Variable speed hydropower plant with virtual inertia control for provision of fast frequency reserves

In this paper, five virtual inertia control structures are implemented and tested on a variable speed hydropower (VSHP) plant. The results show that all five can deliver fast power reserves to maintain grid stability after disturbances after a disturbance. The VSHP is well suited for the purposed since its output power can be changed almost instantaneously by utilizing the rotational energy of the turbine and generator. This will cause the turbine rotational speed to deviate from its optimal value temporarily. Then the governor control will regain the turbine rotational speed by controlling the guide vane opening and thereby the turbine flow and mechanical power. With that, the VSHP output power can be changed permanently to contribute with primarily frequency reserves. Dynamic and eigenvalue analyses are performed to compare five different versions of the basic VSG and VSM control structures; VSG, power-frequency PID-controller with permanent droop (VSG-PID), VSM, VSM with power-frequency PD-controller (VSM-PD), and VSM with power-frequency PID-controller and permanent droop (VSM-PID). They are evaluated by two main criteria; their ability to deliver instantaneous power (inertia) to reduce the rate of change of frequency (ROCOF) and their contribution to frequency containment control (steady-state frequency droop response

Variable speed pumped storage hydropower for integration of wind energy in isolated grids : case description and control strategies

This paper presents the use of variable speed pumped storage hydropower plants for balancing power fluctuations from wind power in an isolated grid. A topology based on a synchronous machine and a full scale back-to-back voltage source converter is suggested for obtaining variable speed operation of a pump-turbine unit. This topology has not been previously investigated for variable speed pumped storage power plants, but can now be considered relevant for small and medium sized pumped storage units because of the development of voltage source converter drives for higher voltage levels. A possible case for implementation of such a system is described based on the situation on the Faroe Islands, where controllable energy storage can help to allow for a higher share of renewable energy in the power system and by that to reduce the dependency on fossil fuels. Power control of the pumped storage unit by load following for direct compensation of the fluctuations in power output from a wind farm will limit the influence on the operation of the rest of the grid. By utilizing the pumped storage to take part in the primary frequency control of the power system, the frequency response to other changes in production or load will also be improved.reviewe

Achieving Enhanced Phasor POD Performance by Introducing a Control-Input Model

In this paper, an enhancement to the well known Phasor Power Oscillation Damper is proposed, aiming to improve its performance. Fundamental to the functioning of this controller is the estimation of a phasor representing oscillations at a particular frequency in a measured signal. The phasor is transformed to time domain and applied as a setpoint signal to a controllable device. The contribution in this paper specifically targets the estimation algorithm of the controller: It is found that improved estimation accuracy and thereby enhanced damping performance can be achieved by introducing a prediction-correction scheme for the estimator, in the form of a Kalman Filter. The prediction of the phasor at the next step is performed based on the control signal that is applied at the current step. This enables more precise damping of the targeted mode. The presented results, which are obtained from simulations on a Single-Machine Infinite Bus system and the IEEE 39-Bus system, indicate that the proposed enhancement improves the performance of this type of controller.Achieving Enhanced Phasor POD Performance by Introducing a Control-Input ModelacceptedVersio