Dezso Sera

PV panel model based on datasheet values

This work presents the construction of a model for a PV panel using the single-diode five-parameters model, based exclusively on data-sheet parameters. The model takes into account the series and parallel (shunt) resistance of the panel. The equivalent circuit and the basic equations of the PV cell/panel in Standard Test Conditions (STC)1 are shown, as well as the parameters extraction from the data-sheet values. The temperature dependence of the cell dark saturation current is expressed with an alternative formula, which gives better correlation with the datasheet values of the power temperature dependence. Based on these equations, a PV panel model, which is able to predict the panel behavior in different temperature and irradiance conditions, is built and tested.

Optimized Maximum Power Point Tracker for Fast-Changing Environmental Conditions

This paper presents a high-performance maximum power point tracker (MPPT) optimized for fast cloudy conditions, e.g., rapidly changing irradiation on the photovoltaic panels. The rapidly changing conditions are tracked by an optimized hill-climbing MPPT method called dP-P&O. This algorithm separates the effects of the irradiation change from the effect of the trackers perturbation and uses this information to optimize the tracking according to the irradiation change. The knowledge of the direction of the irradiation change enables the MPPT to use different optimized tracking schemes for the different cases of increasing, decreasing, or steady irradiance. When the irradiance is changing rapidly this strategy leads to faster and better tracking, while in steady-state conditions it leads to lower oscillations around the MPP. The simulations and experimental results show that the proposed dP-P&O MPPT provides a quick and accurate tracking even in very fast changing environmental conditions.

On the Perturb-and-Observe and Incremental Conductance MPPT Methods for PV Systems

This paper presents a detailed analysis of the two most well-known hill-climbing maximum power point tracking (MPPT) algorithms: the perturb-and-observe (P&O) and incremental conductance (INC). The purpose of the analysis is to clarify some common misconceptions in the literature regarding these two trackers, therefore helping the selection process for a suitable MPPT for both researchers and industry. The two methods are thoroughly analyzed both from a mathematical and practical implementation point of view. Their mathematical analysis reveals that there is no difference between the two. This has been confirmed by experimental tests according to the EN 50530 standard, resulting in a deviation between their efficiencies of 0.13% in dynamic and as low as 0.02% under static conditions. The results show that despite the common opinion in the literature, the P&O and INC are equivalent.

Local Reactive Power Control Methods for Overvoltage Prevention of Distributed Solar Inverters in Low-Voltage Grids

The main objective of this study is to increase the penetration level of photovoltaic (PV) power production in low-voltage (LV) grids by means of solar inverters with reactive power control capability. This paper underlines weak points of standard reactive power strategies which are already imposed by certain grid codes, and then, the study introduces a new reactive power control method that is based on sensitivity analysis. The sensitivity analysis shows that the same amount of reactive power becomes more effective for grid voltage support if the solar inverter is located at the end of a feeder. Based on this fundamental knowledge, a location-dependent power factor set value can be assigned to each inverter, and the grid voltage support can be achieved with less total reactive power consumption. In order to prevent unnecessary reactive power absorption from the grid during admissible voltage range or to increase reactive power contribution from the inverters that are closest to the transformer during grid overvoltage condition, the proposed method combines two droop functions that are inherited from the standard cos φ(P) and Q(U) strategies. Its performance comparison in terms of grid losses and voltage variation with different reactive power strategies is provided by modeling and simulating a real suburban LV network.

Improved MPPT Algorithms for Rapidly Changing Environmental Conditions

The first part of this paper intends to give an overview of the maximum power point tracking methods for photovoltaic (PV) inverters presently reported in the literature. The most well-known and popular methods, like the perturb and observe (P&O), the incremental conductance (INC) and the constant voltage (CV), are presented. These methods, especially the P&O, have been treated by many works, which aim to overcome their shortcomings, either by optimizing the methods, or by combining them. In the second part of the paper an improvement for the P&O and INC method is proposed, which prevents these algorithms to get confused during rapidly changing irradiation conditions, and it considerably increases the efficiency of the MPPT

Improved MPPT method for rapidly changing environmental conditions

A well-known limitation of the perturb and observe (P&O) MPPT method is that it can get confused and track in wrong direction during rapidly changing irradiation. The present work offers a simple and effective solution to this problem, by using an additional measurement of the solar arrays power in the middle of the MPPT sampling period. The method has been experimentally tested and compared with the traditional P&O method

Evaluation of the voltage support strategies for the low voltage grid connected PV generators

Admissible range of grid voltage is one of the strictest constraints for the penetration of distributed photovoltaic (PV) generators especially connection to low voltage (LV) public networks. Voltage limits are usually fulfilled either by network reinforcements or limiting of power injections from PVs. In order to increase PV penetration level further, new voltage support control functions for individual inverters are required. This paper investigates distributed reactive power regulation and active power curtailment strategies regarding the development of PV connection capacity by evaluation of reactive power efforts and requirement of minimum active power curtailment. Furthermore, a small scale experimental setup is built to reflect real grid interaction in the laboratory by achieving critical types of grid (weak and sufficiently stiff).

PV inverter test setup for European efficiency, static and dynamic MPPT efficiency evaluation

This paper concerns the evaluation of performance of grid-connected PV inverters in terms of conversion efficiency, European efficiency, static and dynamic MPP efficiency. Semi-automated tests were performed in the PV laboratory of the Institute of Energy Technology at the Aalborg University (Denmark) on a commercial transformerless PV inverter. Thanks to the available experimental test setups, that provide the required high measuring accuracy, and the developed PV simulator, which is required for MPPT performance evaluation, PV Inverters can be pretested before being tested by accredited laboratories.

Low-cost digital implementation of proportional-resonant current controllers for PV inverter applications using delta operator

The performances of the P+Resonant controller in case of current control for a single phase grid connected inverter have been proved to be superior to the PI controller, since it is able to remove the phase error of the control at the fundamental frequency of the grid. It offers also the possibility of selective harmonic compensation. However, in case of digital implementation on a low-cost fixed-point DSP, the limited computational power and the limited numerical representation precision can restrict the utilization of it. The present paper proposes a different way of digital implementation of the P+Resonant controller with selective harmonic compensation on a low-cost fixed-point DSP. The resonant part of the P+R has been implemented as a second order filter based on delta operator. The current controller, together with harmonic compensation for the 3/sup rd/, 5/sup th/, and 7/sup th/ harmonics has been successfully tested in practice with a 1.5 KW PV inverter, achieving a 1.2% total harmonic distortion (THD) of the grid current.

Power Electronics and Control of Renewable Energy Systems

The global electrical energy consumption is still rising and there is a demand to double the power capacity within 20 years. The production, distribution and use of energy should be as technological efficient as possible and incentives to save energy at the end-user should also be set up. Deregulation of energy has in the past lowered the investment in larger power plants, which means the need for new electrical power sources may be very high in the near future. Two major technologies will play important roles to solve the future problems. One is to change the electrical power production sources from the conventional, fossil (and short term) based energy sources to renewable energy resources. Another is to use high efficient power electronics in power generation, power transmission/distribution and end-user application. This paper discuss some of the most emerging renewable energy sources, wind energy and photovoltaics, which by means of power electronics are changing from being minor energy sources to be acting as important power sources in the energy system.