Maintaining the power balance in an 'empty network'

This paper presents the concept of an "empty network" and shows how the power balance can be maintained in such a system. In this study, an "empty network" is defined as a power system in which no rotating mass is present; all generators are grid-connected via power electronic interfaces, so that the possible inertia of the generators is 'hidden' from the network. One generator creates a neat 50 Hz voltage that serves as a frequency reference for the other generators. Conventional power systems are mainly supplied by large centralized synchronous generators. These generators are connected directly to the grid so that there is a coupling between the generator rotor speed, and thus the system frequency, and the power balance in the system. Therefore, an unbalance manifests itself by an altered system frequency. In the empty network, the frequency is fixed, as it is created by a power electronic device, and an unbalance cannot be detected in the classical way. In this paper, an empty network is simulated on an RTDS (real time digital simulator). Voltage deviations are used to detect the power unbalances. Simple test systems that consist of 1,2 and 3 buses are applied, in which all generators are modeled as current sources, except for the frequency reference, which is a voltage source. A load jump is simulated to cause a power unbalance in the system. The study shows that by using voltage deviations as control signals, the power balance can be maintained in an empty network.