Frequency Domain Specifications Research Articles

A decentralized optimal PID controller with disk margin-based robust stability analysis for higher-order industrial systems

ABSTRACT Decentralized control systems are frequently employed to tackle control challenges in multi-input multi-output (MIMO) systems. Hence, this paper proposes a decentralized PID controller that relies on frequency domain specifications. This controller is designed to minimize the loop interactions and fulfill the design criteria of the MIMO system. The PID parameters are calculated based on gain and phase margin specifications. Additionally, a first-order plus dead time model is derived for each of the decoupled subsystems. Furthermore, robust stability is analysed using disc margin analysis, which overcomes the constraints of traditional margins. Moreover, the paper determines a secure range of uncertainty for various levels of gain and phase uncertainties. The findings suggest that the proposed controller achieves robust stability over a broader range of margins when compared to alternative control methods.

Spectral changes in skin blood flow during pressure manipulations or sympathetic stimulation.

Skin blood flow is commonly determined by laser Doppler flowmetry (LDF). It has been suggested that pathophysiological conditions can be assessed by analysis of specific frequency domains of the LDF signals. We tested whether physiological stimuli that activate myogenic and neurogenic mechanisms would affect relevant portions of the laser Doppler spectrum. LDF sensors were placed on the right forearm of 14 healthy volunteers for myogenic (six females) and 13 for neurogenic challenge (five females). Myogenic responses were tested by positioning the arm ∼50° above/below heart level. Neurogenic responses were tested by immersing the left hand into an ice slurry with and without topical application of local anaesthetic. Short-time Fourier analyses were computed over the range of 0.06 to 0.15Hz for myogenic and 0.02 to 0.06Hz for neurogenic. No significant differences in spectral density were observed (P=0.40) in the myogenic range with arm above (7±54×10-4dB) and below heart (7±14×10-4dB). Neurogenic spectral density showed no significant increase from baseline to cold pressor test (0.0017±0.0013 and 0.0038±0.0039dB; P=0.087, effect size 0.47). After application of anaesthetic, neurogenic spectral density was unchanged between the baseline and cold pressor test (0.0014±0.0025 and 0.0006±0.0005dB; P=0.173). These results suggest that changes in the myogenic and neurogenic spectral density of LDF signals did not fully reflect the skin vascular function activated by pressure manipulation and sympathetic stimulation. Therefore, LDF myogenic and neurogenic spectral density data should be interpreted with caution.

A fractional‐order active disturbance rejection control for permanent magnet synchronous motor position servo system

AbstractThis paper introduces a novel control scheme for the permanent magnet synchronous motor (PMSM) position servo system using a fractional‐order active disturbance rejection control (ADRC) approach. Specifically, a first‐order ADRC is employed in the current loop, while a fractional‐order ADRC is designed for the position loop. In the latter, a linear extended state observer (LESO) is utilized to estimate and compensate for disturbances, while a fractional‐order proportional derivative (FO[PD]) feedback controller is employed to enhance the control performance. Moreover, a parameter tuning method is presented based on frequency domain specifications. This technique utilizes the flat phase constraint as a design constraint to ensure that the phase is flat near the gain crossover frequency, thus ensuring that the closed‐loop system remains robust to loop gain variations. Simulation and experimental results demonstrate that the proposed fractional‐order ADRC control scheme yields improved dynamic response, disturbance rejection, and robustness to loop gain variations.

Individually Addressable Multitouch Sensors Using a Sweep Signal for Minimal Wiring Complexity

Although touch sensing has been developed rapidly, it is difficult to design a simple circuit or a system that contains many sensors; the numbers of wires increase in proportion to the number of sensors. Although efforts have been made to reduce the number of wires, multi-touch measurements are still challenging because it is difficult to decouple multi-touch signals. Here, we apply FDM (Frequency Division Multiplexing) to SFCS (Swept Frequency Capacitive Sensing) when developing a sensor system capable of multi-touch with minimal wiring complexity. The sensor system can be extended in series and arrays by connecting multiple sensors using only two wires. A signal generated via frequency sweeping is expressed as a unique response in a specific frequency domain using a multi-band band-stop filter. Considering such unique touch responses, each capacitive multi-touch sensor is individually addressable, thereby allowing touch to be detected regardless of sensor location.

Toward Automated Gust Load Alleviation Control Design via Discrete Gust Impulse Filters

In the context of active gust- and turbulence-load alleviation function design, control designers optimize the response of the closed-loop system to satisfy the relevant certification specifications (e.g., European Union Aviation Safety Agency (EASA) CS-25.341 and Federal Aviation Regulations (FAR) Part 25, Sec. 341). These include time-domain criteria specifying the peak response to discrete gusts as well as frequency-domain continuous-turbulence criteria. Both types of criteria cannot be easily considered simultaneously with commonly available control design software. A frequency-domain formulation of 1−cosine discrete gust criteria based on a low-order, parameterized linear filter is proposed and demonstrated on a publicly available gust load alleviation benchmark. One example demonstrates its application in combination with continuous-turbulence specifications, and in principle, it can also be combined with other relevant frequency-domain specifications, such as passenger comfort metrics. This technique is shown to work well, producing the desired results with a simple, systematic design procedure, and should help reduce the time and effort required to obtain satisfactory control specifications.

Generalized adaptive singular spectrum decomposition and its application in fault diagnosis of rotating machinery under varying speed

Rotating machinery fault signals often consist of multiple components with time varying frequencies under variable speed conditions. Spectral overlap exists among these components, making it difficult to independently separate the features of the components. Singular spectrum decomposition (SSD), a singular spectrum analysis-based signal decomposition method, has shown its great potential in suppressing background noise and extracting fault-related components in complex background noise environments. However, SSD is a frequency domain decomposition method with equivalent filtering characteristics, and it is susceptible to the mode mixing when processing signals with spectral overlap. Moreover, the choice of a key parameter in the iteration decomposition process of SSD, the embedding dimension, is determined using an empirical formula, which might cause suboptimal decomposition outcomes. To address these issues, this paper proposes a generalized adaptive singular spectrum decomposition (GASSD) method, which combines generalized demodulation with improved embedding dimension selection for SSD. GASSD incorporates SSD into the framework of adaptive generalized demodulation to separate specific frequency domain features. Firstly, for an effective generalized demodulation analysis, a region block synchronous ridge extraction method is proposed to accurately estimate the instantaneous frequency ridges from the time-frequency plane, which helps construct proper demodulation phase functions. Secondly, to achieve optimal analysis of SSD, a Gini moderation decomposition index is designed to improve the construction of the trajectory matrix by determining an appropriate embedding dimension. Finally, the reliability of the proposed method is demonstrated by analyzing wind turbine generator bearing fault signals and rotor rubbing fault signals.

An adaptive fractional order controller design: A realization for liquid level regulation in liquid level plant

In this paper, an adaptive FO − IλD1−λ controller design is proposed using a frequency domain approach. The proposed adaptive controller parameters are tuned based on the frequency domain specifications. To realize the velocity error constant for the proposed controller, Oustaloup Recursive Approximation (ORA) method is employed. The proposed controller is realized for liquid level regulation in the Liquid Level Plant (LLP). An identification technique is proposed to identify a linear adaptable parameter transfer function (LAPTF) model of LLP. The performance of the proposed controller is compared with the existing works. It is observed that the proposed controller outperforms the existing controllers in the literature.

Practical Automatic Tuning of Lag-lead Compensators for Feedback Control Systems

This paper proposes a scheme for auto-tuning a lag-lead compensator to satisfy frequency-domain specifications of a feedback control system. Most previous studies proposed algorithms for tuning either lag or lead compensators. A study presented a self-tuning lag-lead compensator whose proportional gain, however, needs to be set manually. In contrast to previous studies, a fully automated tuning process for a lag-lead compensator is devised in this paper. In the proposed scheme, the plant's frequency responses at specific frequencies are first estimated, and an iterative algorithm adapts all controller parameters. To facilitate the estimation of high loop gain at a low frequency, a notch filter is introduced to the control loop while estimating this high low-frequency loop gain. Without this mechanism, a real-time data acquisition system of a wide dynamic range would be required. In addition to fulfilling the requirements for the low-frequency loop gain and phase margin, another feature of the proposed scheme is the satisfaction of the required gain-crossover frequency. However, the proposed method supposes that the frequency-domain specifications can be met for a plant using a lag-lead compensator, which is the plant's requirement for the proposed method. Experimental results for controlling a voice-coil motor are reported in this paper, showing that the proposed auto-tuner can practically provide a lag-lead compensated system satisfying frequency-domain performance requirements.

Fractional-order PID controller design via optimal selection strategy of frequency domain specifications

In this paper, a novel fractional-order Proportional-Integral Derivative (PID) controller design depending on optimal selection of frequency domain specifications is proposed for time delay systems. The frequency domain specification sets, namely, (i) phase margin and gain crossover frequency and (ii) phase margin and gain margin are determined so that the reference model is optimal according to three time domain performance indices, i.e. Integral Square Error (ISE), Integral Time Square Error (ITSE) and Integral Absolute Error (IAE). Here, the delayed Bode's ideal transfer function is employed in the reference model. Moreover, the stability region of the reference model is given via a theorem. In simulation studies, the proposed methodology is compared with other two different methods using the same frequency domain specifications. It is observed that the proposed optimal fractional-order PID controllers outperform according to the mentioned performance indices, and they also possess considerably acceptable performance in terms of other time domain specifications such as overshoot, settling time, etc.

A graphical technique of controller design and selection of lower and upper bounds in controller design using optimization techniques

AbstractThe regulation and stabilization of a system's output to achieve desired performance and ensure system reliability require the use of different controllers, but selecting appropriate control parameters presents a challenge in ensuring robustness and stability. Proportional–integral–derivative (PID) controllers are popularly used due to their simplicity and effectiveness in addressing these challenges. In this paper, a simple, effective, and efficient, novel graphical technique is proposed to design PID and its variants (PI/PD) controllers, which addresses the challenges in selecting appropriate control parameters. The method involves creating three equispaced vectors for controller parameters , and obtaining a 3D (2D in PI/PD) Cartesian grid of these vectors. All nodes in the grid provide several possible controllers, and integral time squared error (ITSE) is calculated for each controller from the closed‐loop step response of the system. The obtained ITSE is plotted in a 4D (PID) or 3D (PI/PD) graph, and controller parameters corresponding to the minimum value of ITSE are identified. Furthermore, the proposed graphical technique aids in choosing the lower and upper bounds (LB and UB) if the controller is designed using optimization techniques. The better selection of LB and UB reduces the search space resulting in lesser execution time and fewer iterations. To validate the proposed graphical technique, we designed various controllers for widely‐used brush‐less DC and switch reluctance motors in electric vehicles. Additionally, by choosing the LB and UB with the proposed technique, controllers are also designed using three optimization techniques: particle swarm optimization, black widow optimization algorithm, and honey badger algorithm. The obtained controllers using the graphical technique outperformed the optimization techniques in terms of time and frequency domain specifications, and the proposed selection of lower and upper bounds resulted in improved performance in terms of iterations and execution time.

Design of a robust and practicable SSI damping controller using H[formula omitted] technique for series compensated DFIG-based wind farms

This paper designs a robust and practicable subsynchronous interaction (SSI) damping controller using H∞ technique for the safe operation of series capacitor compensated wind farms (WFs) with doubly-fed induction generator (DFIG) wind turbines (WTs). Mixed sensitivity control design together with pole placement are formulated into a set of linear matrix inequalities (LMIs) to obtain the controller parameters. The LMI technique allows to include both desirable frequency and time domain specifications. The proposed damping controller is integrated into the WT controller (WTC) and receives the DFIG converter currents as inputs. The implementation of the proposed controller does not require any communication links between the WTs and WF secondary control layer. The controller output signals are applied to the inner control loops of DFIG converters and are dynamically limited for the desired fault-ride-through (FRT) performance. The effectiveness of the damping controller is verified through detailed electromagnetic transient (EMT) simulations. In these simulations, the complete medium-voltage (MV) collector grid is modeled with all details, and it is assumed that the wind speed at the location of each turbine follows a Gaussian distribution. The collected results confirm the accuracy of the modeling of the entire WF as an aggregated WT with the average wind speed.

Static Output Feedback-Based DFIG Controller Design for the Wind-Driven Scheme

This paper presents DFIG-based WT schemes for WECS that are necessitated the appropriate control systems to get better performance with an efficient operation of the DFIG system. During the DFIG functioning both rotor and grid side converters play a very important role because these converters have controllers that control the DFIG-based WT system. The wind energy general idea and the DFIG working principle have been discussed properly. The sixth-order transfer function (T.F) DFIG model (considered a plant model) has been applied for controller design to the DFIG system in terms of Static Output Feedback Technique (SOF) and Genetic Algorithm (GA)-based optimization techniques. The SOF- and GA-based designed controllers have been implemented in the DFIG-based WT Simulink model for their performance analysis, in terms of output responses of three-phase terminal voltage, active power delivery and reactive power requirement to the grid along with DC-Link voltage. Also, these designed controllers are applied in the sixth-order DFIG system T.F model and get output responses concerning time and frequency domain specifications. At last, after the comparisons of output responses of both controllers in DFIG Simulink and T.F model cases it has been found that the SOF-based controller design scheme is better than GA-based technique for the DFIG-based WT system. Hence the SOF technique is the better alternative to designing a controller for (higher-order) DFIG-based WT systems. Abbreviations: Tr: Rise Time, Tp: Peak Time, Ts: Settling Time, Mp: Maximum Overshoot, Pc: Peak, GM: Gain Margin, PM: Phase Margin, Wgc: Gain crossover frequency, Wpc: Phase crossover frequency

Analytical Fractional-Order PID Controller Design With Bode’s Ideal Cutoff Filter for PMSM Speed Servo System

In this article, a speed control scheme based on an analytically designed fractional-order PID with Bode’s ideal cutoff (FOPID-BICO) filter is proposed. The FOPID controller is designed to track the speed references and the BICO suppress is applied to filter the high-frequency noise. Considering the difficulty of parameters tuning of the FOPID controller, a comprehensive analytical design method based on frequency specifications-defined loop-shaping for the FOPID-BICO controller is first proposed for the permanent magnet synchronous motor speed control. The designed speed servo system satisfies five frequency-domain specifications: gain crossover frequency, phase margin, phase crossover frequency, gain margin, and a “flat phase” constraint. Moreover, the influence of phase crossover frequency on control system is fully exposed through the frequency-domain analysis. The proposed designed method ensures that the control system is robust to loop gain variations and guarantees the optimal performance on rejecting noise in high-frequency and disturbance in low-frequency. The effectiveness of the proposed FOPID-BICO controller has been verified by experimental results.

Design of decentralised PI/PID control algorithm for a benchmark continuously stirred tank reactor system using frequency domain specifications

Design of decentralised PI/PID control algorithm for a benchmark continuously stirred tank reactor system using frequency domain specifications

Design of a decentralised PI/PID control algorithm for a benchmark continuously stirred tank reactor system using frequency domain specifications

Design of a decentralised PI/PID control algorithm for a benchmark continuously stirred tank reactor system using frequency domain specifications

Dynamic Feedforward-Based Fractional Order Impedance Control for Robot Manipulator

Impedance control is widely applied in contact force control for robot manipulators. The traditional impedance model is linear, and has limitations in describing the actual impedance force. In addition, time-varying and dynamic coupling characteristics pose critical challenges to high-speed and high-precision impedance control. In this paper, a fractional order impedance controller (FOIC) is proposed for industrial robot manipulator control and a systematic FOIC parameters tuning strategy based on frequency-domain specifications is presented. In order to improve performance under dynamic disturbances, a dynamic feedforward-based fractional order impedance controller (DFF-FOIC) is further developed. The robot manipulator dynamics are investigated and the effectiveness of the DFF-FOIC is illustrated by simulation. Then, the DFF-FOIC is applied on a physical robot manipulator prototype. Our step force tracking test results show that the proposed FOIC has better control performance than an integer order impedance controller (IOIC), achieving a better step response with lower overshoot, less settling time, and smaller integral time absolute error (ITAE) than the IOIC under fair comparison conditions.

Frequency- and Time-Domain Yield Optimization of a Power Delivery Network Subject to Large Decoupling Capacitor Tolerances

Suboptimal design of power delivery networks (PDNs) may cause performance deterioration and severe functional failures on high-speed computer platforms. Voltage regulators (VRs) distribute controlled voltage in the PDN to the active devices, providing a steady power supply at a desired DC voltage level with an acceptable noise level or ripple. Unacceptable voltage drops can be caused by transient switching currents at the devices. Many decoupling capacitors are commonly used to lower the PDN impedance profile in order to reduce power supply noise and to supply fast transient current to switching devices. However, commercially available decoupling capacitors typically present large manufacturing variability. In this article, we first propose an optimization methodology that gradually finds the best compensation parameter values of a buck converter VR to meet suitable stability criteria. Simultaneously, the number of parallel decoupling capacitors in the PDN is minimized while meeting a frequency-domain impedance profile specification and a time-domain minimum voltage droop requirement under nominal parameter values. Finally, a statistical analysis, yield estimation, and yield optimization of the nominally optimized PDN subject to large decoupling capacitor tolerances is presented. We consider the impedance profile, transient voltage droop, and VR stability as the responses of interest for yield calculation.

Tissue-like electrophysiological electrode interface construction by multiple crosslinked polysaccharide-based hydrogel

A reliable electrophysiological electrode interface (EEI) between bioelectronic devices and biological tissues is indispensable to achieve the high fidelity recording of bioelectricity. However, there is an inherent tradeoff among EEI's electrochemical characteristics, mechanical properties and biocompatibility when considering the desired nanostructure and optimum composition. Here, we proposed a mechanically matched, highly conductive and biocompatible EEI, a tissue-like metal-doped hydrogel which could enable excellent electro-biosensing, by bringing disulfide modified silver nanowires into difunctional hyaluronan/carboxymethyl chitosan composite. The intensity of cortical signals at specific frequency domain recorded by the hydrogel-based EEI is doubled, which is significant for the diagnosis of epilepsy. Furthermore, the natural gel matrix could lead to seamless bio-integration between EEI and the tissue site of interest, minimizing signal dissipation without causing obvious inflammatory response. Overall, the EEI we designed contributes to improving tissue-device integration as well as bioelectronic device's performance and further leads to more effective human-computer interfaces.

Frequency-Weighted Singular Spectrum Analysis for Time Series

Singular spectrum analysis (SSA) is a nonparametric spectral decomposition of a time series. A time series is exactly separated into arbitrary number of additive subsequences with the singular value decomposition. Previously, we have shown that SSA algorithm can equivalently be formulated as an optimality condition for the generation of adaptive filters. In this paper, based on our optimal-filter viewpoint, we show that the spectral weight factor can naturally be introduced into the SSA algorithm. With this extension, we can selectively focus on the specific frequency domain of the time series, and then the detailed study of the time series with complicated spectral structure becomes possible.

Stabilizing Sets of Current PI Controllers for IM Drives With and Without LC Filter

Connection of an LC filter to the output of voltage source inverter (VSI) in squirrel cage induction motor (SQIM) drive converts the pulse-width modulated (PWM) voltages into smooth sinusoidal voltages. However, this connection may lead to closed-loop instability in the rotor flux-oriented (RFO) vector-controlled (VC) SQIM system. The closed-loop stability of the combined SQIM + LC filter (SQLC) system is complex and has not been analyzed properly in the literature. In this paper, a detailed closed-loop stability analysis of the SQLC system has been presented based on stability region (SR) and accordingly the PI gains of VC has been designed. The SR method is adopted to derive the common stability regions for the SQIM system and SQLC system. Thereby, the paper proves that connecting an LC filter in-between the VSI and the SQIM system does not always destabilize the closed-loop system. Further, for an SQLC system, the complete range of current controller gains is obtained at various operating points. The frequency-domain specifications have been used to select a proper stabilizing set and the effect of parametric variation of LC filter on the stabilizing set has also been discussed. The experimental results are provided to validate the analysis.