Abstract: Provided is a method for suppressing a circulating current in a modular multi-level converter for a high voltage direction-current (HVDC) transmission system. The HVDC transmission system converts an alternating current (AC) into a direct current (DC) and vice versa, transmits energy using a DC cable, and including a modular multilevel converter generating a high voltage source by stacking a plurality of sub-modules in series. In the circulating current suppression method, a circulating current (idiffj; j=a,b,c) of a,b,c phase in an abc 3-phase stationary reference frame, a DC current (idc) flowing in a DC cable, a current reference value (i*dc) of a DC component that needs to flow in the DC cable are inputted. The circulating current (idiffj) of the a,b,c phase is controlled to become zero. A compensation value (V*diffj) for suppressing a harmonic component of the circulating current is outputted.

Abstract: The present invention relates to a driving method for a modular multi-level converter. The driving method include inputting a current reference value (i*pj2) of the upper valve of the modular multi-level converter, measuring a current value (ipj2) of the valve, calculating an error value (errpj2) between the current reference value and the measured current value of the upper valve, measuring a DC link voltage value (Vdc2) of the modular multi-level converter, measuring a AC-grid voltage value (Esj) of the modular multi-level converter, and calculating a voltage reference value (u*pj2) using the current reference value (i*pj2), the measured current value (ipj2), the error value (errpj2), the DC link voltage value (Vdc2), and the AC-grid voltage value (Esj).

Abstract: The present invention relates to a driving method for a modular multi-level converter. The driving method include inputting a current reference value (i*pj2) of the upper valve of the modular multi-level converter, measuring a current value (ipj2) of the valve, calculating an error value (errpj2) between the current reference value and the measured current value of the upper valve, measuring a DC link voltage value (Vdc2) of the modular multi-level converter, measuring a AC-grid voltage value (Esj) of the modular multi-level converter, and calculating a voltage reference value (u*pj2) using the current reference value (i*pj2), the measured current value (ipj2), the error value (errpj2), the DC link voltage value (Vdc2), and the AC-grid voltage value (Esj).

Abstract: A photovoltaic power conditioning system and method is provided. The system includes an isolated DC/DC converter (41), a DC/AC inverter (42), and a sine filter (43). The isolated DC/DC converter (41) receives a DC voltage from a solar cell through a parallel connection structure and converts the DC voltage into another DC voltage and then outputs the converted DC voltage through a series connection structure. The DC/AC inverter (42) converts the DC voltage output from the isolated DC/DC converter into an AC voltage. The sine filter (43) performs sine filtering on the AC voltage output from the DC/AC inverter and outputs the filtered AC voltage. The system employs a topology allowing it to be responsible for part of the output capacity, thereby significantly reducing the required capacity and increasing the system efficiency, so that the system can be applied to small and large-capacity photovoltaic power generation.

Abstract: Provided is a method for suppressing a circulating current in a modular multi-level converter for a high voltage direction-current (HVDC) transmission system. The HVDC transmission system converts an alternating current (AC) into a direct current (DC) and vice versa, transmits energy using a DC cable, and including a modular multilevel converter generating a high voltage source by stacking a plurality of sub-modules in series. In the circulating current suppression method, a circulating current (idiffj; j=a,b,c) of a,b,c phase in an abc 3-phase stationary reference frame, a DC current (idc) flowing in a DC cable, a current reference value (i*dc) of a DC component that needs to flow in the DC cable are inputted. The circulating current (idiffj) of the a,b,c phase is controlled to become zero. A compensation value (V*diffj) for suppressing a harmonic component of the circulating current is outputted.

Abstract: A photovoltaic power conditioning system and method is provided. The system includes an isolated DC/DC converter (41), a DC/AC inverter (42), and a sine filter (43). The isolated DC/DC converter (41) receives a DC voltage from a solar cell through a parallel connection structure and converts the DC voltage into another DC voltage and then outputs the converted DC voltage through a series connection structure. The DC/AC inverter (42) converts the DC voltage output from the isolated DC/DC converter into an AC voltage. The sine filter (43) performs sine filtering on the AC voltage output from the DC/AC inverter and outputs the filtered AC voltage. The system employs a topology allowing it to be responsible for part of the output capacity, thereby significantly reducing the required capacity and increasing the system efficiency, so that the system can be applied to small and large-capacity photovoltaic power generation.

Abstract: The present invention relates to a passive auxiliary circuit for driving power switches connected in series for much higher rating of a power system. The passive auxiliary circuit for an IGBT power switch connected in series with another, comprises two capacitors, which are connected in series across the IGBT; two resistors dividing a voltage applied across the IGBT, each resistor being connected in parallel with each capacitor; and a diode and a third resistor which are connected in series between a gate terminal of the IGBT and a node connecting the two capacitors, wherein the diode is placed such that its cathode is directed to the gate. This passive auxiliary circuit, whose structure is so simple, is able to distribute a supplied high voltage equally over series-connected IGBTs, to reduce additional power loss remarkably, and to relieve transient overvoltage like as a conventional active gate circuit.