Lisa Ruttledge

System-wide inertial response from fixed speed and variable speed wind turbines

As wind penetration levels on power systems increase worldwide, the dynamic characteristics of these systems are changing due to the displacement of synchronous generation. One issue, of particular concern, is the resulting reduction in system inertia. Modern, variable speed wind turbines are controlled by power electronics and so do not inherently contribute to the inertial response of the system. Such devices can however be fitted with a control loop which provides an active power response to significant frequency deviations, similar to the inertial response of fixed speed wind turbines and synchronous generation. However, the response of variable speed turbines is dependent on local wind speeds and so cannot be quantified deterministically by system operators. This paper examines the potential for wind generation to contribute to system inertial response and considers the aggregated inertial response capabilities of fixed speed and variable speed wind generation.

Emulated Inertial Response From Wind Turbines: Gain Scheduling and Resource Coordination

With increasing wind penetration levels on power systems worldwide, conventional thermal plant, along with the ancillary services they provide are being displaced. To address this issue, modern variable speed wind turbines can offer a short-term controlled response to temporary power imbalances, by harnessing their stored rotational energy, a so called emulated, or synthetic, inertial response. However, unlike conventional frequency response services, the emulated inertial response is dependent on the wind turbine operating condition and provides a response which is distinct to that from synchronously connected plant. While much research has investigated the harnessing of such a response from wind turbines and its effect on system frequency, this paper investigates potential issues associated with the system-wide integration of the technology at scale. The ability for wind generation to provide frequency support through emulated inertia is assessed, as well as the potential for tuning such a distributed response resource to ensure timely and effective frequency recovery under different system conditions. It is shown that the frequency response capability of future systems and the operating protocols for system participants, including wind generation, will require development if emulated inertia technology is adopted at scale.

System-wide contribution to frequency response from variable speed wind turbines

Due to the differing electromechanical characteristics of modern variable speed wind turbines to conventional generators, the provision of ancillary services from wind generation is likely to change the nature of the frequency response of power systems to contingency events. This paper explores the aggregate contribution from wind turbines to the frequency response of future power systems, considering both emulated inertial and governor controls. In particular, the potential issues that may arise as a result of the changing nature of the system frequency response due to the uncertainty over the distribution of ancillary services from embedded generation on the network, are examined in the context of future power system requirements.

Load Inertia Estimation Using White and Grey-Box Estimators for Power Systems with High Wind Penetration

Abstract The increasing penetration of wind farms in power systems has increased concerns over the frequency behaviour and control of synchronous power systems due to a low contribution from modern wind turbines to overall system inertia. With this trend of conventional generators being displaced by variable speed wind turbines, the contribution from load inertia becomes more significant. The need for greater consideration towards load inertia estimation, or even on-line tracking of load inertia, seems to be required. A white-box method for estimation of load inertia is examined using system frequency and generator output power signals from previous generator forced outages. A grey-box identification method is also applied to estimate the inertia of synchronous generators. The impact of sampling rates, time shifting and signal averaging on parameter estimation is also considered. The method is shown to be robust enough to be applied for load inertia estimation in control centres.