Comparação do controle do inversor trifásico conectado à rede com filtro LCL considerando o amortecimento passivo e ativo

Distributed generation systems must fulfill standards specifications of current harmonics injected to the grid. In order to satisfy these grid requirements, passive filters are connected between inverter and grid. This work compares the characteristic response of the traditional inductive (L) filter with the inductive-capacitive-inductive (LCL) filter. It is shown that increasing the inductance L leads to a good ripple current suppression around the inverter switching frequency. The LCL filter provides better harmonic attenuation and reduces the filter size. The main drawback is the LCL filter impedance, which is characterized by a typical resonance peak, which must be damped to avoid instability. Passive or active techniques can be used to damp the LCL resonance. To address this issue, this dissertation presents a comparison of current control for PV grid-tied inverters with L filter and LCL filter and also discuss the use of active and passive damping for different regions of resonance frequency. From the mathematical models, a design methodology of the controllers was developed and the dynamic behavior of the system operating in closed loop was investigated. To validate the studies developed during this work, experimental results are presented using a three-phase 5kW experimental platform. The main components and their functions are discussed in this work. Experimental results are given to support the theoretical analysis and to illustrate the performance of grid-connected PV inverter system. It is shown that the resonant frequency of the system, and sampling frequency can be associated in order to calculate a critical frequency, below which is essential to perform the damping of the LCL filter. Also, the experimental results show that the active buffer per virtual resistor, although with a simple development, is effective to damp the resonance of the LCL filter and allow the system to operate stable within predetermined parameters.

Avaliação de um sistema de resfriamento passivo para o clima de Curitiba

Direct evaporative cooling systems (DECS) based on sprinkling water indoors in the form of droplets and indirect evaporative cooling systems (IECS), characterized by the use of wetted roof or wall surfaces for cooling without increasing the indoor air moisture, consist of interesting bioclimatic strategies still not quite explored in Brazil. This study aims to evaluate the use of a particular form of IECS (which combines evaporative cooling and thermal mass brought about by a water reservoir) for indoor thermal control in warm conditions in Curitiba, Two test cells were initially built, monitored and compared to each other: a control module (CM) and an experimental module (EM), the latter provided with an evaporative pond. A subsequent configuration of the system which cancels out the evaporative function of the system and that is solely based on the increase of thermal mass, was tested in a second monitoring round. A third configuration of EM combinig evaporative cooling and the increase of termal mass was tested. Results showed a higher effectiveness of the IECS for the indoor cooling of the tested cells. The average temperature in EM was reduced in 2.5°C and the maximum temperature was reduced in 8.0°C in comparison with the CM. Results also showed a strong relation between the wet-bulb temperature depression and the internal temperature decrease achieved by the evaporative cooling strategy.