Power Modules for Dual Active Bridge DC-DC Converters

Dual active bridge (DAB) converters have become a standard choice wherever a design needs galvanic isolation and power flow in both directions: DC fast chargers, battery energy storage, and solid-state transformer stages. The topology is simple on paper, but its efficiency, switching frequency, and thermal margin are set almost entirely by the power modules in the two bridges.

At HIITIO, we design and manufacture IGBT modules, SiC modules and gate drivers for these applications. This article walks through how a DAB loads its modules, what published reference designs show, and how to match a module and driver to your own converter.

How a DAB Converter Loads Its Power Modules

A DAB connects two full bridges through a high-frequency transformer and a series inductance, often supplied by the transformer’s leakage inductance. According to Texas Instruments’ application note on the topology, the direction and amount of power are set by the phase angle between the two bridges, and one bridge’s lagging current helps achieve zero-voltage turn-on (ZVS). That gives the modules three practical requirements:

• Both bridges are working bridges. Because power can reverse, the modules on each side must be rated for full current and loss, not only the load side.
• Soft switching is not guaranteed. A study in IEEE Transactions on Power Electronics shows that ZVS range can be lost at light load under phase-shift control, especially when one port runs at high voltage. Switching losses at light load therefore still matter.
• Modulation affects the stress. Extended, dual and triple phase-shift schemes can widen the ZVS range, but they change the RMS current and turn-off current the modules see.

Why SiC Modules Suit DAB Designs

SiC MOSFET modules are widely used in DAB stages for several reasons:

• Higher switching frequency. Lower switching loss allows higher frequency, which shrinks the transformer and inductor. ST’s 25 kW reference design cites passive-component size and weight reduction as a direct benefit of high-frequency SiC operation.
• No tail current. MOSFET turn-off is faster and cleaner than IGBT turn-off, which helps when ZVS is partially lost.
• Thermal headroom. Junction temperatures up to 175 °C, as listed on HIITIO’s SiC module pages, widen the design margin.

IGBT modules remain reasonable at lower frequencies and cost-sensitive high-power designs. For the broader device trade-offs, see HIITIO’s guide to SiC vs IGBT vs MOSFET for solid-state circuit breakers.

Table 1. Published DAB Designs and the Modules They Use

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FAQ

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SiC modules switch with lower loss and without tail current, which allows higher frequency and smaller magnetics. IGBT modules can still be a sound choice at lower frequencies where cost dominates.

What voltage class should I choose for an 800 V DAB?

ST’s 25 kW reference design uses 1200 V SiC modules with an 800 V nominal input. If your bus is higher or you need more margin, evaluate 1700 V devices such as the HCS400FH170A2C1.

How many power modules does a DAB need?

Each full bridge needs four switches. With half-bridge modules, that means two modules per bridge and four for a single-phase DAB, unless a full-bridge module is used.

Can a DAB lose soft switching?

Yes. Under phase-shift control, ZVS can be lost at light load or large voltage mismatch. Advanced modulation can extend the range, and module switching characteristics still matter in those conditions.

Which gate driver should I use with HIITIO SiC modules?

It depends on your switching frequency and gate power. HIITIO’s standard core and plug-and-play drivers are specified up to 30 kHz, so higher-frequency designs should be reviewed with our engineering team.