SYSTEM AND METHOD FOR POWER CONVERSION

• US 20150303819A1
• Filed: 04/16/2015
• Published: 10/22/2015
• Est. Priority Date: 04/18/2014
• Status: Active Grant

• Current Assignee: GE Energy Power Conversion Technology Limited (GE Vernova, Inc.)
• Original Assignee: General Electric Company
• Inventors: ZHANG, Yingqi, ZHANG, Ying, QU, Bo, SHEN, Jie, CHEN, Kunlun
• Granted Patent: US 10,003,279 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H02M 1/0095 Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
• CPC Class Codes: H02M 1/327 against abnormal temperatures
• CPC Class Codes: H02M 7/4837 Flying capacitor converters
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters

Abstract

A method used to control the operation of a converting device such that it can provide multi-level output voltage for loads. This method comprises at least the steps of: determine whether the load which the converter is providing electricity for is operating under the first condition or the second condition; generate the first pulse signal after determining that this load is operating under the first condition, select at least one of at least three different current paths, such that when the converter is selecting any of the current paths, it can provide output voltage at the same level; as well as generate the second pulse signal after determining that this load is operating under the second condition, such that the converter can perform the regular energy conversion operations.

Claims

1. A power conversion system, comprising:

a multi-level power converter comprising switches operable to provide a multi-level output voltage having at least one positive voltage level, a zero voltage level, and at least one negative voltage level; and

a controller in communication with the multi-level power converter and capable of being operated under at least a normal modulation mode and a thermal balancing modulation mode depending at least on the magnitude of the multi-level output voltage, wherein the controller is operable to send control signals to the multi-level power converter to select among at least three different current paths therein for controlling the multi-level power converter to provide the zero level output voltage in the thermal balancing modulation mode while reducing thermal stress on the switches of the multi-level power converter.

2. The power conversion system of claim 1, wherein the multi-level power converter is configured to provide a 2n+1 level output voltage, where n is equal to and larger than two.

3. The power conversion system of claim 1, wherein the multi-level power converter comprises:

a first converter module comprising a first switch unit, a second switch unit, and a third switch unit; and

a second converter module coupled to the first converter module, the second converter module comprising a fourth switch unit, a fifth switch unit, and a sixth switch unit.

4. The power conversion system of claim 3, wherein one of the at least three different current paths is through the second and sixth switch units.

5. The power conversion system of claim 4, wherein another of the at least three different current paths is through the third and fifth switch units.

6. The power conversion system of claim 3, wherein each of the first and fourth switch units comprise:

a first switching device controllable to allow a first electric current to flow therethrough along a first direction;

a first diode coupled in parallel to the first switching device, the first diode arranged to allow a second electric current to flow therethrough along a second direction opposite to the first direction;

a second switching device controllable to allow the second electric current to flow therethrough along the second direction; and

a second diode coupled in parallel to the second switching device, the second diode arranged to allow the first electric current to flow therethrough along the first direction.

7. The power conversion system of claim 3, wherein at least one of the second, third, fifth, and sixth switch units comprise at least two switching devices connected in series.

8. The power conversion system of claim 3, further comprising:

a DC link comprising a first DC capacitor and a second DC capacitor; and

a flying-cap link comprising a first flying capacitor and a second flying capacitor;

wherein the three different current paths corresponding to the zero voltage level comprise;

a first current path comprising the first and third switch units;

a second current path comprising the first DC capacitor, the second switch unit, the first flying capacitor, the second flying capacitor, and the sixth switch unit; and

a third current path comprising the second DC capacitor, the third switch unit, the second flying capacitor, the first flying capacitor, and the fifth switch unit.

9. The power conversion system of claim 8, wherein the controller is further operable to send control signals to the multi-level power converter to select the three different current paths in a manner to balance the voltages at the first and second flying capacitors in the thermal balancing modulation mode.

10. A power conversion system, comprising:

a multi-level power converter comprising a plurality of switching devices operable to convert a direct-current (DC) voltage at a DC link to a multi-level alternating-current (AC) voltage for use by a motor; and

a controller in communication with the multi-level converter, the controller comprising;

a modulation mode selection unit for generating a first modulation mode signal upon determining the motor is operating under a first condition and generating a second modulation mode signal upon determining the motor is operating under a second condition;

a first pulse pattern distributor (304) coupled to the modulation mode selection unit and operable to generate first pulse signals for controlling the plurality of switching devices to substantially balance the thermal conditions of the plurality of switching devices according to the first modulation mode signal; and

a second pulse pattern distributor (306) coupled to the modulation mode selection unit and operable to generate second pulse signals for controlling the plurality of switching devices to perform normal power conversion operations according to the second modulation mode signal.

11. The power conversion system of claim 10, wherein the modulation mode selection unit is operable to identify that the motor is operating under the first condition upon determining that an actual AC output voltage of the multi-level power converter is less than a voltage threshold and an actual AC output current from the multi-level power converter is greater than a current threshold.

12. The power conversion system of claim 10, wherein the modulation mode selection unit is operable to identify that the motor is operating under the first condition upon determining that an AC output command voltage indicative of a desired AC output voltage of the multi-level power converter is less than a voltage threshold and an AC output command current indicative of a desired AC output current of the multi-level power converter is greater than a current threshold.

13. The power conversion system of claim 10, wherein modulation mode selection unit is to generate the first modulation mode signal upon determining a modulation index is less than a threshold value.

14. The power conversion system of claim 10, wherein the first pulse pattern distributor is operable to modify the first pulse signals if the voltages at the flying capacitors are not balanced according to pre-set criteria.

15. A method for operating a power converter capable of providing a multi-level output voltage to a load, comprising:

determining whether the load powered by the power converter is operating under a first condition or a second condition;

generating first pulse signals to select among at least three different current paths when the load is operating under the first condition to allow the power converter to provide a same level output voltage; and

generating second pulse signals to allow the power converter to perform normal power conversion operations when the load is operating under the second condition.

16. The method of claim 15, wherein determining whether the load is operating under a first condition or a second condition comprises:

determining whether an actual output voltage of the power converter is less than a voltage threshold;

determining whether an actual output current of the power converter is greater than a current threshold; and

generating a first signal indicating that the load is operating under the first condition upon determining that the actual output voltage is less than the voltage threshold and the actual output current is greater than the current threshold.

17. The method of claim 15, wherein determining whether the load is operating under a first condition or a second condition comprises:

determining whether an output command voltage indicating a desired output voltage of the power converter is less than a voltage threshold;

determining whether an output command current indicating a desired output current of the power converter is greater than a current threshold; and

generating a first signal indicating that the load is operating under the first condition upon determining that the output command voltage is less than the voltage threshold and the output command current is greater than the current threshold.

18. The method of claim 15, wherein determining whether the load is operating under a first condition or a second condition comprises:

determining whether a modulation index in association with the power converter is less than a threshold value; and

generating a first signal indicating that the load is operating under the first condition upon determining that the modulation index is less than the threshold value.

19. The method of claim 15, further comprising:

determining whether the voltages at flying capacitors in association with the power converter are balanced;

modifying the first pulse signals upon determining that the voltages at the flying capacitors are not balanced.

20. The method of claim 15, wherein the same level output voltage is zero.