Voltage Tracking Error Research Articles

Asymptotic voltage restoration in islanded microgrids via an adaptive asynchronous event-triggered finite-time fault-tolerant control

As the actuators of distributed generators involved in Microgrids (MGs) may experience different faults, it is highly recommended to design an appropriate secondary Fault Tolerant (FT) controller to provide resilience and robustness with respect to these malicious events. Meanwhile, the reduction of communication network workload from controller-to-actuator may be helpful to mitigate actuators stress. By virtue of the above, this article aims at introducing a novel distributed adaptive FT-Event-Triggered Control (FT-ETC) scheme for secondary voltage regulation control in AC islanded MG able to compensate faulty actuators effects while reducing the waste of communication network resources. The proposed control scheme is derived with the aid of the backstepping method and the ETC theory, whose combination ensures resilience with respect to possible faulty signals, while no knowledge of global information is required. Adaptive mechanisms are derived by exploiting Lyapunov theory, while Zeno-freeness property is proven by contradiction. Compared with the existing state-of-the-art on FT-ETC in islanded MG, here the main novelty relies in achieving the asymptotic rather than the practical stability of the voltage tracking errors despite an unhealthy environment, while the remaining adaptive signals involved in the closed-loop systems are bounded in finite-time. Finally, an extensive simulation analysis, also involving real-time Hardware In-the-Loop (HIL) experiments, confirms the theoretical derivation.

Adaptive Supplementary Control of VSG Based on Virtual Impedance for Current Limiting in Grid-Connected and Islanded Microgrids

By applying virtual synchronous generator (VSG) method in high penetration level microgrids, current limiting issue under fault condition has become an important challenge. The main objective of this paper is to propose a novel current limiting strategy which has the capability of voltage tracking error reduction to avoid voltage controller saturation. This purpose is obtained by adaptive virtual impedance-based reference voltage correction during fault condition. Furthermore, positive and negative peak detection-based current limiting method implemented in double loop control system prepares soft transition ability. Moreover, this current limiting method generates the adaptive term of virtual impedance part. In contrast to conventional VSG methods, the proposed approach provides high quality voltage and current for microgrid in both grid-connected and islanded modes during fault conditions. The offline and hardware in the loop (HIL) simulation results confirm that the peak current of the inverter is restricted to the threshold value under symmetrical and asymmetrical faults for two operating modes of microgrid.

Model-Free Predictive Current Control of Five-Phase PMSM Drives

Model predictive control is highly dependent on accurate models and the parameters of electric motor drives. Multiphase permanent magnet synchronous motors (PMSMs) contain nonlinear parameters and mutual cross-coupling dynamics, resulting in challenges in modeling and parameter acquisition. To lessen the parameter dependence of current predictions, a model-free predictive current control (MFPCC) strategy based on an ultra-local model and motor outputs is proposed for five-phase PMSM drives. The ultra-local model is constructed according to the differential equation of current. The inherent relation between the parameters in the predictive current model and the ultra-local model is analyzed in detail. The unknowns of the ultra-local model are estimated using the motor current and voltage at different time instants without requiring motor parameters or observers. Moreover, space vector modulation technology is employed to minimize the voltage tracking error. Finally, simulations and experiments are conducted to verify the effectiveness of the MFPCC with space vector modulation. The results confirm that the proposed method can effectively eliminate the impact of motor parameters and improve steady-state performance. Moreover, this control strategy demonstrates good robustness against load variations.

Improved lumped electrical characteristic modeling and adaptive forgetting factor recursive least squares-linearized particle swarm optimization full-parameter identification strategy for lithium-ion batteries considering the hysteresis component effect

Electric vehicles, as a new green mode of transportation, have put forward higher demand indicators for accurate modeling and efficient parameter identification strategies for lithium-ion batteries. In this paper, a lumped electrical characteristic model is constructed for lithium-ion batteries considering the hysteresis component effect based on a proposed adaptive forgetting factor recursive least squares-linearized particle swarm optimization (AFFRLS-LPSO) algorithm with strong working condition characterization capability for full parameter identification. First, to characterize the relationship accurately and intuitively between the external characteristics and the internal state quantities of the battery, the charging and discharging measurement information is captured, and the difference in the open circuit voltage (OCV) caused by the hysteresis phenomenon is resolved. Then, the complex working condition experiments is conducted, and through online inspection of experimental data, the fusion strategy concept is introduced to prevent the phenomenon of “filter saturation” and improve the ability of the algorithm to track the variable characteristic parameters of the battery. The full parameter identification results and terminal voltage tracking effects under different identification strategies are compared. Also, the consistency verification results of the adaptive parameter identification strategy under different working conditions are further analyzed. The experimental results show that the voltage tracking error of the model with an added hysteresis component is significantly smaller than the error without hysteresis. Furthermore, at an ambient temperature of 15 °C, the root mean squared error and mean absolute percentage error of the AFFRLS-LPSO algorithm are reduced by 0.0037 V and 0.300 %, respectively, under the dynamic stress test and Beijing bus dynamic stress test working conditions, and the consistency accuracy of the unconstrained parameter estimation is improved by 9.9 %. The fusion strategy provides a theoretical basis for real-time parameter identification models for lithium-ion batteries with high precision and adaptability for electric vehicles.

SRFPI-LADRC Based Control Strategy for Off-Grid Single-Phase Inverter: Design, Analysis, and Verification

Linear active disturbance rejection control (LADRC) has been extensively used in various areas due to its excellent disturbance suppression capability. When LADRC is applied to a single-phase inverter for tracking a sinusoidal reference signal, there is an inherent tracking inaccuracy problem. The steady-state error can be removed with the synchronous reference frame proportional-integral (SRFPI) control, which generates two orthogonal signals. In this paper, a modified control method based on compound SRFPI and LADRC for an off-grid single-phase inverter is put forward, where both output signals of SRFPI are employed as the reference signals of LADRC. Furthermore, a selective harmonic compensation method is performed by paralleling multiple SRFPI controllers to further reduce the selective harmonic components. Detailed theoretical analyses including system stability, robustness, performance of voltage tracking error and disturbance rejection are presented, which indicate that this organic combination fuses the merits of both SRFPI and LADRC without complicating the control design. Additionally, contrast experiments are conducted to demonstrate its effectiveness and superiority. These findings demonstrate that the system realizes a slight voltage tracking error and steady-state error, rapid dynamic response, and low total harmonic distortion (THD), especially under highly nonlinear load conditions.

ELM-Based Adaptive Practical Fixed-Time Voltage Regulation in Wireless Power Transfer System

This paper proposes an extreme learning machine (ELM)-based adaptive sliding mode control strategy for the receiver-side buck converter system in the wireless power transfer system subjecting to the lumped uncertainty. The proposed control strategy utilizes a singularity-free fixed-time sliding mode (FTSM) feedback control, which ensures a fixed-time convergence for both the sliding variable and voltage tracking error. An ELM-based uncertainty bound estimator is further designed to learn the uncertainty bound information in real-time, which opportunely loosens the constraint of bound information requirement for sliding mode control design. The global stability of the closed-loop system is rigidly analyzed, and the good performance of the proposed control strategy is validated by comparison experiments which exhibit ideal overshoot elimination, 45.70–51.72% reduction of settling time, and 13.65–36.96% reduction of the root mean square value for voltage tracking error with respect to different load types.

Design of Adaptive Fuzzy Sliding-Mode Control for High-Performance Islanded Inverter in Micro-Grid

In this paper, an adaptive fuzzy sliding-mode control (AFSMC) system is investigated for an islanded inverter to achieve a high-performance power supply. A sliding mode control (SMC) law is designed initially to obtain both the voltage tracking error and the current tracking error of the inverter involved, to realize both the output-voltage regulation and the current protection with global stability. Moreover, to deal with uncertainties in the practical inverter system without the chattering phenomenon, an adaptive fuzzy system embedded with a self-adjustive translation width is developed to replace the switch term of the SMC. In addition, the adaptation laws, derived from the Lyapunov stability theorem, adjust the AFSMC parameters online to guarantee optimal and robust performance. Furthermore, the superior control performance of the proposed AFSMC is verified by a numerical simulation in MATLAB, producing experimental results on the prototype in comparison with the conventional SMC.

Analysis and Verification of Compound SRFPI-LADRC Strategy for an Off-Grid Single-Phase Inverter

Summary. The linear active disturbance rejection control (LADRC) is mainly applied for tracking a step signal, and it is inadequate to realize satisfactory performance in the control of a single-phase inverter whose reference signal is sinusoidal. In this paper, an improved voltage control strategy based on compound synchronous reference frame proportional-integral (SRFPI) control and LADRC is proposed. The SRFPI and LADRC remain relatively independent without complicating the control parameter design. Detailed theoretical analyses on the compound strategy and its performance are presented, indicating that it inherits the advantages of the two controllers. Moreover, contrast experiments are carried out to verify the feasibility and superiority of the proposed control strategy. The results show that the system achieves a small steady-state error, voltage tracking error, fast transient response, and low total harmonic distortion (THD) when feeding a highly nonlinear load.

Comments on “Fractional-Order Sliding Mode Approach of Buck Converters With Mismatched Disturbances”

In this letter, it is verified that the main result of the above article <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> on converging the voltage tracking error of a buck converter controlled by a fractional-order sliding mode controller cannot be logically justified. The root cause of this inconsistency, which is an improper use of an inequality, is discussed.

Prescribed Performance Voltage Control Strategy of LC Inverter

Aiming at the voltage tracking problem of the LC inverter, a new prescribed performance controller is proposed. In order to make the voltage tracking error converge entirely according to the trajectory described by the performance function, a new state variable is introduced referring to the integral sliding surface. The specific form of the voltage controller is obtained according to the voltage equation in the dq coordinate frame and the system stability requirement. The adopted control law is easy to implement. It does not need to adjust the parameters repeatedly so that the inverter’s steady-state and dynamic performance indicators can be close to the prescribed values. The MATLAB/Simulink platform simulation experiment verifies the feasibility and effectiveness of the proposed new prescribed performance control strategy.

Internal Model Principle Method to Robust Output Voltage Tracking Control for Single-Phase UPS Inverters With Its SPWM Implementation

This article investigates output voltage tracking control, and harmonic distortion suppression in single-phase voltage-source uninterruptible power supply (UPS) inverters with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> -filter. The control scheme is based on sensing the output voltage across the UPS load, and using the voltage tracking error in a feedback loop of the internal model principle (IMP) framework. A robust controller is designed to drive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> -filter to operate with an adjustable amplitude, and adaptive resonant frequency. Specifically, the proposed controller basically employs an internal model with a filter to examine the incremental dynamics of the voltage tracking error, and regulate the voltage modulating signal in sine pulse width modulation (SPWM). With such a stable operation of the controlled UPS system, the inverter is able to achieve fast dynamics of voltage tracking, which results in the minimum harmonics while approaching the zero-error steady state under the external loads. The Matlab/Simulink simulation, and experimental validation are both provided for the prototype controlled UPS inverter under the closed-loop operation. It is shown that the controller offers improved performance over the existing schemes. By merely using the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">voltage error</i> to adjust the output voltage, the controlled inverter produces nearly perfect sinusoidal voltage at moderate switching frequency under a wide range of filter parameters, and consequently, the UPS operation has excellent dynamic response with both high voltage utilization of the DC source, and high power quality.

Finite-time disturbance observer–based funnel voltage control strategy for vehicle-to-grid inverter in islanded mode

Based on vehicle-to-grid technology, electric vehicles can be used as power sources in the case of power failure. With the aim to reduce voltage overshoot and improve the anti-disturbance ability of the vehicle-to-grid inverter, a high-performance voltage control strategy based on funnel control and finite-time disturbance observer is developed. First, the dynamic model of the inverter in dq-frame is established, and the lumped disturbance including the unmodeled part is considered. Next, a novel funnel variable is proposed to ensure that the voltage tracking error can be stabilized within the prescribed funnel boundary, and thus enhance the transient performance. Then, a novel finite-time disturbance observer is designed to estimate the lumped disturbance in the system such as load fluctuations, and improve the anti-disturbance ability of the controller. Moreover, the second-order sliding mode differentiator is introduced to estimate the derivative of the virtual control law and eliminate the explosion of complexity problem in the derivation process. Finally, the finite-time stability of the proposed voltage control strategy is analyzed via the Lyapunov theory. The effectiveness of the proposed control strategy is verified by two cases.

A Novel Command-Filtered Adaptive Backstepping Control Strategy with Prescribed Performance for Photovoltaic Grid-Connected Systems

With the aim of solving the power fluctuation and bus voltage instability problems caused by external environment variations in the photovoltaic grid-connected system, a prescribed performance-based adaptive backstepping controller is proposed for the system to regulate the bus voltage and the inverter current. First, the mathematical model of the grid-connected inverter is established, in which the uncertain system parameters are estimated via a designed projection-based adaptive law. Then, the command-filtered backstepping sliding mode control method is applied to the system for power regulation. In order to achieve favorable tracking performance, the prescribed performance technique is introduced in the voltage regulation strategy by constraining the compensated voltage tracking error within a certain range from a novel point of view. Finally, the simulation is carried out considering the variations of environmental situations, and the obtained results demonstrate the sound performance of the prescribed performance-based control strategy with respect to the photovoltaic grid-connected system.

Bat Algorithm Based an Adaptive PID Controller Design for Buck Converter Model

The aim of this paper is to design a PID controller based on an on-line tuning bat optimization algorithm for the step-down DC/DC buck converter system which is used in the battery operation of the mobile applications. In this paper, the bat optimization algorithm has been utilized to obtain the optimal parameters of the PID controller as a simple and fast on-line tuning technique to get the best control action for the system. The simulation results using (Matlab Package) show the robustness and the effectiveness of the proposed control system in terms of obtaining a suitable voltage control action as a smooth and unsaturated state of the buck converter input voltage of ( ) volt that will stabilize the buck converter system performance. The simulation results show also that the proposed control system when compared with the other controllers results has the capability of minimizing the rising time to ( sec) and the settling time to ( sec) in the transient response and minimizing the voltage tracking error of the system output to ( ) volt at the steady state response. Furthermore, the number of fitness evaluations is decreased.

A Neural Network Assistance AMPPT Solar Energy Harvesting System With 89.39% Efficiency and 0.01–0.5% Tracking Errors

This paper presents a high-performance solar energy harvesting system with improved adaptive maximum power point tracking (AMPPT) method utilizing neural network (NN) model as assistance. Under the guidance of the negative feedback control (NFC) model, a BJT based voltage control oscillator with three off-chip reconfigurable resistors is designed in this paper to improve the reusability of the solar energy harvesting system. Meanwhile, the AMPPT accuracy has much improvement by co-simulation of MATLAB/Simulink and Virtuoso with the help of NN model of Photovoltaic (PV) Cell. The complete system with output voltage of 4.2V to power the battery is designed and fabricated in $0.18~\mu \text{m}$ CMOS technology. According to the test results, the system can track the maximum power points (MPP) successfully with average voltage tracking errors of 0.23% (0.01-0.51%) of PV cell 1 and 0.29% (0.01-0.5%) of PV cell 2 when the light intensity changes from 3000lux to 10000lux. Without power hungry current sensor or voltage sensor and other complicated control circuits, the peak efficiency is about 89.39% @ 3000lux.

Adaptive Resilient Secondary Control for Islanded AC Microgrids With Sensor Faults

In this article, we investigate the adaptive resilient secondary voltage and frequency control problem for islanded ac microgrids (MG) in the presence of sensor faults. Sensor faults or data attacks have a great impact on the stability and quality of MG. Existing methods commonly assume that the sensing information from distributed generations (DGs) is healthy or satisfies some ideal conditions. To achieve resilient secondary voltage restoration, a novel adaptive fault tolerant control scheme is proposed. Since the bounds of the time-varying faults are unknown, sufficient conditions are first derived to guarantee the voltage tracking errors to be uniformly ultimately bounded. It is also theoretically shown that the frequency restoration and power sharing can be ensured stable of the overall ac MG system by using the same control scheme. Compared with the existing distributed control methods for secondary control of MG, the considered problem with unknown boundaries sensor faults is more challenging and still not well explored.

Predictive Duty Cycle Control for Four-Leg Inverters With ${LC}$ Output Filter

Three-phase four-leg inverter is a well-known solution to handle unbalanced and nonlinear loading conditions in three-phase transformerless uninterruptible power supply applications. For such power converters, finite control set model predictive control (FCS-MPC) is considered as a promising control alternative due to its simplicity, fast dynamic response, and capability to include nonlinearities and constraints. However, the absence of modulator in FCS-MPC implementation leads to several shortcomings, such as higher load voltage total harmonic distortion (THD), large tracking error of control objectives, and variable switching frequency. Furthermore, the fourth leg operates with a higher average switching frequency than the other three main legs, which complicates the $LC$ filter design. To overcome the aforementioned shortcomings, a new predictive duty cycle control is proposed in this article. Extensive experimental results are shown to verify that the proposed method can achieve enhanced steady-state performance with significant reduced load voltage THD and tracking error under different operating conditions, such as nonlinear single-/three-phase unbalanced load and single-phase short-circuit fault, while preserving the fast dynamic performance of FCS-MPC. Steady-state and dynamic performances of the proposed method are compared to FCS-MPC and double-vector MPC approaches to validate the superiority of the proposed scheme.

An Adaptive Nonsingular Terminal Sliding Mode Control for Bidirectional DC–DC Converter in Hybrid Energy Storage Systems

In order to improve transient response and robust tracking performance, an adaptive nonsingular terminal sliding mode control (ANTSMC) strategy is developed for bidirectional dc–dc converter (BDC) of hybrid energy storage systems (HESSs). By using the adaptive rules, the estimated values of load variations, external input voltage, input current, and output voltage can be obtained. Then, the voltage tracking error can be calculated based on the estimated value and the actual value. The fast terminal SMC strategy is proposed such that the tracking error converges in a finite time. Simulation results, compared with conventional PID, second-order sliding mode, show that output voltage can robustly track the reference voltage with fast response.

An Improved Sliding Mode Control Technique to Mitigate Mismatched Parameter Uncertainties of Three-Phase Voltage Source Inverters

This paper proposes a theoretical and experimental implementation of an advanced sliding mode control (SMC) for a three-phase voltage source inverter (VSI) to achieve robustness against the unknown uncertainties of an LC filter. The significant contributions of the proposed SMC are summarized as considerations for the matched and mismatched uncertainties of the LC filter, more relaxed norm-bounds, dynamic characterization of sliding surface, and unique stability analysis. Unlike the conventional SMC techniques with matched uncertainties, the mismatched uncertainties in the state matrix are taken for the design of the proposed SMC. Also, the relaxed norm-bound designed for matched and mismatched uncertainties allows a wide range of variations in the values of LC filter. The voltage tracking errors are significantly reduced and the total harmonic distortions (THDs) are highly suppressed by characterizing the sliding surface in terms of flexible linear matrix inequalities (LMIs). Next, the stability analysis and reachability conditions are given using the Lyapunov criterion. The authenticity of the proposed SMC method is proved by TMS320LF28335 DSP based experimental results with a prototype 1-kVA test-bed. The comparative experimental results and analysis for the proposed SMC scheme, the conventional SMC scheme, and the conventional PI-PI control scheme are presented under the load step change, unbalanced load, and non-linear load step change with the parameter uncertainties to demonstrate the excellent performance of the proposed controller such as fast transient response, small steady-state error, and low THD.

Active realization of fractional order Butterworth lowpass filter using DVCC

This paper presents an active realization of fraction order Butterworth lowpass filter using a differential voltage current conveyor (DVCC) and two fractance devices (FDs). Initially, the DVCC based fractional order system transfer function is developed. Then, the transfer function of the developed system is equated with the standard fractional order Butterworth equation. By equating this, the generalized condition is obtained for which the developed system behaves like a fractional order Butterworth filter. Further, the effect of current and voltage tracking errors of DVCC, on the system response is investigated using Monte Carlo analysis. Stability of the proposed fractional order Butterworth filter is investigated by pole-zero analysis in complex W-plane. Moreover, the dependency of filter cutoff frequency, on various circuit parameters are investigated using 3D plots. Finally to validate the theoretical results, proposed fractional order Butterworth filter is simulated using R-C ladder network based fractional order capacitor, in PSpice environment using 0.5 μm MIETEC CMOS technology.