ABSTRACT:
At present, the disturbances like the voltage fluctuations, resulting from the grid's complexities and unbalanced load conditions, create severe power quality concerns like total harmonic distortion (THD) and voltage unbalance factor (VUF) of the grid voltage. Though the custom power devices such as distribution-static compensators (D-STATCOMs) improve these power quality concerns, however, the accompanying controller plays the substantial role. Therefore, this paper proposes a fractional-order sliding mode control (FOSMC) for a D-STATCOM to compensate the low power distribution system by injecting/absorbing a specific extent of the reactive power under disturbances. FOSMC is a non-linear robust control in which the sliding surface is designed by using the Riemann-Liouville (RL) function and the chattering phenomenon is minimized by using the exponential reaching law. The stability of FOSMC is evidenced by employing the Lyapunov stability criteria. Moreover, the performance of the proposed FOSMC is further accessed while doing its parametric variations. The complete system is demonstrated with a model of 400V, 180kVA radial distributor along with D-STATCOM under two test scenarios in MATLAB/Simulink environment. The results of the proposed controller are compared with the fixed frequency sliding mode control (FFSMC) and conventional proportional-integral (PI) control. The results validate the superiority of the proposed controller in terms of rapid tracking, fast convergence, and overall damping with very low THD and VUF.
KEYWORDS:
1. Power
quality
2. Custom
power devices
3. Distribution
static compensator
4. Fractional
order
5. Sliding
mode control
6. Total
harmonic distortion
7. Voltage
unbalance factor
SOFTWARE: MATLAB/SIMULINK
SCHEMATIC DIAGRAM:
Figure 1. Simplified Model Of D-Statcom Configuration.
EXPECTED SIMULATION RESULTS:
Figure 2. (A) Three-Phase Voltage
At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid (B) Rms Voltage At Lv Ac Bus
Under Voltage Sag/Swell Of Main Grid (C) Load Active And Reactive Power Under
Voltage Sag/Swell Of
Main
Grid.
Figure 3. (A) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Pi Control (B) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Pi Control (C) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Ffsmc (D) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Ffsmc (E) Three-Phase Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Fosmc (F) Rms Voltage At Lv Ac Bus Under Voltage Sag/Swell Of Main Grid With D-Statcom While Employing Fosmc.
Figure 4. (A) Load Active And
Reactive Power Under Voltage Sag/Swell With D-Statcom While Employing Pi
Control (B) Load Active And Reactive Power Under Voltage Sag/Swell With
D-Statcom While Employing Ffsmc (C) Load Active And Reactive Power Under
Voltage Sag/Swell With D-Statcom While Employing Fosmc.
Figure 5. (A) Injected/Absorbed
Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Pi Control
(B) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell While
Employing Ffsmc.
Figure 6. (A) Injected/Absorbed
Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Fosmc With
_ D 0:2 And Kd , Kq D 5 _ 106 (B) Injected/Absorbed Reactive Power By D-Statcom
Under Voltage Sag/Swell While Employing Fosmc With _ D 0:5 And Kd ; Kq D 5 _
106 (C) Injected/Absorbed Reactive Power By D-Statcom Under Voltage Sag/Swell
While Employing Fosmc With _ D 0:8 And Kd , Kq D 5 _ 106 (D) Injected/Absorbed
Reactive Power By D-Statcom Under Voltage Sag/Swell While Employing Fosmc With
_ D 0:5 And Kd , Kq D 3 _ 104:
CONCLUSION:
In this paper, the authors have proposed a FOSMC based DSTATCOM to compensate the low power distribution system under disturbances such as voltage sag/swell and unbalanced load conditions. Besides, the performance of the FOSMC under its parametric variations is discussed as well. The complete system is demonstrated with a model of 400V, 180kVA radial distributor along with D-STATCOM under two test scenarios in MATLAB/Simulink environment. In the first test scenario, the grid transients (voltage sag/swell) are considered at the LV AC bus. Likewise, in the second test scenario, the unbalanced load conditions are considered at the LV AC bus. D-STATCOM sustains the voltage at LV AC bus by injecting/absorbing a certain extent of reactive power under voltage sag/swell and unbalanced load conditions. The results of the proposed controller are compared with fixed frequency sliding mode control (FFSMC) and conventional proportional-integral (PI) control. The results validate the superiority of the proposed controller in terms of rapid tracking, fast convergence, and overall damping with very low THD, and VUF. In the first test scenario, the voltage THD of proposed FOSMC during voltage sag/swell results in 0.52% in contrast to FFSMC and PI control which have THD of 0.84% and 2.17% respectively. In the second test scenario, the voltage THD of proposed FOSMC during unbalanced load conditions results in 0.97% in contrast to FFSMC and PI control which have THD of 1.96% and 3.63%. Likewise, the VUF under unbalanced load conditions with proposed FOSMC is 0.0014% in contrast to FFSMC and PI control which have VUF of 0.02% and 0.71%. In terms of assessment with existing SMC schemes, the proposed FOSMC has a very high response time, very high accuracy, very high robustness, lowest chattering along with low THD and VUF. The proposed model could be realized on the hardware platform for real-time verification purposes in future applications.
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