‘Power’ printed circuit boards (pcbs) will carry the gate drive circuits, a power supply, current measurement circuits and an inrush circuit. The power supply is complicated because it must supply the drive circuits at different, high voltages, as well as the control and interface circuits at ‘safe’ low voltages. Power terminals – supply and motor connections- are also mounted on the power boards. A separate control board often includes the control terminals as well as the display and push buttons to set up and control the variable frequency drive.
The complete assembly may be mounted in a plastic case or, for higher power variable frequency drives, in strong steel case. IP20 versions are suitable for mounting in a cubicle or machine, while IP55 or IP66 versions may be offered for more exposed applications.
In the next article we’ll look at drive selection, installation, and commissioning.