Projeto e desenvolvimento de um microinversor buck de elevado rendimento conectado à rede elétrica com filtro LCL

Abstract

Micro-inverters are small single-phase photovoltaic power generation modules that connect directly to a photovoltaic panel and the electrical grid, which typically consist of a DC-DC stage and a DC-AC stage. The topology of the chosen microinverter is DC link, for its simplicity and to ensure that only high frequency current components flow through the DC-DC stage transformer. In this work, a topology of MIC is presented, highlighting the CC-CA stage, where it presents a contribution in the development of microinverters with high energy conversion efficiency. One of the main goals is to reduce losses in the CC-CA stage by using a buck inverter in conjunction with an LCL filter. The buck-type inverter consists of the inclusion of only one switch in series with the H-bridge of switches. In this way, the additional switch is responsible for producing a (always positive) sine wave current that is unfolded by the switches on the H-bridge. Therefore, the system operates with only one highfrequency switch to make the pulse width modulation so that all other bridge inverter switches operate at the network frequency, unfolding. In order to increase the power density, the attenuation of the filter must be increased, reducing both the volume of the components and the losses in the conduction of the same. Based on this, a third-order LCL filter having an attenuation of 60 dB / dec was chosen. Current control uses a multi-resonant controller which tracks the sine-wave reference at 60 Hz and also compensates for current harmonic components present in the multiple frequencies of the 3rd and 5th fundamental. In addition, in order to overcome the stability problems related to the LCL filter response, an active damping loop is proposed, which does not require passive elements or additional sensors to perform the same, which increases efficiency and reduces associated costs to the system. Due to the use of a DC link micro-inverter, an external voltage control grid is implemented to regulate the voltage of the capacitive bus which is composed of a film capacitor instead of an electrolytic capacitor, which tends to increase the useful life of the system. Experimental results of a 200 W prototype demonstrate the feasibility of the proposal. Finally, the comparison between the efficiency of the micro-inverter with active damping and passive damping is evaluated, according to the European efficiency standard.