Tag: Variable Speed Motor Controls

A very common method for directly controlling low flow rates of fluids is to use a device known as a metering pump. A “metering pump” is a pump mechanism, motor, and drive electronics contained in a monolithic package. Simply supply 120 VAC power and a control signal to a metering pump, and it is ready to…

Regulating the electric power sent to an electric motor is a task performed by high-speed switching transistors inside a motor drive, modulating the pulse-width of a high-frequency square wave to the motor. The high-speed switching happening inside of a motor “drive” circuit results in the drive drawing current from the AC power source as high-frequency…

Modern DC and AC motor drives provide features useful when using electric motors as final control elements. Some common features seen in both VSDs and VFDs are listed here: Speed limiting Torque limiting Torque profile curves (used to regulate the amount of torque available at different motor speeds) Acceleration (speed rate-of-change) limiting Deceleration (speed rate-of-change)…

There are several different methods useful for causing an AC induction motor to brake, or slow down: DC injection Dynamic braking Regenerative braking Plugging DC injection uses the technique of energizing the stator windings with low-current DC instead of high-current AC as is the case when the motor runs. Dynamic braking works the motor as a generator, dissipating energy…

AC induction motors are based on the principle of a rotating magnetic field produced by a set of stationary windings (called stator windings) energized by AC power of different phases. The effect is not unlike a series of blinking “chaser” light bulbs which appear to “move” in one direction due to the blinking sequence. If sets of wire coils…

DC electric motors generate torque by a reaction between two magnetic fields: one field established by stationary “field” windings (coils), and the other by windings in the rotating armature. Some DC motors lack field windings, substituting large permanent magnets in their place so that the stationary magnetic field is constant for all operating conditions. In…

An alternative to control valves for adjusting fluid flow is to regulate the speed of the machine(s) motivating fluid to flow. In the case of liquid flow control, this would take the form of variable-speed pumps. In the case of gas flow control, it would mean varying the rotational speed of compressors or blowers. Flow…