Electrical Drives

Motor Controllers - Controller manufacturers are improving features such as protection for motor controllers and brushless dc commutation.

One operation of all motors, whether powered by ac or dc, calls for motor controllers. The simplest of motor controllers, called starters, merely connect and disconnect a motor to a power source. But motor controllers also protect the motor from overload and prevent excessive branch-circuit current. In some cases, motor controllers protect the equipment they power as well as the operators. More sophisticated motor controllers, sometimes called drives, regulate motor torque, speed, or horsepower in response to remote commands.

AC Motor Controllers

Adjustable-speed ac motor controllers offer advantages over dc motor controllers because of the simplicity, high-speed capability, and low-maintenance requirements of squirrel-cage motors. Squirrel-cage motors can also adapt to adverse conditions, such as dirty air, explosive atmospheres, and inaccessible locations.

Ac motor drives: The ac induction motor is sometimes considered a constant-speed motor, and it is when connected to a 60-Hz power source. However, its speed can be adjusted if power is supplied by an adjustable-frequency drive. Speed is also adjustable by means of eddy-current drives. The primary elements of an adjustable-frequency drive are a rectifier and an inverter that convert 60-Hz power to adjustable-frequency ac. Two ways to provide this conversion are the six-step and PWM methods.

Two conversion methods are hard to compare because there are many variations. However, the attributes include:

Six-step method:

Can operate at higher frequencies.
Produces less motor noise.
Produces less stress on motor insulation.

PWM method:

Produces less motor losses in some versions.
Provides low-speed torque without cogging.
Can provide stall torque.

Motor Controllers: Information on Motor Controllers