Smart Metering Of Electric Energy In AC Micro-grid Included Nonlinear Load

With the construction of a new power system with new energy as the main body,distributed power has become an important supplement to the development of a new power system due to its advantages such as flexible power generation,local consumption,and green cleanliness.As an effective way to improve the utilization of distributed power,AC microgrid have the characteristics of uninterrupted power supply,flexible operation mode,and can be used for emergency power supply of important loads.However,due to the characteristics of randomness and uncertainty of a large number of nonlinear loads,their flexibly connected to the AC micro-grid and the bidirectional flow of electric energy between users and the AC micro-grid,not only leads to the disadvantage of poor anti-interference ability of micro-grid system,but also reduces the accuracy of electric energy metering.Therefore,the research on the smart metering of electric energy of AC micro-grid with nonlinear load has important academic value and engineering practical significance to improve the accuracy of electric energy metering.The dissertation mainly takes the AC micro-grid with nonlinear load as the research object.To solve the problem of electric energy metering inaccuracy caused by nonlinear load access,it carries out research on harmonics and inter-harmonics detection,three-phase unbalance analysis and optimization,electric energy compensation algorithm,load access regulation by real-time price and so on.1)Firstly,the topology of each micro-source in the AC micro-grid system is analyzed,and the equivalent circuit model of the AC micro-grid with nonlinear loads is established on the basis of considering the principle of bidirectional electric energy metering and the nonlinear and unbalanced characteristics caused by nonlinear load access.Based on this model,the influence of nonlinear characteristics,unbalance characteristics,fault power characteristics and electric energy are studied in detail,and the accurate electric energy metering scheme is designed.2)For harmonics and inter-harmonics generated by the connection of non-linear loads to AC micro-grids easily cause inaccuracy of electric energy metering,combined with the characteristics of dynamic changes of harmonics and inter-harmonics in micro-grid,the inter-harmonic electric energy metering of generalized d_k-q_k coordinate transformation is adopted to realize the effectively extract any k^th inter-harmonics.Based on this,a harmonic detection method based on the combination of deep belief network and ensemble empirical mode decomposition is proposed,which overcomes the modal aliasing problem in the analysis of harmonic dynamic signals by classical empirical mode decomposition in the analysis of harmonic dynamic signals,and realizes the adaptive extraction of harmonic signals and smart metering ofelectric energy.3)Aiming at solving the problem of voltage unbalance at the electric energy metering point caused by the randomness of AC microgrid load access and the unbalanced output of micro-source,an improved electric energy metering method of forward push back generation power flow calculation is proposed.This method quantitatively analyzes the influence of voltage change caused by random load access in micro-grid,which affects the accuracy of electric energy metering.Based on this,taking the minimum three-phase voltage unbalance as the objective function,the simulated annealing algorithm is used to optimize the phase sequence of the load access,which reduces the impact of three-phase voltage imbalance on the accuracy of electric energy metering.4)In order to solve the problem that the electric energy cannot be accurately metering and compensated in time caused by the fault of the electric energy metering device in the AC micro-grid,the structural parameters of the deep belief network are optimized with the help of the standard particle swarm algorithm,and smart compensation algorithm for missing electric energy based on the combination of deep belief network and standard particle swarm optimization algorithm is proposed.Compared with the traditional electric energy compensation method,the proposed algorithm can accurately compensate the missing electric energy data,and the accuracy of the proposed algorithm is verified by comparing the power fitting curves before and after optimization.5)When the load is randomly connected to AC micro-grid,the load will be too low or too high,so that the measurement range of electric energy metering device can exceed the rated measurement requirements.A real time price optimization model aiming at minimizing the electric energy expenditure of load access users is proposed,and the improved sunflower algorithm is used for optimization and solution.The results show that the proposed method optimizes the load access timing sequence in the AC micro-grid through real time price adjustment,and can adjust the load to the measurement range specified in the regulation of electric energy metering device.Based on this model,the influence of load access change before and after optimization on the accuracy of electric energy metering device is analyzed,and it is verified that the proposed model can improve the accuracy of electric energy metering by means of real time price optimization.