Suppression Scheme Research Articles

Inhibition of microbunching instability in the Shanghai soft X-ray Free-Electron Laser User Facility

A microbunching instability (MBI) driven by beam collective effects can deteriorate electron beam quality in advanced x-ray free electron lasers. In this paper, we demonstrate a scheme to suppress microbunching instability by adjusting the compression ratio of two-stage bunch compressor in linear accelerator of the Shanghai soft X-ray Free-Electron Laser User Facility (SXFEL-UF). The calculation of the microbunching instability gain and the mechanism of MBI suppression scheme can be revealed by the theoretical model in this paper. Numerical simulations are presented to verify the analytical results. Furthermore, benefit by the high temporal resolution of transverse deflecting structure (TDS), beam experiments for direct analysis of MBI were carried out at SXFEL-UF. Theoretical calculations as well as simulation and consistent experimental results illustrate that the suppression of microbunching instability can be achieved by increasing the first stage compression ratio of the linac in the SXFEL-UF. The feasible theme provides a promising beam optimization method for future X-FEL facilities.

Research on Energy Dissipation Technology and AC Overvoltage Suppression of Sending End in UHVDC Transmission

For suppress the amplitude of overvoltage from HVDC sending terminal, an overvoltage suppression scheme based on the principle of controllable energy dissipation was proposed. The overvoltage mechanism of a weak AC system under the fault of the DC system was analyzed, and the method and operating principle of the CSREDD were proposed. Prototype of the develop CSREDD was tested, which proved correctness about the design. The controllable energy dissipation device has been successfully applied to the ±800kV Lu-Gu UHVDC transmission project. The operation results show that the controllable energy dissipation device can effectively suppress the AC overvoltage.

Low-Complexity Iterative Adaptive Approach Based on Range–Doppler Matched Filter Outputs

This article presents a computationally efficient iterative adaptive approach based on range–Doppler matched filter outputs for sidelobe suppression and range–Doppler imaging. A sidelobe suppression scheme, named as dimension reduction based fast iterative adaptive approach (DR-FIAA), is designed by adopting a small processing window on range–Doppler matched filter outputs to eliminate the masking of weak targets by strong targets nearby with low computational complexity. Two specific methods are proposed under this scheme, namely synchronous FIAA (SY-FIAA) and sequential FIAA (SE-FIAA). Compared to SY-FIAA, SE-FIAA has lower computational complexity at the cost of some performance loss. Based on the structure relationships among covariance matrices, further reduced computational complexity can be achieved by SY-FIAA and SE-FIAA. Numerical examples for different scenarios are included to demonstrate the effectiveness of the proposed designs.

Multi-sliding mode current disturbance suppression scheme based model reference adaptive system for sensorless control of permanent magnet synchronous motor

In order to improve the accuracy of the speed and angle estimation of the permanent magnet synchronous motor (PMSM) in the sensorless mode, this paper firstly proposes a multi-sliding mode scheme based on model reference adaptive system (MRAS) with proportional integral (PI) control. The current disturbance of the sensorless method is suppressed by the multi-sliding mode based on MRAS method, thus reducing the disturbance of the current to the PI and indirectly improving the current anti-interference of the PI. Meanwhile, the quantitative analysis of the current disturbance by the MRAS based on multi-sliding mode scheme is presented in detail. Then, the suppression capability of different sliding-mode schemes is discussed. Finally, various experiments are designed to verify the feasibility of the scheme and the correctness of the theory.

Study on coordinated multi-objective reactive control system of AC/DC power grid based on new-generation synchronous condenser

With rapid development of HVDC transmission system, the coupling relationship between the AC and DC power grid has become increasingly stronger. Especially, the problem of voltage instability is prominent in HVDC receiving-end system, the dynamic reactive power performance of the receiving-end power grid is inadequate. Therefore, the new-generation synchronous condenser (NGSC) as ‘a strong reactive power support device” is widely applied to high-capacity DC transmission system. However, there is a lack of coordination control strategy between the NGSCs and AC/DC power grid, so it is difficult to give full play to the reactive power supporting capacity of the NGSCs. In this paper, a coordinated multi-objective reactive control strategy between the NGSCs and the AC/DC power grid is proposed . In steady state, the initial reactive power optimization method of a NGSC is proposed. In transient state, a commutation failure suppression scheme of DC system based on the NGSCs and the DC control system is proposed. In transition process, the coordinated control strategy of the NGSCs with capacitance and reactance is studied. The research results provide theoretical basis for subsequent study on the safety and stability of AC/DC power grid.

Annual Characteristic Analysis of Ionosphere Reflection From Middle-Latitude HF Over-the-Horizon Radar in the Northern Hemisphere

The dynamically changing ionospheric conditions are the biggest impediment to realizing ideal performance in long-range for over-the-horizon radar (OTHR). Most related studies focus on developing the signal processing techniques and antenna arrays design. However, ionosphere clutter derives from the interaction between radar signal and the ionosphere, it exhibits different behaviors in three dimensions. OTHR should have the ability to sense when and where (in range) a certain type of ionosphere clutter appears before proposing the appropriate suppression scheme. Therefore, this report aims at identifying the various types of ionosphere clutter in Earth’s middle-latitude regions and characterizing them in terms of temporal, Doppler, azimuth, range and overall amplitude distribution domain, thereby establishing a multi-dimensional information profile. An experimental OTHR has been developed to monitor the surrounding oceans in middle-latitude area, we collected a sufficient real radar return data for two years running and then selected data specifically designed to observe ionosphere clutter. Then, we identify the various types of ionosphere clutter and catalogue their multi-dimensional characteristics. A knowledge of where a certain type of ionosphere clutter appears and pertinent information are essential for developing the appropriate clutter mitigation scheme in real time.

A novel premium power supply scheme against harmonic suppression for non-linear park

• A method for harmonic-suppression needs identification is proposed to guide non-linear customers to actively participate in harmonic mitigation. • The novel premium power supply scheme against harmonic suppression for non-linear park can effectively solve the harmonic problems with the situations that all the participants are satisfied. • A DEA-based method is proposed to reasonably realize allocation of the scheme costs. • The proposed scheme provides the possibility for the power grid and customers to jointly control harmonic problems. With the continuous development of power grids, the power electronization rates of power systems are increasing, and problems caused by harmonic pollution are becoming major concerns. Generally, harmonic problems result from the electric utility and non-linear customers, thus the mutual collaboration of both parties is crucial to addressing these problems. However, due to the indeterminate needs of non-linear customers for harmonic suppression and high investment pressure for harmonic suppression, customers are reluctant to participate in mitigation, which makes harmonic suppression appear prevarication. As a result, harmonic suppression cannot be carried out smoothly. To solve this problem, a novel premium power supply scheme against harmonic suppression for non-linear park is proposed. Firstly, this paper presents a method for harmonic-suppression needs identification based on super-efficiency interval model to attract customers to participate in harmonic suppression. Secondly, a premium power supply scheme is proposed, which consists of harmonic-suppression needs identification, suppression strategy design and scheme cost allocation. Furthermore, to reasonably allocate the scheme costs among each participant, this paper proposes a data envelopment analysis (DEA) based method considering the influence of both harmonic contribution and harmonic-suppression needs. Finally, case studies are used to verify the effectiveness and correctness of the proposed methods and the scheme.

A Novel Scheme for Suppression of Human Motion Effects in Non-Contact Heart Rate Detection

A Novel Scheme for Suppression of Human Motion Effects in Non-Contact Heart Rate Detection

Harmonic State-Space Based AC-Side Impedance Model of MMC and High Frequency Oscillation Characteristics Analysis

Recently, high-frequency oscillation of the modular multilevel converter (MMC) based high-voltage direct current (HVDC) projects has attracted great attentions. In order to analyze the small-signal stability, this paper uses the harmonic state-space (HSS) method to establish a detailed frequency domain impedance model of the AC-side of the HVDC transmission system, which considers the internal dynamic characteristics. In addition, the suggested model is also used to assess the system's high-frequency oscillation mechanism, and the effects of the MMC current inner loop control, feedforward voltage links, and control delay on the high-frequency impedance characteristics and the effect of higher harmonic components. Finally, three oscillation suppression schemes are analyzed for the oscillation problems occurring in actual engineering, and a simplified impedance model considering only the high-frequency impedance characteristics is established to compare the suppression effect with the detailed impedance model to prove its reliability.

A Barrage Jamming Suppression Scheme for DBF-SAR System Based on Elevation Multichannel Cancellation

A Barrage Jamming Suppression Scheme for DBF-SAR System Based on Elevation Multichannel Cancellation

A modified modal sensitivity method for resonance analysis in power electronic systems

Modal sensitivity analysis (MSA) is an essential resonance influencing factor analysis tool in a power electronic system for quantifying the sensitivity of resonance modes to parameters. Unfortunately, in the conventional MSA, the calculation result of modal frequency sensitivity (MFS) is influenced by the frequency resolution, and the modal impedance sensitivity (MIS) could only be quantified under a specific frequency, posing damage to the MSA accuracy. In this paper, a modified MFS calculation method is proposed by solving the critical variable expression with non-homogeneous formula, which avoids the influence of frequency resolution and the accuracy is significantly improved. Furthermore, a new concept of modal resonance sensitivity (MRS) is proposed for quantifying the sensitivity of resonance peak impedance to parameters, which shows good adaptability for the resonance frequency changing and offers a supplement to MIS analysis. Both the proposed method provides precise guidance for designing resonance mitigation and suppression schemes in power electronic systems. Time domain simulations with multiple converters are carried out to verify the proposed method.

Water irradiation devoid pulses enhance the sensitivity of 1H,1H nuclear Overhauser effects.

The nuclear Overhauser effect (NOE) is one of NMR spectroscopy's most important and versatile parameters. NOE is routinely utilized to determine the structures of medium-to-large size biomolecules and characterize protein-protein, protein-RNA, protein-DNA, and protein-ligand interactions in aqueous solutions. Typical [1H,1H] NOESY pulse sequences incorporate water suppression schemes to reduce the water signal that dominates 1H-detected spectra and minimize NOE intensity losses due to unwanted polarization exchange between water and labile protons. However, at high- and ultra-high magnetic fields, the excitation of the water signal during the execution of the NOESY pulse sequences may cause significant attenuation of NOE cross-peak intensities. Using an evolutionary algorithm coupled with artificial intelligence, we recently designed high-fidelity pulses [Water irrAdiation DEvoid (WADE) pulses] that elude water excitation and irradiate broader bandwidths relative to commonly used pulses. Here, we demonstrate that WADE pulses, implemented into the 2D [1H,1H] NOESY experiments, increase the intensity of the NOE cross-peaks for labile and, to a lesser extent, non-exchangeable protons. We applied the new 2D [1H,1H] WADE-NOESY pulse sequence to two well-folded, medium-size proteins, i.e., the K48C mutant of ubiquitin and the Raf kinase inhibitor protein. We observed a net increase of the NOE intensities varying from 30 to 170% compared to the commonly used NOESY experiments. The new WADE pulses can be easily engineered into 2D and 3D homo- and hetero-nuclear NOESY pulse sequences to boost their sensitivity.

A multi-level coordinated DC overcurrent suppression scheme for symmetrical bipolar MMC-HVDC integrated offshore wind farms

This paper proposes a multi-level coordinated control (MLCC) scheme for symmetrical bipolar modular multilevel converter based high voltage direct current (MMC-HVDC) integrated offshore wind farms. MLCC makes full use of the energy control capability of MMCs to effectively suppress DC overcurrent triggered by submarine cable breakage. This MLCC scheme consists of four control levels. The first level is for the offshore fault pole MMC. Once a DC submarine cable is broken, the fault pole MMC of the offshore converter station passively absorbs power from wind farms using the storage capacity of internal sub-module capacitors. This buys time for the rest of the control to start. The second level is for the onshore non-faulty pole MMC, which can actively raise the DC voltage to suppress DC overcurrent. The third level is for offshore non-fault pole MMC, which balances the power delivered to the DC system in real-time based on the power received from wind farms. The fourth level is for offshore wind farms, which reduce power to restore the non-fault pole submarine cable transmission power and current to the allowed state. The correctness and effectiveness of the proposed MLCC in different scenarios are verified using the PSCAD/EMTDC.

Multi-hop data dissemination using a multi-metric contention-based broadcast suppression strategy in VANETs

Vehicular Ad-hoc Networks (VANETs) are highly dynamic and self-organized ad hoc wireless networks that enable vehicles to set up and maintain communication without any central base station. In multi-hop-based VANETs, messages are disseminated throughout the network through a relaying. However, the dissemination of time-critical emergency warning messages remains challenging due to the broadcast storm problem. The widely proposed broadcast suppression strategies are either beacon-based, which demands extra bandwidth or do not scale well under different traffic conditions. Thus, this paper proposes a multi-criteria-based broadcast suppression scheme for multi-hop VANETS. The proposed scheme utilizes multiple node attributes, including relative velocity, traffic density, lane weight (moving lane), link stability, movement angle and distance to sender, to estimate a node's quality. Upon receiving a new message, each node can contend for the next-hop relay position using its quality value such that a high-quality node is granted the earliest channel access to broadcast the data packet. The performance of the proposed scheme is validated using data generated from traffic simulation in the OMNET++ environment under different traffic conditions. The results from the simulation claim that the proposed strategy alleviates broadcast overhead by 30% and significantly improves the overall dissemination efficiency by 48.97% compared to the bench-marked methods. The results showed that the objectives are met by significantly improving dissemination efficiency with increased reachability, reduced broadcast overhead and end-to-end delay. Moreover, the scheme enables each receiving node to evaluate its broadcasting suitability autonomously, making the relay selection process dynamic and adaptive to any traffic condition.

Crosstalk Suppression in Individually Addressed Two-Qubit Gates in a Trapped-Ion Quantum Computer.

Crosstalk between target and neighboring spectator qubits due to spillover of control signals represents a major error source limiting the fidelity of two-qubit entangling gates in quantum computers. We show that in our laser-driven trapped-ion system coherent crosstalk error can be modeled as residual Xσ[over ^]_{ϕ} interaction and can be actively canceled by single-qubit echoing pulses. We propose and demonstrate a crosstalk suppression scheme that eliminates all first-order crosstalk utilizing only local control of target qubits, as opposed to an existing scheme which requires control over all neighboring qubits. We report a two-qubit Bell state fidelity of 99.52(6)% with the echoing pulses applied after collective gates and 99.37(5)% with the echoing pulses applied to each gate in a five-ion chain. This scheme is widely applicable to other platforms with analogous interaction Hamiltonians.

Microvibration transfer and suppression of satellite under multi-source coupling disturbances based on energy flow analysis

The accuracy of satellites is extremely dependent on the control of the micro-vibration while the transmission paths among multiple vibration sources are complex. To reduce the impact of micro-vibration on the payloads of satellites effectively, the transmission characteristics of micro-vibrations under multi-source disturbances were analyzed, and a specific vibration suppression scheme was proposed. Based on the theoretical derivation and energy flow analysis method, the coupling transmission characteristics of micro-vibrations in the satellite under single- and multi-source disturbances were compared. The transmission characteristics of the vibration in the satellite under multi-source disturbance were obtained to determine the main transfer path. The contributions of different waveforms for elastic waves generated by vibration, namely bending wave, longitudinal wave and shear wave, to the target point were obtained by calculating the net transfer ratio to find out the dominant transfer waveform of the vibration. The vibration along the main transmission path was blocked by means of stiffened plates and an optimal vibration isolation scheme was determined by comparing the fluctuations in the vibrational energy of the payload under various stiffened ways. The results showed that the vibration energy under multi-source disturbances could not be obtained by the superposition of that under the single source. The longitudinal wave was the dominant transfer waveform of vibration with the energy to the payload accounting for 92.26%. The optimal vibration isolation treatment on the main transmission path can reduce the vibration by 79.25% on average, up to one order of magnitude.

A Trigger Signals Modification Scheme for Common-Mode Conducted EMI Reduction of Modular Multilevel Converter

Modular multilevel converter (MMC), due to its features of modularization, high efficiency, and so on, has gradually become the mainstream multilevel converter. However, it can induce large electromagnetic interference (EMI) because of the high-level <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$dv/dt$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$di/dt$ </tex-math></inline-formula> during its commutation transient. Therefore, it is significant to analyze the characteristics of common-mode (CM) conducted EMI of MMC and propose a suppression scheme accordingly. In this article, considering the voltage to ground of submodule (SM) as a direct noise source, the relationship between CM current and equivalent noise source of one phase, as well as that between the equivalent noise source of one phase and switching action of each SM are deduced. Furthermore, a trigger signals modification (TSM) scheme is proposed, which can effectively suppress the CM conducted EMI on the dc side without obviously affecting the operating performance of MMC. In particular, this scheme manipulates the trigger signals already generated by the modulation and capacitor voltage balancing control, thus enabling good applicability. Finally, experimental results verify the validity of the analysis and the effectiveness of the proposed TSM scheme.

Digital SI Cancellation Based on LSTM for Co-frequency Co-time Full Duplex Communication Systems

To address the high self-interference (SI) in co-frequency co-time full duplex (CCFD) communication systems, a digital SI suppression method based on deep learning is proposed. A memory polynomial is firstly utilized to simulate the SI channel. Then a long short-term memory network (LSTM) is used to reconstruct the SI signal. The clean signal after interference suppression can be achieved by subtracting the SI signal at the receiver. To better reflect the changes of the SI signals after being transmitted through the multiple channels and reduce dependence on data volume, feature preprocessing and feature reconstruction are performed at the input of the LSTM. We use the multi-segment delayed transmitted signal as the multiple features and utilize the brainstorm optimization (BSO) technique to estimate the ideal time delay. We verify the proposed SI suppression scheme in the OFDM transmission system. The experimental results show that compared with the traditional least squares estimation (LS) and adaptive filter least mean square (LMS) algorithms, the proposed scheme has a significant performance boost. A SI signal suppression capability of 47.19 dB is achieved.

Clutter Jamming Suppression for Airborne Distributed Coherent Aperture Radar Based on Prior Clutter Subspace Projection

Airborne distributed coherent aperture radar is of great significance for expanding the detection capability of the system. However, the extra observation dimension introduced by its sparse configuration also deteriorates the performance of traditional adaptive processing in a non-uniform environment. This paper focuses on moving target detection when the system works in a clutter–jamming-coexisting environment. In order to make full use of the specific low-rank structure to reduce the requirement for training data, this paper proposes a two-stage adaptive scheme that cancels jamming and clutter separately. The proposed suppression scheme first excludes the mainlobe jamming component from the training data based on the prior clutter subspace projection and performs intra-node clutter suppression. Then, the remaining jamming is jointly canceled based on the covariance obtained with its inter-pulse mixture model. Numerical examples show that this scheme can effectively reduce the blocking effect of main lobe jamming on high-speed targets but, due to the inaccuracy of the prior subspace, there is a certain additional loss of signal-to-noise ratio for near stationary targets. The simulation also shows that the proposed scheme is equally applicable to systems with a time-varying distributed geometry.

Demonstration of Tunable Three-Body Interactions between Superconducting Qubits.

Nonpairwise multiqubit interactions present a useful resource for quantum information processors. Their implementation would facilitate more efficient quantum simulations of molecules and combinatorial optimization problems, and they could simplify error suppression and error correction schemes. Here, we present a superconducting circuit architecture in which a coupling module mediates two-local and three-local interactions between three flux qubits by design. The system Hamiltonian is estimated via multiqubit pulse sequences that implement Ramsey-type interferometry between all neighboring excitation manifolds in the system. The three-local interaction is coherently tunable over several MHz via the coupler flux biases and can be turned off, which is important for applications in quantum annealing, analog quantum simulation, and gate-model quantum computation.