# A Consideration on Maximum Efficiency of Resonant Circuit of Inductive Power Transfer System with Soft-Switching Operation

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## Abstract

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## 1. Introduction

## 2. System Overview

#### 2.1. Derivation of Voltage and Current in a Bi-Directional inductive power transfer (IPT) System

#### 2.2. Transmission Power and Efficiency

## 3. Influences of Soft-Switching Operation

#### 3.1. Requirement for Soft-Switching Operation

#### 3.2. Analysis for Efficiency of the Resonant Circuit

## 4. Experiments

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Abbreviations

EV | Electric vehicle |

IPT | Inductive power transfer |

## References

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**Figure 2.**Relationships between the gating signals and the output waveforms of the active bridges with soft-switching operation. (

**a**) operation waveforms of the primary-side active bridge; (

**b**) operation waveforms of the secondary-side active bridge.

**Figure 4.**Transition diagram of the operation mode focusing on turning ${\mathrm{S}}_{11}$ on with soft switching.

**Figure 5.**Efficiency map of the resonant circuit with each operation mode. (

**a**) At ${I}_{\mathrm{charge}}=8$ A, ${E}_{1}=200$ V and ${E}_{2}=150$ V; (

**b**) At ${I}_{\mathrm{charge}}=8$ A, ${E}_{1}=200$ V and ${E}_{2}=200$ V.

**Figure 6.**Loci of the maximum efficiency points of the resonant circuit where ${I}_{\mathrm{charge}}$ is varied.

**Figure 9.**Efficiency of the overall system. (

**a**) ${E}_{1}=200$ V, ${E}_{2}=150$ V; (

**b**) ${E}_{1}=200$ V, ${E}_{2}=200$ V.

**Figure 10.**Waveforms of voltages and currents in the resonant circuit at ${E}_{1}=200$ V, ${E}_{2}=150$ V, and ${I}_{charging}=8$ A. (

**a**) hard-switching operation; (

**b**) soft-switching operation.

Switching frequency of the active bridges f | 85 kHz |

Angle equivalent to dead-time length ${\theta}_{\mathrm{d}}$ | 0.427 rad (@${\theta}_{\mathrm{d}}=800$ ns) |

Primary-side direct current (DC) voltage ${E}_{1}$ | 200 V |

Secondary-side DC voltage ${E}_{2}$ | 150 V, 200 V |

Charging DC current for battery ${I}_{\mathrm{charge}}$ | 8 A |

Inductance of primary-side coil ${L}_{1}$, secondary-side coil ${L}_{2}$ | 67.7 uH, 68.6 uH |

ESR of primary-side coil ${r}_{1}$, secondary-side coil ${r}_{2}$ | 95 m$\mathsf{\Omega}$, 103 m$\mathsf{\Omega}$ |

Coupling coefficient k | 0.3 |

Software programing language | C++ language |

Switching frequency of the active bridges f | 85 kHz |

Angle equivalent to dead-time length ${\theta}_{\mathrm{d}}$ | 0.427 rad (@${\theta}_{\mathrm{d}}=800$ ns) |

Primary-side DC voltage ${E}_{1}$ | 200 V |

Secondary-side DC voltage ${E}_{2}$ | 150 V, 200 V |

Inductance of primary-side coil ${L}_{1}$, secondary-side coil ${L}_{2}$ | 67.7 uH, 68.6 uH |

ESR of primary-side coil ${r}_{1}$, secondary-side coil ${r}_{2}$ | 95 m$\mathsf{\Omega}$, 103 m$\mathsf{\Omega}$ |

Snubber capacitor | None (parasitic) |

Coupling coefficient k | 0.3 |

Switching devices | ROHM BSM080D12P2C008 |

Oscilloscope | Tektronix MDO4034C |

Power meter | HIOKI PW6001 |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Ota, R.; Sudarmo Nugroho, D.; Hoshi, N.
A Consideration on Maximum Efficiency of Resonant Circuit of Inductive Power Transfer System with Soft-Switching Operation. *World Electr. Veh. J.* **2019**, *10*, 54.
https://doi.org/10.3390/wevj10030054

**AMA Style**

Ota R, Sudarmo Nugroho D, Hoshi N.
A Consideration on Maximum Efficiency of Resonant Circuit of Inductive Power Transfer System with Soft-Switching Operation. *World Electric Vehicle Journal*. 2019; 10(3):54.
https://doi.org/10.3390/wevj10030054

**Chicago/Turabian Style**

Ota, Ryosuke, Dannisworo Sudarmo Nugroho, and Nobukazu Hoshi.
2019. "A Consideration on Maximum Efficiency of Resonant Circuit of Inductive Power Transfer System with Soft-Switching Operation" *World Electric Vehicle Journal* 10, no. 3: 54.
https://doi.org/10.3390/wevj10030054