Search

This paper presents a need-based distributed coordination strategy (NDCS) for multiple electric vehicle (EV) storages in an islanded commercial hybrid alternating-current (AC)/direct-current (DC) microgrid. The control capacity of the interlinking converter is enhanced by incorporating combined power-droop and voltage-droop strategies to leverage the coupling of AC and DC voltages. Therefore, the AC bus voltage can be regulated simultaneously by regulating only the DC bus voltage without affecting the power-sharing capabilities of the converter. The NDCS is proposed to coordinate the EV storages to regulate the DC bus voltage. The main objective of the NDCS is to decide whether the coordination of the available EV storages is to be done in a decentralised or a distributed manner. The mathematical model and the algorithm to deploy NDCS are developed to realise its application to a real system. The effectiveness of the control system is verified in a commercial hybrid AC/DC microgrid comprising one photovoltaic unit and four EV storages directly connected to the DC bus via DC/DC converters and four distributed-generation (DG) units connected to the AC bus using the conventional droop-control scheme. The performance of both controllers is tested under variable irradiation, commercial loading, and various fault conditions. The results of the case studies demonstrate the efficacy of the overall system in terms of robustness for a variable generation-demand scenario, time delay, EV plug-and-play, and fault conditions.

Growing electricity demand and scarcity of energy sources are the driving force of exploration of renewable energy sources. However, uncertain energy production of these sources creates difficulties in their control and operation with or without a grid utility connection. This paper proposes a novel power control strategy which employs a voltage band in the DC-link voltage to maintain voltage stability and thereby improve the power quality during temporary disturbances in a network. It is applied to act as an inverter's inertia and obtain maximum benefit from the storage system, based on the features of a DC busbar to avoid a voltage limit violation. It also proposes a demand dispatch strategy based on a client's terminal voltage, which avoids the complexity of communication lines, to balance the network power during power shortages. The developed control algorithm is tested on an IEEE 16 bus test feeder with multiple DG units and from the results it is found that the proposed control methods provide effective control of the voltage and power quality during transient conditions and scarce power generation.

Equal power-rating inverters operating with different power set-points in either an islanded or grid-connected mode may lead to inter-unit circulating power caused by a large mismatch between power generation and demand during network contingencies (faults on the heavy load side or unintentional islanding). This circulating power may violate the dc-link voltage limit and, as a result, the protection scheme may shut down the inverter and reduce the microgrids reliability. This paper proposes a regulator for controlling the dc-link voltage of the microgrid's inverter during a period of circulating power. It includes a discharging resistor with a series-connected switch across the dc-link capacitor which is turned on through a control algorithm if the dc-link voltage exceeds its pre-defined limit. Case studies of parallel-connected inverters are conducted and their stability assessed through a small-signal analysis. In addition, a realistic microgrid is designed as a low-voltage (LV) network and tested to verify the concept and regulator actions presented. The simulation results validate the effectiveness of the proposed regulator during network contingencies.

This paper presents a new robust nonlinear excitation controller design for synchronous generators in multimachine power systems to enhance the transient stability. The mismatches between the original power system model and formulated mathematical model are considered as uncertainties, which are modeled through the satisfaction of matching conditions. The exogenous noises appearing from measurements are incorporated with the power system model including the two-axis model of synchronous generators. The partial feedback linearization technique is used to design the controller which transforms the original nonlinear multimachine power system model into several reduced-order linear and autonomous subsystems. The desired control law is obtained for each subsystem and implemented in a decentralized manner provided that the dynamics of the autonomous subsystems have no effects on the overall stability of the system. The analysis related to the dynamics of noisy autonomous subsystems is also included and the proposed controller has the excellent capability to decouple these noises. Finally, the performance of the proposed control scheme is evaluated on an IEEE 39-bus benchmark power system following different types of large disturbances. The performance of the proposed controller is compared to that of a partial feedback linearizing controller, which is designed without robustness properties, to verify the effectiveness of the proposed control scheme.

In this paper, a robust controller for the positioning of a piezoelectric tube scanner (PTS) used in an atomic force microscope (AFM) is proposed. A minimax linear quadratic Gaussian (LQG) controller is designed based on an uncertain system model which is constructed by measuring modeling error between the measured and model frequency response. This controller is robust against uncertainties introduced as a result of spillover dynamics of the scanner at frequencies higher than the first resonance frequency (900 Hz) of the scanner and the variation of plant transfer function due to temperature, humidity, and duration of operation. The proposed controller is applied to the PTS in the AFM used in the experiments to evaluate the performance of the proposed method. It is observed that the proposed scheme provides up to 12 dB closed-loop damping of the resonant mode to track the reference triangular signal. The robust performance of the proposed controller has been investigated for 0–1.96 g sample mass variation. A high positioning accuracy up to 125 Hz frequency is achieved by reducing scanner's vibration and tracking error. Higher-quality imaging up to 125 Hz scanning frequency is achieved compared to the existing PI controller and some other existing methods. This control technique may be applied to control vibration for the systems with changing frequency response due to uncertainties, such as vibration control of disc-drive system. Refereed/Peer-reviewed

In this paper, a data driven controller is designed for the positioning control of a piezoelectric tube scanner (PTS) used in an atomic force microscope (AFM). A single-input single-output (SISO) model-based data driven controller is synthesized by using a mixed negative imaginary (NI) and small gain (SG) approach. The controller is implemented on an AFM and gives significant damping and tracking performance, with 16.64 dB and 19.33 dB damping at the resonance frequency of the X and Y-axes of the PTS, respectively. Moreover, this type of controller design is an effective approach to give intuition about how the controller frequency response should, depending on the design constraints being applied, which ensures optimized performance in vibration control. Refereed/Peer-reviewed

In this paper, a data-driven controller is synthesised for systems with negative imaginary (NI) properties such as the piezoelectric tube scanner (PTS) of an atomic force microscopy (AFM). The scanning speed of an AFM is limited by the dynamic behaviours of its scanning unit. The controller aims to damp vibrations, increase the closed-loop bandwidth and track reference signals with high accuracy. The measured frequency response of the PTS is used to calculate the controller frequency response at each frequency by minimising a cost function. The data-driven control optimisation problem is constrained by NI properties to guarantee that the controller is stable and identifiable. The designed controller is implemented on the AFM using a dSPACE ds1103 real-time prototyping system. Experimental results show that the controller is able to significantly damp the resonances in the scanner's lateral axes, provide a high-bandwidth closed-loop system and allow reference signal tracking. Refereed/Peer-reviewed

Over the last two decades, increasing the scanning speed of an atomic force microscopy (AFM) has been attempted either by applying novel controllers, using alternative scanning methods, or by modifying the hardware setup. This paper demonstrates, the first two approaches to achieve high-speed AFM image scanning. A robust minimax linear quadratic Gaussian (LQG) controller is designed and spiral scanning is considered as an alternative scanning method rather than conventional raster scanning. The minimax LQG controller is designed based on an uncertain system model which is constructed by measuring the plant variations due to variations in sample mass and also modeling error between the measured and model frequency responses. This controller is also robust against uncertainties introduced as a result of variations of sample mass, spillover dynamics of the scanner at frequencies higher than the first resonance frequency of the scanner, and variation in plant transfer functions due to temperature and humidity. The designed controller is experimentally implemented on an AFM using a dSPACE ds-1103 real-time prototyping system and open-loop and closed-loop spiral imaging performances are evaluated. The proposed controller provides sufficient damping at the resonant modes to accurately track the sinusoidal reference signal and generate vibration free images. Also, creep, hysteresis, and cross-coupling effects are significantly reduced. The experimental results show that the proposed scheme outperforms the open-loop case and some other existing approaches. Refereed/Peer-reviewed

In this paper, the design of a data driven controller using a small-gain theorem approach for improving the positioning accuracy of a piezoelectric tube scanner (PTS) is demonstrated. Open-loop frequency responses of both the X-PTS and Y-PTS are measured using a band-limited sweep sine signal and are used as primary data for this control design. The frequency response of the controllers is synthesized by the application of the small-gain theorem constraints over the entire frequency range for both the axes. The experimental implementation of this feedback data driven controller provides significant vibration reduction, with 19 dB and 15 dB damping at the resonance frequencies of the X and Y-axes of the PTS, respectively. A comparison between the open-loop and closed-loop tracking performance for triangular signals shows significant improvement up to the scanning frequency of 150 Hz. Moreover, the design of this data driven controller is less complex than conventional controller design methods as it does not need a system model. Refereed/Peer-reviewed

This paper presents the high-precision lateral positioning of a piezoelectric tube scanner (PTS) used in an atomic force microscope (AFM). The operation of the PTS is affected by various nonlinearities depending upon its operating conditions. An internal reference model-based optimal linear quadratic Gaussian (LQG) controller with a vibration compensator is designed and implemented on the AFM to reduce creep, hysteresis, induced vibration, and cross coupling. This proposed controller has integral action on the error state which makes it possible to track the reference signal and the vibration compensator achieves significant damping of the resonant modes of the PTS in the X- and Y-axes. It also compensates the cross coupling between the X-Y axes dynamics of the AFM system, reducing the artifacts instigated by the system dynamic behavior at high scan rates. The closed-loop frequency responses for both the axes have a high bandwidth. The experimental results are presented which demonstrate the efficacy of the proposed method. Refereed/Peer-reviewed

This paper presents an approach for designing a robust vibration control system for a piezoelectric tube scanner (PTS) used in an atomic force microscope (AFM). In this control design, an uncertainty system model is constructed by measuring modeling error between the measured and model frequency response data. Then a minimax linear quadratic Gaussian (LQG) control technique is used to design a controller which minimizes scanner vibration at its resonant mode. This controller is robust against uncertainties introduced as a result of truncating higher order modes of the scanner, variation of plant transfer function due to temperature and humidity and measurement noise from the position sensors. The experimental results show that the proposed controller is able to reduce the vibration at its resonant mode and track the reference signal. Refereed/Peer-reviewed

In this paper, we present a spiral scanning method using an atomic force microscope (AFM). A spiral motion is generated by applying slowly varying amplitude sine wave in the X-axis and cosine wave in the Y-axis of the piezoelectric tube (PZT) scanner of the AFM. An LQG controller also designed for damping the resonant mode of the PZT scanner for the lateral positioning of the AFM scanner stage. In this control design, an internal model of the reference sinusoidal signal is introduced with the plant model and an integrator with the system error is introduced. A vibration compensator is also designed and included in the feedback loop with the plant to suppress the vibration of the PZT at the resonant frequency. Experimental results demonstrate the effectiveness of the proposed scheme Refereed/Peer-reviewed

In this article the design and experimental implementation of an observer based model predictive control (OMPC) scheme for active damping of the first two resonant modes of a smart structure is presented. The design of this controller is based on an identified model of the plant. A Kalman filter is used to obtain full state information. The experimental results verify the efficacy of the proposed controller Refereed/Peer-reviewed

This article presents the design and experimental implementation of an observer-based model predictive control (OMPC) scheme with a notch filter which aims to compensate for the effects of creep, hysteresis, cross-coupling, and vibration in piezoactuators in order to improve the nanopositioning of an atomic force microscope (AFM). The controller design is based on an identified model of the piezoelectric tube scanner (PTS) for which the control scheme achieves significant compensation of its creep, hysteresis, cross-coupling, and vibration effects and ensures better tracking of the reference signal. A Kalman filter is used to obtain full-state information of the plant. The experimental results exemplify the use of this proposed control scheme. Refereed/Peer-reviewed

In this paper we describe the cross-coupling effect between X-Y axes of piezoelectric tube (PZT) scanner used in an atomic force microscope (AFM). During raster scanning X-Y axes induced cross-coupling effect in the lateral positioning of the scanner stage of the AFM and as a result, it produces blurred or distorted images. To address this effect, an LQG controller is designed and implemented on AFM which minimizes the cross-coupling effect between the axes mainly at the resonance frequency of the scanner tube. The proposed controller has an integral action with the error signal which makes it possible to track the reference signal and a significant damping of the resonant modes of the PZT in the X and Y axes. This controller compensates the cross-coupling between X-Y axes dynamics of the AFM system, reducing the artifacts instigating by the system dynamic behavior at high scan rates. The closed-loop frequency responses for both the axes have achieved high bandwidth. Consequently, scanned results are evaluated as a better one than the open-loop of the AFM. Refereed/Peer-reviewed

An atomic force microscope (AFM) is an extremely versatile investigative tool in the field of nanotechnology, the performance of which is significantly influenced by its conventional zig-zag raster pattern scanning method. In this paper, we consider the use of a spiral scanning method with an improved model predictive control (MPC) scheme for its faster scanning. The proposed MPC controller reduces the phase error between the input and output sinusoids and provides better tracking of the reference signal. Also, a notch filter is designed and included in the feedback loop with the plant to suppress vibrations of the piezoelectric tube scanner (PTS) at the resonant frequency. Consequently, the proposed controller achieves a higher closed-loop bandwidth and significant damping of the resonant mode of the AFM's PTS. Experimental results show that, by using the proposed method, the AFM's scanning speed is significantly increased to up to 180 Hz and produces improved image quality. Refereed/Peer-reviewed

This paper presents a design of an internal reference model based optimal linear quadratic Gaussian controller (LQG) for a piezoelectric tube (PZT) actuator used in the atomic force microscope (AFM). This control scheme minimizes the steady-state error and provides improved closed-loop bandwidth and enables the controller to track reference triangular signal. The proposed scheme places the closed-loop poles in the left half of the s-plane such that significant damping of the resonant modes of the PZT actuator can be achieved. Experimental results with the AFM show that the proposed control approach is able to scan faster and improves the quality of images by minimizing blurring, tilting, and edge distortion of the image as compared to the existing PI controller of the AFM. Refereed/Peer-reviewed

This paper demonstrates the design and experimental implementation of an observer based model predictive control (OMPC) with a notch filter for the positioning of the piezoelectric tube (PZT) scanner of an atomic force microscope (AFM). This control scheme achieves active damping of the resonant mode of the PZT scanner and accurate tracking of a reference triangular signal. Kalman filter is used to obtain full-state information in the presence of position sensor noise. The experimental results confirm the efficacy of the proposed controller. Refereed/Peer-reviewed

This paper presents the design of an LQG controller for the lateral positioning of a piezoelectric tube actuator (PZT) used in an atomic force microscope (AFM). In the proposed control scheme, an internal model of the reference signal is included in the plant model and an integrator with the system error is introduced. As a result, it reduces the steady-state tracking error. A vibration compensator is also designed and included in a feed-back loop with the plant to suppress the vibration of the PZT at the resonance frequency. Consequently, the proposed controller achieves higher closed-loop bandwidth and significant damping of the resonant mode of the PZT, which enables the tracking of a reference triangular signal. Experimental results show the significant improvement of the scanned images as compared to the in-built PI controller of the AFM. Refereed/Peer-reviewed