Current control of three level neutral point clamped voltage source rectifiers using selective harmonic elimination

The growing availability of high power semiconductor devices and the increasing necessity of high power converters in power systems and industry applications demand the use of multilevel converters topologies, such as the 3-level neutral point clamped voltage source converter. The tradeoff in designing this kind of converter is between switching losses and fast dynamic control. The size and cost of passive filters is also an important technological barrier, mainly when dealing with active rectifiers. Among the well-known pulse width modulation strategies, selective harmonic elimination (SHE) techniques has proven their advantages in producing the lowest harmonic content waveform for a low switching frequency. The main drawbacks of these methods are the assumption of steady-state conditions for switching angles calculation and the storage of switching angles' tables of considerable size. This paper deals with these two issues by proposing the application of the correlation factor method to reduce these tables, analyzing the frequency response of the modulator and implementing a current control scheme in dq frame. These methodologies are also applied to a true unity power factor (TUPF) rectifier which eliminates the use of input filters. Simulation results show the efficiency of these proposals.

I. Introduction

The use of three phase power converters has already become common in industry applications and power systems applications, e.g. motor drives, converters for wind turbines, etc. Among all types of converters available, the more common in use is the voltage source converter (VSC). High power converters, otherwise were introduced quite early employing current source converters (CSC) due to the limitations of the power electronic switches available at the beginning (thyristor for instance) [1].