Minimization of harmonics in photovoltaic inverters

DE PAULA, M.; SANCHEZ REINOSO, C.R.; AVILA, L.

Congreso; Conference on Sustainable Development of Energy, Water and Environment Systems; 2017

International Centre for Sustainable Development of Energy, Water and Environment Systems

When tackling the design of a photovoltaic system, some papers try to optimize it using estimation methods for the inverter-array sizing. There are also works that adopt other approaches, but all of them focus on the key role of the inverter to improve the system. Multilevel inverters are widely used in photovoltaic applications due to the fact that they present less harmonic distortion than mono-level inverters and can utilize several photovoltaic modules as inputs. However, it would also be desirable to reduce the harmonic content in the multilevel inverters output. There are methods used to eliminate the harmonic distortion that allow the characterization of the harmonic content; then, the problem can be converted into polynomial equations to be solved analytically. The polynomial degree increases with the number of direct current sources and the number of harmonics to be eliminated. Therefore, as the problem size increases, more complex expressions are obtained and the calculation time of the optimal switching angles also increases. To decrease the computational cost some methods were proposed but the solutions they yield are discontinuous at some points, thus creating problems to find the possible switching angles at said points. In addition to that, it is required a great number of switching to eliminate high order harmonics, causing high switching losses.This paper proposes a methodology to minimize the harmonic content in a multilevel inverter output. A swarm particle based optimization algorithm is proposed to reduce the total harmonic distortion, subject to restrictions over the allowed harmonic content. This approach could be useful to obtain the most convenient angles for different modulation indexes and could prevent discontinuity issues in the solution of the non-linear functions.For different modulation indexes the results obtained show that the proposed methodology reduces the harmonic distortion and finds all the solutions sets for the non-linear equations, and solving the problem of the discontinuities for cascade multilevel inverters. The optimal vector obtained, composed by the best switching angles, is suitable to be used in online applications.