Periodic Steady-state Operation Research Articles

Periodic Steady State Assessment of Microgrids with Photovoltaic Generation Using Limit Cycle Extrapolation and Cubic Splines

This paper proposes a fast and accurate time domain (TD) methodology for the assessment of the dynamic and periodic steady state operation of microgrids with photovoltaic (PV) energy sources. The proposed methodology uses the trapezoidal rule (TR) technique to integrate the set of first-order differential algebraic equations (DAE), generated by the entire electrical system. The Numerical Differentiation (ND) method is used to significantly speed-up the process of convergence of the state variables to the limit cycle with the fewest number of possible time steps per cycle. After that, the cubic spline interpolation (CSI) algorithm is used to reconstruct the steady state waveform obtained from the ND method and to increase the efficiency of the conventional TR method. This curve-fitting algorithm is used only once at the end part of the algorithm. The ND-CSI can be used to assess stability, power quality, dynamic and periodic steady state operation, fault and transient conditions, among other issues, of microgrids with PV sources. The results are successfully validated through direct comparison against those obtained with the PSCAD/EMTDC simulator, widely accepted by the power industry.

Weakly Nonlinear Propagation in Thermoacoustic Engines: A Numerical Study of Higher Harmonics Generation up to the Appearance of Shock Waves

Though thermoacoustic engines usually operate at high acoustic amplitude, they rarely exhibit strong deformation of the wavefront due to nonlinear propagation. It has however been demonstrated experimentally that obtaining shock waves in thermoacoustic engines is possible under specific con-ditions. This paper aims at presenting a simple description of the periodic steady-state operation of thermoacoustic engines describing the wave steepening process leading to shock wave formation. Results of numerical simulations are compared to experimental data in different engine configura-tions, and model improvements are proposed to reach a realistic description of the weakly nonlinear propagation in thermoacoustic engines.

Cavity dumping versus stationary output coupling in repetitively Q-switched solid-state lasers

A comparative theoretical analysis of continuously pumped actively Q-switched solid-state lasers differing in output coupling methods (cavity dumping versus a partially transmitting cavity mirror) is presented. Basic performance characteristics of the optimally coupled laser for periodic steady-state operation are expressed analytically. The instability effects are shown to fundamentally inhere in cavity dumping in contrast to ordinary Q-switching. The space of system parameters permitting stable operation and the maximum average power attainable as a train of regular energy pulses are determined numerically and verified experimentally. Cavity dumping is demonstrated to be the coupling method allowing Q-switched lasers to reach extremely high repetition rates.

Impact of Heat Transport on the Electrical Characteristics of a GaAs MESFET under Periodic Steady-State Operation.

Two dimensional numerical calculation of heat generation and transport in GaAs MESFETs with high frequency gate bias has been performed. In order to study the conjugate nature of electronic and thermal phenomena in the semiconductor devices, electron particles, momentum and energy equations, and the energy equations of optical and acoustic phonons as well as Poisson equation are solved simultaneously. Calculated results exhibited the effect of temperature distributions to the current charactreistics as high frequency gate voltage variation.