Active Damping Methods Research Articles

Voltage Modulation Using Virtual Positive Impedance Concept for Active Damping of Small DC-Link Drive System

Small dc-link drive systems, built with film capacitors in the dc-link, present a new trend in many industrial applications and are obtaining increasing interests. It has the advantages of longer lifetime and the possibility to achieve a more compact design of the capacitor bank, especially at medium and high power rates. However, it could exhibit instability problems, mainly in the form of oscillations. The unexpected oscillation may result in overvoltage and shorten the lifetime of the power devices and the dc-link capacitors; increase the total harmonic distortion and also the partially weighted harmonic distortion of the grid supply current. Therefore, active damping methods are usually needed in order to stabilize such drive systems. This paper first analyzes the system characteristics and the principles of existing active damping methods. Then, a new voltage modulation based method named as “virtual positive impedance” method is introduced to guarantee the dc-link stability. This new approach is simple to apply and its implementation does not require the knowledge of system parameters and machine operating conditions. The proposed method is analyzed in details and verified by experiments.

Active Disturbance Rejection Control of LCL-Filtered Grid-Connected Inverter Using Padé Approximation

In this paper, a simplified robust control is proposed to improve the performance of a three-phase current controlled voltage source inverter connected to the grid through an inductive–capacitive–inductive ( LCL ) filter. The presence of the LCL -filter resonance complicates the dynamics of the control system and limits its overall performance, particularly when disturbances and parametric uncertainty are considered. To solve this problem, a robust active damping method based on the linear active disturbance rejection control (LADRC) is proposed. The simplification is made possible by order reduction in the plant transfer function using Pade approximation. Simulation results show that the proposed LADRC-based current controller achieves high power quality and good dynamic performance, in the presence of parameters uncertainties as well as external disturbances. An experimental prototype is built to verify the effectiveness and practicality of the proposed control strategy.

Inverter-Current-Feedback Resonance-Suppression Method for LCL-Type DG System to Reduce Resonance-Frequency Offset and Grid-Inductance Effect

For the LCL-type grid-connected distributed generation system, the grid-current-feedback active damping (GCFAD) methods have a conflict between the resonance-suppression ability and harmonic-currents amplification. For this, an inverter-current-feedback reso-nance-suppression (ICFRS) method without additional sensors is proposed to reduce resonance-frequency offset and grid-inductance effect due to its unattenuated damping characteristic under high-frequency bandwidth. By analyzing two types of equivalent impedance models of ICFRS and GCFAD with a high-pass filter (HPF), GCFAD can suppress the resonance peak well only with a large resonance-frequency offset and might result in a narrow control bandwidth. However, ICFRS can suppress the resonance peak well with smaller resonance-frequency offset and maintain a high power quality compared with GCFAD. Considering the influence of control delay and grid inductance, the positive/negative critical point of an equivalent virtual resistance of ICFRS derived in the interval of [1/6, 1/3) is obtained, and a robust ICFRS is further proposed to improve system stability by maintaining a positive resistance regardless of grid-inductance variation. The stable-state and dynamic properties of the overall system are analyzed in detail in this paper, and its proper control parameters are selected without a complicated trial. Finally, simulation and experimental results verify the validity of the proposed method.

A comprehensive control system for multi-parallel grid-connected inverters with LCL filter in weak grid condition

Active damping methods are used for resonance damping in grid-connected inverters with LCL filter. In microgrids, parallel grid-connected inverters are coupled due to grid impedance introducing multiple resonances. In general, such coupling effect is not taken into account for modeling and controller design. For single grid-connected inverter, despite good performance, the system tends to become instable with parallel connection of other inverters. Moreover, the grid injected current can be distorted by the grid voltage harmonics. In traditional control system, grid voltage is used as a feedforward signal to achieve harmonic rejection capability by boosting the inverter output impedance. However, this method introduces negative phase angle which could lead to control system instability. In this paper, the control system design for multi-parallel grid-connected inverters using active damping is clarified. Inverters with different characteristics are also modeled in a weak grid as a multivariable system while coupling effect with a wide variation of grid impedance is taken into account. An improved grid voltage feedforward method is proposed to eliminate negative aspects of the traditional method. The simulation results in MATLAB/SIMULINK software demonstrate the effectiveness of the proposed control system.

The evaluation of two methods for active vibration damping using RUS Hexapod platform

This paper presents a study on active vibration Isolation using RUS (revolute joint, universal joint, spherical joint) structure of Stewart platform, as it is less expensive and easier to build than PSS (prismatic joint, spherical joint, spherical joint) structure, which is used a lot in this field. Two control methods are proposed; the fuzzy logic method and the adaptive feed forward control method with multiple error least mean square. Results are evaluated using the SimMechanics toolbox under Matlab 2014 with white noise signals to simulate vibrations. In addition, practical measured accelerations are applied and results are evaluated. Both strategies use a proportional–integral–derivative (PID) controller in parallel to control displacements of the Hexapod as vibrations at low frequencies generate high variations in displacements. The results prove that using a Hexapod with RUS structure can degrade vibrations and guarantee a good behavior for many applications, which is the main aim of this research.

Enhanced Resonant Current Controller for Grid-Connected Converters With LCL Filter

Conventional resonant controllers (RCs) are commonly used in the current control of grid-tied converters with LCL filter due to their advantages, such as zero steady-state error at both fundamental sequences, easy design process, and straightforward implementation. Nevertheless, these traditional solutions do not permit to place the closed-loop poles of the system in convenient locations when dealing with a fourth-order plant model such as the LCL filter plus the computation delay. Therefore, the reference tracking and the disturbance rejection are deficient in terms of transient behavior and depend on the LCL filter. Furthermore, an additional active damping method usually has to be designed in order to ensure stability. This paper presents an enhanced current RC with stable and fast response, negligible overshoot, good disturbance rejection, and low controller effort for grid-tied converters with LCL filter. The developed solution uses a direct discrete-time pole-placement strategy from the classical control theory (using transfer functions), involving two extra filters, to enhance the performance of the RC. In this manner, the complexity of state-space methods from modern control theory is avoided. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme.

Improved adaptive notch filter-based active damping method for shunt active power filter with LCL-filter

The LCL-filter has been recently used with grid-connected converters to mitigate switching ripple harmonics. The LCL-filter presents a better attenuation performance for switching ripple harmonics in comparison with L- and LC-type filters. However, the application of LCL-filter has two basic constraints on the circuit design and the resonance problem. These constraints can be effortlessly overcome for grid-connected converters which operate on the utility fundamental frequency. On the other hand, these constraints become a challenging issue when the LCL-filter is used with shunt active power filter (SAPF) because of the wide operation frequency bandwidth of SAPF. This wide operation bandwidth of SAPF causes a narrow bandwidth for the selection of LCL-filter cutoff frequency and the resonance damping control. In this paper, the application constraints of LCL-filter are discussed and the LCL-filter design is provided for SAPF. In addition, an adaptive notch filter-based single-loop active damping method is developed considering the wide operation bandwidth of SAPF. The proposed method consists of a grid impedance estimation algorithm in order to update notch filter parameters adaptively against grid impedance variations. By the help of the single-loop active damping strategy, the proposed controller does not require any additional sensor for the current measurement of LCL-filter capacitor to damp resonance currents. The stability analysis of proposed controller is performed through pole–zero maps. The proposed method is tested, and its performance is verified with comprehensive case studies of a 400-V 80-kVA SAPF simulation model through MATLAB/Simulink.

Analysis and Stabilization of a Smart Transformer-Fed Grid

The stability of the grid-connected inverters adopted in distributed energy resources (DERs) highly depends on the characteristics of the grid impedance. Hence, various active damping methods and adaptive control algorithms have been proposed for the control of the grid inverters. Differently from those existing solutions, this paper proposes to use a smart transformer (ST) to shape the grid impedance to interact with the controllers of local inverters, aiming at improving the stability of the local controllers as well as the overall grid. A main advantage of this solution is that it offers a pervasive service to all the available DERs, reducing the cost and design effort of the local controllers. Three active damping methods are presented in this paper and the implementation issues in the ST LV-side voltage controller are given. Moreover, the design criteria of the active damping methods considering the control performance of ST and the stability requirements of local DERs are presented. Analysis and experiments are carried out to verify the effectiveness of the proposed solution.

All-Pass-Filter-Based Active Damping for VSCs With LCL Filters Connected to Weak Grids

LCL filters are commonly used to connect voltage-sourced converters (VSCs) to the grid. This type of filter is cheaper than a single inductor for the same current total harmonic distortion (THD), but it generates resonance problems if no active or passive damping method is applied. Active damping methods are becoming popular in the literature because they improve efficiency, but they are sometimes difficult to implement and additional measurements are required. This paper proposes an active damping method for VSCs connected to weak grids, which is based on making the open-loop phase zero at the resonance frequency. It will be shown that this strategy provides adequate damping of oscillations and that it can be achieved in two different ways: at the design stage (if the design constraints make it possible) or with an all-pass filter in series with the current controller. Two methods to design the all-pass filter are proposed. Also, the proposed active damping technique is compared with three alternatives already proposed in the literature. All the control algorithms are verified by simulation and in a 15-kW prototype of a three-phase VSC connected to a configurable weak grid via an LCL filter.

Effect Of Improving Damping Ratio On Surface Finish By Filling Particulate Reinforced Polymer Composites In Machine Tool Structures

It is proven that the structural damping plays an important role in determining machine tool precision. Machine tool industries are trying to increase the machine tool precision by various passive and active damping methods with no appreciable success. However, research involving polymer composites, particularly particulate reinforced polymer composites (widely known as polymer concrete) in machine tool structures have shown promising results in terms of better damping, reduced mass and comparable stiffness. In this study, particulate reinforced polymer composites with different compositions have been studied for machine tool structural application. Influence of particulate composition (polymeric resin type and proportion) on damping ratio and elastic modulus has been investigated by carrying out impulse hammer vibration test. In comparison to cast iron and steel polymer composite with quartz of up to 2 mm size with 30% polyester showed 80 times higher damping ratio. As stiffness of polymer composite was moderate to use for machine tool structures, the composition which exhibited highest damping ratio was filled into steel structure in order to compensate for stiffness while increasing damping. Ratio of polymer composite to Steel volume in the hybrid structure was increased upto75% and its response for vibration was studied. The results revealed that addition of particulate reinforced polymer composite which showed highest damping ratio, increased damping of the structure by large amount with negligible reduction in stiffness. In order to investigate its effect on machine tool precision, the hybrid structures were ground under similar condition and its surface finish were tested. The results revealed that the stiffness acts in combination with damping ratio to improve the surface finish and hence location of addition of polymer composite in the steel structure is important to consider.

Effect of Active Damping on Output Impedance of Three-Phase Grid-Connected Converter

LCL-filter is commonly used to attenuate the switching harmonics of grid-connected converters. LCL -filter creates resonances in the converter dynamics which shall be damped for ensuring robust performance of the converter. Active damping methods can be used to attenuate the resonant behavior effectively. Accordingly, the output impedance is affected and the grid-interaction sensitivity of the converter varies with the active damping design. In order to carry out impedance-based stability analysis or assessment of the harmonic rejection capability, an accurate analytical model to predict the output impedance is necessary. This paper investigates the output impedance properties of capacitor-current-feedback active damping, which are so far not considered thoroughly in the literature. The output impedance modification with the active damping design is explained, thus, the stability and harmonic rejection capability of the converter can be improved. Furthermore, in order to validate the model, experimental measurements of the output impedance with active damping are presented for the first time in the literature.

Robust Active Damping Methods for LCL Filter-Based Grid-Connected Converters

Grid-connected converters (GcCs) employ LCL filters instead of simple L filters in order to meet new grid codes and their on-going changes in the near future. Active damping methods, without power losses, are preferred to passive ones for solving the resonance problems of LCL -filter-based GcCs ( LCL -GcCs). However, large changes in the grid inductance (typically under weak grid conditions and in rural areas) may compromise the system stability. Moreover, the delay of digital controllers will change system phase-frequency characteristics and consequently will affect the system stability. In view of this, this paper proposes a systematic design procedure for the active damping of voltage-oriented PI control for LCL- GcCs. The procedure considers active damping methods based on capacitor current feedback and is aimed to ensure stable operation under severe grid inductance variations while taking into account the influence of digital control delay and LCL filter parameters changes on the system stability. Simulation and experimental results are presented and discussed in order to validate the proposed design procedure.

Modeling and Resonance Control of Modular Three-Level Shunt Active Power Filter

Compared with the conventional central shunt active power filter (SAPF), modular designed SAPF can track the harmonics more precisely and quickly with a compact and expandable structure, which makes it a better solution for harmonic mitigation. But there are very few paper discussed about the modeling and parallel resonance issues of modular SAPF parallel system. This paper provides a modeling of three-level SAPF, aiming to guide the modular design and research the parallel resonance control method. First, a simplified modular three-level SAPF modeling is proposed based on averaging impedance modeling and small signal linearization techniques. Then, the coupling issues between modules are researched, and a self-adaptive active damping method is proposed to suppress the system resonance. Based on the modeling results, an improved three-level SAPF module topology is proposed to construct the modular system. The theoretical analysis and experimental results verify that the module topology improvement together with the damping strategy can promise the compensating bandwidth, reliability, and fast, precise harmonics tracking ability.

Positive- and Negative-Sequence Current Controller With Direct Discrete-Time Pole Placement for Grid-Tied Converters With LCL Filter

Traditionally, the current control of grid-tied converters with LCL filter is based on proportional-resonant or proportional-integral controllers, which often need an additional active damping method to achieve stability. These solutions do not permit to place the closed-loop poles in convenient locations when dealing with such high-order plants. This constraint results in degraded reference-tracking and disturbance-rejection responses. On the other hand, the existing methods based on direct pole placement or other modern control strategies, do not control with zero steady-state error both positive and negative sequences of the grid current, but only the positive one. This limitation is undesirable under unbalanced grid conditions. This paper presents a current controller for grid-tied converters with LCL filters based on direct discrete-time pole placement. The proposed controller makes it possible to control both positive and negative sequences of the grid-side current with zero steady-state error. Contrarily to the classical resonant controllers, the closed-loop poles can be placed in convenient locations, yielding a fast response with negligible overshoot and low controller effort. Moreover, no additional damping methods of the resonance are necessary to achieve stable operation, regardless of the switching frequency and LCL filter used. Simulation and experimental results that validate the proposal are presented.

Study of a Current Control Strategy Based on Multisampling for High-Power Grid-Connected Inverters With an LCL filter

The high-power grid-connected inverters with LCL filters have been widely used. Current control plays a key role in the grid-connected inverter control system. To cope with the inherent resonance of the LCL filter, active damping (AD) methods are usually employed. However, the AD performance is impaired by control delays which are introduced in the digital control implementation process. Besides, the lag phase due to control delays limits the system bandwidth and stability margin. The effects of control delays are more noteworthy in the high-power grid-connected inverter due to its low switching frequency. This paper investigates the current control strategy based on multisampling for the high-power grid-connected inverter with the LCL filter. First, the multisampled AD scheme is studied, which can reduce control delays effectively and improve AD performance. Besides, the multisampled control without additional damping whether passive or active is researched. Through the inverter-side current feedback, the system can realize single-current-loop control based on multisampling. Thus, the control system is simplified and it can be stable, and achieve better dynamic performance. Finally, experimental results show that the proposed control schemes are effective.

An Active Damping Method Based on a Supercapacitor Energy Storage System to Overcome the Destabilizing Effect of Instantaneous Constant Power Loads in DC Microgrids

This paper presents a novel active damping method to overcome instability problems of dc microgrids (MGs) caused by constant power loads (CPLs). This method is implemented based on the existing energy storage system (ESS) in the dc MGs. As an indispensable part in the dc MGs, the ESS in this paper is used for more than just compensating the conventional power unbalance in the system, it has taken an additional responsibility and is used for adjusting the system damping to deal with the instability problems induced by the CPLs as well. First, the stability criteria of a simplified dc MG are analyzed. Based on this, an active damping method that aims at virtually reshaping the loads in the dc MG is introduced. With the proposed method, which is realized by a supercapacitor ESS in this paper, the CPLs in the system are virtually reduced and the resistive loads are virtually increased. Therefore, the destabilizing effect of the CPLs in the dc MG is eliminated. Simulations and experiments are conducted and the effectiveness of the proposed method is verified. This method is suitable to be applied in the dc MG with various elements and variable operation modes.

About One Method of Active Dynamic Damping

In this article questions of active clearing of vibrations of system are considered. The paper deals with the active damping of the system's oscillations. Considering that the system is constrained by servosvyazami, for a single-mass system it is proposed to perform servosviaz by changing the mass of the absorber. For this it is proposed to build a digital tracking system.

相対加速度を利用した帯域制限外乱/内乱相殺による振動抑制制御

This study presents the method of active vibration damping in cutting using relative acceleration, which is intended for full-closed controlled ball-screw-driven stage. Disturbance against rigid body motion is canceled out by using multi-encoder-based disturbance observer. Disturbance/internal disturbance against relative motion is canceled out by using relative acceleration instead of relative velocity or displacement. The use of acceleration signal recovers phase lag and leads to suppress vibration in higher frequencies. In addition, it enhances low-frequency cutoff characteristics in extracting relative motion, which enables band-limited vibration control separating the rigid body and the relative motion. By introducing suitable phase lead filter which makes phase shift zero between load force and current response, vibration of the table can be effectively suppressed without significantly changing the resonance frequency. The results of end milling tests show that the vibration near the resonance frequency is suppressed by relative acceleration feedback.

A Time Delay Compensation Method Based on Area Equivalence For Active Damping of an <italic>LCL</italic> -Type Converter

Control of the LCL -type three-phase grid-connected converter is difficult due to high resonance peak of the LCL filter. Active damping is the state-of-the-art solution to this problem, but the damping performance will be affected by the inherent time delay of digital control, especially for high-power low switching frequency applications. Based on a discrete-time stability analysis of an LCL -type converter with capacitor-current-feedback active damping, a simple and effective time delay compensation method, which is based on area equalization concept, is proposed. The method can reduce the negative impact of the computation delay significantly. It has the potential to serve as a general solution to time delay compensation of a digitally controlled PWM converter. The validity of the proposed method is proved by experimental results.

Dynamic Resonance Analysis and Oscillation Damping of Multiterminal DC Grids

Voltage-source converter-based multiterminal high-voltage direct current (VSC-MTDC) systems/grids are prone to system instability. This critical issue is overlooked in the literature. In order to improve system stability, this paper proposes an effective active damping method as a remedy to suppress voltage and power resonances in the VSC-MTDC grids by injecting damping signals into the inner current loops of VSC-MTDC stations. With dynamic regulation of the damping current, resonance is suppressed by power converter controllers without any additional current and voltage measurement. In this paper, modeling and stability analysis of the VSC-MTDC system/grid is presented considering the dc-side energy storage components, and control with a droop control structure. Then, single-frequency and multifrequency resonance mechanisms of dc-bus voltage and power in the event of transients are analyzed. Later, the stability effect of the MTDC system/grid inductance and capacitance values to the resonance amplitude and frequency droop coefficients is investigated. A PSCAD/EMTDC platform is developed to conduct dynamic simulations, and a scaled-down four-terminal 20-kW experimental prototype is used to validate the effectiveness of the proposed control methodology.