Subscribe Now Subscribe Today
Research Article
 

Research of the Constant Current Characteristic of Symmetric AC-AC Inductive Coupled Power Transfer System



Lu Zhang, Yue Sun, Zhihui Wang and Chunsen Tang
 
Facebook Twitter Digg Reddit Linkedin StumbleUpon E-mail
ABSTRACT

This study proposes a novel symmetric AC-AC converter for Inductive Power Transfer (ICPT) system which has simple and symmetric circuit topology without requiring large filter capacitor and rectifier. It takes 50 Hz sinusoidal mains input and generates 50 Hz sinusoidal mains output. The constant current characteristic of the system is verified by theoretical analysis based on impulse theorem. The parameter of the resonant link is also derived to ensure the frequency stability of system. Preliminary Simulation and experimental results have verified the validity of the system.

Services
Related Articles in ASCI
Similar Articles in this Journal
Search in Google Scholar
View Citation
Report Citation

 
  How to cite this article:

Lu Zhang, Yue Sun, Zhihui Wang and Chunsen Tang, 2014. Research of the Constant Current Characteristic of Symmetric AC-AC Inductive Coupled Power Transfer System. Journal of Applied Sciences, 14: 144-150.

DOI: 10.3923/jas.2014.144.150

URL: https://scialert.net/abstract/?doi=jas.2014.144.150
 
Received: September 27, 2013; Accepted: November 19, 2013; Published: February 01, 2014



INTRODUCTION

Inductively coupled power transfer (ICPT) technology allows electrical energy to be transferred from a stationary primary source to one or more movable secondary loads over relatively large air gaps (Si et al., 2008; Li et al., 2008). Due to the elimination of physical electric contacts, it is widely used in special fields, such as inflammable and explosive areas and wet or undersea environment (Sample et al., 2011; Li et al., 2012a, 2013; Dai and Sun, 2011; Tang et al., 2009). Moreover, in most industrial ICPT applications, only ac mains are available, so several research have been done to achieve AC output (Boys et al., 2008; Keeling et al., 2010; Sun et al., 2012).

Normally, in order to generate a high-frequency current on the primary side, an AC-DC-AC two-stage power conversion is employed in ICPT systems (Wang et al., 2010, 2011). However, extra semiconductor switches and large DC electrolytic capacitors can be costly and bulky (Safaee et al., 2012; Wu et al., 2011a) which also compromises system reliability. Meanwhile, for high power application, power factor correction circuitry is usually employed along with the rectification stage.

Recently, one of the options to design a direct AC-AC ICPT system is to generate a high-frequency current on the primary side based on free oscillation and energy injection control (Li et al., 2012b). The converter is simplicity but neglect the envelop characteristic of the track current and the design of the pickup. Moreover, it has been pointed out that a low energy storage power supply can be used to achieve AC-AC conversion (Wu et al., 2011b). Such technique can directly generate high frequency track currents whereas the AC-DC stage is still used because that such technique needs a small filter capacitor after the rectifier to reduce the energy storage of the power supply.

In this study, a novel direct sinusoidal input/output AC-AC ICPT system is presented without energy storage links. Compared with the traditional AC-DC-AC ICPT system, its structure and control are simple and the cost is lower. This technique combines the primary direct AC-AC converter with a secondary AC-AC converter based on energy injection control that converts the high frequency AC directly to a low frequency AC output. The expression for the steady load current based on impulse theorem has been discussed in detail. Simulations and experiments have been carried out to verify the theoretical results.

BASIC CIRCUIT OPERATION

The ICPT system can be classified by voltage-fed system and current-fed system. The voltage-fed system normally matches series tuned types of resonant tanks, while current-fed system matches parallel tuned types of resonant tanks. This study uses a typical voltage-fed resonant tank as an example. The main AC-AC topology of voltage-fed ICPT system can be shown in Fig. 1.

As shown in Fig. 1, the system has the symmetric circuit topology from primary part to secondary part. The series resonant network of the primary part consisting of a capacitor Cp in series with an inductor Lp, such series resonant tank is assumed to be driven to produce a high-frequency sinusoidal current with low distortion directly from input AC supply. This sinusoidal current provide the Zero Current Switching (ZCS) conditions for IGBT switches (P1~P4).

Fig. 1: Symmetric AC-AC voltage-fed ICPT system

The secondary part consists the pick up coil Ls which is completely tuned by the series capacitor Cs and the M is the mutual inductance between Lp and Ls, such series resonant tank receives the high-frequency energy by the magnetic fields coupling. The symmetric AC-AC converter that includes four switches (S1~S4) converts the induced high frequency AC directly to a low frequency AC output to the load RL.

Primary AC-AC converter operation (the energy injection and free oscillation control method): The four IGBTs (P1~P4) and four anti-parallel diodes (PD1~PD4) constitute two pairs bidirectional switch to convert the input AC supply into a series of the high frequency rectangular voltage waveform whose amplitude changed according to sinusoidal law (Fig. 2). The primary AC-AC converter operate based on energy injection mode and free oscillation mode: When the polarity of the input AC supply and the resonant current is positive, P1 switched “on”, while other switches (P2~P4) be “off” and the energy is injected into the primary resonant tank, as the polarity of resonant current is negative then P2 switched “on”, while other switches (P1, P3, P4) be “off” and the energy free oscillate in the resonant tank. The signals and waves corresponding to the principle are seen as Fig. 2.

Impulse theorem: There is a very important conclusion called impulse theorem in sample control theory which is the narrow pulses of equal impulse and different shape have the same effect when added to the inertia link. Impulse is the area of narrow pulses and the same effect means to get the same output response wave (Zheng et al., 2010).

Based on the impulse theorem (also called equivalent area principle), in order to make the output voltage waveform equivalent with the desired voltage waveform, the area sum of surrounded by sinusoid half wave with power grid frequency within the half output voltage period must be equal to the one of desired output voltage wave. It especially needs to be pointed that the wave of sinusoid half wave of the input supply is chopped by high frequency pulse signals based on energy injection and free oscillation principal (Fig. 3).

Fig. 2(a-g): Control sequence of the AC-AC resonant soft-switched converter of primary part, (a) Input voltage waveform, (b) Control pulse waveform of P1, (c) Control pulse waveform of P2, (d) Control pulse waveform of P3, (e) Control pulse waveform of P4, (f) Output voltage waveform of the primary inverter and (g) Resonant current waveform of the LP

Fig. 3: Output voltage waveform of primary AC-AC inverter

From Fig. 3, let the amplitude of the input AC supply be Vam, frequency be fa, period be Ta, then the voltage waveform of the input AC supply can be expressed as follow:

(1)

In order to facilitate analysis of the circuit and highlight the main issues, supposed the resonant frequency fc is large enough, then the area of each trapezoidal curve (SABCE) can be replaced by the rectangle area (SABCD), then each area of the voltage Sj can be expressed as:

(2)

where, Vi(j) is the length of the rectangle (SABCD) that is replaced by the instantaneous voltage (t = j) and the width of the rectangle is the half resonant period (0.5Tc). The zero phase frequency must be equal to the secondary resonant frequency so that the maximum output power could be achieved (Wang et al., 2004). Therefore, the resonant period Tc should be:

(3)

where, the ω0 is the zero phase angular frequency of the system, as shown in Fig. 3, the area of surrounded by every sinusoid half wave with the input power after inverted by the high frequency control pulse (S) is expressed as follow:

(4)

where, the N is:

(5)

Then the voltage injected into the primary resonant tank should be:

(6)

The resonant current of primary part iLp can be derived as:

(7)

where the reflected impedance Rr that is dependent on the transformer coupling and operating frequency is given by:

(8)

where, Zs is the impedance of the secondary part and M is the mutual inductance between primary coil and secondary coil.

Secondary AC-AC converter operation: Similarly, the working principle of the secondary part is also based on the energy injection and free oscillation mode, it is the inverse process of the primary part. The high frequency resonant current induced from the primary part is converted into low frequency current waveform whose amplitude changed according to sinusoidal law, the signals and waves corresponding to above principle are seen as Fig. 4.

The equivalent circuit of the secondary part based on the mutual induction model is shown in Fig. 5.

According to the AC impedance model of system resonant tank, the induced voltage Voc of the secondary resonant inductance Ls can be:

(9)

Then, the current of the secondary inductance iLs should be :

(10)

where, Req is the equivalent resistance of the output port of the secondary resonant link and Rs is the inherent resistance of inductor Ls. Substituting Eq.7-9 into Eq.10, the secondary inductance current iLs is derived as:

(11)

It can be seen from Eq.11 that the iLs is independent of the load RL, in addition, the on-and-off period of the switch SL is equal, suppose the working time of the circuit is σ, the expression of the equation as follow can be given according to energy conservation principle:

(12)

Then substituting Eq.12 into Eq.11, the load current iL can be obtained as follow:

(13)

Fig. 4(a-g): Control sequence of the AC-AC resonant soft-switched converter of secondary part, (a) Resonant current waveform of the LS, (b) Control pulse waveform of S1, (c) Control pulse waveform of S2, (d) Control pulse waveform of S3, (e) Control pulse waveform of S4, (f) Output voltage waveform of the primary inverter and (g) Load current waveform of the secondary

From Eq.13, it can been obviously seen that the load current iL is completely independent of the load RL, in other words, the system exactly has the constant current characteristic.

Frequency stability: Form Eq. 13, it can be seen that the constant current characteristic of the system depend on the resonant frequency fc. In order to ensure there is only one zero phase angle frequency, parameters of the system should be satisfied as follow (Zhang et al., 2013):

Fig. 5: Equivalent circuit diagram of the AC-AC resonant soft-switched converter of secondary part

(14)

where the expression of the coupling coefficient k is given by:

(15)

The M is the mutual inductance between primary coil and secondary coil. In addition the Γ is defined as shown below:

(16)

SIMULATION AND EXPERIMENTAL RESULTS

Simulation analysis: On the basis of the analysis discussed above, the simulation model in MATLAB/SIMULINK software of the proposed AC-AC ICPT system can be easily built with the parameters shown in Table 1.

The simulation waveforms of the system are as shown in Fig. 6 and 7. It can be seen from Fig. 6b that the primary resonant current iLp can be directly generated by the input AC supply that is shown in Fig. 6a. The steady-state waveform is achieved after 5 msec and the envelope of the resonant current is in good quality by using the energy injection and free oscillation control method, the current amplitude of iLp is 20 A. The enlarged drawing of the resonant current (39.5~40.5 msec) shown as Fig. 6c shows that the frequency of current iLp is 20 kHz and made to be a low distortion sinusoidal shape, the system operates at ZCS condition because the control pulse waveform of P1 is in phase with iLp.

Fig. 6(a-c): Input AC voltage, resonant current and control pulse waveform of primary part, (a) Primary input ac supply, (b) Resonant current and (c) Enlarged drawing of the resonant current

Fig. 7(a-b): Resonant current waveform of primary part and load

Table 1: Parameters of proposed AC-AC ICPT system

The resonant current waveform of primary part and load current waveform of secondary part with dynamic load switching is shown as Fig. 7.

Current waveform of secondary part with dynamic load switching (a) Primary resonant current waveform with the load RL1 = 400 Ω varying from RL2 = 200 Ω and (b) Load current waveform with the load RL1 = 400 Ω varying from RL2 = 200 Ω.

From Fig. 7a, as the load RL varies from RL1 = 400 Ω to RL2 = 200 Ω the primary resonant current iLp varies from 20 to 10 A, simultaneously, the load current iL shown as Fig. 7b keeps at 2 A, this proves that the symmetric AC-AC ICPT system exactly has the constant current characteristic.

It also can be seen from Fig. 7b that the load current iL is 50 Hz and made in good quality by the low-pass filtering tank followed of the inverter.

DISCUSSION

The symmetric AC-AC ICPT system shown in Fig. 1 has been implemented in a laboratory scale. The inverter consists of four IGBTs (International Rectifier IRGBC40K). The zero-crossing points of inductance current are detected by the current sense transformers (Talema AS-103).

Fig. 8: Experimental waveforms of proposed symmetric AC-AC ICPT system with the load RL1 = 400 Ω varying from RL2 = 200 Ω. (CH1: Control pulse of P1-5 V/div; CH2: Current of the primary inductor iLp-10 A/div; CH3: Current of the load iL-2 A/div)

Phase-locked loop (CD4046) is selected to achieve the ZCS operation for the converter with variable frequency. According to the parameters in Table 1. The experimental results of the proposed ICPT system are shown below.

Figure 8 shows the experimental waveforms the symmetric AC-AC ICPT system, the primary resonant current iLp is controlled based on the energy injection and free oscillation mode, it can be seen from Fig. 8 that the peak resonant current iLp decrease from 8 to 14.9 A as the load RL is switched from 400 to 200 Ω, while the amplitude of the output load current iL still remains at 1.86 A and the frequency keeps at 49.8 Hz. Considering the coil resistance and conduction loss in actual system, the experimental results are lower than the simulation value which is obtained under ideal situation. In addition, the load current iL shown in Fig. 8 (CH3) has slight ripple which is caused by the output filter capacitor Cfs whose discharge time is affected by the sudden change of the load resistance. However, compared with the fact that the power of the system decreased by 50% under dynamic load switching condition, such slight current ripple will not affect our conclusion that the system does have the constant current characteristic.

From Fig. 9, it can be seen that the system has achieved ZCS as the resonant current iLp is in phase with control pulse of P1. It also can be seen that the experimental curve of the current iLp deviates of by about 0.8 kHz from the theoretical value. This is caused by deviations in actual component values from the nominal values. The theoretical results are based on the simplifications in the model that ignores losses in the capacitors and electromagnetic structure.

Fig. 9: Steady-state experimental waveforms of the resonant current and control pulse of primary part (CH1: Control pulse of P1-5 V/div; CH2: Current of the primary inductor iLp-10 A/div; CH3: Current of the load iL-2 A/div)

Therefore, this error in practice doesn’t affect the analyzed results above this section.

CONCLUSION

This study put forward a symmetric AC-AC ICPT system without requiring energy storage links. The expression for the steady load current based on impulse theorem has been discussed in detail under dynamic load switching condition. Simulations and experiments have been carried out to validate the constant current characteristic of the system and it realizes 50 Hz sinusoidal mains input and generates 50 Hz sinusoidal mains output without any large filter capacitor and rectifier, this could save cost and volume of the ICPT system and the system complexity is also been reduced.

ACKNOWLEDGMENTS

This study is financially supported by National Natural Science Foundation of China (No. 51207173, 51277192). I also would like to give my special thanks to the anonymous reviewers for their contributions to this study.

REFERENCES
1:  Boys, J.T., C.Y. Huang and G.A. Covic, 2008. Single-phase unity power-factor inductive power transfer system. Proceedings of the IEEE Power Electronics Specialists Conference, June 15-19, 2008, Rhodes, Greece, pp: 3701-3706.

2:  Dai, X. and Y. Sun, 2011. Study on energy injection control method for inductive power transfer system. J. Univ. Electron. Sci. Technol. China, 40: 69-72.

3:  Keeling, N.A., G.A. Covic and J.T. Boys, 2010. A unity-power-factor IPT pickup for high-power applications. IEEE Trans. Ind. Electron., 57: 744-751.
CrossRef  |  

4:  Li, H.L., A.P. Hu and G.A. Covic, 2012. A direct AC-AC converter for inductive power-transfer systems. IEEE Trans. Power Electron., 27: 661-668.
CrossRef  |  

5:  Li, H.L., A.P. Hu and G.A. Covic, 2008. FPGA controlled high frequency resonant converter for contactless power transfer. Proceedings of the IEEE Power Electronics Specialists Conference, June 15-19, 2008, Rhodes, Greece, pp: 3642-3647.

6:  Li, Y.L., Y. Sun and X. Dai, 2012. Controller design for an uncertain contactless power transfer system. Inform. Technol. J., 11: 971-979.
CrossRef  |  

7:  Li, Y.L., Y. Sun and X. Dai, 2013. μ-Synthesis for frequency uncertainty of the ICPT system. IEEE Trans. Ind. Electron., 60: 291-300.
CrossRef  |  

8:  Safaee, A., D. Yazdani, A. Bakhshai and P.K. Jain, 2012. Multiblock soft-switched bidirectional AC-AC converter using a single loss-less active snubber block. IEEE Trans. Power Electron., 27: 2260-2272.
CrossRef  |  

9:  Sample, A.P., D.A. Meyer and J.R. Smith, 2011. Analysis, experimental results and range adaptation of magnetically coupled resonators for wireless power transfer. IEEE Trans. Ind. Electron., 58: 544-554.
CrossRef  |  

10:  Si, P., A.P. Hu, S. Malpas and D. Budgett, 2008. A frequency control method for regulating wireless power to implantable devices. IEEE Trans. Biomed. Circuits Syst., 2: 22-29.
CrossRef  |  Direct Link  |  

11:  Sun, Y., X. Lv, Z. Wang and C. Tang, 2012. A quasi sliding mode output control for inductively coupled power transfer system. Inform. Technol. J., 11: 1744-1750.
CrossRef  |  Direct Link  |  

12:  Tang, C.S., Y. Sun, Y.G. Su, S.K. Nguang and A.P. Hu, 2009. Determining multiple Steady-state ZCS operating points of a Switch-mode contactless power transfer system. IEEE Trans. Power Electron., 24: 416-425.
CrossRef  |  

13:  Wang, C.S., G.A. Covic and O.H. Stielau, 2004. Power transfer capability and bifurcation phenomena of loosely coupled inductive power transfer systems. IEEE Trans. Ind. Electron., 51: 148-157.
CrossRef  |  

14:  Wang, Z.H., Y. Sun, X. Dai and C.S. Tang, 2011. Design of converter of DC-AC type contactless power transfer system. J. Chongqing Univ., 34: 38-43.
Direct Link  |  

15:  Wang, Z.H., Y. Sun, Y.G. Su, X. Dai and C.S. Tang, 2010. A new type AC/DC/AC converter for contactless power transfer system. Trans. China Electrotech. Soc., 25: 84-89.

16:  Wu, H.H., G.A. Covic, J.T. Boys and D.J. Robertson, 2011. A series-tuned inductive-power-transfer pickup with a controllable AC-voltage output. IEEE Trans. Power Electron., 26: 98-109.
CrossRef  |  

17:  Wu, H.H., G.A. Covic and J. Boys, 2011. A low energy storage IPT system using AC processing controllers. Proceedings of the 6th IEEE Conference on Industrial Electronics and Applications, June 21-23, 2011, Beijing, China, pp: 351-356.

18:  Zhang, L., Y. Sun, Z. Wang and C. Tang, 2013. Analysis of bifurcation phenomena of voltage-fed inductively coupled power transfer system varying with coupling coefficient. Inform. Technol. J., 12: 1176-1183.
CrossRef  |  Direct Link  |  

19:  Zheng, S.C., Q.Z. Zhou, X.H. Cao and H. Zhu, 2010. Principle of single phase AC/AC converter based on plugged pulse fashion and PWM control. Trans. China Electrotech. Soc., 25: 136-141.
Direct Link  |  

©  2021 Science Alert. All Rights Reserved