Ernesto Ruppert Filho

Comprehensive Approach to Modeling and Simulation of Photovoltaic Arrays

This paper proposes a method of modeling and simulation of photovoltaic arrays. The main objective is to find the parameters of the nonlinear I-V equation by adjusting the curve at three points: open circuit, maximum power, and short circuit. Given these three points, which are provided by all commercial array data sheets, the method finds the best I-V equation for the single-diode photovoltaic (PV) model including the effect of the series and parallel resistances, and warranties that the maximum power of the model matches with the maximum power of the real array. With the parameters of the adjusted I-V equation, one can build a PV circuit model with any circuit simulator by using basic math blocks. The modeling method and the proposed circuit model are useful for power electronics designers who need a simple, fast, accurate, and easy-to-use modeling method for using in simulations of PV systems. In the first pages, the reader will find a tutorial on PV devices and will understand the parameters that compose the single-diode PV model. The modeling method is then introduced and presented in details. The model is validated with experimental data of commercial PV arrays.

Modeling and circuit-based simulation of photovoltaic arrays

This paper presents an easy and accurate method of modeling photovoltaic arrays. The method is used to obtain the parameters of the array model using information from the datasheet. The photovoltaic array model can be simulated with any circuit simulator. The equations of the model are presented in details and the model is validated with experimental data. Finally, simulation examples are presented. This paper is useful for power electronics designers and researchers who need an effective and straightforward way to model and simulate photovoltaic arrays.

A Predictive Power Control for Wind Energy

The doubly fed induction generator (DFIG) is widely used in wind energy. This paper proposes a model-based predictive controller for a power control of DFIG. The control law is derived by optimization of an objective function that considers the control effort and the difference between the predicted outputs (active and reactive power) and the references. The prediction was calculated using a linearized state-space model of DFIG. As the generator leakage inductance and resistance information were required for this control method, the influence of the estimation errors for these parameters was also investigated. Simulation results are presented to validate the proposed controller.

Model-Based Predictive Control Applied to the Doubly-Fed Induction Generator Direct Power Control

This paper proposes a model-based predictive controller for doubly-fed induction generator direct power control. The control law is derived by optimization of an objective function that considers the control effort and the difference between the predicted outputs (active and reactive power) and the specific references, with predicted outputs calculated using a linearized state-space model. In this case, the controller uses active and reactive power loop directly for the generator power control. Because the generator leakage inductance and resistance information were required for this control method, the influence of the estimation errors for these parameters was also investigated. Simulation results are carried out to validate the proposed controller.

Dynamic analysis of the input-controlled buck converter fed by a photovoltaic array

The control of the input voltage of DC-DC converters is frequently required in photovoltaic applications. In this spe cial situation, unlike conventional converters, the output vol tage is constant and the input voltage is controlled. This paper deals with the analysis and the control of the buck converter with constant output voltage and variable input.

Fault Current Limiter Using YBCO Coated Conductor—The Limiting Factor and Its Recovery Time

A fault current limiter (FCL) based on an arrangement of parallel connected high temperature superconducting tapes constituting a limiter element was designed and tested in 220 V line for a fault current peak between 1 kA to 2 kA. The limiter employed second generation (2G) HTS tapes of YBCO coated conductor reinforced with stainless steel. Four tapes were electrically connected in parallel with 0.4 m effective length per element wherein 16 elements connected in series constitutes a single-phase unit. The FCL performance was evaluated through over-current and current fault tests. Its recovery characteristics were used to design the shunt protection. The designed limiting ratio is 4 for 16 elements and the experimental result for one element showed a 20% limiting ratio. For the fault current test one element can withstand five cycles of fault without degradation. It was observed recovery times below 0.5 s under nominal load using a shunt resistance of 173 mOmega.

A control method for voltage source inverter without dc link capacitor

Voltage source inverter plays an important role in modern industry. Conventional voltage source inverter has a large electrolytic capacitor as energy store element in order to keep the dc link voltage constant. However, a large electrolytic capacitor increases the input current distortion. Replacing the large electrolytic capacitor by a small film capacitor the input current quality is improved but the output currents are distorted by low order harmonics. This paper proposes a simple current control method for a voltage source inverter without the use of a large electrolytic capacitor in the dc link in order to compensate the low order harmonics in the output currents. The proposed current control scheme employs just one PI regulator and since that the space vector modulation is used in this control the switching frequency of the converter is kept constant.

Evaluation of Electrical Properties of Lap Joints for BSCCO and YBCO Tapes

The joint process between tapes of coated conductors is a critical issue for the most of the applications of high temperature superconductors (HTS). Using different fabrication techniques joints of YBCO coated superconductors were prepared and characterized through electrical measurements. For soldering material low melting point eutectic alloys, such as In-Sn (m.p. 116degC) and Sn-Pb (m.p. 189degC) were selected to prepare lap joints with effective length between 1 to 20 cm. The splice resistance and the critical current of the joints were evaluated by I-V curve measurements with the maximum current strength above the critical current, in order to evaluate the degree of degradation for each joint method. Pressed lap joints prepared with tapes without external reinforcement presented low resistance lap joint nevertheless some critical current degradation occurs when strong pressing is applied. When mechanical pressure is applied during the soldering process we can reduce the thickness of the solder alloy and a residual resistance arises from contributions of high resistivity matrix and external reinforcement. The lap joints for reinforced tape were prepared using two methods: the first, using ldquoas-suppliedrdquo tape and the other after reinforcement-removal; in the latter case, the tapes were resoldered using Sn-Pb alloy. The results using several joint geometries, distinct surface preparation processes and different soldering materials are presented and analysed. The solder alloy with lower melting point and the longer joint length presented the smallest joint resistance.

Detailed implementation of a current controller with 3D space vectors for four wire active filters

This research presents the detailed implementation of a current controller with three-dimension (3D) space vector pulse width modulation (SVPWM) for active filters used in four-wire unbalanced power systems. Many techniques of current control are widely known for three-wire balanced systems. However some modifications must be done in the original techniques when the system is unbalanced and has a neutral conductor. Few works are explicit and detailed on this subject. This paper shows the complete process of implementation of a four-wire current controller with a three-leg inverter and makes a comparison of its performance with the performance of the conventional hysteresis-based current controller.

Test of a Modular Fault Current Limiter for 220 V Line Using YBCO Coated Conductor Tapes With Shunt Protection

A modular superconducting fault current limiter (SFCL) consisting of 16 elements was constructed and tested in a 220 V line for a fault current between 1 kA to 7.4 kA. The elements are made up of second generation (2G) YBCO-coated conductor tapes with stainless steel reinforcement. For each element four tapes were electrically connected in parallel with effective length of 0.4 m per element, totaling 16 elements connected in series. The evaluation of SFCL performance was carried out under DC and AC tests. The DC test was performed through pulsed current tests and its recovery characteristics under load current were analysed by changing the shunt resistor value. The AC test performed using a 3 MVA/220 V/60 Hz transformer has shown the current limiting ratio achieved a factor higher than 10 during fault of up to five cycles without conductor degradation. The measurement of the voltage for each element during the AC test showed that in this modular SFCL the quench is homogeneous and the transition occurs similarly in all the elements.