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Control of Three-phase UPS with Nonlinear Load Using Disturbance Observer Considering Transformer Concerns

Shahriari, Zohair | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53210 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Tahami, Farzad
  7. Abstract:
  8. Nowadays, non-linear loads comprise an important part of electrical grids. One of the most essential sources of nonlinear loads is switching power supplies, which mainly include power electronic rectifiers. When power outage occurs, Uninterruptible Power Supplies (UPS) must be able to supply these loads. The nonlinearity of the load has a significant effect on the Total Harmonic Distortion (THD) of the output voltage, which may not be easily reduced, especially in three-phase inverters. Furthermore, the presence of isolating transformers in these power supplies limits the control of harmonics and intensifies the nonlinear effects of the system.In this Master Thesis, a disturbance observer is used to eliminate the effect of nonlinear load on uninterruptible power supply. The disturbance observer not only eliminates the nonlinear dynamics of load and transformer, but also makes the control system robust enough to load changes. The disturbance observer that is widely used in robotics is a device to remove disturbances. In linear control methods, the output load current is considered as disturbance and this causes the reduction of the output voltage quality. Using the disturbance observer, output load current is estimated and is added to the system input with a reverse sign. Using the proposed method and proper design of the disturbance observer filters, voltage THD is significantly reduced. The optimal filter design, the selection of the winding arrangement and the appropriate structure for the isolating transformer should be considered in the design of the system. Both simulation and experimental results verify the validity of the optimal filter design and the proposed control strategy using disturbance observer to limit the nonlinear dynamics and disturbances on UPS
  9. Keywords:
  10. Uninterruptible Power Supplies ; Transformers ; Disturbance Observer ; Total Harmonic Distortion ; Nonlinear Load

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