Electric Control Substituting Pitch Control for Large Wind Turbines

A completely electrical control of a variable speed wind turbine is experimentally verified. A vertical axis wind turbine with a direct driven generator and an electrical system with diode rectification and full inverter connected to the electric grid is presented. This is the first paper that presents this novel 200？kW wind power plant erected at the west coast of Sweden. The turbine has fixed pitch and is only controlled electrically accommodated by passive stall of the blades. By electrically controlling the generator rotational speed with the inverter, passive stall regulation is enabled. The first results on experimental verification of stall regulation in gusty wind speeds are presented. The experiments show that the control system can keep the turbine rotational speed constant even at very gusty winds. It is concluded that electrical control accommodated by passive stall is sufficient as control of the wind turbine even at high wind speeds and can substitute mechanical control such as blade pitch. 1. Introduction Increased amount of electricity produced from wind power is one of the ways to reach the goal of lowering emissions of greenhouse gases from energy production. Installed wind turbines and wind power plants have increased both in size and number in the last 25 years. However, research is still needed, in order to increase the reliability of turbines [1]. The research in wind power at the division of electricity at Uppsala University is focused at vertical axis wind turbines of straight-bladed Darrieus type. Darrieus turbines are described in [2]. The novel concept with an all-electric control and a variable speed turbine connected to a direct driven PM generator placed on ground reduces the number of moving parts compared to conventional wind turbines. Hence, the maintenance cost is expected to be lower than for conventional wind turbines. The turbine is controlled electrically by controlling the power output and rotational speed of the generator; that is, no mechanical control as described in [3] is needed. In wind speeds above nominal, the electrical system is accommodated by passive stall. Passive stall has also been used historically in fixed speed horizontal axis wind turbines [4]. However, in this concept it is used together with a variable speed turbine instead of fixed speed. In conventional horizontal axis wind turbines, the gearbox, pitch, and yaw system stand for a substantial part of the downtime [5]. Further, by placing the generator on ground, it is easier to mount and maintain it. The generator can be designed for