## Harmonics Created by AC Frequency Converters

Harmonic currents generated by power electronics based devices create serious power quality problems in facilities. Particularly 3 phase AC frequency converters used for engine control generate harmonic currents during operation due to rectifier layer available in its topological structure. In this study, examination was focused on how harmonics generated by a 3 phase AC frequency converter changes according to frequency converter structure and filtering type. Current harmonic distortion (THDI%) values are compared depending on different load and application types.

*converters are assessed. Advantages and disadvantages of solution methods are assessed.*

**AC frequency**More Interested: Braking Resistor

## General Information on Harmonics

Harmonic current and voltages are generated by loads containing semi-conductors connected to grid [1,2]. Harmonic distortion caused by harmonic currents’ exceeding certain limit values creates various problems in a facility.

Below given information is valid when the line inductance value can be negligible according to DC reactor inductance. Harmonic levels are calculated based on the below given formula:

Variation of wave shape created by adding harmonic currents to basic component current is indicated in Image 2. Only 5th Harmonic current was added to the basic component.

### Harmonic Sources and Effects on the Grid

## Structure and Dimensioning of 3 Phase 6 Pulse Frequency Converter

**Harmonic**currents cause distortion in busbar voltage. If grid impedances and harmonic currents are known, theoretically voltage harmonics of any point on the grid can be calculated. The circuit diagram given in Image 3 indicates frequency converter fed from the grid and other components. ABB DriveSize software was used during frequency converter harmonic distortion calculations.

### Limit Values Related with Current Harmonics

### Reduction of Harmonics Through Structural Changes to be Performed in AC Frequency Converter

Table .2 Factors affecting harmonic distortion and their effects

Factor |
Effect |

Larger Engine | Higher current harmonic |

Higher engine load | Higher current harmonic |

Higher DC or AC inductance | Lower current harmonic |

Higher pulse rectifier | Lower current harmonic |

Larger transformer impedance | Lower voltage harmonic |

Smaller transformer impedance | Lower voltage harmonic |

Larger grid short circuit power | Lower current harmonic |

### Pulse Rectifier Usage

### 12 Pulse or 24 Pulse Diode Rectifier Usage

**More Interested: Load Banks**

### Phase Controlled Thyristor Rectifier Usage

### IGBT Bridge Usage

### DC or AC Coils With Higher Inductance

Amount of the voltage harmonic depending on the current harmonic shall be changed based on grid short circuit rate (Rsc). Higher rate shall mean lower voltage distortion. Voltage harmonic distortion amounts to be created based on the grid circuit rate are seen in Image 14.

## Other Methods for Reducing Harmonics

### Single Arm Tuned Passive Filters

### Multiple Arm Tuned Passive Filters

### Active Filters

**Active filter**measures the dirty current withdrawn by the pollutant load and analyze harmonics on this current based on their frequencies, then generate the reverse phase current with same amplitude and frequency with these harmonic currents and gives into the grid. Therefore, the part starting from active filter connection point until the grid shall be purified from harmonics.

## Comparing Methods Related with Harmonic Reduction

## Conclusion

**AC frequency**converters those are used for engine control almost in every application emit harmonic currents to the grid during operations due to semi-conductor components in their structures. Amplitude and frequencies of emitted harmonic currents varies depending on used topology and filtration method. Current harmonics emitted by frequency converters are multiplied with grid and system impedances and cause harmonic voltages. These induced voltages reveal failures depending on harmonics.

## Sources

*[1] C.Kocatepe, M.Uzunoğlu, R.Yumurtacı, A.Karakaş, O.Arıkan, Elektrik Tesislerinde Harmonikler, İstanbul: Birsen Yayınevi, 2003.*

*[2] R.C.Dugan, M.F.McGranaghan,S. Santoso,H.W. Beaty “Electrical Power Systems Quality, Second Edition”, McGraw-Hill, 2004*

*[3] The ABB Group – Automation and Power Technologies, Guide to Harmonics with AC Drives, 2002. http://www08.abb.com/global/scot/scot201.nsf/veritydisplay/cedba3af94239d90c1257b0f004712c4/$file/ABB_Technical_guide_No_6_REVD.pdf*

*[4] C.Kocatepe, “Sinüzoidal Olmayan Yükleri İçeren Enerji sistemlerinde*

*Harmonik Yük Akışı Analizi ve Simülasyonu”, Yıldız Teknik Üniversitesi, Fen Bilimleri Enstitüsü Doktora Tezi, İstanbul, 1995.*

*[5] M.Bilge, “Güç Sistemlerinde Harmoniklerin Pasif Filtrelerle Eliminasyonu”, Kahramanmaraş Sütçü İmam Üniversitesi, Fen Bilimleri Enstitüsü Yüksek Lisans Tezi, Kahramanmaraş, 2008.*

*[6] IEEE519-2014 Standardı, “IEEE Recommended practices and requirements for harmonic control in electrical power systems”*

*[7] IEC 61800-3 Standardı, “Adjustable speed electrical power drive systems”*

Uğur YaşaAktif Kompanzasyon ve Harmonik Filtre Sistemleri Sanayi ve Ticaret A.Ş.ugur.yasa@aktif.net