Power system stability enhancement by WAMS-based supplementary control of multi-terminal HVDC networks

This paper deals with supplementary control of a MTDC network designed for the stability enhancement of a AC power system. The proposed control is a WAMS-based control modulating the real and reactive power at the terminals of the DC network. Relevant control formulas have been derived for a linear multi-machine system model with the application of the direct Lyapunov method. Validity and robustness of the proposed control has been verified by computer simulation for a multi-machine test system using a nonlinear model and detailed modeling of power system components. The proposed control is robust and insensitive to changes in the network configuration and loading conditions in the AC power system. In the case, when more of the MTDC networks and/or the HVDC links are used in one interconnected power system the proposed stabilizing control produces additive damping i.e. each controlled network element contributes to the positive damping. Some practical aspects have also been discussed. The proposed WAMS-based stabilizing control of the MTDC network is innovative by both its main concept and the derivation of control formulas using the direct Lyapunov method.     

Hybrid DPWM implementation using coarse and fine programmable ADLL

In the paper we propose a novel architecture and implementation of 11-bit Digital Pulse Width Modulator (DPWM) circuit based on previously known building blocks. Linearized Class-AD Double-sided (LADD) algorithm has been used to calculate the DPWM signals of the 11-bit resolution hybrid DPWM for a Class-AD digital audio amplifier. Noise-shaping process is used to support high fidelity with practical values of time resolution. The proposed DPWM circuit is composed of 8-bit counter and Analog Delay Locked Loop (ADLL) using 4-bit tapped delay line. A dual ADLL employing coarse and fine programmable delay element is used to adjust the delay time of delay line and lock it to required time. The coarse- as well as fine-delay lines are implemented as a cascade of variable-delay elements based on shunt capacitor delay element or single-ended Schmitt trigger. The proposed 11-bit DPWM circuit, at a switching frequency of 352.8 kHz and clock generator frequency of 90.3 MHz allows us to attain SNR of 120 dB and THD of the output signal less than 0.1% within the audio baseband and modulation index M=0.95. Basic verification of circuit manufacturability and simulation results (Monte Carlo analysis) for real CMOS process are presented.     

External subsystem equivalent model for steady-state and dynamicsecurity assessment

A method for external subsystem model reduction is proposed. The reduction process starts with the load node elimination, resulting in a Ward-PV equivalent which contains all boundary and generator nodes. The number of the generator nodes is significantly decreased by aggregation. This is done by the Zhukov method, which replaces each selected group of the generator nodes by one equivalent generator node. The obtained equivalent is called the reduced Ward-PV equivalent. All generating units attached to the aggregated generator nodes are also aggregated into equivalent generating units. The equivalent obtained by such a method may be used for both steady-state and dynamic security analysis. The reduced Ward-PV equivalent retains the static and dynamic properties of the original Ward-PV equivalent if the aggregated generator nodes are grouped for aggregation on the base of coherency. The Yugoslav electrical power system was used as the sample system for testing the proposed method     

A bipolar charge measurement system for aerosol characterization

This paper reports the development of a bipolar charge measurement system for aerosol characterization. The system incorporates a front-end cylindrical arrangement consisting of two “D”-shaped precipitation sections. Each of these sections incorporates wire electrodes maintained at a high potential of opposite polarity. The interface between the two “D” sections is a thin wedge, the front-end of which acts as a bifurcation for the incoming aerosol. The test aerosol is drawn through the bifurcation separator using a suction pump, and subject to an appropriate electric field. Depending on the electric field distribution and air-flow characteristics, particles of the same polarity as that of the potential applied to the wire electrodes are deflected toward an outer collecting wall and give up their charge. This precipitation section is connected to a series of five “D”-shaped electrodes (open-ended Faraday chambers) to collect the charged aerosol of different charge to mass ratio. Both analytical and numerical calculations were performed to optimize the design of the manufactured system. Preliminary tests were carried out with an aerosol of known size and charge distribution. The results obtained are in good agreement with the theoretical predictions     

Electrical characteristics of an electrostatic valve used for bulktransport of agricultural seeds

In an electrostatic valve used for bulk transport of agricultural seeds, the interparticulate electroclamping forces can be established by applying electric potential gradient between a separated pair of conducting electrode grids placed perpendicularly across the flow. The flow control of particulate material is thus achieved using no moving parts. When an electric field is applied, several types of electric field forces are generated, depending on the bulk and surface resistivities of the particles, the geometry of the electrodes, the applied field, and the geometry and the conductivity of the materials used for the transport channel. In this study the current-voltage characteristics of the valve were experimentally investigated for different flow control parameters. The triboelectrification of turnip seeds caused by the frictional contact on the channel walls was investigated and compared with the valve current. A range of wall liner materials with different electrical properties conductive to insulating were tested. The materials used for the wall liner did not significantly influence the current characteristics of the electrostatic valve. The effect of pulse duration of the applied potential on charge-to-mass ratio of the discharged material was studied. The results obtained show that the level of net charge acquired by the particles could be controlled by controlling the duty cycle of the electroclamping field     

ORGANIC GEOCHEMISTRY OF MIDDLE MIOCENE (BADENIAN – SARMATIAN) SOURCE ROCKS AND MATURATION MODELLING IN THE POLISH AND UKRAINIAN SECTORS OF THE EXTERNAL CARPATHIAN FOREDEEP

The Carpathian Foredeep to the north and NE of the Carpathian orogenic belt in SE Poland and NW Ukraine is divided into internal and external sectors. In the narrow internal foredeep, Lower and Middle Miocene shales, sandstones and interbedded evaporites are tightly folded. By contrast the external foredeep is characterized by the presence of a thick, unfolded Middle Miocene molasse succession. This ranges in thickness from a few hundred metres in the north of the external foredeep to >5000 m in the south, near the Carpathian thrust front. Middle Miocene sandstones in the external foredeep form a major reservoir for biogenic gas at fields in Poland and Ukraine. The Middle Miocene molasse succession in the external Carpathian Foredeep also contains organic-rich intervals which have source rock potential. For this paper, core samples (n = 670) of Badenian and Sarmatian mudstones from 43 boreholes in the Polish sector of the external foredeep were analysed to investigate their organic geochemistry and hydrocarbon potential. Results show that the samples analysed in general have low to fair (but locally high) total organic carbon (TOC) contents which range up 4.6 wt.% although the average is only 0.7 wt.%. Rock-Eval (S₁+S₂) values are poor to fair and the hydrogen index is also low with a mean value of less than 100 mg/g TOC. The samples analysed are dominated by gas-prone Type III kerogen and this is consistent with previous studies of time-equivalent samples from the Ukrainian part of the external foredeep. The organic matter is in general thermally immature and is interpreted to have been deposited in anoxic and/or sub-oxic conditions. However in the Polish part of the external foredeep, thermal maturities may locally reach the initial phase of the oil window where the Middle Miocene source rocks have been buried deeply beneath the Carpathian thrust front. The burial history and thermal evolution of the Middle Miocene succession were reconstructed by means of 1-D modelling at nine boreholes located in both the Polish and Ukrainian parts of the external Carpathian foredeep. The modelling indicated that Middle Miocene source rocks have only entered the initial phase of the oil window locally where they are buried beneath the flysch nappes of the Carpathian foldbelt. At these locations the generation of thermogenic gas may have begun at depths of more than 3 km. However, Middle Miocene source rocks are still immature at depths of >4000 m in some boreholes in the Ukrainian part of the study area. The absence of accumulations of thermogenic natural gas is consistent with the observed low levels of source rock maturity.     

State-variable control of shunt FACTS devices using phasor measurements

This paper addresses the problem of state-variable stabilizing control of power system using shunt FACTS devices. This stabilizing control is activated in the transient state of a power system and is supplementary with respect to the main steady-state control of a FACTS device. Stabilizing control laws have been derived for a non-linear multi-machine system model using direct Lyapunov method with the aim to maximize the rate of energy dissipation during power swings and therefore maximization of damping. The proposed control strategy is executed by a non-linear multi-loop controller with rotor angles and speed deviations of synchronous generators used as the input signals. The input signals, obtained from a phasor measurement system, are necessary only from a small area around the controlled shunt FACTS device. Validity of the proposed state-variable control has been confirmed by computer simulation for a small multi-machine test system.     

Electrostatic atomization of conducting liquids using ACsuperimposed on DC fields

The objective of this study is to investigate the possibility of using electrostatic atomization to produce fine ceramic particles starting from highly conducting ceramic precursor solutions. The work was directed towards carrying out experimental investigation for the production of uniform droplets formed by the breakup of a permanent jet extending from the capillary nozzle. To control the atomization process an AC field (sine wave) was superimposed on a DC field. For given parameters of electrostatic field, capillary diameters, resistivity of liquids, and flowrate, the jet formation and breakup process was investigated. Several regimes were observed to be in synchronization with the applied potentials and frequencies. In these regimes uniform droplets were produced. Optical techniques were employed to study the breakup process     

Design of traveling-wave field panel for pharmaceutical powdersbased on computer simulation of particle trajectories

A fundamental study of charged particle levitation and transport in a traveling-wave field was carried out with a view to design and manufacture a series of flatbed panels with embedded electrode arrangement. Fourier transformation technique has been used to provide boundary conditions for the numerical calculations of particle trajectories. From the analysis, a potential function can be extracted which gives a better approximation compared to the one given by Masuda's early work. The numerical method using finite element and finite difference technique to solve field and trajectories, respectively, has been employed with a well-designed user interface. The user interface for integrating both methods is of universal value on its own. Based on this study, a computer program is under development with three levels of accuracy. The first level with consideration of the first spatial harmonic is presented in this paper, which is sufficient for designing panel electrode arrangements for the confinement and transport of dry powders. For the advanced study of particle trajectories under higher harmonic vectors, levels 2 and 3 (currently under development) may be utilized to serve different user requirement of accuracy. A series of panel electrodes have been designed and manufactured based on the analyses presented in this paper. Using these panels, lactose powder samples were successfully levitated and transported in the desired direction. Experimental observation is in good agreement with the numerical results