Generalized formulation of multilevel selective harmonic elimination PWM: Case I-Non-Equal DC Sources

The paper presents optimal solutions for eliminating harmonics from the output waveform of a multilevel staircase pulse-width modulation (PWM) method with non-equal dc sources. Therefore, the degrees of freedom for specifying the cost function increased without physical changes as compared to the conventional stepped waveform. The paper discusses an efficient hybrid real coded genetic algorithm (HRCGA) that reduces significantly the computational burden resulting in fast convergence. An objective function describing a measure of effectiveness of eliminating selected order of harmonics while controlling the fundamental for any number of levels and for any number of switching angels is derived. It is confirmed that multiple independent sets of solutions exist and the ones that offer better harmonic performance are identified. Different operating points including five- and seven-level inverters are investigated and simulated. Selected experimental results are reported to verify and validate the effectiveness of the proposed method

On abolishing symmetry requirements in the formulation of a five-level selective harmonic elimination pulse-width modulation technique

Selective harmonic elimination pulse width modulation (SHE-PWM) techniques offer a tight control of the harmonic spectrum of a given voltage waveform generated by a power electronic converter along with a low number of switching transitions. These optimal switching transitions can be calculated through Fourier theory, and for a number of years quarter-wave and half-wave symmetries have been assumed when formulating the problem. It was shown recently that symmetry requirements can be relaxed as a constraint. This changes the way the problem is formulated, and different solutions can be found without a compromise. This letter reports solutions to the switching transitions of a five-level SHE-PWM when both the quarter- and half-wave symmetry are abolished. Only the region of high-modulation indices is reported since the low-modulation indices region requires a unipolar waveform to be realized. Selected simulation and experimental results are reported to show the effectiveness of the proposed method

A hybrid genetic algorithm for selective harmonic elimination control of a multilevel inverter with non-equal DC sources

The paper presents an optimal solution for eliminating pre-specified order of harmonics from a stepped waveform of a multilevel cascaded inverter topology with non-equal dc sources. The main challenge of solving the associated nonlinear equations, which are transcendental in nature and therefore have multiple solutions, is the convergence of the relevant algorithms and therefore an initial point selected considerably close to the exact solution is required. The paper discusses an efficient hybrid real coded genetic algorithm (HRCGA) that reduces significantly the computational burden resulting in fast convergence. An objective function describing a measure of effectiveness of eliminating selected order of harmonics while controlling the fundamental component is derived. Different cases including seven- and nine-level inverters with different values of modulation indices are reported. The theoretical findings are validated through simulation studie