Power receiving device and contactless power transmission system

Abstract

To suppress a power increase when a short circuit is formed by an operation of switching elements.SOLUTION: A power reception device includes: a power reception coil that receives power transmitted from a power transmission coil in a non-contact manner; and a control device that executes a short-circuit mode in which a plurality of switching elements provided between the power reception coil and a load are caused to perform switching operations to short-circuit between output terminals of the power reception coil. When a phase of a current and a phase of a voltage in the power reception device are deviated from each other, the control device determines switching timings of the switching elements to the short-circuit mode in a manner that the phase of the voltage is shifted in a direction in which a power factor of power supplied to the load is deteriorated.SELECTED DRAWING: Figure 12

Description

[Technical Field]

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

[0002] Patent document 1 discloses that a switching element for power control is provided in the power receiving device of a contactless power transmission system, and when the voltage on the power receiving device side exceeds a reference value, the operation of the switching element is controlled to form a short circuit, thereby interrupting charging and avoiding excessive voltage rise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6361818 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have discovered that when power suppression control is performed to form a short circuit in a switching element, a phenomenon known as overshooting occurs, in which power suddenly increases and exceeds the target value. Exceeding the rated value due to overshooting can lead to battery degradation or failure. In this case, it is conceivable to provide a safety margin between the rated value and the target value of power control, assuming that overshooting will occur, but this leads to a decrease in the received power during wireless charging.

[0005] The present invention has been made in consideration of the above circumstances, and aims to provide a power receiving device and a contactless power transmission system that can suppress an increase in power when a short circuit is formed by the operation of a switching element. [Means for solving the problem]

[0006] The power receiving device of the present invention comprises a power receiving coil that receives power transmitted contactlessly from a power transmitting coil, and a control device that executes a short-circuit mode in which a switching element provided between the power receiving coil and a load is switched to perform a switching operation to short-circuit the output terminals of the power receiving coil, wherein the control device is characterized in that, when the phase of the current and the phase of the voltage in the power receiving device are out of phase, the control device determines the switching timing of the switching element in the short-circuit mode so that the phase of the voltage is shifted in a direction that deteriorates the power factor of the power supplied to the load.

[0007] According to this configuration, the power factor of the electric power can be deteriorated by executing the short circuit mode, and therefore an increase in the electric power due to the switching operation can be suppressed.

[0008] In addition, the control device may determine the switching timing of the switching element in the short-circuit mode so that the right side of the voltage rectangular wave is reduced more than the left side when the phase of the current lags the phase of the voltage, and may determine the switching timing of the switching element in the short-circuit mode so that the left side of the voltage rectangular wave is reduced more than the right side when the phase of the current leads the phase of the voltage.

[0009] With this configuration, when the current phase lags behind the voltage phase, the phase of the short-circuit mode can be determined so that the right side of the voltage rectangular wave is cut off more. This prevents the power factor from deteriorating due to the phase shift, and suppresses the increase in power due to switching operation.

[0010] Furthermore, when the current and the voltage are not out of phase with each other, the control device may determine the switching timing of the switching elements in the short-circuit mode so as to symmetrically reduce the voltage rectangular wave.

[0011] With this configuration, when the current phase leads the voltage phase, the phase of the short-circuit mode can be determined so that the left side of the voltage rectangular wave is cut off more. This means that the power factor deteriorates due to the phase shift, and the increase in power due to switching operation can be suppressed.

[0012] A contactless power transfer system according to the present invention includes the power receiving device of the above invention and a power transmitting device having the power transmitting coil.

[0013] According to this configuration, in a contactless power transmission system including a power transmitting device and a power receiving device, the power factor can be worsened by executing a short-circuit mode on the power receiving device side, thereby suppressing the increase in power due to switching operation. [Effects of the Invention]

[0014] In the present invention, the power factor of the power can be deteriorated by executing the short circuit mode, so that an increase in power due to switching operations can be suppressed. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram schematically illustrating a contactless power transmission system according to an embodiment. [Figure 2] FIG. 2 is a diagram for explaining a current path in the diode mode. [Figure 3] FIG. 3 is a diagram for explaining a current path in the short-circuit mode. [Figure 4] FIG. 4 is a diagram showing the voltage and current on the input side of the rectifier and the received power supplied to the battery when the short-circuit mode is executed. [Figure 5] FIG. 5 is a diagram showing the relationship between the duty and the received power in the short-circuit mode. [Figure 6] FIG. 6 shows the results of a wireless power supply test using an actual vehicle. [Figure 7] FIG. 7 is a diagram showing the relationship between the received power of the battery and the phase and duty in the short-circuit mode. [Figure 8] FIG. 8 is a diagram for explaining a change in inductance depending on the positional relationship between the power transmitting coil and the power receiving coil. [Figure 9] FIG. 9 is a diagram showing an example of a case where power control is performed in a state where the phase of the current lags behind the phase of the voltage. [Figure 10] FIG. 10 is a diagram for explaining a phase shift of the voltage fundamental wave that occurs when the short-circuit mode is executed in a short-circuit phase that cuts off the left side of the voltage rectangular wave as power control. [Figure 11] FIG. 11 is a diagram for explaining a phase shift of a voltage fundamental wave that occurs when a short-circuit mode is executed as power control in a short-circuit phase that cuts off the right side of a voltage rectangular wave. [Figure 12] FIG. 12 is a flowchart showing the power control flow. [Figure 13] FIG. 13 is a diagram showing a case where the short-circuit mode is executed with a short-circuit phase that cuts off a large amount of the right side of the voltage rectangular wave when the current phase lags behind the voltage phase. [Figure 14] FIG. 14 is a diagram showing a case where the short-circuit mode is executed with a short-circuit phase that cuts off a large amount of the left side of the voltage rectangular wave when the current phase leads the voltage phase. [Figure 15] FIG. 15 is a diagram showing a case where the short-circuit mode is executed with a short-circuit phase that cuts off the voltage rectangular wave symmetrically when the current phase and the voltage phase are in phase. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, a power receiving device and a contactless power transfer system according to an embodiment of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the embodiment described below.

[0017] 1 is a diagram schematically illustrating a contactless power transfer system according to an embodiment. The contactless power transfer system 1 includes a power transmitting device 10 and a power receiving device 20. The contactless power transfer system 1 is a wireless power transfer system that transfers power contactlessly from a power transmitting coil L10 of the power transmitting device 10 to a power receiving coil L20 of the power receiving device 20. A battery 30, which is a load on the power receiving side, is electrically connected to the power receiving device 20.

[0018] The power transmitting device 10 includes a DC power supply 11, a smoothing capacitor C11, an inverter 12, a filter circuit 13, and a power transmitting side resonant circuit 14.

[0019] A DC power supply 11 supplies DC power to an inverter 12. A smoothing capacitor C11 is provided between the DC power supply 11 and the inverter 12. The smoothing capacitor C11 is connected in parallel with the inverter 12.

[0020] The inverter 12 is a power conversion device that converts DC power supplied from the DC power supply 11 into AC power. The inverter 12 is configured as a full-bridge circuit in which four switching elements SW11, SW12, SW13, and SW14 are fully bridge-connected. A diode is connected in parallel to each of the switching elements SW11 to SW14. Each of the switching elements SW11 to SW14 is configured by an IGBT, and performs switching operation in response to a control signal. The inverter 12 supplies the converted AC power to the filter circuit 13.

[0021] The filter circuit 13 removes noise contained in the AC current input from the inverter 12, and outputs the AC power from which the noise has been removed to the power transmitting side resonant circuit 14. The filter circuit 13 is a T-type filter in which a coil L11, a capacitor C12, and a coil L12 are arranged in a T shape.

[0022] The power transmitting side resonant circuit 14 includes a power transmitting coil L10 and a resonant capacitor C13. The power transmitting coil L10 transmits AC power supplied from the filter circuit 13 to the power receiving device 20 in a contactless manner. The power transmitting coil L10 and the resonant capacitor C13 form an LC resonant circuit. The resonant capacitor C13 is connected in series to one end of the power transmitting coil L10 and adjusts the resonant frequency of the LC resonant circuit.

[0023] The power receiving device 20 includes a power receiving-side resonant circuit 21, a filter circuit 22, a rectifier 23, a smoothing capacitor C21, a current sensor 24, a voltage sensor 25, and a control device 26. The power receiving device 20 receives power from the power transmitting device 10 in a contactless manner.

[0024] The power receiving side resonant circuit 21 includes a power receiving coil L20 and a resonant capacitor C22. The power receiving coil L20 receives power transmitted contactlessly from the power transmitting coil L10. The power receiving coil L20 and the resonant capacitor C22 form an LC resonant circuit. The resonant capacitor C22 adjusts the resonant frequency of the LC resonant circuit.

[0025] The filter circuit 22 removes noise contained in the AC current input from the power receiving side resonant circuit 21, and outputs the AC power from which the noise has been removed to the rectifier 23. The filter circuit 22 is a T-type filter in which a coil L21, a capacitor C23, and a coil L22 are arranged in a T shape.

[0026] The rectifier 23 is a rectifier circuit that converts the AC power input from the filter circuit 22 into DC power and outputs it to the battery 30. The rectifier 23 is configured as a full-bridge circuit in which four diodes D21, D22, D23, and D24 are fully bridge-connected as rectifying elements. One end of the filter circuit 22 is connected to the connection point between the anode of the diode D21 and the cathode of the diode D22. The other end of the filter circuit 22 is connected to the connection point between the anode of the diode D23 and the cathode of the diode D24.

[0027] A switching element is connected in parallel to each of the diodes D21, D22, D23, and D24. A switching element SW21 is connected in parallel to the diode D21. A switching element SW22 is connected in parallel to the diode D22. A switching element SW23 is connected in parallel to the diode D23. A switching element SW24 is connected in parallel to the diode D24. Each of the switching elements SW21 to SW24 is formed by an IGBT, and performs switching operation in response to a control signal from the control device 26.

[0028] The rectifier supplies the converted DC power to the battery 30. A smoothing capacitor C21 is provided between the rectifier and the battery 30. The smoothing capacitor C21 is connected to the rectifier in parallel.

[0029] The current sensor 24 detects the input current of the rectifier 23. The current sensor 24 is provided between the filter circuit 22 and the rectifier 23. The current sensor 24 detects the current flowing through the rectifier 23 and outputs a detection signal to the control device 26.

[0030] The voltage sensor 25 detects the input voltage of the rectifier 23. The voltage sensor 25 is provided between the filter circuit 22 and the rectifier 23, and is connected in parallel with the rectifier 23. The voltage sensor 25 detects the voltage input to the rectifier 23, and outputs the detection signal to the control device 26.

[0031] The control device 26 is an electronic control device that controls the rectifier 23. Signals from various sensors provided in the power receiving device 20 are input to the control device 26. Then, the control device 26 executes various controls based on the signals input from the various sensors.

[0032] For example, the control device 26 executes power control to control the power supplied to the battery 30 during contactless charging. In the contactless power transmission system 1, in order to protect the load on the power receiving side, a short circuit path is formed using the switching elements SW21 to SW24 of the power receiving device 20 during contactless charging, thereby suppressing the amount of power supplied to the load. Therefore, the control device 26 executes power control during contactless charging, and controls the switching elements SW21 to SW24 of the rectifier 23.

[0033] The power control includes a diode mode and a short circuit mode, and the controller 26 can switch between the diode mode and the short circuit mode.

[0034] The diode mode is a control mode in which a current flows to the battery 30 and received power is supplied from the power receiving device 20 to the battery 30. In the diode mode, all of the switching elements SW21, SW22, SW23, and SW24 of the rectifier 23 are controlled to be in the off state. The current path in the diode mode is a return path via the diode D21, the battery 30, and the diode D24, as shown by the arrow in FIG. 2. Note that the current sensor 24 and the voltage sensor 25 are omitted in FIG. 2. The current of the battery 30 may also be referred to as a battery current.

[0035] The short-circuit mode is a control mode in which current circulates and does not flow into the battery 30. That is, the short-circuit mode is a mode in which current circulates from the rectifier 23 to the receiving coil L20. In the short-circuit mode, the switching elements SW21, SW22, and SW24 of the rectifier 23 are controlled to the off state, and the switching element SW23 is controlled to the on state. In the short-circuit mode, the current path is a return path via the diode D21 and the switching element SW23, as shown by the arrow in FIG. 3. Note that the current sensor 24 and the voltage sensor 25 are omitted from FIG. 3.

[0036] The control device 26 executes the short-circuit mode, thereby reducing the amount of power supplied to the battery 30. The control device 26 executes control to switch between the diode mode and the short-circuit mode when reducing the power received by the battery 30. As shown in Fig. 3, the control device 26 executes switching control to switch the switching element S23 between an off state and an on state.

[0037] 4, the current waveform on the input side of rectifier 23 does not change significantly, and the voltage becomes zero. That is, the current waveform in rectifier 23 does not change significantly between diode mode and short-circuit mode. Furthermore, during the short-circuit mode, the output voltage of rectifier 23 becomes zero, and therefore the received power of battery 30 becomes zero.

[0038] Furthermore, the control device 26 controls the duty, which is the proportion of the short circuit mode in the voltage square wave, to 0 to 100%. As shown in Fig. 5, the control device 26 controls the received power of the battery 30 between 0% and 100% by manipulating the duty of the short circuit mode.

[0039] In the contactless power transmission system 1 configured in this manner, the control device 26 executes power control during contactless charging, thereby suppressing an increase in power of the battery 30 and protecting the battery 30.

[0040] For example, when the power transmitting device 10 is a ground-side unit installed on the ground and the power receiving device 20 is a vehicle-side unit mounted on a vehicle, the contactless power transmission system 1 is a system configured to be able to wirelessly supply power to a traveling vehicle. Because this vehicle is an electric vehicle equipped with a battery 30, regeneration while traveling allows regenerative charging of the battery 30. Therefore, if regeneration and contactless charging are performed simultaneously while traveling, excessive power will be supplied to the battery 30, which may cause deterioration or failure of the battery 30. To prevent this, the control device 26 performs power control to reduce the power received by contactless charging. In other words, the control device 26 controls the vehicle to prioritize regeneration and refrain from contactless charging.

[0041] However, when the inventors conducted a wireless power supply test using an actual vehicle, they found that when they attempted to control power using a switching element on the power receiving device 20 side, an overshoot occurred in which the received power of the battery 30 exceeded the target value by nearly two times.

[0042] FIG. 6 shows the results of a wireless power transfer test using an actual vehicle. FIG. 6 illustrates the test results of in-motion power transfer when a vehicle equipped with a receiving coil L20 passes over a transmitting coil L10. The upper part of FIG. 6 shows the change in battery current depending on whether or not power control is performed. The middle part of FIG. 6 is an enlarged view of a portion of the upper part of FIG. 6, showing the change in battery current when power control is performed. The lower part of FIG. 6 shows the change in duty corresponding to the change in the middle part of FIG. 6.

[0043] 6, if power control is not executed during contactless charging, the current of battery 30 (battery current) will increase beyond the upper limit and will increase naturally, causing the received power of battery 30 to increase naturally. If power control is executed during contactless charging to avoid this, control device 26 will start power control when the battery current reaches the upper limit during contactless charging (time t1).

[0044] However, just after time t1, the control device 26 started power control and began increasing the duty, which is the manipulated variable of the rectifier 23. At that moment, the battery current began to increase rapidly, and the received power began to increase. At that time, the battery current exceeded the upper limit by nearly two times. Specifically, while the duty was increasing from 0% to nearly 50%, especially around 10% to 20%, the battery current continued to increase rapidly, reaching a value nearly twice the upper limit. When the increase in duty subsided, the battery current decreased to a value close to the upper limit. During this period, the received power increased in accordance with the increase in the battery current. Regarding this phenomenon, the momentum of the power increase was unique compared to the power waveform when a vehicle passed over the power transmitting coil L10 without power control being executed. From this, it is believed that the execution of the short-circuit mode using the rectifier 23 caused a power increase, contrary to its intended purpose (power reduction).

[0045] Therefore, the present inventors have studied the mechanism by which the formation of a short circuit by the rectifier 23 causes an increase in received power.

[0046] First, the inventors focused on the phenomenon that the received power increases when the duty in the short circuit mode increases, and studied the relationship between the magnitude of the duty and the received power. As a result, as shown in Figure 7, it was found that there are combinations of duty and phase that cause an increase in the received power when the duty is 0%, even when the duty is greater than 0%.

[0047] For example, when the duty is 60% or higher, i.e., when the duty is relatively large, the received power decreases in all phases. On the other hand, when the duty is 40% or lower, i.e., when the duty is small, the received power increases in certain phases. It was found that the power increase is particularly large when the duty is between 10 and 20%. Furthermore, the phases where the power increase occurs include the ranges of 0 to 40 degrees and 160 to 180 degrees.

[0048] That is, the first factor is that when the duty is small, there are conditions in a specific phase where the received power is greater than when the duty is 0%. When the duty is controlled to 50% by power control, the duty gradually increases from 0%, as shown in Figure 6. During this process, the duty passes through a range of 40% or less, which causes an increase in the received power, as shown in Figure 7. Within this range, as shown in Figure 7, there are conditions where the received power is greater than when the duty is 0%, depending on the phase (switching timing) in which the short circuit mode is executed. Therefore, if the phase of the short circuit mode is set to 0 to 40 degrees or 160 to 180 degrees when the duty passes through this range, the received power will increase due to power control.

[0049] Furthermore, the inventors continued to study the mechanism by which the formation of a short circuit by the rectifier 23 causes an increase in received power, and as a result, the following second to fifth factors were identified.

[0050] The second factor is variations in characteristics due to factors such as the capacitance of the capacitor and the number of coil turns, as well as interactions between the ferrite cores of the transmitting coil L10 and the receiving coil L20. These variations in characteristics and interactions between the ferrite cores cause circuit constants such as inductance to deviate from their designed values, causing the resonant frequency of the circuit to deviate from the drive frequency of the inverter 12. For example, if the drive frequency of the inverter 12 is fixed at 85 kHz, the resonant frequency of the transmitting-side resonant circuit 14 will deviate to 84 kHz or 83 kHz, and the resonant frequency of the receiving-side resonant circuit 21 will deviate to 84 kHz or 83 kHz.

[0051] As shown in Figure 8, when a power receiving device 20 mounted on a vehicle 100 passes over a power transmitting coil L10 installed on the ground, the positional relationship between the ferrite core 15 of the power transmitting coil L10 and the ferrite core 27 of the power receiving coil L20 changes, and the inductance deviates from the design value due to the interaction between the ferrite cores.

[0052] The third factor is that deviations from the design values of the circuit constants due to the second factor cause the waveform of the current flowing through the circuit to become distorted, resulting in a phase shift between the fundamental component of the current and the fundamental component of the voltage, lowering the power factor of the received power. The power factor of the received power is expressed as the cosine of the phase shift. The formula for received power is "P=I·N·cosΔθ", where Δθ represents the phase shift (phase difference). cosΔθ represents the power factor.

[0053] As shown in Figure 8, when the circuit constants deviate from the design values and the current waveform becomes distorted, a phase shift Δθ occurs, such that the fundamental wave component of the current (fundamental current wave) lags behind the phase of the fundamental wave component of the voltage (fundamental voltage wave), as shown in Figure 9, for example. The power factor of the received power decreases in accordance with this phase shift Δθ. When the power factor decreases, the received power decreases.

[0054] A fourth factor is that when power control is performed and a short circuit is formed in rectifier 23, a period occurs in which the voltage square wave is zero, but this causes the voltage fundamental wave to be pushed to the left or right (phase shifted). This phase shift includes a direction that worsens the power factor and a direction that improves the power factor.

[0055] As shown in Figure 9, when power control is performed in a state where the current phase lags behind the voltage phase, if the voltage fundamental wave is pushed to the right by the phase of the short-circuit mode, the voltage fundamental wave will shift in phase in a direction that eliminates the phase shift Δθ with the current fundamental wave, and the power factor that was reduced by the third factor will improve.

[0056] As shown in FIG. 9, the voltage waveform (rectangular voltage wave) is a waveform that includes two peaks (a positive voltage peak and a negative voltage peak) in one cycle. In this explanation, with respect to one peak of the rectangular voltage wave, the left side is referred to as the phase lead side, and the right side is referred to as the phase lag side. When referring to the right side of the rectangular voltage wave, this refers to both the right side of the positive voltage peak and the right side of the negative voltage peak. When referring to the left side of the rectangular voltage wave, this refers to both the left side of the positive voltage peak and the left side of the negative voltage peak.

[0057] For example, as shown in Figure 10, when the phase of the short-circuit mode is set to shave off the left side of the voltage square wave and power control is performed, a phase shift occurs in which the voltage fundamental wave is pushed to the right.As shown in Figure 11, when the phase of the short-circuit mode is set to shave off the right side of the voltage square wave and power control is performed, a phase shift occurs in which the voltage fundamental wave is pushed to the left.

[0058] Furthermore, when power control is performed, the longer the period (duty) during which the voltage square wave is zero, the smaller the amplitude of the voltage fundamental wave. As shown in Figure 9, the amplitude of the voltage fundamental wave during power control (when the duty is greater than 0%) is smaller than the amplitude of the voltage fundamental wave before power control is performed (when the duty is 0%).

[0059] The fifth factor is an increase in received power due to the formation of a short circuit by the rectifier 23 when conditions are met in which the power factor improvement effect due to the fourth factor is dominant. The received power during power control is determined by multiplying the reduction in amplitude of the voltage fundamental wave by the power factor improvement effect or power factor deterioration effect due to the phase shift. When power control begins, the duty is increased so that the received power falls within the target value. However, during this increase, if conditions are met in which the power factor improvement effect is dominant over the reduction in amplitude of the voltage fundamental wave, the power will increase unintentionally.

[0060] In particular, when the fifth factor and the first factor overlap, there is a possibility that a sudden increase in battery current, i.e., a sudden increase in power supplied to the battery 30, may occur as shown in Fig. 6. To address this, the contactless power transfer system 1 is configured to suppress the power increase due to the formation of a short circuit path by suppressing the power increase due to the fifth factor.

[0061] Therefore, control device 26 controls the switching timing (short-circuit phase) for forming a short circuit during contactless charging so that it is a phase that does not cause an increase in power. To this end, control device 26 includes a first detection unit that detects the phase of the current in rectifier 23, a second detection unit that detects the phase of the voltage in rectifier 23, a determination unit that determines whether or not there is a shift between the phase of the current and the phase of the voltage, a determination unit that determines the short-circuit phase, and a control unit that executes power control according to the short-circuit phase.

[0062] The first detection unit detects the phase of the current on the input side of the rectifier 23 based on a signal from the current sensor 24. The current sensor 24 functions as a sensor for detecting the phase of the current. The first detection unit detects the phase of the current flowing into the rectifier 23 in real time.

[0063] The second detection unit detects the phase of the voltage on the input side of the rectifier 23 based on a signal from the voltage sensor 25. The voltage sensor 25 functions as a sensor for detecting the phase of the voltage. The second detection unit detects the phase of the voltage input to the rectifier 23 in real time.

[0064] The determination unit determines whether or not the phase of the current is shifted from the phase of the voltage, based on the phase of the current detected by the first detection unit and the phase of the voltage detected by the second detection unit.

[0065] The determination unit determines, in accordance with the phase shift determined by the determination unit, a phase that will result in a power factor deterioration effect as a short-circuit mode phase (short-circuit phase) when the short-circuit mode is executed for the phase shift. The short-circuit phase is determined so that the phase shift caused by executing the short-circuit mode will result in a power factor deterioration effect.

[0066] The control unit executes power control based on the short-circuit phase determined by the determination unit and the duty of the short-circuit mode.

[0067] 12 is a flowchart showing the power control flow. The control shown in FIG.

[0068] The control device 26 detects the phase of the current on the input side of the rectifier 23 (step S1). In step S1, the first detection unit detects the phase of the current flowing into the rectifier 23 in real time based on the signal input from the current sensor 24 to the control device 26.

[0069] Control device 26 detects the phase of the voltage on the input side of rectifier 23 (step S2). In step S2, based on the signal input from voltage sensor 25 to control device 26, the second detection unit detects the phase of the voltage input to rectifier 23 in real time.

[0070] Based on the phase of the current detected by the first detector and the phase of the voltage detected by the second detector, the control device 26 determines whether the phase of the current lags behind the phase of the voltage in the rectifier 23 (step S3). In step S3, the determination unit determines whether the phase of the current lags behind the phase of the voltage.

[0071] If rectifier 23 determines that the current phase lags the voltage phase (step S3: Yes), control device 26 determines the short-circuit phase so as to reduce the right side (phase-lag side) of the voltage square wave more (step S4). In step S4, the determination unit determines the short-circuit phase to be a switching timing that reduces the right side (phase-lag side) of the voltage square wave more, within a range in which the power factor deterioration effect due to the phase shift can be obtained. The control unit of control device 26 executes the short-circuit mode based on the short-circuit phase determined in the processing of step S4.

[0072] As shown in Figure 13, the control device 26 performs power control to reduce the right side of the voltage square wave. As a result, the voltage fundamental wave undergoes a phase shift in the direction that increases the phase difference with the current fundamental. In other words, the voltage fundamental wave shifts in the direction that worsens the power factor of the received power.

[0073] If it is determined that the phase of the current in rectifier 23 does not lag behind the phase of the voltage (step S3: No), control device 26 determines whether the phase of the current in rectifier 23 leads the phase of the voltage (step S5). In step S5, the determination unit determines whether the phase of the current leads the phase of the voltage.

[0074] If it is determined that the phase of the current in rectifier 23 leads the phase of the voltage (step S5: Yes), control device 26 determines the short-circuit phase so as to reduce the left side (phase lead side) of the voltage rectangular wave more (step S6). In step S6, the determination unit determines the short-circuit phase to be a switching timing that reduces the left side (phase lead side) of the voltage rectangular wave more, within a range in which the power factor deterioration effect due to the phase shift can be obtained. Then, the control unit of control device 26 executes the short-circuit mode based on the short-circuit phase determined in the processing of step S6.

[0075] As shown in Figure 14, the control device 26 performs power control to reduce the left side of the voltage square wave. As a result, the voltage fundamental wave undergoes a phase shift in the direction that increases the phase difference with the current fundamental. In other words, the voltage fundamental wave shifts in the direction that worsens the power factor of the received power.

[0076] If it is determined that the current phase in rectifier 23 does not lead the voltage phase (step S5: No), control device 26 determines that the current phase and the voltage phase are in phase and determines the short-circuit phase so as to symmetrically cut the voltage rectangular wave (step S7). In step S7, the determination unit determines the short-circuit phase to be a switching timing that symmetrically cuts both the left and right sides of the voltage rectangular wave so as not to produce a power factor improvement effect due to phase shift. Then, the control unit of control device 26 executes the short-circuit mode based on the short-circuit phase determined in the processing of step S7.

[0077] 15, the control device 26 performs power control to reduce the left and right sides of the voltage square wave symmetrically, resulting in no phase shift in the voltage fundamental wave and no power factor improvement effect.

[0078] As described above, according to the embodiment, it is possible to suppress an unintended increase in power when performing power control using a switching element provided in the power receiving device 20. This makes it possible to protect the load on the power receiving side when performing contactless charging.

[0079] Alternatively, the current sensor 24 may detect the phase of the current and output the detection signal to the control device 26. The control device 26 obtains information relating to the phase of the current contained in the signal from the current sensor 24.

[0080] Furthermore, there are no particular limitations on the locations where current sensor 24 and voltage sensor 25 are installed. For example, control device 26 can estimate the current flowing through rectifier 23 and the voltage applied to rectifier 23. In other words, control device 26 only needs to be able to acquire current value information that allows it to estimate the current flowing through rectifier 23, and there are no particular limitations on the location where current sensor 24 is connected. Similarly, there are no particular limitations on the location where voltage sensor 25 is connected, and there is no particular limitation on the location where control device 26 only needs to acquire voltage information that allows it to estimate the voltage applied to rectifier 23.

[0081] Furthermore, switching elements do not have to be connected in parallel to all diodes in the rectifier 23. For example, when switching elements are connected in parallel to the diodes D21 and D23 in the rectifier 23, switching elements do not have to be connected in parallel to the diodes D22 and D24 in the rectifier 23. Similarly, when switching elements are connected in parallel to the diodes D22 and D24 in the rectifier 23, switching elements do not have to be connected in parallel to the diodes D21 and D23 in the rectifier 23.

[0082] Furthermore, in the contactless power transfer system 1 in which the power transmitting device 10 is installed on the ground and the power receiving device 20 is mounted on the vehicle 100, contactless charging can be performed not only while the vehicle 100 is moving, but also while the vehicle 100 is stopped. In other words, the mechanism by which the formation of a short circuit by the rectifier 23 causes an increase in received power applies not only to power supply while the vehicle is moving, but also to power supply while the vehicle is stopped. Therefore, when the vehicle 100 receives power contactlessly from the power transmitting device 10 on the ground while stopped, the control device 26 can control the switching elements of the rectifier 23 to execute the short-circuit mode. In this case, the control device 26 can determine the switching timing in the short-circuit mode so as to generate a phase shift in a direction that deteriorates the power factor of the received power.

[0083] Furthermore, the control device 26 is not limited to shaving only the left side of the voltage rectangular wave or shaving only the right side of the voltage rectangular wave when switching the switching elements in the short-circuit mode. In other words, the control device 26 can set the short-circuit phase so that the left side of the voltage rectangular wave is shaved more than the right side, and can also set the short-circuit phase so that the right side of the voltage rectangular wave is shaved more than the left side. When the current phase lags the voltage phase, the control device 26 can determine the switching timing of the switching elements of the rectifier 23 so that the right side of the voltage rectangular wave is shaved more than the left side. When the current phase leads the voltage phase, the control device 26 can determine the switching timing of the switching elements of the rectifier 23 so that the left side of the voltage rectangular wave is shaved more than the right side. [Explanation of symbols]

[0084] 1. Contactless power transmission system 10 Power transmission equipment 11 DC power supply 12 inverters 13 Filter Circuit 14 Power transmission side resonant circuit 20 Power receiving device 21 Receiving side resonant circuit 22 Filter Circuit 23 Rectifier 24 Current Sensor 25 Voltage Sensor 26 Control device 100 vehicles L10 transmitting coil L20 receiving coil D21, D22, D23, D24 diodes SW21, SW22, SW23, SW24 switching elements

Claims

1. a receiving coil that receives power transmitted contactlessly from the transmitting coil; a control device that executes a short-circuit mode in which a switching element provided between the power receiving coil and a load is switched on and off to short-circuit the output terminals of the power receiving coil; In a power receiving device comprising: When the phase of the current and the phase of the voltage in the power receiving device are out of phase, the control device determines the switching timing of the switching element in the short-circuit mode so that the phase of the voltage is shifted in a direction that deteriorates the power factor of the power supplied to the load in the short-circuit mode. A power receiving device characterized by:

2. The control device determining a switching timing of the switching element in the short-circuit mode so that the right side of the voltage rectangular wave is more significantly reduced than the left side when the phase of the current lags behind the phase of the voltage; When the phase of the current leads the phase of the voltage, the switching timing of the switching element in the short-circuit mode is determined so that the left side of the voltage rectangular wave is reduced more than the right side. The power receiving device according to claim 1 .

3. When the current and the voltage are not out of phase with each other, the control device determines the switching timing of the switching element in the short-circuit mode so as to symmetrically cut off the voltage rectangular wave. The power receiving device according to claim 2 .

4. A power receiving device comprising: the power receiving device according to any one of claims 1 to 3; and a power transmitting device having the power transmitting coil. A contactless power transmission system.

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