Power Mismatch Research Articles

New Passive Loss of Mains Detection Scheme Using Characteristics of Differential Impedance of Series Inductor

Nowadays, renewable energy sources (RESs) are widely used as distributed generation sources, leading to issues such as unintentional islanding, protection concerns, and reverse power flow. Unintentional islanding is dangerous because it can endanger utility workers, damage DG units, and jeopardize grid stability. To overcome these issues, Researchers are developing islanding detection schemes. This article proposes a novel passive technique for islanding detection of multi-bust test systems, based on the differential impedance of a series inductor. The differential impedance changes during islanding and non-islanding events. However, in grid-connected mode, the voltage and frequency of the microgrid are handled by the utility grid. Therefore, no significant changes in differential impedance occur. The voltage and frequency of the microgrid are not handled by the power grid while in islanded mode. Therefore, the differential impedance varies significantly. The islanding is detected if the value of differential impedance is greater than the predefined threshold. This scheme detects islanding in 24 ms at zero mismatch power, has no impact on power quality, and is computationally simple. The proposed approach easily discriminates between islanding and non-islanding events. The distribution test system is simulated in MATLAB/Simulink environment. Additionally, the novel passive technique has been validated on an OPAL-RT real-time platform.

Zero power mismatch islanding detection algorithm for hybrid distributed generating system

Distributed generation is essential for both keeping up with the rising power demand and reducing the amount of money spent on fossil fuels. There is widespread agreement that the world should prioritize the development of renewable energy systems such as wind and solar energy. This study describes the design and utility-grid integration of a hybrid distributed generating system that utilizes photovoltaic and wind-driven permanent magnet synchronous generators (hybrid PMSG-PV systems). To prevent damage to the grid, hybrid distributed generation systems, consumer devices, and line workers must be protected from islanding. Detection of islanding in hybrid DG systems has been suggested using passive islanding and time-spectral analysis. Measuring and amplifying the ripple content present in voltage at point of common coupling (PCC) about 0.4 seconds after the permissible delay time after the circuit breaker opens on the utility grid side is how islanding is discovered using this method. Compared to other methods, the proposed method has smoother islanding detection waveforms owing to increases in both the window size and threshold limit. The suggested method detects islanding in 40 ms and is verified in a variety of non-islanding scenarios, such as fault occurrence, parallel feeder loss, and load shift. In addition, the cost is reduced, the response time is rapid, and there is no non-detection zone (NDZ) when using these methods. Unlike active islanding detection methods, their function is unaffected by the size, quantity, or type of distributed generators linked to the utility grid; hence, there are no power quality concerns.

A Sizing Procedure for the DC-Side Capacitor of a Three-Phase Modular Multilevel Converter

The integration of photovoltaic (PV) modules with a modular multilevel converter (MMC) is very interesting because it allows us to exploit the intrinsic advantages of that converter, such as modularity and high voltage quality, and to implement distributed maximum power point tracking algorithms. The latter can appropriately be performed through controlling the circulating currents. In the literature, some control strategies for both the AC and DC circulating currents were proposed to manage the power mismatch among the legs and between the arms of the MMC. In a previous work, the authors proposed a novel control strategy for the circulating current components and inserted a capacitor on the DC side of a three-phase MMC with integrated PV panels. In the present work, it is shown how the correct sizing of this capacitor is essential to optimize the AC circulating voltages and minimize converter losses. A sizing procedure is proposed, deeply analyzed, and validated through numerical simulations.

The Scheme of Movable DC Ice Melting Device Based on the Engine-Generator Topology

In this article, an entire scheme of DC ice-melting devices based on the engine-generator topology is proposed to solve the problem of poor portability caused by the current devices. It is found that the engine-generator topology suffers from a power mismatch when starting with load, which may eventually lead to starting failure. A soft-start strategy is proposed to control the power required by the load by controlling the duty cycle of the switching tube to achieve real-time power matching. Compared with the most popular phase-controlled rectifier DC ice melting device, the entire scheme of the device is proposed, which not only achieves continuous voltage and current adjustment but also effectively reduces the ripple of the output and control complexity. The feasibility of the proposed soft-start strategy and the entire scheme of the device is verified by simulation results.

Performance of Osprey Optimization Algorithm for Solving Economic Load Dispatch Problem

The osprey optimization algorithm (OOA) is a new metaheuristic motivated by the strategy of hunting fish in seas. In this study, the OOA is applied to solve one of the main items in a power system called economic load dispatch (ELD). The ELD has two types. The first type takes into consideration the minimization of the cost of fuel consumption, this type is called ELD. The second type takes into consideration the cost of fuel consumption and the cost of emission, this type is called combined emission and economic dispatch (CEED). The performance of the OOA is compared against several techniques to evaluate its reliability. These methods include elephant herding optimization (EHO), the rime-ice algorithm (RIME), the tunicate swarm algorithm (TSA), and the slime mould algorithm (SMA) for the same case study. Also, the OOA is compared with other techniques in the literature, such as an artificial bee colony (ABO), the sine cosine algorithm (SCA), the moth search algorithm (MSA), the chimp optimization algorithm (ChOA), and monarch butterfly optimization (MBO). Power mismatch is the main item used in the evaluation of the OOA with all of these methods. There are six cases used in this work: 6 units for the ELD problem at three different loads, and 6 units for the CEED problem at three different loads. Evaluation of the techniques was performed for 30 various runs based on measuring the standard deviation, minimum fitness function, and maximum mean values. The superiority of the OOA is achieved according to the obtained results for the ELD and CEED compared to all competitor algorithms.

Control techniques for operation of roof-top solar photovoltaics based microgrid in islanded mode

This paper presents the control techniques for the operation of roof-top solar photovoltaics based single-phase ac microgrid in islanded mode. The proposed microgrid consists of four roof-top photovoltaics on various buildings, battery energy storage system in each building, and loads. In each building, the roof-top photovoltaic system is connected to the single-phase ac loads and proposed single-phase ac microgrid through the two-stage converter, which consists of dc-dc boost converter and bidirectional single-phase voltage source converter. A bidirectional dc-dc converter is used to connect the battery energy storage system to the photovoltaic system. The control technique of the bidirectional single-phase voltage source converter, using the feed-forward and feed-back control signals, has been suggested into a rotating d-q synchronous reference frame, with the dual controllers, for controlling the power mismatch and rated sinusoidal ac voltage of the microgrid. The control technique of the bidirectional dc-dc converter, used for the battery energy storage system, is implemented with two voltage controllers and one current controller for managing of the power mismatch in the proposed microgrid system. In this work, the power control algorithms have also been developed, which are aimed to manage the power balance in the single roof-top PV based building as well as in the proposed microgrid, under islanded mode, for various operating scenarios including fault condition.

Performance improvement of reconfiguration strategies in photovoltaic array by replacement of blocking diodes with MOSFETs

ABSTRACT The power from photovoltaic array (PVA) is affected by temperature, solar irradiation, dust concentration, wind velocity, photovoltaic array configuration (PVAC) and shading pattern. The problem of partial shading (PS) is recognized as a major concern which decreases the PVA output power and represents multiple peak power points in the PV characteristic. Different PVACs respond differently with regard to their mismatch power loss (MPL) and fill factor (FF) under partial shaded condition (PSC). The conventional PVACs, such as SP-diode (Series-Parallel), TCT-diode (Total-Cross-Tied), BL-diode (Bridge-Link) and HC-diode (Honey-Comb), use blocking diodes (B-diodes) to block the reverse current. On the other hand, the proposed PVACs, including SP-MOSFET, TCT-MOSFET, BL-MOSFET and HC-MOSFET, replace the B-diodes with Blocking P-MOSFETs (BP-MOSFETs). The improvement in power output of the PVA is examined for four different configurations with B-diode and BP-MOSFET under changing illumination conditions. It is observed that TCT-MOSFET configuration shows better performance with least power losses and maximum efficiency under PSCs.

Power Mismatches Elimination Strategy for MMC-Based Photovoltaic System and Lightweight Design

For the modular multilevel converter (MMC) based photovoltaic system (MMC-PV), when the sub-modules (SMs) of MMC are connected to distributed photovoltaic (PV), power mismatches between legs and arms is the inherent problem. To eliminate the power mismatches, this article proposes a lightweight MMC-based grid-connected energy router (MGER) integrated PV and energy storage (ES). Large-scale PV and centralized ES are connected to horizontal three SMs through four-terminal dual-active-bridges (FDAB). The primary three full-bridges of which adopts synchronous switching to achieve mismatch power elimination between horizontal SMs, so legs power balance can be realized. In addition, the SMs three-phase symmetrical ripple-power can also cancels each other out under synchronous switching of primary FDAB, so as to achieve low capacitance and lightweight of MGER, and the MMC arms 2nd-order circulating current can be also eliminated from root cause. In this article, the power mismatches analysis, MGER configuration, power mismatches elimination, control method, and lightweight implementation are discussed in detail. Finally, the correctness and effectiveness of proposed scheme are verified by simulation and experiment.

Multi-Agent Distributed Reinforcement Learning Algorithm for Free-Model Economic-Environmental Power and CHP Dispatch Problems

In conventional methods for Economic Dispatch Problem (EDP) and Economic-Environmental Dispatch Problem (EEDP), a full connection between the units and the control center is considered, while some faults in the communication system are possible in practical conditions. Hence, an intelligent and high-speed distributed method that is robust against disconnection is needed. In this paper, a Multi-Agent Distributed Reinforcement Learning (MADRL) algorithm based on consensus control for EDP and EEDP is presented. In this method, the incremental cost of units is optimized based on Lagrange method and the reinforcement learning algorithm. Thus, a performance index is defined for each agent in proposed algorithm to be independent of the unit model. The performance index of each agent is the sum of two terms, including i) the difference between the previous performance index value and local power and heat mismatch values and ii) the sum of the difference between the incremental cost of the unit with other neighboring units. In other words, optimizing the defined performance indexes of the agents eliminates the need for the system model. The MADRL method is tested on several grids and compared with other methods. The numerical results show an improvement in the algorithm speed and optimal point.

Consensus-Based Energy Management of Microgrid With Random Packet Drops

Decentralized energy management using consensus-based algorithm is a vibrant research field since it can promote the local accommodation of the renewable energy generation without raising privacy and scalability issues. Most of the existing methods assume that the communication links are reliable, which might not be true in real-world implementations. This paper focuses on tackling the problem of random packet drops. We first formulate the models of the energy management problem in the microgrid and the information packet drop in the communication network. Based on the models, we conclude that losing the information about incremental electricity cost estimation is tolerable, while losing the information about the power mismatch estimation is not. We propose a novel consensus algorithm that tracks and exchanges the accumulated value of the power mismatch estimation so that the information loss can be recovered. An equivalent form of the proposed method is established by augmenting the communication links with virtual buffering nodes. Based on the augmented communication topology, we theoretically prove the convergence of the proposed algorithm and the optimality of the solution. Several case studies are provided to validate the effectiveness of the proposed algorithm.

Performance Enhancement of Single-Phase Two-Stage AC-DC Converter With Reduced DC-Link Capacitance

Single-phase two-stage AC-DC converters employed in electric vehicle (EV) chargers have the tendency to produce low frequency ripple due to input/ output power mismatch, making it necessary to use bulky DC-link capacitors. High voltage ripple at DC-link due to reduced capacitance, prompts poor input power quality and high low-line frequency ripple at the output of secondary-stage. In state-of-art, input power quality in converters with low DC-link capacitance is enhanced by using a digital low-pass filter (LPF). However, employing LPF to sensed DC-link voltage results in a non-optimum dynamic response and deteriorated stability margins. With the objective to improve input power quality, enhance dynamic performance and reduce secondary-side ripple for low valued DC-link capacitance AC-DC converters, a modified unit-template based model predictive (MUT-MPC) and a DC-link feedforward (DFF) controls are presented in this paper. The current feed-forward for the unit-template is controlled by predictive voltage error through an optimization process of cost function to improve input power quality and dynamic performance for primary AC-DC converter. Furthermore, a DC-link feedforward (DFF) control is implemented for secondary DC-DC stage, which reduces the low-frequency current ripple at the load. Finally, to verify the effectiveness of presented multi-objective control method in comparison with traditional controls, MATLAB simulations and experimental results are provided.

The Effects of Non-Uniformly-Aged Photovoltaic Array on Mismatch Power Loss: A Practical Investigation towards Novel Hybrid Array Configurations

One of the most important causes of a reduction in power generation in PV panels is the non-uniform aging of photovoltaic (PV) modules. The increase in the current–voltage (I–V) mismatch among the array modules is the primary cause of this kind of degradation. There have been several array configurations investigated over the years to reduce mismatch power loss (MPL) caused by shadowing, but there have not been any experimental studies that have specifically examined the impact of various hybrid array topologies taking PV module aging into consideration. This research examines the influence of the non-uniform aging scenario on the performance of solar PV modules with various interconnection strategies. Experiments have been carried out on a 4 × 10, 400 W array with 12 possible configurations, including three proposed configurations (LD-TCT, SP-LD, and LD-SP), to detect the electrical characteristics of a PV system. Finally, the performances of different module configurations are analyzed where the newly proposed configurations (SP-LD and LD-SP) show 15.80% and 15.94% higher recoverable energy (RE), respectively, than the most-adopted configuration (SP). Moreover, among the twelve configurations, the SP configuration shows the highest percentage of MPL, which is about 17.96%, whereas LD-SP shows the lowest MPL at about 4.88%.

Island detection for grid connected photovoltaic distributed generations via integrated signal processing and machine learning approach

The applications of distributed generators in distribution networks have proven to be highly reliable and cost-effective. Accidental islanding is currently regarded as an undesirable operational mode in utility practice because it can harm individuals and connected systems. Therefore, the occurrence of islanding must be detected, and then distributed generators must be disconnected from the main network. In this article, a fast and accurate island detection method is proposed for photovoltaic distributed generations with a near-zero non-detection zone. A new island detection approach is developed by combining signal processing and machine learning techniques. Variational mode decomposition is used as a signal processing technique. Whereas the ensemble bagged-trees method is used as a machine learning technique. Variational mode decomposition is used to process positive- and negative-sequence component voltage signals along with power signal measurements acquired from the point of common coupling in order to identify intrinsic-mode functions. Next, the ensemble bagged-trees method is utilized to detect islanding during active and reactive power mismatch events and inconvenient quality factors. The results demonstrate that the suggested technique is able to discriminate between islanding and non-islanding events such as capacitive switching, fault emulation, and distribution generation cut-off. Besides, it has a minimum non-detection zone of less than 4% and a 4.8 ms detection time. Therefore, it is a reliable and reasonable solution for the distribution grid.

Optimal PV array reconfiguration under partial shading condition through dynamic leader based collective intelligence

This paper applies the innovative idea of DLCI to PV array reconfiguration under various PSCs to capture the maximum output power of a PV generation system. DLCI is a hybrid algorithm that integrates multiple meta-heuristic algorithms. Through the competition and cooperation of the search mechanisms of different metaheuristic algorithms, the local exploration and global development of the algorithm can be effectively improved to avoid power mismatch of the PV system caused by the algorithm falling into a local optimum. A series of discrete operations are performed on DLCI to solve the discrete optimization problem of PV array reconfiguration. Two structures (DLCI-I and DLCI-II) are designed to verify the effect of increasing the number of sub-optimizers on the optimized performance of DLCI by simulation based on 10 cases of PSCs. The simulation shows that the increase of the number of sub-optimizers only gives a relatively small improvement on the DLCI optimization performance. DLCI has a significant effect on the reduction in the number of power peaks caused by PSC. The PV array-based reconstruction system of DLCI-II is reduced by 4.05%, 1.88%, 1.68%, 0.99% and 3.39%, when compared to the secondary optimization algorithms.

Comparison of Meta-Heuristic Optimization Algorithms for Global Maximum Power Point Tracking of Partially Shaded Solar Photovoltaic Systems

Partial shading conditions lead to power mismatches among photovoltaic (PV) panels, resulting in the generation of multiple peak power points on the P-V curve. At this point, conventional MPPT algorithms fail to operate effectively. This research work mainly focuses on the exploration of performance optimization and harnessing more power during the partial shading environment of solar PV systems with a single-objective non-linear optimization problem subjected to different operations formulated and solved using recent metaheuristic algorithms such as Cat Swarm Optimization (CSO), Grey Wolf Optimization (GWO) and the proposed Chimp Optimization algorithm (ChOA). This research work is implemented on a test system with the help of MATLAB/SIMULINK, and the obtained results are discussed. From the overall results, the metaheuristic methods used by the trackers based on their analysis showed convergence towards the global Maximum Power Point (MPP). Additionally, the proposed ChOA technique shows improved performance over other existing algorithms.

Parabolic Mirror‐Assisted Thermoelectric and Radiative Cooling System for Maximizing Power Generation Utilizing Solar and Outer Space Thermodynamic Resources

AbstractRadiative cooling technology is extensively researched as a green technology, leveraging outer space as a thermodynamic resource. Recently, integrating thermoelectric generators (TEGs) and radiative coolers (RCs) are proposed to generate power using the temperature difference between the ambient and the radiative cooler. However, current TEG‐RC systems only utilize one thermodynamic resource, resulting in suboptimal efficiency. It proposes a parabolic mirror‐assisted TEG‐RC system that fully utilizes both the Sun and outer space as thermodynamic resources. The system places the hot side of the TEG, covered by a solar absorber (SA), at the focal point of the parabolic mirror, while the RC is located on the cold side of the TEG. Theoretical and experimental results reveal the optimal ratio between the RC and SA sizes to balance the power mismatch between cooling and heating powers. It also finds that the number of TEG stacks significantly affects power generation efficiency and determines the optimal number. Outdoor measurements demonstrate exceptional power generation during the daytime, which is an unprecedented achievement. This study also demonstrates the further enhancement in power generation efficiency when the proposed system is integrated with concentrated solar cells instead of the SA.

Modeling and performance analysis of novel quad‐tied PV array configuration under partial shading conditions

AbstractA photovoltaic (PV) cell is the smallest unit in an array that exhibits nonlinear characteristic curves. To gather the maximum amount of energy from a PV array under partial shading conditions (PSCs), it is necessary to follow the largest peak in the power–voltage (P–V) curve. PV cells are partially or totally shaded due to atmospheric conditions, which show multiple peaks in the PV curve. To overcome the losses occurring due to PSCs, PV array reconfiguration action is advisable. The authors of this work proposed a novel quad‐tied PV array configuration and compared its performance to that of other current configurations such as series‐parallel, total‐cross tied, and others in terms of global maximum power point tracking, mismatch loss, fill factor, and efficiency. The MATLAB/Simulink 2020a platform was used to generate PV array curves under various shading conditions.

Methods for increasing the potential of integration of EV chargers into the DC catenary of electric transport grids: A trolleygrid case study

The traction substations of urban electric transport grids are oversized and underutilized in terms of their capacity. While their over-sizing is an unfortunate waste, their under-utilization creates the major hurdle for the integration of renewables into these grids due to the lack of a base load. Therefore, integrating smart grid loads such as EV chargers is not only an opportunity but a necessity for the sustainable transport grid of the future.This paper examines six methods for increasing the potential of EV chargers in three case studies of a trolleygrid, namely a higher substation no-load voltage, a higher substation power capacity, a smart charging method, adding a third overheard parallel line, adding a bilateral connection, and installing a multi-port converter between two substations. From the case studies, the most promising and cost-effective method seems to be introducing a bilateral connection, bringing a charging capacity for up to 175 electric cars per day. Meanwhile, other costly and complex methods, such as smart charging with grid state sensors and communication, can offer charging room for over 200 electric cars per day. Furthermore, using solar PV systems to power the grid showed a more than doubling of the directly utilized energy by installing a 150kW charger, from 19% to 41%. This reduces the power mismatch between the trolleygrid and the PV system from 81% to 59% and thereby reduces the severe economic need for storage, AC grid power exchange, or PV power curtailment while allowing a high penetration of renewables.

Innovative Methodologies for Higher Global MPP of Photovoltaic Arrays under PSCs: Experimental Validation

Partial shading conditions (PSCs) are responsible for the root causes of photovoltaic (PV) system performance deprivation such as hotspots (damaged PV cells), mismatch power losses and multiple power maxima. Recently, PV array reconfiguration strategies have proven to be beneficial in improving PV system performance and achieving improved shade dispersion properties. This research analyzes the improved Su-Do-Ku (I-SDK) PV array configuration in order to counteract the shading effect. This approach implements a 6 × 6 size PV array configuration and performance evaluation under different realistic shading scenarios. The performance of the I-SDK configuration is assessed and compared to that of the total-cross-tied (TCT) and Su-Do-Ku (SDK) arrangements. The performance indices such as power loss (PL), power at global maximum power point (GMPP), fill-factor (FF), performance ratio (PR), power enhancement (PE) and execution ratio (ER) are analyzed to show comprehensive comparison. An experimental analysis confirms the MATLAB/Simulink findings, demonstrating that the I-SDK configuration outperforms both the TCT and SDK array setups. The GMPP values of 143.5 W, 141.7 W, 138.1 W and 129.3 W also show the superiority of I-SDK during four shading instances compared to conventional SP, TCT, SDK and SM arrangements. Moreover, under similar PSCs, higher %FF (74.61%, 76.10%, 77.1%, 75.92%) and lower PL (36.7 W, 38.5 W, 42.1 W, 50.9 W) support the adoptability of I-SDK for experimental validation/commercial viability.

Passive Island Detection Method Based on Positive Sequence Components for Grid-Connected Solar–Wind Hybrid Distributed Generation System

This paper presents the development and practical implementation of a new passive island detection method for grid-connected hybrid distributed generating systems. The method employs positive sequence voltage and current components at the point of common coupling. The product of the difference in positive sequence voltage and the difference in positive sequence current is used to produce the Islanding Detection Index (IDI). Islanding is identified when the IDI magnitude surpasses a predefined threshold over a predefined delay time. Even in the case of a zero power mismatch condition, the proposed method can identify the islanding condition in under 70 msec. Its effectiveness is validated under various operating circumstances. It provides excellent stability against various non-islanding situations, avoiding unwanted tripping. The suggested method also has the advantages of being simple and inexpensive to implement, having no adverse effects on output power quality, not requiring a classifier, not being system-dependent, and working regardless of the quantity and type of distributed generation connected to the utility grid. The obtained detection timings were compared to those previously reported in the literature, confirming the proposed approach’s superiority. The suggested work utilizes the OPAL-RT real-time hardware-in-loop environment and MATLAB/Simulink.