Abstract
The drawback of modulation ratio limitation in selective harmonic elimination pulse width modulation (SHEPWM) technology based on Walsh function transformation. In order to solve this problem, a multiband SHEPWM control technology method for a multilevel inverter based on Walsh functions is proposed. By analyzing multiband SHEPWM for multilevel inverter voltage waveforms under a Fourier series transform, the unified nonlinear multiband SHEPWM equations for a multilevel inverter with a modulation index varying from 0 to 1 can be generalized. The equations can be solved by Walsh function transform. In this way, the difficulties faced in expanding the modulation index, online calculation, and real-time control are resolved simultaneously. A seven-level inverter is taken as the example, for which the piecewise linear equations of Walsh functions under different bands and the trajectories of switching angles are given. Meanwhile, the conditions for multiple sets of solutions at such a point where the modulation index is switched over are also taken into account. The feasibility of the proposed method is verified by simulation based on MATLAB and SIMULINK. Finally, the feasibility of the practical application is proved by the experiment based on Digital Signal Processor (DSP).
Highlights
The cascaded H-bridge (CHB) multilevel inverter is one of the popular converter topologies used in high-power medium-voltage (MV) drives [1]
selected harmonics elimination pulse width modulation (SHEPWM) control method based on the Walsh function transform for the multilevel inverter
By combining the Walsh function transformation with the multiband SHEPWM control method for the multilevel inverter, the regulation operation range of the inverter can be expanded to 0–1
Summary
The cascaded H-bridge (CHB) multilevel inverter is one of the popular converter topologies used in high-power medium-voltage (MV) drives [1]. The core issue of the SHEPWM control is the solution of nonlinear equations of the multilevel inverter, including the selection of initial values and the selection of iterative algorithms. As it is easy to solve nonlinear equations by using Walsh functions and they have a low dependence on the initial solution, a kind of transformation method is proposed, for which the multilevel inverter modulation index of the multiband SHEPWM modulation scheme [14] can be broadened and combined with Walsh functions. The SHEPWM voltage waveforms of the multilevel inverter in different waveform band modes are analyzed and the multiband SHEPWM solution model with modulation indexes ranging from high to low is established.
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