Lesław Gołębiowski

Inverters operation in rigid and autonomous grid

Purpose – The aim of this paper is to develop the method of optimal control of the three‐phase inverter system for autonomous and power grid operation. The presented method will also allow the cooperation of several inverters creating an autonomous network. This system should also be able to reduce demanded higher harmonics in power voltage according to the list of numbers of these harmonics. In this article the authors describe a system that is used to create a symmetrical three‐phase voltage. The supply power is taken from the renewal source. The inverter system as well as cooperation of several such systems to create an autonomous network is under consideration. The generated three‐phase voltage should be symmetrical even when the RL load is not symmetrical or else it changes in impulse. Cooperation of the system with the autonomous network is also under consideration. The task is to supply the set current of the basic harmonic to the power grid and possibly to reduce voltage higher harmonics on output...

Voltages in the Shaft of the Induction Motor in 3D FEM Formulation

A 3D model reflecting entire internal structure of the asynchronous machine using finite elements method, has been presented here. Nodal finite elements have been used to approximate scalar potential and edge finite elements to approximate vector magnetic potential. This model includes both the skew of the rotor bars as well cross current flowing through the rotor iron laminates. The three-phase stator winding is supplied with four-lead mains voltage. The axial flux was calculated by integration of the vector potential around the shaft of the machine. Making isolation between I a mine worse in the area of tooth stator, was leading to the voltage in the rotor shaft, this voltage was used for diagnostics. Plots were calculated following the switching on the machine at various speeds. Bar as well as ring fractures were simulated. The simulation results have been confirmed by the theoretical anticipations.

Detection of broken bars and rings in induction machines

Determining the number of broken bars due to the failure or the number of ring segments of the rotor cage of induction motor is an important problem during the operation of such machine. The Unscented Kalman Filter (UKF), used to achieve this goal, provides precise information on numbers of broken bars and ring segments. To generate such information, the filter requires measurements of the stator currents and currents of additional single-winding coils located at the stator teeth and loaded with large resistances (~1 kΩ). The measurement of the rotational speed of the rotor and the related angle of the machine shaft rotation is also needed. The method of determining the numbers of broken bars and ring segments of the rotor and the method of detecting only the broken bars of the rotor cage were tested. The presented method can be used for the protection of large and expensive induction drives.

Autotransformer rectifier circuits with parallel connection without the use of IPT chokes - review

When using many rectifying devices, higher harmonic components of currents absorbed by them from the grid become significantly important. They can cause very harmful phenomena connected with grid voltage drop, glimmering of lights or significant power losses. The presented 18 pulse rectifier circuits enable to lower the content of higher harmonics of the grid currents. When considering leakage inductance of autotransformers and supplying grid these rectifier circuits may be classified to the ‘clean power’ circuit type. Due to instability of ITP type chokes and their vulnerability to magnetic circuits saturation it was decided to resign from their application. Different 18 pulse rectifier circuits were analyzed and diode currents waveforms were calculated and their characteristic parameters were presented. These results may simplify the process of designing such circuits.

Rectifier circuits with magnetically non-coupled chokes

When using many rectifying devices, higher harmonic components of currents absorbed by them from the grid become significantly important. They can cause very harmful phenomena connected with grid power outages, glimmering of lights or significant heat losses. The 18 pulse rectifier circuits presented in the article enable to lower the content of higher harmonics of the current absorbed from a grid. When considering appropriate values of leakage inductance of chokes and the supplying grid these rectifier circuits may be classified to the ‘clean power’ circuit type. Due to instability of ITP type chokes and their vulnerability to magnetic circuits saturation it was decided to resign from their application. Autotransformer or ZSBT chokes were replaced with magnetically non-coupled chokes. These presented results may simplify the process of designing such circuits.

Thermal Coupling Analysis of the Permanent Magnet Synchronous Generator

The construction and thermal analysis of the 2 KW generator designed for a small wind power station with vertical axis of rotation was presented in this article. The analysis is required in order to determine temperature distribution inside the machine to avoid magnets demagnetization and insulation damage. The presented thermal analysis of synchronous generator prototype was made using Computational Fluid Dynamics (CFD) Ansys Fluent analysis. In order to determine losses at the machine components Ansys Maxwell system was used. The analysis was made for three variants of the air flow speed around the generator frame. The lowest speed corresponds to the conditions of air flow during the study at the test stand, while higher speeds simulate the normal generator operation.

Study of the dynamic stability for small power plants

This paper focuses on the changing requirements for small power units connected to the grid and the task of stability studies to ensure the adherence of this requirements. Belong the coupled simulation of grid faults to determine the critical fault clearing time of a machine the main influences on the ability of a machine on keeping connected to the grid during a fault with deep voltage transients are discussed. This influences are especially important to know, if a synchronous generator does not fulfill the stability requirements and has to be optimized.