Circulating Current Suppression in Parallel Connected ANPC Converters using Advanced PWM Switching Patterns

This work presents an advanced switching pattern shift control approach to enhance line-voltage quality and mitigate circulating current jumps and flux issues in magnetic cores for parallel connected Active Neutral-Point Clamped (ANPC) converters using interleaved switching. The interleaved switching technique is crucial for achieving multilevel line-voltages but introduces circulating currents between parallel connected legs and low line-voltage quality. To address the line-voltage quality problem associated with interleaved switching in standard phase-shift pulse width modulation (PS-PWM), an enhanced phase-shift (EPS-PWM) technique with uncontrolled carrier phase transition is used. However, EPS-PWM introduces jump and dc offset issues in inductor flux and circulating current, leading to increased current stress on the switching devices, higher power losses, and larger passive components. The advanced switching pattern shift control approach provides a non-complex yet effective solution to eliminate the dc offset in inductor flux and circulating currents by solely controlling PWM switching patterns. Compared with uncontrolled carrier transition, the peak value of circulating currents and flux are reduced by over two times, resulting in decreased size/weight of magnetic components and increases power converter efficiency. The viability of this approach is validated through detailed analysis, simulations, and experimental results on a 3-phase parallel connected ANPC Voltage Source Converter (VSC) system.