Maria Gabriella Cimoroni

Analytical Method for Pattern Generation in Five-Level Cascaded H-Bridge Inverter Using Selective Harmonic Elimination

This paper proposes an analytical procedure for computation of all pairs of valid switching angles used in pattern generation in five-level H-bridge cascaded inverters. The proposed procedure eliminates harmonic components from inverter output voltage and, for each harmonic, returns the exact boundaries of all valid modulation index intervals. Due to its simple mathematical formulation, it can be easily implemented in real time using a digital signal processor or a field-programmable gate array. In this paper, after a detailed description of the method, simulation and experimental results demonstrate the high quality of achievable results.

Harmonics elimination in 5-level converters operating at very low switching frequency

This paper deals with the problem of harmonics reduction in cascaded multilevel converters throught Selective Harmonic Elimination. The method consists of an analytical procedure for identifying a set of switching angles capable of eliminating the desired harmonics and a graphical analysis tool allowing the identification of all valid solutions. Because of their industrial interest, relatively complex 5-level inverters have been considered, however the proposed method can be easily extended to a higher number of levels, too. The main advantage of the proposed approach is its simple implemention, which can be accomplished by using low cost digital signal processors. Simulations and experiments are presented for demonstrating the achievable results.

Harmonic mitigation technique for multilevel inverters in power systems

A new procedure to mitigate some harmonics is presented for a 5-level cascaded inverter, varying the modulation index. The two switching angles α1 and α2 are computed by using a procedure based on graphycal analysis by using Chebyshev polynomials and the Warings formulae. The proposed mitigation technique is applied to reduce a pair of harmonics among third, fifth and seventh in inverter output voltage according to standard code requirements. Experimental results are also extracted by the prototype built at the laboratory. The measured results confirm the quality of the presented procedure.

Investigation about numerical methods for Selective Harmonics Elimination in cascaded multilevel inverters

Selective Harmonic Elimination (SHE) is a technique allowing the elimination of well defined harmonics by a complex signal, thus improving the quality of inverter output waveforms. SHE algorithms are very complex from a computational point as they consist of the solution of a set of nonlinear equations. This paper proposes two new approaches: (i) an analytical approach consisting of a graphical analysis allowing, in a 5-level inverter, the identification of all valid solutions; (ii) an iterative fixed point method applicable to 7-level inverters. Both the approaches, which can be easily implemented in real-time using digital controllers have been successfully verified through numerical simulations.

An analytical algorithm for Selective Harmonic Elimination and efficient control in five-level inverters

Traditional methods, such as Modulating-Functios, Space-Vectors and Feedback Methods present the disadvantage of high residual harmonics. Selective Harmonic Elimination (SHE) generates trains of pulses such as the fundamental component of the resulting waveform has a specified frequency and amplitude while selected order harmonics are eliminated. To achieve this goal, a set of nonlinear equations must be solved. SHE offers many distinctive features including high quality of the output waveform, low switching frequency at fundamental frequency ratios, possibility to select the harmonics to be deleted and the ability to leave triplen harmonics uncontrolled. On the other side, the main drawbacks of SHE methods are their computational burden and the subsequent need of complicated hardware. This paper proposes a new analytical algorithm for SHE in a 5-level cascaded inverter. The proposed method transforms the trascendental system in a polinomial one resulting that analytical solution can be easy obtained using a typical Digital Signal Controller. The achievable results are demonstrated by both simulation and experimental results.

A Selective Harmonic Elimination Method for Five-Level Converters for Distributed Generation

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.

Selective harmonic elimination in a seven level cascaded multilevel inverter based on graphical analysis

One of the big concerns in power conversion systems is the amount of harmonic content. This paper considers a seven level cascaded inverter and proposes a simple graphical approach, useful to obtain three switching angles which, if applied to the inverter, eliminates two harmonics. The method has been further improved for mitigating some additional harmonics. The effect of modulation index on variation of angles is also investigated and total harmonic distortion (THD) is calculated for selected modulation indexes. The proposed modulation operates at fundamental frequency, which means high inverter efficiency due to reduced power losses. Simulation and experimental results are obtained to show the effectiveness of the proposed procedure.

Performance analysis and simulation of unbalanced DC sources five level inverter topology

The harmonic contents of the output waveform of the power converters is a very important factor in electrical power quality. In this paper a five-level cascaded inverter with unequal DC sources is considered and a selective harmonic elimination technique at fundamental frequency, based on the graphical separation of functions zeros, is considered to reduce total harmonic distortion in the inverter output waveform.

SHE formulation for five level inverters with unequal DC sources

Because of their numerous advantages including high voltage operations and limited harmonics content, multilevel inverters are often used in high power applications. However, dc sources supplying the inverter do not always have the same voltage, thus resulting voltage unbalances and performance deterioration. In order to solve such a problem, this paper proposes a modulation technique based on a harmonic elimination method developed for five level inverters with unequal dc link voltages. The approach is based on the analytical solution of non linear equations associated with the inverter. After a description of the method, an analysis on the computed switching angles and on their impact on total harmonic distortion is reported with the support of simulation results.

A deterministic harmonics mitigation technique for five-level inverters

A deterministic algorithm aiming at reduction of harmonic content in three phase, five-level cascaded inverters is proposed. The procedure starts from a non-linear system consisting of disequations and, using Chebyshev polynomials and Warings formula, for any assigned modulation index computes those switching angles α1 and α2 reducing harmonics amplitude such as to fulfill grid code specifications. Simulation and experimental results demonstrate the achievable results.