Csaba Szabo

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.

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.

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.

Incremental Encoder in Electrical Drives: Modeling and Simulation

Incremental encoders are electro-mechanical devices used as position sensors in electrical drives. They provide electrical pulses when their shaft is rotating. The number of pulses is proportional to the angular position of the shaft. The paper focuses on the modeling and simulation of an incremental encoder, and associated units serving for direction identification and position computing. Matlab-Simulink® structure was realized and tested. The proposed structure identifies the direction of the rotation in an angular interval equal to a quarter of the angular step of encoder graduation. The incremental encoder was integrated into the simulation structure of an induction motor based drive control system in order to provide the position of the motor shaft. Experimental results are also presented.

Flat-Top space-vector modulation implemented on a fixed-point DSP

The paper presents the method and implementation steps for space-vector (space-phasor) pulse width modulation, on a fixed-point digital signal processor using MATLABs Simulink® and the eZdsp development board. Besides the implementation of the simple suboptimal method, there are implemented 4 different Flat-Top (discontinuous) procedures. The simulation results show the improvements brought by the Flat-Top techniques: less commutations, even inside a sampling period, the ability to choose a Flat-Top method in correlation with the character of the inverters load in order to reduce furthermore the commutation losses. Also, the design of these Flat-Top techniques is improved by computing the position of the reference phasor without any trigonometric function, by using p.u. values for the on-times of basic vectors and by using the DC link voltage value, which can be compensated in case of the voltage ripples.

Run-Time Reconfiguration of Tandem Inverter for Induction Motor Drives

The paper presents a short introduction to reconfigurable systems and why are they used or should be used in control of AC drives. The reconfigurable vector control system is introduced and there are treated the reconfiguration problems. There is analyzed the reconfigurable control system and it is motivated the need for reconfiguration in motor control. The control of the induction motor fed by the tandem inverter needs reconfiguration if the supply is made only from one inverter instead of the both component ones. Finally a simulation and fast prototyping method is shown using Field Programmable Gate Arrays.

ECOLOGICAL POWER SYSTEM WITH LOCAL DISTRIBUTION DC-LINE FOR AC-DRIVE CONSUMERS

Abstract The paper deals with the simulation and implementation of AC-drives with synchronous and induction motors fed by a local distribution DC-line, which is supplied from an autonomous vector controlled synchronous generator. The main AC-grid is connected to DC-line the via ecological power electronic converters with bi-directional power flow, like the AC-drives and the generator. Solutions are proposed for sine-wave rectifying and inverting of the energy accomplishing grid-side unity power-factor with active power-filtering of the AC-grid- and motorside currents for different transferred energy levels. The energy-efficiency of the drives is achieved by means of vector control structures.

Double field oriented sensorless control of cage induction motor

The paper presents a vector control strategy for induction motor without mechanical sensor using double field-orientation procedure. It combines the advantages of both, rotor-and stator-field orientation. As a consequence the computation of control variables and also the speed identification calculus is independent of the rotor resistance, which improves the performance/robustness of the system.

Current-controlled PWM strategy with carrier wave for constant switching frequency

The most common current-control methods uses hysteresis controllers. With these conventional controllers it is inherently impossible to achieve constant switching frequency and current-error minimization at the same time. A method to realize constant switching frequency is to add a triangular carrier wave with constant amplitude and frequency to the reference signal. The error between the obtained signal and current feedback determines the constant PWM switching logic. However, unwanted switching occurs. The paper proposes an improved current-controlled PWM strategy with carrier wave for constant switching frequency, which is easy to implement. Its mathematical expression and validation is illustrated by means of simulation. Also a comparison between the proposed current-controlled PWM strategy and the well-known voltage-controlled PWM procedure is made from point of view of harmonic distortion.