Research On Frequency Control Strategy And Method Of The Interconnected Power Grid With Smart Grid Circumstances

With the development of global modern power network interconnection andintelligent, not only regional power grid need support from interconnection network,but also power grid itself needs to be coordinated with new energy development. Theaccess of new energy, such as intermittent energy, has brought new problems to theoperation of power grids that complicate structure, operation and control of the powergrid. Meaning while, with the development of society, more and more seriousrequirements are put forward to smart grid environment. Based on steady operation,power grid should became more economic and green gradually. These presentsituation and development requirements put forward new problems and higherrequirements to the power quality achieved through the grid frequency control duringpower grid running. Therefore it also brings new opportunities and challenges to theresearch of control mechanism of power grid frequency.In the background and the new situation of the power development mentionedabove, the paper studies the modern interconnected grid frequency control mechanismunder the smart grid environment. In this paper, according to the running environmentof power grid interconnection and new energy access, also to evaluation of the smartgrid index, base on control theory, the frequency control system of interconnected gridregarded as a large system to analysis its structure and performances. The studybegins with frequency optimal control algorithm strategy of the grid layer, as well asaims at create a healthy running smart grid and ensure the excellence of power quality.The main work is summarized as follows:Firstly, this paper proposes the theoretical basisbased on modern interconnectedpower grid frequency control mechanism Systematically, then describesinterconnected power grid hierarchical double-layer multivariable frequency controlstructure under the smart grid environment, then hierarchical analyses the controlmechanism of power grid layer and multiple group unit layer that regards the formeras frequency control optimization target and regards the latter as mathematical modelof equivalent object structure, and analyzes the evaluation index of the smart gridfrequency control. This section finally establishes system simulation platform ofinterconnected power grid multi-area and multivariable frequency control andevaluation index. This establishment lays the foundation of the interconnected powergrid frequency control theory algorithm and simulation study. The Second section proposes optimal allocation principles and algorithm ofAGC (Automation the Generator Control) demands as the network layer’s controloutput in multiple group unit layer. In this section, a multi-objective function based ondistribution principle swhich considering rapidity, economy, and environmentalprotection is established. Then the normalization and intelligent optimizationalgorithm are given to realize controllable optimal allocation value of each AGC units.Then using CPS’s (Control Performance Standard) performance evaluation index forfrequency Control to improve the allocation principles in the rationality of theunit-scheduling phase. Furthermore, due to randomness of the smart grid, theoptimal load distribution strategy and implementation algorithm between the unitsthat based on Q reinforcement learning method to adapt to changes in gridenvironment are provided. And it is used in optimal allocation algorithm simulationstudy of AGC command with interconnected power grid of multi-area systemsimulation platform. Simulation results confirm its effectiveness.Thirdly, in order to adapt to the coordinated development of the smart grid andnew energy, as for the random characteristics for power system load and theintermittent characteristics of the new energy grid, A syllabification Algorithm whichmodified by Markov chain is proposed. This algorithm is used for forecast ultra shortterm load that contains intermittent power which is handled as a negative load. Studydemonstrates that prediction algorithm prompts the unknown load disturbances andintermittent sources to predictable the load disturbance that lays the foundation for thestudy of the design of predictive control and provides the scientific evidence for thefurther consumptive of full percentage of intermittent power to smart grid.Fourthly, instead of using a second frequency regulation PI controller, thedesign of predictive controller used for the interconnected multi-area’s frequencycontrol is proposed in this section. In the case of avoiding adopting frequencyresponse coefficient, the state prediction model, rolling optimization performanceindicators and mathematical model for predictive control with constraints areestablished. Furthermore, gross electric output and its changing rate are regard asconstraints. Then quadrics QP problem used to solve nonlinear problems caused byconstraints, as a result, optimal control law which is the optimal AGC demand isobtained. And the stability and robustness of the system is analyzed. Finally, thecontroller is experimented on the interconnected power grid of multi-area systemsimulation platform. By verifying the research results, it is demonstrated that thedesign achieves remarkable optimization results of frequency control. This research has been partially carried out in some power grid companies, andgradually implemented the promotion.With the increase of network capacity and thedegree of interconnection, and the access of intermittent new energy, this researchresults shows a substantial application prospect in the interconnected power gridfrequency control for good quality.