Research On Distributed Coordination Control Strategy For Microgrids Community In Grid-connected Operation Mode

The microgrids community(MGC)is established based on microgrids technology,connecting the adjacent microgrids and consumption network to the distributed network,which is the important form to improve the permeability of renewable energy generation and furtherly promote the development of microgrid technology.Different from single microgrid,the MGC is more complicated,and due to the limitation of control variable dimensions and prediction accuracy in operation,there is big challenges of MGC coordinated control in the area of distributed power optimization,system power balance,system economic optimal operation as well as voltage stability control.Therefore,this paper studies on the MGC coordinated control technology under the gridconnected mode from the two dimensionalities: device-level and system-level,normal mode and emergency mode,which has the important theoretical significance and engineering application value to ensure MGC safe and reliable operation and operating economics enhancement.The main contributions of this paper are as follows,(1)As the operation modes of the wind turbine are complicated,and the output power fluctuation is high,a model predictive control strategy is proposed covering the whole speed region,which takes into account the power smoothing in the transition zone.The state space equation and objective function are built covering all wind condition including partial-load and full-load regions,a smooth switching strategy is designed with loop-back characteristic,on the premise of guaranteeing multi-objective control in the partial-load/full-load regions,the power fluctuation in the transition zone near the rated wind speed is effectively suppressed.(2)The hierarchical power coordinated optimal control considering battery storage operating modes for MGC is proposed,in order to protect the health of battery storage system,eliminate the power imbalance caused by distributed generation and load forecasting errors,and ensure the safe and stable operation of MGC.By introducing the integer variable describing the limited current and constant voltage control modes of battery storage system,the mathematical model and constraint equations of MGC are constructed,and the scheduling programming is presented as the mixed integer linear programming;the distributed compensation strategy is designed to dynamically offset the power imbalance caused by the prediction error.(3)A distributed coordinated control strategy considering economic operation is proposed adopting the virtual hierarchy concept,to rolling optimize the operation cost of the whole system,and at the same time simplify the power variable complication.Firstly,a virtual hierarchy strategy based on general MGC architecture is designed,and a distributed model predictive hierarchical control framework is constructed to reduce the complexity and variables dimension of power exchanging.By constructing the model of subsystem,the local model predictive controller and global sharing objective function are built,and the distributed logarithmic barrier method is introduced to solve this optimization problem.The proposed strategy not only has the global optimal solution of centralized economic optimization,but also overcomes the shortcoming of poor real-time performance of centralized optimization strategy.(4)In emergency mode,a voltage stability control strategy based on distributed power collaboration is presented considering the adjustable ratio of sub-microgrid and spatial location.Firstly,two stage control structure for MGC is constructed,and the voltage dynamic equation is built based on Newton-Raphson method.Secondly,the ratio of adjustable resource is defined,and the cooperative voltage control strategy based on adjustable ratio is proposed.Each microgrid solves its own dynamic voltage equation based on the adjustable resource ratio and spatial location,directly determines its active and reactive power increments.The proposed strategy guarantees that the voltage can be quickly restored to safe range,while taking into account the principle of “do what you can” in sub-microgrid.