Jiri Bendl

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.

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.

Influence of space harmonics on properties of six-phase induction machine - Part II. simulation and experiments

The experimental verification of the results of the mathematical analysis of a six-phase induction machine is presented in this paper. The verification is based on the measurement of the currents and torques at the feeding of stator winding by voltages which correspond only to a selected symmetrical component. The measured values are compared with the results of theoretical calculations. A single-phase short-circuit is simulated as an example of unbalanced feeding. Also in this case, the simulated currents are compared with measured currents.

Optimal Control of Input Rectifier in Voltage-Source Inverter Supplied from Unbalanced Power Grid

Operation of voltage-source inverter with fully controlled front-end stage supplied from an unbalanced power grid has been investigated and analyzed. A method of finding optimal switching functions based on various optimizing criteria has been investigated that generates the demanded output DC-link current. The overall power factor and current unbalance have been used as the optimizing criteria. The individual cases were simulated by a numerical model

Limitation of adjustable-speed drive operation by unbalanced voltage supply

Operation of the 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.

Operation of induction machine with combined star delta stator winding

An induction machine with combined star-delta stator winding is analyzed in the paper. This type of winding is used in order to suppress the selected groups of higher spatial harmonics of the current layer, magnetic flux density in the air gap, and the flux in the yoke and thus lower the losses and improve the energy efficiency. The mathematical model of the machine has been developed. The possibility to suppress higher harmonics in such machines has been demonstrated. The validity of the equations has been verified by experimental measurements on a physical model of the machine.