A New Design of Selective Harmonic Elimination for Adjustable Speed Operation of AC Motors in Mining Industry

This paper presents an appropriate design of selective harmonic elimination for a high performance adjustable speed operation of ac motors in mining industry. These motors are normally old machines and/or fed by long cable and require pure sinusoidal voltages. A passive filter is employed between the machine and a three-level NPC converter. Owing to its higher frequency band free of harmonics the selective harmonic elimination was chosen to command the converter. Therefore it is required the operation of selective harmonic elimination in variable fundamental frequency conditions. It then brings the noneliminated harmonics to the low frequency region. A new design of selective harmonic elimination consists of a technical criterion of changing the set of pulse pattern in a more economical way in order to maintain the low frequency harmonic content far from the fundamental frequency range still keeping high system efficiency, fast acceleration and less torque pulsation and feasible digital implementation. The technical criterion also simplifies the passive filter design letting enough space to allocate cutoff and resonant frequencies inside the band free of harmonics. All the discussion of this work is supported by simulation and experimental results of a prototype which is aimed to confirm the feasibility of the above ideas.