We have newly developed (110)-surface strained-silicon-on-insulator (SOI) n-and p-MOSFETs on (110)-surface relaxed-SiGe-on-insulator substrates with the Ge content of 25%, fabricated by applying the Ge condensation technique to SiGe layers grown on (110)-surface SOI wafers. We have demonstrated that the electron and the hole mobility enhancement of (110)-surface strained-SOI devices amounts to 23% and 50%, respectively, against the mobilities of (110)-surface unstrained MOSFETs. As a result, the electron and the hole mobility ratios of (110)-surface strained-SOI MOSFETs to the universal mobility of (100)-surface bulk-MOSFETs increase up to 81% and 203%, respectively. Therefore, the current drive imbalance between n-and p-MOS can be reduced. Moreover, both the electron and the hole mobilities of the (110)-surface strained-SOIs strongly depend on the drain current flow direction, which is qualitatively explained by the anisotropic effective mass characteristics of the carriers on a (110)-surface Si. As a result, the (110)-surface strained-SOI technology with optimization of the current flow directions of nand p-MOS is promising for realizing higher speed scaled CMOS.

In this paper, design of a primary resonant tank for resonant converters compensation in an Inductive Power Transfer (IPT) system is analyzed and some criteria for selecting its reactive components are established. The optimization goal is to maximize the transferred power, while limiting the number of compensation components to no more than two reactive components. Additionally, VA limits of the inverter are taken into consideration. Current track requirements are relaxed and instead of constant track current, small track load dependency is allowed, which is acceptable in practice. The theoretical investigations and calculations, as well as simulations for two important practical cases considered are presented in the paper. It is shown that LC compensation structure allows maximum delivered power, but not for the case when the impedances of compensation elements are the same as it would be expected. Additionally, the impact of converter ratings and allowed load dependent track current variation on the optimal design are investigated through the set of numerical simulations.

Power grids worldwide are undergoing a revolutionary transition as so-called "smart grids" that exploit renewable energy sources are emerging. As such distributed power generation requires networked control, future power systems will become more exposed to cyber attacks. This paper discusses cyber security challenges for a future power grid. It highlights deficiencies and shortcomings of existing power devices and identifies areas of urgent need particularly on the software side to establish security as a first-class paradigm in cyber-physical control systems. Such actions are urgent as a cyber compromise of power systems can lead to physical outages or even damaged power devices. Hence, security and fault resilience of power as a utility must be a prime objective for power grids. Security compromises should be contained to only present themselves as localized faults and to prevent faults from cascading. We expose these challenges in detail and also highlight novel opportunities for cyber security specifically for a smarter power grid, which can be generalized to the wider domain of cyber-physical control systems.

T his article deals with shunt-type active power filters (APFs) and shunt compensation. Some traditional methods of generating reference currents are reviewed, and a fast technique using a form of hybrid genetic algorithm (hGA) is discussed. The proposed method exploits an artificial neural network (ANN)-based proportional integral (PI) controller to generate an initial estimate of the reference current followed by refinement of the same through hGA. Investigations using MATLAB-/ Simulink-based simulations with supporting results from an experimental prototype confirm the usefulness of the proposed technique. In addition to the problems of unbalance and reactive power loading, the power system distribution network is also facing challenges because of harmonic loading in the system. This is due to the increasing use of nonlinear loads, namely adjustable speed drives (ASDs), arc furnaces, switched mode power supply (SMPS), uninterruptible power supply (UPS) systems, etc. Harmonics not only increases the losses in the system but also produces unwanted disturbance to the communication network, voltage, current stress, etc. This has motivated the introduction of an APF for improving the power quality [1]-[50]. Shunt APF is used to eliminate the current harmonics, whereas series compensation does the same job for voltage harmonics. Three major areas are to be considered for a shunt-type APF. First is to estimate the compensating current [1]-[35], [46], second is to look for possible power-converter topologies [1], [2], [42]-[45], [50] that may be used, and third is to explore pulse-modulation techniques that may actually generate and track the corresponding reference currents [1], [36]-[41]. This work deals with referencegeneration techniques. A standard pulsewidth modulation (PWM-type) voltage source inverter (VSI) is used. Figure 1 shows a schematic diagram of the controller. Modern techniques based on soft computing are covered in this

Recently, renewable wind energy is enjoying a rapid growth globally to become an important green electricity source to replace polluting and exhausting fossil fuel. However, with wind being an uncontrollable resource and the nature of distributed wind induction generators, integrating a large-scale wind-farm into a power system poses challenges, particularly in a weak power system. In the paper, the impact of STATCOM to facilitate the integration of a large wind farm into a weak power system is studied. First, an actual weak power system with two nearby large wind farms is introduced. Based on the field SCADA data analysis, the power quality issues are highlighted and a centralized STATCOM is proposed to solve them, particularly the short-term (seconds to minutes) voltage fluctuations. Second, a model of the system, wind farm and STATCOM for steady-state and dynamic impact study is presented, and the model is validated by comparing with the actual field data. Using simulated PV and QV curves, voltage control and stability issues are analyzed, and the size and location of STATCOM are assessed. Finally, a STATCOM control strategy for voltage fluctuation suppression is presented and dynamic simulations verify the performance of proposed STATCOM and its control strategy.

This paper presents the performance of capacitorcharging-type inverters. Both single-and three-phase inverters are considered. A simple technique to design the L-C elements of such an inverter is introduced. The switching devices are operated in the discontinuous conduction mode to reduce the size of the inductor and also for better dynamic performance. The inverter is simulated in PSPICE. An experimental prototype is produced to verify the results from simulation. Experimentations have been conducted for single-phase and three-phase systems. The inverter is found to operate satisfactorily for various types of load including unbalanced load. Index Terms-Controlled capacitor charging (CCC), discontinuous conduction mode (DCM), inverters, zero-current switching (ZCS).

This paper presents a new feedback control strategy for balancing individual dc capacitor voltages in a three-phase cascade multilevel inverter-based static synchronous compensator. The design of the control strategy is based on the detailed smallsignal model. The key part of the proposed controller is a compensator to cancel the variation parts in the model. The controller can balance individual dc capacitor voltages when H-bridges run with different switching patterns and have parameter variations. It has two advantages: 1) the controller can work well in all operation modes (the capacitive mode, the inductive mode, and the standby mode) and 2) the impact of the individual dc voltage controller on the voltage quality is small. Simulation results and experimental results verify the performance of the controller.

This paper presents a new control scheme for a parallel hybrid active filter system intended for harmonic compensation of large nonlinear loads up to 50 MVA, to meet IEEE 519 recommended harmonic standards. The active filter is small rated, 2%-3% of load kilovoltampere rating. The control scheme is based on the concept of synthesizing a dynamically variable inductance, and its usefulness is demonstrated for an active filtering application. A synchronous reference frame (SRF) controller implements the dynamically varying negative or positive inductance by generating active filter inverter voltage commands. This variable inductance controller parallel hybrid active filter system can selectively synthesize multiple "active inductances" at dominant harmonic frequencies without affecting passive filter impedances at all other frequencies. This controller also provides a "current limiting" function to prevent passive filter overloading under ambient harmonic loads and/or supply voltage distortions. Three implementation variations of a parallel hybrid active filter system are presented. This paper also proposes the use of power factor correction capacitors as low cost passive filters for a parallel hybrid active filter system, which are controlled to provide either single or multiple tuned harmonic sinks and to increase cost effectiveness for high power applications. Simulation results with small rated pulsewidth modulated (PWM) and square-wave active filter inverters validate the proposed variable inductance controller operation for mistuned passive filters, to provide single and multiple frequency tuning to achieve harmonic compensation of a 325 kVA harmonic load under supply voltage harmonics and ambient harmonic loads.

This paper presents a new control scheme for a hybrid parallel active filter (HPAF) system intended for highpower applications-up to 100-MW nonlinear loads-to meet IEEE 519 recommended harmonic standards. The active filter inverter is realized with small-rated (1%-2% of the load rating) square-wave inverters operating at the dominant harmonic frequencies. The proposed system achieves harmonic isolation at desired dominant harmonic frequencies, such as the fifth and seventh, even in the presence of supply voltage harmonic distortions. A novel method of active filter inverter dc-bus control, as proposed here, achieves power balancing by exchanging energy at the fundamental frequency and at the dominant harmonic frequency (such as the fifth). The proposed square-wave inverterbased HPAF system provides improved filtering characteristics as compared to the conventional passive filter and is expected to be cost effective for high-power nonlinear loads compared to the conventional passive filter or other active filtering solutions. The concept of harmonic isolation at dominant harmonic frequencies by square-wave inverters with the proposed control scheme is validated by simulation results.

This paper presents laboratory test results of the Dominant Harmonic Active Filter (DHAF) prototype. The DHAF system achieves harmonic isolation at the dominant harmonics using square-wave active filter inverters. The key advantages of the DHAF system are the low rating and low bandwidth requirements of the active filter inverter. Such characteristics allow cost-effective and viable applications of the DHAF system to mitigate harmonic problems for high-power nonlinear loads (10-100 MW and above). Several practical situations, including source-sink resonance, ambient harmonic interferences, and unbalanced grid voltages are applied to the DHAF prototype to validate its performance. The operation principles of the DHAF system and the synchronous-reference-frame-based controller are discussed to explain how harmonic isolation at the dominant harmonics is accomplished. A design example of the DHAF system for a 20-MVA rectifier load at an industrial site is also given to illustrate its application.

Voltage sags have become one of the most important power quality concerns in recent years. According to survey results across the U.S., voltage sags and short-duration power outages account for 92% of power quality problems encountered by industrial customers. Voltage sags often cause undervoltage faults in various sensitive loads and subsequently interrupt the manufacturing processes. Such interruptions often inflict severe losses for industries. In Taiwan, R.O.C., most high-tech manufacturers use uninterruptible power supplies to avoid interruptions, but the cost effectiveness of such an approach remains unclear. As the utility grid continues to improve the reliability of electric power, the inverter-based voltage sag compensator has become a viable solution to prevent production interruptions resulting from voltage sags. The existing sag compensation systems accomplish a fast response within a small fraction of a fundamental cycle by tracking the line voltages closely, and switch on the compensator whenever the voltage waveforms deviate from the normal values. However, the utility voltages often contain transient spikes with amplitudes up to 200% resulting from switching of power-factor-correction capacitors, circuit breakers switchings, lightning strikes, and so on. Such transient disturbances may trigger the sag compensator into operation if its controller is very sensitive. The switching frequency of the sag compensator inverter is inadequate to compensate the narrow pulses of voltage spikes. Furthermore, the power semiconductor devices (like insulated gate bipolar transistors)of the inverter may also be damaged due to overvoltage by the surges. In this paper, a brief overview of power quality issues of a high-tech industry park in Taiwan will be provided to validate the need for ride-through technologies. A synchronous-reference-frame-based controller for the inverter-based voltage sag compensator is also presented. A sag detection mechanism is included in the controller for correct and prompt identification of voltage sags. Disturbances like voltage spikes are attenuated to avoid any false triggering of the compensator. The overall system responds to voltage sags and restores the voltage back to balanced 1.0 pu for critical loads within one-eighth to one-fourth of a cycle, which meet the requirement of industry standards like the SEMI-F47 standard. Simulation and laboratory test results are presented to verify the functionality of the proposed system.

A synchronous-reference-frame (SRF)-based controller for the dominant harmonic active filter (DHAF) system has already been proposed by the authors.The SRF controller is designed to achieve harmonic isolation at the dominant harmonic frequencies (such as at the 5th and/or 7th) between the supply and load. This allows implementation of the DHAF system by square-wave inverters switching at the 5th or 7th harmonic frequency. Compared to conventional active filter systems which require high-switching-frequency pulsewidth modulation inverters, the square-wave-inverter-based DHAF system provides a viable and cost-effective solution to achieve harmonic isolation for high-power nonlinear loads (10 MW and above) or cluster of nonlinear loads, to meet the IEEE 519 recommended harmonic standard. In this paper, a new feedforward command of the SRF controller is proposed which provides better dynamic performance. The improved feedforward command of the SRF controller can suppress any system resonances at the dominant harmonic frequencies and meet IEEE 519 harmonic current limits. Experimental results are presented to validate the effectiveness of the SRF controller and the DHAF system.

A discrete model of the IEC 61000-4-15 flickermeter is developed for use with the Matlab-Simulink simulation software package. The discrete model is a faithful reproduction of a flickermeter defined by the IEC Standard; it duplicates the functional blocks described by the standard and operates in the same way as the standardized instrument to assure complete fidelity of results. The model is intended to be used within larger simulations that contain discrete model blocks, either alone or in combination with the Simulink SimPowerSystems blockset, to provide direct quantification of flicker. The model is fully developed, and all model parameters are provided for use with 60-Hz systems. A discrete calibrator is described that duplicates the test waveforms described by the IEC Standard.

We have experimentally proven the Cerenkov generation of optical phonons by drifting electrons in a semiconductor. We observe an instability of the polar optical phonons in nanoscale semiconductors that occurs when electrons are accelerated to very high velocities by intense electric fields. The instability is observed when the electron drift velocity is larger than the phase velocity of optical phonons and rather resembles a ''sonic boom'' for optical phonons. The effect is demonstrated in p-in semiconductor nanostructures by using subpicosecond Raman spectroscopy.

This study addresses the timely issues of modelling, and defining selection criteria for, a solid-state fault isolation device (FID) intended for use in power electronics-based distribution systems (PEDS). This work subsequently derives the FID parameters by mapping the characteristics of a conventional medium-voltage distribution system onto that of the PEDS envisioned under a new multiuniversity Engineering Research Centre. When conventional circuit breakers are used in distribution systems, they have a relatively long clearing time, causing the voltage to collapse for a significant time. A semiconductor circuit breaker, however, is expected to be able to switch fast enough to keep a voltage disturbance within acceptable limits. The main focus of this study is to address the operational issues of the interaction between the power electronic converters and the solid-state FID. The utilisation of rate of current decrease (di/dt) control during turn-off in conjunction with passive clamping devices to manage the overvoltage that results from very fast circuit breaker operation is introduced. In contrast to a simple conventional RC-snubber circuit, the proposed overvoltage management avoids high leakage current, which is the undesirable drawback of RC-snubber circuits. The presented prototype is experimentally verified with low and medium-voltage test circuits. List of abbreviations AFU active front-end unit DESD distributed energy-storage devices DRER distributed renewable energy resources IGBT insulated gate bipolar transistor FID fault isolation device LTI linear time-invariant MOV metal oxide varistor PEBB power electronics building block PEDS power electronics-based distribution system PWM pulse-width modulation RTDS real-time digital simulator SST solid-state transformer TRV transient recovery voltage VCB vacuum circuit breaker VSI voltage-source inverter VVS variable voltage source

While conventional mobile substations are used to bypass the whole substation in case of loss or maintenance of power transformers, Active Mobile Substations (AMS) can be used both in normal conditions as a power router and in contingencies as a recovery transformer. The AMS is a mobile substation with integrated power electronics. By controlling its throughput power, it can be connected across different transformers of the grid. This paper explores transmission-level active mobile substations that provide backup in case of power transformer failure or forced reduced operation scenarios in addition to power flow control for seasonal renewable energy transmission. The AMS must be designed to operate satisfactorily under typical fault and unbalanced conditions. In this paper, component design considerations in development of the AMS under unbalanced operating condition will be provided, and a new control strategy is proposed to control AMS under unbalanced operating conditions when component design is not sufficient to prevent overcurrent and trips. Detailed PSCAD simulation for the proposed control scheme is performed and results are presented. Experimental results are also shown to verify the proposed control method under unbalanced operating conditions.