Sul Ademi

A New Sensorless Speed Control Scheme for Doubly Fed Reluctance Generators

This paper presents the development and experimental validation of a novel angular velocity observer-based field-oriented control algorithm for a promising low-cost brushless doubly fed reluctance generator (BDFRG) in wind power applications. The BDFRG has been receiving increasing attention because of the use of partially rated power electronics, the high reliability of brushless design, and competitive performance to its popular slip-ring counterpart, the doubly fed induction generator. The controller viability has been demonstrated on a BDFRG laboratory test facility for emulation of variable speed and loading conditions of wind turbines or pump drives.

Comparisons of Vector Control Algorithms for Doubly-Fed Reluctance Wind Generators

This chapter presents a comparative development and thorough assessment of vector control methodologies for a promising brushless doubly-fed reluctance generator (BDFRG) technology for adjustable speed wind turbines. The BDFRG has been receiving increasing attention in research and industrial communities due to the low operation & maintenance costs afforded by the partially-rated power electronics and the high reliability of brushless construction, while offering competitive performance to its commercially popular and well-known slip-ring counterpart, the doubly-fed induction generator (DFIG). The two robust, machine parameter independent control schemes, one with flux (field) vector orientation (FOC) and the other voltage vector-oriented (VOC), have been built and their response examined by realistic simulation studies on a custom-designed BDFRG fed from a conventional ‘back-to-back’ IGBT converter. The high quality of the simulation results has been experimentally validated on a laboratory BDFRG test facility under VOC conditions as a preferred control option at large-scale wind power levels.

Nonlinear H-infinity control for the rotary pendulum

The rotary (Furutas) pendulum is used to analyzed the performance of a new nonlinear optimal (H-infinity) control for underactuated robotic systems. After applying partial feedback linearization, the pendulums dynamic model is first transformed to an equivalent form. The later description of the pendulums dynamics undergoes approximate linearization which takes place round a temporary operating point (equilibrium) recomputed at each iteration of the control algorithm. The linearization makes use of Taylor series expansion of the state-space model of the system and of computation of the associated Jacobian matrices. For the approximately linearized model of the pendulum an H-infinity feedback controller is developed. Through the repetitive solution of an algebraic Riccati equation which is also performed at each step of the control method, the controllers gain is computed. The stability features of the control loop are proven with Lyapunov analysis. First it is shown that the control loop satisfies the H-infinity tracking performance condition. Next, under moderate conditions it is also shown that the global asymptotic stability of the control loop can be assured.

Flatness-based adaptive fuzzy control of brushless doubly-fed reluctance machines

The article proposes an adaptive control approach that is capable of compensating for model uncertainty and parametric changes of the doubly-fed reluctance machines (DFRMs), as well as for the lack of measurements about the DFRMs state vector elements. First it is proven that the DFRMs model is a differentially flat one. By exploiting differential flatness properties it is shown that the DFRM model can be transformed into the linear canonical form. For the latter description, the new control inputs comprise unknown nonlinear functions which can be identified with the use of neurofuzzy approximators. The estimated dynamics of the generator is used by a feedback controller thus establishing an indirect adaptive control scheme. Moreover, to robustify the control loop, a supplementary control term is computed using H-infinity control theory. Another problem that has to be dealt with comes from partial measurements of the state vector of the generator. Thus, a state observer is implemented in the control loop. The stability of the considered observer-based adaptive control approach is proven using Lyapunov analysis. Moreover, the performance of the control scheme is evaluated through simulation experiments.

A nonlinear optimal control methoc for autonomous submarines' diving

A nonlinear H-infinity (optimal) control method is developed for the problem of simultaneous control of the depth and heading angle of an autonomous submarine. This is a multi-variable nonlinear control problem and its solution allows for precise underwater navigation of the submarine. The submarines dynamic model undergoes approximate linearization around a temporary equilibrium that is recmputed at each iteration of the control algorithm. The linearization procedure is based on Taylor series expansion and on the computation of the submarines model Jacobian matrices. For the approximately linearized model, the optimal control problem is solved through the design of an H-infinity feedback controller. The computation of the controllers gain requires the solution of an algebraic Riccati equstion, which is repetitively performed at each step of the control method. The stability of the control scheme is proven through Lyapunov analysis. First, it is demonstrated that for the submarines control loop, the H-infinity tracking performance criterion holds. Moroever, under moderate conditions it is shown that that the control scheme is globally asymptotically stable.

A novel direct power control for open-winding brushless doubly-fed reluctance generators fed by dual two-level converters using a common DC bus

A new direct power control (DPC) strategy for open-winding brushless doubly-fed reluctance generators (BDFRGs) with variable speed constant frequency is proposed. The control winding is open-circuited and fed by dual traditional two-level three phase converters using a common DC bus, and the DPC strategy aiming at maximum power point tracking and common mode voltage elimination is designed. Compared to the traditional three-level converter systems, the DC bus voltage, the voltage rating of power devices and capacity of the single two-level converter are all reduced by 50% while the reliability, redundancy and fault tolerance of the proposed system still greatly improved. Consequently its effectiveness is evaluated by simulation tests on a 42 kW prototype generator in MATLAB/SIMULINK.

Nonlinear optimal control for the VSC-HVDC transmission system

A nonlinear H-infinity (optimal) control method is proposed for the problem of control of the VSC-HVDC transmission system (Voltage Source Converter - High Voltage DC transmission system). Approximate linearization, round a local operating point, is performed for the dynamic model of the VSC-HVDC transmission system. This local equilibrium consists of the present value of the state vector of the VSC-HVDC model and of the last value of the control input that was exerted on it, and is re-calculated at each time instant. To accomplish this linearization, Taylor series expansion and the computation of the associated Jacobian matrices are performed. The robustness of the control scheme allows to compensate for the modelling error which is due to truncation of higher order terms from the Taylor expansion. Next, an H-infinity feedback controller is designed. After solving an algebraic Riccati equation at each iteration of the control algorithm, the feedback gain is computed. Lyapunov stability analysis is used to prove that the control loop satisfies an H-infinity tracking performance criterion. This also indicates elevated robustness to model uncertainty and external perturbations. Moreover, under moderate conditions it is proven that the control loop is globally asymptotically stable.

Nonlinear optimal control for the synchronization of chaotic and hyperchaotic finance systems

It is possible to make specific finance systems get synchronized to other finance systems exhibiting chaotic and hyperchaotic dynamics, by applying nonlinear optimal (H-infinity) control. This signifies that chaotic behavior can be generated in finance systems by exerting a suitable control input. Actually, a lead financial system is considered which exhibits inherently chaotic dynamics. Moreover, a follower finance system is introduced having parameters in its model that inherently prohibit the appearance of chaotic dynamics. Through the application of a suitable nonlinear optimal (H-infinity) control input it is proven that the follower finance system can replicate the chaotic dynamics of the lead finance system. By applying Lyapunov analysis it is proven that asymptotically the follower finance system gets synchronized with the lead system and that the tracking error between the state variables of the two systems vanishes.

Simulation and practical studies of doubly-fed reluctance drives operation and control

The doubly-fed reluctance machine is a viable substitute for the widely used wound rotor doubly-fed induction machine (DFIM) in adjustable speed slip power recovery applications (e.g. pump-type drives, high-inertia loads, wind turbines etc.). It may offer competitive performance to DFIM at equally low capital expenditure by adopting a similar fractional converter, but contributing further with much reduced operation and maintenance costs of reliable brushless construction and a simpler, more compact, rugged 2-stage gearbox. The comparative simulation results for the two robust angular velocity and power factor control schemes executed in flux and/or voltage vector oriented reference frames have been experimentally validated on a custom-built prototype for variable loading characteristics.

Parameter independent vector control of brushless Doubly-fed reluctance generators

The paper is concerned with voltage vector oriented control of a brushless doubly-fed reluctance generator (BDFRG) having grid-connected wind turbines as one of the main target applications. By using a fractional inverter, this promising generator technology could offer competitive performance and similar cost savings to its commercially popular slip-ring cousin, the doubly-fed induction generator (DFIG), but with the additional bonuses of maintenance-free operation and high reliability of brushless structure. The presented simulation and laboratory test results for an entirely machine parameter independent speed and reactive power control algorithm under various loading conditions of the BDFRG prototype, including those typically encountered in wind energy conversion systems, have been shown to be in good agreement clearly demonstrating the controller effectiveness and accuracy of the simulation model.