Analysis On UHVDC Transmission Voltage Stability For Large-scale Wind/photovoltaic Power

Large-scale wind/photovoltaic power generation by the UHVDC long-distance transmission to the load side, in improving the efficiency of the wind/pv given at the same time, also to the power grid has brought a certain degree of negative impact. Wind power, photovoltaic, thermal power, ultra high voltage dc and ac s ystem voltage coupling effect, make out a system voltage characteristic is more complex, this complex voltage characteristic has become we have to focus.At first, this paper studied the doubly- fed induction generator, permanent magnet direct drive synchro nous generator and the mathematical model of photovoltaic cells, on the basis of the mathematical model of grid-connected wind farms is studied two kinds of different system and control model of grid-connected photovoltaic(pv) system and the model of low voltage across, in DIgSILENT simulation software to build the wind/photovoltaic grid-connected system, and studied the low voltage through characteristics. UHVDC transmission, the mathematical model was deduced and the hierarchical level control of the UHVDC transmission system are studied, the inverter control strategy, control strategy of converter transformer tap and ac filter control strategy, and in DIgSILENT simulation model is established. O f large-scale wind/light volts high- voltage dc conveying system static voltage stability is analyzed, the main research sending dc thermal power of form a complete set of power of different circumstances on the sending end converter bus reactive short-circuit ratio, effective use of PV and VQ curve continuous power flow calculation, reactive power effective short-circuit ratio is different foreign send system static voltage stability are analyzed; UHVDC system is studied under different operation modes, different reactive power allocation scheme external static voltage stability of the system. O f large-scale wind/light volts high- voltage dc conveying system transient voltage stability is analyzed, studied 750 kv ac line three permanent fault cases of N-1、N-2wind farm is LVRT characteristics foreign sent transient voltage stability of the system, and put forward the use of measures to reduce the dc power to be delivered to the outside, improve the fault cases of system voltage stability to be delivered to the outside; Wind/photovoltaic power station is studied in diffe rent low voltage through the characteristics of foreign send transient voltage stability of the system; Studied the wind/photovoltaic power station power fluctuations in case foreign to the influence of the system voltage stability.