Three voltage levels are better than two

Yaskawa is promising a variety of benefits from a new inverter which is says is the first general-purpose 400V inverter to offer three-level PWM (pulse width modulation) control. The suggested benefits include improved protection against surge voltages, low acoustic and electrical noise levels, extremely high efficiency, and protection against damage caused by bearing currents.

Unlike conventional inverters which produce two levels of phase voltage and three-level output waveforms, the new G7 inverter provides three levels of phase voltage, allowing a five-level output voltage. This, in turn, allows an output waveform which approaches an ideal sine shape.

The new inverter, which had its European debut at the recent SPS/IPC/Drives exhibition in Germany, can drive standard motors without needing any surge suppression filters. Its energy-saving performance is said to approach the theoretical maximum, while the drive can deliver 150% of full load torque at 0.3Hz in the open-loop vector control mode. A precise torque limit function provides accurate control of the output torque, protecting motors against sudden load fluctuations.

The G7 drive is being produced in ratings from 0.4-110kW at 200V, and up to 300kW for 400V operation.