Jaime W. Zapata

Model predictive control of interleaved dc-dc stage for photovoltaic microconverters

The development of different configurations and topologies implemented in photovoltaic (PV) plants have made possible the increase of efficiency of the system. The traditional configurations of grid-connected PV systems, centralized, string, multi-string and ac-module, have been analyzed and actually most of them are controlled using classic PI control. Furthermore, each of them has different efficiency values due to the inherent associated problems. The large-scale PV plants do not work properly when the modules do not work at the same conditions, for example when some atmospheric and environmental problems are involved, it reduces the reliability of the system. The traditional small-scale PV configurations have a low efficiency due to the dc-boosting stage in order to reach the grid levels. This work presents a grid-connected PV configuration, focused in the improve of the efficiency of the traditional ac-module configuration, a flyback topology for the dc-side and a H-bridge topology for the grid connection will be implemented. Moreover, the proposed control scheme is based on FCS-MPC algorithm.

Design of a Cleaning Program for a PV Plant Based on Analysis of Energy Losses

Solar photovoltaic (PV) energy has grown significantly over the past few years. However, despite the increase in installed capacity, this energy source still raises important concerns related to the variability of power production. The short-term effects such as cloud shadowing and supply interruptions, as well as long-term effects such as dust accumulation, seasonal variation, and ageing of PV modules, can cause variability of power production. Therefore, the analysis of all the variability sources in order to provide statistically consistent power production data is an important challenge. This study presents a methodology to analyze data from a PV plant in order to have an independent evaluation of the different effects of variability, identifying dust deposition, and proposing a cost-based optimal cleaning program for a PV plant installed in the northern region of Chile.

Partial power DC-DC converter for large-scale photovoltaic systems

In photovoltaic (PV) systems, a wide variety of power converter topologies and PV configurations have been developed in order to increase the system efficiency. Traditionally, grid-connected PV systems use one or two conversion stages. The single conversion stage is mainly used for large-scale PV systems working with only a DC-AC converter. Whereas, for small and medium-scale, two conversion stages are used. The advantages working with a DC-stage are mainly the distributed maximum power point tracking (MPPT) algorithm and the elevation capability, but it presents a reduced conversion efficiency compared with the single stage configurations. On the other hand, the single conversion stage presents a reduced overall efficiency produced by partial shading. The proposed work presents a Partial Power DC-DC converter (PPC) which process only a portion of the whole power, reducing the conversion losses. It includes the benefits of two stage configurations so that it performs individual MPPT. Besides, due to the modularity of the architecture, it allows the parallel connection of many strings as required to use in large-scale PV systems. Simulations are performed in order to evaluate the converter performance.

Partial power DC-DC converter for photovoltaic two-stage string inverters

In order to increase the conversion efficiency in photovoltaic (PV) systems, different configurations and topologies were developed. Depending on the application, the converters used for grid connection are built using one or two conversion stages. The advantages of the converters with a DC-stage are mainly the distributed maximum power point tracking algorithm per PV string, a wider range of operation, higher energy yield and, when required for grid connection, the possibility of voltage regulation. However, the conversion efficiency is lower than configurations with a single stage as the central inverter. Therefore, the proposed work presents a Partial Power DC-DC converter (PPC) which process part of the entire system power, and the surplus power is directly supplied to the output side. A topology is proposed and the details of its operation are explained based on the operating principle. Simulations are performed in order to evaluate the converter performance.

Partial power DC-DC converter for photovoltaic microinverters

In order to increase the conversion efficiency in photovoltaic (PV) systems, different configurations and topologies were developed. Depending on the application, the converters used for grid connection are built using one or two conversion stages. The advantages of the converters with a DC-stage are mainly the distributed maximum power point tracking algorithm per PV string or PV module and, when required for grid connection, the possibility of voltage elevation. However, the conversion efficiency is lower than configurations with a single-stage as the central inverter. Therefore, the proposed work presents a Partial Power DC-DC converter (PPC) which process part of the entire system power, and the remaining power is directly supplied to the output side. A topology is proposed and the details of its operation are explained based on the operating principle. Simulations are performed in order to evaluate the converter performance.

Analysis of short-term and long-term characteristics of PV power production

Solar photovoltaic (PV) energy has one of the fastest growth among renewable energies, reaching an installed capacity of 100 GW in year 2012, mainly due by the cost reduction of PV panels. However, one of the main disadvantages of this kind of energy source is their highly variability. The main source of variability is, of course, the day/night cycle. Nevertheless, short-term effects such as cloud shadowing and supply interruptions and long-term effects such as dust accumulation, seasonal variation and ageing of panels will also appear as sources of variability. The combined effect of all these variability sources makes the analysis of the power production data very complex. The reliability and accuracy of this data analysis could becomes significant because it is required to expand the PV plant size, to design a new one, to incorporate energy storage for power smoothing or to economically evaluate the PV system. This work presents a methodology to obtain statistically consistent data from a PV plant, in order to evaluate all the mentioned effects separately. The method is based on the correlation of PV power production data with an ideal value of solar power obtained from geographical and astronomical data. The proposed methodology is applied to data obtained from a PV plant located in northern Chile.

Multi-channel partial power DC-DC converter for current balancing of LED strings

The light-emitting diode (LED) technology is reaching a high penetration in commercial applications oriented to illumination. However, there are some problems associated when the application requires a high output power. The problems are related to the connection of several LED units to reach the voltage and current levels. The voltage-current characteristic of the LEDs is not always the same, specially when a failure occurs. Therefore, when some strings are connected in parallel, the illumination is not uniform if the same voltage is applied to all strings. For that reason, in this paper a multi-channel current balancing driver is proposed. The driver is based on a partial power DC-DC converter architecture. It performs current balancing handling only a portion of the total power delivered by the source, reaching an increased efficiency. Besides, due to the modularity of the architecture, it allows the parallel connection of as many strings as required to use for high power application. Simulations are performed in order to evaluate the converter performance.

Evaluation of output connections of interleaved dc-converter stage for photovoltaic ac-module configurations

The continuous increased installation of solar photovoltaic (PV) systems have made possible the interest in their development, oriented to reach a high efficiency system. There are four traditional configurations of grid-connected PV systems depending of the size of the plant,each of them has different efficiency values due to the inherent associated problems. The large-scale PV plants have problems when the modules do not work at the same conditions, for example when some atmospheric and environmental problems are involved, it reduces the reliability of the system. The traditional small-scale PV configurations have a low efficiency due to the dc-boosting stage in order to reach the grid levels. This work presents a grid-connected PV configuration, focused in the improve of the efficiency of the traditional ac-module configuration, a flyback topology for the dc-side and, a H-bridge topology for the grid connection will be implemented.

Design of a cleaning program for a PV plant based on the analysis of short-term and long-term effects

Solar photovoltaic (PV) energy has grown significantly during the last years. However, despite of the increase in installed capacity penetration, this energy source still arises important concerns due to the variability of power production. The short-term effects such as cloud shadowing and supply interruptions, as well as long-term effects such as dust accumulation, seasonal variation and ageing of PV modules can generate variability of power production. Therefore, the analysis of all the variability sources in order to provide a statistically consistent power production data represents an important challenge. This work presents a methodology to analyze data from a PV plant located in Chile by isolating the effect produced by soiling and, with this information a cost based cleaning program is proposed.