Compensation Mode Research Articles

Flexible Compensation of Voltage and Current Unbalance and Harmonics in Microgrids

In recent years, the harmonics and unbalance problems endanger the voltage and current quality of power systems, due to increasing usage of nonlinear and unbalanced loads. Use of Distributed Generation (DG)-interfacing inverters is proposed for voltage or current compensation. In this paper, a flexible control method is proposed to compensate voltage and current unbalance and harmonics using the distributed generation (DG)-interfacing inverters. This method is applicable to both grid-connected and islanded Microgrids (MGs). In the proposed method, not only the proper control of active and reactive powers can be achieved, but also there is flexibility in compensating the voltage or current quality problems at DG terminals or Points of Common Coupling (PCCs). This control strategy consists of active and reactive power controllers and a voltage/current quality-improvement block. The controller is designed in a stationary (αβ) frame. An extensive simulation study has been performed and the results demonstrate the effectiveness of the proposed control scheme. Depending on the compensation modes, the harmonics and unbalance compensation of DG output current, MG-injected current to the grid, as well as PCC and DG voltages, can be achieved in grid-connected operation of MG while in the islanded operation, and the PCC and DG voltages compensation can be obtained through the proposed control scheme.

A new model predictive control algorithm by reducing the computing time of cost function minimization for NPC inverter in three-phase power grids

This paper presents a new control strategy based on finite-control-set model-predictive control (FCS-MPC) for Neutral-point-clamped (NPC) three-level converters. Containing some advantages like fast dynamic response, easy inclusion of constraints and simple control loop, makes the FCS-MPC method attractive to use as a switching strategy for converters. However, the large amount of required calculations is a problem in the widespread of this method. In this way, to resolve this problem this paper presents a modified method that effectively reduces the computation load compare with conventional FCS-MPC method and at the same time does not affect on control performance. The proposed method can be used for exchanging power between electrical grid and DC resources by providing active and reactive power compensations. Experiments on three-level converter for three Power Factor Correction (PFC), inductive and capacitive compensation modes verify the good and comparable performance. The results have been simulated using MATLAB/SIMULINK software.

Comparison of viability and osteogenic potential of mesenchymal stem cells on fibrin glue or fibronectin coated ceraform®

The application of biocalorimetry to fermentation processes offers advantageous insights, while being less complex compared to other, sophisticated PAT solutions. Although the general concept is established, calorimetric methods vary in detail. In this work, a special approach, called heat compensation calorimetry, was applied to an E. coli fed-batch process. Much work has been done for batch processes, proving the validity and accuracy of this calorimetric mode. However, the adaption of this strategy to fed-batch processes has some implications. In the first section of this work, batch fermentations were performed, comparing heat capacity calorimetry to the compensation mode. Both processes showed very good agreement by means of growth behavior. The heat related differences, e.g. temperature profiles, were obvious. In addition, the impact of the chosen mode on the calculation of in-process heat transfer coefficients was shown. Finally, a fed-batch fermentation was performed. The compensation mode was kept sufficiently, up to the point where the metabolic heat production accelerated strongly. Controller tuning was a neuralgic point, which would have needed further optimization under these conditions. Nevertheless, in the present work it was possible to realize a working compensation process while demonstrating critical aspects that must be considered when establishing such approach.

Supervisory adaptive fault‐tolerant control against actuator failures with application to an aircraft

SummaryIn this paper, a supervisory adaptive fault‐tolerant control scheme is proposed for a class of uncertain nonlinear systems with multiple inputs. The multiple inputs are the outputs of an actuator group that may act either on one control surface or on multiple control surfaces and may fail during operation. With some actuator groups as backups, the supervisory adaptive control includes 2 modes: the adaptive compensation mode and the switching mode. The former is used to compensate for the failure of an actuator group as long as at least one actuator of the group works normally, and the latter, to switch the controller from a failed group to a healthy one when the failure is detected by one of the monitoring functions that are constructed to supervise some variables related to system stability. It is shown that with the proposed scheme, all signals of the closed‐loop system are bounded, and prescribed transient and steady state performance of the tracking error can be guaranteed. An aircraft example is used to demonstrate the application of the proposed scheme.

Study on the system design and control method of a semi-active heave compensation system

ABSTRACTThe heave compensation system is essential for the installation of subsea equipment. A new semi-active heave compensation system is designed and the control system is analysed, with the aim of solving heave movement problems during deep-water installation. The heave compensation is implemented with a pulley block system and actuated by a compound hydraulic cylinder. The control system can switch between passive compensation mode and semi-active compensation mode. The state-space equations of both modes are set up based on the mechanical and hydraulic system models of the compensation system. With the state-space equations, three control strategies are compared based on the classic Proportion Integration Differentiation (PID) control, and the limitations of PID control are also analysed. In order to avoid defects of the PID controller, the active disturbance rejection control (ADRC) technology is introduced, and a newly developed second-order ADRC controller is applied in the tension control strategy for heave compensation, which results in improved compensation effect.

Digital impedance pilot relaying scheme for STATCOM compensated TL for fault phase classification with fault location

This study presents calculation of fundamental frequency-based per phase digital impedance pilot relaying (DIPR) scheme for static synchronous compensator (STATCOM) compensated transmission line (TL) using two end synchronised measurement. DIPR involves computation of absolute value of ratio of estimated phasor sum of voltages to the phasor sum of currents of both ends. DIPR inherently differentiate between internal and external faults on the line. For all internal faults, computed value of DIPR ratio is equivalent to system and TL impedance value whereas for external faults, it is equal to line capacitance impedance value. This novel pilot relaying scheme is easy to set once the system parameters are estimated and has the ability to detect all types of faults and correctly classify faulty phase with mid-point connected STATCOM on TL. This scheme is immune to effect of STATCOM compensation mode, level of injection and its dynamic response. Also it is not affected by line charging capacitive current and fault transient resistance. The fault distance is estimated using the STATCOM current injection information for various types of fault with high accuracy, considering maximum fault resistance of 20 Ω. Accuracy and effectiveness of this scheme is evaluated in EMTDC/PSCAD simulation for 230 kV, 300 km, mid-point STATCOM compensated TL and in hardware setup with mid-point STATCOM on 100 V supply voltage having 200 km TL in offline mode. Results bring out the robustness, reliability and superiority of proposed novel pilot relaying scheme with fault location algorithm.

A Witricity-Based High-Power Device for Wireless Charging of Electric Vehicles

In this paper, a Witricity-based high-power device is proposed for wireless charging of electric vehicles. According to the specific requirements of three-stage charging for electric vehicles, four compensation modes of the Witricity system are analyzed by the Loosely Coupled Theory among transformer coils and the Substitution Theorem in circuit theory. In addition, when combining voltage withstand levels, the current withstand capability, the switching frequency of electronic switching tubes, and the features of the resonant circuit, the series-parallel (SP) compensation mode is selected as the best compensation mode for matching the capacitor of the system. The performances of coils with different ferrite core arrangements are compared by simulations and models. The feasibility of the system is verified theoretically and the system functions are evaluated by the joint simulation of Simplorer and Maxwell. Finally, a Witricity-based high-power device is proposed as designed, and the correctness of theoretical analyses and simulation results are verified.

Web Service Compensation at Runtime: Formal Modeling and Verification Using the Event-B Refinement and Proof Based Formal Method

One of the key interests in web services is the ability to compose them in order to build more powerful and complex ones running in an interoperable and distributed setting. Several languages, like BPEL, that describe such services have been proposed. Similar to the usual complex systems, web service compositions may exhibit inappropriate behaviors in the presence of failures. Compensation mechanisms are available to express running services recovery in case of failures. This paper addresses the problem of the correct design of web service compositions in case of failures. It presents a novel correct-by-construction formal approach based on refinement using the Event-B method. The proposed approach defines a compensation mechanism to repair failed services at runtime. It addresses not only behavioral aspects but also, functional ones through the introduction of repairing invariants whose persistence is enforced during compensation at runtime. Different compensation scenarios and modes are addressed. A formal model for equivalent, degraded and upgraded service compensations relying on the Event-B formalization is defined. The proposal is illustrated on a case study.

梧州市下小河流域水生态补偿初探及政策建议

以梧州市下小河流域为例，提出了下小河流域水生态补偿内容、途径、方式、补偿主体与客体和标准，从补偿范围、类型、内容和方式4个方面初步建立了下小河流域水生态补偿框架体系。结合目前国内关于水生态补偿的现状和研究成果，提出了实施水生态补偿的6点政策建议：一是建立健全水生态补偿立法；二是把握水生态补偿的几个重要关系；三是提高财政转移支付力度，拓宽资金来源；四是完善水生态补偿的管理体制；五是加强公众对水生态补偿的认知与参与；六是加强水生态补偿科学研究与试点工作。水生态补偿作为生态补偿的关键环节，关系到我国水生态文明建设实施的具体成效。研究结果可为梧州市水生态补偿乃至区域水生态补偿机制构建提供一定的科学依据。 The content, way, method, subject and object and standard of water ecological compensation were put forward, and the framework of water ecological compensation system in the Xiaxiaohe basin was established from four aspects of compensation scope, type, content and mode. Combination the present situation and research results of water ecological compensation in China, six policy suggestions on the implementation of water ecological compensation were proposed. The first is to establish and improve water ecological compensation legislation, the second is to grasp several important ecological compensation, the third is to increase the ecological compensation for the financial transfer payments, the fourth is to improve the management system of water ecological compensation, the fifth is to strengthen publicity and education, to enhance the stakeholders of water ecological compensation awareness and participation, and the sixth is to strengthen the scientific research and experimental work of water ecological compensation. As the key link of ecological compensation, water ecological compensation is related to the implementation of water ecological civilization construction in China. It will provide a scientific basis for the construction of water ecological compensation in Wuzhou city and region.

Investigation of the Pathway for Targeted Medical Measures for Poverty Alleviation in the Context of Building an Overall Well-Off Society in China

Health forms the basis of an overall well-off society. In order to eliminate the phenomenon of “poverty caused by illness”, China must implement targeted medical measures for poverty alleviation. To achieve this, China should adhere to the medical and health policies of prevention first, the medical spending for poverty alleviation should be precise, the medical compensation mode needs to be de-marketized, the access to the medical market should be more marketized, and the medial and health resources should be supplied to the countryside, thereby “focusing our medical and health work on rural areas” substantially.

Circulating current derivation and comprehensive compensation of cascaded STATCOM under asymmetrical voltage conditions

Cascaded static synchronous compensator (STATCOM) with delta-connected configuration is an effective solution to compensate reactive and negative-sequence currents. This study focuses on the circulating current and compensation method of delta-connected STATCOM under asymmetrical voltage conditions. According to the phasor analysis, constrains of voltage phasors and current phasors under reactive current compensation mode, negative-sequence current compensation mode and comprehensive compensation mode are deduced. On the basis of this, the analytical expressions of circulating current under the three modes are derived. Furthermore, a comprehensive compensation method for delta-connected STATCOM is proposed. In the proposed method, phase current references are calculated directly with the instantaneous voltage and current signals, which could enhance the dynamic behaviour and cluster-balancing control performance especially under asymmetrical voltage conditions. Finally, simulation and experiment results have been given to verify the effectiveness and feasibility of the proposed control method.

Multilevel Cascaded-Type Dynamic Voltage Restorer With Fault Current-Limiting Function

This paper presents a new multilevel cascaded-type dynamic voltage restorer (MCDVR) with a fault current-limiting function. This topology can operate in two operational modes: 1) a compensation mode for voltage fluctuations and unbalances and 2) short-circuit current-limiting mode. The current-limiting function of the MCDVR is performed by activating antiparallel thyristors during the short-circuit fault, and deactivating them during normal operation. The mathematical model of the MCDVR system is also established in this paper. The control scheme design and optimal parameter selection are outlined based on the detailed theoretical analysis of the converter. The transient states of the MCDVR in the compensation mode and current-limiting mode are also analyzed. Simulation results based on the PSCAD/EMTDC software, and experimental results on a laboratory setup help to validate the proposed topology and the theoretical analysis.

Dielectric properties and defect chemistry of barium titanate ceramics co-doped R and Dy ions (R=Eu, Gd, Tb)

The structure, microstructure, dielectric behavior, point defects, mixed valence states, site occupations, and defect chemistry of nominal (Ba1−xRx)(Ti1−xDyx)O3 (x=0.06, R=Eu, Gd, Tb) (BRTD) ceramics were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, electron paramagnetic resonance (EPR), dielectric and resistivity measurements. BRTD exhibited a tetragonal perovskite structure, a higher ceramic density of ρr=91% of theoretical density, a diffuse phase transition (DPT) behavior, and a nonlinear shift in dielectric-peak temperature (Tm) with the kind of doping ions. The feature of mixed valence states associated with site occupation is responsible for this abnormal Tm-shift rate. BRTD with R=Tb exhibited a lowest dielectric loss of tan δ=0.025 at 1kHz and a nearly frequency-independent stability up to 107Hz at room temperature. A double-site compensation mode of GdBa•-DyTi' could be formed and led to a rapid Tm-shift rate of approximately −10°C/%(Gd-Dy). A symmetrical EPR signal at g=1.985 was designated as Gd3+ (4f7) Kramers ions. The mixed valence states of Ba-site Eu3+/Eu2+ (4f7) and Ba-site Tb3+/Ti-site Tb4+ (4f7) appeared in BRTD owing to the metastable nature of the 4f7 electron configuration. The Raman spectra in a high-wavenumber region of 1500–6700cm−1 were discovered and might be likely linked to the 4f7 doping ions, such as Eu2+, Gd3+, and Tb4+ ions. The defect chemistry is discussed.

An adaptive control algorithm for grid-interfacing inverters in renewable energy based distributed generation systems

This paper proposes an adaptive control algorithm for grid-interfacing inverters in renewable energy-based distributed generation systems. The proposed control algorithm functions in two different modes: basic power generation mode, harmonics compensation mode. In basic power generation mode, the inverter pumps desired amounts of active and reactive powers into the grid at the point of common coupling. In harmonics compensation mode, the control algorithm ensures sinusoidal grid current through load current harmonics mitigation in addition to desired power generation. Moreover, the proposed control algorithm does not use any detection methods for compensation of harmonic currents. Hence, it results in low computational burden. Based on the requirements, the proposed control algorithm can be operated in either of the modes. A proportional–integral controller-based closed loop control is employed for accurate control of the power injected into the grid. A frequency adaptive notch filter is used to synchronize the grid-interfacing inverter with the fundamental component of grid voltage without using any phase locked loop. The effectiveness of the proposed control algorithm in reference active and reactive powers generation, current harmonics compensation is demonstrated successfully by simulation and experimental results.

A novel motion classification based intermode selection strategy for HEVC performance improvement

High Efficiency Video Coding (HEVC) standard adopts several new approaches to achieve higher coding efficiency (approximately 50% bit-rate reduction) compared to its predecessor H.264/AVC with same perceptual image quality. Huge computational time has also increased due to the algorithmic complexity of HEVC compared to H.264/AVC. However, it is really a demanding task to reduce the encoding time while preserving the similar quality of the video sequences. In this paper, we propose a novel efficient intermode selection technique and incorporate into HEVC framework to predict motion estimation and motion compensation modes between current and reference blocks and perform faster inter mode selection based on three dissimilar motion types in divergent video sequences. Instead of exploring and traversing all the modes exhaustively, we merely select a subset of candidate modes and the final mode from the selected subset is determined based on their lowest Lagrangian cost function. The experimental results reveal that average encoding time can be downscaled by 40% with similar rate-distortion performance compared to the exhaustive mode selection strategy in HEVC.

Outage Probability Analysis of a Coherent FSO Amplify-and-Forward Relaying System

In this letter, we propose and analyze an amplify-and-forward (AF) relaying system for coherent free-space optics (FSOs) applications. In particular, we derive, in series expressions, the lower bound of the outage probability of the proposed system using modal compensation to mitigate the atmospheric turbulence-induced amplitude fluctuation and phase aberration. The performance of the derived lower bound of the outage probability is confirmed by the very tight Monte-Carlo simulation result. We show that the coherent FSO AF relaying system could be used for practical applications in case of Zernike compensation mode $J = 20$ , requiring the SNR of 32.5 dB in the outage probability of $10^{-6}$ . It is also noted that the AF relaying system is comparable in performance with the DF relaying system.

A Fault-Tolerant Three-Phase Adjustable Speed Drive Topology With Active Common-Mode Voltage Suppression

A fault-tolerant adjustable speed drive (ASD) topology is introduced in this paper. A conventional ASD topology is modified to address: 1) drive vulnerability to semiconductor device faults; 2) input voltage sags; 3) motor vulnerability to effects of long leads; and 4) minimization of common-mode (CM) voltage applied to the motor terminals. These objectives are attained by inclusion of an auxiliary IGBT inverter leg, three auxiliary diodes, and isolation-reconfiguration circuit. The design and operation of the proposed topology modifications are described for different modes: 1) fault mode, 2) active CM suppression mode, and 3) auxiliary sag compensation (ASC) mode. In case of fault and sag, the isolation and hardware reconfiguration are performed in a controlled manner using triacs/antiparallel thyristors. In normal operation, the auxiliary leg is controlled to actively suppress CM voltage. For inverter IGBT failures (short circuit and open circuit), the auxiliary leg is used as a redundant leg. During voltage sags, the auxiliary leg, along with auxiliary diodes, is operated as a boost converter. A current-shaping control strategy is proposed for the ASC mode. A detailed analysis of CM performance of the proposed topology is provided, and a new figure of merit, CM distortion ratio (CMDR), is introduced to compare the attenuation of CM voltage with that of a conventional ASD topology. The output filter design procedure is outlined. A design example is presented for an 80 kW ASD system, and simulation results validate the proposed auxiliary leg based fault-tolerant scheme. Experimental results from a scaled prototype rated at 1 hp are discussed in this paper.

A Multi-Mode Control Strategy for VAr Support by Solar PV Inverters in Distribution Networks

This paper proposes a multi-purpose VAr control strategy for solar PV inverters for voltage support in distribution networks. The proposed strategy can be applied under various PV power generation conditions. The inverters will normally operate in a dynamic VAr compensation mode for voltage support (including low PV and no PV periods). During mid-day when PV has surplus power, the proposed strategy will control the PV inverters to absorb VAr for voltage rise mitigation using a droop characteristic approach. During passing clouds, the strategy will mitigate voltage fluctuations by ramp-rate control of inverter VAr output. A dynamic model of the proposed PV inverter control has been developed to analyze its performance in terms of fast VAr control and voltage support under various PV generation conditions. The results of the analysis performed on an Australian distribution system show that the proposed VAr control strategy can mitigate voltage rise, and improve the voltage profile despite potential vast changes in the sun irradiation during passing cloud and also in the absence of PV output during the evening.

Common sense at the Swedish Tax Agency: Transactional boundaries that separate taxable and tax-free income

Abstract How does a tax collecting agency distinguish between taxable and tax-free income when the law says that all exchanges having value, regardless of compensation mode, are seen to constitute income? “By using our common sense” proposed one of the Swedish Tax Agency's legal experts. Common sense is here used as a frame for the boundary work that the Agency engages in-based on legislation, courtroom decisions, and praxis-while it pays attention to what Swedish taxpayers see as legitimate to tax. Six transactional boundaries are proposed that in different constellations distinguish the taxable trade from a helping hand. The analysis is based on an ethnography of publicly available documentation, rules, and regulations regarding income tax at the Agency's website. An ethnographic approach to these documents that are available to all taxpayers represents an apprehension of, and empathy for, the analytical concerns of both Agency and taxpayers. These documents represent the Agency as a collective of voices with a diligent aim to convey the same message for all taxpayers.

Advanced compensation mode for cascade multilevel static synchronous compensator under unbalanced voltage

An improved control scheme for delta-connected cascade multilevel static synchronous compensator (STATCOM) operating under unbalanced conditions is proposed. The individual phase instantaneous current control is suitable for delta-connected cascade multilevel STATCOM which can be equivalent to three single-phase inverters. To compensate the system imbalance, the reactive control mode and the voltage control mode are studied, and the discrete current loop controller has been designed. Accordingly, the cascade multilevel STATCOM can maintain normal operation under unbalanced voltage by using the individual phase instantaneous current control strategy while the unbalanced system can be effectively compensated by the two modified compensation modes. The proposed control scheme has been verified by simulation and experimental results based on a three-phase 36-chain cascade multilevel STATCOM laboratory prototype are shown.