Dependable Control for Wireless Distributed Control Systems

Abstract

Abstract:The use of wireless communications for real-time control applications poses several problems related to the comparatively low reliability of the communication channels. This paper is concerned with adaptive and predictive application-level strategies for ameliorating the effects of packet losses and burst errors in industrial sampled-data Distributed Control Systems (DCSs), which are implemented via one or more wireless and/or wired links, possibly spanning multiple hops. The paper describes an adaptive compensator that reconstructs the best estimates (in a least squares sense) of a sequence of one or more missing sensor node data packets in the controller node. At each sample time, the controller node calculates the current control, and a prediction of future controls to apply over a short time horizon; these controls are forwarded to the actuator node every sample time step. A simple design method for a digital Proportional Integral Derivative (PID)-like adaptive controller is also described for use in the controller node. Together these mechanisms give robustness to packet losses around the control loop; in addition, the majority of the computational overhead resides in the controller node. An implementation of the proposed techniques is applied to a case study using a Hardware in the Loop (HIL) test facility, and favorable results (in terms of both performance and computational overheads) are found when compared to an existing robust control method for a DCS experiencing artificially induced burst errors.

Exploring the Limits of Floating-Point Resolution for Hardware-In-the-Loop Implemented with FPGAs

“…Table 3 summarizes the theoretically minimum floating-point format needed for every load. These widths have been calculated using Equations (7) and (8) and the scenarios of Table 2. Regardless of the calculated widths, all scenarios have been simulated with significand widths between 24 and 32 bits.…”

“…The problem in power converter HIL models is not the number of exponent bits, as the magnitudes are not extremely big or small, but the number of bits of the significand. Therefore, only the significand field should be enlarged reaching the number of bits calculated using Equations (7) and (8).…”

“…HIL simulation presents numerous advantages such as having a safe environment to test controllers, allowing the use of the controller in its final implementation, even before building the real plant to be controlled. HIL techniques are being increasingly implemented using computers [6][7][8][9][10][11] and also digital devices like FPGAs (Field Programmable Gate Array) [12][13][14][15][16][17]. The latter make it possible to perform complex calculations faster.…”

A Control Methodology for Load Sharing System Restoration in Islanded DC Micro Grid with Faulty Communication Links

“…Therefore, DC microgrids avoid cumbersome DC-AC-DC generation [1][2][3][4]. However, the usage of DC microgrids at distribution scale is increasing with the collaboration of various renewable resources due to the higher penetration of electric vehicles [5][6][7].…”