Προσομοίωση σε πραγματικό χρόνο επιδράσεων διεσπαρμένης παραγωγής σε δίκτυα διανομής με χρήση ψηφιακών μοντέλων και πραγματικού εξοπλισμού

Abstract

The subject of this doctoral thesis is the use of real-time simulation and specifically Power Hardware in the Loop (PHIL) simulation, to study the impact of distributed generation on the distribution network. PHIL simulation allows the connection of hardware power equipment (e.g. photovoltaic inverter) to a simulated network. The potential future role of PHIL simulation for laboratory testing and studying of phenomena in power systems is explained. The stability and accuracy issues of PHIL simulation, the main methods for evaluating and achieving stability and methods for accuracy estimation are presented. A new method to achieve stability is proposed, which maintains sufficient accuracy, while it allows the connection of a scaled-down device to analyse the behaviour of the full-scale device. Stability considerations are provided and the accuracy improvement by using the proposed method is quantified. Next, modern functions for the provision of ancillary services by distributed generation are presented concerning voltage control (cosφ(P), Q(V) control) and frequency control (P(f) control, virtual inertia). The stability issue of Q(V) control is explained. A review of recent international standards/guidelines is performed, concerning steady-state voltage support, dynamic network support and frequency control, which includes a comparative analysis and identification of gaps. Advanced testing procedures using conventional approaches are proposed, along with PHIL test procedures. Subsequently, the development of the PHIL environment at the Electric Energy Systems laboratory of NTUA is described, which includes the protection schemes applied and preliminary PHIL experiments are presented. Α benchmark system for PHIL testing is proposed, which includes reference test procedure, setup and network. Problematic interactions between local voltage controller of distributed generation and On-Load Tap Changer (OLTC) are examined with pure digital simulations. The proposed method to achieve stability and accuracy is applied and PHIL tests are executed using a scaled-down photovoltaic inverter to analyse the behaviour of the full-scale inverter. The PHIL tests show interactions that were not visible at the pure digital simulations, which demonstrate the value of the PHIL approach. The model of the voltage controller of the inverter is validated by comparing the results of the PHIL tests and the pure digital simulations. PHIL tests on frequency control are performed to study the impact of droop control and virtual inertia. Next, PHIL simulation is employed for laboratory education of students on important topics of the operation of the modern power system. A double PHIL setup is developed, creating two work benches, which provides hands-on experience to the students in small groups and allows experiential learning. The assessment of the laboratory exercises by the students was clearly positive. Finally, the electromagnetic interference from inverters of distributed generation on electronic meters is analysed, which can result in energy measurement errors. A detailed review of standards/guidelines is performed, which highlights the gap in the 2 kHz - 150 kHz range and reports recent developments and remaining issues. Laboratory setups for testing immunity and emissions are described and immunity tests on electronic meters and emissions tests on inverters are performed.