Hybrid MMC with Low Voltage Operations and DC Fault Ride-through Capabilities Based on Auxiliary Full-bridge Converter

The hybrid modular multilevel converter(MMC)based on half-bridge sub-modules(HBSMs)and full-bridge submodules(FBSMs)can operate at low DC voltages and clear DC side fault currents.However,the costs and power losses are much higher in hybrid converters.An auxiliary full-bridge converter(AFC)is designed to reconstruct the converter structure in the arm level,and the HBSMs output capacitor voltage through the AFC can attain similar capabilities to hybrid MMCs.The operational principle of the auxiliary full-bridge converter is discussed,and the low voltage operation and non-blocking fault ride through control are verified in a two-terminal DC network simulation.Through economic analysis,the power loss of the AFC is similar to a HBSM MMC but the total investment is lower than a hybrid MMC,making the AFC a promising solution to improve the existing HBSM converter with more controllability.

An Approach to the Ultimate Goal of Power Grid Development—Constant Voltage Operation

The concept of constant voltage operation is proposed in this paper and it is demonstrated that the ultimate goal of power grid development is constant voltage operation.The topic is expanded into three aspects:the benefits of constant voltage operation,the technology and equipment to realize constant voltage operation,and the reactive power compensation capacity needed for constant voltage operation.The benefits of constant voltage operation have four aspects:1)Constant voltage operation is the ultimate presentation of the strong smart grid;2)Constant voltage operation can resist grid disturbances in the most powerful manner and greatly improve the power system stability;3)Constant voltage operation can effectively eliminate the voltage fluctuation problem involved with the integration of large scale renewable energy;4)Constant voltage operation can minimize the grid power loss.The means to realize constant voltage operation is primarily the modular multilevel converter based STATCOM(MMC-STATCOM),which has encountered great acceptance during recent years.Simualtion verifications are run in a modified IEEE 300-bus system and the Pearl River Delta grid in PSS/E.The results indicate that constant voltage operation can greatly improve the stability of power systems and the capacity of installed MMC-STATCOMs is within an acceptable range.

Lowering the Operational Voltage of Single-Layer Polymer Electroluminescent Devices by Using CuO_x Modifying Indium-Tin Oxide Electrode

In this study it is demonstrated that oxygen-plasma-generated CuOx can enhance the holes injection from ITO anode into polymer layer in single-layer polymer EL devices. The possible reason for this enhancement is because the ITO anode modified with CuOx possesses much higher work function than pure ITO anode, which reduces the barrier for hole-injection and further lowers the operational voltage of the polymer EL devices. The work function shift is probable due to the oxygen-plasma-generated CuOx can store more releasable oxygen, and the releasable oxygen in turn changes the oxygen concentration just near ITO surface, which will shift the work function of ITO anode.

Low Gate Voltage Operated Multi-emitter-dot H^+ Ion-Sensitive Gated Lateral Bipolar Junction Transistor

A low gate voltage operated multi-emitter-dot gated lateral bipolar junction transistor （BJT） ion sensor is proposed. The proposed device is composed of an arrayed gated lateral BJT, which is driven in the metal-oxidesemiconductor field-effect transistor （MOSFET）-BJT hybrid operation mode. Further, it has multiple emitter dots linked to each other in parallel to improve ionic sensitivity. Using hydrogen ionic solutions as reference solutions, we conduct experiments in which we compare the sensitivity and threshold voltage of the multi-emitter-dot gated lateral BJT with that of the single-emitter-dot gated lateral BJT. The multi-emitter-dot gated lateral BJT not only shows increased sensitivity but, more importantly, the proposed device can be operated under very low gate voltage, whereas the conventional ion-sensitive field-effect transistors cannot. This special characteristic is significant for low power devices and for function devices in which the provision of a gate voltage is difficult.

A Hybrid Dielectric Ink Consisting of up to 50 wt% of TiO2 Nanoparticles in Polyvinyl Alcohol （PVA）

PVA （Polyvinyl Alcohol） is a water soluble organic dielectric, easily solution processed to fabricate films by spin coating, dip coating or inkjet printing. It has been used as a dielectric layer in OTFTs （organic thin film transistors）, and its dielectric constant is around 3.5-10. For OTFTs operating at lower voltage, it is desirable to increase the dielectric constant. Here, we report a technique to incorporate upto 50 wt% of TiO2 nanoparticles （15-25 nm） in PVA to increase its dielectric constant. Rutile phase of TiO2 is used, because of its higher dielectric constant （e = 114） compared to anatase phase （E = 31）. We have made inks containing 10 and 50 wt% （of PVA） TiO2 nanoparticles, which is stable upto six months. PVA-TiO2 dispersions and PVA （without TiO2） were spin coated on indium tin oxide coated polyethylene terephthalate substrate. Film structure was studied using SEM （scanning electron microscopy）. Absorption study of the films confirms presence of TiO2 nanoparticles. M-I-M capacitors were fabricated by thermally evaporating aluminium on top of the dielectric films. We observed enhancement in dielectric constant by a factor of 2 for PVA containing 50 wt% TiO2 in comparison to PVA＇s dielectric constant. There is no concomitant increase in the leakage current.

Voltage Security Operation Region Calculation Based on Improved Particle Swarm Optimization and Recursive Least Square Hybrid Algorithm

Large-scale voltage collapse incidences, which result in power outages over large regions and extensive economic losses, are presently common occurrences worldwide. To avoid voltage collapse and operate more safely and reliably, it is necessary to analyze the voltage security operation region(VSOR) of power systems, which has become a topic of increasing interest lately. In this paper, a novel improved particle swarm optimization and recursive least square(IPSO-RLS) hybrid algorithm is proposed to determine the VSOR of a power system. Also, stability analysis on the proposed algorithm is carried out by analyzing the errors and convergence accuracy of the obtained results. Firstly, the voltage stability and VSOR-surface of a power system are analyzed in this paper. Secondly, the two algorithms,namely IPSO and RLS algorithms, are studied individually.Based on this understanding, a novel IPSO-RLS hybrid algorithm is proposed to optimize the active and reactive power,and the voltage allowed to identify the VSOR-surface accurately. Finally, the proposed algorithm is validated by using a simulation case study on three wind farm regions of actual Hami Power Grid of China in DIg SILENT/Power Factory software.The error and accuracy of the obtained simulation results are analyzed and compared with those of the particle swarm optimization(PSO), IPSO and IPSO-RLS hybrid algorithms.

A low-voltage sense amplifier with two-stage operational amplifier clamping for flash memory

A low-voltage sense amplifier with reference current generator utilizing two-stage operational amplifier clamp structure for flash memory is presented in this paper,capable of operating with minimum supply voltage at1 V.A new reference current generation circuit composed of a reference cell and a two-stage operational amplifier clamping the drain pole of the reference cell is used to generate the reference current,which avoids the threshold limitation caused by current mirror transistor in the traditional sense amplifier.A novel reference voltage generation circuit using dummy bit-line structure without pull-down current is also adopted,which not only improves the sense window enhancing read precision but also saves power consumption.The sense amplifier was implemented in a flash realized in 90 run flash technology.Experimental results show the access time is 14.7 ns with power supply of 1.2 V and slow corner at 125℃.

Bosonic Operator Realization of Hamiltonian for a Superconducting QuantumInterference Device

Based on the appropriate bosonic phase operator diagonalized in the entangled state representation we construct the Hamiltonian operator model for a superconducting quantum interference device. The current operator and voltage operator equations are derived.

Promoting operating voltage to 2.3 V by a superconcentrated aqueous electrolyte in carbon-based supercapacitor

Aqueous supercapacitors(SCs)have attracted more and more attention for their safety,fast charge/discharge capability and ultra-long life.However,the application of aqueous SCs is limited by the low working voltage due to the narrow electrochemical stability window(ESW)of wate r.Herein,we report a new"water in salt"(WIS)electrolyte by dissolving potassium bis(fluorosulfonyl)amide(KFSI)in water with an ultra-high mass molar concentration of 37 mol/kg.The highly concentrated electrolyte can achieve a wide ESW of 2.8 V.The WIS electrolyte enables a safe carbon-based symmetrical supercapacitor to operate stably at 2.3 V with an ultra-long cycle life and excellent rate performance.The energy density reaches 20.5 Wh/kg at 2300 W/kg,and the capacity retention is 83.5%after 50,000 cycles at a current density of 5 A/g.This new electrolyte will be a promising candidate for future high-voltage aqueous supercapacitors.

Intrinsically ionic conductive nanofibrils for ultra-thin bio-memristor with low operating voltage

Memristors integrated with low operating voltage,good stability,and environmental benignity play an important role in data storage and logical circuit technology,but their fabrication still faces challenges.This study reports an ultra-thin bio-memristor based on pristine environmentfriendly silk nanofibrils(SNFs).The intrinsic ionic conductivity,combined with high dielectric performance and nanoscale thickness,lowers the operation voltage down to0.1-0.2 V,and enables stable switching and retention time over 180 times and 10^(5)s,respectively.Furthermore,the SNFbased memristor device in a crossbar array achieves stable memristive performance,and thus realizes the functions of memorizing image and logic operation.By carrying out variable-temperature electrical experiments and Kelvin probe force microscopy,the space charge-limited conduction mechanism is revealed.Integrating with low operating voltage,good stability,and ultra-thin thickness makes the SNF-based memristors excellent candidates in bioelectronics.

Transmission Line Distance Protection Under Current Transformer Saturation

Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current,operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-ahalf configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.