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Research was conducted on reduction of circuit inductance for the purpose of reducing the surge voltage generated during switching by FET (field effect transistor / semiconductor device) in the power modules of motor controllers for golf carts (Fig. 1) and other electric vehicles.
The motor control system is composed of the battery, the motor controller, the motor, and the wirings that connect them, and the inductance exists in them altogether.
It became clear from simulation analysis and measurements from a prototype that only the inductance within the motor controller among these composition parts influences the surge voltage. And it became clear that there is a correlation between surge voltage and the sum of the inductance of the electrolytic capacitor inside the power module and the inductance of the circuit by which current is supplied from the electrolytic capacitor to the FET.
Therefore, circuit inductance was successfully reduced by reducing the parasitic inductance of the patterns by employing a laminated structure for the power source patterns, while also minimizing the length of the bonding wires of the COB (chip on board) mounted FETs, on a metal-based circuit board serving as a component of the power module.
These measures in combination with reducing the inductance at the location where the electrolytic capacitor is mounted made it possible to reduce surge voltage to roughly one-half the level of conventional power modules.