Application of Fast Frequency Response to improve Primary Frequency Control in Tasmania

摘要

This paper investigates the use of Fast Frequency Response (FFR) sources to support the high penetration of Renewable Energy Systems (RES) that interface to AC power networks via Asynchronous Generating (AG) units. Specific focus is given to the application of a Frequency Stabiliser (FS) device supplied by super-capacitors to the Tasmanian power system [1]. The maximum level of secure penetration of renewable energy with AG depends on services supplied by Synchronous Generating (SG) units. SG are directly and strongly coupled to the power system providing the bulk of the power system's inertia and are also the traditional source of Frequency Control Ancillary Services (FCAS), in particular fast raise 6 s and 60 s reserves (R6 and R60). Inertial response is natural and faster than R6 and it opposes changes in system frequency which is critical in limiting the allowable Rate of Change of Frequency (RoCoF) in a power system. The complementary R6 and R60 services limit the frequency nadir and drive frequency recovery following the loss of generation. These factors, which are global quantities across each AC network, become more critical as the proportion of SG falls. In addition, SG provide significantly more "fault level" than AG which is important for stable operation of local control and protection systems, especially those associated with power electronics based AG. As SG units get displaced from real time dispatch by AG, a number of critical services offered by SG can become scarce. Given the crucial role played by SG in the overall stability of AC power systems, their displacement has triggered the development of new technologies to perform equivalent roles. The advantage offered by the FS is its ability to inject high levels of active power into the AC system over a 0.5 to 10 s timeframe which overlaps with inertial and R6 responses and is fast enough to limit the frequency nadir. This compensates for the reduction in inertia and Primary Frequency Control (PFC), i.e. R6 offered by SG. The FS also has a strong reactive power capability which helps voltage control in localities with low fault level. In Tasmania, additional inertia and reactive power services can be supplied by hydro plant operating in Synchronous Condenser (SC) mode although long-term operation of machines as SC is costly due to plant deterioration and energy losses of 1-2%. Although the FS has a relatively small energy store available (approximately 400 MW.s), the speed of its injection is an excellent complement to the slow responding mechanical power of hydro units making an elegant solution for a predominantly hydro based system which has limited R6 but very good R60 delivery capability.