Inertia Emulation in Multiterminal HVDC Networks

In this paper the supporting action of a multi-terminal HVDC network to one AC grid is investigated. A three-terminal HVDC network is considered, which is connected to three independent AC networks by means of a Master converter and two Slave converters. The Master converter controls the DC link voltage, while the Slave converters are controlled to exchange a predetermined power. A derivative Inertia Emulation Control (INEC) algorithm is proposed for the Master converter, allowing it to both control DC voltage and limit the AC grid ROCOF (Rate Of Change Of Frequency). Two possible solutions to improve the control effectiveness in limiting frequency deviation are considered, namely further DC link capacitors oversizing and introduction of a P-V droop characteristic on one Slave converter. Simulation results are presented to substantiate the proposed control effectiveness.