*5.1. Experiment Setup Description*

To verify the above analysis and design methodology, a 30 kW three-phase D3L inverter fed open-end winding transformer prototype based on DSP TMS320F28377D controller is constructed, as shown in Figure 17. The D3L inverter is supplied by two rectifiers (DC Source 1 and 2) with the DC voltage *v*dc = 850 V. The switching frequency of the inverter is 5 kHz. For the OEW transformer, the phase voltage ratio is 364 V/380 V, the leakage inductance is about 0.025 p.u., we compensate it to 0.06 p.u. through adding extra inductors.

The designed parameters of the three kinds of filters tabulated in Table 2 are tested by experiment. Here the D3L inverter with different filters are divided into three cases, where Case-1 represents the D3L inverter with the Type-1 filter, Case-2 represents the D3L inverter with the Type-2 filter, and Case-3 represents the D3L inverter with the Type-3 filter. In addition, the experimental analysis is carried out in two operating modes. One is the two inverters of the D3L inverter working at the power balance mode. Another one is the two inverters of the D3L inverter working at the power unbalance

mode. Here, the power ratio of the two inverters is chosen as 3/2, corresponding to a relatively large imbalance ratio of 33.33%. Besides, to suppress the resonance caused by the high order filter, the filter based active damping method [36] is used here.

**Figure 17.** Experimental platform of the DI-OEWT grid-tied system.
