High-voltage direct current (HVDC) transmission technology has become the core means for long-distance and large-capacity power transmission due to its advantages such as large transmission capacity, low loss, and strong stability. Traditional HVDC technology based on line-commutated converters (LCC) has inherent defects such as the limitation of the short-circuit capacity of the receiving-end system and the inability to achieve multi-terminal interconnection. Although the flexible DC technology based on voltage-source converters (VSC) has the capability to connect renewable energy, it is constrained by component costs and technical maturity. As a new converter topology integrating the technical advantages of LCC and VSC, SLCC (Half-Bridge Modular Multilevel Converter) enhances system flexibility and reduces fault current levels through optimized control strategies, while maintaining high engineering economy. This paper aims to explore the operational characteristics and engineering application feasibility of SLCC technology in HVDC projects.

To address the issues of large footprint, complex configuration, and lack of flexibility in switching associated with traditional passive filters in high-voltage direct current (HVDC) systems, this paper proposes a hybrid active power filter (HAPF) solution. The HAPF integrates a passive filter and a voltage source converter (VSC) in series, employing two control strategies: current control to compensate harmonic currents and impedance control to enhance low-impedance filtering performance. One HAPF is capable to filter multiple harmonics, and can reach a filtering rate 95

This paper addresses the challenges posed by voltage fluctuations during the commutation process of Flexible Line Commutated Converters (FLCC), in which an MMC is in series between the transformer and LCC valve, and their impact on system insulation coordination. An optimized arrester configuration scheme is proposed based on voltage fluctuation analysis. During the commutation process, the voltage across the LCC valve and transformer is influenced by changes in commutation angle and MMC voltage, which may lead to high peak voltage on both rectifier and inverter sides, and high arrester reference voltage. Steady-state voltage simulations and calculations are conducted to analyze voltage peaks under different operating conditions. Based on this, a new arrester configuration is designed, in which the transformer side of the MMC is allocated a grounded arrester, and the valve side of the MMC is protected by valve arrester, to ensure minimum arrester number and reduce energy demands, in consideration of the energy distribution after fault and possible arrester combination scheme. The arrester ratio of CCOV and the reference voltage is optimized to enhance the low arrester protective level. Simulation results demonstrate that the optimized scheme effectively mitigates the impact of voltage fluctuations on equipment withstand voltage, improving the system's resilience and safety, thus providing theoretical support for the design and application of FLCCs.

Ultra high voltage direct current transmission is the main In this paper, the principle and topology of APF are compared firstly, and then the scheme of adding APF is designed according to the phenomenon that the 5th harmonic of Jinhua converter station exceeds the standard. The control target of APF is studied, and the minimum current output capability of APF is calculated by mathematical formula, and the specific control strategy is designed based on the result of control target. Finally, the simulation model of PSCAD is built to verify the correctness of the control strategy. The results show that the scheme of adding active filter can effectively reduce the low order harmonics of converter station.

Ultra high voltage direct current transmission is the main technical means for large-scale energy bases in western China to remotely transmit power resources to the central and eastern load centers. With the continuous development of new power systems, the power grid has put forward higher requirements for the operation reliability, control flexibility, and equipment safety of ultra-high voltage direct current transmission. With the large-scale integration of new energy into ultra-high voltage DC systems, frequent voltage fluctuations and stability issues in converter stations are prominent. When the DC power or voltage repeatedly deviates from the target value, it will cause continuous action of tap changer, resulting in safety hazards for converter and on load tap changer equipment. Therefore, it is necessary to conduct research on optimization strategies for frequent operation of tap changers in ultra-high voltage direct current projects.

A novel scheme for a frequency 32-tupling millimeter wave (MMW) radio over fiber(ROF) system without the bit walk-off effect is proposed. The operation principle and feasibility of our proposed scheme are theoretically analyzed and verified with simulation experiments. The main part of our scheme is a ±16th order sidebands generator (SG) which is constructed by eight Mach-Zehnder modulators (MZM) connected in parallel. In the back-to-back(BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±16th order sidebands are generated by the SG. In the data transmission case, the data signal is split into two beams first, one of which modulates the RF drive signal with an electrical phase modulator (PM), and the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can be modulated only to the +16th order sideband of the output of the SG. The optical carrier from the CW laser is split into two paths, one is sent into the SG, and the other is used as a pilot. The output signal of SG is combined with the pilot signal and is transmitted to the base station(BS) via optical fiber. In BS, the pilot signal is filtered out by an FBG and used as the carrier for uplink for carrier reuse. After filtering out the pilot, the signal from the FBG which is ±16th order sidebands is injected into the photodetector, and a frequency 32-tupling MMW with downlink data is generated. The influence on the bit error rate (BER) and Q factor by the key parameters in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion, greatly increase the fiber transmission distance, but also effectively improve the performance of the downlink, it has important application prospects in ROF systems.

With the large-scale development of new energy, the high proportion of wind and solar renewable energy sources and power electronic devices profoundly affect the dynamic behavior of the power system, further posing challenges to the safe and stable operation of the DC system. Traditional ultra-high voltage direct current (UHVDC) engineering converter stations are equipped with a large number of AC filters. During the switching process of AC filters, there is a dead zone of reactive power in the AC/DC system, and there is always a certain amount of reactive power exchange. According to engineering experience, the dead zone range is about 0.8 times the maximum capacity of a single AC filter group. When the AC filter group is large, the reactive power exchange value between the AC/DC systems also increases. Under the continuous development of new energy in the future, the reactive power support capacity of the communication system may become increasingly limited. At the same time, there are a large number of power electronic devices in the network, and the reactive power injected into the communication system may also pose operational risks to the stability of the communication system. This article mainly proposes a control strategy to reduce the reactive power exchange in the AC/DC system in the case of a large dead zone of reactive power under low power in the Matiari-Lahore DC project. By comparing the reactive power exchange during the lifting process and the number of switching times, the possible applicable solutions and risk points of the current DC transmission system are analyzed, providing feasible solutions for the safe and stable operation of DC transmission projects in the future new power grid.

In HVDC transmission project, it is necessary to carry out AC filter tuning test before the AC filter is put into operation to ensure that the error between actual tuning frequency and design tuning frequency is within 1% (refer to Q/GDW 11750.5-2017 Sub-system test standard in UHV converter station Part 5: Sub-system test for AC filter field). Taking the HP24/36 filter of Shanghaimiao station as an example, the tuning frequencies are designed to be 1200 Hz and 1800 Hz. However, the on-site measured tuning frequency of HP24/36 filter is 1179 Hz and 1775 Hz respectively. After research, it was found that the main reasons for the error in the measured tuning frequency of AC filters are as follows:(1) The element value of AC filter has deviation; (2) Considering the resistance element in the filter, there is a small deviation between the actual tuning frequency and the designed tuning frequency; (3) There are measurement errors in measuring instruments; (4) The stray inductance of the connecting wire used in the measurement results in the measurement error. Therefore, it is recommended to take the filter tuning frequency obtained by the tuning characteristic tester (such as Bodian PF3000) as the reference, and take the tuning frequency calculated by the measured value of each filter element as the final result. When the error between the design tuning frequency and the calculated tuning frequency is less than 1%, it can be considered that the tuning test is passed.

A novel inserting pilot scheme to generate and distribute a frequency 16-tupling millimeter wave (MMW) radio over fiber (ROF) system without the bit walk-off effect via Mach–Zehnder modulators (MZMs) is proposed. The operation principle is analyzed and the feasibility of our proposed scheme is verified by simulation test. The main part of our scheme is a ±8th-order sidebands generator (SG), which is constructed by four MZMs connected in parallel. In the back-to-back (BTB) transmission case, by properly adjusting the voltage and initial phase of the radio frequency (RF) drive signals of the MZMs, ±8th-order sidebands are generated by the SG. In the data transmission case, the data signal is first split into two beams, one of which modulates the RF drive signal with an electrical phase modulator (PM) while the other is amplified by an electrical gainer (EG), and then the two beams are combined into one and used as the composite RF drive signal of the MZMs. By adjusting the modulation index of the PM and the gain of the EG, the data signal can only be modulated to the +8th-order sideband of the output of the SG. The optical carrier from the continuous wave (CW) laser is split into two paths: one is sent into the SG, and the other is used as a pilot signal. The output signal of SG is combined with the pilot signal and is transmitted to the base station (BS) via optical fiber. At the BS, the pilot signal is filtered out by a fiber Bragg grating (FBG) and used as the carrier for the uplink for carrier reuse. After filtering out the pilot, the signal from the FBG, which is composed of ±8th-order sidebands, is injected into a photodetector, and a frequency 16-tupling MMW with downlink data is generated. The key parameters’ influence on the bit error rate (BER) and Q factor in the system is also analyzed. Our scheme can not only effectively overcome the bit walk-off effect caused by optical fiber chromatic dispersion and greatly increase the fiber transmission distance but can also effectively improve the performance and the tunability of system. Therefore, it has important application prospects in ROF systems.

In this article, a compact distributed septuple-band negative group delay circuit (NGDC) is proposed and analyzed. It is mainly composed of a high–low–high step-impedance microstrip line with an E-shaped groove and two T-shaped open stubs. This NGDC was first simulated and then fabricated by using a conventional printed circuit board (PCB) process with the substrate of RO4350. To investigate the operational mechanism of the NGDC, an equivalent circuit, consisting of nine transmission lines, four series–parallel LC resonant circuits, and two T-type series LC resonant circuits, has been developed and analyzed. It is found that the theoretical group delay characteristic calculated from the equivalent circuit agrees well both with the simulated data by using ADS as well as HFSS and with the experimental results. The measured seven NGD resonant frequencies occur at 2.03, 2.84, 8.14, 8.74, 13.0, 16.02, and 18.46 GHz, and the corresponding NGD values read −3.65, −3.04, −1.73, −3.23, −1.16, −1.20, and −1.47 ns. The dimensions of the presented passive NGDC are only 25 mm $\times22$ mm without using any lumped components.

With the development of electric vehicles in China, the fault monitoring and warning systems for the charging process of electric vehicles have received the industry’s attention. A method for the monitoring and warning of electric vehicle charging faults based on a battery model is proposed in this paper. Through online estimation of the state of charge of the power battery model and battery electromotive force, parameters such as battery state of charge, voltage, and temperature can be adjusted in real time to simulate the charging response of the power battery, which can simulate power batteries of different types, specifications, and parameters. During the charging process, CAN (Controller Area Network) bus monitoring technology is used to receive and analyze the charging information of the charger, as well as the battery charging information and battery charging demand information. The charging response information simulated by the battery model is compared with the battery charging state information, and the charging state information of the charger is compared with the battery charging demand information to determine whether the charging process is normal. When it is judged that a charging fault occurs, a fault warning signal is sent. This method can identify more than 10 types of faults, including the failure of the BMS (Battery Management System) function. The comparison and analysis of actual charging accident data and power battery model data verifies the feasibility of the charging fault monitoring method proposed in this paper.

In this paper, a novel super-wideband multiple-input multiple-output (SWB-MIMO) antenna system with high isolation has been proposed, each antenna element consisting of a spade-shaped radiation patch, a defected ground structure (DGS) as well as a windmill-shaped decoupling structure. The elliptical slot etched on the radiation patch and the rectangular DGS are jointly utilized to make better the radiation performance and impedance bandwidth. Both of four-element and eight-element SWB-MIMO antenna systems are simulated and analyzed, respectively. A prototype of the four-element SWB-MIMO antenna system with total dimensions of 58 mm $\times58$ mm $\times 1$ mm was fabricated to verify the concept of design using an FR4 material substrate. Measurement and simulation results indicate that the proposed SWB-MIMO antenna system can work in the frequency band ranging from 2.9 to 40 GHz with a mutual coupling of lower than–17 dB. Also, excellent performance has been achieved with a low envelop correlation coefficient (ECC) of lower than 0.04, high multiplexing efficiency ( $\eta _{\mathrm {mux}}$ ) of more than–3.0 dB, stable gain of up to 13.5 dBi as well as quasi-omnidirectional radiation properties. This design provides an important guideline for obtaining a super-wide MIMO antenna.

Here, a silicon-substrate-based four element antenna system is investigated by using a coplanar frequency selective surface (FSS) as a novel parallel reflector to improve radiation and transmission characteristics of the antennas. The four antennas are arranged around the square FSS, and one of the antennas is used as the transmitting element, while the other three as the receiving ones. It is found that, owing to the stopband filtering and the linearly changing reflection phase of the designed coplanar FSS, the gain and directivity of the transmitting antenna have been greatly improved, and that the antenna system transmission coefficients, including S-21, S-31 and S-41, have been significantly increased. Two types of the antenna systems have been designed and fabricated on a P-type silicon wafer substrate for the cases with and without a coplanar FSS reflector. The measured S-parameters are essentially consistent with those simulated. In comparison with the case without the FSS, the transmission coefficients of S-21, S-31 and S-41 for the system with the FSS have been increased about 6.42, 5.97 and 5.89 dB at the center frequency of 5.42 GHz, respectively. Furthermore, the proposed coplanar FSS exhibits distinct advantage of low-profile compared to the conventional vertical FSS reflector.

Performance status evaluation is essential for the safe running of electric vehicle (EV) charging infrastructure. With the development of the EV industry, the EV charging infrastructure industry has advanced considerably. Safe and reliable operation of the charging infrastructure is important for the development of EVs. As such, we propose a comprehensive evaluation method to assess the performance condition of an EV charging infrastructure. First, based on the analysis of the existing EV charging principles, we established an evaluation index system for EV charging infrastructure. Second, the subjective weight, objective weight, and comprehensive weight of the index system were determined through analytic hierarchy processes (AHP) and the entropy weight method. Then, we used fuzzy comprehensive evaluation to appraise the performance of the charging infrastructure through expert investigation. Finally, based on the actual data from an EV charger, the performance conditions of the EV charging infrastructure were evaluated to demonstrate the feasibility of the method and the reliability of the index system.

With the continuous development and promotion of electric vehicles, the safety and reliability of electric vehicle charging facilities are paid more attention. In order to serve users better, this paper analyzes the existing charging facilities and clarifies the technical requirements for on-site detection, and an on-site detection system of electric vehicle charging facilities is proposed based on the analysis. The practical application proves that the system can detect the electrical performance, protection characteristics and restriction characteristics effectively, which could provide reference for the operation and maintenance of the charging facilities.

An electric vehicle power battery simulation system simulating different power battery packs for the field test of the off-board charger is designed, which can be used to test the performance of an off-board charger. Specifically, the improved power battery model is combined with the improved lightweight charging load and the online estimation of the state of charge as well as the electromotive force of the battery model are used to adjust charging load parameters in real time to simulate the charging response. An acceleration coefficient is introduced into the traditional battery model to improve test efficiency, and the type, specification, temperature and voltage parameters of the battery can be set online according to the test requirements. An improved charging load scheme is proposed, in which a DC converter cascaded power battery pack of the mobile test vehicle is used to form a lightweight charging load with the mode of constant voltage, constant current, constant power and constant resistance and the ability to be adjusted continuously within the rated range. As a result, the size and weight of the charging load are reduced and the autonomous test of the off-board charger is realized. The performances of the proposed battery simulation system are validated through the various experimental results.

Owing to the particular distribution of energy and load, the high-voltage direct current transmission system has been greatly developed in China. A number of areas have formed the multi-infeed direct current (MIDC) transmission systems. In MIDC transmission systems, the electrical distance between the inverter stations is close and the coupling effect is strong, therefore, the interaction influence of harmonics is complex. In order to analyse this complex interaction influence, this study first introduces the influence factors multi-infeed influence factors of power (MIIF-Pd) and multi-infeed total harmonic voltage distortion (MITHDu), which are used to describe the interaction influence degree of harmonics between inverter stations. Then based on the Shanghai power grid, a simulation model of the MIDC transmission systems was built in PSCAD/EMTDC, and the interaction influence degree of harmonics in MIDC transmission systems was studied in the case of large disturbance and small disturbance exists in the inverter stations. The results show that the interaction influence of harmonics between inverter stations is related to the electrical distance, the style of disturbance, transmission power and so on. Meanwhile, the disturbance on a commutation bus mainly leads to the increase of the harmonic distortion rate in this inverter station, and has less influence on the other stations.

A novel tricyclic nested electromagnetic bandgap (TN-EBG) structure has been proposed to restrain the simultaneous switching noise (SSN) in high-speed digital systems. The presented TN-EBG structure was fabricated and measured based on the simulated performance of the configuration. It is found that the measured S-parameters are in good agreement with the simulated ones. Also, it is observed that an ultra-wide bandgap has been achieved, which almost ranges from 1 to 27 GHz with the noise suppression at -50 dB. Especially for the stopband width spanning from 1.1 to 21.6 GHz, the suppression depth level reaches up to-60 dB. The derived electric field distribution images have clearly exhibited the operation mechanism of the TN-EBG structure for SSN mitigation within the different frequency regions.

The lack of inertia and damping mechanism of photovoltaic (PV) grid-connected systems controlled by maximum power point tracking (MPPT) poses a challenge for the safety and stability of the grid. Virtual synchronous generator (VSG) technology has attracted wide attention, since it can make PV grid-connected inverter present the external characteristics of a synchronous generator (SG). Nevertheless, traditional PV-VSG is generally equipped with an energy storage device, which leads to many problems, such as increased costs, space occupation, and post-maintenance. Thus, this paper proposes a two-stage improved PV-VSG control method based on an adaptive-MPPT algorithm. When PV power is adequate, the adaptive-MPPT allows the PV to change the operating point within a stable operation area to actualize system supply-demand, matching in accordance to the load or dispatching power demand; when PV power is insufficient, PV achieves traditional MPPT control to reduce power shortage; simultaneously, improved VSG control prevents the DC bus voltage from falling continuously to ensure its stability. The proposed control approach enables the two-stage PV-VSG to supply power to loads or connect to the grid without adding additional energy storage devices, the effectiveness of which in off-grid and grid-connected modes is demonstrated by typical simulation conditions.

The fundamental reason of the commutation failure caused by harmonics is analyzed based on the mechanism of commutation failure.This paper presents a method of voltage time area,meanwhile defines and calculates the commutation failure critical deviation angle and critical proportion coefficient of 5th,7th,1 1 th,13th order dominant harmonic.In addition,the actual example of Shanghai power grid is given,then through equivalent harmonic model and Ward equivalent algorithm of power network,voltage deviation of the DC access point caused by background harmonic and the critical condition of commutation failure can be calculated by Matlab software,all the results are checked by simulation.Finally,conditions of preventing commutation failure caused by harmonic in engineering are proposed.The conclusions have a practical guiding role on planning and operation of AC/DC power grid.