Report on system modelling, simulation and advanced controllers for enhanced functionalities and services provision from multiport converters

This Deliverable illustrates the work carried out on operation and control of distribution grids with multiport converters (MPCs) in the context of iPLUG project. MPCs are power electronics devices with multiple input and output ports, enabling the simultaneous interconnection of different distributed energy resources (DER) and grids. The main objective of WP4 is to demonstrate the capability of integrating MPCs into the distribution grid seamlessly. This integration requires the development of grid models and average or reduced MPC more suitable for large-scale power system analysis. The most suitable application of MPCs for grid operation and control is the Soft Open Point (SOP). SOPs are enhanced versions of traditional switches: in addition to grid reconfiguration to enhance reliability, they allow precise control of active and reactive power setpoints at each port. This deliverable focuses on SOPs, in particular MPC-enabled ones, i.e. SOPs whose DCDC conversion stages are handled through MPCs. The introduction, in Chapter 2, reviews SOP applications in distribution grids and the role of MPCs in these applications. The subsequent chapters follow the structure of WP4. • Chapter 3 summarizes the work carried out in Task 4.1 on grid modelling and simulation. The chapter is divided into two case studies: one focusing on voltage analysisand voltage profile improvement through an MPC integrated into grid, and another on the evaluation of potential stability issues due to the grid integration of MPCs. Each case study presents the respective grid model, MPC average model, and lastly their integration for system-level studies. • Chapter 4 describes the work associated with Task 4.2, mainly the development of local controllers for MPC-based SOPs, that ensure system stability and provide gridservices. This chapter analyses both isolated and non-isolated MPCs. After a review of the main control strategies, a small-signal stability analysis is detailed for an isolated three-port soft open point (SOP) based on the triple active bridge. The modeling derivation is presented, and a sensitivity analysis is used to evaluate the impact of several control and grid parameters on the small-signal stability of the system. Furthermore, a control strategy is proposed for the operation of a three-port non-isolated SOP under abnormal grid conditions using both grid following and grid forming controls. Finally, a grid forming control implementation based on the unified voltage oscillator control concept is presented for MPCs together with a study on the impact of the grid conditions on grid forming control for distribution networks with different X/R ratios. • Chapter, 5, reporting work from Task 4.3, focuses on centralized coordination through high-level optimization studies. The optimal power flow (OPF) problem for optimizing the operation of MPC-based SOPs is formulated to improve grid performances. Two main objective functions are evaluated, mainly grid energy losses and voltage deviation minimization. Furthermore, the frequency support service provided by in MPC-interfaced microgrids is assessed based on a centralized model predictive control strategy.