable resistance Ras shown in Fig. (b). The field winding is, however, left connected across the supply undisturbed. The braking effect is controlled by varying the series resistance R.

The selection of the correct motor for an application depends on the type of duty cycle it will experience. This is described by the "classes of motor duty." The classes of motor duty refer to the type of load the motor will experience and the duration of the load. For example, a motor used for a continuous duty application, such as a fan or pump, will need to have a higher power rating than a motor used for an intermittent duty application, such as a crane. The duty cycle is also important to consider. For example, a short time duty motor might operate at high power for short periods with long intervals of rest. A continuous duty motor will operate at a lower power level but for much longer durations. The selection of the right motor is important for ensuring that the motor is not overloaded and that it can operate reliably over the long term.

An electromechanical device converting electrical energy into mechanical energy to power machines and mechanisms for tasks like driving fans, lifting goods, running conveyors, and powering vehicles.

A single motor driving multiple machines or mechanisms connected by shafts, belts, or gears. This offers cost savings but has reduced flexibility and increased risk of downtime if the motor fails.

A motor driving a single specific machine or mechanism, granting individual control but potentially costing more.

The ability to move the motor in all four quadrants of the speed-torque plane, including forward motoring, forward braking, reverse motoring, and reverse braking. This allows for flexible control of the motor's direction and speed.

A load characterized by the force opposing motion, and it's magnitude depends on the speed of the driven machine. Examples include friction, wind resistance, and some types of brakes.

A load where the force opposing motion depends on the speed of the driven machine. Examples include fans, blowers, and pumps. The faster they go, the more resistance.

The state where the motor's speed and torque are constant over time, without significant change. This is a goal for stable electric drive operation.

The ability of a motor to operate at its full power rating for extended periods, as defined on the machine's nameplate.

The ability of a motor to operate above its full power rating for short durations. Often used for starting, braking, or specific operating situations.

A factor that influences the choice of electric drives, representing the actual power needed to operate the system at any given time, taking into account the load's variability.

The torque directly proportional to the motor's speed in the steady state. Examples include fans and blowers.

The torque that is independent of the motor's speed in the steady state. Examples include lifting loads or running conveyors.

The operation of a motor where it runs at a speed higher than the synchronous speed (for induction motors) or the field speed (for DC motors), resulting in the generator mode and returning energy to the power source.

The operation of a motor where the armature is disconnected from the supply and connected across a resistor. This creates a braking torque by dissipating the energy in the resistor.

The operation of a motor where the armature connections are reversed. By reversing the current flow, the applied voltage and back EMF work together to create a braking torque.

The operation of a motor where the rotor speed is controlled by adjusting the frequency of the voltage applied to the stator, while maintaining the ratio of voltage to frequency constant.

A method of controlling the speed of an induction motor by adjusting the voltage applied to the stator, without changing the frequency. This can be used for reducing the motor's speed, but it comes with limitations in terms of maximum torque.

A type of drive system used for controlling induction motors, relying on a current source inverter to feed the motor. This approach provides inherent short-circuit protection but has limitations in terms of speed range and dynamic response.

A type of drive system used for controlling induction motors, employing a voltage source inverter. This approach offers flexibility and faster response but has limitations in terms of short-circuit protection.

A method for speed controlling an induction motor using a static Scherbius drive, utilizing a slip-ring motor and a separately excited DC motor to control speed.

The moment of inertia of the motor and its connected load, representing the resistance to change in rotation. It affects how quickly the motor accelerates or decelerates.

A component used in electric drives to smooth out fluctuations in speed and torque. It stores energy when the torque is high and releases it when the torque is low, helping to stabilize the drive's performance.

A component in electric drives that allows for adjustment of the motor's voltage. This is often used for speed control by controlling the voltage supplied to the motor.

A component in electric drives that provides instructions and commands to the motor, managing its speed, torque, and other operating parameters. It often incorporates feedback mechanisms for closed-loop control.

The speed of a motor below which it operates in a constant torque mode, and above which it operates in a constant power mode.

The point on the motor's speed-torque curve where the torque is at its maximum value.

The operation of a motor where the speed is controlled by adjusting both voltage and frequency, ensuring that the ratio of voltage to frequency remains constant. This helps to maintain a constant flux in the motor, providing efficient speed control over a wide range.

The speed of a motor where the slip (the difference between synchronous speed and rotor speed) is at its rated value. This corresponds to the motor's normal operating speed.