Efficiency analysis of electrical vehicle drive circuit with high resolution

Ever increasing demand for energy along with the scarcity of energy resources has given an impetus to studies focusing on energy efficiency in various areas including transportation sector. It is known that the electric motors exhibit significantly higher efficiencies than the internal combustion engines. In parallel with this fact, the electric vehicles have started to draw wide attention. An electric vehicle is mainly composed of a battery pack and an electric motor which is powered and controlled by a DC-AC converter (inverter). In this thesis, conducted within the context of TUBITAK 1003 project, an inverter circuit is designed to control three-phase induction machine. Moreover, the efficiency analysis of the designed inverter circuit is also carried out. Inverter, in which semiconductor switches such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used, is a power electronic circuit that transforms the direct current (DC) into the alternating current (AC). Semiconductor switches are commonly controlled by high frequency pulse width modulation technique which allows obtaining an AC voltage with the desired amplitude and frequency. Since semiconductor switches used in inverters are not ideal, inevitable losses take place during the conduction and switching instants in case of hard switching. In addition to switching losses, challenges arise from the wide frequency spectrum of the output current and voltage waveforms as a result of pulse width modulation. Therefore, accurate measurement of the inverter efficiency becomes a major problem in such inverter circuits. In power electronic systems, efficiency measurements are performed by using electrical input-output method, power analyzer and calorimeter system. Power analyzers that are capable of measuring the efficiency with minimum error rate are very expensive. On the other hand, calorimeter systems are costly and occupy large space; furthermore, they result in extended measurement duration. In this study, a digital system for efficiency measurement is established by using a DAQ card with high sampling frequency. The established measurement system is capable of obtaining the efficiency of the inverter accurately by measuring the sampled current and voltage components with high frequency (approximately 125 times of switching frequency). According to the test results and cost analysis given in this thesis, it can be stated that the proposed system presents several superiorities such as higher sampling rate and more sensitive measurement compared to power analyzer use and offers a more cost-effective solution.