Requirements for control strategies of grid‐connected converters in the future power system

Abstract

The increasing penetration of converter-based generation in many power systems around the world has sparked a discussion about how to operate these power systems with the usual levels of efficiency, reliability and cost-effectiveness. Current grid-following converter-based generators have proven to run stably in parallel to one another, even if there are thousands of them connected in a power system, and even in very small isolated power systems with extremely low system inertia. Discussions around the necessity of additional converter performance, usually under the 'grid-forming' and 'Virtual Synchronous Machines' concepts, have recently been transferred from the academic sphere to national and international industry fora. Formal discussions have started in Great Britain, in Germany and at ENTSO-E level. However, there is still a lot of uncertainty about the real and not simulated performance of grid-forming converters, whilst the needs case for requiring this radically different control method has not been adequately justified. With the present paper we raise key questions that will serve towards an objective discussion about power system needs, grid infeed technologies and their interaction. This section summarises the recent developments in the discussions around the control strategies needed for the future power system that is dominated by converter-based generation. The European Network of Transmission System Operators for Electricity (ENTSO-E) at a European level and National Grid Electricity System Operator (NGESO) in Great Britain spearhead the discussions, with the German SOs exploring the grid-forming concept but so far in a less formal context.

An overview of stability challenges for power‐electronic‐dominated power systems: The grid‐forming approach

“…A general idea of the GFM control is to present an ideal voltage source with a given voltage amplitude and frequency at its terminal, as shown in Figure 1 [58].…”

“…FIGURE 1Basic concepts of a grid-forming converter: (a) With, and (b) without grid supporting functionalities[58] …”

Coupling analysis on power‐frequency control loops for virtual synchronous generator based on relative gain array and Prony method

“…The increasing penetration of distributed power leads to a gradual decrease in the installed proportion of traditional synchronous generators (SGs), meanwhile, the access of a large number of distributed power sources will seriously affect the stability of power system [4,5]. In order to maintain the voltage and frequency stability of the system, conventional fossil-based generators are gradually being replaced by grid-forming inverters [6,7]. These power electronic converters can establish the AC voltage and provide inertial support for frequency regulation of power grid [8][9].…”