A. Ba-Razzouk

Implementation of a DSP based real-time estimator of induction motors rotor time constant

Implementation of ac drives insensitive to parameter variations is an important need in the field of high performance drives. For drives controlled by the indirect rotor flux oriented control method (IRFOC), the rotor time constant (/spl tau//sub r/ = L/sub r//R/sub r/) exerts a dominant role in the loss of dynamic performance and its variation results in an undesirable coupling between flux and torque of the machine. This paper presents a new scheme for on-line estimation of rotor time constant using dq representation of the model in the stationary reference frame and measurements of accessible motor variables only (voltages, currents and speed). The estimator is tested by simulation in the MATLAB/SIMULINK environment and validated experimentally on a 1/4 hp squirrel cage motor and a 1/4 hp wound rotor motor with implementation on a TMS320C31 digital signal processor.

Accurate adaptive integration algorithms for induction machine drive over a wide speed range

This paper presents three new architectures for designing accurate adaptive integration algorithms (AAIA) for quasi exact flux position and magnitude estimation of induction machines over a wide speed range. Pure integrators are in practice affected by DC-offset and DC-drift problems while estimating flux position and magnitude from the back electromotive force (emf). Modified integration algorithms based on low pass filter (LPF) or programmable LPF are also known to be affected by the cut-off frequency. The proposed architectures are based on the association of high pass filters (HPF) and pure integrators. DC-offsets and drift problems are eliminated by the HPFs before integration. The HPF characteristics are used for magnitude (gain) and position (angle) compensation. The HPF cut-off frequency can be chosen far from the inverse of stator time constant without affecting the estimation of low frequency signals resulting into good accuracy over a wide speed range. A strong agreement is observed between the simulation and experimental results that demonstrate the accuracy of the proposed architectures. The proposed AAIA can be used for any kind of induction machine (IM) since they are independent from the IM parameters. The AAIA can also be used to estimate stator flux in order to estimate the IM parameters online, as required for adaptive control in indirect rotor flux oriented control (IRFOC) schemes

A unified method for modeling and simulation of three phase induction motor drives

This paper presents a new approach for modeling and simulating the dynamic behavior of a large, interconnected, nonlinear, time-varying physical system consisting of a three-phase induction motor drive. An example of a vector-controlled induction motor shows that the proposed method is very accurate and very fast. The proposed simulation method and algorithm are expected to overcome some of the disadvantages of the existing methods. Simulation results are presented to illustrate the capabilities and flexibility of the simulation technique. A comparative evaluation with PSIM results is also provided to confirm the simplicity and the accuracy of the proposed unified method.

Application of the current-injected modeling approach to quasi-resonant converters

This paper describes how the current-injected (CI) method, which has been applied only to pulse-width modulation (PWM) DC-DC power converters, can be extended to quasi-resonant (QR) power converters. The methodology for extending this small-signal modeling approach is described in detail. It is also shown that QR dynamic models are easy to obtain since they are derived directly from PWM power converter models. These new models result in a unified block diagram from which zero-voltage-switching (ZVS) or zero-current-switching (ZCS) transfer functions of the basic topologies, such as buck, boost, and buck-boost operated in half-wave (HW) or full-wave (FW) modes, are found. As an application of this method, a ZVS boost power converter and ZCS boost power converter were fabricated and tested. In addition, small-signal models of these power converters were derived with the help of the state-space averaging (SSA) method. The agreement of the CI method simulations with the experimental results for the two QR power converters is comparable or better than that of the SSA method.

Decoupled parallel simulation of power electronics systems using Matlab-Simulink

This work presents an efficient parallel simulation method, namely the Discrete Time Model Segmentation Approach (DTMSA) which could be applied to simulate a complex system using simple Simulink block diagram models. In this approach, a complex system, like motor drives, can be decoupled into many smaller subsystems. Each subsystem is then formulated with a smaller matrix and simulated with in the same program. This technique reduces the memory requirements and computation time. In addition, this approach is easily implementable on parallel computers and is structured to take full advantage of parallel processing. This parallel simulation method allows significant speed improvement compared to normal sequential simulation.

An improved estimation of eddy-current losses distribution for squirrel cage induction motor using finite element method

In the proposed paper, an improved approach for the estimation of eddy-current losses distribution in a sheet from a squirrel cage induction motor is presented. The principle consists of combining finite element analysis with experimental measurements to determine the equivalent transverse electrical conductivity of a single sheet. The calculation is based on the assumption that the eddy-current losses are the same under the same flux density condition. The experimental conditions are reproduced in the simulation. Saturation effects have been taken into account. Varying the conductivity value step by step, the simulation repeats until eddy-current losses match that obtained in the experimental case. The 2D-finite element method is applied to obtain the flux density waveform at all points of a sheet. Eddy-current losses are determined on the basis of the field analysis. The equivalent conductivity obtained in this way can be used for modeling the magnetic circuit of an induction motor. The sheets used in this paper are taken from a 50-HP squirrel cage induction motor.

Real time flux and torque estimator for induction machines

This paper presents a novel method for flux and torque estimation. Based on the observation and analysis of the behaviour of the classical torque and flux estimator structure in an indirect rotor flux oriented control (IRFOC) of a voltage fed squirrel cage asynchronous machine, the proposed structure is fully independent of the stator resistance. Implemented in dq coordinates, the estimator is based on simple calculus of signal averages. Only stator voltages and currents are required for the estimation, along with maximum and minimum detectors. Flux position and magnitude are estimated separately, and dq fluxes are rebuilt for torque estimation. The estimator is designed for systems running above 0.5 Hz, making it available for induction machine (IM) applications running over a wide range of speed. Simulations are performed on SimPowerSystems.

Numerical simulation in power electronics using the MATLAB-SIMULINK program

In this article we present a new method of numerical simulation of systems composed of static converters. This method is based on a new approach to modelling of a power interrupter. The resolution of the equations is based on a constant matrix despite the changes of state of the interrupter. The article presents the method of modelling the power interrupters in the MATLAB-SIMULINK environment. The placing of equations is wholly automatic supported by nodal analysis of circuits. This approach implanted in the MATLAB program permits us to benefit from this powerful tool for which this application is the principle subject; and presents a very interesting capacity of interactive work for the user. This method applied in an actual static converter simulator gives very good results, and possess an appreciable advantage concerning speed of calculation, and the precision and viability of the results obtained. The illustration of the formalism proposed is tested on a three phase system assuring an alternative-continuous transformation based on an optimisation of the current spectrum quality entering by the injection of the third harmonic (Minnesota converter).

Application of the current-injected modelling approach to quasi-resonant converters

Until now, the injected current method has been applied only to DC-DC power converters. This paper describes how this method can be extended to quasi-resonant power converters. It is shown that quasi-resonant models are easy to obtain since they are derived directly from the PWM power converter models. These new models result in a unified block diagram from which zero voltage switching or zero current switching transfer functions of the basic topologies such as buck, boost and buck-boost operated in half-wave or full-wave are found. As an application of this method, a zero voltage switching boost power converter and a zero current switching boost power converter are fabricated and tested. Experimental results are compared to computer simulations obtained with this method and with the state-space averaging method.<<ETX>>