Power converter apparatus and methods using neutral coupling circuits with interleaved operation
A power converter apparatus, such as an uninterruptible power supply (UPS), includes an inverter having an input coupled to a first DC bus and a second DC bus and configured to generate an AC output with respect to a neutral terminal at a phase output terminal thereof. The apparatus further includes first and second neutral coupling circuits, each configured to selectively couple the first DC bus and the second DC bus to the neutral terminal, and a control circuit configured to cause interleaved operation of the neutral coupling circuits.
1. A power converter apparatus comprising:
a rectifier having an input coupled to an AC source and an output coupled to a first DC bus and a second DC bus and configured to generate a DC voltage across the first and second DC busses;
an inverter having an input coupled to the first DC bus and the second DC bus and configured to generate an AC output with respect to a neutral terminal at a phase output terminal;
parallel first and second neutral coupling circuits, each configured to selectively couple the first DC bus and the second DC bus to the neutral terminal; and
a control circuit configured to cause interleaved operation of the neutral coupling circuits while the rectifier is generating the DC voltage across the first and second DC busses.
2. The apparatus of claim 1 , wherein the control circuit is configured to operate the neutral coupling circuits to shift a voltage range between the first DC bus and the second DC bus with respect to the neutral terminal.
3. The apparatus of claim 1 , wherein the control circuit comprises:
a pulse width modulation circuit configured to generate a pulse train signal; and
a drive circuit configured to drive respective ones of the neutral coupling circuits responsive to respective interleaved sets of pulses of the pulse train signal.
4. The apparatus of claim 3 , wherein the pulse train signal comprises a first pulse train signal and wherein the drive circuit comprises:
a pulse separation circuit configured to generate second and third pulse train signals comprising respective trains of pulses corresponding to respective ones of the interleaved sets of pulses; and
respective first and second drive circuits that drive respective ones of the neutral coupling circuits responsive to respective ones of the second and third pulse train signals.
5. The apparatus of claim 4 , wherein the pulses of the second and third pulse train signals have pulse widths that are integer multiples of pulse widths of the corresponding pulses of the first pulse train signal.
6. The apparatus of claim 1 , wherein the inverter comprises first and second parallel-connected phase coupling circuits configured to selectively couple the first DC bus and the second DC bus to the phase output terminal in an interleaved manner.
7. The apparatus of claim 1 , wherein respective ones of the first and second neutral coupling circuits are configured to selectively couple the first DC bus and the second DC bus to the neutral terminal via respective first and second inductors that are not magnetically coupled.
8. An uninterruptible power supply (UPS), comprising:
a phase output terminal;
a neutral terminal;
a first DC bus and a second DC bus;
a rectifier having an input coupled to an AC source and an output coupled to the first DC bus and the second DC bus and configured to generate a DC voltage across the first and second DC busses;
a common mode inductor having a first terminal coupled to one of the first DC bus and the second DC bus and a second terminal configured to be coupled to a battery;
a filter capacitor coupled between the second terminal of the common mode inductor and the neutral terminal;
an inverter coupled to the first DC bus and second DC bus and configured to generate an AC output with respect to the neutral terminal at the phase output terminal;
parallel first and second neutral coupling circuits coupled in parallel between the first DC bus and the second DC bus and each configured to selectively couple the first DC bus and the second DC bus to the neutral terminal; and
a control circuit configured to cause interleaved operation of the neutral coupling circuits while the rectifier is generating the DC voltage across the first and second DC busses.
9. The UPS of claim 8 , wherein the control circuit is configured to cause the neutral coupling circuits to shift a voltage range between the first DC bus and the second DC bus with respect to the neutral terminal.
10. The UPS of claim 8 , wherein the control circuit comprises:
a pulse width modulation circuit configured to generate a pulse train signal; and
a drive circuit configured to drive respective ones of the neutral coupling circuits responsive to respective interleaved sets of pulses of the pulse train signal.
11. The UPS of claim 10 , wherein the pulse train signal comprises a first pulse train signal and wherein the drive circuit comprises:
a pulse separation circuit configured to generate second and third pulse train signals comprising respective first and second trains of pulses corresponding to respective ones of the interleaved sets of pulse; and
respective first and second drive circuits that drive respective ones of the neutral coupling circuits responsive to respective ones of the second and third pulse train signals.
12. The UPS of claim 11 , wherein the pulses of the second and third pulse train signals have pulse widths that are integer multiples of the pulse widths of the corresponding pulses of the first pulse train signal.
13. The UPS of claim 8 :
wherein the common mode inductor comprises:
a first common mode inductor configured to be coupled between the first DC bus and a first terminal of the battery; and
a second common mode inductor configured to be coupled between the second DC bus and a second terminal of the battery; and
wherein the filter capacitor comprises:
a first filter capacitor coupled between the first common mode inductor and the neutral; and
a second filter capacitor coupled between the second common mode inductor and the neutral.
14. The UPS of claim 8 , wherein the inverter comprises first and second parallel-connected phase coupling circuits configured to selectively couple the first DC bus and the second DC bus to the phase output terminal in an interleaved manner.
15. The UPS of claim 8 , wherein respective ones of the first and second neutral coupling circuits are configured to selectively couple the first DC bus and the second DC bus to the neutral terminal via respective first and second inductors that are not magnetically coupled.
16. A method of operating a power conversion apparatus comprising a rectifier having an input coupled to an AC source and an output coupled to a first DC bus and a second DC bus and configured to generate a DC voltage across the first and second DC busses and an inverter coupled to the first and second DC busses and configured to generate an AC output with respect to a neutral terminal at a phase output terminal, the method comprising:
providing parallel first and second neutral coupling circuits, each configured to selectively couple the first DC bus and the second DC bus to a neutral terminal; and
interleaving operations of the first and second neutral coupling circuits while operating the rectifier to generate the DC voltage across the first and second DC busses and operating the inverter to generate the AC voltage with respect to the neutral terminal.
17. The method of claim 16 , further comprising operating the neutral coupling circuits to cause a voltage range between the first DC bus and the second DC bus to shift with respect to the neutral terminal.
18. The method of claim 16 , wherein interleaving operations of the first and second neutral coupling circuits while operating the rectifier to generate the DC voltage across the first and second DC busses and operating the inverter to generate the AC voltage with respect to the neutral terminal comprises:
generating a pulse train signal comprising a series of pulses having widths that vary responsive to a control variable; and
driving respective ones of the neutral coupling circuits responsive to respective interleaved sets of pulses of the pulse train signal.
19. The method of claim 18 , wherein driving respective ones of the neutral coupling circuits responsive to respective interleaved sets of pulses of the pulse train signal comprises:
generating second and third pulse train signals comprising respective trains of pulses corresponding to respective ones of the interleaved sets of pulse; and
driving respective ones of the neutral coupling circuits responsive to respective ones of the second and third pulse train signals.
20. The method of claim 19 , wherein the pulses of the second and third pulse train signals have pulse widths that are a integer multiple of the pulse widths of the corresponding pulses of the first pulse train signal.
21. The method of claim 16 , wherein respective ones of the first and second neutral coupling circuits are configured to selectively couple the first DC bus and the second DC bus to the neutral terminal via respective first and second inductors that are not magnetically coupled.