4.4 Discussion of the Simulation Results
The proposed system has been examined under balanced and unbalanced loading conditions for load levelling and balancing. Power quality disturbances are also mitigated using the proposed approach. The indirect current control (ICCT) theory is implemented to generate switching signals for the shunt connected DSTATCOM-based BESS, as illustrated in Figure 4.4.
Figure 4.4 MATLAB simulation of indirect current control theory controlled for the DSTATCOM-BESS system.
4.5 Results Analysis under a Balanced System
The proposed system is analyzed under a balanced system condition that considers linear, nonlinear, and induction motor loads for demonstrating the performance on harmonic eliminations. The system is analyzed for source voltage (Vs), terminal voltage (Vt), source current (Is), compensating current (Ic), load currents (Il), battery voltage (Vbb), and battery current (Ibb) based signals. The parameters under the system consideration are as follows:
Source: Vpeak = 415 V, 3-Phase, 50 Hz
Linear load: Resistiveload = 1000 Ω, Inductiveload = 1e−3H
Nonlinear load: Rectifier-based inductive load with Rload = 1000 Ω, Lload = 1e−3H
Induction motor load: Nominal power = 3730VA, 415 V, 50 Hz and Tm = 10, hysteresis controller band 0.1
Battery and controller parameter: VOC = 720 V, Rb1 = 0.1 Ω, Rb2 = 1000 Ω, Cb2 = 1688 F, Cdc = 5000 F, I*smd = 35
PI controller: Proportional constant = 043, Integrator constant = 0.15
4.5.1 Response of DSTATCOM-BESS under a Balanced Linear Load
The response of the DSTATCOM-BESS system with a balanced linear load is as depicted in Figure 4.5. The linear load varies from 1000 Ω to 1 Ω to test the battery charging operation. It has been perceived that the source voltage (Vs) and currents (Isa) are balanced and in-phase under the battery charging condition (Ibb). Load currents (Il) are observed to be balanced when keeping the balanced terminal at its reference voltage. Also during the operation the compensating current (Ic) is in balance and continuously provides the required current.
Figure 4.5 Response of DSTATCOM-BESS under a balanced linear load.
4.5.2 Response of DSTATCOM-BESS under a Nonlinear Load
The response of the DSTATCOM-BESS system with the nonlinear load is depicted in Figure 4.6. It has been visualized that the ICCT is initially fixed in the constant current control mode operation. Hence, the system’s other load is removed in order to demonstrate the off-peak condition and under this condition, batteries are now starting to charge. Also, due to efficient control, the reference voltage is regulated in order to maintain a constant charging current. It has also been seen that the DSTATCOM provides a compensating current to maintain the source current and voltage sinusoidal and is balanced by keeping the terminal voltage at its calculated reference voltage. Moreover, the source current harmonics and load current harmonics are illustrated in Figures 4.7 and 4.8 and are visualized at 0.44% and 30.31%, respectively, which shows the proposed system’s superiority.
Figure 4.6 Response of DSTATCOM-BESS under a nonlinear load.
Figure 4.7 Source side frequency spectrum.
Figure 4.8 Load side frequency spectrum.
4.5.3 Response of DSTATCOM-BESS under an Induction Motor (IM) Load
The response of the DSTATCOM-BESS system with an IM load is as depicted in Figure 4.9. It is well known that if Tm is positive, the machine operates as a motor, and if it is negative, the machine operates as a generator. Hence, the sign of the mechanical torque directs the mode of operation. It has been visualized that the motor takes a large starting current at the time of starting. Accordingly, DSTATCOM injects the compensating current to maintain the voltage at PCC and current sinusoidal. During this condition, the terminal voltage is also kept at its reference voltage and the battery starts charging. Also, the grid side and load side harmonics are depicted in Figures 4.10 and 4.11, respectively. The obtained harmonics are well below the international standard IEEE519-2014. Moreover, Table 4.1 illustrates the harmonics-based comparative analysis of all considered loads. The perceived results establish the performance of the DSTATCOM-BESS system.
Figure 4.9 Response of DSTATCOM-BESS under an induction motor load.
Figure 4.10 Source side frequency spectrum.
Figure 4.11 Load side frequency spectrum.
Table 4.1 Harmonics analysis under balanced loads.
| S. No. | Type of load | Indirect current control theory controlled DSTATCOM-BESS | |
|---|---|---|---|
| Source side THD | Load side THD | ||
| 1 | Linear load | 0.57% |
|