SAFACTIVE FILTER - COMAR CONDENSATORI SpA

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Only harmonic compensation HP Filter Load current Line current ref. Total compensation Vdc_ref + Vdc feedback – PI Regulator + – + – I_SAF feedback Hysteresis control SAF current transducer SAF DC voltage transducer Control filter chart The hysteresis control The typical current emitted by Active Filter with a PWM modulation and hysteresis control is shown in the figure below where the current has a triangular shape with a carrier frequency of 10 kHz: This current is then modulated with the next rule: it changes continuously between the upper band and the bottom band, where it is forced to change. These two bands are shaped from the regulation block based on the load harmonic current and the internal regulation PWM control rules. Then a DC internal bus composed by two electrolytic capacitor banks, one with a positive potential and the other with a negative potential is the current source for the filter (so when the inverter block of the filter injects on to the network the “correcting” current it takes it from this bus). When SAF works, it switch on the upper side of the semiconductor bridge, the current flows to the load with an amplitude up to the upper band of the control shaped waveform (see t1 time in figure). Then this upper semiconductor is switched off and the lower side IGBT is switched on: so the current 8 http://www.comarcond.com
flows to the load from the negative potential, reaching the lower side of the band control shaped (t2 time in figure) With this operations a current wave shape as the calculated one is flowing to the network, after that the waveform is filtering by the induction coil working in high frequency. In the same way (with the same method of control) the filter can generate current to correct the reactive power of the load, giving at the same time correcting the harmonics. In order to give a full power factor correction of the load, where it is necessary a reactive power greater than the one available in the active filter, it is possible to connect external capacitor banks to satisfy the full reactive power demand. The control of these banks can be performed by the filter with a command from a volt free contact of a relay. Other important feature of the filter is the possibility to adapt itself to the maximum possible current. So that when a current higher than the rated one is needed, SAF doesn’t stop the operations and continue to give the current to correct the harmonic absorption of the load, limiting it’s self to the maximum rating without cutting out (this could introduce distortion on the network) but modelling in the best way possible the emission of the current. The critical condition is displayed with an alarm. SAF interface In the base version SAF is equipped with an easy interface, based on led indication and can effectively monitor the active filter operation, all the internal conditions, to allow for a fast diagnosis of any fault. It is also possible to use a volt free contact on the relay to give a remote indication of the alarm, the state of the filter, the control of other values or the control to switch-on the filter. The values shown in the display are also a part of all the possible state that the active filter can monitoring as security value, control variable, value of current or voltage of the network. A microprocessor continuously monitoring all the parameters of the system and the filter is working under its control every time. Sophisticated algorithms allow the equipment to work in the best condition possible so the internal components are always without electrical stress and consequently this increases their life. This kind of control: ‣ limits the maximum current flowing; ‣ keeps under control the voltage of the system and of the active filter; ‣ runs in a security way the inverter switch by the control of the “blanking time” and the “dead time” inside with a precision about a microsecond; ‣ monitors the three phase supply voltage of the network; ‣ controls the current flowing when the power is the maximum rated even if the load is absorbing a current greater than the rated (so the filter doesn’t turn off); ‣ checks the maximum temperature In addition to this basic easy version of the interface, Comar Condensatori S.p.A. provides an advanced interface that can monitor the values of all the parameters run by SAF: an alphanumeric display updated continuously in real time the changing values of: ‣ network rms voltage and THD v ‣ cosϕ ‣ bus voltage DC ‣ load rms current THD i ‣ filter rms current ‣ power absorption by the filter and the load ‣ current rms value before the load connection So it possible to see the efficiency of the filter, monitoring the current before the load and the current after it. It is also possible to check the fault history in order to analyze them for fast error diagnostics. http://www.comarcond.com 9
Page 1 and 2: UNI EN ISO 9001:2000 C E R T I F MA
Page 3 and 4: Index • Introduction ............
Page 5 and 6: The presence of harmonic current in
Page 7: Active Filter block schematic • I
Page 11 and 12: Power factor correction: It is poss
Page 13 and 14: The SAF system The active filter ha
Page 16: Grafica Junior - Tel. 051.733020 CO

SAFACTIVE FILTER - COMAR CONDENSATORI SpA

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