Background

Modular multilevel converters (MMCs) have a combination of issues related to their use. The capacitors are large and unreliable, they have no isolation and must resort to large and unwieldy transformers if isolation is required, and they are infeasible when it comes to variable-frequency operation. Additionally, central controllers in MMCs are vulnerable to failure and perform key functions such as capacitor-balancing, current control, and PWM. Medium voltage alternating current (MVACs) on the other hand are collection systems, power is processed through several stages (ac-dc, dc-ac, low-frequency transformers) thus yielding lower efficiency, increasing cooling requirements, and increases in overall system weight and cost.

Technology Overview

To combat some of these disadvantages, researchers at the University of Colorado has proposed concept bridges advances in wide-bandgap devices with breakthroughs in distributed and decentralized control to produce next-generation medium voltage power conversion circuits that are scalable in both architecture and control. Taken together, the proposed circuit designs and accompanying control strategies will yield integrated circuit + control (C²) blocks, each comprising a local controller and converter, that can be assembled in a modular fashion to obtain highly distributed conversion interfaces for next-generation renewable system architectures. By utilizing SiC devices to obtain C² blocks that each operate at a voltage and power in excess of 1kV and 100kW respectively, such that ensembles of series-connected blocks perform direct ac-dc conversion at medium voltages. By leveraging SiC devices operating at high switching frequencies, cascaded circuit structures will yield transformative performance gains in efficiency while eliminating bulky capacitors and low-frequency transformers. From a reliability standpoint, the elimination of large capacitor banks coupled with online reliability monitoring and wear-mitigation enabled by digital control will increase system lifetime. Contemporary advances in decentralized and distributed control will be leveraged to circumvent single points of failure and afford an overall resilient system that functions despite faults at the block level. The envisioned project outcome is a suite of dc-dc, dc-ac, and ac-dc architectures that can be applied to a variety of renewable energy applications.

Stage of Development

Lab Prototype.

CU4377B

Modular and Scalable Power Architecture for Medium-Voltage Power Conversion (MVPC)