The possibility to adjust the reactive power at the point of connection of battery systems will enhance flexibility provision in future renewable-based grids. Therefore, Grid Codes require verification of the reactive power capability of battery systems, which can be exploited by system operators. This paper proposes standardized testing procedures to verify reactive power functions for Grid Code compliance of battery systems. The investigated control functions are (i) reactive power control, (ii) power factor control, and (iii) automatic power factor control. The designed procedures detect the reactive power capability of battery systems thoroughly, and they verify the battery system against Grid Code compliance following three success criteria: accuracy, sensitivity, response time. The experimental testbed allows to validate a 33.5 kW / 95 kWh battery system following the requirements in the Danish Grid Code. Results show that the battery system follows the Grid Code, satisfying both reactive power capability requirements and success criteria.
To insure a stable and reliable operation of the existing and future grids, it is important to study the stability of the power electronic based converters’ controls which can replace synchronous generation. Most existing studies use a Thévenin equivalent model of the grid to test the grid following controls. The present article demonstrates the limits of these studies. An alternative setup is proposed and is shown to provide more insight into the underlying mechanisms of the grid following control behaviour in weak grids, using a linearized state space model. These insights are exploited to propose further improvements to the control. These improvements are shown to extend the stability of the control while reducing the interactions among converters.
This paper provides the HVDC electrical design of three existing UK HVAC overhead lines, two of which constitute 85% of the UK transmission overhead line system. The designs are based on CIGRE and IEC recommendations. Also, the verification of the electrical stress requirements on the insulators is performed by means of finite element simulations. The paper shows that the HVDC converted tower lines would carry 1.6 to 2.9 times the power of the original HVAC lines, depending on tower type, insulation arrangement, and environmental conditions.
