Active Damping Methods Research Articles

Dynamic Modelling and Control of Flexible Link Manipulators: Methods and Scope - Part 2

Objectives: This paper addresses two key issues in the area of flexible robotics. The issues are vibration control of flexible links and trajectory control of flexible robots. A brief, yet, significant review is provided that addresses these two issues. Methods: For vibration control of flexible links, possibilities of the use of passive and active damping methods are explored in the literature. After that, the effect of proper trajectory planning to ensure positional accuracy at the end-effector is studied. Findings: After a review of 181 research papers from the year 1970 to 2021, it has been found that the vibration suppression of flexible links can be achieved through the application of viscoelastic materials, piezoelectric materials, and optimum trajectory planning. Recent trends in research in the area of flexible manipulators show that an optimal trajectory can significantly help in reduction of link vibrations and achievement of positional accuracy simultaneously. Novelty: The novelty of the present work lies in exploring the possible application of passive and active damping control methods for vibration suppression of flexible link manipulators. Besides that, the survey also highlights how well planned trajectory may help achieve accurate tip positioning of flexible robots. Keywords: Flexible manipulator; viscoelastic damping; active vibration control; trajectory planning and control

Robust Active Damping Strategy for DFIG Wind Turbines

Doubly fed induction generators (DFIGs) with an LCL filter are widely used for wind power generation. In these energy conversion systems, there is an interaction between the grid-side converter (GSC) and the rotor-side converter (RSC) control loops, the generator and the LCL filter that must be properly modeled. Such interaction between the GSC and the RSC proves to have a significant influence on the stability. Several active damping (AD) methods for grid-connected converters with an LCL filter have been proposed, nevertheless, the application of these techniques to a DFIG wind turbine is not straightforward, as revealed in this article. To achieve a robust damping irrespective of the grid inductance, this article proposes an AD strategy based on the capacitor current feedback and the adjustment of the control delays to emulate a virtual impedance, in parallel with the filter capacitor, with a dominant resistive component in the range of possible resonance frequencies. This work also proves that, by applying the AD strategy in both converters simultaneously, the damping of the system resonant poles is maximized when a specific value of the grid inductance is considered. Experimental results show the interaction between the GSC and the RSC and validate the proposed AD strategy.

A Novel DC-Link Voltage Feedback Active Damping Control Method for IPMSM Drives With Small DC-Link Capacitors

In a small dc-link drive system, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance is a typical phenomenon caused by the negative inverter admittance related to the constant power load, which is considered an instability problem that needs to be resolved well. In this article, a novel dc-link voltage feedback active damping control method is proposed to improve system stability. First, the feedback control loop with time delay is established. Based on the inverter admittance, the feedback gain is designed to handle various operating conditions properly. Meanwhile, the inverter equivalent admittance can be changed into positive to improve the system stability. Then, the oversampling method is proposed to reduce the digital control delay time and improve the damping current precision. Therefore, the system damping performance is further enhanced. Finally, the damping current modification is applied, in which the damping current is modified to negative in the motor regenerative braking mode to improve the grid power factor. Compared with the conventional active damping method, the power factor is increased to 0.989 and the grid current harmonics are reduced to satisfy the requirements of EN61000-3-2. The effectiveness of the proposed active damping method is also verified by the experimental results.

Active damping method for voltage source inverter-based distributed generator using multivariable finite-control-set model predictive control

Despite its advantages, the LCL filter can significantly distort the grid current and constitute a substantially more complex control issue for the grid-connected distributed generators (DGs). This paper presents an active damping approach to deal with the LCL filter's oscillation for the finite-control-set model predictive control (FCS-MPC)-three-phase voltage source inverters (VSIs)-based DG. The new approaches use the multivariable control of the inverter side's filter current and capacitor voltage to suppress the LCL filter resonance. The proposed method has been tested in steady-state and under grid voltage disturbances. The comparative study was also conducted with the existing virtual resistance active damping approaches for an FCS-MPC algorithm. The study validates the developed control schemes' superior performance and shows its ability to eliminate lower-order grid current harmonics and decrease sensitivity to grid voltage distortion.

Source-Side Virtual RC Damper-Based Stabilization Technique for Cascaded Systems in DC Microgrids

Cascaded connection of power converters is a dominant connection form in DC microgrids. In such systems, despite the possible instability caused by the impedance interactions between the individually designed converters, tightly regulated load converters acting as constant power loads (CPLs) tend to destabilize the system owing to their negative resistance characteristics. Hence, this paper proposes a new virtual series RC damper in parallel with the source-side converter's capacitor without compromising the load's dynamic performance. Using this design-oriented active damping method, which utilizes a simple control structure with a more straightforward tuning of the control parameter, the stability and performance of the system are guaranteed. The feasibility and robustness of the suggested active stabilization idea against unanticipated variations in input voltage amplitude, and CPL power rating (load changes) as well as step changes in output voltage reference, are also authenticated. The control and operation principles, as well as the circuit physical meaning realized by the presented technique for three cascaded systems comprising the basic DC/DC converters feeding CPLs, are theoretically analyzed. Simulation and experimental results are provided to validate the effectiveness of the proposed active stabilizer.

Discrete Fundamental AC Voltage Controller for Three-Phase Standalone Converters

Voltage control of standalone converters with LC filter is usually based on proportional-resonant or proportional-integral controllers, which often require further active damping methods to achieve stability. These solutions place design constraints in the selection of the closed-loop pole locations which limit the achievable bandwidth and increase the design complexity. In contrast, in state-space based controllers, the closed-loop poles can be placed freely through state feedback, which makes them particularly suitable for high order plants and/or low sampling frequencies. Among the modern control methods, direct pole placement is a simple technique that enables the establishment of a straightforward relationship between outcome and design, as opposed to more advanced approaches. This paper presents a discrete state-space voltage controller for standalone converters with LC output filter. The proposed method combines the direct pole placement technique with a virtual disturbance observer in order to compensate the effects produced by the load and model mismatches. The design process takes into account both the filter parameters and the sampling frequency, rendering the performance of the obtained controller independent of both. The result is a streamlined design procedure that leads to consistent outcomes for a wide range of plant parameter variations, requiring only one input: the desired closed-loop bandwidth.

Emulating bistabilities in turning to devise gain tuning strategies to actively damp them using a hardware-in-the-loop simulator

Bistabilities in turning are characterized by the process being stable for small perturbations and unstable for larger ones. These bistabilities occur due to nonlinearities in cutting force characteristics. Characterizing these bistabilities can guide selection of cutting parameters to lie outside these zones of conditional instabilities. However, if cutting is targeted in the bistable regions, or in regions that are globally unstable, active damping methods may need to be pursued to improve the stability envelopes. Since gain tuning for active damping of chatter vibrations is usually based on linear stability analysis, it would be useful to know if those gains are adequate for damping chatter in the presence of bistabilities that occur in processes prone to strong perturbations. However, experimentation on machines to investigate these bistabilities and/or tune gains to meet targeted productivity levels with active damping is difficult due to the destructive nature of chatter. This paper hence discusses the use of a hardware-in-the-loop (HiL) simulator to emulate bistabilities and to serve as a test bench for gain tuning in the presence of bistabilities. The HiL simulator has a hardware layer comprising a flexure representing a flexible workpiece, and two actuators. One emulates the cutting force calculated in real-time in the software layer. Another serves as the active damper operating with a velocity feedback control law. Bistabilities for three different nonlinear force models are experimentally illustrated on this HiL simulator. We show that active damping can stabilize these bistable regions. Since the width of the bistable regions depend on the nonlinear force characteristics, our investigations reveal that gains must be tuned for the force model and the static chip thickness under consideration. These results are useful and can instruct active damping strategies during more realistic cutting processes with nonlinear force characteristics that exhibit conditional instabilities in the presence of strong perturbations.

Active/Passive Method-Based Hybrid High-Frequency Damping Design for MMCs

High-frequency resonance (HFR) is a key issue of power electronics-based systems. Two solutions can be applied for addressing HFRs, including active damping method and passive damping method. For modular multilevel converters (MMCs), most of the existing harmonic resonance suppression methods are focused on active methods, including active filtering and virtual resistance. However, the active filtering may lead to negative damping in its attenuation band and the virtual resistance may become negative in high-frequency range when influenced by control delay. In order to avoid the negative effects of control delay and increase the damping of MMCs in high-frequency range, this article reconsiders the arm inductor in MMCs and proposes a passive damper design method for MMCs. With the coordinated design between active controller and passive damper, the negative damping of MMCs in high-frequency range can be effectively eliminated and the system stability can be improved. Also, the proposed passive damper has little impact on the steady-state operation and increases few losses of the MMC. The effectiveness of the proposed passive damper is validated by electromagnetic transient (EMT) simulations in PSCAD/EMTDC.

Dynamic impact of hydraulic systems using pressure feedback for active damping

Pressure feedback has been an effective method for active damping and oscillation reduction in hydraulic systems. However, this study reveals a dynamic impact problem of a larger velocity overshoot and slower convergence excited by an external force/torque disturbance once pressure feedback is introduced for active damping. This problem is introduced through a theoretical analysis, and then illustrated by a numerical simulation. The solutions to this problem are analysed for a hydraulic system with a symmetric cylinder. For a trade-off between the active damping effect and reduction in dynamic impact, a multi-objective optimization method is proposed to determine the control parameters (gain and time constant) of the high-pass pressure filter. The multi-objective optimization method is validated by a simulation model with the symmetric cylinder under different disturbances. Moreover, an analysis is carried out for the system with an asymmetric cylinder or hydraulic motor. The theoretical analysis shows that the mathematical forms of the two systems are similar to that of the symmetric cylinder system. Therefore, the dynamic impact problem also exists in the two systems. The proposed method is also effective for the damping improvement and mitigation of the dynamic impact.

A Simple Method for Passivity Enhancement of Current Controlled Grid-Connected Inverters

Grid-connected inverters with LCL filter work stable using active damping methods. However, the stability of the control system can be threatened easily by grid impedance variation. On the other hand, delay in digitally-controlled systems shrinks the stable region. Therefore, it is very probable that by variation of grid impedance, resonance frequency located in the unstable region. To address this problem, a simple but effective method based on converter-side current feedback is proposed in this letter. This method does not need any extra sensors for active damping, which increases reliability and reduces the cost. The proposed method expands the stable region and guarantees the stability of the inverter against the grid impedance variation. It is shown that the proposed method is effective in the case of multiparalleled inverters whiles normally coupling effect among inverters makes the stability condition worse. The effectiveness of the proposed method is verified through experimental results.

Design, control and comparative analysis of an LCLC coupling hybrid active power filter

This study provides the design, control and comparative analysis of the proposed LCLC coupling hybrid active power filter (LCLC-HAPF). Compared with the conventional L filter coupling active power filters (APFs), LC filter and LCL filter coupling HAPFs (LC-HAPFs and LCL-HAPFs), the proposed LCLC-HAPF provides better switching frequency harmonics elimination, lower dc-link voltage rating and switching loss. Although the LCLC-HAPF has some advantages, two main challenges will still be confronted in practical implementations. Those are stability problems caused by resonance of LCLC filter, and parameter design for the LCLC filter. In this study, a new active damping method is proposed to overcome the high order resonance problem existing in the proposed LCLC-HAPF. After that, the stability analysis and parameter design are given for the proposed LCLC-HAPF. Finally, the effectiveness of the proposed LCLC-HAPF topology is validated through both simulation and experimental studies in comparison with the conventional APFs and HAPFs.

Enhanced robustness with damping interval widening strategy of LCL-type converter under weak grid condition

Active damping methods are widely adopted to present a damping effect on the resonance phenomenon without the power loss of LCL-type converters connected to a grid. However, extra sensors are used to implement the damping strategy. In this paper, a sensorless damping strategy where only the grid current is sampled has been proposed. Furthermore, the inner relationship between the tradition capacitor current feedback strategy and the proposed strategy has been clarified. Considering the digital delay and a weak grid, a robust method that uses unit delay feedback to mitigate the phase lag and to widen the effective damping interval has been developed. With this simple measure, stability is enhanced during the Nyquist frequency and robustness is improved when the LCL parameters vary and grid impedance exists. Finally, simulation and experimental results are presented to verify the feasibility and engineering significance of the proposed strategy.

Active damping method based self‐adjust notch filter for current source converter

Inductor–capacitor (LC) filter in current source converter (CSC) exits resonance peak, which result in reducing control stability and amplifying harmonic component near resonance frequency. This study proposed a simply self-adjust notch filter active damping method for CSC. A notch filter is inserted into control loop to damp the control gain at resonance frequency, no need of additional sensor. The grid inductance varies as power system operating conditions change, which deteriorates notch filter damping performance because of resonance frequency changing. The harmonic impedance estimation method is used in the paper to estimate grid inductance and actively adjust notch filter centre frequency. Both simulation and experimental results verified the effectiveness and robustness of the proposed method.

Elimination of current oscillation in isolated three‐port power converters using active damping method

Double switching frequency components of the input current in the isolated three-port converter (TPC) can be effectively mitigated using an LC circuit at the input side of the converter. Although the LC circuit prevents the high-frequency current flow into the system, there is a resonant peak in the port current control model that can degrade the control performance and even give rise to instability issues. In this article, an active damping method (ADM) is proposed to enhance the damping ratio of the current control system and decrease the resonance amplitude of the LC circuit. The proposed ADM is fully implemented within the converter control system without any additional circuits or components and as such is seen as a cost-effective and efficient method. Simulation and experiment results show the effectiveness of the proposed method on the input current oscillation elimination in an isolated TPC.

Performance comparison of passive series R and shunt R‐C damped LCL filter for grid‐connected inverters

LCL filters are widely used in distributed power-generation systems to attenuate high-frequency harmonics caused by pulse-width modulation switching of grid-connected inverters. A resonance occurs due to the series-connected reactive components. In order to damp resonance effects, active and passive damping methods are used. Lower switching frequencies are typically preferred to decrease switching power losses with high-power applications. Thus, control bandwidth of the system is limited and implementation of active damping gets harder. As a result, passive damping methods are commonly used in high-power applications. In this study, performances of two most commonly used passive damping methods which are series R damped and shunt R-C damped are analysed and compared in terms of resonance damping, grid current attenuation at high frequencies, and power losses on damping circuits.

Hybrid vibration control of a Two-Link Flexible manipulator

This research work deals with tip vibration control of a Two-Link Flexible manipulator using hybrid control technique. This technique involves the implementation of unconstrained viscoelastic damping layer on the links in conjunction with active damping using piezoelectric sensors and actuators. Mathematical modelling of the complete system is done using the finite element approach in the inertial frame. Viscoelastic damping is modelled using Kelvin–Voigt elements for which a damping matrix is derived. Active damping is modelled as time-dependent uniformly distributed load applied by the piezoelectric actuator on the flexible link working under feedback control. The angular and linear velocities of the tips of flexible links are used for direct feedback. The unconstrained viscoelastic damping layer effectively reduces the vibrations of the system. The effectiveness of the active control depends upon the relative position of sensors and actuators on the links. The novelty of the work lies in control of torsional and flexural vibrations through the application of passive and active damping methods to the non-inertial frames represented by the manipulator links.

A novel control approach for damping of resonance in a grid interfaced inverter system-fuzzy control approach

ABSTRACT LCL (Inductor, Capacitor and Inductor) filters are commonly employed in grid allied system, provide better harmonic attenuation than L (Inductor) and LC (Inductor and Capacitor) filters. They bring resonance in addition to oscillations into grid coupled system. With the intention to mitigate the resonance that brings instability problems in the system, active damping control strategies are adopted. Active damping method based fuzzy logic control to ease control action on the considered scheme is focused in this article. The projected controller is compared with the existing injected grid current feedback controller to investigate the resonance damping and stability of grid interfaced LCL filter by multilevel inverter. When compared with injected grid current feedback controller, satisfactory performance based on harmonic content, resonance peak and stability is met by the fuzzy logic control approach. Simulation analyses justify the design strategies and the efficacy of fuzzy logic control.

An intelligent control approach for resonance damping in a grid-connected inverter system

Photovoltaic power generation has transformed into the most reassuring strategy for power generation among the renewable sources in view of its intrinsic favorable circumstances. The significant snag that photovoltaic system poses like other inexhaustible sources is the power intermittency in regard to atmospheric conditions like irradiation and temperature. These photovoltaic systems are interfaced to the grid through filters via inverters to prevent harmonics getting in to the grid. Generally, inductor–capacitor–inductor filters are employed in grid-connected system, as they provide better harmonic attenuation than inductor and inductor-capacitor filters. However, they bring resonance as well as oscillations into the grid-connected system. So, in order to suppress the resonance that brings instability problems in the system, active damping control strategies are adopted. But these conventional active damping methods increase the complexity of the system as they need extra sensors. This article proposes a fuzzy logic control-based active damping method to ease the control activity. The proposed controller is contrasted with the injected grid current feedback controller to investigate the resonance damping and the stability of grid interfaced multilevel inverter with inductor–capacitor–inductor filter. When compared with the injected grid current feedback controller, the fuzzy logic control approach promises satisfactory performance based on harmonic content, resonance peak, and stability analysis. The compliance according to the industrial standard in terms of harmonics is met in this article and is duly documented within the manuscript. Simulation results verify the design strategies and the effectiveness of the proposed fuzzy logic control strategy.

Inductor Current Feedback Active Damping Method for Reduced DC-Link Capacitance IPMSM Drives

The LC resonance between the line inductor and the dc-link film capacitor is an important concern in the reduced dc-link capacitance interior permanent magnet synchronous motor drive system. In this paper, an active damping method based on the virtual damping resistor is applied to suppress the LC resonance and improve the drive system stability. The performance of the damping resistor is analyzed in a systematic level, and possible configurations have been analyzed to obtain the optimal solution, which is proved to be the inductor current feedback (ICF) damping method. In order to realize the equivalent damping effect, the dc-link voltage feedback is applied to emulate the ICF-based active damping method by a step-by-step approach. Meanwhile, the grid voltage distortion will stimulate additional harmonics of the grid current in the reduced dc-link capacitance motor drives. Hence a feedforward compensation method is applied to suppress the grid current distortion arising from the distorted grid voltage, which has not been investigated in the previous related researches. Harmonics of the grid current are reduced and requirements of EN61000-3-2 can be satisfied by applying the proposed method. Experiments on a compressor drive platform equipped with the reduced dc-link capacitance are performed to verify the effectiveness of the proposed method.

ОПТИМАЛЬНОЕ ГАШЕНИЕ ПОПЕРЕЧНЫХ КОЛЕБАНИЙ КОНСОЛЬНОЙ БАЛКИ

The multicriteria problem of transverse vibrations damping of a console beam is colved by the active and passive damping methods. The mathematical model of beam is provided by Bernoulli-Euler's hypotheses with the linear viscosity. Perturbation acting on the beam belongs to a class L2 of functions. The beam mode is described by Krylov functions. The normal form method is used to convert to the main coordinates. A model of active vibration isolation applied along the entire length of the console beam and a model connected to a vertical base at one point were constructed. The task of transverse vibrations damping is a state feedback control problem with two controlled outputs. Two criteria are introduced: the level of the control force and the maximum deflection of the beam. The generalized H2-norm is used as a measure of functional evaluation in the synthesis of optimal regulators. The search for optimal feedback is based on the use of linear matrix inequalities and efficient algorithms for solving, implemented in the MATLAB package. Synthesis of Pareto optimal control is implemented on the basis of Germeyer convolution. The optimal values of the functional under distributed and concentrated vibration isolations are given with respect to two criteria for active and passive damping methods. The paper includes a comparison of vibration isolation for different damping methods.