# Cascaded H-Bridge Multilevel Converter Applied to a Wind Energy Conversion System with Open-End Winding

^{*}

## Abstract

**:**

## 1. Introduction

^{®}software and considering a $1.67$ MW WECS.

## 2. System Description

#### 2.1. Wind Energy Conversion System

#### 2.2. Generator

#### 2.3. Multilevel Converter and Electric Machines with Open-End Windings

## 3. Proposed System

#### 3.1. Modulation Strategy

#### 3.2. Control Strategies

## 4. Results and Discussion

^{®}software.

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## Abbreviations

CHB | Cascaded H-Bridge |

FC | Flying Capacitor |

GSC | Grid-side Converter |

MSC | Machine-side Converter |

NPC | Neutral Point Clamped |

OEW | Open-end Winding |

SCIM | Squirrel-Cage Induction Machine |

WECS | Wind Energy Conversion System |

## References

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**Figure 1.**Evolution of wind energy around the world [1].

**Figure 3.**CHB multilevel converter. (

**a**) Structure of five-level CHB multilevel converter. (

**b**) Waveforms of the output voltage of the individual H-bridges (${v}_{a1}$ and ${v}_{a2}$) and the CHB arrangement (${v}_{aN}$).

**Figure 5.**WECS with CHB five-level back-to-back converters (MSC and GSC) driving an asynchronous generator with open-end windings.

**Figure 6.**Modulation technique (PS-PWM) used in the switching of CHB multilevel converters. (

**a**) Two-cell (five-level) control diagram for CHB. (

**b**) Reference signal and carriers waveforms for five-level CHB. (Adapted from [6]).

**Figure 7.**Induction machine rotor flux position estimation for control orientation. (The superscript ∗ refers to reference value).

**Figure 10.**Behavior of the DC-link voltage, where ${V}_{dc}^{*}$ refers to DC-link voltage reference, while ${V}_{dc}$ is the measured value. (

**a**) DC-link voltage phase A. (

**b**) Detail, zoomed in, showing the maximum oscillation of the DC-link voltage.

**Figure 11.**Machine side-converter currents, where ${I}_{sd}^{*}$ and ${I}_{sq}^{*}$ are the direct and quadrature current reference; ${I}_{sd}$ and ${I}_{sq}$ are the measured value. (

**a**) Direct axis component. (

**b**) Quadrature axis component.

**Figure 12.**Machine speed, where the reference value is ${\omega}_{ref}^{*}$ and the measured value is ${\omega}_{machine}$.

**Figure 13.**Turbine and machine electromagnetic torques. (

**a**) Behavior of torques throughout the simulation. (

**b**) Detail, zoomed in, showing abrupt variation in wind speed, reflecting on turbine torque and, consequently, on electromagnetic torque.

**Figure 14.**Active power in generator and converters. (

**a**) Behavior of total active power throughout the simulation. (

**b**) Distribution of active power among GSC.

**Figure 18.**Harmonic spectrum of machine current. (

**a**) Overview of the harmonic content of currents at the machine terminals. (

**b**) Detail, in zoom, showing the low harmonic content in currents of the machine.

**Figure 19.**Harmonic spectrum of grid current. (

**a**) Overview of the harmonic content of the currents at the grid. (

**b**) Detail, zoomed in, showing the lowest harmonic content in currents flowing in the grid.

Switching States | Output Voltage (Phase A) | |||
---|---|---|---|---|

${S}_{11}$ | ${S}_{12}$ | ${S}_{21}$ | ${S}_{22}$ | ${v}_{aN}$ |

1 | 0 | 1 | 0 | $2{V}_{dc}$ |

0 | 0 | 1 | 0 | ${V}_{dc}$ |

1 | 0 | 0 | 0 | |

1 | 0 | 1 | 1 | |

1 | 1 | 1 | 0 | |

0 | 0 | 0 | 0 | 0 |

0 | 0 | 1 | 1 | |

0 | 1 | 1 | 0 | |

1 | 0 | 0 | 1 | |

1 | 1 | 0 | 0 | |

1 | 1 | 1 | 1 | |

0 | 0 | 0 | 1 | $-{V}_{dc}$ |

0 | 1 | 0 | 0 | |

0 | 1 | 1 | 1 | |

1 | 1 | 0 | 1 | |

0 | 1 | 0 | 1 | $-2{V}_{dc}$ |

Multilevel Converter | Advantages | Disadvantage |
---|---|---|

NPC | ||

FC | - -
- Flying capacitor cost is high for low and medium switching frequency operation [25]
- -
- High number of cells [25]
- -
- As levels increase, the number of capacitors increases [34]
- -
- Complexity in the control strategy due to capacitor voltage regulation [34]
- -
- Pre-charge of the capacitors, which implies in the decrease of the performance of the system [34]
| |

CHB |

**Table 3.**Parameters of squirrel-cage induction machine [45], LCL filter and converters.

Parameter | Value |
---|---|

Rated output power | 1677 kW |

Nominal line stator voltage | 2300 V(rms) |

Nominal stator current | 421.2 A(rms) |

Nominal Frequency | 60 Hz |

Nominal rotor speed | 1786 rpm |

Number of poles pairs | 2 |

Rated mechanical torque | 8.9 kNm |

Stator winding resistance, ${R}_{s}$ | 29 m$\mathsf{\Omega}$ |

Rotor winding resistance, ${R}_{r}$ | 22 m$\mathsf{\Omega}$ |

Stator leakage reactance, ${L}_{ls}$ | 0.226 m$\mathsf{\Omega}$ |

Rotor leakage reactance, ${L}_{lr}$ | 0.226 m$\mathsf{\Omega}$ |

Magnetization reactance, ${L}_{m}$ | 13.04 m$\mathsf{\Omega}$ |

Moment of inertia | 63.87 kgm${}^{2}$ |

Nominal line grid voltage | 1150 V(rms) |

Nominal grid frequency | 60 Hz |

DC-link Voltage | 2100 V |

DC-link Capacitance | 12 mF |

Switching frequency (MSC and GSC) | 5 kHz |

Converter side inductor, ${L}_{f}$ | 6.3 mH |

Converter side resistor, ${R}_{f}$ | 23.8 m$\mathsf{\Omega}$ |

Grid side inductor, ${L}_{g}$ | 0.63 mH |

Grid side resistor, ${R}_{g}$ | 23.8 m$\mathsf{\Omega}$ |

Parallel capacitor, C | 10.03 $\mathsf{\mu}F$ |

Damping resistor, ${R}_{d}$ | 2.52 m$\mathsf{\Omega}$ |

Description | Time |
---|---|

Start of simulation | 0.0 s |

Machine magnetization start at | 1.2 s |

Machine acceleration starts at | 1.8 s |

Machine reaches the rated speed at | 5.0 s |

Reduce equivalent to $20\%$ in machine torque at | 8.3 s |

Increase of approximately $17\%$ in machine torque at | 11.3 s |

Reactive power injection at | 13.0 s |

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## Share and Cite

**MDPI and ACS Style**

Bettoni, S.d.S.; Ramos, H.d.O.; Matos, F.F.; Mendes, V.F.
Cascaded H-Bridge Multilevel Converter Applied to a Wind Energy Conversion System with Open-End Winding. *Wind* **2023**, *3*, 232-252.
https://doi.org/10.3390/wind3020014

**AMA Style**

Bettoni SdS, Ramos HdO, Matos FF, Mendes VF.
Cascaded H-Bridge Multilevel Converter Applied to a Wind Energy Conversion System with Open-End Winding. *Wind*. 2023; 3(2):232-252.
https://doi.org/10.3390/wind3020014

**Chicago/Turabian Style**

Bettoni, Samuel dos Santos, Herbert de Oliveira Ramos, Frederico F. Matos, and Victor Flores Mendes.
2023. "Cascaded H-Bridge Multilevel Converter Applied to a Wind Energy Conversion System with Open-End Winding" *Wind* 3, no. 2: 232-252.
https://doi.org/10.3390/wind3020014