Analysis and suppression of switching-frequency harmonics in variable-output-voltage inverters

In many practical applications such as motor drives, the inverter is required to produce a variable output voltage within a wide range (e.g., 0.1 to 1 pu). In such cases, when the inverter operates in low modulation index (low output voltage), the harmonic distortion of the output voltage increases due to considerable reduction in the magnitude of the fundamental component. Also, the ratio of the switching losses to the output power will be high in the low modulation index. In this paper, a simple solution is proposed to overcome the problems. The principle of the proposed solution is to adjust the DC-link voltage so that the modulation index of the inverter remains within a specific high range. Different practical ways of obtaining controlled DC-link voltage are presented. Also, for operation of the DC-DC converter used for DC-link voltage control, three strategies are proposed. The proposed solution is simple, and it is very effective and feasible to implement. To the best of the authors' knowledge, the idea has not been presented in this form previously. In order to verify the proposed solution, the simulation and experimental results are presented and discussed. In this paper, a simple solution is proposed to overcome the problem of deteriorated output voltage and current quality in low modulation index operation range of the voltage source inverters. The principle of the proposed solution is to adjust the DC-link voltage so that the modulation index of the inverter remains within a specific high range. Different practical ways of obtaining controlled DC-link voltage are presented. Also, for operation of the DC-DC converter used for DC-link voltage control, three strategies are proposed. The proposed solution is simple, and it is very effective and feasible to implement.image