Dr. Aty Edris Principal Consultant abdel-aty.edris@siemens.com

Dr. Aty Edris recently led a study investigating integration of novel Permanent Magnet Hydro Synchronous Generators (PMSGs) to the Alberta Interconnected System in Canada. The work was initiated by Canadian Hydro Developers and was a collaboration among Siemens PTI in the US, Andritz Hydro in Austria, and the Alberta Electric System Operator in Canada.

A PMSG is a robust, very low maintenance, energy efficient generator; however, due to its inherently very low inertia and lack of excitation control feature, it imposes the challenge of maintaining its synchronous stability when connected to a utility grid. The major challenge for the integration of a PMSG to a utility grid is not losing its synchronism under low-voltage conditions as a result of fault conditions. Power System Operators dictate a Low Voltage Ride Through (LVRT) requirement, which is a requirement to ensure that the generator will not fall out of synchronism following a transmission voltage dip to a certain level for a specific period of time. Therefore, a PMSG would require compensating stability controllers to fulfill the LVRT requirement dictated by the Power System Operator.

A comprehensive design study aimed at improving stability performance of PMSGs was recently conducted. The study approach first looked at optimization of the PMSG design parameters (moment of inertia, generator reactances, and time constants) using systematic dynamic study analysis. Then, various Voltage Sourced Converter technology-based stability controllers, compensating for the lack of excitation control of the PMSG, were analyzed and evaluated. The analyses concluded with an innovative concept providing an unprecedented and robust connection solution enabling the PMSG to fulfill all regulation criteria for a generator’s connection to utility grids.

The study finding is illustrated in the figure below, which compares the generator speed responses for different fault durations.

Generator Speed Deviation, from Synchronous Speed, in Response to Different
Durations of a Three-Phase Fault at the Point of Common Coupling

This successful application for HVDC Plus, for generator interconnection and dynamic reactive power compensation, demonstrates broader potential to reliably integrate renewable generation to the grid, particularly at weaker interconnection points.

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