this link may help you.you just have to download the files, unzip  and run in matlab.

(http://in.mathworks.com/matlabcentral/fileexchange/index?utf8=%E2%9C%93&term=12+pulse+converter+type%3A%22Model%22)

of course, you gotta build it, unless you mean to model it, then you need the overall structure model - for each switching source and pwm or firing circuits... .like an integrator is a capacitor but represented as 1/s -unless you want to use somebody elses work the above link should work great