# Droop Control Strategy of Utility-Scale Photovoltaic Systems Using Adaptive Dead Band

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## Abstract

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^{®}E program to analyze the short term voltage stability and display the results for various dead bands. The proposed modeling and operational strategy are validated in simulation using a modified IEEE 39 bus system. The results provide useful information, indicating that the control scheme through an adaptive dead band enables more stable system operation than that through a fixed dead band.

## 1. Introduction

- Estimation of required reactive power for each bus in the transmission system through the calculation of voltage sensitivity in an offline study.
- Achievement of more accurate voltage regulation between the DGs and plant controller by using the adaptive dead band strategy.
- Provision of a suitable solution to the voltage problem by injecting an accurate reactive power into each POI.
- Achievement of flexibility and redundancy using the architecture, even with unforeseen network topology changes.

## 2. Reactive Power–Voltage Droop Control Method

#### 2.1. Conventional Reactive Power–Voltage Droop Control Method

- If the voltage drops significantly when the system strength is weak, it is difficult to recover the voltage because sufficient capacitive reactive power is not supplied owing to a fixed dead band.
- If an overvoltage occurs when the system strength is strong, an overshoot appears because sufficient inductive reactive power is not produced because of the use of a fixed dead band.
- An unnecessary converter operation may occur frequently because of the voltage fluctuations.
- Frequent switching for multiple converters to deal with power quality issues may even cause resonance and transient overvoltage.

#### 2.2. Proposed Reactive Power–Voltage Droop Control Method

## 3. Simulation Study and Analysis

#### 3.1. System Description

#### 3.2. System Disturbance

- Small disturbance: Network voltage is maintained within the range of 0.95–1.05 p.u after disturbance
- Large disturbance: Network voltage is out of the voltage maintenance range after disturbance

#### 3.3. Simulation Results

## 4. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## Appendix A

## References

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**Figure 13.**(

**a**) Voltage profile, and (

**b**) reactive and (

**c**) active power result obtained by large disturbance.

Nomenclature | Description |
---|---|

${Q}_{branch}$ | Regulated branch initial reactive power flow (p.u) |

${K}_{c}$ | Reactive droop (p.u) |

${V}_{reg}$ | Regulated bus voltage (p.u) |

${T}_{fltr}$ | Voltage and reactive power filter time constants (s) |

${V}_{ref}$ | Regulated bus initial voltage (p.u) |

${e}_{max}$ | Maximum Volt/VAR error (p.u) |

${e}_{min}$ | Minimum Volt/VAR error (p.u) |

${K}_{p}$ | Volt/VAR regulator proportional gain |

${K}_{i}$ | Volt/VAR regulator integral gain |

${Q}_{max}$ | Maximum plant reactive power command (p.u) |

${Q}_{min}$ | Minimum plant reactive power command (p.u) |

${T}_{ft}$ | Plant controller Q output lead time constant (s) |

${T}_{fv}$ | Plant controller Q output lag time constant (s) |

${Q}_{ext}$ | Reactive power command from plant controller (p.u) |

Parameter | Small Disturbance | Large Disturbance |
---|---|---|

${t}_{\mathrm{rise}}$ (s) | <1–30 | <0.2 |

Overshoot (%) | <5 | <3 |

Stability Indicator(SI) | <0.0 | <0.05 |

Parameter | Dead Band (p.u) | ||
---|---|---|---|

0.02 | 0.04 | 0.06 | |

${t}_{\mathrm{rise}}$ (s) | 0.161 | 0.162 | 0.163 |

Overshoot (%) | 3.0909 | 2.9691 | 2.7517 |

Stability Indicator(SI) | 0.0417 | 0.0417 | 0.0417 |

Parameter | Dead Band (p.u) | |||
---|---|---|---|---|

0.00 | 0.032 | 0.08 | 0.20 | |

${t}_{\mathrm{rise}}$ (s) | 0.177 | 0.179 | 0.185 | 0.235 |

Overshoot (%) | 3.0985 | 2.9866 | 2.5117 | 2.9359 |

Stability Indicator(SI) | 0.0437 | 0.0438 | 0.0438 | 0.0440 |

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**MDPI and ACS Style**

Kim, W.; Song, S.; Jang, G.
Droop Control Strategy of Utility-Scale Photovoltaic Systems Using Adaptive Dead Band. *Appl. Sci.* **2020**, *10*, 8032.
https://doi.org/10.3390/app10228032

**AMA Style**

Kim W, Song S, Jang G.
Droop Control Strategy of Utility-Scale Photovoltaic Systems Using Adaptive Dead Band. *Applied Sciences*. 2020; 10(22):8032.
https://doi.org/10.3390/app10228032

**Chicago/Turabian Style**

Kim, Woosung, Sungyoon Song, and Gilsoo Jang.
2020. "Droop Control Strategy of Utility-Scale Photovoltaic Systems Using Adaptive Dead Band" *Applied Sciences* 10, no. 22: 8032.
https://doi.org/10.3390/app10228032