Transmission lines’ non-negligible distributed capacitance can increase the risk of broadband resonance in power systems. However, the distributed parameter characteristics and frequency-dependent characteristics are commonly ignored in the transmission line modeling during the analysis of resonance, which may lead to inaccurate stability assessment and pseudo oscillations in simulations. In this article, a harmonic frequency range transmission line model suitable for real-time simulation (RTS) is proposed. First, a simplified calculation method of parameters based on system structures is expanded. Afterward, a detailed equivalent circuit of the multi-phase model is implemented in RTS to meet the requirements of decoupling and parallel computing. Finally, the electrical parameters are modified based on the harmonic frequency to improve the Bergeron model and the proposed model (PM) is developed accordingly. Simulation results show that the PM is highly suitable for time-domain simulation and high-order harmonic analysis.

Converter valve-side single-phase-to-ground (SPG) faults are among the most critical issues affecting the secure operation of modular multilevel converters (MMCs). However, the fault characteristics of these faults in symmetrical monopolar MMCs have not been thoroughly explored. This paper aims to fill this gay by theoretically investigating SPG faults in such systems. The analysis considers various influencing factors, including MMC grounding schemes and dc line types. The findings demonstrate that valve-side SPG faults cause dc voltage oscillations and therefore, large discharging currents from the distributed capacitors of dc lines. These scenarios are examined through mathematical analyses and verified through simulations of a generic MMC-HVDC system using PSCAD/EMTDC. The results accurately reveal the fault behaviors under different system conditions, providing valuable insights for the design of protection systems and insulation coordination for internal ac grounding faults in MMC stations.

Valve-side, single-phase-to-ground (SPG) faults in bipolar high-voltage direct current (HVDC) systems based on half-bridge modular multilevel converters (HB-MMCs) result in i) significant upper arm overvoltage, and ii) non-zero-crossing currents in the grid-side ac circuit breaker (ACCB). In this paper, a dc-link thyristor-based protection scheme is proposed to address both issues. The dc-link thyristor branches are installed in the dc terminal of each station. A dc short-circuit loop is formed following triggering the thyristor branch, redirecting currents from the upper arms to the branch, thus preventing continuous capacitor charging in the upper arms. Moreover, the creation of the dc short-circuit loop induces symmetrical components in the grid-side currents, which ensure current zero-crossings in the grid-side ACCB. The peak current flowing into the dc-link thyristor branch is also calculated to facilitate the design of the thyristor branch. The effectiveness of the proposed protection scheme is validated in an HB-MMC HVDC system simulated in PSCAD/EMTDC.

In voltage source converter-based low-voltage dc systems (LVDC), the fault current of the dc-link capacitor is considerably high and destructive to system infrastructure. It is necessary to develop effective fault detection methods with sufficient sensitivity and accuracy. To achieve these targets, a complex domain analysis-based fault detection method is proposed in this article. Specifically, the proposed method first fits the transient current into a linear combination of exponential functions, which is solved in the Z-domain-based on the Padé approximation. Second, exponents of the fitted function are projected into the complex plane. A state circle centered on the origin is defined on the complex plane to detect dc faults according to the position of projection points relative to the state circle. The proposed method can differentiate several typical situations via theoretical analysis, including fault line transients, healthy line transients, and load switching. The performance of proposed method is validated with an experimental multiterminal LVDC system to reveal its effective performance compared with present frequency domain based methods, including the wavelet transform, the short-time Fourier transform, the S transform, and the Hilbert–Huang transform.

For distributed solid electricity thermal storage aggregators (DSETSA), the uncertainty of the marginal clearing price may lead to the problem of multibidding scenarios (including successful, part successful, and failed biddings) in the electricity spot market. Moreover, the marginal operating cost affecting the bidding revenue in the spot market is not considered in the existing methods, which challenge the bidding of the aggregators. To address the challenge, this article proposes an optimized operation framework for DSETSA. First, based on the incomplete information characteristics of the spot market, an optimal bidding model which incorporates marginal operating cost constraints for DSETSA under multibidding scenarios is proposed to increase the operation profit. Second, the DSETSA's multibidding scenario problem induced by the uncertainty of the marginal clearing price in the electricity spot market is cast into a probability distribution representation using the Bayesian incomplete information theory to increase the chances of winning bids. Finally, framework establishes the relationship between the bidding price, electricity demand, and public traded electricity in the spot market. The effectiveness of the proposed framework is demonstrated through simulations.

Various DC circuit breakers (DCCBs) have been widely proposed for the DC fault protection of high-voltage direct-current (HVDC) grids. In recent years, hybrid DCCBs (HCBs) have been paid significant attentions due to their features of low power losses and fast dynamic response. However, several aspects regarding the design of HCB should be further addressed. For instance, the requirement of deploying a large surge arrester to dissipate the large fault current energy should be further addressed and the strategy to perform zero-voltage switching (ZVS) of semiconductor devices during the post-fault restoration processes should be investigated. In this paper, a dual-bridge hybrid DC circuit breaker (DB-HCB) with freewheeling diode branches is proposed to address the above issues. The operation principle of the proposed DB-HCB for pole-to-ground and pole-to-pole faults is presented. Compared with other HCBs, the capacity of the surge arrester is obviously reduced, so that the capital cost and volume of the proposed DB-HCB is decreased. Moreover, the ZVS is implemented during the post-fault restoration processes. Simulation results in PSCAD/EMTDC are given to validate the effectiveness of the proposed DB-HCB.

This paper proposes a novel T-type multilevel inverter (MLI) based on the switched-capacitor technique. The proposed inverter not only achieves that the maximum voltage stress of the switches is less than the input voltage but also has a voltage boost capability, which makes it suitable in high voltage applications. It is worth mentioning that the proposed inverter features two topology extension schemes which help it achieve a higher output level and voltage gain. With the merit of low voltage stress and reduced power devices, a seven-level inverter can be achieved using only two capacitors. Moreover, capacitor voltage self-balancing capability can simplify the complexity of the circuit and control. The topology, operating principle, modulation strategy and analysis of the capacitor of the inverter are presented. The superiorities of the proposed inverter are investigated by comparing with recently proposed hybrid MLIs and switched-capacitor MLIs. Finally, a seven-level prototype is constructed to validate the correctness of the theoretical analysis and the feasibility and effectiveness of the proposed inverter.

global localization is essential for pose initialization and pose recovery. However, for the lack of prior information, global localization is always unreliable and time consuming, especially in featureless and dynamic industry environment. To alleviate the negative influence of such environment, this paper uses reflector as landmarks. Then, several maps including labeled occupancy grid map and multi-resolution likelihood field are proposed to model the positions of landmarks as well as ordinary obstacles. Furthermore, a branch and bound method is employed to achieve fast global search based on those proposed maps. Through experiments in a real industry application, the reliability and efficiency of our proposed global localization method is verified.

This paper proposes an efficient and robust localization recovery method considering time variation for Monte Carlo localization (MCL), which can handle the kidnapped robot problem (KRP) with improved recovery speed and success rate. The presence of particles near the real robot’s pose is necessary for the localization recovery of MCL. Therefore, the generation number and position of random particles are the vital factors to solve KRP. It is generally assumed that the robot cannot move instantaneously, so the size of the search space where robot may appear should be time-dependent after the KRP occurs. Given these considerations, a restricted search space is firstly constructed as a set subject to a time-varying normal distribution, which can effectively narrow the search space and estimate the probability that the robot may appear. In addition, a short-long term random particle generation strategy considering time variation is designed to availably determine the number of random particles according to the change of the likelihood and time. And then, the random particles are spread into the restricted search space. Finally, the above particle set is integrated into the MCL for localization recovery. The effectiveness of the proposed method is verified through real scene experiments.

Medium-voltage dc (MVdc) power distribution grid is a key link to build dc power networks. In this article, a novel input-series-output-parallel modular dc transformer (DCT) with the high-frequency-link (HFL) voltage buck-boost matching strategy is proposed for MVdc grids application. The proposed DCT is composed of a current-fed switched capacitor structure and corresponding dual-active-bridge converters, and they need to operate collaboratively to achieve the great property. Comparing with the traditional switched capacitor-based DCT (SCDCT), the most salient merits of the proposed DCT include the HFL voltage buck-boost adaptive regulation, the low conducting and switching current in switches and the capacitor voltages self-balance characteristic. These merits are all beneficial for the improvement of efficiency, operating reliability, switching performance, and cost of DCT systems. Meanwhile, the proposed DCT reserves the advantages of SCDCT including redundant submodule design and dc fault isolating capability. The topology, buck-boost modulation principle, capacitor voltage self-balance analysis, switching behaviors, and comprehensive comparison with the traditional SCDCT are completed in detail. Finally, the experimental results validate the effectiveness and correctness of the proposed solution.

One of the most significant obstacles preventing the large-scale application of direct-current (DC) technology in medium voltage (MV) distribution networks is their fault protection. The existing AC relay protection needs to be changed or redesigned to protect the future overlay MVAC and MVDC distribution networks. Therefore, a comprehensive understanding of the dynamic and fault behavior and post-fault restoration strategies of MVAC and MVDC systems are critically important. Moreover, a comparison of MVAC and MVDC systems during a fault will also contribute to designing the protection systems of hybrid MV AC/DC systems. In this paper, the challenges of protecting DC faults of MVDC systems and possible solutions are first introduced. Then, the fault characteristics and post-fault restoration of MVDC and MVAC distribution systems are compared and investigated through case studies. Time-domain simulations have been conducted in PSCAD/EMTDC. The work in this paper will be valuable for the protection design for future hybrid MV AC/DC systems.