Parallel Operation of Voltage Source Converters without Filter Inductors: Control of the Circulating Current

Scalable large-scale power systems can be managed by paralleling of multiple power converters, possibly arranged in interleaved configurations. State-of-the-art in reduction of the circulating current indicates the ubiquitous use of filter inductors, which are placed at each parallel converter output. This paper presents a new control algorithm to remove those filters, relying only on the natural parasitic inductance at each connection point. Multiple cells in parallel are modeled to investigate the transient behavior of the load signals and their group dynamics in case of a large number of units. A two-step control strategy is proposed: a narrow-bandwidth communication interface is used to synchronize coarsely the units, then a high-speed closed-loop control on the converter current tracks the difference in samples taken by the Double Edge Sampler (DES). Correction is achieved by means of high-resolution parametric delays, cascaded to the traditional PWM modulator. Each converter controls its own current without the need of information from his neighbors. The potential of this technology is envisioned in the automotive field, where modular powertrains can be designed for different vehicle targets. The effects of the proposed approach can improve power per unit of volume and weight, thanks to the removal of the bulky output filters.