Research On Several Issues Of AC Side Basic Design Of MTDC Transmission System

Compared with traditional two-terminal HVDC system, Multi-terminal HVDC transmission system (MTDC) has greater potential in further development for its technological advantage and economic efficiency. It is significant to study the issues of MTDC system primary design, which is useful for MTDC project design. Based on a four-terminal LCC-MTDC system, this paper introduces the calculation method and program design technology of system reactive power management, AC harmonic current calculation and AC side filters design.Firstly, a few MTDC projects are introduced and the key technology of MTDC system are summarized in this paper, including its topology, operation mode and control method. Then it come to a conclusion that parallel MTDC system is superior to series MTDC system by comparing their insulation coordination, adjust range, system expansion flexibility, etc.Then the basic reactive power management principle is put forward and different reactive power balance strategies are analyzed in the next chapter. Besides, detailed computing procedure is described to calculate the switching order of reactive power compensation equipment. Based on a MTDC system, the reactive power change rule is analyzed and the switching order is computed under different load changing way.Next, a fast decoupled calculation method based on time domain piecewise method is proposed to calculate AC harmonic current in each converter station respectively, considering different system operation mode, system control method and DC load level. Based on the harmonics calculation results, the procedure of AC side filters design is carried out and the method is tested by a four-terminal MTDC system later in this paper.