Development of DC-Biased Enhanced Unipolar Modulation Topology for DC -AC Power Converter-fed Single-phase Induction Motor

Abstract This work presents development of DC-biased enhanced unipolar modulation topology for DC -AC power converter-fed single-phase induction motor. The system is modeled and simulated in MATLAB/Simulink environment to single-phase induction motor. It presents a comparative analysis on the output parameters with the inverter fed of the same induction motor. The proposed approach on triggering multilevel DC-AC power switches is based on an enhanced unipolar modulation scheme. This scheme consists of two modulating signals phase-shifted at180 degrees from each other and two DC-biased triangular carriers that were combined to generate firing signals. The outcome of the comparison between the carriers and reference sinewave produces switching signals used for firing the switches of conventional single-phase full bridge diode-clamped multilevel inverter. This scheme was designed to reduce the number of carrier waves and minimize the overall modulation circuit to obtain a stabilized output voltage waveforms. Unlike the conventional multicarrier sinusoidal pulse width modulation that uses four triangular waves and one modulating sine wave for the same inverter type, the proposed system has only two triangular waves and two reference sinewaves. This means that the proposed system has total of 4 while conventional modulations have 5. The proposed modulation scheme has advantages of reduced number of components therefore reduced cost of implementation and can easily be packaged. It also possesses all its carrier waves operating in continuous current mode which makes it unique from other multicarrier and other related modulation schemes. Output voltage of 200V and current of 20A with corresponding total harmonic distortions of 0.4075% and 0.2509% at Frequency of 50Hz with the output power of 4kw were the results obtained from the simulation and that was validated with experimental prototype. And the practical wave forms were displayed.