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 of a power transmission device in a non-contact manner; a rectifier circuit provided between the power reception coil and a load; a smoothing capacitor provided between the rectifier circuit and the load; and a control device that executes a short-circuit mode in which a plurality of switching elements provided in the smoothing capacitor are caused to perform switching operations to short-circuit between output terminals of the power reception coil. A control device includes an acquisition unit that acquires information indicating a drive frequency of an inverter provided in the power transmission device, a setting unit that sets a switching frequency of the rectifier circuit to a value different from the drive frequency of the inverter, and a control unit that executes the short-circuit mode on the basis of the switching frequency set by the setting unit.SELECTED DRAWING: Figure 13

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 is a power receiving device comprising: a receiving coil that receives power transmitted contactlessly from a power transmitting coil of a power transmitting device; a rectifier circuit provided between the receiving coil and a load; a smoothing capacitor provided between the rectifier circuit and the load; and a control device that executes a short-circuit mode that short-circuits the output terminals of the receiving coil by switching a switching element provided in the rectifier circuit, wherein the control device comprises: an acquisition unit that acquires information indicating the driving frequency of an inverter provided in the power transmitting device; a setting unit that sets the switching frequency of the rectifier circuit to a value different from the driving frequency of the inverter; and a control unit that executes the short-circuit mode based on the switching frequency set by the setting unit.

[0007] According to this configuration, by setting the switching frequency of the rectifier circuit to a value different from the drive frequency of the inverter on the power transmission side, it is possible to suppress an increase in power when a short circuit is formed by the operation of the switching element.

[0008] The switching frequency may be a value greater than the drive frequency, and may be a frequency that sweeps between 0 and 180°, gradually shifting the phase at which the short circuit mode occurs relative to the voltage square wave of the rectifier circuit.

[0009] With this configuration, the switching frequency is higher than the drive frequency, and the phase at which the short-circuit mode occurs gradually shifts, resulting in both power factor improvement and power factor deterioration due to the phase shift. This periodic fluctuation in power is smoothed by the smoothing capacitor, so the power supplied to the load ultimately decreases uniformly.

[0010] The switching frequency may be a value greater than the drive frequency, and may be a frequency at which the number of times the short circuit mode occurs per one cycle of the voltage square wave of the rectifier circuit is an odd number of times, 3 or more.

[0011] With this configuration, the switching frequency is higher than the drive frequency and occurs three or more times in one cycle of the voltage square wave, which reduces the amount of phase shift of the fundamental wave component, thereby suppressing the increase in power consumption due to the phase shift.

[0012] The control unit may also insert a plurality of the short circuit modes at equal intervals in one cycle of the voltage rectangular wave, and insert the short circuit modes at the same phase in each cycle of the voltage rectangular wave.

[0013] According to this configuration, even if the short circuit mode occurs at the same phase every time with respect to the voltage square wave, it is possible to suppress the increase in power.

[0014] 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.

[0015] According to this configuration, in a contactless power transmission system equipped with a power transmitting device and a power receiving device, by setting the switching frequency of the rectifier circuit to a value different from the driving frequency of the inverter on the power transmitting side, it is possible to suppress the increase in power when a short circuit is formed by the operation of the switching element. [Effects of the Invention]

[0016] In the present invention, by setting the switching frequency of the rectifier circuit to a value different from the drive frequency of the inverter on the power transmission side, it is possible to suppress an increase in power when a short circuit is formed by the operation of the switching element. [Brief explanation of the drawings]

[0017] [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 diagram for explaining the phase shift in which the short circuit mode occurs with respect to the voltage rectangular wave. [Figure 13] FIG. 13 is a diagram for explaining the phase in which the short-circuit mode occurs with respect to the voltage rectangular wave. [Figure 14] FIG. 14 is a diagram for explaining the decrease in received power. [Figure 15] FIG. 15 is a diagram for comparing the amount of phase shift that occurs when the short circuit mode occurs two times per cycle of the voltage rectangular wave with the amount of phase shift that occurs when the short circuit mode occurs three times per cycle. [Figure 16] FIG. 16 is a diagram showing the relationship between the number of times the short circuit mode occurs per one cycle of the voltage rectangular wave and the amount of phase shift of the fundamental wave component. [Figure 17]FIG. 17 is a diagram for explaining a case where the short circuit mode occurs twice in one cycle of the voltage rectangular wave. DETAILED DESCRIPTION OF THE INVENTION

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The power receiving device 20 includes a power receiving-side resonant circuit 21, a filter circuit 22, a rectifier 23, a smoothing capacitor C21, and a control device 24. The power receiving device 20 receives power from the power transmitting device 10 in a contactless manner.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 made up of an IGBT, and performs switching operation in response to a control signal from the control device 24.

[0030] 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.

[0031] The control device 24 is an electronic control device that controls the rectifier 23. Signals are input to the control device 24 from various sensors provided in the power receiving device 20. The control device 24 then executes various controls based on the signals input from the various sensors.

[0032] For example, the control device 24 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 24 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 24 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 feedback path via the diode D21, the battery 30, and the diode D24, as shown by the arrow in FIG. 2. The current of the battery 30 may also be referred to as the 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 feedback path via the diode D21 and the switching element SW23, as shown by the arrow in FIG. 3.

[0036] The control device 24 executes the short-circuit mode, thereby reducing the amount of power supplied to the battery 30. The control device 24 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 24 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 24 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 24 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 24 executes power control during contactless charging, thereby suppressing an increase in power of the battery 30 and protecting the battery 30.

[0040] For example, if 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 24 performs power control to reduce the power received by contactless charging. In other words, the control device 24 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 performed during contactless charging, the current of the battery 30 (battery current) will increase beyond the upper limit and will increase naturally, causing the received power of the battery 30 to increase naturally. If power control is performed during contactless charging to avoid this, the control device 24 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 24 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 along 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 wave component of the current and the fundamental wave 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·V·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, when performing power control to form a short circuit during contactless charging, in order to suppress an increase in power due to switching, control device 24 controls the switching frequency of rectifier 23 to a value different from the drive frequency of inverter 12. Control device 24 acquires information indicating the drive frequency of inverter 12 on the power transmission side in advance, and intentionally sets the switching frequency to a value different from the drive frequency.

[0062] Specifically, the control device 24 includes an acquisition unit that acquires the drive frequency of the inverter 12, a setting unit that sets the switching frequency of the rectifier 23 in the short-circuit mode, and a control unit that performs power control according to the switching frequency.

[0063] The acquisition unit acquires information indicating the drive frequency of the inverter 12. The power receiving device 20 includes a communication unit that performs wireless communication with the infrastructure. The communication unit receives information about the power transmitting device 10 through wireless communication with the infrastructure. The received information about the power transmitting device 10 includes information indicating the drive frequency of the inverter 12. The control device 24 can know the drive frequency of the inverter 12 before performing power control by using the received information indicating the drive frequency of the inverter 12. The acquisition unit acquires information indicating the drive frequency of the inverter 12 before the control unit performs power control.

[0064] The setting unit sets the switching frequency of the rectifier 23 in the short-circuit mode to a value different from the drive frequency based on the drive frequency of the inverter 12 acquired by the acquisition unit. The control device 24 does not control the switching frequency to be the same as the drive frequency in power control, but intentionally controls the switching frequency to be a value different from the drive frequency. For example, the setting unit sets the switching frequency of the rectifier 23 to a value higher than the drive frequency of the inverter 12.

[0065] More specifically, the setting unit sets the switching frequency to a frequency at which the short circuit mode occurs twice per cycle of the voltage square wave. The switching frequency can be determined by the number of times the short circuit mode occurs per cycle of the voltage square wave. The switching frequency is greater than the drive frequency and, as shown in FIG. 12, is a frequency at which the phase (switching timing) at which the short circuit mode occurs gradually shifts relative to the voltage square wave of the rectifier 23 and sweeps between 0 and 180°. In the example shown in FIG. 12, the phase at which the short circuit mode occurs sweeps between 0 and 180° over nine cycles of the voltage square wave. In this way, the control device 24 can set the switching frequency to a value greater than an integer multiple of the drive frequency of the inverter 12. In the example shown in FIG. 12, the switching frequency is greater than twice the drive frequency of the inverter 12. Note that the portion of the voltage square wave shown in FIG. 12 enclosed by the dashed line is enlarged in FIG. 13.

[0066] As shown in Figure 13, the short-circuit mode occurs when the switching element SW23 of the rectifier 23 switches from an OFF state to an ON state. The switching frequency is set so that the short-circuit mode occurs twice per cycle T1 of the rectangular voltage wave of the rectifier 23. In other words, the switching cycle T2 is shorter than one cycle T1 of the rectangular voltage wave and longer than half the cycle T1 / 2 of the rectangular voltage wave. In other words, the switching frequency is higher than the drive frequency of the inverter 12 and lower than twice the drive frequency of the inverter 12. Therefore, the phase at which the short-circuit mode occurs gradually shifts relative to the rectangular voltage wave of the rectifier 23.

[0067] The control unit executes power control based on the switching frequency set by the setting unit. As the power control, the control unit executes control such that the phase at which the short circuit mode occurs is gradually shifted relative to the voltage square wave excited in the rectifier 23, as shown in Figs. 12 and 13 .

[0068] When the control device 24 executes power control, the timing at which the short circuit mode enters gradually shifts relative to the voltage square wave of the rectifier 23. The frequency of the voltage square wave excited in the rectifier 23 is set to the same value as the drive frequency of the inverter 12. The voltage square wave of the rectifier 23 is a wave synchronized with the drive frequency of the inverter 12. In response to this, the control device 24 performs switching control of the rectifier 23 at a frequency higher than the drive frequency, gradually shifting the phase at which the short circuit mode enters relative to the voltage square wave, and finally completing a full cycle.

[0069] Furthermore, when the control device 24 executes power control, the phase in which the short circuit mode is initiated passes through both a region that improves the phase shift between the current and voltage and a region that worsens the phase shift between the current and voltage, resulting in alternating power increases and decreases. As the phase in which the short circuit mode is initiated cycles through the range from 0 to 180°, power decreases and increases are periodically repeated. Furthermore, the smoothing capacitor C21, located immediately before the battery 30, averages out the alternating power increases and decreases. As a result, the power increases and decreases due to the improvement and worsening of the phase shift are canceled out. That is, the power fluctuations due to the short circuit mode phase are canceled out over time, and the amplitude of the fundamental wave component is reduced. Therefore, as shown in FIG. 14, the power supplied to the battery 30 is ultimately uniformly reduced. Thus, ultimately, only the reduction in the amplitude of the voltage fundamental wave and the resulting power reduction—the original purpose of the short circuit mode—remains.

[0070] As described above, according to the embodiment, when power control is performed using a switching element provided in the power receiving device 20, the switching frequency is set to a value different from the drive frequency, so that the timing at which the short-circuit mode is entered gradually shifts with respect to the voltage square wave of the rectifier 23. This makes it possible to prevent an unintended increase in power during power control. As a result, it is possible to protect the load on the power receiving side when performing contactless charging.

[0071] Furthermore, the phenomenon of increased power consumption due to the short circuit mode can be eliminated without using a costly and low-robust method such as adding a sensor for precisely managing the phase of the short circuit mode.

[0072] It should be noted that the rectifier 23 does not require that switching elements be connected in parallel to all diodes. For example, when the rectifier 23 has switching elements connected in parallel to the diodes D21 and D23, it does not require that switching elements be connected in parallel to the diodes D22 and D24. Similarly, when the rectifier 23 has switching elements connected in parallel to the diodes D22 and D24, it does not require that switching elements be connected in parallel to the diodes D21 and D23.

[0073] 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 is applicable 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 24 can control the switching element of the rectifier 23 to execute the short-circuit mode.

[0074] Furthermore, although the configuration in which the communication unit of the power receiving device 20 communicates wirelessly with the infrastructure has been described, the present invention is not limited to this. For example, the power receiving device 20 can communicate wirelessly with an external server. Alternatively, the power receiving device 20 can communicate wirelessly with the power transmitting device 10. There is no particular limitation on the method for acquiring in advance the information indicating the drive frequency of the inverter 12 on the power transmitting side.

[0075] As a modification of the embodiment, it is possible to configure the control device 24 so that the short-circuit mode is entered at the same phase with respect to the voltage square wave every time. Here, a modification of the control device 24 will be described.

[0076] The control device 24 of the modified example sets the number of times the short circuit mode is applied to the voltage rectangular wave to an odd number equal to or greater than 3. Furthermore, the control device 24 applies a plurality of short circuit modes at equal intervals for one cycle of the voltage rectangular wave, and applies the short circuit mode at the same phase for each cycle of the voltage rectangular wave.

[0077] Specifically, the setting unit sets the switching frequency to a frequency at which the short circuit mode occurs an odd number of times (three or more) per cycle (two waves) of the voltage square wave. When performing power control, the control unit controls the short circuit mode so that it occurs periodically, i.e., at equal intervals, with respect to the voltage square wave. In this case, the short circuit mode occurs an odd number of times (three or more) per cycle of the voltage square wave. To compare an odd number of times (three or more) with an even number of times, Figure 15 shows voltage waveforms when the short circuit mode occurs two times (N=2) and when the short circuit mode occurs three times (N=3). Note that N represents the number of times the short circuit mode is initiated per cycle of the voltage square wave. In other words, N represents the number of times the short circuit phase is set within one cycle of the voltage square wave.

[0078] As shown in Figure 15, when the short circuit mode occurs twice (N=2), the short circuit mode occurs at a position shifted to the left relative to one wave of the voltage square wave, resulting in a total of two short circuit modes occurring per cycle (two waves) of the voltage square wave. When the short circuit mode is shifted to the left, a phase shift of Δθ2 occurs, pushing the fundamental wave component of the voltage waveform to the right. Also, when the short circuit mode occurs twice (N=2), the short circuit mode may occur at a position shifted to the right relative to one wave of the voltage square wave, as shown in Figure 11. When the short circuit mode is shifted to the right, a phase shift occurs, pushing the fundamental wave component of the voltage to the left. In other words, when the number of short circuit modes occurring per cycle of the voltage square wave is even, the thinning position (short circuit mode period) is shifted to either the left or right. The same is true for an even number of times greater than two, i.e., an even number greater than four.

[0079] If the phase shift direction is such that the phase difference between the current fundamental wave and the voltage fundamental wave is reduced, the power factor of the received power will improve, ultimately leading to an increase in power. On the other hand, if the phase shift direction is such that the phase difference between the current fundamental wave and the voltage fundamental wave is increased, the power factor of the received power will deteriorate, resulting in a decrease in power. In other words, even if the phase shift of the voltage fundamental wave occurs in a direction that improves the power factor, the increase in power can be suppressed by reducing the amount of phase shift.

[0080] When the short circuit mode occurs three times (N=3), the short circuit mode occurs three times per cycle (two waves) of the voltage square wave, and is located on the left, center, and right sides of the voltage square wave. When the short circuit mode occurs three times, the short circuit mode occurs in more dispersed positions to the left and right than when the short circuit mode occurs twice. A phase shift of Δθ3 occurs, pushing the fundamental wave component of the voltage waveform to the right. The phase shift Δθ3 when the short circuit mode occurs three times is smaller than the phase shift Δθ2 when the short circuit mode occurs twice. This suppresses the amount of phase shift of the voltage fundamental wave pushed to the left and right. As a result, power factor improvement and power increase due to the phase shift are less likely to occur.

[0081] Fig. 16 is a diagram showing the relationship between the amount of phase shift of the fundamental wave component and the number of times the short circuit mode is entered. Note that N represents the number of times the short circuit mode is entered per one cycle (two waves) of the voltage square wave. Also, multiple points are plotted in Fig. 16, which show the results of entering the short circuit mode at different phases when the number of times the short circuit mode is entered is the same, as shown in Fig. 17.

[0082] As shown in Figure 16, when N = 2, the maximum phase shift of the voltage fundamental wave was approximately ±17 degrees. In contrast, when N = 3, the phase shift of the voltage fundamental wave was approximately ±5 degrees. Comparing the cases where the short circuit mode occurs two times and three times, the amount of phase shift can be significantly reduced when it occurs three times. This was also true for odd numbers of N greater than or equal to five, such as 5 or 7. In this way, when the number of occurrences is an odd number greater than or equal to three, the amount of phase shift of the voltage fundamental wave is reduced compared to when the number of occurrences is an even number.

[0083] According to this modification, by inserting the short circuit mode three, five, seven, or any other odd number of times during one cycle of the voltage square wave, the phase shift of the voltage fundamental wave can be reduced compared to when the short circuit mode is inserted twice, thereby suppressing the increase in power consumption due to the execution of the short circuit mode. [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 Control device 100 vehicles L10 transmitting coil L20 receiving coil D21, D22, D23, D24 diodes SW21, SW22, SW23, SW24 switching elements

Claims

1. a power receiving coil that receives power transmitted in a contactless manner from a power transmitting coil of a power transmitting device; a rectifier circuit provided between the receiving coil and a load; a smoothing capacitor provided between the rectifier circuit and the load; a control device that executes a short-circuit mode in which a switching element provided in the rectifier circuit is switched on and off to short-circuit the output terminals of the power receiving coil; In a power receiving device comprising: The control device an acquisition unit that acquires information indicating a drive frequency of an inverter provided in the power transmission device; a setting unit that sets a switching frequency of the rectifier circuit to a value different from a drive frequency of the inverter; a control unit that executes the short-circuit mode based on the switching frequency set by the setting unit; A power receiving device comprising:

2. The switching frequency is a value greater than the drive frequency, and the phase at which the short circuit mode occurs is gradually shifted relative to the voltage square wave of the rectifier circuit, sweeping between 0 and 180 degrees. The power receiving device according to claim 1 .

3. The switching frequency is a frequency that is greater than the drive frequency and that causes the number of times the short circuit mode occurs per one cycle of the voltage square wave of the rectifier circuit to be an odd number of times equal to or greater than 3. The power receiving device according to claim 1 .

4. The control unit inserts a plurality of the short circuit modes at equal intervals in one cycle of the voltage rectangular wave, and inserts the short circuit modes at the same phase in each cycle of the voltage rectangular wave. The power receiving device according to claim 3 .

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

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