Maria Imecs

Vector control schemes for Tandem-converter fed induction motor drives

The tandem converter is an arrangement of two inverters connected in parallel: a high-power pulse-amplitude modulated current-source inverter and a low-power pulse-width modulated voltage-source inverter. In comparison with an equivalent single voltage-source inverter, this structure offers several advantages, significant reduction of switching losses in particular. Results of experiments with a tandem inverter, and those of computer simulations of induction motor drives with that converter, are presented. Three vector control schemes for such drives were investigated: a) rotor-flux orientation with a voltage-controlled tandem converter, b) rotor-flux orientation with a current-controlled tandem converter, and c) stator-flux orientation with a voltage-controlled tandem converter. Performance characteristics of the described control schemes are discussed.

Comparative analysis of PWM techniques: Simulation and DSP implementation

The paper presents an overview of the pulse width modulation (PWM) techniques for a feed-forward voltage source inverter. Classical and optimized modulation methods are treated regarding the ease of implementation, harmonic spectra, maximum modulation index and switching losses. Classical PWM procedures like naturally sampled with saw-tooth or symmetrical triangle-carrier-wave, regular sampled and space vector modulation (SVM) or optimized methods like third harmonic reference injection and flat-top discontinuous SVM are simulated using MATLAB-Simulink® development package. An eZdsp development board was used to implement various PWM strategies on a fixed point DSP and compare their performances.

An improved speed identification method using incremental encoder in electric drives

The paper presents a variable sampling time method for speed identification using generated pulses from an incremental encoder. The most common procedures for speed identification are: in low speed range the period-measurement-and in high speed range the frequency-measurement-based method. Considering the error that occurs in the classical frequency method for speed calculation, the proposed procedure eliminates that error by increasing the sampling period with the necessarily amount of time in order to synchronize the sampling period with the generated encoder pulses. There are presented simulation results obtained with Matlab/Simulink® structures.

Vector Control of Induction Motor Drives with Model Based Predictive Current Controller

The paper presents the design of a model-based predictive current controller (MPC) for induction motor (IM) drive application. Using an input-output linearized model, a systematic design of the long-range predictive current controllers is introduced. The resulting explicit MPC controller achieves the same performance like classical MPC, but with less computational effort, offering the possibility for real-time implementation. The results are compared to the state of the art current controllers, showing the performance of the new controller.

Vector control of the synchronous motor operating at unity power factor

The paper deals with n resultant stator-field-oriented vector control of a voltage-source-inverter-fed synchronous motor with variable excitation, controlled speed, and controlled flux, operating at unity power factor. These instructions give you basic guidelines for preparing camera-ready papers for conference proceedings. Simulation (using Matlab/Simulink environment) and implementations (on an experimental rig based on a dSPACE DS1104 controller card) were carried out.

Error compensation methods in speed identification using incremental encoder

This paper presents a comparative analyze between several methods that compensate or reduce the errors that occurs in speed identification using incremental encoder. The errors are caused by the lack of synchronization between encoder pulses and sampling time in fixed-time measurement and fixed-position measurement, and also due to the delay between the reference speed and the calculated speed from the incremental encoder pulses. Simulation results, using Matlab/Simulink® structures are presented and discussed.

Dual field orientation for vector controlled cage induction motors

The presented vector control structure combines the advantages of two types of field-oriented procedure. It is proposed for the short-circuited induction motor supplied from a voltage-source inverter (VSI) with voltage-feedforward (carrier-wave or space-vector) PWM. The speed and flux controllers generate directly the rotor-field-oriented components of the stator-current. The computation of the stator-voltage control variables of the inverter is made in the simplest manner in the stator-field oriented coordinate frame. As a consequence the control structure became motor parameter independent. There are presented simulation results and implementation possibilities.

Voltage-Hertz Control of the Synchronous Machine with Variable Excitation

In spite of the development of the vector control methods for the AC machines, the scalar control also finds his place in various industrial applications. Generally, the scalar control is used in reduced speed-range applications where is no need for exceptional dynamic behaviour. In order to achieve the highest torque per ampere ratio, the flux amplitude has to be maintained at his rated value. This can be achieved by adjusting in a proper way the US amplitude and the fS frequency of the stator-voltage. The working frequency is determined by the parameters of the application, so the constant flux operation can be maintained by adjusting the supply voltage amplitude. The first control method, which assures loss-less operation for the motor is the so-called constant voltage-Hertz operation. The only control variable is the stator-voltage frequency, while the voltage is computed based on the simplified steady-state equivalent circuit of the stator. Nevertheless, the main drawback of the constant volt/Hertz procedure consists on the effects of the voltage which can cause problems at low speed operation. These voltage drops at low frequencies has the same order of magnitude with the computed voltage, which makes the method inadequate at low speed. This can be eliminated by adopting different techniques, for the voltage drop compensation. The paper deals with current-feedback-based voltage-drop computation procedures for a salient-pole synchronous motor, with variable excitation. In addition to the known current-feedback compensation method, in this case also the excitation voltage is controlled, is order to improve the dynamic behaviour of the system

Rotor Fault Detection in Induction Machines: Methods and Techniques - State-of-the-Art

Fault detection, on-line condition monitoring and fault diagnosis of induction machines have received considerable attention in the last twenty years. Despite of various, more or less questionable practical results obtained, the topic increased in interest especially concerning those methods and techniques which are related to rotor fault detection case. Although the recent trend is toward the non-invasive, potentially sensorless methods (that use more and more sophisticated mathematical models in order to avoid false alarms), the present paper takes also into consideration the traditional, dedicated techniques in use. However, most of these methods in use are limited to the case of the three-phase squirrel cage induction motor. A wide range of literature is cited in order to provide appropriate references. Some critical comments regarding the new achievements are also included

Implementation of a configurable controller for an AC drive control: a case study

There are several different approaches to defining reconfigurable systems. Reconfigurable computing is also often called Custom or Adaptive. The significant potential for the acceleration of computing in general-purpose applications has been demonstrated (S. Hauck, 1998; J. Villasnor and W.H. Mangionesmith, 1997). Reconfigurable systems are those computing platforms whose architecture is modified by the software to suit the application at hand. J.M. Maciejowski (1997) gave another definition for reconfigurable systems. According to him, the reconfigurable (control) systems are important when a major failure occurs. The paper combines both approaches of reconfiguration in trying to give a solution implementing a reconfigurable embedded controller for the vector control of an AC drive.