Corinne Alonso

Adaptive digital MPPT control for photovoltaic applications

Maximum Power Point Tracker (MPPT) is often used to increase the energy conversion efficiency for intermittent energy sources. Numerous of research teams work today to improve this type of algorithms. We had developed real-time MPPT controls based on the Extremum Seeking Control principle first implemented on analogical circuit. Today, to be more flexible and adaptive with several structures of power static converters, our new MPPT algorithms are implemented on numerical circuits. Our aim is to obtain high performances. To achieve a high quality matching between sources and loads, our new MPPT control adjusts continually the static converter duty cycle. Transitory effects are immediately detected and new MPP rapidly recovered. In addition, this digital control has an adjustment delay which allows an adaptation to a large power range from high to low points and then a real optimisation. Experimental results validate the global behaviour of this control for photovoltaic systems.

Practical Implementation of a High-Frequency Current-Sense Technique for VRM

To track the inductor current in high-frequency dc/dc converters is not effortless, particularly when high output currents and low output voltages are demanded by the load. This paper proposes a simple technique to obtain a good accuracy in the inductor current measurement in voltage regulator module (VRM) applications. The main idea is to obtain an equivalent voltage image which can be used for the high-frequency pulsewidth modulation controller to generate the converter control law. This strategy of measurement is generic, and it has been previously validated by simulations. Afterward, some experimental results are obtained by using several prototypes of dc/dc converters delivering a very low output voltage and owning several loads from 10-mA to 100-A currents. This wide range covers the power requirements of portable and embedded VRM applications. Moreover, this sense technique has also been validated in a digital high-frequency current-mode-controlled dc/dc converter.

Paralleling DC–DC Switching Converters by Means of Power Gyrators

In this paper, the problem of paralleling DC-DC switching converters is solved by means of power gyrators. The key element of the parallel connection is a buck converter with input filter acting as a power gyrator of type G with controlled output current, i.e., with its DC output current being proportional to its DC input voltage. electromagnetic interference minimization, current distribution among converters, stability, and voltage regulation are ensured by this approach. It is shown that a voltage regulator based on the parallel operation of power gyrators with democratic current sharing is always stable regardless of the number of connected modules. Experimental results of a DC-DC voltage regulator based on the parallel connection of three power gyrators with democratic current sharing are in perfect agreement with the theoretical predictions.

Self-oscillating DC-to-DC switching converters with transformer characteristics

Fourth-order converters with both input and output filters are analyzed in self-oscillating sliding mode. The boost converter with output filter and the Cuk converter are shown to have stable dynamics and an equilibrium point with transformer characteristics. The analytical predictions are verified by experimental results.

Dynamic performance of maximum power point tracking circuits using sinusoidal extremum seeking control for photovoltaic generation

The article studies the dynamic performance of a family of maximum power point tracking circuits used for photovoltaic generation. It revisits the sinusoidal extremum seeking control (ESC) technique which can be considered as a particular subgroup of the Perturb and Observe algorithms. The sinusoidal ESC technique consists of adding a small sinusoidal disturbance to the input and processing the perturbed output to drive the operating point at its maximum. The output processing involves a synchronous multiplication and a filtering stage. The filter instance determines the dynamic performance of the MPPT based on sinusoidal ESC principle. The approach uses the well-known root-locus method to give insight about damping degree and settlement time of maximum-seeking waveforms. This article shows the transient waveforms in three different filter instances to illustrate the approach. Finally, an experimental prototype corroborates the dynamic analysis.

Four Switch Buck-Boost Converter for Photovoltaic DC-DC power applications

Photovoltaic energy is a wide kind of green energy. A high performance on these systems is needed to make the most of energy produced by solar cells. Also, there must be a constant adaptation due to the continuous variation of power production. Control techniques for Power Converters like the MPPT algorithm (Maximum Power Point Tracking) present very good results on photovoltaic chains. Nevertheless, losses on power elements reduce global performance and the voltage/current adaptation is not always possible. In this paper, the use of the high efficiency structure Four Switch Buck-Boost for Photovoltaic systems is addressed. FSBB Converters present some advantages regarding other Power Converter structures: it has few electrical components, output voltage can be higher or lower than input voltage, and it presents a non-inverted output voltage as happens with others Buck-Boost Converters. A prototype of FSBB has been developed in order to exploit these new capabilities for a Photovoltaic DC-DC power application (solar module: 0V to 20V input voltage and different resistive loads). The implemented MPPT digital control chooses between a Buck or Boost mode, depending on the working conditions. Firstly, an introduction and the FSBB operating mode are addressed. Then, the adaptive MPPT control algorithm is detailed. And finally, the experimental results and conclusion are presented.

Improved photovoltaic conversion chain with interleaved method

This paper presents a parallel connection of three-cell interleaved boost converters used as an adaptation stage dedicated to photovoltaic applications. Indeed, this structure associated to a MPPT control improves the efficiency and reliability of a photovoltaic power conversion chain. An additional current sharing control has been incorporated to assure a uniform distribution of power between each DC-DC converter. Every voltage and current ripples present on the load and photovoltaic (PV) source implying the switch stresses are reduced with this technique compared to a classical structure. Finally; experimental results show that the proposed technique can be used for impedance matching of a PV array.

New adaptive supervision unit to manage photovoltaic batteries

In the context of photovoltaic (PV) research, the use of a storage function in such intermittent power supply systems is crucial in order to get better adequacy between the peaks of energetic consumption and production. On the one hand, a research algorithm of the optimal power to charge and discharge advanced batteries for photovoltaic application is necessary to obtain an optimum electronic management system. On the other hand, a balancing and a protection unit are incorporated into the electronic control unit, to optimize the lifetime of the battery. The new adaptive supervision unit to manage PV batteries presented in this paper aims to optimize the use of the battery making the overall system more reliable and cost effective. A new concept of an integrated supervision unit for different battery technologies using new control algorithms is described.

A new method for fault detection and identification of shadows based on electrical signature of defects

Good diagnosis and monitoring of PV systems are key points to maximize PV production. The main objective of this work is focus on the development of a new tool able to detect faults of PV systems on real-time, with a particular care for the detection of shadows. The proposed detection method is based only on DC power measurements.

LED lighting — Reduce the power consumption and increase the users comfort

With the vanishing of the fossil primary resources and the carbon impact issues, the efficient use of energy has become a major priority. Lighting is an important element of expenditure as it is easy to act on it. The Light Emitting Diode (LED) technology opens many perspectives in this field due to its higher energy efficiency. LED could indeed become in a near future a replacement for fluorescent tubes. LEDs tubes have specific thermal and electrical needs; this work is focused therefore on optimization studies in terms of association topologies: serial versus parallel. The starting point is electrical equivalent models extracted from single LED. The choice of combinations is guided by the required performance in terms of light quality by paying attention to the overall consumption of the lighting system. The final target is the evaluation of losses reduction when the individual AC/DC conversion circuits integrated in the lamp bases are replaced by a DC/DC global distribution scheme. This approach was adopted to power the lighting of single room from a low DC voltage weakly regulated power grid.