Transient Analysis Of Load Shock And Coping Strategy For High Penetration Micro-grid

Developing and utilizing renewable energy is essential for solving the problems of energy shortage and environmental pollution.The distributed generation(DG)has the characteristics of randomness and uncertainty,and most DGs are connected to the micro-grid in the form of power electronic interface,which leads to the small inertia and poor anti-interference ability.Loads such as an induction motor and an electric vehicle will consume a large amount of reactive power and inject harmonic currents,and thus produce shock load and affect the stability of the micro-grid.When penetration of DGs in micro-grid is increasing,the fluctuation smoothing and dynamic balance of micro-grid system depend on itself.Therefore,it's of great significance to study the influence caused by shock load in high penetration micro-grid,to analyze flow distribution before and after the load shock and reveal the mechanism of shock load and fault propagation,to deal with shock load and micro-grid internal balance storage allocation strategy,and improve the stability of micro-grid operation and the ability of DGs consumption.This paper focuses on the research of transient analysis and energy storage strategies of high penetration micro-grid.And the main research contents are as follows:First of all,the frequency,amplitude and phase of the power quality transient signal in the process of load shock change with time and contain complex transient phenomena.In order to solve the problem of Hilbert Huang Transform(HHT)when analyzing transient power quality signal during load shock,a new method combining statistic feature vector symbolic(SFVS)and Hilbert Huang Transform(HHT)is proposed.And using the new method to analyze the transient signal in high penetration micro-grid during load shock is also included in this study.The experimental results demonstrate that the proposed method is accurate and the transient component in power quality signals can be extracted accurately,the instantaneous amplitude,instantaneous frequency and the moment of waveform mutation of power quality transient signal are obtained.Secondly,according to the topology of micro-grid system power flow calculation of complex structure,three-phase unbalance and weak ring network problems,a method based on augmented loop correlation matrix is proposed to establish the power flow calculation node reactance matrix,combined with the operation characteristics of DGs,a power flow calculation model of micro-grid is established.The Z-bus method has been adopted to solve the power flow calculation model of the power flow,and the reactive power is corrected by the voltage deviation of PV nodes in the iterative process for the Z-bus method is weak to process on PV nodes.The proposed method is verified by IEEE13 test system and 7 nodes micro-grid system.And the influence of the load shock on the power flow distribution in micro-grid with different penetration is studied on the EU low voltage micro-grid system and the micro-grid experimental platform.The results show that the proposed method is accurate in the calculation of the power flow of the micro-grid system with DGs and weak ring network.The higher the penetration,the higher the impact of the load shock on the voltage amplitude of the micro-grid;the PV type DG is conducive to the micro-grid reducing voltage fluctuations when the load shocks.Thirdly,in order to solve the problem of DGs voltage Ride-Through in micro-grid,a control strategy based on instantaneous value predictive control algorithm is proposed,and the method is suitable for DGs with power electronic interface.An experimental prototype is built to verify the algorithm,which based on the DSC digital signal control chip TMS320F28 XXX as the main control unit,the Fuji 2MBI100VA120-50 100A/1200 V IGBT module as the inverter bridge,the proposed instantaneous voltage predictive control algorithm as the inverter control strategy.The results show that the inverter can realize low and high voltage ride through and recovery when the system's voltage is in fluctuations,and the active and reactive power adjustment can be completed within several cycles.The islanding protection can also be realized.Fourthly,strategy of energy storage configuration is proposed to deal with the load shock and internal power balance of micro-grid.The optimal configuration model of the energy storage system with high penetration of micro-grid considering the PCC point power constraint is established,and an optimization method based on the voltage sensitivity coefficient is proposed.The model takes into account the micro-grid topology,line parameters,temperature,irradiance and other factors.And the optimal solution of the model is the minimum power capacity and the optimal node deployment scheme,with the aim of satisfying the micro-grid voltage fluctuation meets the national standards of power quality.The proposed method can be applied to deal with the PV power fluctuation and the load shock,which is helpful to evaluate the capability of the micro grid system for the photovoltaic power supply.Finally,the effectiveness of the proposed method is demonstrated by the EU low voltage micro-grid system and a micro-grid experimental platform.This paper presents the method of analyzing the transient signal of load shock in high penetration micro-grid,the calculation method of flow distribution and storage strategies.The research results provide a theoretical tool and a basis for the study of power quality analysis and control of micro-grid,which is beneficial to the configuration and system design of micro-grid,and the realization of the self-balancing control system.The AC / DC hybrid micro-grid and micro-grid autonomous self-healing strategy can be further researched in future.