Maximum power point tracking (MPPT) techniques are used in photovoltaic (PV) systems to maximize the PV array output power by tracking continuously the maximum power point (MPP) which depends on panels temperature and on irradiance conditions. The issue of MPPT has been addressed in different ways in the literature but, especially for low-cost implementations, the perturb and observe (PO moreover, it is well known that the P&O algorithm can be confused during those time intervals characterized by rapidly changing atmospheric conditions. In this paper it is shown that, in order to limit the negative effects associated to the above drawbacks, the P&O MPPT parameters must be customized to the dynamic behavior of the specific converter adopted. A theoretical analysis allowing the optimal choice of such parameters is also carried out. Results of experimental measurements are in agreement with the predictions of theoretical analysis.

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Optimization of perturb and observe maximum power point tracking method

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.

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

Review of the maximum power point tracking algorithms for stand-alone photovoltaic systems

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 simulation and hardware implementation of incremental conductance (IncCond) maximum power point tracking (MPPT) used in solar array power systems with direct control method. The main difference of the proposed system to existing MPPT systems includes elimination of the proportional-integral control loop and investigation of the effect of simplifying the control circuit. Contributions are made in several aspects of the whole system, including converter design, system simulation, controller programming, and experimental setup. The resultant system is capable of tracking MPPs accurately and rapidly without steady-state oscillation, and also, its dynamic performance is satisfactory. The IncCond algorithm is used to track MPPs because it performs precise control under rapidly changing atmospheric conditions. MATLAB and Simulink were employed for simulation studies, and Code Composer Studio v3.1 was used to program a TMS320F2812 digital signal processor. The proposed system was developed and tested successfully on a photovoltaic solar panel in the laboratory. Experimental results indicate the feasibility and improved functionality of the system.

Simulation and Hardware Implementation of Incremental Conductance MPPT With Direct Control Method Using Cuk Converter

Photovoltaic systems normally use a maximum power point tracking (MPPT) technique to continuously deliver the highest possible power to the load when variations in the insulation and temperature occur. It overcomes the problem of mismatch between the solar arrays and the given load. A simple method of tracking the maximum power points (MPPs) and forcing the system to operate close to these points is presented. The principle of energy conservation is used to derive the large- and small-signal model and transfer function. By using the proposed model, the drawbacks of the state-space-averaging method can be overcome. The TI320C25 digital signal processor (DSP) was used to implement the proposed MPPT controller, which controls the DC/DC converter in the photovoltaic system. Simulations and experimental results show excellent performance.

Implementation of a DSP-controlled photovoltaic system with peak power tracking

A cascaded-like high-step-down converter (CHSDC) is proposed in this article, which can steeply convert a high voltage to a much lower level without the utilizing of extreme turns ratio or duty ratio. The proposed converter integrates two buck-boost converters and one forward converter to form a single-stage architecture containing only a single low-side driving switch, which, as a result, can lower the cost and reduce the complexity of the associated control driver. Even in a single-stage single-switch structure, the ability to step down input voltage is as effective as the cascade of two buck-boosts and one forward converter. Meanwhile, the proposed converter can avoid the low efficiency caused by a cascaded structure. Without an additional clamp circuit, the leakage energy stored in the transformer of the CHSDC can be still recycled so as to raise the efficiency of the converter and suppress voltage spikes at the power switch. Converter operation principle and key parameter design are discussed. Moreover, a 200 W prototype is built and then tested to validate the proposed converter and verify the theoretical analysis.

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Cascaded-like High-Step-Down Converter with Single Switch and Leakage Energy Recycling in Single-Stage Structure

In this article, a novel multi-port multi-directional converter (MPMDC) is proposed. Even though the power stage of the MPMDC belongs to a single-stage structure, it can control power flow direction handily among ports and achieve converter operation in up to five modes. The MPMDC has the feature of galvanic isolation and can obtain a high voltage conversion ratio even under the adoption of only one inductor and one transformer. The leakage energy of the transform can be recycled to improve overall efficiency. Once the MPMDC is applied to deal with renewable energy, battery, and bus energy, the advantage of multi-directional control of power flow can advance an energy storage system to perfectly function power conditioning feature. In addition to the discussion of converter operation, voltage gain, voltage stress, current stress, and inductance design are analyzed theoretically. Comparisons with some of the latest similar converters are also carried out. A 200-W prototype is built and measured. According to the practical results, it is verified that the hardware measurements meet the theoretical derivations and the MPMDC is validated. The maximum efficiency of the converter is up to 94%.

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Chihming Shen

Papers

Implementation of a DSP-controlled photovoltaic system with peak power tracking

Cascaded-like High-Step-Down Converter with Single Switch and Leakage Energy Recycling in Single-Stage Structure

Multi-Port Multi-Directional Converter with Multi-Mode Operation and Leakage Energy Recycling for Green Energy Processing