Tower Electric Motor Company carries quality Variable Frequency Drives from Weg, Baldor, Leeson and many other quality brands. Our Variable Frequency Drives have a wide range of available controls, protective features and displays. TEMCo has a full range of motor controls and drives including variable frequency drives, soft starters, etc., to meet your motor starting, protection, and variable speed application needs.

Call (510)490-2187 for additional variable frequency drive details and to order.
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Variable Frequency Drives

An overview of the development and application of Variable Frequency Drives.  

Several common applications that require speed control are conveyors, large pumps, boiler fans and many others.  In the past variable motor speed was achieved with several inefficient means such as wound rotor motors and variable rotor resistors.  The new more efficient and effective way to achieve this variable speed today is with variable frequency drives.

The speed at which and electric motor spins is directly relations to the frequency, phase and number of poles that and electric motor uses.  These three electrical factors do determine the speed of an electric motors rotating electric field.  In the US the standard frequency of most utility supplied ac power is 60Hz.  

By developing the technology to vary the frequency of the current supplied to special AC electric motors in modern time we have developed the much more efficient variable frequency drives. 

This technology became affordable to produce variable-speed drives which are now possible because of modern advances in solid-state electronics. A new product developed called an insulated gate bipolar transistor (IGBT) made it possible to switch large current levels at high-kHz rates, this lead to pulse-width-modulated (PWM) inverter drives. These units have relatively low distortion, are compact in form factor and have high operating efficiency.

Pulse-Width-Modulated-Inverters (PWM inverters) control the kHz-chopping rate of a wave; varying its envelope in voltage and fundamental frequency; to control the motor acceleration and running of the induction motor. The pulse rate can be set high enough to make audible noise of vibration, stimulated in the motor by the Variable Frequency Drive (VFD), inaudible. You can arrange the range of fundamental frequencies through which the drive accelerates and operates the electric motor to skip critical frequencies where resonance in the mechanical equipment and structural supports might be excited to levels that could cause damage.

The circuitry of a variable frequency is similar to other system applications of solid-state motor controllers and uninterruptible power supply systems, as used for large computer systems and data centers.

Variable Frequency Drive Categories

There are two general categories of Variable Frequency Drives (VFD) designs: Voltage source inverter (VSI) and Current source inverter (CSI.) Manufacturers of Variable Frequency Drives VFDs seemed to use one style or the other. The two types differ in the manner in which power is passed to the motor after being processed by the drive. The VSI drive treats the motor as a parallel-connected load and controls the overall performance envelope by adjustments to the output voltage of the drive. The CSI drive centers on motor impedance (inductive reactance) since it is driving current through the motor as part of the performance envelope. You must match CSI drives with their motors.

This motor matching is less important for VSI drives. Some use Variable Frequency Drives (VFDs) with motors of unknown origin, particularly in retrofits. However, one source should specify, purchase, and install Variable Frequency Drives (VFDs) with their associated motors whenever possible. Keep track of the thermal budget for the operating motor, and even for rooms housing large groups of drives.