Low Voltage Solution Research Articles

Table of Contents and Foreword

This issue of the Journal of Integrated Circuits and Systems (JICS) features a very broad content, including papers on RF, AMS and digital design, presenting low voltage, low power and low noise solutions, improving the circuit robustness against attacks, proposing new approaches for video compression and dealing with reconfigurability, SAT solvers and energy harvesting. Six of these papers have been selected from the presentations given at SBCCI2010 (23rd Symposium on Integrated Circuits and Systems Design), which has been held in São Paulo, Brazil in 2010. Among the contributions presented at the Symposium, only a few best rated were selected by the JICS Editorial Board and have been invited to submit an extended version to the Journal. These papers have been reviewed by external experts and have been accepted for the special section on best SBCCI2010 papers. In addition to the best papers presented at the conference, three spontaneous submissions passed through the usual reviewing process and have been accepted as regular papers. We would like to thank the authors for their effort in preparing these high quality papers, as well as the reviewers for their help on paper selection, which guarantees the scientific level of this issue.We sincerely hope that JICS readers will enjoy these contributions.
 Marcelo Lubaszewski - JICS Editor-in-chief
 Marcelo Pavanello - JICS Co-Editor

Double Dose Reduction in the Equilibrium Phase of Chest-Pelvic CT With Low Tube Voltage and Forward-Projected Model-Based Iterative Reconstruction Solution.

ObjectivesThis study aimed to examine whether a new imaging method (80-kV forward-projected model-based iterative reconstruction solution [FIRST] protocol) that uses a combination of low tube voltage and FIRST can reduce radiation dose and contrast medium volume by comparing the quality of the resulting image with that of the image obtained by 120-kV adaptive iterative dose reduction 3D protocol in the equilibrium phase of chest-pelvic computed tomography (CT).Subjects and methodsTwenty-seven patients underwent CT by both protocols on different days. Two radiologists subjectively assessed image quality by scoring axial images for sharpness, contrast enhancement, noise, artifacts, and overall quality. The mean CT values, standard deviations, contrast-to-noise ratios, and signal-to-noise ratios in the liver, aorta, and erector spinae muscles were used for objective assessment. Radiation dose parameters included the CT dose index volume, dose-length product, effective dose, and size-specific dose estimate. Results were compared for different body mass index categories.ResultsThe 80-kV FIRST protocol helped achieve mean reductions of 36.3%, 35.7%, and 36.6% in CT dose index volume, effective dose, and size-specific dose estimate, respectively (p < 0.01). Therefore, this protocol was regarded as comparable to the conventional protocol in image quality, except for visual sharpness.ConclusionsThe 80-kV FIRST protocol is capable of reducing radiation dose and contrast medium volume compared to the adaptive iterative dose reduction 3D protocol in the equilibrium phase of chest-pelvic CT.

Low Operating Voltage Solution Processed (Li₂ZnO₂) Dielectric and (SnO₂) Channel-Based Medium Wave UV-B Phototransistor for Application in Phototherapy

UV lamps used for phototherapy for the treatment of several skin diseases do not have uniform output. This makes the treatment difficult and less responsive. A Ultraviolet B (UV-B) sensitive thin-film phototransistor has been fabricated and characterized to monitor the intensity of UV radiation in phototherapy of skin diseases like psoriasis, vitiligo, and atopic dermatitis. Phototherapy with UV-B ranges from 280 to 320 nm, safe and very effective for skin disease treatment. Hence, to make it portable and affordable for medical technologies, we have demonstrated the fabrication process of a low-operational (≤2V), low-cost solution-processed Li2ZnO2 (dielectric)/SnO2 (channel)-based phototransistor that shows very high photosensitivity at around ~300 nm of UV-B region. The working principle depends on the passage of UV-B light through a window followed by striking a micrometer-scale semiconductor phototransistor. The responsivity and external quantum efficiency (EQE) of the fabricated phototransistor was found to be about 0.12 A/W and 40.12% at 300 nm, respectively, at a notably low operating voltage (≤2 V). High sensitivity (>200%) with fast response time (7 s) was also achieved with UV-B irradiation of 650 $\mu \text{W}$ /cm2. For in-depth performance analysis of the fabricated device, modeling has also been done, and the outcome matched well with the experimental results.

Nano CMOS Charge Pump for Readerless RFID PLL

Readerless RFID has become more significant for reliable wireless communication. The Phase Locked Loop (PLLs) are among the most crucial functional blocks in the Readerless RFID where the PLL performance greatly depend on the Charge Pump (CP). Conventional CP circuits suffer from current mismatching characteristics which generate phase offset and spurs in the PLL output signals. In order to overcome these problems, the CP current mismatch has to be minimized. An enhanced CP circuit with zero current mismatch is presented in this article adopting an ideal current mirror technique and an additional inverter to provide a rail-to-rail voltage. The post-layout simulation shows that the proposed CP maintain the steady current over a wide range of output voltage from 0.1-1.8 V consuming the substantially lower power of 0.178 µW. The CP circuit is designed in 130 nm CMOS process that operates at 1.8 V and the core occupies 17 x 59.5 μm 2 . The proposed CP will be a good solution for low voltage, high-frequency PLL structure which suffers from poor performances.

A Complex-Valued Three-Phase Load Flow for Radial Networks: High-Performance and Low-Voltage Solution Capability

Load flow methods for distribution networks, such as backward forward sweep (BFS) have a good computational performance and can find solutions with accuracy. However, some studies may demand the determination of low voltage solutions, and this poses a problem for these methods since they cannot find these solutions due to convergence issues. This paper presents a load flow method based on a novel complex-valued formulation developed for distribution networks, which works well on radial topologies by using an incidence matrix to avoid complicated series element models, allow high-performance and low-voltage solution capability. The formulation is solved by Newton's method via Wirtinger's calculus. To prove the low-voltage solution capability, both sides of QV curves, i.e., unstable and stable regions were traced on balanced and unbalanced networks. Performance tests in the IEEE test feeders show that the runtime is less than or equal to the runtime of the BFS method. Furthermore, the line R/X ratio and the number of controlled voltage node or volt-var functions do not affect the computational performance, yielding advantages over the classic Newton and BFS methods.

TC48: A low‐cost 48 V integrated drive for mild hybrid electric vehicles

The TC48 drive is a low-cost, low-voltage integrated motor-drive solution suitable for mild hybrid electric vehicles, off-highway traction, and any application where a compact, highly torque-dense machine is required. Low-voltage solutions for electric vehicles are attractive to manufacturers due to lower insulation requirements, and hence lower cost. The package is based on a six-phase switched reluctance machine, which uses a novel stator topology and unique winding design to achieve high torque density. The power electronics converter hardware is integrated into the motor housing, giving a physically, electrically, and thermally optimised solution. The complete package has been designed to be suitable for manufacturing in high volumes. This study describes the electromagnetic design of the motor, the mechanical innovations used to physically realise this design, and the cooling system which makes the high power density possible. The integration of the power electronics and their control is also discussed. The project is the result of collaboration between Newcastle and Loughbosrough Universities, RDM Ltd., Productiv, Infineon, Tata Steel, and Libralato.

Efficient method to compute all the type‐1 low‐voltage power flow solutions in distribution systems

The power flow equations usually have multiple solutions including a high-voltage solution and many low-voltage solutions, among which only the type-1 solutions (where the power flow Jacobian matrix has only one positive real-part eigenvalue) are closely related to the voltage instability phenomenon. This study proposes an efficient method to compute all the type-1 low-voltage power flow solutions in distribution systems. First, the geometric properties of the power flow solution space of distribution systems have been studied. Second, the propositions which can guarantee to locate all the type-1 power flow solutions have been suggested and proved. Finally, the conventional implicit Z-bus method is modified to compute all the type-1 germ solutions, based on the suggested propositions; and then the Newton–Raphson method is utilised to trace all the type-1 low-voltage power flow solution branches which originate from the known type-1 germ solutions. The 7-node, 33-node, and 69-node systems are used to validate and demonstrate the proposed method.

Lower Cost Solution for Medium Voltage Heater Control: An Affordable Evolution Using Variable Voltage Transformers

Power electronic devices are the standard solution for lowvoltage (LV) heater control; however, cost and harmonic issues are amplified for medium-voltage (MV) heater applications. To provide an MV alternative at a significantly lower cost, this article details modifications and testing that will evolve part-range and load-tap-changing voltage regulators into full-range variable voltage transformers (VVT) for MV heater control. From the initial minor modifications that converted autotransformers into 16-tap isolation transformers, the development moves on to the inclusion of secondary base windings that bring 32 taps into play for refined control. Three-phase solutions and the addition of MV interrupters from the utility industry provide an economical solution for a stand-alone MV heater operation that avoids the harmonic issues of other heater control technologies.

Negative Reactance Impacts on the Eigenvalues of the Jacobian Matrix in Power Flow and Type-1 Low-Voltage Power-Flow Solutions

It was usually considered in power systems that power flow equations had multiple solutions and all the eigenvalues of Jacobian matrix at the high-voltage operable solution should have negative real parts. Accordingly, type-1 low-voltage power flow solutions are defined in the case that the Jacobian matrix has only one positive real-part eigenvalue. However, an important issue that has not been well addressed yet is that the “negative reactance” may appear in the practical power system models. Thus, the negative real-part eigenvalues of the Jacobian matrix at the high-voltage operable solution may be positive and also the type-1 low-voltage solutions could have more than one positive real-part eigenvalues, being a major challenge. Therefore, in this paper, the recognition of the type-1 low-voltage power flow solutions is re-examined with the presence of negative reactance. Selected IEEE standard power system models and the real-world Polish power systems are then tested to verify the analysis. The results reveal that the negative reactance in the practical power systems has a significant impact on the negative real-part eigenvalues of the Jacobian matrix at the high-voltage operable solution as well as the number of positive real-part eigenvalues at the type-1 low-voltage power flow solutions.

0.3‐V bulk‐driven programmable gain amplifier in 0.18‐µm CMOS

SummaryA new solution for an ultra low voltage bulk‐driven programmable gain amplifier (PGA) is described in the paper. While implemented in a standard n‐well 0.18‐µm complementary metal–oxide–semiconductor (CMOS) process, the circuit operates from 0.3 V supply, and its voltage gain can be regulated from 0 to 18 dB with 6‐dB steps. At minimum gain, the PGA offers nearly rail‐to‐rail input/output swing and the input referred thermal noise of 2.37 μV/Hz1/2, which results in a 63‐dB dynamic range (DR). Besides, the total power consumption is 96 nW, the signal bandwidth is 2.95 kHz at 5‐pF load capacitance and the third‐order input intercept point (IIP3) is 1.62 V. The circuit performance was simulated with LTspice. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Energy function applied to voltage stability studies – Discussion on low voltage solutions with the help of tangent vector

Two main topics regarding the energy function approach for voltage stability analysis are addressed in this paper. First, the problem of the critical low voltage solution identification is discussed. For this sake, the ability of the tangent vector method to correctly identify the low voltage solution that ultimately coalesce with the power system operating solution is investigated. It is shown that the methodology is consistent with the mechanism of the low voltage solutions. Second, the definition of the group of buses related to the weak area of a system is addressed. It is shown that the combined use of the low voltage solution methodology and the tangent vector technique yields good results. Tests were carried out in the IEEE-30, IEEE-57 and IEEE-118 bus test systems.

Optimal multiplier load flow method using concavity theory

This paper utilises concavity properties in the optimal multiplier load flow method (OMLFM) to find the most suitable low voltage solution (LVS) for the systems having multiple LVS at the maximum loading point. In the previous method, the calculation of the optimal multiplier is based on only one remaining low voltage solution at the vicinity of voltage collapse point. However, this does not provide the best convergence for multi-low voltage solutions at the maximum loading point. Therefore, in this paper, concavity properties of the cost function in OMLFM are presented as the indicator to find the most suitable optimal multiplier in order to determine the most suitable low voltage solutions at the maximum loading point. The proposed method uses polar coordinate system instead of the rectangular coordinate system, which simplifies the task further and by keeping PV type buses. The polar coordinate in this method is based on the second order load flow equation in order to reduce the calculation time. The proposed method has been validated by the results obtained from the tests on the IEEE 57, 118 and 300-bus systems for well-conditioned systems and at the maximum loading point.

Dual-&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$V_{\rm th}$ &lt;/tex-math&gt;&lt;/inline-formula&gt; Low-Voltage Solution Processed Organic Thin-Film Transistors With a Thick Polymer Dielectric Layer

Threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) control using different metal gates (aluminum and gold) was applied to realize dual-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> low-voltage solution processed organic thin film transistors (OTFTs). In the devices, the low-operation voltage was realized based on a channel engineering approach instead of using large gate dielectric capacitance, therefore, a relatively thick and low-dielectric constant polymer dielectric layer can be used. The devices present a mobility about 1.0 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /(V·s), ON/OFF ratio of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and small subthreshold swing of 100 mV/decade with the maximum processing temperature not exceeding 100 °C. It was found that, even with a 400-nm thick polymer dielectric layer, since possible charge trapping effects was effectively suppressed by the crosslinking processes, well controlled V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> was achieved. Both unipolar single-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> and dual-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> inverters were fabricated, clearly showing the influence of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> on the circuit operation and improved performance with the dual-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> OTFT technology.

Quadratic Discriminant Index for Optimal Multiplier Load Flow Method in ill conditioned system

In ill conditioned power systems, the classical Optimal Multiplier Load Flow Method (OMLFM) can only calculate Low Voltage Solutions (LVS) at the vicinity of the maximum loading point (MLP). It cannot determine the boundary zone between solvable and unsolvable cases of load flow equations solution. Considering this limitation, this paper proposed the Quadratic Discriminant Index (QDI) based on the properties of quadratic form of load flow equations to enhance OMLFM to find LVS at the MLP in polar coordinate form. These properties can describe all straight lines through two distinct state variables solution as Multiple Load Flow Solutions (MLFS) in OMLFM. The trajectory of these lines approaches MLP in term of loading factor. Furthermore, in this process, MLP in well, ill and unsolvable operation zones can also be determined. The test results of a single-machine system and IEEE 14, 57 and 118-bus test systems demonstrate the validity of the proposed method.

Improved Step Size Newton Raphson Method using quadratic equations properties in ill-conditioned power system

SUMMARY The Step Size of the Newton Raphson Method (SSNRM) is based on the optimal multiplier that is used to determine the Multiple Load Flow Solutions (MLFS) for an ill-conditioned power system. However, the SSNRM is incapable of determining the desirable Low Voltage Solution (LVS) from the MLFS at the Maximum Loading Point (MLP), due to the fact that when the load demand increases, the LVSs moves closer to each other at the MLP. Commonly, the smallest optimal multiplier was used to calculate the LVS at the MLP under this condition. However, this paper proves the fact that using the smallest optimal multiplier to determine the most suitable LVS for the systems having multiple solutions at the MLP will not guarantee a favourable outcome. Therefore, this paper investigates the application of the properties of scalar quadratic equations (PSQE) that enhances the function of the SSNRM at the MLP. Thus, an indicator, based on PSQE, is introduced in this work, which amends the existing SSNRM for the purpose of finding the desirable LVS at the MLP. The closest optimal multiplier to the proposed indicator is selected in order to determine the desirable LVS from all possible solutions at the MLP. The proposed method has been tested on a three-bus and IEEE 30-bus systems at the MLP for verification purposes. Additionally, the continuation power flow method is also utilized in order to compare it to the proposed method for the IEEE 30-bus system at the MLP. Copyright © 2013 John Wiley & Sons, Ltd.

Grid Code Requirements for Wind Power Integration in Europe

As the capacity of wind power continues to increase globally, stricter requirements regarding grid connection of wind generators are introduced by system operators. The development of wind turbine technology is inevitably affected by the new grid codes, and wind power plants are expected to support the grid and provide ancillary services much like conventional power plants. The most demanding regulations are found in Europe where wind penetration levels are higher. This paper presents the main aspects of current grid code requirements for the integration of wind power in European countries and suggests performance characteristics in order to satisfy the most demanding requirements. The dynamic behavior of wind turbines with doubly fed induction generators is investigated and a solution for low voltage ride through compliance is presented.

A Highly Linear Low-Voltage Source-Degeneration Transconductor Based on Unity-Gain Buffer

A complementary metal oxide semiconductor (CMOS) transconductor based on a high performance unity-gain buffer driving the degeneration resistor was used to obtain a highly linear voltage-to-current conversion with considerable reduction of the supply voltage. Simulations show that the transconductor using an 0.18-μm standard CMOS process with a 1.2-V supply voltage has less than −80 dB total harmonic distortion (THD) for a 1-MHz 0.4-V p-p differential input signal. The third-order intermodulation is less than −63 dB for 0.25 V p-p differential inputs at 1 MHz. The DC power consumption in the transconductor core is 240 μW. This topology is a feasible solution for low voltage and low power applications.

Multiple low voltage power flow solutions using hybrid PSO and optimal multiplier method

In this paper a method for computing multiple power flow solutions of power system is proposed. The proposed method determines the multiple solutions in pairs. Particle Swarm Optimization (PSO) technique is used to find the starting values of the rectangular Newton–Raphson power flow. From these starting values, the rectangular Newton–Raphson load flow determines a low voltage solution close to the first one. Optimal multipliers are then used to determine a second low voltage solution. Test results of standard IEEE 14 bus system have been shown.

A Linear Voltage Stability Index to Estimate the Distance to Voltage Collapse

This paper proposes a new voltage stability index (VSI) that has a more or less linear characteristic, and thus can provide better estimation of the distance to voltage collapse. It requires only the normal power flow solution and the type-1 low voltage solution of the critical or weakest bus of the system. The effectiveness of the proposed VSI in estimating the distance to voltage collapse is tested on a 5-bus system and the IEEE 14- and 30-bus systems. The results obtained through the proposed VSI are then compared with those found by other methods, as well as with the corresponding actual values found by repetitive power flow simulations.

Design of a 1-V 1-MS/s Track&Hold circuit based on the switched opamp approach

A very low voltage solution for the realization of the hold capacitor in a Track&Hold circuit based on an open-loop architecture is introduced. The circuit is a modification based on the switched opamp approach of the Track&Hold circuit using Miller Capacitance. Simulations show that the circuit is able to operate at 1V 1MS/s with a Total Harmonic Distortion of −64 dB @ 100 kHz and a very low power consumption of 80 µW.