Design Of Harmonic Suppression Grid-connected Inverter For Distributed Power Generation System

With the development of distributed generation,more and more new energy sources are connected to the power grid,which brings more power and promotes the development of new energy.In the power grid,due to the large amount of input of nonlinear load,current harmonics will be generated.Based on the problem of harmonics in the power grid,this paper can not only provide more power but also suppress harmonics in the grid when grid-connected inverters are connected to the grid.Waves not only improve power quality,but also improve equipment utilization,which is very practical for the power grid.Therefore,this paper focuses on the harmonic suppression function of grid-connected inverters.The specific research content of the paper includes the following aspects:Firstly,the principle and topology of the grid-connected inverter are analyzed.The full-bridge inverter is selected as the research object,and then the modulation method of the grid-connected inverter is analyzed.The SVPWM modulation method is adopted.The double closed-loop control strategy is selected,and it is added to the double closed-loop strategy for harmonic suppression.The voltage outer loop and current inner loop are designed specifically to determine its parameters,and the overall simulation model is established on Matlab.Secondly,the algorithm of harmonic detection is studied.Based on the theory of instantaneous reactive power,the theory of instantaneous reactive power is analyzed and introduced,and the low-pass filter is further analyzed.Low-pass filters generally use Butterworth filters,but they are limited by the shortcomings of real-time and accuracy.It is better to use a sliding filter to analyze the harmonics.After that,the detected harmonics are compensated,and the core algorithm of the compensation adopts repeated control,which has good stability,but has the disadvantage of slow adjustment speed,and the current inner loop generally adopts PI control with fast adjustment speed,therefore,the repetitive controller and the current PI controller are connected in parallel as the current inner loop to control theharmonic current.Simulation shows that this method has better suppression effect than the double closed loop.It is also analyzed that the harmonics in the load-side current in the design of the lead are mostly odd harmonics,so the algorithm of PI+odd harmonic repetitive control is proposed,which is intended to eliminate odd harmonics and better suppress harmonic currents.Through simulation,relying on the simulation model,it is found that the effect of suppressing harmonic content is better.Finally,the hardware and software design of the grid-connected inverter was carried out.The hardware part has completed the design of the main circuit and the detection circuit.The software part is designed for the main program,harmonic calculation subroutine and so on.By constructing the physical object and verifying the experimental results,the effectiveness of the design of the grid-connected inverter to compensate the harmonics is tested.