Circulating current control of MMC-fed induction motor drive under entire speed range operation

ABSTRACT

A modular multilevel converter (MMC) is reflected to be an emerging multilevel topology for medium- to high-power induction motor drives due to its highly reliable structure, modularity and scalability. However, large circulating current produced in the phase arm of MMC during low-speed operation of induction motor drive is a major drawback of MMC, which leads to affect the size of a sub-module capacitor, inductor and switch rating. To mitigate the circulating current and improve the performance of MMC-fed induction motor drive, this paper proposed a new circulating current error compensator (CCEC) technique with reduced arm current peak. By proper control of instantaneous voltage between arms and DC link current, second-order fundamental frequency current harmonic from circulating current is eliminated which leads to a significant reduction in circulating current. A comparative evaluation between conventional control scheme and the proposed CCEC control scheme is presented. The performance and effectiveness of the proposed CCEC technique are validated using a MATLAB-based simulation. Scale-down laboratory experimental setup is also developed to check the effectiveness of the proposed CCEC control technique. Reduction in circulating current for entire speed range with improved DC link current profile is observed as compared to conventional circulating current suppression control.

KEYWORDS:

• Modular multilevel converter
• circulating current
• field orientation control
• sub-module capacitor voltage ripple
• variable frequency drive

Disclosure statement

No potential conflict of interest was reported by the author(s).