F. T. Fernandes

Variable speed wind turbine using the squirrel cage induction generator with reduced converter power rating for stand-alone energy systems

This paper presents a new configuration for a wind energy conversion system (WECS) with variable speed, using a squirrel cage induction generator (SCIG) for stand-alone energy system applications. The Proposed configuration utilizes converters with reduced power rating, operates with MPPT to maximum wind energy extraction, uses battery bank for energy storage and can operate with non-linear and unbalanced loads. Energy storage characteristic is desirable for wind energy conversion systems isolated from the mains since an energy interruption does not stop of the entire system. Also, the power rating of the converters is reduced compared to the generator and load power rating due to the low power requirements of the power converters to SCIG excitation control and to supply the load. It is presented also the whole proposed WECS and the system operation modes according the turbine speed. It is presented also the whole proposed system and the system operation modes according the turbine speed. The simulation of the proposed WECS is performed in conjunction with the dynamic wind turbine model of 1 kW and the results confirm the effectiveness to supply unbalanced and non-linear loads, the converters power rating reduction and operation with variable turbine speed. Simulation results show the effectiveness of the system to supply unbalanced and non-linear stand alone loads.

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.

FC and PV emulation by buck converter based on experimental VxI curves and dynamic response

This paper presents an emulation of fuel cell and photovoltaic modules based on the buck converter as a replacement of actual power sources for bench tests. This approach is suitable for power electronic designs involving power converters to interface source and DC loads or source and mains grid, without having available the real source. The output voltage of the buck converter is referred to lookup tables/equations with experimental data from actual sources under load variation to determinate the biasing curves and dynamic response. To validate the results, a comparison between simulated and practical results obtained from laboratory test with actual sources is performed. The energy source emulations with buck converters is a simple, safe, versatile, and effective way of physically representing DC sources for various laboratory tests.

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.

Integration of alternative sources of energy as current sources

This work proposes an integration of alternative energy sources having the different generating modules connected as current sources. These sources were configured to inject current into a common DC bus. This feature avoids current circulation among sources due to the voltage differences, reducing the stress in the individual generators. A battery bank is a system part, used as an energy accumulator for periods when there is primary energy depletion. The bus voltage is controlled by modulation of a secondary load in parallel with the main load. A DC-DC Boost converter connects each primary source to a common bus, except for the storage system that uses a DC-DC Buck-Boost converter. Finally, it is presented a mathematical analysis through simulated results to show the sources behavior and overall performance when turned into current sources.