The growth of online services and digital data being uploaded to the Internet has led to an increase in the number of data centers. From an electrical point of view, data centers are very sensitive loads that require a very reliable power supply. For this reason, they are equipped with uninterruptible power supplies (UPS). In specific areas with high concentration of these services, such as Dublin, Ireland, there is a massive concentration of data centers. The strict connection requirements of these systems can lead to the simultaneous disconnection of an important share of the consumption in response to relatively small oscillations/disturbances in the power grid. As a consequence, power oscillations are aggravated, and the frequency of the grid can experience important fluctuations. This constitutes an important challenge for the corresponding Transmission System Operators (TSO).

As a solution, the UPS behavior is changed to remain connected during these disturbances by modifying the control to behave as a pure resistive impedance during these events, thus achieving a predictive and stabilizing behavior of the data centers, i.e. Uninterruptible Power Supply (UPS) systems. The controller of the mains side of the UPS (rectifier) is adapted by adding a virtual resistive impedance, which is activated when the grid oscillation reaches the trigger value. A PLL maintains synchronization with the grid, which is chosen to be immune to voltage variations due to the presence of oscillating voltages during these events.

The virtual resistor approach has been tested in simulation on a UPS connected to an infinite power grid. For the aforementioned case, the power consumption of the UPS in response to a voltage dip in the grid turns predictable. In fact, its behavior becomes equivalent to that of a resistor after just 20 ms (settling time). When the voltage returns to its nominal values, the load returns to its nominal steady state according to the power control loop bandwidth. The experimental tests, using a second inverter in back-to-back configuration to emulate the grid, are currently ongoing.