Frequency analysis and stability enhancement of DTC controlled PMSM drive with input LC filter

This paper presents a new method of frequency characteristic measurement for ac drives connected to a dc trolley-wire. The input part of a drive is composed of an input LC filter. The LC filter is a naturally almost undamped circuit and any change in the circuit (e.g. voltage drop or constant power taken from the circuit) causes dangerous capacitor voltage oscillations. This method helps to find dangerous resonant frequencies of the whole traction drive and it allows finding possible danger oscillations of the dc-link voltage appearing due the motor drive operation. Furthermore a method for dc-link capacitor voltage stabilization has been designed and employed in the permanent magnet synchronous motor drive. The stabilization effect of this method is verified in a using the direct torque control of the permanent magnet synchronous motor by simulations as well as by experimental evidence at a laboratory prototype of the traction drive with rated power 10 kW using the frequency characteristic measurement.