CHS loads require configurations which include elements parallel to load (PAF, PPAF, SAPPF).
WAVESURFER 424 OSCILLSCOPE SERIES
In this case, the hybrid configuration presents better results than only series active filter.
The analysis of experimental results has allowed next conclusions to be obtained: - VHS loads require active compensator which includes a series active power filter (SAF, SAPPF). In all compensation equipments, the active filter control was designed to mitigate load harmonics. In each case, voltage and current waveforms were recorded and measures were made before and after harmonic compensation using each configuration. Thus, an experimental analysis has been carried out about three different cases corresponding to the connection of a three-phase rectifier with smoothing DC capacitor, a three-phase regulator or a set constituted by both loads. It allows the availability of non-linear loads with different harmonic production. A test bank has been designed composed of a harmonic voltage source (HVS) load and another harmonic current source (HCS) load, with the possibility of individual or joint connection. They are series active filter SAF, parallel active filter PAF, parallel passive-active filter PPAF and series active and parallel passive filter SAPPF. C ONCLUSION Four different active filter topologies to eliminate harmonics have been analyzed. The rest of configurations hardly aim to decrease THD values. The SAPPF decreases the same parameter to a value of 2%. It can be noticed as SAF configuration achieves the decreasing of current THD from 19.2% to 5.8%. Table IV presents the measures THD and RMS values. In this case, only the configurations with series APF aim the reduction of distortion in a meaningful way. 13 shows voltage and current waveforms before and after compensation for each APF topology. Thus, with K1 on and K2 on, the load is composed of a 1.18 kVA three- phase rectifier and a 0.98 kVA three-phase regulator. In this case both loads have been simultaneously connected, and the load presents an intermediate behavior.
The first one is voltage harmonic source and the second one current harmonic source. Case 1 and 2 present the experimental results corresponding to two types of non-linear loads whose harmonic characteristics are dual. Numerical results confirm the preliminary analysis obtained looking at system waveforms, Fig. Table III presents the results of THD and RMS values measured before and after compensation. Only SAF configuration does not allow current harmonics cancellation, because of series compensator topology and load harmonic character. The three topologies that include components in parallel to the load achieve to mitigate the current harmonics produced by a CHS type load. In this case three of four configurations aim an important reduction in voltage and current distortion. 12 b), c), d) and e) present voltage and current waveforms after compensation using each topology. 12 a) shows voltage and current waveforms before compensation. This is a HCS type load because of source impedance has little effect on the current harmonics.
In this case the power system is only constituted by the load composed of a three-phase regulator. Table II includes voltage and current THD and RMS values measured with the EPQ Fluke 434 analyzer. With respect to this type of load, shunt connection configurations, PAF and PPAF are not effective from the point of view of harmonic compensation. Thus, line current harmonics amplitude strongly depends on the source impedance, while voltage in its terminals practically does not depend on the ac impedance. A rectifier with smoothing DC capacitor is a HVS nonlinear load. SAF topology aims the mitigation of the distortion in a considerable level, while the rest of configurations do not achieve to significantly reduce distortion. SAPPF topology aims waveforms practically sinusoidal. A preliminary analysis of the waveforms shows that those configurations which include a series active filter achieve the improvement of voltage and current distortion. Figures 11 b), c), d) and e) present the voltage and current waveforms, when each harmonic compensation equipment is connected. 11 a) presents the voltage waveform in PCC and the supply current corresponding to the phase “a” obtained from a LECROY Wavesurfer 424 oscilloscope. 10 before and after compensation are presented, when the load connected is the three-phase rectifier with a capacitive load on DC side. As first case, results corresponding to the power system shown in Fig. Three cases have been analyzed according to the switch states of the Fig. The four configurations of harmonic compensation are considered. P RACTICAL R ESULTS In this section, voltage and current waveforms and THD values in PCC are presented.
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