Harmonic Analysis Of Rectifiers Based On Probability Model

Power electronic circuits are widely applied and highly required in the industry,but the circuits will make the grid current waveform distortion.However when the rectifier circuit,which takes the largest share of the power electronic circuit,is treated as the load while the grid operates,it will have a great harmonic current injecting into the grid and affect the power quality of the grid.And it also affects the social production and other power consuming load.So harmonic current generated by the rectifier circuit can not be ignored.Thyristor rectifier circuits take a large development market and a solid foundation for development.And as a harmonic source which can not be ignored,analysis and suppression of the harmonic current generated by thyristor rectifier circuit have a very important practical significance.In this thesis,three-phase bridge rectifier circuit is treated as the research object.model establishment,harmonic characteristics analysis,harmonic suppression and simulation verification are mainly analyzed.First,the circuit model of three-phase uncontrolled rectifier circuit,three-phase half-wave bridge rectifier circuit,three-phase bridge full-control rectifier circuit and 12-pulse rectifier circuit are respectively built by the simulation platform of Matlab/Simulink.And the harmonic current characteristics,which include the harmonic components and the relative content,of the network side are analyzed.So the harmonic distribution of the three-phase rectifier circuit and the multi-pulse rectifier circuit are well understanded,and some basic research for the following in-depth analysis is done.Then,the method of mathematics and probability theory is used to establish the analytic model of three-phase bridge rectifier circuit under symmetry and asymmetry of three-phase power supply.And based on the probability model of random variables,the Monte Carlo simulation method is used to establish the probability model of the harmonic current amplitude and phase angle on the network side.The probability density curves of the harmonic current amplitude and phase angle on the network side are acquired and probability value of harmonic current amplitude and phase angle in the proper interval is clerified.Compared with the simulation results of the three models,the correctness of the analysis is verified and the possibility of harmonic prediction is also provided.Subsequently,the analytic model and probability model of 12-pulse rectifier circuit are established.The results obtained from the analysis of the amplitude and phase of the harmonic current on the network side are in agreement with the ones of the circuit model.The correctness of the analytical method and the coincidence of the three methods are verified,which provides the theoretical basis for the application of circuit model to analyze the harmonic suppression effect of multi-pulse rectifier circuit.Finally,the harmonics suppression method is adopted to suppress the harmonics produced by the three-phase bridge rectifier circuit,including multi-pulse rectifier circuit and DC side harmonic suppression technique.For the multi-pulse rectifier circuit,12-pulse rectifier circuit which is a wide range of applications and relatively simple structure is chose for analysis and research.By,respectively,analyzing the circuit model of the three-phase bridge rectifier circuit and the 12-pulse rectifier circuit,and comparing the simulation results,a good harmonic suppression effect was observed.For the DC-side harmonic suppression technique,a circuit model of the third-harmonic injection suppression method is established.The harmonic current value change of the three-phase bridge rectifier circuit after the introduction of the third harmonic current is analyzed and compared,and the harmonic suppression effect of the third harmonic injection is verified.