Control of a Synchronous Machine

Abstract: The VAWT project at Uppsala University has successfully managed to develop a vertical axis wind turbine (VAWT). The VAWT has many benefits compared to the Horizontal axis wind turbines (HAWT) which are the most common wind turbine design today. One of the many advantages with the VAWT is that it allows the generator to be located on the ground level. That reduces the required tower strength. The wind turbine is not self starting, i.e. the turbine needs a certain speed before the wind can force the turbine to revolve. The wind turbine is therefore in need of special start procedure. During the start, power electronics is used to operate the generator as a motor. Today Hall latches are located in the air gap of the generator which provides the signals that govern the power electronics. However, there is a demand to have a start that does not require Hall latches. Such controller would increase the reliability of the starter system. The design of the wind turbine could be even more simplified. Hence, the diploma work treats a programmed microcontroller to control the start-up without using any sensors at all. A hub motor was obtained for laboratory work, a driver and an inverter were constructed to drive the motor using a microcontroller. The finished start-up program has the ability to start the hub motor both sensorless and using Hall sensors. The microcontroller controls the motor by measuring the phase voltages of the motor. This information is used to decide which phases of the motor the electric current should go through. The current to the motor is limited using pulse width modulation strategy (PWM). Current limitation is necessary to protect the power electronics and limit the torque during the start. The result of start-ups using both Hall sensor and sensorless showed that the two start strategies are able to accelerate the rotor at the same rate. However, the start-ups using Hall sensors reached a higher top speed than the sensorless starts. However, the wind turbine is not in need of a higher speed than what the sensorless start was able to reach. Thus, the sensorless start is considered to be as good as the start using Hall sensors.