Abstract
The continuous improvement of new energy penetration reduces the inertia of the system, which leads to the frequency deviation and the rate of change of frequency (RoCoF) being easily exceeded. To improve the frequency stability of sending-end power systems with large-scale renewable energy access via ultra-high voltage direct current (UHVDC), the coordinated frequency control for UHVDC participating in system frequency regulation (FR) including primary FR and system inertial response is presented. Based on the simplified system model, the mechanism of UHVDC participation in system frequency support and its influence on receiving-end system frequency response characteristics are analyzed. Compared with the inertia response and primary FR of traditional synchronous generators, the parameter calculating method of UHVDC coordinated frequency response control is proposed. Based on the system root trajectory analysis, the influence of the frequency response control parameters on the sending-end system’s stability is analyzed, and the constraints of UHVDC participating in the system frequency response control are analyzed. Then, based on the RTDS verification platform containing the Lingshao ±800 kV UHVDC control and protection system, the system frequency response characteristics under different control strategies, operating conditions and control parameters are verified and analyzed. The experimental results show that the UHVDC frequency coordinated control can effectively increase the equivalent inertia of the sending-end system, restrain the RoCoF and the frequency deviation, and increase the FR capability of the UHVDC system.
Highlights
Renewable energy, such as wind and solar energy, in China is mainly distributed in the western and northern regions, while the load centers of China’s power grids are mainly located in the eastern and southern regions
After the large-scale integrations of photovoltaic (PV) and wind turbines (WT) to the sending-end power system with grid-connected inverters as the circuit interface, the PV and wind generators usually operate at the maximum power tracking mode [5,6], resulting in the inability of generation units to respond to changes in system frequency and their inability to participate in system frequency regulation (FR) [7]
WT provide inertial support to the system through rotor kinetic energy, which leads to mechanical fatigue of the rotor, reducing the reliability and service life of the equipment provide inertial support to the system through rotor kinetic energy, which leads to me2 of 23 chanical fatigue of the rotor, reducing the reliability and service life of the equipment significantly [8,9]
Summary
Renewable energy, such as wind and solar energy, in China is mainly distributed in the western and northern regions, while the load centers of China’s power grids are mainly located in the eastern and southern regions. The limited renewable energy participate in the factors as wind speed,light and the capacity ofsystem a singlecan generating unit, resystem FR to a certain extent.participant. Due to thewith constraints uncontrollable factors such newable energy generation systems grid FRof must use standby control or as wind speed, light and the limited capacity of a single generating unit, renewable energy be equipped with certain energy storage systems [14]. There are to major chalcoordinated control between multiple machines, even between renewable energy and lenges such as limited regulation capacity, high regulation costs and complex coordinatraditional generating units to participate in FR. AFC based on droop controller is used in the sending-end tem that is a regional power grid.
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