Converter pulse width modulation strategies for three phase regenerative drives
A three-phase regenerative drive employing multiple converter pulse width modulation (PWM) strategies. The drive includes a three-phase converter having inputs for connection to a three-phase AC source, the three-phase converter having three phase legs, a DC bus operably connected to the three-phase converter wherein the three phase converter is configured to direct current from the three-phase AC source to the DC bus, and a three-phase inverter operably connected to the DC bus and a motor, the three phase inverter configured to draw current from the DC bus and provide three phase command signals to the motor. The three-phase converter employs a first PWM strategy to supply current to the DC bus, and the converter employs a second PWM strategy to supply current to the DC bus if a total current in the three phase legs exceeds a selected threshold.
1. A three-phase regenerative drive employing multiple converter pulse width modulation (PWM) strategies, the drive comprising:
a three-phase converter having inputs for connection to a three-phase AC source, the three-phase converter having three phase legs;
a DC bus operably connected to the three-phase converter wherein the three phase converter is configured to direct current from the three-phase AC source to the DC bus;
a three-phase inverter operably connected to the DC bus and a motor, the three phase inverter configured to draw current from the DC bus and provide three phase command signals to the motor; and
wherein the three-phase converter employs a first PWM strategy to supply current to the DC bus, and the three-phase converter employs a second PWM strategy to supply current to the DC bus if a total current in the three phase legs exceeds a selected current threshold.
2. The three-phase regenerative drive of claim 1 , wherein the each phase leg of the three phase legs of the three-phase converter includes a first and a second switching device, each of the thee phase legs having an emitter side resistor configured to sense phase current for each phase leg of the three phase legs.
3. The three-phase regenerative drive of claim 1 , further including a controller for providing converter PWM signals to the three-phase converter based on at least one of the first PWM strategy and the second PWM strategy.
4. The three-phase regenerative drive of claim 3 , wherein the first PWM strategy is based on at least one of a space vector PWM and a hybrid space vector PWM technique.
5. The three-phase regenerative drive of claim 3 , further including the controller configured to generate inverter PWM control signals to the three-phase inverter.
6. The three-phase regenerative drive of claim 5 , wherein the converter PWM control signals are at a different frequency than the inverter PWM control signals.
7. The three-phase regenerative drive of claim 6 , wherein the converter PWM control signals are at twice the frequency than the inverter PWM control signals.
8. The three-phase regenerative drive of claim 1 , wherein the second PWM strategy is based on at least one of a discontinuous PWM technique and a space vector PWM technique.
9. The three-phase regenerative drive of claim 1 , further comprising a filter interposed between the AC source and the three-phase converter.
10. The three-phase regenerative drive of claim 9 wherein the filter comprises at least two series reactances configured to transfer current from the AC source to each phase leg of the three phase converter.
11. The three-phase regenerative drive of claim 1 , wherein the converter PWM strategy provides a drive that is about 25% more efficient than a three-phase regenerative drive employing space vector PWM techniques alone.
12. A method of operating a three phase regenerative drive to drive a motor from a three phase AC source, the drive comprising a three-phase converter having three phase legs, a three phase inverter, and a DC bus connected between the converter and the inverter, and a controller, the controller executing the method comprising:
determining a total current in the three phase legs;
controlling the three phase converter with a first pulse width modulation (PWM) technique to cause the three phase converter to supply power to the DC bus;
if a total current in the three phase legs exceeds a selected threshold, controlling the three-phase converter to employs a second PWM strategy to supply current to the DC bus.
13. The method of claim 12 , wherein the each phase leg of the three phase legs of the three-phase converter includes a first and a second switching device, each of the thee phase legs having an emitter side resistor, wherein the measuring is based on a voltage induced on the emitter side sense resistors.
14. The method of claim 12 , further including the controller providing converter PWM control signals to the three-phase converter based on at least one of the first PWM strategy and the second PWM strategy.
15. The method of claim 14 , wherein the wherein the first PWM strategy is based on at least one of a space vector PWM and a hybrid space vector PWM technique.
16. The method of claim 12 , wherein the second PWM strategy is based on at least one of a discontinuous PWM technique and a space vector PWM technique.
17. The method of claim 12 , further including generating inverter PWM control signals to the three-phase inverter to generate three phase command signals from the DC bus to supply the motor.
18. The method of claim 17 , wherein the converter PWM control signals are at a different frequency than the inverter PWM control signals.
19. The method of claim 12 , wherein the converter PWM control signals are at twice the frequency than the inverter PWM control signals.
20. The method of claim 12 , further comprising interposing a filter between the AC source and the three-phase converter.
21. The method of claim 20 wherein the filter comprises at least two series reactances configured to transfer current from the AC source to each phase leg of the three phase converter.
22. The method of claim 12 further including, wherein the converter PWM strategy provides a drive that is about 25% more efficient than a three-phase regenerative drive employing space vector PWM techniques alone.