difference between simulink models composed of simulink library components and self-built ones

Hi everyone,

I have a question about MATLAB simulink modeling. Take the generator as an example. Basically you can use components from simpower library to build the generator. Or you can build it according to i.e. the four order dynamic equations by using s-function. For a single-machine system. The difference is not so big in respect with the controllability. However, if you build a multi-machine system, like a power system. Here comes the question. After adding controllers on this mathematic-equation based power system.the simulation runs very slowly! I AM NOT SURE the feasibility of this hand-building method. I once thought of replacing 4-order with higher order more complete ones or using more complex controllers. Actually this further increases the computation time. I want to know how to design this kind of multi-order systems using s function and at the same time improve its simulation efficiency.Thanks!