# Configurations, Power Topologies and Applications of Hybrid Distribution Transformers

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## Abstract

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## 1. Introduction

## 2. Hybrid Transformer Configurations

#### 2.1. Self-Supported Hybrid Transformers

#### 2.2. Hybrid Transformers Connected to Auxiliary Windings

#### 2.3. Hybrid Transformers Connected to Transformer Windings

#### 2.4. Three-Stage Configuration

#### 2.5. Additional HDT Configurations

## 3. Power Converter Topologies Employed for Hybrid Transformers

#### 3.1. DC/AC Power Converter Topologies

#### 3.2. AC/AC Power Converter Topologies

#### 3.2.1. AC/AC Converters Based on Direct Converters

#### 3.2.2. AC/AC Converters with a DC-Link Stage

#### 3.2.3. AC/AC Converters with Galvanic Isolation

## 4. Analysis of Hybrid Transformers

#### 4.1. Operating Region

#### 4.1.1. Reactive Power Injection

#### 4.1.2. Restricted Active and Reactive Power Injection

#### 4.1.3. Unrestricted Active and Reactive Power Injection

#### 4.1.4. Use of Tap Changers Systems to Extend the HDT Operating Region

#### 4.2. Power Converter Location Effects

#### 4.2.1. Shunt Converter Location

#### 4.2.2. Series Converter Location

#### 4.2.3. Combined Compensation and Circulating Active Power Flow

#### 4.3. Losses in Distribution Transformers

#### 4.4. LFT Protection

#### 4.4.1. Self-Supported HDT

#### 4.4.2. HDT Connected to Auxiliary Windings

#### 4.4.3. HDT Connected to the LFT Primary or Secondary Windings

#### 4.5. HDT Reliability

## 5. Ancillary Services Provided by Hybrid Transformers

#### 5.1. Distribution Transformer Inrush Current Mitigation

#### 5.2. Distribution Transformer Additional Capacity

#### 5.3. Hybrid Transformers to Provide Virtual Inertia

#### 5.4. Renewable Energy Systems and New Kind of Loads Integration

#### 5.5. Decentralized Control of a HDT for Voltage Regulation in Active Networks

## 6. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 2.**HDT configurations. (

**a**) Power converter connected in series without a coupling transformer (CT). (

**b**) Power converter connected in series with CT. (

**c**) Power converter connected to the low-frequency transformer (LFT) core. (

**d**) Power converter connected in shunt configuration. (

**e**) Power converter connected to auxiliary windings (AWs) and in series without CT. (

**f**) Power converter connected to AWs and in series with CT. (

**g**) Power converter connected to two AWs. (

**h**) Power converter connected to the secondary-side and in series without CT. (

**i**) Power converter connected to the secondary-side and in series with CT. (

**j**) Power converter connected to both sides of the LFT in shunt configuration.

**Figure 4.**Additional HDT configurations. (

**a**) Series connection to the high voltage taps. (

**b**) Series connection to the low voltage taps. (

**c**) Shunt connection to both phases of a single-phase with central tap grid.

**Figure 6.**DC/AC power converter topologies. (

**a**) Three-phase two-level converter. (

**b**) Three-phase two-level converter with CTs. (

**c**) Three-phase two-level converter with split capacitor and CTs. (

**d**) H-bridge converter per phase with common DC-Link. (

**e**) H-bridge converter per phase with independent DC-Link. (

**f**) Cascaded H-bridge converter.

**Figure 7.**Single-phase representation AC choppers. (

**a**) AC buck converter. (

**b**) AC buck-boost converter. (

**c**) AC Ćuk converter. (

**d**) AC bipolar buck converter.

**Figure 9.**AC/AC converter with intermediate DC-Link stage. (

**a**) Back-to-back half-bridge converter. (

**b**) Back-to-back H bridge converter. (

**c**) Back-to-back three-phase two-level converter. (

**d**) Back-to-back three-phase two-level converter for four-wire grids. (

**e**) Single-phase representation of a three-phase two-level converter and H-bridge converter in back-to-back configuration. (

**f**) Back-to-back neutral pointed clamped (NPC) converter for four-wire grids.

**Figure 10.**Power converter topologies with galvanic isolation. (

**a**) Three-stage power converter with DAB DC/DC converter. (

**b**) Three-stage power converter based on a indirect matrix converter. (

**c**) Single-stage cascaded AC/AC full-bridges in input series and output parallel (ISOP) configuration. (

**d**) Three-stage power converter with dual-active bridge (DAB) in ISOP configuration for series and shunt (four-wire) compensation.

**Figure 11.**Operating region of HDTs whose power converters inject reactive power, exclusively. (

**a**) Active and reactive power (PQ) operating region. (

**b**) Series voltage injection. (

**c**) Shunt current injection.

**Figure 12.**Operating region of HDTs whose power converters are capable to inject restricted active and reactive power. (

**a**) PQ operating region. (

**b**) Complex plane operating region for voltage compensation.

**Figure 13.**Operating region of HDTs whose power converters are capable of injecting active and reactive power. (

**a**) PQ operating region. (

**b**) Complex plane operating region for voltage compensation.

**Figure 14.**HDT with taps changers. (

**a**) Diagram of a HDT configuration with taps changers systems (

**b**) Operating region of the HDT output voltage versus the power converter converter output voltage (

**c**) Complex plane operating region.

**Figure 15.**Shunt converter locations. (

**a**) Primary-side. (

**b**) Secondary-side. (

**c**) Connected to an auxiliary winding.

**Figure 16.**Series converter locations. (

**a**) Primary-side. (

**b**) Secondary-side. (

**c**) Connected to an auxiliary winding.

**Figure 17.**Circulating active power flow scenarios. (

**a**) No circulating power between the LFT and the power converter. (

**b**) Circulating power flow between the LFT and power converter.

**Figure 19.**Hybrid transformer of configuration Figure 2e with bypass switch.

**Figure 23.**HDTs for the integration of renewable systems and new kind of loads. (

**a**) Renewable systems integration. (

**b**) Electric vehicle charging station.

Compensation | ||||||
---|---|---|---|---|---|---|

Series | Series (CT) | Shunt | Magnetic | |||

Energy source | Capacitor | (a) | x | |||

(b) | x | |||||

(c) | x | |||||

(d) | x | |||||

Aux wind. | (e) | x | x | |||

(f) | x | x | ||||

(g) | x | |||||

(h) | x | x | ||||

Wind. | (i) | x | x | |||

(j) | x |

Power Converter | Ideal Voltage Gain |
---|---|

AC Buck | D |

AC Buck-Boost | $\frac{1}{1-D}$ |

AC Ćuk | $\frac{1}{1-D}$ |

AC bipolar Buck | $2D-1$ |

Compensation | |||||
---|---|---|---|---|---|

Reactive Power | Restricted PQ | Unrestricted PQ | |||

Power converter topology | Figure 6 | (a) | x | ||

(b) | x | ||||

(c) | x | ||||

(d) | x | ||||

(e) | x | ||||

(f) | x | ||||

Figure 7 | (a) | x | |||

(b) | x | ||||

(c) | x | ||||

(d) | x | ||||

Figure 8 | x | ||||

Figure 9 | (a) | x | |||

(b) | x | ||||

(c) | x | ||||

(d) | x | ||||

(e) | x | ||||

(f) | x | ||||

Figure 10 | (a) | x | |||

(b) | x | ||||

(c) | x | ||||

(d) | x |

Motive | Assessment |
---|---|

Circulating active power flow | –1 |

Magnetic compensation (Q) | 1 |

Magnetic compensation (P + Q) | 2 |

Series converter on primary-side (Q) | 2 |

Shunt converter on secondary-side (Q) | 2 |

Series converter on primary-side (P + Q) | 3 |

Shunt converter on secondary-side (P + Q) | 3 |

LFT Protection | |||||
---|---|---|---|---|---|

No Ser. | Ser. sec. | Ser. pri. | Ser. mag. | ||

Capacitor | (a) | - | 0 | 2 | - |

(b) | - | 0 | 2 | - | |

(c) | 1 | - | - | - | |

(d) | 2 | - | - | - | |

Aux wind. | (e) | - | 1 | 3 | - |

(f) | - | 1 | 3 | - | |

(g) | - | - | - | 3 | |

Wind. | (h) | - | 2 | 4 | - |

(i) | - | 2 | 4 | - | |

(j) | 3 | - | - | - |

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## Share and Cite

**MDPI and ACS Style**

Carreno, A.; Perez, M.; Baier, C.; Huang, A.; Rajendran, S.; Malinowski, M.
Configurations, Power Topologies and Applications of Hybrid Distribution Transformers. *Energies* **2021**, *14*, 1215.
https://doi.org/10.3390/en14051215

**AMA Style**

Carreno A, Perez M, Baier C, Huang A, Rajendran S, Malinowski M.
Configurations, Power Topologies and Applications of Hybrid Distribution Transformers. *Energies*. 2021; 14(5):1215.
https://doi.org/10.3390/en14051215

**Chicago/Turabian Style**

Carreno, Alvaro, Marcelo Perez, Carlos Baier, Alex Huang, Sanjay Rajendran, and Mariusz Malinowski.
2021. "Configurations, Power Topologies and Applications of Hybrid Distribution Transformers" *Energies* 14, no. 5: 1215.
https://doi.org/10.3390/en14051215