Abstract
The connection mode of the direct current (DC) power distribution system and the alternating current (AC) system is the foundation of system design, and it is also one of key technologies of the DC power distribution network. Based on the topology structure, grounding method, main equipment parameters, load parameters and system control protection strategy of the DC power distribution system, this paper establishes the system simulation model in the case of configuring the connection transformer and not configuring the connection transformer. Simulation results show that, when no connecting transformer is installed, the interaction between AC and DC systems will be great when faults occur, and the cost of converter valves and DC reactors will be increased. When connecting transformers are installed, the interaction between AC and DC systems can be effectively isolated, and the operation reliability of the system will be greatly improved while the cost is saved. Therefore, it is recommended to configure an independent connection transformer in the DC distribution system.
Highlights
The direct current (DC) power distribution network has many advantages, it can improve the power quality, decrease the power loss and running cost, harmonize the contradiction between the power grid and distributed power supply effectively [1,2,3,4,5,6,7]
When the bipolar short-circuit fault occurs on the DC side, the maximum overcurrent of the converter valve and the bridge-arm reactor flows through the converter valve is 1.79 kA without considering the blocking of the converter valve and the action of the DC circuit breaker, and the maximum current transmitted to the 10 kV alternating current (AC) bus is 1.89 kA
The configuration of the connection transformer can effectively isolate the interaction between the AC and the DC system, and can ensure that the continuous operation under the DC single-pole ground fault without affecting the operation of the 10 kV AC bus, thereby greatly improving the reliability of the power supply of the AC–DC hybrid power distribution system
Summary
The direct current (DC) power distribution network has many advantages, it can improve the power quality, decrease the power loss and running cost, harmonize the contradiction between the power grid and distributed power supply effectively [1,2,3,4,5,6,7]. In reference [11], the fault mechanism of the modular multilevel converter (MMC) DC-side bipolar short circuit is analyzed, and the circuit model of overcurrent analysis is established. In reference [12], the transient characteristics of the MMChigh-voltage direct current (HVDC) DC-side fault are studied, and the equivalent circuit model under short-circuit fault is established. In reference [16], a general calculation method of the fault current is proposed for the DC-side bipolar short-circuit fault of the flexible DC grid. This paper uses the method of fault simulation analysis to study the connection mode between the DC distribution system and the AC system. Simulation analysis is conducted for the connection mode of the DC power distribution system and the AC network. The AC-side fault simulation analysis and DC-side fault simulation analysis are carried out to study the influence of whether to configure the connection transformer on the system characteristics
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