Analysis and Design of Wireless Charging System based on SSC

Yaya Wang

1, a

, Guokun Xie

, Kai Zheng

Electrical Automation, Xi`an Traffic Engineering Institute, Mei Bei west road, Binhe new district, Xian, China

Keywords: Resonance, wireless charging, coupling coil, chopper frequency.

Abstract: Based on the series resonance compensation topology structure as the research foundation, taking charging

electric cars as the object, using the simulation software to build a wireless charging system T model

equivalent circuit, by dealing with choosing the right frequency sweep chopping frequency, using the

method of regulating control, solves the problem of wireless power transmission efficiency is low and the

rate of change, and finally the use of Ansoft electromagnetic simulation software Maxwell3D theory

analyses the mutual inductance coil and the relationship between the transmission distance, to the study of

wireless charging of electric cars, has very important significance.

1 INTRODUCTION

Comrade Xi Jinping pointed out in the report to the

19th national congress that "clear water and green

mountains are golden mountains", adhering to the

basic state policy of resource conservation and

environmental protection, electric energy as a kind

of clean energy is widely used in all walks of life,

and electric vehicles as a new type of energy

transportation is an inevitable development trend. As

a safe, convenient and adaptable Power Charging

technology, Wireless Power Transfer (WPT) is the

key technology for the development of pure electric

vehicles in the future. If we master this technology,

we will have the right to speak in this field. Many

companies have designed wireless charging systems

with power up to 3kw (

L. Chen, S. Liu, Y. C. Zhou

and T. J. Cui

, 2011), but there are still some

research points that need to be improved, such as:

how to reduce the coil size to reduce the system cost

when the same power is transmitted, how to make

the system better adapt to the complex situation of

different coil displacements, how to improve the

transmission efficiency while reducing the loss, etc.,

are hot issues in current research. Based on previous

studies, this paper adopts the transformer wireless

charging control system to regulate the output

power, and mainly analyzes the influence of the

characteristics, frequency characteristics and

coupling coefficient of the series-series resonant

topological switch on the output power and

transmission efficiency.

2 S-S RESONANT TOPOLOGY

MODEL ANALYSIS

The main principle of wireless charging technology

is that the transmitter coil and the receiver coil have

the same resonant frequency. To achieve this

purpose, an appropriate resonant compensation

capacitor is usually added to the two coils.

According to the transmitting terminaland receiving

terminal network connection relationship, WPT

system topology structure can be divided into series

-series (S-S), series and parallel (S-P), parallel and

series (P-S), parallel-parallel (P-P) of these four

basic structure, the series-series(S-S) resonant

topology is the best power wireless transmission

resonant topology (Yongsheng Fu, Lei Shi,

Kevin(hua) Bai, 2014). Figure 1 is transformer

equivalent model of (S-S) resonant.

Figure 1. S-Stransformer equivalent model.

It is assumed from figure 1 that:

336

Wang, Y., Xie, G. and Zheng, K.

Analysis and Design of Wireless Charging System based on SSC.

DOI: 10.5220/0008480903360340

In Proceedings of 5th International Conference on Vehicle, Mechanical and Electrical Engineering (ICVMEE 2019), pages 336-340

ISBN: 978-989-758-412-1

111

LwjRZ 

(1)

222

LwjRRZ



(2)

LwX *

(3)

LwjZ **

(4)

Where, R1 is the internal resistance of L1 of the

primary coil, R2 is the internal resistance of L2 of

the secondary coil, and RL is the load, C1 and C2

are the resonant capacitors of the primary side and

the secondary side respectively. Lm is the mutual

inductance of the primary and secondary coil.

Therefore, it can be known from the transformer

principle that:









0**

221

211

ZIZI

UIZIZ

inm

(5)

Equation 5 shows that:



















)*(*

***

)*(*

inm

LwZZ

ULwj

LwZZ

(6)

Total power input of circuit:



cos*

|)*(*|

||*

)*Re(

inin

LwZZ

IUP





(7)

Total power output of circuit:

|])*(*[|

)*(**

*||

mLin

Lout

LwZZ

LwRU

RIP





(8)

Total circuit efficiency:





cos*|])*(*[*|

*)*(

212

out

LwZZZ

RLw





(9)

Maximum transmission efficiency:

%100*

])*()()[(

*)*(

212

mLL

LwRRRRR

RLw







(10)

3 COIL MODEL AND CIRCUIT

SIMULATION

3.1 Coil Model

By equation (10) with known as in resonance circuit

and load coil of the case, the transmission efficiency

of circuit is only related to the mutual inductance

coil, the greater the mutual inductance transmission

efficiency is higher. According to the principle of

magnetic coupling, when the same wire is used to

form a coil, the larger the coil area, the greater the

mutual inductance value and mutual inductance

coefficient will be. So the method to improve the

transmission efficiency of system is within the

allowed space set up the large area of the coil.

This design by using the finite element analysis

software Ansys/Maxwell circuit parameters of the

simulation to get the best parameters based on figure

2 inject 50 KHZ high frequency ac signal to the coil,

the magnetic field lines toward the trend and

magnetic field strength.

3.2 Principles of WPT

Principle of electric vehicle charging system: power

frequency alternating current (ac) is obtained by

rectifying filtering first stable direct current (A.K.

RamRakhyani, S.Mirrabbasi, and C.Mu, 2018), then

through high frequency inverter for high frequency

square wave ac, repass transmitter resonant

compensating network and launch coil to make work

in resonant state, when transmitting circuit

frequency and receiving coil and the receiver equals

the compensating network frequency, magnetic field

energy can be transmitted through magnetic

resonance (NMR), receiving coil get electricity

finally through the high frequency output rectifier to

the electric car battery.

3.3 Circuit Simulation

For s - s resonant topology, switch frequency

directly affects the system's output power to the total

loss, so the simulation of the system do sweep with

the equivalent circuit of transformer, zero point of

resonance analysis impedance has two, as shown in

figure 3 so this design choice than 50 KHZ and

chopping frequency can be changed as a resonance

point, make the output power under control.

Analysis and Design of Wireless Charging System based on SSC

337

Figure 2. Lines of magnetic force coupling coil and the magnetic field intensity distribution.

Figure 3. System total impedance and phase VS switch frequency.

According to the working principle of WPT and

simulation of coil parameters, the system simulation

waveform is shown in figure 4.

Simulation waveform shows by the figure 4

system of charging: when adjusting the input dc

voltage of 220 v, the charging power of about 345

ICVMEE 2019 - 5th International Conference on Vehicle, Mechanical and Electrical Engineering

338

w, system about 60 ms into a stable state, the

charging waveform smooth system safe and reliable

operation.

Figure 4. System simulation waveform.

4 COUPLING COEFFICIENT

MEASUREMENT AND

ANALYSIS

Coupling coefficient is the physical quantity that

reflects the coupling degree of transmitting coil and

receiving coil most directly. The coupling

coefficient varies with the transmission distance of

the system. The change of coupling coefficient

directly affects the output power and transmission

efficiency of the system.

Can be seen from the figure 5, the farther the

transmission distance, the smaller the mutual

inductance between the two coils M, the smaller the

coupling coefficient k, and the smaller the coupling

coefficient of output power and transmission

efficiency is smaller, so, choose appropriate

transmission distance is the factors affecting the

output power and the transmission efficiency is very

important.

5 CONCLUSION

Based on the s-s resonant topological structure, the

design obtains the model parameters and chopper

frequency of the wireless charging system through

simulation analysis, and obtains the charging

simulation waveform by simulating the T equivalent

circuit diagram of the wireless charging system. It is

pointed out that the system must detect the changes

of coil mutual inductance and leakage inductance in

real time according to the changes of relative

displacements between coils in order to charge

stable. The relationship between coil mutual

inductance M and transmission distance d is

analyzed theoretically.

ACKNOWLEDGEMENTS

Scientific research project of Shaanxi provincial

education department in 2019, search and design of

voltage regulating wireless charging system based

on SSC.

REFERENCES

A.K. RamRakhyani, S.Mirrabbasi, and C.Mu, “Design and

Optimization of Resonance-Based Efficient Wireless

Power Delivery System for Bionmedical Implants,”

IEEE Trans. Biomed. Circuit Syst., vol.5, pp. 48-63.

Http: // info. xcar. com. cn/ 201501/news _ 1750736 _

1.html.

L. Chen, S. Liu, Y. C. Zhou and T. J. Cui, “An

optimizable circuit structure for high-efficiency

wireless power transfer”, IEEE Trans. Ind.

Electron.,vol.60, no.1, 2011, pp. 339 –349.

Yongsheng Fu, Lei Shi, Kevin (hua) Bai. “High-

Frequency Wireless Charging System Study Based on

Normally-off GaN HEMTs,” IEEE Wide Bandgap

Device and Application Conference (WiPDA 2014-

10).

Analysis and Design of Wireless Charging System based on SSC

339

Figure 5. Relation curve between coupling coefficient and

transmission distance.

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340