Improved direct torque control using Kalman filter: application to a doubly-fed machine

Direct Torque Control (DTC) has been extensively researched and applied during the last two decades. However, it has only first been applied to the Brushless Doubly Fed Reluctance Machine (BDFRM) a few years ago in its basic form inheriting its intrinsic flux estimation problems that propagate throughout the algorithm and hence compromise the DTC performance. In this paper, we propose the use of Kalman Filter (KF) as an alternative to improve the estimation and consequently the control performance of the DTC. The KF is designed around a nominal model, but is shown to be reliable over the whole operating range of the BDFRM. Moreover, we use a modified robust exact differentiator based on Sliding Mode (SM) techniques to calculate the angular velocity from an angular position encoder. Computer simulations are meticulously designed to take into account real-world physical constraints and thus show illustrative supporting results as expected from an experimental setup

Flux observer algorithms for direct torque control of brushless doubly-fed reluctance machines

Direct Torque Control (DTC) has been extensively researched and applied to most AC machines during the last two decades. Its first application to the Brushless Doubly-Fed Reluctance Machine (BDFRM), a promising cost-effective candidate for drive and generator systems with limited variable speed ranges (such as large pumps or wind turbines), has only been reported a few years ago. However, the original DTC scheme has experienced flux estimation problems and compromised performance under the maximum torque per inverter ampere (MTPIA) conditions. This deficiency at low current and torque levels may be overcome and much higher accuracy achieved by alternative estimation approaches discussed in this paper using Kalman Filter (KF) and/or Sliding Mode Observer (SMO). Computer simulations accounting for real-time constraints (e.g. measurement noise, transducer DC offset etc.) have produced realistic results similar to those one would expect from an experimental setup

Wind power applications of doubly-fed reluctance generators with parameter-free hysteresis control

The development and practical implementation aspects of a novel scheme for fast power control of the doubly-fed reluctance generator with a low-cost partially-rated converter, a promising brushless candidate for limited speed ranges of wind turbines, are presented in this paper. The proposed concept is derived from the fundamental dynamic analogies between the controllable and measurable properties of the machine: electro-magnetic torque and electrical power, and flux and reactive power. The algorithm is applied in a stationary reference frame without any knowledge of the machine parameters, including rotor angular position or velocity. It is then structurally simpler, easier to realize in real-time and more tolerant of the system operating uncertainties than model-based or proportional-integral control alternatives. Experimental results have demonstrated the excellent controller response for a variety of speed, load and/or power factor states of a custom-built generator prototype

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

Power control of brushless doubly-fed reluctance drive and generator systems

A new algorithm for shaft position sensor-less independent control of real and reactive power of the Brushless Doubly-Fed Reluctance Machine (BDFRM), an emerging competitive for applications with limited variable speed ranges (e.g. pumps or wind turbines), is proposed and experimentally verified in this paper. The algorithm is inspired by the fundamental operating principles of the machine and does not depend on any parameters. Therefore, it is more robust than model-based control approaches which often suffer from sensitivity issues and performance trade-offs associated with machine parameter variations or their inaccurate identification. In turn, the considered control method merely relies on the grid-connected winding voltage and current signals. Practical studies including speed tracking, power factor regulation and load response have demonstrated high performance of the scheme on a custom designed 1.5 kW prototype

A new sensorless torque and reactive power controller for doubly-fed machines

A novel sensor-less algorithm for decoupled control of torque and reactive power of a class of doubly-fed machines like the conventional wound rotor induction machine (DFIM) or the emerging brushless reluctance machine (BDFRM), has been proposed in this paper. The control concept has been derived from the first principles of torque production and magnetisation of the machines and requires only the grid-connected winding measurements. The sensitivity analysis presented has shown an inherent robustness of the flux estimator to resistance variations making the overall control scheme practically parameter independent and structurally simple and as such suitable for implementation using low cost DSP platforms or micro-controllers. Potential target applications include variable speed drive and generator systems with limited speed ranges (e.g. large pumps and/or wind turbines) where the cost benefits of partially-rated power electronics can be fully exploited. A custom-designed BDFRM prototype has served as a case study to illustrate the good control performance through computer simulations

Direct power control of brushless doubly-fed reluctance machines

A new algorithm for independent shaft position sensor-less control of real and reactive power (and therefore power factor) of the Brushless Doubly-Fed Reluctance Machine (BDFRM), a promising cost-effective candidate for applications with limited variable speed capability (e.g. pumps or wind turbines), has been proposed in this paper. The algorithm is inspired by the fundamental dynamic and magnetising principles of the machine and does not require knowledge of any parameters. As such, it should be more robust than model-based control approaches which often suffer from sensitivity issues and performance trade-offs associated with machine parameter variations or their inaccurate identification. In turn, the proposed control method (termed as 'Direct Power Control' due to conceptual similarities with traditional 'Direct Torque Control') merely relies on the grid-connected winding voltage and current information. Simulation studies have demonstrated excellent potential of the DPC scheme for generating operating mode of the custom designed BDFRM at maximum power factor

Towards a Generic Torque and Reactive Power Controller for Doubly-Fed Machines

A novel shaft-position sensorless algorithm for decoupled control of torque and reactive power (TRPC) of doublyfed machines like the classical wound rotor induction machine (DFIM) and the emerging brushless reluctance machine (BDFRM), has been discussed and experimentally verified in this paper. The underlying control concept is derived from first principles of magnetization and torque production in the machines. For control purposes, only the grid-connected winding measurements and rough knowledge of its resistance value are required. Such a weak parameter dependence makes the TRPC inherently robust, structurally simple and fast to execute even on low-cost DSPs. A variety of applications is possible including drive and generator systems with limited variable speed ranges (e.g. large pumps and wind turbines) where cost savings of using partially-rated power electronics are significant. Two customdesigned and built BDFRM prototypes have served as case studies to evaluate the controller performance by computer simulations and through laboratory experiments

Second order sliding mode control of a DC drive with uncertain parameters and load conditions

The Higher Order Sliding Mode (HOSM) is considered as a generalization of standard sliding modes that attenuates the chattering phenomenon. The main problem in implementation of the HOSM is the increasing information demand. In this work we implement two recent non-linear robust control schemes on a DC drive emphasizing their ability to tackle realistic situations in which the drive parameters are subject to variation, in addition to a time varying load constraint. Namely, we consider the Twisting algorithm which requires the first time derivative of the sliding variable to be known. In addition to that, we use the Super Twisting algorithm, which unlike other HOSM algorithms merely requires measurements of the sliding variable. Simulation results are given to support the approach