International Conference on Power Plants, 30.10-02.11.2012, Zlatibor, Serbia THE SPECTRAL COMPOSITION OF THE INPUT CURRENT OF REGULATED VIBRATORY CONVEYING DRIVES (RVCD) AND THEIR EFFECT ON POWER SUPPLY NETWORK Željko.V.Despotović*, zeljko.despotovic@pupin.rs Marija Janković*, Vladimir M. Šinik** Institute “Mihajlo Pupin”, University of Belgrade, Serbia* Technical Faculty “Mihajlo Pupin”- Zrenjanin, University of Novi Sad **

INTRODUCTION Vibratory conveying drives are the most efficient way to transport bulk and particulate materials. The use of an appropriate power converter can provide amplitude and frequency control of vibratory conveying. The range of the required amplitude of the load carrying element is 0.1mm-5mm, while the required frequency is in the range 5Hz-150Hz. A switching converter topologies can provide these requirements. Despite all the advantages, this topology significantly impairs the quality of the input current of the whole vibratory conveying drive, which is powered from the grid. A measure of the impact this current can make is the spectral composition of the input current. The lecture presents the experimental results for the most critical cases: when the excitation frequency is equal to the network supply frequency-50 Hz and when it is higher or lower by a few hertz. Based on the experimentally obtained spectra, a solution for the power factor correction circuit which provides a sinusoidal input current is proposed.

SCR PHASE CONTROL POWER CONVERTER IN REGULATED VIBRATORY CONVEYING DRIVES (RVCD) In this type of converter the thyristor is triggered only during positive half-periods. In this way the network voltage of frequency 50(60) Hz at the input is converted to a pulsating direct current (DC) supplying the EVA coil which generates a discrete spectrum of vibrations: 3000 (3600) cycles/min, 1500(1800) cycles/min, 1000(1200) cycles/min, 750(900) cycles/min, 600(720) cycles/min, 500(600) cycles/min, etc., depending upon the instant of triggering of the thyristor

SPECTRAL COMPOSITION –SCR PHASE CONTROL REGULATED VIBRATORY CONVEYING DRIVES (RVCD) Unidirectional-single SCR (a) 3000 cycles/min, (b) 1500 cycles/min, (c) 600 cycles/min and bidirectional-triac or anti parallel SCR (d) 6000 cycles/min

SWITCH MODE POWER CONVERTER IN REGULATED VIBRATORY CONVEYING DRIVES (RVCD) (a)-two switch forward converter, (b) - symmetrical half bridge and (c)-full bridge

AC/DC TOPOLOGY IN REGULATED VIBRATORY CONVEYING DRIVES Power converter AC/DC topology to study the spectral composition of switch mode RVCD to the supplying network

INFLUENCE of SWITCH MODE RVCD on POWER SUPPLY NETWORK (driving frequency of EVA is 50Hz)- simulation results (a) phase shift of EVA current pulses 0º, (b) phase shift of EVA current pulses 180º

INFLUENCE of SWITCH MODE RVCD on POWER SUPPLY NETWORK (driving frequency of EVA is 50Hz)- simulation results (a) phase shift of EVA current pulses 90º, (b) FFT spectrum, (c) FFT spectrum range 0-100Hz.

INFLUENCE of SWITCH MODE RVCD on POWER SUPPLY NETWORK (driving frequency of EVA is 48Hz)- simulation results (a) input current waveform, (b) FFT spectrum

INFLUENCE of SWITCH MODE RVCD on POWER SUPPLY NETWORK (driving frequency of EVA is 52Hz)- simulation results (a) input current waveform, (b) FFT spectrum

INFLUENCE of SWITCH MODE RVCD on POWER SUPPLY NETWORK; USING INPUT CHOKE (driving frequency of EVA is 50Hz)- simulation results (a) input voltage and current waveforms, DC link voltage waveform (b) FFT spectrum.

In all the cases presented so far, it can be concluded that a switch-mode RVCD for all its advantages, generally has a negative impact on the supply network. The solution that arises in this case is an input power factor correction (PFC) converter which must be placed between the mains and the output power converter which drives EVA.

Principle block scheme of the PFC control circuit for supplying switch mode RVCD

THE EXPERIMENTAL RESULTS Oscilloscopic records of the mains voltage and current for different driving frequencies of EVA: without input inductance (a) 48Hz, (b) 52Hz, (c) 50Hz and with input inductance (d) 50Hz

THE EXPERIMENTAL RESULTS Oscilloscopic records of the mains voltage, current, and DC link voltage for the PFC converter of a RVCD: the driving frequency of EVA (a) 48Hz and (b) 52Hz

THE EXPERIMENTAL RESULTS Input current FFT spectrum of the PFC converter of RVCD for EVA driving frequency of 48Hz

CONCLUSIONS In a power network, RVCD's (involving both SCR and switch-mode) generate mainly unfavorable AC pulses, but under certain conditions they can also generate pulsating DC pulses. Owing to this, they represent significant sources of higher harmonics which adversely affect the operation of other consumers. The impact on a power network is more drastic if a number of RVCD’s is used. In fact, this is quite common in practice, where, for technological reasons, a processing line is fed from a number of conveying devices in order to form a final mixture of a required homogeneity. For this reason it is necessary to carry out an additional optimization of switch mode RVCD’s i.e. optimization of the input (AC/DC) rectifying circuit. A solution for the power factor correction circuit which provides a sinusoidal input current is proposed. For this case the presented experimental results clearly show the benefits of the proposed PFC circuit for applications in the control of vibratory conveying drives.

ACKNOWLEDGEMENTS The presented investigation, has been carried out with the technical and financial supports of the Serbian Ministry of Science-Project of technological development -grant No: TR33022.

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