HV Precharge & Bus-Sequencing Controller

One rig hosted an 11 kW three-port triple active bridge (TAB) converter — 300–700 V input, 890–1250 V high-voltage output, and 36–48 V low-voltage output — researched for 1.25 kV on-board-charger and 48 V auxiliary-power-module applications. Both rigs needed a controlled way to bring their DC links up from a stiff high-voltage source.

A converter's DC-link capacitance starts at 0 V. Closing a contactor straight onto the source puts the full bus voltage across only the wiring and capacitor ESR, so the inrush is limited by a few milliohms — enough to weld contactor tips, blow fuses, and stress the capacitors. A precharge path inserts a resistor first:

Peak current becomes $V_{bus}/R$, and the link reaches over 99 % of the bus after about $5\tau = 5RC$. Sizing the resistor is a trade between that charge time, the peak current, and the resistor's pulse-energy rating — the stored energy $\tfrac{1}{2}CV_{bus}^2$ is dissipated in it during every precharge.

The Arduino sequences the rig in a fixed order — precharge the DC link through the resistor, switch the bus over to the main path, then run — and an emergency stop de-energizes the rig from any stage.