Agusti Egea-Alvarez

Voltage Control of Multiterminal VSC-HVDC Transmission Systems for Offshore Wind Power Plants: Design and Implementation in a Scaled Platform

This paper deals with multiterminal voltage source converter (VSC) HVDC transmission systems for the connection of offshore wind power plants to the main land ac grid. A droop-based control scheme is considered. The droop controllers have been designed base on a mixed sensitivity criterion by solving a convex optimization problem with linear matrix inequalities. The system is analyzed by means of simulations and experimentally in a scaled platform. Simulations show the control performance during a wind speed change and a voltage sag in the main ac grid. Experimental results include wind power changes (increase and decrease) and an eventual VSC loss (both considering grid-side and wind farm VSC loss). In all the cases, the simulation and the experimental results have shown a good system performance.

Advanced Vector Control for Voltage Source Converters Connected to Weak Grids

This paper addresses an advanced vector current control for a voltage source converter (VSC) connected to a weak grid. The proposed control methodology permits high-performance regulation of the active power and the voltage for the feasible VSC range of operation. First, the steady state characteristics for a power converter connected to a very weak system with a short circuit ratio (SCR) of 1 are discussed in order to identify the system limits. Then, the conventional vector control (inner loop) and the conventional power/voltage control (outer loop) stability and frequency responses are analyzed. From the analysis of the classic structure, an enhanced outer loop based on a decoupled and gain-scheduling controller is presented and its stability is analyzed. The proposed control is validated by means of dynamic simulations and it is compared with classic vector current control. Simulation results illustrate that the proposed control system could provide a promising approach to tackle the challenging problem of VSC in connection with weak AC grids.

DC Voltage Droop Control Design for Multiterminal HVDC Systems Considering AC and DC Grid Dynamics

This paper focuses on the droop-based dc voltage control design for multiterminal VSC-HVDC grid systems, considering the ac and the dc system dynamics. The droop control design relies on detailed linearized models of the complete multiterminal grid, including the different system dynamics, such as the dc grid, the ac grid, the ac connection filters, and the converter inner controllers. Based on the derived linear models, classical and modern control techniques are applied to design the different controllers, including a multivariable frequency analysis to design the grid voltage droop control. In combination with the droop control, a dc oscillation damping scheme is proposed in order to improve system performance. The control design is validated through simulations of a three-terminal system.

Multiterminal HVDC-VSC for offshore wind power integration

The different operation modes of multiterminal HVDC-VSC systems for large offshore wind farms are analyzed. Control schemes for each power converter are proposed. The wind farm VSCs inject the power to the HVDC grid and are controlled as ideal voltage sources that absorb all the incoming power in normal operation, and reduce the injected power whenever a fault occurs and the DC voltage rises. The grid-side VSC inject the power to the main grid and control the DC voltage using a droop control scheme. The proposed controllers are tested in a case study by means of dynamic simulations with a four terminal system. The results show good performance for changing wind speeds, a voltage sag and a loss of a converter.

Active and Reactive Power Control of Grid Connected Distributed Generation Systems

The present chapter describes active and reactive power control for distributed generation and storage systems connected to the grid by means of voltage source converters. Renewable generation and storage systems connected to a three-phase three-wire grid are considered. The different system components are described and modelled. The overall active and reactive power control scheme based on the instantaneous power theory is described. The fundamental necessary control blocks are detailed including the phase locked loop, current controllers, current references calculation and DC bus voltage controllers. Simulations results are provided to exemplify the described control approach.

Experimental implementation of a voltage control for a Multiterminal VSC-HVDC offshore transmission system

This paper presents the design and implementation of a Multiterminal VSC-HVDC (Voltage Sources Converter, High Voltage Direct Current) experimental platform. Operational points considering offshore wind farms and a droop-based controller are described. In addition, the experimental platform has been tested under several conditions as: normal operation, grid side converter disconnection and wind farm converter disconnection.

Protection system remote laboratory

Remote laboratories are a learning tool that allows carrying out tutorials without being physically present in the laboratory facilities. Such sort of platforms can be useful to complement students learning with some practical activities. Timetables flexibility is the main advantage of remote laboratories for both students and teachers, since these laboratories are in operation 24 hours per day without requiring any supervisory assistance. The protection and distribution power systems have recently changed by the effect of the new information and communication technologies. As these changes have been carried out in such a short period of time, professionals with knowledge in these topics are required. Additionally it would be needed to include distribution automation concepts in current subjects and finally create didactic material to be used in practical sessions. This paper presents an e-laboratory of electrical protections that emulates the structure and conditions of a distribution grid. This laboratory is used to perform practical activities in degree and master subjects and professional courses dealing with electrical protections, automation and communications.

Multiterminal-HVDC scaled platform for offshore wind transmission systems emulation

This paper presents a Multiterminal VSC-HVDC (Voltage Sources Converter, High Voltage Direct Current) emulation platform. Design details of the scaled platform are discussed. A DC grid droop-based voltage control method designed following Lyapunov control theory has been adopted. In addition, operational points of the Multiterminal HVDC grid are described. The emulation platform have been tested under wind power change and power converter disconnection scenarios. The emulation results has been verified by means of simulations.

Operation and Control of VSC-HVDC Multiterminal Grids for Offshore Wind

The control and operation of a multiterminal VSC-HVDC grid for offshore wind power under normal and fault conditions are described. The paper addresses maintaining the DC voltage during electrical faults and power reduction methods using fixed speed induction generators.

Advanced vector control for voltage source converters connected to weak grids

This paper addresses an advanced vector current control for a voltage source converter (VSC) connected to a weak grid. The proposed control methodology permits high-performance regulation of the active power and the voltage for the feasible VSC range of operation. First, the steady state characteristics for a power converter connected to a very weak system with a short circuit ratio (SCR) of 1 are discussed in order to identify the system limits. Then, the conventional vector control (inner loop) and the conventional power/voltage control (outer loop) stability and frequency responses are analyzed. From the analysis of the classic structure, an enhanced outer loop based on a decoupled and gain-scheduling controller is presented and its stability is analyzed. The proposed control is validated by means of dynamic simulations and it is compared with classic vector current control. Simulation results illustrate that the proposed control system could provide a promising approach to tackle the challenging problem of VSC in connection with weak AC grids.