New Inverter Supplies for High Horsepower Drives

A review of basic ac induction motor characteristics establishes the requirements of a static ac variable-speed drive. Both voltage and frequency impressed onto an ac motor must be programmed in correct proportion if required operating torque is to be maintained. The means of voltage control used characterizes the various inverter designs and likewise dictates their limitations. Pulsewidth modulation for variable voltage control eliminates many of the restrictions heretofore placed on inverters. Their operating capabilities, while not economically favorable in every case, are technically equal to or better than those of a dc system.