Abstract
This paper proposes an efficient PWM modulation method in a three-phase PWM inverter which optimally reduces switching (SW) losses for one switch cycle according to the two-phase modulation. It selects the optimum switching vector (SV) pattern on-line which minimizes an estimation function based on switching losses considering phase currents among possible reduction patterns for one switching cycle. The estimation is composed of two types of SW losses. The first one is a PWM SW loss due to the two-phase modulation composed of three SVs for one switch cycle. The second one is a transition loss between one of six switch modes from I to VI to another. The proposed SW loss estimation is defined as ol-line subtraction of the first loss saving from the second loss locally for one switching cycle. The optimum switch pattern (SP) is defined as one with the lowest estimation and it can reduce SW losses most effectively. The proposed optimum PWM principle was experimentally investigated for output voltages of the two-level and three-level inverters connected with an universal load. It reduced number of switching times of the largest or secondly largest current. It can automatically adapt to various conditions of current amplitudes which are dependent on power factors of loads.
