Power balance control for a two-stage solar inverter with Low Voltage Ride Through capability

The latest grid codes require the renewable energy sources (RES) to provide ancillary services during fault and post fault conditions. More specifically, in case of a short-duration voltage dip, the grid-tied photovoltaic (PV) system should stay connected and support the grid by injecting reactive power. However, meeting these requirements during voltage sags is a challenge for two-stage systems, due to the power imbalance between the dc/dc converter and the inverter, resulting in dc-link voltage excursions and output current overshoots. In this paper, a power balance control scheme is proposed, by which, a successful low voltage ride through (LVRT) and smooth dclink voltage variation are achieved, while the output current is kept within the predefined limits. Two reactive power injection strategies are investigated that exhibit different dynamic response during voltage sags. The effectiveness of the proposed LVRT control is verified though simulations of a 2 kVA solar system

A MPPT algorithm for partial shading conditions employing curve fitting

Standard maximum power point tracking (MPPT) algorithms often fail to locate the global maximum of a photovoltaic (PV) system under partial shading conditions, while other more sophisticated approaches usually involve extra perturbation of the operating point, which entails undesired output power fluctuation. In this paper, a new MPPT method is introduced, which continuously detects the shading parameters and estimates all power peaks (MPPs) on the P-V curve, guaranteeing continuous operation at the global maximum. The algorithm applies least squares (LSQ) curve fitting (CF) to measurements at the current MPP, utilizing the inherent ripple, without the need for additional perturbation on the operating point. The calculations performed are entirely mathematical and no extra measurement equipment is required, such as irradiance or temperature sensors. The method is designed for PV strings illuminated at two irradiance levels

Enhanced MPPT control of a two-stage grid-connected PV system under fast-changing irradiance conditions

In this paper, an enhanced Maximum Power Point Tracking (MPPT) strategy for a two-stage gridconnected PV system is proposed, which enables accurate tracking of the maximum power point irrespective of the rate of change in solar irradiance levels. The analysis is performed both in the frequency and time domains, using a suitable linearized model of the system. A comparative assessment of the proposed MPPT strategy versus a conventional Perturbation and Observation (P&amp;O) method is carried out for operation under trapezoidal irradiance profiles.<br/

A partial shading detection technique for MPPT algorithms in PV systems

In this paper, a simple algorithmic enhancement for MPPT methods is introduced, which mathematically determines if the PV system is shaded, thus avoiding unnecessary curve scanning to locate the global maximum if it is unshaded. The proposed technique improves the overall efficiency and applies to any PV system at any irradiance distribution, using only a common temperature sensor

Electrical vehicle load modelling for distribution system considering future scenarios

Electric vehicles (EVs) are a valuable means of reducing our reliance on traditional fossil fuel based transportation. In recent years, the market share of EVs is increasing, which raises some important questions: what is the impact of EVs on the electrical load of our electricity distribution systems, and how can we adequately model it? Some researches have been done to model the EV loads and influence, but they are limited in applications due to complexity and requirements of data. This paper proposes a model for EV loads which takes into account diversity of EV loads and difficulties in applications, and provides analysis of the EV loads in modern and future grids. Efficacy of the proposed model has been demonstrated using real EV-datasets, which provides valuable statistical analysis

Interfacing synchronous machine model including stator transients with network for stability studies

A detailed multi-time scale model of synchronous machines (SM) with stator transients is necessary to capture the complex interactions in inverter-integrated power systems. The conventional detailed SM model, including stator transients is incompatible with that of the step-up transformer in the domain as both are modelled as current sources in series. This letter proposes an efficient approach for interfacing the detailed SM model with the transformer by reformulating the SM model as a voltage source without accuracy loss. MATLAB/Simulink numerical simulations using New England 39-bus test system validate the computational efficiency of the proposed approach

Noise-scaled euclidean distance: A metric for maximum likelihood estimation of the PV model parameters

This article revisits the objective function (or metric) used in the extraction of photovoltaic (PV) model parameters. A theoretical investigation shows that the widely used current distance (CD) metric does not yield the maximum likelihood estimates (MLE) of the model parameters when there is noise in both voltage and current samples. It demonstrates that the Euclidean distance (ED) should be used instead, when the voltage and current noise powers are equal. For the general case, a new noise-scaled Euclidean distance (NSED) metric is proposed as a weighted variation of ED, which is shown to fetch the MLE of the parameters at any noise conditions. This metric requires the noise ratio (i.e., ratio of the two noise variances) as an additional input, which can be estimated by a new noise estimation (NE) method introduced in this study. One application of the new metric is to employ NSED regression as a follow-up step to existing parameter extraction methods toward fine-tuning of their outputs. Results on synthetic and experimental data show that the so-called NSED regression &amp;#x201C;add-on&amp;#x201D; improves the accuracy of five such methods and validate the merits of the NSED metric