The Improved Wavelet Modulation And Its Application On Inverter

Wavelet modulation(WM)was proposed in recent years.WM has the advantages of low total harmonic distortion(THD),low switching loss,high magnitude of fundamental component,high dc voltage utilization ratio and simple digital implementation.However,once sample groups D and scale parameter j of WM are determined,the output voltage of WM is fixed and cannot be changed.This disadvantage sets great limitation on the widely application of WM.To solve the above problems,this thesis improves the WM technique from the following two aspects:Firstly,this thesis puts forward the WM technique for multilevel inverter.To solve the switching angles,this thesis proposes two methods and apply the WM technique on multilevel inverter successfully.Secondly,this thesis proposes an amplitude-controllable wavelet modulation(ACWM)technique.By introducing the modulation ratio,the pulse width of the ACWM can be adjusted.Thus,the ACWM can not only maintain the advantages of the original WM,but also adjust the amplitude of output voltage flexibly.This thesis applies the ACWM on Z-source inverter,and solves the contradiction between the boost factor and the harmonic contents successfully.The main research contents of this thesis are as follows:(1)Introduces the principle of WM briefly,and reviews the development history of wavelet analysis;(2)Introduces the basis of WM technique: the concept of multi-resolution analysis and non-uniform recurrent sampling as well as the linear synthesis scaling function;(3)Puts forward a method to apply the WM technique to multilevel inverter.Aiming at the switching angle problem,this paper proposes two methods: time-priority algorithm and lowest-THD-priority algorithm;(4)To solve the problem that WM can’t regulate the output voltage,this thesis proposes the amplitude-controllable wavelet modulation;(5)Explore the feasibility of ACWM on z-source inverter.By mathematical derivation,simulation and experimental results,it was proved that the ACWM for Z-source inverter can reduce THD and the voltage stress across the switching elements significantly.