# Non-Conventional, Non-Permanent Magnet Wind Generator Candidates

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

- Firstly, a robust hub structure that would overcome gusty wind conditions;
- Secondly, an economical size that favours larger offshore wind turbines capacities within the range of 5–10 MW;
- Thirdly, the use of a variable speed design that improves operation efficiency compared to that of fixed speed wind turbines which only operate efficiently at a particular peak speed;
- Fourthly, the elimination of gearboxes in the design of wind turbines to alleviate maintenance costs;
- Fifthly, the use of permanent magnets (PMs), which are constituted of the rare-earth materials—Neodymium-based powerful magnets used for manufacturing of the more efficient and high-torque density wind generators;
- Lastly, the use of superconductors or advance materials/design technologies to reduce the size and mass of wind generators, hence improving the levelized cost of energy (LCOE).

## 2. Conventional Non-PM Wind Generators

#### 2.1. Squirrel Cage Induction Generators (SCIG)

#### 2.2. Wound Rotor Induction Generators (WRIGs)

#### 2.3. Doubly Fed Induction Generators (DFIG)

#### 2.4. Electrically Excited Synchronous Generators (EESG)

**Figure 6.**EESG with full-scale power converter [46].

## 3. Non-Conventional Non-PM Electrical Machines

#### 3.1. Reluctance Synchronous Machine (RSM)

#### 3.1.1. Torque Ripple

#### 3.1.2. Power Factor

#### 3.1.3. Control

#### 3.2. DC-Excited Vernier Reluctance Machine (DC-VRM)

#### 3.3. Wound-Field Flux Switching Machine (WF-FSM)

#### 3.4. Double-Salient DC Machine (DSDCM)

#### 3.5. DC-Field Excited Flux Reversal Machine (DC-FRM)

#### 3.6. Brushless Doubly-Fed Machines

## 4. Comparative Analysis of Non-Conventional Non-PM Electrical Machines

## 5. Conclusions

^{3}, which is reasonable when compared to a conventional PMSG operating at 150 r/min, which yielded 24 kNm/m

^{3}. The predicted torque density of the DC-VRM is because it operates on the flux modulation principle and as such, can provide high torque capability based on magnetic gearing effects [15,16]. Meanwhile, it is observed that the torque ripple of the DC-VRM is 2.5 times that of the PMSG, and this is usually the Achilles’ heel of FMMs because of their double-salient design. Additionally, due to high saturation effects and cross-magnetic fields of the stator-mounted field and armature windings, the power factor of the DC-VRM is poorer, as seen in this case. It is not surprising that the presence of field windings, among other things, also meant that the efficiency of the DC-VRM is much lower (87.4%) compared to that of the PMSG (94.4%). In addition, the speed regimes of the studied brushless wound-field wind generators are suggestive of ranges in the low- and medium-speed wind generator drivetrains, a trend that could be somehow associated with their characteristic high pole numbers.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

AFDSM | Axial Flux Doubly Salient Machine |

ARSM | Assisted Reluctance Synchronous Machine |

ASP | Asymmetric Stator Pole |

BDFIM | Brushless Doubly-Fed Induction Machines |

BDFRM | Brushless Doubly-Fed Reluctance Machines |

BLAC | Brushless Alternating Current |

BLDC | Brushless Direct Current |

BSMM | Brushless Stator Mounted Machine |

CPSR | Constant Power Speed Range |

CRSM | Compensated Reluctance Synchronous Machine |

DC | Direct Current |

DFIG | Doubly Fed Induction Generator |

DSDCM | Double-Salient Direct Current Machine |

DSM | Double-Salient Machine |

DSPM | Double-Salient Permanent Magnet Machine |

EESG | Electrically Excited Synchronous Generator |

EMF | Electromotive Force |

FEM | Finite Element Method |

FMM | Flux Modulation Machine |

FRM | Flux Reversal Machine |

FRT | Fault Ride Through |

FSG | Flux Switching Generator |

FSM | Flux Switching Machine |

HS | High Speed |

HTS | High Temperature Superconducting |

HVDC | High Voltage Direct Current |

kW | Kilowatt |

LCOE | Levelized Cost of Energy |

MFB | Multiple Flux Barriers |

MW | Megawatt |

OBD | Optimized Benchmark Design |

PM | Permanent Magnet |

PMSG | Permanent Magnet Synchronous Generator |

RSG | Reluctance Synchronous Generator |

RSM | Reluctance Synchronous Machine |

SCIG | Squirrel Cage Induction Generator |

SRM | Switched Reluctance Machine |

UMF | Unbalanced Magnetic Force |

USD | US Dollar |

VRM | Vernier Reluctance Machine |

WECS | Wind Energy Conversion System |

WF | Wound Field |

WRIG | Wound Rotor Induction Generator |

WRSM | Wound Rotor Synchronous Machine |

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**Figure 1.**Wind power global capacity and annual additions, 2010–2020 [1].

**Figure 9.**Structure of three-phase DSDCM: (

**a**) 6/8-pole [k = 1, N = 2]; (

**b**) 12/16-pole [k = 2; N = 2]; (

**c**) 6/16-pole [k = 1; N = 4] and (

**d**) 24/16-pole [conventional topology, k = 4].

**Table 1.**PM-FRM vs. DC-FRM (adapted from [24] with costs from 2015).

Items | PM-FRM | DC-FRM | |
---|---|---|---|

No. of armature phases | 3 | 4 | 4 |

Power (kW) | 58 | 64 | 22 |

Power Density (MW/m^{3}) | 1.98 | 2.10 | 0.71 |

Flux Controllability | Low | Low | High |

Material Cost (USD) | 1245 | 1398 | 308 |

Cost-effectiveness | 46.6 | 45.8 | 71.4 |

Type | Torque Density (kNm/m^{3}) | Average Torque (Nm) | Torque Ripple (%) | Power Factor | Cost | Efficiency (%) | Speed (r/min) |
---|---|---|---|---|---|---|---|

RSG [64] | 18.5 | 97.7 × 10^{3} | 4.92 | 0.54 | Low | 97.94 | 500 |

DC-VRM [85] | 17.39 | 732.0 | 8.5 | 0.8 | Low | 87.4 | 200 |

WF-FSM [110] | 31.6 | 77.8 × 10^{3} | 3.74 | 0.8 | Low | 97.0 | 360 |

DSDCM [113] | 3.92 | 38.22 | 7.46 | - | Low | 89.3 | 500 |

DC-FRM [24] | 6.68 | 179.9 | 6.28 | - | Low | 72.5 | 900 |

PMSG (kW) [90] | 24.01 | 1011.1 | 3.42 | 0.97 | High | 94.4 | 150 |

PMSG (MW) [121] | 109.25 | 2789 × 10^{3} | 2.06 | 0.94 | High | 95.0 | 15 |

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**MDPI and ACS Style**

Udosen, D.; Kalengo, K.; Akuru, U.B.; Popoola, O.; Munda, J.L.
Non-Conventional, Non-Permanent Magnet Wind Generator Candidates. *Wind* **2022**, *2*, 429-450.
https://doi.org/10.3390/wind2030023

**AMA Style**

Udosen D, Kalengo K, Akuru UB, Popoola O, Munda JL.
Non-Conventional, Non-Permanent Magnet Wind Generator Candidates. *Wind*. 2022; 2(3):429-450.
https://doi.org/10.3390/wind2030023

**Chicago/Turabian Style**

Udosen, David, Kundanji Kalengo, Udochukwu B. Akuru, Olawale Popoola, and Josiah L. Munda.
2022. "Non-Conventional, Non-Permanent Magnet Wind Generator Candidates" *Wind* 2, no. 3: 429-450.
https://doi.org/10.3390/wind2030023