The history of technology combines engineering with economic, social, and political factors. Technology seems to advance in waves. Small advances accumulate slowly until a critical level of technological success and economic advantage is achieved. Throughout technological history is found the idea of feedback control. Like all ideas, feedback control impacts technology only when it is embodied therein; it is not tied to any specific innovation or invention. The article describes innovations that either use feedback control or allow it to be exploited. They are simple but their impact on technology is profound. It is shown that they played a crucial role in facilitating the truly great waves of technological and scientific development. They are the escapement (a significant part of the paper is about mechanical clocks), the governor, the aileron, the gyro, and the amplifier.

Feedback control: an invisible thread in the history of technology

An interactive tool for introductory nonlinear control systems education

In this article, a methodology of chattering analysis of Sliding Mode/Higher Order Sliding Mode (SM/HOSM) control systems in the frequency domain is presented. A numerical method for computing the Describing Functions (DFs) of HOSM control algorithms is given. The algorithm for predicted chattering parameters in dynamically perturbed system via the Describing Function-Harmonic Balance (DF-HB) technique is proposed. The stability conditions for limit cycles in dynamically perturbed HOSM control systems are presented. The concepts of Practical Stability Phase Margin ( PSPM ) and Practical Stability Gain Margin ( PSGM ) as the robustness metrics to unmodeled dynamics in HOSM control systems are introduced. The methodologies for computing PSPM and PSGM via DF-HB technique are provided. The accuracy of the proposed chattering analysis techniques is confirmed via computer simulations.

Chattering Analysis of HOSM Controlled Systems: Frequency Domain Approach

Isochronous controlled battery energy storage system (ESS) can maintain constant frequency in an islanded ac microgrid, but its power and state of charge (SoC) may go beyond limit due to intermittent renewable energy resources and impact load change. This paper introduces a control strategy integrated with bang-bang and backlash mechanism to coordinate distributed energy resources (DERs). When overloading will take place, ESS will change from isochronous control to droop control, with droop gain varying based on bang-bang control, by which the overloaded power will be spontaneously transferred from ESS to other DERs. Moreover, frequency will be automatically restored when impact load disappears, which eliminates the effort of secondary frequency control. When SoC of ESS comes to limit, the diesel generator will change from droop control to isochronous control, whereas ESS will adopt virtual inertia and grid-supporting droop control to help stabilize frequency. A backlash mechanism is also employed to latch the control mode near SoC limit. Comprehensive tests on real-time simulator demonstrated the effectiveness of the proposed control strategy.

Adaptive Coordination for Power and SoC Limiting Control of Energy Storage in an Islanded AC Microgrid With Impact Load

This study presents an average sliding control (ASC) method to be used in power factor correction (PFC) circuits to decrease the total harmonic distortion (THD) of the input current by eliminating the input current harmonics. The ASC algorithm is adapted to TMS320F2812 digital signal processor (DSP) owing to its well-known properties, such as robustness, stability and good regulation in a wide range of operating conditions. The control approach is operated in continuous conduction mode. In this approach, a sinusoidal signal is generated by the DSP and is used as reference in controlling the converter switch to obtain a sinusoidal input current based on zero-crossing points of input voltage. The feed-forward is also used in the control algorithm using maximum value of the input voltage. The implementation of feed-forward improves the converter's performance to obtain a near-unity PFC with a lower input current THD. The converter used in the simulation and experimental studies is a bridgeless converter. The conduction losses of the switches of this converter are lower compared with the similar PFC converters. The experiments performed in the laboratory for different cases of operation verify the theoretical and simulation studies. The experimental results are satisfied by IEC 61000-3-2 current harmonic standard.

Average sliding control method applied on power factor correction converter for decreasing input current total harmonic distortion using digital signal processor

This article uses computer-aided design tools to develop a describing function analysis of a pendulum clock. We design the escapement as a control system that allows the pendulum to provide the required time keeping and, at the same time, add enough energy to the pendulum to overcome the damping caused by friction. We use analysis tools in the MATLAB Control System Toolbox to accomplish the design and analysis. A by-product of our analysis is a simple MATLAB/Simulink model and a script that generates describing functions for any arbitrary nonlinear system (including systems with multiple nonlinearities and with frequency-dependent describing functions). We also develop a Simulink model of the clock to verify the results of the analysis. The analysis described here uses some object-oriented programming features of MATLAB.

C. Schwartz

Papers

Describing function analysis using MATLAB and Simulink