Static VAr Compensators (SVC) are power devices that can modify the reactive power in different ways, in order to compensate either reactive power or line voltages, depending on the application at hand. For instance, SVC include thyristor controlled reactors and thyristor controlled switched capacitors that can compensate reactive power produced by variable predominantly inductive/capacitive loads. Due to the increasing number of variable loads and the new regulations in the Mexican electrical grid, these devices have acquired the attention of the Power Quality firms such as Diram, S.A. de C.V. Therefore, they sponsored the industrial SVC controller development.In this thesis, it is developed a closed-loop implementation of an industrial SVC. It compensates for the reactive power under sinusoidal and balanced conditions using the quadrature currents as the feedback signal. Also, the main power theories found in literature are reviewedand it is presented a formal definition of the reactive power using an optimization problem with constrains. Then, it is used this formal definition to obtain the main AC power theories.