https://hdl.handle.net/1721.1/89011 Fri, 03 Apr 2026 21:04:16 GMT 2026-04-03T21:04:16Z https://hdl.handle.net/1721.1/120117 A Systems and Control Perspective of CPS Security Dibaji, Seyed Mehran; Pirani, Mohammad; Flamholz, David Bezalel; Annaswamy, Anuradha M.; Johansson, Karl Henrik; Chakrabortty, Aranya Abstract—The comprehensive integration of instrumentation, communication, and control into physical systems has led to the study of Cyber-Physical Systems (CPS), a field that has recently garnered increased attention. A key concern that is ubiquitous in CPS is a need to ensure security in the face of cyber attacks. In this paper, we carry out a survey of systems and control methods that have been proposed for the security of CPS. We classify these methods into three categories based on the type of defense proposed against the cyberattacks: prevention, resilience, and detection & isolation. A unified threat assessment metric is proposed in order to evaluate how CPS security is achieved in each of these three cases. Also surveyed are risk assessment tools and the effect of network topology on CPS security. An emphasis has been placed on power and transportation applications in the overall survey. Tue, 22 Jan 2019 00:00:00 GMT https://hdl.handle.net/1721.1/120117 2019-01-22T00:00:00Z https://hdl.handle.net/1721.1/107969 Delay-Aware Control Designs of Wide-Area Power Networks: Proofs of the Results Dibaji, Seyed Mehran; Yildiz, Yildiray; Annaswamy, Anuradha; Chakrabortty, Aranya; Soudbakhsh, Damoon The purpose of this document is to provide proofs of the results in Dibaji et al. (2017). Fri, 07 Apr 2017 00:00:00 GMT https://hdl.handle.net/1721.1/107969 2017-04-07T00:00:00Z https://hdl.handle.net/1721.1/107408 Towards Resilient Cyber-Physical Energy Systems Baros, Stefanos; Shiltz, Dylan; Jaipuria, Prateek; Hussain, Alefiya; Annaswamy, Anuradha M. In this paper, we develop a system-of-systems framework to address cyber-physical resilience, the ability to withstand the combined presence of both cyber attacks and physi-cal faults. This framework incorporates a definition of re-silience, a resilience metric as well as a resilient control de-sign methodology. The resilient control architecture utilizes a hybrid optimal control methodology combined with a dy-namic regulation market mechanism (DRMM), and is evalu-ated in the context of frequency regulation at a transmission grid. The framework enables the evaluation of both the clas-sical robust control properties and emerging resilient control properties under both cyber attacks and physical faults. The proposed framework is used to assess resilience of a Cyber-Physical Energy System (CPES) when subjected to both cyber and physical faults via DETERLab. DETERLab, a testbed capable of emulating high fidelity, cybersecure, net-worked systems, is used to construct critical scenarios with physical faults emulated in the form of generator outages and cyber faults emulated in the form of Denial of Service (DoS) attacks. Under these scenarios, the resilience and per-formance of a CPES that is comprised of 56 generators and 99 consumers is evaluated using the hybrid-DRMM control methodology. Tue, 14 Mar 2017 00:00:00 GMT https://hdl.handle.net/1721.1/107408 2017-03-14T00:00:00Z https://hdl.handle.net/1721.1/101750 Supplementary Materials to "Adaptive Output-Feedback Control for A Class of Multi-Input-Multi-Output Plants with Applications to Very Flexible Aircraft" Qu, Zheng; Annaswamy, Anuradha; Lavretsky, Eugene A dominant presence of parametric model uncertainties motivates an adaptive approach for control of very flexible aircraft (VFA). This paper proposes an adaptive controller that includes a baseline design based on observers and parameter adaptation based on a closed-loop reference model (CRM), and is applicable for a class of multi-input multi-output (MIMO) plants where number of outputs exceeds number of inputs. In particular, the proposed controller allows the plant to have first-order actuator dynamics and parametric uncertainties in both plant and actuator dynamics. Conditions are delineated under which this controller can guarantee stability and asymptotic reference tracking, and the overall design is validated on a nonlinear VFA model. Tue, 22 Mar 2016 00:00:00 GMT https://hdl.handle.net/1721.1/101750 2016-03-22T00:00:00Z https://hdl.handle.net/1721.1/101661 Adaptive Control of a Generic Hypersonic Vehicle Wiese, Daniel P.; Annaswamy, Anuradha M.; Muse, Jonathan A.; Bolender, Michael A.; Lavretsky, Eugene This paper presents an adaptive augmented, gain-scheduled baseline LQR-PI controller applied to the Road Runner six-degree-of-freedom generic hypersonic vehicle model. Uncertainty in control effectiveness, longitudinal center of gravity location, and aerodynamic coefficients are introduced in the model, as well as sensor bias and noise, and input time delays. The performance of the baseline controller is compared to the same design augmented with one of two different model-reference adaptive controllers: a classical open- loop reference model design, and modified closed-loop reference model design. Both adaptive controllers show improved command tracking and stability over the baseline controller when subject to these uncertainties. The closed-loop reference model controller offers the best performance, tolerating a reduced control effectiveness of 50%, rearward center of gravity shift of up to -1.6 feet (11% of vehicle length), aerodynamic coefficient uncertainty scaled 4× the nominal value, and sensor bias of up to +3.2 degrees on sideslip angle measurement. The closed-loop reference model adaptive controller maintains at least 70% of the delay margin provided by the robust baseline design when subject to varying levels of uncertainty, tolerating input time delays of between 15-41 ms during 3 degree angle of attack doublet, and 80 degree roll step commands. Thu, 10 Mar 2016 00:00:00 GMT https://hdl.handle.net/1721.1/101661 2016-03-10T00:00:00Z https://hdl.handle.net/1721.1/101648 Adaptive Output Feedback Based on Closed-Loop Reference Models for Hypersonic Vehicles Wiese, Daniel P.; Annaswamy, Anuradha M.; Muse, Jonathan A.; Bolender, Michael A.; Lavretsky, Eugene This paper presents a new method of synthesizing an output feedback adaptive controller for a class of uncertain, non-square, multi-input multi-output systems that often occur in hypersonic vehicle models. The main challenge that needs to be addressed is the determination of a corresponding square and strictly positive real transfer function. This paper proposes a new procedure to synthesize two gain matrices that allows the realization of such a transfer function, thereby allowing a globally stable adaptive output feedback law to be generated. The unique features of this output feedback adaptive controller are a baseline controller that uses a Luen- berger observer, a closed-loop reference model, manipulations of a bilinear matrix inequality, and the Kalman- Yakubovich Lemma. Using these features, a simple design procedure is proposed for the adaptive controller, and the corresponding stability property is established. The proposed adaptive controller is compared to the classical multi-input multi-output adaptive controller. A numerical example based on a 6 degree-of-freedom nonlinear, scramjet powered, blended wing-body generic hypersonic vehicle model is presented. The adaptive output feedback controller is applied to result in stable tracking of uncertainties that destabilize the baseline linear output feedback controller. Wed, 09 Mar 2016 00:00:00 GMT https://hdl.handle.net/1721.1/101648 2016-03-09T00:00:00Z https://hdl.handle.net/1721.1/101647 Sequential Loop Closure Based Adaptive Autopilot Design for a Hypersonic Vehicle Wiese, Daniel P.; Annaswamy, Anuradha M.; Muse, Jonathan A.; Bolender, Michael A.; Lavretsky, Eugene This paper presents a sequential loop closure approach to designing a velocity and altitude tracking au- topilot for a hypersonic vehicle. The control architecture consists of two decoupled control subsystems, one for velocity, the other for altitude. The velocity control subsystem consists of an adaptive augmented baseline controller. The altitude control subsystem consists of an adaptive inner-loop designed to accommodate uncer- tainties in the stability and control derivatives of the aircraft, and track pitch-rate commands. The outer-loop is designed independent of the inner loop, and guarantees stability of the closed-loop system. The outer-loop uses components of a closed-loop reference model, and generates the appropriate pitch-rate commands for the inner loop such that the hypersonic vehicle tracks the desired altitude. A numerical example based on a scram- jet powered, blended wing-body generic hypersonic vehicle model is presented, demonstrating the efficacy of the proposed control design. Wed, 09 Mar 2016 00:00:00 GMT https://hdl.handle.net/1721.1/101647 2016-03-09T00:00:00Z https://hdl.handle.net/1721.1/99356 A Practical Integration of Automatic Generation Control and Demand Response Shiltz, Dylan; Annaswamy, Anuradha For a power grid to operate properly, electrical frequency must be continuously maintained close to its nominal value. Increasing penetration of distributed generation, such as solar and wind generation, introduces fluctuations in active power while also reducing the natural inertial response of the electricity grid, creating reliability concerns. While frequency regulation has traditionally been achieved by controlling generators, the control of Demand Response resources has been recognized in recent smart grid literature as an efficient means for providing additional regulation capability. To this end, several control methodologies have been proposed recently, but various features of these proposals make their practical implementations difficult. In this paper, we propose a new control algorithm that facilitates optimal frequency regulation through direct control of both generators and Demand Response, while addressing several issues that prevent practical implementation of other proposals. In particular, i) our algorithm is ideal for control over a large, low-bandwidth network as communication and measurement is only required every 2 seconds, ii) it enables Demand Response resources to recover energy lost during system transients, and iii) it accommodates both measured disturbances and unmeasured disturbances. We demonstrate the viability of our approach through dynamic simulations on a 118-bus grid model. Fri, 16 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99356 2015-10-16T00:00:00Z https://hdl.handle.net/1721.1/99198 Adaptive Output-Feedback Control for A Class of Multi-Input-Multi-Output Plants with Applications to Very Flexible Aircraft Qu, Zheng; Annaswamy, Anuradha; Lavretsky, Eugene A dominant presence of parametric model uncertainties necessitates an adaptive approach for control of very flexible aircraft (VFA). This paper proposes an adaptive controller that includes a baseline design based on observers and parameter adaptation based on a closed-loop reference model (CRM), and is applicable for a class of multi-input multi-output (MIMO) plants where number of outputs exceeds number of inputs. In particular, the proposed controller allows the plant to have first-order actuator dynamics and parametric uncertainties in both plant and actuator dynamics. Conditions are delineated under which this controller can guarantee stability and asymptotic reference tracking, and the overall design is validated using simulations on a nonlinear VFA model. Wed, 07 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99198 2015-10-07T00:00:00Z https://hdl.handle.net/1721.1/99197 A Model-based Dynamic Toll Pricing Strategy for Controlling Highway Traffic Phan, Thao; Annaswamy, Anuradha; Yanakiev, Diana; Tseng, Eric A model-based approach to dynamic toll pricing has been developed to provide a systematic method for determining optimal freeway pricing schemes. A novel approach is suggested for alleviating congestion, which utilizes identified models of driver behavior and traffic flow, as well as optimization of the target density to maximize throughput. Real-time traffic information from on-road sensors is integrated with historical information to provide feedback and preview for the dynamic toll price controller. The algorithm developed here provides an opportunity to improve on existing toll policy by guaranteeing minimum speeds for toll lane drivers, maintaining consistent traffic flow for the other drivers, and optimizing the overall traffic throughput Wed, 07 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99197 2015-10-07T00:00:00Z https://hdl.handle.net/1721.1/99196 Utilization-Aware Adaptive Back-Pressure Traffic Signal Control Chang, Wanli; Chakraborty, Samarjit; Annaswamy, Anuradha Back-pressure control of traffic signal, which computes the control phase to apply based on the real-time queue lengths, has been proposed recently. Features of it include (i) provably maximum stability, (ii) low computational complexity, (iii) no requirement of prior knowledge in traffic demand, and (iv) requirement of only local information at each intersection. The latter three points enable it to be completely distributed over intersections. However, one major issue preventing backpressure control from being used in practice is the utilization of the intersection, especially if the control phase period is fixed, as is considered in existing works. In this paper, we propose a utilization-aware adaptive algorithm of back-pressure traffic signal control, which makes the duration of the control phase adaptively dependent on the real-time queue lengths and strives for high utilization of the intersection. While advantages embedded in the back-pressure control are kept, we prove that this algorithm is work-conserving and achieves the maximum utilization. Simulation results on an isolated intersection show that the proposed adaptive algorithm has better control performance than the fixed-period back-pressure control presented in previous works. Wed, 07 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99196 2015-10-07T00:00:00Z https://hdl.handle.net/1721.1/99195 Foundations of Infrastructure CPS Annaswamy, Anuradha; Hussain, Alefiya; Chakrabortty, Aranya; Cvetkovic, Milos Infrastructures have been around as long as urban centers, supporting a society’s needs for its planning, operation, and safety. As we move deeper into the 21st century, these infrastructures are becoming smart – they monitor themselves, communicate, and most importantly self-govern, which we denote as Infrastructure CPS. Cyber-physical systems are now becoming increasingly prevalent and possibly even mainstream. With the basics of CPS in place, such as stability, robustness, and reliability properties at a systems level, and hybrid, switched, and eventtriggered properties at a network level, we believe that the time is right to go to the next step, Infrastructure CPS, which forms the focus of the proposed tutorial. We discuss three different foundations, (i) Human Empowerment, (ii) Transactive Control, and (iii) Resilience. This will be followed by two examples, one on the nexus between power and communication infrastructure, and the other between natural gas and electricity, both of which have been investigated extensively of late, and are emerging to be apt illustrations of Infrastructure CPS. Wed, 07 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99195 2015-10-07T00:00:00Z https://hdl.handle.net/1721.1/99194 Frequency Control using Cooperative Demand Response through Accumulated Energy Cvetkovic, Milos; Annaswamy, Anuradha This paper proposes a hierarchical control architecture for engaging demand into providing primary frequency response services. The proposed architecture relies on the use of information about accumulated energy for the aggregation of demand capabilities and dissagregation of demand responsibilities. Since the accumulated energy has a distinct additive property, the aggregation/disaggregation of demand becomes straightforward. Additional unique features of the proposed architecture are that it: i) includes the information of inflexible load in the aggregated demand, ii) allows for intuitive cooperation between load aggregators. Conditions for stability under cooperating load aggregators are derived. Finally, simulations are carried out on the IEEE 39-bus system to illustrate the proposed concepts of aggregation, disaggregation and cooperation. Wed, 07 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99194 2015-10-07T00:00:00Z https://hdl.handle.net/1721.1/99193 Analysis of Slow Convergence Regions in Adaptive Systems Nouwens, Oscar; Annaswamy, Anuradha; Lavretsky, Eugene We examine convergence properties of errors in a class of adaptive systems that corresponds to adaptive control of linear time-invariant plants with state variables accessible. We demonstrate the existence of a sticking region in the error space where the state errors move with a finite velocity independent of their magnitude. We show that these properties are also exhibited by adaptive systems with closed-loop reference models which have been demonstrated to exhibit improved transient performance as well as those that include an integral control in the inner-loop. Simulation and numerical studies are included to illustrate the size of this sticking region and its dependence on various system parameters Wed, 07 Oct 2015 00:00:00 GMT https://hdl.handle.net/1721.1/99193 2015-10-07T00:00:00Z https://hdl.handle.net/1721.1/98917 Squaring-Up Method for Relative Degree Two Plants Qu, Zheng; Annaswamy, Anuradha; Lavretsky, Eugene Abstract--- Non-square multi-input-multi-output (MIMO) plants are becoming increasingly common, as the addition of multiple sensors is becoming prevalent. However, square systems are needed sometimes as an leverage when it comes to design and analysis, as they possess desirable properties such as strict positive realness. This paper presents a squaring up method that adds artificial inputs to a class of MIMO plants with relative degree two and stable transmission zeros, where number of outputs exceeds number of inputs. The proposed method is able to produce a square plant that has stable transmission zeros and uniform/nonuniform relative degree, and is used to carry out adaptive control of this class of plants and shown to lead to satisfactory performance in a numerical study. Mon, 28 Sep 2015 00:00:00 GMT https://hdl.handle.net/1721.1/98917 2015-09-28T00:00:00Z https://hdl.handle.net/1721.1/98482 Supplementary Materials to "Adaptive Output-Feedback Control for Relative Degree Two Systems Based on Closed-Loop Reference Models" Qu, Zheng Abstract--- In this paper, a new adaptive output-feedback controller for multi-input-multi-output (MIMO) linear plant models with relative degree two is developed. The adaptive controller includes a baseline design based on observers and parameter adaptation based on a closed-loop reference model (CRM). The overall design guarantees robust stability and tracking performance in the presence of parametric uncertainties that are commonly seen in aircraft applications. Supplementary materials for the CDC paper. Mon, 14 Sep 2015 00:00:00 GMT https://hdl.handle.net/1721.1/98482 2015-09-14T00:00:00Z https://hdl.handle.net/1721.1/97541 A Delay-Aware Cyber-Physical Architecture for Wide-Area Control of Power Systems Soudbakhsh, Damoon; Chakrabortty, Aranya; Alvarez, Francisco; Annaswamy, Anuradha In this paper we address the problem of widearea control of power systems in presence of different classes of network delays. We pose the control objective as an LQR minimization of the electro-mechanical states of the swing equations, and exploit flexibilities and transparencies of the communication network such as scheduling policies, bandwidth to co-design a delay-aware state feedback control law. Hence, unlike the traditional robust control designs, our design is delayaware, not delay-tolerant. A key feature of our method is to retain the samples of the control input until a desired time instant using shapers before releasing them for actuation to regulate the delays entering the controller. In addition, our codesign includes an overrun management strategy to guarantee stability of the closed-loop power system model in case of occasional PMU data losses. This strategy allows dropping messages with very large delays, reducing resource utilization during busy network times, and improving overall performance of the system. We illustrate our results using a 50-bus, 14- generator, 4-area power system model, and show how the proposed arbitrated controller can guarantee significantly better closed-loop performance than traditional robust controllers. Sun, 28 Jun 2015 00:00:00 GMT https://hdl.handle.net/1721.1/97541 2015-06-28T00:00:00Z https://hdl.handle.net/1721.1/97540 Co-Design of Arbitrated Network Control Systems with Overrun Strategies Soudbakhsh, Damoon; Phan, Linh; Annaswamy, Anuradha; Sokolsky, Oleg This paper addresses co-design of platform and control of multiple control applications in a network control system. Limited and shared resources among control and noncontrol applications introduce delays in transmitted messages. These delays in turn can degrade system performance and cause instabilities. In this paper, we propose an overrun framework together with a co-design to achieve both optimal control performance and efficient resource utilization. The starting point for this framework is an Arbitrated Network Control System (ANCS) approach, where flexibility and transparency in the network are utilized to arbitrate control messages. Using a two-parameter model for delays experienced by control messages that classifies them as nominal, medium, and large, we propose a controller that switches between nominal, skip and abort strategies. An automata-theoretic technique is introduced to derive analytical bounds on the abort and skip rates. A co-design algorithm is proposed to optimize the selection of the overrun parameters. A case study is presented that demonstrates the ANCS approach, the overrun framework and the overall co-design. Sun, 28 Jun 2015 00:00:00 GMT https://hdl.handle.net/1721.1/97540 2015-06-28T00:00:00Z https://hdl.handle.net/1721.1/96684 A Dynamic Market Mechanism for Integration of Renewables and Demand Response Knudsen, Jesper; Hansen, Jacob; Annaswamy, Anuradha M. The most formidable challenge in assembling a Smart Grid is the integration of a high penetration of renewables. Demand Response, a largely promising concept, is increasingly discussed as a means to cope with the intermittent and uncertain renewables. In this paper, we propose a dynamic market mech- anism that reaches the market equilibrium through continuous negotiations between key market players. In addition to incor- porating renewables, this market mechanism also incorporates a quantitative taxonomy of demand response devices, based on the inherent magnitude, run-time, and integral constraints of demands. The dynamic market mechanism is evaluated on an IEEE 118 Bus system, a high fidelity simulation model of the Midwestern United States power grid. The results show how the proposed mechanism can be utilized to determine combinations of demand response devices in the presence of intermittent and uncertain renewables with varying levels of penetration so as to result in a desired level of Social Welfare. Tue, 21 Apr 2015 00:00:00 GMT https://hdl.handle.net/1721.1/96684 2015-04-21T00:00:00Z https://hdl.handle.net/1721.1/96683 An Integrated Dynamic Market Mechanism for Real-time Markets and Frequency Regulation Shiltz, Dylan; Cvetkovic, Milos; Annaswamy, Anuradha M. Tue, 21 Apr 2015 00:00:00 GMT https://hdl.handle.net/1721.1/96683 2015-04-21T00:00:00Z https://hdl.handle.net/1721.1/96429 Adaptive Output Feedback Based on Closed-Loop Reference Models for Hypersonic Vehicles Annaswamy, Anuradha M.; Wiese, Daniel P.; Muse, Jonathan A.; Bolender, Michael A.; Lavretksy, Eugene This paper presents a new method of synthesizing an output feedback adaptive controller for a class of uncertain, non-square, multi-input multi-output systems that often occur in hypersonic vehicle models. The main challenge that needs to be addressed is the determination of a corresponding square and strictly positive real transfer function. This paper proposes a new procedure to synthesize two gain matrices that allows the realization of such a transfer function, thereby allowing a globally stable adaptive output feedback law to be generated. The unique features of this output feedback adaptive controller are a baseline controller that uses a Luenberger observer, a closed-loop reference model, manipulations of a bilinear matrix inequality, and the Kalman-Yakubovich Lemma. Using these features, a simple design procedure is proposed for the adaptive controller, and the corresponding stability property is established. The proposed adaptive controller is compared to the classical multi-input multi-output adaptive controller. A numerical example based on a scramjet powered, blended wing-body generic hypersonic vehicle model is presented. The 6 degree-of-freedom nonlinear vehicle model is linearized, giving the design model for which the controller is synthesized. The adaptive output feedback controller is then applied to an evaluation model, which is nonlinear, coupled, and includes actuator dynamics, and is shown to result in stable tracking in the presence of uncertainties that destabilize the baseline linear output feedback controller. Tue, 07 Apr 2015 00:00:00 GMT https://hdl.handle.net/1721.1/96429 2015-04-07T00:00:00Z https://hdl.handle.net/1721.1/96428 Adaptive Output-Feedback Control with Closed-Loop Reference Models and Applications to Very Flexible Aircraft Qu, Zheng; Anuradha, Annaswamy This paper proposes an adaptive controller for a class of multi-input multi-output (MIMO) plants where the number of outputs is larger than the number of inputs, an example of which is very-flexible aircraft (VFA). A dominant presence of model uncertainties and actuator anomalies necessitates an adaptive approach for control of VFA. The proposed controller, denoted as the adaptive SPR/LTR controller, combines a baseline observer-based design with loop transfer recovery (LTR) properties and an adaptive design based on strictly positive real (SPR) transfer functions. In addition to accommodating the absence of full state measurements, the controller includes a reference model that also plays the role of an observer through a closed-loop component. Conditions are delineated under which this controller, can guarantee asymptotic reference tracking, and the control design is validated using a VFA model around a single equilibrium flight condition with 707 states, 12 outputs and 2 control inputs. Simulation results show that the adaptive controller not only ensures stability but also recovers a nominal performance both in time domain and in frequency domain despite the presence of varying wing shape and actuator anomalies. Preprint of JGCD 2015-01-G001282 paper. Tue, 07 Apr 2015 00:00:00 GMT https://hdl.handle.net/1721.1/96428 2015-04-07T00:00:00Z