Nistor Daniel Trip

Increase of the Efficiency for a Solar Renewable Source Using a Soft Switched DC-DC Boost Converter

An important role in the solar renewable energy sources play a DC-DC power converter that transforms the electric energy provided by a photovoltaic (PV) system in DC energy to be used for DC loads or to be stored in high capacity battery. This paper presents a new type of active snubber for DC-DC boost converters that can be used in solar renewable sources. The main purpose of this new circuit is to assure a soft turn-off switching of the power switch in a switched mode boost power supply. The efficiency of the switched mode power supply is negatively influenced by the hard switching of its power semiconductor devices. This effect is easier observed in power supply that uses IGBTs as main power switches. The active snubber presented in this work offers a soft switching at the turn-off of the IGBT. The whole energy accumulated by the proposed snubber in the first part of an operation cycle is transferred to the load in the last part of the operating cycle. The simulation results are in very good agreement with the theoretical analysis of the active snubber. This paper also presents experimental results that validate the discussed operation principle.

A geothermal thermo-electric energy converter for charging lithium-ion battery

The paper analyzes the optimal conditions for thermal power conversion system. Geothermal water source heat and thermo-electrical conversion is performed with cells TEG (thermo electric generators) based on the Seebeck effect. This study developed in the frame of a national research project is useful for ensuring the energy conversion in conjunction with storage Li-Ion battery. Design method uses Matlab-Simulink program and can be generalized for various thermo-electric cells. Batteries inserted into the simulation scheme can be modified by constructive parametric values. Software solution developed can be extended to numerous applications with efficient electronic conversion. Implemented electronic converter has high efficiency as an integrated electronic structure.

Considerations on the use of thermoelectric generators at low temperatures to recover waste geothermal energy

This paper presents considerations on the possibility to use thermoelectric generators at low temperatures to recover waste heat recovery applications, especially from geothermal energy. Thermoelectric generators have a satisfactory efficiency, when they are usually used in conditions with high gradient of temperatures. However, there are many applications, which lose important quantities of energy even at low temperatures, in the order of tens of degrees. To evaluate the operation of a thermoelectric generators modules set, the authors have realized an experimental prototype and investigate its electrical output characteristic at low temperature differences. The purpose of this study was to investigate the possibility to obtain electricity, into an isolated place, but with practical possibility to assure temperature gradients.

Considerations on efficiency increase for power electronic circuits that interconnect renewable energy sources to the grid

This paper presents some considerations regarding the efficiency increase for a circuit that assures the interconnection of a renewable energy source that produces electricity to the grid. The authors use as a link between the renewable source and the grid a quasi-resonant zero current switching half wave buck converter, in order to decrease the switching losses for the main switch of the circuit and to improve the overall efficiency of the system. The simulation results confirm the operation of the circuit proposed by the authors.

DSP based interconnection circuit of the renewable energy sources to a smart grid

This paper presents general considerations on a DSP based control circuit that can be used to connect different types of renewable energy sources that supply electrical energy into a smart grid, where the droop control method is involved for an efficient energy management. The main purpose of the circuit is to control the amount of energy transferred from the renewable energy sources to the smart gird, following in the same time and taking into account the smart grid frequency. When the management system of the smart grid uses droop control technique to allow the activation of different renewable energy sources connected to the grid, the grid frequency shift is small. In order to determine with high accuracy the smart grid frequency and also to assure a proper PWM control of the power inverter, the authors take into considerations a digital signal processor that offer to this problem a convenient practical solution.

Considerations on the use of a MPPT circuit for a thermoelectric generator

This paper presents some considerations on the use of a Maximum Power Point Tracking circuit for a thermoelectric generator. The authors present experimental results obtained with a thermoelectric generator that comprises an array of thermoelectric generation modules used then to model and simulate a circuit that extracts the maximum output electric power for a low temperature difference range. The circuit that assures an interface between thermoelectric generator and a DC load is a boost switched mode power supply. This paper do not cover the stabilization of the output voltage or current of the power supply, but emphasize on the match between output resistance of the TEG array and the input of the switched mode power supply. The paper presents also a set of simulation results that shown the operation mode of the proposed circuit.

An photovoltaic system tester with three-phase off-grid supply

The system is designed dimensioning the area with photovoltaic panels, in conditions of available consumer in a house. The MPPT (Maximum Power Point Tracking) algorithm ensures efficiency and is included in Boost converter. At the output, there is used a multi-level inverter which forms a three-phase supply off-grid.

Thermal treatment of ferromagnetic pieces at medium frequency

The paper is a continuation of the research reported by the authors regarding the eddy-current heating analysis of a ferromagnetic piece heating equipment. The previous results were dedicated to circular conductors, whereas, in the present paper bars of any the cross-section shape are considered. The electromagnetic field depth of penetration being sufficiently small in comparison with the other geometrical dimensions of the bar, we will take into account only a zone in the vicinity of the bar surface, having a thickness of five times the depth of penetration. Along this depth, the problem is one-dimensional and a combined numerical and analytical approach will result in an extremely efficient procedure for the analysis of the electromagnetic field problem coupled with the thermal diffusion one.

A geothermal generator for grid greenhouse electrical power generator for supplying microgrid

For the integration of more renewable energy in a micro-grid greenhouse we have conducted a research for geothermal energy conversion into electricity. Thermal energy conversion uses a steam turbine providing mechanical torque on the shaft of a permanent magnet synchronous motor. Electronic conversion of alternating current to continuous current is performed with conventional modules. Finally, an inverter controlled by electronic management system will ensure stable values for electricity supply grid in single-phase system at European standards. We used real data available of the geothermal source and the real parameters of the electronic components for testing in simulation.