# Inductive Power Transfer Systems for Bus-Stop-Powered Electric Vehicles

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Inductive Power Transfer System

_{dc}, the DC-AC H-bridge inverter is utilized to generate the high frequency square wave voltage V

_{in}. The EE-shaped ferrite cores are utilized to transfer the power to secondary side load (by pick-up coil and receiver). The primary inductance and secondary inductance are L

_{p}and L

_{s}. The mutual inductance is M (=L

_{m}). The coupling coefficient (k) is defined as in (1):

^{−7}H/m). Figure 2c shows the equivalent circuit of the primary series resonant and secondary parallel resonant (SP) topology IPT system and Figure 2d shows the secondary parallel resonant (P) topology IPT system, respectively.

_{m}) and the equivalent resistance of core loss is R

_{m}. The primary and secondary leakage inductances are L

_{lp}and L

_{ls}as in (2).

_{lp}= (1−k)L

_{p}, L

_{ls}= (1−k)L

_{s}

_{p}and r

_{s}. The load is simplified as R

_{L}. The primary series resonant capacitor is C

_{P}and the secondary parallel resonant capacitor is Cs. The transfer function of the SP topology IPT system is given as in (3):

_{H}) operated at the high frequency domain is as in (4):

_{H}) is as in (4) and the low frequency pole (s = −P

_{L}) is as in (8):

## 3. Frequency Response of the IPT System

_{P}(0.2 μF) and the secondary parallel resonant capacitor is Cs (0.2 μF). The resistances r

_{p}and r

_{s}are 0.72 Ω. The load resistance R

_{L}is 100 Ω.

_{r1}and ω

_{r2}move to each other as the air gap is increased as shown in Figure 3a. In P topology, the resonant peak value is decreased as the air gap is increased as shown in Figure 3b. Therefore, the SP topology is suitable for a large air gap IPT system and the P topology suits a small air gap IPT system. The coupling coefficient and resonant frequency of the IPT system with varied air gap are given in Table 1.

_{dc}: 30 V). The resonant frequencies of the IPT system are 15 kHz (ω

_{r1}) and 23 kHz (ω

_{r2}) under air gap 5 mm, 17 kHz (ω

_{r1}) and 22 kHz (ω

_{r2}) under air gap 10 mm, and 20 kHz (ω

_{r1,2}) under air gap 20 mm, respectively. The input power and output power are increased and the efficiency is decreased as air gap increased. The measurement results of the SP topology IPT system are given in Table 2. Figure 3d shows the input power and output power of the P topology IPT system with varied air gap (test results; V

_{dc}: 30 V). The input power, output power, and the efficiency are decreased as air gap increased. The measurement results of the P topology IPT system are given in Table 2. As shown in Figure 3, the measurement results agree with the simulation results produced by using MATLAB.

## 4. Simulation and Experimental Results

#### 4.1. Air Gap

_{dc}: 150 V; fsw: 20 kHz). The efficiency, input power, and output power of the P topology IPT system are 85%, 150 W, and 128 W under load 100 Ω (gap: 10 mm). The efficiency, input power, and output power of the P topology IPT system are 79%, 150 W, and 119 W under load 200 Ω (gap: 15 mm). The efficiency, input power, and output power of the P topology IPT system are 72%, 120 W, and 86 W under load 300 Ω (gap: 20 mm). The efficiency of the P topology IPT system is affected by the load and air gap.

#### 4.2. Displacement

#### 4.3. Dislocation

#### 4.4. Motion

_{s}) and current (i

_{s}) waveforms of the IPT system are varied seriously.

_{s}) and current (i

_{s}) waveforms of mode 2H are high and stable due to the adequate overlap operation for three H-bridge inverters. Compared Figure 10 (mode 2H) with Figure 9 (mode 1H), mode 2H exhibits high efficiency 76%, stable input power and output power. Therefore, the P topology IPT system operated at mode 2H is validated to meet the requirements for bus-stop-powered EVs.

## 5. IPT System Operated at Large Air Gap

_{p}(147 μH) and L

_{s}(147 μH). The primary series capacitor and secondary parallel capacitor are C

_{p}(0.43 μF) and C

_{s}(0.43 μF). Therefore, the resonant frequency is designed as 20 kHz.

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

- Miller, J.M.; Onar, O.C.; Chinthavali, M. Primary-side power flow control of wireless power transfer for electric vehicle charging. IEEE J. Emerg. Sel. Top. Power Electron.
**2015**, 3, 147–162. [Google Scholar] [CrossRef] - Wang, C.; Stielau, O.H.; Covic, G.A. Design considerations for a contactless electric vehicle battery charger. IEEE Trans. Ind. Electron.
**2005**, 52, 1308–1314. [Google Scholar] [CrossRef] - Li, S.; Mi, C.C. Wireless power transfer for electric vehicle applications. IEEE J. Emerg. Sel. Top. Power Electron.
**2015**, 3, 4–17. [Google Scholar] - Choi, S.Y.; Gu, B.W.; Jeong, S.Y.; Rim, C.T. Advances in wireless power transfer systems for roadway-powered electric vehicles. IEEE J. Emerg. Sel. Top. Power Electron.
**2015**, 3, 18–36. [Google Scholar] [CrossRef] - Zhang, W.; Wong, S.; Tse, C.K.; Chen, Q. An optimized track length in roadway inductive power transfer systems. IEEE J. Emerg. Sel. Top. Power Electron.
**2014**, 2, 598–608. [Google Scholar] [CrossRef] - Shin, J.; Shin, S.; Kim, Y.; Ahn, S.; Lee, S.; Jung, G.; Jeon, S.; Cho, D. Design and implementation of shaped magnetic-resonance-based wireless power transfer system for roadway-powered moving electric vehicles. IEEE Trans. Ind. Electron.
**2014**, 61, 1179–1192. [Google Scholar] [CrossRef] - Chen, L.; Nagendra, G.R.; Boys, J.T.; Covic, G.A. Double-coupled systems for IPT roadway applications. IEEE J. Emerg. Sel. Top. Power Electron.
**2015**, 3, 37–49. [Google Scholar] [CrossRef] - Nagendra, G.R.; Chen, L.; Covic, G.A.; Boys, J.T. Detection of EVs on IPT highways. IEEE J. Emerg. Sel. Top. Power Electron.
**2014**, 2, 584–597. [Google Scholar] [CrossRef] - Kurs, A.; Karalis, A.; Moffatt, R.; Joannopoulos, J.D.; Fisher, P.; Soljacic, M. Wireless power transfer via strongly coupled magnetic resonances. Science
**2007**, 317, 83–86. [Google Scholar] [CrossRef] [PubMed] - Zhang, W.; Wong, S.; Tse, C.K.; Chen, Q. Analysis and comparison of secondary series- and parallel-compensated inductive power transfer systems operating for optimal efficiency and load-independent voltage-transfer ratio. IEEE Trans. Power Electron.
**2014**, 29, 2979–2990. [Google Scholar] [CrossRef] - Aldhaher, S.; Luk, P.C.; Whidborne, J.F. Electronic tuning of misaligned coils in wireless power transfer systems. IEEE Trans. Power Electron.
**2014**, 29, 5975–5982. [Google Scholar] [CrossRef] - Pantic, Z.; Lee, K.; Lukic, S.M. Multifrequency inductive power transfer. IEEE Trans. Power Electron.
**2014**, 29, 5995–6005. [Google Scholar] [CrossRef] - Pinuela, M.; Yates, D.C.; Lucyszyn, S.; Mitcheson, P.D. Maximizing dc-to-load efficiency for inductive power transfer. IEEE Trans. Power Electron.
**2013**, 28, 2437–2447. [Google Scholar] [CrossRef] [Green Version] - Musavi, F.; Eberle, W. Overview of wireless power transfer technologies for electric vehicle battery charging. IET Power Electron.
**2013**, 7, 60–66. [Google Scholar] [CrossRef]

**Figure 2.**Simplified inductive power transfer system. (

**a**) Circuit of the IPT system; (

**b**) EE-shaped cores; (

**c**) Equivalent circuit of the SP topology; (

**d**) Equivalent circuit of the P topology.

**Figure 3.**Frequency response of the IPT system based on EE-shaped cores with varied air gap. (

**a**) SP topology (MATLAB); (

**b**) P topology (MATLAB); (

**c**) Input power and output power of SP topology (test results; V

_{dc}: 30 V); (

**d**) Input power and output power of P topology (test results; V

_{dc}: 30 V).

**Figure 4.**Prototype of measurement for the P topology IPT system. (

**a**) multi-H-bridge inverters (

**b**) prototype of measurement.

**Figure 5.**Efficiency, input power, and output power of the P topology IPT system with varied air gap and frequency (V

_{dc}: 150 V; R

_{L}: 100 Ω). (

**a**) Efficiency, input power, and output power; (

**b**) Varied air gap from 5 mm to 65 mm (20 kHz); (

**c**) Varied load (20 kHz).

**Figure 6.**Displacement effect of the IPT system with varied air gap from 5 mm to 40 mm (V

_{dc}: 150 V; fsw: 20 kHz). (

**a**) Efficiency, input power; and output power (

**b**) Displacement.

**Figure 7.**Dislocation effect of the IPT system with varied air gap from 5 mm to 40 mm (fsw: 20 kHz). (

**a**) Efficiency, input power; and output power (

**b**) Dislocation.

**Figure 8.**Efficiency, input power, and output power of the IPT system in motion. (

**a**) Air gap: 10 mm (

**b**) Air gap: 20 mm.

**Figure 9.**Waveforms of the P topology IPT system operated at mode 1H (air gap: 10 mm; time: 100 ms/div.; voltage: 200 v/div.; current i

_{p1}, i

_{p2}, and i

_{p3}: 5 A/div.; current i

_{s}: 2 A/div.). (

**a**) Voltages; (

**b**) Currents.

**Figure 10.**Waveforms of the P topology IPT system operated at mode 2H (air gap: 10 mm; time: 100 ms/div.; voltage: 200 v/div.; current i

_{p1}, i

_{p2}, and i

_{p3}: 5 A/div.; current i

_{s}: 2 A/div.) (

**a**) Voltages; (

**b**) Currents.

**Figure 11.**IPT system based on finite element analysis (V

_{dc}: 300 V; fsw: 20 kHz; air gap: 150 mm). (

**a**) 3D Model of EE-shaped ferrite cores; (

**b**) Circuit of the SP topology.

**Figure 12.**Waveforms of the IPT system based on finite element analysis (V

_{dc}: 300 V; fsw: 20 kHz; air gap: 150 mm). (

**a**) Input and output voltages of SP topology; (

**b**) Input and output currents of SP topology; (

**c**) Input and output voltages of P topology; (

**d**) Input and output currents of P topology.

Gap | 5 mm | 10 mm | 20 mm |
---|---|---|---|

L_{lp} | 217.7 μH | 237.2 μH | 282.7 μH |

L_{ls} | 217.7 μH | 237.2 μH | 282.7 μH |

L_{m} | 107.3 μH | 87.8 μH | 42.3 μH |

k | 0.33 | 0.27 | 0.13 |

ω_{r1} | 15 kHz | 17 kHz | 20 kHz |

ω_{r2} | 23 kHz | 22 kHz | 20 kHz |

ω_{r} | 20 kHz | 20 kHz | 20 kHz |

SP topology | Gap | 5 mm ω_{r1}: 15 kHz | 5 mm ω_{r2}: 23 kHz | 10 mm ω_{r1}: 17 kHz | 10 mm ω_{r2}: 22 kHz | 20 mm ω_{r1,2}: 20 kHz |

Input power | 30 W | 66 W | 45 W | 72 W | 177 W | |

Output power | 28 W | 59.3 W | 38.4 W | 64 W | 136.9 W | |

Efficiency | 94% | 90% | 85% | 89% | 77% | |

P topology | Gap | 5 mm ω_{r}: 20 kHz | 10 mm ω_{r}: 20 kHz | 20 mm ω_{r}: 20 kHz | ||

Input power | 13.2 W | 7.2 W | 3.9 W | |||

Output power | 11.9 W | 5.5 W | 1.6 W | |||

Efficiency | 90% | 77% | 40% |

Air Gap (mm) | 5 | 10 | 20 |
---|---|---|---|

Efficiency | 93% | 85% | 60% |

Input Power(W) | 300 | 150 | 54 |

Output Power(W) | 278 | 128 | 32 |

**Table 4.**Displacement effect of the IPT system with varied air gap from 5 mm to 40 mm (fsw: 20 kHz).

Displacement | Air Gap (mm) | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 |
---|---|---|---|---|---|---|---|---|---|

Displacement: 10 mm | Efficiency | 86.8% | 73.2% | 61.4% | 49.5% | 33.3% | 22.9% | 14.8% | 7.4% |

Input power (W) | 219 | 105 | 72 | 49.5 | 37.5 | 31.5 | 28.5 | 27 | |

Output power (W) | 191.1 | 77.2 | 44.1 | 24.5 | 12.5 | 7.2 | 4.2 | 2 | |

Displacement: 20 mm | Efficiency | 76.3% | 62.7% | 45.4% | 33.3% | 24.2% | 15.0% | 10.6% | 6.0% |

Input power (W) | 97.5 | 64.5 | 46.5 | 37.5 | 33 | 30 | 27 | 27 | |

Output power (W) | 74.4 | 40.5 | 21.1 | 12.5 | 8 | 4.5 | 2.9 | 1.6 |

Dislocation | Air Gap (mm) | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 |
---|---|---|---|---|---|---|---|---|---|

Dislocation: 10 mm | Efficiency | 87.5% | 72.1% | 54.7% | 41.4% | 28.1% | 17.1% | 11% | 7.4% |

Input power (W) | 171 | 87 | 58.5 | 43.3 | 36 | 30 | 28.5 | 27 | |

Output power (W) | 147.9 | 62.7 | 32 | 18 | 10.1 | 5.1 | 3.1 | 2 | |

Dislocation: 20 mm | Efficiency | 41.8% | 31.2% | 21.7% | 18.1% | 11.8% | 8.1% | 6.0% | 4.4% |

Input power (W) | 37.5 | 34.5 | 31.5 | 30 | 28.5 | 27 | 27 | 25.5 | |

Output power (W) | 15.7 | 10.8 | 6.8 | 5.4 | 3.3 | 2.2 | 1.6 | 1.1 |

Air Gap | X-Axis (mm) | −40 | −30 | −20 | −10 | 0 | 10 | 20 | 30 | 40 |
---|---|---|---|---|---|---|---|---|---|---|

Air Gap: 10 mm | Efficiency | 85% | 81% | 0% | 78% | 85% | 78% | 0% | 81% | 85% |

Input power (W) | 150 | 117 | 0 | 98 | 150 | 98 | 0 | 117 | 150 | |

Output power (W) | 128 | 95 | 0 | 77 | 128 | 77 | 0 | 95 | 128 | |

Air Gap: 20 mm | Efficiency | 56% | 49% | 0% | 43% | 56% | 43% | 0% | 49% | 56% |

Input power (W) | 54 | 49 | 0 | 45 | 54 | 45 | 0 | 49 | 54 | |

Output power (W) | 30 | 24 | 0 | 19 | 30 | 19 | 0 | 24 | 30 |

Air Gap | X-Axis (mm) | −40 | −30 | −20 | −10 | 0 | 10 | 20 | 30 | 40 |
---|---|---|---|---|---|---|---|---|---|---|

Air Gap: 10 mm | Efficiency | 76% | 76% | 75% | 75% | 76% | 75% | 75% | 76% | 76% |

Input power (W) | 238 | 240 | 230 | 230 | 224 | 230 | 230 | 240 | 238 | |

Output power (W) | 181 | 182 | 173 | 173 | 169 | 173 | 173 | 182 | 181 | |

Air Gap: 20 mm | Efficiency | 52% | 51% | 50% | 49% | 51% | 49% | 50% | 51% | 52% |

Input power (W) | 115 | 114 | 114 | 113 | 107 | 113 | 114 | 114 | 115 | |

Output power (W) | 59.4 | 58.3 | 57.2 | 55.1 | 54.1 | 55.1 | 57.2 | 58.3 | 59.4 |

Air Gap | X-Axis (mm) | −40 | −30 | −20 | −10 | 0 | 10 | 20 | 30 | 40 |
---|---|---|---|---|---|---|---|---|---|---|

Air Gap: 10 mm | Efficiency | 58.1% | 59.4% | 59.7% | 62.4% | 63.0% | 62.4% | 59.7% | 59.4% | 58.1% |

Input power (W) | 237 | 246 | 250.5 | 268.5 | 277.5 | 268.5 | 250.5 | 246 | 237 | |

Output power (W) | 137.8 | 146.2 | 149.6 | 167.4 | 174.8 | 167.4 | 149.6 | 146.2 | 137.8 | |

Air Gap: 20 mm | Efficiency | 31.3% | 33.7% | 34.4% | 36.1% | 37.5% | 36.1% | 34.4% | 33.7% | 31.3% |

Input power (W) | 135 | 142.5 | 145.5 | 150 | 150 | 150 | 145.5 | 142.5 | 135 | |

Output power (W) | 42.3 | 48.0 | 50.0 | 54.1 | 56.2 | 54.1 | 50.0 | 48.0 | 42.3 |

© 2016 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/).

## Share and Cite

**MDPI and ACS Style**

Hou, C.-C.; Chang, K.-Y.
Inductive Power Transfer Systems for Bus-Stop-Powered Electric Vehicles. *Energies* **2016**, *9*, 512.
https://doi.org/10.3390/en9070512

**AMA Style**

Hou C-C, Chang K-Y.
Inductive Power Transfer Systems for Bus-Stop-Powered Electric Vehicles. *Energies*. 2016; 9(7):512.
https://doi.org/10.3390/en9070512

**Chicago/Turabian Style**

Hou, Chung-Chuan, and Kuei-Yuan Chang.
2016. "Inductive Power Transfer Systems for Bus-Stop-Powered Electric Vehicles" *Energies* 9, no. 7: 512.
https://doi.org/10.3390/en9070512