Multi-level inverter topologies for medium- and high-voltage applications

1. A power switching circuit comprising:

a first DC bus and a second DC bus;

a first DC/DC converter having a first input coupled to the first DC bus and configured to receive a first input DC voltage corresponding to a first allocated portion of an input DC voltage between the first DC bus and the second DC bus and an output configured to provide a first output DC voltage;

a second DC/DC converter having a first input coupled to the second DC bus and configured to receive a second input DC voltage corresponding to a second allocated portion of the input DC voltage between the first DC bus and the second DC bus and an output configured to provide a second output DC voltage;

a DC/AC inverter having a first input coupled to the output of the first DC/DC converter and a second input coupled to the output of the second DC/DC converter, the DC/AC inverter including n (n>2) switching legs, each switching leg having k switching cells coupled between the first input and the second input; and

at least one controller coupled to the first DC/DC converter, the second DC/DC converter, and the DC/AC inverter, the at least one controller configured to operate the DC/AC inverter to provide n AC signals to at least one load coupled to the DC/AC inverter by

operating, at no time during a complete cycle of at least one of the n AC signals, fewer than two of the n switching legs in a static state, and

operating, at no time during the complete cycle of the at least one of the n AC signals, fewer than a remaining n−2 of the n switching legs in a transition state,

wherein the at least one controller operates each switching leg of the n switching legs in either the static state or the transition state at any given time during the complete cycle of the at least one of the n AC signals.

2. The power switching circuit of claim 1 , further comprising:

a first DC voltage source and a second DC voltage source coupled between the first DC bus and the second DC bus, the first DC voltage source configured to provide the first input DC voltage to the first DC/DC converter and the second DC voltage source configured to provide the second input DC voltage to the second DC/DC converter.

3. The power switching circuit of claim 2 , wherein the first DC bus is a positive DC bus and the second DC bus is a negative DC bus.

4. The power switching circuit of claim 1 , wherein the first and second DC/DC converters each include m switching cells, and each switching cell of the m switching cells includes at least a first switch and a second switch, the first and second switches being configured to operate in complementary states.

5. The power switching circuit of claim 1 , wherein the controller is further configured to operate the first DC/DC converter such that the first output DC voltage is a positive variable DC voltage having a first duty cycle and to operate the second DC/DC converter such that the second output DC voltage is a negative variable DC voltage having a second duty cycle.

6. The power switching circuit of claim 5 , wherein the first input of the DC/AC inverter is coupled directly to the output of the first DC/DC converter to receive the positive variable DC voltage and the second input of the DC/AC inverter is coupled directly to the output of the second DC/DC converter to receive negative variable DC voltage.

7. The power switching circuit of claim 6 , wherein each switching leg operating in the static state is configured to provide a static output voltage to the load derived from one of the positive DC variable voltage and the negative DC variable voltage, the static output voltage corresponding to one of the most positive and most negative portions of the n AC signals.

8. The power switching circuit of claim 7 , wherein an output of each switching leg operating in the static state is coupled via at least one of the k switching cells to one of the first and second inputs of the DC/AC inverter.

9. The power switching circuit of claim 6 , wherein each switching leg operating in the transition state is configured to provide a transition output voltage to the at least one load derived from the positive DC variable voltage and the negative variable DC voltage, the transition output voltage corresponding to intermediate portions of the n AC signals.

10. The power switching circuit of claim 9 , wherein an output of each switching leg operating in the transition state is switched via at least one of the k switching cells between at least the first and second inputs of the DC/AC inverter.

11. A non-transitory computer-readable medium storing thereon sequences of computer-executable instructions for operating a power switching circuit, the sequences of computer-executable instructions including instructions that instruct at least one processor to:

receive a first input DC voltage at an input of a first DC/DC converter coupled to a first DC bus, and a second input DC voltage at an input of a second DC/DC converter coupled to a second DC bus, the first input DC voltage corresponding to a first allocated portion of an input DC voltage between the first DC bus and the second DC bus and the second input DC voltage corresponding to a second allocated portion of the input DC voltage between the first DC bus and the second DC bus;

control the first DC/DC converter to provide a first DC voltage and the second DC/DC converter to provide a second DC voltage;

receive the first DC voltage at a first input of a DC/AC inverter and receiving the second DC voltage at a second input of the DC/AC inverter, the DC/AC inverter having n (n>2) switching legs having k switching cells; and

control the DC/AC inverter to provide n AC output signals derived from the first and second DC voltages by

operating, at no time during a complete cycle of at least one of the n AC signals, fewer than two of the n switching legs in a static state, and

operating, at no time during the complete cycle of the at least one of the n AC signals, fewer than a remaining n−2 switching legs in a transition state,

wherein the at least one controller operates each switching leg of the n switching legs in either the static state or the transition state at any given time during the complete cycle of the at least one of the n AC signals.

12. The non-transitory computer-readable medium of claim 11 , wherein controlling the first DC/DC converter to provide the first DC voltage further includes operating the first DC/DC converter such that the first DC voltage is a first variable DC voltage having a first duty cycle and controlling the second DC/DC converter to provide the second DC voltage further includes operating the second DC/DC converter such that the second DC voltage is a second variable DC voltage having a second duty cycle.

13. The non-transitory computer-readable medium of claim 12 , wherein operating each respective switching leg in the static state includes controlling the switching leg to provide a static output voltage derived from one of the first variable DC voltage and the second variable DC voltage, the static output voltage corresponding to one of the most positive and most negative portions of the n AC output signals.

14. The non-transitory computer-readable medium of claim 12 , wherein operating each respective switching leg in the transition state includes controlling the switching leg to provide an output voltage derived from the first variable DC voltage and the second variable DC voltage, the transition output voltage corresponding to intermediate portions of the n AC output signals.

15. An Uninterruptible Power Supply (UPS) system, the UPS system comprising:

an input configured to be coupled to an AC source and to receive input AC power from the AC source;

an output configured to provide output AC power to a load;

a converter coupled to the input and configured to convert the input AC power into DC power;

a first DC bus and a second DC bus coupled to the converter and configured to receive DC power from the converter;

a first DC/DC converter having a first input coupled to the first DC bus and configured to receive a first input DC voltage corresponding to a first allocated portion of an input DC voltage between the first DC bus and the second DC bus and an output configured to provide a first output DC voltage;

a second DC/DC converter having a first input coupled to the second DC bus and configured to receive a second input DC voltage corresponding to a second allocated portion of the input DC voltage between the first DC bus and the second DC bus and an output configured to provide a second output DC voltage;

at least one DC/AC inverter having a first input coupled to the output of the first DC/DC converter and a second input coupled to the output of the second DC/DC converter, the at least one DC/AC inverter including n (n>2) switching legs, each switching leg having k switching cells coupled between the first input and the second input; and

at least one controller coupled to the first DC/DC converter, the second DC/DC converter, and the DC/AC inverter, the at least one controller configured to operate the at least one DC/AC inverter to provide n AC signals to the output coupled to the at least one DC/AC inverter by

operating, at no time during a complete cycle of at least one of the n AC signals, fewer than two of the n switching legs in a static state, and

operating, at no time during the complete cycle of the at least one of the n AC signals, fewer than a remaining n−2 of the n switching legs in a transition state,

wherein the at least one controller operates each switching leg of the n switching legs in either the static state or the transition state at any given time during the complete cycle of the at least one of the n AC signals.

16. The UPS system of claim 15 , further comprising:

a first DC voltage source and a second DC voltage source coupled between the first DC bus and the second DC bus, the first DC voltage source configured to provide the first input DC voltage to the first DC/DC converter and the second DC voltage source configured to provide the second input DC voltage to the second DC/DC converter.

17. The UPS system of claim 16 , wherein the first DC bus is a positive DC bus and the second DC bus is a negative DC bus.

18. The UPS system of claim 15 , wherein the controller is further configured to operate the first DC/DC converter such that the first output DC voltage is a positive variable DC voltage having a first duty cycle and to operate the second DC/DC converter such that the second output DC voltage is a negative variable DC voltage having a second duty cycle.

19. The UPS system of claim 18 , wherein each switching leg operating in the static state is configured to provide a static output voltage to the output derived from one of the positive DC variable voltage and the negative DC variable voltage, the static output voltage corresponding to one of the most positive and most negative portions of the n AC signals.

20. The UPS system of claim 18 , wherein each switching leg operating in the transition state is configured to provide a transition output voltage to the output derived from the positive DC variable voltage and the negative variable DC voltage, the transition output voltage corresponding to intermediate portions of the n AC signals.