STATCOM is an effective equipment to operate electric power system flexibly. But further development of STATCOM is expected such as lower loss and the active filter operation etc.Authors are also developing STATCOM using the new inverter system that consists of series connected three inverters with different output voltage. Figure 1 shows the system configuration and operation. We call this "Inverter System with Controlled Gradational Voltage", and it aims at highly effective and low harmonic component.However, there is a problem that the entire system control becomes complex because three inverters are cooperatively operated by a suitable method for the application, and the energy adjustment of individual DC power is also necessary.
Fig. 1. System configuration and operationTo these problems, we select these method that only the inverter of smallest capacity operates by high switching frequency, and that STATCOM output negative sequence current corresponding to no equilibrium of the system voltage to adjust the voltage of the capacitor.By use of the proposed control technique, we made the prototype of 3-phase 200 V class STATCOM. It was tested about power factor improvement and a harmonics current suppression. Figure 2 and Fig. 3 shows the examination result. We confirmed right operation of STATCOM from these result.
SUMMARYThis paper presents the STATCOM using the new concept of an inverter system which consists of three inverter units connected in series, and each inverter unit generates a different input voltage such as V C , 2V C , 4V C .This inverter system can output a high-quality voltage by a low-frequency switching oper ation. Thus, it can combine low loss and high quality. In this paper, we show the technique to apply STATCOM which uses the inverter system, and examination results.
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