JP7568269B2 - High frequency inverter, rectifier circuit and wireless power transmission system - Google Patents

Description

The present invention relates to a high-frequency inverter and rectifier circuit that can output a constant voltage or current even when the load resistance fluctuates, and a wireless power transmission system that uses them.

High-frequency inverters are used in induction heaters, plasma generators, and wireless power transmission due to their high efficiency and high power. Inverters with high output and high efficiency, such as class E inverters, achieve zero voltage switching (ZVS) and zero voltage derivative switching (ZVDS). However, class E inverters achieve the above ZVS and ZVDS at a load resistance that is assumed. Therefore, if the load resistance fluctuates, ZVS is not achieved, resulting in a decrease in efficiency. Therefore, an inverter method that achieves ZVS at a constant voltage (CV) output has been developed (see non-patent document 1).

JP 2020-010414 A JP 2015-023686 A JP 2013-013288 A

R.E.Zulinski and K.J.Grady, “Load-independent class E power inverter. I. Theoretical development”, IEEE Trans. Circuits Syst. I, vol. 37, No.8, pp.1010-1018, Aug. 1990.

The technology disclosed in the above-mentioned non-patent document 1 achieves ZVS in inverter output with a constant voltage, but the design theory is complicated, and the voltage conversion ratio is inevitably large when converting from a DC voltage source to a high-frequency voltage. As a result, it has not been practical. Therefore, a method has been proposed to achieve ZVS in a high-frequency switching circuit by using two switching elements and correcting the dead time from when one switching element is turned off to when the other switching element is turned on (see patent document 1).

The technology disclosed in Patent Document 1 provides a control circuit with a chargeable and dischargeable capacitor, and when the capacitor voltage reaches an upper limit set voltage, turns off two switching elements, and when the capacitor voltage reaches a lower limit set voltage, turns on one or the other switching element alternately, requiring a control unit for this purpose. It also requires a correction unit that increases the amount of discharge per unit time during the discharge period in which the capacitor is discharged, thereby quickly bringing the capacitor voltage to the lower limit set voltage. However, the above switching circuit does not achieve ZVS when the load resistance fluctuates.

On the other hand, depending on the type of load, a constant voltage or constant current power supply is desired, and switching power supplies capable of obtaining a constant voltage output have been developed (see Patent Document 2), and constant current power supplies have also been developed (see Patent Document 3).

The technology disclosed in Patent Document 2 controls the output voltage of a boost converter, and when converting an input voltage to a predetermined voltage, the input voltage is converted to the predetermined output voltage by correcting the error between the measured value (detection signal) of the input voltage and the output voltage. Therefore, the above technology is a switching power supply device that includes a boost converter, and cannot be applied to a class E inverter or rectifier circuit.

The technology disclosed in Patent Document 3 is a constant current circuit having a switch element, in which the switch element is controlled by a control unit according to the drain current of the switch element, and the purpose is to suppress output current ripple. Therefore, the above technology is also not applicable to class E inverters or rectifier circuits.

The present invention has been made in consideration of the above points, and its purpose is to provide an inverter circuit and a rectifier circuit that can output a constant voltage or a constant current even when the load resistance changes, and to provide a wireless power transmission system that uses these.

The present invention, which relates to a high-frequency inverter circuit, is a high-frequency inverter circuit that supplies power at a constant voltage or constant current to a load whose load resistance varies, and includes a switching circuit having a switching element that is switched at a predetermined duty ratio and an output capacitor connected in parallel to the switching element, and a passive circuit that converts the output impedance of the switching circuit, and the passive circuit uses the output impedance when the switching voltage, which is determined based on the configuration and setting values of each element provided in the output side circuit including the switching circuit and the actual load, achieves ZVS and ZVDS as a reference impedance, converts the output impedance at the actual load to the reference impedance, and converts the output impedance so that the switching voltage falls within the range in which ZVS is achieved within the range of the varying load.

According to the above configuration, the DC voltage can be converted into a high-frequency AC voltage by the operation of the switching element, and then output. At this time, the switching voltage rises when the switch is in the off state and then falls, so it is preferable that the voltage is zero (V) at the moment the switch is turned on (achieving ZVS), and it is even more preferable that the slope of the voltage change curve is zero (achieving ZVDS). This is also true when the load resistance changes and the switching voltage changes according to the fluctuating load. Therefore, by providing a passive circuit, it is possible to at least achieve ZVS when the load resistance fluctuates.

The passive circuit assumes an inverter (hereinafter sometimes referred to as a class E inverter) in which the switching voltage achieves ZVS and ZVDS in the configuration of the output side circuit including the actual load (optimum load), and uses the output impedance at that time as a reference impedance. The output impedance at the actual load is converted to the reference impedance, and the output impedance within the range of the fluctuating load is converted so that it is within a range that achieves ZVS. This makes it possible to achieve ZVS even if the load resistance fluctuates. At this time, impedance parameters suitable for impedance conversion by the passive circuit are found, and the passive circuit is constructed to satisfy those impedance parameters.

In this way, by converting the impedance of the output circuit including the load, ZVS is achieved even when the load resistance fluctuates, so the switching voltage becomes zero (V) when the switching element switches from the off state to the on state, and switching losses can be significantly reduced. And because switching losses are so minimal, it can become a constant voltage source when outputting as an AC voltage source, and a constant current source when outputting as an AC current.

In the invention of the above configuration, the passive circuit can be constructed as a circuit that obtains impedance parameters that can perform impedance conversion from the load real axis variation geodesic curve drawn on the Smith chart to the ZVS geodesic curve that achieves ZVS drawn on the Smith chart, and satisfies the impedance parameters.

Here, a geodesic line is a line that connects the shortest distance between two points (geometric length by Poincaré measurement using non-Euclidean geometry), and may be a straight line, a circle, or an arc. Furthermore, the impedance transformation can be a Möbius transformation, which transforms from circle to circle, but a straight line can be transformed by considering it as a circle with a radius of ∞. The real axis fluctuation geodesic line of the load is calculated by calculating the impedance parameters for transforming 0 Ω to ∞ Ω into a ZVS geodesic line when a constant voltage is output, and ∞ Ω to 0 Ω into a ZVS geodesic line when a constant current is output, in the impedance values in the range of 0 Ω to ∞ Ω, including the impedance that achieves ZVS and ZVDS in the optimal load. Therefore, although the impedance parameters differ between the case of constant voltage output and the case of constant current output, a passive circuit with a circuit configuration that satisfies each of these is provided.

According to the above configuration, when selectively outputting either a constant voltage or a constant current, an appropriate passive circuit can be provided according to the selected output. With regard to constant current output, when focusing on the switching current, it is known that zero current switching (ZCS) can reduce switch loss. However, in this case, in order to output a constant current, we will determine impedance parameters that achieve ZVS while focusing on the switch voltage. This makes it possible to output a constant current even when the load fluctuates.

The present invention relates to a rectifier circuit that rectifies AC power supplied by a constant voltage or a constant current and outputs DC as a constant voltage or a constant current to a load whose load resistance varies. The rectifier circuit includes a switching element that is switched at a predetermined duty ratio while adjusting the phase with the AC voltage input from an AC voltage source, and an output capacitor connected in parallel to the switching element, and a passive circuit that converts the input impedance to the switching circuit. The passive circuit converts the input impedance at the actual load to the reference impedance, and converts the input impedance so that the fall voltage of the switching voltage, which is determined based on the configuration and setting value of each element provided in the output side circuit including the switching circuit and the actual load, falls within a range in which ZVS and ZVDS are achieved.

According to the above configuration, the AC voltage source supplied can be rectified by operating the switching element with a suitable duty ratio. At this time, the falling voltage of the switch voltage does not achieve ZVS due to fluctuations in the load of the output side circuit, so a passive circuit is provided to achieve at least ZVS for that falling voltage. The configuration of the passive circuit is the same as that of the passive circuit in the high-frequency inverter circuit described above, but the switching element, output capacitor, and configuration within the passive circuit are basically constructed to be symmetrical to the inverter circuit. This is because the achievement of ZVS in the inverter circuit is an event when the switching voltage converges to zero (V), whereas in the rectifier circuit, it is an event at the falling voltage of the switching voltage. By providing a passive circuit configured in this way, the rectified voltage or current becomes a constant voltage or constant current.

In the invention having the above configuration, the passive circuit can be constructed as a circuit that obtains an impedance parameter that can perform impedance conversion from the load real axis variation geodesic line drawn on the Smith chart to the ZVS geodesic line that achieves ZVS drawn on the Smith chart, and satisfies the impedance parameter. This is similar to the case of an inverter circuit, and when selectively outputting either a constant voltage or a constant current as a direct current after rectification, an appropriate passive circuit can be provided according to the selected output.

The invention of each of the above configurations may further include a control unit that controls the switching operation of the switching element, and the control unit may control the switching operation while correcting a phase difference that occurs with the period of the input voltage or input current when the input impedance is converted by the passive circuit.

According to the above configuration, the power input to the switching element changes in phase due to the action of the passive circuit, etc., and the phase difference can be corrected by the control unit.

The present invention, which relates to a wireless power transmission system, is characterized in that it has a high-frequency inverter circuit having any of the above configurations as the power supply side, a rectifier circuit having any of the above configurations as the power receiving side, and a coupler provided between the two circuits.

According to the above configuration, the DC voltage source can be output as a high-frequency constant voltage or constant current by the inverter circuit, and this can be transmitted as the supply side to the receiving side via the coupler. On the other hand, on the receiving side, the power supplied as a high-frequency constant voltage or constant current can be rectified as a constant voltage or constant current and supplied to the load. Note that the coupler can be a magnetic field coupling type or an electric field coupling type, and a transformer or gyrator can be constructed, but the type and configuration are not important here.

According to the present invention, in both the high-frequency inverter circuit and the rectifier circuit, even if the load resistance changes, the switching voltage at least achieves ZVS, so the output voltage or output current is stable and can be output as a constant voltage or constant current.

In addition, a wireless power transmission system that uses these devices enables wireless transmission while converting a DC voltage source into a constant voltage or constant current, and efficient power transmission is achieved by the operation of a phase-adjusted switching element in the rectifier circuit.

FIG. 1 is an explanatory diagram showing an embodiment of a high-frequency inverter circuit. 1A and 1B are diagrams for explaining a design method, in which FIG. 1A shows a class E inverter and FIG. 1B shows a Smith chart. 1A and 1B are diagrams for explaining a design method, in which FIG. 1A shows a two-terminal pair circuit, and FIG. 1B shows an example of transformation of a geodesic line. 1A and 1B are diagrams showing impedance parameters for a constant voltage output in a high-frequency inverter circuit, where FIG. 1A is a Smith chart and FIG. 1B shows an example of a T-type circuit. 1A and 1B are diagrams showing impedance parameters for constant current output in a high-frequency inverter circuit, where FIG. 1A is a Smith chart and FIG. 1B shows an example of a T-type circuit. FIG. 1 is an explanatory diagram illustrating an embodiment of a rectifier circuit. FIG. 1 is an explanatory diagram illustrating an embodiment of a wireless power transmission system. FIG. 1A is a diagram showing an embodiment of a high-frequency inverter circuit for constant voltage output, and FIG. 1B is a diagram showing an embodiment of a high-frequency inverter circuit for constant current output. 6 is a graph showing simulation results for an embodiment of a high-frequency inverter circuit, in which (a) shows the results for only a class E inverter, (b) shows the results for a high-frequency inverter circuit for constant voltage output, and (c) shows the results for a high-frequency inverter circuit for constant current output. 13 is a graph showing the results of measuring a switching voltage (shunt capacitor voltage). 1A is a diagram showing an embodiment of a rectifier circuit for constant voltage output, and FIG. 1B is a graph showing the results of a simulation. 10A is a diagram showing another embodiment of a rectifier circuit for constant voltage output, and FIG. 10B is a graph showing the results of a simulation. 1A is a diagram showing an embodiment of a rectifier circuit for constant current output, and FIG. 1B is a graph showing the results of a simulation. 10A is a diagram showing another embodiment of a rectifier circuit for constant current output, and FIG. 10B is a graph showing the results of a simulation. FIG. 1 illustrates an embodiment of a wireless power transmission system. 11 is a graph showing a simulation result in the embodiment of the wireless power transmission system.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
<Configuration of high frequency inverter circuit>
Fig. 1 shows an outline of a high-frequency inverter circuit according to an embodiment of the present invention. The high-frequency inverter circuit 100 shown in Fig. 1 includes a switching circuit 10 and a load circuit 20, and a passive circuit (circuit network) 30 between the switching circuit 10 and the load circuit 20.

The switching circuit 10 includes an input inductor 12 connected to the positive side of the DC voltage source 11, a switching element 13 connected in parallel to the DC voltage source 11 and switched at a predetermined duty ratio, an output capacitor 14 connected in parallel to the switching element 13, and a series LC resonant filter 15 connected to the power transmission wiring.

The switching element 13 is switched between the on and off states by a cycle controlled by PWM, and a typical duty ratio is 1/2 of the cycle T, so in this embodiment the duty ratio is also set to 1/2 of the cycle T. A transistor or MOS-FET can be used for this switching element 13.

The input inductor 12 connected to the DC voltage source 11 supplies DC current to the circuit following the switching element. The series LC resonant filter 15 is an LC resonant circuit that resonates the output of the power transmission side wiring, and is connected as a low-pass filter to pass only the fundamental wave and suppress harmonics. Note that if the passive circuit is to have a low-pass effect, this series LC resonant filter 15 can be omitted.

The output capacitor 14 stores charge when the switching element 13 is in the off state and releases the charge when it is in the on state. ZVS can be achieved by releasing all the accumulated charge before the switching element 13 transitions from the off state to the on state. At this time, ZVDS can be achieved by designing the discharge of charge, which changes over time, i.e., the amount of change in voltage (switching voltage) (slope on the graph), to be zero. When ZVS is achieved, switching losses are reduced, and when ZVDS is also achieved, further reductions in harmonics of the switching voltage are expected. An inverter circuit that achieves both ZVS and ZVDS is called class E and is distinguished from other inverter circuits.

In order for the voltage (switching voltage) of the output capacitor 14 to achieve ZVS and ZVDS, the output impedance _Z0 in the switching circuit 10 must be set to a predetermined value. In this case, the output impedance _Z0 is set on the premise that the load 21 is an optimum load, or an optimum load is calculated according to the value of the output impedance _Z0 set by the configuration of the switching circuit 10, and the load 21 with that value is used.

However, in either of the above cases, if the resistance value of the load 21 fluctuates, ZVS and ZVDS cannot be achieved. This is because if the resistance value of the load 21 is smaller than the optimal value, the charge stored in the output capacitor 14 is released quickly, and the output voltage (switching voltage) becomes negative when the switching element 13 is turned on. Conversely, if the resistance value of the load 21 is greater than the optimal value, not all of the charge is released, and the output voltage (switching voltage) becomes positive.

Therefore, in this embodiment, a passive circuit (circuit network) 30 is provided between the switching circuit 10 and the load side circuit 20, and this passive circuit 30 achieves ZVS by releasing all the charge stored in the output capacitor 14 so that the voltage (switching voltage) of the output capacitor 14 becomes zero (V) when the switching element 13 is turned on, even if the load 21 fluctuates.

<Circuit design method>
A technique for designing the network of passive circuit 30 is described below.
First, in a typical class E inverter as shown in FIG. 2(a), the output current (i ₁ (t)) and the voltage (v ₁ (t)) of the output capacitor (shunt capacitor) can be expressed by the following equation.

Now, based on the above equation, the following equation can be obtained by harmonic balance analysis.

And under ZVS and ZVDS conditions with t = T/2, the following equation can be obtained:

Now, by substituting the above formula (6) into the above formulas (4) and (5) and deleting θ, we obtain the following formulas (7) and (8).

In this case, the impedance ( _Z0 = _R0 + _jX0 ) that satisfies the above (7) and (8) appears as two arc-shaped curves on the Smith chart as shown in FIG. 2(b), and the two curves intersect at the point _Z00 . This intersecting point _Z00 is expressed by the following equation. Note that the above-mentioned arc-shaped curve is called a geodesic point in hyperbolic geometry. Here, the above equation (7) represents the ZVS geodesic curve, and the above equation (8) represents the ZVDS geodesic curve.

Such arc-shaped curves on the Smith chart (ZVS geodesic or ZVDS geodesic) change due to actual load fluctuations, and in this case, it is possible to convert the real axis load fluctuation geodesic to a ZVS geodesic. This conversion is done using a Möbius transformation. A Möbius transformation can map from a circle to a circle, and a straight line can be considered to be a circle of radius ∞, so it is possible to convert a straight line into a circle (or an arc-shaped curve).

Here, let us assume a typical black box model in which the load fluctuates in a two-terminal pair circuit as shown in Fig. 3(a). This black box converts the load impedance _ZL to an input impedance _Z0 . The input impedance _Z0 converted by the impedance parameters _Z11 , _Z12 , _Z21 , and _Z22 in the black box at this time can be expressed by the following formula.

Furthermore, if the black box is lossless and consists of reciprocal components, the above equation (10) can be expressed as the following equation:

The input impedance _Z0 converted as described above converts the load impedance _ZL from a real axis load variation geodesic curve to a ZVS geodesic curve as shown in FIG. 3(b). When impedances at three points are extracted from each geodesic curve, each impedance is expressed by the following formula.

By solving the above equation, the individual parameters (Z ₁₁ , Z ₂₂ , Z ₂₁ (=Z ₁₂ )) constituting the impedance parameters of the black box can be obtained. These individual parameters can be expressed by the following equations.

By substituting the respective values for the impedance parameters of the black box shown above, the individual parameters (Z ₁₁ , Z ₂₂ , Z ₂₁ (=Z ₁₂ )) are determined, and a specific network of the passive circuit 30 can be designed.

<Passive circuit design for constant voltage (CV) output>
Next, a method for designing the passive circuit 30 with a constant voltage output (hereinafter sometimes abbreviated as CV output) will be described with reference to the above design method. As described above, the formula expressing the ZVS geodesic curve is as shown in the above formula (7). In this formula (7), when R ₀ =0, X ₀ becomes the following formula (18), and Z _0a and Z _0b become the following formulas (19) and (20). Note that the intersection (Z ₀₀ ) of the ZVS geodesic curve and the ZVDS geodesic curve is the above formula (9).

On the other hand, as shown in FIG. 4(a), for the loads Z _La , Z _Lb , and Z _L0 on the real axis, the horizontal axis of the Smith chart indicates the load resistance R _L , which can be regarded as a geodesic line of the load resistance, with both ends being 0 and ∞. The load resistance R _L is an arbitrary point in the range from 0 to ∞, and impedance parameters for constant voltage output can be obtained by setting Z _La = 0, Z _Lb = ∞, and Z _L0 = R _L0, respectively. By substituting these calculation formulas into the above formulas (15) to (17), the individual parameters (Z ₁₁ , Z ₂₂ , Z ₂₁ (= Z ₁₂ )) can be obtained. The result is as shown in the following formula.

Furthermore, since Z ₁₁ =jX ₁₁ , Z ₂₂ =jX ₂₂ , and Z ₂₁ =jX ₂₁ , the respective reactances X ₁₁ , X ₂₁ , and X ₂₂ can be expressed by the following equations.

When configuring the T-type circuit shown in Figure 4(b), by substituting the above equations (22) to (24) into the reactance values in Figure 4(b), four different circuits can be configured depending on the polarity of _X21 and the range of R _L0 . The range of R _L0 is also influenced by ωC _s . These four types of circuit configurations are shown in the table below.

Therefore, with the above four types of circuit configurations, ZVS can be achieved regardless of the load resistance R _L. When the load resistance R _L =R _L0 , ZVS and ZVDS are achieved.
Furthermore, by substituting the above expressions (22) to (24) into the above expression (11), the following expression can be obtained.

Therefore, the current resonance width _I1 can be calculated from the above equation (25) and the previously described equations (3) to (5), as shown below.

Furthermore, if the voltage resonance width _V2 of the output voltage is calculated from the above equation (25) and the impedance parameters, the following equation is obtained.

As is clear from the above equation (27), the voltage amplitude width _V2 of the output voltage is constant regardless of the load resistance R _L , so that a constant voltage output can be achieved.

<Passive circuit design for constant current (CC) output>
Next, a method for designing the passive circuit 30 for constant current output (hereinafter sometimes abbreviated as CC output) will be described. The design method for constant current output is the same as that for constant voltage output, where _X0 is given by the above formula (18), _Z0a and _Z0b are given by the above formulas (19) and (20), and the intersection ( _Z00 ) of the ZVS geodesic line and the ZVDS geodesic line is given by the above formula (9).

5A, in the case of constant current output, the horizontal axis of the Smith chart indicates the load resistance R _L for the loads Z _La , Z _Lb , and Z _L0 on the real axis. This is regarded as a geodesic curve of the load resistance, as in the case of constant voltage output, and both ends are 0 and ∞.

Here, the load resistance R _L is an arbitrary point in the range from 0 to ∞, but when determining the impedance parameters for constant current output, the two ends of the geodesic line of the load resistance, "0" and "∞", are the opposite values to those for constant voltage output. In other words, the impedance parameters for constant current output can be obtained by setting Z _La = ∞, Z _Lb = 0, and Z _L0 = R _L0 . By substituting these calculation formulas into the above formulas (15) to (17), the individual parameters (Z ₁₁ , Z ₂₂ , Z ₂₁ (=Z ₁₂ )) can be obtained. The result is as shown in the following formula.

Furthermore, since Z ₁₁ =jX ₁₁ , Z ₂₂ =jX ₂₂ , and Z ₂₁ =jX ₂₁ , the respective reactances X ₁₁ , X ₂₁ , and X ₂₂ can be expressed by the following equations.

As with the constant voltage output, when configuring the T-type circuit shown in Fig. 5(b), substituting the above equations (29) to (31) for the reactance in the figure, four different circuits can be configured depending on the polarity of _X21 and the range of R _L0 . The range of R _L0 is also influenced by ωC _s . These four types of circuit configurations are shown in the table below.

In the above four types of circuit configurations, ZVS can be achieved regardless of the load resistance R _L. When the load resistance R _L =R _L0 , ZVS and ZVDS are achieved. This is the same as in the case of constant voltage output.

Furthermore, by substituting the above formulas (22) to (24) into the above formula (11), the following formula (32) can be obtained, and the current resonance width _I1 can be obtained as the following formula (33) from this formula (32) and the above formulas (3) to (5). Furthermore, by calculating the current resonance width _I2 of the output current from this formula (33) and the impedance parameters, the following formula (34) is obtained.

As is clear from the above equation (34), the current amplitude width _I2 of the output current is constant regardless of the load resistance R _L , so that a constant current output can be achieved.

<Summary of high frequency inverter circuit>
As described above, a class E switching circuit 10 that achieves ZVS and ZVDS at an optimal load is configured, and the output impedance for the optimal load is used as a base, and the output impedance for a fluctuating actual load is converted to a base impedance, thereby making it possible to achieve a constant voltage output or a constant current output even when the load resistance R _L of the actual load is changed in various ways. In this case, a passive circuit 30 having desired impedance parameters can be provided for each of the cases of constant voltage output and constant current output by the design method described above.

<Rectification circuit>
Fig. 6 shows an outline of an embodiment of the present invention relating to a rectifier circuit. The rectifier circuit 200 shown in Fig. 6 has a configuration inverted from the high-frequency inverter circuit (Fig. 1) described above. That is, a passive circuit (circuit network) 30 is provided between an input side circuit (power supply circuit) 40 and a switching circuit 50 for rectification.

The switching circuit 50 includes a switching element 53 and an output capacitor (shunt capacitor) connected in parallel to the switching element 53, and a series LC resonant filter 55 is provided in the power transmission wiring. An output inductor 52 is provided in series with the load 60. Note that the series LC resonant filter 55 can also be omitted in the rectifier circuit 220 if the passive circuit is to have a low-pass effect.

The switching element 53 is switched between the on and off states by a cycle controlled by PWM, and a typical duty ratio is 1/2 of the cycle T, so in this embodiment the duty ratio is also set to 1/2 of the cycle T. However, as described below, a phase difference may occur with the power supply voltage, so the switching element 53 is controlled to adjust the phase. Note that a transistor or MOS-FET can be used as the switching element 53.

In a rectifier circuit using a switching element 53, the AC supplied from an AC voltage source is converted to DC by the switching operation of the switching element 53. The switching voltage rises when the switching element 53 switches from the ON state to the OFF state. The rising voltage at this time rises from 0 (V) when ZVS and ZVDS are achieved.

In the rectifier circuit 200 using the switching element 53, similar to the inverter circuit described above, by providing a passive circuit 30 configured with a predetermined impedance parameter, ZVS can be achieved even when the load fluctuates. Then, by adjusting the impedance parameter, a constant voltage or constant current can be output.

<Rectifier circuit design method>
The design method of the rectifier circuit is the same as that of the high-frequency inverter circuit described above. That is, as shown in FIG. 6, the configuration of each element constituting the rectifier circuit 200 is an inverse configuration in which the inverter circuit is inverted. With such an inverse configuration, the voltage at each element (element, etc.) can be considered to be the same as that of the inverter circuit. In this case, each impedance or reactance, etc. can be calculated in the same way. The same applies to the movement of each point of the geodesic line. Therefore, the impedance parameters can be obtained by the same design method.

Here, if the load conditions and output conditions are the same as those of the inverter circuit, the internal configuration of the passive circuit 30 can also be inverted and inverted. For example, if an LLC circuit is used as the T-type circuit, a CLL circuit with left and right inversion can be configured. The inductance or capacitance of each element can also be set in the same way. On the other hand, if the load conditions are different, a different circuit configuration can be used while using the same design method. For example, if the inverter circuit has a CV output but the rectifier circuit is changed to a CC output, the passive circuit 30 will inevitably have a different configuration. Even in this case, the design method can be the same as that of the inverter circuit described above.

Therefore, the design method is the same, so it will not be described again here, but in the case of constant voltage output and constant current output, the impedance parameters are obtained by the same method to configure a passive circuit. However, since a phase difference occurs between the input voltage and the drive signal of the switching element, this phase difference must be fixed to an appropriate value. This phase difference is determined by the polarity of a specific reactance _X21 among the individual parameters of the impedance parameters in the passive circuit. Note that this reactance _X21 is the same as the reactance in the inverter circuit.

For example, in the case of inputting a constant AC voltage and outputting a DC voltage CV, the phase difference is +180° when _X21 >0 and the phase difference is 0° when _X21 <0. In addition, in the case of outputting a DC voltage CC, the phase difference is -90° when _X21 >0 and the phase difference is +90° when _X21 <0.

<Wireless power transmission system>
Next, a wireless power transmission system will be described. By using the above-mentioned high-frequency inverter circuit and rectifier circuit, it is possible to construct a wireless power transmission system that can achieve ZVS and CV output or CC output in each circuit.

Figure 7 shows an example of an embodiment of a wireless power transmission system. As shown in this figure, in the wireless power transmission system, the high-frequency inverter circuit is composed of a switching circuit and a passive circuit, and the rectifier circuit is also composed of a switching circuit and a passive circuit. The high-frequency inverter circuit and the rectifier circuit are wirelessly coupled by a coupler.

The coupler used may be an electric field coupler or a magnetic field coupler, and these include the transformer type and the gyrator type. The transformer type is used when CV input is to be a CV output, or when CC input is to be a CC output, and the gyrator type is used when CV input is to be a CC output, or when CC input is to be a CV output.

The high-frequency inverter circuit and rectifier circuit configured here are as described above, and specifically, the two are configured symmetrically to each other. In other words, the high-frequency inverter circuit and rectifier circuit are arranged with the configurations of the high-frequency inverter circuit and rectifier circuit inverted (symmetrically positioned) around the coupler. Therefore, for example, the high-frequency inverter circuit may be configured as shown in Figure 1, and the rectifier circuit may be configured as shown in Figure 6, and they may be coupled by a coupler.

Now, a high-frequency inverter circuit converts DC to high-frequency, a coupler transmits high-frequency wirelessly without converting it, and a rectifier circuit converts high-frequency to DC; in these conversions, when a CV input is converted to a CV output, or when a CC input is converted to a CC output, it is recognized as a transformer characteristic. On the other hand, when a CV input is converted to a CC output, or when a CC input is converted to a CV output, it is recognized as a gyrator characteristic. Therefore, when the high-frequency inverter circuit and the rectifier circuit both have transformer characteristics, or when both have gyrator characteristics, the impedance parameters of the passive circuits can be configured similarly, and each element can be inverted (symmetrical). On the other hand, when one has transformer characteristics and the other has gyrator characteristics, the impedance parameters of the passive circuits are different, and separate passive circuits are configured.

Even if the high-frequency inverter circuit and rectifier circuit are inverted (symmetrically arranged), a phase difference occurs between the output voltage from the high-frequency inverter (input voltage to the rectifier circuit) and the drive signal for the switching element in the rectifier circuit, and as mentioned above, this phase difference must be fixed to an appropriate value. Therefore, in order to control the drive signal for the switching element of the rectifier circuit, the phase is controlled by the means shown in Figures 7(a) to 8(b).

To demonstrate that the above configuration can achieve CV output characteristics or CC output characteristics, experiments were conducted on specific circuit configurations. The experiments were conducted using a simulator, and the configurations and experimental results were as follows.

<Example of high frequency inverter circuit>
A circuit for CV output in a high-frequency inverter was designed with the configuration shown in Fig. 8(a). The specifications of the switching circuit in this case are as shown in the table below, and the passive circuit is a T-type LLC circuit, set as shown in the table below. The load resistance is set to 50 Ω, which corresponds to the optimal load for achieving ZVS and ZVDS in a class E inverter circuit without a passive circuit.

In addition, the configuration shown in Figure 8(b) was designed as a circuit for CC output in the high-frequency inverter. The specifications of the switching circuit in this case are the same as for CV output, and the passive circuit is a T-type LCL circuit, set as shown in the table below.

For the high-frequency inverter circuit for CV output and the high-frequency inverter circuit for CC output described above, the changes over time were detected for the switching voltage (shunt capacitor voltage), output voltage, and output current for one cycle from the OFF state to the ON state of the switching element when the load resistance was the optimal load (50 Ω) and when it was changed (25 Ω and 100 Ω). For reference, the voltages and currents were also detected in the same way for a simple E-class inverter without a passive circuit.

These results are shown in Figure 9. (a) shows the results for only the class E inverter, (b) shows the results for a high-frequency inverter circuit equipped with a passive circuit to enable CV output, and (c) shows the results for a high-frequency inverter circuit equipped with a passive circuit to enable CC output. As shown in these figures, according to the switching voltage (shunt capacitor voltage), when the load resistance is the optimal load (50 Ω), ZVS and ZVDS are achieved in each circuit configuration. Furthermore, when only the class E inverter is used, ZVS is not achieved when the load resistance fluctuates, but ZVS is achieved in the high-frequency inverter circuits for CV output and CC output.

Furthermore, in an inverter circuit for CV output, even if the load resistance is changed, there is no change in the amplitude of the output voltage, and a constant voltage is output. On the other hand, in an inverter circuit for CC output, even if the load resistance is changed, there is no change in the amplitude of the output current, and a constant current is output.

To confirm the achievement of ZVS in the load resistance range of 5Ω to 500Ω (1/10 to 10 times the optimal load), the switching voltage (shunt capacitor voltage) at the timing when the switching element switches from the OFF state to the ON state was measured for the above three types of circuits. The results are shown in Figure 10. In the figure, "G2G" indicates a configuration in which the above-mentioned passive circuit is provided, and "Conventional" indicates an E-class inverter circuit with a conventional configuration.

As is clear from the results shown in Figure 10, in each circuit for CV output and CC output, the switching voltage (shunt capacitor voltage) is 0 (V) at the timing when the switching element is turned on for each load resistance, which matches the theoretical ZVS situation. In reference to this result, it can be determined that the high-frequency inverter circuit configured as in this embodiment enables CV output or CC output over a wide range, without being limited to the above-mentioned 25 Ω and 100 Ω.

<Example of rectifier circuit>
As a circuit for CV output in a rectifier circuit, a configuration as shown in FIG. 11(a) was designed. The circuit shown in this figure is a case where the polarity of the impedance parameter _X21 described above is positive, and the specifications when the polarity of the impedance parameter _X21 is positive are as shown in the table below. As shown in the table below, the input high frequency voltage amplitude was set to 51.6 V (6.78 MHz), the output voltage was designed to be 48 V, and the optimal load was designed to be 86.6 Ω. The passive circuit in this case was a T-type CLL circuit, and each element was set as shown in the table below. Since the input voltage was a high frequency (RF) voltage with a frequency of 6.78 MHz, the switching frequency of the switching element was set to 6.78 MHz, and the phase difference was fixed to 180°.

The experimental results for the rectifier circuit configured as above are shown in Figure 11 (b). As shown in this figure, by operating the switching element while fixing the phase at 180° with respect to the radio frequency (RF) input voltage, the falling voltage of the switching voltage (shunt capacitor voltage) achieved ZVS. As a result, the DC output voltage became a constant voltage.

Next, a rectifier circuit was designed for CV output when the polarity of the impedance parameter _X21 is negative. The configuration is shown in Fig. 12(a). The specifications of the switching circuit in this case are the same as those in Table 5 above, and only the passive circuit was changed. The passive circuit was a T-type LCL circuit, and was set as shown in the table below.

The experimental results for the rectifier circuit of the above configuration are shown in Fig. 12(b). When the polarity of the impedance parameter _X21 is negative, no phase difference occurs with respect to the radio frequency (RF) input voltage, so that as shown in the figure, the falling voltage of the switching voltage (shunt capacitor voltage) achieves ZVS by operating the switching element without adjusting the phase. As a result, the DC output voltage becomes a constant voltage.

On the other hand, a configuration as shown in FIG. 13(a) was designed as a circuit for CC output. This illustrates the case where the polarity of the impedance parameter _X21 is positive. The specifications of this circuit are as shown in the table below. The input high frequency voltage amplitude was set to 51.6 V (6.78 MHz), the optimum load was set to 86.6 Ω, as in the case of CV output, and the output current was designed to be 0.55 A. The passive circuit in this case was a T-type LCL circuit, and each element was set as shown in the table below. The switching frequency of the switching element was set to 6.78 MHz, and the phase difference was fixed to -90°.

The experimental results for the rectifier circuit configured as above are shown in Figure 13(b). As shown in this figure, by operating the switching element while fixing the phase at -90° with respect to the radio frequency (RF) input voltage, the falling voltage of the switching voltage (shunt capacitor voltage) achieved ZVS. As a result, the DC output current became a constant current.

Next, a rectifier circuit was designed for CC output when the polarity of the impedance parameter _X21 is negative. The configuration is shown in Fig. 14(a). The specifications of the switching circuit in this case are the same as those in Table 7 above, and only the passive circuit was changed. The passive circuit was a T-type CLC circuit, and was set as shown in the table below.

The experimental results for the rectifier circuit of the above configuration are shown in Fig. 14(b). When the polarity of the impedance parameter _X21 is negative, the falling voltage of the switching voltage (shunt capacitor voltage) achieves ZVS by operating the switching element while correcting the phase of the switching voltage by +90° with respect to the radio frequency (RF) input voltage. As a result, the DC output current becomes a constant current.

<Example of wireless power transmission system>
As a circuit for constructing a wireless power transmission system, a configuration as shown in FIG. 15 was designed. Basically, it is composed of an inverter circuit, a coupling circuit, and a rectifier circuit. The specifications of the inverter circuit are as shown in Table 9 below, and the rectifier circuit is as shown in Table 10 below. The coupler is configured as shown in FIG. 15, and the specifications are shown in Table 11 below. The input voltage is 100V from a constant voltage source, and this is made into a constant voltage output by the inverter circuit. The coupler adopts a gyrator method, and is configured to output a constant current from a constant voltage input. Furthermore, the rectifier circuit is configured to output a constant voltage from a constant current input. In this case, the assumed output voltage is designed to be a constant voltage of 100V, and the result is shown in FIG. 16.

From the results in Figure 16, it was found that the output from the inverter circuit was a high-frequency constant voltage of 300V, and that a high-frequency constant current of 600mA was input to the rectifier circuit via the coupler. Furthermore, it was found that the high-frequency constant current of 600mA was rectified in the rectifier circuit, and a constant DC voltage of 100V was output.

<Summary>
As described above, for both the high frequency inverter circuit and the rectifier circuit, by appropriately configuring the passive circuit, it is possible to achieve CV output or CC output even when the load fluctuates. Furthermore, by using these and coupling them with a coupler, a wireless power transmission system can be constructed, in which CV output or CC output is realized in the high frequency inverter circuit, wireless transmission is performed by a wireless coupler, and finally, CV output or CC output by DC is possible regardless of the load by a rectifier.

As a result, it is possible to supply the desired power to various loads. In other words, it is possible to provide a stable power supply to loads that require a constant voltage supply and loads that require a constant current supply, and by setting the optimal load in advance and providing a passive circuit, it is possible to reduce switching losses for any load fluctuation.

Although the embodiments and examples 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 embodiments, etc., or to add other configurations. For example, a representative passive circuit configuration is shown, but other configurations may be used as long as the circuit configuration can obtain the impedance parameters that the passive circuit should have. Also, although one example of the coupler is shown in the example, other configurations may be used.

10, 50 Switching circuit 11 DC voltage source 12 Input inductor 13, 53 Switching element 14, 54 Output capacitor (shunt capacitor)
15, 55 Series LC resonant filter 20 Load circuit (output side circuit)
21, 60 Load 30 Passive circuit 40 Power supply circuit (input side circuit)
52 Output inductor 100 High frequency inverter circuit 200 Rectifier circuit

Claims (8)

A high-frequency inverter circuit that supplies power at a constant voltage or a constant current to a load whose load resistance varies,
a switching circuit including a switching element that is switched on and off at a predetermined duty ratio and an output capacitor that is connected in parallel to the switching element;
a passive circuit for converting an output impedance of the switching circuit;
The passive circuit uses an output impedance when a switching voltage, which is determined based on the configuration and setting values of each element provided in an output side circuit including the switching circuit and an actual load, achieves ZVS and ZVDS as a reference impedance, converts an output impedance at an actual load to the reference impedance, and converts the output impedance so that the switching voltage falls within a range in which ZVS is achieved within a fluctuating load range. The high-frequency inverter circuit according to claim 1, wherein the passive circuit is constructed as a circuit that satisfies an impedance parameter that can convert the impedance from the load real axis variation geodesic line drawn on the Smith chart to a ZVS geodesic line that achieves ZVS drawn on the Smith chart. A rectifier circuit that rectifies AC power supplied at a constant voltage or a constant current and outputs DC power as a constant voltage or a constant current to a load whose load resistance varies,
a switching circuit including a switching element which is switched at a predetermined duty ratio while adjusting a phase with an AC voltage input from an AC voltage source, and an output capacitor which is connected in parallel with the switching element;
a passive circuit for converting an input impedance of the switching circuit;
The passive circuit is characterized in that it uses an input impedance when the rise voltage of the switching voltage, which is determined based on the configuration and setting values of each element provided in an output side circuit including the switching circuit and an actual load, achieves ZVS and ZVDS as a reference impedance, converts the input impedance in the actual load to the reference impedance, and converts the input impedance so that, within the fluctuating range of the load, the fall voltage of the switching voltage falls within a range where ZVS is achieved. The rectifier circuit according to claim 3, wherein the passive circuit is constructed as a circuit that satisfies an impedance parameter that can perform impedance conversion from the load real axis variation geodesic curve drawn on the Smith chart to the ZVS geodesic curve that achieves ZVS drawn on the Smith chart. Further, a control unit is provided for controlling the switching operation of the switching element,
5. The rectifier circuit according to claim 3, wherein the control unit controls switching operation while correcting a phase difference that occurs between the input voltage or input current period when the input impedance is converted by the passive circuit. A wireless power transmission system comprising a high-frequency inverter circuit according to claim 1 or 2 as a power supply side, which is coupled to a rectifier circuit via a coupler. A wireless power transmission system comprising a rectifier circuit according to any one of claims 3 to 5 on the power receiving side, which is coupled to a high-frequency inverter circuit via a coupler. A wireless power transmission system comprising a high-frequency inverter circuit according to claim 1 or 2 as a power supply side, a rectifier circuit according to any one of claims 3 to 5 as a power receiving side, and a coupler provided between the high-frequency inverter circuit and the rectifier circuit .

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