# 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

- Lasseter, R.H. Certs microgrid. In Proceedings of the IEEE International Conference on System of Systems Engineering, San Antonio, TX, USA, 16–18 April 2007; pp. 1–5. [Google Scholar]
- Ackermann, T.; Andersson, G.; Soder, L. Electricity market regulations and their impact on distributed generation. In Proceedings of the Electric Utility Deregulation and Restructuring and Power Technologies, London, UK, 4–7 April 2000; pp. 608–613. [Google Scholar]
- Parlak, K.S.; Ozdemir, M.; Aydemir, M.T. Active and reactive power sharing and frequency restoration in a distributed power systme consisting of two UPS units. Electr. Power Energy Syst.
**2009**, 31, 220–226. [Google Scholar] [CrossRef] - Hatziargyriou, N.; Asano, H.; Iravani, R.; Marnay, C. Microgrids. IEEE Power Energy Mag.
**2007**, 5, 78–94. [Google Scholar] [CrossRef] - Walling, R.A.; Saint, R.; Dugan, R.C.; Burke, J.; Kojovic, L.A. Summary of distributed resources impact on power delivery systems. IEEE Trans. Power Deliv.
**2008**, 23, 1636–1644. [Google Scholar] [CrossRef] - Moreira, C.L.; Resende, F.O.; Lopes, J.A.P. Using low voltage microgrids for service restoration. IEEE Trans. Power Syst.
**2007**, 22, 395–403. [Google Scholar] [CrossRef] - Fortescue, C.L. Method of symmetrical coordinates applied to the solution of polyphase networks. AIEE Trans.
**1918**, 37, 1027–1140. [Google Scholar] - Hague, B. The method of symmetrical coordinates in the theory of polyphaser circuits. Sel. Eng. Pap.
**1926**, 1. [Google Scholar] [CrossRef] - El-Barbari, S.; Hofmann, W. Digital control of a four leg inverter for standalone photovoltaic systems with unbalance load. In Proceedings of the Twenty-sixth Annual conference of IEEE Industrial Electronics Society (IECON 2000), Nagoya, Japan, 22–28 October 2000; pp. 729–734. [Google Scholar]
- Vechiu, I.; Curea, O.; Camblong, H. Transient operation of a four-leg inverter for autonomous applications with unbalance load. IEEE Trans. Power Electron.
**2010**, 25, 399–407. [Google Scholar] [CrossRef] - Doan, V.T.; Kim, K.Y.; Choi, W.; Kim, D.W. Design of a hybrid controller for the three-phase four-leg voltage-source inverter with unbalance load. J. Power Electron.
**2017**, 17, 181–189. [Google Scholar] [CrossRef] - Priya, N.A.; Mabel, M.C. Control methods for four-leg voltage source inverter. In Proceedings of the International Conference on Devices, Circuits and Systems (ICDCS), Coimbatore, India, 15–16 March 2012; pp. 44–48. [Google Scholar]
- Senjyu, T.; Nakaji, T.; Uezato, K.; Funabashi, T. A hybrid power system using alternative energy facilities in isolated island. IEEE Trans. Energy Convers.
**2005**, 20, 406–414. [Google Scholar] [CrossRef] - Jo, H.; Cho, S.; Shin, C.; Cha, H. Zero sequence impedance of Yg-Yg three phase core type transformer. Trans. Korean Inst. Electr. Eng.
**2016**, 65, 940–945. [Google Scholar] [CrossRef] - Shin, D.Y.; Park, Y.W.; Cha, H.J. A case study on malfunction of OCGR and inaccuracy of watt-hour meter in distributed generation system. Trans. Korean Inst. Electr. Eng.
**2008**, 57, 1349–1355. [Google Scholar] - Shin, D.Y.; Yun, D.H.; Cha, H.J. Problem analysis by iron core structure of the transformer on asymmetric three phase lines and prevention measures. Trans. Korean Inst. Electr. Eng.
**2012**, 61, 1536–1541. [Google Scholar] [CrossRef] - Sin, C.; Lim, K.; Petrus, S.D.; Choi, J. Controller design of stand-alone or grid-connected inverter to compensate harmonics caused by nonlinear load. Trans. Korean Inst. Power Electron.
**2017**, 22, 440–448. [Google Scholar] - Rodriuez, P.; Luna, A.; Candlea, I.; Mujal, R.; Teodorescu, R.; Blaabjerg, F. Multiresonant frequency-locked loop for grid synchronization of power converters under distorted grid conditions. IEEE Trans. Ind. Electron.
**2011**, 58, 127–138. [Google Scholar] [CrossRef] [Green Version] - He, J.; Li, Y.W.; Blaabjerg, F.; Wang, X. Active harmonic filtering using current-controlled, grid-connected DG units with closed-loop power control. IEEE Trans. Power Electron.
**2014**, 29, 642–653. [Google Scholar] - He, J.; Li, Y.W. Hybrid voltage and current control approach for DG Grid interfacing converters with LCL filters. IEEE Trans. Ind. Electron.
**2013**, 60, 1797–1809. [Google Scholar] [CrossRef] - Lim, K.; Choi, J. PR control based cascaded current and voltage control for seamless transfer of microgrid. In Proceedings of the International Future Energy Electronics Conference (IFEEC’2015), Taipei, Taiwan, 1–4 November 2015; pp. 1–6. [Google Scholar]
- Bhattacharya, S.; Divan, D.M. Synchronous frame based controller implementation for a hybrid series active filter system. In Proceedings of the Thirtieth IAS Annual Meeting Industry Applications Conference, Orlando, FL, USA, 8–12 October 1995; pp. 2531–2540. [Google Scholar]
- Bhattacharya, S.; Divan, D.M.; Banerjee, B. Synchronous reference frame based harmonic isolator using series active filter. In Proceedings of the EPE (European Power Electronics and drives), Florence, Italy, 1991; Volume 3, pp. 30–35. [Google Scholar]
- Choi, H.S.; Choi, S.J. An effective gyrator-based transformer modeling using PSIM. Trans. Korean Inst. Power Electron.
**2016**, 21, 207–214. [Google Scholar] [CrossRef] - Chiniforoosh, S.; Atighechi, H.; Davoudi, A.; Jatskevich, J.; Yazdani, A.; Filizadeh, S.; Saeedifard, M.; Martinez, J.A.; Sood, V.; Strunz, K.; et al. Dynamic average modeling of front-end diode rectifier loads considering discontinuous conduction mode and unbalanced operation. IEEE Trans. Power Deliv.
**2012**, 27, 421–429. [Google Scholar] [CrossRef] - Takahashu, I. Power factor improvement of a diode rectifier circuit by dither signal. In Proceedings of the IEEE Industry Applications Society Annual Meeting, Seattle, WA, USA, 7–12 October 1990; pp. 1289–1294. [Google Scholar]
- Villablanca, M.E.; Nadal, J.I. Current distortion reduction in six-phase parallel-connected AC/DC rectifiers. IEEE Trans. Power Deliv.
**2008**, 23, 953–959. [Google Scholar] [CrossRef]

**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