AC Disturbances Research Articles

Estimation of multi-infeed HVDC inter converter direct current interaction in close electric proximity

This paper aims at investigating the direct current interaction between various converters of High Voltage Direct Current (HVDC) system, which lie in close electric proximity within the multi-infeed configuration. The interaction between converters in multi-infeed DC system are highly possible events which need to be evaluated in order to avoid the adverse operational results. The various indices such as multi-infeed interaction factor (MIIF) considering AC busbar voltages, local and concurrent commutation failures (CF) in converter stations under different AC disturbances, influence of AC system’s strength on fault recovery time (FRT), transient over-voltage (TOV) under permanent DC faults, voltage and power stability of multi-infeed DC system are comprehensively illustrated in literatures. However, there is lack of literature regarding the investigation of current interaction in multi-infeed DC system. Therefore, in this paper, a power flow approach is adopted to estimate the inter converter direct current interaction. An index, multi-infeed current interaction factor (MICIF) is proposed that can effectively depicts the interaction between converters. The MICIF index is verified through electromagnetic transient simulations of dual infeed HVDC system developed in PSCAD/EMTDC. The results show that MICIF index can accurately assess the interaction between different converter stations of HVDC system under steady and transient states.

Adaptive Control Strategy for Three-Phase Three-Level T-Type Rectifier Based on Online Disturbance Estimation and Compensation

This paper proposes an adaptive control technique (ACT) for a three-phase, three-level, T-type rectifier based on online disturbance estimation and compensation. The proposed solution also regulates the DC-link voltage and grid currents under uncertainties, disturbances, measurement noises, and unbalanced grid voltages without cascaded control. The proposed controller consists of two layers; the first one is responsible for estimating nonlinearities and model uncertainties based on Kalman Filter Algorithm (KFA). The second layer is responsible for controlling both grid currents and DC link voltage using Linear Quadratic Regulator (LQR). The proposed controller is analyzed theoretically, validated experimentally, and the performance of the proposed controller is compared with two other controllers. The simulation and experimental results prove the superiority of the proposed controller and show that the proposed controller can ensure fast-tracking performance with almost zero steady-state error. The proposed controller has the ability to overcome severe disturbances such as AC and DC side disturbances, measurement noises, and mathematical model’s uncertainties even up to 400%.

Model predictive control and protection of MMC-based MTDC power systems

Meshed offshore grids (MOGs) present a viable option for a reliable bulk power transmission topology. The station-level control of MOGs requires faster dynamics along with multiple objective functions, which is realized by the model predictive control (MPC). This paper provides control, and protection design for the Modular Multilevel Converter (MMC) based multi-terminal DC (MTDC) power system using MPC. MPC is defined using a quadratic cost function, and a dqz rotating frame voltage inputs are represented using Laguerre orthonormal functions. MPC has been applied for the control of both grid forming and grid following converters in a four-terminal MTDC setup, implemented for real-time Electromagnetic Transient (EMT) simulation. By applying numerous time-domain simulations, the advantages of the MPC when dealing with AC and DC side disturbances are investigated. The investigation highlights the MPC’s inherent feature of fast response and high damping during- and post-disturbance, which is compared to the traditional PI controller performance. The analysis provides a comprehensive insight into the transient behavior of the MTDC during disturbances.

Discrete-Time Repetitive Control-Based ADRC for Current Loop Disturbances Suppression of PMSM Drives

The current loop is the key to realizing high-precision permanent magnet synchronous motor (PMSM) drives. However, the performance of the current loop is deteriorated by the dc and ac disturbances. To deal with the problem, this article proposes a discrete-time repetitive control-based active disturbance rejection control (ADRC) for the current loop. The discrete-time repetitive controller is embedded in the control law of the ADRC and operates in parallel with the discrete-time extended state observer (DESO), which is the core of the ADRC. The repetitive controller is designed to compensate for the ac disturbance, while the DESO is designed to suppress the dc disturbance. The stability and antidisturbance capability of the studied scheme are analyzed theoretically in the discrete-time domain, which can guide the tuning of control parameters. Compared with the existing ADRC-based PMSM control schemes, the studied scheme can suppress the dc and ac disturbances simultaneously, thereby improving dynamic- and steady-state performance of the current loop. Finally, the effectiveness of the studied scheme is validated on a 4.4-kW PMSM drive platform.

Maximum-variance gradiometer technique for removal of spacecraft-generated disturbances from magnetic field data

Abstract. In situ measurement of the magnetic field using spaceborne instruments requires a magnetically clean platform and/or a very long boom for accommodating magnetometer sensors at a large distance from the spacecraft body. This significantly drives up the costs and the time required to build a spacecraft. Here we present an alternative sensor configuration and a technique allowing for removal of the spacecraft-generated AC disturbances from the magnetic field measurements, thus lessening the need for a magnetic cleanliness programme and allowing for shorter boom length. The final expression of the corrected data takes the form of a linear combination of the measurements from all sensors, allowing for simple onboard software implementation. The proposed technique is applied to the Service Oriented Spacecraft Magnetometer (SOSMAG) on board the Korean geostationary satellite GeoKompsat-2A (GK2A). In contrast to other missions where multi-sensor measurements were used to clean the data on the ground, the SOSMAG instrument performs the cleaning on board and transmits the corrected data in real time, as needed by space weather applications. The successful elimination of the AC disturbances originating from several sources validates the proposed cleaning technique.

Advanced automated emergency control strategy for embedded VSC-HVDC links

This paper proposes an advanced emergency control strategy for embedded VSC-HVDC links after AC disturbances, such as line tripping and generation loss. The control goals are to minimize the impact of the disturbance on the AC-network, which includes improving the long-term voltage stability with utilizing possible unloading capacity of parallel AC elements. The proposed algorithm is evaluated against other control strategies for embedded VSC-HVDC links by applying it to a simple demonstration network. The test system includes all necessary VSC converter dynamics, the VSC-HVDC link current and voltage limits and simple load recovery characteristics for an evaluation of the long term voltage stability. The simulation results are explained and the advantages of the proposed emergency control strategy are discussed.

A Novel System for Measuring Alternating Current Impedance Spectra of Series-Connected Lithium-Ion Batteries With a High-Power Dual Active Bridge Converter and Distributed Sampling Units

Alternating current (ac) impedance spectra facilitate lithium-ion battery management. Realizing a low-cost and low-complexity onboard impedance measuring system is a vital issue for the management based on the ac impedance. In the article, a novel impedance measuring system combined with a high-power dual active bridge (DAB) converter and distributed sampling units is proposed and verified. The DAB converter is designed to generate the ac disturbance to ensure a quasi-steady measurement of the battery impedance. The distributed signal sampling units simultaneously measure the voltage and current of all the series-connected battery cells in a module to measure their impedance. The measured impedance in a frequency range of 0.1-500 Hz shows the feasibility of the system. The root-mean-square errors of the measured impedance phase from 0.2 to 200 Hz and the magnitude from 0.1 to 500 Hz are less than 6.9% and 4.0%, respectively. The errors in some frequency ranges are slightly larger, which are analyzed. The novelty is reflected in that the system is easily integrated into a bidirectional onboard charger and compatible with the battery management system, thus reducing costs and complexity. It provides a basis for the onboard application of the battery impedance.

Quasi-Z source inverter control of PV grid-connected based on fuzzy PCI

Photovoltaic grid-connected inverter is an important interface between the photovoltaic power generation system and power grid. Its high-quality operation is directly related to the output power quality of the power grid. In order to further optimize the control effect of the quasi-Z source grid-connected photovoltaic inverter, a fuzzy proportional complex integral control (PCI) method was proposed for the current internal loop control. This method can eliminate the steady-state error, and has the characteristic of zero steady-state error adjustment for the AC disturbance signal of a specific frequency. The LCL filter is adopted in the grid-connected circuit, and the feedback capacitive current is taken as the control variable of the inner loop to form the active damping control method, which can not only effectively suppress the resonance of the LCL circuit, but also significantly inhibit the high-order harmonics in the grid-connected current. Finally, a system simulation model is built in MATLAB/Simulink to verify the superiority and effectiveness of the proposed method.

A Coordinated Marginal Current Control Method for LCC-HVDC

Line-commutated-converter-based HVdc (LCC-HVdc) is extensively used in modern power systems. Most of the LCC-HVdcs are implemented with the control strategy termed marginal current control method (MCCM), while their operation is sensitive to disturbance from the ac part of the system. This paper originally reveals the mechanism of two types of oscillations induced by the MCCM after ac disturbances, i.e., the current boundary induced oscillation and the current error induced oscillation. A coordinated marginal current control method (CMCCM) is proposed, aiming at suppressing the aforementioned oscillations and enhancing HVdc recovery performance. Compared to the MCCM that responds only to dc voltage, the CMCCM additionally considers ac voltage, ac current, and power factor of the converter. AC grid's parameters are also taken into account. With a more considerate design, the empirical current boundary determined by the MCCM is replaced with an analytical one to coordinately control dc current. Therefore, better performance of HVdc is achieved. Simulations in RTDS reveal that the proposed CMCCM can suppress the oscillations, speed up HVdc recovery process, and moderate transient over voltage of HVdc.

Robust Flux Estimation Method for Linear Induction Motors Based on Improved Extended State Observers

Flux estimation is of great importance for high-performance linear induction motor (LIM) drives. However, due to the end effects of LIMs, range of variation in mutual inductance and secondary resistance is quite high with the change in operating condition, and the flux estimation suffers from these LIM parameter variations. To alleviate the influence of these parameter variations, this paper proposes a new flux estimation algorithm based on two improved extended state observers (ESOs) with expanded bandwidth for observing disturbances. One of them is especially designed to observe the ac disturbance at certain frequency. Taking advantage of the improved ESOs, the robustness of the flux observer to parameter deviations can be significantly strengthened, and the vector control strategy based on this new flux observer can achieve better dynamic performance. Finally, the effectiveness of the proposed method is validated by both simulation and experimental results on an LIM prototype.

Comparative Performance Study of Dynamic Reactive Power Compensators on Operating Characteristics of LCC Based UHVDC System Under Hierarchical Connection Mode

This paper compares the performance of different dynamic reactive power compensators (DRPCs) on transient characteristics of LCC based UHVDC system under hierarchical connection mode (LCC-UHVDC-HCM). The different DRPCs considered are Synchronous Condenser (SC), STATCOM and combination of both SC and STATCOM (hybrid dynamic reactive power compensator, HDRPC). Various transient indices like commutation failure immunity index (CFII), commutation failure probability index (CFPI) and fault recovery time (FRT) of LCC-UHVDC-HCM system are undertaken in order to evaluate the comparative performance of various DRPCs. The LCC-UHVDC-HCM system along with different DRPCs is developed in PSCAD/EMTDC and numerous simulations are done to observe the transient phenomena. The results indicate that performance of DRPCs changes during various AC disturbances such as single phase to ground fault and three phase to ground fault for different fault severity. It is examined that STATCOM is better than other dynamic compensators in improving CFII and CFPI. SC and HDRPC show almost same behavior in improving CFII. However, in case of CFPI, HDRPC is superior to SC. The performance of SC is better than STATCOM and HDRPC in improving FRT under severe fault conditions. However, under low fault conditions, all DRPCs have equal performance in reducing FRT.

Adaptive Backstepping Control with Online Parameter Estimator for a Plug-and-Play Parallel Converter System in a Power Switcher

This study aims to address the inherent uncertainty in plug loads and load extraction, distributed generation, and the inevitable circulating current in a parallel structure. Therefore, in this paper, an adaptive backstepping control scheme with an online parameter estimator (OPE) for a plug-and-play parallel converter system in a four-port power switcher is proposed. The adaptive backstepping control method was designed in the dq0 coordinate system to suppress the circulating current in the zero-component; the circulating current can be suppressed by using an embedded algorithm and omitting the extra controller. An adaptive update law was designed to weaken the influence of the arbitrary plug and extraction operations in the DC and AC buses to realize the plug-and-play function. The transient tracking performance is governed by the limitation of maximum total errors in the voltage and current. As a result, the settling times of the voltage, current, and power decreased. Additionally, to further improve the system robustness, an online inductance and resistance estimator was established using an optimal algorithm that solves the weighted least squares problem. In the estimator, there are no additional voltage and current sensors needed, and the mean squared error (MSE) of the estimation can be minimized. Simulation studies on a two-converter parallel system with a plug-and-play function were conducted using MATLAB/SIMULINK (R2018b, MathWorks, Natick, MA, USA) to verify the effectiveness of the proposed adaptive backstepping control strategy. The results show that this strategy improves system performance over that of a system with unbalanced parameters among a parallel structure with AC and DC system disturbances caused by arbitrary plug and extraction operations.

Analysis for DC transmission line harmonics originated from AC transformer inrush current and improved method for DC harmonic protection

Large-scale electricity has fed into Central and Southern China through DC transmission lines. Any one of the DC transmission lines suddenly outage will result in a large proportion of power-shortage. Recently, there are many DC harmonic protection misoperations caused by AC disturbance, resulting in DC transmission line exit operation. Therefore, it is necessary to analyse the effect of AC disturbance on DC harmonics and study methods for DC harmonic protections. In this study, based on the theory of switching function, the harmonics interaction in AC–DC systems is studied. The cause of DC line harmonic protection misoperation during unusual AC disturbances, such as inrush current and short circuit, is revealed. The DC line 50 Hz harmonic protection misoperates frequently due to inrush current on site. Taking it for example, an improved method using the second harmonic voltage in AC system bus is proposed. In this method, the 50 Hz harmonics generated by inrush current can be accurately identified by judging the correlation between the AC harmonic voltage and the DC line harmonic current. By automatically adjusting the threshold value of protection, the misoperation can be prevented effectively without affecting the original protection performance. The simulation results verify the correctness of the method.

Disturbance of harbour porpoises during construction of the first seven offshore wind farms in Germany

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 596:213-232 (2018) - DOI: https://doi.org/10.3354/meps12560 Disturbance of harbour porpoises during construction of the first seven offshore wind farms in Germany Miriam J. Brandt1,*, Anne-Cecile Dragon1, Ansgar Diederichs1, Michael A. Bellmann2, Veronika Wahl3, Werner Piper4, Jacob Nabe-Nielsen5, Georg Nehls1 1BioConsult SH GmbH&Co.KG, 25813 Husum, Germany 2Institute of Technical and Applied Physics (itap) GmbH, 26129 Oldenburg, Germany 3IBL Umweltplanung GmbH, 26122 Oldenburg, Germany 4Institute for Applied Ecosystem Research (IfAÖ) GmbH, 20357 Hamburg, Germany 5Department of Bioscience, Section for Marine Mammal Research, Aarhus University, 4000 Roskilde, Denmark *Corresponding author: m.brandt@bioconsult-sh.de ABSTRACT: We investigated the disturbance effects of offshore windfarm construction on harbour porpoises Phocoena phocoena using acoustic porpoise monitoring data and noise measurements during construction of the first 7 large-scale offshore wind farms in the German Bight between 2010 and 2013. At 6 wind farms, active noise mitigation systems (NMS) were applied during most piling events, and 1 was constructed without. Based on generalized additive modelling analyses, we describe a clear gradient in the decline of porpoise detections after piling, depending on noise level and distance to piling. Declines were found at sound levels exceeding 143 dB re 1 µPa2s (the sound exposure level exceeded during 5% of piling time, SEL05) and up to 17 km from piling. When only considering piling events with NMS, the maximum effect distance was 14 km. Compared to 24-48 h before piling, porpoise detections declined more strongly during unmitigated piling events at all distances: at 10-15 km declines were around 50% during piling without NMS, but only 17% when NMS were applied. Within the vicinity (up to about 2 km) of the construction site, porpoise detections declined several hours before the start of piling and were reduced for about 1-2 d after piling, while at the maximum effect distance, avoidance was only found during the hours of piling. The application of first generation NMS thus reduced the effect range of pile driving and led to a lower decline of porpoise detections over all distances. However, NMS were still under development and did not always work with equal efficiency. As NMS have further developed since, future investigations are expected to show additional reduction of disturbance effects. KEY WORDS: Acoustic monitoring · Acoustics · Anthropogenic impact · Behaviour · Marine mammal · PAM · Phocoena phocoena · Spatial scale · Wind turbine · Pile driving Full text in pdf format PreviousNextCite this article as: Brandt MJ, Dragon AC, Diederichs A, Bellmann MA and others (2018) Disturbance of harbour porpoises during construction of the first seven offshore wind farms in Germany. Mar Ecol Prog Ser 596:213-232. https://doi.org/10.3354/meps12560 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 596. Online publication date: May 28, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Optimal Design and Real Time Implementation of Autonomous Microgrid Including Active Load

Controller gains and power-sharing parameters are the main parameters affect the dynamic performance of the microgrid. Considering an active load to the autonomous microgrid, the stability problem will be more involved. In this paper, the active load effect on microgrid dynamic stability is explored. An autonomous microgrid including three inverter-based distributed generations (DGs) with an active load is modeled and the associated controllers are designed. Controller gains of the inverters and active load as well as Phase Locked Loop (PLL) parameters are optimally tuned to guarantee overall system stability. A weighted objective function is proposed to minimize the error in both measured active power and DC voltage based on time-domain simulations. Different AC and DC disturbances are applied to verify and assess the effectiveness of the proposed control strategy. The results demonstrate the potential of the proposed controller to enhance the microgrid stability and to provide efficient damping characteristics. Additionally, the proposed controller is compared with the literature to demonstrate its superiority. Finally, the microgrid considered has been established and implemented on real time digital simulator (RTDS). The experimental results validate the simulation results and approve the effectiveness of the proposed controllers to enrich the stability of the considered microgrid.

Synchronized measurement technology supported AC and HVDC online disturbance detection

In electric power system, disturbance detection has become an important part of grid operation and refers to the detection of a voltage and current excursion caused by the wide variety of electromagnetic phenomena. This paper proposes a computationally efficient and robust algorithm for synchronized measurement technology (SMT) supported online disturbance detection, suitable for AC and HVDC grids. The proposed algorithm is based on the robust median absolute deviation sample dispersion measure to locate dataset outliers. The algorithm is capable of identifying the disturbance occurrence and clearance measurement sample based on the dynamic criteria, driven by present power system conditions. The effectiveness of the proposed algorithm is verified by real-time simulations using a cyber-physical simulation platform, as a co-simulation between the SMT supported electric power system model and underlying ICT infrastructure. The presented results demonstrate effectiveness of the proposed algorithm, making it suitable for an AC and HVDC online disturbance detection application or as a pre-step of backup protection schemes.

The use of Tikhonov regularization method for calculating the distribution function of relaxation times in impedance spectroscopy

The state-of-the-art in realization of the method of distribution of relaxation times (DRT) as applied to the analysis of data of electrochemical impedance spectroscopy is briefly surveyed. The theoretical fundamentals of the DRT method are described, the methods of solving the Fredholm equation of the 1st order with respect to the unknown DRT function are considered as an ill-defined problem. The Tikhonov regularization method presently considered as the most suitable for solving this equation is discussed. For several numerical experiments, the high resolution of the DRT method and its stability with respect to noise in impedance spectra are demonstrated. Among the problems and limitations of the DRT methods, the choice of the optimal regularization coefficient is considered as the most significant. Particularly, it is shown that in those cases where several relaxation processes with the constant phase angle appear in the response of objects under study to ac disturbances, different regularization coefficients should be selected for each of these elements in order to obtain adequate results.

Effects of AC Disturbance on Cowinding HTS Coils According to the Inserted Materials

Alternating field causes energy loss due to induced back electromotive force (EMF) to high-temperature superconducting (HTS) coils in the superconducting electric machines. Therefore, a method of reducing the effects of the alternating fields on the HTS coils in superconducting machines according to the winding insulation conditions has been investigated. In addition, the HTS coils cowound with turn-to-turn inserted materials to control the time constant has been proposed. The charge-discharge delay can be determined with the time constant, also the time constant is related to the radial directional resistance of the no-insulation coil. The variation of the radial resistance would affect the reduction effect of ac disturbance on the no-insulation coil. Therefore, trade-off between the reduction effect of the alternating disturbance and charge-discharge delay could be considered. In this paper, we evaluated the effects of alternating magnetic fields on the HTS coils according to the varying radial resistance caused by cowinding method with metal tapes in liquid nitrogen. Four types of the HTS coils are: 1) no-insulation coil, 2) cowound coil with copper tape, 3) cowound coil with stainless steel tape and 4) insulation coil which have different radial resistance respectively. The experimental result shows that the co-winding method can be applicable in the superconducting electric machines.

The Efficient Solution of Parasitic Voltage Annulment in Electronic Low Resistance Comparator

The article describes an efficient solution of parasitic voltage annulment applied in low resistance comparison. By development and design the low resistance comparator with many measuring ranges, occurred some difficulties with parasitic voltages. Theirs influence on measuring result is not negligible. To eliminate those disturbances, the analog voltage integration method is used. That is the way to nullify the parasitic voltages. Also, this electric circuit eliminates the influence of AC disturbances, which are consequence of network power supply (50 Hz frequency), independently of intensity of voltage amplifying. Ill. 6, bibl. 10, tabl. 1 (in English; abstracts in English and Lithuanian). DOI: http://dx.doi.org/10.5755/j01.eee.121.5.1653

Superconducting Permanent Magnet Made by a Bulk ${\rm MgB}_{2}$ Ring

The bulk superconductors can be used as permanent magnets of very high magnetic induction, provided that a feasible way of magnetization is identified and that the superconducting material can withstand the magnetic forces induced by high trapped fields. Here it has been considered as superconducting permanent magnet a bulk MgB2 ring, obtained by the Reactive Liquid Infiltration (RLI) process. This material offers several advantages with respect to the well known YBCO textured material, even if its application temperature will be far lower, around 20-30 K. First of all, MgB2 does not require grain orientation to reach enough current density, it can be produced in a quite straight forward way, it is lightweight and it is mechanically robust. To magnetize the MgB2 ring, we have applied a DC magnetic field with a superconducting magnet, using a step wise, field cooling type, procedure. The induced magnetization of the bulk MgB2 ring, at 4 K, is around 2 T in its vicinity. It has been verified that the magnetization is very stable during the time and it can withstand also AC disturbances of several Hz in frequency.