Alan F. Lynch

Experimental Validation of Nonlinear Control for a Voltage Source Converter

In this brief, we consider reactive power and DC voltage tracking control of a three-phase voltage source converter (VSC). This control problem is important in many power system applications including power factor correction for a distribution static synchronous compensator (D-STATCOM). Traditional approaches to this problem are often based on a linearized model of the VSC and proportional-integral (PI) feedback. In order to improve performance, a flatness-based tracking control for the VSC is proposed where the nonlinear model is directly compensated without a linear approximation. Flatness leads to straightforward open-loop control design. A full experimental validation is given as well as a comparison with the industry-standard decoupled vector control. Robustness of the flatness-based control is investigated and setpoint regulation for unbalanced three-phase voltage is considered.

Flatness-Based Feedback Control of an Automotive Solenoid Valve

This brief considers the control of solenoid valve actuators used for gas exchange in internal combustion engines. Although solenoid valves offer performance benefits over traditional camshaft-based valve systems, maintaining low impact velocity is a critical performance requirement. Flatness provides a convenient framework for meeting a number of performance specifications on the valves end motion. The proposed control design incorporates voltage constraints, nonlinear magnetic effects, and various motion planning requirements. A flat output acts as a design parameter and is parameterized with a spline basis. A nonlinear feasibility problem is solved to obtain optimal spline coefficients such that performance requirements are met. The resulting flat output provides an open-loop control which is augmented with feedback so that a linear stable tracking error system results. The proposed control scheme is demonstrated in simulation and on an experimental testbed. The performance of a proportional-integral controller is compared experimentally to the flatness-based method

Modeling automotive gas-exchange solenoid valve actuators

We develop a finite-element analysis (FEA) model to describe transient and static operation of gas-exchange valves. Such valves, directly controlled by solenoids, are a promising method for enhancing automotive engine efficiency. The FEA model is validated by experimental testing on an actual automotive prototype valve. We show that a nonlinear lumped-parameter model that uses FEA results also closely matches experimental data. The lumped-parameter model is suitable for optimization of design and can be readily used for closed-loop simulation. We present a simplified lumped-parameter model to facilitate controller design. Finally, we compare a dynamic open-loop simulation with experimental results.

Nonlinear observers with approximately linear error dynamics: the multivariable case

Exact error linearization uses nonlinear input-output injection to design observers with linear error dynamics in certain coordinates. This approach can only be applied nongenerically. We propose an observer for a wider class of multivariable systems which uniformly minimizes the nonlinear part of the system that cannot be canceled by nonlinear input-output injection. Our approach is numerical, constructive, and provides locally exponentially stable error dynamics. An example compares our design with a high-gain method.

Nonlinear tension observers for web machines

Precise regulation of span tension in web-handling machines is critical to ensure product quality. Elevated tension causes web fracture during operation; depressed or highly variable tension leads to irregular and unacceptable spool. Web-handling machines typically employ costly load cell sensors to measure span tension. This work investigates the use of nonlinear estimators or observers to provide cost-effective span tension estimates from system measurements. After presenting the dynamic equations of a web-handling machine, their structure is exploited to design a reduced-order, nonlinear observer with linear time-varying error dynamics. Exponential stability of the error dynamics is demonstrated. Performance of the estimator is experimentally compared with two competing designs on a real web-handling machine.

Precision Tracking of a Rotating Shaft With Magnetic Bearings by Nonlinear Decoupled Disturbance Observers

Static offset and synchronous vibration are obstacles to precision tracking of a rotating shaft supported by active magnetic bearings (AMBs). A constant and harmonic disturbance observer is an effective approach to estimate and suppress these undesired effects. A disturbance observer is particularly well-suited for tracking applications since it can directly compensate for AMB force nonlinearity. In this paper, we propose a nonlinear reduced-order disturbance observer which is incorporated into a flatness-based tracking control. Since a reduced-order approach requires knowledge of velocity, we design an inner-loop velocity observer which can achieve convergence at a faster rate than the disturbance observer. This hierarchical observer simplifies the control because disturbance estimates are decoupled for each degree of freedom (DOF) and disturbance compensation is modularized. Experimental results on a commercially available 5-DOF system demonstrate accurate position tracking over the bearing air gap for a wide range of shaft velocities.

Experimental Validation of a Helicopter Autopilot Design using Model-Based PID Control

Autonomous helicopter flight provides a challenging control problem. In order to evaluate control designs, an experimental platform must be developed in order to conduct flight tests. However, the literature describing existing platforms focuses on the hardware details, while little information is given regarding software design and control algorithm implementation. This paper presents the design, implementation, and validation of an experimental helicopter platform with a primary focus on a software framework optimized for controller development. In order to validate the operation of this platform and provide a basis for comparison with more sophisticated nonlinear designs, a PID controller with feedforward gravity compensation is derived using the generally accepted small helicopter model and tested experimentally.

Integration of a Triaxial Magnetometer into a Helicopter UAV GPS-Aided INS

The University of Albertas Applied Nonlinear Controls Lab (ANCL) helicopter unmanned aerial vehicles (UAVs) existing GPS-aided inertial navigation system (INS) does not provide observability of heading angle during hover. This motivates the integration of a triaxial magnetometer aiding sensor into the extended Kalman filter (EKF)-based navigation algorithm. A novel magnetometer calibration procedure is implemented and compared with conventional approaches. Experimental results in ground and flight testing confirm that the observability issue is resolved and demonstrate improvements in attitude estimation.

Invariant Observer Design for a Helicopter UAV Aided Inertial Navigation System

The invariant observer is a recently introduced constructive nonlinear design method for symmetry-possessing systems such as the magnetometer-plus-global positioning system (GPS)-aided inertial navigation system (INS) example considered in this paper. The resulting observer guarantees a simplified form of the nonlinear estimation error dynamics, which can be stabilized by a proper choice of observer gains using a nonlinear analysis. A systematic approach to this step is the invariant Extended Kalman Filter (EKF), which is modified from its originally proposed form and applied to the aided INS example to obtain the observer gains. The resulting invariant observer is implemented onboard an outdoor helicopter unmanned aerial vehicle platform and successfully validated in experiment and demonstrates an improvement in performance over a conventional (non-invariant) EKF design.

Adaptive Control of a Voltage Source Converter for Power Factor Correction

In this study an adaptive control is designed for a three-phase voltage source converter (VSC) acting as a static synchronous compensator to provide power factor compensation. The proposed method relies on an approximate third-order nonlinear model of the VSC that accounts for uncertainty in three system parameters. The design ensures asymptotic tracking of q-axis current and dc-voltage reference trajectories. Simulation and experimental results verify the performance of the controller relative to an established vector control method.