Desired Crossover Frequency Research Articles

Analytical Factorized Model for Stability Analysis and Optimization of Shunt RC Damped LCL Filter for Grid-Connected Voltage Source Inverters

In this article, an optimal design procedure of shunt RC damped LCL filter is discussed. The proposed design procedure finds the minimum damping resistance to guarantee the stability of the grid-current controller without affecting the effectiveness of the filter. This minimum value is derived using the factorized filter input admittance and filter forward transadmittance. The proposed factorization procedure allows us to have an analytical expression of system poles and zeros. Moreover, the minimum damping resistor is determined upon the desired crossover frequency and the desired phase margin of the grid-current controller. After that, an objective function is assumed, and an optimization problem is formulated to minimize the physical size of the filter by minimizing the total capacitance and inductance and by minimizing the filter ripple content as well. Accordingly, the proposed objective function minimizes the filter physical size and filter power losses and, hence, enhances filter's efficiency. A prototype demonstrates and validates the proposed filter design and analysis experimentally.

DC/DC 컨버터의 파라미터 변화를 고려한 구간분석법 기반 제어기 설계

By performing interval analysis on the system transfer function, we propose an improved method of control loop design for a DC/DC converter. In conventional design methods, the effect of system parameter change due to the specified range of operating conditions and production tolerances in power components should be checked a posteriori, because this may result in a transfer function shift and performance degradation. In the proposed method, a possible parameter change is considered a priori in the design step in order that the desired crossover frequency and sufficient phase margin can be achieved even in the worst case condition. As an illustrative example, a buck dc/dc converter is designed by two different methods and performance comparisons are performed to verify the feasibility of the proposed scheme.

Simulation of Pilot Workload for a Helicopter Operating in a Turbulent Ship Airwake

This article describes a recent study in helicopter/ship dynamic interface simulation to examine pilot workload in the presence of a ship's airwake. The flight dynamics model represents a UH-60 helicopter and is based on the GENHEL software. This flight model has been updated to include a high-order dynamic inflow model and gust penetration effects of the time-varying ship airwake. The airwake model is derived from time-accurate computational fluid dynamics (CFD) solutions and provides an appropriately detailed level of fidelity to capture its effect on pilot workload. To simulate pilot control inputs for shipboard approach operations, an optimal control model of the human pilot is developed. The pilot model can be easily tuned to achieve different tracking performances, based on a desired crossover frequency, in each control axis and is designed to operate over a range of airspeeds using a simple gain scheduling algorithm. The pilot model is used to predict pilot workload for shipboard approaches in two different wind-over-deck conditions. Validation studies are conducted using both time and frequency domain analyses. The pilot control input autospectra predicted from the simulation model are compared to those of flight test data from the Joint Shipboard Helicopter Integration Process program. The paper also discusses the application of a stochastic airwake model for more efficient simulation. This new airwake model is derived from the simulation with the full CFD airwake by extracting an equivalent six-dimensional gust vector. The spectral properties of the gust components are then analysed, and shaping filters are designed to simulate the gusts when driven by white noise. It is proposed that the stochastic gust model can be used to optimize the automatic flight control system in order to improve disturbance rejection properties of the aircraft.

Power-complementary IIR filter pairs with an adjustable crossover frequency

This paper introduces two classes of power-complementary recursive low-pass/high-pass filter pairs with an adjustable crossover frequency in such a way that the stopband attenuation of both filters remains the same. For each class, the filter pair is constructed using two all-pass sub-filters as building blocks. Based on the properties elliptic minimal Q-factors transfer functions, simple expressions are derived for evaluating the coefficients in all-pass sections in order to achieve the desired crossover frequency. The design procedures are developed for synthesizing power-complementary filter pairs implemented as a parallel connection of two all-pass sub-filters and for the tapped cascaded interconnections of two identical all-pass sub-filters. The direct parallel connection has both the power-complementary and all-pass complementary property. The second class of filters constructed using several identical copies of the two all-pass filters possesses the power-complementary property.