TB Wood's WFC1000 Series, Installation, Operation And Maintenance Instructions

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1.6 AC Inverter Fundamentals
The principle of operation of the WFC HT , or any AC inverter, is to provide both an adjustable voltage and an
adjustable frequency to the AC motor. The WFC HT automatically maintains the required volts/hertz ratio,
allowing the AC motor to run at its optimum efficiency and providing rated torque capability throughout the
motor’s speed range. The basic formula that relates the output frequency to motor speed is:
Ns = 120 x f
Ns = Synchronous Speed (RPM)
P f = Frequency (Hertz)
P = Number of Poles in Motor
For Induction Motors:
Motor RPM = Synchronous Speed – Motor Slip (RPM)
The number of poles of a particular motor, and the amount of slip for a given load torque, are set by the
motor’s design and manufacturer.
1.7 Description of Operation
The primary functional blocks of the inverter are outlined in Figure 1.7.
The ultimate goal of any inverter is to accept fixed voltage and frequency from a power source and convert this
power into variable voltage and frequency to control a three phase AC induction motor. The WFC
HT does this
and much more. It allows the user to interface into the very powerful electronics necessary to provide variable
speed control of the motor, in a very friendly fashion.
Signals can be introduced to the terminal strip for full or partial control of the inverter. The powerful serial input
output (SIO) link is available for total communication and programming. The keypad provides total control of
programming and drive operation.
FIGURE 1.7
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