Control of Virtually Synchronous AC and DC Coupled Networks with Distributed Generation
ref. ENE2016-79493-R
National public
Initial date: 2016-12-30
Final date: 2019-12-29


The electrical networks have grown in complexity and heterogeneity over the recent years. The increasing penetration of different generation systems at different levels, the continuous increase in energy demand, the emergence of transmission systems in DC and the higher interaction with consumers have made necessary to rethink the control structures in order to ensure the stability of the network under all kind of scenarios, without limiting its evolution.

In this regard, the main objective of the project is to provide control solutions that maintain or even increase, the synchronous nature of the grid despite the tendency to increase the ratio of generating devices connected to network not based on classical synchronous generators, increasing thus its stability.

The project will propose, analyze and validate a set of control strategies which are oriented to guarantee the stability of the synchronous network. This synchronous network is considered to be one where all the elements are synchronized and work harmoniously based on the power flow equilibrium. In the proposal the integration of different power grids in both AC and DC are carefullly treated. Moreover, the project aims to extend the synchronous control strategies developed in previous projects, and more oriente to generation and storage systems, to the control of AC and DC networks links.

A special case of interconnection between AC and DC buses is the case of HVDC interconnections, that connect DC systems with AC networks in two or more nodes. Moreover, this interconnection is combined with generation or consumption within the DC network. In this regard, the project will devote several efforts in the analysis of AC networks control and how this methodology can be translated into a synchronous control at the DC side, giving rise finally to a single system that can be treated as a single virtually synchronous network. This approach would contribute to increase the staibilty and power flow control.

Within the category of interconnection devices, or electronic based generation, power conversion systems that interconnect DC bus with AC buses with power flow in either direction they will be considered. This type of interconnection includes different technologies and dynamics, as for example the offshore wind farms (photovoltaic in some cases); the interconnection of energy storage devices and interconnections between networks with AC converter and DC among others. The project aims to integrate all these devices into a common control framework to share a dynamic side AC and form a virtually synchronous network.

With this, the project aims to demonstrate that a virtually synchronous grid can be stable itsefl,  at phase, frequency and voltage levels, based solely on synchronous interconnection devices. As a basic hypothesis it will be assumed that the network has sufficient energy reserves guaranteed by a secondary and tertiary network control and additional energy storage elements. Although the study of this energy reserve is not included in the project its dynamics, technical limitations and variability of each technology will be considered. The main objectives are focused on:

- Scaling the virtual synchronous generation concept in the interconnection of DC and AC networks
- Performing the analysis of stability criteria in AC and DC networks, considering the AC-equivalent model in DC networks
- Analyzing different scenarios, considering different network configurations


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Universitat Politècnica de Catalunya (UPC) - BarcelonaTech