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The effects of DC source voltage unbalance on the CHB inverter, if not properly managed, reduce the efficiency of the whole power system and generate unwanted harmonics in the output voltage with increased THD. In this paper, an SHE technique operating at the fundamental frequency has been proposed for unbalanced five-level CHB inverters to fix the amplitude of the fundamental harmonic, set the amplitude of the lower order harmonics to zero and achieve high efficiency performance. A preliminary off-line graphical approach was used to determine the switching angles at some modulation index values. Subsequently, a real-time interpolating Lagrange polynomial-based approach is proposed to obtain a continuous modulation index range. The study has been preliminarily analyzed in a simulation environment and subsequently validated experimentally.

This article considers ${l}$ -level cascaded H-bridge (CHB) inverters and proposes a new modulation method based on pulse active width modulation (PAWM), capable to minimize all harmonics with order $n< 2l+1$ and to satisfy the European harmonic standards for medium-voltage-level applications EN 50 160 and CIGRE WG 36-05. A mathematical theorem and its proof are presented, stating the features of the procedure, which is an improvement of the selective harmonic elimination (SHE) PAWM proposed by Buccella et al. After a detailed description of the method, simulation and experimental results have been included, showing its capability to reduce low-order harmonics.

A recursive method that eliminates $n+1$ harmonics and their respective multiples from the output voltage of a cascaded H-bridge (CHB) multilevel inverters with $s=2^{n}$ dc sources $(n=1,2,3,\ldots)$ is proposed. It solves $2 \times 2$ linear systems with no singular matrices and always gives an exact solution with very low computational effort. Simulated results in three-phase five-, nine-, 17-, and 33-level CHB inverters, and experimental results in a five-level inverter demonstrate the validity of the method.

In this paper, a new modulation technique is proposed for three-phase voltage-source inverters (VSIs). It is based on time partition obtained by Chebyshev polynomials’ zeros of the first kind which are used to build up nonuniform recursive sampling. A detailed mathematical description of the method and its implementation are given. Obtained results show that the proposed technique gives a total harmonic distortion factor lesser than conventional sinusoidal pulsewidth modulation under the same loading conditions. By comparing results obtained by proposed technique with results carried out by the wavelet modulation method, it is shown that they are very close. The proposed modulation returns lesser switching losses in comparison to sinusoidal pulsewidth modulation and space vector modulation. A MATLAB code that generates switching pulses to activate a Simulink model of the three-phase VSIs is developed to implement the proposed Chebyshev modulation technique. Experiments verify the correctness of the proposed method.

In distributed generation, high power capability and high efficiency are very important requirements. For this reason, this paper proposes a new analytical procedure for selective harmonic elimination in five-level inverters operating at fundamental frequency. For each modulation index, the proposed method calculates all possible switching angles eliminating a specified odd harmonic from the output voltage. The method has limited computational complexity, simple and cost-effective real-time implementation, and full capability of integration with closed loop control. Simulation and experimental results highlight full elimination of selected harmonic.