Showing papers on "Voltage regulator published in 2021"

Deep Reinforcement Learning Based Volt-VAR Optimization in Smart Distribution Systems

Abstract: This paper develops a model-free volt-VAR optimization (VVO) algorithm via multi-agent deep reinforcement learning (DRL) in unbalanced distribution systems. This method is novel since we cast the VVO problem in distribution networks to an intelligent deep Q-network (DQN) framework, which avoids solving a specific optimization model directly when facing time-varying operating conditions in the systems. We consider statuses/ratios of switchable capacitors, voltage regulators, and smart inverters installed at distributed generators as the action variables of the agents. A delicately designed reward function guides these agents to interact with the distribution system, in the direction of reinforcing voltage regulation and power loss reduction simultaneously. The forward-backward sweep method for radial three-phase distribution systems provides accurate power flow results within a few iterations to the DRL environment. The proposed method realizes the dual goals for VVO. We test this algorithm on the unbalanced IEEE 13-bus and 123-bus systems. Numerical simulations validate the excellent performance of this method in voltage regulation and power loss reduction.

Optimal Coordinated Allocation of Distributed Generation Units/ Capacitor Banks/ Voltage Regulators by EGWA

Abstract: Enhancing the distribution systems performance is an important target for system operators. This article proposes an enhanced grey wolf algorithm (EGWA) for allocating the distributed generation units (DGUs) which is coordinated with the capacitor banks (CBs) and the voltage regulators (VRs) to achieve the target. Diversified tasks aim at minimizing the investment expenses of the coordinated equipment, and maximizing the benefits resulted from power losses reduction and the purchased power from the grid. In the technical direction, it is investigated through ameliorating the voltage profile and the loading capacity. Also, the loading variations are incorporated via light, shoulder, and peak levels of demand. A dynamic adaptation mechanism is used for updating the control parameters of the GWA. The proposed EGWA is employed for solving the optimal allocation problem (OAP) for two Egyptian distribution systems. Simulation results declare the proposed EGWA capability for solving the coordinated allocation of CBs, DGUs, and VRs. Great reduction of power losses is achieved with high improvement of the minimum voltage and loading capacity. Also, a comparative and statistical analysis is executed for the application of the proposed EGWA with different optimization techniques, which derives superior capabilities of the proposed EGWA over the others in the literature.

Robust Model Predictive Control Paradigm for Automatic Voltage Regulators against Uncertainty Based on Optimization Algorithms

Abstract: This paper introduces a robust model predictive controller (MPC) to operate an automatic voltage regulator (AVR). The design strategy tends to handle the uncertainty issue of the AVR parameters. Frequency domain conditions are derived from the Hermite–Biehler theorem to maintain the stability of the perturbed system. The tuning of the MPC parameters is performed based on a new evolutionary algorithm named arithmetic optimization algorithm (AOA), while the expert designers use trial and error methods to achieve this target. The stability constraints are handled during the tuning process. An effective time-domain objective is formulated to guarantee good performance for the AVR by minimizing the voltage maximum overshoot and the response settling time simultaneously. The results of the suggested AOA-based robust MPC are compared with various techniques in the literature. The system response demonstrates the effectiveness and robustness of the proposed strategy with low control effort against the voltage variations and the parameters’ uncertainty compared with other techniques.

Sliding Mode Control of Grid-Connected NPC Converters Via High-Gain Observer

Abstract: In this paper, a nonlinear high-gain observer (NHGO) based second-order sliding mode (SOSM) control strategy is proposed for the three-phase three-level neutral-point-clamped (NPC) converter. This controller applies the advanced SOSM algorithm both in the voltage regulation loop and in power tracking loop, which provides a fast dynamic for the dc-link voltage, and also assures a good steady state behavior for the NPC converter. Additionally, a NHGO technique is implemented in the voltage regulator combining with the SOSM algorithm. The conventional observer-based controllers suffer from the destructive effects of measurement noise, and it can only be addressed by diminishing the observer gain, which sacrifices the observer property. The NHGO technique adopts a time varying gain, that is, high gain in transient while low gain in steady state, which minimizes the adverse influence of measurement noise. The tuning method of the proposed NHGO-based SOSM controller is given to simplify the implementation process. Finally, the simulation and experimental results of the proposed control scheme for the NPC converter are given and compared with the conventional PI controller as well as the well-known linear extended state observer-based control method, which validates the feasibility and superiority of the proposed controller.

Predictive Coordinated and Cooperative Voltage Control for Systems With High Penetration of PV

Abstract: This article proposes a predictive coordinated and cooperative voltage control method in a power distribution system with high penetration of photovoltaic (PV) units. First, an integrated coordinated voltage control of voltage regulators (VRs) tap positions and cooperative distributed control of the reactive power output from PV inverters are used to maintain system voltages within an appropriate bandwidth. Next, solar power forecasting is applied to predict voltage changes, which are used to set the VR tap positions and capacitor switch status to prevent large voltage fluctuations. The fine tuning of voltage adjustment is then achieved by cooperative control of PV inverters to maintain a uniform voltage profile across the system. The proposed method is tested on a modified IEEE 123-node test feeder with high penetration of PVs using real measurement data and compared with the base case. Simulation results demonstrate the effectiveness of the integrated voltage control, as well as the enhancement from the predictive control through solar power forecasting-enabled voltage change estimates. Comparison to previous work in the literature shows significant improvement in terms of voltage deviation and reduction in excessive tap changes.

Optimal design of Fractional order PID controller based Automatic voltage regulator system using gradient-based optimization algorithm

Abstract: Considering the superior control characteristics and increased tuning flexibility of the Fractional-Order Proportional Integral Derivative (FOPID) controller than the conventional PID regulator, this article attempts to explore its application in the optimal design of the Automatic Voltage Regulator (AVR). Since FOPID has two additional tuning parameters (µ and ʎ) than its mentioned conventional counterpart, its tuning process is comparatively difficult. To overcome the stated issue, a self-regulated off-line optimal tuning method based on the Gradient-Based Optimization (GBO) algorithm is adopted in the current study. The optimal FOPID gains are obtained by minimizing the selected Fitness Function (FF) that is chosen as Integral Time Absolute Error (ITAE) in the current study. The simulations are performed using MATLAB/SIMULINK 2018a to test and compare the performance of the proposed GBO-based optimal AVR design based on the dynamic response, stability, and robustness evaluation metrics with some of the recently published metaheuristic optimization algorithm based optimal AVR designs in the literature. The results show that the proposed AVR design provides the most optimal dynamic response and enhanced stability among the considered AVR designs, thus proves its efficacy and essence.

Simultaneous design of fuzzy PSS and fuzzy STATCOM controllers for power system stability enhancement

Abstract: The low frequency oscillations have always been the main problem of power system and can lead to power angle instability, limiting the maximum power to be transmitted on tie-lines and system separation. For boosting power system stability limits, the most effectiveness way is to install supplementary excitation control, power system stabilizer (PSS) to add a supplementary feedback stabilizing signal into the automatic voltage regulator (AVR). This article investigates the coordination and optimization of fuzzy controllers for designing PSS and STATCOM controllers for more attenuation of power system fluctuations. The designed fuzzy controller replaces the STATCOM AC voltage regulator. Moreover, for more damping a fuzzy power system stabilizer (FPSS) is placed on all machines. Coordination between Fuzzy Based STATCOM (FSTATCOM) and FPSS is achieved by Self-Adaptive Learning Bat Algorithm (SALBA) in two stages. At first, scaling factors and then fuzzy sets of membership functions (MFs) will be tuned based on a performance index. To indicate the effectiveness of the proposed scheme, the coordinated optimized FPSS and FSTATCOM are compared with conventional design approaches like conventional PSS (CPSS) and proportional-integral controller based STATCOM (PISTATCOM). The simulations clearly demonstrate the effectiveness of the coordinated fuzzy controllers in terms of transient and dynamic stability.

Vulnerability Assessment of Conservation Voltage Reduction to Load Redistribution Attack in Unbalanced Active Distribution Networks

Abstract: This article proposes a new type of load redistribution attack on a closed-loop conservation voltage reduction (CVR) in an unbalanced three-phase distribution network having voltage regulators (an on-load tap changer (OLTC) and capacitor bank), smart inverters for solar photovoltaic and energy storage systems, and smart meters. The objective of the proposed attack strategy using a bilevel optimization problem is to maximize three-phase active power flow from the substation (upper level) while guaranteeing normal CVR operation (lower level) through the injection of malicious data into smart meters. The bilevel optimization problem is finally transformed into a single-level optimization problem based on Karush–Kuhn–Tucker conditions of the lower level optimization problem. An IEEE 13-node distribution feeder is used to quantify the performance of the proposed attack in terms of voltage level, OLTC tap position, PV penetration rate, and attack effort.

Minimizing Energy Storage Utilization in a Stand-Alone DC Microgrid Using Photovoltaic Flexible Power Control

Abstract: DC microgrids (dcMGs) are gaining popularity for photovoltaic (PV) applications as the demand for PV generation continues to grow exponentially. A hybrid control strategy for a PV and battery energy storage system (BESS) in a stand-alone dcMG is proposed in this paper. In contrast to the conventional control strategies that regulate the dc-link voltage only with the BESS, the proposed control strategy exploits both the PV system and the BESS to regulate the dc-link voltage. The PV acts as the primary dc voltage regulator allowing for the battery to remain standby as a secondary dc voltage regulating resource. As a result, the proposed control strategy minimizes the utilization of the BESS in order to prolong its lifetime while maintaining the state-of-charge (SoC) of the battery within a desired range. To achieve that, the flexible power point tracking (FPPT) concept is applied to the PV system to enhance the dynamic performance of the dcMG by adaptively adjusting the PV output power according to the load profile. The performance of the proposed control strategy is verified with experimental results. Furthermore, the effectiveness of the proposed control strategy on prolonging the lifetime of a lithium-ion battery and a lead-acid battery is investigated via a simulation case study with one-day load and irradiance curve profiles.

Performance evaluation of a novel improved slime mould algorithm for direct current motor and automatic voltage regulator systems

Abstract: This study deals with the controlling the speed of a direct current (DC) motor via a fractional order proportional–integral–derivative (FOPID) controller and maintaining the terminal voltage level ...

Operational planning steps in smart electric power delivery system.

Abstract: This paper presents a comprehensive review of advanced technologies with various control approaches in terms of their respective merits and outcomes for power grids. Distributed energy storage control is classified into automatic voltage regulator and load frequency control according to corresponding functionalities. These control strategies maintain a power balance between generation and demand. Besides, three basic electric vehicle charging technologies can be distinguished, i.e. stationary, quasi-dynamic and dynamic control. For realizing charge-sustaining operation at minimum cost quasi-dynamic and dynamic strategies are adopted for in-route charging, while stationary control can only be utilized when the electric vehicle is in stationary mode. Moreover, power system frequency stability and stabilization techniques in non-synchronous generator systems are reviewed in the paper. Specifically, a synchronverter can damp power system oscillations and ensure stability by providing virtual inertia. Furthermore, it is crucial to manage the massive information and ensure its security in the smart grid. Therefore, several attack detection and mitigation schemes against cyber-attacks are further presented to achieve reliable, resilient, and stable operation of the cyber-physical power system. Thus, bidirectional electrical power flows with two-way digital control and communication capabilities have poised the energy producers and utilities to restructure the conventional power system into a robust smart distribution grid. These new functionalities and applications provide a pathway for clean energy technology. Finally, future research trends on smart grids such as IoT-based communication infrastructure, distributed demand-response with artificial intelligence and machine learning solutions, and synchrophasor-based wide-area monitoring protection and control (WAMPC) are examined in the present study.

Online Learning Based Voltage and Power Regulator for AC Microgrids

Abstract: In this brief, an online learning-based adaptive secondary controller with extended state observer (ESO) is proposed for regulating the voltage and allocating the reactive power in an islanded microgrid. With the active disturbance rejection properties of the ESO technique, two delicately designed neural networks via online learning approaches are proposed to compensate for the unknown/uncertain dynamics (UD) in the microgrid and attenuate the impact of external disturbance. Moreover, a vector of switching factors is introduced to unify the voltage recovery of the critical bus and accurate reactive power-sharing into a single framework. It is also worth noting that the devised approach is deployed in a distributed fashion, which enables the microgrid to acquire the plug-and-play capability. Extensive simulations are conducted to verify the effectiveness of the proposed controller for several cases including islanding and sudden load changing.

Distributed Power Sharing Control for Islanded Single-/Three-Phase Microgrids With Admissible Voltage and Energy Storage Constraints

Abstract: This article investigates power sharing and power quality improvement issues of islanded single-/three-phase microgrids (S/T-MGs) where both sources and loads are unbalanced. A hierarchical distributed control approach is proposed, which consists of 1) a phase-independent virtual synchronous generator (P-VSG) control used for primary control of distributed generators (DGs), 2) a distributed secondary power flow regulator used for power sharing control among DGs and among phases, and 3) a distributed secondary voltage regulator used for voltage restoration and power quality improvement. Compared with conventional methods, the proposed control has several salient features: 1) the P-VSG control allows for independent and flexible power control and voltage regulation for each phase and accurate phase shifts; 2) distributed containment control proposed in the secondary power control and voltage regulation layer guarantees admissible output phase powers, voltage profiles and power quality; 3) the constraint operator developed for the secondary controllers makes charging/discharging power of the energy storage system (ESS) within permitted values; 4) communication delays are also considered in the proposed distributed approach. Simulation results are presented to demonstrate the proposed control method.

Maiden Application of Fuzzy-2DOFTID Controller in Unified Voltage-Frequency Control of Power System

Abstract: This article presents an amalgamated pattern of automatic load frequency control (ALFC) and automatic voltage regulator (AVR) system in a three-area interconnected power system using the Fuzzy two-...

HHO-based Model Predictive Controller for Combined Voltage and Frequency Control Problem Including SMES

Abstract: This paper discusses the modelling and control of a combined load frequency control (LFC) and automatic voltage regulator (AVR) system for a multi-area power system network with each generating are...

Fully Integrated Switched-Inductor-Capacitor Voltage Regulator With 0.82-A/mm 2 Peak Current Density and 78% Peak Power Efficiency

Abstract: Fully integrated voltage regulators (FIVRs) can improve the performance and reduce the power consumption of a system-on-chip (SoC) by providing point-of-load voltage regulation with dynamic voltage scaling. The desirable attributes of FIVRs include high power efficiency, high power density, and fast transient response, which are difficult to achieve due to on-chip area constraint and parasitic effects. Low-quality and low-density on-chip inductors and capacitors are currently the main performance-limiting factors. This article presents a switched-inductor-capacitor (SIC) voltage converter that can operate more efficiently with compact on-chip air-cored metal-tracked inductors than existing step-down voltage converters. The SIC converter consists of an inductor, a flying capacitor, and three power switches, and it can provide fine-grained voltage regulation by using pulsewidth-modulation (PWM) control. The unique SIC converter topology eases the on-chip inductor integration by positioning the inductor at the input power supply and reducing the current stress of the inductor. A proof-of-concept fully integrated SIC voltage regulator is fabricated in a 65-nm CMOS process, with an area of 1.3 mm $\times $ 0.5 mm excluding pads. The output voltage can be regulated from 0.6 to 0.9 V given a 1.2-V input power supply. The output voltage ripple is below 56 mV over the entire range of output voltages and load currents. The peak power efficiency is 78% at an output of 0.9 V and 406 mA. The peak power density is 730 mW/mm2, and the peak current density is 820 mA/mm2.

Optimal Restoration of Active Distribution Systems With Voltage Control and Closed-Loop Operation

Abstract: This article presents a new mixed-integer second-order cone programming model for solving the restoration problem in active distribution systems considering the optimal control of distributed generators (DGs), voltage regulators (VRs), on-load tap changers (OLTCs), and capacitor banks (CBs). In contrast to most of the works found in the literature, temporary loops may be formed in the network during the restorative operation state. This operating condition allows restoring the service to more loads. In this way, the objective function of the problem minimizes (i) the total load not supplied, (ii) the number of switching operations, (iii) the changes in the statuses of the voltage control devices and in the dispatch of the DGs, and (iv) the number of basic loops formed in the system. Several tests are carried out using a 53-node system for single-fault and multiple-fault scenarios. The results obtained with the proposed approach outperform the solutions achieved when only radial configurations are allowed in the problem. Moreover, it is also verified that the voltage control allows for more efficient restoration schemes.

Event-triggered distributed model predictive control for resilient voltage control of an islanded microgrid

Abstract: This article addresses the problem of distributed secondary voltage control of an islanded microgrid (MG) from a cyber‐physical perspective. An event‐triggered distributed model predictive control (DMPC) scheme is designed to regulate the voltage magnitude of each distributed generators (DGs) in order to achieve a better trade‐off between the control performance and communication and computation burdens. By using two novel event triggering conditions that can be easily embedded into the DMPC for the application of MG control, the computation and communication burdens are significantly reduced with negligible compromise of control performance. In addition, to reduce the sensor cost and to eliminate the negative effects of nonlinearity, an adaptive nonasymptotic observer is utilized to estimate the internal and output signals of each DG. Thanks to the deadbeat observation property, the observer can be applied periodically to cooperate with the DMPC‐based voltage regulator. Finally, the effectiveness of the proposed control method has been tested on a simple configuration with four DGs and the modified IEEE‐13 test system through several representative scenarios.

Reliability Analysis of Capacitors in Voltage Regulator Modules With Consecutive Load Transients

Abstract: Capacitors are critical in voltage regulator modules (VRMs), which contribute to store energy and stabilize the output voltage during load transients. Usually, VRMs work with consecutive load transients, which would bring more electrothermal stress to capacitors and affect the reliability of capacitors compared with the steady-state operation. Recently, some efforts have been made to investigate the reliability of capacitors in power electronic converters. Unfortunately, transient processes are commonly ignored, which can impair the accuracy of the lifetime estimation. Regarding this issue, this letter investigates the influence of transients on the damage of capacitors in VRMs. A 150-W VRM is introduced as a case study. First, the electrothermal stresses during steady state and transients are analyzed. Then, the lifetime calculation is considered from a single capacitor to hybrid capacitor banks. In addition, a suitable capacitor configuration of capacitor banks is also provided in order to maximize its lifetime.

Applying Synchronous Condenser for Damping Provision in Converter-dominated Power System

Abstract: The dynamic characteristics of converter-dominated systems are governed by controlling power converters and the interactions between converter systems and conventional alternators. Frequency oscillations can appear under dynamic operation conditions caused by the phase-locked loop dynamics and interactions among the converter control systems. The oscillations may be poorly damped, which can result in reduced power generation, longer settling time, or disconnections of sensitive components. It is foreseeable that damping services will be critical for power grid stabilization in the future with high penetration of renewable generation. In this work, synchronous condensers (SCs) are evaluated and applied to provide damping services to the power grid under post-event conditions. An innovative supplementary controller for the automatic voltage regulator of SCs is proposed to improve the frequency stabilization in a converter-dominated system after disturbances. Using local and remote measurements, SCs are able to modulate the reactive power output and hence, the terminal bus voltage, which further impacts the power flow in the system; therefore, damping can be provided to the frequency oscillations. The control is implemented on an industrial-level hardware platform, and the performance is verified by the hardware-in-the-loop simulation.

Control and Implementation of a Multifunctional Solar PV-BES-DEGS Based Microgrid

Abstract: A three-phase four-wire microgrid comprising of a solar photovoltaic (PV) array—battery energy storage—a diesel engine generator set (DEGS) is presented in this article. Here an enhanced adaptive filter (EAF) control and an incremental conductance (INC) maximum power point tracking algorithm are used to improve the power quality and to extract the maximum power from the PV array. The EAF control provides higher disturbance rejection capability over other controls. The EAF control is applied to the voltage source converter (VSC) to improve the power quality, such as compensation of harmonics, reactive power, and load unbalance. The INC control is used to harvest the PV array maximum power. For controlling the voltage output of the DEGS, an electronic automatic voltage regulator is provided at the synchronous generator field winding. The neutral current compensation is achieved by controlling the fourth-leg of VSC. This microgrid is simulated using MATLAB/Simulink tool. The robustness of the EAF control strategy is tested on a developed system prototype in the laboratory.