| Compared with the traditional HVDC, the ultra HVDC (UHVDC) has more complex configuration, more components and operation modes. Therefore, the traditional frequency and duration (F&D) method and hierarchical models for HVDC cannot simply be applied to UHVDC, for which it is hard to model and to directly compute parameter sensitivity. So this paper does a research on UHVDC state space modeling, reliability index calculation and sensitivity analysis etc. which are shown as follows:An improved F&D method is firstly proposed to yield direct relationship of the states before and after equivalence, which need not manual search and calculating transition frequencies and acquiring transition rates one by one. The improved F&D method is called matrix description of F&D method which greatly improves the efficiency of equivalent calculation and provides the basis for UHVDC model refinement and calculation.Then based on the improved F&D method, the state space of UHVDC considering the six operation modes, the converter transformers of Y/Y and Y/△ types and standby mode is established and calculated.The derivation of matrix description of F&D method is given to deduce the analytical sensitivity of transition rate matrices, state probabilities, frequencies and durations after multi-step equivalence. Based on the UHVDC modeling, a new sensitivity model of UHVDC is proposed and its validity is verified by continuously changing the parameters. The analytical method of sensitivity is extended to unified power flow controller in this paper.Finally, in order to quantify impact of the UHVDC inner components’ random failure on the reliability of the power system, a new UHVDC power flow calculation model is firstly established and then a method for calculating sensitivity relationship between the power system and UHVDC inner component parameters are proposed. The feasibility and effectiveness of the method are verified by a numerical example to upgrade the RTS IEEE test system. |
PDF Full Text Request