Fast Irradiation Changes Research Articles

Transient Differentiation Maximum Power Point Tracker (Td-MPPT) for Optimized Tracking under Very Fast-Changing Irradiance: A Theoretical Approach for Mobile PV Applications

This work presents an algorithm for Maximum Power Point Tracking (MPPT) that measures transitory states to prevent drift issues and that can reduce steady-state oscillations. The traditional MPPT algorithms can become confused under very fast-changing irradiance and perform tracking in the wrong direction. Errors occur because these algorithms operate under the assumption that power changes in the system are triggered exclusively due to perturbations introduced by them. However, the power increase triggered by irradiance changes could be more significant than those caused by the perturbation effect. The proposed method modifies the Perturb and Observe algorithm (P&O) with an additional measurement stage performed close to the maximum overshoot peak after the perturbation stage. By comparing power changes between three measurement points, the algorithm can accurately identify whether the perturbation was made in the correct direction or not. Furthermore, the algorithm can use additional information to determine if the operating point after the perturbation stage is beyond the maximum power point (MPP) and perturb in the opposite direction for the next iteration. Thus, the proposed algorithm shows reduced steady-state oscillations and improved tracking under fast irradiance changes compared to conventional P&O and P&O with power differences (dP-P&O). The design is validated via simulations using fast-changing irradiance tests based on the standard EN 50530 accelerated by a factor of 100×. The proposed algorithm achieved 99.74% of global efficiency versus 97.4% of the classical P&O and 99.54% of the dP-P&O under the tested conditions.

An Adaptive Power Ramp Rate Control Method for Photovoltaic Systems

Photovoltaic (PV) power fluctuations, caused by fast irradiance changes, because of passing clouds, may pose challenges to the stability and reliability of power systems with high penetration of PV inverters. In this regard, new standards impose power ramp rate control (PRRC) on grid-connected PV systems. Available solutions in the literature lack the capability of fast measurement for power ramp rate and fast dynamics under rapid irradiance changes. This article proposes an adaptive flexible power point tracking-based PRRC strategy to obtain fast dynamics. The proposed algorithm in this article performs an additional measurement in the middle of each computation step to detect rapid irradiance changes and subsequently to measure the power ramp rate quickly. Afterward, the voltage step undergoes adaptive calculations to constrain the power ramp rate to the predefined value. Comparison between simulations of the proposed strategy and conventional solutions reveals the superiority of the proposed algorithm for limiting the ramp rate under the influence of rapid irradiance changes. The results gained on experimental grounds on a 2.5-kW PV system are provided to validate the performance of the proposed PRRC algorithm under various operating conditions.

Grid-connected photovoltaic system with power smoothing

This paper analyzes the power smoothing of grid-connected photovoltaic (PV) systems under fast irradiance changes. The analyzed converter is composed of a triple active bridge series-resonant (TABSR) DC-DC converter cascaded with a voltage source inverter (VSI). Two controlled variables are considered: battery current and the PV voltage. The TABSR DC-DC converter is modeled as controlled current sources for the battery and the PV ports. The ramp rate (RR) control algorithm is used to smooth the PV output power profile enhancing the power delivered to the grid. Four ramp rates (10%, 5%, 2% and 1%) are used to evaluate the RR control algorithm and the battery state of charge (SOC) response. Therefore, the battery can be sized appropriately. Real data for irradiance and temperature in an overcast day is used to verify the effectiveness of the proposed system.

Modified Levy Flight Optimization for a Maximum Power Point Tracking Algorithm under Partial Shading

This paper presents a novel modified Levy flight optimization for a photovoltaic PV solar energy system. Conventionally, the Perturb and Observe (P&O) algorithm has been widely deployed in most applications due to its simplicity and ease of implementation. However, P&O suffers from steady-state oscillation and stability, besides its failure in tracking the optimum power under partial shading conditions and fast irradiance changes. Therefore, a modified Levy flight optimization is proposed by incorporating a global search of beta parameters, which can significantly improve the tracking capability in local and global searches compared to the conventional methods. The proposed modified Levy flight optimization is verified with simulations and experiments under uniform, non-uniform, and dynamic conditions. All results prove the advantages of the proposed modified Levy flight optimization in extracting the optimal power with a fast response and high efficiency from the PV arrays.

A novel fast MPPT strategy used for grid-connected residential PV system applied in morocco

Regardless its significant potential for generating renewable energy, Moroccan government prohibited the injection of production surplus into the low voltage (LV) network because it still lack the implementing decreases, that represents one of the principal challenges for residential self-production in the country. The focus of this paper work is to introduce and analyze a novel fast MPPT strategy applied in an improved grid-connected Residential PV system respecting the current legislative framework in Morocco, which allow to the consumer being an actor in the energy transition towards a low-carbon society by reducing his dependence to the electrical grid and managing his own energy consumption efficiently by a good switching between photovoltaic (PV) source and the grid and therefore making a framework of smart residence management system. The overall system is designed to improve the energy control performance with two techniques: the first one uses a novel high performance controller to track the maximum power point (MPP) of a photovoltaic array under fast irradiation and load changes. Among the advantages of this proposed controller is the stability of its output voltage with fast response speed to the required parameters. The second one uses a Power Factor Correction (PFC) circuit to ensure the power quality regulation in the grid side via a predictive current control method. Finally, the stability of a closed-loop system is simulated and analyzed using commercial software offering sufficient conditions to validate a practical stability and robustness of the proposed overall designed system.

MODIFICATIONS OF MAXIMUM POWER POINT TRACKING P&O METHOD FOR PHOTOVOLTAIC PANEL

Perturbation and Observe method for maximum power point tracking is presented in this paper. Three method modifications have been proposed, which allow satisfying tracking efficiency, even for very fast and noisy irradiance changes.

An improved MPPT scheme employing adaptive integral derivative sliding mode control for photovoltaic systems under fast irradiation changes

Maximum power point tracking (MPPT) is necessary to achieve an optimal exploitation of photovoltaic (PV) system. This paper presents a novel voltage-oriented MPPT (VO-MPPT) method, where the conventional perturb and observe (P&O) algorithm is combined with the proposed external voltage control based on an adaptive integral derivative sliding mode (AIDSM). It is designed with new sliding surface, in addition, the derivative and integral terms are chosen to eliminate the overshoot during fast changes in solar irradiation and to minimize the steady-state fluctuation. Furthermore, an adaptation mechanism is joined to adjust the controller gains under each irradiation level. The proposed MPPT is tested and compared with the most widely used MPPT methods by simulations using MATLAB/SimulinkTM and real time hardware in the loop (HIL) implementation. The results obtained with the proposed MPPT show excellent dynamic performance under fast irradiation changes.

Solar Irradiation Independent Expression for Photovoltaic Generator Maximum Power Line

In order to enhance maximum power point tracking (MPPT) speed of photovoltaic generators (PVGs) upon fast irradiation changes, maximum power line (MPL)-based control is often used. MPL is a curve, linking all possible MPP coordinates for a given temperature. In the literature so far, PVG MPL was either assumed linear, which is inaccurate for all irradiation levels, or possessed photocurrent dependence, requiring real-time estimation of the latter. In this letter, an irradiation-independent explicit expression for PVG MPL is derived, valid for all practical irradiation levels, thus allowing real-time implementation without the need of photocurrent estimation.

Power Ramp Limitation Capabilities of Large PV Power Plants With Active Power Reserves

Power ramp limitation (PRL) is likely to become a requirement for large-scale photovoltaic power plants (LPVPPs) in order to allow the increase of PV penetration levels. Especially in islands with reduced inertia capability, this problem is more stringent: high-power ramp can be caused by either fast irradiance changes or other participant generators for example wind power, or loads. In order to compensate for the power mismatch, LPVPPs must use active power reserve (APR), by either curtailment or auxiliary storage. The paper proposes a PRL control structure for dynamic APR sizing and deployment. The selected test case is the power system of Puerto Rico (PREPA), modeled using the modified IEEE 12 bus benchmark system, with different levels of PV penetration. It is shown that LPVPP with PRL can effectively reduce the ramping rate of the participating generators. Considering that the large area of LPVPPs acts as a filter against fast irradiance changes, the study also reveals the required plant size for which an auxiliary storage is no longer needed in order to comply with PRL requirements—an important economical aspect.

Mitigation of Fast Voltage Variations During Cloud Transients in Distribution Systems With PV Solar Farms

Since photovoltaic (PV) generators have no mechanical inertia, fast solar irradiance changes associated with cloud transients cause instantaneous variations in PV power output, resulting in rapid and possibly significant voltage changes in systems with high penetration of PV generators. In addition to characterizing this emerging power-quality issue, this paper proposes and investigates techniques to mitigate these fast voltage variations caused by cloud transients in distribution system with PV solar farms. The investigated approaches are based on the PV inverter capacity for fast reactive power compensation without the need to oversize the inverter or curtail the active power by using only the available reserve. Real measurement data characterize the issue and time-series power-flow simulations evaluate the mitigation techniques.

Multi String Grid-Connected PV System with LLC Resonant DC/DC Converter

This paper presents a grid-connected multi string photovoltaic (PV) system with a three level voltage source converter using double closed loop control strategy. The outer DC voltage control loop regulates the DC bus voltage while the inner current control loop synchronizes the output current with the grid voltage, thus ensuring unity power factor. In the proposed configuration, LLC resonant DC/DC converter is used to extract the maximum power and to boost the PV array voltage. It is intrinsically isolated by a high frequency transformer, so that the parasitic capacitance of the PV panels to ground could not be of concern; furthermore, because of soft switching technique, LLC converter operates at high frequency with low switching losses. Size and cost of the magnetic components and DC-link capacitor are decreased compared with traditional boost converters. An incremental conductance method integrated with PI controller is developed on LLC resonant converter to extract maximum power. Simulation studies confirm that the control design approaches taken are robust and the dynamic performance of the proposed system during fast solar irradiation changes is acceptable.

Voltage-Oriented Input-Output Linearization Controller as Maximum Power Point Tracking Technique for Photovoltaic Systems

This paper presents a robust input-output linearization controller as maximum power point tracking (MPPT) technique in a photovoltaic (PV) buck dc-dc converter with applications to dc microgrids, solar vehicles, or stand-alone systems. Due to the control structure proposed in this paper, the MPPT control system is able to track very fast irradiance changes. Meanwhile, the internal stability of the overall closed-loop system is guaranteed for different load scenarios. A sector condition is only required for the load current, which is satisfied for most of the current PV applications. In turn, this condition implies the robustness against oscillations in the dc bus voltage. Finally, the MPPT control system is validated through experimental results, where the closed-loop performance is evaluated under abrupt irradiance and set-point changes, parametric uncertainty, and dc bus load variations.

Improved Synthesis of Global Irradiance with One-Minute Resolution for PV System Simulations

High resolution global irradiance time series are needed for accurate simulations of photovoltaic (PV) systems, since the typical volatile PV power output induced by fast irradiance changes cannot be simulated properly with commonly available hourly averages of global irradiance. We present a two-step algorithm that is capable of synthesizing one-minute global irradiance time series based on hourly averaged datasets. The algorithm is initialized by deriving characteristic transition probability matrices (TPM) for different weather conditions (cloudless, broken clouds and overcast) from a large number of high resolution measurements. Once initialized, the algorithm is location-independent and capable of synthesizing one-minute values based on hourly averaged global irradiance of any desired location. The one-minute time series are derived by discrete-time Markov chains based on a TPM that matches the weather condition of the input dataset. One-minute time series generated with the presented algorithm are compared with measured high resolution data and show a better agreement compared to two existing synthesizing algorithms in terms of temporal variability and characteristic frequency distributions of global irradiance and clearness index values. A comparison based on measurements performed in Lindenberg, Germany, and Carpentras, France, shows a reduction of the frequency distribution root mean square errors of more than 60% compared to the two existing synthesizing algorithms.

Outdoor PV Module Performance under Fluctuating Irradiance Conditions in Tropical Climates

Tropical climates (such as in Singapore) are characterised by fast-changing irradiance conditions due to high variations in cloud coverage. Different photovoltaic (PV) technologies possibly react differently to these variations of irradiance conditions, which in turn will also influence the module performance. In this study, a novel method is introduced to systematically investigate the fluctuating irradiance and its influence on module performance. Taking the Adnot clear-sky irradiance model as reference, the fluctuating irradiance is separated into high and low irradiance levels using the Typical Meteorological Day (TMD) irradiance values of 2011. These two irradiance groups are then analysed individually for the impact of the fluctuation frequency (defined via the number of minutes of constant irradiance) on the following module parameters: short-circuit current, module temperature and efficiency. The distribution of fluctuating irradiance over a whole year in Singapore and its impact on 5 different module technologies (monocrystalline Si, hetero-junction Si wafer, a-Si single junction, a-Si double junction and micromorph Si) are presented. The results show that the efficiency of wafer-based Si modules is not much influenced by the fast irradiance changes and dominated by the temperature effect at high irradiance. In contrast, Si-based thin-film technologies are stronger impacted by the fluctuations. Amorphous Si technologies show higher efficiencies at low irradiances, while micromorph Si modules react similar to monocrystalline Si at high irradiances, however with a slight drop in efficiency at low irradiances. This study gives valuable insights into the PV module response to varying irradiance.