小岩 健太

Crowbar is a popular device used to facilitate the fault ride-through of doubly fed induction generator (DFIG), which protects the power converter from the damage of overcurrent/overvoltage. The crowbar is activated once an overcurrent/overvoltage is detected, and it is desirable to release the crowbar as soon as possible in order to output active/reactive powers to the grid. But releasing the crowbar at an inappropriate timing may result in the recurrence of overcurrent. So, it is important to release the crowbar at an adequate timing. To this end, we analytically investigate the behavior of rotor current, and reveal that the current amplitude fluctuates periodically with a decaying magnitude. Hence, there is a set of release timings which may prevent overcurrent/overvoltage. Further, it is shown that these release timings are robust to the variations of voltage dip depth, generator parameters as well as wind speed. This analysis not only provides a justification for existing release algorithms, but also forms a solid basis for further improvement of crowbar operation. Finally, an algorithm is proposed for the crowbar operation which can prevent overcurrent/overvoltage while minimizing the adverse impact on the grid. The analysis is validated and compared via detailed simulations.

Passive power filters are indispensable for grid-connected inverters (GCIs) to eliminate current harmonics. However, typical filters require large inductance, which not only increases the filter dimension and costs but also leads to slower current response and a high voltage drop across the filter. This article proposes a novel filter called LCTCL filter, which effectively attenuates harmonics with small inductance. In addition, this article presents a controller synthesis to the GCI with LCTCL filter without an additional resistor. We demonstrate the effectiveness of the proposed LCTCL filter through comparative analysis with typical filters via simulations and experiments. We clarify that the proposed LCTCL filter has excellent features in terms of filter dimension, frequency characteristics, robustness for parameter variations, harmonic suppression, and total harmonic distortion.