# Stand-Alone Microgrid Inverter Controller Design for Nonlinear, Unbalanced Load with Output Transformer

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## Abstract

**:**

## 1. Introduction

## 2. Stand-Alone Inverter Design Considering Output Transformer

#### 2.1. Changes in Zero Sequence Component According to Transformer Structure

#### 2.2. Zero-Sequence-Component Control Technique in a Five-Limb Core-Type Transformer

_{a}= 20 Ω, R

_{b}= 12 Ω, and R

_{c}= 200 Ω). Labels a1, a2, b1, b2, c1, c2 of simulation are connected to the equivalent model of the transformer shown in Figure 6a or Figure 6b.

#### 2.3. Negative-Sequence-Component Control Technique

#### 2.4. Nonlinear Compensation Using PI + MR Controller

#### 2.5. Microgrid Inverter Controller Design

## 3. Simulation

## 4. Conclusions

## Author Contributions

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 3.**Zero sequence flux of transformer core type. (

**a**) Three-limb core-type transformer, and (

**b**) five-limb core-type transformer.

**Figure 6.**Transformer simulation using PSIM magnetic element: (

**a**) three-limb core-type transformer and (

**b**) five-limb core-type transformer.

**Figure 9.**Simulation results of the five-limb core-type transformer (conventional proportional-integral (PI) controller).

**Figure 14.**Fast Fourier transform (FFT) analysis result of microgrid inverter. (

**a**) Conventional PI controller; (

**b**) PI + R controller.

**Figure 19.**Simulation results of a five-limb core-type transformer under unbalanced load conditions. (

**a**) dq controller; (

**b**) dq0 controller.

**Figure 20.**Simulation results of resonant controller under an unbalanced load. (

**a**) Conventional controller; (

**b**) Resonant controller.

**Figure 21.**FFT analysis of resonant controller under an unbalanced load. (

**a**) Conventional controller; (

**b**) Resonant controller.

**Figure 22.**Simulation result of resonant controller under a nonlinear load. (

**a**) Conventional controller; (

**b**) Resonant controller.

**Figure 23.**FFT analysis of PI + MR control inverter under a nonlinear load. (

**a**) Conventional controller; (

**b**) Resonant controller.

Parameter | Value |
---|---|

Rated power | 200 kW |

Output voltage | 380 V |

Line frequency | 50 Hz |

Inverter | Three-phase, four-wire |

Transformer core type | Five-lime core transformer |

Balance load | 20 Ω |

Unbalanced load | 20 Ω, 12 Ω, 200 Ω |

Nonlinear load | Three-phase diode rectifier |

Filter inductor | 2 mH |

Output capacitor | 100 μF |

Voltage controller bandwidth | 15 Hz |

Current controller bandwidth | 1 kHz |

Resonant controller gain (2th, 6th, 12th) | 10, 6, 4 |

THD | Conventional Controller | Resonant Controller |
---|---|---|

Voltage | 0.08 | 0.05 |

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**MDPI and ACS Style**

Lim, J.-U.; Kim, H.-W.; Cho, K.-Y.; Bae, J.-H. Stand-Alone Microgrid Inverter Controller Design for Nonlinear, Unbalanced Load with Output Transformer. *Electronics* **2018**, *7*, 55.
https://doi.org/10.3390/electronics7040055

**AMA Style**

Lim J-U, Kim H-W, Cho K-Y, Bae J-H. Stand-Alone Microgrid Inverter Controller Design for Nonlinear, Unbalanced Load with Output Transformer. *Electronics*. 2018; 7(4):55.
https://doi.org/10.3390/electronics7040055

**Chicago/Turabian Style**

Lim, Jae-Uk, Hag-Won Kim, Kwan-Yuhl Cho, and Joung-Hwan Bae. 2018. "Stand-Alone Microgrid Inverter Controller Design for Nonlinear, Unbalanced Load with Output Transformer" *Electronics* 7, no. 4: 55.
https://doi.org/10.3390/electronics7040055