Recent Developments of Electrical Drives - Part 39. The book stating the recent developments of electrical drives, can be useful for engineers and researchers investigating and designing electrical and electronic devices as well as for students and young researchers dealing with electrical and electronic engineering, computer sciences (advanced computer modelling, sophisticated control systems with artificial intelligence tools applied, optimal design bye use of classical and genetic algorithms employed), applied mathematics and all the topics where electromagnetic, thermal, mechanical phenomena occur | . Static and Dynamic Measurements 381 300 -200 -100 0 -100 -200 -300 t ms 60 40 - 20 0 -20 _ -40 600 650 700 750 800 850 900 950 t ms Figure 7. Stator voltage Vs and stator current Is vs. time after switching on the grid voltage. At 700 ms the stator voltage V changes to the value of the grid voltage with a peak value of here 300 V In the plot of the stator current we can recognize decaying electric transients until around 800 ms. Later we find oscillations caused by the transient condition of the magnet rotor. The next plot in Fig. 8 shows the magnet rotor speed over a longer period up to 2000 ms. The magnet rotor speed oscillates sinusoidal around synchronous speed which is caused by an oscillation of the magnet rotor around the static load angle at no load. Because of the aluminum cylinder which can be regarded as a damper circuit the oscillations have exponential decaying amplitude until the system is stable again. If the PMIM will work as a wind generator this test represents a starting procedure for the wind turbine. Finally the results of the acceleration process from standstill are presented after the PMIM is directly connected to the grid. Fig. 9 compares the rotor speed and the magnet rotor speed. Because of the higher inertia the asynchronous rotor blue line accelerates slower than the magnet rotor. The magnet rotor like a synchronous machine can only perform an asynchronous run up with the help of its damper circuit. Because the stator field rotates much faster than the field of the permanent magnets during acceleration the magnet rotor sees an oscillating torque. In the plot we can find these oscillations transferred to the magnet rotor speed. The smaller the slip of the magnet rotor becomes and thus the smaller the frequency of the oscillating torque the stronger is its influence. Thus the amplitude of the speed oscillations 1600 1500 1400 1300 E 600 800 1000 1200 1400 1600 1800 t ms Figure 8. Magnet rotor speed wMR vs. time after switching on
