Gilney Damm

Supervisory hybrid model predictive control for voltage stability of power networks

Emergency voltage control problems in electric power networks have stimulated the interest for the implementation of online optimal control techniques. Briefly stated, voltage instability stems from the attempt of load dynamics to restore power consumption beyond the capability of the transmission and generation system. Typically, this situation occurs after the outage of one or more components in the network, such that the system cannot satisfy the load demand with the given inputs at a physically sustainable voltage profile. For a particular network, a supervisory control strategy based on model predictive control is proposed, which provides at discrete time steps inputs and set-points to lower-layer primary controllers based on the predicted behavior of a model featuring hybrid dynamics of the loads and the generation system.

Unmanned Aerial Vehicle Speed Estimation via Nonlinear Adaptive Observers

In this paper the problem of the speed estimation of an unmanned aerial vehicle is addressed, when acceleration, the angles and the angular speeds are available for measurement. We focus our analysis on a prototype drone - a 4 rotors helicopter robot- which is not equipped with GPS related devices and relies on the inertial measurement unit (IMU) only. A global exponential solution to this open problem is provided in the framework of adaptive observation theory when exact measurements are available. A modified estimator is presented to enhance robustness in velocity estimation in the realistic case of noisy acceleration measurements.

DC transformer for DC/DC connection in HVDC network

This paper presents the modeling and control of a multilevel DC/DC bidirectional converter suitable for medium voltage and power applications, with a special interest in wind-power applications. The proposed multilevel topology has a modular structure constituted by base DC/DC converter cells. The multilevel converter is consequently based on Dual Active Bridge (DAB). The overall control of the DC/DC converter is achieved by using a nonlinear control based in Lyapunov theory.

Robust transient stabilisation problem for a synchronous generator in a power network

The robust transient stabilisation problem (with stability proof) of a synchronous generator in an uncertain power network with transfer conductances is rigorously formulated and solved. The generator angular speed and electrical power are required to be kept close, when mechanical and electrical perturbations occur, to the synchronous speed and mechanical input power, respectively, while the generator terminal voltage is to be regulated, when perturbations are removed, to its pre-fault reference constant value. A robust adaptive nonlinear feedback control algorithm is designed on the basis of a third-order model of the synchronous machine: only two system parameters (synchronous machine damping and inertia constants) along with upper and lower bounds on the remaining uncertain ones are supposed to be known. The conditions to be satisfied by the remote network dynamics for guaranteeing ℒ2 and ℒ∞ robustness and asymptotic relative speed and voltage regulation to zero are weaker than those required by the single machine-infinite bus approximation: dynamic interactions between the local deviations of the generator states from the corresponding equilibrium values and the remote generators states are allowed.

Adaptive nonlinear excitation control of synchronous generators

In this paper, continuing the line of our previous works, a nonlinear adaptive excitation control is designed for a synchronous generator modeled by a standard third order model on the basis of the physically available measurements of relative angular speed, active electric power and terminal voltage. The power angle, which is a crucial variable for the excitation control, is not assumed to be available for feedback, as mechanical power is also considered as an unknown variable. The feedback control is supposed to achieve transient stabilization and voltage regulation when faults occur to the turbines so that the mechanical power may permanently take any (unknown) value within its physical bounds. Transient stabilization and voltage regulation are achieved by a nonlinear adaptive controller, which generates both on-line converging estimates of the mechanical power and a trajectory to be followed by the power angle that converges to the new equilibrium point compatible with the required terminal voltage. The main contributions here, compared with our previous works, is the use of on-line computation and tracking of equilibrium power angle, and the proof of exponential stability of the closed loop system for states and parameter estimates, instead of the previous asymptotical one.

DC /DC converters as DC circuit-breakers in HVDC networks operation

This paper presents the modeling and control of a DC/DC bidirectional converter suitable for medium voltage and power applications in Multi-Terminals HVDC (MT-HVDC) grids. Moreover its use as DC circuit-breaker is described. This is a new concept, against the contemporary studies of DC breakers, which could help for the implementation of MT-HVDC networks. The proposed multilevel topology is based on Dual Active Bridge (DAB). The overall control of the DC/DC converter is achieved by using a nonlinear control based in Lyapunov theory.

Nonlinear Control of a DC MicroGrid for the Integration of Photovoltaic Panels

New connection constraints for the power network (grid codes) require more flexible and reliable systems, with robust solutions to cope with uncertainties and intermittence from renewable energy sources (renewables), such as photovoltaic (PV) arrays. The interconnection of such renewables with storage systems through a direct current (DC) MicroGrid can fulfill these requirements. A “Plug and Play” approach based on the “System of Systems” philosophy using distributed control methodologies is developed in this paper. This approach allows to interconnect a number of elements to a DC MicroGrid as power sources, such as PV arrays, storage systems in different time scales, such as batteries and supercapacitors, and loads, such as electric vehicles and the main ac grid. The proposed scheme can easily be scalable to a much larger number of elements.

Modeling and conditional integrator control of an unmanned aerial vehicle for airlaunch

A satellite launching procedure known as air-launch is modeled and simulated at the staging phase, where a reusable unmanned aerial vehicle airlaunchs a second (rocket) stage. The airlaunch is modeled as a hybrid system with instantaneous jumps. This paper presents the effects of the variations in mass, inertia and aerodynamic coefficients on the stability of the airlaunch system at the stage separation. The airlaunch phase implies on perturbations on aerodynamic forces and moments that may bring the system unstable. For this reason a robust conditional integrator controller is designed with the objective of stabilizing the system during the airlaunch. Performance of the proposed control algorithm is illustrated through computer simulations.

Multi-time-scale stability analysis and design conditions of a VSC terminal with DC voltage droop control for HVDC networks

This paper addresses the problem of analyzing the dynamic limitations of a VSC terminal with DC voltage droop control. Thanks to its fast response, DC voltage droop control is usually used to adjust the DC voltage in case of power imbalance. To ensure the stability of the VSC terminal, the dynamics between the dq currents (il,dq) and the DC voltage (uc) must be well distinguished. Therefore, the choice of the droop control gain Ku and the dq current control gains Kdq is still a challenging problem. First, we assume that there exist Ku and Kdq such that a slow and a fast dynamics can be imposed on uc and il,dq, respectively. Then, we propose a novel methodology based on separation of dynamics to prove the existence of these control gains. Subsequently, a detailed stability analysis is carried out via Lyapunov theory, from which a necessary condition and a sufficient condition are derived for the control gains. To verify this methodology, numerical simulations are carried out in MATLAB/SIMULINK.

Discussion on: "Identification of frequency of biased harmonic signal"

Frequency estimation is a classical and difficult problem that has drawn much attention in the last decades, as may be seen in its extensive literature. It is as interesting from the application as from the theoretical point of view. Indeed there are many applications for such estimators in the fields of rotating systems control like disk drives; active vibration control for helicopters, planes and offshore oil platforms; reduction of acoustic noise produced by fans in air systems; among many others.