Research On Cascaded High Frequency Inverter Based On Specific Harmonic Elimination

High frequency inverter has been widely used in ultrasonic technology,aviation power supply,new energy development and other fields because of its high power density and good reliability.In the field of ultrasonic,high frequency inverter is the core device of driving power supply of ultrasonic transducer.At present,there are still many shortcomings in technology.Usually,the square wave or modulation wave with a large number of harmonics is directly output,and the low-order harmonic with high amplitude and great harm will not only produce serious electromagnetic interference to the ultrasonic transducer,but if the transducer is directly driven without filtering,it will also cause large harmonic losses;Moreover,the commonly used resonant inverter cannot achieve wide-band output,which limits their applicability.Aiming at the harmonic problems and wide-band output requirements of high frequency inverter,this dissertation conducts an in-depth study on the modulation method and topology of high frequency inverter.The essence of the specific harmonic elimination technology is to eliminate the specific harmonic by optimizing the switching time.Because its application is not limited by the fundamental frequency,it provides favorable conditions for the inverter wide-band output.Multilevel specific harmonic cancellation technology can obtain the highest output power quality at low switching frequencies theoretically.Because of the difficulty of modeling and the complexity of model calculation,this technology is rarely used in practice.Cascaded inverter has small switching stress and good output waveform quality,which is the common topological structure of multilevel inverter.In this thesis,the specific harmonic elimination technology is applied to the cascaded inverter,and a model of image residual harmonic elimination is proposed,the second inverter harmonic is taken as the image harmonic of the first inverter harmonic,which simplifies the multi-level specific harmonic elimination model.The specific harmonic elimination model is a set of nonlinear transcendental equations.Because of its difficult initial value selection,complex solution process and poor convergence,it becomes a bottleneck in the application of specific harmonic elimination technology.In this thesis,an improved particle swarm optimization algorithm is proposed.The linear decreasing inertia weight factor is combined with the sign function to form a new weight factor,which can avoid the problem that the algorithm is easy to fall into the local optimum in the later iteration.In order to overcome the common problem of low precision due to the randomness of search in intelligent algorithm,the improved particle swarm optimization algorithm is combined with Newton iterative method,which not only avoids the difficulty of initial value selection,but also improves the accuracy of the algorithm.Finally,a high frequency inverter experimental platform with two H-bridge cascades as the topology is built,and the advantages of the proposed image residual harmonic model,the accuracy of Newton iterative particle swarm optimization algorithm and the broadband output performance of the inverter are verified by simulation and experiment.The results show that the image residual harmonic elimination model is not only simple and easy to calculate,but also has a very good harmonic elimination effect.Newton iteration improved particle swarm optimization algorithm not only avoids the influence of initial value on the algorithm convergence,but also improves the accuracy of the algorithm.The application of specific harmonic elimination technology in cascaded multilevel inverter not only eliminates the low harmonics,but also realizes the wide frequency output,which provides a new method for the optimal design of high frequency inverter.