arXiv subjects

Kang Ma

Publications and source records attributed to Kang Ma.

16 recordsLinked to original sources

arXiv2026

Design and Verification of a New Current Source for Tsinghua Tabletop Kibble Balance

This paper presents an ultra-stable current source tailored for the one-mode, two-phase (OMTP) measurement scheme in Tsinghua tabletop Kibble balances. To achieve simultaneous high resolution and nA/A-level stability, a composite 'coarse-fine' control topology is proposed, utilizing a dual-DAC architecture and an active digital feedback loop. Experimental results show that the Allan deviation reaches 1 nA/A at an integration time of approximately 3 minutes, representing a tenfold improvement in measurement speed compared to commercial-source-based setups. Furthermore, the design offers a significant cost advantage, providing a satisfying option for high-precision, cost-effective mass realization.

physics.ins-det↗

arXiv2026

An Optical System for Monitoring Coil Parasitic Motion and Mass Position for Tsinghua Tabletop Kibble Balance

This paper presents a novel seven-channel optical measurement system for monitoring coil parasitic motion and mass position in the Tsinghua Tabletop Kibble balance. The system employs seven spectrally-confocal displacement sensors arranged in a distributed configuration to simultaneously measure the coil's translational ($x_{\rm{c}}, y_{\rm{c}}$), rotational ($\theta_x,\theta_y$) degrees of freedom, and the mass position offset ($x_{\rm{m}}, y_{\rm{m}}$) due to corner errors. Three vertically oriented sensors target an equilateral triangle target rigidly connected to the coil, enabling real-time calculation of tilt angles through geometric relationships. Two horizontally oriented sensors measure the translational displacement of a frame target on the coil assembly. Two additional horizontal sensors monitor the mass position to quantify corner errors. The initial experimental setup has been completed, featuring sufficient resolution and minimal signal loss, providing a new approach for alignment adjustment and corner error compensation in high-precision Kibble balances.

physics.ins-det↗

arXiv2026

Status of the Tsinghua Tabletop Kibble Balance

This paper reports on the status of the Tsinghua tabletop Kibble balance experiment, aiming to deliver a mass calibration instrument for kilogram realizations in accordance with the new International System of Units (SI). Major progress since 2024 in different aspects, i.e., electrical, magnetic, mechanical, and optical, is presented. The primary weighing and velocity measurement results are discussed.

physics.ins-det↗

arXiv2026

Recent Advances in Tabletop Kibble Balance -- KBmini

This paper presents recent advances in the KBmini Kibble balance, a tabletop system for E2-accuracy mass calibration up to 1 kg. The $Bl(z)$ profile is characterized by manually setting the magnet at different vertical positions, and the extremum point is selected as the weighing position. The spring constant of the weighing cell around this point is measured. With a new coil of a larger number of turns and a multi-harmonic excitation technique, a near-constant velocity profile over a moving range of 180 $\mu$m, producing an induced-voltage flat-top region exceeding 1 V, is achieved. These results establish a foundation for subsequent mass calibration experiments.

physics.ins-det↗

arXiv2025

Black-Start Power Capacity Sizing and Control Strategy for an Islanded DFIG Wind-to-Hydrogen System

This paper proposes a black-start method for an off-grid wind-to-hydrogen (W2H) system comprising a wind farm based on Doubly-Fed Induction Generators (DFIGs), proton exchange membrane fuel cells (PEMFCs) serving as the black-start power source, and a hydrogen production industry. The PEMFC is installed within the hydrogen industry to facilitate direct access to hydrogen fuel. Based on the microgrid topology and black-start scheme, this study innovatively sizes the rated capacity of the PEMFC through power flow analysis. The capacity must be sufficient to charge passive components such as transmission lines and transformers, provide rotor excitation, and supply wind turbine (WT) and electrolyzer (ELZ) auxiliaries during startup. The proposed system integrates wind-hydrogen coordinated control (WHCC) and hydrogen-storage coordinated control (HSCC). Under maximum power point tracking (MPPT) of the WTs, the ELZ follows power fluctuations to absorb wind output, ensuring stable voltage and frequency. Fixed-frequency control applied to either the DFIG or PEMFC converters enables DFIGs to retain conventional grid-following (GFL) operation, reducing converter development costs. For both control modes, this paper establishes the black-start sequence and formulates a comprehensive coordinated control strategy for the entire system. The entire control system is validated through simulations in MATLAB/Simulink. Results confirm that the calculated PEMFC capacity supports reliable black-start, while the black-start control strategy ensures smooth system self-startup. Furthermore, the coordinated control strategy maintains stable frequency and voltage under fluctuating wind power, demonstrating the practicality and robustness of the proposed approach.

eess.SY↗

arXiv2025

Self-Error Correcting Method for Magnetic-Array-Type Current Sensors in Multi-Core Cable Applications

Data-driven methods enable online assessment of error states in magnetic-array-type current sensors, and long-term measurement stability can be enhanced through further self-error correction. However, when the magnetic-array-type current sensors are applied to multi-conductor systems such as multi-core cables, the time-varying correlations among conductor currents may degrade the performance of multi-latent-variable data-driven models for error evaluation. To address this issue, this paper proposes a robust self-error correcting method for magnetic-array-type current sensors even under significant variations in phase current correlations (e.g., large fluctuations in three-phase current imbalance). By incorporating phase current decoupling and principal component analysis (PCA), the correlation analysis of multi-latent variables (i.e., multi-conductor currents) is transformed into a single-latent-variable (corresponding to single phase current) modeling problem. Experimental results demonstrate that the proposed method effectively detects error drifts of magnetic field sensors as low as $2\times10^{-3}$ in relative error and $2\times10^{-3}$ rad in phase error. Accurate evaluation and correction of each magnetic field sensor's error drifts substantially eliminates the overall error drift in the magnetic-array-type current sensor, validating the feasibility and effectiveness of the proposed self-error correcting method.

physics.ins-det↗

arXiv2025

Metering Error Estimation of Fast-Charging Stations Using Charging Data Analytics

Accurate electric energy metering (EEM) of fast charging stations (FCSs), serving as critical infrastructure in the electric vehicle (EV) industry and as significant carriers of vehicle-to-grid (V2G) technology, is the cornerstone for ensuring fair electric energy transactions. Traditional on-site verification methods, constrained by their high costs and low efficiency, struggle to keep pace with the rapid global expansion of FCSs. In response, this paper adopts a data-driven approach and proposes the measuring performance comparison (MPC) method. By utilizing the estimation value of state-of-charge (SOC) as a medium, MPC establishes comparison chains of EEM performance of multiple FCSs. Therefore, the estimation of EEM errors for FCSs with high efficiency is enabled. Moreover, this paper summarizes the interfering factors of estimation results and establishes corresponding error models and uncertainty models. Also, a method for discriminating whether there are EEM performance defects in FCSs is proposed. Finally, the feasibility of MPC method is validated, with results indicating that for FCSs with an accuracy grade of 2\%, the discriminative accuracy exceeds 95\%. The MPC provides a viable approach for the online monitoring of EEM performance for FCSs, laying a foundation for a fair and just electricity trading market.

eess.SP↗

arXiv2025

Achieving Stability and Optimality: Control Strategy for a Wind Turbine Supplying an Electrolyzer in the Islanded Storage-less Microgrid

Wind power generation supplying electrolyzers in islanded microgrids is an essential technical pathway for green hydrogen production, attracting growing attention in the transition towards net zero carbon emissions. Both academia and industry widely recognize that islanded AC microgrids normally rely on battery energy storage systems (BESSs) for grid-forming functions. However, the high cost of BESS significantly increases the levelized cost of hydrogen (LCOH), compromising economic feasibility. To address this challenge and reduce the LCOH, this paper focuses on a wind turbine (WT) supplying an electrolyzer in a storage-less microgrid and identifies a unique characteristic that challenges the conventional understanding of this microgrid: active power is coupled with microgrid voltage rather than frequency, the latter being entirely decoupled from active power balance. Based on this unique characteristic, this paper develops a new control strategy that maintains power balance, stabilizes the voltage and frequency, and maximizes hydrogen production. The effectiveness of the control strategy is validated through case studies conducted in Matlab/Simulink, especially its capability to maintain stability while maximizing hydrogen production under various conditions.

eess.SY↗

arXiv2024

Updates on the Tsinghua Tabletop Kibble Balance

With the adoption of the revised International System of Units (SI), the Kibble balance has become a pivotal instrument for mass calibrations against the Planck constant, $h$. One of the major focuses in the Kibble balance community is prioritizing experiments that achieve both high accuracy and compactness. The Tsinghua tabletop Kibble balance experiment seeks to develop a compact, high-precision, user-friendly, cost-effective, and open-hardware apparatus for mass realization, specifically within the kilogram range. This paper reports on the progress of the Tsinghua tabletop Kibble balance project over the past two years. Various aspects of the Tsinghua tabletop system, including electrical, magnetic, mechanical, and optical components, are summarized. Key achievements, such as the construction and characterization of the magnet system, determination of absolute gravitational acceleration, investigation of a capacitor-sensor-based weighing unit, and development of a high-precision current source, are presented to provide a comprehensive understanding of the experiment's status.

physics.ins-det↗

arXiv2024

A Compact Magnet System for the Tsinghua Tabletop Kibble Balance

Although the so-called magnetic geometrical factor, $Bl$, of a Kibble balance does not appear in the Kibble equations, it offers the precision link between electrical and mechanical quantities and furthers a quasi-quantum traceability path for mass metrology. This feature makes the magnet system, supplying the $Bl$ in Kibble equations, play a core role in Kibble balances. Following the open-hardware idea, we report here on the design, manufacture, assembly, optimization, and finally performance of a compact magnet system for the Tsinghua tabletop Kibble balance. Notably, the magnet system showcased in this study facilitates a straightforward upper levitation of splitting through a streamlined mechanism guide, substantially enhancing the ease of open and close operations. Experimental tests show the realized magnet systems can yield a high $Bl$ value (e.g., 400 Tm for a bifilar coil and 800 Tm for a single coil with a wire gauge of 0.2 mm) meanwhile a low volume/weight (40 kg) thanks to the uniformity improvement of magnetic profiles. Furthermore, important parameters related to systematic effects, such as the current effect, are checked, aiming for a final mass-realization accuracy at the $10^{-8}$ level.

physics.ins-det↗

arXiv2024

A Bi-polar Current Source with High Short-term Stability for Tsinghua Tabletop Kibble Balance

A high-precision current source, capable of supporting weighing measurements with a relative uncertainty at the $10^{-9}$ level, is essential for Kibble balance experiments. However, most current sources utilized in Kibble balances to date are homemade and not commercially available. In this paper, we introduce a digital-feedback, two-stage current source designed for the Tsinghua tabletop Kibble balance, relying solely on commercially available sources and voltmeters. A high-resolution, small-range current source is employed to digitally compensate for current output fluctuations from a large-range current source. Experimental tests show the proposal can offer an easy realization of a current source with nA/A stability to support Kibble balance measurements.

physics.ins-det↗

arXiv2024

Multi-Object Tracking in the Dark

Low-light scenes are prevalent in real-world applications (e.g. autonomous driving and surveillance at night). Recently, multi-object tracking in various practical use cases have received much attention, but multi-object tracking in dark scenes is rarely considered. In this paper, we focus on multi-object tracking in dark scenes. To address the lack of datasets, we first build a Low-light Multi-Object Tracking (LMOT) dataset. LMOT provides well-aligned low-light video pairs captured by our dual-camera system, and high-quality multi-object tracking annotations for all videos. Then, we propose a low-light multi-object tracking method, termed as LTrack. We introduce the adaptive low-pass downsample module to enhance low-frequency components of images outside the sensor noises. The degradation suppression learning strategy enables the model to learn invariant information under noise disturbance and image quality degradation. These components improve the robustness of multi-object tracking in dark scenes. We conducted a comprehensive analysis of our LMOT dataset and proposed LTrack. Experimental results demonstrate the superiority of the proposed method and its competitiveness in real night low-light scenes. Dataset and Code: https: //github.com/ying-fu/LMOT

cs.CV↗

arXiv2024

A Self-Healing Magnetic-Array-Type Current Sensor with Data-Driven Identification of Abnormal Magnetic Measurement Units

Magnetic-array-type current sensors have garnered increasing popularity owing to their notable advantages, including broadband functionality, a large dynamic range, cost-effectiveness, and compact dimensions. However, the susceptibility of the measurement error of one or more magnetic measurement units (MMUs) within the current sensor to drift significantly from the nominal value due to environmental factors poses a potential threat to the measurement accuracy of the current sensor. In light of the need to ensure sustained measurement accuracy over the long term, this paper proposes an innovative self-healing approach rooted in cyber-physics correlation. This approach aims to identify MMUs exhibiting abnormal measurement errors, allowing for the exclusive utilization of the remaining unaffected MMUs in the current measurement process. To achieve this, principal component analysis (PCA) is employed to discern the primary component, arising from fluctuations of the measured current, from the residual component, attributed to the drift in measurement error. This analysis is conducted by scrutinizing the measured data obtained from the MMUs. Subsequently, the squared prediction error (SPE) statistic (also called $Q$ statistic) is deployed to individually identify any MMU displaying abnormal behavior. The experimental results demonstrate the successful online identification of abnormal MMUs without the need for a standard magnetic field sensor. By eliminating the contributions from the identified abnormal MMUs, the accuracy of the current measurement is effectively preserved.

eess.SP↗

arXiv2021

Learning Rich Features for Gait Recognition by Integrating Skeletons and Silhouettes

Gait recognition captures gait patterns from the walking sequence of an individual for identification. Most existing gait recognition methods learn features from silhouettes or skeletons for the robustness to clothing, carrying, and other exterior factors. The combination of the two data modalities, however, is not fully exploited. Previous multimodal gait recognition methods mainly employ the skeleton to assist the local feature extraction where the intrinsic discrimination of the skeleton data is ignored. This paper proposes a simple yet effective Bimodal Fusion (BiFusion) network which mines discriminative gait patterns in skeletons and integrates with silhouette representations to learn rich features for identification. Particularly, the inherent hierarchical semantics of body joints in a skeleton is leveraged to design a novel Multi-Scale Gait Graph (MSGG) network for the feature extraction of skeletons. Extensive experiments on CASIA-B and OUMVLP demonstrate both the superiority of the proposed MSGG network in modeling skeletons and the effectiveness of the bimodal fusion for gait recognition. Under the most challenging condition of walking in different clothes on CASIA-B, our method achieves the rank-1 accuracy of 92.1%.

cs.CV↗

arXiv2019

Energy Management of Airport Service Electric Vehicles to Match Renewable Generation through Rollout Approach

Traditional diesel-based airport service vehicles are characterized by a heavy-duty, high-usage-frequency nature and a high carbon intensity per vehicle per hour. Transforming these vehicles into electric vehicles would reduce CO2 emissions and potentially save energy costs in the context of rising fuel prices, if a proper energy management of airport service electric vehicles (ASEVs) is performed. To perform such an energy management, this paper proposes a new customized rollout approach, as a near-optimal control method for a new ASEV dynamics model, which models the ASEV states, their transitions over time, and how control decisions affect them. The rollout approach yields a near-optimal control strategy for the ASEVs to transport luggage and to charge batteries, with the objective to minimize the operation cost, which incentivizes the charging of the ASEVs to match renewable generation. Case studies demonstrate that the rollout approach effectively overcomes the "curse of dimensionality". On both typical summer and winter days, the rollout algorithm results in a total cost approximately 10% less than that of the underlying "greedy charging" heuristic, which charges a battery whenever its state of charge is not the maximum. The rollout algorithm is proven to be adaptive towards flight schedule changes at short notice.

eess.SY↗

arXiv2018

Dynamic Game-based Maintenance Scheduling of Integrated Electric and Natural Gas Grids with a Bilevel Approach

This paper proposes a dynamic game-based maintenance scheduling mechanism for the asset owners of the natural gas grid and the power grid by using a bilevel approach. In the upper level, the asset owners of the natural gas grid and the power grid schedule maintenance to maximize their own revenues. This level is modeled as a dynamic game problem, which is solved by the backward induction algorithm. In the lower level, the independent system operator (ISO) dispatches the system to minimize the loss of power load and natural gas load in consideration of the system operating conditions under maintenance plans from the asset owners in the upper level. This is modeled as a mixed integer linear programming problem. For the model of the natural gas grid, a piecewise linear approximation associated with the big-M approach is used to transform the original nonlinear model into the mixed integer linear model. Numerical tests on a 6-bus system with a 4-node gas grid show the effectiveness of the proposed model.

math.OC↗