Power quality becomes the important problems of power systems recently due to the increase of the sensitive equipments to power qualities, such as personal computers and product facilities of semiconductors. Though the active filter is the most effective countermeasure for the power quality improvement, it cannot control the active power because its stored energy is too small. On the other hand, seeing form the AC system side, SMIES (Superconducting magnetic energy storage) with the voltage type inverter-converter unit has the same configuration as the active filter. Therefore, SMES can work as well as the active filter. The difference is its stored energy.
In this paper, using EMTP-ATP, the effect of the power quality improvement by SMES, such as the harmonics current compensation, voltage sag compensation, UPS and three-phase balancing, is examined. These functions are achieved by the basically same control system. Therefore, a couple of these functions are achieved at the same time. To make sure, SMES is modeled on EMTP by PWM converter, DC reversible chopper and inductance. The control system is presented on MODELS of EMTP-ATP. Thus the simulation results are made clear that the control system achieves a couple of these functions at the same time.
Next, the coil current of SMES is investigated when these functions are activated. To damp harmonics current and to balance three-phase components, it is found that the coil current is vibrating, because the output of SMES in each phase is different. Though the other functions such as voltage sag compensation and UPS need large energy, these functions do not need large energy. Nevertheless, even for the functions of harmonics current compensation and three-phase balancing, SMES should have amount of stored energy in order to damp the vibration in the coil current.