Inversor Push-Pull não isolado com autotransformador

Abstract

This work presents a novel non isolated voltage source inverter (VSI) topology using an autotransformer, which provides an ac output voltage whose rms value is twice the one provided by a conventional half-bridge inverter considering the same modulation index. As advantages, there is the fact that the converter uses only one DC voltage source, the SPWM (Sinusoidal pulse width modulation - sinusoidal PWM modulation) modulation can be applied in the control of the switches and as these are in the same reference, it is used more simplified non-isolated control circuits, it has a PWM voltage at the output equal to twice the input voltage and uses only two switches. With disadvantages we have the asymmetry in the windings of the autotransformer that cause an undesired DC level in the magnetic flux of the core, leading to saturation. Additionally, we have voltage spikes in the switches when turned off, due to the action of the dispersion inductance present in the autotransformer. In a steady state, the reverse voltage on the switches will be twice the DC supply voltage, being recommended for low voltage applications. A low-pass LC filter is connected at the inverter output to provide a nearly sinusoidal voltage with low harmonic content. The qualitative and quantitative analyzes of the proposed converter are presented in detail, from which it is possible to design and analyze it. Simulation and experimental results are presented and discussed through a prototype with nominal power of 100 W, input voltage of 40 V, voltage in the inductors of the 80 V autotransformer, effective output voltage of 56.57 V, switching frequency of 20 kHz and cut-off frequency designed for the 2 kHz LC output filter. This aims to validate theoretical considerations and identify the main advantages and disadvantages of this topology.