In this method, a solid state variable frequency inverter is used to start the motor. With the variable frequency power source, the motor can supply full load torque at full load current for the duration of the acceleration. The initial applied frequency is very low, and the frequency is gradually increased to the running speed desired.

Variable Frequency Starting

Starting Characteristics:

Can be programmed similarly to the solid state starter to respond to current limits, speed control, or internal ramping function. Current and torque are a function of the programming.

Applications:

Usually used only when the inverter is necessary to supply variable frequency as a speed control. Generally, is too expensive to use just for starting purposes, but may be because it does have the very best starting characteristics relative to the burden it places on the power system during acceleration.