Non-contact power transmission system

Abstract

The invention provides a non-contact power transmission system capable of realizing reduction of loss in rectification operation on a power receiving side and reduction of required cooling capability. A non-contact power transmission system is provided with a power receiving unit, a received power conversion unit, a current sensor, and a control device. The power receiving unit is provided with a secondary-side coil that acquires AC power transmitted in a non-contact manner from the primary-side coil of the power transmission device. The power reception power conversion unit converts the AC power acquired by the power reception unit into DC power. The current sensor detects a current flowing between the power receiving unit and the received power conversion unit. When the detection value of the current output from the current sensor is equal to or greater than a predetermined threshold value, the control device performs a synchronous rectification operation by synchronously driving a plurality of switching elements of the received power conversion unit in accordance with the phase of the current.

Description

Technical Field

[0001] The present invention relates to a contactless power transmission system. Background Art

[0002] In recent years, in order to ensure that more people can obtain reliable, sustainable and advanced energy that is suitable for them, research and development related to charging stations in vehicles equipped with secondary batteries that contribute to energy efficiency has been carried out.

[0003] Conventionally, there is known a system that switches on and off a rectifying element on the power receiving side in contactless power transmission depending on whether a current detected on the power receiving side is equal to or greater than a predetermined threshold (see, for example, Patent Document 1 listed below).

[0004] Patent Document 1: Japanese Patent Application Publication No. 2001-309580 Summary of the invention

[0005] In the technology related to the charging station in a vehicle equipped with a secondary battery, when non-contact power transmission is performed to the vehicle, it is desired to reduce the loss in the rectification operation on the power receiving side and reduce the required cooling capacity. For example, in the non-contact power transmission system of the above-mentioned conventional technology, the rectifying element does not conduct until the current on the power receiving side becomes more than a predetermined threshold value, so the current waveform becomes distorted from the sine wave shape, and the rectification efficiency cannot be improved.

[0006] The present invention has been made in consideration of such a situation, and its object is to provide a contactless power transmission system that can reduce the loss in the rectification operation on the power receiving side and reduce the required cooling capacity, and further contribute to energy efficiency.

[0007] In order to solve the above-mentioned problems and achieve the relevant objects, the present invention adopts the following means.

[0008] (1) A contactless power transmission system according to one aspect of the present invention comprises: a power receiving unit having a coil that receives AC power transmitted from a power transmitting device in a contactless manner; a power conversion unit having 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; and a control device that controls switching operations of the plurality of switching elements based on a detection value of the current output from the current sensor, wherein the control device causes the power conversion unit to perform a synchronous rectification operation when the detection value of the current is greater than or equal to a predetermined threshold value, in which the plurality of switching elements are synchronously driven according to a phase of the current, thereby rectifying the AC power.

[0009] (2) In the above scheme (1), the control device may prohibit the synchronous rectification action when the detected value of the current is less than the predetermined threshold value, and allow the action of rectifying the AC power using the plurality of rectifying elements.

[0010] (3) In the above scheme (1) or (2), the control device may stop the synchronous rectification action and transfer the power receiving unit and the power conversion unit to a standby state when the detected value of the current is less than the prescribed threshold value during the execution of the synchronous rectification action.

[0011] According to the above solution (1), a control device is provided which starts execution of synchronous rectification operation according to a predetermined threshold value for current and controls the timing of switching operation in synchronous rectification according to the phase of current, thereby reducing the loss in rectification operation on the power receiving side and the required cooling capacity.

[0012] In the case of the above scheme (2), switching between a rectification operation that does not require a signal to instruct a switching operation and is performed by a plurality of rectifying elements, and a synchronous rectification operation can be set based on a predetermined threshold value for the current, so that the synchronous rectification operation can be appropriately performed even when a moving object such as a vehicle equipped with the power receiving unit is moving.

[0013] In the case of the above-mentioned means (3), when a mobile object such as a vehicle equipped with the power receiving unit leaves the power transmission section, the synchronous rectification operation can be stopped and the state can be shifted to the standby state, thereby enabling appropriate operation switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a diagram showing a configuration of a contactless power transmission system according to an embodiment of the present invention.

[0015] Figure 2 It is a diagram showing the details of the configuration of the contactless power transmission system according to the embodiment of the present invention.

[0016] Figure 3 It is a diagram showing the configuration of a power transmission unit and a power reception unit of a contactless power transmission system according to an embodiment of the present invention.

[0017] Figure 4 1 is a flowchart showing a process on the power receiving side of the contactless power transmission system according to the embodiment of the present invention.

[0018] Figure 5 yes Figure 4 The flowchart of power receiving control is shown.

[0019] Figure 6This is a diagram showing an example of the correspondence relationship among the power transmission side voltage, the power transmission side current, the power reception side voltage, the power reception side current, the drive signal, and the synchronous rectification flag in the contactless power transmission system according to the embodiment of the present invention.

[0020] Figure 7 1 is a flowchart showing a process on the power transmission side of the contactless power transmission system according to the embodiment of the present invention. DETAILED DESCRIPTION

[0021] Hereinafter, a non-contact power transmission system according to an embodiment of the present invention will be described with reference to the drawings.

[0022] Figure 1 and Figure 2 1 is a diagram showing a configuration of a contactless power transmission system 1 according to an embodiment. Figure 3 1 is a diagram showing the configuration of the power transmission unit 8 and the power reception unit 15 of the contactless power transmission system 1 according to the embodiment.

[0023] The contactless power transmission system 1 of the embodiment supplies power to a moving object such as a vehicle from outside the moving object by contactless power transmission. The vehicle is, for example, an electric vehicle such as an electric vehicle, a hybrid vehicle, or a fuel cell vehicle.

[0024] (Contactless power transmission system)

[0025] like Figure 1 and Figure 2 As shown, the contactless power transmission system 1 of the embodiment includes, for example, a power transmission device 2 installed on a travel path of a vehicle, a drive control device 3 and a power receiving device 4 mounted on a mobile body such as a vehicle, and a communication system M. It should be noted that the contactless power transmission system 1 of the embodiment may include at least only components mounted on the mobile body (such as the drive control device 3 and the power receiving device 4), or may perform contactless power transmission by combining components external to the mobile body (such as the power transmission device 2 and the communication system M) with the contactless power transmission system 1 mounted on the mobile body.

[0026] The communication system M includes, for example, at least one roadside communication device Ma and a communication control device Mb. The communication system M constitutes at least a part of an electronic toll collection system such as ETC (Electronic Toll Collection System) in a toll road.

[0027] The roadside communication device Ma is arranged, for example, at a predetermined distance from the upstream side of the coupling section (communication section and power transmission section) described later in the travel path of the vehicle. The roadside communication device Ma is equipped with an antenna for wireless communication, etc., and communicates with the vehicle-mounted communication device 18 described later, which is mounted on a mobile body such as a vehicle, by wireless. When the roadside communication device Ma obtains information required for payment and settlement for power transmission from the power transmission device 2 to the mobile body such as a vehicle from the vehicle-mounted communication device 18, for example, it transmits key information required for starting power transmission and information related to the installation of the power transmission device 2 to the vehicle-mounted communication device 18. The information required for payment and settlement is, for example, information inherent to a mobile body such as a vehicle, such as the presence or absence of an IC card or a vehicle-mounted transponder for charging and an identifier. The key information is, for example, information generated while being updated at a predetermined period in a different manner for each mobile body (i.e., a vehicle, etc., for which execution of power transmission is permitted) that has passed through a predetermined power transmission section. The key information is information required for the power transmission device 2 to authenticate the power receiving device 4 described later of the mobile body such as a vehicle. The information on the installation of the power transmission device 2 is, for example, information on the installation intervals of the plurality of power transmission units 8 described later.

[0028] The communication control device Mb controls the actions of all roadside communication devices Ma with which corresponding relationships have been established in advance. The communication control device Mb is a software function unit that performs its functions by executing a specified program by a processor such as a CPU (Central Processing Unit). The software function unit is an ECU, which has a processor such as a CPU, a ROM (Read Only Memory) for storing programs, a RAM (Random Access Memory) for temporarily storing data, and an electronic circuit such as a timer. It should be noted that at least a part of the communication control device Mb can also be an integrated circuit such as an LSI (Large Scale Integration).

[0029] For example, the communication control device Mb attempts to obtain the information required for payment and settlement through communication between the roadside communication device Ma and the on-board communication device 18 of a mobile body such as a surrounding vehicle at a predetermined period. When the communication control device Mb obtains the information required for payment and settlement from the on-board communication device 18 and confirms that electronic settlement can be performed, it sends permission information indicating that electronic settlement can be performed and key information required to start power transmission to the on-board communication device 18. When the key information is sent from the roadside communication device Ma to the on-board communication device 18, the communication control device Mb sends the same key information to the power transmission side control device 9 described later.

[0030] The power transmission device 2 includes, for example, a power supply unit 6, a power transmission power conversion unit 7, a power transmission unit 8, and a power transmission-side control device 9. The power transmission device 2 may include at least a plurality of power transmission units 8 in a predetermined coupling section in a vehicle travel path.

[0031] The power supply unit 6 includes, for example, an AC power supply such as a commercial power supply, an AC-DC converter for converting AC power into DC power, and a capacitor for power smoothing. The power supply unit 6 converts AC power supplied from the AC power supply into DC power by the AC-DC converter.

[0032] The power transmission power conversion unit 7, for example, includes an inverter that converts DC power into AC power. The inverter of the power transmission power conversion unit 7 includes, for example, a bridge circuit formed by a plurality of switching elements and rectifying elements connected in a two-phase bridge, and a capacitor for voltage smoothing. Each switching element is, for example, a transistor such as a MOSFET (Metal Oxide Semi-conductor Field Effect Transistor) of SiC (Silicon Carbide). The plurality of switching elements are transistors 7a and 7b of the high-side arm and the low-side arm of each phase. The rectifying element is, for example, a freewheeling diode connected in parallel with each transistor 7a and 7b. The capacitor 7c for voltage smoothing is connected in parallel with the bridge circuit.

[0033] The power transmission unit 8 transmits power by means of a change in a high-frequency magnetic field through magnetic field coupling such as magnetic field resonance or electromagnetic induction. Figure 3 As shown, the power transmission unit 8 includes, for example, a resonance circuit formed by a primary coil 8a, a primary resistor 8b, and a primary capacitor 8c connected in series. The power transmission unit 8 includes, for example, a sensor such as a current sensor for detecting a current It flowing in the resonance circuit.

[0034] The power transmission side control device 9 comprehensively controls the power transmission device 2. The power transmission side control device 9 is a software function unit that performs its functions by executing a predetermined program by a processor such as a CPU (Central Processing Unit). The software function unit is an ECU, which has a processor such as a CPU, a ROM (Read Only Memory) for storing programs, a RAM (Random Access Memory) for temporarily storing data, and an electronic circuit such as a timer. It should be noted that at least a part of the power transmission side control device 9 can also be an integrated circuit such as an LSI (Large Scale Integration).

[0035] For example, the power transmission side control device 9 controls the switching operation of the switching elements of the power transmission power conversion unit 7 to be turned on (conducted) and off (cut off) according to a preset driving frequency or information on the required frequency obtained from the power receiving device 4, thereby transmitting power to the power receiving device 4 of the vehicle.

[0036] For example, when the power transmission side control device 9 obtains the key information from the communication control device Mb, it grasps that the same key information is transmitted from the roadside communication device Ma to the vehicle-mounted communication device 18 of the mobile body, and shifts the power transmission device 2 from the stop state to the reception standby state. The stop state of the power transmission device 2 is, for example, a state in which the switching operation in the power transmission power conversion unit 7 is stopped, such as maintaining each switching element of the power transmission power conversion unit 7 to be disconnected (cut off). The reception standby state of the power transmission device 2 is a state in which information transmission from the power receiving device 4 of the mobile body such as a vehicle is detected. The reception standby state of the power transmission device 2 is, for example, a short-circuit state of the power transmission power conversion unit 7.

[0037] The transmission-side control device 9 short-circuits the primary-side coil 8a by setting the transistor 7b of the low-side arm of each phase to be turned on in the short-circuited state of the transmission power conversion unit 7. As a result, when the primary-side transmission device 2 is viewed from the secondary-side reception device 4, the impedance of the primary side becomes a very large value, but when the magnetic field is generated by the secondary-side coil 15a of the reception device 4 at the time of PING transmission described later, the communication from the reception device 4 is detected by the voltage induced in the primary-side coil 8a of the transmission device 2.

[0038] For example, when the power transmission side control device 9 obtains information such as the key information and the required frequency of power transmission from the power receiving device 4, it compares the key information obtained from the communication control device Mb with the key information obtained from the power receiving device 4. When the key information is consistent, the power transmission side control device 9 causes the power transmission device 2 to shift from the reception standby state to the power transmission state. The power transmission state of the power transmission device 2 is, for example, a state in which power transmission of the required frequency of the power receiving device 4 is performed.

[0039] like Figure 1 and Figure 2 As shown, the drive control device 3 of a mobile body such as a vehicle includes, for example, a power storage device 11, a power conversion unit 13, and a rotary electric machine 14. The power receiving device 4 of the mobile body includes, for example, a power receiving unit 15 and a power receiving 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, a vehicle-mounted communication device 18.

[0040] The power storage device 11 is connected to a power conversion unit 13 and a power receiving power conversion unit 16 described later. The power storage device 11 is charged by power transmitted in a contactless manner from a power transmission device 2 outside the vehicle. The power storage device 11 exchanges power with the rotating electric machine 14 via the power conversion unit 13.

[0041] The power storage device 11 includes, for example, a storage battery such as a lithium ion storage battery, a current sensor for detecting the current of the storage battery, and a voltage sensor for detecting the voltage of the storage battery.

[0042] 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 DC power into AC power. The power converter includes, for example, a second element module and a capacitor for voltage smoothing.

[0043] The second element module, for example, includes a second bridge circuit formed by a plurality of switching elements and a rectifier element connected in a three-phase bridge. Each switching element is, for example, a transistor such as a SiC MOSFET. The plurality of switching elements are transistors 13a and 13b of a high-side arm and a low-side arm of each phase pair. The rectifier element is, for example, a freewheeling diode connected in parallel with each transistor 13a and 13b. A capacitor 13c for voltage smoothing is connected in parallel with the second bridge circuit.

[0044] The second element module controls the operation of the rotating electric machine 14 by transferring power. For example, when the rotating electric machine 14 is powered, the second element module converts the DC power input from the positive and negative DC terminals 13p and 13n into three-phase AC power and supplies the three-phase AC power from the three-phase AC terminal 13d to the rotating electric machine 14. The second element module generates a rotational driving force by sequentially commutating the power supplied to the three-phase stator winding of the rotating electric machine 14.

[0045] The second element module converts the three-phase AC power input from the three-phase stator winding into DC power by driving the switching elements of each phase to be turned on (conducted) and off (cut off) in synchronization with the rotation of the rotating electric machine 14, for example, during the regeneration of the rotating electric machine 14. The second element module can supply the DC power obtained by converting the three-phase AC power to the power storage device 11.

[0046] The rotating electric machine 14 is, for example, a three-phase AC brushless DC motor provided for driving the vehicle. The rotating electric machine 14 includes a rotor having a permanent magnet for excitation and a stator having a three-phase stator winding for generating a rotating magnetic field for rotating the rotor. The three-phase stator winding is connected to the three-phase AC terminals 13d of the power conversion unit 13.

[0047] The rotating electric machine 14 generates a rotational driving force by performing a power traction operation under the action of the electric power supplied from the electric power conversion unit 13. For example, when the rotating electric machine 14 can be connected to the wheels of the vehicle, it generates a driving force by performing a power traction operation under the action of the electric power supplied from the electric power conversion unit 13. The rotating electric machine 14 can also generate power by performing a regenerative operation under the action of the rotational power input from the wheel side of the vehicle. When the rotating electric machine 14 can be connected to the internal combustion engine of the vehicle, it can also generate power by the power of the internal combustion engine.

[0048] The power receiving unit 15 is connected to the power receiving power conversion unit 16. The power receiving unit 15 obtains power by using the change of the high-frequency magnetic field transmitted from the power transmitting unit 8 through magnetic field coupling such as magnetic field resonance or electromagnetic induction. Figure 3 As shown, the power receiving unit 15 includes, for example, a resonance circuit formed by a secondary coil 15a, a secondary resistor 15b, and a secondary capacitor 15c connected in series. The power receiving unit 15 includes, for example, a sensor such as a current sensor that detects the current Ir flowing in the resonance circuit.

[0049] Figure 1 and Figure 2 The receiving power conversion unit 16 shown is connected to the power conversion unit 13. The receiving power conversion unit 16 includes a so-called non-full-bridge type (or non-bridge type and totem pole type) power factor correction (PFC: Power Factor Correction) circuit that converts AC power into DC power. The so-called non-bridge type PFC is a PFC that does not include a bridge rectifier implemented by a plurality of diodes connected by a bridge, and the so-called totem pole PFC is a PFC that includes a pair of switching elements of the same conductivity type connected in series in the same direction (totem pole connection).

[0050] The receiving power conversion unit 16 includes, for example, a third bridge circuit formed by a plurality of switching elements and a rectifying element connected in a two-phase bridge, and a capacitor for voltage smoothing. Each switching element is, for example, a transistor such as a SiC MOSFET. The plurality of switching elements are transistors 16a and 16b of the high-side arm and the low-side arm of each phase pair. The rectifying element is, for example, a freewheeling diode connected in parallel with each transistor 16a and 16b. The capacitor 16c for voltage smoothing is connected in parallel with the third bridge circuit.

[0051] For example, the power receiving device 4 including the power receiving unit 15 and the power receiving power conversion unit 16 controls the switching operation of turning on (conducting) and turning off (cutting off) each switching element of the power receiving power conversion unit 16 based on the information of the frequency of power transmission performed by the power transmitting device 2, thereby obtaining the power transmitted from the power transmitting device 2.

[0052] The control device 17 comprehensively controls the drive control device 3, the power receiving device 4, and the vehicle-mounted communication device 18 of a mobile body such as a vehicle. The control device 17 is a software function unit that performs functions by executing a predetermined program by a processor such as a CPU (Central Processing Unit). The software function unit is an ECU, which has a processor such as a CPU, a ROM (Read Only Memory) for storing programs, a RAM (Random Access Memory) for temporarily storing data, and an electronic circuit such as a timer. It should be noted that at least a part of the control device 17 can also be an integrated circuit such as an LSI (Large Scale Integration).

[0053] The control device 17 generates, for example, a control signal indicating a timing to drive each switching element to be turned on (conducting) or turned off (cutting off), and generates a gate signal for actually driving each switching element to be turned on or off based on the control signal.

[0054] For example, the control device 17 controls the switching operation 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 and perform power factor correction of the input voltage and input current.

[0055] For example, the control device 17 controls the switching operations of the plurality of switching elements of the receiving power conversion unit 16 based on the detection value of the current output from the current sensor 17 a that detects the current flowing between the power receiving unit 15 and the receiving power conversion unit 16 .

[0056] For example, the control device 17 controls the output according to the target output by performing a synchronous rectification operation of synchronously driving a plurality of switching elements of the power receiving device 4 to turn on and off, and a short-circuiting operation of short-circuiting the secondary side coil 15 a .

[0057] For example, the control device 17 controls the synchronous rectification operation according to the magnitude and phase of the current Ir flowing in the secondary coil 15a, which is generated in the power receiving unit 15 due to the power transmitted from the power transmission device 2. The control device 17 controls the plurality of switching elements of the power receiving power conversion unit 16 by a soft switching operation called zero voltage switching operation (ZVS). In the zero voltage switching operation (ZVS), each switching element performs an operation of turning on (switching from an off state to an on state) after the voltage across the two ends is set to zero by discharging the output capacitance (parasitic capacitance) in the off state during the dead time of each phase.

[0058] 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 synchronous rectification operation of the zero voltage switching operation (ZVS) in the high-side arm of each phase of the power receiving power conversion unit 16. The control device 17 increases the impedance of the secondary side when the power receiving device 4 on the secondary side is viewed from the power transmitting device 2 on the primary side by short-circuiting the secondary side coil 15a, thereby reducing the current on the primary side (power transmission current: current It flowing in the primary side coil 8a). The control device 17 controls the current of the power transmitting device 2 on the primary side by using the power receiving device 4 on the secondary side, thereby performing independent power control such as power transmission stop on the power receiving device 4 side.

[0059] For example, the control device 17 sets a communication section for communication and a power transmission section for power transmission in a coupling section where the degree of coupling between the primary coil 8a of the power transmitting device 2 and the secondary coil 15a of the power receiving device 4 is greater than or equal to a predetermined value in the vicinity of the power transmitting device 2. For example, when the control device 17 acquires key information through communication between the roadside communication device Ma and the vehicle-mounted communication device 18 at a time before reaching the coupling section, the control device 17 transmits information related to 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 start of power transmission by the power transmitting device 2 in the power transmission section.

[0060] For example, when the control device 17 sets a first communication interval and a second communication interval before and after the power transmission interval along the moving direction of a mobile body (such as a vehicle V), information related to power transmission is sent from the power receiving device 4 to the power transmitting device 2 in the first communication interval as the initial communication interval.

[0061] The information related to power transmission includes, for example, key information obtained from the roadside communication device Ma, the required frequency of power transmission, target output (power consumption) for fail safe, and information related to various abnormalities.

[0062] The required frequency of power transmission is set to suppress the reduction of power transmission efficiency and output (power) based on, for example, the minimum ground height of the moving body associated with the distance between the primary coil 8a and the secondary coil 15a and the mounting layout of the power receiving device 4 in the moving body. The control device 17 may also set the required frequency according to the state of power transmission between the power transmitting device 2 and the power receiving device 4.

[0063] It should be noted that the control device 17 can also send information indicating the stop of power transmission in the power transmission interval and communication in the communication interval 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, for example, when the primary side coil 8a is present in the last communication interval (for example, the second communication interval, etc.) of the coupling interval.

[0064] For example, when the control device 17 acquires the key information through the communication between the roadside communication device Ma and the vehicle-mounted communication device 18, the control device 17 transmits information by transmitting power from the power receiving device 4 to the power transmitting device 2 in the reception standby state as a so-called Internet packet search (PING) signal in the communication section of the coupling section. The power receiving device 4 communicates by using the voltage induced in the primary coil 8a of the power transmitting device 2 by the magnetic field generated by the secondary coil 15a through the energization switching operation based on the switching operation in the power receiving power conversion unit 16. The control device 17 performs PING transmission by, for example, switching the carrier used for non-contact power transmission from the power receiving device 4 to the power transmitting device 2 at a predetermined duty cycle to generate two levels of digital signals, namely, dominant (superior) and recessive (inferior). The predetermined duty cycle is, for example, a predetermined minimum to 50%. It should be noted that the control device 17 may also transmit information by, for example, amplitude modulation of the carrier based on the duty cycle of the switching operation.

[0065] The control device 17 performs PING transmission at a predetermined period of, for example, several tens of μs to several ms, and upon receiving a response signal to the PING transmission from the power transmission device 2 , starts power reception control for power transmission from the power transmission device 2 in the power transmission section.

[0066] The control device 17 sets the timing of PING transmission, for example, based on information related to the installation of the power transmission device 2 acquired from the roadside communication device Ma and the movement state of the mobile body (for example, the vehicle V) (that is, the movement state of the power receiving device 4), so that the communication (that is, the transmission and reception between each other) between the power transmission device 2 and the power receiving device 4 in the communication section is appropriately completed. For example, the control device 17 sets the transmission cycle based on information such as the installation interval of the plurality of power transmission units 8 and the speed of the mobile body (for example, the speed of the vehicle V) in order to complete at least a predetermined number of PING transmissions (one time, etc.) in the communication section.

[0067] It should be noted that, for example, even when the execution of PING transmission in the communication interval is permitted, the control device 17 shifts to a standby state for stopping the execution of PING transmission outside the communication interval. For example, the control device 17 may start the execution of PING transmission from before the initial communication interval immediately before reaching the next coupling interval in the standby state for PING transmission as the moving body moves.

[0068] Hereinafter, as the operation of the contactless power transmission system 1 , processing executed by the power transmission-side control device 9 and the control device 17 will be described.

[0069] Figure 41 is a flowchart showing a power receiving-side process executed by the control device 17 of the contactless power transmission system 1 according to the embodiment.

[0070] First, in Figure 4 In step S01 shown, the control device 17 determines whether electronic settlement for power transmission from the power transmission device 2 to the mobile body can be performed by sending and receiving information (payment communication) based on wireless communication between the roadside communication device Ma and the vehicle-mounted communication device 18. If the result of its determination is "no", the control device 17 repeatedly performs the processing of step S01. On the other hand, if the result of its determination is "yes", the control device 17 advances the processing to step S02.

[0071] Then, in step S02, the control device 17 obtains key information necessary for starting power transmission from the roadside communication device Ma.

[0072] Next, in step S03 , the control device 17 generates a signal for PING transmission to be performed by transmitting electric power from the power receiving device 4 to the power transmitting device 2 .

[0073] Next, in step S04 , the control device 17 executes PING transmission at a predetermined cycle in the first communication section of the coupling section.

[0074] Next, in step S05, the control device 17 determines whether a response signal to the PING transmission is received from the power transmission device 2. If the determination result is "No", the control device 17 repeats the process of step S05. On the other hand, if the determination result is "Yes", the control device 17 advances the process to step S06.

[0075] Then, in step S06 , the control device 17 starts power reception control, which will be described later, for power transmission from the power transmission device 2 in the power transmission section.

[0076] Next, in step S07, the control device 17 determines whether the coupling section has ended. If the determination result is "No", the control device 17 returns to step S04. On the other hand, if the determination result is "Yes", the control device 17 ends the process.

[0077] Figure 5 yes Figure 4 The flowchart of power receiving control is shown.

[0078] First, in Figure 5In step S11 shown, the control device 17 starts magnetic resonance coupling between the power transmission unit 8 and the power reception unit 15 by allowing the diode rectification operation of the power reception device 4. The diode rectification operation is a full-wave rectification operation performed by the rectification element of the third bridge circuit of the power reception power conversion unit 16 (the freewheeling diode connected in parallel with each transistor 16a, 16b).

[0079] Next, in step S12, the control device 17 determines whether the detected value of the current output from the current sensor 17a is greater than or equal to a predetermined threshold value. If the determination result is "No", the control device 17 repeatedly performs the process of step S12. On the other hand, if the determination result is "Yes", the control device 17 advances the process to step S13. The predetermined threshold value is set based on, for example, the output classification of the power receiving power conversion unit 16.

[0080] 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 for instructing the high-side arm of the power receiving power conversion unit 16 and the pulse for instructing the low-side arm of the power receiving power conversion unit 16 every time the phase of the detected value of the current output from the current sensor 17a crosses zero (0°).

[0081] 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 value. If the determination result is "No", the control device 17 repeats the process of step S14. On the other hand, if the determination result is "Yes", the control device 17 advances the process to step S15.

[0082] 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 synchronous rectification operation is switched to the diode rectification operation, the control device 17 switches the power receiving device 4 to the standby state according to a predetermined condition. 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 the power transmission by, for example, performing a short-circuit operation of short-circuiting the secondary side coil 15a. Then, the control device 17 returns the process.

[0083] Figure 6 1 is a diagram showing an example of the correspondence relationship among the power transmission side voltage, the power transmission side current, the power reception side voltage, the power reception side current, the drive signal, and the synchronous rectification flag in the contactless power transmission system 1 according to the embodiment.

[0084] First, for example, Figure 6Before the time t1 shown, after the power transmission control of the power transmitting device 2 is started by sending a PING from the power receiving device 4 to the power transmitting device 2, the amplitude of the secondary side current (power receiving side current: for example, the current detected by the current sensor 17a, etc.) gradually increases due to the diode rectification action of the power receiving device 4.

[0085] Then, for example, when the power receiving side current exceeds a predetermined threshold value Ith at time t1, the synchronous rectification operation of the power receiving device 4 starts with the flag value of the synchronous rectification flag changing from "0" to "1". The predetermined threshold value Ith of the power receiving side current is set, for example, for a steady state in which the current amplitude gradually increases due to the start of the diode rectification operation and becomes constant after an appropriate time.

[0086] In the synchronous rectification operation after time t1, for example, as shown at each time t2, t4, t6, t8, and t10, the pulse (driving signal: dotted line) indicating the driving of the low-side arm of the receiving power conversion unit 16 or the pulse (driving signal: solid line) indicating the driving of the high-side arm of the receiving power conversion unit 16 is reversed from active (ON) to inactive (OFF) every time the phase of the waveform of the receiving-side current crosses zero (0°). In addition, for example, as shown at each time t3, t5, t7, and t9, the driving signal (dotted line) of the low-side arm of the receiving power conversion unit 16 and the driving signal (solid line) of the high-side arm of the receiving power conversion unit 16 are alternately switched from active (ON) to inactive (OFF), and then reversed from inactive (OFF) to active (ON) after a predetermined delay time corresponding to the internal inductance value, etc. By the synchronous rectification operation, the waveform of the receiving-side current becomes a sine wave in the 180° section.

[0087] Figure 7 1 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 according to the embodiment.

[0088] First, in Figure 7 In step S21 shown, the power transmission side control device 9 determines whether the key information is transmitted from the roadside communication device Ma to the power receiving device 4. If the result of its determination is "No", the power transmission side control device 9 advances the process to step S22. On the other hand, if the result of its determination is "Yes", the power transmission side control device 9 advances the process to step S23.

[0089] Then, in step S22 , the power transmission-side control device 9 maintains the stopped state of the power transmission device 2 , and returns the process to step S21 .

[0090] Then, in step S23 , the power transmitting-side control device 9 shifts the power transmitting device 2 from the stopped state to the reception standby state.

[0091] Next, in step S24, the power transmission side control device 9 determines whether a PING signal based on power transmission from the power receiving device 4 to the power transmission device 2 is received in the first communication section of the coupling section. If the result of its determination is "No", the power transmission side control device 9 repeats the process of step S24. On the other hand, if the result of its determination is "Yes", the power transmission side control device 9 advances the process to step S25.

[0092] Next, in step S25 , the power transmission-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 .

[0093] Next, in step S26, the power transmission side control device 9 determines whether the key information obtained from the communication control device Mb is consistent with the key information obtained from the power receiving device 4. If the result of its determination is "No", the power transmission side control device 9 ends the process. On the other hand, if the result of its determination is "Yes", the power transmission side control device 9 enters step S27.

[0094] Next, in step S27 , the power transmission-side control device 9 transmits a response signal in response to the PING transmission to the power receiving device 4 through the power transmission from the power transmitting device 2 to the power receiving device 4 in the communication section.

[0095] Next, in step S28, the power transmission-side control device 9 starts power transmission control for power transmission to the power receiving device 4 at the requested frequency acquired from the power receiving device 4 in the power transmission section. Then, the control device 17 ends the process.

[0096] As described above, according to the contactless power transmission system 1 of the embodiment, the control device 17 is provided to start the synchronous rectification operation according to the predetermined threshold value Ith of the power receiving side current and to control the switching operation according to the phase of the power receiving side current, thereby reducing the loss and the required cooling capacity in the rectification operation on the power receiving side.

[0097] By alternately reversing the drive signals of the low-side arm and the high-side arm each time the phase of the waveform of the power receiving side current crosses zero (0°), the waveform of the power receiving side current can be made sinusoidal in the 180° interval, and the efficiency of power conversion can be improved. For example, compared with the case where the reversal of the drive vibration is switched according to whether the power receiving side current exceeds a predetermined threshold, the duty cycle of power conversion can be increased, and the output can be improved.

[0098] The diode rectification operation and the synchronous rectification operation can be switched according to a predetermined threshold value Ith of the power receiving-side current, and the synchronous rectification operation can be appropriately performed even when a moving object such as a vehicle equipped with the power receiving device 4 is moving.

[0099] When a mobile object 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, thereby enabling appropriate operation switching.

[0100] (Variation Example)

[0101] In the above-described embodiment, the contactless power transmission system 1 may include a power storage voltage conversion unit that converts input and output power of the power storage device 11 in the case of a hybrid vehicle that uses the power storage device 11 and an internal combustion engine as power sources.

[0102] 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 can be omitted, replaced, and changed in various ways without departing from the scope of the invention. These embodiments and their variations are included in the invention described in the technical solution and its equivalent scope, as are the solutions included in the scope and the main purpose of the invention.

Claims

1. A contactless power transmission system, wherein: The contactless power transmission system comprises: a power receiving unit having a coil for receiving AC power transmitted from the power transmitting device in a contactless manner; a power conversion unit having a plurality of switching elements and a plurality of rectifying elements connected to the coil and converting the AC power obtained by the power receiving unit into DC power; a current sensor for detecting a current flowing between the power receiving unit and the power conversion unit; as well as a control device for controlling the switching operation of the plurality of switching elements based on the detection value of the current output from the current sensor, When the detected value of the current is equal to or greater than a predetermined threshold value, the control device causes the power conversion unit to perform a synchronous rectification operation in which the plurality of switching elements are synchronously driven according to a phase of the current to thereby rectify the AC power.

2. The contactless power transmission system according to claim 1, wherein: The control device prohibits the synchronous rectification operation and permits the operation of rectifying the AC power by using the plurality of rectifying elements when the detected value of the current is smaller than the predetermined threshold value.

3. The contactless power transmission system according to claim 1 or 2, wherein: The control device stops the synchronous rectification operation and shifts the power receiving unit and the power conversion unit to a standby state when the detected value of the current is smaller than the predetermined threshold value during execution of the synchronous rectification operation.

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