One of the most important cares of the power electronic designer is the reduction of the harmonics created by converters. These harmonics are attenuated by passive elements whose size is directly linked to the frequencies which have to be filtered. For this reason, the technique of Pulse Width Modulation (PWM) is widely used. This principle of modulation does not lead to a reduction of the harmonic distortion factor (THD) of the waveform directly generated by the converter (it even leads to a slight increase of it [1]) but it permits an increase of the frequency of the disturbing harmonics. In this way the size and the weight of the filters associated to the converters can be reduced.
Unfortunately this method introduces some problems: switching losses become more and more important when the frequency increases. So it is necessary to use faster electronic components to obtain quicker commutations. But this choice leads to the generation of very high frequency EMI, due on one hand to quick variations of the electrical values during the commutations [2] and on the other hand to high frequency working [3]. Nowadays these EMI can not be tolerated because of the new EMI standards.
In order to overcome these constraints (without any increase of the filter size) multilevel converters can be used. Actually the converters of this kind are known to generate less harmonics than the classical ones [4]. So it is possible, using multilevel techniques, to reduce the THD of the PWM waveform when an increase of the modulation frequency is not possible anymore.
Unfortunately, as the number of levels increases, the structure becomes more and more complex. This is a drawback which can be lowered in the case of rectifiers: as the bipolar energy flow is needed, structures can be simplified.
This paper deals with a new non-reversible monophase multilevel rectifier using Pulse Width Modulation and drawing up a sinusoidal and in phase mains current [5, 6]. Its working and the constraints involved by this choice are defined. Afterwards, the particular voltage balancing loop and the process of generating semiconductor control signals are studied with the help of a formalism developed in our laboratory [7]. Finally the experimental results, obtained with a 3 kW prototype, confirm the simulation of the model and validate this study.
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