This disclosure relates to minimising the losses in a power drive system. In particular it relates to detecting excess power and automatically activating and deactivating a system to redirect the excess power away from the power drive system into the suppl...

An a.c. elevator of the invention has a commercial power source (1), an inverter (3) operable with the power from the commercial power source (1) for generating a.c. power, and an electric motor to be driven with the a.c. power generated by the inverter (3...