Eftichios Koutroulis

Development of a microcontroller-based, photovoltaic maximum power point tracking control system

Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m/sup 2/ and 25/spl deg/C.

Design of a maximum power tracking system for wind-energy-conversion applications

A wind-generator (WG) maximum-power-point-tracking (MPPT) system is presented, consisting of a high-efficiency buck-type dc/dc converter and a microcontroller-based control unit running the MPPT function. The advantages of the proposed MPPT method are that no knowledge of the WG optimal power characteristic or measurement of the wind speed is required and the WG operates at a variable speed. Thus, the system features higher reliability, lower complexity and cost, and less mechanical stress of the WG. Experimental results of the proposed system indicate near-optimal WG output power, increased by 11%-50% compared to a WG directly connected via a rectifier to the battery bank. Thus, better exploitation of the available wind energy is achieved, especially under low wind speeds.

A New Technique for Tracking the Global Maximum Power Point of PV Arrays Operating Under Partial-Shading Conditions

The power-voltage characteristic of photovoltaic (PV) arrays operating under partial-shading conditions exhibits multiple local maximum power points (MPPs). In this paper, a new method to track the global MPP is presented, which is based on controlling a dc/dc converter connected at the PV array output, such that it behaves as a constant input-power load. The proposed method has the advantage that it can be applied in either stand-alone or grid-connected PV systems comprising PV arrays with unknown electrical characteristics and does not require knowledge about the PV modules configuration within the PV array. The experimental results verify that the proposed global MPP method guarantees convergence to the global MPP under any partial-shading conditions. Compared with past-proposed methods, the global MPP tracking process is accomplished after far fewer PV array power perturbation steps.

Design optimization of transformerless grid-connected PV inverters including reliability

This paper presents a new methodology for optimal design of transformerless Photovoltaic (PV) inverters targeting a cost-effective deployment of grid-connected PV systems. The optimal values and types of the PV inverter components are calculated such that the PV inverter Levelized Cost Of the Electricity (LCOE) generated during the PV system lifetime period is minimized. The LCOE is calculated also considering the failure rates of the components, which affect the reliability performance and lifetime maintenance cost of the PV inverter. A design example is presented, demonstrating that compared to the non-optimized PV inverter structures, the PV inverters designed using the proposed optimization methodology exhibit lower total manufacturing and lifetime maintenance cost and inject more energy into the electric-grid and by that minimizing LCOE.

Development of an integrated data-acquisition system for renewable energy sources systems monitoring

Data-acquisition systems are widely used in renewable energy source (RES) applications in order to collect data regarding the installed system performance, for evaluation purposes. In this paper, the development of a computer-based system for RES systems monitoring is described. The proposed system consists of a set of sensors for measuring both meteorological (e.g. temperature, humidity etc.) and electrical parameters (photovoltaics voltage and current etc.). The collected data are first conditioned using precision electronic circuits and then interfaced to a PC using a data-acquisition card. The LABVIEW program is used to further process, display and store the collected data in the PC disk. The proposed architecture permits the rapid system development and has the advantage of flexibility in the case of changes, while it can be easily extended for controlling the RES system operation.

High-frequency pulse width modulation implementation using FPGA and CPLD ICs

Pulse width modulation (PWM) has been widely used in power converter control. Most high power level converters operate at switching frequencies up to 500 kHz, while operating frequencies in excess of 1 MHz at high power levels can be achieved using the planar transformer technology. The contribution of this paper is the development of a high-frequency PWM generator architecture for power converter control using FPGA and CPLD ICs. The resulting PWM frequency depends on the target FPGA or CPLD device speed grade and the duty cycle resolution requirements. The post-layout timing simulation results are presented, showing that PWM frequencies up to 3.985 MHz can be produced with a duty cycle resolution of 1.56%. Additionally, experimental results are also presented for low cost functional verification of the proposed architecture.

Development of an FPGA-based System for Real-Time Simulation of Photovoltaic Modules

Photovoltaic (PV) simulators are indispensable for the laboratory operational evaluation of PV energy production system components (e.g. battery chargers, DC/AC inverters etc.), in order to avoid the time-consuming and expensive field-testing process. In this paper, the development of a novel real-time PV simulator based on Field Programmable Gate Arrays (FPGAs), is presented. The proposed system consists of a Buck-type DC/DC power converter, which is controlled by an FPGA-based unit using the Pulse Width Modulation (PWM) principle. The system operator is able to define both the PV module type to be simulated and the environmental conditions under which the selected PV module operates. The proposed design method enhances the rapid system prototyping capability and enables the reduction of the power converter size and cost due to the high clock speed feature of the FPGA-based control unit. The experimental results indicate that using the proposed method the PV module current-voltage characteristics are simulated with an average accuracy of 1.03%.

Development of a data acquisition system for remote monitoring of renewable energy systems

The widespread application of Renewable Energy Sources (RES) requires the use of data acquisition units both for monitoring system operation and control of its operation. In this paper, the development of a data acquisition system for remote monitoring and control of RES plants is presented. It is based on the Client/Server architecture and it does not require the physical connection of the monitored systems to the data collection server. This feature is essential in RES plants since they are usually installed in inaccessible areas. The measured parameters are available on-line over the Internet to any user.

Optimal Design of Modern Transformerless PV Inverter Topologies

The design optimization of H5, H6, neutral point clamped, active-neutral point clamped, and conergy-NPC transformerless photovoltaic (PV) inverters is presented in this paper. The components reliability in terms of the corresponding malfunctions, affecting the PV inverter maintenance cost during the operational lifetime period of the PV installation, is also considered in the optimization process. According to the results of the proposed design method, different optimal values of the PV inverter design variables are derived for each PV inverter topology and installation site. The H5, H6, neutral point clamped, active-neutral point clamped and conergy-NPC PV inverters designed using the proposed optimization process feature lower levelized cost of generated electricity and lifetime cost, longer mean time between failures and inject more PV-generated energy into the electric grid than their nonoptimized counterparts, thus maximizing the total economic benefit obtained during the operational time of the PV system.

Development of an FPGA-based system for real-time simulation of photovoltaic modules

Photovoltaic (PV) simulators are indispensable for the laboratory operational evaluation of PV energy production system components (e.g. battery chargers, DC/AC inverters etc.), in order to avoid the time-consuming and expensive field-testing process. In this paper, the development of a novel real-time PV simulator based on field programmable gate arrays (FPGAs), is presented. The proposed system consists of a buck-type DC/DC power converter, which is controlled by an FPGA-based unit using the pulse width modulation (PWM) principle. The system operator is able to define both the PV module type to be simulated and the environmental conditions under which the selected PV module operates. The proposed design method enhances the rapid system prototyping capability and enables the reduction of the power converter size and cost due to the high clock speed feature of the FPGA-based control unit. The experimental results indicate that using the proposed method the PV module current-voltage characteristics are simulated with an average accuracy of 1.03%