Resumen
The calculation of variations initially it was a technique that was born in the field of physics and its great contributions have been taken advantage of by the engineering sciences in problems that involve finding a minimum trajectory that minimizes time, energy among other variables of interest. The following document will show how to find an optimal control law in order to minimize the time to bring the system that in this case is a direct current motor from a known initial state to a desired final state, using the Bang-control technique. Bang In direct current motor, the variables to be controlled are the field current, the input voltage and the angular velocity developed by the motor. For all the above, the control technique is not only innovative but also useful and practical for energy systems.