# A Real-Car Experiment of a Dynamic Wireless Power Transfer System Based on Parallel-Series Resonant Topology

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Experimental Setup

#### 2.1. Circuit Configurations

#### 2.2. WPT Coil Specifications

#### 2.3. WPT Coil Parameters

_{N}and vehicle-side coil L

_{S}were 23.5 and 655 μH, respectively, while the subscript “N” stands for the number of ground-side coils as shown in Figure 1. Winding resistances r

_{N}and r

_{S}take into account skin and proximity effects and equivalent resistance for a ferrite core loss. The coupling coefficient k between the ground-side coil and the vehicle-side coil at a 170-mm air-gap is 0.235.

_{N}and L

_{S}in this experiment were 3.1% and 4.8%, respectively. Similarly, r

_{N}and r

_{S}were 8.4% and 2.9%. Mutual inductance between L

_{N}and L

_{S}at x = 300 mm decreases to half of the original value (x = 0 mm). Consequently, the mutual inductance is almost zero at x = 900 mm.

## 3. Results

#### 3.1. Transformer Analysis

#### 3.1.1. Stationary System Analysis

_{IN}and ω, assuming a sinusoidal voltage. The self-inductances of the ground-side coil and the vehicle-side coil are defined as L

_{P}and L

_{S}, respectively. The mutual inductance between the ground-side and vehicle-side coils is defined as M

_{PS}. The current and voltage directions are defined as shown in Figure 4.

_{IN}and V

_{O}are given as

_{P}and C

_{S}are determined as

_{O}increases linearly with the input voltage V

_{IN}. This is similar to ideal transformer behavior but different in coefficient. The output voltage also increases the mutual inductances or coupling factor, as shown in Equation (1). If the input and output voltage is approximately equivalent, the self-inductance value of the secondary (vehicle-side) coil needs to be much higher than that of the primary (ground-side) coil.

#### 3.1.2. Dynamic System Analysis

_{1}, L

_{2}and L

_{S}, respectively. The mutual inductances between coil 1 and coil 2, between coil 1 and the vehicle-side coil, and between coil 2 and the vehicle-side coil are defined as M

_{12}, M

_{1S}and M

_{2S}, respectively.

_{IN}and V

_{O}are given as

_{1}and L

_{2}have the same values as L, because the ground-side coils have identical shapes and windings. To achieve effective power transfer, the input power factor approximates unity. The resonant capacitors defined C

_{P1},C

_{P2}and C

_{S}are determined as

_{O}increases linearly with the input voltage V

_{IN}in a similar fashion as for the stationary system but, with a difference of a coupling factor term. The term is the sum of the coupling factors which the vehicle-side coil interlinks with. In this case, the two ground-side coils. From this equation, the design concept of the vehicle-side coil is the same as the stationary WPT system, and the vehicle-side coil is able to use both the stationary and dynamic coils.

#### 3.2. Experimental Results

#### 3.2.1. Stationary WPT System Results

_{IN}. The circuit topology used was consistent with the topology detailed in Figure 1, and the number of ground-side coils, N, was one. Table 4 lists the experimental circuit parameters. The position of the vehicle-side coil was kept at a nominal air-gap of 170 mm without misalignment. The operating frequency in the inverter was set to 85 kHz and was constant throughout the stationary experiment. The input voltage V

_{DC}was proportional to the load voltage V

_{L}, as shown in Equation (4). Load power P

_{L}was 25 kW and efficiency was measured as 85.5% at V

_{IN}= 485.6 V

_{DC}in Figure 1. The theoretical output voltage V’

_{L}calculated by Equation (4) using Table 3 is 413.4 V. However, the experimental output voltage V

_{L}was 398.4 V. The difference between the theoretical and experimental voltage may be explained by the decision not to take into account the winding resistances within the WPT coils and the misalignment of resonant capacitors in theoretical value.

#### 3.2.2. Dynamic WPT System Test Bench Results

_{DC}and frequency were controlled to be constant values of 240 V and 85 kHz, respectively. No other feedback loop was installed in this system.

_{L}of 265 V. As can be seen from Figure 9, there are times when the output power is equal to zero. This phenomenon results from PS characteristics and connecting a battery load. The transferred output voltage is also lower than the load voltage with a low coupling factor. The loss from the road power (i.e., ground-side coils), the filter and the inverter, was 1600 W in this system. The receiving energy of the vehicle from one ground-side coil to the next coil was around 28 Wh for this experiment’s conditions. The total energy conversion efficiency from the center of the first ground-side coil to the center of the fifth coil was 56.92%.

#### 3.2.3. Dynamic WPT System Real-Car Test Results

## 4. Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Photographs of the WPT coils tested in this paper. (

**a**) Ground-side coil, (

**b**) vehicle-side coil.

**Figure 3.**Experimental parameters of the WPT coils in case of the occurrence of misalignment. (

**a**) Measured self and mutual inductances. (

**b**) Measured equivalent resistances.

**Figure 6.**Experimental results of the stationary WPT system at the aligned condition as a function of input voltage V

_{DC}.

**Figure 11.**Experimental results of the load voltages and currents in the real-car test at vehicle velocity v

_{x}= 19 km/h.

**Figure 12.**Experimental results of the load voltages and currents in the real-car test at vehicle velocity v

_{x}= 52 km/h.

System Components | Specifications |
---|---|

Output power | Max 25 kW |

Air gap | 170 mm |

Frequency | 85 kHz |

AC/DC converter | Variable output voltage ^{1} |

Inverter | Full SiC FETs ^{2} |

Rectifier | Double current rectifier |

Vehicle-side coil cooling | Water cooling |

^{1}power-factor-correction (PFC) function is included;

^{2}FET means field effect transistor.

Side of Coil | Size (mm) | Winding |
---|---|---|

Ground-side | 620 × 600 × 40 | 6 T × 10 p ^{1} |

Vehicle-side | 430 × 374 × 38.5 | 45 T × 1 p |

^{1}“p” stands for parallel connection.

L_{N} | L_{S} | r_{N} | r_{S} | k |
---|---|---|---|---|

22.4 μH | 658 μH | 51.6 mΩ | 1360 mΩ | 0.235 |

C_{N} | C_{S} | L_{L1} | L_{L2} | R_{L} |
---|---|---|---|---|

17.3 nF | 13.7 nF | 300 μH | 300 μH | 7.6 Ω |

C_{N} | C_{S} | L_{1} | L_{2} | V_{L} |
---|---|---|---|---|

17.3 nF | 13.7 nF | 300 H | 300 H | 260 V |

Test Result in this Paper | Receiving Power (kW) | Efficiency | Total Energy Conversion Efficiency | Total Received Energy (Wh) |
---|---|---|---|---|

Stationary WPT system | 25 | 85.5% | -- | -- |

Bench test for Resistance | 10.6 | 79.1% | 72.45% | 301 |

Bench test for Battery | 10.1 | 79.2% | 56.92% | 149 |

Real-car test (v_{x} = 19 km/h) | 6.5 | NA | NA | 2.14 |

Real-car test (v_{x} = 52 km/h) | 5.9 | NA | NA | 0.5 |

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## Share and Cite

**MDPI and ACS Style**

Fujita, T.; Kishi, H.; Uno, H.; Kaneko, Y.
A Real-Car Experiment of a Dynamic Wireless Power Transfer System Based on Parallel-Series Resonant Topology. *World Electr. Veh. J.* **2019**, *10*, 49.
https://doi.org/10.3390/wevj10030049

**AMA Style**

Fujita T, Kishi H, Uno H, Kaneko Y.
A Real-Car Experiment of a Dynamic Wireless Power Transfer System Based on Parallel-Series Resonant Topology. *World Electric Vehicle Journal*. 2019; 10(3):49.
https://doi.org/10.3390/wevj10030049

**Chicago/Turabian Style**

Fujita, Toshiyuki, Hiroyuki Kishi, Hiroshi Uno, and Yasuyoshi Kaneko.
2019. "A Real-Car Experiment of a Dynamic Wireless Power Transfer System Based on Parallel-Series Resonant Topology" *World Electric Vehicle Journal* 10, no. 3: 49.
https://doi.org/10.3390/wevj10030049