Analysis of Circuit for Dynamic Wireless Power Transfer by Stepping Stone System

Transcription

1 Analysis of Circuit for Dynamic Wireless Poer Transfer by Stepping Stone System 6mm Hiroshi Uno ) Jun Yamada ) Yasuyoshi Kaneko ) Toshiyuki Fujita ) Hiroyuki Kishi ) ) Saitama University, Graduate school of Science and Engineering, 55 Shimo-Okubo, Sakura-ku, Saitama-shi, Saitama, , Japan ( h.uno.48@ms.saitama-u.ac.jp) ) Technova Inc., 3th Fl. The Imperial Hotel Toer, - Uchisaiai-cho, -chome, Chiyoda-ku, Tokyo, -, Japan Presented at EVS 3 & EVTeC 8, Kobe, Japan, October - 3, 8 ABSTRACT: Electric Vehicles (EVs) has risen to prominence as a research topic due to contemporary environmental concerns and the resultant need for energy conservation. One of the challenges in designing EVs is extending their cruising distance. An approach to address this problem is dynamic ireless poer transfer. This paper aims to provide a really simple model dynamic ireless poer transfer system. Specific attention is given to verifying the coupling coefficient hen the secondary coil is misaligned. The model is used to analyze voltage and current characteristics in to different in to topologies, series-series (SS) and parallel series (PS). Findings are tested validated via a simulation and an experiment. KEY WORDS: Wireless Poer Transfer, Dynamic Wireless Poer Transfer, Circuit Topology. INTRODUCTION Contemporary environmental concerns and the resultant need for energy conservation has highlighted electric vehicles (EVs) as one of cars orthy of siginificant research focus. One of the biggest problems presented by EVs is that the cruising distance is shorter and fueling time is longer than that of a car poered by fuels. Dynamic ireless poer transfer (DWPT) () is proposed as a method for solving these problems. To main approaches exist, namely the loop coll approach (), and the location ith spacing approach ()(3)(4)(5), ithin hich there are specific different methods. This paper dras on the stepping stone system method proposed in references () and (3). Compared ith the loop coil method, the stepping stone system is expected to be cheaper and easier to implement, in terms of the laying of the ground coils (). Proposed DWPT circuit topologies in the stepping stone system are series-series (SS) and parallel-series (PS). The SS topology is one of the most common circuit topologies used to implement ireless poer transfer (WPT). Previous studies used this topology for constant current (), poer supply, in the repeater coil method (3), for comparison ith a stationary system (4). With respect to the PS topology, one of the characteristics is that the input impedance approaches infinity hen the secondary side of the topology is absent. DWPT is proposed to take advantage of this characteristic (5). Very fe previous orks have analyzed both topologies including variable voltage and current by misalignment of running direction; if all possible phenomena are included, the analysis becomes complicated and it is very difficult to make any predictions. In this paper, the aim is to construct as simple a model of a DWPT system as possible. This paper focuses on the verification of the coupling coefficient hen the secondary coil is misaligned, providing insight into the common tendency of voltage and current fluctuation in such circuits. To topologies are analyzed: series SS topology, specifically a series connection of primary coils connected in series to resonant capacitors, and parallel PS topology, specifically the parallel connection of primary coils connected in parallel to resonant capacitors, ith to primary coils and a secondary coil. These topological approaches are validated via an electrical circuit simulator and via an experiment. The structure of this paper is as follos. Section gives an overvie of the SS and PS topologies as this applies to a primary

2 coil and a secondary coil. Section 3 provides results and analysis of input and output data for voltage, current and output poer using the series SS and parallel PS topologies and considering misalignment in the running direction, and describes relevant features. Section 4 details the circuit simulator, and Section 5 describes the result of the experiment. Finally, Section 6 summarizes the research and presents conclusions.. Circuit topology of a primary coil and a secondary coil This section examines basic characteristic of the SS and PS topologies using a primary and secondary coil. In this paper, ind resistance is much smaller than reactance at the resonant frequency. Moreover, the input of square ave voltage for actual applications has little influence on the higher harmonics of current because WPT is a resonant circuit. Therefore, only the root mean square (RMS) of the fundamental ave component is considered... SS topology This section describes the SS topology, hich, as previously mentioned, is one of the most idely used in WPT. A circuit diagram ith an SS topology is shon in Fig.. Fig. SS topology In this circuit, for resonant capacitors C s, C s, C C S s, C s, () here the input and output characteristics are given by æ - jm ö æ ö - jk æv in ö æv ö æv ö, () è I ø in è I ø è I ø è jm ø è jk ø and the input impedance is given by ( M ) M (k ) Zin R R C S I R V. (3) From Eq. (), the SS topology has immittance converter (6) hich outputs a constant current hen input remains at a constant voltage. From Eq. (3), hen the coupling coefficient k decreases due to misalignment of the secondary coil, input impedance approaches zero... PS topology This section describes the PS topology, shon in Fig.. M Fig. PS topology In the figure shon in this figure, for resonant capacitors, C P, C s, Cp, C, (4) s ( - M ) ( - k ) here the input and output characteristics are given by æ æ ö æv in ö æ ö M V k è I ø M in è ø I è ø è and input impedance is given by R C P C S V ö æv ö, (5) è I k ø ø æ ö Zin R R. (6) M è ø k From Eq. (5), the PS topology has the ideal transformer hich outputs a constant voltage hen input remains at a constant voltage. If the primary coil and secondary coil have the same shape, is the turn ratio beteen the primary side and the secondary side. It is necessary to increase the number of turns on the secondary side hen taking voltage and current at the same ratio as the primary side, because the coefficient coupling k causes secondary self-inductance. From Eq. (6), hen the coupling coefficient k decreases due to misalignment of the secondary coil, input impedance approaches infinity. The PS topology enables the performance of passive sitching. 3. Analysis of circuit topology for to primary coils and a secondary coil Fig. 3 shos the series SS topology circuit, and Fig. 4 shos the parallel PS topology circuit. I

3 Table. The voltage and current characteristics for constant input voltage Table. The voltage and current characteristics for constant input current Series SS topology Constant R V in R V j I j ( k3 + k3) 3 P R 3 3 V in 3 Parallel PS topology Constant 3 R + j 3 3 V in ( k - k - k ) R R + j( k - k3 - k3) 3 3 k3 + k3 R + j( k - k3 - k3) 3 3 R R ( k - k - k ) 3 Series SS topology V in ( 3 + k3) R V I P k 3 Constant Parallel PS topology R j( k - k - k ) j( k3 + k3) 3 ( k k ) j R 3 3 R ( k3 + k3 ) Constant R 3 k3 + k3 3 k3 + k3 R 3 ( k3 + k3) C S I M 3 (k 3 ) I 3 C S3 I Car side (secondary coil) xmm x6mm C S V I 3 V3 V R 35mm moving direction x V M 3 (k 3 ) Fig.3 Series SS topology Road side (primary coils) Fig.5 Pattern diagram I I CP M 3 (k 3 ) I 3 V C P in V I 3 V3 I CP C P V M 3 (k 3 ) Fig.4 Parallel PS topology C S V I R coupling coefficient [-] k k 3 k 3 k 3 +k 3 In the circuit analysis of Figs. 3 and 4, the folloing conditions are taken into consideration for simplicity. l When the separation beteen the primary coils is suitable, mutual coupling is ignored. l Winding resistances are suitably smaller than reactances. l All primary coils are the same shape and perform the same. ( ) l Resonant capacitors apply the resonance condition of inductances at the mm point, and do not change on the ay. (Fig. 5) When applying the conditions, the capacitance in the series SS topology are determined as follos: CS CS, C S3, (7) 3 and the capacitance in the parallel PS topology are determined as follos: self inductance [µh] distance [mm] Fig.6 Variable coupling coeffient distance [mm] Fig.7 Variable self inductance 3

4 Table 3. Specifications of solenoid coils Gap[mm] 35 Coil type H-shaped core Size[mm] Ground side Core Size[mm] Ground side Winding Size[mm] Ground side Winding[mm] Ground side T p T p C, (8) P CP, C S ( - k ) 3 here k represents the coupling coefficient k 3 +k 3 at the mm point setting on the secondary side. Tables and list the voltage and current characteristics for constant input voltage, and constant input current, respectively. From Tables and, the sum of coupling coefficients k 3, k 3 shos a large fluctuation on voltage and current. For example, hen k 3+k 3 decreases, the value increases if this parameter is the numerator, and hen k 3+k 3 decreases, the value increases if this parameter is the denominator. Furthermore, the parallel PS topology has a bigger misalignment influence than the series SS topology because an imaginary component appears in the equations in this topology hen the secondary coil moves from the mm point. 4. Simulation The simulation is run using by PSIM, a circuit simulator, to validate the equations presented in Section 3.The coils uses an H- shaped solenoid, hich has high misalignment performance (7). The coil shape parameters are listed in Table 3. In this paper, the value obtained by actually measuring the constant of the coil at intervals of mm beteen and 6 mm as used. The coil parameters obtained by measurement are given in Figs. 6 and 7. Moreover, Table 4 lists the various constants used in the simulation. The value of capacitors use parameters at mm point from Fig. 5. A simulation is carried out using the above values. The output ave form of the inverter source uses a sine ave, and the load uses only pure resistance ithout a rectifier. Figs. 8 and 9 shos the output poer using the series SS and parallel PS topologies, respectively, as ell as input poer factors, and sho ho the calculated value is reproduced approximately in the simulation. There are places here the values deviate in Fig. 8 at the time of constant input voltage and Fig. 9 at the time of constant input current. This may be due to loss caused by inding resistance, not considered by analysis, and/or due an output poer[w] output poer[w] 5 Table 4. Simulation parameters Gap[mm] 35 Frequency[kHz] 85 oad Resistance[W] 7 C s,c s[µf](ss).4 C s3[µf](ss).49 C p,c p[µf](ps).4 C s[µf](ps).6 max[v] 4. SSmax[A] 5. PSmax[A] Fig.8 Output poer of series SS topology(simulation) theoretical(const ) simulation(const ) theoretical(const ) simulation(const ) Poer factor(simulation) theoretical(const ) simulation(const ) theoretical(const ) simulation(const ) Poer factor(experiment) Fig.9 Output poer of parallel PS topology(simulation) Table 5. Experiment parameters Gap[mm] 35 Frequency[kHz] 85 DC oad Resistance R d[w] 8.7 C s,c s[µf](ss).7 C s3[µf](ss).49 [V] SS[A] 5. error that increases as the total value of the coupling coefficient decreases. 5. Experiment An experiment is carried out to validate the equations calculated in Sections 3 and 4, ith experimental verification limited to the poer factor[-] poer factor[-]

5 series SS topology. Fig. shos experiment circuit of SS topology. The experimental circuit is shon in Fig.. Additionally, Table 5 lists various constants used in the experiment. The input ave uses the RMS (square ave), converted beteen square ave voltage v and fundamental ave voltage, as v. (9) p Moreover, a load R uses a combination of DC electronic resistance and a full bridge rectifier. The conversion formula (8) is 8 R R d. () p The result for output poer of the series SS topology is shon in Fig.. There is a large difference beteen the calculated theoretical values and the experimental values in Fig. (a). They may be due to a variation of the poer factor by an invisible factor during the analysis. The larger the change in values, the greater the influence of the poer factor change becomes; the smaller the change in values, the smaller the influence of the poer factor change. Nevertheless, the qualitative changes are in approximate agreement. 6. CONCUSION This paper analyzes the input voltage and current, and the output voltage, current, and poer of the series SS and the parallel PS topologies using to primary coils and a secondary coil, ith a focus on the series SS topology for experimental verification. The trends of the theoretical equation and the circuit simulation value are in approximately agreement. There are places here the values deviate significantly hen constant voltage is input, probably because of a variation of the poer factor caused by an invisible factor in the analysis. In the future, this ork ill be extended to include experimental verification of the parallel PS topology, including parallel SS topology, i.e., Fig. Experiment circuit of series SS topology output poer[w] output poer[w] theoretical(const ) experiment(const ) Poer factor(experiment) (a) constant theoretical(const ). experiment(const ) Poer factor(experiment) (b) constant Fig. Output poer of series SS topology(experiment) parallel connection of primary coils in series to resonant capacitors, and perform a comparative analysis of the results on the series SS and parallel PS topologies. Moreover, it ill analyze the impact of increasing the number of primary coils. REFERENCES () T.Yasuda, T. Fujita, and M, Sato, Proposed dynamic contactless poer transfer system, in Proc. EVS8, 5, vol. B5-, pp poer factor[-] poer factor[-]

6 () Y. Chen, S. Park, J. Kim, H. Kim, K. Hang, J. Kim, and S. Ahn, System and electromagnetic compatibility of resonance coupling ireless poer transfer in on-line electric vehicle, -in Proc. ISAP,, no. E3-, pp (3) K. K. Kim, T. Imura, and Y. Hori, Ne ireless poer transfer via magnetic resonant coupling for charging moving electric vehicle, in Proc. EVTeC and APE 4, 4, no. 446, pp. 5. (4) T. Fujita, T. Yasuda, and H. Akagi, A dynamic ireless poer transfer system applicable to a stationary system, IEEE Trans. Industry Applications, vol. 53, no 4, pp , Jun. 7 (5) J. Yamada, K Tsuda, R. Kobayashi, Y. Kaneko, Circuit analysis and characterization of contactless poer transfer system ith variable impedance, IEEJ Trans. Industry Applications, vol. 37 no., pp , Nom. 7 (in japanese) (6) H.Irie and Y. Yamada, Immittance converter suitable for poer electronics, Elect. Eng. Japan, vol. 4, no., pp. 53 6, Jul. 998 (7) C. Kato, K. Tsuda, T. Matsumura, Y. Kaneko, T. Fujita, and T. Yasuda, Investigation of ireless poer transfer system ith spaced arranged primary H-shaped core coils for moving EVs, in Proc. IEEE IECON 5, 5, pp (8) R.. Steigerald, A comparison of half-bridge resonant converter topologies, IEEE Trans. Poer Electronics, vol. 3, no., pp. 74 8, Apl. 988