Laboratoris remots i virtuals per assignatures de l'àmbit de l''enginyeria elèctrica

Peer Reviewe

Sensorless control of a power converter for a cluster of small wind turbines

This study presents a new sensorless control for small wind turbine clusters with a single power converter with a direct torque control algorithm. The proposed system consists of a wind farm connected to a back-to-back power converter that interfaces the wind farm with the AC grid. The studied wind turbines are based on fixed-speed wind turbines equipped with squirrel cage induction generators with individual pitch control. The presented structure permits to reduce the number of converters and allows to accomplish the grid codes (fault ride through capability and reactive power support). Furthermore, the generated active power can be reduced according to grid operator requirements. The presented control scheme can be applied to wind turbine repowering projects, wind farms connected to a microgrid, even, new small onshore and offshore power plants. The system performance and stability is studied and validated by means of dynamic simulations.Postprint (author's final draft

Assessment of grid-connected wind turbines with an inertia response by considering internal dynamics

This paper presents a small-signal analysis of different grid side controllers for full power converter wind turbines with inertia response capability. In real wind turbines, the DC link controller, the drivetrain damping controller and the inertial response might present contradictory control actions in a close bandwidth range. This situation might lead to reduced control performance, increased component stress and non-compliance of connection agreements. The paper presents an analysis of the internal wind turbine dynamics by considering different grid-side converter control topologies: standard current control used in the wind industry, standard current control with inertia emulation capabilities and virtual synchronous machines. Comments are made on the similarities between each topology and the negative effects and limits, and possible remedies are discussed. Finally, the conclusion poses that the inclusion of a DC link voltage controller reduces the ability of a converter to respond to external frequency events without energy storage. The degradation increases with the DC link voltage control speed

Superredes, las redes eléctricas del futuro

Peer Reviewe

Stability limits and tuning recommendation of the classical current control providing inertia support

The drastic increase in renewable energy sources in power grids has raised stability concerns. A particular concern exists in the ability of the converters to preserve frequency stability, due to their inherent lack of inertia provision. Grid forming converters have been presented as a solution to this issue, however the control structure for such converters is significantly different from the vector current control structures utilized by most installed control-converter systems. The classical current controller with a Phase Locked Loop (PLL) can be modified to provide inertia by including an additional control loop that injects active power in the case of a frequency event. This paper presents a detailed stability study, using a small signal model, and presents a set of controller tuning recommendations for the classical current controller with inertia emulation capability. The investigation found that the classical current and PLL tuning decreases the power that can be provided using the inertia emulation loop. Reducing the current loop time constant can allow for stable inertia emulation with classical vector current control

Review and comparison of single and dual active bridge converters for MVDC-connected wind turbines

A key component for all-DC wind farms is the DC/DC converter. The converter must have multi-megawatt power capability, a high step-up ratio, provide galvanic isolation, and operate efficiently while being able to fit in the wind turbine nacelle. The single active bridge (SAB) and dual active bridge (DAB) converters in standalone or cascaded configuration are promising topologies that have the potential to meet these requirements. This paper reviews the operation and control of these converters, and compares their volume, weight, and efficiency for a 15 MW wind turbine with 80 kV DC connection. The results show that the standalone topologies are significantly smaller and lighter than their cascaded counterparts. However, all topologies fit inside the wind turbine nacelle. The SAB designs are the most efficient and robust, as they use diodes in the output bridge. The DAB topologies have the advantage of bidirectional power flow at the cost of additional switches and losses. The standalone DAB requires series-connected switches in the output bridge, which may difficult to implement. The cascaded topologies offer higher reliability without significantly increasing losses, making them the most attractive option for future DC wind turbines

Superredes, las redes eléctricas del futuro

Peer Reviewe

Power reduction coordinated scheme for wind power plants connected with VSC-HVDC

This article introduces a novel power coordination method for the operation under restricted conditions of offshore wind power plants connected with VSC-HVDC without the use of communications between converter stations. The proposed method consists of the coordination of the Dynamic Braking Resistor (DBR) located in the Grid Side Converter (GSC) and the wind power plant in order to maintain the DC voltage stability. The coordination is achieved by means of two droop controllers, one for the GSC-DBR and another one for the offshore wind power plant. These droop gains are selected to avoid limit cycles using the describing function approach. The proposed power coordination scheme is tested and verified by means of dynamic simulations

Sensorless control of a power converter for a cluster of small wind turbines

This study presents a new sensorless control for small wind turbine clusters with a single power converter with a direct torque control algorithm. The proposed system consists of a wind farm connected to a back-to-back power converter that interfaces the wind farm with the AC grid. The studied wind turbines are based on fixed-speed wind turbines equipped with squirrel cage induction generators with individual pitch control. The presented structure permits to reduce the number of converters and allows to accomplish the grid codes (fault ride through capability and reactive power support). Furthermore, the generated active power can be reduced according to grid operator requirements. The presented control scheme can be applied to wind turbine repowering projects, wind farms connected to a microgrid, even, new small onshore and offshore power plants. The system performance and stability is studied and validated by means of dynamic simulations