PhD defence by Yacine Terriche on Power Quality and Voltage Stability Enhancement of Terrestrial Grids and Shipboard Microgrids
12.11.2020 kl. 13.00 - 16.00
Yacine Terriche, Department of Energy Technology, will defend the thesis "Power Quality and Voltage Stability Enhancement of Terrestrial Grids and Shipboard Microgrids"
Power Quality and Voltage Stability Enhancement of Terrestrial Grids and Shipboard Microgrids
Professor Josep. M. Guerrero
Assistant Professor Yonghao Gui
Associate Professor Samuel Simon Araya
Associate Professor Samuel Simon Araya, Dept. of Energy Technology, Aalborg University (Chairman)
Professor Haitham A. Abu-Rub, Texas A&M University at Qatar, Qatar
Professor Jose Rodriguez, Universidad Andres Bello, Santiago, Chile.
Harmonic contamination is becoming a vital subject in electrical power systems (EPSs). It is inoffensive as long as its level is not significant. However, due to the large increase in the installation of power electronic converters, mainly the nonlinear loads such as AC and DC variable speed drives, harmonics are severely finding their way into shipboard and offshore applications.
Ensuring a good power quality of ships is not only earmarked to avoid serious damage of the EPSs, but also to avoid the severe possible accidents that might provoke the blackout of the ship. Hence, improving the safety of the passengers and/or crew with a privileged level of security, as well as reduces the specific emissions and fuel consumption. Therefore, harmonics generated by these nonlinear loads can be a potential risk if they are not well studied and mitigated, as they can also affect the voltage via the transmission lines’ impedance and the sub-transient reactance of the synchronous generators, and thereby cause malfunction and fail of other loads.
The voltage stability is another issue, which can threaten the EPSs. The voltage stability hypothesis can be described as the attempt of the loads to absorb a larger power than the power supplies and transmission lines can deliver. If the load demand varies suddenly due to certain disturbances such as short circuits, the system might lose the equilibrium and results in the voltage collapse. Since the ships are characterized by the heavy variable loads that consume a large amount of power in a short duration, their EPS is prone to the voltage drop. If this drop exceeds the standards, it can cause the voltage collapse that can result in the blackout of the ship.
To deal with these issues, several static VAR compensators and filters have been suggested in the literature. The traditional method to reduce the harmonics and compensate for the power factor (PF) is to install the passive power filters (PPFs). Though these filters are featured by the low cost and ease of implementation, improving their harmonics rejection capability did not attract much attention. Hence, in this project, improving the harmonic attenuation factor and the filters sensitivity factor have been investigated.
Recently, based on the development of power converters, the application of the active power filters (APFs) is becoming an alternative solution to the PPFs. The main advantages gained from the APFs are the flexibility and fast dynamic response during the load variation, the capability to improve the current waveform using only one single filter, the ability to regulate the current/voltage unbalance, voltage sags, and PF. Therefore, in this project, the application of APFs and PPFs to improve the power quality issues of the EPSs of terrestrial grids and shipboard power systems (SPSs) has been investigated. Moreover, in order to enhance the filtering capability, flexibility, and the dynamic response of the APFs, new algorithms such as the matrix pencil method and least square solutions are developed to extract the reference compensating currents. Furthermore, controlling the APF needs precise information about the voltage phase to perform the synchronization. Hence, some open-loop and closed-loop synchronization methods are developed to enhance the dynamic response of the APF.
Accurate assessment of harmonics provides substantial information on their circulation’s danger, thus enables the engineers to verify if the harmonic distortion complies with the standards or requires interfering. Moreover, precise assessment of the harmonics helps the engineers to design the suitable filters, taking into consideration some important criteria such as the type of harmonics (odd/even harmonics, integer/non-integer multiple of the fundamental frequency), and the level of harmonic distortion. Furthermore, harmonics/interharmonics analysis can provide a comprehension diagnosis for fault detection, and fault location of the synchronous generators and motors. There are enormous techniques for estimating the harmonics of distorted signals. However, most of these techniques are frequency-dependent techniques, which implies that their performance degrades in the existence of interharmonics or frequency drifts. The dominant standards in the power quality field recommend the application of the discrete Fourier transform (DFT) with an aggregation of consecutive 12 cycle time intervals for a 60 Hz power system frequency. However, since the DFT can only operate in the steady-state condition, a window width of 12 cycles of a steady-state current is not practical for SMGs due to the large variation in the frequency and load in a short duration. Hence, following the standards recommendation may not be very practical for SMGs. In this regard, two signal periodicity-independent algorithms that can assess the harmonics/interharmonics accurately with a fast transient response under large frequency drifts are proposed in this project. The evaluation of these algorithms is carried out under MATLAB software and validated via analyzing the electrical power system current of a bulk carrier ship and a container ship during the operation of the mooring winches and the windlass, then the results are compared with the traditional methods.
The defence will be in english - all are welcome
Streaming info tbd.
Department of Energy Technology
Pontoppidanstræde 105, Room 4.127