Study On Transient Stability And Unit-tripping Strategy Of Wind-photovoltaic-thermal-bundled Power Transmission System

The transmission mode of wind-photovoltaic-thermal-bundled power not only solves the problem of wind and photovoltaic power abandonment in China to a certain extent,realizes the cross regional transmission of new energy,but also solves the problem of reverse distribution between China’s energy base and load center,which greatly saves the transmission cost.However,the connection of win d and photovoltaic power into the power system will produce a large number of coupling effects,affect the power flow distribution of the system,and further affect the transient stability of the power system.Therefore,this paper mainly studies the problems of the transient stability and the unit-tripping strategy of wind-photovoltaic-thermal-bundled power transmission system.Firstly,The transient stability of wind-photovoltaic-thermal-bundled power transmission system is studied.Based on the PSD-BPA simulation software,a typical model of wind-photovoltaic-thermal-bundled power transmission system is constructed.Based on the extended equal area criterion(EEAC),the problems related to the transient stability of the wind-photovoltaic-thermal-bundled power transmission system are deduced and analyzed.Based on the established typical model of wind-photovoltaic-thermal-bundled power transmission system,the typical operation mode,separate wind and photovoltaic power access,different proportion of wind,photovoltaic and thermal power,different reactive power control modes of new energy units,different standby capacity of thermal power unit after serious AC fault are simulated and analyzed to study the influence of transient stability of the system.It is mainly analyzes and explains the relevant characteristics of the wind-photovoltaic-thermal-bundled power transmission system from the aspects of the power angle,acceleration power of the thermal power unit and bus voltage.Secondly,the transient stability analysis of wind-photovoltaic-thermal-bundled power transmission system in North China is carried out.Under the initial operation mode,a serious AC fault is set,and the transient stability analysis is carried out.On this basis,the output proportion of new energy is increased,and the influence law on the transient stability of the system is verified.Based on the actual power grid,the effects of fault location and the distance between new energy power station and parallel node on system transient stability are simulated and analyzed,including power angle stability and voltage stability.Finally,the unit-tripping strategy formulation problem of wind-photovoltaic-thermal-bundled power transmission system is studied.The impact of wind power,photovoltaic power and thermal power unit-tripping on system stability is studied,and the improvement effects of different types of generator unit-tripping on system transient stability are compared.On this basis,the selection principle of unit-tripping is given,and the emergency unit-tripping strategy formulation model of wind-photovoltaic-thermal power coordination with the minimum total unit-tripping volume as the goal and the constraints of transient safety,static safety,system damping ratio and unit-tripping ratio is proposed.The emergency unit-tripping strategy is formulated for a practical example in North China.Based on the comparison of emergency unit-tripping strategy of wind-photovoltaic-thermal power coordination and emergency unit-tripping strategies of new energy units and thermal units,the wind-photovoltaic-thermal power coordinated emergency unit-tripping strategy not only has small unit-tripping volume,but also has good economy.Therefore,this strategy is selected as the optimal unit-tripping strategy.The emergency unit-tripping strategy formulation method of wind-photovoltaic-thermal power coordination has a certain engineering application value,and can provide guidance for making the unit-tripping strategy for actual system.