| In recent years,due to energy transformation and environmental problems,China has vigorously developed scenery storage and transportation.As a result,the new energy power generation technology has advanced by leaps and bounds,but photovoltaic power generation is affected by factors such as illumination,temperature and MPPT control algorithm,and has power fluctuation characteristics.In addition,a large number of nonlinear loads and power electronic equipment are connected to the power grid,which aggravates the harmonic pollution.These harmonics are prone to resonance amplification through long-distance transmission lines.Usually,virtual resistors are embedded in photovoltaic inverters to suppress resonance.Considering the power fluctuation of photovoltaic power generation,the disturbance step size and sampling frequency will be adjusted,and then interharmonics will be generated.Coupling interharmonics through AC and DC sides will seriously affect the suppression effect.In order to make up for the defects,this paper proposes a long-distance transmission line harmonic resonance suppression scheme based on photovoltaic power generation system with hybrid energy storage system.The DC side is equipped with storage battery and super capacitor to compensate the fluctuation of photovoltaic output,and the equivalent infinite transmission line control strategy is embedded in photovoltaic inverter to suppress the resonance amplification of AC side.In this thesis,firstly,the photovoltaic cell system is modeled,and the maximum power tracking technology is used to maintain the power generation efficiency.According to the literature parameters,the long-distance transmission line is modeled,its equivalent impedance expression is deduced,and its Bode diagram is drawn.When the output impedance of the inverter is the same as the transmission line impedance,and the phase difference is 180,the output current will produce multi-resonance phenomenon.Based on the analysis of active power filter and the derivation of equivalent wireless length theory,the control strategy of multi-function grid-connected inverter is proposed to solve the problem of harmonic oscillation amplification while grid-connected Through the change of disturbance step size and sampling frequency in MPPT control caused by DC side power fluctuation,the generation mechanism of interharmonics is analyzed.Through the analysis of the coupling characteristics between DC side harmonics and AC side,it is concluded that the interharmonics will reduce the effectiveness of the strategy when they are transmitted to AC side,and the battery super capacitor hybrid energy storage system is introduced to stabilize the power fluctuation of DC side.Based on MATLAB/Simulink simulation,it is verified that the harmonic resonance suppression strategy proposed in this thesis can suppress the total harmonic distortion rate to a lower level.Finally,a 9km transmission line model is builted.With the power converter Eval-M5-E1B1245N-Si C as the inverter platform,the Speedgoat real-time target machine simulates the hybrid energy storage system for power compensation.The converter platform is controlled by program compilation,which verifies the correctness and effectiveness of the proposed harmonic resonance suppression strategy for long-distance transmission lines of photovoltaic power generation based on hybrid energy storage system. |
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