(b)
Fig. 9 . VCM operation of DSTATCOM (a) Source voltage (b) Load voltage
Fig. 9 shows the VCM operation of DSTATCOM under voltage unbalance condition. It is seen from fig 9 (a) that an unbalance in the source voltage is applied from 0.2 to 0.45 seconds. At this time interval the RMS value of source voltage in phase a, b, c are found to be 208V, 235V, 253V with an unbalance factor of 11.25%. This unbalance in voltages is removed by use of DSTATCOM at the load side and it is seen that the load voltage is still maintained at 1 p.u. even if the source voltage is unbalanced. Fig.10 (a) shows the RMS value of source voltage and fig. 10(b) shows the RMS value of load voltage. It is observed that the load voltages are maintained at 1 p.u. in all the three phases even though the source voltage is unbalanced.
Fig. 11 shows the operation of Dual Function DSTATCOM which works in both condition i.e. in CCM and VCM. From fig 11(a) it is seen that during normal operation, DSTATCOM works in CCM mode of operation i.e. it maintains the source current sinusoidal and in phase with the load current. This can be seen in fig. 11(b). Now, after 0.2s the voltage unbalance is experienced in the system and during this period the source current becomes highly unbalanced as seen in fig 11(a).