Power-Cell Switching-Cycle Capacitor Voltage Control for Modular Multi-Level Converters

摘要

In a modular multi-level power converter, additional switching states are interleaved between main switching states that control output voltage or waveform. The additional switching states provide current from a DC-link to charge capacitors in respective modules or cells to an offset voltage from which the capacitor voltages are controlled toward a reference voltage during each switching cycle rather than being allowed to build up over a period of an output waveform of variable line frequency, possibly including zero frequency. Since the switching cycle is much shorter than the duration of a line frequency cycle and the capacitor voltages are balanced during each switching cycle, output voltage ripple can be limited as desired with a capacitor of much smaller value and size than would otherwise be required.

主权项

1. A power converter having an upper arm and a lower arm, each said upper and lower arm comprising a switch constituted by a series connected pair of transistors and a capacitor, said power converter module being operated using at least two main switching states for controlling average value of phase current and two further switching states interleaved alternately between said main switching states during which said capacitor is either bypassed or connected to a voltage to charge said capacitor to an offset voltage value such that voltage across said capacitor is controlled toward a reference voltage during said main switching states.