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 configured to:
receive a reference voltage vector and an angle;
identify a sector among sectors of a multi-level inverter including at least two levels, yielding an identified sector;
identify a region among regions of the multi-level inverter based on the reference voltage vector and angle, yielding an identified region; and
select a switching sequence and turn-on time values based on the identified sector and the identified region; and
a circuit configured to generate pulse width modulation (PWM) switching signals for the regions of the multi-level inverter and the sectors of the multi-level inverter based on the turn-on time values and the switching sequence,
wherein each of the regions includes a same number of the sectors.
2. The control system according to claim 1 , further comprising a counter configured to count from 0 to Ts/2 and then from Ts/2 to 0, where Ts is a sampling period.
3. 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).
4. The control system of claim 1 , wherein the processor and the memory are implemented by a digital signal processor (DSP).
5. The control system of claim 1 , 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 based on the X and Y coordinate point values.
6. The control system of claim 5 , 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 5 , 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 sectors are sectors A-F.
10. A method of controlling a multi-level inverter, comprising:
receiving a reference voltage vector and an angle;
identifying a sector among sectors of a multi-level inverter including at least two levels, yielding an identified sector;
identifying a region among regions of the multi-level inverter based on the reference voltage vector and the angle, yielding an identified region;
selecting a switching sequence and turn-on time values based on the identified region; and
generating pulse width modulation (PWM) switching signals for the regions of the multi-level inverter and the sectors of the multi-level inverter based on the turn-on time values and the switching sequence,
wherein each of the regions includes a same number of the sectors.
11. 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.
12. The method of claim 11 , 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 time 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, the multi-level inverter including at least two levels; and
a controller for the multi-level inverter, the controller comprising:
a processor and a memory configured to:
receive a reference voltage vector and an angle;
identify a sector among sectors of the multi-level inverter and a region among regions of the multi-level inverter based on the reference voltage vector and the angle, yielding an identified sector and an identified region; and
select a switching sequence and turn-on time values based on the identified sector and the identified region; and
a circuit configured to generate pulse width modulation (PWM) switching signals for the regions of the multi-level inverter and the sectors of the multi-level inverter based on the turn-on time values and the switching sequence,
wherein each of the regions includes a same number of the sectors.