Abstract
High modularity, easy scalability, and superior harmonic performance, comprising the topology with the most potential for medium- to high-voltage high-power applications, are representative features of a modular multilevel converter (MMC). Each application of a MMC requires a proper scheme such that it conforms to control objectives such as correct submodule capacitor voltage balancing control and the suppression of circulating current. Over the past few years, various studies have been presented that meet the MMC requirements through both classical control-based pulse-width modulation and model predictive control, although some drawbacks exist for both control concepts. The dynamic performance of the classical control methods with proportional-integral or proportional-resonant controllers is unsatisfactory, and the requirement of proportional-integral parameters tuning procedure makes converter operation performance depends on proportional-integral parameters adjustment. Meanwhile, model predictive control performance depends significantly on the mathematical model of a system, and weighting factor selection is tedious. In this paper, we propose an improved phase-shifted carrier pulse-width modulation method and capacitor voltage balancing control that inherits the merits from both classical control and model predictive control. Meanwhile, the proposed control method eliminates the requirement of the tedious proportional-integral parameters tuning procedure and improves the dynamic performance compared with the conventional phase-shifted carrier pulse-width modulation-based proportional-integral controller method. Simulations and experiments were conducted to demonstrate the proposed method's properness.
Highlights
In recent years, there has been a growing trend toward using multilevel converters in the industry
In terms of high-power and highvoltage applications, the 3L-NPC and flying capacitor converter (FC) topologies require a dramatic increase in the number of clamping diodes or FCs, which leads to high complexity in controlling the capacitor voltage [1], [4], [5]
In this paper, we present a method for the control of modular multilevel converter (MMC) where the proposed improved phase-shifted carrier PWM (PSC-PWM) and the capacitor voltage balancing control method inherit the merits of both the classical control and model predictive control (MPC) methods and have distinctive features
Summary
There has been a growing trend toward using multilevel converters in the industry. We propose an improved PSC-PWM method and a new capacitor voltage balancing control scheme for controlling MMC where regulating the AC output current and circulating current has been implemented with their predicted values substituted for reference ones. The proposed method has the following advantages: 1) no requirement for PI controllers to achieve objectives, which allows avoiding the PI parameters tuning procedure and dependence of operation performance on PI parameters adjustment; 2) improved dynamic performance of the PSC-PWM method compared with conventional PSC-PWM-based PI controllers; 3) achieving capacitor voltage balancing control in a closed-loop manner; and 4) avoiding unwanted switching actions. Unlike the conventional PSC-PWM control scheme method based on PI controllers [8], the proposed method is easy to realize with a straightforward approach because the PI parameters tuning procedure is unnecessary, permitting a significantly improved dynamic performance
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