E. Durán

Analog Current Control Techniques for Power Control in PEM Fuel-Cell Hybrid Systems: A Critical Review and a Practical Application

This paper presents a prototype of a proton exchange membrane (PEM) fuel-cell hybrid system, with a bus connection set by a dc battery bank and all the power electronics and control needed to manage the system. The system power control is based on analog current control. To choose the topology of the controller, a critical review of all the topologies of analog current controllers for dc/dc converters has been done. This review was necessary because there is no literature found that shows a similar compilation. In the experimental part, the proper functioning of the controlled hybrid system is reflected on one hand and the way to solve the known problem of starvation on the other hand. A very important aspect of the system is its scalability. It can be developed in parallel to implement a whole system that handles power levels higher than the rate power of each single fuel-cell system.

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.

A new approach to obtain I-V and P-V curves of photovoltaic modules by using DC-DC converters

The achievement of I-V and P-V curves of photovoltaic modules gives the possibility of obtaining their characteristic parameters: the short-circuit current (I/sub sc/), the open-circuit voltage (V/sub oc/), the maximum power point (MPP) and the fill factor (FF). These values are significant for the design of a photovoltaic system. These curves depend on the global irradiance (G), the temperature (T) and the spectral distribution of the solar irradiation. In this paper, a new methodology to determine the afore mentioned curves by using DC-DC converters is proposed. This methodology allows carrying out the complete sweep of the voltage and the current (including V/sub oc/ and I/sub sc/). Regarding the traditional methods, this new one provides the following advantages: a) minimum power loss with regard to the systems that operate in lineal zone (active zone); this implies several advantages in size and cost; and b) this new method allows an automatic adaptation of the interpolation interval.

A new application of the coupled-inductors SEPIC converter to obtain I-V and P-V curves of photovoltaic modules

The achievement of I-V and P-V curves of photovoltaic modules gives the possibility to obtain the exact operation point, the short-circuit current (Isc), the open-circuit voltage (Voc), the maximum power point (MPP) and the fill factor (FF). These are significant parameters for the design and for the start-up of a photovoltaic installation. In this paper, we propose and analyse by means of simulation the capacity of the SEPIC (single-ended primary inductance converter) structure to implement I-V and P-V curves tracers of photovoltaic modules, mainly because the SEPIC topology presents the capability of buck-boost conversion. Thanks to this property, a complete sweep of the voltage and the current given by a photovoltaic panel can be made, including Voc and Isc . This structure is implemented by coupled inductors and presents two fundamental advantages: 1) it allows to emulate a resistance at the input converter within the range [0,infin) and 2) it guarantees a null ripple in the input current when the magnetic coupling of his two inductors fulfils ZRC (zero ripple condition)

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.

I–V and P-V curves measuring system for PV modules based on DC-DC converters and portable graphical environment

The photovoltaic (PV) modules or arrays can be characterized by their I–V and P-V curves. These curves depend on solar irradiance and temperature. There are many ways to obtain these curves, but the using of DC-DC converters as variable resistance offers advantages over the rest. This paper presents a circuit solution based on scaled DC-DC converter using IGBT to obtain the I–V and P-V curves of the PV modules or arrays. A portable graphical environment (virtual instrument, VI) has been developed to adjust the parameters of the developed measuring system and show the I–V and P-V curves together and other parameters in real time. The experimental results for the system proposed using 1 kW single-ended primary inductance converter (SEPIC) are shown.

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.

Determination of PV Generator I-V/P-V Characteristic Curves Using a DC-DC Converter Controlled by a Virtual Instrument

A versatile measurement system for systematic testing and measurement of the evolution of the I-V characteristic curves of photovoltaic panels or arrays (PV generators) is proposed in this paper. The measurement system uses a circuit solution based on DC-DC converters that involves several advantages relative to traditional methods: simple structure, scalability, fast response, and low cost. The measurement of the desired characteristics of PV generators includes high speed of response and high fidelity. The prototype system built is governed by a microcontroller, and experimental results prove the proposed measurement system useful. A virtual instrument (VI) was developed for full system control from a computer. The developed system enables monitoring the suitable operation of a PV generator in real time, since it allows comparing its actual curves with those provided by the manufacturer.

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.