Pradeep Gillella

Time-Varying Internal Model-Based Control of a Camless Engine Valve Actuation System

This paper focuses on the motion control of a camless engine valve actuation system during both steady state and transient engine operation. The precise tracking performance obtained using controllers based on the internal model principle for the constant speed case motivates the investigation under engine speed transients. The cyclic but aperiodic reference signal to be tracked is modeled using two different methods, i.e., as a combination of frequency varying sinusoids in the time domain or as a repetitive (periodic) signal in the rotational angle domain. The recently developed time-varying internal model-based controller is ideally suited for both the approaches. The details associated with the design of the controller for each of the approaches are first documented. A quantitative analysis comparing various performance metrics for both the approaches helps to highlight the relative advantages of each method. The experimental results from a prototype camless engine valve actuation system are then presented to help in validating the overall effectiveness of the proposed control method.

Design, Modeling, and Control of a Camless Valve Actuation System With Internal Feedback

This paper presents the modeling and control design of a new fully flexible engine valve actuation system, which is an enabler for camless engines. Unlike existing electromechanical or servo-actuated electrohydraulic valve actuation systems, precise valve motion control is achieved using a very stiff hydromechanical internal-feedback mechanism. The entire feedback mechanism is built into the physical design of the system. The external control only activates or deactivates the feedback mechanism in real time using simple two-state valves. This helps reduce the system cost, and thus enables mass production. The trajectory of the closed-loop system is purely dependent on the design parameters of the internal-feedback system. A mathematical model of the system has been developed and validated with experimental results from a prototype system. The “area-schedule” is identified as the most critical design feature, which affects the trajectory of the closed-loop system and, therefore, needs to be designed systematically to optimize the performance of the system as well as improve its robustness. By treating this feature as the feedback-control variable, the design problem is transformed into a nonlinear optimal control problem and solved numerically using dynamic programming. The effectiveness of the proposed design procedure is verified with case studies.

Robust stabilization of discrete linear time varying internal model based system

This paper focuses on a low order robust stabilizer design for linear time varying (LTV) internal model based system in the discrete time domain. While adopting the output feedback gain injection based stabilization structure for continuous LTV systems, the discrete stabilization synthesis has its unique challenges, and the approach formulated in the continuous domain cannot be directly applied. Therefore, in this paper, the stabilization for LTV internal model based control in the discrete setting is formulated. Its challenges are revealed and methods to convert it into a convex optimization based synthesis are proposed. The approach is then validated through simulation analysis and experimental investigations.Copyright

A new stabilizer for ltv internal model based system and its application to camless engine valve actuation

This paper focuses on the stabilization of an internal model based control system for reference tracking/disturbance rejection, where the physical plant is linear time invariant while the generating dynamics of the reference/disturbance is time varying. Given the inevitable linear time varying (LTV) nature of the internal model unit resulting from the time varying generating dynamics, a critical problem to be addressed is the design of a low order and robust stabilizer for the entire augmented system. While a parameter-dependent output injection based stabilizer was introduced in our previous work, the new method proposed in this paper reduces the conservativeness in the control synthesis and thus enables a more effective control design especially for the problem involving LTI physical plant with LTV internal model dynamics. The proposed approach is then validated through experimental investigations on a camless engine valve actuation system, where robust and precise tracking performance is demonstrated.

Modeling and control design of a camless valve actuation system

This paper presents the modeling and control design of a new fully flexible engine valve actuation system which is an enabler for camless engines. Unlike existing electromechanical or servo actuated electro-hydraulic valve actuation systems, precise valve motion control is achieved with a hydromechanical internal feedback mechanism. This feedback mechanism can be turned on or off in real-time using simple two state valves which helps reduce the system cost and enables mass production. Since the external control only activates or deactivates the internal feedback mechanism, the trajectory of the entire closed-loop system is purely dependent on the design parameters of the internal feedback system. A mathematical model of the system is developed to evaluate the effect of each of the design parameters. The “Area-schedule” is identified as the key design feature which affects the trajectory of the closed-loop system. It needs to be designed systematically to optimize the performance of the system as well as improve its robustness. By treating this feature as the feedback control variable, the design problem is transformed into a nonlinear optimal control problem which is later solved using the numerical dynamic programming method. The effectiveness of the designed area-schedules is verified with simulations.

Low-Order Stabilizer Design for Discrete Linear Time-Varying Internal Model-Based System

This paper focuses on the low-order stabilizer design for linear time-varying (LTV) internal model-based system in the discrete time domain. While an output feedback gain injection-based stabilizer was proposed for continuous LTV systems in previous work, the synthesis in discrete domain has its unique challenges, and the approach formulated in the continuous domain cannot be directly applied. In this paper, the stabilization for LTV internal model-based control in the discrete setting is formulated, its challenges are revealed, and two control synthesis methods are presented. The merits and limitations of both approaches are discussed and then further studied through simulation and experimental investigations.

Transient control of a camless valve actuation system using a time-varying repetitive controller

Camless valve actuation systems, also referred to as Fully Flexible Valve Actuation systems, use electronically controlled actuators to replace the camshaft in an internal combustion engine. This paper presents the control design for such an actuation system to enable the precise valve motion control during engine speed transients. The desired valve motion (reference) remains periodic in the crank angle domain, but becomes cyclic and aperiodic in the time domain when the engine speed changes in real-time. This phenomenon motivates the control design in the rotational angle domain. However, this approach results in a time-varying model for the plant. A systematic method for obtaining the discrete time-varying Input/Output representation of higher order systems is developed to enable the application of the newly developed time-varying repetitive control to plants with complex dynamics. The use of a variable sampling rate helps accurately represent complex reference signals using low dimensional models. The implementation of the simulations on a rapid control prototyping system helps identify and address potential issues that influence the controller execution time which directly affects the maximum engine speed at which it can be used.Copyright

Investigation of time-varying internal model based control for camless engine valve actuation

This research focuses on the tracking control design for a camless engine valve actuator during engine speed transients. The cyclic but aperiodic valve reference signal to be tracked can be modeled using two different methods, i.e., as a combination of frequency varying sinusoids in the time domain or as a repetitive (periodic) signal in the rotational angle domain. The recently developed time-varying internal model based controller is ideally suited for both the approaches. Investigation of the continuous time and discrete domain implementations uncovers some unique characteristics resulting from the time-varying nature of the system which favor working in the discrete domain. A quantitative analysis comparing various performance metrics for the different approaches of modeling the reference signal helps highlight the relative advantages of each method. Finally, experimental results from a prototype camless engine valve actuation system help validate the overall effectiveness of the proposed approach.

Iterative learning control of a camless valve actuation system with internal feedback

This paper presents the iterative learning control of an electro-hydraulic fully flexible engine valve actuation system. The specific camless system has a unique hydro-mechanical feedback mechanism that simplifies the external control to the choice of triggering timings for three two-state valves. All the critical parameters describing the engine valve event, i.e. lift, duration, timing, and seating velocity, can be continuously varied by controlling these timings. Initial testing of a prototype experimental setup reveals that the performance of the system (transient tracking and steady-state variability) is influenced purely by the state of the system when the internal feedback mechanism is activated. This feature, along with the cyclic nature of the engine valve operation, motivates the development of a iterative-learning-based feedback and feed-forward controller to identify and set the optimal operating point in real time using the output of the previous cycle and the desired performance. The learning control implementation presented here is unique in that, instead of calculating a control signal (sequence) for each cycle, it sets the triggering timings for each of the on-off valves, which directly affect the initial conditions for the internal feedback loop. Experimental results demonstrate that the controller is able to minimize lift and closing time errors while satisfying the seating velocity constraint even during aggressive transient operation.

Tracking Control of Periodic Signals With Varying Magnitude and Its Application to Hybrid Powertrain

Internal model based repetitive control for linear time invariant (LTI) system has been widely applied to track or reject periodic signals with only the period known. It is well understood that the discrete generating dynamics of the periodic signal can be obtained by finite sampling, and embedding it as the internal model will yield asymptotic performance. However, the traditional repetitive control framework will no longer work for periodic signals with varying peak to peak amplitude. As will be revealed in this paper, the generating dynamics of this kind of signals is time varying, and thus simply embedding its generating dynamics as the internal model will no longer ensure asymptotic performance. The necessity of investigating tracking or rejecting varying magnitude periodic signals comes from a wide class of anticipated applications, one example of which is the hybrid vehicle powetrain vibration reduction. In the hybrid vehicles, engine starting and stopping occur frequently to switch between power sources, which could cause driveline vibration. With proper formulation, the oscillation signal becomes periodic with varying magnitude. To suppress such vibration, in this paper, the generating dynamics of this unique signal is first derived, and then its corresponding controller design method is presented. After a series of simulations and case studies, the proposed control framework is demonstrated to be a promising solution for the hybrid powertrain vibration reduction problem.Copyright