Browsing by Author "Haro-Larrode, Marta"
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Item Impact of proportional resonant controller parameters of VSC connected to AC grids with variable X/R characteristic on the small signal stability(2020-06) Haro-Larrode, Marta; Santos-Mugica, Maider; Eguia, Pablo; Rodriguez-Sanchez, Raul; Gil-de-Muro, Asier; Tecnalia Research & Innovation; POWER SYSTEMS; POWER ELECTRONICS AND SYSTEM EQUIPMENTThe purpose of this paper is to assess the impact of proportional resonant controller (PR) parameters of a Voltage Source Converter (VSC) and AC grid topology on the small signal stability of a VSC-AC system. Based on this, a small signal model is constructed, step by step, and validated against EMT simulations. Following this validation, several scenarios containing different PR controller gains are proposed and compared by means of trajectory of eigenvalues. A discussion of the best adequacy of PR controller parameters and AC grid strength in combination with inductive-resistive characteristic (X/R) is developed to ensure the stability of the system. The previous eigenvalue analysis is verified in time domain by means of EMT simulations. The analysis performed concludes that, while the AC grid strength in combination with PR controller parameters plays an important role in determination of stability, variations in the inductive-resistive AC grid characteristic need to be included in the analysis, since further instabilities can appear even when the PR controller is well designed for a specific AC grid configuration.Item Methodology for Tuning MTDC Supervisory and Frequency-Response Control Systems at Terminal Level under Over-Frequency Events(2020-06) Haro-Larrode, Marta; Santos-Mugica, Maider; Etxegarai, Agurtzane; Eguia, Pablo; Tecnalia Research & Innovation; POWER SYSTEMSThis paper proposes a methodology for tuning a supervisory and frequency-response outer loop control system of a multi-terminal direct current (MTDC) grid designed to transmit o_shore wind energy to an onshore AC grid, and to provide frequency support during over-frequency events. The control structure is based on a master–slave scheme and ensures the achievement of frequency response, with specific implementation of the UK national grid code limited-frequency sensitive (LFSM) and frequency-sensitive (FSM) modes. The onshore AC grid is modelled with an equivalent frequency-response model to simulate the onshore AC grid dynamics under frequency deviations. The main innovation of this paper is the development of a methodology for tuning simultaneously two hierarchical levels of a MTDC coordinated control structure, i.e., the MTDC supervisor, given by the active power set point for slave terminal, and the slope of frequency-response functions at onshore terminals. Based on these two hierarchical levels, di_erent strategies are evaluated in terms of frequency peak reductions and change of the frequency order type. Moreover, tuning guidance is given when a di_erent MTDC control structure or di_erent synchronous generator characteristics of the onshore AC grid are considered.Item On the tuning of fractional order resonant controllers for a voltage source converter in a weak AC grid context(2021-03) Haro-Larrode, Marta; Bergna-Diaz, Gilbert; Eguia, Pablo; Santos-Mugica, Maider; Tecnalia Research & Innovation; POWER SYSTEMSThis paper proposes a method for tuning the fractional exponent of different types of fractional order resonant controllers for a voltage source converter in a weak AC grid context. The main objective is to ensure the stability of the controlled system in a weak AC grid environment and to achieve an adequate dynamic response under disturbances. Therefore, six commonly used integer order proportional resonant (PR) control structures are selected from the literature and compared with each other according to their frequency behaviour. Afterwards, a rational approximation for the fractional order term is selected based on continuous fraction expansion technique. The inclusion of a fractional exponent in each integer order PR structure generates the fractional order proportional resonant (FPR) control transfer functions. Once the FPR controllers have been obtained, their closed-loop responses are tested via eigenvalue trajectory analysis. For each FPR control structure, a range of the fractional exponent that ensures stability is obtained. The conclusions of eigenvalue trajectory analysis are tested by implementing the FPR control structures in an specific application consisting in a modular multi-level converter (MMC) connected to a weak AC grid with adjustable short-circuit ratio. By means of time-domain simulations, not only the previous eigenvalue analyses are validated, but also new tuning criteria are given for the fractional exponent in combination with other control parameters, such as the damping frequency and the inductance of the complementary feedback branch. Moreover, a sensitivity analysis of the tuning criteria is carried out for other sizes of the AC filter inductance.