Srikanthan Sridharan with Adviser P. T. Krein
The duality between the two-level voltage sourced inverter (VSI) and the current sourced inverter (CSI) is examined for performance and efficiency enhancement of induction motor drives over wide operating conditions. A loss minimization algorithm is developed using a comprehensive loss model to achieve optimum flux for minimizing system-level drive losses. Total losses obtained are lower for the proposed system-based minimization than for previously reported machine-based minimization algorithms. A minimum-inverter-dc-bus-current technique is devised using the output filter capacitor.Figure 2 shows the optimum flux profiles and the losses obtained for the system and machine-based minimization methods for a fan load. Total loss as a function of flux and filter capacitance is shown in Fig. 3.
The literature reports higher performance for VSI drives than for CSI, but comparisons are not based on identical standards. Because high-frequency pulse-width modulation methods are adopted for VSI and more basic quasi-square pulse or selective harmonic elimination methods for CSI, CSI drives show poor power factor and harmonic distortions in the output. This work adopts comparable standards using space vector pulse width modulation control with a combinational logic map to translate switching pulses from VSI to CSI. Results indicate that comparable efficiencies can be achieved exploiting the functional and topological duality between the VSI and CSI drives.
This research is supported by Rolls Royce account 2012-05196.