Research On Islanded Microgrid Model Reduction And Distributed Secondary Control Strategy

The islanding operation of microgrid is an effective measure to ensure reliable power supply and safely system operation for sensitive loads.Based on multi inverter-interfaced distributed generator(IIDG)parallel microgrid under the island mode due to the small power supply capacity,space truss structure is weak,and lack of inertia,easy stability problems.Due to its small power capacity,weak grid structure and lack of inertia,the microgrid in island mode with multi inverter-interfaced distributed generators(IIDGs)paralleling can easier get stability problems.However,if the stability problem is studied based on the full order model of IIDG,it is easy to cause dimension disaster.Therefore,it is necessary to study the model reduction methods for IIDG-based mcirogrids.In addition,how to improve the stability of islanded microgrid based on hierarchical control while effectively improving the dynamic performance of the system is also the main focus of microgrid research.Based on the support of national natural science foundation of China(51277184),in terms of order reduction of microgrid model,the model reduction method of IIDG-based island microgrid is studied.On the basis of order reduction model analysis,a nonlinear bounded distributed secondary control method based on continuous communication is proposed for the abundant communication network.And for the limited communication network resources,there may be communication network delay and packet loss problem and network attack problem.In order to solve the problem of communication network delay packet loss and network attack,a distributed secondary control method and a distributed secondary control method considering communication network attack are proposed respectively.The main contributions of this paper are as follows:(1)The multi-time scale order reduction method for IIDGs-based islanded microgrid is studied.Firstly,by taking the droop control-based IIDG in microgrid as the research object,a complete model of IIDG including power droop controller,voltage and current double-loop controller,filter and line is established.Then,according to the singular perturbation theory,the features of the complete model of IIDG are divided into multiple time scales,and the model is treated with fast dynamic order reduction.Finally,through feature extraction of IIDG small signal model,the static stability consistency of IIDG model before and after order reduction is proved;using the quadratic approximation method of the the system stability domain boundary,the transient stability consistency of the IIDG model before and after order reduction is proved.(2)As for the abundant communication resource condtion,a class of sliding model based finite-time control have chattering problem in the steady state,thus,an improved nonlinear,bounded and lipschitz continuous distributed secondary control method is proposed.Firstly,by analyzing distributed secondary control principle and based on the consistency control algorithm and the lipschitz continuous condition theory,the nonlinear dynamic distribution function inspired by Beta cumulative distribution funciton is introduced to improve the convergence speed of the consensus control and suppress the transient overshoot.Then,the effectiveness towards suppressing chattering phenomenon of proposed algorithm is proved through comparing with the sliding mode based finite-time consensus algorithm.Finally,the stability of the control strategy is proved by using the stability determination function of Lyapunov.(3)As for the limited communication resource condtion,the communication time and data dropout may happen,thus,an improved event-tiggered based distributed secondary control method is proposed to solve the time-delay and packet loss problems in communication networks.Firstly,by analyzing the basic principle and classification of event-triggered control method,and considering the influence of communication delay and data packet loss on the event triggering conditions,an event trigger control algorithm based on state-independent event trigger function is designed to improve the robustness of the algorithm.Then,the delay and packet loss mechanism of communication network is studied and the minimum triggering time interval and the maximum allowable communication delay are estimated.Finally,the stability of the proposed control strategy is proved by theoretical derivation,and the effectiveness of the improved algorithm is proved through comparing with the state-dependent based event-triggered control algorithm.(4)As for the limited communication resource condtion,the communication cyberattack may happen,thus,an improved event-triggered based distributed secondary control method is proposed considering the communication environment having deceptive cyberattacks problems.Firstly,the basic principle of cyberattack is analyzed,and the probability model of successful penetration of deceptive cyberattack into microgrid protection devices is built by setting the ratio.Then,considering the concealment and randomness characteristics of deceptive cyberattack,the event-triggered based control is designed by using the fixed triggering function upper limit.Finally,the basic theory of stochastic stability is analyzed,the convergence consensus in mean square senses of the proposed method is proved through the Lyapunov method,and the relation between convergent upper limit function and several key parameters is studied and the corresponding adjustable range is presented.