On the electrical power side there has been a clear trend over the lifetime of modern wind power technology. The traditional Danish windmill was designed to operate with constant speed and as simple an electrical system as possible. While today's large turbines run exclusively with variable speed. The main reasons for this are the reduced mechanical stress that comes with being able to vary the speed at high winds, reduced noise from the turbine in low winds is also an important factor, and low speed in low winds also makes the turbine's ability to convert the wind's motion into mechanical rotation more effective.
To achieve variable speed operation electronic power converters are currently used in, these are connected between the generator and grid to disengage the generator's frequency/speed from the grid's fixed 50Hz frequency. Today the DFIG system (double-fed induction generator) dominates the market, but the trend is clearly toward full effect converters gaining market share. The main reasons are that the power electronics of the frequency converters become more cost effective and the system with full power effect converters have greater manoeuvrability, especially in the event of a fault on the power grid. Grid knowledge is becoming increasingly important as network companies are making ever increasing demands on wind turbines. Grid companies around the world describe their grid codes in official documents. They are available at a national and international level. It is essential that wind turbines meet these requirements in order to ensure safe operation of the power grid, especially in the future when we will have a much greater amount of wind power connected. Connection requirements are constantly evolving and wind power producers must be able to test their wind turbines to demonstrate compliance.
Issues within Power and Control Systems are:
Can new converter topologies with unique control be an advantage given the power quality, minimal bearing currents, ageing of the coil insulation and electronics components?
What does the optimal generator system look like, taking into account converter topology, power generation, controllability, power quality, maintenance and noise?
To what extent the choice of generator system, control of the system and fault scenarios affect the mechanical loads on the wind turbine?
How can the development of new magnetic materials affect generator structure, can new power semiconductor devices lead to improved converter technology?
Can high voltage DC technology be a good electrical system inside the turbine, in the collection network within a wind farm and for the transmission of the wind farm's total power to the national grid?
How can the demands of the grid to control the effect be met and thus support the frequency of the network through advanced control of wind turbine and/or wind farm?
Control of wind farms has been shown to be a promising solution for the integration of wind power into the grid. What control algorithms can be used and can they be implemented in a realistic way?
The following projects within the Centre fall under Theme group 1:
TG1-2 Models of electrical drives for wind turbines
TG1-4 Model verification and testing of wind turbines systems by VSC-based testing equipment
TG1-21 Electromagnetic Transient study of wind farms connected by HVDC