Christian Sasse

Grid Integration of Large DFIG-Based Wind Farms Using VSC Transmission

This paper describes the use of voltage source converter (VSC)-based HVDC transmission system (VSC transmission) technology for connecting large doubly fed induction generator (DFIG)-based wind farms over long distance. The operation principles of the proposed system are described, and new control strategies for normal and grid fault conditions are proposed. To obtain smooth operation, the wind farm side VSC (WFVSC) is controlled as an infinite voltage source that automatically absorbs power generated by the wind farm and maintains a stable local ac network. Fault ride through of the system during grid ac faults is achieved by ensuring automatic power balancing through frequency modulation using WFVSC and frequency control using DFIG. PSCAD/EMTDC simulations are presented to demonstrate robust performance during wind speed and power variations and to validate the fault ride through capability of the proposed system.

Comparison of Using SVC and STATCOM for Wind Farm Integration

This paper studies system stability of wind farms based on fixed speed induction generators (FSIG) and investigates the use of the static Var compensator (SVC) and static synchronous compensator (STATCOM) for wind farm integration. Due to the nature of asynchronous operation, system instability of wind farms based on FSIG is largely caused by the excessive reactive power absorption by FSIG after fault due to the large rotor slip gained during fault. Wind farm models based on FSIG and equipped with either SVC or STATCOM are developed in PSCAD/EMTDC. It was found that the SVC and STATCOM considerably improve the system stability during and after disturbances, especially when the network is weak. Compared to SVC, STATCOM gave a much better dynamic performance, and provided a better reactive power support to the network, as its maximum reactive current output was virtually independent of the voltage at the point of common coupling (PCC).

Grid Frequency Control Design for Offshore Wind Farms with Naturally Commutated HVDC Link Connection

This paper considers the formal design for the offshore grid frequency control in an LCC HVDC connected wind farm. The control paradigm is based on using the grid frequency control to regulate the HVDC rectifier angle and hence control the power flow in the system. The dynamics of the system are derived and a grid frequency controller is designed. The mathematical analysis and the control design are verified through PSCAD simulation. Good modeling agreement is obtained for both open and closed loop systems and the work provides a good basis for wider research investigation into wind farm operation including fault behaviour.

STATCOM-controlled HVDC Power Transmission for Large Offshore Wind Farms: Engineering Issues

The paper considers a solution for integration of large offshore DFIG-based wind farms with a common collection bus controlled by a STATCOM into the main onshore grid using line-commutated HVDC connection. A design procedure is described and the controlled system is validated using PSCAD/EMTDC simulations confirming high performance of the proposed control strategy in both normal operation conditions and faults. Engineering issues related to STATCOM capacitor sizing and reduction of STATCOM rating are considered and their effectiveness is confirmed

Power Electronics Options for Large Wind Farm Integration: VSC-Based HVDC Transmission

This paper describes the use of voltage source converter based HVDC transmission (VSC transmission) system for grid integration of large wind farms over long distance. The wind farms can be based on either doubly-fed induction generator (DFIG) or fixed speed induction generator (FSIG). The paper describes the operation principles and control strategies of the proposed system. Automatic power balancing during network AC fault is achieved without communication between the two converters. PSCAD/EMTDC simulations are presented to demonstrate the robust performance and to validate the proposed system during various operating conditions such as variations of generation and AC fault conditions. The proposed VSC transmission system has technical and economic advantages over a conventional AC connection for integrating large wind farms over long distance

Electricity networks of the future

In May 2005 the European Commission Research Directorate-General defined an initial scope for the creation of a technology platform for the electricity networks of the future. This was namely to increase the efficiency, safety and reliability of European electricity transmission and distribution systems and to remove obstacles to the large-scale integration of distributed and renewable energy sources, in line with the proposed priority for smart energy networks in the Research Directorate-Generals Framework Program 7 (FP7). In January 2006, the platforms vision paper was published. This paper presents an overview of the initial issues raised

Immunity research of wireless communication in switch cabinet monitoring and control

With the wide spread use of wireless data transmission technologies in offices and houses, and also due to the flaws of wired communication in LV wiring system in switchgear, the prospect of the application of existing wireless data transmission technologies to replace LV wiring in switchgear is attracting more and more researchers and manufacturers. The cost of using readily available wireless data transmission technologies to replace some or all of the low voltage wiring in switchgear is currently thought to be very low. The wireless communication doesn’t need transmitting media, so it can prevent the damage caused by conducted interference, and will not take up more space when the number of monitoring parameters increase. So it is easier to install and maintain. However, currently very little research has been carried out about its possible application in substation and MV switchgear, where electromagnetic interferences are rather complicated and of uncertain amplitude. There is still a scope to investigate the possibility of using such a low cost wireless data transmission technology in switchgear. One of the remaining challenges is to choose a proper wireless technology and prove its reliability in switchgears. This paper studies the feasibility of applying the Bluetooth and 802.11b wireless data transmission technologies for the purpose of Medium Voltage (MV) switchgear monitoring and control. In particular, a series of experiments are carried out to test the reliability of both Bluetooth and 802.11b devices for applications in switchgear under various interference conditions, and the immunity property of the two candidates is obtained preliminarily from experimental results. All results are presented and discussed in the paper.

Reliability Test of Using 802.11b Technology In Switchgear for Measurement and Control

In this paper the typical interference sources for wireless communication in medium voltage (MV) switchgear are first studied and summarized, and the gap breakdown is then chosen as the primary interference source for IEEE 802.11b communication. The immunity tests to the interference of gap breakdown and narrow-band signals are carried out. The results show that both SF6 and vacuum gap breakdown have remarkable impacts on IEEE 802.11b communication. It is found that when the strength of radio signal is strong enough, it will also cause 802.11b working abnormally. According to the test results, the reliability performance of 802.11b devices is assessed preliminary.

Scattering phase function measurements on single particles and on particle ensembles

We present measurements of the light-scattering phase function of selected carbon and ash particles in the geometric-optics regime in which the particle diameter is much larger than the wavelength of the light source. Measurements were performed on both single particles and particle ensembles. This was accomplished with two separate methodologies: an electrodynamic levitator for single-particle measurements and a particle feeder for the ensemble measurements. For each methodology, two irradiation sources were utilized: an argon-ion laser (lambda = 496 nm) and a xenon lamp. Results of the normalized phase functions are presented.