Voltage Regulation Loop Research Articles

A distributed double-layer control algorithm for medium voltage regulation and state of charge consensus of autonomous battery energy storage systems in distribution networks

The increasing integration of Distributed Generation (DG) based on Renewable Energy Sources (RES) in traditional distribution systems necessitates the adoption of smart grid strategies. These strategies rely heavily on energy storage actuation to manage the inherent variability of RES and ensure autonomous operation. This article presents a hierarchical digital control strategy for managing distribution power systems, utilizing Battery Energy Storage Systems (BESS) to regulate voltage amplitude and enhance overall behavior for efficient energy management. At the primary control level, operating at a minute-scale actuation rate, an integral voltage regulation loop determines the BESS power injection or consumption, refined by a fuzzy conditioning of signals that accounts for the state of charge and operational modes of each device. Laplacian and random switching secondary consensus control strategies, operating at a slower rate, ensure coordinated action among individual units. The convergence of these strategies is analytically validated using Lyapunov’s theory under idealized conditions. Extensive dynamic simulations over a 24-hour period demonstrate the proposed strategy’s effectiveness in improving power quality and coordinating voltage regulation, particularly in terms of enhancing the power factor and reducing the standard deviation of voltage and power variables over time in a coordinated manner.

Analysis of proportional-resonant damping factors in the parallel operation of UPSs

Accurate load-sharing and circulating current mitigation is a particular problem in parallel-connected inverters without intercommunication. This paper analyzes how using multiple-resonant controllers in the voltage regulation loop impacts the parallel operation of uninterruptible power supplies (UPSs) with droop control. It is shown how adding damping factors of all modes of the resonant controller reduces the circulating current between the UPSs, also improving the power-sharing closed-loop stability and performance. Moreover, the proper choice of these damping coefficients can replicate the effects of adding virtual resistance loops to the droop controller structure. An analysis of such coefficients on the stability margins of the voltage regulation system is carried out and the methodology is validated by experimental results considering the parallelism of two 3.5 kVA UPSs with parametric differences in their LC filters.

High-performance finite-time adaptive control strategy for three-level T-type converters

Three-level T-type converters are necessary interfaces for distributed energy resources to interact with the public grid. Naturally, designing a control strategy, featuring superior dynamics and strong robustness, is a promising solution to guarantee the efficient operation of converters. This article presents an improved finite-time control (IFTC) strategy for three-level T-type converters to enhance the dynamic performance and anti-disturbance capacity. The IFTC strategy integrates a dual-loop structure to regulate the dc-link voltage and grid currents. Specifically, the voltage regulation loop employs a finite-time adaptive controller that can counteract load disturbances without relying on current sensors. In the current tracking loop, finite-time controllers combined with a command filter are constructed to obtain fast and accurate current tracking. In this loop, the command filter is utilized to avoid calculating the derivative of current references. Theoretical analysis and experimental results demonstrate the IFTC strategy’s effectiveness.

Frequency and Voltage Stabilization of Multiarea Hybrid Power System by Considering the Impact of Communication Time Delay

The integration of renewable energy sources (RES) with conventional sources plays a vital role in global energy systems. With the integration of RES, frequency and voltage variations are the major issues, which degrade system performance. In this study, an optimal controller is designed to mitigate these frequency and voltage variations by considering the effect of communication time delays in the multisource two-area power system. Area-1 comprises conventional generation units (i.e., thermal, hydro, and gas) whereas area-2 comprises wind, solar, and diesel power plants. Frequency oscillations are mitigated by a load frequency control loop and variations in terminal voltage are regulated by an automatic voltage regulation loop. To enhance the system response, redox flow batteries, and interline power flow controllers are integrated in the system. Moreover, physical constraints, i.e., generation rate constraint is accounted in reheat thermal and hydropower plants. The proposed sine cosine algorithm tuned Proportional Integral Derivative controller ensures that variations of frequencies, terminal voltages, and exchange of tie-line power will remain within tolerance limits. The system response on random loading is evaluated and a comparison is done with state-of-the-art controllers. As a result, the proposed controller provides better performance by minimizing the fluctuations of frequency and voltages.

A Novel Frequency Compensation Scheme for Heavy Load LDO with Improved Load Regulation and High Open Loop Gain

This paper presents a novel frequency compensation scheme for the stability of low dropout regulator (LDO). The proposed compensation scheme introduces a zero in the voltage regulation loop to enlarge gain and phase margin at high‐frequencies. As a result, high open‐loop‐gain and improved load regulation performances are achieved, and a particular resistor is introduced in the compensation structure to cancel the voltage drop originating from cable resistances at the output to further improve the load regulation performance. The proposed LDO with wide input/output range and high‐power supply rejection is designed and implemented in a 180 nm CMOS process. The LDO operates with an input voltage range of 4–16 V, an output voltage range of 1.5–5 V and an output current range of 0–1000 mA. High open loop gain and high bandwidth are achieved, and the simulated performances of load regulation and line regulation are less than 32 μV/mA and less than 3 mV/V over the whole operation range, respectively. The on‐chip compensation capacitor required by the compensation module is only 1.8 pF. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Load Frequency Control and Automatic Voltage Regulation in Four-Area Interconnected Power Systems Using a Gradient-Based Optimizer

Existing interconnected power systems (IPSs) are being overloaded by the expansion of the industrial and residential sectors together with the incorporation of renewable energy sources, which cause serious fluctuations in frequency, voltage, and tie-line power. The automatic voltage regulation (AVR) and load frequency control (LFC) loops provide high quality power to all consumers with nominal frequency, voltage, and tie-line power deviation, ensuring the stability and security of IPS in these conditions. In this paper, a proportional integral derivative (PID) controller is investigated for the effective control of a four-area IPS. Each IPS area has five generating units including gas, thermal reheat, hydro, and two renewable energy sources, namely wind and solar photovoltaic plants. The PID controller was tuned by a meta-heuristic optimization algorithm known as a gradient-based optimizer (GBO). The integral of time multiplied by squared value of error (ITSE) was utilized as an error criterion for the evaluation of the fitness function. The voltage, frequency, and tie-line power responses of GBO-PID were evaluated and compared with integral–proportional derivative (GBO-I-PD), tilt integral derivative (GBO-TID), and integral–proportional (GBO-I-P) controllers with 5% step load perturbation (SLP) provided in each of the four areas. Comprehensive comparisons between GBO-PID and other control methodologies revealed that the proposed GBO-PID controller provides superior voltage, frequency, and tie-line power responses in each area. The reliability and efficacy of GBO-PID methodology were further validated with variations in the turbine time constant and speed regulation over a range of  ± 25%. It is evident from the outcomes of the sensitivity analysis that the proposed GBO-PID control methodology is very reliable and can successfully stabilize the deviations in terminal voltage, load frequency, and tie-line power with a shorter settling time in a four-area IPS.

Passivity-Based Control for Output Voltage Regulation in a Fuel Cell/Boost Converter System.

In this paper, a passivity-based control (PBC) scheme for output voltage regulation in a fuel-cell/boost converter system is designed and validated through real-time numerical results. The proposed control scheme is designed as a current-mode control (CMC) scheme with an outer loop (voltage) for voltage regulation and an inner loop (current) for current reference tracking. The inner loop's design considers the Euler-Lagrange (E-L) formulation to implement a standard PBC and the outer loop is implemented through a standard PI controller. Furthermore, an adaptive law based on immersion and invariance (I&I) theory is designed to enhance the closed-loop system behavior through asymptotic approximation of uncertain parameters such as load and inductor parasitic resistance. The closed-loop system is tested under two scenarios using real-time simulations, where precision and robustness are shown with respect to variations in the fuel cell voltage, load, and output voltage reference.

A 4.2–13.2 V, on-chip, regulated, DC–DC converter in a standard 1.8V/3.3V CMOS process

This paper presents a fully on-chip HV-regulated DC–DC boost converter for the power management unit of an electrical neural stimulator. The core of the DC–DC converter consists of a 4x4 array of individually-configurable charge pumps. The rows and columns of the array can be dynamically enabled or disabled, thus extending the range of suitable output voltages and load currents. Additionally, the converter includes a feedback loop for output voltage regulation which allows responding to abrupt changes in the load current within a few microseconds. The circuit has been designed in a standard 180 nm 1.8V/3.3V CMOS process and occupies an active area of 2.1mm2. An exhaustive experimental characterization of the proposed circuit was carried out. Experimental results demonstrate that, for an input voltage of 3V, the DC–DC converter’s regulated output ranges from 4.2V to 13.2V under load currents of 0.1–4 mA. Maximum delivered power is around 48mW. The power efficiency of the converter at the highest achievable output voltage under a 4 mA load current is higher than 65% for input voltages above 2.4V.

An Ultra-Low-Voltage Single-Crystal Oscillator-Timer (XO-Timer) Delivering 16-MHz and 32.258-kHz Clocks for Sub-0.5-V Energy-Harvesting BLE Radios in 28-nm CMOS

This paper reports an ultra-low-voltage (ULV) single-crystal oscillator-timer (XO-Timer) for sub-0.5 V Bluetooth low-energy (BLE) radios that aims for self-powering by harvesting the ambient energies. Specifically, we tailor an on-chip micropower manager (lPM) to customize the voltage and current budgets for each sub-function of the XO-Timer. Such lPM shows a high power efficiency by introducing a 3-stage cascaded structure and a single voltage-regulation loop; they together uphold the performance of the XO-Timer amid supply-voltage and temperature variations. The core amplifier of the XO-Timer is ULV-enabled, and is reconfigurable (i.e., 1-stage and 3-stage gm) to balance between the power budget and performance under the high-performance mode (HPM) and low-power mode (LPM). Fabricated in 28-nm CMOS, the XO-Timer in HPM generates a 16-MHz clock with a power of 24.3 lW, and a phase noise of.133.8 dBc/Hz at 1-kHz offset, resulting in a Figure-of-Merit (FoM1) of.236 dBc/Hz. In the LPM, the XO-Timer delivers a 32.258-kHz clock while consuming 11.4 lW. The sleep-timer FoM2 is 14.8 lW and the Allan deviation is 35.1 ppb, achieving the lowest supply voltage (0.25 V) not only for a dual-mode XO-Timer but also for a MHz-range XO.

SMES-GCSC Coordination for Frequency and Voltage Regulation in a Multi-Area and Multi-Source Power System with Penetration of Electric Vehicles and Renewable Energy Sources

Frequency, tie-line power, and the terminal voltages of synchronized generators must all be kept within prescribed limits to ensure the stability of an interconnected power grid through combined automatic generation control (AGC) and automatic voltage regulator (AVR) loops. Thermal power plants, electric vehicles, and renewable energy sources—including solar and wind, geothermal, and solar thermal power plants—form the two-area integrated power system in present research. A new cascade controller named the cascaded proportional integral derivative (PID) and fractional-order PID (CPID-FOPID) controller is proposed for the first time, whose performance is compared with the PID and FOPID controller. The results show that the proposed cascade controller outperforms PID and FOPID in delivering superior dynamic characteristics, including short settling times and low oscillation amplitudes. A new metaheuristic algorithm named the coot algorithm was applied to optimize the parameters of these controllers. The suggested controller outperforms FOPID in the combined AGC and AVR problem under uncertain conditions (random load disturbance, variable input of solar irradiation, and wind power). Robustness of the controller is tested with significant variation in the turbine time constant of the thermal and geothermal power plant. In this study, authors also investigated the best possible coordination between the superconducting magnetic energy storage (SMES) and gate-controlled series capacitor (GCSC) devices to control both voltage and frequency simultaneously. The effect of communication time to the power system is analyzed in this study. Additionally, the obtained results are satisfactorily validated using OPAL-RT real-time digital simulator.

An Inductor-First Single-Inductor Multiple-Output Hybrid DC–DC Converter With Integrated Flying Capacitor for SoC Applications

With the increasing complexity of highly integrated system on chips (SoCs), the power management system (PMS) is required to provide several power supplies efficiently for individual blocks. This paper presents a single-inductor multiple-output (SIMO) inductor-first hybrid converter that generates three outputs between 0.4V and 1.6V from a 1.8V input. The proposed multiple-output hybrid power stage can improve the conversion efficiency by reducing inductor current while extending the output voltage range compared with the existing hybrid topologies. In addition, the proposed converter employs an on-chip switched-capacitor power stage (SCPS) with a dual-switching frequency technique, resulting in a fast response time, low cross-regulation, and reduced number of on-chip pads. Measurement results show that the converter achieves a peak efficiency of 87.5% with the maximum output current of 450mA. The converter is integrated with a fast voltage regulation loop with 500MHz system clock to achieve a less than 0.01mA/mV cross-regulation and a maximum 20mV overshoot at full-load transient response. The design is fabricated in the standard 180nm CMOS technology.

Fuzzy Sliding-Mode Control for Three-Level NPC AFE Rectifiers: A Chattering Alleviation Approach

Due to the high-performance requirements of power converters in industrial applications, sliding-mode control has drawn extensive research attention for its insensitivity against external disturbances. In order to ensure this advantage while suppressing the chattering problem caused by discontinuous switching functions, in this article, a fuzzy sliding-mode control (FSMC) strategy consisting of three control loops is proposed for three-phase three-level neutral-point-clamped active front-end rectifiers. In the power tracking loop, an improved super-twisting algorithm is proposed to enforce the tracking errors of active power and reactive power to bounded regions in finite time and guarantee the transient performance. Next, in the dc-link voltage regulation loop, the regulation error of dc-link voltage converges to a bounded region with a super-twisting extended state observer-based FSMC strategy. A simple but efficient proportional-integral controller is employed in dc-link voltage balancing loop to reduce the voltage difference between two dc-link capacitors. The proposed controller is characterized by attenuated chattering phenomenon and improved the dc-link voltage regulation performance, disturbance rejection ability, and power tracking performance. Experimental results are provided to verify the effectiveness and superiority of the proposed strategy.

Load Frequency Control and Automatic Voltage Regulation in a Multi-Area Interconnected Power System Using Nature-Inspired Computation-Based Control Methodology

The stability control of nominal frequency and terminal voltage in an interconnected power system (IPS) is always a challenging task for researchers. The load variation or any disturbance affects the active and reactive power demands, which badly influence the normal working of IPS. In order to maintain frequency and terminal voltage at rated values, controllers are installed at generating stations to keep these parameters within the prescribed limits by varying the active and reactive power demands. This is accomplished by load frequency control (LFC) and automatic voltage regulator (AVR) loops, which are coupled to each other. Due to the complexity of the combined AVR-LFC model, the simultaneous control of frequency and terminal voltage in an IPS requires an intelligent control strategy. The performance of IPS solely depends upon the working of the controllers. This work presents the exploration of control methodology based on a proportional integral–proportional derivative (PI-PD) controller with combined LFC-AVR in a multi-area IPS. The PI-PD controller was tuned with recently developed nature-inspired computation algorithms including the Archimedes optimization algorithm (AOA), learner performance-based behavior optimization (LPBO), and modified particle swarm optimization (MPSO). In the earlier part of this work, the proposed methodology was applied to a two-area IPS, and the output responses of LPBO-PI-PD, AOA-PI-PD, and MPSO-PI-PD control schemes were compared with an existing nonlinear threshold-accepting algorithm-based PID (NLTA-PID) controller. After achieving satisfactory results in the two-area IPS, the proposed scheme was examined in a three-area IPS with combined AVR and LFC. Finally, the reliability and efficacy of the proposed methodology was investigated on a three-area IPS with LFC-AVR with variations in the system parameters over a range of  ± 50%. The simulation results and a comprehensive comparison between the controllers clearly demonstrates that the proposed control schemes including LPBO-PI-PD, AOA-PI-PD, and MPSO-PI-PD are very reliable, and they can effectively stabilize the frequency and terminal voltage in a multi-area IPS with combined LFC and AVR.

Fuzzy Logic System-Based Sliding-Mode Control for Three-Level NPC Converters

Nowadays, power converters have become the key to overcoming many challenges, so as to achieve more efficient transportation systems. Sliding-mode control (SMC) has become one of the preferred choices for power conversion applications because of its insensitivity to external disturbances. However, it is a challenge to suppress the chattering phenomenon. To solve this problem, in this article, a fuzzy logic system-based SMC strategy is proposed for three-phase three-level neutral-point-clamped power converters to improve the disturbance rejection ability, dc-link voltage regulation ability, and power tracking ability with good chattering suppression ability. The proposed controller is composed of three control loops. In the power tracking loop, a fuzzy super-twisting algorithm is proposed to force the active power and reactive power tracking their reference values. A fuzzy observer-based fuzzy SMC method is used in the dc-link voltage regulation loop to regulate the dc-link voltage to the reference value. Then, in the dc-link voltage balancing loop, a simple proportional–integral control strategy is utilized to balance the voltages of two dc-link capacitors. Finally, three groups of experiments are provided to validate the effectiveness and superiority of the proposed strategy.

Sliding Mode Control of Grid-Connected Neutral-Point-Clamped Converters Via High-Gain Observer

In this article, 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 the 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, an 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.

An enhanced implementation of SRF and DDSRF-PLL for three-phase converters in weak grid

Abstract Renewable energy generation systems connected to utility grid require perfect synchronization to grid which is one of the most important issues that needs to be taken into consideration. This paper proposed a hardware-accelerated implementation for the decoupled double synchronous reference frame phase-locked loop (DDSFR-PLL) for grid synchronization in grid-connected converters in weak grid that suffers from phase voltage-unbalance, variable phase and frequency conditions. Since the transformations and filtering of this method is computationally intensive and needs to be executed as fast as possible by the microcontroller unit (MCU) and Due to the presence of other current and voltage regulation loops in the same interrupt service routine (ISR) with high frequency rate, a hardware-based acceleration using the STM32G4x4 MCU built-in filter, filter math accelerator (FMAC) and coordinate rotation digital computer (CORDIC) is used to speed the execution time. This study addresses the description, derivation and implementation of the both DQ-PLL and DDSRF-PLL algorithms. The performance of both pure-software and accelerated implementation is demonstrated, compared and run on a three-level active neutral point clamped (ANPC) converter board. In proposed method, CPU load dropped from 80.5% by using the conventional software implementation to 23.6% (70% load reduction).This reduction in CPU load enables the addition of more features and more advanced current and voltage control algorithms.

The concept of direct adaptive control for improving voltage and frequency regulation loops in several power system applications

This article presents the idea of direct adaptive control for several power system applications such as the Egyptian power system (EPS), a three-zone interconnected microgrid (MG), and a single machine connected to the grid (SMIB). The main concept of the proposed adaptive method is built on the tuning of the controller gains using Harris hawks optimizer (HHO). In order to maintain the frequency and voltage at their nominal values, a modified virtual rotor (virtual inertia + virtual damping) is investigated as a tertiary control loop within the proposed EPS and the 3-area MG system. For SMIB application, a secondary automatic voltage regulator (AVR) has been added to the primary AVR within the excitation system to offer more adequate damping characteristics for the synchronous generator of the studied system. Where the proportional-integral-derivative power system stabilizer (PID-PSS) is connected to the excitation system for a single machine tied to the grid to significantly mitigate low-frequency oscillations due to various expected faults and undesirable operating conditions. The proposed direct adaptive control strategy has been used to tune the integral controller of the secondary AVR and PID for SMIB application, and also to adjust the virtual rotor in the EPS and the 3-area MG applications. The operative performance of the introduced adaptive secondary AVR is assessed against the conventional system (no PSS), Lead-Lag PSS, and PSS type 2 based PSO and WECC standard under the effect of a 3-φ short-circuit fault subjected at the grid bus considering solar photovoltaic (PV) farm-based grid. Moreover, the EPS system and 3-area MG are evaluated under the effect of load change conditions and partial injection of PV and random loads. The final findings prove that the direct adaptive concept can provide robust performance and effectively maintain the dynamic stability of the main grid against fluctuations.

Experimental validation of advanced SP-SAF based on intelligent controllers for power quality enhancement

In this paper, an intelligent control of the single-phase shunt active filter (SP-SAF) for power quality improvement is proposed. The developed approach is essentially composed of two controllers based on the fuzzy logic theory. The first fuzzy proportional derivative (PD) controller with integral (I) action replacing the standard PI regulator, intervenes in the DC voltage regulation loop of the depollution device. In addition, it effectively participates in the delivery of the reference source current. The second controller represented by a fuzzy hysteresis regulator ensures better control of the filter current. Moreover, it acts as an intelligent governance decision maker of the (DC/AC) converter constituting the filtering system. The strategy offers a source current of sinusoidal shape respecting the imposed international standards and the operation of the treated system under a power factor very close to unity. The effectiveness of the new proposed control strategy has been tested through MATLAB/Simulink software and practically validated via the dSPACE 1104 card under various operating conditions. Finally, the experimental results show that the proposed control paradigm outperformed the existing control schemes.

Adaptive Second-Order Sliding Mode Control for Grid-Connected NPC Converters With Enhanced Disturbance Rejection

In this article, a two-stage control scheme consisting of an adaptive-gain second-order sliding mode (SOSM) controller and a switched high-gain observer (HGO) is proposed for the three-level neutral-point-clamped (NPC) converter. The adaptive-gain SOSM control method is applied both in the voltage regulation loop and instantaneous power tracking loop, thus, the boundary of the disturbance derivative does not need to be known <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> . Compared with the fixed-gain SOSM, it provides a faster dynamic and a better steady-state response for the NPC converter. On the other hand, the conventional disturbance compensation observer used in the power system suffers from the adverse effects of measurement noise, which limits the performance of the observer. A switched HGO is combined with the adaptive-gain SOSM controller in the voltage regulation loop to address this issue. By using a switched observer gain, the switched HGO greatly diminishes the performance degradation induced by the inevitable measurement noise. Finally, several experiments between the representative extended state observer-based SOSM control scheme and the proposed control method are carried out for a comparison. The results demonstrate the feasibility and effectiveness of the proposed approach.

Flatness-SVPWM Control for Three-Phase Shunt Active Power Filter Based on Five-Level NPC Inverter

The increasing use in the industry of nonlinear loads based on power electronic elements has introduced serious perturbation problems in the electric power distribution grids. These nonlinear loads generate non-sinusoidal currents to the mains which degrade the system's performance. Active power filters have been developed over the years to solve these problems and improve power quality. This study focuses on the use of a shunt active power filter to compensate nonlinear load's current harmonics and reactive power. To this end, a regulator based on the flatness control technique combined with an SVPWM strategy for a three-phase shunt active power filter based on a five-level neutral-point-clamped (NPC) inverter is used. The control objectives of this work are twofold: i. compensating the current harmonics and the reactive power produced by the nonlinear loads, and ii. regulating the inverter's DC capacitor voltage. To achieve these objectives, two cascaded loops are designed; an inner loop for the reactive and harmonic currents compensation based on a flatness controller and an outer loop for the DC voltage regulation based on a PI regulator. The simulation results are developed under MATLAB/Simulink environment to prove the satisfactory performance of the proposed controlled system.