# A Two-Grid Interline Dynamic Voltage Restorer Based on Two Three-Phase Input Matrix Converters
## 2 Operation of the TI-IDVR  
The IDVR system consists of several DVRs connected by different feeders, which share a common dc-link. The proposed TI-IDVR system shown in Figure 2 employs two DVRs connected to two different feeders originating from two network substations. These two feeders can have the same voltage level or have different voltage levels. The system consists of two independent feeders, a sensitive load on each feeder, a TTI-MC, two CSIs to synthesize the voltage to be injected into the grid, two injection transformers, two input filters and two output filters. As shown in Figure 2, the proposed TI-IDVR presents the configuration of two DVRs (without energy storage systems) connected on the source side without a capacitor on the dc-link. The merge of the two DVRs is done by replacing the two shunt converters of the DVRs with a TTI-MC. In this way, the considerations related to this topology are taken [7]:  
Figure 2: Schematic diagram of the proposed two input interline dynamic voltage regulator (TI-IDVR). CSI: current source inverter; TTI-MC: two three-phase input matrix converter. Where, SF are the switches that connect and disconnect the feeders and Sn are the switching elements of the TTI-MC and the CSIs, with n = 1, 2... and n = a, b, c, respectively. (a) when a voltage sag occurs, the shunt converter takes the remaining voltage and current from the feeder to maintain the full load power at nominal voltage; (b) a saving is obtained in the energy storage system; (c) there is the capacity to compensate for long-term voltage sags; (d) it is recommended that the feeders be robust since these topologies draw more current from the line during the fault. In this sense, even if the feeders are robust and capable of providing high currents, in practice, the available current could be limited by the overcurrent protection devices in the distribution line transformers; and (e) a saving is obtained by not using energy storage devices on the dc-link. It should be mentioned that although the use of TTI-MCs has not been widely adopted in IDVR topologies, it provides the benefit of expanding the compensation range by integrating the two feeders to power the TI-IDVR's virtual dc-link. Functionally, depending on the type of disturbance to compensate for, the proposed TI-IDVR can perform as a conventional DVR or as an IDVR. When a voltage swell appears in one of the feeders, the TI-IDVR behaves like a DVR and draws excess power from the failed feeder to compensate for the disturbance and keep the load voltage at its nominal value. In this way, the TI-IDVR does not draw power from the healthy feeder to compensate for the voltage swell in the faulty feeder. On the other hand, when the disturbance is a voltage sag, the TI-IDVR behaves like an IDVR and draws power from the two feeders to compensate for the disturbance and to keep the voltage on the load at its nominal value. In this case, the TI-IDVR integrates the power from the two feeders and is therefore capable of compensating for deep and long-term voltage sags. In terms of the modes of operation of the converters, when a disturbance occurs in one of the feeders, the series converter (CSI) corresponding to the failed feeder operates in compensation mode and mitigates the disturbance. At the same time, the shunt converter (TTI-MC) operates in power flow control mode. If the disturbance is a voltage swell, the TTI-MC transfers the excess power from the faulty feeder to the virtual dc-link. If the disturbance is a voltage sag, the TTI-MC integrates the power from the two feeders and transfers it to the virtual dc-link. The CSI that is operating in compensation mode takes power from the virtual dc-link and builds the compensation voltage to mitigate the disturbance in the faulty feeder. On the other hand, since the two feeders of the TI-IDVR system in Figure 2 are connected to two different grid substations, it is reasonable to suppose that a disturbance in one of the feeders would have a negligible impact on the other feeder [17].