Modular Multilevel Converter with Sensorless Diode-Clamped Balancing through Level-Adjusted Phase-Shifted Modulation

TL;DR

This paper introduces a sensorless, cost-effective balancing method for diode-clamped modular multilevel converters using level-adjusted phase-shifted modulation, eliminating the need for extensive sensors and complex control.

Contribution

It presents a novel balancing technique exploiting arm current's dc component with a simple modulation scheme, enabling sensorless operation and reducing control complexity.

Findings

Effective voltage balancing achieved without sensors.

Simulation and experimental results validate the method.

Low-cost and simple implementation demonstrated.

Abstract

Cascaded H-bridge and modular multilevel converters (MMC) are on the rise with emerging applications in renewable energy generation, energy storage, and electric motor drives. However, their well-known advantages come at the price of complicated balancing, high-bandwidth isolated monitoring, and numerous sensors that can prevent MMCs from expanding into highly cost driven markets. Therefore, an obvious trend in research is developing control and topologies that depend less on measurements and benefit from simpler control. Diode-clamped topologies are considered among the more applicable solutions. The main problem with a diode-clamped topology is that it can only balance the module voltages of a string in one direction; therefore, it cannot provide a completely balanced operation. This paper proposes an effective balancing technique for the diode-clamped topology. The proposed solution exploits the dc component of the arm current by introducing a symmetrically level-adjusted phase-shifted modulation scheme, and ensures the balancing current flow is always in the correct direction. The main advantages of this method are sensorless operation, no added computation and control effort, and low overall cost. Analysis and detailed simulations provide insight into the operation of the system as well as the new balancing technique and the experimental results confirm the provided discussions.