Synthetic inertia analysis

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Dr. Vokony István
Department of Electric Power Engineering

The growing share of renewable energy sources - especially wind and solar – basically transforms the electric power grid. The decentralized structure opens up new technical challenges in the system operation and control. One of the most serious questions is the reduction of power system inertia. Most of the emerging technologies are connecting to the grid via power converters so they are practically decoupled from the system and its frequency changes. The electric power system has not been designed for that: stability relied heavily on the inertial response of synchronous generators which decreases the rate of change of frequency (ROCOF). The rotating mass of those generators is directly coupled to the system and functions as a kinetic energy storage component during the disturbances.

The concept of synthetic inertia is that the power converters of the non-synchronous generators should be controlled in a way to mimic the effects of the rotating mass. This means that these generators would emulate the behavior of synchronous generators.

My thesis starts with a literature review with a purpose to summarize the problem of the reduction of inertia as well as the concept and technological possibilities of synthetic inertia through the review of research papers. The appendix contains all the related definitions and a resumé of the swing equation. After that the composition of self-developed controlling architectures (with DigSilent Power Factory 15.1 software) are described in detail, with the introduction of different parameter setting possibilities and selectivity options. An evaluation criterion is being proposed and tested on two different system models with electromechanical transient simulations with a wide-range of different settings. Integration of synthetic inertia into currently used operation and control and further development possibilities are also described. The parameter selections are validated throughout a laboratory measurement of a power electronic converter.

As a result, frequency stability is examined considering the high penetration of non-synchronous generation. The effects could be quantified in detail with the composed methods. The proposed modeling approach could be used for composing complex planning and evaluation processes, as well as to implement the stability preservation enhancement with synthetic inertia in practice.


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