Current control of modular multilevel converters with phase‐shifted pwm using a daisy‐chained distributed control system

Abstract

A modular multilevel converter (MMC) with a conventional centralized control system has many optical fibers for gate signals. A daisy‐chained distributed control system that consists of a primary controller and daisy‐chained cell controllers can reduce the fibers effectively. However, communication delays occur between the controllers and affect the current control performance. This article reveals the current control model of an MMC with phase‐shifted pulse width modulation using the daisy‐chained distributed control system considering the communication delays. We derived a generalized pulse transfer function of the current control and verified it with numerical analyses and circuit simulations. The impacts of the communication delays on the current control and its gain design method are also discussed and analyzed. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Synchronization for an MMC Distributed Control System Considering Disturbances Introduced by Submodule Asynchrony

“…Also the voltage diverging is directly related to the square of the frequency error accumulating period, which means that the capacitor voltage might diverge dramatically and significantly deteriorate the control performance of the capacitor voltage balancing loop, and eventually lead to the malfunction of the MMC in a short period of time. It is worth noting that the capacitor voltage deviations are not considered while calculating the circulating current ripple in (10). The approximate model is adopted to sufficiently evaluate the SM capacitor voltage deviation with simplicity in this paper.…”

“…In HVDC applications, hundreds of SMs are typically required for the MMCs to handle a high voltage (hundreds of kilovolts) with relatively low-voltage rating power devices. In favor of properly manipulating such large number of SMs, distributed controls with phase-shifted (PS) PWM scheme for MMCs are proposed in [7][8][9][10][11], in order to improve the modularity of the MMC system in terms of software and distributing the computational burden into different digital controllers. However, an inherent problem along with a distributed control system for MMCs is the asynchrony of SM controllers, due to the manufacturing tolerance of crystal oscillators that provide controller clocks.…”

A level enhanced voltage balancing method for modular multilevel converter without using sensors

“…12 Therefore, the carrier based high-switching frequency methods such as phase disposition PWM (PDPWM) and phase-shifted carrier PWM (PSCPWM) are the alternative and widely applied on MMCs. [13][14][15][16][17][18] The PDPWM has better harmonic performance but suffers from uneven power distribution. 19 This is solved by sorting the capacitors and generated 2N + 1 levels.…”

“…However, the reduced switching frequency methods demand the large size capacitors to minimize the capacitor voltage fluctuations 12 . Therefore, the carrier based high‐switching frequency methods such as phase disposition PWM (PDPWM) and phase‐shifted carrier PWM (PSCPWM) are the alternative and widely applied on MMCs 13–18 …”

Interleaving Clusters of Submodules to Enhance Scalability of Modular Multilevel Converters for High-Voltage Applications

“…Among these efforts, reduced communication burden through distributed control schemes was highlighted in [18]. A daisy-chained distributed control system was presented in [19]. An example of an industry implementation of distributed control scheme was discussed in [20].…”