Theory Analysis And Dynamic Modeling Of Wide-band Harmonic In Distributed Photovoltaic Grid-connected System

In the era when the state vigorously advocates the policy and strategy of low-carbon environmental protection and sustainable development,vigorous development of new energy is an important means to solve the production contradictions and enhance competitiveness of our country.Distributed energy generation is the product of the application of new energy technology in the field of electricity.Improving the level of clean energy transmission and absorption through technological innovation can solve the bottleneck of renewable energy development and optimize the energy industry structure.However,with the popularization of new energy generation and micro-grid technology,it also brings new harmonic problems with wide frequency domain,multi-type and strong interaction to the main power grid,which poses a great challenge to the power quality of the power system.In this paper,the broadband harmonics of distributed photovoltaic grid-connected systems are studied as follows:(1)Inverter,as the key equipment of photovoltaic energy and power grid interface,studies its output characteristics;studies the influence of non-linear factors such as dead-time effect on output according to the characteristics of switching devices;proposes a dead-time compensation strategy based on AC side inductance current ripple characteristics;combines grid-connected filter circuit parameters,inverter output control technology and harmonic active compensation technology to photovoltaic inversion.The harmonic source model of grid-connected photovoltaic inverters is established based on the influence of output current waveform of grid-connected converters.(2)Analyzing the working characteristics of power components in wide-frequency harmonic domain in distributed photovoltaic grid-connected system,combining with the harmonic domain characteristics of power components,the power frequency model is improved,and the wide-frequency domain harmonic model of power components such as transmission lines and power transformers is proposed.(3)Combining the broadband harmonic models of power devices in distributed photovoltaic system,the dissemination and interaction rules between the output harmonics and background harmonics of the main grid in grid-connected operation mode are analyzed.The resonance law between the output harmonics of photovoltaic power station and background harmonics of the grid is analyzed by two-port model,and the influence law of system parameters on the broadband harmonic resonance is studied.(4)Establish a broadband harmonic impedance model of hybrid active power filter in distributed PV grid-connected system,analyze the influence of active power filter operation status on the suppression effect of broadband harmonics,and verify the correctness and validity of broadband harmonic theory research and harmonic source modeling through simulation analysis.