arXiv subjects

Friederich Kupzog

Publications and source records attributed to Friederich Kupzog.

3 recordsLinked to original sources

arXiv2020

Frequency Stability of Synchronous Machines and Grid-Forming Power Converters

An inevitable consequence of the global power system transition towards nearly 100% renewable-based generation is the loss of conventional bulk generation by synchronous machines, their inertia, and accompanying frequency and voltage control mechanisms. This gradual transformation of the power system to a low-inertia system leads to critical challenges in maintaining system stability. Novel control techniques for converters, so-called grid-forming strategies, are expected to address these challenges and replicate functionalities that so far have been provided by synchronous machines. This article presents a low-inertia case study that includes synchronous machines and converters controlled under various grid-forming techniques. In this work 1) the positive impact of the grid-forming converters on the frequency stability of synchronous machines is highlighted, 2) a qualitative analysis which provides insights into the frequency stability of the system is presented, 3) we explore the behavior of the grid-forming controls when imposing the converter dc and ac current limitations, 4) the importance of the dc dynamics in grid-forming control design as well as the critical need for an effective ac current limitation scheme are reported, and lastly 5) we analyze how and when the interaction between the fast grid-forming converter and the slow synchronous machine dynamics can contribute to the system instability

eess.SY↗

arXiv2019

Beyond low-inertia systems: Massive integration of grid-forming power converters in transmission grids

As renewable sources increasingly replace existing conventional generation, the dynamics of the grid drastically changes, posing new challenges for transmission system operations, but also arising new opportunities as converter-based generation is highly controllable in faster timescales. This paper investigates grid stability under the massive integration of grid-forming converters. We utilize detailed converter and synchronous machine models and describe frequency behavior under different penetration levels. First, we show that the transition from 0% to 100% can be achieved from a frequency stability point of view. This is achieved by re-tuning power system stabilizers at high penetration values. Second, we explore the evolution of the nadir and RoCoF for each generator as a function of the amount of inverter-based generation in the grid. This work sheds some light on two major challenges in low and no-inertia systems: defining novel performance metrics that better characterize grid behaviour, and adapting present paradigms in PSS design.

eess.SY↗

arXiv2019

Interactions of Grid-Forming Power Converters and Synchronous Machines

An inevitable consequence of the global power system transition towards nearly 100% renewable-based generation is the loss of conventional bulk generation by synchronous machines, their inertia, and accompanying frequency and voltage control mechanisms. This gradual transformation of the power system to a low-inertia system leads to critical challenges in maintaining system stability. Novel control techniques for converters, so-called grid-forming strategies, are expected to address these challenges and replicate functionalities that so far have been provided by synchronous machines. We present a low-inertia high-fidelity case study that includes synchronous machines and models of grid-forming converters. We study interactions between synchronous machines and converters and analyze the response of various grid-forming control approaches to contingencies, i.e., large changes in load and the loss of a synchronous machine. Our case study highlights the positive impact of the grid-forming converters on frequency stability and analyze the potential limitations of each control technique when interacting with synchronous machines. Our studies also analyze how and when the interaction between the fast grid-forming converter, the dc source and ac current limitations, and the slow synchronous machine dynamics contributes to system instability. Lastly, we introduce an effective solution to address the instability issues due to the GFCs ac and dc current limitation.

math.OC↗