Multi-string Photovoltaic Research Articles

An adapted model predictive control MPPT for validation of optimum GMPP tracking under partial shading conditions

The energy generation efficiency of photovoltaic (PV) systems is compromised by partial shading conditions (PSCs) of solar irradiance with many maximum power points (MPPs) while tracking output power. Addressing this challenge in the PV system, this article proposes an adapted hybrid control algorithm that tracks the global maximum power point (GMPP) by preventing it from settling at different local maximum power points (LMPPs). The proposed scheme involves the deployment of a 3 × 3 multi-string PV array with a single modified boost converter model and an adapted perturb and observe-based model predictive control (APO-MPC) algorithm. In contrast to traditional strategies, this technique effectively extracts and stabilizes the output power by predicting upcoming future states through the computation of reference current. The boost converter regulates voltage and current levels of the whole PV array, while the proposed algorithm dynamically adjusts the converter's operation to track the GMPP by minimizing the cost function of MPC. Additionally, it reduces hardware costs by eliminating the need for an output current sensor, all while ensuring effective tracking across a variety of climatic profiles. The research illustrates the efficient validation of the proposed method with accurate and stable convergence towards the GMPP with minimal sensors, consequently reducing overall hardware expenses. Simulation and hardware-based outcomes reveal that this approach outperforms classical techniques in terms of both cost-effectiveness and power extraction efficiency, even under PSCs of constant, rapidly changing, and linearly changing irradiances.

Investigation of single and multiple MPPT structures of solar PV-system under partial shading conditions considering direct duty-cycle controller

Partial shading of solar panels diminishes their operating efficiency and energy synthesized as it disrupts the uniform absorption of sunlight. To tackle the issue of partial shading in photovoltaic (PV) systems, this article puts forward a comprehensive control strategy that takes into account a range of contributing factors. The proposed control approach is based on using multi-string PV system configuration in place of a central-type PV inverter for all PV modules with a single DC-DC converter. This adaptation enhances overall efficiency across varying radiation levels. Also, the proposed technique minimizes the overall system cost by reducing the required sensors number by utilizing a radiation estimation strategy. The converter switching strategy is synthesized considering direct duty-cycle control method to establish the maximum power point (MPP) location on the P–V curve. The direct duty-cycle tracking approach simplifies the control system and improves the system’s response during sudden partial shading restrictions. To validate the effectiveness of the suggested MPPT method, two system configurations were constructed using MATLAB/SIMULINK software and assessed under various partial shading scenarios. Additionally, a multi-string system was subjected to real irradiance conditions. The sensor-less MPPT algorithm proposed achieved an impressive system efficiency of 99.81% with a peak-to-peak ripple voltage of 1.3V. This solution offers clear advantages over alternative approaches by reducing tracking time and enhancing system efficiency. The system findings undoubtedly support the theoretical scrutiny of the intended technique.

Integrated Duty Cycle Control for Multiple Renewable Energy Sources in a Grid Connected System

Due to their abundance, affordability, and clean energy production, Renewable Energy Sources (RESs) have emerged as crucial sources of electricity production. As a result, considerable effort has been made to integrate renewable energy sources into the grid to help it meet energy demands. One of the challenges is the Maximum Power Extraction (MPE), where the maximum power needs to be extracted from each RES. The cost of implementation rises linearly with the number of RESs if the MPE arrangements are being made for each RES individually. Additionally, the MPE through multiple RES systems gets more challenging, especially when several PhotoVoltaic (PV) strings are connected and each PV string receive non-uniform irradiance. This paper proposes an integrated MPE control system for a multi-RES grid-connected system. The proposed solution uses a single microcontroller to maximize power from all sources to overcome the linearly growing cost problem. Moreover, we propose an improved Multi-Dimensional Cuckoo (MDC) algorithm for MPE to tackle the non-uniform irradiation problem with multi-string PV, in contrast to prior works with grid-connected multiple sources. The proposed technique is first put up against the individual MPE control system, and then it is put up against the Jaya algorithm that is documented in the literature for a typical one-dimensional MPE.

Analytical Assessment of Time-Varying Reliability and Penetration Limit of PV-Integrated Systems

This article presents a discrete convolution-based method for reliability evaluation of a grid-connected photovoltaic (PV) system, where special consideration is given to the variable availability of PV array components. Along with the negative impacts of variable solar irradiance and ambient temperature on the PV power generation, they affect the reliability of PV system power electronic components. A variable availability model based on the power loss in the semiconductors of PV system components is needed to account for this effect in the reliability analysis. The article proposes a 3-D capacity outage model of a PV farm that accounts for the variable availability and the redundancies associated with the topologically complex multistring PV arrays. The outage model is used to construct a PV capacity outage probability and frequency table (COPAFT), which along with conventional generation COPAFT, is convolved with the distribution of load to determine system reliability. An integration limit assessment tool is also developed within the proposed framework, ensuring that the PV power integration does not violate the system frequency stability. Simulations on the modified IEEE RTS-79 system demonstrate the efficacy of the proposed method.

SOLAR PV SYSTEM WITH MULTI-LEVEL INVERTER USING PI AND FUZZY LOGIC CONTROLLER

This paper presents a single-phase multi-string Nine-level PV inverter topology for grid-connected photovoltaic (PV) systems with a novel PWM control and fuzzy logic scheme. The Multilevel inverters are extensively used due to their increased power rating reduced EMI, improving harmonic performance. Multilevel inverters are switched at low switching frequency when compared to two level inverters, a single-phase multi-string nine-level PV inverter topology for grid-connected photovoltaic (PV) systems using novel PWM control Technology. A photovoltaic (PV) system generates electricity by direct conversion. The PV strings are cascaded together in parallel configuration and connected to a Nine-level inverter to generate output voltage. Two reference sinusoidal signals are identical to each other with an offset equivalent to the amplitude of the triangular carrier signal were used to generate gate signals for the nine level inverter switches and it is to implement this PWM using PI current control algorithm. The proposed nine level inverter offers much less THD and can operate at near unity power factor. the frequency of it will be 50Hz and from the result we minimizes the number of components and devices as well as switching losses are reduced when compared to the conventional multilevel inverter topology and its interconnects for grid utilization. Fuzzy Logic Control (FLC), originating from control theory focused on mathematical representations of the open-loop mechanism to be controlled, is an integral aspect of fuzzy reasoning. Fuzzy Logic Control has been successfully extended to a wide range of practical issues, including warm water control, robot control, heat exchange, traffic junction control, cement kiln control, vehicle speed control, automotive engineering, and mcar parking and turning, power system and nuclear reactor, on-line shopping, washing machines, etc. The validity of the proposed inverter is verified through simulation andcompared with other technique. The output voltage will be in the form of stepped waveform. The proposed system produces less THD and reduction of steady state time KEYWORDS –Maximum Power Point Tracking(MPPT) algorithm, Boost Converter, FLC contreoller, PWM technique.

Design and field implementation of smart grid-integrated control of PV inverters for autonomous voltage regulation and VAR ancillary services

Ancillary services from Photovoltaic (PV) inverters can increase distribution system flexibility and alleviate the voltage regulation challenges associated with high PV penetration levels. However, the required communication infrastructure and smart grid integration challenges limit the broad deployment of PV ancillary services. This paper presents a cost-effective volt/var control (VVC) of multi-string PV inverters for active voltage regulation and reactive power dispatch using the existing smart distribution infrastructure to avoid the upfront costs of providing PV ancillary services. The proposed VVC model is developed in MATLAB/Simulink to adapt PV reactive power compensation according to the X/R characteristics of the distribution feeder. An IEC 61131-3 compliant prototype is designed based on Simulink PLC code and deployed to a commercially available remote terminal unit (RTU) using CODESYS standardization tool to address smart grid integration challenges. The proposed VVC scheme is tested in a real-world grid-connected PV system with multi-string inverters for experimental validation. Quasi-static time-series simulation and experimental results demonstrate the validated effectiveness of the proposed control scheme in controlling fast PV fluctuations, resolving voltage violations, voltage flickers, and enabling higher PV penetration.

Certain investigations of ANFIS assisted CPHO algorithm tuned MPPT controller for PV arrays under partial shading conditions

This paper conceptualizes development of solar energy harvesting in partial shading situations. Two methods, namely Photovoltaic (PV) system topology design and Maximum Power Point Tracking (MPPT) techniques, can well reduce partial shading effects. An active hybrid MPPT controller suggested harvesting PV power called the Adaptive Neuro-Fuzzy Inference System (ANFIS) assisted Crowded Plant Height Optimisation (CPHO) algorithm. In the multi-string PV system configuration, the DC–DC boost converter is operated between the PV string and inverter to maximise the power yield. The duty ratio of converter must be adjusted and kept at an optimal level to obtain maximum power from the PV array. During uniform irradiance condition, the CPHO tuned MPPT controller itself gives the optimal duty cycle. Under partial shading circumstances, the PV array power versus voltage characteristics has several peaks. Hence optimal duty cycle can be obtained in two stages. In the first stage, ANFIS performs estimation of Global Maximum Power Point (GMPP), among multiple Local Maximum Power Point (LMPP) peaks and tracks close to a peak power point. The second stage CPHO algorithm fine-tunes and attains the exact point of GMPP. Hence, the suggested hybrid MPPT controller detects the GMPP more accurately and settles down the oscillations of the duty cycle in a fast manner. The performance enlivened by getting optimal duty cycle, and this proposed approach fortified through the MATLAB/Simulink platform.

Optimal Energy Harvesting From a Multistrings PV Generator Based on Artificial Bee Colony Algorithm

Photovoltaic (PV) systems based on multistring configuration are the best effective solution, given its advantages in terms of system availability, reliability, and energy efficiency. In this particular configuration each substring has its own dc-dc converter and a dedicated maximum power search algorithm which increase the cost and complexity. In this article, an efficient centralized global maximum power tracking (GMPPT) algorithm for multistring PV array subject to partial shading conditions is proposed. The algorithm is based on artificial bee colony (ABC) as an optimization approach to provide the optimal duty cycles allowing the extraction of the optimal global maximum power from each substring. In particular, the proposed approach allows significant reduction of the required sensors to only one pair of current and voltage sensors, at the common point of connection of the overall PV strings. The simulation study has been carried out under Cadence/Pspice and MATLAB/Simulink platforms on the I-V curves to confirm the effectiveness of the proposed algorithm when several shading patterns occur. In addition, complex shading pattern of a daily profile has been also carried out to demonstrate the GMPPT finding in dynamically variable conditions. Performance comparison against particle swarm optimization based maximum power point tracking algorithm and the traditional perturb and observe method has also been carried out. The obtained simulation and experimental results have shown the effectiveness and a good tracking capability of the proposed ABC algorithm in a multistring PV array configuration under uniform and nonuniform irradiance.

All SiC Grid-Connected PV Supply with HF Link MPPT Converter: System Design Methodology and Development of a 20 kHz, 25 kVA Prototype

Design methodology and implementation of an all SiC power semiconductor-based, grid-connected multi-string photovoltaic (PV) supply with an isolated high frequency (HF) link maximum power point tracker (MPPT) have been described. This system configuration makes possible the use of a simple and reliable two-level voltage source inverter (VSI) topology for grid connection, owing to the galvanic isolation provided by the HF transformer. This topology provides a viable alternative to the commonly used non-isolated PV supplies equipped with Si-based boost MPPT converters cascaded with relatively more complex inverter topologies, at competitive efficiency figures and a higher power density. A 20 kHz, 25 kVA prototype system was designed based on the dynamic model of the multi-string PV panels obtained from field tests. Design parameters such as input DC link capacitance, switching frequencies of MPPT converter and voltage source inverter, size and performance of HF transformer with nanocrystalline core, DC link voltage, and LCL filter of the VSI were optimized in view of the site dependent parameters such as the variation ranges of solar insolation, module surface temperature, and grid voltage. A modified synchronous reference frame control was implemented in the VSI by applying the grid voltage feedforward to the reference voltages in abc axes directly, so that zero-sequence components of grid voltages are taken into account in the case of an unbalanced grid. The system was implemented and the proposed design methodology verified satisfactorily in the field on a roof-mounted 23.7 kW multi-string PV system.

Partial Shading Analysis of Multistring PV Arrays and Derivation of Simplified MPP Expressions

In this paper, the electrical response of a partially shaded photovoltaic (PV) array, comprising several strings connected in parallel, is investigated. The PV array is simulated by employing an enhanced version of the widely used single-diode model, reformulated in an explicit manner employing the Lambert W function. The multiple maximum power points (MPPs) that appear on the P-V characteristic of the array in partial shading conditions are analyzed, in terms of their number and properties. Simplified empirical expressions are then derived to calculate the voltage, current, and power for each local MPP, at any irradiance level and temperature, using only datasheet information, in a most simple and straightforward manner, without resorting to detailed modeling and simulations. The derived formulae are validated using both simulation and experimental results.

Single-Stage Multistring PV Inverter With an Isolated High-Frequency Link and Soft-Switching Operation

A grid-tied multistring photovoltaic (PV) inverter with a high-frequency ac (HFAC) link, soft-switching operation, and high-frequency (HF) galvanic isolation is introduced. This single-stage topology can handle an arbitrary number of PV strings with different electrical parameters, locations, and orientations. Using a dedicated maximum power point tracker for each PV string, this inverter can harvest the highest possible power from each string independently, even though they might be at dissimilar irradiance levels and operating temperatures. The isolated HFAC link is formed by the magnetizing inductance of a small-sized HF transformer and two small ac capacitors without the use of bulky short-life electrolytic capacitors. The link is responsible for transferring the PV strings' power to the grid along with creating zero-voltage switching for the power devices. Therefore, the converter has the advantages of high power density, high reliability, as well as high efficiency. After describing the control scheme and the operating algorithm of the proposed multistring inverter, a detailed analysis is carried out. The experimental results of the developed 1-kW two-string prototype with different PV strings at various PV conditions are also shown. The results verify the effectiveness of the topology in tracking the maximum power of each string independently without affecting the operating condition and control of the other string.