Electronically commutated serial-parallel switching for motor windings
A method and a circuit for controlling an ac machine comprises controlling a full bridge network of commutation switches which are connected between a multiphase voltage source and the phase windings to switch the phase windings between a parallel connection and a series connection while providing commutation discharge paths for electrical current resulting from inductance in the phase windings. This provides extra torque for starting a vehicle from lower battery current.
1. A circuit for controlling an ac machine having a stator with a plurality of phase windings for each phase and a rotor, the circuit comprising:
a switching device which is connected between a multiphase voltage source and the phase windings, the switching device having a set of contacts for conducting load currents of a magnitude conducted in the windings of the ac machine; and
a full bridge network of solid state commutation switches connected to the switching device to provide commutation discharge paths for electrical current resulting from inductance in the phase windings when the phase windings are switched between a parallel connection and a series connection.
2. The circuit of claim 1 , wherein the solid state commutation switches are SCRs with a low steady state operating current rating of up to and including approximately 25 amps and a high pulse rating of at least approximately 350 amps.
3. The circuit of claim 1 , wherein the commutation switches are in addition to switches in a power inverter supplying multi-phase power to the ac machine.
4. The circuit of claim 1 , wherein the ac machine is a motor.
5. The circuit of claim 1 , wherein the ac machine is a three-phase machine with a plurality of phase windings for phase A, for phase B and for phase C, respectively.
6. The circuit of claim 1 , wherein the switching device has a plurality of contacts for electrical connection to multiphase voltage source and has a plurality of contacts for connection to the phase windings for changing the connection of the phase windings in each phase between a parallel connection and a serial connection.
7. A method of controlling a multiphase ac machine having a stator with a plurality of phase windings for each phase and a rotor, the method comprising:
supplying phase voltages to the phase windings from a multi-phase voltage source;
providing an additional switching device between the phase windings and the multi-phase source; and
controlling the additional switching device to switch the phase windings between a parallel connection and a series connection; and
providing commutation discharge paths for electrical current resulting from inductance in the phase windings passing through the additional switching device, when the phase windings are switched between a parallel connection and a serial connection.
8. The method of claim 7 , wherein the commutation discharge paths are provided by a full bridge network of SCRs with a low steady state operating current rating of no more than approximately 25 amps or less and a high pulse rating of at least approximately 350 amps.
9. The method of claim 7 , wherein the commutation switches are in addition to switches in a power inverter supplying multi-phase power to the ac machine.
10. The method of claim 7 , wherein the ac machine is a motor.
11. The method of claim 7 , wherein the ac machine is a three-phase machine with a plurality of phase windings for phase A, for phase B and for phase C, respectively.