# A Two-Grid Interline Dynamic Voltage Restorer Based on Two Three-Phase Input Matrix Converters
## 7 Simulation Results and Discussion
### Case 2: Unbalanced Voltage Swell  
A swell is defined as an increase in the rms value of voltage or current of around 1.1 to 1.8 pu, with a duration from 0.5 cycles to 1 min. It is said that a three-phase voltage system is unbalanced if the magnitudes of the phase or line voltages are different from each other. In this section, the performance of the proposed TI-IDVR in the compensation of unbalanced voltage swell in the feeders is verified. To simulate these disturbances, the peak voltage of the feeders is increased from 100 Vp to 115 Vp in phase \(a\), to 130 Vp in phase \(b\), and to 145 Vp in phase \(c\). Figure 12: System waveforms in the compensation of voltage sags and harmonic distortion. (**a–d**) System waveforms (phase \(a\)); (**e–h**) system waveforms without TI-IDVR. When this disturbance arises, the TI-IDVR behaves like a conventional DVR. That is, the TTI-MC only takes power from the feeder that presents the unbalanced swell voltage for the TI-IDVR to perform the proper compensation. It is worth mentioning that this mode of operation is an important feature of the proposed TI-IDVR, unlike other IDVRs that draw power from the feeder without failure to compensate for the disturbance. The voltage and current waveforms of the entire system are shown in Figures 13 and 14. Figure 14 shows the waveforms of the system without TI-IDVR. The disturbance occurs at feeder 1 in the 50 ms to 100 ms time interval as shown in Figure 13. In this time interval, the TTI-MC only takes power from feeder 1 and transfers it to the virtual dc-link. The CSI 1 takes this power and builds the compensation voltage as shown in Figure 13. In this way, the unbalanced voltage swell is successfully compensated and the voltage at sensitive load 1 remains stable. The behavior of the TI-IDVR in compensating for this disturbance in feeder 2 is shown in Figure 13. The difference is that the TTI-MC draws power from feeder 2, and CSI 2 synthesizes the proper injection voltage to adequately compensate for the unbalanced voltage swell in feeder 2 and keeps the voltage at sensitive load 2 stable. The phase \(a\) voltage and current waveforms of the system are shown in Figure 14. When the event occurs in feeder 1, the voltages and currents of feeder 2 and sensitive load 2 remain unchanged. Furthermore, it can be clearly seen in the figure that the voltage and current in sensitive load 1 remain stable despite the disturbance. The figure also shows that the voltages and currents in the feeders and the sensitive loads are in phase. Therefore, it can be concluded that the proposed TI-IDVR is capable of maintaining a unit power factor in feeders and sensitive loads despite this type of feeder disturbance. System behavior without a TI-IDVR is shown in Figure 14. Comparing Figures 13 and 14, the effectiveness of the proposed TI-IDVR in the compensation of unbalanced voltage swells can be appreciated. from a faultless grid to a faulty grid. Needless to say, this is a feature that conventional IDVRs lack. To simulate a voltage interruption in the feeders, the peak voltage of all phases is reduced from 100 to 5 Vp for 50 ms. The waveforms of system voltages and currents are shown in Figures 15 and 16. In the 50 to 100 ms time interval, the voltage interruption in feeder 1 is simulated. The voltage interruption of feeder 2 is simulated in the time range of 150 to 200 ms. In this case, in order to hold the voltage stable in sensitive load 1, the TI-IDVR transfers the necessary power from feeder 2 to feeder 1. The voltage interruption in feeder 1, the virtual dc-link voltage and the injected voltage are shown in Figure 15. The figure shows that the TTI-MC transfers the power from the feeder without fail to the virtual dc-link. The CSI 1 takes this power and synthesizes the compensation voltage. The peak value of the injected voltage is 95 Vp. The figure shows that the voltages of load 1 remain stable at their nominal values despite the voltage interruption. Figure 15 shows a similar behavior of the TI-IDVR when the disturbance occurs in feeder 2.