This paper presents the effects on output voltage and current total harmonic distortion (THD) response with increasing the arm inductance (smooth reactor for HVDC) for the modular multilevel converter (MMC) behavior based on a closed loop-needless PID controller control. Also, it presents the effects on MMC quantities, such as a circulating current ripple, maximum output voltage, and submodule capacitor ripple responses with increasing the value of arm inductance. Because increasing arm inductor size could reduce the THD and circulating current ripple waveforms of the MMC, this effect will be investigated in this paper. The closed loop-needless PID controller control is presented first. Second, an examination of the effect of changing the arm inductor for MMC behavior is carried out based on many simulation results in this paper in order to analyze the change in THD for all MMC quantities, including circulating current, upper arm current and voltage, lower arm current and voltage, and AC output voltage and current. Third, arm inductance relationships with output voltage and current THD are shown. Also, arm inductance relationships with a circulating current ripple and submodule capacitor ripple are presented. As a part of this study, the relationship between arm inductance and maximum output voltage is explained. Finally, the hardware design and software design of the prototype are presented to verify the arm inductor value effect on MMC experimentally. The experimental results are also documented in this paper. (C) 2015 Elsevier B.V. All rights reserved.