7. Linear Modulation Region Expansion Strategy

This chapter delves into the challenges posed by DC-link voltage fluctuations in electrolytic capacitorless motor drives, focusing on their impact on modulation index harmonics and motor performance. The text introduces a linear modulation margin enhancement strategy designed to improve voltage utilization by suppressing these harmonics. It provides a detailed analysis of modulation fluctuation caused by DC-link voltage pulsation and presents a voltage vector angle adjustment method to mitigate these effects. The chapter also explores the use of an impedance model to analyze and verify the suppression effects of the control strategy on modulation index and current harmonics. Additionally, it discusses an adaptive suppression method for fluctuations in the modulation index under field-weakening control, aiming to maximize voltage utilization in the linear modulation region. The text concludes with experimental results that demonstrate the effectiveness of the proposed strategies in enhancing linear modulation margin, voltage utilization, and motor performance, even under varying operating conditions and input voltages.