*4.3. Summary and Discussion*

The designed parameters of the three kinds of filters, as well as the applicability of the presented fault-tolerant scheme on the filters, are summarized in Table 2.


**Table 2.** Comparison of the three kinds of filters.

Note: Tr represents the OEW transformer.

From analyzing the table, the followings can be seen.

(1) The Type-1 and Type-2 filter have the same filter parameters, but the inverter-side inductor of the Type-1 filter needs two magnetic cores while the Type-2 filter only needs one, which means the Type-2 filter has a smaller size and cost than the Type-1 filter.

(2) Besides the transformer leakage inductance, the value of the extra inductance requirement of the Type-3 filter is reduced by a factor of 58.35%, while the capacitance requirement is increased about 50%, compared to the Type-1 and Type-2 filter.

(3) The total inductance of the Type-1 and Type-2 filter is more than 10% of the system base inductance, which may cause a larger fundamental voltage drop across the inductor and increase the DC voltage lower limit value.

(4) Unlike the Type-1 and Type-3 filter, the DI-OEWT topology with the Type-2 filter cannot realize fault-tolerant operations with the presented fault tolerate scheme.

(5) In terms of the inductance requirement, magnetic cores numbers and the fault-tolerant applicability, the proposed Type-3 filter has a certain advantage over the existing Type-1 and Type-2 filter.
