Study Of AGC Method Used In Power Grid With Wind Power Based On Virtual Unit

With the increasing consumption of global energy,it is imperative to develop renewable energies.The wind energy,a kind of renewable clean energy,has developed rapidly in recent years.However,the randomness and volatility of wind power generation will cause many problems about active power security and stability,such as decrease of operation level,increase of frequency disturbance and active power fluctuation of tie-line.In order to guarantee the safe and stable operation of power network,wind energy is abandoned in some way and the integration of wind power is limited.In this case,with the integration of wind power,how to improve the performance of automatic generation control to meet the requirements of frequency quality and safe operation has become an urgent problem of wind power utilization.Along with the rapid growth of installed wind capacity,energy structure of power system is changing.Although traditional hydropower and thermal power units are still dominant,wind power is taking the place of conventional power and playing the more important role gradually.Because wind power is distributed in the network and local concentration,the large scale wind power accessing to grid will bring many problems to AGC.On the one hand,it influences on the frequency regulation of power system.Wind power fluctuations lead to the fluctuation of active power in short time,which causes the shortage of AGC regulation capacity,degradation of CPS,as well as decreasing of frequency distribution index.On the other hand,it has affects on the tie-line of local power network.In the concentration accessing areas,the fluctuations of local clustering wind power will cause local transmission congestion and security overload of the tie-line.Focus on the problems above,this paper proposes a method of automatic generation control with virtual unit which is suitable for frequency control with the integration of wind power.According to regional power features,a great number of adjustable small hydro-power units participate in frequency control as an equivalent virtual AGC unit,which can improve the adjustable capacity and regulation rate of system.In the process of modeling the equivalent virtual AGC unit,beside conventional unit constraints,the tie-line security constraints and vibration area constraints of hydropower unit are taken into consideration to ensure the security and stability of tie-line and generation units.Based on the analysis of wind power fluctuation characteristics,the regulation capacity of AGC is set to make the virtual AGC unit fit the local wind characteristics better.In order to improve the tie-line transmission condition further,this paper proposes a method of unit distribution based on section sensitivity factor to implement the second distribution of virtual AGC among the group of small hydropower units.With the goal of getting tie-line's maximum transmission margin,the optimal dispatch model of small hydro-power units is established considering the influence that small hydro-power outputs have on tie-line transmission power.Section sensitivity factor of small hydro-power units are defined according to the objective function of this model,and the optimal solution method is converted to a priority optimal dispatch problem with section sensitivity factors.According to this model,small hydro-power units participating in automatic generation control is realized and the transmission margin of tie-line increases,which reserves regulation capacity for the wind power fluctuations.Finally,the model of automatic generation control including virtual units is simulated based on the actual parameters of power grid in Guizhou province.The simulation results are compared with traditional method in improving the performance of frequency controlling and tie-line transmission limit.Simulation result shows the validity of the proposed method in power grid with wind farms and small hydro-power units.