Proceedings of the 6th IIAE International Conference on Industrial Application Engineering 2018
Simulation of Electrical Characteristics for Misalignment of Coil in Wireless Power Transfer System Using Repeating Coil
Akihiro Imakiire a,* , Hideaki Tokunaga a, Akihiro Kawagoe a, Masahiro Kozako a, Masayuki Hikita a
aKyushu Institute of Technology, 1 1 Sensui cho, Tobata ku, Kitakyushu, 804 8550, Japan
*Corresponding Author: [email protected]
Abstract characteristic against misalignment of the coil is important to transmit power to the load with high efficiency. The This paper compares the electrical characteristics of the electrical characteristics of other coil types along with the S P type and the repeating coil type wireless power transfer S P type, and the repeating coil type have been compared (WPT) system. The features of the two types of WPT by many researchers (1, 4). However, it is difficult to compare systems are described if the output power is same value the electrical characteristics in the same condition, because using the same coil model. The current and voltage values all the types have different features, circuit configurations, of resonance capacitor are high, and the output power and coil shapes. Thus it becomes difficult to determine a decrease when misalignment of coil occurs. Therefore, condition that is suitable for both types of the WPT system. compensation method for misalignment is investigated to Moreover, several different parameters and electrical suppress this burden of resonance capacitor when characteristics exist, consuming lot of time to conduct a misalignment of coil occurs. These results are calculated simulation and investigation. from circuit equations based on the results of This paper compares the electrical characteristics of the electromagnetic analysis and are investigated for automatic S P type and the repeating type WPT system. The features guided vehicle (AGV) applications. Thus, if the repeating of the two types WPT system are described if the output coil maintains the center position between the primary and power is the same value using same coil model. The current secondary coils, the repeating coil type can suppress the and voltage values of the resonance capacitor are high when burden of the resonance capacitor and improve the misalignment of the coli occurs. Therefore, compensation transmission power. method is investigated to suppress this burden of resonance capacitor when misalignment of coil occurs. These results Keywords : wireless power transfer, repeating coil, are calculated from circuit equations based on the results of automatic guided vehicle, relay coil. electromagnetic analysis and are investigated for automatic guided vehicle (AGV) applications. It is useful to search for 1. Introduction optimum design conditions in the WPT system. In literature (5), the burden of the resonance capacitor in In recent years, the wireless power transfer (WPT) the WPT system was investigated. In literatures (6) and (7), system has been researched for various applications, such compensation method for misalignment using control or as electric vehicles (EV). There are numerous circuit coil shapes were studied. In addition, The Literature configurations with different electrical characteristics(1 4). (8) (10) showed the two types dynamic wireless power The circuit configuration of the S P type WPT system is transfer system such as using parallel line feeder or relay commonly used for EV applications, which has two coil(repeating coil), respectively. On the other hand, we resonance capacitors: one is connected in series with the have been studied the WPT system using the repeating coil primary coil, and the other is connected in parallel with the which is controlled the position (11 12). In this paper, we secondary coil. On the other hand, the WPT system with a investigate the electrical characteristics, compensation repeating coil (repeating coil type) is well known for its method, and the burden of the capacitor, when the repeating robust performance in the coil position. The electrical
DOI: 10.12792/iciae2018.018 81 © 2018 The Institute of Industrial Applications Engineers, Japan. S S S S Gap 7 1 3 5 S P type i L D D D D 20 mm Secondary coil L1 1 7 1 3 5 IPM S 8 S S S 2 4 6 Primary coil V D D D D batt 8 2 4 6 0 x (Misalignment) mm PM motor driving system for AGV M S S 12 Gap 9 11 C L L C L Repeating coil type 1 1 r r 2 D D V 20 mm 1 3 dc Secondary coil Repeating coil S S 10 12 Primary coil D D r r r 2 4 1 r 2 M1r Mr2 x (Misalignment) mm Wireless power transfer system for AGV 0 (a) System configuration (b) Coils model, and motion of repeating coil and secondary
Fig. 1. Wireless Power Transfer System with Repeating Coil for Automatic Guided Vehicle.
Table 1. Simulation condition. 2. Wireless power transfer system Parameters Value configuration for automatic guided vehicle
Input voltage V1 (S P type) 141 Vrms
Input voltage V1 (Repeating coil type) 141 Vrms 2.1 Overall WPT system for AGV Input voltage V ’ (Repeating coil type) 1 Figures 1 (a) and (b) show the WPT system for AGV The output power is same value in the S P type 254 V rms investigated thus far. Figure 1(a), shows the voltage booster and the repeating coil type that controls the battery current, DC link capacitor used V Frequency of input voltage 1 25 kHz commonly in the WPT system, and three phase inverter for G Gap length 20 mm motor of AGV. Figure 1 (b) shows the coil model and X Misalignment 0－80 mm motions of repeating coil and secondary coils. The R Load resistance L 100 secondary coil position means the AGV position. In L Inductance 1(S P type)@No misalignment 638 H contrast, the repeating coil is set at the center between the L Inductance 2(S P type)@No misalignment 637 H primary and secondary coils to keep the output voltage L Inductance 1(Repeating coil type) constant. In other words, the repeating coil is controlled to 573 H @No misalignment suppress the decrease in the output power.
Inductance Lr(Repeating coil type) 638 H 2.2 Simulation model of the S-P type and the @No misalignment repeating coil type Inductance L2(Repeating coil type) 638 H @No misalignment Figure 2 shows the simulation model of the S P type and
Resonance capacitor C1(S P type) 92 nF the repeating coil type. In both these types, the coil shape
Resonance capacitor C2(S P type) 64 nF and the number of turns are similar. However, with addition
Resonance capacitor C1(Repeating coil type) 71 nF of the repeating coil type, the repeating coil is set at the
Resonance capacitor Cr(Repeating coil type) 71 nF center of the primary and secondary coils. The gap length
Internal resistance of coil r1, rr, r2 0.173 and misalignment is defined in Fig. (1). In the simulation, Relative permeability of ferrite core 2300 misalignment is a parameter. The simulation condition, 125 ×125 ×5 physical property values, and size of coil are summarized in Ferrite core size [mm] Table 1. In addition, the input voltage V1 and the load R Diameter of coil Φ175 mm resistance L were set as sine waveforms and 100 , Number of turns of coil 75 respectively, in the simulation. First, the output voltage and current of coil were simulated using electromagnetic analysis (ANSYS, coil maintains at the center of the primary and secondary Maxwell and Simplorer), and the inductance and mutual coils. inductance were calculated as parameters as shown in Fig.
82 Circuit simulation model
(1) I2 I1 I1 I2
VVout V out 1V1
(2) Coil model
2 ωMr 2 ωM 1rMr 2 L2 − M 12 − L − M 1 − 1 2 12 C ωLr − ωLr − 1 ωCr ωCr
2 C (a) The S P type ωM 1r ωM 1rMr 2 L1 − M 12 − 2 1 − 1 R ωLr − ωLr − L ωCr ωCr Circuit simulation model L − M 1 12
Irr ωM 1rMr 2 VVr M 12 − r 1 ∞ ωLr − ωCr
I1 I2 I I L1 − M12 L2 − M12 1 2 1 RL C = 1 ω 2 (L + L − 2M ) 1 2 12 Vout V1 Vout V1 Coil model Fig. 3 Equivalent circuit model of the repeating coil type.
2.3 Equation model of the S-P type and the repeating coil type
Equations of the S P type and the repeating coil type are expressed as (1) and (2), respectively. The resonance (b) The repeating coil type capacitor value is decided to set the power factor of circuit Fig. 2 Simulation model using electromagnetic analysis. at 1.0. In addition, the equivalent circuit model of repeating type is shown in Fig. 3. It can be seen that the equivalent 2. circuit model of repeating coil type is similar to that of the Next, the simulation results using electromagnetic S P type system. Furthermore, if the mutual inductances software and the calculation results using circuit equations M1r and Mr2 have the same value, and the repeating were compared. As a result, the validity of calculation resonance capacitor value is chosen as the resonance results was confirmed using circuit equations. Note that the frequency with repeating coil Lr, the output voltage can be calculation results derived using parameters such as constant. In this condition, resonance capacitor C2 is not inductance and mutual inductance were simulated using needed. Therefore, if the repeating coil position controls the electromagnetic software. The circuit equations are useful center between the primary and secondary coils, the output to design the WPT system when the influence of the voltage can be maintained constant with the input voltage parameter on the electrical characteristics of the WPT value Vin . Therefore, in the simulation of the repeating coil system is investigated. type, the resonance capacitor C2 was not used, as reported Finally, the S P type and repeating coil type calculation in previous investigation (12). The system used repeating results were compared and discussed. In addition, a resonance capacitor and secondary resonance capacitor. compensation method is described. However, electrical characteristics of the S P type and
83 repeating coil type have not compared in detail with similar 300 conditions when the repeating coil is controlled at the 250 center of the primary and secondary coils intentionally. Therefore, in this paper each WPT system is designed 200 with the same output power, using the same coil model. In 150 addition, the burden of each resonance capacitor was 100 investigated. Furthermore, the change in the impedance Output [V] Output voltage 50 Ectromagnetic analysis locus was observed according to the increase in the Equation(1) misalignment. 0 0 10 20 30 40 50 60 70 80 90 100 Thus, the parameters and the electrical characteristics are Misalignment [mm] large. Thus, we used the circuit equations based on the electromagnetic analysis. However, it is necessary to (a) Output voltage consider that the S P type has higher voltage than the 20 repeating coil type as follows. 18 Ectromagnetic analysis I1 16 Ectromagnetic analysis I2 L 14 V = 2 V I1 Equation(1) out M 1 (3) 12 12 I2 Equation(1) 10 8 Vout = V1 (4) 6
Coil current [A] 4 The S P type and repeating coil type output voltages are 2 0 expressed as (3) and (4), respectively. In the simulation 0 10 20 30 40 50 60 70 80 90 100 condition, output power value is the same, i.e., the Misalignment [mm] repeating coil type needs higher voltage inverter than the (b) Coil current S P type to provide the same output power. Fig. 4 Simulation results of the S P type. 3. Simulation results and discussion 160 Figures 4 and 5 show the output voltage and coil current 140 120 characteristics of the S P type and the repeating coil type 100 from the electromagnetic analysis and equations (1) and (2), 80 Ectromagnetic analysis respectively. As shown in the figures, the results obtained 60 Equation(2) from the electromagnetic analysis and the equations are 40 Output voltage[V] Output 20 almost similar. It was confirmed that the validity of the 0 results of equations from the results of comparison between 0 10 20 30 40 50 60 70 80 90 100 Misalignment [mm] the simulation (Fig. 2) and equations. Thus, other characteristics such as coil efficiency, output power, output (a) Output voltage voltage, and coil current can be calculated by the equations. 20 The inductance and mutual inductance were calculated 18 Ectromagnetic analysis I1 16 Ectromagnetic analysis Ir from the electromagnetic analysis. 14 Ectromagnetic analysis I2 Figures 6 (a) and (b) show the output power 12 10 Equation(2) I1 characteristics for misalignment. For this, the load was set 8 Equation(2) Ir at 100 . In addition, Figs. 6 (a) and (b) are different in 6 Equation(2) I2 4 Coil current [A] terms of the input voltage Vin of repeating coil type. In Fig. 2 0 6 (a), input voltage Vin of the repeating coil type was set at 0 10 20 30 40 50 60 70 80 90 100 the same value as that of the S P type. In (b), input voltage Misalignment [mm]
Vin of the repeating coil type was set about two times that of the S P type to adjust the same output power of the S P type (b) Coil current under the no misalignment. Fig. 5 Simulation results of the repeating coil type.
84 800 100.0 S P type 700 98.0 Repeating coil type 96.0 600 94.0 S P type 500 92.0 Repeating coil type 400 90.0 300 88.0 86.0 200 84.0 Output power Output [W] power 100 [%] Coil efficiency 82.0 0 80.0 0 10 20 30 40 50 60 70 80 0 20 40 60 80 Misalignment [mm] Misalignment [mm]
(a) Input voltage value is same the S P type. Fig. 7 Coil efficiency for misalignment of the two types 800 of WPT system. 700 600 7 500 I1(S P) 6 I2(S P) 400 I1(Repeating coil type) 300 5 Ir(Repeating coil type) S P type I2(Repeating coil type) 200 Repeating coil type 4 Output power [W] Output 100 3 0 2 0 10 20 30 40 50 60 70 80
Misalignment [mm] Capacitor current [A] 1 0 (b) Input voltage value of repeating coil type is two times of that of the 0 10 20 30 40 50 60 70 80 S P type Misalignment [mm] Fig. 6 Output power for misalignment of two types of (a) Resonance capacitor current
WPT system. 500 Vc1(S P) 450 Vc2(S P) 400 Vc1(Repeating coil type) From Fig. 6 (a), it was confirmed that the repeating coil 350 Vcr(Repeating coil type) 300 type is a more low output voltage and low output power 250 system than the S P type. These results are expressed by 200 150 equations (3) and (4). The S P type is superior to the 100 V Capacitor voltage [V] 50 repeating coil type at the same input voltage in . However, 0 as shown the Fig. 6 (b), if the output power of the repeating 0 10 20 30 40 50 60 70 80 coil type has the same value as the S P type, then the Misalignment [mm] repeating coil type can be superior to the S P type in low (b) Resonance capacitor voltage output power area. For example, observing 400 W, the S P Fig. 8 Resonance capacitor’s burden for misalignment of type can transmit the power about 40 mm of misalignment. the two types of WPT system. In contrast, the repeating coil type can transmit the power 150.0 about two times of misalignment than the S P type. 100.0 Next, we compared the coil efficiency of the two types of 80 mm WPT system. The coil efficiency defined only copper loss 50.0 80 mm of coil. 40 mm 40 mm 0 mm Figure 7 shows the coil efficiency of the S P type and the 0.0 0 mm 150.0 100.0 50.0 0.0 50.0 100.0 150.0 repeating coil type. The repeating coil type has greater 50.0 efficiency than the S P type by increasing the misalignment. [ ] patt Imaginary
This is because the S P type rapidly decreases the output 100.0 S P power, thereby increasing the reactive power. On the other Repeating coil type hand, the repeating coil type maintains high efficiency even 150.0 Real part [ ] with low output power. Figures 8 (a) and (b) show the resonance capacitance Fig. 9 Impedance locus for misalignment of the two types burden for misalignment depicting the resonance capacitor of WPT system.
85 current and voltage characteristics, respectively. The 80 repeating coil type’s input voltage V was set two times that in 70 of the S P type. Thus, the burden of the primary resonance 60 capacitor increased more than that of the secondary 50 resonance capacitor in the S P type. In addition, in the 40 repeating coil type, the burden of the repeating resonance C1 30 capacitor increased more than that of the primary resonance Cr 20 capacitor. Therefore, when designing the repeating coil type, 10 this result of the repeating resonance capacitor’s burden capacitance[nF] resonance Ideal 0 should be considered. 0 20 40 60 80 100 Next, we compared the impedance locus for Misalignment [mm] misalignment of the two types WPT system. Figure 9 shows Fig. 10 Ideal resonance capacitor value for misalignment the impedance viewed from the primary side. The circles of repeating coil type. and triangles indicate the impedances of the S P type and the repeating coil type, respectively. The result explains the robustness of the repeating coil type. If a misalignment 400 occurs, the leakage inductance increases, and leads to an 350 increase in the reactive power. As shown in Fig. 9, the S P 300 type shows the almost inductive load at 80 mm of 250 200 misalignment. On the other hand, the repeating coil type 150 S P Repeating coil type does not the completely show inductive load at 80 mm of 100 C2=Cr misalignment. The features of the S P type and the 50
Output voltage[V] Output C2=10%Cr repeating coil type differ for the impedance locus. 0 From the equivalent circuit of the repeating coil type as 0 10 20 30 40 50 60 70 80 Misalignment [mm] shown in Fig. 3, if the mutual inductances M1r and Mr2 are of the same value and the repeating resonance capacitor’s Fig. 11 Output voltage for misalignment of the two types value is chosen as the resonance frequency with repeating of WPT system when the resonance capacitor C2 is added. coil Lr, then the output voltage can be constant. However, the output power (output voltage) gently decreases for misalignment, as shown in Fig. 6. 100% Cr. As a result, the output voltage was increased
Figure 10 shows the ideal resonance capacitor value for according to the increase in the value of C2. Thus, the misalignment of the repeating coil type. As a result, it was output power increased for misalignment. The output confirmed that the change of in ideal C1 and Cr values voltage characteristic of the repeating coil type resembles decrease, so the output voltage decrease because it deviates the S P type output voltage characteristic with the increase from the designed value. Therefore, additional control is in the value of C2. However, the advantage of flat needed to maintain the output voltage. characteristic of the output voltage for misalignment in the
repeating coil type is lost on adding C2. In addition, the
4. Compensation method of misalignment burden of the C1, Cr, and C2, such as current and voltage and burden for resonance capacitor characteristics, must be considered for misalignment. Next, compensation method of misalignment is In this section, compensation method of misalignment investigated by controlling the magnitude of input voltage and burden for resonance capacitor is investigated. In the Vin and the frequency of input voltage. As shown in Fig. 9, above simulation, C2 was not used in the repeating coil type the impedances from the viewpoint of primary side were because C2 does not need to adjust the power factor set at resistance and inductive load for misalignment.
1.0 in no misalignment condition. Therefore, if the frequency of input voltage Vin is Figure 11 shows the output voltage for misalignment of controlled to decrease, then the impedance will change only repeating coil type when the secondary resonance capacitor resistance, and the power factor of the circuit will be
C2 is added. The C2 was set at the value of 10% Cr and controlled at 1.0. However, the control causes an increase in
86 the burden of resonance capacitors C1 and Cr. In particular, 30.0 the current and voltage of C1 directly increases more than 25.0 0 mm that of Cr because, the impedance from the viewpoint of 20.0 40 mm primary side changed to low value by controlling the 15.0 frequency. 80 mm Figures 12 and 13 show the primary current 10.0 characteristic for the frequency and impedance locus for 5.0 Primary coil current [A] Primarycoilcurrent misalignment of repeating coil type when the frequency 0.0 changed, respectively. As a result, it can be seen that the 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95100 Frequency [kHz] impedance from the viewpoint of primary side changed only the resistance by controlling the frequency. In addition, Fig. 12 Primary coil current for misalignment of the it was confirmed that primary current increased with repeating coil type. decreasing frequency. Figure 14 shows the input and output voltages for misalignment of repeating coil type when the frequency and 150.0 input voltage was changed. The input voltage was with control controlled to keep the output power constant. Although two without control 100.0 control parameters exist, such as magnitude of input voltage 50.0 and the frequency, the output power can be controlled to remain constant. 0.0 Figure 15 shows the resonance capacitor voltage for 150.0 100.0 50.0 0.0 50.0 100.0 150.0 misalignment of repeating coil type when the frequency and patt[ ] Imaginary 50.0 input voltage was changed. As a, results, the voltage and 100.0 20.1 kHz current of C1 over that of Cr. The voltage of C1 reached 80 mm of misalignment, which was about four times of 0 mm 150.0 C of misalignment. The burden of r characteristics is similar Real part [ ] to that of C1. Fig. 13 Impedance locus for misalignment of the Finally, the advantages of the repeating coil type is repeating coil type when the input voltage and frequency described reflecting the simulation results. By controlling were adjusted. the position of the repeating coil, the output voltage can be kept almost constant. Even if misalignment occurs, the 5. Conclusions output voltage changes in a safe direction. In addition, the burden of the resonance capacitor for repeating coil is This paper compares the electrical characteristics of both always maximized, thus, the system design is simple. the S P type and the repeating coil type WPT system. The In particular, an advantage is that the efficiency of the features of the two types was described if the output power repeating coil type can be kept high even when is the same using the same coil model when the repeating misalignment occurs. This is also the case when the output coil was controlled center of the primary and secondary power decreases. Therefore, even if the power factor 1 coils intentionally. control is not performed, there is no problem if the In particular, an advantage is that the efficiency of the allowable position range is considered, and the output repeating coil type can be kept high even when voltage is designed to achieve the required voltage at that misalignment occurs. This is also the case when the output point. power decreases. Therefore, even if the power factor 1 If the power factor 1 control is used, the burden of the control is not performed, there is no problem if the primary side resonance capacitor is maximized, and it allowable position range is considered, and the output becomes several times the voltage of the resonance voltage is designed to achieve the required voltage at that capacitor and the current at the condition of no point. In addition, the repeating coil type features, such as misalignment. Therefore, when designing the WPT system resonance capacitor burden and impedance locus of repeating coil, the above limitations must be considered. characteristics, are indicated to design the WPT system.
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