JP2017221020A - System and method for power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply power to a secondary side load using power supplied from the primary side to the secondary side in a non-contact manner, without exchanging power supply information between the primary side and the secondary side without controlling a primary voltage.SOLUTION: Control means 24 of a power supply system 10 controls to supply power from a secondary side coil 22 to a secondary battery 26. In this case, the control means 24 controls to supply power from the secondary side coil 22 to the secondary battery 26 in such a manner that, starting from an initial state in which a load resistance value when viewing the secondary battery 26 from the secondary side coil 22 becomes substantially infinite in a current region having an input current Iin smaller than and including an input current value Iinmax, the load resistance value decreases as time elapses.SELECTED DRAWING: Figure 1

Description

  When the primary side coil connected to the primary side power source and the secondary side coil connected to the secondary side load are arranged with a gap therebetween, the present invention The present invention relates to a power supply system and a power supply method for supplying power to a secondary coil in a contactless manner.

  In recent years, a primary coil connected to a primary power supply and a secondary coil connected to a secondary load are arranged with a gap therebetween, and the primary coil is not connected to the secondary coil. A technique for performing non-contact power feeding (non-contact power transmission) from a power source to a load by supplying power by contact has been developed.

  One such non-contact power feeding method uses electromagnetic induction. In this power feeding method, for example, a primary side (power feeding side) power source is an AC power source, and a secondary side (power receiving side) load is a power storage device provided in the electric vehicle. A power storage device such as a secondary battery or a capacitor is charged using electromagnetic induction between the provided primary coil and the secondary coil provided in the electric vehicle on the power receiving side.

  For example, Patent Documents 1 and 2 are disclosed as conventional techniques of the non-contact power feeding method.

  In Patent Document 1, in order to transmit power supply information such as a charging instruction and required power from the power reception side to the power supply side in the case of non-contact power supply, a communication device is provided in the primary side coil and the secondary side coil. It is disclosed that contactless power feeding is performed from a power feeding side to a power receiving side based on the power feeding information by transmitting and receiving power feeding information.

  On the other hand, in Patent Document 2, in the non-contact power feeding method in which the tolerance for the positional deviation between the primary side coil and the secondary side coil at the time of non-contact power feeding and the fluctuation of the gap length between both coils is large, between the two coils. The subject that the ratio of a primary voltage and a secondary voltage fluctuates with the fluctuation | variation of positional relationship of is disclosed. Further, in Patent Document 2, in order to solve this problem, if power supply information is exchanged by communication between a primary side coil (power supply side coil) and a secondary side coil (power reception side coil), It is disclosed that interference, communication error, communication noise due to a power transmission magnetic field, and the like occur, and that the installation of the communication device hinders the reduction in size and weight on the power receiving side. In order to solve such a problem, the technique disclosed in Patent Document 2 realizes constant secondary voltage by controlling the primary voltage without using a communication device.

JP 2008-288889 A JP 2011-45195 A

  In the technology of Patent Document 2, from the viewpoint that the charging voltage to the power storage device is preferably a constant voltage, the secondary voltage is made constant by controlling the primary voltage without using a communication device to make the secondary voltage constant. Charge. However, when power is supplied to a load that is a power storage device such as a secondary battery, a simpler control method, specifically, a secondary load without controlling the primary voltage. It is preferable that non-contact power supply can be performed.

  The present invention has been made in consideration of such problems, and without exchanging power supply information between a primary side which is a power supply side and a secondary side which is a power reception side, and 1 To provide an electric power supply system and an electric power supply method capable of supplying electric power to a load on the secondary side using electric power supplied in a non-contact manner from the primary side to the secondary side without controlling the secondary voltage. Objective.

  In the present invention, a primary side coil connected to a primary side power source and a secondary side coil connected to a secondary side load are arranged with a gap therebetween, and the secondary side coil is connected to the secondary side coil. The present invention relates to a power supply system and a power supply method for supplying power to a side coil in a contactless manner.

  And in order to achieve said objective, the electric power supply system which concerns on this invention is provided between the said secondary side coil and the said load, Control which controls the electric power supply from the said secondary side coil to the said load Means. In this case, the control means is configured to output the load from the secondary coil to the load in a current region where the output current flowing from the secondary coil to the load is equal to or less than the current value corresponding to the maximum power operating point of the secondary coil. Starting from an initial state in which the load resistance value is almost infinite, the power supply from the secondary coil to the load is controlled so that the load resistance value decreases with time. .

  In order to achieve the above object, in the power supply method according to the present invention, power is supplied from the secondary coil to the load by the control means provided between the secondary coil and the load. In the current region where the output current flowing from the secondary coil to the load is equal to or less than the current value corresponding to the maximum power operating point of the secondary coil, the load is viewed from the secondary coil. The power supply from the secondary coil to the load is controlled so that the load resistance value decreases as time elapses, starting from an initial state where the load resistance value at that time is substantially infinite.

  Thus, in the present invention, the control means controls the power supply from the secondary coil to the load by reducing the load resistance value from approximately infinity with the passage of time. Therefore, in the present invention, it is possible to control the power supply to the load without exchanging power supply information between the primary side and the secondary side and without controlling the primary voltage. . That is, the control for the power supply to the load is completed on the secondary side regardless of the state on the primary side. As a result, it is possible to supply power to the load by simple control on the secondary side using the power supplied from the primary side coil to the secondary side coil without contact.

  Therefore, in the present invention, feedback means (communication device or the like) from the secondary side to the primary side is unnecessary. Further, it becomes unnecessary to ensure compatibility between the primary side and the secondary side by providing a communication device, and to perform an interoperability test for ensuring compatibility. In this way, many processes for ensuring compatibility are not required. Therefore, in the present invention, the cost of the power supply system can be reduced.

  Here, the control means rectifies the output voltage and output current of the secondary coil, and performs voltage conversion on the output voltage after rectification, and a DC voltage that is the output voltage after conversion. A voltage conversion circuit that supplies the voltage conversion circuit to the load, and a control unit that controls the voltage conversion circuit. In this case, the control unit corresponds to the output current after rectification and the DC current flowing from the voltage conversion circuit to the load substantially matches a target current value, and the DC voltage substantially matches a target voltage value, And / or it is preferable to control the voltage conversion circuit so that the output power multiplied by the output voltage and the output current after rectification substantially coincides with the maximum power value.

  In this way, feedback control is performed so that the DC current substantially matches the target current value, the DC voltage substantially matches the target voltage value, and / or the output power substantially matches the maximum power value. By doing so, it is possible to easily control the power supply to the load. As a result, it is possible to perform control to efficiently extract power that can be acquired from the primary side.

  In this case, the control unit first reaches the target current value among the direct current, the direct current voltage, and the output power, or the direct current voltage reaches the target voltage value first. Or when the output power first reaches the maximum power value, the direct current, the DC voltage, or the output power that has first reached the target current value, the target voltage value, or the maximum power value. It is preferable that the power supply to the load is continued in a controlled state.

  When the load is a power storage device such as a secondary battery, the DC current, the DC voltage, or the output power that has reached first is controlled to the target current value, the target voltage value, or the maximum power value. By continuing the power supply to the load, the power storage device can be easily charged.

  Further, the voltage conversion circuit includes a switching element, and in the initial state, the control unit turns the switching element off to make the load resistance value substantially infinite, and thereafter every predetermined unit time. Preferably, the load resistance value is gradually decreased by increasing the on-time of the switching element. Thereby, the electric power supply with respect to the said load can be performed easily.

  Specifically, the control unit may control power supply to the load as follows.

  That is, when the direct current reaches the target current value, the control unit controls the direct current to the target current value while increasing or decreasing the duty of the switching element. Thereafter, when the output power reaches the maximum power value, the control unit controls the output power to the maximum power value while increasing or decreasing the duty. Further, the control unit turns off the switching element when the DC voltage reaches the target voltage value and the DC voltage reaches the target voltage value continuously within a specified time, The control on the voltage conversion circuit is terminated.

  Thereby, when the load is a power storage device such as a secondary battery, when the SOC (charge rate) is low, non-contact power feeding to the power storage device can be easily performed to complete charging.

  Further, when the DC voltage reaches the target voltage value, the control unit controls the DC voltage to the target voltage value while increasing or decreasing the duty of the switching element, and then the DC voltage is within a specified time. When the target voltage value is reached continuously, the switching element may be turned off to end the control on the voltage conversion circuit. Thereby, when the load is a power storage device, the contactless power feeding to the power storage device can be completed in a short time if the SOC is sufficiently large.

  Further, when the output power reaches the maximum power value, the control unit controls the output power to the maximum power value while increasing or decreasing the duty of the switching element, and then the DC voltage is set to the target voltage. When the DC voltage reaches the target voltage value continuously within a specified time after reaching the value, the switching element may be turned off to end the control on the voltage conversion circuit. As a result, when the load is a power storage device, the power storage device can be easily configured even if the maximum power value is set small due to a positional deviation between the primary side coil and the secondary side coil. Can be contactlessly fed. As a result, the maximum power obtainable from the primary side can be supplied to the power storage device easily and efficiently.

  In each of the above inventions, the switching element is preferably a field effect transistor. Thereby, voltage conversion from the output voltage to the DC voltage in the voltage conversion circuit can be quickly performed while suppressing power consumption in the voltage conversion circuit.

  Further, the output power increases with a decrease in the output voltage after rectification, and reaches the maximum power value at the maximum power operating point at which the product of the output current and the output voltage is maximized. It has a drooping characteristic that decreases when the output voltage is lowered. On the other hand, the output current after rectification has a characteristic of decreasing as the output voltage increases. In this case, in the initial state, the load resistance value becomes substantially infinite, so that the output voltage becomes a no-load voltage as a maximum voltage value and the output current becomes a minimum value. Therefore, the control unit may start from the no-load voltage in the current region and control the voltage conversion circuit between the no-load voltage and the output voltage value corresponding to the maximum power operating point. .

  In the current region, the loss (copper loss) of the internal resistance on the secondary side is small, and the power use efficiency is high. Therefore, by controlling the voltage conversion circuit between the no-load voltage and the output voltage value corresponding to the maximum power operating point, while reducing the loss accompanying the power supply on the secondary side, It is possible to perform non-contact power supply to the load. In addition, even if the power that can be supplied to the load is restricted due to the occurrence of a positional deviation between the primary coil and the secondary coil or the increase in the gap length, the It is possible to supply the maximum power to the load under the restricted conditions.

  Furthermore, it is preferable that the primary side coil and the secondary side coil are electromagnetic induction coils. Thereby, the power supply to the load can be easily controlled.

  According to the present invention, the control means controls the power supply from the secondary coil to the load by decreasing the load resistance value from about infinity with time. Therefore, in the present invention, it is possible to control power supply to the load without exchanging power supply information between the primary side and the secondary side and without controlling the primary voltage. That is, the control for power supply to the load is completed on the secondary side regardless of the state on the primary side. As a result, it is possible to supply power to the load by simple control on the secondary side using the power supplied from the primary side coil to the secondary side coil without contact.

It is a circuit diagram of the electric power supply system concerning this embodiment. It is a circuit diagram which shows the equivalent circuit of the primary side coil of FIG. 1, and a secondary side coil. It is a graph which shows the relationship between the input voltage with respect to a voltage conversion circuit, input current, and input power. It is a graph which shows the relationship between an input electric current, an input voltage, a request voltage, input electric power, and a duty. It is a flowchart explaining operation | movement of the electric power supply system of FIG. 3 is a timing chart of the first embodiment. It is a timing chart of 2nd Example. It is a timing chart of 3rd Example. It is a circuit diagram which shows the modification of the electric power supply system of FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a power supply system and a power supply method according to the present invention will be described with reference to the accompanying drawings.

[Configuration of this embodiment]
As shown in FIG. 1, the power supply system 10 according to the present embodiment is a system that performs non-contact power supply (non-contact power transmission) from the primary side 12 that is the power supply side to the secondary side 14 that is the power reception side. .

  Specifically, on the primary side 12, a series circuit of a resistor 18 and a primary side coil 20 is connected to the AC power supply 16. On the other hand, on the secondary side 14, a control unit 24 and a secondary battery 26 as a load are connected in parallel to the secondary side coil 22.

  In the control means 24, a rectifier circuit 28, a first smoothing circuit 30, a voltage conversion circuit 32, and a second smoothing circuit 34 are parallel to the secondary coil 22 from the secondary coil 22 toward the secondary battery 26. It is connected to the.

  The rectifier circuit 28 is a diode bridge composed of four diodes 36. The first smoothing circuit 30 has a capacitor 38. The voltage conversion circuit 32 includes a MOSFET (metal oxide semiconductor field effect transistor) 40 as a switching element, a diode 42 and a coil 44.

  In this case, a series circuit of the MOSFET 40 and the diode 42 is connected in parallel to the capacitor 38. That is, the drain terminal of the MOSFET 40 is connected to one end of the capacitor 38, the source terminal is connected to the cathode of the diode 42, and the anode of the diode 42 is connected to the other end of the capacitor 38. One end of a coil 44 is connected to the source terminal of the MOSFET 40 and the cathode of the diode 42, and the other end of the coil 44 is connected to one end of a capacitor 46 constituting the second smoothing circuit 34.

  One end of the capacitor 46 is connected to the positive electrode of the secondary battery 26, and the other end of the capacitor 46 is connected to the negative electrode of the secondary battery 26. In this case, the other end of the capacitor 46, the anode of the diode 42, and the other end of the capacitor 38 are connected to the negative electrode of the secondary battery 26.

  In the control means 24, a current sensor 48 is connected between one end of the capacitor 38 and the drain terminal of the MOSFET 40. A voltage sensor 50 is connected in parallel to the capacitor 38. Further, a current sensor 52 is connected between one end of the capacitor 46 and the positive electrode of the secondary battery 26. Furthermore, a voltage sensor 54 is connected to the capacitor 46 and the secondary battery 26 in parallel. The control unit 24 further includes a charge control unit 56 and a step-down control unit 58 as control units for the MOSFET 40.

  And the electric power supply system 10 is applied to the non-contact electric power feeding with respect to the electrical storage apparatus (secondary battery 26) with which the electric vehicle which is not illustrated is equipped, for example. In this case, the primary coil 20 is a coil on the power supply side (ground side), and the secondary coil 22 is a coil on the electric vehicle side. That is, when the electric vehicle moves above the ground side primary side coil 20, the primary side coil 20 and the secondary side coil 22 are arranged with a predetermined gap therebetween. Then, by electromagnetic induction between the primary side coil 20 and the secondary side coil 22, power is supplied from the primary side coil 20 to the secondary side coil 22 in a non-contact manner, and the AC power supply 16 receives non-contact power feeding (non-contact) The secondary battery 26 can be charged by contact power transmission.

  Due to the electromagnetic induction, a mutual inductance M is generated between the primary side coil 20 having the self inductance L1 and the secondary side coil 22 having the self inductance L2. An equivalent circuit between the primary side coil 20 and the secondary side coil 22 in this case is shown in FIG.

Here, when the primary current I1 flows from the AC power supply 16 through the resistor 18 to the primary coil 20 and the primary voltage V1 is applied to the primary coil 20, the secondary coil 22 has Due to electromagnetic induction, a secondary voltage V2 of an alternating voltage as an electromotive force is generated, and a secondary current I2 as an alternating current flows. And there exists a relationship of following (1)-(3) formula between the primary voltage V1 and the primary current I1, and the secondary voltage V2 and the secondary current I2.
V1 = jω × L1 × I1-jω × M × I2 (1)
V2 = jω × M × I1−jω × L2 × I2 (2)
M = k × (L1 × L2) ^1/2 (3)

  Note that j is an imaginary unit, and ω is an angular frequency. K is a coupling coefficient (k <1).

From the above formulas (1) to (3), the secondary voltage V2 can be expressed by the following formula (4). Further, the power P2 of the secondary coil 22 can be expressed by the following equation (5).
V2 = jω × I2 × {(M ² −L1 × L2) / L1}
+ V1 × (M / L1) (4)
P2 = V2 × I2 (5)

  The rectifier circuit 28 rectifies the secondary voltage V2 and the secondary current I2 and converts them into a pulsating voltage and a pulsating current, respectively. The first smoothing circuit 30 generates a DC voltage (output voltage) Vin and a DC current (output current) Iin, which are electromotive forces, by smoothing the pulsating voltage and the pulsating current.

  The DC voltage Vin is a DC voltage corresponding to the secondary voltage V2 that is the output voltage of the secondary coil 22 and an input voltage applied to the input side of the voltage conversion circuit 32. The direct current Iin is a direct current corresponding to the secondary current I2 that is the output current of the secondary coil 22, and is an input current that flows to the input side of the voltage conversion circuit 32. Therefore, in the following description, the DC voltage (output voltage) Vin may be referred to as the input voltage Vin, and the DC current (output current) Iin may be referred to as the input current Iin.

  In FIG. 1, the voltage conversion circuit 32 is a step-down chopper, and steps down the input voltage Vin by turning on or off the MOSFET 40. Since the step-down chopper having the configuration shown in FIG. 1 is well known, detailed description thereof will be omitted.

  The input voltage Vin is stepped down, smoothed by the second smoothing circuit 34, and supplied to the secondary battery 26 as an output voltage (DC voltage) Vout. An output current (DC current) Iout corresponding to the input current Iin also flows from the second smoothing circuit 34 to the secondary battery 26. As a result, the secondary battery 26 is charged.

  The current sensor 48 detects the input current Iin and outputs a detection signal corresponding to the detected input current Iin to the charge control unit 56. The voltage sensor 50 detects the input voltage Vin and outputs a detection signal corresponding to the detected input voltage Vin to the charge control unit 56. The current sensor 52 detects the output current Iout and outputs a detection signal corresponding to the detected output current Iout to the charge control unit 56. The voltage sensor 54 detects the output voltage Vout and outputs a detection signal corresponding to the detected output voltage Vout to the charge control unit 56.

  The charging control unit 56 determines the voltage value (required voltage) and current necessary for charging the secondary battery 26 based on the input detection signals (input voltage Vin, input current Iin, output voltage Vout, output current Iout). A value (required current) is calculated, and a command signal corresponding to the calculated required voltage and required current is output to the step-down control unit 58.

  The step-down control unit 58 controls the on / off of the MOSFET 40 by supplying a control signal to the gate terminal of the MOSFET 40 based on a command signal from the charge control unit 56. Note that the step-down control unit 58 controls on / off of the MOSFET 40 by PWM (Pulse Width Modulation) control. Details of the PWM control will be described later.

  FIG. 3 shows the qualitative relationship of the aforementioned input voltage Vin, input current Iin, and DC power (output power) Pin (Pin = Vin × Iin) obtained by multiplying the input voltage Vin and the input current Iin. Note that the DC power Pin is input power to the voltage conversion circuit 32, and therefore may be referred to as input power Pin in the following description.

  In FIG. 3, V0 is a no-load voltage. The no-load voltage V0 is a value of the input voltage Vin (electromotive force) when the load resistance value is substantially infinite when the secondary battery 26 that is a load is viewed from the secondary coil 22. If the MOSFET 40 is turned off and the conduction between the drain terminal and the source terminal is interrupted, the load resistance value becomes substantially infinite.

  Here, when the primary side coil 20 and the secondary side coil 22 are coupled by electromagnetic induction and the input power Pin is consumed by a load such as the secondary battery 26, the input voltage Vin is reduced from the no-load voltage V0. As a result, the input power Pin increases. When the input voltage Vin is further decreased, the value of the input power Pin becomes the maximum power Pmax (maximum power value). That is, in the characteristics of the input power Pin, the operating point at the maximum power Pmax is the maximum power operating point of the secondary coil 22.

  Thereafter, when the input voltage Vin is further decreased from the input voltage value Vinmax (output voltage value corresponding to the maximum power operating point) corresponding to the maximum power Pmax, the input power Pin is decreased. That is, the input power Pin has a drooping characteristic that changes parabolically with respect to the input voltage Vin.

  Note that reducing the input voltage Vin from the no-load voltage V0 can be translated into increasing the load from 0, while reducing the load resistance value from infinity.

  In such drooping characteristics of the input power Pin, there are a total of two values of the input voltage Vin corresponding to an arbitrary input power Pin, one on each of the left and right sides of FIG. On the other hand, the input current Iin has a characteristic of decreasing as the input voltage Vin increases. Therefore, when the input current Iin is smaller, the loss (copper loss) due to the internal resistance of the circuit on the secondary side 14 becomes smaller, and the utilization efficiency of the input power Pin becomes higher.

  Therefore, in the power supply system 10, the secondary battery 26 is charged in a current region equal to or less than the input current value Iinmax corresponding to the maximum power Pmax, that is, a voltage region between the no-load voltage V0 and the input voltage value Vinmax. Is called. That is, in this voltage region (current region), since the input current Iin is small and the input voltage Vin is high, the load is small and the load resistance value is high. Therefore, in this charging control, the operating point of the secondary coil 22 changes between the no-load voltage V0 and the maximum power Pmax (input voltage value Vinmax) due to the drooping characteristics of the input power Pin.

  FIG. 4 is a graph showing the relationship between the input current Iin, the input voltage Vin, and the input power Pin, the required voltage, and the duty of the MOSFET 40.

  As described above, in the power supply system 10, charging control for the secondary battery 26 is performed in a voltage region between the no-load voltage V0 and the input voltage value Vinmax (current region equal to or smaller than the input current value Iinmax). Therefore, the required voltage is set between the charge end voltage Vobj and the discharge end voltage according to the voltage region and the current region. In FIG. 4, the required voltage is set within the range illustrated by the triangles in the voltage region and the current region.

  The duty is also set to 0% at the no-load voltage V0 and X% at the input voltage value Vinmax. Therefore, in the voltage region and the current region, the duty of the control signal supplied from the step-down control unit 58 to the MOSFET 40 can be changed within the range of 0% to X%. The duty of X% is a duty corresponding to the maximum value Tonmax of the on-time Ton of the MOSFET 40.

  In this case, the input voltage Vin can be changed from the no-load voltage V0 to the input voltage value Vinmax by gradually increasing the duty from 0% corresponding to the no-load voltage V0 in the initial state toward X%. it can. In other words, by increasing the duty, the load resistance value (equivalent impedance) when the secondary battery 26 is viewed from the secondary coil 22 can be reduced. Such charge control makes it possible to charge the SOC (charge rate) of the secondary battery 26 within a range of 0% to 100%.

[Operation of this embodiment]
Next, the operation (power supply method) of the power supply system 10 according to the present embodiment will be described with reference to FIGS. In this description of operation, it will be described with reference to FIGS.

  As described above, in the power supply system 10 of FIG. 1, the voltage conversion circuit 32 is a step-down chopper. In this case, the end-of-charge voltage Vobj, which is the maximum value of the charging voltage of the secondary battery 26, is set to a voltage value equal to or less than the no-load voltage V0. Therefore, in the charge control for the secondary battery 26, the target is to increase the output voltage Vout to the end-of-charge voltage Vobj. On the other hand, the target current Iobj of the output current Iout varies depending on the charging condition of the secondary battery 26. In this case, the target current Iobj is preferably, for example, a maximum current value that can charge the secondary battery 26.

  Then, the step-down control unit 58 turns the MOSFET 40 on or off by PWM control based on the command signal from the charge control unit 56. In this case, the period of the control signal is τ.

  FIG. 5 is a flowchart showing the operation of the power supply system 10. In the power supply method according to this flowchart, the following three embodiments (first to third embodiments) can be applied.

  The first embodiment (see FIG. 6) shows a case where the output current Iout first reaches the target current Iobj among the output current Iout, the output voltage Vout and the input power Pin used for charging the secondary battery 26. . 1st Example assumes the case where the secondary battery 26 in which SOC fell is charged to full charge (SOC: 100%).

  In the second embodiment (see FIG. 7), the output voltage Vout first reaches the charge end voltage Vobj among the output current Iout, the output voltage Vout, and the input power Pin. 2nd Example assumes the case where the secondary battery 26 near full charge is charged.

  The third embodiment (see FIG. 8) shows a case where the input power Pin first reaches the maximum power Pmax among the output current Iout, the output voltage Vout, and the input power Pin. The third embodiment assumes a case where the maximum power Pmax is set low due to a positional shift between the primary coil 20 and the secondary coil 22, a large gap length, or the like.

  The first to third examples are examples of the present embodiment. Actually, which of the output current Iout and the output voltage Vout first reaches the target value, or the input power Pin is the first. Whether the maximum power Pmax is reached depends on the state of the secondary battery 26 at the time of charge control, the coupling state between the primary side coil 20 and the secondary side coil 22 (the magnitude of the coupling coefficient k), and the like. Note that.

[First embodiment]
The first embodiment will be described with reference to FIGS.

  First, in order to charge the secondary battery 26, the power feeding side (primary side 12) and the power receiving side (secondary side 14) are set at predetermined positions, and the primary side coil 20 and the secondary side coil 22 are connected. They are arranged at a predetermined gap length.

  Next, at time t0 in FIG. 6, a switch (not shown) on the primary side 12 is turned on, so that AC power is supplied from the AC power supply 16 to the primary coil 20 via the resistor 18. Thereby, the secondary voltage V2 is generated in the secondary coil 22 by electromagnetic induction between the primary coil 20 and the secondary coil 22, and AC power is generated. As a result, power supply (charging) to the secondary battery 26 by internal control on the secondary side 14 becomes possible.

  In this case, in step S1 of FIG. 5 before time t0, the charging control unit 56 first supplies a command signal for setting the ON time Ton to 0 to the step-down control unit 58. The step-down control unit 58 keeps the MOSFET 40 off based on the command signal. Thereby, the connection between the input side and the output side of the voltage conversion circuit 32 is cut off, and the load resistance value when the secondary battery 26 is viewed from the secondary coil 22 becomes infinite. That is, a no-load state is established in which the connection with the secondary battery 26 is released. Note that the no-load state set by the process of step S <b> 1 is the initial state of the power supply system 10.

  In the next step S <b> 2, the charging control unit 56 acquires the output voltage Vout from the voltage sensor 54 and acquires the output current Iout from the current sensor 52. In step S <b> 3, the charging control unit 56 acquires the input voltage Vin from the voltage sensor 50 and acquires the input current Iin from the current sensor 48. In step S4, the charging control unit 56 calculates the input power Pin by multiplying the input voltage Vin and the input current Iin.

  In the next step S5, the charging control unit 56 determines whether or not the current input power Pin calculated in step S4 is larger than the previous input power Pin value (hereinafter also referred to as the previous value Pinold). .

  When the current input power Pin is larger than the previous value Pinold (step S5: YES, Pin> Pinold), in the next step S6, the charge control unit 56 performs control to increase the duty of the MOSFET 40 in the previous charge control process. It is determined whether or not (hereinafter referred to as duty up control) has been executed. That is, in step S6, the charging control unit 56 determines whether or not the processing in step S9 described later for incrementing the on time Ton by the unit time Δτ is executed in the previous charging control processing.

  The unit time Δτ is the minimum unit time when the on-time Ton is changed. For example, when the on-time Ton can be changed in n stages including 0, Δτ = τ / (n− 1).

  If the determination result of step S6 is affirmative (step S6: YES), the charge control unit 56 determines whether or not the output voltage Vout is lower than the charge end voltage Vobj as the target voltage in the next step S7. .

  Since Vout <Vobj at time t0 (step S7: YES), the charging control unit 56 determines whether or not the output current Iout is smaller than the target current Iobj in the next step S8.

  Since Iout <Iobj at the time point t0 (step S8: YES), the charging control unit 56 increments the on-time Ton by the unit time Δτ in the next step S9. In this case, since the control means 24 has a feedback control configuration, incrementing the on-time Ton by the unit time Δτ means that the load resistance value is controlled to decrease from infinity in the initial state. To do. That is, the flowchart of FIG. 5 shows the processing content for performing charging control on the secondary battery 26 so that the load resistance value decreases with time.

  In the next step S10, the charging control unit 56 sets the current input power (current value) Pin to the previous value Pinold. In step S <b> 11, the charging control unit 56 determines whether or not charging control for the secondary battery 26 should be terminated.

  When charging control is continued (step S11: NO), the charging control unit 56 outputs a command signal corresponding to the on-time Ton incremented in step S9 to the step-down control unit 58. The step-down control unit 58 supplies a control signal having a duty corresponding to the ON time Ton to the gate terminal of the MOSFET 40 based on the command signal from the charge control unit 56, thereby turning the MOSFET 40 on or off. Thereafter, the process returns to step S2. That is, until it is determined in step S11 that charging control is finished (step S11: YES), the processes in steps S2 to S10 are repeatedly executed.

  As described above, by repeatedly executing the processes of steps S2 to S10, the output current Iout, the output voltage Vout, the input power Pin, and the duty (on time Ton) have elapsed since the time point t0. Along with each increase.

  Then, at time t1 when time T1 has elapsed from time t0, first, the output current Iout reaches the target current Iobj. Note that the target current Iobj is preferably a maximum current value that can charge the secondary battery 26, for example, as described above.

  Accordingly, since a negative determination result is obtained in step S8 (step S8: NO, Iout ≧ Iobj), in the next step S12, the charging control unit 56 decrements the on-time Ton by the unit time Δτ. In the next step S13, the charging control unit 56 determines whether or not the on-time Ton after decrement becomes a negative value.

  Usually, since Ton> 0 (step S13: NO), the charging control unit 56 executes the processes of steps S10 and S11, returns to step S2, and executes the processes after step S2 again.

  That is, when the output current Iout reaches the target current Iobj at time t1, the output current Iout is equal to the target current Iobj by repeatedly performing the increment (step S9) or decrement (step S12) of the on-time Ton. It is controlled to be constant. Along with such control, the SOC and the output voltage Vout gradually increase with time. At the same time, the input power Pin increases toward the maximum power Pmax. Further, the duty slightly increases with time.

  At time t2 when time T2 has elapsed from time t1, the input power Pin reaches the maximum power Pmax. In this case, since Pin = Pinold, a negative determination result is obtained in step S5. Therefore, in the next step S14, the charging control unit 56 determines whether or not the duty up control has been executed in the previous process.

  When the previous process is duty-up control (step S14: YES), the charging control unit 56 executes step S12 and decrements the on-time Ton by the unit time Δτ. On the other hand, when the previous process is not duty up control (step S14: NO), the charging control unit 56 executes step S9 after executing the determination process of steps S7 and S8, and increments the on-time Ton by the unit time Δτ. To do.

  After executing the process of step S9 or step S12, the charging control unit 56 executes the processes of steps S10 and S11, returns to step S2, and executes the processes after step S2 again.

  That is, when the input power Pin reaches the maximum power Pmax at the time point t2, the on-time Ton increment (step S9) or decrement (step S12) is repeatedly performed, so that the input power Pin is equal to the maximum power Pmax. It is controlled to be constant. Along with this control, the SOC and the output voltage Vout gradually increase with time, while the output current Iout gradually decreases. Further, the duty slightly decreases with time.

  At time point t3 when time T3 has elapsed from time point t2, the output voltage Vout reaches the charge end voltage Vobj, which is a control target (target voltage) of the secondary battery 26. In this case, since a negative determination result is obtained in step S7 (step S7: NO, Vout = Vobj), in the next step S12, the charging control unit 56 decrements the on-time Ton by the unit time Δτ. Thereafter, the charging control unit 56 sequentially executes the processes of steps S13, S10, and S11, returns to step S2, and executes the processes after step S2 again.

  However, since the output voltage Vout has reached the end-of-charge voltage Vobj, a negative determination result is obtained in step S7 even in the subsequent processing (step S7: NO). Accordingly, the decrement process in step S12 is performed every time the output voltage Vout reaches the charge end voltage Vobj during a predetermined time. As a result, when the output voltage Vout continuously reaches the end-of-charge voltage Vobj and a positive determination result is obtained in step S13 (step S13: YES), in the next step S15, the charge control unit 56 It is determined that the charging of the secondary battery 26 has been completed, and the on time Ton is set to zero.

  Thereafter, the charge control unit 56 executes the processes of steps S10 and S11 (step S11: YES), and outputs a command signal indicating Ton = 0 to the step-down control unit 58. The step-down control unit 58 supplies a control signal having a duty of 0 to the MOSFET 40 based on the command signal, and turns off the MOSFET 40.

  Therefore, by the decrement process for the on-time Ton described above, the output current Iout, the input power Pin, and the duty decrease from time t3 with time, and become 0 at time t4 after time T3 has elapsed. .

  In the first embodiment, when step S6 in FIG. 5 is a negative determination result (step S6: NO), the input power Pin has increased, but the duty-up control has not been executed last time. It is. In this case, in the drooping characteristic of the input power Pin of FIG. 3, the input power out of two electromotive forces (input voltage Vin) corresponding to the input power Pin that exists one on each of the left and right sides with the maximum power Pmax interposed therebetween. This is a case where the input voltage Vin is present on the lower voltage side than the voltage value Vinmax (the operating point is moving).

  Therefore, in step S12, the charging control unit 56 performs control to return the input voltage Vin to a higher voltage side than the input voltage value Vinmax by decrementing the on time Ton.

  Further, if Pin ≦ Pinold (step S5: NO) in step S5 and a negative determination result (step S14: NO) is obtained by the determination process in step S14, the charging control unit 56 increases the duty. It is determined that the input power Pin is decreasing by not executing the control last time. Thereafter, the charging control unit 56 performs feedback control according to the output voltage Vout and the like after step S7.

  On the other hand, when an affirmative determination result (step S14: YES) is obtained in step S14, the charge control unit 56 performs the duty up control last time, so that the input power Pin decreases and the input voltage Vin is input. It is determined that the voltage value Vinmax is moving to a lower voltage side. In step S12, the charging control unit 56 decrements the on time Ton and performs feedback control to return the input voltage Vin to the high voltage side.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIGS. In addition, about the process which is common in 1st Example, description is abbreviate | omitted or description is simplified. Further, in the second embodiment, as described above, since the secondary battery 26 is charged in a state close to full charge (SOC: 100%), the secondary battery 26 is compared with the first embodiment. Note that the charging time is short.

  Also in the second embodiment, the primary side coil 20 and the secondary side coil 22 are arranged with a gap length therebetween, and a switch (not shown) on the primary side 12 is turned on at time t5 in FIG. Electric power can be supplied to the secondary battery 26 by internal control of the secondary side 14.

  Also in this case, similarly to the first embodiment, the on-time Ton is set to 0 in Step S1, and then the processing of Steps S2 to S11 is repeatedly performed. The output voltage Vout, the input power Pin, and the duty (on time Ton) increase.

  However, in the second embodiment, the output voltage Vout first reaches the end-of-charge voltage Vobj that is the control target (target voltage) of the secondary battery 26 at time t6 when time T5 has elapsed from time t5.

  In this case, since a negative determination result is obtained in step S7 (step S7: NO, Vout = Vobj), the charging control unit 56 decrements the on time Ton by the unit time Δτ in the next step S12. Next, the charging control unit 56 performs the determination process in step S13. Normally, Ton> 0 (step S13: NO), the process returns to step S2 through steps S10 and S11.

  Thus, when the output voltage Vout reaches the end-of-charge voltage Vobj, the on time Ton increment (step S9) or decrement (step S12) is repeated, and the output voltage Vout becomes constant at the end-of-charge voltage Vobj. To be controlled.

  Thereafter, when the output voltage Vout continuously reaches the end-of-charge voltage Vobj during a predetermined time period and Ton <0 (step S13: YES), the charge control unit 56 charges the secondary battery 26. Is determined to be complete. As a result, the on-time Ton is set to 0 in step S15, and it is determined in step S11 that charging has ended (step S11: YES).

  In the second embodiment, the subsequent processing when a negative determination result is obtained in step S6 or when Pin <Pinold is determined in step S5 is the same as in the first embodiment. In FIG. 7, the output voltage Vout is controlled to be constant at the charge end voltage Vobj at time T6 from time t6 to time t7. Further, the decrement process for the on time Ton is executed from the time t7, and the charging of the secondary battery 26 is finished at the time t8 when the time T7 has elapsed from the time t7.

[Third embodiment]
Next, a third embodiment will be described with reference to FIGS. In addition, about the process which is common in 1st Example and 2nd Example, description is abbreviate | omitted or description is simplified. In the third embodiment, as described above, the maximum power Pmax is limited to a low value due to a positional shift between the primary side coil 20 and the secondary side coil 22 and a large gap length. Therefore, it should be noted that it is necessary to charge the secondary battery 26 more time than the first embodiment and the second embodiment.

  Also in the third embodiment, as in the first and second embodiments, the primary coil 20 and the secondary coil 22 are arranged with a gap length therebetween, and the primary coil at time t9 in FIG. Due to the switch (not shown) on the side 12 being turned on, power can be supplied to the secondary battery 26 by the internal control of the secondary side 14. Further, as in the first and second embodiments, the on-time Ton is set to 0 in step S1, and then the processes in steps S2 to S11 are repeated, so that the time elapses from time t9. The output current Iout, the output voltage Vout, the input power Pin, and the duty (on time Ton) increase.

  However, in the third embodiment, the input power Pin first reaches the maximum power Pmax at time t10 when time T8 has elapsed from time t9.

  In this case, since a negative determination result is obtained in step S5 (step S5: NO, Pin = Pinold), the charging control unit 56 determines whether or not the duty up control was previously executed in the next step S14.

  When a negative determination result (step S14: NO) is obtained in step S14, the charge control unit 56 performs a process of incrementing the on time Ton by the unit time Δτ in step S9 after the processes of steps S7 and S8. . On the other hand, when a positive determination result (step S14: YES) is obtained in step S14, the charging control unit 56 performs a process of decrementing the on time Ton by the unit time Δτ in step S12. As a result, the input power Pin is controlled to be constant at the maximum power Pmax.

  With such control, the SOC and the output voltage Vout gradually increase with time after the time t10, while the output current Iout gradually decreases. Further, the duty slightly decreases with time. Then, at time t11 when time T9 has elapsed from time t10, the output voltage Vout reaches the end-of-charge voltage Vobj.

  In this case, when the output voltage Vout continuously reaches the end-of-charge voltage Vobj during a predetermined time that is predetermined and Ton <0 (step S13: YES), the charge control unit 56 controls the secondary battery 26. Judge that charging is complete. As a result, the on-time Ton is set to 0 in step S15, and it is determined in step S11 that charging has ended (step S11: YES).

  In the third example, the subsequent processing when a negative determination result is obtained in step S6 or when Pin <Pinold is determined in step S5 is the same as in the first example. In FIG. 8, the decrement process for the on time Ton is performed from the time point t11, and the charging of the secondary battery 26 ends at the time point t12 when the time T10 has elapsed from the time point t11.

[Modification of this embodiment]
A modification of the power supply system 10 according to the present embodiment is shown in FIG. In this modification, the voltage conversion circuit 32 is a step-up chopper, and the control unit that controls the on / off of the MOSFET 40 is a charge control unit 56 and a step-up control unit 60, and is different from the configuration of FIG.

  In this case, the voltage conversion circuit 32 as a boost chopper boosts the input voltage Vin from the first smoothing circuit 30. Since the step-up chopper is well known, detailed description thereof is omitted.

  Further, the boost control unit 60 controls on / off of the MOSFET 40 based on a command signal from the charge control unit 56. In this case, the boost control unit 60 controls the MOSFET 40 by PWM control.

  Also in this modified example, the input power Pin has the drooping characteristic of FIG. 3 as in the configuration of FIG. In the charging control for the secondary battery 26, as shown in FIGS. 2 and 3, the control is performed in a voltage region and a current region between the no-load voltage V0 and the input voltage value Vinmax.

  However, in this modification, since the voltage conversion circuit 32 is a step-up chopper, the discharge end voltage is designed to be equal to or higher than the no-load voltage V0. Since other configurations and operations are the same as those in the case of FIG. 1, detailed description thereof is omitted.

  In this modification, a diode 42 is connected between the coil 44 and the positive electrode of the secondary battery 26. Thereby, the backflow from the secondary battery 26 in the state where the voltage conversion circuit 32 stops the boosting operation is prevented, and inadvertent discharge of the secondary battery 26 can be prevented.

[Effect of this embodiment]
According to the power supply system 10 and the power supply method according to the present embodiment, the control unit 24 reduces the load resistance value from the initial state of approximately infinity as time elapses, so that the secondary coil 22 generates a load. The power supply to the secondary battery 26 is controlled. Therefore, in this embodiment, power is supplied to the secondary battery 26 without exchanging power supply information between the primary side 12 and the secondary side 14 and without controlling the primary voltage V1. Can be controlled. That is, the control on the power supply to the secondary battery 26 is completed on the secondary side 14 regardless of the state of the primary side 12. As a result, it is possible to supply power to the secondary battery 26 by simple control on the secondary side 14 using the power supplied from the primary side coil 20 to the secondary side coil 22 without contact. it can.

  Therefore, in this embodiment, feedback means (communication device or the like) from the secondary side 14 to the primary side 12 is unnecessary. In addition, it is not necessary to ensure compatibility between the primary side 12 and the secondary side 14 by providing a communication device, or to perform an interoperability test for ensuring compatibility. In this way, many processes for ensuring compatibility are not required. Therefore, in this embodiment, the cost of the power supply system 10 can be reduced.

  Further, in the control means 24, feedback such that the output current Iout substantially coincides with the target current Iobj, the output voltage Vout substantially coincides with the charge end voltage Vobj, and / or the input power Pin substantially coincides with the maximum power Pmax. By performing the control, it is possible to easily control the power supply to the secondary battery 26. As a result, it is possible to perform control to efficiently extract power that can be acquired from the primary side 12.

  In this case, among the output current Iout, the output voltage Vout, and the input power Pin, the output current Iout first reaches the target current Iobj, the output voltage Vout first reaches the charge end voltage Vobj, or the input power When Pin first reaches the maximum power Pmax, the control unit 24 controls the output current Iout, the output voltage Vout, or the input power Pin that has first reached the target current Iobj, the charge end voltage Vobj, or the maximum power Pmax. Thus, the power supply to the secondary battery 26 is continued. Thereby, the secondary battery 26 can be easily charged.

  Further, in the initial state, the load resistance value is made almost infinite by turning off the MOSFET 40 which is a switching element, and then the load resistance value is gradually decreased by increasing the on-time Ton of the MOSFET 40 every unit time Δτ. The power supply to the secondary battery 26 can be easily performed.

  Specifically, in the first embodiment of FIG. 6, when the output current Iout reaches the target current Iobj, the output current Iout is controlled to the target current Iobj while increasing or decreasing the duty of the MOSFET 40, and then the input power Pin is maximized. When the power Pmax is reached, the input power Pin is controlled to the maximum power Pmax while increasing or decreasing the duty. Further, when the output voltage Vout reaches the charge end voltage Vobj and the output voltage Vout reaches the charge end voltage Vobj continuously within the specified time, the MOSFET 40 is turned off to control the voltage conversion circuit 32. finish. Thereby, when the SOC of the secondary battery 26 is low, non-contact power feeding to the secondary battery 26 can be easily performed to complete the charging.

  In the second embodiment of FIG. 7, when the output voltage Vout reaches the charge end voltage Vobj, the output voltage Vout is controlled to the charge end voltage Vobj while increasing or decreasing the duty of the MOSFET 40, and then the output voltage Vout is defined. When the end-of-charge voltage Vobj is reached continuously within the time, the MOSFET 40 is turned off and the control on the voltage conversion circuit 32 is finished. Thereby, if SOC is sufficiently large, the non-contact electric power feeding to the secondary battery 26 can be completed in a short time.

  Further, in the third embodiment of FIG. 8, when the input power Pin reaches the maximum power Pmax, the input power Pin is controlled to the maximum power Pmax while increasing / decreasing the duty of the MOSFET 40, and then the output voltage Vout is the charge end voltage. When Vobj is reached and the output voltage Vout reaches the end-of-charge voltage Vobj continuously within the specified time, the MOSFET 40 is turned off and the control on the voltage conversion circuit 32 is finished. Thereby, even if the maximum power Pmax is set to be small due to a positional deviation between the primary side coil 20 and the secondary side coil 22, non-contact power feeding can be easily performed to the secondary battery 26. it can. As a result, the maximum power obtainable from the primary side 12 can be supplied to the secondary battery 26 easily and efficiently.

  In addition, since the voltage conversion circuit 32 includes the MOSFET 40, voltage conversion from the input voltage Vin to the output voltage Vout in the voltage conversion circuit 32 can be quickly performed while suppressing power consumption in the voltage conversion circuit 32.

  In the voltage region (current region) between the no-load voltage V0 and the input voltage value Vinmax, the loss of the internal resistance on the secondary side 14 is small, and the power use efficiency is high. Therefore, by controlling the voltage conversion circuit 32 in this region, it is possible to perform non-contact power supply to the secondary battery 26 while reducing a loss due to power supply on the secondary side 14. Further, even if the power that can be supplied to the secondary battery 26 is restricted due to the occurrence of positional deviation between the primary coil 20 and the secondary coil 22 or the increase in the gap length, it is given. It is possible to supply the maximum power to the secondary battery 26 under the restricted conditions.

  Furthermore, since the primary side coil 20 and the secondary side coil 22 are electromagnetic induction coils, the power supply to the secondary battery 26 can be easily controlled.

  It should be noted that the present invention is not limited to the above-described embodiment, and it is naturally possible to adopt various configurations without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10 ... Electric power supply system 12 ... Primary side 14 ... Secondary side 16 ... AC power supply 18 ... Resistor 20 ... Primary side coil 22 ... Secondary side coil 24 ... Control means 26 ... Secondary battery 28 ... Rectifier circuit 30 ... First smoothing circuit 32 ... Voltage conversion circuit 34 ... Second smoothing circuit 36, 42 ... Diode 38, 46 ... Capacitor 40 ... MOSFET
44 ... Coil 48, 52 ... Current sensor 50, 54 ... Voltage sensor 56 ... Charge control unit 58 ... Step-down control unit 60 ... Step-up control unit

Claims (11)

A primary side coil connected to the primary side power source and a secondary side coil connected to the secondary side load are arranged with a gap therebetween, and the primary side coil is not connected to the secondary side coil. In a power supply system that supplies power by contact,
A control means provided between the secondary coil and the load, for controlling power supply from the secondary coil to the load;
The control means views the load from the secondary coil in a current region where an output current flowing from the secondary coil to the load is equal to or less than a current value corresponding to a maximum power operating point of the secondary coil. Starting from an initial state where the load resistance value is almost infinite, and controlling the power supply from the secondary coil to the load so that the load resistance value decreases with time. And power supply system. The power supply system according to claim 1, wherein
The control means rectifies the output voltage and output current of the secondary coil, performs voltage conversion on the rectified output voltage, and converts the DC voltage that is the converted output voltage to the load. A voltage conversion circuit to be supplied to, and a control unit for controlling the voltage conversion circuit,
The control unit corresponds to the output current after rectification and a DC current flowing from the voltage conversion circuit to the load substantially matches a target current value, and the DC voltage substantially matches a target voltage value, and / or The power supply system controls the voltage conversion circuit so that an output power obtained by multiplying the output voltage and the output current after rectification substantially coincides with a maximum power value. The power supply system according to claim 2,
The control unit is configured to determine whether the DC current first reaches the target current value among the DC current, the DC voltage, and the output power, or the DC voltage first reaches the target voltage value, or When the output power first reaches the maximum power value, the direct current, the DC voltage, or the output power that has reached first is controlled to the target current value, the target voltage value, or the maximum power value. A power supply system that continues power supply to the load in a state. The power supply system according to claim 2 or 3,
The voltage conversion circuit includes a switching element,
In the initial state, the control unit makes the load resistance value substantially infinite by turning off the switching element, and then increases the on-time of the switching element every predetermined unit time. A power supply system characterized by gradually decreasing a resistance value. The power supply system according to claim 4, wherein
The controller is
When the direct current reaches the target current value, the direct current is controlled to the target current value while increasing or decreasing the duty of the switching element,
Thereafter, when the output power reaches the maximum power value, the output power is controlled to the maximum power value while increasing or decreasing the duty.
Further, when the DC voltage reaches the target voltage value and the DC voltage reaches the target voltage value continuously within a specified time, the switching element is turned off to An electric power supply system characterized by terminating control. The power supply system according to claim 4, wherein
The controller is
When the DC voltage reaches the target voltage value, the DC voltage is controlled to the target voltage value while increasing or decreasing the duty of the switching element,
After that, when the DC voltage reaches the target voltage value continuously within a specified time, the switching element is turned off and the control for the voltage conversion circuit is ended. The power supply system according to claim 4, wherein
The controller is
When the output power reaches the maximum power value, the output power is controlled to the maximum power value while increasing or decreasing the duty of the switching element,
Thereafter, when the DC voltage reaches the target voltage value and the DC voltage reaches the target voltage value continuously within a specified time, the switching element is turned off to An electric power supply system characterized by terminating control. In the electric power supply system of any one of Claims 4-7,
The power supply system, wherein the switching element is a field effect transistor. The power supply system according to any one of claims 2 to 8,
The output power increases with a decrease in the output voltage after rectification, reaches the maximum power value at the maximum power operating point at which the product of the output current and the output voltage is maximized, and the output voltage Has a drooping characteristic that decreases when the
The output current after rectification has a characteristic of decreasing with an increase in the output voltage,
In the initial state, the load resistance value is substantially infinite, the output voltage becomes a no-load voltage as a maximum voltage value, and the output current becomes a minimum value,
The control unit starts from the no-load voltage in the current region, and controls the voltage conversion circuit between the no-load voltage and an output voltage value corresponding to the maximum power operating point. Power supply system. In the electric power supply system of any one of Claims 1-9,
The power supply system, wherein the primary side coil and the secondary side coil are electromagnetic induction coils. A primary side coil connected to the primary side power source and a secondary side coil connected to the secondary side load are arranged with a gap therebetween, and the primary side coil is not connected to the secondary side coil. In a power supply method for supplying power by contact,
When controlling the power supply from the secondary coil to the load by the control means provided between the secondary coil and the load,
Load resistance value when the load is viewed from the secondary coil in a current region where the output current flowing from the secondary coil to the load is equal to or less than the current value corresponding to the maximum power operating point of the secondary coil Starting from an initial state where the power becomes substantially infinite, and the power supply from the secondary coil to the load is controlled so that the load resistance value decreases as time elapses. .

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