Systems and methods for controlling multi-level diode-clamped inverters using space vector pulse width modulation (SVPWM)
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.
1. A control system for a multi-level inverter, comprising:
a processor; and
a memory having stored thereon instructions, which, when executed by the processor, cause the processor 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 from a look-up table stored in the memory 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 for the multi-level inverter according to claim 1 , wherein each of the plurality of regions includes a same number of the plurality of sectors.
3. The control system according to claim 1 , further comprising an up/down counter configured to count from 0 to T S /2 and then from T S /2 to 0, where T S 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 instructions, when executed by the processor, further cause the processor to:
convert the reference voltage vector and the angle into X and Y coordinate point values in the identified sector; and
identify a region based on the X and Y coordinate point values.
7. The control system of claim 6 , 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.
8. The control system of claim 6 , wherein the turn-on time values and the switching sequence are predetermined for each sector and region.
9. The control system of claim 1 , wherein the plurality of sectors are sectors A through 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 and a region among a plurality of regions of the multi-level inverter based on the sampled reference voltage vector and the sampled angle;
selecting a switching sequence and a plurality of turn-on time values, which are predetermined for each sector and region, 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 according to claim 10 , wherein each of the plurality of regions includes a same number of the plurality of sectors.
12. The method of claim 10 , further comprising:
converting the reference voltage vector and the angle into X and Y coordinate point values; and
identifying the region based on the X and Y coordinate point values.
13. The method of claim 12 , 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.
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 having stored thereon instructions, which, when executed by the processor, cause the controller 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 from a look-up table stored in the memory 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.