Improved Wind Turbine Control Strategies for Maximizing Power Output and Minimizing Power Flicker

For reducing the cost of energy (COE) for wind power, controls techniques are important for enhancing energy yield, reducing structural load and improving power quality. This thesis presents the control strategies studies for wind turbine both from the perspectives of both maximizing power output and reducing power flicker and structural load, First, a self-optimizing robust control scheme is developed with the objective of maximizing the power output of a variable speed wind turbine with doubly-fed induction generator (DFIG) operated in Region 2. Wind power generation can be divided into two stages: conversion from aerodynamic power to rotor (mechanical) power and conversion from rotor power to the electrical (grid) power. In this work, the maximization of power generation is achieved by a two-loop control structure in which the power control for each stage has intrinsic synergy. The outer loop is an Extremum Seeking Control (ESC) based generator torque regulation via the rotor power feedback. The ESC can search for the optimal torque constant to maximize the rotor power without wind measurement or accurate knowledge of power map. The inner loop is a vector-control based scheme that can both regulate the generator torque requested by the ESC and also maximize the conversion from the rotor power to grid power. In particular, an ∞ controller is synthesized for maximizing, with performance specifications defined based upon the spectrum of the rotor power obtained by the ESC. Also, the controller is designed to be robust against the variations of some generator parameters. The proposed control strategy is validated via simulation study based on the synergy of several software packages including the TurbSim and FAST developed by NREL, Simulink and SimPowerSystems. Then, a bumpless transfer scheme is proposed for inter-region controller switching scheme in order to reduce the power fluctuation and structural load under fluctuating wind conditions. This study considers the division of Region 2, Region 2.5 and Region 3 in the neighborhood of the rated wind speed. When wind, varies around the rated wind speed, the switching of control can lead to significant fluctuation in power and voltage supply, as well as structural loading. To smooth the switch and improve the tracking, two different bumpless transfer methods, Conditioning and Linear Quadratic techniques, are employed for different inter-region switching situations. The conditioning bumpless transfer approach adopted for switching between Region 2 maximum power capture controls to Region 2.5 rotor speed regulation via generator torque. For the switch between Region 2.5 and Region 3, the generator torque windup at rated value and pitch controller become online to limit the load of wind turbine. LQ technique is posed to reduce the discontinuity at the switch between torque controller and pitch controller by using an extra compensator. The flicker emission of the turbine during the switching is calculated to evaluate power fluctuation. The simulation results demonstrated the effectiveness of the proposed scheme of inter-region switching, with significant reduction of power flicker as well as the damage equivalent load

Speculative Thread Framework for Transient Management and Bumpless Transfer in Reconfigurable Digital Filters

There are many methods developed to mitigate transients induced when abruptly changing dynamic algorithms such as those found in digital filters or controllers. These "bumpless transfer" methods have a computational burden to them and take time to implement, causing a delay in the desired switching time. This paper develops a method that automatically reconfigures the computational resources in order to implement a transient management method without any delay in switching times. The method spawns a speculative thread when it predicts if a switch in algorithms is imminent so that the calculations are done prior to the switch being made. The software framework is described and experimental results are shown for a switching between filters in a filter bank.Comment: 6 pages, 7 figures, to be presented at American Controls Conference 201

A cascade MPC control structure for PMSM with speed ripple minimization

This paper addresses the problem of reducing the impact of periodic disturbances arising from the current sensor offset error on the speed control of a PMSM. The new results are based on a cascade model predictive control scheme with embedded disturbance model, where the per unit model is utilized to improve the numerical condition of the scheme. Results from an experimental application are given to support the design

Automatic Mode Switching for A Multi-functional Variable Refrigerant Flow System

Multi-functional variable refrigerant flow system (MFVRF) is designed to realize simultaneous heating and cooling for individual zones. It is desirable to use existing measurements to determine switching between different modes under changes of ambient and load conditions, i.e. reversing the mode of indoor unit (IDU) and/or outdoor unit (ODU) heat exchangers (HX), as well as the bumpless transfer for controller switching. In this study, a set of mode switching logic is proposed for a four-zone MFVRF system, which involves both IDU and ODU mode switching actions. For the ODU-HX mode switching, thermodynamic analysis under different load changes reveals the qualitative trend for the air-side and refrigerant-side characteristics as the operation approaches to marginal scenarios. The ODU mode switching is thus based on the air-side temperature difference. Mode switching involving IDU action only is studied with a 1H3C (one heating three cooling) mode, in which IDU-1 is in heating mode and IDU-2, IDU-3 and IDU-4 are in cooling mode. For a given zone load conditions, when the zone temperature of IDU is higher than upper limit of a preset cooling mode hysteresis band, IDU enters the cooling mode by simultaneously opening all related cooling mode valves and closing heating-mode valves within time duration. On the other hand, the cooling mode is turned off by closing all related cooling valves when the zone temperature is lower than the lower limit of the cooling mode temperature band. Similarly, when the zone temperature is lower than lower limit of heating mode temperature band, IDU enters its heating mode. When the zone temperature for IDU is higher than the upper limit of heating mode temperature band, the heating mode is turned off. For ODU Mode Switching, it is proposed in this paper to use the temperature difference between the inlet and outlet air of the ODU HX. To justify the use of ODU air-side temperature differential as the indicator variable for ODU mode switching, several cases of 2H2C (two-heating two-cooling) mode are first simulated, in which the IDU-1 and IDU-2 are operated in heating mode and IDU-3 and IDU-4 are operated in cooling mode. A negative ramp of load change applied to IDU-3 within 1000 seconds. For the ODU-HX, the air inlet temperature is fixed at the ambient 20oC, while the air outlet temperature approaches closer and closer to 20oC under reducing cooling load in IDU-3. Simulation results have revealed the decreasing trend of COP. The T-s diagram for the refrigerant cycle of 2H2C mode is evaluated under several scenarios of reduction in IDU-3 cooling load. It reveals that a decreasing temperature difference at the air side or refrigerant side can be candidate probing variables for mode switching of ODU HX. Also, similar study is conducted when the ODU HX works as evaporator, with the MFVRF system operated in 3H1C (three heating one cooling) mode. Simulations for ODU HX mode switch case have been performed, and the results validate the effectiveness of the proposed scheme of mode switching

Bumpless transfer for switched systems

Tres estrategias de transferencia sin perturbaciones fueron evaluadas para sistemas conmutados. Un método de transferencia sin perturbaciones basado en control predictivo fue desarrollado y dos teoremas para la estabilidad interna del sistema incluyendo las primeras dos estrategias de transferencia sin perturbaciones fueron encontrados y demostrados. Finalmente, los métodos de transferencia sin perturbaciones y las condiciones de estabilidad fueron aplicados sobre un sistema de cintas magnéticas.Three bumpless transfer strategies were evaluated for switched systems. A bumpless transfer method based on predictive control was developed and two theorems for the internal stability of the overall system with the first two bumpless transfer methods were found and demonstrated. Finally, the bumpless transfer methods and the stability conditions were applied on a web winding system.Magíster en Ingeniería ElectrónicaMaestrí

Superheat control for air conditioning and refrigeration systems: Simulation and experiments

Ever since the invention of air conditioning and refrigeration in the late nineteenth century, there has been tremendous interest in increasing system efficiency to reduce the impact these systems have on global energy consumption. Efficiency improvements have been accomplished through component design, refrigerant design, and most recently control system design. The emergence of the electronic expansion valve and variable speed drives has made immense impacts on the ability to regulate system parameters, resulting in important strides towards efficiency improvement. This research presents tools and methodologies for model development and controller design for air conditioning and refrigeration systems. In this thesis, control-oriented nonlinear dynamic models are developed and validated with test data collected from a fully instrumented experimental system. These models enable the design of advanced control configurations which supplement the performance of the commonly used proportional-integral-derivative (PID) controller. Evaporator superheat is a key parameter considered in this research since precise control optimizes evaporator efficiency while protecting the system from component damage. The controllers developed in this thesis ultimately provide better transient and steady state performance which increases system efficiency through low superheat set point design. The developed controllers also address the classical performance versus robustness tradeoff through design which preserves transients while prolonging the lifetime of the electronic expansion valve. Another notable contribution of this thesis is the development of hardware-in-the-loop load emulation which provides a method to test component and software control loop performance. This method alleviates the costs associated with the current method of testing using environmental test chambers

An antiwindup approach to power controller switching in an ambient healthcare network

This paper proposes a methodology for improved power controller switching in mobile Body Area Networks operating within the ambient healthcare environment. The work extends Anti-windup and Bumpless transfer results to provide a solution to the ambulatory networking problem that ensures sufficient biometric data can always be regenerated at the base station. The solution thereby guarantees satisfactory quality of service for healthcare providers. Compensation is provided for the nonlinear hardware constraints that are a typical feature of the type of network under consideration and graceful performance degradation in the face of hardware output power saturation is demonstrated, thus conserving network energy in an optimal fashion

Model and control of a solar tower for energy production

Supervisors: Prof./Dr. João Manuel Lage de Miranda Lemos; Prof./Dr. Bertinho Manuel D’Andrade da Costa. Examination Committee: Chairperson: Prof./Dr. João Fernando Cardoso Silva Sequeira;Supervisor: Prof./Dr. João Manuel Lage de Miranda Lemos. Members of the Committee: BGEN/ENGEL Luis Filipe Basto Damásio; TCOR/ENGEL Ana Paula da Silva Jorge; Prof./Dr. Alexandre José Malheiro BernardinSolar towers are electrical power production systems that use highly concentrated solar radiation as energy source that is collected by means of a heat-transfer fluid. This master thesis studies the application of several control strategies with the aim of maintaining the working fluid at a temperature that maximizes the electrical production. The main difficulties are the nonlinear fluid temperature dynamics, plant thermal constrains, and a variable energy source that cannot be manipulated. The temperature dynamics flow dependence demands for a changing parameter controller that results from a gain scheduling scheme or from a multi-model adaptive control strategy, in which the manipulated variable is adjusted by one of the set of local controllers designed for different operating regimes. The former is accomplished through a Proportional-Integral Controller (PI) control and the latter via Linear Quadratic Gaussian (LQG) optimal control. In addition, the Multistep Multivariable Adaptive Regulator (MUSMAR) control algorithm that adjusts its gains to every plant dynamic change, including parameters, is tested. Although the mentioned control concepts are applied considering the flow as the only manipulated variable, the combination of the latter with the radiation flux reflected by the heliostat field is also studied through PI control. The solar tower electrical power production has a maximum for a given outlet temperature that changes with plant parameters and disturbances. The improvement of production levels is conducted by adjusting the temperature reference with a static optimization procedure.As torres solares são sistemas de produção de energia elétrica que utilizam a radiação solar concentrada como fonte primária. A última, é absorvida por um fluído que percorre o permutador de calor em que a radiação incide. A presente dissertação estuda a aplicação de várias estratégias de controlo com o objetivo de manter a temperatura do fluido no valor que maximiza a produção de energia. As dificuldades principais centram-se na não linearidade da dinâmica da temperatura do fluído, nos limites térmicos do sistema e na incapacidade de manipular a radiação solar. A alteração da dinâmica da temperatura com o caudal requer a utilização de um controlador de parâmetros variáveis que resulta de um esquema de escalonamento de ganhos ou da associação de diversos controladores projetados para diferentes pontos de operação. O primeiro método é desenvolvido com controlo PI enquanto que o último recorre ao controlo LQG. Em adição, é estudada a aplicação do algoritmo de controlo MUSMAR, em que os ganhos são adaptados para qualquer alteração da dinâmica do sistema, incluindo a variação de parâmetros do modelo. Embora as estratégias de controlo referidas considerem apenas o caudal como variável manipulável, a combinação da última com o fluxo de radiação é tambem estudada com um controlador PI. A produção de energia de uma torre solar possui um máximo para uma dada temperatura que se altera com os parâmetros da planta e perturbações. O aumento da produção é conseguida pela determinação da referência de temperatura através de um algoritmo de otimização estática.N/

Multiple model adaptive control of functional electrical stimulation

This paper establishes the feasibility of multiple-model switched adaptive control to regulate functional electrical stimulation for upper limb stroke rehabilitation. An estimation-based multiple-model switched adaptive control (EMMSAC) framework for nonlinear time-invariant systems is described, and extensions are presented to enable application to time-varying Hammerstein structures that can accurately represent the stimulated arm. A principled design procedure is then developed to construct both a suitable set of candidate models from experimental data and a corresponding set of tracking controllers. The procedure is applied to a sample of able-bodied young participants to produce a general EMMSAC controller. This is then applied to a different sample of the population during an isometric nonvoluntary trajectory tracking task. The results show that it is possible to eliminate model identification while employing closed-loop controllers that maintain high performance in the presence of rapidly changing system dynamics. This paper hence addresses critical limitations to effective stroke rehabilitation in a clinical setting