Introduction of Multi-functional Power Quality Improvement Energy Storage System to Power Systems

近年来，由于对电能质量敏感的设备如个人计算机和半导体生产设备的增加，电能质量成为电力系统的重要问题。虽然有源滤波器是改善电能质量最有效的措施，但由于其储能太小，无法控制有功功率。另一方面，从AC系统侧来看，具有电压型逆变器-转换器单元的SMIES（超导磁能量存储）具有与有源滤波器相同的配置。因此，SMES可以像有源滤波器一样工作。本文利用EMTP-ATP软件，对超导储能系统（SMES）的谐波电流补偿、电压暂降补偿、UPS和三相平衡等改善电能质量的作用进行了研究。这些功能通过基本相同的控制系统来实现。因此，这些功能可以同时实现。为了保证SMES的可靠性，在EMTP上建立了由PWM变换器、直流可逆斩波器和电感组成的SMES模型。该控制系统基于EMTP-ATP模型。仿真结果表明，该控制系统同时实现了上述几种功能。接下来，研究了这些功能被激活时超导磁储能系统线圈电流的变化规律。为了抑制谐波电流和平衡三相分量，发现由于超导磁储能系统各相输出功率不同，线圈电流是振荡的。虽然其他功能，如电压骤降补偿和UPS需要大量的能量，这些功能并不需要大量的能量。然而，即使是谐波电流补偿和三相平衡功能，超导磁储能系统也应该有一定的储能量，以阻尼线圈电流的振荡。

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.