Plenary session

Plenary lecture „Micro windmills - design and control” will be given by professor Zbigniew Krzemiński

Microturbines, according to definition provided in the Renewable Energy Sources Act, have the power of not more than 40 kW. Relevant in this context are the limits of the power of 3 kW and 10 kW due to the price of the mandatory purchase of electricity. Micro windmill structures must meet the economic viability of the investment, which imposes the use of rotor blades with fixed pitch angle and stall controlled speed. On the basis of cost analysis it can be shown that for low power and high speed it is economical to use a synchronous generator with permanent magnets, and higher power require a application of the induction generator and gearbox. The construction and parameters of a wind turbine depend on the choice of wind speed, above which the power of the generator is limited. This speed, which is the rated speed of the windmill, is selected on the basis of the distribution curve analysis for the wind speed in selected area. On the basis of the rated speed and power characteristics of the proposed wind turbine the rated power and the rated speed of the generator is selected. Design process of the micro windmill is known, but there are no relationships in the literature, which must be taken into account in order to ensure maximum production of electricity. Microwindmill is controlled in accordance to several rules depending on wind speed. In the first range specified for small wind speed the control sets operating point at maximum power. The second range is transitory, with a constant generator speed ensuring safe operation of the plant. In the third range, for the high-speed wind, power limitation of windmill occurs. In the second and third ranges a stall effect is used for braking, the plant can operate on unstable parts of the mechanical characteristic. In addition the fourth type of control is introduced for variable but limited wind speed, enabling fuller use of wind energy. Design parameters of a wind turbine together with a method of control makes it possible to specify the power curve and the production of electricity at a certain distribution of wind speed. The construction of the windmill imposes the use of sensorless control methods for the generator with a wide action range of the observer speed. Lowering the cost of micro power converters leads to economically justifiable use of devices build on a basis of silicon carbide. Construction of modern micro wind power plant combines aerodynamic issues with advanced methods of regulation and the latest developments in the field of power electronics. Test results for the micro wind power plant with a capacity of 40 kW put into production will be presented in the paper.