Conference Agenda

The growing penetration of converter-interfaced renewable energy sources (CI-RES) has revealed several challenges related to the stability of the electrical grids. To mitigate these issues, there is an ongoing research regarding the concept of virtual synchronous generators, where new control schemes are employed to enable CI-RES with integrated fast-acting energy storage system (ESS) to provide ancillary services to the grid, e.g., inertial response (IR). Although several solutions have been proposed in the literature, the proper integration and energy management of the ESS towards IR provision remains an open research topic. In this paper, an holistic control approach is presented regarding IR provision by a system comprising of a CI-RES and an ultracapacitor (UC). The proposed approach is supplemented by an efficient energy management system allowing the UC to release/absorb energy during IR provision while always ensuring the operation of the UC voltage within its technical limits. The robustness and the performance of the proposed method are experimentally evaluated in a lab setup, where all the components of the proposed system, i.e., CI-RES and UC have been analytically implemented.

The advent of renewable energy sources (RESs) has posed several technical challenges related to the operation of modern power systems. These can be classified into two main categories: a) problems at the power system level, and b) local problems at the distribution network (DN). To solve these issues, there is a strong need for the development of innovative control schemes that can be employed by converter-based network assets, e.g., battery energy storage (BES) systems and distributed RES. In this context, a unified control system (UCS) for the provision of ancillary services (ASs) by distributed RES-BES systems within a multi-services perspective is introduced in this paper. The proposed UCS comprises different algorithms to provide ASs related to voltage regulation, voltage unbalance mitigation and frequency support. The UCS is implemented in 3-phase, 4-leg converters (3Ph4LCs) to ensure the provision of ASs in unbalanced DNs. In addition, at the dc side of the 3Ph4LC a series dc-dc converter for BES support allows the implementation of the proposed UCS in weak DNs. The transient operational performance of the proposed UCS is evaluated by conducting time-domain simulations.

Grid forming converters are expected to become the main voltage source for electrical power systems in future grids, as many of the conventional power plants based on synchronous generators are being replaced by renewable generating plants interfacing with grids via converters. This paper evaluates network energisation via grid forming converter based on multi-loop droop control, focusing on transformer inrush and switching overvoltages. The evaluation utilizes simulation conducted in PSCAD-EMTDC to investigate the scenarios of using a 50 MVA battery energy storage plant with grid forming converters to sequentially energise part of a 132 kV network. The results are analysed and compared with those obtained under the scenario of energising the same network via a 50 MVA synchronous generator. The studies serve to identify the potential differences between grid forming converters and synchronous generators in terms of their impacts on transformer inrush transients and cable switching overvoltages. In addition, the influences of grid forming converter aggregation, controller parameter settings and current limiter settings on the inrush and switching transients are investigated.

This paper introduces a grid forming (GFM) control method – detailed synchronous machine emulation virtual synchronous generator (VSG). The proposed method makes a voltage source converter exactly emulate a synchronous generator (SG), using a current source interface. The precise emulation of an SG gives tighter control over overcurrent and improved transient damping. Electromagnetic Transients (EMT) simulation is used to demonstrate the operation, and small signal model is used to assess the stability performance. Small signal analysis shows that the resulting VSG operates stably, and oscillatory modes can be damped by appropriate optimization of the virtual damping windings resistances.

The growing use of renewable energy sources such as wind and solar in distribution networks (DNs) poses a challenge for DN protection. Inverter-based resources (IBRs) have fault responses that differ from conventional generators, which can have a significant impact on how the DN is protected and lead to misoperations, such as blinding. Use of simplified inverter models may result in incorrect relay settings and relay misoperations. This paper leverages a comprehensive grid-following inverter with dynamic reactive current (DRC) limiting model. The inverter with DRC model is combined with distribution system equations, to form a nonlinear differential and algebraic equations (NDAE) model, in which the fault response is verified. The grid-following inverter with DRC limiting is then implemented in a distribution system with protection elements and compared with a simplified fault response model based on frozen control. The system is tested under varying irradiance conditions, as well as varying dynamic factor K of the DRC limiting model. The effect of the DRC current limiting model on protection blinding is investigated as well. The case study reveals that precise modeling of the PV inverter including the DRC limiter is indeed required to properly identify and predict blinding scenarios in the DN.