Ludek Schreier

Torque and current ripple analytical investigation in space-vector PWM inverter fed induction motor drive under DC-bus voltage pulsation

Analytical investigation of the current and electromagnetic torque ripples in the three-phase voltage source inverter fed induction motor drive under DC-link voltage pulsation is presented in this paper. The analytical expressions for the voltage and current space-vectors as a function of the DC-link voltage pulsation are derived. The analytical results are verified by the experiments.

Influence of space harmonics on properties of six-phase induction machine - Part I. analysis

The paper deals with analysis of the situation in a six-phase induction machine. The method of space vectors is used for this purpose. The necessity to consider higher space harmonic waves of a current layer, flux density and flux in the stator yoke is shown in the case of feeding by unbalanced stator voltages. Equations of a six-phase machine are derived and the relation between symmetrical components of instantaneous values of a six-phase machine with a group of space harmonics of the field in the air gap is shown.

Compensation of unbalanced three-phase voltage supply in voltage source inverter

A control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC link of a voltage source inverter is investigated. Such a pulsating current can have detrimental effects on operating properties of the drive as well as on the quality of power supply in the electrical vicinity of the inverter. A feasible range of control parameters is determined based on the required level of immunity against unbalanced voltage supply and on the parameters of the system. The impact of the control method on the power factors and current amplitudes in individual input phases for the available range of control parameters is analyzed and discussed. Examples of numerical simulations illustrate operation of the system under investigation both with and without the compensation method used.

Working regions of adjustable-speed units with doubly fed machines

The working regions of an adjustable-speed generation unit with a doubly fed machine connected to the power grid are determined. The analytical relations for the control range of the rotor voltage phasor due to the maximal permissible values of currents and voltages of the machine and supply cycloconverter are presented. Simulation results are shown to illustrate the operation of the system.

Operation of Adjustable Speed Drives under Non Standard Supply Conditions

The demands on the robustness and reliability of electrical drives have been steadily rising during the last decade. In some applications, the users require the drive to continue in operation even under certain non-standard conditions. The discusses various types of non-standard conditions and analyzes what impact these non-standard conditions have on the voltage- source inverter and what countermeasures can be taken in order to minimize their negative impacts on operation of the drive. Special attention is paid to the voltage-source unbalances and control methods eliminating these unbalances are discussed.

Operating regions of PWM rectifier under unbalanced voltage supply

Operation of electric drives may be negatively affected by non-standard conditions in the power network such as voltage unbalance, which may arise in three-phase power networks. The unbalance can be caused by a failure in the network or by unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source inverter cause pulsations in the DC-link voltage when not properly taken care of. This may result in reduced power capabilities of the drive. The paper deals with the methods to address this problem and with the limitations placed on the drive when operated from the unbalanced voltage supply.

Influence of circuit parameters on operating regions of PWM rectifier under unbalanced voltage supply

Electric drives may be negatively affected by non-standard conditions in the power network such as voltage unbalance, which may arise in three-phase power networks. The unbalance can be caused by a failure in the network or by unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source inverter cause pulsations in the DC-link voltage when not properly taken care of. This may result in reduced power capabilities of the drive. The paper deals with the methods to address this problem and with the limitations placed on the drive when operated from the unbalanced voltage supply. Influence of circuit parameters on the operating regions and their constraints are particularly dealt with.

Optimal control of power unit with doubly fed machine

An adjustable-speed unit with a doubly-fed machine running both in generator and pump modes is dealt with. Operation of a power unit with a doubly fed machine driven by a Francis turbine regulated at the optimal speed is analyzed and compared to the cases when the speed is kept constant. The response of the system to changes in demanded active power command has been investigated. Control of active power consumed in pump mode is analyzed. The effect of a high voltage distribution line on the operation of the system has been taken into consideration.

Additional asynchronous and pulsating torque analysis of 3-phase induction machine

This document contains possibilities of additional asynchronous torque development due to the high harmonics and their general derivation. Also, there is calculated a pulsating torque of 3-phase induction machine with power 1.1kW from electromagnetic field and example of additional asynchronous torque calculation. Whole analysis is done by finite element method in ANSYS. The torque is calculated via a circular path integral of the Maxwell stress tensor. The Maxwell stress tensor provides a convenient way of computing forces acting on bodies by evaluating a surface integral.

Power factor correction in voltage source inverter under unbalanced three-phase voltage supply conditions

The power factor correction achieved with a control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC link of a voltage source inverter is investigated and analyzed. A feasible range of control parameters is determined based on the required level of immunity against unbalanced voltage supply and on the parameters of the system. The impact of the control method on the current amplitudes in individual input phases for the available range of control parameters is analyzed and discussed. Examples of numerical simulations and experimental measurements illustrate operation of the system under investigation both with and without the compensation method used.