126 research outputs found
Adaptive and predictive controllers applied to onshore wind energy conversion system
This paper presents a simulation of onshore energy conversion system connected to the electric grid and under an event-based supervisor control based on deterministic version of a finite state machine. The onshore energy conversion system is composed by a variable speed wind turbine, a mechanical transmission system described by a two-mass drive train, a gearbox, a doubly fed induction generator rotor and by a two-level converter. First, mathematical models of a variable speed wind turbine with pitch control are studied, followed by the study of different controller types such as adaptive controllers and predictive controllers. The study of an event-based supervisor based on finite state machines is also studied. The control and supervision strategy proposed for the onshore energy conversion system is based on a hierarchical structure with two levels, execution level where the adaptive and predictive controllers are included, and the supervision level where the event-based supervisor is included. The objective is to control the electric output power around the reference power and also to analyze the operational states according to the wind speed. The studied mathematical models are integrated into computer simulations for the onshore energy conversion system and the obtained numerical results allow for the performance assessment of the system connected to the electric grid. A comparison of the onshore energy conversion system performance without or with the supervisor is carried out to access the influence of the control and supervision strategy on the performance
Linear Parameter Varying Power Regulation of Variable Speed Pitch Manipulated Wind Turbine in the Full Load Regime
In a wind energy conversion system (WECS), changing the pitch angle of the
wind turbine blades is a typical practice to regulate the electrical power
generation in the full-load regime. Due to the turbulent nature of the wind and
the large variations of the mean wind speed during the day, the rotary elements
of the WECS are subjected to significant mechanical stresses and fatigue,
resulting in conceivably mechanical failures and higher maintenance costs.
Consequently, it is imperative to design a control system capable of handling
continuous wind changes. In this work, Linear Parameter Varying (LPV) H_inf
controller is used to cope with wind variations and turbulent winds with a
turbulence intensity greater than 10%. The proposed controller is designed to
regulate the rotational rotor speed and generator torque, thus, regulating the
output power via pitch angle manipulations. In addition, a PI-Fuzzy control
system is designed to be compared with the proposed control system. The
closed-loop simulations of both controllers established the robustness and
stability of the suggested LPV controller under large wind velocity variations,
with minute power fluctuations compared to the PI-Fuzzy controller. The results
show that in the presence of turbulent wind speed variations, the proposed LPV
controller achieves improved transient and steady-state performance along with
reduced mechanical loads in the above-rated wind speed region.Comment: 12 pages, 10 figure
Contributions to impedance shaping control techniques for power electronic converters
El conformado de la impedancia o admitancia mediante control para convertidores electrónicos de potencia permite alcanzar entre otros objetivos: mejora de la robustez de los controles diseñados, amortiguación de la dinámica de la tensión en caso de cambios de carga, y optimización del filtro de red y del controlador en un solo paso (co-diseño). La conformación de la impedancia debe ir siempre acompañada de un buen seguimiento de referencias. Por tanto, la idea principal es diseñar controladores con una estructura sencilla que equilibren la consecución de los objetivos marcados en cada caso. Este diseño se realiza mediante técnicas modernas, cuya resolución (síntesis del controlador) requiere de herramientas de optimización. La principal ventaja de estas técnicas sobre las clásicas, es decir, las basadas en soluciones algebraicas, es su capacidad para tratar problemas de control complejos (plantas de alto orden y/o varios objetivos) de una forma considerablemente sistemática. El primer problema de control por conformación de la impedancia consiste en reducir el sobreimpulso de tensión ante cambios de carga y minimizar el tamaño de los componentes del filtro pasivo en los convertidores DC-DC. Posteriormente, se diseñan controladores de corriente y tensión para un inversor DC-AC trifásico que logren una estabilidad robusta del sistema para una amplia variedad de filtros. La condición de estabilidad robusta menos conservadora, siendo la impedancia de la red la principal fuente de incertidumbre, es el índice de pasividad. En el caso de los controladores de corriente, el impacto de los lazos superiores en la estabilidad basada en la impedancia también se analiza mediante un índice adicional: máximo valor singular. Cada uno de los índices se aplica a un rango de frecuencias determinado. Finalmente, estas condiciones se incluyen en el diseño en un solo paso del controlador de un convertidor back-to-back utilizado para operar generadores de inducción doblemente alimentados (aerogeneradores tipo 3) presentes en algunos parques eólicos. Esta solución evita los problemas de oscilación subsíncrona, derivados de las líneas de transmisión con condensadores de compensación en serie, a los que se enfrentan estos parques eólicos. Los resultados de simulación y experimentales demuestran la eficacia y versatilidad de la propuesta.Impedance or admittance shaping by control for power electronic converters allows to
achieve among other objectives: robustness enhancement of the designed controls, damped
voltage dynamics in case of load changes, and grid filter and controller optimization in
a single step (co-design). Impedance shaping must always be accompanied by a correct
reference tracking performance. Therefore, the main idea is to design controllers with a
simple structure that balance the achievement of the objectives set in each case. This
design is carried out using modern techniques, whose resolution (controller synthesis)
requires optimization tools. The main advantage of these techniques over the classical
ones, i.e. those based on algebraic solutions, is their ability to deal with complex control
problems (high order plants and/or several objectives) in a considerably systematic way.
The first impedance shaping control problem is to reduce voltage overshoot under load
changes and minimize the size of passive filter components in DC-DC converters. Subsequently,
current and voltage controllers for a three-phase DC-AC inverter are designed
to achieve robust system stability for a wide variety of filters. The least conservative
robust stability condition, with grid impedance being the main source of uncertainty, is
the passivity index. In the case of current controllers, the impact of higher loops on
impedance-based stability is also analyzed by an additional index: maximum singular
value. Each of the indices is applied to a given frequency range. Finally, these conditions
are included in the one-step design of the controller of a back-to-back converter used
to operate doubly fed induction generators (type-3 wind turbines) present in some wind
farms. This solution avoids the sub-synchronous oscillation problems, derived from transmission
lines with series compensation capacitors, faced by these wind farms. Simulation
and experimental results demonstrate the effectiveness and versatility of the proposa
Multi-Objective Optimisation-Based Tuning of Two Second-Order Sliding-Mode Controller Variants for DFIGs Connected to Non-Ideal Grid Voltage
In this paper, a posteriori multi-objective optimisation (MOO) is applied to tune the parameters of a second-order sliding-mode control (2-SMC) scheme commanding the grid-side converter (GSC) of a doubly-fed induction generator (DFIG) subject to unbalanced and harmonically distorted grid voltage. Two variants (i.e., design concepts) of the same 2-SMC algorithm are assessed, which only differ in the format of their switching functions and which contain six and four parameters to be adjusted, respectively. A single set of parameters which stays valid for nine different operating regimes of the DFIG is also sought. As two objectives, related to control performances of grid active and reactive powers, are established for each operating regime, the optimisation process considers 18 objectives simultaneously. A six-parameter set derived in a previous work without applying MOO is taken as reference solution. MOO results reveal that both the six- and four-parameter versions can be tuned to overcome said reference solution in each and every objective, as well as showing that performances comparable to those of the six-parameter variant can be achieved by adopting the four-parameter one. Overall, the experimental results confirm the latter and prove that the performance of the reference parameter set can be significantly improved by using either of the six- or four-parameter versions.This research was co-funded by the Spanish Ministry of Economy and Competitiveness—project codes DPI2015-64985-R and RTI2018-096904-B-I00—and FEDER Funds, EU. The authors from the University of the Basque Country UPV/EHU are with the “Intelligent Systems and Energy (SI+E)” research group, funded by UPV/EHU—research grant GIU16/54—and the Basque Government—research grant IT1256-19
Optimized state feedback regulation of 3DOF helicopter system via extremum seeking
In this paper, an optimized state feedback regulation of a 3 degree of freedom (DOF) helicopter is designed via extremum seeking (ES) technique. Multi-parameter ES is applied to optimize the tracking performance via tuning State Vector Feedback with Integration of the Control Error (SVFBICE).
Discrete multivariable version of ES is developed to minimize a cost function that measures the performance of the controller. The cost function is a function of the error between the actual and desired axis positions. The controller parameters are updated online as the optimization takes place. This method significantly decreases the time in obtaining optimal controller parameters. Simulations were conducted for the online optimization under both fixed and varying operating conditions. The results demonstrate the usefulness of using ES for preserving the maximum attainable performance
Multi-Objective Control Strategies and Prognostic-Based Lifetime Extension of Utility-Scale Wind Turbines
Windenergie wird zunehmend als erneuerbare Energiequellen attraktiv, da Wind
nachhaltig genutzt werden kann. In vielen Ländern gibt es umfangreiche Anstrengungen,
die Produktion von elektrischer Energie aus Wind zu steigern. Im Vergleich
zu anderen erneuerbaren Energiequellen wie Sonne, Gezeiten, Wasserkraft
o.ä. ist die Energiegewinnung aus Wind technologisch ausgereifter. Daher ist die
Energiegewinnung aus Wind stärker gewachsen ist als andere Technologien. Windkraft
verursacht weniger nachteilige Auswirkungen auf die Umwelt als konventionelle
Energiequellen. Aufgrund der vergleichsweise hohen Investitions-, Betriebs- und
Wartungskosten sind trotz einer weltweit starken Verbreitung von Windenergieanlagen
die Produktionskosten von Windenergie im Vergleich mit anderen alternativen
Energiequellen hoch.
Um die wachsende Nachfrage nachWindkraft zu befriedigen, werdenWindkraftanlagen
in Größe und Leistung zunehmend skaliert. Bei zunehmender Größe dominieren
die strukturellen Lasten der Turbine. Dies führt vermehrt zu Materialermüdung
und Ausfällen. Ein weiterer Schwerpunkt in der Entwicklung von Windtechologie
ist die Forderung nach Senkung der Produktionskosten, um einen Wettbewerbsvorteil
gegenüber anderen alternativen Energiequellen zu schaffen. Im Bereich der
Steuerung können niedrigere Produktionskosten durch den Betrieb der Windturbine
am/oder in der Nähe der optimalen Energieeffizienz im Teillastbetrieb erreicht
werden. Dies erhöht die Zuverlässigkeit durch Verringerung des Verschleißes und
die erzeugte Nennleistung auf ihrem Nennwert im hohen Windregime. Häufig ist
es schwierig, einen Steueralgorithmus zu realisieren, der sowohl Effizienz als auch
Zuverlässigkeit gewährleistet, da diese beiden Ziele widersprechen.
In dieser Arbeit werden Mehrzielsteuerungsstrategien sowohl für den Teillastbereich
als auch für hohe Windgeschwindigkeits bereiche vorgestellt. Im Bereich geringer
Windgeschwindigkeiten ist eine Steuerungsstrategie so zu konzipieren, dass die Stromerzeugung
sowie die strukturelle Belastung im Sinne einer Balance zwischen maximalen
Stromproduktion und verlängerter Lebensdauer der Windturbine optimal ist.
Für den Bereich hoher Windgeschwindigkeiten wird ein multivariates Steuerungsverfahren
vorgeschlagen, um das Verhältnis von Leistung/Geschwindigkeit und struktureller
Lastreduzierung zu optimieren. Es wird ein Regler zur Einzelblattverstellung
entworfen, um sowohl die unausgewogene Strukturlasten als auch durch die Variation
des Windgeschwindigkeit verursachte Rotorscheibe, vertikale Windscherung
und Gierversatz fehler zu reduzieren.
Um die Zuverlässigkeit derWindturbine zu gewährleisten, ist ein Online-Schadensbewertungsmodell
in den Hauptwindturbinenregelkreis integriert, so dass die Windturbine
entsprechend ihres aktuellen Verschleißzustandes betrieben wird. In Abhängigkeit
von der akkumulierten Schadenshöhe werden Regler zur Einzelblattverstellung
mit unterschiedlichen Lastreduktionen und Kompromissen bei der Stromerzeugung eingesetzt, um zwischen den beiden Zielen verlängerte Lebensdauer und Leistungsregelung
einen geeigneten Kompromiss zu erzielten. Aufgrund der Herausforderungen
die mit Offshore-Windpark Standorten verbunden sind, ist diese Art von prognose-basierter
Regelung im Windturbinenbetrieb vor allem im Offshore-Einsatz vorteilhaft.
Insbesondere im Kontext output-basierter Vertragsformen z.B. power purchase
agreement (PPA) kann dieser Ansatz zur Optimierung der Wartungsplanung genutzt
werden.
Die Ergebnisse zeigen, dass die vorgeschlagenen Strategien die Auflast auf Windturbinen
reduzieren kann ohne sich auf andere Ziele wie die Leistungsoptimierung
und Leistung/Drehzahlregelung auszuwirken. Es konnte außerdem gezeigt werden,
dass eine prognostisch basierte Steuerung effektiv die Lebensdauer von Windenergieanalagen
verlängern kann, ohne das Ziel der Leistungsregelung einzuschränken.Wind energy is one of the rapidly growing renewable sources of energy due to the
fact that wind is abundantly available and unlikely to be exhausted like fossil fuel.
Additionally, there are deliberate effort to sensitize many countries to develop polices
that support production of electrical power from wind. Maturity of wind energy
technology has made power production from wind grow significantly compared to
other renewable energy sources such as solar, tidal, hydro among others. Like many
other renewable energy sources, production of power from wind has less adverse
effects on the environment. Despite the growth of global cumulative installed wind
capacity, its cost of production is still higher compared to other alternative energy
sources due to high initial investment cost and high operation and maintenance
(O&M) costs.
To meet the growing demand of wind power, wind turbines are being scaled up both
in size and power rating. However, as the size increases, the structural loads of
the turbine become more dominant, causing increased fatigue stress on the turbine
components and consequent loss of functionality before the end of lifetime. Another
area of focus in wind power production is lowering its production cost; hence, making
it more competitive compared to other alternative power sources. From the control
point of view, low production cost of wind energy can be achieved by operating
wind turbine at/or near the optimum power efficiency during partial load regime,
regulating generated power to its rated value in the high wind regime as well as
mitigating structural loads so as to guarantee extended lifetime. Often, it is difficult
to realize a control algorithm that can effectively guarantee both efficiency and
reliability because these two aspects involve conflicting objective. Therefore, it is
important to optimize the trade-off between these competing control objectives.
In this thesis, multi-objective control strategies for both the partial load region and
high wind speed region are presented. During low wind speed, a control strategy
that optimizes power production as well as mitigating structural load is designed
to balance between power production maximization and extended lifetime of wind
turbine. On the other hand, a multivariate control method to balance between
power/speed regulation and structural load reduction is proposed for high wind
speed region. More specifically, an individual blade pitch controller is designed to
eliminate the unbalanced deterministic structural loads across rotor disc caused by
variation in wind speed, vertical wind shear, and yaw misalignment error.
To guarantee reliability in wind turbine, an online damage evaluation model is also
integrated into the main wind turbine control loop such that wind turbine is operated
accordance to its structural health status in order to tolerate fault or to extend
its service lifetime by a given period of time. Depending on the accumulated damage
level, individual pitch controllers with different degrees of load reduction and
power production compromise are employed to balance between extended lifetime and power regulation objective. This kind of prognostic-based control is useful in
wind turbine operation, especially in offshore application due to challenges associated
with offshore wind farm sites. Additionally, in wind farms that are managed
through output-based contracts such as power purchase agreement (PPA), this approach
can be utilized to optimize maintenance scheduling to avoid unscheduled
downtime.
The results demonstrated that the proposed multi-objective control strategies can
reduce structural load on wind turbine without adversely affecting other objectives
of power optimization and power/speed regulation. It has also be shown that a
prognostic-based control can be effectively used to extend the lifetime of wind turbine
without sacrificing the objective of power regulation
Sliding Mode Control
The main objective of this monograph is to present a broad range of well worked out, recent application studies as well as theoretical contributions in the field of sliding mode control system analysis and design. The contributions presented here include new theoretical developments as well as successful applications of variable structure controllers primarily in the field of power electronics, electric drives and motion steering systems. They enrich the current state of the art, and motivate and encourage new ideas and solutions in the sliding mode control area
Active disturbance rejection control of three-phase LCL power conversion system under non-ideal grid conditions
Under non-ideal grid operating conditions such as unbalanced grid voltage and harmonic grid that are commonly found in microgrid conditions, the negative sequence components of the microgrid voltage interfere with the active and reactive current controls in the power conversion system, leading to an increase in the harmonic content of the grid-side current and affecting the power quality of the microgrid system. To solve these problems, firstly, the mathematical model of the LCL-type power conversion system is analyzed, and a linear active disturbance rejection control based on model compensation is designed. Secondly, the influence of non-ideal power grid conditions on the control of the LCL-type power conversion system is analyzed, and the active disturbance rejection control strategy of the LCL-type power conversion system based on frequency-locked loops with harmonic cancellation modules (HCM-FLL) is proposed, which speeds up the system, improves the system’s robustness, and reduces the harmonic content of the network measurement current under the condition of power grid voltage unbalance and harmonic power grid. Finally, by using the verification of MATLAB/Simulink simulation, the current power quality obviously under the condition of voltage unbalance and harmonic power grid is evidently improved by the proposed control strategy. When compared to the traditional control methods, the control strategy proposed in this study features a simple control structure, making it easy to implement in engineering without requiring high controller performance or additional circuits. This reduces design costs and provides a wide range of controller parameters, ensuring strong anti-interference performance without the need for frequent controller parameter adjustments
Internal Model Control (IMC) design for a stall-regulated variable-speed wind turbine system
A stall-regulated wind turbine with fixed-speed operation provides a configuration which is one of the cheapest and simplest forms of wind generation and configurations. This type of turbine, however, is non-optimal at low winds, stresses the component structure and gives rise to significant power peaks during early stall conditions at high wind speeds. These problems can be overcome by having a properly designed generator speed control. Therefore, to track the maximum power locus curve at low winds, suppress the power peaks at medium winds, limit the power at a rated level at high winds and obtain a satisfactory power-wind speed curve performance (that closely resembles the ideal power-wind speed curve) with minimum stress torque simultaneously over the whole range of the wind speed variations, the availability of active control is vital. The main purpose of this study is to develop an internal model control (IMC) design for the squirrel-cage induction generator (SCIG), coupled with a full-rated power converter of a small (25 kW), stall-regulated, variable-speed wind-turbine (SRVSWT) system, which is subject to variations in the generator speed, electromagnetic torque and rotor flux. The study was done using simulations only. The objective of the controller was to optimise the generator speed to maximise the active power generated during the partial load region and maintain or restrict the generator speed to reduce/control the torque stress and the power-peaking between the partial and full load regions, before power was limited at the rated value of 25 kW at the full load region. The considered investigation involved estimating the proportional-integral (PI) and integral-proportional (IP) controllers parameter values used to track the stator-current producing torque, the rotor flux and the angular mechanical generator speed, before being used in the indirect vector control (IVC) and the sensorless indirect vector control (SLIVC) model algorithms of the SCIG system. The design of the PI and IP controllers was based on the fourth-order model of the SCIG, which is directly coupled to the full-rated power converter through the machine stator, whereas the machine rotor is connected to the turbine rotor via a gearbox. Both step and realistic wind speed profiles were considered. The IMC-based PI and IP controllers (IMC-PI-IP) tuning rule was proven to have smoothened the power curve and shown to give better estimation results compared to the IMC-based PI controllers (IMC-PI), Ziegler-Nichols (ZN) and Tyreus-Luyben (ZN) tuning rules. The findings also showed that for the SRVSWT system that employed the IVC model algorithm with the IMC-PI-IP tuning rule, considering the application of a maintained/constant speed (CS) strategy at the intermediate load region is more profitable than utilizing SRVSWT with the modified power tracking (MoPT) strategy. Besides that, the finding also suggested that, for the IMC-PI-IP approach, the IVC does provide better power tracking performance than the SLIVC model algorithm
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