## 4 Results in Practical Cases
### Experimental Results  
Harnessing the potential of ANNs requires their implementation in a specific integrated circuit. However, a laboratory setup based on data acquisition cards has allowed for a first experimental validation in obtaining compensation currents with ANNs. Thus, a modular system based on dSpace cards was developed. Specifically, the set includes a DS1005 PPC control card developed from a PowerPC 750 GX 1 GHz processor that runs the control program in real time. This card manages the inputs and outputs from/to the power system through a DS2004 card with 16 input channels, and a DS5101 DWO card with 16 TTL pulse outputs. The input signals to the DS2004 card are from a set of Hall effect LEM sensors: LV-25-P sensors for voltage signals and LA35-NP sensors for current signals. The APF power circuit consists of a three-phase inverter with IGBTs, the Semikron SKM50 GB123D. It is a three-leg inverter with two capacitors on the DC side at whose  
Figure 11: Dynamic response with UpfC control, applying at \(t=0.1\) s a load change: nonlinear load increase. Up: one phase load current. Middle: source currents, with _ITHD_ = 3.3% after the change. Down: one phase source current and voltage, showing the _PF_ compensation. midpoint the neutral connection can be made. More details on the experimental prototype can be found in [2]. A three-phase diode rectifier with capacitive filtering on the DC side was connected to the 400 V, 50 Hz distribution network (230 V phase voltage). This frequently constitutes the input circuit of a variable speed drive of an asynchronous motor. Figure 14 shows the phase voltage waveforms of the grid, which present the distortion and unbalance typical of a low voltage supply. It also shows the voltage and current of the load for the same phase  
Figure 12: Performance of the UpfC control at different frequencies in a wide interval around the nominal 50 Hz value. Up: load and source _ITHD_. Down: source _PF_. Figure 13: Dynamic response with frequency changes, showing the source current and voltage waveforms. Top graph: change from 50 to 50.5 Hz at \(t=0.09\) s. Bottom graph: change from 50 to 49.5 Hz at \(t=0.09\) s.  
(phase _a_), where it can be observed the high current distortion corresponding to an _ITHD_ of 144%. The UpfC strategy was executed on the control card, which has allowed determining the compensation currents. Figure 15, upper graph, shows the compensation current generated by the ANN control circuit. The middle graph shows the resulting sinusoidal source currents, where the _ITHD_ value is 3.9%. Finally, Figure 15, bottom graph, contains the supply voltage and current waveforms in the same phase after compensation. As a result, theses voltages and currents are collinear, reaching a power factor close to unity. The unbalanced load performance was also tested. According to (8), the UpfC strategy will produce source currents proportional to the source voltages. Therefore, in most real cases, where not much voltage unbalance is present, the compensation will give rise to balanced three-phase source currents. Figure 16 shows a load change from the previous load features to lower impedance values, and different for each phase. Thus, the current amplitudes become higher and show some unbalance. The load _ITHD_ is over 140% in every phase. In Figure 17, the UpfC compensation results are presented. The top graph shows the compensation current in one of the phases. The middle graph shows the sinusoidal source currents, with the correction one cycle after the change, becoming quickly stationary and almost balanced. The slight unbalance that can be appreciated is due to the small voltage unbalance. The source _ITHD_ values fall into 4.0%, 4.1%, and 3.8% for the phases \(a\), \(b\), and \(c\), respectively. Finally, Figure 17, bottom graph, contains the supply voltage and current waveforms, which highlights the power factor correction. After all these tests were carried out, it is important to highlight some relations with the reference works.