Three-phase electric spring (TPES) was originally proposed to solve three-phase imbalance issues in power systems. So far, several attempts have been reported on proposing power control methods for ...it. However, existing solutions on TPES either depend on circuit parameters or have relatively slow dynamic responses. In this article, a novel power control strategy that incorporates the advantages of direct power control (DPC) is proposed to solve the above issues. It might be the first attempt to propose a simple power control strategy with rapid dynamic response and independent with circuit parameters for TPES. Besides, the relationship between power operating range and circuit parameters is well analyzed, which provides a way for parameter optimization. To restrain the resonance phenomenon caused by the TPES topology, the passive and active damping methods are compared, revealing that power quality of the control objective can be greatly improved with the active damping. Finally, the proposed DPC with both damping methods is validated by simulations and experimental results.
MMC converters are widely used in power grid. Different types of MMC-based cascaded converters will face stability problems. Through the impedance modeling of typical MMC-based AC/DC converter and ...DC/DC, the small signal model is established at the steady-state point, so as to obtain the output impedance of the front-end converter and the input impedance of the back-end converter.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A higher order passive power filter (LLCL filter) for the grid-tied inverter is becoming attractive for industrial applications due to the possibility to reduce the cost of the copper and the ...magnetic material. However, similar to the conventional LCL filter, the grid-tied inverter is facing control challenges. An active or a passive damping measure can be adopted to suppress the possible resonances between the grid and the inverter. For an application with a stiff grid, a passive damping method is often preferred for its simpleness and low cost. This paper introduces a new passive damping scheme with low power loss for the LLCL filter. Also, a simple engineering design criterion is proposed to find the optimized damping resistor value, which is both effective for the LCL filter and the LLCL filter. The control analysis and the power loss comparison for different filter cases are given. All these are verified through the experiments on a 2-kW single-phase grid-tied inverter prototype using proportional resonant controllers. It is concluded that, compared with the LCL filter, the proposed passive damped LLCL filter can not only save the total filter inductance and reduce the volume of the filter but also reduce the damping power losses for a stiff grid application.
In this paper, the methodology of Desoyer and Slibar, for an approximate analytical solution of the nonlinear differential equations governing the dynamics of a circular centrifugal pendulum, has ...been herein extended to the case of cycloidal and epicycloidal pendula paths. Another distinctive feature treatment of this investigation is the use of parametric cartesian equations of the mass pendulum for the cycloidal and epicycloidal paths. The tuning conditions for the three cases of circular, cycloidal and epicycloidal centrifugal pendula have been deduced. These are consistent with the findings of Denman. Due to the tautochronism associated with these paths, the centrifugal pendula with such paths demonstrated a damping capabilities also under large oscillations. The numerical examples discussed confirm such features.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Passive damping is the most adopted method to guarantee the stability of LCL-filter-based grid converters. The method is simple and, if the switching and sampling frequencies are sufficiently high, ...the damping losses are negligible. This letter proposes the tuning of different passive damping methods and an analytical estimation of the damping losses allowing the choice of the minimum resistor value resulting in a stable current control and not compromising the LCL-filter effectiveness. Stability, including variations in the grid inductance, is studied through root locus analysis in the z -plane. The analysis is validated both with simulation and with experiments.
•The characteristics of high-frequency oscillation in MMC-HVDC systems are analyzed and summarized by impedance method.•The influence of the parameters of passive filters on impedance shaping effect ...is analyzed and summarized.•A passive damping parameter design method which can be implemented based on “black box” model or simplified theoretical model of MMC station is presented in detail.•The proposed method reduces the capacity of the passive damping device while ensuring system stability margin.
Recent years, there have been several high-frequency oscillation events in modular multilevel converter (MMC) based DC current projects. Considering the wideband oscillation characteristics of this issue, passive MMC impedance shaping methods are superior solutions for their advantages over the active methods in enhancing the broadband damping level. However, the optimization of parallel passive devices mainly focused on reactive power compensation and the suppression of characteristic harmonics generated by low-level inverters, which is not applicable to MMC systems. To address the optimization design problem of passive damping devices, this paper proposes an optimized design method for passive filters by analyzing the relationship between the passive damping device and the impedance shaping effect of the inverter. The proposed method reduces the capacity of the passive damping device while ensuring system stability margin. Finally, the effectiveness of the proposed passive impedance shaping strategy is verified through time-domain simulations considering changes in AC side operating conditions and power reduction operation of the MMC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, a simple and efficient finite element model is applied to the vibration analysis of active–passive damped multilayer sandwich plates/shells with a viscoelastic core, sandwiched between ...functionally graded material (FGM) layers, and including piezoelectric layers. Both the FGM and the piezoelectric layers are modelled using the classical plate theory and the core is modelled using Reddy’s third-order shear deformation theory. The sandwich finite element is obtained performing the assembling of N “elements” through the thickness, by using specific assumptions on the displacement continuity at the interfaces between layers. To achieve a mechanism for the active control of the structural dynamics response, a feedback control algorithm is used, coupling the sensor and active piezoelectric layers. The dynamic analysis of the sandwich plate/shell structures is conducted in the frequency domain to obtain the natural frequencies and the loss factors of the viscoelastic core and in time domain for the steady state harmonic motion. For both analyses, a finite element code has been implemented. The model is applied in the solution of some illustrative examples and the results are presented and discussed.
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Enhancing the vibration suppression performance of cutting tools is crucial for achieving high-performance cutting of difficult-to-machine materials. This paper presents a novel cutting tool as well ...as its design method for vibration suppression in milling process. By incorporating a high-damping lattice structure into the cutting tool, the dynamic stiffness of the spindle-holder-tool system can be effectively increased based on the dynamic absorber effect. To achieve this goal, the natural frequency of the cutting tool filled with metallic lattice is tuned with the spindle-holder subassembly by altering the geometric parameters of the metallic lattice. A comprehensive dynamic model of the spindle-holder-tool system, considering the complex tool geometries, is developed to accurately analyze this system’s behavior and a design procedure is proposed to optimize the cutting tool. The geometric parameters of the lattice structure in the cutting tool are optimized based on the dynamic model, while the cell type of the high-damping lattice is selected by experiments. The proposed cutting tool is additively manufactured using the selective laser melting technique, and a comparison is made with a conventional indexable cutting tool with a solid tool body. Both simulations and impact hammer tests demonstrate an increase of 18.3% in the dynamic stiffness of the proposed cutting tool filled with metallic lattice compared with the conventional indexable cutting tool. Furthermore, a large number of milling tests are carried out on titanium alloy Ti-6Al-4V to validate the vibration suppression performance of the cutting tool filled with metallic lattice. Experimental results show that the stability limit corresponding to the proposed cutting tool can be doubled compared with the conventional indexable cutting tool.
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•A new cutting tool filled with metallic lattice for vibration suppression is presented.•The critical mode of the cutting system can be suppressed by the proposed tool based on dynamic absorber effect.•A dynamic model of the cutting system with complex tool geometries is developed for design of the lattice structures.•Experiments and simulations validate the vibration suppression performance of the proposed cutting tool.•The stability limit can be increased by 100% at least using the proposed tool compared with the conventional tool.
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Switching ripple filters (SRF) is one of the significant part of grid connected voltage source converters (VSC) that have been a backbone of the most of renewable energy systems for the last decade. ...SRFs have two main features for the grid connected VSC systems. One of these is to maintain a coupling connection and integration between grid and VSC. The other one is to prevent the penetration of switching ripple currents to the grid by filtering them. Several SRF topologies named as L, LC, LCL and LLCL type are presented in literature. In order to maintain effective switching ripple filtering, higher order SRF topologies are developed. However, these high order SRFs have resonance problems. To overcome resonance problems of higher order SRFs, passive and active damping methods are applied to SRFs. This paper presents a comprehensive review of SRFs used in grid connected VSCs. In the scope of this paper, the characteristics and the design procedures of SRFs are investigated. Also, both passive and active damping methods applied to the higher order SRFs are classified in detail with the latest studies presented in literature.
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