Marius Biriescu

Experimental determination of synchronous machines reactances from DC decay at standstill

Measurement of parameters of high-power synchronous machines from steady-state or transient AC operational tests requires a great deal of electrical power. This paper presents a new application of a floating-point analog-to-digital converter which is employed in a microcomputer-embedded system that implements a standstill time response method to measure synchronous machine parameters. Floating-point quantization of the stator current response of a locked-rotor synchronous machine to a step signal is used to find the direct-axis and quadrature-axis reactances. Compared to previous solutions, this testing technique is characterized by higher precision, while still reducing the required power and minimizing the testing time. Simulated and experimental results are finally presented to compare the precision of this system with current state-of-the-art solutions.

Effects of stator slot magnetic wedges on the induction motor performances

The paper presents some aspects of magnetic wedges application in electrical machines. The slot opening distorts the waveform of the air-gap flux density and produces high order space harmonics, which causes increased additional losses and torque ripples and reduces both the power factor and efficiency of the machines. FEM-analysis is used in order to investigate some effects of stator slot magnetic wedges on an induction motor performances. The test results and FEM-simulations are very close and prove that the utilization of magnetic wedges is a good solution to improve the performances of the induction motor with open stator slots.

Testing of electrical machines in periodical and quasi-periodical conditions, using a data acquisition and processing system

The paper presents the procedures and the results of electrical machine testing accomplished by these authors using a specialized data acquisition and processing system (DAPS), they designed and built. This DAPS is aimed to measure and monitor electrical machines while operating in transient or steady state regimes. The architecture of the DAPS and the functionality of its components are described in the first part of the paper. To emphasize the versatility of the DAPS, some examples of testing electrical machines for periodic and dumped periodic regimes are given. The hardware programmability of the DAPS signal adapter and the modularity of the related software can extend the DAPS applicability to testing any electric high power equipment.

Rotation Speed and Wind Speed Indirect Measurement Methods for the Control of Windmills with Fixed Blades Turbine

The implementation complexity of classical algorithms for wind turbines control limits the utilization of low-end microcontrollers for such applications. We conceived an original method that aims to optimize the efficiency of windmills with fixed blades with the variation of the wind speed. In the paper we present an original method to determine generators efficiency values using measurements that were performed at the prototypes homologation, along with original simplified models of wind turbine and of wind turbine - generator assembly. Measured values of the frequency, voltage and current of the generator are applied to determine the turbine rotation speed and the wind speed, reducing thus the number of needed sensors. A couple of families of regression functions were derived and tuned accordingly to the factory experimental characteristics to allow for a facile calculation of the generators efficiency database table. To further speedup the assessment of the optimum /safety value of the windmill rotation speed, the generators model is considered to provide the rotation as a function of the wind speed in a tabular format that is further used at run-time as a look-table for rapid interpolations in the control loop. The main advantages of the proposed approach are the simplicity and robustness of the implementation, being easily portable to low-end microcontroller platforms.

Emergent exploration and resource gathering in collaborative robotic environments

The last years demonstrated a significant increase in the interest for emergent, collaborative robotics as a viable alternative to the more centralized classic approach. The design and implementation of a system of numerous cheaper robots have become more attractive than the construction of a larger, more expensive robot. This paper describes the algorithm which is used by a collaborative system of autonomous robots to find food sources (resources) on an unknown territory. As a case study, the implementations of this algorithm using a robotic collective composed of LEGO Mindstorm robots is discussed in this article. Some of the more interesting experimental results are also presented.

Low speed PM generator for direct-drive wind applications

The paper deals with the design, FEM analysis, and testing of a surface-mounting permanent magnet (PM) generator with an inner rotor for wind applications. The purpose of this work has been to build a PM generator with simple structure, good performances and very low cogging torque. The paper presents the main design aspects and the performance characteristics of a 5 kW, 120 rpm and some test results of the PM generator prototype. Good agreement between simulated and experimental results has been achieved.

Computer Aided Testing of Electrical Machines

The paper presents a computer controlled platform that authors devised and built for testing electrical machines both in laboratory and in industrial environments. The hardware and software architecture of the system were developed to address the testing specifications required by standards or requested by customers. Also, the results of several significant measurements that were performed with this automatic test-bench are presented. The testing platform was employed for testing electrical machines in various settings like mixed-frequency alternate current regime, amplitude modulated quasi-periodic regime, aperiodic transitory regime, to name just the most relevant ones. Prototype tests were carried out over medium power induction motors and synchronous machines, and the results of these measurements are presented here.

Experimental model of a hydrogenerator with static excitation

In this paper is presented an experimental model for an hydro aggregate with synchronous generator having static excitation. The model was designed and achieved in the laboratory at reduced scale, of 12 kVA, using a VI — LabVIEW environment. With the help of this model there might be experimentally studied the dynamic conditions of the real hydro generators in function.

Experimental Investigation of Rotor Currents Distribution in the Healthy and Faulty Cage of Induction Motors at Standstill

This paper simply investigates experimentally multiple “rotor” bar current waveforms at standstill, on a dedicated inverted induction motor prototype as a basis to analyze the bar currents distribution in the symmetrical and unsymmetrical cage. A phasor calculus scheme based on primary magneto-motive-force space harmonics is developed to explain this asymmetry of bar currents system at standstill even for a symmetrical cage. The results of the paper should be a strong experimental foundation to investigate thoroughly the effects of rotor speed and loading and of broken bars on additional losses, torque pulsations, noise, and vibrations in high performance induction machines.

Performances analysis of an induction motor with stator slot magnetic wedges

The medium and high power induction machines are usually built with prefabricated insulated coils. In these cases, by technological reason, the stator is designed with rectangular shape open slots. Because of the large width of the open slot, the air-gap magnetic field is distorted (comparatively with the situation of other types of slots shape), having high order space harmonics with significant amplitudes. Consequently, the pulsating torque components, noises and vibrations appear, and both the power factor and the efficiency decreases. To avoid these unfavorable effects of the open slots, the magnetic wedges are used. In this work, some aspects concerning the influence of the magnetic wedges on the performances of induction motor with open slots are analyzed. In this purpose the finite element method (FEM) and tests are used. It comes out that between the experimental results and FEM simulation results is a good concordance. This analysis confirms that the use of magnetic wedges in the case of an induction motors with open slots is a suitable solution to improve the electrical machines performances.