Quasi multi-level converter

A method of operating a power converter, wherein the power converter comprises:

• at least one phase leg, comprising:
• direct-current (DC) terminals connectable to a DC source or load;
• an alternating-current (AC) terminal connectable to an AC load or source;
• and
• at least one module serially connecting the DC and AC terminals of the respective phase leg, the at least one module respectively comprising:
• a first, a second, and a third AC terminal;
• a first, a second, and a third DC terminal;
• capacitive energy storage devices serially connecting the first, second, and third DC terminals;
• at least one first power switch serially connecting the first DC terminal and the first AC terminal;
• at least one switching cell serially connecting the second DC terminal and the second AC terminal, the at least one switching cell respectively comprising:
• at least one energy storage device, and
• pairs of second power switches connected anti-serially, one of the pairs of the second power switches comprising main second power switches and another one of the pairs of the second power switches comprising auxiliary second power switches;
• and
• at least one (N≥1) third power switch serially connecting the third DC terminal and the third AC terminal;
• wherein the first and third DC terminals of a first one of the at least one serially connected module forming the DC terminals of the respective phase leg;
• and
• wherein the AC terminals of a last one of the at least one serially connected module connected to one another and forming the AC terminal of the respective phase leg,
• the method comprising:
• establishing first drive signals of the at least one first power switch of a respective module and third drive signals of the at least one third power switch of the respective module in accordance with a first pulse-width modulation (PWM) scheme and in dependence on a predetermined AC voltage modulation waveform;
• establishing second drive signals of the at least one switching cell of the respective module in accordance with a second PWM scheme and in dependence on the first and third drive signals;
• synchronously switching the at least one first power switch of the respective module based on the first drive signals;
• synchronously switching the at least one third power switch of the respective module based on the third drive signals;
• and
• asynchronously switching the at least one switching cell of the respective module based on the second drive signals by:
• switching the at least one switching cell of the respective module complementary to the drive signals of both the at least one first power switch and the at least one third power switch of the respective module,
• switching the main second power switches of the at least one switching cell of the respective module staggered in time in accordance with respective dwell times, and
• adjusting the respective dwell times to adjust the switching of the main second power switches.

A method of operating a power converter, wherein the power converter comprises:

• at least one phase leg, comprising:
• direct-current (DC) terminals connectable to a DC source or load;
• an alternating-current (AC) terminal connectable to an AC load or source;
• and
• at least one module serially connecting the DC and AC terminals of the respective phase leg, the at least one module respectively comprising:
• a first, a second, and a third AC terminal;
• a first, a second, and a third DC terminal;
• capacitive energy storage devices serially connecting the first, second, and third DC terminals;
• at least one first power switch serially connecting the first DC terminal and the first AC terminal;
• at least one switching cell serially connecting the second DC terminal and the second AC terminal, the at least one switching cell respectively comprising:
• at least one energy storage device, and
• pairs of second power switches connected anti-serially, one of the pairs of the second power switches comprising main second power switches and another one of the pairs of the second power switches comprising auxiliary second power switches;
• and
• at least one (N≥1) third power switch serially connecting the third DC terminal and the third AC terminal;
• wherein the first and third DC terminals of a first one of the at least one serially connected module forming the DC terminals of the respective phase leg;
• and
• wherein the AC terminals of a last one of the at least one serially connected module connected to one another and forming the AC terminal of the respective phase leg,
• the method comprising:
• establishing first drive signals of the at least one first power switch of a respective module and third drive signals of the at least one third power switch of the respective module in accordance with a first pulse-width modulation (PWM) scheme and in dependence on a predetermined AC voltage modulation waveform;
• establishing second drive signals of the at least one switching cell of the respective module in accordance with a second PWM scheme and in dependence on the first and third drive signals;
• synchronously switching the at least one first power switch of the respective module based on the first drive signals;
• synchronously switching the at least one third power switch of the respective module based on the third drive signals;
• and
• asynchronously switching the at least one switching cell of the respective module based on the second drive signals by:
• switching the main second power switches of the at least one switching cell of the respective module complementary to the at least one first power switch or the at least one third power switch of the respective module having a same voltage blocking direction.