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

The many different techniques for maximum power point tracking of photovoltaic (PV) arrays are discussed. The techniques are taken from the literature dating back to the earliest methods. It is shown that at least 19 distinct methods have been introduced in the literature, with many variations on implementation. This paper should serve as a convenient reference for future work in PV power generation.

/pdf/comparison-of-photovoltaic-array-maximum-power-point-2nci76j6n4.pdf

Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques

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

Power electronics

Review of the maximum power point tracking algorithms for stand-alone photovoltaic systems

This paper proposes a hybrid ac/dc micro grid to reduce the processes of multiple dc-ac-dc or ac-dc-ac conversions in an individual ac or dc grid. The hybrid grid consists of both ac and dc networks connected together by multi-bidirectional converters. AC sources and loads are connected to the ac network whereas dc sources and loads are tied to the dc network. Energy storage systems can be connected to dc or ac links. The proposed hybrid grid can operate in a grid-tied or autonomous mode. The coordination control algorithms are proposed for smooth power transfer between ac and dc links and for stable system operation under various generation and load conditions. Uncertainty and intermittent characteristics of wind speed, solar irradiation level, ambient temperature, and load are also considered in system control and operation. A small hybrid grid has been modeled and simulated using the Simulink in the MATLAB. The simulation results show that the system can maintain stable operation under the proposed coordination control schemes when the grid is switched from one operating condition to another.

A Hybrid AC/DC Microgrid and Its Coordination Control

Power quality and availability are becoming important issues for critical and sensitive loads. UPS is a complete solution for power quality problems, but high capital and running cost makes it an expensive solution. A series dynamic voltage restorer (DVR) provides load voltage support with a power rating equal to only a fraction of the load. At present, most of DVRs use feed-forward control because of the compensation response time requirement, this kind of control may introduce steady state error and on-site calibration problems. Although closed-loop PI regulation could not meet the dynamic response requirement, this paper demonstrates that a closed-loop nonlinear state variable control algorithm is a viable industrial solution. Practical issues, such as fault type analysis and controller design method, are included in the paper. The dynamic performance is analyzed and verified through simulation and experimental tests on a 2 kVA prototype.

A nonlinear control method of dynamic voltage restorers

Anti-islanding protection is a mandatory feature for grid-connected inverters. The effectiveness of passive islanding detection methods (IDMs) is usually demonstrated by means of non-detection zones (NDZs) represented in a power mismatch space (/spl Delta/P /spl times/ /spl Delta/Q). A number of active type IDMs with improved performance have been presented but their effectiveness cannot be compared using the /spl Delta/P /spl times/ /spl Delta/Q space. This paper proposes a new load parameter space for comparing the effectiveness of IDMs where the influence of the load resistance can be easily assessed. Equations that represent NDZs for the /spl Delta/P /spl times/ /spl Delta/Q and proposed load parameter space are derived and verified by simulation.

Analysis and comparison of islanding detection methods using a new load parameter space

High-power current source converters (CSCs) are usually implemented with gate turn off thyristors (GTOs) or integrated gate commutated thyristors (IGCTs) that present a maximum switching frequency of a few kilohertz. Space vector modulation (SVM) offers a very elegant way of generating CSC gating signals online with increased gain and reduced switching frequency. However, for very low switching frequency, SVM results in low-order (5th and 7th) noncharacteristic harmonics complicating the design of the input filter. The reduction of the magnitude of these harmonics has been sought mostly through new sequences of space vectors (states) that present better performance for different ranges of modulation index and power factor. Moderate improvement can be obtained by calculating the statespsila on times for the reference vector in the middle of an SVM cycle. This paper proposes calculating the statespsila on times as the reference vector rotates. Simulation results show that this approach results in a significant reduction in the harmonic distortion of these two components, which, for a selected sequence of states, can be limited to 0.3% of the fundamental component as the modulation index varies from 0.05 to 1.0. Experimental results obtained with a digital signal processor development kit are also provided to show the superior performance of the proposed techniques.

Space Vector Modulation for Low Switching Frequency Current Source Converters With Reduced Low-Order Noncharacteristic Harmonics

https://hal.archives-ouvertes.fr/hal-02090612/document

Nonlinear control of a DC MicroGrid for the integration of distributed generation based on different time scales

Electricity is usually supplied by diesel generators in remote communities at high costs. In such a case, renewable energy sources (RESs), such as wind and photovoltaics (PV), can be cost effective to meet part of the energy needs. However, the integration of RESs may lead to large power fluctuations and to the operation of the diesel genset under-loaded. Traditionally, energy storage devices have been used to provide power smoothing and frequency regulations, but this solution is quite costly.
In this thesis, electric water heaters (EWH) are used to assist with power balancing and frequency regulation and to prevent the diesel genset from operating under-loaded, in a PV-diesel hybrid mini-grid.
The characteristics of the diesel genset, PV, and the EWH are studied. An EWH is modeled using Matlab/SIMULINK. Approximate linear equations are derived and used for estimating the amount of power an EWH can take or drop, by varying the set point temperature Td. 
A review of methods used to control the EWH are then presented. A basic integrated control of the EWH, which varies the set point temperature (Td), using the system frequency is studied. Issues using this control in a small power system are investigated, and a modified integrated control is proposed to solve them. 
The effectiveness of basic and modified integrated controls is validated using a hybrid PV-diesel mini-grid benchmark implemented in PSCAD. Moreover, the impact of the PV on fuel consumption, and frequency variations is observed. Simulation results indicate that the modified integrated control is effective for frequency regulations, peak shavings, and for preventing genset operates under loaded.

/pdf/using-electric-water-heaters-ewhs-for-power-balancing-and-2aa81lfrkc.pdf

Luiz A. C. Lopes

Papers

A nonlinear control method of dynamic voltage restorers

Analysis and comparison of islanding detection methods using a new load parameter space

Space Vector Modulation for Low Switching Frequency Current Source Converters With Reduced Low-Order Noncharacteristic Harmonics

Nonlinear control of a DC MicroGrid for the integration of distributed generation based on different time scales

Using Electric Water Heaters (EWHs) for Power Balancing and Frequency Control in PV-Diesel Hybrid Mini-Grids