Systems and methods for reducing AC drive common-mode currents

• US 7,881,081 B1
• Filed: 04/16/2010
• Issued: 02/01/2011
• Est. Priority Date: 04/16/2010
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Kirschnik, David W., Tallam, Rangarajan M., Leggate, David, Lukaszewski, Richard A.
• Primary Examiner(s): Riley; Shawn
• Application Number:
  US12/761,893
• Time in Patent Office: 291 Days
• Field of Search: 363/41, 363/40, 363/131, 363/132
• US Class Current: 363/41
• CPC Class Codes: H02M 1/123 Suppression of common mode voltage or current
• CPC Class Codes: H02M 1/44 Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
• CPC Class Codes: H02M 7/53876 based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
• CPC Class Codes: H02M 7/5395 by pulse-width modulation

Abstract

Control systems, methods and power conversion systems are presented for controlling common mode currents in power converters, in which feedback signals used in pulse width modulated inverter switching control are selectively adjusted to ensure minimum differences between the resulting common mode compensated feedback signals according to a common mode dwell time in each pulse width modulation period, with the common mode dwell time being adjusted according to modulation index.

Claims

1. A power conversion system, comprising:

a DC circuit comprising first and second DC current paths;

an inverter comprising a multi-phase AC connection having a plurality of AC terminals for supplying AC electrical power, and a switching network comprising a plurality of switching devices individually coupled between one of the DC current paths and one of the AC terminals, the switching devices individually operable to selectively electrically couple the corresponding DC current path with the corresponding AC terminal according to a corresponding switching control signal; and

a switch control system operative to provide the switching control signals by pulse width modulation at least partially according feedback signals or values representing AC phase outputs and according to the position of a reference vector in a space vector modulation diagram having a plurality of stationary active space vectors around the periphery of the diagram and two stationary zero vectors at an origin of the diagram, the vectors representing unique switching states for the switching network and defining a plurality of triangular sectors positioned around the origin, the sectors each being defined by a unique set of two active vectors and the zero vectors at the corners of the corresponding triangular sector, the switch control system providing the switching control signals according to a switching sequence corresponding to the diagram sector in which the reference vector is currently located, the switch control system comprising a common mode reduction component operative in each pulse width modulation period to determine max, mid, and min ones of the feedback signals or values, and to selectively adjust one or more feedback signals or values higher or lower to provide common mode compensated feedback signals or values having minimum differences therebetween based at least partially on a common mode dwell time.

2. The power conversion system of claim 1, wherein the common mode reduction component is operative in each pulse width modulation period to selectively adjust one or more of the feedback signals or values φ

higher or lower according to the formulas (max−

mid)≧

2(T<sub>dwell—

CM</sub>/T_PWM) and (mid−

min)≧

2(T<sub>dwell—

CM</sub>/T_PWM) to provide the common mode compensated feedback signals or values, where T<sub>dwell—

CM</sub> is the common mode dwell time and where T_PWM is the pulse width modulation period.

3. The power conversion system of claim 2, wherein the switch control system is operative in each pulse width modulation period to accumulate common mode adjustment amounts for each feedback signal or value and to adjust one or more feedback signals or values higher or lower in a subsequent pulse width modulation period to compensate for the common mode reduction adjustments made in a previous pulse width modulation period.

4. The power conversion system of claim 3, wherein the switch control system is operative to selectively adjust the common mode dwell time at least partially according to a modulation index associated with the position of the reference vector in the space vector modulation diagram.

5. The power conversion system of claim 4, wherein the switch control system is operative to receive the common mode dwell time from an external source.

6. The power conversion system of claim 4, wherein the switch control system further comprises a reflected wave compensation component operative to selectively adjust one or more of the common mode compensated feedback signals or values higher or lower to provide reflected wave compensated signals or values based at least partially on at least one reflected wave compensation limit value.

7. The power conversion system of claim 6, wherein the reflected wave compensation component is operative to selectively adjust one or more of the common mode compensated feedback signals or values higher or lower according to the following formula:

φ

″

=φ

′

if (RWC_min<

=φ

′

<

=RWC_max), φ

″

=1 if (φ

′

>

RWC_max), φ

″

=0 if (φ

′

<

RWC_min), where φ

′

are the common mode compensated feedback signals or values, φ

″

are the reflected wave compensated signals or values, RWC_min is a lower reflected wave compensation limit value, and RWC_max is an upper reflected wave compensation limit value.

8. The power conversion system of claim 6, wherein the switch control system further comprises a deadtime compensation component operative to selectively adjust one or more of the common mode compensated feedback signals or values or to selectively adjust one or more of the reflected wave compensated signals or values to provide deadtime compensated signals or values based at least partially on a deadtime value.

9. The power conversion system of claim 8, wherein the deadtime compensation component is operative to selectively adjust one or more of the common mode compensated feedback signals or values or to selectively adjust one or more of the reflected wave compensated signals or values φ

″

to provide the deadtime compensated signals or values φ

′

″

according to the following formula;

φ

′

″

=φ

″

+sign(i<sub>φ

′</sub>

)·

(Td/T_PWM), where i<sub>φ

′</sub>

is a corresponding phase current, Td is the deadtime value, and T_PWM is a pulse width modulation period.

10. The power conversion system of claim 4, wherein the switch control system further comprises a deadtime compensation component operative to selectively adjust one or more of the common mode compensated feedback signals or values φ

′

based at least partially on a deadtime value.

11. The power conversion system of claim 1, wherein the switch control system is operative to selectively adjust the common mode dwell time at least partially according to a modulation index associated with the position of the reference vector in the space vector modulation diagram.

12. The power conversion system of claim 11, wherein the switch control system is operative to receive the common mode dwell time from an external source.

13. The power conversion system of claim 1, wherein the switch control system is operative to receive the common mode dwell time from an external source.

14. The power conversion system of claim 1, wherein the switch control system further comprises a reflected wave compensation component operative to selectively adjust one or more of the common mode compensated feedback signals or values higher or lower to provide reflected wave compensated signals or values based at least partially on at least one reflected wave compensation limit value.

15. The power conversion system of claim 14, wherein the switch control system further comprises a deadtime compensation component operative to selectively adjust one or more of the common mode compensated feedback signals or values or to selectively adjust one or more of the reflected wave compensated signals or values to provide deadtime compensated signals or values based at least partially on a deadtime value.

16. The power conversion system of claim 1, wherein the switch control system further comprises a deadtime compensation component operative to selectively adjust one or more of the common mode compensated feedback signals or values to provide deadtime compensated signals or values based at least partially on a deadtime value.

17. The power conversion system of claim 1, wherein the switch control system comprises a carrier-based pulse width modulation system including a carrier wave generator, at least one comparator operative to compare a carrier wave from the generator with the one or more feedback signals or values, and a set of switching sequences to provide the switching control signals by pulse width modulation based on an output of the at least one comparator.

18. A method for mitigating common mode currents in a power conversion system having a switching inverter, the method comprising:

providing pulse width modulated inverter switching control signals to a plurality of inverter switching devices of the switching inverter to convert DC power to cause the inverter to selectively provide multi-phase AC electrical output power at least partially according feedback signals or values representing AC phase outputs and according to the position of a reference vector in a space vector modulation diagram;

determining max, mid, and min ones of the feedback signals or values in each pulse width modulation period; and

selectively adjusting one or more feedback signals or values higher or lower to provide common mode compensated feedback signals or values having minimum differences therebetween based at least partially on a common mode dwell time in each pulse width modulation period.

19. The method of claim 18, wherein one or more of the feedback signals or values are adjusted higher or lower according to the formulas (max−

mid)≧

2(T<sub>dwell—

CM</sub>/T_PWM) and (mid−

min)≧

2(T<sub>dwell—

CM</sub>/T_PWM), where T<sub>dwell—

CM</sub> is the common mode dwell time and where T_PWM is the pulse width modulation period.

20. The method of claim 18, further comprising:

accumulating common mode adjustment amounts for each feedback signal or value φ

in each pulse width modulation period; and

adjusting one or more feedback signals or values higher or lower in a subsequent pulse width modulation period to compensate for the common mode reduction adjustments made in a previous pulse width modulation period.

21. The method of claim 18, further comprising selectively adjusting the common mode dwell time at least partially according to a modulation index associated with the position of the reference vector in the space vector modulation diagram.

22. The method of claim 21, further comprising receiving the common mode dwell time from an external source.

23. The method of claim 18, further comprising receiving the common mode dwell time from an external source.