ADVANCED SHEPWM TECHNIQUE FOR AC TRACTION DRIVES

The advantages of the selected harmonic elimination (SHE) PWM technique for ac traction drives are described, which include the mitigation of the electromagnetic interference and a notable reduction in the size of the dc link filters. Using the Newton Raphson method, the nonlinear SHE equations have been solved up to 35 degrees of freedom and the multiple solutions have been obtained. These multiple solutions are then evaluated by a performance index which reflects the ratio of the harmonic current to the fundamental current in the motor. The evaluation shows that among the multiple solutions there exists an optimal solution which results in the minimum harmonic current. In the experiment as many as 34 kinds of the lower order harmonics have been eliminated by the SHEPWM technique from the output voltages of the inverter.