Closed loop control of AC drive with LC filter

In electric drives with frequency converter a LC filter is used to smooth the voltages and currents supplying the AC motors. Unfortunately the LC filter introduces the phase shift and voltage drop on input and output of the filter. It makes difficult to implement precise control of the electric motors especially in the case of speed sensorless control methods. It is necessary to change the used control system and the state variables calculate block in case of the drive with the filter. In this paper a method for an asynchronous motor speed sensorless control in the system with inverter and LC output filter is presented. In the proposed system a nonlinear control method of the asynchronous motor and the speed and flux observer structure were modified. The system does not need any additional sensors except these which were previously used in the system without LC filter. The proposed electric drive was realized in simulation and experiment for 1.5 kW asynchronous motor.