Enhancement Design of Multi-phase Transformer for Cascaded H-Bridge Motor Driver

Abstract

The growth of using medium-voltage drivers (MVDs) to control medium-voltage motors has led to more complicated designs to cover the market demand. Multi-phase transformers (MPT) are one of the most preferred components for AC-DC-AC converters. MPT in MVD systems has essential functions: harmonic filtering between the grid and rectifier, Isolation between the grid and rectifier, converting voltage to suitable voltage for the rectifier, and preventing block common-mode voltages, which could cause failure in motor winding insulation. MPTs are critical to motor drivers because of their pure sine wave, low THD, grid isolation from the motor, efficacy, and cost-effectiveness. This work addresses the configuration, winding turn ratios, selection factors, and calculations of power, weight, and design procedure for shifting transformers. The proposal design is confirmed by simulation results, which support the experimental studies validated by different load levels. The result determines the inductance value for cost-effectiveness, low-harmonics, and power factor improvement. This work provides an experimental method to specify the IPT inductance value, which improves the power rating and reduces the THD. Mathematical specification, an experimental method, was applied to calculate the optimal value of the IPT inductance. The simulation and experimental results analysis were studied and verified. The optimal value of inductance obtained by the simulation result is 25mH; at this value, the THD equals 4.6%.