Reducing the Harmonics Level in a Three-Level Single-Phase Autonomous Inverter without Pulse-Width Modulation

Abstract

An autonomous multilevel single-phase inverter with no applied pulse-width modulation (PWM) and capacitive voltage dividers, the output voltage curve of which is close to a sine-wave shape and corresponds to the contemporary standards of electrical energy quality for 0.38-kV networks is considered. As compared with inverters with the use of PWM, the proposed inverter, owing to the use of low switching frequencies for power semiconductors at a level of the industrial frequency of 50 Hz and due to the optimal use of different-level amplitudes, should not generate significant electromagnetic interference and not cause accelerated wear in the insulation of connected equipment. Studies that have been performed with mathematical and physical models have demonstrated the potentiality of obtaining a voltage with a permissible harmonic coefficient at a level of K_HU amounting to about 6.36% for 0.38-kV networks with the use of a three-level autonomous inverter constructed based on a three-core magnetic circuit of the transformer with a passive LC filter containing a sequential resonant circuit.