# Reduced-Capacity Inrush Current Suppressor Using a Matrix Converter in a Wind Power Generation System with Squirrel-Cage Induction Machines

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## Abstract

**:**

## 1. Introduction

## 2. Inrush Current Suppressor Using MC

_{100}or S’

_{400}.

_{u}of the output u-phase and the input phase. The duty ratios are decided by comparing the duty ratio d

_{u}and the carrier signal v

_{tri}. In the case of Pattern I, when d

_{u}is larger than v

_{tri}, MX is connected. MN is connected when d

_{u}is smaller than v

_{tri}in T

_{1}. MD is connected when d

_{u}is smaller than v

_{tri}in T

_{2}. In the case of Pattern II, when d

_{u}is smaller than v

_{tri}, MN is connected. MX is connected when d

_{u}is larger than v

_{tri}in T

_{1}. MD is connected when d

_{u}is larger than v

_{tri}in T

_{2}. n, which is used for input current synthesis, is defined as T

_{1}/T

_{s}. The T

_{u1}∼ T

_{u4}of Figure 2 are decided by comparison of the carrier signal and the duty ratio d

_{u}. Similarly, the T

_{v1}∼ T

_{v4}, T

_{w1}∼ T

_{w4}are decided, as well. Logic Circuit A of Figure 1 chooses which T

_{u1}∼ T

_{u4}, T

_{v1}∼ T

_{v4}and T

_{w1}∼ T

_{w4}to connect MX, MD and MN under the conditions of Patterns I and II. Logic Circuit B of Figure 1 decides the timing that connects the input with output.

## 3. Simulation Results

_{s}is 0.1 mH, which is about 5% relative to the rated impedance of 400 kW SCIM. Figure 3 shows the simulation condition. The 100-kW SCIM is connected to the grid from 3 to 8 m/s. The 400-kW SCIM is connected to the grid over 8 m/s.

#### 3.1. Simulation Results of Direct Connection

_{Tr}is the r-phase receiving-end voltage; i

_{Tr}is the source current; SP

_{100}is the rotating speed; and v

_{w}is the wind speed. From Figure 4, the maximum value of the inrush current is 1145 A. The voltage sag is about 6.89%. Figure 5 shows simulated waveforms for the 400-kW SCIM. From Figure 5, the maximum value of the inrush current is 3873 A. The voltage sag is about 15.28%. In general, a soft-starter is used to avoid the voltage sag caused by the inrush current.

#### 3.2. Conventional Inrush Current Suppressors

_{100}and R

_{400}are 0.715 and 0.577 Ω, respectively. Figure 12 shows the simulation waveform of the source current for the 100-kW SCIM with external resistors. From this simulation result, no inrush current nor harmonic current occurs by using external resistors. Figure 13 shows the simulation waveform of the source current for the 400-kW SCIM with external resistors. From this simulation result, no inrush current nor harmonic current occurs by using external resistors. However, large energy losses in series-connected external resistors occur during the start-up condition. The r-phase maximum losses are 119.0 and 212.6 kW for the 100-kW and 400-kW SCIM, respectively. The large power losses are brought the increase of the volume of the external resistors.

#### 3.3. Simulation Results with the Proposed Inrush Current Suppressor

_{Tr}is the r-phase receiving-end voltage; i

_{Tr}is the source current; i

_{MTr}is the r-phase input current of the MC; i

_{MOr100}is the r-phase output voltage of the MC; i

_{mr100}is the r-phase SCIM current; SP

_{100}is the rotating speed; and v

_{w}is the wind speed. From Figure 14, the output voltage of the MC and SCIM current is in phase. This means that the output side of the MC performs as the resistor in each phase. Therefore, the maximum SCIM current is 558 A, and the voltage sag is about 1.5%. The active power flows into the MC during the inrush current suppression. The active power is about 47.8 kW. The receiving-end voltage v

_{Tr}is opposite in phase to the input current i

_{MTr}of the MC. The active power is regenerated to the grid. The regenerated power is about 33.6 kW. In this simulation, the stationary losses of power devices and the resistors of the passive filters are included. From this simulation result, the inrush current of the 100-kW SCIM is reduced by about 50%, and the voltage sag of the 100-kW SCIM is reduced by about 78% by connecting the proposed inrush current suppressor.

_{Tr}is also opposite in phase to the input current i

_{MTr}of the MC. The regenerated power at the input side of the MC is about 79.8 kW. From this simulation result, the inrush current of the 400-kW SCIM is reduced by about 80%, and the voltage sag of the 400 kW-SCIM is reduced by about 95% by using the proposed inrush current suppressor. Thus, the validity of the proposed inrush current suppressor is confirmed by the simulation results.

#### 3.4. Reduction of the Capacity for the Proposed Inrush Current Suppressor

_{eq}is the equivalent resistance of the output side of the proposed inrush current suppressor; I

_{mr100}is the r-phase maximum SCIM current; U

_{100}is the capacity of the proposed inrush current suppressor; and RP

_{100}is the ratio of the regenerated power through the MC. The horizontal axis represents the number of turns on the secondary side of the matching transformer. The number of turns on primary side of the matching transformer is always one. Figure 16b shows the relationship between the turn ratio and the proposed inrush current suppressor for the 400-kW SCIM. From these relationships, the capacity of the MC decreases by increasing the turns of the secondary side of the matching transformer. However, the ratio of the regenerated power through the MC is reduced by increasing the turns. Furthermore, the change in slop of the capacity of the MC decreases gradually from the turn ratio of 1:4. Thus, the appropriate turn ratio is 1:4.

_{Tr}is the r-phase receiving-end voltage; i

_{Tr}is the r-phase source current; i

_{MTr}is r-phase input current of the MC; v

_{MOr100}is the r-phase output voltage of the MC; i

_{mr100}is the r-phase SCIM current; SP

_{100}is the rotating speed; and v

_{w}is the wind speed. From Figure 17, the maximum source current is 146 A. The voltage sag is about 1.01%. The active power that flows into the MC is about 17.1 kW. The receiving-end voltage v

_{Tr}is also opposite in phase to the input current of the MC i

_{MTr}. The regenerated-power at the input side of the MC is about 10.6 kW. Figure 18 shows the simulation results with the proposed inrush current suppressor for the 400-kW SCIM when the turn ratio is 1:4. From Figure 18, the maximum source current is 158 A. The voltage sag is about 0.51%. The active power that flows into the MC is about 22.6 kW. The receiving-end voltage v

_{Tr}is also opposite in phase to the input current of the MC i

_{MTr}. The regenerated power at the input side of the MC is about 13.4 kW.

## 4. Conclusions

## Author Contributions

## Conflicts of Interest

## References

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**Figure 1.**System configuration with the proposed inrush current suppressor using matrix converter (MC) in a large-capacity wind power generation system (WPGS).

**Figure 2.**Switching states in Pattern I and Pattern II in the direct duty ratio pulse width modulation (DDRPWM) method.

**Figure 8.**Source current total harmonic distortion (THD) of the soft-starter for the 100-kW SCIM in Figure 7.

**Figure 10.**Source current THD of the soft-starter for the 400-kW SCIM in Figure 9.

**Figure 16.**Relationship between the number of turns on the secondary side of the matching transformer and the proposed inrush current suppressor. (

**a**) For the 100-kW SCIM; (

**b**) For the 400-kW SCIM.

**Figure 17.**Simulation results with the proposed inrush current suppressor for the 100-kW SCIM when turn ratio is 1:4.

**Figure 18.**Simulation results with the proposed inrush current suppressor for the 400-kW SCIM when the turn ratio is 1:4.

Item | 100-kW SCIM | 400-kW SCIM |
---|---|---|

Rated power (kW) | 100 | 400 |

Rated phase voltage (V) | 277.13 | 277.13 |

Rated phase current (A) | 120.28 | 481.12 |

Rated frequency (Hz) | 50 | 50 |

Number of pole | 6 | 4 |

Synchronous speed (rpm) | 1000 | 1500 |

Rated wind speed (m/s) | 8 | 15 |

Item | Value |
---|---|

Source voltage V_{s} (V) | 480 |

Source frequency f (Hz) | 50 |

Source inductor L_{s} (mH) | 0.1 |

Inductor of input filter L_{fi} (mH) | 1 |

Capacitor of input filter C_{fi} (μF) | 25 |

Inductor of output filter L_{fo} (mH) | 0.25 |

Capacitor of output filter C_{fo} (μF) | 100 |

Resistor of output filter R_{fo} (Ω) | 1 |

Resistor of clamp circuit R_{c} (Ω) | 1000 |

Capacitor of clamp circuit C_{c} (μF) | 500 |

Item | Inrush Current (A) | Voltage Sag (%) | THD of Source Current (%) | Losses (kW) | |
---|---|---|---|---|---|

Direct connection | 100-kW SCIM | 1145 | 6.9 | 0.08 | - |

400-kW SCIM | 3873 | 15.3 | 1.1 | - | |

Proposed inrush current suppressor (turn ratio is 1:1) | 100-kW SCIM | 558 | 1.5 | 7.71 | 14.2 |

400-kW SCIM | 718 | 0.76 | 15.6 | 38.7 | |

Proposed inrush current suppressor (turn ratio is 1:4) | 100-kW SCIM | 146 | 1.0 | 20.9 | 6.5 |

400-kW SCIM | 158 | 0.5 | 23.9 | 9.2 | |

Soft-starter | 100-kW SCIM | 649 | 6.6 | 328.8 | - |

400-kW SCIM | 1941 | 13.8 | 329.9 6 | - | |

External resistors | 100–kW SCIM | 512 | 1.0 | - | 119.0 |

400 kW-SCIM | 609 | 0.8 | - | 212.6 |

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**MDPI and ACS Style**

Shibata, S.; Yamada, H.; Tanaka, T.; Okamoto, M.
Reduced-Capacity Inrush Current Suppressor Using a Matrix Converter in a Wind Power Generation System with Squirrel-Cage Induction Machines. *Energies* **2016**, *9*, 223.
https://doi.org/10.3390/en9030223

**AMA Style**

Shibata S, Yamada H, Tanaka T, Okamoto M.
Reduced-Capacity Inrush Current Suppressor Using a Matrix Converter in a Wind Power Generation System with Squirrel-Cage Induction Machines. *Energies*. 2016; 9(3):223.
https://doi.org/10.3390/en9030223

**Chicago/Turabian Style**

Shibata, Sho, Hiroaki Yamada, Toshihiko Tanaka, and Masayuki Okamoto.
2016. "Reduced-Capacity Inrush Current Suppressor Using a Matrix Converter in a Wind Power Generation System with Squirrel-Cage Induction Machines" *Energies* 9, no. 3: 223.
https://doi.org/10.3390/en9030223