Abstract
Large-scale wind-thermal-bundled power that is transmitted by mixed ultra-high voltage direct current (UHVDC)/ultra-high voltage alternating current (UHVAC) systems has become crucial for large-scale wind farms in China. Equations describing the electromagnetic power characteristics under short circuits for UHVAC lines and UHVDC blocks are derived based on an analysis of the external characteristics of a doubly fed wind farm and UHVDC systems. The effect of wind power penetration ratio on rotor angle transient stability is analysed, and the optimal wind power penetration ratio under the constraint of rotor angle transient stability is determined. The effects of system parameters, such as the UHVDC transmission capacity and the reactance of UHVAC lines on the optimal wind power penetration ratio are discussed. The trend of rotor angle stability varies from a monotonic deterioration to concave, and the optimal wind power penetration ratio increases from 0 to 30% under an UHVDC block when the reactance of UHVAC lines increases from 0.005 to 0.02. The optimal wind power penetration ratio under a short circuit increases from 40% to 60% when the reactance of UHVAC lines decreases from 0.02 to 0.006 and decreases from 40% to 30% when the capacity of UHVDC decreases from 3200 MW to 1600 MW. The analysis is verified by simulating an actual system in China’s Northwest Power Grid.
Highlights
In recent years, wind power has developed rapidly in China
An ultra-high voltage direct current (UHVDC) system offers the advantages of enormous transmission capacity, low transmission loss, and a narrow corridor; it is the clear choice for large-scale wind farms in northern China [4]
Lines is concave with an increasing k, and the optimal wind power penetration ratio kn is affected by the reactance of the ultra-high voltage alternating current (UHVAC) lines and the capacity of the UHVDC system
Summary
Wind power has developed rapidly in China. Several gigawatts of wind farms have been planned and constructed in North China, Northwest China and Northeast China (Three-North area) [1]. Wind-thermal-bundled power transmitted by an UHVDC system mixed with existing UHVAC systems has become an effective scheme for large-scale wind farms in China. The influence of wind power penetration ratio on rotor angle transient stability of a wind-thermal-bundled system after a short-circuit fault is analysed in [17]. The electromagnetic power equations of a typical wind-thermal-bundled system under a UHVDC block and short circuit of UHVAC lines are derived, respectively, based on an analysis of the transient external characteristics of a wind farm and UHVDC system.
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