Dynamic Power Flow Algorithm Considering Larvge Scale Renewable Power Generation

As a fundamental function part of DTS(Dispatcher Training System),dynamic power flow(DPF)calculation focuses on the power flow solution under the circum-stance of power disturbance occurrence and frequency deviation.According to the method,the disturbance power is distributed to all generators and loads that have fre-quency regulation ability,instead of the only generator at slack bus which is assigned randomly by conventional power flow calculation.Therefore,the results of dynamic power flow are more accurate and reliable.In recent years,the installed capacity of renewable power grows extremely fast which results in the higher penetration of them in power systems.Consequently,to consider large scale renewable power model in dynamic power flow calculation has been quite necessary.Firstly,based on the introduction of operational traits of currently used renew-able power generation units,the frequency regulation characteristics of them that rep-resented by wind turbines and photovoltaic arrays are discussed.The rotor speed of squirrel-caged induction generator(SCIG)wind turbines is coupled to system fre-quency,therefore its power-frequency characteristics can be obtained through math-ematic deduction directly under reasonable assumption;For the doubly fed induction generator(DFIG)wind turbines and photovoltaic arrays which normally under maxi-mum power tracking(MPPT)mode,the integrated control strategy is put forward to let them participate in frequency regulation steadily.Like the conventional generator,the mathematical expression of static frequency regulation coefficient is given and the setting link in control strategy is also deducted.According to the works above,this paper proposes a frequency response calcula-tion model based-dynamic power flow method considering renewable power genera-tion(R-DPF).The proposed calculation method adopts the form of alternate calcula-tion between conventional power flow calculation and frequency response calculation.Specifically,the frequency calculation is executed following a power disturbance.After the a period of primary frequency regulation process,the active output of con-ventional generators,renewable power units and load at all buses are updated.The conventional power flow calculation is executed to determine the new state of system.Then the system waits for the next disturbance information.It is noteworthy the con-ventional power flow calculation adopts the combined iteration of newton-raphson method and PQ decoupled method.During the iteration,the renewable power genera-tion units are considered as different bus types according to their control strategies.The frequency calculation is based on specific frequency response model and the pre-set frequency regulation coefficient of renewable power is counted in it.As a part of results of proposed power flow calculation,the frequency curves reflect the dynamic frequency characteristics of power system with high penetration of renewable power generation.For application,the proposed calculation method is programmed in Fortran lan-guage.In a specific case study,the IEEE 30-bus system is modified to verify the pro-posed method considering different renewable power penetration.Finally,the power flow calculation results are compared and analyzed.