| Power electronic technology uses the power electronic devices for powerconversion and control. Variety of power converters are widely used in high voltagedc transmission, static reactive power compensation, power locomotive traction,ac/dc power transmission, electrolysis, excitation, etc. Modulation strategy as thecore part of the power converter control method, has great influence on the workingperformance of power converter. Good modulation strategies for reducing harmonicpollution to power network and loss of the switch action caused by the switch,increasing the voltage utilization plays an important role.Although the existing modulation technology plays an important role in theindustrial production, scholars still hope to develop new modulation strategy tofurther improve the working efficiency of the power converter. Wavelet Modulation(WM) as a novel modulation strategy is compared with the existing modulationstrategy can significantly reduce the output voltage total harmonic distortion rateand switch loss, widen the linear modulation range and easily digital realization.This paper presents a method to calculate the output voltage modulation indexof a new type of inverter modulation strategy-wavelet modulation. The paper willfirst analyze the basic principle of wavelet modulation, and then analyze the linearrange of its voltage modulation index (M) and deduce the solution method of M.The correctness of the analysis is verified by simulation and experiment.Comparisons are also made of output line voltage’s spectrum when invertersrespectively controlled by wavelet modulation, SPWM and SVPWM and the Mlinear modulation range of these three methods. The results show that, the analys isof wavelet modulation’s voltage M is reasonable; wavelet modulation can outputbetter quality of line voltage compared to SPWM and SVPWM modulation when Mboth up to the maximum; wavelet modulation also has small voltage harmonicdistortion compared to other modulations with the same M. By introducing ancoefficient to its sampling function, the improved wavelet-modulation can reducelow-order harmonic contents of the output voltage and enhance continuouslycontrollability of modulation index.According to the basic principle Fourier series theory, Fourier decomposition ismade of the output waveform of the single phase WM VS rectifier to get theanalytic expression of the output dc voltage and every harmonic voltage. Acomparison is made of SVPWM and SPWM rectifier when supplying three phasesymmetric and asymmetric voltage source. The simulation results show that theanalysis of single phase WM voltage rectifier is reasonable, and compared to SVPWM and SPWM, wavelet modulation rectifier has advantages of reduced inputcurrent harmonics, small distortion rate of DC output voltage and when high inputpower factor is close to1, DC output voltage is larger.Base on the theory analys is and simulation, hardware and software of thecontrol system, applied DSP TMS320F2812, the modulation that duty ratio is basedon WM and the improved WM modulation is realized. All the work of this article issummarized in the last part. |
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