Non-contact power transmission system

Abstract

To provide a non-contact power transmission system that can reduce loss in a rectification operation on a power receiving side and can reduce required cooling capacity.SOLUTION: A non-contact power transmission system 1 comprises a power receiving unit 15, a received power conversion unit 16, a current sensor, and a control unit 17. The power receiving unit 15 includes a secondary-side coil that receives AC power transmitted from a primary-side coil of a power transmitting device 2 in a non-contact manner. The received power conversion unit 16 converts the AC power received by the power receiving unit 15 into DC power. The current sensor detects current flowing between the power receiving unit 15 and the received power conversion unit 16. When a detection value of current output from the current sensor is equal to or more than a predetermined threshold Ith, the control unit 17 drives a plurality of switching elements of the received power conversion unit 16 in a synchronized manner according to the phase of the current to cause the received power conversion unit to execute a synchronous rectification operation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a contactless power transfer system. [Background technology]

[0002] In recent years, research and development has been conducted into charging vehicles equipped with secondary batteries that contribute to energy efficiency, in order to ensure that more people have access to affordable, reliable, sustainable and advanced energy. Conventionally, in contactless power transmission, a system is known in which a rectifying element on the power receiving side is switched ON or OFF depending on whether or not the current detected on the power receiving side is equal to or greater than a predetermined threshold (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-309580 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology for charging and supplying power to a vehicle equipped with a secondary battery, it is desirable to reduce the loss in the rectification operation on the power receiving side and the required cooling capacity when transmitting power to the vehicle contactlessly. For example, in the contactless power transmission system of the above-mentioned conventional technology, the rectifying element does not turn on until the current on the power receiving side reaches or exceeds a predetermined threshold, which causes the current waveform to change from a sinusoidal waveform to a distorted waveform, resulting in the problem that rectification efficiency cannot be improved.

[0005] An object of the present invention is to provide a contactless power transfer system that can reduce losses in the rectification operation on the power receiving side and reduce the required cooling capacity, thereby contributing to energy efficiency. [Means for solving the problem]

[0006] In order to solve the above problems and achieve the above object, the present invention employs the following aspects. (1): A contactless power transmission system according to one aspect of the present invention (e.g., contactless power transmission system 1 in the embodiment) includes a power receiving unit (e.g., power receiving unit 15 in the embodiment) having a coil (e.g., secondary coil 15a in the embodiment) that receives AC power transmitted contactlessly from a power transmitting device (e.g., power transmitting device 2 in the embodiment), and a power conversion unit (e.g., power receiving power conversion unit 1 in the embodiment) that has a plurality of switching elements (e.g., transistors 16a and 16b in the embodiment) and a plurality of rectifying elements connected to the coil, and that converts the AC power received by the power receiving unit into DC power. 6), a current sensor (e.g., current sensor 17a in the embodiment) that detects the current flowing between the power receiving unit and the power conversion unit, and a control device (e.g., control device 17 in the embodiment) that controls the switching operation of the plurality of switching elements based on the detected value of the current output from the current sensor, and when the detected value of the current is equal to or greater than a predetermined threshold value (e.g., predetermined threshold value Ith in the embodiment), the control device causes the power conversion unit to perform a synchronous rectification operation that rectifies the AC power by synchronously driving the plurality of switching elements in accordance with the phase of the current.

[0007] (2): In the contactless power transmission system described in (1) above, when the detected value of the current is less than the predetermined threshold, the control device may prohibit the synchronous rectification operation and allow the operation of rectifying the AC power by the multiple rectifying elements (e.g., diode rectification operation in the embodiment).

[0008] (3) In the contactless power transmission system described in (1) or (2) above, when the detected value of the current is less than the predetermined threshold value during the synchronous rectification operation, the control device may stop the synchronous rectification operation and transition the power receiving unit and the power conversion unit to a standby state. [Effects of the Invention]

[0009] According to (1) above, by providing a control device that starts the execution of synchronous rectification operation in response to a predetermined threshold value for the current and controls the timing of the switching operation in synchronous rectification in response to the phase of the current, it is possible to reduce losses in the rectification operation on the receiving side and the required cooling capacity.

[0010] In the case of (2) above, switching between the rectification operation performed by multiple rectification elements and the synchronous rectification operation can be set according to a predetermined threshold value for the current without requiring a signal to instruct the switching operation, and the synchronous rectification operation can be performed appropriately even when a mobile object such as a vehicle equipped with the power receiving unit is moving.

[0011] In the case of (3) above, when a moving body such as a vehicle equipped with a power receiving unit leaves the power transmission section, the synchronous rectification operation can be stopped and the device can transition to a standby state, allowing appropriate operation switching to be performed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a diagram showing a configuration of a contactless power transmission system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing details of the configuration of a contactless power transmission system according to an embodiment of the present invention. [Figure 3] 1 is a diagram showing the configuration of a power transmitting unit and a power receiving unit of a contactless power transfer system according to an embodiment of the present invention. [Figure 4] 4 is a flowchart showing a power receiving side process of the contactless power transmission system according to the embodiment of the present invention. [Figure 5] 5 is a flowchart of the power reception control shown in FIG. 4. [Figure 6] 4 is a diagram showing an example of a correspondence relationship between a power transmitting side voltage, a power transmitting side current, a power receiving side voltage, a power receiving side current, a drive signal, and a synchronous rectification flag in the contactless power transfer system according to the embodiment of the present invention. FIG. [Figure 7] 4 is a flowchart showing a power transmission side process of the contactless power transmission system according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a contactless power transfer system according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 and 2 are diagrams showing the configuration of a contactless power transfer system 1 according to an embodiment. Fig. 3 is a diagram showing the configurations of a power transmitting unit 8 and a power receiving unit 15 of the contactless power transfer system 1 according to an embodiment. A contactless power transfer system 1 according to the embodiment supplies power to a moving body such as a vehicle from outside the moving body by contactless power transfer. The vehicle may be, for example, an electric vehicle, a hybrid vehicle, a fuel cell vehicle, or other electrically powered vehicle.

[0014] (contactless power transmission system) 1 and 2, a contactless power transfer system 1 according to an embodiment includes, for example, a power transmitting device 2 installed on a vehicle's running path or the like, a drive control device 3 and a power receiving device 4 mounted on a moving body such as a vehicle, and a communication system M. Note that the contactless power transfer system 1 according to an embodiment may include at least only the components mounted on the moving body (for example, the drive control device 3 and the power receiving device 4), or contactless power transfer may be performed by combining components external to the moving body (for example, the power transmitting device 2 and the communication system M) with the contactless power transfer system 1 mounted on the moving body.

[0015] The communication system M includes, for example, at least one roadside communication device Ma and a communication control device Mb. The communication system 1 constitutes at least a part of a system for electronically collecting tolls, such as an ETC (Electronic Toll Collection System) on a toll road.

[0016] The roadside communication device Ma is disposed, for example, at a predetermined distance upstream of a coupling section (communication section and power transmission section) described later on a roadway or the like along which the vehicle travels. The roadside communication device Ma includes an antenna for wireless communication and wirelessly communicates with an on-board communication device 18 (described later) mounted on a mobile object such as a vehicle. For example, when the roadside communication device Ma acquires information necessary for billing and settlement for power transmission from the power transmission device 2 to the mobile object such as a vehicle from the on-board communication device 18, the roadside communication device Ma transmits key information necessary for starting power transmission and information about the installation of the power transmission device 2 to the on-board communication device 18. The information necessary for billing and settlement is information specific to the mobile object such as a vehicle, such as the presence or absence and identifier of an IC card or on-board transponder for toll collection. The key information is, for example, information generated and updated at a predetermined interval so as to be different for each authorized mobile object (i.e., a vehicle permitted to perform power transmission) passing through a predetermined power transmission section. The key information is information necessary for the power transmission device 2 to authenticate a power receiving device 4 (described later) of the mobile object such as a vehicle. The information relating to the installation of the power transmission device 2 is, for example, information such as the installation intervals of the plurality of power transmission units 8, which will be described later.

[0017] The communication control device Mb controls the operation of all roadside communication devices Ma that are associated with it in advance. The communication control device Mb is a software function unit that functions when a processor such as a CPU (Central Processing Unit) executes a predetermined program. The software function unit is an ECU that includes a processor such as a CPU, a ROM (Read Only Memory) that stores programs, a RAM (Random Access Memory) that temporarily stores data, and electronic circuits such as a timer. At least a part of the communication control device Mb may be an integrated circuit such as an LSI (Large Scale Integration). For example, the communication control device Mb attempts to acquire information necessary for billing and settlement by communicating with the roadside communication device Ma and the in-vehicle communication device 18 of a mobile body such as a nearby vehicle at a predetermined period, etc. When the communication control device Mb acquires the information necessary for billing and settlement from the in-vehicle communication device 18 and confirms that electronic settlement is possible, it transmits permission information indicating that electronic settlement is possible and key information necessary for starting power transmission to the in-vehicle communication device 18. When the communication control device Mb transmits key information from the roadside communication device Ma to the in-vehicle communication device 18, it transmits the same key information to the power transmission side control device 9 described below.

[0018] The power transmission device 2 includes, for example, a power supply unit 6, a transmission power conversion unit 7, a power transmission unit 8, and a power transmission side control device 9. Note that the power transmission device 2 may include at least a plurality of power transmission units 8 in a predetermined coupling section on a vehicle travel path or the like. The power supply unit 6 includes, for example, an AC power supply such as a commercial power supply, an AC-DC converter that converts AC power into DC power, and a power smoothing capacitor. The power supply unit 6 converts AC power supplied from the AC power supply into DC power using the AC-DC converter.

[0019] The transmission power conversion unit 7 includes, for example, an inverter that converts DC power into AC power. The inverter of the transmission power conversion unit 7 includes, for example, a bridge circuit formed by a plurality of switching elements and rectifying elements bridge-connected in two phases, and a voltage-smoothing capacitor. Each switching element is, for example, a transistor such as a SiC (Silicon Carbide) MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The plurality of switching elements are high-side arm and low-side arm transistors 7a and 7b that form a pair in each phase. The rectifying element is, for example, a freewheeling diode connected in parallel to each of the transistors 7a and 7b. A voltage-smoothing capacitor 7c is connected in parallel to the bridge circuit.

[0020] The power transmitting unit 8 transmits power by changing a high-frequency magnetic field, for example, through magnetic field coupling such as magnetic resonance or electromagnetic induction. As shown in Fig. 3, the power transmitting unit 8 includes a resonant circuit formed by, for example, a primary coil 8a, a primary resistor 8b, and a primary capacitor 8c connected in series. The power transmitting unit 8 also includes a sensor, such as a current sensor, that detects the current It flowing through the resonant circuit.

[0021] The power transmitting side control device 9 comprehensively controls the power transmitting devices 2. The power transmitting side control device 9 is a software function unit that functions when a processor such as a CPU (Central Processing Unit) executes a predetermined program. The software function unit is an ECU that includes a processor such as a CPU, a ROM (Read Only Memory) that stores programs, a RAM (Random Access Memory) that temporarily stores data, and electronic circuits such as a timer. At least a part of the power transmitting side control device 9 may be an integrated circuit such as an LSI (Large Scale Integration).

[0022] For example, the power transmission side control device 9 transmits power to the vehicle's power receiving device 4 by controlling the on (conduction) and off (cutoff) switching of each switching element of the power transmission power conversion unit 7 according to a preset drive frequency or information on a required frequency received from the power receiving device 4. For example, when the power transmitting side control device 9 receives key information from the communication control device Mb, it recognizes that the same key information has been transmitted from the roadside communication device Ma to the in-vehicle communication device 18 of the mobile object, and transitions the power transmitting device 2 from a stopped state to a reception standby state. The stopped state of the power transmitting device 2 is a state in which the switching operation of the power transmitting power conversion unit 7 is stopped, for example, by maintaining each switching element of the power transmitting power conversion unit 7 in an off (blocked) state. The reception standby state of the power transmitting device 2 is a state in which information transmission from the power receiving device 4 of the mobile object, such as a vehicle, is detected. The reception standby state of the power transmitting device 2 is, for example, a short-circuit state of the power transmitting power conversion unit 7.

[0023] When the power transmission power converter 7 is short-circuited, the power transmission side control device 9 short-circuits the primary coil 8a by turning on the low-side arm transistor 7b of each phase. As a result, when the primary power transmission device 2 is viewed from the secondary power reception device 4, the impedance of the primary side becomes very large. However, when a magnetic field is generated by the secondary coil 15a of the power reception device 4 during PING transmission (described later), communication from the power reception device 4 is detected by the voltage induced in the primary coil 8a of the power transmission device 2.

[0024] For example, when the power transmitting side control device 9 receives information such as key information and a requested frequency for power transmission from the power receiving device 4, it compares the key information received from the communication control device Mb with the key information received from the power receiving device 4. If the key information matches, the power transmitting side control device 9 transitions the power transmitting device 2 from a reception standby state to a power transmission state. The power transmission state of the power transmitting device 2 is, for example, a state in which power is transmitted at the requested frequency of the power receiving device 4.

[0025] 1 and 2, a drive control device 3 of a moving body such as a vehicle includes, for example, a power storage device 11, a power conversion unit 13, and a rotating electric machine 14. A power receiving device 4 of the moving body includes, for example, a power receiving unit 15 and a received power conversion unit 16. The drive control device 3 and the power receiving device 4 include, for example, a common control device 17. The control device 17 includes, for example, an on-board communication device 18.

[0026] The power storage device 11 is connected to a power conversion unit 13 and a received power conversion unit 16, which will be described later. The power storage device 11 is charged by power transmitted contactlessly from a power transmission device 2 outside the vehicle. The power storage device 11 exchanges power with a rotating electric machine 14 via the power conversion unit 13. The power storage device 11 includes a battery such as a lithium ion battery, a current sensor that detects the current of the battery, and a voltage sensor that detects the voltage of the battery.

[0027] The power conversion unit 13 is connected to the rotating electric machine 14. The power conversion unit 13 includes, for example, a power converter that converts between DC power and AC power. The power converter includes, for example, a second element module and a capacitor for voltage smoothing. The second element module includes, for example, a second bridge circuit formed by a plurality of switching elements and rectifying elements bridge-connected in three phases. Each switching element is, for example, a transistor such as a SiC MOSFET. The plurality of switching elements are high-side arm and low-side arm transistors 13a and 13b that form a pair in each phase. The rectifying elements are, for example, freewheeling diodes connected in parallel to each of the transistors 13a and 13b. A voltage smoothing capacitor 13c is connected in parallel to the second bridge circuit.

[0028] The second element module controls the operation of the rotating electric machine 14 by receiving and sending electric power. For example, when the rotating electric machine 14 is powered, the second element module converts DC power input from the positive and negative DC terminals 13p, 13n into three-phase AC power and supplies the three-phase AC power from the three-phase AC terminals 13d to the rotating electric machine 14. The second element module generates a rotational driving force by sequentially commutating the current to the three-phase stator windings of the rotating electric machine 14. For example, during regeneration of the rotating electric machine 14, the second element module converts three-phase AC power input from the three-phase stator windings into DC power by driving the switching elements of each phase to turn on (conduct) and off (cut) in synchronization with the rotation of the rotating electric machine 14. The second element module can supply the DC power converted from the three-phase AC power to the power storage device 11.

[0029] The rotating electric machine 14 is, for example, a three-phase AC brushless DC motor provided for driving a vehicle. The rotating electric machine 14 includes a rotor having a permanent magnet for a field, and a stator having three-phase stator windings that generate a rotating magnetic field that rotates the rotor. The three-phase stator windings are connected to three-phase AC terminals 13d of the power conversion unit 13. The rotating electric machine 14 generates rotational driving force by power running using the electric power supplied from the electric power conversion unit 13. For example, if the rotating electric machine 14 can be connected to the wheels of a vehicle, it generates driving force by power running using the electric power supplied from the electric power conversion unit 13. The rotating electric machine 14 may generate electric power by performing regenerative operation using rotational power input from the wheels of the vehicle. If the rotating electric machine 14 can be connected to an internal combustion engine of the vehicle, it may generate electric power using the power of the internal combustion engine.

[0030] The power receiving unit 15 is connected to the receiving power conversion unit 16. The power receiving unit 15 receives power by changes in the high-frequency magnetic field transmitted from the power transmitting unit 8, for example, through magnetic field coupling such as magnetic resonance or electromagnetic induction. As shown in FIG. 3, the power receiving unit 15 includes a resonant circuit formed by, for example, a secondary coil 15a, a secondary resistor 15b, and a secondary capacitor 15c connected in series. The power receiving unit 15 also includes a sensor such as a current sensor that detects a current Ir flowing through the resonant circuit.

[0031] 1 and 2 is connected to the power conversion unit 13. The receiving power conversion unit 16 includes a so-called full-bridgeless (or bridgeless and totem-pole) power factor correction (PFC) circuit that converts AC power into DC power. The so-called bridgeless PFC is a PFC that does not include a bridge rectifier made up of multiple bridge-connected diodes, and the so-called totem-pole PFC is a PFC that includes a pair of switching elements of the same conductivity type that are connected in series in the same direction (totem-pole connection).

[0032] The receiving power conversion unit 16 includes, for example, a third bridge circuit formed by a plurality of switching elements and rectifying elements bridge-connected in two phases, and a voltage smoothing capacitor. Each switching element is, for example, a transistor such as a SiC MOSFET. The plurality of switching elements are high-side arm and low-side arm transistors 16a, 16b that form a pair in each phase. The rectifying element is, for example, a freewheeling diode connected in parallel to each of the transistors 16a, 16b. A voltage smoothing capacitor 16c is connected in parallel to the third bridge circuit.

[0033] For example, a power receiving device 4 equipped with a power receiving unit 15 and a power receiving power conversion unit 16 receives power transmitted from the power transmitting device 2 by controlling the on (conduction) and off (cutoff) switching of each switching element of the power receiving power conversion unit 16 in accordance with information on the frequency of power transmission by the power transmitting device 2.

[0034] The control device 17 comprehensively controls, for example, the drive control device 3, the power receiving device 4, and the in-vehicle communication device 18 of a mobile body such as a vehicle. The control device 17 is a software function unit that functions when a predetermined program is executed by a processor such as a CPU (Central Processing Unit). The software function unit is an ECU that includes a processor such as a CPU, a ROM (Read Only Memory) that stores programs, a RAM (Random Access Memory) that temporarily stores data, and electronic circuits such as a timer. At least a part of the control device 17 may be an integrated circuit such as an LSI (Large Scale Integration).

[0035] The control device 17 generates, for example, control signals indicating the timing for driving each switching element on (conducting) and off (blocking), and also generates gate signals for actually driving each switching element on and off based on the control signals. For example, the control device 17 controls the switching of each switching element of the power receiving device 4 to rectify the AC power received from the power transmitting device 2 into DC power, while improving the power factor of the input voltage and input current. For example, the control device 17 controls the switching operation of multiple switching elements of the receiving power conversion unit 16 based on the current detection value output from a current sensor 17a that detects the current flowing between the receiving unit 15 and the receiving power conversion unit 16.

[0036] For example, the control device 17 controls the output according to the target output by a synchronous rectification operation that synchronously drives a plurality of switching elements of the power receiving device 4 to turn on and off, and a short-circuit operation that short-circuits the secondary coil 15a. For example, the control device 17 controls the synchronous rectification operation in accordance with the magnitude and phase of a current generated in the power receiving unit 15 by the power transmitted from the power transmitting device 2, i.e., a current Ir flowing through the secondary coil 15a. The control device 17 controls the multiple switching elements of the receiving power conversion unit 16 by soft switching of so-called zero voltage switching (ZVS). In zero voltage switching (ZVS), each switching element is turned on (switched from an off state to an on state) after the voltage across both ends of the switching element is made zero by discharging the output capacitance (parasitic capacitance) in the off state during the dead time period of each phase.

[0037] For example, the control device 17 controls the short-circuit operation by turning on only the low-side arm of each phase while continuing the zero-voltage switching (ZVS) synchronous rectification operation in the high-side arm of each phase of the receiving power conversion unit 16. By short-circuiting the secondary coil 15a, the control device 17 increases the secondary-side impedance when the secondary-side power receiving device 4 is viewed from the primary-side power transmitting device 2, thereby reducing the primary-side current (transmitting current: current It flowing through the primary-side coil 8a). The control device 17 controls the current of the primary-side power transmitting device 2 by the secondary-side power receiving device 4, thereby performing independent power control, such as stopping power transmission, on the power receiving device 4 side.

[0038] For example, the control device 17 sets a communication section for communication and a power transmission section for power transmission in a coupling section near the power transmitting device 2 where the degree of coupling between the primary side coil 8a of the power transmitting device 2 and the secondary side coil 15a of the power receiving device 4 is equal to or greater than a predetermined level. For example, when the control device 17 receives key information through communication between the roadside communication device Ma and the in-vehicle communication device 18 before arriving at the coupling section, the control device 17 sends information about power transmission in the power transmission section from the power receiving device 4 to the power transmitting device 2 in the communication section before the power transmitting device 2 starts transmitting power in the power transmission section. For example, when the control device 17 sets a first communication section and a second communication section before and after the power transmission section along the direction of movement of a moving body (e.g., a vehicle V), the control device 17 sends information regarding power transmission from the power receiving device 4 to the power transmitting device 2 in the first communication section, which is the first communication section.

[0039] The information relating to power transmission includes, for example, key information acquired from the roadside communication device Ma, a required frequency for power transmission, a target output (power consumption) for fail-safe purposes, and information relating to various abnormalities. The required frequency of power transmission is set so as to suppress a decrease in the efficiency of power transmission and output (power) based on, for example, the minimum ground clearance of the mobile body, which is related to the distance between the primary coil 8a and the secondary coil 15a, and the mounting layout of the power receiving device 4 on the mobile body. The control device 17 may set the required frequency depending on the state of power transmission between the power transmitting device 2 and the power receiving device 4. In addition, the control device 17 may, for example, when the primary side coil 8a is present in the last communication section of the coupling section (e.g., the second communication section, etc.), send information indicating the stop of power transmission in the power transmission section and communication in the communication section from the power receiving device 4 to the power transmitting device 2 through communication between the power transmitting device 2 and the power receiving device 4.

[0040] For example, when the control device 17 receives key information through communication between the roadside communication device Ma and the in-vehicle communication device 18, it transmits information by transmitting power from the power receiving device 4 to the power transmitting device 2 in a reception standby state as a so-called ping signal in the communication section of the coupled section. The power receiving device 4 communicates using a voltage induced in the primary coil 8a of the power transmitting device 2 by a magnetic field generated in the secondary coil 15a by a current switching operation performed by switching in the receiving power conversion unit 16. The control device 17 executes the ping transmission by, for example, switching a carrier wave for contactlessly transmitting power from the power receiving device 4 to the power transmitting device 2 at a predetermined duty ratio to generate a two-level digital signal, so-called dominant and recessive. The predetermined duty ratio is, for example, a predetermined minimum to approximately 50%. Note that the control device 17 may transmit information by, for example, amplitude modulating the carrier wave by changing the switching duty ratio.

[0041] The control device 17 transmits a PING signal at a predetermined interval, for example, from several tens of microseconds to several milliseconds, and when it receives a response signal to the PING signal from the power transmitter 2, starts power reception control for power transmission from the power transmitter 2 in the power transmission section. The control device 17 sets the timing of PING transmission according to, for example, information about the installation of the power transmission device 2 received from the roadside communication device Ma and the moving state of the moving body (e.g., vehicle V) (i.e., the moving state of the power receiving device 4) so ​​that communication (i.e., mutual transmission and reception) between the power transmission device 2 and the power receiving device 4 in the communication section is properly completed. For example, the control device 17 sets the transmission period according to information such as the installation intervals of the multiple power transmission units 8 and the speed of the moving body (e.g., the speed of the vehicle V) so that PING transmission is completed at least a predetermined number of times (e.g., once) in the communication section. Note that, for example, even if the control device 17 permits the execution of PING transmission in the communication section, it transitions to a standby state in which the execution of PING transmission is stopped outside the communication section. For example, in the standby state for PING transmission, the control device 17 may start the execution of PING transmission immediately before the mobile object reaches the first communication section of the next connection section as the mobile object moves.

[0042] Hereinafter, as the operation of the contactless power transfer system 1, the processes executed by the power transmission side control device 9 and the control device 17 will be described. FIG. 4 is a flowchart showing a power receiving side process executed by the control device 17 of the contactless power transfer system 1 in the embodiment. 4, the control device 17 determines whether electronic payment for power transmission from the power transmitting device 2 to the mobile object is possible through wireless communication (billing communication) between the roadside communication device Ma and the in-vehicle communication device 18. If the determination result is "NO," the control device 17 repeats the processing of step S01. On the other hand, if the determination result is "YES," the control device 17 proceeds to step S02.

[0043] Then, in step S02, the control device 17 acquires key information required to start power transmission from the roadside communication device Ma. Next, in step S03, the control device 17 generates a signal for PING transmission by power transmission from the power receiving device 4 to the power transmitting device 2. Next, in step S04, the control device 17 executes PING transmission at a predetermined cycle in the first communication section of the coupled section. Next, in step S05, the control device 17 determines whether or not a response signal to the PING transmission has been received from the power transmitting device 2. If the result of this determination is "NO", the control device 17 repeats the process of step S05. On the other hand, if the result of this determination is "YES", the control device 17 proceeds to step S06. Then, in step S06, the control device 17 starts the power reception control, which will be described later, for the power transmission from the power transmission device 2 in the power transmission section. Next, in step S07, the control device 17 determines whether the combined section has ended. If the result of this determination is "NO", the control device 17 returns to step S04. On the other hand, if the result of this determination is "YES", the control device 17 advances the processing to the end.

[0044] FIG. 5 is a flowchart of the power reception control shown in FIG. 5, the control device 17 starts magnetic resonant coupling between the power transmitting unit 8 and the power receiving unit 15 by allowing the power receiving device 4 to perform diode rectification. The diode rectification is a full-wave rectification operation performed by the rectifying elements (freewheeling diodes connected in parallel to each of the transistors 16a and 16b) of the third bridge circuit of the receiving power conversion unit 16. Next, in step S12, the control device 17 determines whether the detected value of the current output from the current sensor 17a is equal to or greater than a predetermined threshold. If the result of this determination is "NO," the control device 17 repeats the process of step S12. On the other hand, if the result of this determination is "YES," the control device 17 proceeds to step S13. The predetermined threshold is set, for example, according to the output classification of the receiving power conversion unit 16.

[0045] Next, in step S13, the control device 17 starts the synchronous rectification operation of the power receiving device 4. For example, the control device 17 inverts the pulse instructing the high-side arm of the receiving power conversion unit 16 to drive and the pulse instructing the low-side arm to drive each time the phase of the detected value of the current output from the current sensor 17a crosses zero (0°). Next, in step S14, the control device 17 determines whether the detected value of the current output from the current sensor 17a is less than a predetermined threshold. If the result of this determination is "NO", the control device 17 repeats the process of step S14. On the other hand, if the result of this determination is "YES", the control device 17 proceeds to step S15.

[0046] Then, in step S15, the control device 17 stops the synchronous rectification operation of the power receiving device 4 and allows the diode rectification operation of the power receiving device 4. After the transition from synchronous rectification operation to diode rectification operation, the control device 17 transitions the power receiving device 4 to a standby state according to predetermined conditions. In the standby state of the power receiving device 4, the control device 17 controls the current of the primary-side power transmitting device 2, such as reducing the output or stopping power transmission, by, for example, short-circuiting the secondary-side coil 15a. Then, the control device 17 returns to the process.

[0047] FIG. 6 is a diagram showing an example of the correspondence relationship between the power transmitting side voltage, the power transmitting side current, the power receiving side voltage, the power receiving side current, the drive signal, and the synchronous rectification flag in the contactless power transfer system 1 of the embodiment. First, for example, before time t1 shown in Figure 6, after power transmission control of the power transmitter 2 is started in response to a PING transmission from the power receiver 4 to the power transmitter 2, the amplitude of the secondary side current (power receiver side current: for example, the current detected by the current sensor 17a) gradually increases due to the diode rectification operation of the power receiver 4. Then, for example, at time t1, when the power receiving-side current exceeds a predetermined threshold Ith, the flag value of the synchronous rectification flag is changed from "0" to "1," and the synchronous rectification operation of the power receiving device 4 is started. The predetermined threshold Ith of the power receiving-side current is set, for example, for a steady state in which the current amplitude, which gradually increases due to the start of diode rectification operation, becomes constant after an appropriate time.

[0048] During the synchronous rectification operation after time t1, for example, as shown at times t2, t4, t6, t8, and t10, the pulse (drive signal: dashed line) instructing the drive of the low-side arm or the pulse (drive signal: solid line) instructing the drive of the high-side arm of the receiving power conversion unit 16 is inverted from ON to OFF each time the phase of the waveform of the power receiving side current crosses zero (0°). Furthermore, as shown at times t3, t5, t7, and t9, the drive signal (dashed line) for the low-side arm and the drive signal (solid line) for the high-side arm of the power receiving power conversion unit 16 are alternately switched from ON to OFF, and then inverted from OFF to ON after a predetermined delay time corresponding to the internal inductance value, etc. Due to the synchronous rectification operation, the waveform of the power receiving side current becomes sinusoidal over a 180° interval.

[0049] FIG. 7 is a flowchart showing a power transmission side process executed by the power transmission side control device 9 of the contactless power transmission system 1 in the embodiment. 7, the power transmitting side control device 9 determines whether or not key information has been transmitted from the roadside communication device Ma to the power receiving device 4. If the determination result is "NO", the power transmitting side control device 9 proceeds to step S22. On the other hand, if the determination result is "YES", the power transmitting side control device 9 proceeds to step S23. Then, in step S22, the power transmitting side control device 9 maintains the stopped state of the power transmitting device 2, and returns the process to step S21. Then, in step S23, the power transmitting side control device 9 causes the power transmitting device 2 to transition from the stopped state to the reception standby state.

[0050] Next, in step S24, the power transmitting side control device 9 determines whether or not a PING signal due to power transmission from the power receiving device 4 to the power transmitting device 2 has been received in the first communication section of the coupling section. If the determination result is "NO", the power transmitting side control device 9 repeats the process of step S24. On the other hand, if the determination result is "YES", the power transmitting side control device 9 proceeds to step S25. Next, in step S25, the power transmitting side control device 9 compares the key information received from the communication control device Mb with the key information received from the power receiving device 4.

[0051] Next, in step S26, the power transmitting side control device 9 determines whether the key information received from the communication control device Mb matches the key information received from the power receiving device 4. If the result of this determination is "NO", the power transmitting side control device 9 proceeds to end the process. On the other hand, if the result of this determination is "YES", the power transmitting side control device 9 proceeds to step S27. Next, in step S27, the power transmitting side control device 9 transmits a response signal to the power receiving device 4 in response to the PING transmission by transmitting power from the power transmitting device 2 to the power receiving device 4 in the communication section. Next, in step S28, the power transmitting side control device 9 starts power transmission control in the power transmission section for power transmission to the power receiving device 4 at the requested frequency received from the power receiving device 4. Then, the control device 17 advances the process to END.

[0052] As described above, according to the contactless power transfer system 1 of the embodiment, the control device 17 starts synchronous rectification operation in response to a predetermined threshold value Ith of the receiving-side current and controls switching operation in response to the phase of the receiving-side current, thereby making it possible to reduce losses in the rectification operation on the receiving side and the required cooling capacity. By alternately inverting the drive signals of the low-side arm and the high-side arm every time the phase of the waveform of the receiving-side current crosses zero (0°), the waveform of the receiving-side current can be made sinusoidal over a 180° interval, thereby improving the efficiency of power conversion. For example, compared to a case where the inversion of the drive oscillation is switched depending on whether the receiving-side current exceeds a predetermined threshold, the duty of the power conversion can be increased and output can be improved.

[0053] It is possible to switch between diode rectification operation and synchronous rectification operation depending on a predetermined threshold Ith of the receiving side current, and it is possible to appropriately perform synchronous rectification operation even when a moving body such as a vehicle on which the power receiving device 4 is mounted is moving. When a moving body such as a vehicle on which the power receiving device 4 is mounted leaves the power transmission section, the synchronous rectification operation can be stopped and the state can be shifted to a standby state, and an appropriate operation switching can be performed.

[0054] (Variation) In the above-described embodiment, the contactless power transfer system 1 may include a storage voltage converter that converts input and output power of the power storage device 11, for example, in the case of a hybrid vehicle or the like that is driven by the power storage device 11 and an internal combustion engine as a power source.

[0055] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as the inventions described in the claims and their equivalents. [Explanation of symbols]

[0056] 1...contactless power transfer system, 2...power transmission device, 3...drive control device, 4...power receiving device, 6...power supply unit, 7...transmission power conversion unit, 8...power transmission unit, 8a...primary side coil, 9...transmission side control device, 11...energy storage device, 13...power conversion unit, 14...rotating electric machine, 15...power receiving unit, 15a...secondary side coil (coil), 16...receiving power conversion unit (power conversion unit), 16a, 16b...transistor (switching element), 17...control device, 17a...current sensor, 18...on-vehicle communication device, M...communication system, Ma...roadside communication device (communication device), Mb...communication control device.

Claims

1. a power receiving unit having a coil for receiving AC power transmitted from a power transmitting device in a non-contact manner; a power conversion unit including a plurality of switching elements and a plurality of rectifying elements connected to the coil, and converting the AC power received by the power receiving unit into DC power; a current sensor that detects a current flowing between the power receiving unit and the power conversion unit; a control device that controls a switching operation of the plurality of switching elements based on a detection value of the current output from the current sensor; Equipped with The control device includes: When the detected value of the current is equal to or greater than a predetermined threshold, the power conversion unit executes a synchronous rectification operation for rectifying the AC power by synchronously driving the plurality of switching elements in accordance with a phase of the current. Contactless power transmission system.

2. The control device includes: When the detected value of the current is less than the predetermined threshold, the synchronous rectification operation is prohibited and an operation of rectifying the AC power by the plurality of rectifier elements is permitted. The contactless power transfer system according to claim 1 .

3. The control device includes: When the detected value of the current is less than the predetermined threshold value during the execution of the synchronous rectification operation, the synchronous rectification operation is stopped, and the power receiving unit and the power conversion unit are shifted to a standby state. The contactless power transfer system according to claim 1 or 2.

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