A motor system includes a motor, first and second power rails connected to a DC voltage input terminal, and a DC bus capacitor connected between the first and second power rails. An inverter circuit has a first inverter leg, a second inverter leg and a third inverter leg, each of which includes first and second power switches connected in series between the first and second power rails. The inverter circuit is configured to selectively output energization signals to phase windings of the motor. A DC link discharge circuit is configured to monitor a voltage level of the DC bus capacitor, and a bus switching circuit is configured to selectively output one of a first DC voltage level or a second DC voltage level to the DC voltage input terminal in response to an output of the DC link discharge circuit.

A system for controlling an electric motor by implementing a synchronized bidirectional rotary dual active bridge, comprising a rotary transformer having a primary side and a secondary side; a first inverter being a first full active bridge, connected between an AC power source and the primary side; a second inverter being a second full active bridge, connected to the secondary side and feeding the load current to the rotor of an electric motor via the secondary side; a control circuit, for transmitting square wave synchronization pulses at the switching frequency of the inverters, to operate the second full active bridge independent of the first full active bridge. At the primary side, the phase and the operating duty cycle of the first full active bridge are controlled to be in synchronization with the synchronization pulses, to thereby vary the current provided by the second full active bridge to the rotor.

A system for controlling an electric motor by implementing a synchronized bidirectional rotary dual active bridge, comprising a rotary transformer having a primary side and a secondary side; a first inverter being a first full active bridge, connected between an AC power source and the primary side; a second inverter being a second full active bridge, connected to the secondary side and feeding the load current to the rotor of an electric motor via the secondary side; a control circuit, for transmitting square wave synchronization pulses at the switching frequency of the inverters, to operate the second full active bridge independent of the first full active bridge. At the primary side, the phase and the operating duty cycle of the first full active bridge are controlled to be in synchronization with the synchronization pulses, to thereby vary the current provided by the second full active bridge to the rotor.