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Rapporto RSE 18000005

VSC-HVDC Multi-terminal grids: control logics for synthetic inertia support.

This report shows simulation results performed on HVDC-VSC systems, bi-terminal and multi-terminal, to study and evaluate INEC (Inertia Emulation Control) algorithm performances on direct current transmission lines.

Object of the analysis is INEC (Inertia Emulation Control) synthetic inertia algorithm applied to VSC (Voltage Source Converter) converters in a multi-terminal HVDC (High Voltage Direct Current) network. Research main focuses on the INEC control implementation in the same HVDC network (bi-terminal) already used and the comparison between INEC inertial action and the "classical" synthetic inertia control; INEC system has been then implemented on a multi-terminal HVDC network, using further control algorithms (droop voltage / power) to modulate the propagation of a frequency disturbance across different synchronous areas.

At first, INEC system configuration was identified, in order to provide an energetically equivalent action respect to “classical” control; through simulations comparison, critical issues emerged regarding INEC response, in particular about ROCOF (Rate Of Change Of Frequency) in the very first moments of transient; different INEC tuning did not produce appreciable improvements, therefore a derivative INEC algorithm was implemented, in order to compensate and reduce transient delays.

Simulation results showed a good response by INEC derivativecontrol, and it was inserted in a multi-terminal HVDC network. Additional control systems have been added to conversion stations; in particular, appropriate calibration of a droop control between voltage and power allows HVDC system to "distribute" (therefore in some ways mitigate) frequency disturbance over multiple synchronous areas. Vice versa, properly controlled VSC converter can "protect" a network from disturbances on other synchronous areas.