Frequency Response Control Research Articles

Data Driven Controller Design for Positioning Control of an AFM Scanner

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.

A Negative Imaginary Theory-based Controller Synthesis for Vibration Control of a Piezoelectric Tube Scanner

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.

Frequency response control of semiconductor laser by using hybrid modulation scheme.

A hybrid modulation scheme that simultaneously applies the direct current modulation and intra-cavity loss modulation to a semiconductor laser is proposed. Both numerical calculations using rate equations and experiments using a fabricated laser show that the hybrid modulation scheme can control the frequency response of the laser by changing a modulation ratio and time delay between the two modulations. The modulation ratio and time delay provide the degree of signal mixing of the two modulations and an optimum condition is found when a non-flat frequency response for the intra-cavity loss modulation is compensated by that for the direct current modulation. We experimentally confirm a 8.64-dB improvement of the modulation sensitivity at 20 GHz compared with the pure direct current modulation with a 0.7-dB relaxation oscillation peak.

Controller synthesis for negative imaginary systems: a data driven approach

The negative imaginary (NI) property occurs in many important applications. For instance, flexible structure systems with collocated force actuators and position sensors can be modelled as negative imaginary systems. In this study, a data-driven controller synthesis methodology for NI systems is presented. In this approach, measured frequency response data of the plant is used to construct the controller frequency response at every frequency by minimising a cost function. Then, this controller response is used to identify the controller transfer function using system identification methods.

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The Joint Adequacy of AGC and Primary Frequency Response in Single Balancing Authority Systems

This paper generalizes previous work on automatic generation control (AGC) gain in a single balancing authority system. In previous work, a control performance standard 1 (CPS1)-compliant AGC gain for a single balancing authority interconnection was proposed, assuming that frequency response can be decoupled from AGC dynamics by widening governor dead bands. However, current practices suggest that widening dead bands may not be a wise course to take as it may deteriorate primary frequency response. This paper formulates sufficient conditions for the adequacy of the joint operation of AGC control and primary frequency response to be consistent with frequency response adequacy. Historical data and a simulation of ERCOT are presented to show numerical results.

A generic model of two-stage grid-connected PV systems with primary frequency response and inertia emulation

Photovoltaic (PV) stations are increasingly becoming subject to grid code requirements that include frequency response and active power control capability. The main goal of this paper is to propose a generic model for a two-stage grid-connected PV system with frequency response capability, suitable for power system studies. The proposed model includes a suitable control scheme, which provides both droop and inertial response, as well as the ability to operate at a scheduled active power reserve, enabling thus the provision of under-frequency response. A linearized small-signal model is developed to assess the stability of the proposed PV power control loop when the PV generator provides frequency response, whereas time-domain simulations are performed in order to quantify the benefits achieved by droop-type and inertia frequency controllers, including a discussion on the selection of their parameters. The analysis demonstrates the satisfactory performance of the proposed PV system model, which provides all functionality required by grid codes in the context of active power control.

Mitigating Voltage and Frequency Fluctuation in Microgrids Using Electric Springs

Voltage and frequency fluctuation associated with renewable integration have been well identified by power system operators and planners. At the microgrid level, a novel device for the implementation of dynamic load response, which is known as the electric springs (ES), has been developed for mitigating both active and reactive power imbalances. In this paper, a comprehensive control strategy is proposed for ES to participate in both voltage and frequency response control. It adopts the phase angle and amplitude control which respectively adjust the active power and the reactive power of the system. The proposed control strategy is validated using a model established with power system computer aided design/electro-magnetic transient in dc system. Results from the case studies show that with appropriate setting and operating strategy, ES can mitigate the voltage and frequency fluctuation caused by wind speed fluctuation, load fluctuation, and generator tripping wherever it is installed in the microgrid.

Taming the Electromagnetic Boundaries via Metasurfaces: From Theory and Fabrication to Functional Devices

As two-dimensional metamaterials, metasurfaces have received rapidly increasing attention from researchers all over the world. Unlike three-dimensional metamaterials, metasurfaces can be utilized to control the electromagnetic waves within one infinitely thin layer, permitting substantial advantages, such as easy fabrication, low cost, and high degree of integration. This paper reviews the history and recent development of metasurfaces, with particular emphasis on the theory and applications relating to the frequency response, phase shift, and polarization state control. Based on the current status of various applications, the challenges and future trends of metasurfaces are discussed.

Assessment of communication-independent grid code compatibility solutions for VSC–HVDC connected offshore wind farms

Abstract Offshore wind farms connected to the mainland through High Voltage DC links based on Voltage Source Converters (VSC–HVDC) are subject to Grid Code (GC) requirements, such as frequency response, Fault Ride Through (FRT) capability, and active and reactive power control. Due to the presence of HVDC links, GC compatibility becomes a challenging task from a control and regulation perspective, since the offshore network AC voltage and frequency are decoupled from the onshore grid voltage and frequency and hence grid-side disturbances are not directly experienced by the Wind Turbines (WTs). To address this challenge of modulating the response of offshore WTs according to the onshore grid conditions, without resorting to dedicated communication schemes, which may introduce delays and reliability concerns, three alternative control strategies are presented and evaluated for the offshore HVDC VSC, which are based only on local measurements. Each strategy can cope with onshore frequency response, FRT and power control requirements at the same time. A coordinated control approach between the WT and HVDC converters is also proposed by integrating a voltage dependent current modulation strategy into the default WT current controllers. Time domain simulations are carried out in DIgSILENT PowerFactory in order to verify the effectiveness of the proposed control schemes.

Novel adaptive fiber-optics collimator for coherent beam combination.

In this manuscript, we experimentally validate a novel design of adaptive fiber-optics collimator (AFOC), which utilizes two levers to enlarge the movable range of the fiber end cap. The enlargement of the range makes the new AFOC possible to compensate the end-cap/tilt aberration in fiber laser beam combining system. The new AFOC based on flexible hinges and levers was fabricated and the performance of the new AFOC was tested carefully, including its control range, frequency response and control accuracy. Coherent beam combination (CBC) of two 5-W fiber amplifiers array with simultaneously end-cap/tilt control and phase-locking control was implemented successfully with the novel AFOC. Experimental results show that the average normalized power in the bucket (PIB) value increases from 0.311 to 0.934 with active phasing and tilt aberration compensation simultaneously, and with both controls on, the fringe contrast improves to more than 82% from 0% for the case with both control off. This work presents a promising structure for tilt aberration control in high power CBC system.

Low complexity and efficient dynamic spectrum learning and tunable bandwidth access for heterogeneous decentralized cognitive radio networks

This paper deals with the design of the low complexity and efficient dynamic spectrum learning and access (DSLA) scheme for next-generation heterogeneous decentralized Cognitive Radio Networks (CRNs) such as Long Term Evolution-Advanced and 5G. Existing DSLA schemes for decentralized CRNs are focused predominantly on the decision making policies which perform the task of orthogonalization of secondary users to optimum vacant subbands of fixed bandwidth. The focus of this paper is the design of DSLA scheme for decentralized CRNs to support the tunable vacant bandwidth requirements of the secondary users while minimizing the computationally intensive subband switchings. We first propose a new low complexity VDF which is designed by modifying second order frequency transformation and subsequently combining it with the interpolation technique. It is referred to as Interpolation and Modified Frequency Transformation based VDF (IMFT-VDF) and it provides tunable bandpass responses anywhere over Nyquist band with complete control over the bandwidth as well as the center frequency. Second, we propose a tunable decision making policy, ρt_rand, consisting of learning and access unit, and is designed to take full advantage of exclusive frequency response control offered by IMFT-VDF. The simulation results verify the superiority of the proposed DSLA scheme over the existing DSLA schemes while complexity comparisons indicate total gate count savings from 11% to as high as 87% over various existing schemes. Also, lower number of subband switchings make the proposed scheme power-efficient and suitable for battery-operated cognitive radio terminals.

Design of Linear Phase Low Pass FIR Filter using Particle Swarm Optimization Algorithm

The everyday broadening field of signal processing has digital filters to play a major role. Linear phase FIR filters are used in vast number of applications due to their nature of phase linearity as well as frequency stability. The traditional nonoptimization methods available for filter design suffer from the problem of need for analog to digital conversion and also the inefficient control of frequency response. The conventional gradient based optimization methods are unable to solve non-differential functions and converges to local optimum solution. Thus this paper presents the evolutionary optimization technique of Particle Swarm Optimization (PSO) for the design of linear phase digital low pass (LP) FIR filter. Given the specifications of desired filter to be realized, PSO algorithm results in an optimal coefficient set for linear phase FIR filter approximating the ideal specifications. In this paper PSO algorithm is used with constriction factor approach to solve the multimodal, highly non-linear filter design problem. This method has the property of parameter independence and thus ensuring convergence while fully exploring the solution space. The velocity and position updating rules of original PSO algorithm is used for the design of low pass FIR filter of order 20. The extensive simulation results obtained from the proposed method shows superiority of the algorithm.

FRF-based structural damage detection of controlled buildings with podium structures: Experimental investigation

Abstract How to use control devices to enhance system identification and damage detection in relation to a structure that requires both vibration control and structural health monitoring is an interesting yet practical topic. In this study, the possibility of using the added stiffness provided by control devices and frequency response functions (FRFs) to detect damage in a building complex was explored experimentally. Scale models of a 12-storey main building and a 3-storey podium structure were built to represent a building complex. Given that the connection between the main building and the podium structure is most susceptible to damage, damage to the building complex was experimentally simulated by changing the connection stiffness. To simulate the added stiffness provided by a semi-active friction damper, a steel circular ring was designed and used to add the related stiffness to the building complex. By varying the connection stiffness using an eccentric wheel excitation system and by adding or not adding the circular ring, eight cases were investigated and eight sets of FRFs were measured. The experimental results were used to detect damage (changes in connection stiffness) using a recently proposed FRF-based damage detection method. The experimental results showed that the FRF-based damage detection method could satisfactorily locate and quantify damage.

Active control of dynamic frequency responses for shell structures

The active control method is a popular way to control mechanical vibration. However, for some industrial needs and military requirements, it does not only need to control vibration, but also has to change the online constant working frequency responses, for example to improve the dynamic performance of mechanical devices and the stealth of military equipment. Because the present active control methods mainly focus on vibration control, the dynamic frequency responses active control method (DFRACM) is constructed to deal with this problem. The constructed DFRACM can not only accomplish vibration control but can also arbitrarily change the dynamic frequency responses of mechanical equipment. Besides, in order to satisfy engineering requirements, the multi-objective DFRACM, which can control the dynamic frequency responses of the controlled object to reach separate specific objectives at different places in one time, is also studied in this paper. The effectiveness of the constructed method is verified through experiments of the open cylindrical shell structure.

Reconfigurable ring filter with controllable frequency response.

Reconfigurable ring filter based on single-side-access ring topology is presented. Using capacitive tuning elements, the electrical length of the ring can be manipulated to shift the nominal center frequency to a desired position. A synthesis is developed to determine the values of the capacitive elements. To show the advantage of the synthesis, it is applied to the reconfigurable filter design using RF lumped capacitors. The concept is further explored by introducing varactor-diodes to continuously tune the center frequency of the ring filter. For demonstration, two prototypes of reconfigurable ring filters are realized using microstrip technology, simulated, and measured to validate the proposed concept. The reconfigured filter using lumped elements is successfully reconfigured from 2 GHz to 984.4 MHz and miniaturized by 71% compared to the filter directly designed at the same reconfigured frequency, while, for the filter using varactor-diodes, the frequency is chosen from 1.10 GHz to 1.38 GHz spreading over 280 MHz frequency range. Both designs are found to be compact with acceptable insertion loss and high selectivity.

Dynamics of cantilever plates and its hybrid vibration control

Applying Lagrange-Germain’s theory of elastic thin plates and Hamiltonian formulation, the dynamics of cantilever plates and the problem of its vibration control are studied, and a general solution is finally given. Based on Hamiltonian and Lagrangian density function, we can obtain the flexural wave equation of the plate and the relationship between the transverse and the longitudinal eigenvalues. Based on eigenfunction expansion, dispersion equations of propagation mode of cantilever plates are deduced. By satisfying the boundary conditions of cantilever plates, the natural frequencies of the cantilever plate structure can be given. Then, analytic solution of the problem in plate structure is obtained. An hybrid wave/mode control approach, which is based on both independent modal space control and wave control methods, is described and adopted to analyze the active vibration control of cantilever plates. The low-order (controlled by modal control) and the high-order (controlled by wave control) frequency response of plates are both improved. The control spillover is avoided and the robustness of the system is also improved. Finally, simulation results are analyzed and discussed.

Controller design for nonlinear systems using the Contoured Robust Controller Bode plot

SUMMARYIn this paper, we develop the Contoured Robust Controller Bode (CRCBode) plot and demonstrate its use in the design of robust controllers for nonlinear single‐input single‐output (SISO) systems. The CRCBode plot shows contours (level sets) of a robust performance quantity on the Bode magnitude and phase plots of the controller. An iterative frequency domain loop‐shaping design approach is employed to eliminate all intersections of the controller frequency response with certain ‘forbidden regions,’ indicating that a standard SISO robust stability and performance criterion is satisfied. Nonlinearities are accounted for by avoiding the maximum forbidden regions over a structured uncertainty set consisting of linearizations of the system dynamics about several operating points. We demonstrate this technique by designing and experimentally verifying a flow‐rate controller for a butterfly‐valve based liquid cooling system, which is robust to valve nonlinearities and flow disturbances. Finally, we compare this compensator with one generated using an automated H ∞ synthesis algorithm and discuss the advantages of the CRCBode approach. Copyright © 2013 John Wiley & Sons, Ltd.

An Experimental Method for the Phase Controlled Frequency Response Measurement of Nonlinear Vibration Systems

AbstractExperimental determination of frequency response function of nonlinear systems is difficult when there exists more than one solution branch. Depending on the system at hand, various types of jump phenomena can be observed and in the example of the well‐known Duffing‐oscillator, it is not possible to experimentally determine the unstable solution branch if the system is excited by a harmonic force. In the present paper we investigate the Duffing‐oscillator and present a method, which allows to reformulate the equation of motion of the system with force‐excitation in the form of an equivalent self‐excited system. Considering the phase between force and response as the input variable, it is possible to evaluate the frequency of the systems vibration for any given phase shift. In the same way the corresponding response amplitude is determined. An experimental set‐up is presented, which is used to validate the performance of the method. Measurements of the backbone curve are performed and discussed on the background of theoretical predictions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Generic Droop Correction IIR Filter Design Algorithm

Cascaded Integrated Comb (CIC) or Multiplier-less Hogenauer structure for multi-rate signal processing has uncontrollable frequency response. State-of-Art (SOA) solution to achieve controllable frequency response is to cascade the Hogenauer filter with a droop-correction Finite Impulse Response (FIR) filter. Although FIR filters are linear phase and inherently stable, Infinite Impulse Response (IIR) filters provide excellent frequency response with the cost of less memory and hence less area and less current consumption, which have never been explored in the context of droop correction. This article introduces a novel algorithm which generates IIR structures to correct droop imposed by Hogenauer structures, which also can be used to save area and power with a better transition and stop-band response in comparison to the equivalent FIR filter. Furthermore, this algorithm can be assimilated as a part of existing algorithm design tool, like MATLAB or SciLab.