In MATLAB R2016a, the simPowerSystems toolbox has been renamed to Simscape Power Systems. Here's how you can open Simscape Power Systems in MATLAB R2016a (a valid license needed):
In R2016a you can access the Simscape Power Systems library by typing pe_lib or powersys (for Specialized Technology) in the MATLAB Command Window and pressing Enter. Alternatively, in the library browser, go to Simscape > Power Systems.