43 research outputs found
External inertia emulation controller for grid-following power converter
The advent of renewable energy has posed difficulties in the operation of power systems whose net inertia is becoming critically low. To face such challenges, grid-forming power has been one of the potential solutions pursued by the industry and research community. Although promising, grid-forming power converters are still immature for mass deployment in power systems. In the meanwhile, an enormous amount of grid-following power converters has been underexploited when it comes to grid-supporting functionalities. Therefore, this article proposes an external inertia emulation controller (eIEC) for grid-following power converter to provide frequency support to the grid. For the purpose of minimizing installation efforts and resources, the controller is designed in such a way that it can be implemented in an external controller communicating with the grid-following power converter via an industrial communication link. This article also investigates the effect of communication delay on the stability performance of the proposed controller. In addition to the detailed analysis, hardware-in-the-loop experiments are also carried out to validate the proposed eIEC.This work was supported by the European Commission under Project FLEXITRANSTORE-H2020-LCE-2016-2017-SGS-774407Peer ReviewedPostprint (author's final draft
Control analysis and design of medium voltage converter with multirate techniques
This work aims to unify the current knowledge about multirate controllers with design
techniques for grid-tied converters, in this occasion, connected to Medium Voltage AC grid. Therefore, the multirate contributions, that have been given so far, are studied, as
well as everything related to modulation techniques for power converters. The temporal
implications of the DSPWM actuator will be correlated to multirate analysis, in
addition to possible alternatives for applications with a lower sampling frequency than
modulation one. Finalizing with explanations and result demonstrations of controllers
working between two frequencies or rates, by means of the available power converter in laboratory.Este trabajo pretende unir el conocimiento actual sobre controladores multitasa o
multifrecuencia (multirate) con técnicas de diseño para convertidores conectados a la red, en este caso concreto, a la red alterna (AC) de Media Tensión. Por tanto, se
estudian las contribuciones multirate realizadas hasta la fecha, asà como todo lo relacionado con la modulación de la señal de control para los convertidores. Las
implicaciones temporales del actuador DSPWM se relacionarán con el análisis
multitasa, asà como se explicarán posibles alternativas para aplicaciones con una
frecuencia de muestreo menor que la de modulación. Finalizando con la explicación y
presentación de resultados de controladores trabajando entre dos frecuencias o tasas,
mediante simulaciones del convertidor disponible en laboratorio.Máster Universitario en IngenierÃa Industrial (M141
Stability Boundaries for Offshore Wind Park Distributed Voltage Control
In order to identify mechanisms causing slow reactive power oscillations observed in an existing offshore wind power plant, and be able to avoid similar events in the future, voltage control is studied in this paper for a plant with a static synchronous compensator, type-4 wind turbines and a park pilot control. Using data from the actual wind power plant, all stabilizing subsystem voltage proportional-integral controller parameters are first characterized based on their Hurwitz signature. Inner loop current control is then designed using Internal Mode Control principles, and guidelines for feed forward filter design are given to obtain required disturbance rejection properties. The paper contributes by providing analytical relations between power plant control, droop, sampling time, electrical parameters and voltage control characteristics, and by assessing frequencies and damping of reactive power modes over a realistic envelope of electrical impedances and control parameters
Coordinated control of parallel DR-HVDC and MMC-HVDC systems for offshore wind energy transmission
Parallel operation of diode rectifier based high-voltage direct current (DR-HVDC) and modular multilevel converter (MMC) based HVDC (MMC-HVDC) for transmitting offshore wind energy is investigated in this paper. An enhanced active power control scheme of the offshore MMC station is proposed to improve the power flow distribution between the MMC-HVDC and DR-HVDC links which are both connected to the offshore wind farm AC network. By regulating the offshore voltage, all the wind powers are transmitted via the DR-HVDC link in low wind conditions while the offshore MMC power is controlled around zero to reduce transmission losses, considering the efficiency superiority of DR-HVDC over its MMC counterpart. When the DR-HVDC is out of service, wind energy is transferred via the MMC-HVDC and the wind turbine generated power is automatically limited by slightly increasing the offshore AC voltage to avoid potential MMC-HVDC overload. A power curtailment control is also proposed which slightly increases the DC voltage of the DR-HVDC to enable autonomous reduction of the generated wind power so as to avoid DR-HVDC overload during MMC-HVDC outage. The proposed coordinated control only uses local measurements and, without the need for communication, can seamlessly handle transitions including various faults. The proposed scheme enables fault ride-through operation and provides a high efficient solution with flexible operation for integrating large offshore wind farms. Simulation results confirm the proposed control strategy
Analysis of Smart Transformer features for electric distribution
The distribution grid is undergoing deep changes created by the integration of new generation resources, such as renewables, and new loads, like electric vehicles. These new actors impact on the distribution grid management, introducing 1) higher variability of the grid power demand and subsequent power unbalance, 2) reverse power flow with increased overvoltage conditions in case of high power production and low power consumption, cables and transformer overload in case of low power production and high power consumption, and 3) decreased system inertia, due to the power electronics-connection of the resources. The Smart Transformer (ST) enables the management of the distribution grid, absolving three main tasks: 1) adapting the voltage level from medium to low voltage grids; 2) managing the distribution grid during the aforementioned issues; and 3) offering higher controllability of distribution and transmission grid. This work describes in details the ST controllers and their tuning, taking into account the services to be provided. The ST enables the direct control of the voltage waveform in the ST-fed grid, varying the voltage amplitude and frequency. This allows to interact with the voltage-sensitive loads power consumption and droop controlled-generators in order to shape the power consumption of the ST-fed grid. Applying this control the ST can offer services to the grid, like limiting the reverse power flow in the medium voltage grid, or managing its overload conditions. The accuracy of these services can be increased if the identification of the grid power sensitivity to voltage and frequency is carried out. The ST, applying a controlled voltage amplitude and frequency variation, performs the on-line load sensitivity identification and evaluates in real time the grid sensitivity. This identification enables the offer of new ancillary services to the distribution and transmission grids
Performance evaluation and control of an MMC active rectifier with half-bridge and full-bridge submodules for HVDC applications
Dissertation (MEng (Electrical Engineering))--University of Pretoria, 2021.The modular multilevel active rectifier was designed and evaluated, whereby the half bridge and the full bridge DC-DC converters as its submodules for the high voltage direct current transmission were compared. It was found that, by taking advantage of the unipolar modulation scheme in the full bridge converter, the switching losses in the two converters are equal when they are both operated in the linear modulation region. Furthermore, operating the full bridge converter in the overmodulation region does not give it a pronounced advantage over the half bridge converter. The conduction losses in the full bridge converter are two times higher than those in the half bridge converter, due to double the number of semiconductor devices. However, using the half bridge converter in the high voltage direct current modular multilevel converter requires an expensive DC-side breaker, while use of the full bridge converter eliminates the need for such a breaker due to the intrinsic DC-side fault current blocking capability. The clear choice between the two requires industry cost data.
A design methodology for the submodule capacitor average voltage loop controllers for phase-shifted carrier modulated modular multilevel converters was carried out from first principles. The methodology enables design of such controllers to be carried out in a step by step and straightforward manner without resorting to simulation or guesswork.
A simple but effective submodule capacitor sizing method was proposed. The resulting submodule capacitor size was shown to be smaller than those resulting from other sizing methods proposed in the literature while achieving the submodule capacitor voltage ripple specifications.
A robust DC bus voltage controller design for modular multilevel rectifiers was presented, whereby a design method for multilevel voltage source converters with DC link capacitors was adopted for modular multilevel rectifiers. Since the modular multilevel converters for HVDC application are designed without the DC-link capacitor to mitigate the effects of a possible DC-side fault current, the submodule capacitors in the modular multilevel converter acted as an equivalent DC link capacitor to accomplish the design.Electrical, Electronic and Computer EngineeringMEng (Electrical Engineering)Unrestricte