Study Of Available Transfer Capability For Ac/dc Systems With VSC-HVDC

Available Transfer Capability(ATC) is not only an evaluation of the power transfer capability of transimision grid, but also an important indicator to measure the safe and stable operation of power grids. Moreover, ATC can guide the optimal allocation of resources market.With the development of power electronics technology, High Voltage Direct Current based on Voltage Source Converter and Pulse Width Modulation (VSC-HVDC) is widely studied. It overcomes many shortcomings of conventional HVDC and extends the application field of HVDC. The structure of power grid becomes more complex and the operation mode of power system changes more flexible due to the addition of VSC-HVDC that causes the difficulty of calculating ATC accurately. Thyristor Controlled Series Capacitor(TCSC) is one of FACTS devices. TCSC can compensate the line reactance partially, regulate the power flow flexibly. Allocating TCSC optimally is able to increase the transfer capability.The voltage source converter is equivalently represented by voltage source model, thus the model of VSC-HVDC system suitable for optimal power flow is developed. The model considers any control mode and operating limits of the converter; moreover, it could be applied to multiterminal VSC-HVDC. The mathematical model of ATC for AC/DC syetems with VSC-HVDC is set up in this paper, in which various methods for optimizing control variables are considered. Sequential quadratic programming method is applied to calculate the ATC. Numerical results illustrate the viability of the proposed model and method applied to the modified EPRI-36 bus system.The steady-state model of TCSC is analysed in this paper. The issue of how to allocate TCSC optimally in network is studied in order to improve available transfer capability. The immune algorithm applicable for the case of containing more TCSC devices is used to determine the location and compensation degree of TCSC and ATC at the same time. Numerical results which are verified by repeated power flow method illustrate the feasibility and validity of the proposed method applied to the IEEE 30-bus and New England 39-bus systems in the end.