Linear Filtering Characteristics Research Articles

Simulation of Brushless DC Motor Speed Control Using Phase Locked Loop Based on Noise Analysis

Based on analyzing the brushless dc motor (BDCM) mathematical model, the BDCM block is built. The speed of the motor is calculated through torque equation. And the back electromotive force (EMF) is obtained by using the piecewise linear method. The permanent magnet brushless motor speed control system is established using phase locked loop (PLL) technology on the basis of the BDCM model in SIMULINK. Two typical noise which will cause speed fluctuations: random load interference and power line interference in motor running is simulated in the control loop. Simulation results clearly show that the PLL control scheme acquires speed accuracy reaching about 1%, which outperforms ordinary speed-current proportional-integral (P-I) regulator control system. It also illustrates that proposed PLL solution has good rejection ratio to noise as the PLL having good linear filtering characteristics of interferences.

Long-period-fiber-grating-based filter configuration enabling arbitrary linear filtering characteristics

The filtering scheme proposed here is based on transmission through a dual long-period-fiber-grating (LPFG) configuration and enables implementation of arbitrary spectral transfer functions using available inverse-scattering design algorithms, such as those widely used for fiber Bragg gratings (FBGs) operating in reflection. Besides the important technical advantage of operation in transmission, the proposed device can reach large spectral bandwidths that would be extremely challenging to reach by, e.g., FBG devices. The proposed concept is demonstrated by designing and fabricating a LPFG-based filter for synthesis of transform-limited 1.5-ps-long square-like pulses.

Processing visual signals with nonlinear spatial filters.

The properties of nonlinear spatial filters as a major part of the peripheral nervous system are investigated with respect to processing of two types of signals: a deterministic stepfunction and Graussian noise. The nonlinearity of the nerve cell is treated as a threshold element. It is shown that certain unfavorable characteristics of linear filters do not occur in such nonlinear filters. The basic nonlinear effects of combined space-time-filtering are demonstrated by using bandpass filters. Time-and space-dependent noise is applied to the nonlinear bandpass. The two subsystems formed by linear bandpass section and the threshold are treated separately. Two examples for the application of nonlinear spatial filtering are given.

A Nonlinear Filter for Independent Gain and Phase (With Applications)

Compensation of control systems by means of linear filters is a basic and well-known art. However, the limitations of linear compensation are also well known. In particular, the interdependence of the phase and gain characteristics of linear filters is always in conflict with the desires of the control-system designer. For example, it is impossible to introduce attenuation into a system without introducing undesirable phase lag as well. The development of a split-path nonlinear filter (SPAN filter) concept promises to yield a practical device which has independent phase and gain characteristics. These characteristics are independent of input signal amplitude. This filter can, therefore, have desirable characteristics which are unattainable with conventional linear filters. The design of the nonlinear filter to meet a desired gain-phase, describing-function specification is simplified by results given in the paper. Analysis and simulation of three sample problems has shown that a great deal of flexibility is available with this nonlinear filter. It is possible to obtain phase lead and amplitude attenuation by a proper choice of linear filtering in the two channels. Analog-computer simulation has verified the analytical work with respect to stability margins, and provided transient-response data, in the absence of analytical methods.