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High-Frequency Isolation Solution for DC distribution Data Center

Fig. 1. Proposed power architecture for future data center.
In both AC and DC data center power architectures, a line-frequency transformer is employed to step-down a medium voltage AC to 480VAC and distribute 480VAC throughout the facilities. With the ever-increasing power consumption of mega data centers, the 480 V AC lines presently carry thousands of amperes of current. This leads to a very bulky and costly transmission bus and large conduction losses within the data center. We propose to utilize a 4.16 kV AC medium voltage line as the distribution bus within the data center facilities, followed by low-voltage solid-state transformers (SST) in a cascade configuration, as shown in Fig. 1. Five cascade H-bridge converters together with high-frequency isolation DC/DC converters are employed to convert medium voltage directly into 380VDC. The inputs of the H-bridges are in series, and the outputs of the DC/DC stages are connected in parallel, as shown in Fig. 2.

With the advent of the new generation of SiC and GaN devices, we propose to operate the DC/DC stage at an unprecedented high frequency: 500 kHz, which is 25 times higher than industry state-of-the-art SSTs. At 500 kHz, the selection of WBG devices and converter topologies are critical. A novel bi-directional CLLC resonant converter will be employed, instead of the popular back-to-back connected dual-active bridge. Each DC/DC module will be designed to handle 15-20kW power.

In order to reduce secondary-side conduction loss, two output sets are paralleled to handle the high output current, as shown in Fig. 3.

For such a 4160V AC to 380V DC system, insulation is critical for the overall system. This function is implemented by the isolated DC/DC converter. Since the insulation design for this high-frequency transformer is crucial, we propose using a sectionalized coil structure to guarantee enough clearance and creepage distance between the primary and secondary windings.

Fig. 2. Three-phase solid state transformer (SST) system.
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