DC Blocking Research Articles

A 5.8-GHz Band Highly Efficient 1-W Rectenna With Short-Stub-Connected High-Impedance Dipole Antenna

This article describes a 5.8-GHz band highly efficient 1-W rectenna that consists of a bridge diode, directly connected to a short-stub-connected high-impedance dipole antenna, with a designed antenna resistance of 580 Ω. The proposed antenna topology realizes circuit functionalities of impedance transform, impedance matching, harmonic reaction, and dc blocking while maintaining a high antenna radiation efficiency. Lossy circuit components between the antenna radiator and the bridge diode can be eliminated for a highly efficient rectification. In experimental investigations, the measured rectification efficiency of the 5.8-GHz band rectifier is 92.8% at an input power of 1 W, and the estimated antenna radiation efficiency from the measured antenna gain is 96.9%, including loss due to circuit functionalities and interconnection. With lesser additional losses, the proposed antenna can be integrated with circuit functionalities to achieve a highly efficient rectenna. The measured rectification efficiency is almost the same as the fundamental limitation restricted by the rectifier diodes' performance.

Analytic assessment of the power system frequency security

Recently, with the increased intermittent renewable energy penetration, many power grids have been incorporated into a large-scale long-distance UHV AC–DC hybrid system. In the actual grid, power disturbances, such as DC blocking faults and trip-off of wind turbines, often occur, resulting in power shortages and large frequency fluctuations. However, the existing approaches to assess the system frequency security are not reliable. This paper proposes an analytic formula for the system frequency response based on a generic system frequency-response (SFR) model, which can be applied to modern large-scale power systems. First, a generic SFR model with a reasonable structure is designed according to the parameter determination strategy. Second, according to the transfer function in the model, the time-domain analytic formula of the frequency response is obtained by realizing the inverse Laplace transform. Moreover, four main indexes are established to represent the characteristics of the frequency dynamic process in different periods, and these indexes are qualitatively and quantitatively analysed. Finally, the New England 10-unit 39-bus power system and East China Power Grid are considered to demonstrate the key features of the proposed method. The results show that the proposed analytic assessment method can be effectively adopted in several applications.

Control of the spatial distribution of ion flux in dual inductively coupled plasmas

The effects of external discharge parameters (applied RF power, operating pressure, and gas flow rate) on ion flux uniformity are investigated in a dual inductively coupled plasma. The ion fluxes and electron temperatures are measured using a Langmuir probe floated by a DC blocking capacitor based on the floating harmonic method. The RF power applied to the top antenna focuses on the total ion flux control throughout the chamber, while the power introduced to the bottom antenna can control the ion flux uniformity in the diffusion chamber. At high pressures, the local electron heating in the vicinity of the bottom antennas results in local maximum ionization, thereby increasing the ion flux near the chamber wall. Furthermore, the ion flux uniformity also can be affected by the gas flow rate and pressure because they are associated with the gas residence time and the electron heating region. A physical understanding of the effects of external discharge parameters on plasma uniformity is useful for optimizing plasma processes.

Fuzzy self-tuning PID control of MC3 LLC resonant LED drivers

An MC3 LLC resonant light-emitting diode (LED) driver is a multi-channel constant current (MC3) output solution based on LLC resonance. Through an effective combination of multiple transformers and a DC block capacitor, this driver allows constant current outputs in multiple channels when the LED channels are unbalanced. This study considers a fuzzy self-tuning proportional integral derivative (PID) control strategy that allows for the self-tuning of PID parameters according to fuzzy inference rules designed using the relationship between the current gain and the switching frequency. Thus, when LED channels are unbalanced, the system allows a constant current output for each of the channels and controls the input voltage disturbances well. Simulation and experimental verifications are carried out, and a 20 W 4-channel constant current power supply design based on LLC resonance is obtained for the LED driver. This realizes soft-switching of the switching device, which reduces system loss and improves system efficiency. Moreover, the adjustment time of the proposed method is half that of fixed-parameter control methods, and the overshoot of the proposed method is smaller than that of fixed-parameter control methods. When compared with PID controllers with fixed parameters, the proposed method is more robust. When a system is disturbed, it recovers faster and has a smaller range of current fluctuation with the proposed method.

Analytical Expression on Transient Overvoltage Peak Value of Converter Bus Caused by DC Faults

This letter proposes an analytical expression on transient overvoltage peak value caused by DC blocking (DCB) and commutation failure (CF). The proposed method can obtain the transient overvoltage risk without modeling the complex AC/DC hybrid system. The method only requires the equivalent parameters of the AC system and the operation parameters of the DC system to effectively calculate the overvoltage without using the dynamic simulation software. The simulation results verify the effectiveness and correctness of the proposed method.

Upgrades to the ion cyclotron emission diagnostic on the DIII-D tokamak.

The ion cyclotron emission diagnostic on the DIII-D tokamak comprises seven single-turn loops that measure high-frequency (1-100MHz) magnetic field fluctuations that are often excited by energetic particles in the plasma. The raw voltage signals induced in the loops in response to these fluctuations travel through a series of cables, isolation transformer DC blocks, low-pass filters, and finally a digitizer before being analyzed in frequency space. The diagnostic has been recently upgraded, most notably to include four additional graphite tile loops and a new eight-channel digitizer. The previous three loops are all on the low-field side of the tokamak. The measurement capabilities of the system have been expanded by the addition of a new horizontally oriented loop on the low-field side, an additional toroidal loop on the low-field side, and two toroidal loops on the high-field side. These loops will be used to provide approximate mode polarization, improved toroidal mode number calculations, and information on modes in inward-shifted plasmas, respectively.

Generalized design of a versatile tri‐frequency Wilkinson power divider

This article presents the design, conceptualization, and validation of a generalized architecture for a Wilkinson Power Divider (WPD). The proposed design strategy highlights the versatility of incorporating a broad variety of dual-band impedance transformers as a part of the WPD, thereby extending its range of applications. As an example, a DC blocking variant of the proposed WPD has also been designed for demonstration. Simple closed-form design equations have been developed and validated with classical examples and case studies. Finally, two prototypes- one ordinary and another DC blocking variant have been fabricated on RO4350 (ɛr = 3.6) substrate and measured. The measurement results are well in accordance with the simulations, thereby validating the proposed design theory.

Reconfigurable broadband printed monopole antenna for portable smart IoT applications

SummaryThe proposed work presents a design of a smart printed monopole antenna separated from a Hexagonal Matching Load (HML) with an air gap. The patch is fed by a coplanar waveguide, while the HML is connected to the ground plane through two pin diodes to realize antenna reconfiguration through controlling the surface current motion. The antenna structure is mounted on FR‐4 epoxy substrate with size of 23 mm × 30 mm to fit the portable devices. After running four different switching scenarios, an observable change in the antenna performance is demonstrated. The proposed antenna provides a gain of 3.1 dBi at 2.45 GHz when the two diodes are switched ON. However, the antenna gain is changed to 1.6 dBi when the two diodes are set OFF. It is demonstrated that the proposed technique shows an effective approach to control the antenna performance without the need for DC blocking capacitor for RF choke. Nevertheless, the Specific Absorption Rate (SAR) effects are evaluated with respect to the human head tissues for all considered scenarios. Finally, the antenna radiation leakages to the human body are also tested numerically and experimentally for validation.

Fixed Frequency Beam-Scanning HMSIW-Based Leaky-Wave Antenna Composed of Circular Slots in V-Shape Configuration

A new reconfigurable slotted antenna is presented in this manuscript. The proposed antenna is realized on a half-mode substrate integrated waveguide (HMSIW). The beam-steering is achieved using embedded varactor diodes in circular cells. Sweeping the bias voltage causes variations of the phase constant, which leads to the fixed frequency beam-scanning. Each reconfigurable cell includes a circular slot at the top plate and varactor switch, DC block, and RF block at the backside of the structure. The operating frequency is chosen as 28.5 GHz in the support of the upcoming 5G mm-wave communications systems. The proposed antenna beam scans 29° of space by switching among different states at 28.5 GHz. The length, width, and height of the antenna are 67 mm, 48 mm, and 0.32 mm, respectively. The proposed antenna’s main novelties are compactness and electronic beam-scanning capability using a single switch per cell. The measured peak realized gain and sidelobe level (SLL) at 28.5 GHz are 8.2 ± 0.6 dBi and 5 dB, respectively. While the impedance bandwidth of the proposed antenna is 1.5 GHz. A good agreement between measured and simulated results is observed. The discrepancies are investigated through a sensitivity analysis. Fixed frequency beam-scanning capability, compactness, simplicity of the assembly, backward radiation, and slight gain variation of the proposed antenna make it a suitable candidate for blind-spot monitoring and 5G vehicle to everything (V2X) communications.

A Novel Suppression Method for Grounding Transformer Against Earth Current From Urban Rail Transit

Earth current generated by the operation of urban rail transit can enter into the neutral point of grounding transformer, which will result in the deterioration of transformer operation performance and cause electrical safety problems. In this article, the neutral current for 220 kV transformers has been measured in the real power system, the characteristics of dc and harmonic current are analyzed, and a novel suppression method for the dc and harmonic current simultaneously combining an active converter with a dc blocking capacitor is proposed, which solves not only the traditional dc bias problem but also the intrusion of the harmonic current from urban rail transit. The active converter is designed to compensate harmonic voltage to suppress harmonic current, and the capacitor provides blocking for the dc current. The protection scheme in case of the high fault current of the neutral point is presented. The improved control method is designed to control the neutral current and adjust the fundamental impedance for the requirements of relay protection. The effectiveness of the proposed method is verified by the digital simulations and the laboratory experiments based on the field working conditions, and the results demonstrate the satisfying performances.

Novel Multifunctional Dual-Band Coupled-Line Coupler With Reuse of Low-Frequency Trans-Directional and High-Frequency Contra-Directional Functions

In this brief, for the first time, a novel multifunctional dual-band coupled-line (CL) coupler with reuse of low-frequency trans-directional (TRD) and high-frequency contra-directional (CTD) functions is presented. It is composed of three cascaded CLs with an overall electrical length of 90° and four shunt capacitors, which achieves a compact circuit configuration in microstrip implementation. Since capacitors are shunted between the CLs, the coupler is easy to realize tight coupling with miniaturized size and has an inherent feature of dc blocking. Moreover, different power ratios can be realized over two designated frequencies. Frequency conversion leads to the location change of the isolation port, which eventually leads to the reuse of the circuit and port function expansion of the coupler. Good agreements between the simulated and measured results verify the design theory.

Systematic Optimization of Multiple-Output DC Distribution Architectures

Complex electronic systems often require a power distribution architecture that provides multiple, separate voltage domains for various subsystem loads, such as microprocessor cores, interface, memory, analog, and radio frequency components. The multiple point-of-load regulated voltages are typically generated using multiple dc–dc converters operating from a single input dc voltage. This article introduces the permutation-graph (PG) method to systematically optimize multiple-voltage-domain dc distribution architectures using commercially available or custom single-input single-output dc–dc converter building blocks. The PG method enumerates possible converter arrangements and selects the converter blocks to achieve the best system figure of merit (FOM) in terms of system efficiency, size, cost, power density, or a combination of these metrics. In representative case study examples, considering a system operating from 48-V input dc voltage and requiring seven regulated point-of-load dc voltages {1, 1.3, 3.3, 5, 12, 24, and 40} V, it is shown how the proposed approach can improve the system FOM by more than 50% compared with solutions offered by a commercially available tool using standard dc–dc blocks. It is also shown how the inclusion of custom dc–dc blocks results in a different optimal arrangement, which yields further system FOM improvements. The approach is validated by experimental results on two 120-W system prototypes, providing five regulated dc voltages {1, 3.3, 5, 12, and 24} V from a 48-V dc bus.

High Output Power SOA Assisted Extended Reach EADFB Laser (AXEL) TOSA for 400-Gbit/s 40-km Fiber-Amplifier-Less Transmission

An AXEL sub-assembly and a 4-channel AXEL TOSA were designed and fabricated. The sub-assembly with a width of less than 0.65 mm was needed to make the width of TOSA applicable to QSFP-DD transceiver. On the other hand, the wire that connects between the terminator and the DC block capacitor must be 0.5 mm or longer to obtain 3-dB bandwidth of over 40 GHz which is enough for 50-Gbaud operation. To become that wire length 0.5 mm or more on the narrow sub-assembly, the AXEL chip was placed between the RF circuit board integrated with the terminator and the DC block capacitor. As a result, the AXEL sub-assembly with a width of only 0.65 mm and with a 3-dB bandwidth of more than 40 GHz was realized. Based on the designed sub-assembly, the 4-channel AXEL TOSA was fabricated. Size of the TOSA is only 18.2 × 6.2 × 5.4 mm (which is suitable for a QSFP-DD transceiver). Optical-modulation amplitudes (OMAs) of the fabricated TOSA exceed +4.7 dBm for all channels. 40-km SMF fiber-amplifier-less transmission of 4-channel × 100-Gbit/s/λ signals was successfully demonstrated by using the fabricated 4-channel AXEL TOSA, 4-channel APD ROSA, and a commercially available DSP. Loss budgets exceed 18 dB for all channels.

Fluoride-ion Conductivity Analysis of Yb-F-S Multiple-anion Compounds

Abstract The mixed-anion fluorosulfide Yb3F4S2 was examined as a solid electrolyte for all-solid-state fluoride-ion batteries. The synthesized Yb3F4S2 compound by solid-state reaction under vacuum contained Yb2O2S impurities, which originated from the starting materials. The conduction properties of Yb3F4S2 are discussed herein based on the electrochemical impedance and DC blocking measurements, which indicate mixed ionic and electrical conduction of Yb3F4S2. Yb L3-edge X-ray absorption measurements demonstrate the mixed valence state of ytterbium ion.

Multichannel Biphasic Muscle Stimulation System for Post Stroke Rehabilitation

We present biphasic stimulator electronics developed for a wearable functional electrical stimulation system. The reported stimulator electronics consist of a twenty four channel biphasic stimulator. The stimulator circuitry is physically smaller per channel and offers a greater degree of control over stimulation parameters than existing functional electrical stimulator systems. The design achieves this by using, off the shelf multichannel high voltage switch integrated circuits combined with discrete current limiting and dc blocking circuitry for the frontend, and field programmable gate array based logic to manage pulse timing. The system has been tested on both healthy adults and those with reduced upper limb function following a stroke. Initial testing on healthy users has shown the stimulator can reliably generate specific target gestures such as palm opening or pointing with an average accuracy of better than 4 degrees across all gestures. Tests on stroke survivors produced some movement but this was limited by the mechanical movement available in those users’ hands.

Dynamic Var Reserve Assessment in Multi-Infeed LCC-HVDC Networks

Recently, multi-infeed line-commutated converter-based high-voltage direct currents (LCC-HVDCs) represent one of the most attractive ways to accommodate large-scale power transfer in main load centers. However, this approach deteriorates the dynamic var reserve (DVR) in the receiving-end power grid, especially in scenarios with heavy loads. If the system does not reserve sufficient dynamic var in advance, a severe voltage dip may occur and further lead to consecutive commutation failures, ultimately resulting in DC blocking and voltage collapse. To address the voltage/var control challenges, a robust DVR assessment method is proposed in this paper. This method is used to determine both the inductive and capacitive DVR and prevent cascading failures. First, continuous dynamic algebraic equations are formulated using a piecewise functional block approximation method for efficient application of second-order trajectory sensitivity analysis (SOTSA). Next, a robust DVR assessment model is formulated, and the corresponding computational strategy is introduced to effectively and accurately solve the large-scale problem. Finally, in numerical simulations, the computational efficiency and accuracy of the proposed method are verified using a simple system and operational data from a real system in the Eastern China Power Grid.

Dynamic Var Reserve-Constrained Coordinated Scheduling of LCC-HVDC Receiving-End System Considering Contingencies and Wind Uncertainties

Sufficient dynamic Var reserve (DVR) can efficiently enhance the immunity against continuous commutation failures (CCF) to avoid DC blocking and further security accidents in the line-commutated converter (LCC) based HVDC receiving-end power system. This article proposes the problem formulation and efficient solution algorithm for the DVR-constrained coordinated scheduling considering contingencies and wind uncertainties. The DVR sufficiency is proposed for the post-contingency CCF immunity in scheduling problems, which combines the voltage sensitivity-based DVR capacity calculation and the off-line DVR requirement tests. HVDC transmission and W/Var sources are coordinately scheduled to accommodate contingencies and wind uncertainties and to improve the operational economy. The reduced event-based algorithm (REA) is developed to subdivide the complex scheduling problem and reduce the considered constraints for efficient calculation. Case studies demonstrate the guaranteed DVR sufficiency, the improved economy, and the enhanced computational efficiency of the proposed methods.

Frequency reconfigurable dual-band filtenna

In this paper, a compact size frequency reconfigurable dual-band filtenna (Filter + Antenna) is proposed for WLAN, WiMaX and C-band applications. The filtenna is designed by a switchable SRR (i.e. Two switches are used in inner and outer split rings) band pass filter (BPF) and a CSRR based antenna. In the process of filtenna design synthesis process is used. The advantages of the reconfigurable filtenna structure are to reduce undesired frequency interference to the system and controllable bandwidth. The antenna is resonated at three frequencies with the bandwidth @ S11 = −10 dB i.e. 2.4 GHz (2.05–2.86 GHz), 3.46 GHz (3.4–3.55 GHz) & 4.36 GHz (4.19–4.65 GHz), whereas the filter is resonated at two frequencies i.e. 2.42 GHz (2.36–2.48 GHz) and 4.41 GHz (4.16–4.77 GHz), When both the designs (i.e. antenna & filter) are combined (i.e. Filtenna), then the joint structure allow only two resonance frequencies i.e. 2.42 GHz (2.37–2.47 GHz) and 4.41 GHz (4.24–4.69 GHz) to pass through and 3.46 GHz frequency is rejected. The rejection is occurred due to dual band filter. Due to the filteration the in band gains are 2.14 dBi and 3.39 dBi, whereas the out of band gain is −4.23 dBi, which justify its rejection behavior and does not effect system performances. Furthermore, the resonances of the resonating structures (SRR and CSRR) are justified by the lump components of the structure.In order to make the filtenna operation re-configurable, PIN diodes with DC block capacitors are connected in the inner and outer split rings of the SRR band pass filter and appropriate dc bias is applied across the PIN diodes to perform either ‘ON’ or ‘OFF’ operation. When inner ring PIN diode is ‘ON’ and outer one is ‘OFF’ then filtenna operates at 2.58 GHz (2.5–2.67 GHz). Similarly, when outer ring PIN diode is ‘ON’ and inner one is ‘OFF’ then the frequency of operation is shifted to 4.45 GHz (4.26–4.85 GHz) band. The realized filtenna at each resonance frequency exhibits bi-directional radiation pattern in E-plane and omni-directional in the H-plane. The simulated performances of the proposed filtenna is verified using the experimental results.

Board-Level Ku-Band Power Amplifier: Design and Challenges

ABSTRACT This paper describes the challenges in the design of board-level Ku-band power amplifier (PA) using the hybrid-MIC technology. The selection of laminates, connectors, cables and RF components, such as DC feed and DC block, is examined from the perspective of Ku-band PA designers. Other key challenges, such as die mounting and wire bonding, are also discussed. Die mounting and wire bonding are critical phenomena and they have a great impact on the working of PA at high frequencies. After several trials, successful die mounting has been achieved and a methodology for reliable die mounting and wire bonding has been proposed. With the help of investigation done for the design of PA at the high operating frequency, a first board-level power amplifier at 17 GHz has been designed using a 250 nm bare die device with a 400 MHz frequency band.

Bi‐level optimised emergency load/generator shedding strategy for AC/DC hybrid system following DC blocking

This study presents a bi-level optimised emergency control strategy, including load and generators shedding following DC blocking. Due to different constraints for networks with different voltages, a bi-level optimised model spanning from the high voltages networks to the lower voltages is put forward. For the higher voltage level network, the overload area is identified and the seriousness of the overload is classified after DC blocking with the help of wide-area measurement systems. Then, the objective function is built with the minimum total amount of load shedding and generator tripping to be solved by improved particle swarm optimisation (IPSO), considering the constraints of frequency and voltage stability, respectively. For the low voltage level networks, the least cost as the objective function with the constraints of load shedding and generator tripping strategy based on the analytic hierarchy process-fuzzy comprehensive evaluation method. The modified 10-machine 39-bus system with HVDC lines is used as the test system. The simulation results demonstrated that the proposed strategy can give good control performance with consideration of different optimisation constraints following the DC line blocking.