4.6 Results Analysis under an Unbalanced System
4.6.1 Response of DSTATCOM-BESS under an Unbalanced Linear Load
The response of the DSTATCOM-BESS system with an unbalanced linear load is as depicted in Figure 4.12. The unbalancing in the linear load starts from 0.25 seconds to 0.5 seconds. The intention of load unbalancing (Il) from three-phase to two-phase and then to one-phase and again reverse illustrates the proposed BESS-based system’s performance. It has been perceived that the source voltage (Vs) and current (Is) are balanced and in-phase during and after the unbalancing. The battery charging is slightly disturbed during unbalancing but maintains a continuous charge (Ibb). The whole operation compensates the current (Ic) from the DSTATCOM continuously injected while keeping the balanced terminal voltage (Vt) at its calculated reference voltage. Also the source and load side current are visualized in Figures 4.13 and 4.14.
Figure 4.12 Response of DSTATCOM-BESS under an unbalanced linear load.
Figure 4.13 Source side frequency spectrum.
Figure 4.14 Load side frequency spectrum.
4.6.2 Response of DSTATCOM-BESS under an Unbalanced Nonlinear Load
The response of the DSTATCOM-BESS system with an unbalanced nonlinear load is as depicted in Figure 4.15. At 0.25 seconds, the three-phase load is transformed to two-phase, and at 0.3 seconds, one-phase and loads are disconnected at 0.35 seconds. The d component of currents is fixed at 35 A. The proposed BESS system supports load levelling and balancing during these loading conditions. The connected nonlinear load is again connected in the same sequence at 0.4, 0.45, and 0.5 seconds. It has been seen that the DSTATCOM provides a compensating current to maintain the source current and voltage sinusoidal and is balanced when keeping the terminal voltage at its calculated reference voltage. Moreover, the source current harmonics and load current harmonics are illustrated in Figures 4.16 and 4.17 and are visualized at 0.19% and 30.31%, respectively, which shows the proposed system’s superiority.
Figure 4.15 Response of DSTATCOM-BESS under an unbalanced nonlinear load.
Figure 4.16 Source side frequency spectrum.
Figure 4.17 Load side frequency spectrum.
4.6.3 Response of DSTATCOM-BESS under an Unbalanced IM Load
The response of the DSTATCOM-BESS system with an unbalanced induction motor (IM) load is depicted in Figure 4.18. It has been visualized that it draws a heavy inrush of current, leading to voltage disturbances. These disturbances were effectively minimized using the proposed DSTATCOM-BESS system by injecting the dynamic reactive power at PCC to regulate the voltage. Similar to previous loading conditions, load unbalancing is created, and it was found that the PCC voltage remains constant during an IM load. During this condition, the terminal voltage is also kept at its reference voltage and the battery starts charging. The grid side and load side harmonics are depicted in Figures 4.19 and 4.20, respectively. The obtained harmonics are well under the international standard IEEE519-2014. Moreover, Table 4.2 illustrates the harmonics-based comparative analysis of all considered loads. The perceived results reveal the performance of the DSTATCOM-BESS system.
Figure 4.18 Response of DSTATCOM-BESS under an unbalanced motor load.
Figure 4.19 Source side frequency spectrum.
Figure 4.20 Load side frequency spectrum.
Table 4.2 Harmonics analysis under load unbalancing.
| S. No. | Type of load | Indirect current control theory controlled DSTATCOM-BESS | |
|---|---|---|---|
| Source side THD | Load side THD | ||
| 1 | Linear load | 0.71% | 0.71% |
| 2 | Nonlinear load | 0.19% | 30.25% |
| 3 | Motor load | 0.31% | 2.43% |
4.7 Conclusion
An indirect current control theory-based control algorithm has been strongly performed for DSTATCOM-BESS to improve power quality in the presence of balanced/unbalanced linear, nonlinear, and induction motor loads. The sudden changes associated with the active power and reactive power, the dc-link voltage, have been considered in designing the ICCT controlled DSTATCOM-BESS system. The particularized working boundaries of the dc-link voltage in the control algorithm ensure the DSTATCOM reliable operation, which protects the inverter during large load fluctuations. The proposed system has been used to solve the challenges associated with the loading conditions of the distribution network. It has been verified that the system’s power quality is mitigated under the IEEE-519-2014.
References