다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

Many grid connected power electronic systems, such as STATCOMs, UPFCs, and distributed generation system interfaces, use a voltage source inverter (VSI) connected to the supply network through a filter. This filter, typically a series inductance, acts to reduce the switching harmonics entering the distribution network. An alternative filter is a LCL network, which can achieve reduced levels of harmonic distortion at lower switching frequencies and with less inductance, and therefore has potential benefits for higher power applications. However, systems incorporating LCL filters require more complex control strategies and are not commonly presented in literature. This paper proposes a robust strategy for regulating the grid current entering a distribution network from a three-phase VSI system connected via a LCL filter. The strategy integrates an outer loop grid current regulator with inner capacitor current regulation to stabilize the system. A synchronous frame PI current regulation strategy is used for the outer grid current control loop. Linear analysis, simulation, and experimental results are used to verify the stability of the control algorithm across a range of operating conditions. Finally, expressions for ""harmonic impedance" of the system are derived to study the effects of supply voltage distortion on the harmonic performance of the system.

Grid current regulation of a three-phase voltage source inverter with an LCL input filter

This paper concentrates on the design and analysis of a controller for multibus microgrid system. The controller proposed for use with each distributed generation (DG) system in the microgrid contains inner voltage and current loops for regulating the three-phase grid-interfacing inverter, and external power control loops for controlling real and reactive power flow and for facilitating power sharing between the paralleled DG systems when a utility fault occurs and the microgrid islands. The controller also incorporates synchronization algorithms for ensuring smooth and safe reconnection of the micro and utility grids when the fault is cleared. With the implementation of the unified controller, the multibus microgrid system is able to switch between islanding and grid-connected modes without disrupting the critical loads connected to it. The performance of this unified controller has been verified in simulation using a real-time digital simulator and experimentally using a scaled laboratory prototype.

Design, analysis, and real-time testing of a controller for multibus microgrid system

This paper presents the analysis and design of a multiple feedback loop control scheme for single-phase voltage-source uninterruptible power supply (UPS) inverters with an L-C filter. The control scheme is based on sensing the current in the capacitor of the load filter and using it in an inner feedback loop. An outer voltage feedback loop is also incorporated to ensure that the load voltage is sinusoidal and well regulated. A general state-space averaged model of the UPS system is first derived and used to establish the steady-steady quiescent point. A linearized small signal dynamic model is then developed from the system general model using perturbation and small-signal approximation. The linearized system model is employed to examine the incremental dynamics of the power circuit and select appropriate feedback variables for stable operation of the closed-loop UPS system. Experimental verification of a laboratory model of the UPS system under the proposed closed-loop operation is provided for both linear and nonlinear loads. It is shown that the control scheme offers improved performance measures over existing schemes, It is simple to implement and capable of producing nearly perfect sinusoidal load voltage waveform at moderate switching frequency and reasonable size of filter parameters. Furthermore, the scheme has excellent dynamic response and high voltage utilization of the DC source.

Analysis and design of a multiple feedback loop control strategy for single-phase voltage-source UPS inverters

This paper investigates the performance of multiple feedback loop control strategy for single-phase voltage-source UPS inverter with an L-C filter. In order to select appropriate feedback variables and assess the stability of the closed loop operation of the overall system, the power circuit (inverter and filter plus load) incremental dynamics is investigated using the state-space averaging technique and root locus method. The results of the stability analysis show that a control scheme which employs the filter capacitor current in an inner feedback loop and the load voltage in an outer voltage control loop results in successful operation of the UPS system. Computer simulation results of a single-phase voltage-source half-bridge UPS inverter with a second order filter and R-L load is presented to demonstrate the performance of the proposed control scheme. Experimental verification of a laboratory model of the UPS system is also provided for both linear and nonlinear loads so as to verify the predicted performance of the system. It is shown that the control scheme offers improved performance measures over existing schemes. It is simple to implement and capable of producing nearly perfect sinusoidal load voltage waveform at moderate switching frequency and reasonable size of filter parameters. Furthermore, the scheme has fast dynamic response and high voltage utilization of the DC source. >

Multiple feedback loop control strategy for single-phase voltage-source UPS inverter

This paper proposes a closed-loop control strategy to operate an off-the-shelf single-phase induction motor (IM) as a symmetrical two-phase IM. The proposed control strategy employs the SFC technique to independently control the stator currents of both the main and auxiliary windings, and make them follow a predefined sinusoidal waveform. Simulation and experimental results show that the proposed scheme is successful in operating the conventional single-phase IM as a symmetrical two-phase IM with fast dynamic and transient responses. In addition, the proposed control system achieves cost-effectiveness in both initial and running costs.

An Unsymmetrical Two-Phase Induction Motor Drive With Slip-Frequency Control

This paper presents the steady-state and dynamic analysis of a novel feedback control strategy for a three-phase voltage-source utility interface power convertor system with a third order T-filter. The control scheme employs an inner capacitor current feedback loop and an outer capacitor voltage control loop to ensure that the harmonic content of both the capacitor voltage and utility current is within the acceptable total harmonic distortion. The utility interface system is analyzed by establishing a general model using state-space analysis. Employing the concept of state-space averaging technique, the steady-state performance of a balanced three-phase system is obtained in terms of system parameters. The dynamic response of the control strategy is then examined by developing a linearized model of the system equations employing perturbation technique and small signal approximation. Based on the bode plot of the system transfer function, a control loop regulator is selected to improve the dynamic response of the system. It is shown in the paper that the proposed scheme offers many advantages for utility interface systems; it is robust and insensitive to parameter variations. In addition, due to the use of the inner current loop, the system has fast dynamic response. Moreover, it is compatible with both large and weak AC network applications and capable of feeding the utility current at any desired power factor. >

Modeling and analysis of a feedback control strategy for three-phase voltage-source utility interface systems

The performance characteristics of the rectangular wave delta modulation (RWDM) scheme for uninterruptible power supply (UPS) applications is investigated. Normalized characteristic curves that show the effect of various modulator parameters on the frequency spectrum of the inverter output voltage are obtained using discrete Fourier transform (DFT) and harmonic analysis techniques. The performance of a single-phase half-bridge inverter with an LC filter is discussed, and experimental results are provided to validate the predicted and simulated results. It is shown that the harmonic content of the inverter output waveform can be controlled through the control of the modulator parameters. >

N. Abdel-Rahim

Papers

Analysis and design of a multiple feedback loop control strategy for single-phase voltage-source UPS inverters

Multiple feedback loop control strategy for single-phase voltage-source UPS inverter

An Unsymmetrical Two-Phase Induction Motor Drive With Slip-Frequency Control

Modeling and analysis of a feedback control strategy for three-phase voltage-source utility interface systems

A single-phase delta-modulated inverter for UPS applications