# Low-Frequency AC Power Transmission and Distribution for Subsea Application Using Hexverter

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## Abstract

**:**

## 1. Introduction

## 2. Modeling of LFAC-Based Subsea T&D Systems

#### 2.1. Hexverter Modeling and Its Control Strategy

_{NO}is the voltage between the neutral point of input system and output system, ${i}_{cir}$ is the zero-sequence circulating current of six arms, and Q1 and Q2 are the hexverter reactive power from AC systems 1 and 2 respectively. Considering the voltage regulation and reactive power demand, the equation Q1 + Q2 ≠ 0 is always satisfied, making the circulating current ${i}_{cir}$ non-zero. It is obvious from research on power electronics converters that the circulating current has a significant impact on the overall power rating and efficiency of the converter because of the huge number of semiconductor devices. Moreover, these semiconductor devices collectively result in a cascaded circulating current, so this novel control strategy optimizes this circulating current to the minimum value. The presence of circulating current increases the switching loss, and therefore reduces the efficiency of the system. In addition to this strict constraint, the reactive power also increases the difficulty of the control strategy.

#### 2.2. Motors, VSD Modeling and Its Control System

#### 2.3. Offshore Wind Farm

#### 2.4. Subsea Transmission Line

- VS and VR are the voltages on the sending and receiving end,
- IS and IR are the currents on the sending and receiving end,
- IL is current in the series impedance,
- R, X and Z are resistance, reactance and total impedance of the cable,
- Y is the admittance.

- P
_{motor}is the motor active power, - ${U}_{ll}$ is line-to-line terminal voltage,
- $\mathrm{cos}\alpha $ is the power factor

## 3. Performance and Discussion of Results

#### 3.1. Wind Farm Simulation Waveforms

#### 3.2. Induction Motor Waveforms Analysis

#### 3.3. S16 Node Waveforms

#### 3.4. Transmission Line Waveforms

#### 3.5. Load-Side Waveforms

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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Parameters | Value | Parameters | Value |
---|---|---|---|

R | 0 Ω | P_{tr} | 10 × 10^{6} W |

L | 10 × 10^{−3} H | V_{s_Ref} | 10 × 10^{3} V |

C_{dc} | 20,000 × 10^{−6} F | V_{m-ref} | 10 × 10^{3} V |

V_{dc0} | 2.0 × 10^{3} V | T_{c} | 1.2 × 10^{−3} s |

V_{dc-ref} | 18 × 10^{3} V | N | 6 |

Parameters | Value |
---|---|

P_{motor} | 5 MW |

P.F | 0.8 |

Line Voltage | 6.6 KV |

Speed | 6000 rpm |

No of Poles | 2 |

3 × 1200 mm^{2} Cu/RM | 3 × 2000 mm^{2} AI RE | |||
---|---|---|---|---|

50 Hz | 16 Hz | 50 Hz | 16 Hz | |

R (Ω/km) | 0.0319 | 0.0204 | 0.0381 | 0.0222 |

L (mh/km) | 0.373 | 0.373 | 0.354 | 0.354 |

C (nf/km) | 191 | 191 | 227 | 227 |

X (mΩ/km | 117.2 | 39.1 | 111.2 | 37.1 |

ωC (ms/km) | 60.0 | 20 | 71.3 | 23.8 |

G (nS/km) | 60 | 20 | 71 | 22 |

I_{max} (KA) | 1.225 | 1.5 | 1.225 | 1.5 |

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## Share and Cite

**MDPI and ACS Style**

Safder, M.U.; Rizvi, S.T.H.; Meng, Y.; Javed, M.Y.; Jaffery, M.H.; Hassan, M.S.
Low-Frequency AC Power Transmission and Distribution for Subsea Application Using Hexverter. *Electronics* **2020**, *9*, 61.
https://doi.org/10.3390/electronics9010061

**AMA Style**

Safder MU, Rizvi STH, Meng Y, Javed MY, Jaffery MH, Hassan MS.
Low-Frequency AC Power Transmission and Distribution for Subsea Application Using Hexverter. *Electronics*. 2020; 9(1):61.
https://doi.org/10.3390/electronics9010061

**Chicago/Turabian Style**

Safder, Muhammad Umair, Syed Tahir Hussain Rizvi, Yongqing Meng, Muhammad Yaqoob Javed, Mujtaba Hussain Jaffery, and Muhammad Sarmad Hassan.
2020. "Low-Frequency AC Power Transmission and Distribution for Subsea Application Using Hexverter" *Electronics* 9, no. 1: 61.
https://doi.org/10.3390/electronics9010061