| The Current source converter(CSC) based Parallel multi-terminal direct current (MTDC) transmission system can connect multiple sending ends with multiple receiving ends through high voltage and large capacity DC transmission lines. And it can connect multiple asynchronous AC systems with each other. Compared with the two-terminal DC transmission system, its topology and operation mode have more flexible and diverse forms, and it’s more economic. With the development of the world power industry and MTDC technology, there are several MTDC transmission projects in operation nowadays. The design of the MTDC transmission system is one of the necessary parts of the MTDC projects. Thus, the main contents of this thesis are as follows:1)The system operation conditions involved in the calculation of the MTDC transmission system parameters are analyzed, including system operation modes, control modes and operation limitations.2)The original parameters which are needed in the calculation of main circuit steady state parameters are discussed, as well as the formulas for calculating basic parameters. The detailed calculation method and procedure of main circuit steady state parameters under the constant current/constant voltage control and angel control are analyzed, based on the given system operation mode and operation limitations. A study case about the calculation of main circuit steady state parameters for a four-terminal HVDC system is presented, and this algorithm is proved effective by the study case.3)The related devices in the DC side network used in the calculation of DC side harmonic current are studied. The three pulse harmonic parameters are calculated by the linear segmenting method. Based on this factors, the calculation method and procedure of DC side harmonic current are analyzed in detail. Compared with the simulation results of PSCAD/EMTDC, this algorithm is proved correct. |
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