Adriano J. Longo

Stand alone self-excited induction generator with reduced excitation capacitors at fixed speed

This paper proposes a reduction of the self-excitation capacitance of induction generators by using an associated Two-Stage Matrix Converter (TSMC). This association regulates load frequency and load voltage in addition to an improved generated voltage. The resistive load affects the self-excited induction generator (SEIG) voltage, but inductive loads cause poor regulating voltage. This trend is due to the opposition between the inductive load reactance and the reactance of the self-excitation capacitors. The TSMC supplies a sinusoidal current with reduced harmonic content. Thus, the matrix converter operates as a resistive load across the IG terminals, improving regulation of the generated voltage. In this text it is included some simulation results of a 1 kW SEIG dynamic model connected either directly to the load or through the TSMC. The simulations are compared with the TSMC prototype for a similar induction machine to prove the effectiveness of the proposed control.

Improved analytical solution to obtain the MPP of PV modules

This paper proposes a mathematical model to obtain an improved analytical determination of the maximum power point (MPP) of silicon photovoltaic panels. The MPP is obtained by considering the 5-parameter PV model to calculate the derivative of the PV panel output current with respect to its output voltage including the shunt and series resistors. Theoretical results are compared to experimental field data to demonstrate the accuracy improvements with respect to lab measurements. Finally, with this model is possible also to observe and predict more accurately the efficiency of photovoltaic panels for the various conditions of load, temperature and solar radiation.

Instrumentation for surface geothermal data acquisition aiming at sustainable heat exchangers

This work discusses the development of a standard multisensor arrangement on a five-meter long rod to be vertically buried underground, using digital temperature sensors. With this purpose, it was assembled a dedicated data acquisition board to allow continuous measurements of the vertical temperatures underground profile of the soil in Santa Maria-RS from Sep 2013 to Jul 2014. It was observed that the soil temperature decreases as the depth increases. In addition, the temperature of the soil tends to become constant with an increasing depth, converging to the average value of the temperature for the location in analysis. The results show that the soil temperature at the depth of five meters, measured in the experimental campus CEESP, varies between 19 °C and 22 °C. During this period, extremes of the ambient temperatures were below 0 °C and above 40 °C and them presented phase delays along the year.

Reduction of electrical load for air conditioning by electronically controlled geothermal energy

This paper describes the design steps of a geothermal system for air conditioning to reduce electricity consumption in residential and small business ambient. To do that it is used surface geothermal energy as one of the heating sources. The geothermal surface is renewable, clean, universal, silent and odorless relying on the circulation of a refrigerant within a pipe hose buried with the aid of a very small size pump, so that the earth absorbs heat in the summer and supplies it to the rooms in the winter. There is a controlled exchange of heat between the one removed from the grounds by a water circulating radiator and a room ventilation system. That is, if the temperature inside the building is above the earth temperature it will tend to level off the temperature with that from ground. A prototype of heat exchanger and electronic control system without any heat pump was built using a hill climbing algorithm to optimize the water pump speed and this heat exchanging system.

Economical Feasibility of Photovoltaic Array Power Increase by Alternative Structures Inclusion

Abstract Photovoltaic panel prices reduced last years. However, module cost per kWh is still expensive when compared with other energy sources. This paper discusses an economic analysis of photovoltaic arrays modified by alternative structures to increase their output power. These structures include increased incident irradiance by solar trackers and/or sun irradiance concentration enhanced by reduction of power losses caused by higher temperatures. Although, modules increased efficiency may demand for more expensive systems. Thus, study cases are presented considering each alternative structure used for photovoltaic power generation increase.

Surface geothermal energy applied to low cost and low power consumption residential air conditioning

The operation of an air-conditioning system, completely powered by geothermal energy, with no other external energy input and no heat pump is described in this paper. This geothermal system can contribute to the reduction of electricity consumption in residences and small businesses, and can retrofit any installation, since it is a surface geothermal energy installation. That is possible because soil temperature, to a certain depth, has a constant temperature throughout the year, with a large mass and heat capacity. Practical tests can be easily conducted with water and underground heat exchangers. This system is designed with a coolant circulating within a serpentine driven by a small hydraulic pump. If the temperature inside the residence is lower or higher than the soil temperature, there is heat exchange between the residence ambient and the soil. Therefore, the surface geothermal energy is used to warm-up or cool-down the room ambient. The prototype described in this paper was implemented with an electronic control to maximize the performance of the heat exchangers. Experiments were made during four months in the winter and in the summer.