This paper investigates the performance of Dynamic Voltage Restorer for compensating different voltage sag levels with various faults and to reduce the Total Harmonic Distortion during the mitigation process. The DVR is implemented with three phase voltage source inverter and is connected at the point of common coupling in order to regulate the load side voltage. The compensation is based on PI and Mamdani Fuzzy Controller. Extensive simulation studies under different magnitude of sag for faults on load side for balanced and unbalanced conditions are conducted using fault generator. Simulation result analysis reveals that DVR performs perfectly with PI and Fuzzy control approach. In addition, capability and performance of DVR for various energy storage capacities and injection transformer rating are also analyzed. The performance of these controllers is validated with simulation results using Matlab/Simulink.
- Dynamic Voltage Restorer (DVR)
- Fuzzy Logic Controller (FLC)
- Total Harmonic Distortion (THD)
- Voltage Sag
Fig. 1. Block Diagram of DVR model
EXPECTED SIMULATION RESULTS:
Fig.2 Unbalanced three-phase to ground fault (PI CONTROL)
Figure 3. Unbalanced three-phase to ground fault (FLC)
Fig.4 Single-line-to-ground fault with 50% sag (PI Control)
Fig.5 Single-line-to-ground fault with 50% sag (FLC)
Fig.6 Balanced three-phase fault with 50% sag (PI CONTROL)
Fig.7 Balanced three-phase fault with 50% sag (FLC)
Fig.8 Three Phase fault with nearly 100% sag (PI)
Fig.9 Three Phase fault with nearly 100% sag (FLC)
The DVR handles both balanced and unbalanced conditions effectively and injects the deviated voltage component under supply disturbances to keep the load voltage balanced and constant at the nominal value. Thus the proposed DVR has the ability to mitigate various levels of voltage sag and different types of faults. Simulation results in MATLAB/SIMULINK prove that the control scheme provides an accurate tracking of the voltage reference and a very fast transient response. Both the controllers exhibits good performance and minimize the THD level. It is found that FLC gives better performance with THD of 0.42% where as PI gives 0.46% THD. The increase in KVA rating of injection transformer and DC storage value effectively compensates the voltage sag and reduce the THD level. However, higher value of DC storage and transformer rating makes it more expensive. The efficacy of a DVR system mainly depends upon the rating of DC storage capacity, injection transformer rating and the load. From the simulation, it clearly shows the importance of these factors and how it affects the performance of DVR is analyzed.
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