Command Governor Approach Research Articles

A command governor approach to set-theoretic model reference adaptive control for enforcing partially adjustable performance guarantees

In feedback control, the presence of system uncertainties cause system state trajectories to deviate from their ideal responses. In practice, a subset of these trajectories can be more critical than the rest due to physical and/or performance characteristics associated with a problem of interest. Hence, it is desired not only to have performance guarantees on the entire system state trajectories but also to be able to adjust the resulting worst-case performance bound for that critical subset. Yet, in model reference adaptive control of uncertain dynamical systems, assigning performance bounds on a subset of system trajectories is not trivial. This paper addresses this gap by proposing a new control architecture that has the capability to enforce a user-defined performance bound on the selected subset of dynamical system trajectories, entitled as partially adjustable performance guarantees. The proposed architecture is predicated on a set-theoretic treatment and utilizes a two-level constructive design framework. In particular, we first form an auxiliary state dynamics in order to construct the auxiliary system error vector between uncertain dynamical system states and this auxiliary dynamics states. This construction aids a control designer to weigh each element of the auxiliary system error vector independently, while enforcing performance bounds on the norm of this error vector. Then, a command governor mechanism is designed for driving a feasible user-selected subset of system states to a close (and user-controllable) neighborhood of the corresponding reference model states. This results in adjustable performance guarantees on a subset of system error trajectories.

A Command Governor Approach for the Voltage Control in Smart Grids with Distributed Generation and Storage Devices

High penetration of Distributed Generation (DG) plants in Medium Voltage (MV) / Load Voltage (LV) power grids may lead to abrupt voltage raises. Typical critical scenarios are represented by either low demand conditions or high power production from renewable sources. Traditional approaches used to face such a situation involve both the disconnection of the distributed generators and the curtailment of the generated power leading to several disadvantages. However, new technologies allow an active orchestration between some controllable devices of the grid, e.g. distributed generators, MV/HV transformers, storage devices in order to maintain relevant system variables within prescribed operative constraints in response to unexpected adverse conditions. This work addresses the online management of distributed generators and storage devices. The approach is based on Command Governor (CG) ideas and is based on the resolution at each time instant of an optimization problem containing explicit constraints related to voltage bounds and operational limits of adopted devices.

Reactive Power Management for Voltage Rise Mitigation in Distribution Networks with Distributed Generation: a Command Governor Approach

Abstract: High penetration of Distributed Generation (DG) in Medium Voltage (MV) power grids is usually a reason of abrupt voltage raises. In this respect critical scenarios are represented by both low demand conditions and high power production from renewable sources. In order to cope with the possibly resulting voltage limits violation, a typical adopted approach is the disconnection of the distributed generators or the curtailment of the generated power leading to several disadvantages. To address this issue an online management of the reactive power of distributed generators is presented. The approach is based on Command Governor (CG) ideas and is aimed at solving a constrained voltage regulation problem in both centralized and distributed ways. The approach foresees an active coordination between some controllable devices of the grid, e.g. distributed generators, MV/HV transformers, in order to maintain relevant system variables within prescribed operative constraints in response to unexpected adverse conditions. Simulation results show that the proposed approach is more effective than approaches suggested by the current Italian norms on reactive power compensation.

A Distributed Multi-Agent Command Governor Strategy for the Coordination of Networked Interconnected Systems

A novel distributed coordination strategy is presented for networked, locally regulated and possibly dynamically coupled, interconnected systems. Such systems are assumed to be connected via data links and subject to pointwise-in-time global constraints on some relevant variables of them, to be enforced as a coordination goal along the overall system evolutions. Such a coordination-by-constraint paradigm is accomplished by resorting to a novel distributed multi-agent Command Governor (CG) approach where each agent is in charge to locally modify, whenever necessary and on the basis of a reduced amount of data exchanged with the other agents, the prescribed set-points to the regulated subsystems so that the coordination constraints are always satisfied. The strategy is described and its main properties analyzed, especially for what it concerns the stability, feasibility and Pareto optimality of the solution. A liveness analysis concerning the possible presence of undesirable Nash equilibria and/or deadlock situations is presented and a discussion on the scalability of the solution with the problem dimension is reported as well. The constrained coordination of a network of interconnected water tanks is presented as a final example in order to show the effectiveness of the proposed strategy.

Collision avoidance command governor for multi-vehicle unmanned systems

SUMMARY In this paper, we consider the problem of coordinating a collection of autonomous unmanned vehicles while guaranteeing collision avoidance. Each vehicle is regulated by a local controller that ensures stability and provides desired path tracking performance in the absence of constraints. The fulfillment of coordination tasks (e.g., collision avoidance) and local constraints (e.g., input saturation constraints) is achieved through a command governor (CG) strategy that, whenever necessary, modifies the nominal paths of the vehicles. First, a centralized CG approach is proposed and fully analyzed. Then, a more interesting distributed implementation requiring low communication rates is discussed. Both approaches make use of a receding horizon strategy and require the on-line solution of mixed-integer optimization programs. Finally, an example is given for illustration purposes. Copyright © 2013 John Wiley & Sons, Ltd.

Sensorless supervision of linear dynamical systems: The Feed-Forward Command Governor approach

This paper proposes a novel class of Command Governor (CG) strategies for input and state-related constrained discrete-time LTI systems subject to bounded disturbances in the absence of explicit state or output measurements. While in traditional CG schemes the set-point manipulation is undertaken on the basis of either the actual measure of the state or its suitable estimation, it is shown here that the CG design problem can be solved, with limited performance degradation and with similar properties, also in the case that such an explicit measure is not available. This approach, which will be referred to as the Feed-Forward CG (FF-CG) approach, may be a convenient alternative CG solution in all situations whereby the cost of measuring the state may be a severe limitation, e.g. in distributed or decentralized applications. In order to evaluate the method proposed here, numerical simulations on a physical example have been undertaken and comparisons with the standard state-based CG solution reported.

Distributed collision avoidance for interacting vehicles: a command governor approach

This paper deals with a distributed coordination problem including collision avoidance. The problem is solved by using a Command Governor strategy based on mixed integer optimization. First, we present an algorithm to find an appropriate command in the centralized case, then a distributed sequential procedure is described. Simulations are reported for comparisons.

Fault tolerance enhancement in distribution power grids: a voltage set-point reconfiguration approach

In this paper we present a supervisory strategy for voltage regulation control problems in electrical power grids based on the Command Governor (CG) approach. The scheme consists of reconfiguring the nominal voltage set-point of the network in the presence of Distributed Generation (DG) units to avoid operative constraint violations in response to unexpected load changes and/or failures. Such a reconfiguration capability allows one to enhance the fault tolerability and to prevent undesirable phenomena from occurring in the electrical power grid. We focus on an electrical Medium Voltage (MV) distribution network subject to coordination constraints on maximum load voltages deviations and possible failures on the on-load tap changers (OLTC). Simulation results show that the CG unit ensures feasible evolutions of the overall network by reconfiguring the nominal voltage set-point, whenever critical events occur.

A PASSIVITY-BASED COMMAND GOVERNOR CONTROL APPROACH

In this paper an extension of the basic Command Governor approach for manipulation of dynamic systems is proposed. This work presents a way to incorporate kinetostatic feedback to the operator maintaining the passivity of the closed-loop system. Preliminary simulation results, without time-delay, are presented showing the theoretically expected effectiveness of the proposed method.

A command governor approach for voltage regulation of medium voltage distribution networks

In this paper a Command Governor strategy is used for voltage regulation in Medium and Low Voltage (MV/LV) distribution networks subject to load voltage drops. The voltage regulation is formulated as a constrained tracking problem by imposing that the voltages at the LV customer loads have minimum deviation from their nominal values, each other compatible with prescribed bounds on their maximum deviations. Simulations studies show the effectiveness of the proposed approach.

A command governor approach to formation flying control problems

This paper provides a solution to a class of satellites' formations reconfiguration and keeping problems under input-saturation and formation accuracy constraints and subject to persistent disturbances. Both relative position and attitude dynamics have been considered. The proposed control scheme aims at producing, provided that the initial conditions are admissible, system evolutions that fulfill the coordination constraints at any time and satisfy desirable control performance. This is accomplished by resorting to the Command Governor approach. An example is provided for showing the effectiveness of the technique.

Control Under Constraints: An Application of the Command Governor Approach to an Inverted Pendulum

The purpose of this paper is to exhibit the relevance of command governor (CG) strategies in real control problems, where consideration has to be given to nonlinearities, model uncertainties, disturbances, input and state-related constraints and requirements of moderate computational complexity. The plant considered is a laboratory cart/rod inverted pendulum for which the control problem consists of regulating vertically its rod subject to motor voltage and rod angle constraints, while providing full-range optimized tracking performance for the cart position. The merits of the proposed CG technique in this application are investigated, and its advantages over classic linear time-invariant design methods are discussed.