Research On Primary Frequency Regulation Scheme Of New Energ

In recent years,the global new energy unit installed capacity in power grid proportion is higher and higher,and the high proportion of new energy will reduce the performance of power grid frequency modulation after interconnection,caused a great influence to the stability of the system frequency.As the sending end of asynchronous network system,Yunnan power grid will face serious high-frequency problems when the outgoing DC transmission channel is locked or the system suddenly loses load.Due to the water hammer effect,In the initial stages of frequency disturbance,power grid frequency fluctuation will be further intensified.Therefore,it is of great significance to study the frequency stability of a high proportion of new energy connected to the grid and the frequency reversal caused by the water hammer effect compensated by new energy units.Firstly,the mathematical modeling of wind turbine,photovoltaic unit and water turbine unit and their frequency control is carried out,and the load model taking into account frequency characteristics adopted in this paper is introduced.The transfer function of wind,light and water when they participate in primary frequency modulation is obtained,which lays a theoretical foundation for the subsequent research.Based on the obtained frequency-modulation transfer function of fan and turbine,a simple mathematical model of the system containing wind,water and load is established.The algebraic differential equation and the system network equation corresponding to the turbine,fan and their frequency modulation strategy are obtained by using the DC power flow method.On the basis of the linearization,the frequency domain analytic expression of the frequency response of the grid-connected node of the turbine and fan is derived.A simple two-machine system containing wind,water and load was built in PSD-BPA,and the susceptance matrix containing wind,water and load nodes was calculated according to the system parameters.The results were substituted into the analytic expression in frequency domain,and the pole diagram and three-dimensional trend diagram of the system frequency response were drawn accordingly.The effects of water hammer effect time constant,turbine frequency modulation control parameters,fan frequency modulation control parameters,wind power response delay and load model on the system frequency characteristics are simulated and analyzed in the two-machine system,and corresponding to the trend diagram.Based on the analysis of high-proportion hydropower in Yunnan region,the time constant and load model of water hammer effect are simulated deeply in the actual power grid model,and the frequency modulation effect is evaluated and analyzed quantitatively by using evaluation indexes.A frequency modulation strategy considering the complementary of water and wind is proposed,and a simple mathematical model of the system containing wind,water,light and load is established.Secondly,combining the algebraic differential equation of the turbine,fan,photovoltaic and their frequency modulation strategy and the system network equation based on the DC power flow,the frequency domain analytic expression of the frequency response of the grid-connected nodes of the turbine,fan and photovoltaic under load disturbance is derived.Based on the analytical analysis of the influence of FM dead zone and FM control parameters on the system frequency,a joint frequency modulation scheme of the water-wind complementary system is proposed.A four-machine system containing wind,light,water and load was constructed in PSD-BPA,and the susceptance matrix containing four nodes including wind,light,water and load was calculated according to the system parameters.The results were substituted into the analytic expression in frequency domain,and the frequency response pole diagram and three-dimensional trend diagram of the system were drawn accordingly.The frequency modulation characteristics of wind,light and water are studied,and a cascade frequency modulation scheme is developed by setting frequency modulation dead zone.The influence of the frequency control parameters of wind,light and water and the load model on the frequency characteristics of the system is simulated and analyzed in the four-engine system.Finally,the power grid model of Yunnan power grid is built,and the new energy units participate in the primary frequency modulation system through sagging control.The influence of the new energy in frequency modulation ratio,frequency modulation amplitude limiting and load model on the frequency and power response of the power grid is analyzed,and the effectiveness of the proposed frequency modulation scheme is verified by simulation.