Monthly Archives: December 2016

On the Implementation of FBD-Theory Concepts in the Control of Active DC-Traction Substations

14 December 2016Fără categoriecburada

Abstract

This paper is focused on the transformation of a classical DC-traction substation with twelve-pulse uncontrolled rectifier into an active traction substation by adding a dedicated system for active filtering and regeneration called SISFREG. The connection of SISFREG to the ACside is performed in the primary of the traction transformer via a passive coupling filter and a recovery transformer, whereas an active separating circuit ensures the connection to the DC-traction line. The new functions added to the DCtraction substation lead to the increasing the energy efficiency of the whole system in both traction and braking regimes of the vehicles’ traction motors. The control of the current provided by the shunt active filter, which is the main component of SISFREG, is achieved in indirect mode, by means of the current upstream the point of common coupling. In the generation of the set current, the concepts of the Fryze-Buchholz-Depenbrock theory are implemented. Thus, an active current is always imposed at the power supply side and the current control loop guarantees almost sinusoidal current and global unity power factor. A complex Simulink model of the whole system, including facilities for energetic analysis, has been developed and the simulation results show good performances in both steady-state and dynamic regimes.

Evaluating RMS of Linearly Variable Magnitude Waveforms by Using FFT and WPT. Theory and Practice

14 December 2016Fără categoriecburada

Abstract

The paper deals with the evaluation of the Root Mean Square (RMS) indices of signals with linearly variable magnitude by using Wavelet Packet Transform (WPT) and Fast Fourier Transform (FFT). Firstly there is presented a synthesis of employed techniques and previous results of the authors with respect to synthetically generated singleharmonic signals. The signals had linearly decreasing/increasing magnitude M. M varies according to a constant slope G. The studied absolute difference between the final and initial values of M belongs to the set {2,5, 5, 7.5 and 10}% from the initial M. Results of the RMS evaluation by using both FFT and WPT in a single harmonic approach are recalled, focusing on the maximum absolute values of percent relative errors. New studies are presented now, firstly considering randomly generated synthetic multiharmonic signals. Three cases are considered, corresponding to harmonic orders belonging to 3 distinct ranges: 3…9, 31…39 and respectively 3…40. The errors associated to the use of FFT and WPT are evaluated for them. Two real multi-harmonic signals are afterward analyzed. Small differences were noticed between the values yielded by FFT and WPT for the total RMS as compared to those computed with Riemann sums. The differences between the RMS yielded by FFT and WPT are also evaluated and discussed.

Study of the Reactive Power Side Effects for Tariff and Compensation Purpose at the Transmission Networks’Users

14 December 2016Fără categoriecburada

Abstract

The reactive power flows affect voltages, losses and transmission capacities. Thus MVAR flows are a matter of increasing concern for the grid operators and the Romanian Regulatory Authority for Energy has established their importance into a specific Order. The latest corresponding regulation for Romania allows the grid operator to exonerate of payment those injections of reactive which affect in a positive manner positively the voltages in the network. Such exemption is difficult to apply since the influence of MVARs on voltages is locational and time dependent. This paper deals with the assessment of reactive powers related to network users for payment and compensation purposes. The drawbacks are evaluated and compared with the benefits for voltage regulation, according to Romanian regulations. Theoretical skills are combined into one organic methodology, and an in-house software package for reactive power assessment is built. This is based on sensitivities of voltage, loss and transmission capacity to reactive injections into nodes. A case study consisting of a real 110kV network of about 2000 nodes was adopted. The survey was conducted for 6000 hours and outlines voltage to sink’s MVARs. The results were used to evaluate the opportunities to compensate and/or to discharge payments the MVARs with positive contribution to voltage regulation. This paper proposes a sensitivity based analysis for a real 110kV network.

Digital Control for the Air Pressure with Multi-Characteristics Selection

14 December 2016Fără categoriecburada

Abstract

The paper deals with a preparatory research stage for controlling the air pressure inside a small tank by various characteristics and algorithms. Basic elements both for the hardware design and for the software support are presented. The experimental platform brings together parallel solutions: a microcontroller board using a PICTM 16F877 chip from Microchip and an industrial controller from HoneywellTM. The functionality of the platform will be tested in this stage by the on-line commutation of the control characteristics IN (pressure error) – OUT (PWM control for the air pump). A set for the available characteristics of the controller is stored in software. For a fast design with simulation and debugging capabilities, the author used FlowcodeTM of Matrix Technology Solutions – an Integrated Development Environment with a Very High Level Programming Language. Future research works are intended for some fuzzy control algorithms that could adapt and optimize the control accordingly the dynamic of the process. The main components of the platform are, besides the controllers mentioned above, an industrial pressure sensor, a compressor, the pressurized container and some standard pneumatic devices for a safe operation. Both the hardware and the software design are made so that besides the research aims, the platform could be a flexible and multi – purpose didactic tool for the students.

Modeling and Torque Ripple Control in Faulty SPMSM

14 December 2016Fără categoriecburada

Abstract

Abstract – This paper presents a model of a Surface Permanent Magnet Synchronous Motor which can be used in a faulty case and a torque ripple control approach developed to be applied if the faulty case is detected. Two faulty cases are considered for study, the first consider an asymmetry between the stator phases of the motor created by unbalanced number of turns and the second a short circuit between the stator windings of the motor. Proposed torque ripple control use a phasor approach to provides the current reference for stator asymmetry and an injection of an inverse current for stator short circuit fault in order to decrease the motor torque ripple. The torque control has been implemented using a model of surface permanent magnet synchronous motor based on the dynamic equations. Simulation and experimental results highlight the link between the faulty and the torque ripple and show the possibility to decrease in this case the torque ripples by changing a balanced sinusoidal current reference by unbalanced one. In practical tests the impact of the unbalanced system of currents in the torque variation is studied using an analysis of vibratory harmonic measured at twice of the supply frequency.

Comparison of the Conservative Power Theory (CPT) with Budeanu’s Power Theory

14 December 2016Fără categoriecburada

Abstract

It is shown in this paper that the Conservative Power Theory (CPT) describes power properties of electrical circuits in a way which has a strong analogy to this description in terms of Budeanu’s power theory which misinterprets the power phenomena in such circuits. Also, similarly as Budeanu’s power theory, the CPT does not create right fundamentals for the power factor improvement by reactive compensation. Moreover, Budeanu’s power theory is no less “conservative” than the Conservative Power Theory, thus both theories can be referred to as conservative ones.