A Method for Motor Synchronous Transfer in Cascaded NPC-Bridge-based Drive Systems

This paper proposes a motor synchronous transfer (MST) method for motor transmission between the VSD and the utility. It has been developed based on the discrete Fourier transformation (DFT), is easily added to the existing motor control strategies, and determines the fundamental component of the grid voltage. As a result, stability against noise, harmonics, and unusual and DC-polluted waveforms is ensured. Unlike the previous algorithms, it lacks filters and additional PI controllers for phase detection. It does not need further hardware like decoupling inductances as the method makes a condition for short-time paralleling of VSD and utility. This article practically evaluates the performance of the proposed method using a cascaded NPC-Bridge inverter. Results confirm that it accurately detects the grid voltage phase and magnitude and transfers the motor with a limited transient overshoot ( 1.5×nominal current), tolerable for the grid and VSD. Also, mathematical operations are reduced by up to 60%.