Exploitation of an Industrial Low-Bandwidth Communication Line for Modulation-Level Synchronization of Voltage Source Converters

Abstract

Parallelization of power electronic converter units is a way to meet the high current requirements of modern electrification applications. In case of voltage source converters, parallel operation can be attained only if the voltages of all the units are equal. In the current state of the art, this voltage synchronization can be achieved at the fundamental frequency, but not at modulation frequency, hence requiring bulky filters to limit circulating currents; this lowers the system performance in terms of cost, volume, weight and sustainability. In this paper, the authors propose a novel approach to synchronization, acting directly at the modulation frequency level, thus removing the need for any filter. This technique relies on the natural parasitic inductance and resistance of the wiring among parallel units. Specifically, this paper presents the first of two synchronization stages required to reach the sub-nanosecond synchronization necessary to completely remove the filters. At start-up, a low-bandwidth industrial communication line, based on the CAN protocol, is exploited to guarantee that the error in the synchronization of PWM signals among all the parallel units is lower than 0.1%. This limits the initial circulating current, supporting the subsequent control stage that achieves sub-nanosecond synchronization. The proposed concept is validated by experiments using a commercial MCU unit with an unadorned CAN peripheral.

Keywords

• circulating current
• initial synchronization
• parallel operation of power converters
• switched mode DC/AC power converter