Candidate: Mehdi Parvizimosaed
Title: Frequency and voltage control in islanded microgrids
Date: March 18, 2019
Time: 1:30 PM
Place: EIT 3155
Supervisor(s): Zhuang, Weihua
Abstract:
Islanded microgrids, featured by distributed energy resources, consumption, and storage, are designed to significantly enhance the self-sustainability of future distribution networks, and to provide energy to remote communities. The islanded microgrid frequency and voltage can experience large excursions due to low system inertia and fast load perturbations in the microgrid. In primary mode control, it is necessary to maintain frequency and voltage in the acceptable ranges. The primary control is not effective to restore frequency and voltage to their desired values due to high variability of renewable generation output power and technical limitations of distributed generation units. To this aim, microgrid central controllers are commonly equipped with optimization to ensure the continuity of load supply and to decrease the cost of energy production. The communication latency and system control delay can affect the performance of islanded microgrid control, and degrade the frequency and voltage stability. This research is to investigate and develop solutions in both primary and secondary frequency-voltage control with consideration of time delay effects. It consists of three research topics:
1) We introduced a distributed frequency and voltage mechanism to tackle some challenges associated with the islanded microgrid control. The proposed controller aims to provide fast and smooth frequency and voltage regulation with the minimum steady-state error, allow distributed power sharing with consideration of generation unit rating and droop characteristics, make a compromise between reactive power sharing and voltage regulation, and decouple active and reactive power controllers. In our preliminary study, we used MATLAB/SIMULINK on a CIGRE benchmark to evaluate the performance of controller.
2) In practice, the generation and controllable load units participating in the frequency and voltage control, can change their outputs within an operation time-interval (e.g., 60s) in response to changes in load and/or renewable energy units. We present a mid-level frequency and voltage controller for islanded microgrids, which unifies the secondary and primary controllers. The proposed dynamic voltage and frequency controller optimally dispatches the generation or controllable load outputs using a unit commitment algorithm in a short-term period between two dispatch intervals while regulating frequency and voltage, and maintaining microgrid stability. To do so, we propose an adaptive critic design approach with technical constraints and look-ahead utility functions to provide a cost-effective and battery lifecycle sparing solution for islanded microgrids
3) We will investigate how communication latency and system control delays impact frequency and voltage control of an islanded microgrid with multiple distributed generators. We will use a small-signal method to determine time delay margin, and to evaluate its relationships with frequency and voltage control gains. A possible solution for time delay management called gain scheduling approach will be also proposed to compensate for the effect of existing time delay, and achieve microgrid control stability