M. Sidrach-de-Cardona

Multiplicative ARMA models to generate hourly series of global irradiation

A methodology to generate hourly series of global irradiation is proposed. The only input parameter which is required is the monthly mean value of daily global irradiation, which is available for most locations. The procedure to obtain new series is based on the use of a multiplicative autoregressive moving-average statistical model for time series with regular and seasonal components. The multiplicative nature of this models enables us to capture the two types of relationships observed in recorded hourly series of global irradiation: on the one hand, the relationship between the value at one hour and the value at the previous hour; and on the other hand, the relationship between the value at one hour in one day and the value at the same hour in the previous day. In this paper the main drawback which arises when using these models to generate new series is solved: namely, the need for available recorded series in order to obtain the three parameters contained in the statistical ARMA model which is proposed (autoregressive coefficient, moving-average coefficient and variance of the error term). Specifically, expressions which enable estimatation of these parameters using only monthly mean values of daily global irradiation are proposed in this paper.

Comparative analysis of buck-boost converters used to obtain I–V characteristic curves of photovoltaic modules

In this paper, the usefulness of several topologies of DC-DC converters for measuring the characteristic curves of photovoltaic (PV) modules is theoretically analyzed. Eight topologies of DC-DC converters with step-down/step-up conversion relation (buck-boost single inductor, CSC (canonical switching cell), Cuk, SEPIC (single-ended primary inductance converter), zeta, flyback, boost-buck-cascaded, and buck-boost-cascaded converters) are compared and evaluated. This application is based on the property of these converters for emulating a resistor when operating in continuous conduction mode. Therefore, they are suitable to implement a system capable of measuring the I-V curve of PV modules. Other properties have been taken into account: input ripple, devices stress, size of magnetic components and input-output isolation. The study determines that SEPIC and Cuk converters are the most suitable for this application mainly due to the low input current ripple, allow input-output insulation and can be connected in parallel in order to measure PV modules o arrays with greater power. CSC topology is also suitable because it uses fewer components but of a larger size. Experimental results validate the comparative analysis.

Different methods to obtain the I–V curve of PV modules: A review

In order to characterize photovoltaic devices a procedure to measure I–V curves is required. The main methods used to perform this task are reviewed. It is shown that at least six distinct methods have been reported in the literature with many variations in implementation. A detailed comparison taking into account typical parameters for measuring systems is accomplished. This paper could be used as a reference for future work on photovoltaic module characterization.

Characterization and simulation of hourly exposure series of global radiation

A statistical model which captures the main features of hourly exposure series of global radiation is proposed. This model is used to obtain a procedure to generate radiation series without imposing, a priori, any restriction on the form of the probability distribution function of the series. The statistical model was taken from the stationary stochastic processes theory. Data were obtained from ten different Spanish locations. As monthly hourly exposure series of global radiation are not stationary, they are modified in order to remove the observed trends. A multiplicative autoregressive moving average model with regular and seasonal components was used. It is statistically accepted that this is the true model which generates most of the analyzed sequences. However, the underlying parameters of the model vary from one location to another and from one month to another. Therefore, it is necessary to examine further the relationship between the parameters of the model and the available data from most locations.

A New Application of the Buck-Boost-Derived Converters to Obtain the I-V Curve of Photovoltaic Modules

A new experimental way to measure the I-V characteristic curve of a solar cell, module or photovoltaic generator by using Buck-Boost-Derived DC-DC converters is proposed. Theoretical analysis shows that the optimal topologies for this purpose are the SEPIC (Single-Ended Primary Inductance Converter) and Cuk converter. The advantages of this method are described, and experimental results show its usefulness.

An application of interleaved DC-DC converters to obtain I-V characteristic curves of photovoltaic modules

The basic operation of a solar cell, module or photovoltaic generator under different irradiation and temperature conditions is characterized by its I-V characteristic curve. Only the experimental measurement of the I-V curve allows us to know the electrical parameters of a photovoltaic cell, module or array. This measure provides very relevant information for the design, installation and maintenance of photovoltaic systems. Currently, the I-V characteristic curve is obtained by connecting a variable charge to the panel terminals in order to achieve that the current of the terminals ranges from zero to the short circuit current. In this paper, a new experimental methodology to measure this characteristic curve by using several SEPIC converters in parallel connection operating in interleaved mode is proposed. This methodology provides two fundamental advantages for this application as regards the use of a single converter: (1) It allows to reproduce I-V curves of higher power (2) It allows to obtain these curves with lower ripple.

Using probabilistic finite automata to simulate hourly series of global radiation

Abstract A model to generate synthetic series of hourly exposure of global radiation is proposed. This model has been constructed using a machine learning approach. It is based on the use of a subclass of probabilistic finite automata which can be used for variable-order Markov processes. This model allows us to represent the different relationships and the representative information observed in the hourly series of global radiation; the variable-order Markov process can be used as a natural way to represent different types of days, and to take into account the “variable memory” of cloudiness. A method to generate new series of hourly global radiation, which incorporates the randomness observed in recorded series, is also proposed. As input data this method only uses the mean monthly value of the daily solar global radiation. We examine if the recorded and simulated series are similar. It can be concluded that both series have the same statistical properties.

An approach to obtain the V-I characteristic of fuel cells by means of DC-DC converters

This paper proposes a new approach to test and evaluate V-I characteristics of fuel cells stacks based on DC-DC converters, which features are simple structure, scalability, fast response and low cost. The measurement of the desired characteristic of fuel cells includes high speed of response, high fidelity and low cost. The obtained results show that all DC-DC topologies are not capable of reproducing this characteristic and that SEPIC (Single-Ended Primary Inductance Converter) converter is optimal for this application. Experimental results show the usefulness of the proposed method.

A New Method to Obtain I-V Characteristics Curves of Photovoltaic Modules Based on SEPIC and Cuk Converters

Abstract The basic operation of a solar cell, module or photovoltaic generator under different irradiation and temperature conditions is characterized by its I-V characteristic curve. Only the experimental measurement of the I-V curve allows us to know with precision the electrical parameters of a photovoltaic cell, module or array. This measure provides very relevant information for the design, installation and maintenance of photovoltaic systems. Currently, the I-V characteristic curve is obtained by connecting a variable charge to the panel terminals in order to achieve that the current of the terminals ranges from zero to the short circuit current. In this paper we propose a new experimental way to measure this characteristic curve by using Buck-Boost-Derived DC-DC converters. It has been proved that the optimal topologies for this purpose are the SEPIC (Single-Ended Primary Inductance Converter) and Cuk converters. The theoretical analysis performed has been validated by means of simulation and experimentally. Additionally, a comparison between three known conventional methods and the proposed one is provided.

A new application of Duty Cycle Sweep based on microcontroller to obtain the I-V characteristic curve of photovoltaic modules

This paper gives a general approach to the development of duty cycle sweep (DCS) in fixed switching frequency pulse width modulated (PWM) strategies based on microcontroller. The flexibility of the PWM signal generated is characterized by: 1) Fixed duty cycle or variable between 0% and 100%. 2) Duty cycle sweep in both directions: increase from 0% to 100% and decrease from 100% to 0%.3) duty cycle sweep between intervals (30% to 50%, etc) with a precision of until 0.5%. Experimental results show that these properties are adequate to control a DC-DC converter and reproduce the I-V curve of photovoltaic (PV) modules.