High frequency rectifier circuit

Abstract

To provide a rectifier circuit that enables a high input impedance while using a coil with a small inductance value, thereby improving power supply efficiency.SOLUTION: There is provided a high frequency rectifier circuit in a non-contact high frequency power supply device by electric field coupling. In a single shunt rectifier circuit including a rectifying element 42 connected in parallel with a load resistor 41, and a choke coil 43 connected in series between the load resistor and the rectifying element, the rectifying element includes a predetermined capacitance by providing an additional capacitor 46 connected in parallel, and the predetermined capacitance of the rectifying element is set to have a size that causes series resonance at an arbitrary frequency on the basis of an inductance value of the choke coil.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a high-frequency rectifier circuit used in a non-contact high-frequency power supply device using an electric field coupling system. [Background technology]

[0002] Non-contact high-frequency power supply devices have been developed as power supply devices for electric vehicles, such as electric mobility, and devices that can supply power appropriately even while driving are attracting particular attention. Non-contact power supply systems include magnetic resonance and electric field coupling systems, and non-contact power supply systems using the electric field coupling system are said to be able to supply power at low cost compared to the magnetic field resonance system because they do not require expensive coils.

[0003] However, in the case of contactless power supply while driving using the electric field coupling method, the power supply efficiency fluctuates due to the rotational movement of the electrode on the power receiving side, which has been a problem. Therefore, in the past, the input impedance of the power receiving side was set high to improve the power supply efficiency (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-032425 A Summary of the Invention [Problem to be solved by the invention]

[0005] The technology disclosed in the above-mentioned Patent Document 1 basically improves power supply efficiency by increasing the impedance on the power receiving side, and therefore it is possible to improve the power receiving efficiency by increasing the input impedance to the rectifier circuit that constitutes the power receiving electrode.

[0006] However, when a single shunt rectifier circuit is used as a general rectifier circuit, a coil with a large inductance value is required to increase the input impedance, and therefore, when increasing the input impedance of the rectifier circuit to improve the power supply efficiency, a ferrite magnetic material is used, and a coil with many turns and a large diameter is used, which increases the weight and volume of the rectifier circuit. This sets back efforts to reduce the weight and size of the rectifier circuit.

[0007] The present invention has been made in consideration of the above-mentioned points, and its object is to provide a rectifier circuit that enables high input impedance while using a coil with a small inductance value, thereby improving power supply efficiency. [Means for solving the problem]

[0008] Therefore, the present invention provides a high-frequency rectifier circuit in a non-contact high-frequency power supply device using electric field coupling, which is a single-shunt rectifier circuit comprising a rectifier element connected in parallel to a load resistance and a choke coil connected in series between the load resistance and the rectifier element, wherein the rectifier element has a predetermined capacitance by providing an additional capacitor connected in parallel, and the predetermined capacitance of the rectifier element is sized to cause series resonance at any frequency based on the inductance value of the choke coil.

[0009] According to the above configuration, the rectifier element constituting the single shunt rectifier circuit functions as a capacitor having a predetermined capacitance between the anode terminal and the cathode terminal. Therefore, when the rectifier element is in the off state and a reverse bias is applied to the rectifier element, an electric charge is accumulated in the capacitor, and when the rectifier element is in the on state, the electric charge is discharged. Then, the capacitor of the rectifier element resonates in series with the choke coil at a predetermined frequency, so that an input impedance according to the value of the load resistance can be obtained without changing the inductance value of the choke coil.

[0010] In this case, a high impedance input is possible by setting the load resistance value larger than the resistance value of the output load, but the load resistance can be adjusted, for example, by a DC / DC converter, depending on the actual output load.

[0011] In the invention having the above configuration, the predetermined capacitance in the rectifying element may be a combined capacitance of a parasitic capacitance of the rectifying element and a capacitance of the additional capacitor.

[0012] According to the above configuration, since a general rectifying element has large and small parasitic capacitances, a predetermined capacitance can be set by combining the parasitic capacitance with an additional capacitor connected in parallel to the rectifying element. By taking into account the parasitic capacitance of the rectifying element, it is possible to cause series resonance with the choke coil.

[0013] In the above configuration, the predetermined capacitance of the rectifier element can be such that the additional capacitor is provided so as to resonate in series when the inductance value of the choke coil is 10 μH or less and the frequency is a high frequency of 5.0 MHz or more. By setting the inductance value to 10 μH or less, the choke coil can be made lightweight and small, and the capacitance of the additional capacitor can be set small. Effect of the Invention

[0014] According to the present invention, it is possible to use a coil with a small inductance value while achieving a high input impedance, thereby improving the power supply efficiency. For example, when a coil with an inductance value of 1 μH is used, if the combined capacitance of the rectifier element is set to 551 pF, resonance occurs at a high frequency of 6.78 MHz. In this case, when the load resistance value is 1000 Ω, the input impedance can be set to 1000 Ω, and power can be supplied with high impedance. Note that a DC / DC converter or the like can be used to adjust the resistance value from the load resistance to the output load. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1A shows an outline of a contactless power supply system using an electric field coupling method, and FIG. 1B is an explanatory diagram showing an embodiment relating to a rectifier circuit. [Diagram 2] 1 is a graph showing the results of Experimental Example 1. [Diagram 3] 1 is a graph showing the results of a comparative experiment for comparison with Experimental Example 1. [Figure 4] FIG. 11 is an explanatory diagram showing a non-contact power transmission circuit by an electric field coupling system used for an experiment and a comparative experiment in Experimental Example 2. [Diagram 5] 1 is a graph showing Experimental Result 1 of Experimental Example 2. [Figure 6] 13 is a graph showing Experimental Result 2 of Experimental Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. <Outline of the non-contact power supply device> 1(a) is a schematic diagram of a non-contact high-frequency power supply device using an electric field coupling method in which a rectifier circuit of the present invention is used. As shown in the figure, the non-contact power supply device using the electric field method has a high-frequency inverter circuit 1 and a matching circuit 2 connected to a power source A on the power transmission side, and a matching circuit 3 and a rectifier circuit 4 on the power receiving side, with an output load B connected to the rectifier circuit 4. The power transmitting side circuits 1 and 2 and the power receiving side circuits 3 and 4 are coupled in a non-contact manner by a coupler 5.

[0017] In order to achieve high efficiency in a power supply device using electric field coupling, both ends of the coupler 5 are made to have high impedance. This is because by increasing the distance between the electrodes of the coupler 5, highly efficient power transmission is possible even if the coupling capacitance is small.

[0018] Matching circuits 2 and 3 for impedance matching are provided between the inverter circuit 1 and the coupler 5, or between the rectifier circuit 4 and the coupler 5. However, if the input and output impedances of the matching circuits 2 and 3 are not adjusted within an appropriate range, losses increase, and there is a limit to sufficiently improving the efficiency of power transmission. In addition, if the matching circuits 2 and 3 are not provided, the output impedance of the inverter circuit 1 and the input impedance of the rectifier circuit 4 are appropriately adjusted for impedance matching. Therefore, the present invention improves the efficiency of power transmission by setting the input impedance of the matching circuit 3 on the power receiving side or the rectifier 4 connected to the coupler 5 within an appropriate range.

[0019] <Rectifier circuit> FIG. 1(b) shows an embodiment of the rectifier circuit 4. As shown in this figure, the basic structure of the rectifier circuit 4 is based on a single-shunt rectifier circuit including a rectifier element (diode) 42 connected in parallel to a load resistor 41, and a choke coil 43 connected in series between the elements 41 and 42. The capacitor 44 connected in parallel to the load resistor 41 is a smoothing capacitor, and the capacitor 45 connected in series to one side of the transmission line is a DC blocking capacitor for preventing the rectified DC component from flowing out. Since the term "single-shunt rectifier circuit" generally refers to a half-wave rectifier circuit including the DC blocking capacitor 45, the present embodiment has a similar configuration. The single-shunt rectifier circuit has an input impedance Z in and the load resistance R L Z in =R L When the input impedance is expressed as / ρ, the circuit operates so that the proportional constant ρ=1. in varies depending on the inductance value of the choke coil 43.

[0020] In this embodiment, an additional capacitor 46 is connected in parallel to the rectifier element (diode) 42. Due to the presence of a depletion layer, the rectifier element (diode) 42 has large and small parasitic capacitances C D Since the additional capacitor 46 has a parasitic capacitance C of the rectifier element (diode) 42, the additional capacitor 46 can be regarded as a type of capacitor (parasitic capacitor) 47. By connecting the additional capacitor 46 in parallel with the rectifier element (diode) 42, the rectifier element (diode) 42 functions as a capacitor having a predetermined capacitance. The predetermined capacitance at this time is the parasitic capacitance C of the rectifier element (diode) 42. D The capacitance of the added capacitor 46 is C Res In other words, the parasitic capacitance C D The capacitance of the additional capacitor 46 is C Res The situation is amplified by the

[0021] In addition, the capacitance C of the additional capacitor 46Res When the rectifier element (diode) 42 is connected to the choke coil 43, the total capacitance (parallel combined capacitance) of the rectifier element (diode) 42 is set to be capable of series resonance with the choke coil 43 at any frequency. The frequency at this time is the frequency of the power transmitted to the power receiving side in a non-contact manner, and the capacitance C Res The following will be selected.

[0022] In this way, since the rectifier element (diode) 42 also functions as a capacitor, when a reverse bias is applied while the rectifier element (diode) 42 is in the off state, charge is accumulated in the capacitor, and when the rectifier element (diode) 42 is in the on state, the charge is released. At this time, the capacitance is adjusted to a predetermined value, and series resonance occurs with the choke coil 43 at an arbitrary frequency, so that the inductor component of the choke coil 43 and the capacitor component of the rectifier element (diode) 43 are cancelled out, and the resistance value R L is the input impedance Z in This is approximately the same as the value of

[0023] Since the present invention is a high-frequency rectifier circuit used in a high-frequency power supply device, any frequency is a high frequency, and when resonating at that frequency, the choke coil 43 can be made small (small inductance) while the capacitance of the additional capacitor 46 can be made small. L However, by providing a DC / DC converter between the output load and the power supply, it is possible to appropriately adjust the load in accordance with the actual output load. EXAMPLES

[0024] <Experimental Example 1> Next, an experiment was conducted to see whether the input impedance can be increased while the choke coil 43 is made smaller according to the embodiment of the present invention. The experimental method was as follows: the circuit configuration was as shown in FIG. 1(b), and the choke coil 43 and the capacitor (C D +C Res The inductance value of the Tuk coil, L s In four types of circuits with inductances of 1 μH, 2 μH, 5 μH, and 10 μH, the resistance value R of the load resistor 41 is L Input impedance Z in was measured. However, the choke coil 43 includes a loss resistance, and the Q value of the coil was set to 100. The smoothing capacitor 44 is an ideal capacitor with infinite capacity. At the same time, the rectification efficiency (output power / input power) was calculated for each circuit with four different inductance values. The respective results are shown in FIG. 2. Note that FIG. 2(a) is a graph of the input impedance value to the rectifier circuit as the load resistance value changes, and FIG. 2(b) is a graph of the rectification efficiency at that time. Note that in both graphs, the dashed lines indicate the ideal state.

[0025] As is clear from the results of FIG. 2(a), when the inductance value of the choke coil 43 is set between 1 μH and 10 μH, the resistance value R L The input impedance increases or decreases with the change in inductance L. This change in input impedance is close to the ideal state. s Therefore, a high input impedance can be obtained even when

[0026] As is clear from the results of FIG. 2(b), the rectification efficiency is also close to the ideal state, and there are some parts where the efficiency exceeds the ideal state. This result of exceeding the ideal state is due to the capacitance C of the additional capacitor 46. ResWith the addition of this, the harmonic processing function has been improved, and it is assumed that the power converted to DC has increased, thereby improving the rectification effect of high frequency power to DC power.

[0027] <Comparative experiment> For comparison with the above experimental results, a circuit was created in which the rectifier element (diode) 42 had no capacitance, and the load resistance value R L and the input impedance Z in The rectification efficiency was calculated. The results are shown in Figure 3. As shown in Figure 3(a), the input impedance Z in is the load resistance R L Although it changes linearly with the magnitude of in In order to increase the inductance L of the choke coil 43, s In addition, the rectification efficiency is affected by the load resistance R L The fluctuation range is small with respect to changes in inductance value L s Increasing the rectification efficiency decreased.

[0028] <Conclusion> According to the results of both of the above experiments, by adding an additional capacitor 46 to the rectifying element (diode 42) and causing series resonance with the choke coil 43, a suitable input impedance Z in It is possible to obtain a high rectification efficiency.

[0029] <Experimental Example 2> Next, an experiment was conducted on the change in power transmission efficiency with respect to the variation in coupling capacitance in the coupler 5. As shown in FIG. 4(a), the experimental circuit was set in a state in which the coupler 5 was interposed between the rectifier circuit 4 shown in the above-mentioned embodiment and an AC power source A. The coupling part of the coupler is a non-contact electric field coupling method in which electrodes are interposed at a predetermined interval between each transmission line, so the coupling capacitance is set to C. Each element shown in the figure is L s = 1μH, C D =20pF, C Res= 531 pF (composite capacitance = 551 pF), and the resonance frequency is 6.78 MHz. s The series loss resistance is included, and the coil Q value is set to 100. p is an ideal capacitor.

[0030] <Comparative experiment> In addition to the above experimental circuit, a comparative experimental circuit 6 was also created. The comparative experimental circuit 6 was created by removing the additional capacitor 46 (capacity C Res ) was deleted. The other elements and conditions were the same as in the experimental circuit, so the result was that the comparative experimental circuit was configured so that it would not resonate even at 6.78MHz.

[0031] <Experimental result 1> In both of the above circuits, the power transfer efficiency was calculated with respect to the change in coupling capacitance. The coupling capacitance C in coupler 5 changes depending on the distance between the electrodes (size of the gap), and the rate of change is set to 0 when the coupling capacitance is C, and 1 when the coupling capacitance is 0. The power transfer efficiency is calculated by dividing the power input from power source A (P in ) to the load resistor 41 (P out ) percentage (P out / P in × 100(%).

[0032] In the above, the resistance value R of the load resistor 41 L The change in power transfer efficiency with respect to the change in coupling capacitance when the coupling capacitance is set to 1000 Ω is shown in Fig. 5. In the figure, "with resonance" indicates the results using the experimental circuit, and "without resonance" indicates the results using the comparative experimental circuit.

[0033] As shown in Fig. 5, in the experimental circuit (with resonance), even if the coupling capacitance fluctuates by about 5%, the power transmission efficiency is maintained at about 80%, and even if the coupling capacitance fluctuates by about 30%, the power transmission efficiency can be secured at about 50%. In contrast, in the comparative experimental circuit (without resonance), the power transmission efficiency drops to about 3% when the coupling capacitance fluctuates by only about 5%. From this result, it can be said that when the rectifier circuit of this embodiment is used, the robustness of the power transmission efficiency against fluctuations in the coupling capacitance is improved.

[0034] <Experimental result 2> Also, under the same conditions as above, the resistance value R of the load resistor 41 L The change in power transmission efficiency with respect to the change in coupling capacitance when the resistance value R of the load resistor 41 is changed was calculated. L The impedance ranges from 50Ω to 10000Ω, specifically, there are six types: 50Ω, 100Ω, 500Ω, 1000Ω, 5000Ω, and 10000Ω.

[0035] The results are shown in Fig. 6. Note that Fig. 6(a) shows the results in the experimental circuit (with resonance), and Fig. 6(b) shows the results in the comparative experimental circuit (without resonance).

[0036] As is clear from the above results, in the case of the comparative experimental circuit (without resonance) (see FIG. 6(b)), the resistance value R L Even if the resistance value R of the load resistor 41 was changed, the power transmission efficiency did not improve significantly. L The results showed that the robustness varied depending on the change in the coupling capacitance. When the range of the coupling capacitance change is predicted in advance, the resistance value R that is appropriate for the change rate is selected. L By setting the value of the power transmission efficiency at the power supply 100 to 1000 V, it is possible to obtain an optimum power transmission efficiency.

[0037] <Summary> As described above, according to the rectifier circuit of this embodiment, by appropriately adjusting the load resistance value without changing the inductance value of the choke coil, it is possible to increase the input impedance, and at the same time improve the rectification efficiency and the robustness of the power transmission efficiency.

[0038] Therefore, in the case of the rectifier circuit of this embodiment, a coil with a small inductance value can be used, which makes it possible to avoid an increase in the size of the choke coil and achieves further miniaturization and weight reduction.

[0039] Although the embodiments of the present invention are as described above, the present invention is not limited to these embodiments or examples. Therefore, it is possible to change the configuration of the above-mentioned embodiments, etc., or to add other configurations. For example, although a diode is shown as a representative example of a rectifying element, other rectifying elements can be used. In addition, the above-mentioned embodiment is premised on the rectifying element having a parasitic capacitance, but even if the parasitic capacitance is small or absent, it can be made to function in the same way by adjusting the capacitance of the additional capacitor 46. Furthermore, although a matching circuit was not used in the experiment on power transmission efficiency, there may be cases where matching circuits are provided on the power transmitting side and the power receiving side. Furthermore, as long as it is a non-contact high-frequency power supply device using an electric field coupling method, a similar rectifying circuit can be used in devices with other configurations. [Explanation of symbols]

[0040] 1 High frequency inverter circuit 2. Transmission side matching circuit 3. Receiving side matching circuit 4 Rectifier circuit 5 Combiner 6 Comparison experiment circuit 41 Load Resistance 42 Rectifier (Diode) 43 Choke coil 44 Smoothing capacitor 45 DC cut capacitor 46 Additional Capacitor 47 Parasitic Capacitors

Claims

1. A high-frequency rectifier circuit in a high-frequency power supply device used for non-contact power supply during driving of an electric vehicle by electric field coupling, A single shunt rectifier circuit including a rectifier element connected in parallel to a load resistor, a choke coil connected in series between the load resistor and the rectifier element and having an inductance value in the range of 1 μH to 10 μH, and a DC blocking capacitor, The rectifying element is provided with an additional capacitor connected in parallel to have a predetermined capacitance, The predetermined capacitance of the rectifying element is set to a value that causes series resonance at a given frequency based on an inductance value of the choke coil, A high-frequency rectifier circuit characterized in that, when a coupler using electric field coupling with a different coupling capacitance is interposed between an AC power source and the high-frequency rectifier circuit, the resistance value of the load resistor is set so as to correspond to the range of variation of the coupling capacitance.

2. 2. The high frequency rectifier circuit according to claim 1, wherein the predetermined capacitance in the rectifier element is a combined capacitance of a parasitic capacitance of the rectifier element and a capacitance of the additional capacitor.

3. A high-frequency rectifier circuit as described in claim 2, wherein the additional capacitor is arranged to resonate in series when the frequency is set to a high frequency of 5.0 MHz or more.

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