The block parameters are different because the Universal Bridge block and the MOSFET block use two different models for the MOSFET device.
When you are using the MOSFET block as a single device, you have to specify the Ron, Lon, Rdiode, and initial current for the device. The single device is modeled as a RL branch in series with a switch that is turned on and off by a logical circuit that mimics the behavior of the MOSFET and its anti-parallel diode.
When you use the Universal Bridge block with the MOSFET as the switching device, you only need to specify the Ron parameter. In this case, the MOSFET is modeled by a resistor in series with a switch. The inductance is not modeled, as it is not really required for the bridge configuration. The difference is also in the logical circuit that controls the switches. Because you know that the MOSFETs are in a bridge configuration, take into account the complementary diodes:
1) Diodes are blocked when complementary MOSFETs are switched on
2) When no snubber capacitances are used (Cs=inf), diodes are triggered when complementary MOSFETs are swithed off
This allows you to better represent a bridge configuration.
In practice, consider the two models almost identical. The behavior of a MOSFET in a Universal bridge block should be the same as the behavior of the single device block.
