Showing papers on "AC power published in 2022"

Power‐frequency oscillation suppression algorithm for AC microgrid with multiple virtual synchronous generators based on fuzzy inference system

Abstract: In the microgrid, virtual synchronous generator technology can significantly enhance the anti-interference characteristics of the system frequency and bus voltage, as well as solve the problems of insufficient damping and low inertia. However, the system frequency and active power oscillation caused by power fluctuations and grid faults threaten the stable operation of the grid seriously. Therefore, for an alternating current (AC) microgrid multi-virtual synchronous generator (VSG) parallel system, an improved virtual synchronous generator control algorithm based on a fuzzy inference system is proposed, which adjusts the values of virtual inertia and damping coefficient dynamically through fuzzy logic rules to realize the coordinated control of the two. The enhanced VSG algorithm described in this research has a substantial influence on power-frequency oscillation suppression, decreases active power and frequency overshoot, shortens the adjustment time, and improves system frequency stability active power, according to simulation and experimental findings.

Distributed Event-Triggered Control for Reactive, Unbalanced, and Harmonic Power Sharing in Islanded AC Microgrids

Abstract: For several reasons, particularly due to the mismatch in the feeder impedance, accurate power sharing in islanded microgrids is a challenging task. To get around this problem, a distributed event-triggered power sharing control strategy is proposed in this article. The suggested technique adaptively regulates the virtual impedances at both fundamental positive/negative sequence and harmonic frequencies and, therefore, accurately share the reactive, unbalanced, and harmonics powers among distributed generation units. The proposed method requires no information of feeder impedance and involves exchanging information among units at only event-triggered times, which reduces the communication burden without affecting the system performance. The stability and interevent interval are analyzed in this article. Finally, experimental results are presented to validate the effectiveness of the proposed scheme.

A Distributed MPC to Exploit Reactive Power V2G for Real-Time Voltage Regulation in Distribution Networks

Abstract: It has been demonstrated theoretically and experimentally that the Vehicle-to-Grid (V2G) enabled electric vehicle (EV) charger is of a reactive power compensation ability with a battery or capacitor connected. To exploit the aggregated reactive power V2G abilities of massively dispersed EV chargers, a distributed model predictive control (DMPC) strategy applying to both balanced and unbalanced distribution networks (DNs) is proposed to integrate them into real-time DN voltage regulation. Firstly, based on the instantaneous power theory and voltage sensitivity matrices, a voltage regulation model considering the reactive response of EV chargers is established without violating the normal EV active charging demands. Then, a completely distributed framework is achieved by DMPC, in which prediction information and calculation results are shared in a Peer-to-Peer (P2P) way to realize the asynchronous broadcast. The proposed model and techniques are validated by numerical results obtained from the IEEE European low voltage test feeder system. The case studies indicate that the proposed DMPC is robust to communication latency (CML) and works effectively in both balanced and unbalanced DNs without any control center, which is a significant advantage for the promotion of real-time reactive power V2G in DNs with irregular user integration and relatively poor communication infrastructure.

An optimal hybrid control scheme to achieve power quality enhancement in micro grid connected system

Abstract: In this manuscript, a novel control scheme is proposed to achieve the power quality (PQ) enhancement of renewable energy sources (RES), such as photovoltaic (PV), wind turbine (WT), fuel cell (FC), and battery. The proposed hybrid technique is the consolidation of both the Improved Bat Algorithm (IBat) and Moth Flame Optimization Algorithm (MFOA), therefore it is known as Improved Bat search Algorithm with Moth Flame Optimization Algorithm (IBatMFOA) control strategy. The crossover and mutation function is utilized to modify the bats search behavior function. Here, MFOA is utilized to enhance the searching behavior of IBat technique by reducing the error function. The main goal of proposed IBatMFOA approach is “to enhance the PQ depending on active with reactive power varience.” To attain the target, MFOA is optimized to lessen the power variation. Moreover, the functioning cost of RESs is diminished based on daily with weekly data forecast, like grid electricity price, electrical load, environmental parameters. By using IBatMFOA technique, the entire system efficiency is enhanced. By then, the proposed method is activated in MATLAB site, then the performance is examined with existing methods, like artificial bee colony, Gravitational Search Algorithm, and Firefly algorithm. The active power controller parameters of proposed technique are 8.8554 and 1.8569. The reactive power controller parameters of proposed technique are 8.1657 and 1.5698.

Observer-Based Sliding-Mode Control for Grid-Connected Power Converters Under Unbalanced Grid Conditions

Abstract: This article proposes a novel robust control strategy for three-phase power converters operated under unbalanced grid conditions. A consolidated control objective is obtained in the stationary $\alpha \beta$ frame, which can be flexibly adjusted according to the degree of oscillation in the active and reactive powers and the balance of the three-phase current. Based on the dynamics of the converter and control objective, a control scheme in a cascaded framework is presented, in which an adaptive observer is applied to estimate the positive and negative sequences of the grid voltage. In the current tracking loop, a super-twisting algorithm current controller coupled with a super-twisting differentiator is implemented to track the current references, featuring rapid dynamics, and improved robustness. Additionally, in the voltage regulation loop, an effective composite controller is developed to regulate the dc-link voltage, where a super-twisting observer is used to estimate the load disturbance, thereby improving the performance of the converter. The experimental results are provided to confirm the effectiveness and superiority of the proposed control strategy.

Analysis, Design, and Implementation of Multi-Quasi-Proportional-Resonant Controller for Thyristor-Controlled LC -Coupling Hybrid Active Power Filter (TCLC-HAPF)

Abstract: Compared with the conventional active power filter, the thyristor-controlled LC -coupling hybrid active power filter (TC LC -HAPF) has a distinct characteristics of low dc-link operating voltage, which can lower the system and operational costs in the medium-voltage-level system. It also has a wider operational range than the conventional hybrid active power filter. Besides that, the TC LC -HAPF can provide reactive, harmonic, and unbalanced powers compensation simultaneously. In this article, the modeling of the TC LC -HAPF is investigated based on the linear control aspect. Then, the analysis, design, and implementation of a multi-quasi-proportional-resonant (MQPR) controller with gain scheduling for the TC LC -HAPF will be proposed, which can automatically change the resonant gain between the inductive and capacitive loads operation to improve its compensation performances. The proposed controller can significantly reduce the TC LC -HAPF steady-state current tracking errors and output current ripple. Finally, the simulation and experimental results are also provided to verify the effectiveness and performance of the MQPR controller for the TC LC -HAPF in comparison with the hysteresis current controller and quasi-proportional-resonant (QPR) controller, which shows superior compensating performances.

An optimized multi-objective reactive power dispatch strategy based on improved genetic algorithm for wind power integrated systems

Abstract: The large uncertainties in wind power generation will bring great challenges to the analysis of optimal reactive power dispatch (ORPD). This paper considers a multi-objective ORPD strategy solved by a heuristic search algorithm that combines the elitist non-dominated sorting genetic algorithm with inheritance (i-NSGA-II) and a roulette wheel selection to optimize the operation of wind power integrated systems. The proposed ORPD strategy employs day-ahead predicted wind energy and load demand data to optimally set of the following control variables: i) optimal tap positions of on-load tap changers (OLTCs), ii) reactive demand set point of reactive power compensators and iii) active and reactive power outputs of wind farms (WFs) with the objectives to minimize: a) voltage deviations, b) active power loss, c) wind turbine harmonic distortions and d) number of switching operations of OLTCs. Because of the uncertainties of wind energy and load demand, hourly modifications of the day-ahead optimal results are also formulated to determine the real-time optimal reactive power dispatch. The proposed new ORPD strategy has been rigorously tested using IEEE 33-bus test system, PG&E 69-bus test system and modified real GB network. Results obtained confirmed the efficacy and applicability of the proposed strategy in both distribution and transmission networks.

Multi-task short-term reactive and active load forecasting method based on attention-LSTM model

Abstract: With the rapid development of power markets, smart grids and large-scale renewable energy generation, it is crucial to be able to accurately predict both reactive and active power loads. In this paper, we propose a novel multi-task load forecasting method for predicting both active and reactive power simultaneously. The long short-term memory (LSTM) architecture is employed in the backbone prediction model, supported by an attention mechanism to prevent performance deterioration. Considering the latent dynamic correlations between the reactive and active loads of a substation, multi-task regression based on hard parameter sharing is adopted to treat the forecasting of both types of loads as parallel subtasks. Meanwhile, we design an adaptive combined-task-wise loss function to optimize the proposed multi-task load forecasting model to avoid biasing of the final model for any subtask. We compare our multi-task attention-LSTM (MTAL) model with other popular single-task load forecasting models and achieve superior accuracy on both subtasks. The results indicate that the proposed method is robust and reliable for practical applications in power systems.

A Two-Stage Parameter Optimization Method for Capacitive Power Transfer Systems

Abstract: Wireless power transfer (WPT) is more convenient and safer than conductive charging for power consumer electronics, biomedical devices, transportation systems, etc. Inductive power transfer is the most widely studied and commercialized WPT technique; however, capacitive power transfer (CPT) is becoming an attractive alternative, offering better misalignment tolerance and lower cost and weight. The electrical-field-resonance-based six-plate coupler system is one of the most typical configurations for high-performance CPT systems, but the associated large number of circuit parameters is always a critical issue for system design. In this article, a parameter optimization method is proposed for this topology. The ratio of the reactive power in the compensation network to the system transferred power is set as the main optimization goal. To solve the high-order optimization problem, a two-stage method is proposed to significantly reduce the optimization complexity while providing the optimized parameters of the whole system. To verify the effectiveness of this method, a 3-kW, 1-MHz CPT system with a 16-pF coupling capacitor is built. Both the simulation and experimental results show that the optimized parameters effectively improve the system efficiency, experimentally achieving 95.7% dc–dc overall efficiency under a 100-mm gap distance at the rated power.

Distributed Event-Triggered Control for Reactive, Unbalanced, and Harmonic Power Sharing in Islanded AC Microgrids

Abstract: For several reasons, particularly due to the mismatch in the feeder impedance, accurate power sharing in islanded microgrids is a challenging task. To get around this problem, a distributed event-triggered power sharing control strategy is proposed in this article. The suggested technique adaptively regulates the virtual impedances at both fundamental positive/negative sequence and harmonic frequencies and, therefore, accurately share the reactive, unbalanced, and harmonics powers among distributed generation units. The proposed method requires no information of feeder impedance and involves exchanging information among units at only event-triggered times, which reduces the communication burden without affecting the system performance. The stability and interevent interval are analyzed in this article. Finally, experimental results are presented to validate the effectiveness of the proposed scheme.

Active Power Backflow Control Strategy for Cascaded Photovoltaic Solid-State Transformer During Low-Voltage Ride Through

Abstract: Different from the conventional photovoltaic (PV) inverters, a three-phase PV solid-state transformer (SST) based on the cascaded H-bridge (CHB) topology can be regarded as consisting of three single-phase CHB inverters in essence. During the low-voltage ride through (LVRT), some phases of three-phase PV SST may inversely absorb active power from ac grid affected by negative-sequence voltages, resulting in that the dc bus voltages of all H-bridges in these phases continue to rise, and that the system will shut down due to overvoltage protection. To deal with this problem, in this article, we study the mechanism of active power backflow during LVRT, analyzes and compares the main methods for suppressing active power backflow, and then proposes an LVRT control strategy based on the zero-sequence voltage compensation, which not only ensures that all modules in three-phase PV SST transmit the almost same active power but also can avoid effectively active power backflow problem even if the total output active of PV array is relatively low. The validity of the proposed method is verified by the simulation and experimental results.

Unified Modeling and Analysis of Dynamic Power Coupling for Grid-Forming Converters

Abstract: Grid-forming converters, taking droop-controlled converters and virtual synchronous generators (VSGs) as typical examples, have shown great promise as the interfaces between renewable energy sources and the future power-electronics-based power system. However, the coupling between active and reactive power will adversely affect the dynamic performance and stability of grid-forming converters. In order to facilitate quantitatively analyzing and assessing the power coupling characteristics of various types of grid-forming strategies, this article develops a unified dynamic power coupling model based on a first amplification coefficient array and a relative gain array in the frequency domain. Then, by using the established unified model, a comprehensive analysis of dynamic power coupling properties for typical VSG control and droop control is presented, which reveals that droop control is helpful in weakening power coupling while VSG control is prone to amplify the coupling. Moreover, the influences of the pivotal control parameters in droop and VSG controllers on power coupling characteristics are discussed in detail, which can provide novel supplementary guidelines for parameter design of droop and VSG controllers. Finally, the experimental results verify the correctness of theoretical modeling and analysis.

MPC-Based Decentralized Voltage Control in Power Distribution Systems With EV and PV Coordination

Abstract: Distribution systems are growing rapidly in size and complexity with increased penetrations of distributed energy resources (DER) and electric vehicles (EVs), leading to operational challenges. Reactive power compensation from photovoltaic (PV) inverters and active power curtailment of PV output are commonly used to mitigate voltage-related problems. However, the charging/discharging flexibility of EVs can be used to avoid PV output curtailment and save energy motivating methods to coordinate EV charging with PVs. Unfortunately, a large number of control variables makes the centralized voltage control computationally expensive. In this work, a decentralized voltage control algorithm which considers the active and reactive power compensation from PV inverters and EVs is presented. The proposed approach helps to solve the voltage issues in a more effective way. The approach involves clustering of the distribution network based on modified modularity, an index that considers EV flexibility and prediction time period. A model predictive control (MPC)-based algorithm is proposed for each cluster to solve the voltage problem using the respective PVs and EVs, while ensuring that the EV charging demand is satisfied while contributing to the voltage regulation. The proposed algorithm is validated using the IEEE 123 node test systems under two PV and EV penetration levels and shown to be effective in solving the voltage regulation problem.

Optimal Distributed Control of AC Microgrids With Coordinated Voltage Regulation and Reactive Power Sharing

Abstract: In this paper, we propose an optimal distributed voltage control for grid-forming (GFM) inverters in islanded AC microgrids. An optimization problem is formulated where the distributed generator (DG) output voltage is considered as the control variable with technical constraints on voltage and reactive power output capacity and an objective function that makes a trade-off between voltage regulation and reactive power sharing. A distributed primal-dual gradient based algorithm is developed to solve the formulated optimization problem to address the challenges due to non-separable objective function, unavailable global average voltage, and globally coupled reactive power constraints. The effectiveness of the proposed optimal distributed control is validated through simulations on the 4-DG test microgrid and the modified IEEE 34-bus distribution test system, and the advantages of the proposed control over existing controls are demonstrated.

A Hybrid Modulation Control for Wireless Power Transfer Systems to Improve Efficiency Under Light-Load Conditions

Abstract: Traditional wireless power transfer (WPT) systems usually adopt the triple-phase-shift control method to maintain a constant output voltage, track the maximum system efficiency point (MEPT), and achieve zero-voltage-switching (ZVS) operation for various applications. However, these three targets are achieved at the cost of high reactive power on both primary and secondary sides, especially under light-load conditions, leading to low efficiency. This has become one of the challenges that hinder a further deployment of WPT technologies in practice. To address this vital problem, in this article, how the reactive power lowers the system efficiency is revealed based on a mathematical model established. Then, a hybrid modulation control strategy based on a proper selection between the full-bridge and half-bridge modes of the inverter and active rectifier is developed. An experimental prototype is constructed to verify the effectiveness of the proposed control method. Experimental results show that the proposed method can reduce the reactive power, maintain a constant output voltage, and realize the MEPT and ZVS operation, with high efficiencies up to 94.29% in a wide load range.

Review of Soft-Switching Topologies for Single-Phase Photovoltaic Inverters

Abstract: Soft switching is one of the effective techniques to improve the efficiency and power density of power electronics converters. This article presents a comprehensive review of the soft-switching topologies used in single-phase photovoltaic (PV) inverters for residential applications. The topologies of single-phase PV inverters are investigated and divided into two types of power conversion stages: the PV interface stage for boosting PV voltage and the grid interface stage for feeding ac power to the grid. The soft-switching topologies for each type of power conversion stage are reviewed and compared, respectively, including the soft-switching mechanisms, efficiency, device ratings, and design challenges. Discussions and recommendations of soft-switching topologies for each stage are also provided. This article is an attempt to provide a helpful reference for engineers working on high-performance single-phase PV inverters.

Reactive Power Markets: a Review

Abstract: Liberalization of the energy system sets the way towards market-based solutions for ancillary service provision. Local reactive power markets are envisioned to achieve more economically and technically efficient reactive power provision to solve voltage control problems in future distribution and transmission grids. However, market-based reactive power procurement is a difficult and yet unsolved problem. This survey provides a comprehensive overview of the characteristics and hardships of reactive power markets. That is followed by a literature overview of reactive power market design, including local markets and markets on system operator level. Further, methods how to analyse reactive power markets are discussed, focusing on market power, game theoretical approaches, Reinforcement Learning, and manipulation of reactive power markets. From this overview, trends and current research gaps are derived and some general research recommendations are given to serve as a guideline for future research in the field of reactive power markets.

Analysis of Distributed Generation Integration Effect on Active Power Losses in Distribution Networks

Abstract: Distributed Generation (DG) is commonly used to reduce active power losses on a distribution network. The optimal location and size of DG will result in minimum active power losses and voltage profile improvement. This research proposes Novel Voltage Sensitivity Index (NVSI) and Stability Index (SI) methods to determine the optimal location and analytical expression to find optimal size and location of DG in Makassar distribution system, Feeder Kima, 76 buses to minimize active power losses and to improve voltage profile. Therefore, DG interconnection has a significant effect on improving the quality of the distribution network. The results show that the sensitivity method does not lead to the best placement DG in reducing active power losses. However, it is an analytical expression, which is very effective in determining optimal location and size of DG to reduce active power losses and to improve voltage profile in Makassar distribution system, Feeder Kima, 76 buses. The most optimal location for DG placement is on Bus 73 (Mega Sakti Pyramid), with a DG size of 0.8515MW. These combinations reduce 45.77% active power losses and increase 1.7336% voltage profile.