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Optimal Design of Output Filter for Low Switching Frequency Multi Level Inverter Based Medium Voltage Induction Motor Drive

Hafezi, Yosef | 2025

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57863 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Zolghadri, Mohammad Reza
  7. Abstract:
  8. In recent years, the use of variable-speed electric drives has gained increasing importance due to their ability to improve the technical performance of systems. However, the rectangular pulses of the inverter's output voltage in these drives introduce challenges such as current ripple, additional losses in the motor and cables, electromagnetic interference, overvoltage on the stator windings, and acoustic noise. Furthermore, the high dv/dt at the motor terminals reduces the motor insulation's lifespan and, when long cables are used to feed the motor, can lead to increased overvoltage at the motor terminals. To address all the aforementioned issues and achieve an appropriate voltage quality at the motor input, the use of a sine wave output filter has emerged as a practical solution in the industry. This thesis focuses on the optimal design of a sine wave filter for a medium-voltage induction motor powered by a low-switching-frequency multilevel inverter. In this process, issues related to resonance and instability are also considered, and based on a novel criterion, the structure and components of a suitable filter are designed. The proposed approach utilizes a genetic algorithm, component modeling, and a cost function that incorporates voltage and current total harmonic distortion (THD), filter parameter costs, and damping resistance losses. Additionally, constraints such as voltage drop across the inductor and damping resistance losses are considered to select the optimal filter configuration. The design results in a sine wave filter with a reduced rf (the ratio of the inverter switching frequency to its resonant frequency). Consequently, the filter's resonant frequency is increased, leading to smaller inductor and capacitor sizes while ensuring improved voltage quality for the motor across all operating frequencies. The impact of cable length on overvoltage at the motor terminals is also separately investigated. Simulations confirm the optimal design of the filter and validate the modeling approach used in the optimization process
  9. Keywords:
  10. Multilevel Inverter ; Optimization ; Filter Parameters ; Low Switching Frequency ; Medium Voltage Induction Motor ; Sine Wave Filter

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