ISSN 1905-7873 Â© 2012 - Maejo International Journal of Science ...

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20 Maejo Int. J. Sci. Technol. 2012, 6(01), 12-27 1000 v ab (V) 0 -1000 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 20 i ga (A) 0 -20 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 10 i rla (A) 0 -10 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 10 i ca (A) 0 -10 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 V dc (V) 800 600 400 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 Time(sec) Figure 4. Performance characteristics of SEIG-STATCOM (cost-effective) system with 0.8-pf static R-L load (Load conditions : 2.2 kW at 2.5 sec., 3.0 kW at 3.0 sec. and 2.2 kW at 3.5 sec.) 1000 v ab (V) 0 -1000 2.4 2.6 2.8 3 3.2 3.4 3.6 20 i ga (A) 0 -20 2.4 2.6 2.8 3 3.2 3.4 3.6 10 i rla (A) 0 -10 2.4 2.6 2.8 3 3.2 3.4 3.6 10 i ca (A) 0 -10 2.4 2.6 2.8 3 3.2 3.4 3.6 800 V dc (V) 600 400 2.4 2.6 2.8 3 3.2 3.4 3.6 Time(sec) Figure 5. Performance characteristics of SEIG-STATCOM (full rating) with 0.8-pf static R-L load (Load conditions: 2.2 kW at 2.5 sec., 3.0 kW at 3.0 sec., and 2.2 kW at 3.5 sec.)
Maejo Int. J. Sci. Technol. 2012, 6(01), 12-27 21 1000 v abc (V) 0 -1000 20 3 3.2 3.4 3.6 3.8 4 4.2 i rlabc (A) i gabc (A) i cabc (A) V dc (V) 0 -20 10 0 -10 5 0 -5 750 700 650 3 3.2 3.4 3.6 3.8 4 4.2 3 3.2 3.4 3.6 3.8 4 4.2 3 3.2 3.4 3.6 3.8 4 4.2 3 3.2 3.4 3.6 3.8 4 4.2 Time(sec) Figure 6. Performance characteristics of SEIG-STATCOM (cost-effective) with unbalanced 0.8-pf R-L load (Load conditions: 3-φ load (2.2 kW, 3.0 kW, 1.0 kW) at 3.0 sec.; load (2.0 kW, 3.0 kW, unloading on ‘c’ phase) at 3.5 sec; and balanced 3-φ loading of 2.2.0 kW at 4.0 sec.) Performance with Motor Load The performance characteristics of the system during the starting and sudden loading of an induction motor are shown in Figures 7 and 8 for cost-effective and full-rating STATCOM respectively. The motor at no load was switched on at 3.0 sec. and was loaded at 4.0 sec. During the starting of the motor, excessive reactive VAR were drawn and therefore the V dc dropped to 300V level with both STATCOM. The V dc quickly rose above the reference 700V before returning to reference level after replenishing the charge on DC bus capacitor. At starting, the transients in v ab , i ga , i ma , T emm and V dc were more visible with cost-effective STATCOM due to its lower rating and the uncharged capacitor connection across the motor load terminals. Because of a lower compensation level, the i ca under steady state was lower compared to the corresponding value with full-rating STATCOM. With cost-effective STATCOM, the SEIG voltage decreased by 10% and the transients were settled in 0.5 sec., whereas these values were 6% and 0.4 sec. respectively for full-rating STATCOM. Without STATCOM, as shown in Figure 3, the decrease in SEIG voltage was 30%. The motor was loaded with rated load torque at 4.0 sec. After small transients, the system response changed accordingly. The increase in i ga , i ma , and T emm and the decrease in rm were observed. The V dc decreased to 670V before returning to steady-state reference value of 700V. The performance of SEIG-IM configuration was compared in the presence and absence of STATCOM and the key parameter indices of the system are summarised in Table 3. The total harmonic distortion (THD) was obtained through fast Fourier transform (FFT) using discrete Fourier transform (DFT) algorithm of MATLAB. The generator-side THD values were within a permissible level, which demonstrated a satisfactory overall system performance.
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