# A Power and Data Decoupled Transmission Method for Wireless Power Transfer Systems via a Shared Inductive Link

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## Abstract

**:**

## 1. Introduction

## 2. System Overview

#### 2.1. Hysteresis Voltage Control

_{p}, C

_{p}and L

_{s}, C

_{s}constitute the primary parallel and secondary series resonant circuits, respectively. D

_{1}~ D

_{4}constitute the rectifier. R

_{eq}is the equivalent input resistance of the rectifier circuit and equals to 8R

_{L}/π

^{2}. C

_{L}is the output filter capacitor and R

_{L}is the load resistance. E and U

_{L}are the input and load DC voltages, respectively.

_{L-req}with a hysteresis tolerance band of ±u

_{t}. S will be switched to the on state when U

_{L}is smaller than U

_{L-req}− u

_{t}and switched to the off state when U

_{L}is larger than U

_{L-req}+ u

_{t}.

#### 2.2. Power and Data Transfer Principle

_{d}is an AC switch composed of two semiconductor switches (e.g., IGBTs or MOSFETs). C

_{sd}is used to compensate L

_{s}at the data carrier frequency. V

_{d}is the injected data carrier while V

_{o}is the received data carrier. L

_{d}and C

_{d}comprise an LC tuning circuit to maximize the output carrier V

_{o}, satisfying ${\omega}_{d}=1/\sqrt{{L}_{d}{C}_{d}}$, where ω

_{d}is the angular frequency of the data carrier. R

_{d}is the input resistance of the data processing circuit. The data transfer topology is shown in Figure 4, where the data transmitter side consists of a modulation module, while the data receiver side consists of a bandpass filter, an operational amplifier and a demodulation module. An amplitude shift keying (ASK) modulation method is used to generate the data carrier. The generation function of the data carrier can be given as:

_{d}and A

_{c}are the frequency and the amplitude of the data carrier, respectively.

_{d}is turned on when S is off). The proposed system has two working modes: (1) when S is on and S

_{d}is off, power is transferred to the load while data transmission is blocked; (2) when S is off and S

_{d}is on, data is transferred from the secondary side to the primary side while the output capacitor C

_{L}is free running. The circuits of these two working modes are shown in Figure 5.

_{d}is selected higher than the power carrier frequency f

_{p}. This is because the extra data transfer channel would not significantly affect the power transfer and the interference of power transfer on data transfer is easy to suppress; (2) the resonant frequencies of the primary and secondary resonant circuits are identical:

## 3. Interference of Extra Data Transfer Channel on Power Transfer

#### 3.1. Interference of Extra Data Transfer Channel on Power Transfer

_{L}whether the data transfer circuit is added or not. The simplified power transfer circuit without and with the data receiver circuit are shown in Figure 6a,b respectively, where i

_{i}is the equivalent input current source.

_{s}is the secondary side loop impedance, given by Z

_{s}= jωL

_{s}+ 1/jωC

_{s}+ R

_{eq}. M is the mutual inductance.

_{p}

_{1}can be derived as:

_{p}

_{1}is the impedance given by Z

_{p}

_{1}= jωL

_{p}+ 1/jωC

_{p}+ Z

_{r}.

_{i}to the output voltage u

_{eq}

_{1}is:

_{p}

_{2}can be rewritten as:

_{p}

_{2}is the impedance given by:

_{d}is the impedance of the data receiver circuit, given by:

_{p2}= jωL

_{p}+ 1/jωC

_{p}+ Z

_{r}+ Z

_{d}, Z

_{d}= 1/(jωC

_{d}+ 1/jωL

_{d}+ 1/R

_{d}).

_{i}to the output voltage u

_{eq}

_{2}can be calculated as:

#### 3.2. Interference of Power Transfer on Data Transfer

_{op}can be expressed as:

_{i}to the data output V

_{op}is:

_{p}, C

_{p}, L

_{s}and C

_{s}satisfy the assumption shown in Equation (2), then Equation (13) can be simplified as:

_{p}, C

_{p}, R

_{eq}(R

_{L}), M and Z

_{d}. In order to reduce the interference, we can increase R

_{L}, Z

_{d}or reasonably decrease ω

_{p}, M and C

_{p}.

#### 3.3. Data Transfer Channel Analysis

_{s}and −jωMi

_{p}, respectively.

_{d}to the output data carrier V

_{od}

_{1}can be expressed as:

_{sd}= jωL

_{s}+ 1/jωC

_{s}+ 1/jωC

_{sd}.

_{s}, C

_{sd}and L

_{d}, C

_{d}resonate at data transfer frequency, so Equation (16) can be simplified as:

_{d}to the output data carrier V

_{od}

_{2}can be expressed as:

_{rp}= jωL

_{p}+ 1/jωC

_{p}, Z

_{rs}= jωL

_{s}+ 1/jωC

_{s}.

#### 3.4. Consideration for the Data Transfer Rate

_{cr}represents the conventional data transfer rate, t

_{off}is the off-state time while t

_{on}is the on-state time in one operation period of the switch S.

_{cr}or t

_{off}. Increasing d

_{cr}can be achieved by increasing the data carrier frequency. As for t

_{off}, it can be calculated by:

_{L}and C

_{L}.

## 4. Simulation Studies

_{p}, C

_{p}, L

_{s}, C

_{s}can be determined accordingly. The load R

_{L}is 10 Ω, and the required voltage is 16 V, with a hysteresis band of ±0.5 V.

#### 4.1. Bode Plot Analysis of Power Transfer with and without Data Transfer

_{pp}

_{1}shown in Equation (6)) from i

_{i}to u

_{eq}

_{1}and power transfer with data transfer (G

_{pp}

_{2}shown in Equation (11)) from i

_{i}to u

_{eq}

_{2}are shown in Figure 8, where we can see that the difference between “with data transfer” and “without data transfer” can be ignored. This verifies that the addition of the data transfer channel has almost no impact on the power transfer.

#### 4.2. Bode Plot of the Interference from Power Transfer to Data Transfer

_{pd}shown in Equation (13)) from i

_{i}to V

_{op}is shown in Figure 9. From Figure 9, we can see that the magnitude of the interference at the power transfer frequency is around −15 dB, which is pretty low for data transfer, therefore, the SNR can remain pretty high.

#### 4.3. Bode Plot Analysis of the Proposed and Traditional Data Transfer Channel

_{dd}

_{1}shown in Equation (16)) from V

_{d}to V

_{od}

_{1}and traditional data transfer channel (G

_{dd}

_{2}shown in Equation (19)) from V

_{d}to V

_{od}

_{2}are shown in Figure 10, which shows that the data transfer capacity of the proposed channel is larger than the traditional channel at the data carrier frequency, so the proposed method for transferring data when power transfer is blocked is more suitable for data transfer.

## 5. Experimental Verification

_{d}. For the data transfer circuit, the modulation is produced by a CD4051 chip; a ceramic filter chip is used as the bandpass filter while a LT1816 chip is used as the operational amplifier. The demodulation circuit consists of an envelope detector to get the envelop of the carrier and a comparator (LM311 chip) to discriminate the data.

#### 5.1. Interference Analysis of the Data Transfer Channel to Power Transfer

_{L}. Figure 12 shows the experiment results with and without data transfer, where channel 1 indicates the output voltage, channel 4 indicates the voltage of C

_{p}, and channel 2 indicates the output data.

_{L}with data transfer is 16.4 V, while Figure 12b shows that the mean value of U

_{L}without data transfer is 16.2 V. Such a small difference indicates the interference of data transfer to power transfer can be ignored. This verifies the Bode plots shown in Figure 8. Furthermore, the system efficiency of Figure 12a is 71%, and the data transfer rate is 560 kbps.

#### 5.2. Comparison between the Proposed and Traditional Data Transfer Method

_{L}, channel 4 indicates the output voltage of the amplifier, and channel 2 indicates the output data.

#### 5.3. Analysis of the Data Transfer Rate

_{d}. Figure 14a shows the case by increasing the conventional data transfer rate, while Figure 14b indicates the case by increasing the conduction duty cycle of S

_{d}.

_{d}.

#### 5.4. Comparasion Results with the Published Literatures

## 6. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 5.**Circuit of the two working modes: (

**a**) S is on and S

_{d}is off; (

**b**) S

_{d}is on and S is off.

**Figure 6.**The simplified power transfer circuit: (

**a**) without data receiver circuit; (

**b**) with data receiver circuit.

**Figure 7.**The simplified data transfer circuit: (

**a**) proposed data transfer circuit; (

**b**) traditional data transfer circuit.

**Figure 11.**Detailed power and data transfer circuit of the experimental prototype: (

**a**) detailed power transfer circuit; (

**b**) detailed data transfer circuit.

**Figure 12.**The monitored interference of data transfer to power transfer: (

**a**) with data transfer; (

**b**) without data transfer.

**Figure 13.**Comparison between the proposed and traditional data transfer: (

**a**) proposed method; (

**b**) traditional circuit.

**Figure 14.**Increasing of the data transfer rate by: (

**a**) increasing the conventional data transfer rate; (

**b**) increasing conduction duty cycle of S

_{d}.

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

L_{p} | 50 μH | L_{s} | 50 μH |

C_{p} | 60 nF | C_{s} | 61 nF |

M | 12.9 μH | E | 20 V |

L_{1},L_{2} | 150 μH | R_{L} | 10 Ω |

f_{p}U _{L-req} | 91 kHz 16 V | f_{d}u _{t} | 10 MHz 0.5 V |

Reference | Bit Rate (kbps) | Transferred Power(W) | Potential Applications |
---|---|---|---|

[13] | 2.16 | 700 | EVs (Electrical Vehicles) |

[14] | 230 | 40 | Peer to peer wireless power transfer (WPT)) with metal shielding such as in EVs |

[15] | 20 | 500 | High power WPT with low frequency such as in EVs |

[16] | 19.2 | 250 | Drilling systems |

[17] | N/A | N/A | Biomedical implants |

[18] | 6 | N/A | N/A |

This paper | 560 | 25 | Robots, biomedical implants, etc. |

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## Share and Cite

**MDPI and ACS Style**

Li, X.; Wang, H.; Dai, X.
A Power and Data Decoupled Transmission Method for Wireless Power Transfer Systems via a Shared Inductive Link. *Energies* **2018**, *11*, 2161.
https://doi.org/10.3390/en11082161

**AMA Style**

Li X, Wang H, Dai X.
A Power and Data Decoupled Transmission Method for Wireless Power Transfer Systems via a Shared Inductive Link. *Energies*. 2018; 11(8):2161.
https://doi.org/10.3390/en11082161

**Chicago/Turabian Style**

Li, Xiaofei, Haichao Wang, and Xin Dai.
2018. "A Power and Data Decoupled Transmission Method for Wireless Power Transfer Systems via a Shared Inductive Link" *Energies* 11, no. 8: 2161.
https://doi.org/10.3390/en11082161