Motor control in industrial applications
Industrial drive applications need to take into account the load on the motor, speed, acceleration, deceleration and duty cycle of the motor. These criteria are used to determine the horsepower and torque requirements. The control of the motor speed and position of the rotor also need to be considered when deciding whether to use constant or variable horsepower.
Variable horsepower / Constant torque
For example, variable horsepower applications with constant torque include gear pumps, cranes and drives for conveyor belts. These often use a constant-speed AC or DC electric motor as the load is constant.
Constant horsepower / Variable torque
A constant horsepower drive with variable torque often uses a DC or servo motor, or an AC motor with a closed-loop control. These can be used for applications such as unwinding and rewinding in roll-to-roll machines.
Variable horsepower / Variable torque
The third approach of variable horsepower and variable torque is often used in centrifugal pumps, fans, mixers and agitators. This is because in these industrial applications the load increases as the speed increases. Naturally a variable frequency drive (VFD) is a suitable solution for such a design. Linear motion drives and actuators often need accurate control of the position of the rotor and stator, while presses and tension control systems can need accurate torque control. These often use an industrial servo drive or stepper motor with a feedback control system to provide high performance.
Industrial drive application examples
There are many different applications for industrial motor control right across the factory floor. Automating industrial processes and connecting the drives up to the cloud are a key part of the move to the next generation of factory automation, often called Industry 4.0. These applications can vary from fans to pumps and from servo drives to linear motors.
AC Drives
An AC drive often uses a single-phase induction motor or three-phase brushless motor with a frequency controller to handle the speed and torque. Control methods such as variable-frequency drive (VFD) or field-oriented control (FOC) can be used, and there are also poly-phase motors that use multiple-phase signals for more accurate control of the drive.
Fans
Fans are of course widely used for ventilation, cooling and fume extraction across a wide range of applications on the factory floor. The mechanical configuration such as the axial, centrifugal and tangential air flow and the size and shape of the blades must be carefully considered, and this leads to the selection of a particular motor. This can be a brushed or brushless DC motor or a single- or three-phase AC induction motor depending on the size of the blades and the speed at which they need to rotate.
Forklift
Electric forklifts use industrial drives in several areas, from driving the wheels to driving the hydraulic pumps that lift the heavy cargo. The powertrain and the hydraulic actuators typically use a permanent-magnet DC motor (PMDC) controlled by high-power low-voltage inverters.
Pumps
Pumps can be found in many industrial environments and depending on the application, the mechanical configuration, size and shape must be carefully selected. Equally, the motor type – whether universal, brushed or brushless DC motor or a single- or three-phase induction motor – and the associated motor drive need to be selected to achieve the overall performance required by the system.
Servo Drives
Industrial servo drives are used to provide the maximum accuracy for a motor's acceleration, speed and position. They are often used in robotics applications where accurate placement is needed at high speed, or where accuracy is needed such as lens autofocus control or antenna positioning. These also make use of sophisticated feedback control loops around a three-phase induction motor drive or BLDC motor.
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