Journal of the Korean Solar Energy Society (한국태양에너지학회 논문집)

The Korean Solar Energy Society (한국태양에너지학회)
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Optimal Design of Notch Filter in Photovoltaic Inverter

태양광 인버터의 노치 필터 최적 설계

  • Received : 2019.03.27
  • Accepted : 2019.04.26
  • Published : 2019.04.30
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Abstract

When Photovoltaic inverter is connected to grid and used as PVPCS (Photovoltaic Power Conditioning System), 120 Hz AC ripple occurs at the dc-link capacitor voltage. This AC ripple reduces the efficiency of PVPCS and shortens the lifetime of the capacitor. In this paper, we design a notch filter to remove AC ripple. As a result, the AC voltage ripple was removed from the dc link and the THD of the PVPCS output current with the notch filter was lowered. This notch filter is determined by the damping coefficient, the bandwidth coefficient, and the switching frequency. Among these, the switching frequency determines the switching loss and the size of the LC filter, and the PVPCS with the high switching frequency has a greater efficiency loss due to the switching loss than the efficiency improvement by the notch filter. Therefore, it is important to set the optimum switching frequency in the PVPCS with the notch filter applied. In this paper, THD and switching loss of PVPCS output current with notch filter are calculated through simulation, and cost function to calculate optimum switching frequency through data is proposed.

Keywords

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Fig. 1 Configuration of residential single-phase PVPCS

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Fig. 2 The bode plot of Notch filter

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Fig. 3 The bode plot of notch filter according to d

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Fig. 4 The bode plot of notch filter according to c

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Fig. 5 Simulation circuit of the single-phase PVPCS

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Fig. 6 Control block diagram of single-phase PVPCS

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Fig. 7 Voltage & Current control block diagram of single-phase PVPCS

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Fig. 8 Dc-link voltage waveform of reference, without and with notch filter

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Fig. 9 Ids, Iqs waveform of without and with notch filter

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Fig. 10 Output current waveform of without and with notch filter

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Fig. 11 FFT analysis of output voltage according to switching frequency

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Fig. 12 Output current waveform according to switching frequency

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Fig. 13 Switching loss waveform according to switching frequency

Table 1 The depth of the notch filter according to the value of d

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Table 2 The bandwidth of the notch filter according to the value of c

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Table 3 THD of output current according to switching frequency

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Table 4 Switching loss value according to switching frequency

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References

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  3. Kotato, H., Design of Digital Notch Filters, IEEE Transactions on Communications, Vol. COM-22, No. 7, 1974.
  4. Yang, S. D., The Compensation of the Grid Current Distortion caused by the Grid Voltage Unbalance and Distortion for 3-Phase Bi-Directional DC to AC Inverter, Journal of the Korean Solar Energy Society, Vol. 32, No. 3, pp. 228-234, 2012. https://doi.org/10.7836/kses.2012.32.spc3.228
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