Abstract: A method for calculating the steady-state fault current of a modular multilevel converter (MMC) comprises calculating the dc-side critical resistance values RA/B, RB/C and RC/D of the MMC based on the bridge arm inductance coefficient k and the ac-side reactance Xac of the MMC; Then, determining the operating modes of the MMC based on RA/B, RB/C and RC/D, and calculating the steady-state dc fault current and the conduction overlap angle respectively under various operating modes without considering the ac-side resistance based on the parameters k, Us, Rdc and the dc-side critical resistance values RA/B, RB/C and RC/D; After that the steady-state AC fault current amplitude and phase angle for each operating mode without considering the AC side resistance are calculated based on the DC current and conduction overlap angle for each operating mode, respectively. Finally, the steady-state AC fault current amplitude and phase angle are calculated for various operating modes considering the AC side resistance.

Abstract: The present disclosure relates to a method for protecting DC line impedance phase based on protection and control coordination, and an application scenario of the method for protecting is a three-terminal flexible DC transmission network. The method uses high controllability of a converter after a fault, injects a characteristic signal at a characteristic frequency, and calculates a phase angle of input impedance to determine a fault interval, which effectively improves protection performance, turns passive to active, and is not affected by nonlinearity of the converter. At the same time, compared with a full-bridge MMC, using a half-bridge MMC does not need to perform fault ride-through first when identifying a fault, and does not need to add additional equipment, it creates fault features and can reliably identify an fault interval; improves protection quickness and at the same time also has better economic benefits.

Abstract: A method for calculating the steady-state fault current of a modular multilevel converter (MMC) comprises calculating the dc-side critical resistance values RA/B, RB/C and RC/D of the MMC based on the bridge arm inductance coefficient k and the ac-side reactance Xac of the MMC; Then, determining the operating modes of the MMC based on RA/B, RB/C and RC/D, and calculating the steady-state dc fault current and the conduction overlap angle respectively under various operating modes without considering the ac-side resistance based on the parameters k, Us, Rdc and the dc-side critical resistance values RA/B, RB/C and RC/D; After that the steady-state AC fault current amplitude and phase angle for each operating mode without considering the AC side resistance are calculated based on the DC current and conduction overlap angle for each operating mode, respectively. Finally, the steady-state AC fault current amplitude and phase angle are calculated for various operating modes considering the AC side resistance.

Abstract: It discloses a ring-connected bridge-type multi-port hybrid DC circuit breaker. When the number of ports is n, n is an integer greater than or equal to 2, the ring-connected bridge-type multi-port hybrid DC circuit breaker includes: an upper DC bus bar, a lower DC bus bar, n thyristor arms, n diode arms, a main breaker branch, and n bypass branches; each thyristor arm connects in series with a diode arm, forming a series circuit; a bypass branch is connected between every two adjacent series circuits, a port is provided at the connection point of the thyristor arm and the diode arm in each series circuit, and the port is used to connect the protected components or the DC lines.

Abstract: It discloses a ring-connected bridge-type multi-port hybrid DC circuit breaker. When the number of ports is n, n is an integer greater than or equal to 2, the ring-connected bridge-type multi-port hybrid DC circuit breaker includes: an upper DC bus bar, a lower DC bus bar, n thyristor arms, n diode arms, a main breaker branch, and n bypass branches; each thyristor arm connects in series with a diode arm, forming a series circuit; a bypass branch is connected between every two adjacent series circuits, a port is provided at the connection point of the thyristor arm and the diode arm in each series circuit, and the port is used to connect the protected components or the DC lines.