This paper presents the concept of an 'empty network' and shows how the power balance can be controlled in such a system. In this study, an 'empty network' is defined as a transmission system in which no rotating mass is present. All generators are connected to distributed systems and 'hidden' behind power electronic interfaces. One generator creates a neat 50 Hz voltage that serves as a frequency reference for the other generators. Consequently, a power imbalance cannot be detected in the classical way, as an altered system frequency. Therefore, a novel control system to maintain the power balance is needed. In this paper, voltage deviations are used to detect power imbalances, and remedies to eliminate the negative consequences of using the voltage deviations to detect the power imbalances are proposed and discussed. Keywords: empty network; power balance control; distributed generation; distribution systems; power electronic interfaces; voltage deviations; power imbalances.@en

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.@en

Nowadays, interest in generating electricity using decentralized generators of relatively small scale ('distributed generation', DG) is increasing. This work deals with the impact of implementing DG on the transmission system transient stability, with the emphasis on a potential transition from a 'vertical power system' to a 'horizontal power system. A problem in power systems is maintaining synchronous operation of all (centralized) synchronous machines. This stability problem associated is called rotor angle stability. In this work, the impact of the DG implementation on this is investigated. The impact of DG levels on the system transient stability when the increasing DG level is followed by a reduction of centralized generators in service resulting in a 'vertical to horizontal' transformation of the power system is also investigated. Furthermore, a stochastic analysis is used to study the transient stability of the power systems. The results show that including the stochastic behavior of DG leads to a more complete and detailed view of the system performance. Finally, the situation when the power system is pushed towards a scenario, where DG penetration reaches a level that covers the total load of the original power system (100% DG level) is investigated. The research performed in this work indicates that from the transmission system stability point of view, if higher DG penetration levels are coming up, sufficient inertia and voltage support must be installed. Furthermore, one should be aware of the fact that the system behaves stochastically, especially with DG. To a certain extent regional balancing of power can be performed by local voltage control.@en