Patent ID: 12191676

DESCRIPTION OF SPECIFIC EMBODIMENTS

In the above known power receiving device, as disclosed in JP-A-2008-259419, the supplied power varies in accordance with the load connected to the power receiving device. Therefore, the power receiving device includes a boost chopper circuit as a voltage control means for making the supplied power constant voltage. The on-duty ratio of the switch of the boost chopper circuit is controlled to control the output voltage to the load side.

When a large amount of power is transmitted or received, such as when power is supplied to an automobile in a contactless manner, the switching loss at the time of turning on and off the booster chopper circuit tends to be large. Conventionally, the driving frequency of the switch has been made to coincide with the frequency of the received power, but it is conceivable to lower the driving frequency in order to reduce the switching loss. However, if the driving frequency is different from the frequency of the received power, the output power of the boost chopper circuit may pulsate. Pulsation in the output power is undesirable because deterioration of the load accelerates, or components for preventing pulsation must be added.

In view of the foregoing, it is desired to have a power receiving device capable of suppressing pulsation of output power while reducing loss even when large power is transmitted and received.

One aspect of the present disclosure provides a power receiving device that receives power from a power transmitting device including a primary coil in a contactless manner and supplies power to a power storage device, the power transmitting device including: a secondary coil that receives AC power of a predetermined frequency from the primary coil; a capacitor connected to the secondary coil and constituting a resonant circuit together with the secondary coil; a rectifier circuit that rectifies output power from the resonant circuit; a power conditioning circuit that is disposed between the power storage device and the rectifier circuit and includes a switch; and a control device that controls the switch using a predetermined driving frequency, wherein the driving frequency is a frequency obtained by dividing the predetermined frequency of the AC power by a natural number equal to or greater than 2.

The secondary coil receives AC power of the predetermined frequency from the primary coil. The power supplied to the storage battery is then conditioned by turning on and off the switch of the power conditioning circuit. The driving frequency of the switch is set to a frequency obtained by dividing the predetermined frequency of the received AC power by a natural number equal to or greater than 2. By setting the of the driving frequency to a frequency obtained by dividing the predetermined frequency of the AC power by a natural number, the power input to the power conditioning circuit can always be switched in the same phase, and pulsation of the power supplied to the power storage device can be suppressed. By using a natural number N equal to or greater than 2, the driving frequency can be lowered, and switching loss can be reduced.

Embodiments

The present embodiment is directed to a power receiving device mounted on a vehicle.FIG.1is a schematic configuration diagram of a contactless power transmission apparatus10according to the present embodiment. A vehicle15is, for example, an automobile driven by an electric vehicle drive device (drive motor or the like), such as an electric vehicle (EV) or a plug-in hybrid vehicle (PEV).

Power transmitting devices20perform, in a contactless state, power transmission (power supply) to a power receiving device30mounted on the vehicle15. The power transmitting devices20are installed on the ground G so as to be buried in the ground G or exposed from the ground G. The power transmitting devices20are installed, for example, in a road traveled by the vehicle15, and are buried in multiple rows along the traveling direction of the vehicle15. The power transmitting devices20transmit power while the vehicle15is traveling.

The power transmitting devices20each includes a primary coil21. The primary coil21is formed by winding a wire (for example, a litz wire) around a core, such as a ferrite core, in a planar shape, for example. The primary coil21is disposed such that its axis is orthogonal to the ground G, that is, the flat face of the wound primary coil21having a planar shape is parallel to the ground G.

The power receiving device30includes a secondary coil31, and the secondary coil31is attached to the vehicle body. More specifically, the secondary coil31is disposed on the vehicle bottom15a.The vehicle bottom15ais a portion forming the lower face of the vehicle15, such as the floor, the under cover, and the like that defines the compartment of the vehicle15.

The secondary coil31is formed by winding a wire (for example, a litz wire) around a core, such as a ferrite core, in a planar shape, for example. The secondary coil31is disposed such that its axis is orthogonal to the ground G, that is, the flat face of the wound secondary coil31having a planar shape is parallel to the ground G and faces parallel to the primary coil21.

The power received by the power receiving device30is supplied to a storage battery16. The storage battery16is, for example, a secondary battery (a lithium-ion battery, a nickel-metal hydride secondary battery, or the like). The storage battery16stores the power supplied from the power receiving device30and supplies the power to the vehicle drive device. Note that the storage battery16corresponds to a “power storage device.”

The power receiving device30is provided with an ECU50that is a control device for controlling the power receiving device30. The ECU50is an electronic control device including a microcomputer including a CPU, a ROM, a RAM, etc., and a peripheral circuit thereof. The ECU50receives the monitoring state of the SOC or the like of the storage battery16. Note that the ECU50may be disposed at the same position as the secondary coil31or the like, or the ECU50may be disposed at another position on the vehicle15.

FIG.2is an electrical circuit diagram of the contactless power transmission apparatus10. The contactless power transmission apparatus10includes a power transmitting device20and a power receiving device30. The power transmitting device20includes a power-transmission-side resonator23, a power-transmission-side filter circuit24, an inverter25, a converter26, and a power-transmission-side drive circuit27.

The power transmitting device20receives power from a power supply unit28. The power supply unit28is an AC power supply that receives power from a power network provided by an electric power company or the like. The power supply unit28supplies AC power of approximately 50 kHz at 3-phase 200 V or 400 V, for example.

The converter26is an AC-to-DC converter that converts the AC power supplied from the power supply unit28into DC power of predetermined voltage, and converts the AC power into DC power through, for example, a switching method. A switch of the converter26is driven by the power-transmission-side drive circuit27.

The inverter25converts the DC power supplied from the converter26into AC power having a predetermined frequency f0. The inverter25converts the DC current into AC current having a predetermined frequency f0by switching the switch. The switch of the inverter25is driven by the power-transmission-side drive circuit27.

It is desirable that the power-transmission-side filter circuit24be provided between the inverter25and the power-transmission-side resonator23. The power-transmission-side filter circuit24is a type of low-pass filter that cuts high-frequency components. In the power-transmission-side filter circuit24, a coil, a capacitor, and a coil are connected in a T-shape and act as an immittance filter.

The power-transmission-side resonator23is a resonant circuit connected in series to the primary coil21and a power-transmission-side capacitor22. When the power-transmission-side resonator23resonates with the input AC power having the predetermined frequency f0, the power-transmission-side resonator23transmits the power to a power-reception-side resonator33.

The power receiving device30includes the power-reception-side resonator33, a power-reception-side filter circuit34, a rectifier circuit35, a power conditioning circuit40, and the ECU50. The power receiving device30supplies power to the storage battery16.

The power-reception-side resonator33is a resonant circuit connected in series to the secondary coil31and a power-reception-side capacitor32. It is desirable that the power-transmission-side resonator23and the power-reception-side resonator33be configured by a series-series (S-S) system. The power-reception-side resonator33is conditioned so as to establish magnetic field resonance with the power-transmission-side resonator23. Specifically, it is desirable that the resonant frequency of the power-reception-side resonator33coincide with the resonant frequency of the power-transmission-side resonator23.

When AC power having the predetermined frequency f0is input from the inverter25in a state in which the power transmitting device20and the power receiving device30are relatively positioned such that magnetic field resonance is established, the power-transmission-side resonator23(the primary coil21) and the power-reception-side resonator33(the secondary coil31) establish magnetic-field resonance. Consequently, the power-reception-side resonator33receives AC power from the power-transmission-side resonator23. Note that the predetermined frequency f0of the AC power input from the inverter25is preferably a frequency that allows power transmission between the power-transmission-side resonator23and the power-reception-side resonator33. Specifically, it is desirable that the predetermined frequency f0of the AC power generated by the inverter25be set to the resonant frequency of the power-transmission-side resonator23and the power-reception-side resonator33.

The power-reception-side filter circuit34is disposed between the power-reception-side resonator33and the rectifier circuit35. The power-reception-side filter circuit34has the same configuration as that of the power-transmission-side filter circuit24. The power-reception-side filter circuit34is a type of low-pass filter that cuts high-frequency components. In the power-reception-side filter circuit34, a coil, a capacitor, and a coil are connected in a T-shape.

By designing the resonant frequency of the power-reception-side filter circuit34based on the predetermined frequency f0, the power-reception-side filter circuit34acts as an immittance filter. The immittance filter (the power-reception-side filter circuit34) is an impedance-to-admittance converter, and is configured so that the impedance in view from the input end of the immittance filter is proportional to the admittance of the load connected to the output end. In the case where the power input to the immittance filter (the power-reception-side filter circuit34) is constant voltage, the power output from the immittance filter is converted into constant current.

The rectifier circuit35has a known configuration for converting AC power into DC power. The rectifier circuit35is composed of, for example, a diode bridge circuit consisting of four diodes. The power output from the rectifier circuit35is the power obtained through full-wave rectification of the AC power.

The output power from the rectifier circuit35is input to the power conditioning circuit40for conditioning the power supplied to the storage battery16. The power conditioning circuit40includes a switch41, a diode42, and a capacitor43. The power conditioning circuit40is a chopper circuit that can energize the storage battery16from the secondary coil31side by turning off the switch41. The switch41is a semiconductor switching element, such as a MOSFET, and is driven by a power-reception-side drive circuit45. The switch41is turned on and off to condition the power level flowing toward the storage battery16. The voltage output from the power conditioning circuit40depends on the battery voltage of the storage battery16.

The power-reception-side drive circuit45performs on-off control of the switch41at a driving frequency f1on the basis of a command from the ECU50. The switch41is controlled by PWM control in which the time of the on-state is controlled predetermined periods, and the output power is conditioned by controlling the on time (on-duty) of the switch41in constant periods.

When a large amount of power is received, such as when power is supplied from the power transmitting device20to the power receiving device30of the vehicle15, and the power to be supplied to PW the storage battery16is conditioned by the power conditioning circuit40, the switching loss at the time of turning on and off the switch41tends to be large. Conventionally, the driving frequency of the switch41has been made to coincide with the frequency of the received power, but it is conceivable to lower the driving frequency of the switch41in order to reduce the switching loss.

FIG.3is a diagram illustrating an example of the power output from the rectifier circuit35when the driving frequency is set not according to the present embodiment. The dashed line inFIG.3indicates the output power from the rectifier circuit35that is obtained by superimposing a frequency component of 170 kHz, which is f0×2, on a predetermined DC power when the predetermined frequency f0is, for example, 85 kHz. The solid line inFIG.3indicates the output passing through the switch41when the switch41is turned on and off at the driving frequency in the comparative example, for example, 30 kHz. Note that, the output waveform of the rectifier circuit35, which performs full-wave rectification, has a frequency component of twice the predetermined frequency f0or f0×2. The rectifier circuit may be a half-wave rectifier circuit, and in such a case, the output waveform from the rectifier circuit has a frequency component of the predetermined frequency f0.

When switching is performed at a frequency unrelated to the predetermined frequency f0as in the driving frequency of the comparative example, the output phase of the rectifier circuit35at the switching timing will be different each time, and the output power will also be different for each switching. Therefore, the output power of the power conditioning circuit40pulsates, as illustrated inFIG.4.FIG.4is a diagram illustrating the waveform of the output power from the power conditioning circuit40to the storage battery16in the comparative example. In the comparative example, pulsation constantly occurs. Such pulsation occurring in the power supplied to the storage battery16is undesirable because deterioration of the storage battery16is accelerated, and components for the purpose of pulsation prevention must be added.

Therefore, in the present embodiment, the driving frequency f1of the switch41is made to be a frequency obtained by dividing the predetermined frequency f0of the received AC power by a natural number N equal to or greater than two.FIG.5is a diagram illustrating the relationship between the output power of the rectifier circuit35and the driving frequency f1in the present embodiment. The dashed line inFIG.5indicates the output power from the rectifier circuit35that is obtained by superimposing a frequency component of a predetermined frequency f0×2, for example, 170 kHz, on a predetermined DC power. The solid line inFIG.5indicates the output passing through the switch41when the switch41is turned on and off at the driving frequency f1in the present embodiment, for example, 28.33 kHz, which is obtained by dividing the predetermined frequency f0(85 kHz) by 3.

When switching is performed at the driving frequency f1obtained by dividing the predetermined frequency f0by a natural number N, as the driving frequency f1in the present embodiment, the output phase of the rectifier circuit35at the switching timing is the same every time, and the output power is also the same every time. Therefore, the switching loss can be reduced without pulsation occurring in the output power of the power conditioning circuit40.FIG.6is a diagram illustrating the waveform of the output power from the power conditioning circuit40to the storage battery16in the present embodiment. In the present embodiment, pulsation does not occur. Also, the switching loss can be suppressed to about ⅓ in comparison with that in the case where the driving frequency is set to the same value as the predetermined frequency f0as in the past.

Note that in the present embodiment, an inductor for energy storage is not provided between the switch41of the power conditioning circuit40and the rectifier circuit35, and thus no loss is caused by lowering the driving frequency f1. The power conditioning circuit40according to the present embodiment is a so-called boost chopper circuit that does not include an inductor for energy storage. When a boost chopper circuit is used, the power input to the switch41must be constant current, but since the input power is generally constant voltage, an inductor is provided in front of the switch41. However, when an inductor is provided in front of the switch41, loss occurs in the inductor as a result of a decrease in the driving frequency f1.

In order to further reduce loss, it is desirable that the power conditioning circuit40does not include an inductor. Accordingly, in the present embodiment, the power-transmission-side resonator23and the power-reception-side resonator33are configured by an S-S system, and the power-reception-side filter circuit34acting as an immittance filter is provided so that constant current is output from the rectifier circuit35. Therefore, it is not necessary to provide an inductor for energy storage between the switch41of the power conditioning circuit40and the rectifier circuit35, and no inductor is provided between the switch41and the rectifier circuit35. Consequently, no loss occurs in the inductor due to the lowering of the driving frequency f1of the switch41, and the loss can be further suppressed by lowering the driving frequency f1.

By lowing the driving frequency f1of the switch41, the switching loss can be reduced, but the controllability of the fluctuation of the received AC power is lowered. In particular, when contactless power supply is performed while the vehicle15is traveling, the received power fluctuates due to various factors. A drop in controllability is undesirable because a drop in controllability leads to fluctuation in power supplied to the storage battery16due to fluctuation in the received power.

Accordingly, the driving frequency f1of the switch41is set to a frequency obtained by dividing the predetermined frequency f0by a natural number N within the range of 2 to 10. Preferably, the natural number N is within the range of 2 to 5. In this range, the controllability of the power conditioning by the power conditioning circuit40can be maintained while the switching loss is reduced.

In order to calculate the driving frequency f1, the natural number N dividing the predetermined frequency f0may be variable. In some cases, it may not be necessary to increase the controllability of the switch41. For example, when the fluctuation of the received power is small, such as when the vehicle15is stopped or when the fluctuation of the output from the storage battery16is small, the controllability does not have to be increased. Accordingly, when the fluctuation of the received power in the secondary coil31is small, the natural number N is made larger than that of when the fluctuation of the received power is large.

FIG.7is a flowchart for setting a driving frequency f1when the driving frequency f1is variable. This process is performed by the ECU50in predetermined cycles.

In step S11, the stability of the received power in the secondary coil31is estimated. The received power fluctuates when the distance between the primary coil21and the secondary coil31changes, for example, due to a change in the vehicle height or the like while the vehicle15is traveling. The received power also fluctuates when the SOC of the storage battery16changes. The SOC of the storage battery16is likely to change while the vehicle15is traveling, particularly while accelerating. Accordingly, the stability of the received power is estimated on the basis of the traveling state, etc., of the vehicle15. For example, in a state where the speed change of the vehicle15is large, the fluctuation of the received power is estimated to be large and the stability is estimated to be small, while in a state where the speed change of the vehicle15is small or in a state where the vehicle is stopped, the fluctuation of the received power is estimated to be small and the stability is estimated to be large. More specifically, if the vehicle speed change rate (i.e., acceleration) is equal to or greater than a predetermined value, the stability is estimated to be small, and if it is equal to or less than the predetermined value, the stability is determined to be large.

In step S12, the driving frequency f1is set on the basis of the stability of the received power. If the fluctuation of the received power is estimated to be small, the natural number N for dividing the predetermined frequency f0is increased. For example, the driving frequency f1is decreased to a value obtained by dividing the predetermined frequency f0by 5. On the other hand, if the fluctuation of the received power is estimated to be large, the natural number N for dividing the predetermined frequency f0is decreased. For example, the driving frequency f1is increased to a value obtained by dividing the predetermined frequency f0by 2. The power-reception-side drive circuit45is then controlled by the calculated driving frequency f1. Consequently, if the controllability does not need to be improved, switching loss can be further suppressed by lowering the driving frequency f1.

In the above-described embodiment, the following effects are achieved.

The secondary coil31receives AC power of the predetermined frequency f0from the primary coil21. The power supplied to the storage battery16is then conditioned by turning on and off the switch41of the power conditioning circuit40. The driving frequency f1of the switch41is then set to a frequency obtained by dividing the predetermined frequency f0of the received AC power by a natural number N equal to or greater than 2. By setting the driving frequency f1to the frequency obtained by dividing the predetermined frequency f0of the AC power by the natural number N, the power input to the power conditioning circuit40can always be switched in the same phase, and pulsation of the power supplied to the storage battery16can be suppressed. By using a natural number N equal to or greater than 2, the driving frequency f1can be lowered, and switching loss can be reduced.

By lowing the driving frequency f1of the switch41, the switching loss can be reduced, but the controllability of the fluctuation of the AC power received by the secondary coil31is lowered. Lowering of the controllability is particularly undesirable when contactless power supply is performed while the vehicle15is traveling because the received power fluctuates due to various factors. Therefore, the driving frequency f1of the switch41is set to a frequency obtained by dividing the predetermined frequency f0of the AC power received by the secondary coil31by a natural number N within the range of 2 to 10. Consequently, controllability can be maintained while switching loss is reduced.

In the present embodiment, a chopper circuit is used as the power conditioning circuit40. For example, in the case where a boost chopper circuit is used, the input power must be constant current, but usually the input power is constant voltage. Therefore, power is conditioned by providing an inductor between the boost chopper circuit and the switch41to store the energy of the input power. However, in the case where an inductor is provided in the power conditioning circuit40, lowering of the driving frequency f1of the switch41causes loss in the inductor.

Accordingly, in the present embodiment, the power-transmission-side resonator23and the power-reception-side resonator33are configured by an S-S system, and the power-reception-side filter circuit34acting as an immittance filter is provided so that constant current is output from the rectifier circuit35. An inductor for energy storage is not provided between the rectifier circuit35and the switch41. Consequently, no loss occurs in the inductor due to the lowering of the driving frequency f1of the switch41, and the loss can be further suppressed by lowering the driving frequency f1.

The driving frequency f1relates to the controllability of the power supplied to the storage battery16, but in some cases, there is no need to increase the controllability of the power supplied to the storage battery16. For example, when the fluctuation of the received power is small, such as when the vehicle15is stopped or when the fluctuation of the output from the storage battery16is small, the controllability does not have to be increased. Accordingly, when the natural number N, i.e., the driving frequency f1, is variable, and the fluctuation of the received power in the secondary coil31is small, the natural number N for division is made larger than that of when the fluctuation of the received power is large. That is, when the fluctuation in the received power is small in the secondary coil31, the driving frequency f1of the switch41is lowered. Consequently, when it is not necessary to increase controllability, loss can be further suppressed by lowering the driving frequency f1.

Other Embodiments

The disclosure is not limited to the above-described embodiment, and, for example, may be implemented as follows.

The primary coil21and the secondary coil31may be multi-phased. For example, the primary coil21and the secondary coil31may be multi-phased into three phases, as illustrated inFIG.8. When the primary coil21and the secondary coil31are multi-phased, the inverter25, the power-transmission-side filter circuit24, the power-reception-side filter circuit34, and the rectifier circuit35are also multi-phased in accordance with the number of phases.

The configuration of the power conditioning circuit40for conditioning the output from the rectifier circuit35is the same even in the case of multi-phase power. Note that in the case of three-phase power, the output power from the rectifier circuit35has a frequency component of the predetermined frequency f0×3 in the predetermined DC power. In such a case, also, the driving frequency f1of the switch41can be set to a value obtained by dividing the predetermined frequency f0by a natural number N, to switch the power input to the power conditioning circuit40always in the same phase, and reduce switching loss while pulsation is suppressed.

The ECU50or microcomputer may detect the frequency of the AC power received by the secondary coil31, and the driving frequency f1may be controlled to a value obtained by dividing the detected frequency by a natural number N equal to or greater than 2. In general, the frequency on the transmission side is maintained constant by the inverter25. However, in rare cases, unexpected fluctuation may occur in the frequency of the AC power generated by the inverter25, or the frequency of the AC power generated by the inverter25may not be known in advance. Therefore, a frequency counter function is provided by the ECU50, the microcomputer, or the like, and the frequency of the received AC power is detected. By detecting the frequency of the received AC power and setting the driving frequency f1on the basis of the detected frequency, loss can be reduced while pulsation is suppressed.

An immittance for energy storage may be provided between the rectifier circuit35and the switch41. When the driving frequency f1is lowered, loss occurs in the immittance, but such loss is smaller than switching loss. Even if an immittance is provided between the rectifier circuit35and the switch41, losses in the power receiving device30can be reduced.

The power receiving device30may be provided on the side of the vehicle15. In such a case, the power transmitting device20may be embedded in a guard rail or the like disposed on the side of the road.

While the disclosure has been described in accordance with the embodiments, it is understood that the disclosure is not limited to such embodiments or structures. The disclosure also encompasses various modifications and variations within the scope of equality. Furthermore, various combinations and modes, as well as other combinations and modes including only one element, more or less, thereof, are also within the scope and idea of the disclosure.