An Optimal ADPWM Based DTC Induction Motor Drive for Reduced Line Current Distortion During High Speed Operations

This paper presents an optimal advanced discontinuous pulse width modulation (ADPWM) based direct torque control (DTC) technique for the induction motor drives operating at high line side voltages. Unlike the existing discontinuous pulse width modulation (DPWM) methods the proposed ADPWM method uses a special category sequences which not only reduces the switching losses but also reduces the line current distortion during high speed operations. The known sequences of this category are 0121 and 7212. This category of DPWM sequences are referred as double switching clamping sequences as they switch individual phase twice in every sub cycle. It can be observed that only the zero state is different in these two sequences. In this paper it is shown that utilizing these two double switching DPWM sequences and by changing the zero state at any spatial angle alpha = gamma where gamma is between 0(0) and 60(0) an infinite number of ADPWM methods can be generated which are categorized as "continual clamping" and "split clamping" sequences. Also, the proposed method will be compared both analytically and through simulation. It will be shown that the proposed ADPWM method is most suilable for the drives operating near rated speedy (voltages) as steady state line current distortion at higher line side voltages is reduced significantly compared with the conventional DTC (CDTC), conventional space vector pulse width modulation (CSVPWM) based DTC as well as the existing DPWM based DTC. Copyright (C) 2009 Praise Worthy Prize S.r.l. - All rights reserved