The many different techniques for maximum power point tracking of photovoltaic (PV) arrays are discussed. The techniques are taken from the literature dating back to the earliest methods. It is shown that at least 19 distinct methods have been introduced in the literature, with many variations on implementation. This paper should serve as a convenient reference for future work in PV power generation.

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Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques

The annual world photovoltaic (PV) cell/module production is growing at almost an exponential rate and has reached 1727 MW in 2005. Building integrated PV (BIPV) projects are emerging as the strongest part of the PV market and grid interactive inverters are a key component in determining the total system cost. Module integrated converter (MIC) technology has become a global trend in grid interactive PV applications and may assist in driving down the balance of system costs to secure an improved total system cost. This paper concentrates on the topology study of the PV MICs in the power range below 500 W and covers most topologies recently proposed for MIC applications. The MIC topologies are classified into three different arrangements based on the dc link configurations. A systematic discussion is also provided at the end of the paper that focuses on the major advantages and disadvantages of each MIC arrangement. These are considered in detail and will provide a useful framework and point of reference for the next generation MIC designs and applications.

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A Review of the Single Phase Photovoltaic Module Integrated Converter Topologies With Three Different DC Link Configurations

Current-voltage and power-voltage characteristics of large photovoltaic (PV) arrays under partially shaded conditions are characterized by multiple steps and peaks. This makes the tracking of the actual maximum power point (MPP) [global peak (GP)] a difficult task. In addition, most of the existing schemes are unable to extract maximum power from the PV array under these conditions. This paper proposes a novel algorithm to track the global power peak under partially shaded conditions. The formulation of the algorithm is based on several critical observations made out of an extensive study of the PV characteristics and the behavior of the global and local peaks under partially shaded conditions. The proposed algorithm works in conjunction with a DC-DC converter to track the GP. In order to accelerate the tracking speed, a feedforward control scheme for operating the DC-DC converter is also proposed, which uses the reference voltage information from the tracking algorithm to shift the operation toward the MPP. The tracking time with this controller is about one-tenth as compared to a conventional controller. All the observations and conclusions, including simulation and experimental results, are presented.

Maximum Power Point Tracking Scheme for PV Systems Operating Under Partially Shaded Conditions

This paper presents an overview of single-phase inverters developed for small distributed power generators. The functions of inverters in distributed power generation (DG) systems include dc-ac conversion, output power quality assurance, various protection mechanisms, and system controls. Unique requirements for small distributed power generation systems include low cost, high efficiency and tolerance for an extremely wide range of input voltage variations. These requirements have driven the inverter development toward simpler topologies and structures, lower component counts, and tighter modular design. Both single-stage and multiple-stage inverters have been developed for power conversion in DG systems. Single-stage inverters offer simple structure and low cost, but suffer from a limited range of input voltage variations and are often characterized by compromised system performance. On the other hand, multiple-stage inverters accept a wide range of input voltage variations, but suffer from high cost, complicated structure and low efficiency. Various circuit topologies are presented, compared, and evaluated against the requirements of power decoupling and dual-grounding, the capabilities for grid-connected or/and stand-alone operations, and specific DG applications in this paper, along with the identification of recent development trends of single-phase inverters for distributed power generators.

Topologies of single-phase inverters for small distributed power generators: an overview

Solar photovoltaic (PV) energy has witnessed double-digit growth in the past decade. The penetration of PV systems as distributed generators in low-voltage grids has also seen significant attention. In addition, the need for higher overall grid efficiency and reliability has boosted the interest in the microgrid concept. High-efficiency PV-based microgrids require maximum power point tracking (MPPT) controllers to maximize the harvested energy due to the nonlinearity in PV module characteristics. Perturb and observe (PO second, no steady-state oscillations around the MPP; and lastly, no need for predefined system-dependent constants, hence provides a generic design core. A design example is presented by experimental implementation of the proposed technique. Practical results for the implemented setup at different irradiance levels are illustrated to validate the proposed technique.

High-Performance Adaptive Perturb and Observe MPPT Technique for Photovoltaic-Based Microgrids

This paper presents a flyback inverter controlled by sensorless current maximum power point tracking (MPPT) for a small photovoltaic (PV) power system. Although the proposed system has small output power such as 300 W, a few sets of small PV power systems can be easily connected in parallel to yield higher output power. When a PV power system is constructed with a number of small power systems, the total system cost will increase and will be a matter of concern. To overcome this difficulty, this paper proposes a PV system that uses no expensive dc current sensor but utilizes the method of estimating the PV current from the PV voltage. The paper shows that the application of this novel sensorless current flyback inverter to an MPPT-operated PV system exhibits satisfactory MPPT performance similar to the one exhibited by the system with a dc current sensor as well. This paper also deals with the design method and the operation of the unique flyback inverter with center-tapped secondary winding.

Flyback inverter controlled by sensorless current MPPT for photovoltaic power system

This paper presents a newly developed transformer-less single phase inverter for a photovoltaic (PV) power system. The proposed system consists of two sets of a PV array and buck-boost type chopper circuit. However, it is afraid that the system has lower "using rate" of PV energy than that of the ordinary PV system, as each PV array is only operated in the half duration of the AC power frequency. In this paper, it is also discussed how to increase this "using rate" by varying the connected capacitor between PV array terminals. The perturbation and observation method is adapted to the maximum power tracking in our PV systems. We adopt the wavelet transform to detect a power outage. The experimental data shows that this new inverter can supply AC power to the utility grid line with the power factor nearly unity.

An inverter using buck-boost type chopper circuits for popular small-scale photovoltaic power system

A zero-voltage transition (ZVT) flyback inverter is proposed. The current in the flyback transformer is controlled in the fixed frequency, and the pulse width is varied to make the inductor current sinusoid. In order to reduce switching losses and noises, a soft-switching technique is adopted. The soft-switching technique is called the switched snubber circuit or the primary current steering technique. It is suitable for the pulse-width modulation (PWM), because the time of the resonant transition is very short and the time is independent of the switching frequency. A laboratory prototype using a digital controller for the ZVT flyback inverter was built. From the simulation using the PSPICE and experimental results, the zero-voltage transition operation of the main switch is confirmed. The proposed inverter is suitable as a power conditioner for PV power systems

Zero-Voltage Transition Flyback Inverter for Small Scale Photovoltaic Power System

This paper presents a perturbation and observation method with an identifier of capacitor for the maximum power point tracking (MPPT) in a photovoltaic power system. Usually, by increasing or decreasing the duty ratio of on-state of switching device, the maximum power point is tracked. The variation of duty ratio is determined by considering its circuit parameters. However, it is known that actual capacitance of an electrolytic capacitor in parallel with the photovoltaic array has 50% error of its nominal value. If the variation of duty ratio is determined based on its nominal value, the performance of MPPT is degraded. Thus, accordingly we must change the variation of duty ratio based on its actual value. In our system, we adapt the model reference adaptive system to identify the capacitor, then we can estimate the accurate capacitance and correct the variation of duty ratio. As a result, we may obtain the high performance of MPPT. Experimental results are shown using a proposed power inverter using buck-boost chopper circuits.

Maximum power point tracking with capacitor identificator for photovoltaic power system

This paper presents a newly developed flyback type inverter for a small scale (low power) photovoltaic power system and a maximum power point tracking (MPPT) controller without a current sensor for this system. As the small scale photovoltaic power systems are used in parallel, cost reduction with high reliability is strongly required. In the proposed inverter, the current is controlled with open loop, and then the generated power of photovoltaic array is calculated by an equation using the voltage of the photovoltaic array. Therefore, the system can obtain the power by detecting only the voltage of the photovoltaic array. As a result, we may obtain the performance of the MPPT without a current sensor as well as with a current sensor.

Nobuyuki Kasa

Papers

Flyback inverter controlled by sensorless current MPPT for photovoltaic power system

An inverter using buck-boost type chopper circuits for popular small-scale photovoltaic power system

Zero-Voltage Transition Flyback Inverter for Small Scale Photovoltaic Power System

Maximum power point tracking with capacitor identificator for photovoltaic power system

Flyback type inverter for small scale photovoltaic power system