Source-network coordination type direct-current (DC) circuit breaker based on pre-charged capacitors for modular multilevel converters (MMC) based DC grid

A source-network coordination type direct-current (DC) circuit breaker based on pre-charged capacitors for a modular multilevel converters (MMC) based DC grid, wherein the MMC based DC grid is provided with four converter stations, each having two converters;

• the converters of the four converter stations are in loop connection through a double-loop DC overhead line;
• two ends of each DC line connecting the converters are separately equipped with the source-network coordination type DC circuit breakers based on pre-charged capacitors which are matched with an MMC active voltage adjusting control strategy in a self-adaptive mode to clear an isolating fault while the DC line has the fault;
• wherein a topological structure of the source-network coordination type DC circuit breaker based on pre-charged capacitors comprises:
• a through-current branch, wherein the through-current branch comprises a quick mechanical switch (Si) and an insulated gate bipolar transistor (IGBT) switching transistor group (Qi) which are sequentially connected in series, and another end of the quick mechanical switch (Si) is connected to a DC bus;
• a pre-charged capacitor branch, wherein the pre-charged capacitor branch comprises a pre-charged capacitor group (Ci), a diode valve group (Di), a thyristor valve group (Ti) and an energy consumption resistor (Ri);
• ends, which are connected to one another in parallel, of the diode valve group (Di), the thyristor valve group (Ti) and the energy consumption resistor (Ri) are connected to a rear end of the IGBT switching transistor group (Qi), and the other ends thereof are connected to one end of the pre-charged capacitor group (Ci) in series while the other end of the pre-charged capacitor group (Ci) is grounded;
• and
• a current-limiting inductor branch, wherein the current-limiting inductor branch comprises a current-limiting inductor (Li), one end of the current-limiting inductor (Li) is connected to a node between the through-current branch and the pre-charged capacitor branch while the other end thereof is connected to the DC line.