Three-phase Infinite Level Inverter

摘要

Pulse width modulated voltage source inverters (PWM-VSI) have many advantages over the traditional bridge inverters; yet there are some challenges encountered by PWM inverters. As power and voltage rating increases; device constraint as well ashigh switching loss creates serious problems. Various pulse width modulated strategies like sinusoidal; 3rd harmonic injection and space vector PWM (SVPWM) employs high frequency switching to obtain quality output voltage with less ripple. Increasing number of voltage levels in a multi-level inverter requires an increase in number of active switches and passive elements. The problem of dead time requirement and shoot-through in PWM inverters distorts the output waveform and transfers less energy to load. A new type of three-phase VSI called three-phase Infinite Level Inverter (ILI) is proposed to mitigate all the above problems to a large extent. The device constraint and switching loss at high frequency is substantially reduced due to lower input DC supply. To get same output voltage; the proposed inverter requires only half of the DC link voltage compared to sine PWM inverter. Also; ILI takes only 0.576 times the input DC voltage compared to 3rd harmonic-injection or SVPWM. This shows that the proposed inverter has the maximum DC link utilization. The number of active switches and passive elements are same for any number of voltage levels. This topology is a multi-level inverter as there are many levels in the output voltage. Shoot-through problem is avoided and thus the proposed inverter doesn't need a dead time; leading to a better system reliability. Hysteresis current control is used for closed loop control. Results obtained from experimental setup and computer simulation using MATLAB/Simulink are presented to verify the above scheme.