Systems and methods for controlling multi-level diode-clamped inverters using Space Vector pulse width modulation (SVPWM)

• US 10,389,272 B2
• Filed: 03/06/2018
• Issued: 08/20/2019
• Est. Priority Date: 10/21/2014
• Status: Active Grant

• Current Assignee: Inertech IP LLC
• Original Assignee: Inertech IP LLC
• Inventors: Mondal, Subrata K.
• Primary Examiner(s): Nash, Gary A
• Application Number:
  US15/913,387
• Publication Number:
  US 20180294741A1
• Time in Patent Office: 532 Days
• Field of Search: 363 40- 43, 363 78, 363 79, 363 97, 363 98, 363131-137
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: H02M 1/0845 digitally controlled (or with digital control)
• CPC Class Codes: H02M 3/04 by static converters
• CPC Class Codes: H02M 7/4835 comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: H02M 7/49 Combination of the output voltage waveforms of a plurality of converters
• CPC Class Codes: H02M 7/53873 with digital control
• CPC Class Codes: H02M 7/53875 with analogue control of three-phase output
• 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

Abstract

Control systems for a multi-level diode-clamped inverter and corresponding methods include a processor and a digital logic circuit forming a hybrid controller. The processor identifies sector and region locations based on a sampled reference voltage vector V* and angle θ_e*. The processor then selects predefined switching sequences and pre-calculated turn-on time values based on the identified sector and region locations. The digital logic circuit generates PWM switching signals for driving power transistors of a multi-level diode-clamped inverter based on the turn-on time values and the selected switching sequences. The control system takes care of the existing capacitor voltage balancing issues of multi-level diode-clamped inverters while supplying both active and reactive power to an IT load. Using the control system, one can generate a symmetrical PWM signal that fully covers the linear under-modulation region.

Claims

1. A control system for a multi-level inverter, comprising:

a processor and a memory configured to;

sample a reference voltage vector and an angle;

identify a sector among a plurality of sectors of the multi-level inverter;

convert the reference voltage vector and the angle into X and Y coordinate point values in the identified sector;

identify a region among a plurality of regions of the multi-level inverter based on the X and Y coordinate point values; and

select a switching sequence and a plurality of turn-on time values based on the identified sector and region; and

a circuit configured to generate pulse width modulation (PWM) switching signals for the plurality of regions of the multi-level inverter and the plurality of sectors of the multi-level inverter based on the turn-on time values and the selected switching sequence.

2. The control system of claim 1, wherein each of the plurality of regions includes a same number of the plurality of sectors.

3. The control system of claim 1, further comprising an up/down counter configured to count from 0 to Ts/2 and then from Ts/2 to 0, where Ts is a sampling period.

4. The control system of claim 1, wherein the circuit is implemented by a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC).

5. The control system of claim 1, wherein the processor and the memory are implemented by a digital signal processor (DSP).

6. The control system of claim 1, wherein the identifying the region includes comparing the X and Y coordinate point values to segments of triangles, which represent regions, in a vector space.

7. The control system of claim 1, wherein the turn-on time values and the switching sequence are predetermined for each sector and region.

8. The control system of claim 1, wherein the turn-on time values and the switching sequence are stored in a look-up table.

9. The control system of claim 1, wherein the plurality of sectors are sectors A-F.

10. A method of controlling a multi-level inverter, comprising:

sampling a reference voltage vector and an angle;

identifying a sector among a plurality of sectors of the multi-level inverter;

converting the reference voltage vector and the angle into X and Y coordinate point values;

identifying a region among a plurality of regions of the multi-level inverter based on the X and Y coordinate point values;

selecting a switching sequence and a plurality of turn-on time values based on the identified region; and

generating pulse width modulation (PWM) switching signals for the plurality of regions of the multi-level inverter and the plurality of sectors of the multi-level inverter based on the turn-on time values and the selected switching sequence.

11. The method of claim 10, wherein each of the plurality of regions includes a same number of the plurality of sectors.

12. The method of claim 10, wherein the identifying the region includes comparing the X and Y coordinate point values to segments of triangles, which represent regions, in a vector space.

13. The method of claim 10, wherein the turn-on time values and switching sequence are predetermined for each sector and region.

14. The method of claim 10, wherein the turn-on values and the switching sequence are stored in a look-up table stored in a storage memory.

15. An energy storage system comprising:

an energy storage device;

a DC-DC converter coupled to the energy storage device;

a multi-level inverter coupled to the DC-DC converter; and

a controller for the multi-level inverter, the controller comprising;

a processor and a memory configured to;

sample a reference voltage vector and an angle;

identify a sector among a plurality of sectors of the multi-level inverter;

convert the reference voltage vector and the angle into X and Y coordinate point values in the identified sector;

identify a region among a plurality of regions of the multi-level inverter based on the X and Y coordinate point values; and

select a switching sequence and a plurality of turn-on time values based on the identified sector and region; and

a circuit configured to generate pulse width modulation (PWM) switching signals for the plurality of regions of the multi-level inverter and the plurality of sectors of the multi-level inverter based on the turn-on time values and the selected switching sequence.

16. The energy storage system of claim 15, wherein the identifying the region includes comparing the X and Y coordinate point values to segments of triangles, which represent regions, in a vector space.

17. A control system for a multi-level inverter, comprising:

a processor and a memory configured to;

sample a reference voltage vector and an angle;

identify a sector among a plurality of sectors of the multi-level inverter and a region among a plurality of regions of the multi-level inverter based on the sampled reference voltage vector and the sampled angle; and

select a switching sequence and a plurality of turn-on time values based on the identified sector and region;

a circuit configured to generate pulse width modulation (PWM) switching signals for the plurality of regions of the multi-level inverter and the plurality of sectors of the multi-level inverter based on the turn-on time values and the selected switching sequence; and

an up/down counter configured to count from 0 to Ts/2 and then from Ts/2 to 0, where Ts is a sampling period.

18. The control system of claim 17, wherein the processor and the memory are further configured to:

convert the reference voltage vector and the angle into X and Y coordinate point values in the identified sector; and

identify a region location based on the X and Y coordinate point values.

19. The control system of claim 18, wherein the identifying the region location includes comparing the X and Y coordinate point values to segments of triangles, which represent regions, in a vector space.

20. The control system of claim 17, further comprising a memory,

wherein the turn-on values and the switching sequence are stored in a look-up table stored in the memory.