Patent ID: 12206335

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, a power conversion apparatus according to an embodiment of the disclosure will be specifically described with reference to the accompanying drawings. The disclosure is not limited to the embodiment described below.

FIG.1is a circuit diagram that shows the power conversion apparatus according to the embodiment. The power conversion apparatus1is mounted on a vehicle Ve that is externally chargeable. The vehicle Ve is an electrified vehicle including a battery allowed to be charged with electric power supplied from an external source and a drive motor configured to be driven by using electric power from the battery. Examples of the vehicle Ve include a plug-in hybrid electric vehicle (PHEV) and a battery electric vehicle (BEV). The power conversion apparatus1is used to supply electric power from an alternating-current power supply, such as a commercial power supply and a domestic power supply, to a battery mounted on the vehicle Ve and to supply alternating-current power from the battery mounted on the vehicle Ve to an electrical apparatus outside the vehicle Ve. In other words, the power conversion apparatus1functions as a charger and an AC feeder.

The power conversion apparatus1supplies electric power among an external power supply2, a main battery3, and an auxiliary battery4. The external power supply2is an alternating-current power supply, such as a commercial power supply (system power supply) and a domestic power supply. The main battery3and the auxiliary battery4are direct-current power supplies mounted on the vehicle Ve. The main battery3is a secondary battery that stores electric power to be supplied to the drive motor. The main battery3supplies motoring electric power to the motor and is charged with electric power generated by regenerative braking with the motor. The auxiliary battery4is a secondary battery that is charged with electric power to be supplied to auxiliaries such as an audio device, a room light, and an air conditioner mounted on the vehicle Ve. The power conversion apparatus1supplies electric power, supplied from the external power supply2, to the main battery3and the auxiliary battery4. The power conversion apparatus1supplies electric power from the main battery3to the auxiliary battery4. In other words, the power conversion apparatus1functions as an auxiliary DC-DC converter in addition to the charger and the AC feeder.

The power conversion apparatus1includes a first switching circuit10, a second switching circuit20, a third switching circuit30, and a transformer40. The main battery3is connected to the second switching circuit20. The auxiliary battery4is connected to the third switching circuit30. When external charging is performed, the external power supply2is connected to the first switching circuit10as shown inFIG.1. The power conversion apparatus1transfers electric power via the transformer40among the external power supply2, the main battery3, and the auxiliary battery4.

The transformer40includes a first winding41, a second winding42, and a third winding43. The first winding41, the second winding42, and the third winding43are magnetically coupled to one another. Both ends of the first winding41are connected to the first switching circuit10. Both ends of the second winding42are connected to the second switching circuit20. Both ends of the third winding43are connected to the third switching circuit30.

The first switching circuit10is connected between the external power supply2and the first winding41. The first switching circuit10supplies the first winding41with electric power supplied from the external power supply2. The first switching circuit10includes a power factor correction (PFC) circuit11, a smoothing capacitor12, a first bridge circuit13, and a relay14.

The PFC circuit11improves the power factor of alternating-current power input from the external power supply2, converts the alternating-current power to direct-current power, and outputs the direct-current power to the first bridge circuit13. During external charging, the external power supply2is connected to alternating-current terminals of the PFC circuit11. The first bridge circuit13is connected to a positive electrode terminal and a negative electrode terminal of the PFC circuit11.

The smoothing capacitor12smooths the voltage of direct-current power output from the PFC circuit11. The smoothing capacitor12is connected to power lines between the PFC circuit11and the first bridge circuit13. The smoothing capacitor12is a first capacitor.

The first bridge circuit13is a full-bridge circuit connected to the positive electrode terminal and negative electrode terminal of the PFC circuit11. The first bridge circuit13includes a switching arm13aand a switching arm13b. The switching arm13aincludes switching elements S1, S2connected in series. The switching arm13bincludes switching elements S3, S4connected in series. The switching arms13a,13bare connected in parallel. The smoothing capacitor12is connected in parallel with the switching arms13a,13b. An upper-side parallel connection point among the switching arms13a,13band the smoothing capacitor12is connected to the positive electrode terminal of the PFC circuit11. A lower-side parallel connection point among the switching arms13a,13band the smoothing capacitor12is connected to the negative electrode terminal of the PFC circuit11. The first winding41is connected between a connection point between the switching element S1and the switching element S2and a connection point between the switching element S3and the switching element S4.

The relay14is provided in a power line between the first bridge circuit13and the first winding41. The relay14is provided in a power line between one end of the first winding41and the connection point between the switching element S3and the switching element S4. When the relay14is in a closed state (ON state), the first winding41and the first switching circuit10are connected such that a current can pass between the first winding41and the first switching circuit10. On the other hand, when the relay14is in an open state (OFF state), the first winding41and the first switching circuit10are interrupted from each other such that no current can pass.

The second switching circuit20is connected between the main battery3and the second winding42. The second switching circuit20supplies the second winding42with electric power from the main battery3. The second switching circuit20includes a main capacitor21and a second bridge circuit22.

The main capacitor21is connected between a positive electrode line and a negative electrode line of the main battery3. The main capacitor21is a second capacitor.

The second bridge circuit22is a full-bridge circuit connected to the positive electrode terminal and negative electrode terminal of the main battery3. The second bridge circuit22includes a switching arm22aand a switching arm22b. The switching arm22aincludes switching elements S5, S6connected in series. The switching arm22bincludes switching elements S7, S8connected in series. The switching arms22a,22bare connected in parallel. The main capacitor21is connected in parallel with the switching arms22a,22b. An upper-side connection point among the switching arms22a,22band the main capacitor21is connected to the positive electrode terminal of the main battery3. A lower-side connection point among the switching arms22a,22band the main capacitor21is connected to the negative electrode terminal of the main battery3. The second winding42is connected between a connection point between the switching element S5and the switching element S6and a connection point between the switching element S7and the switching element S8.

The third switching circuit30is connected between the auxiliary battery4and the third winding43. The third switching circuit30supplies the third winding43with electric power from the auxiliary battery4. The third switching circuit30includes a third bridge circuit31, an intermediate capacitor32, and an auxiliary capacitor33.

The third bridge circuit31includes a switching arm31aand a switching arm31b. The switching arm31aincludes switching elements S9, S10connected in series. The switching arm31bincludes switching elements S11, S12connected in series. The switching arms31a,31bare connected in parallel. The intermediate capacitor32is connected in parallel with the switching arms31a,31b. The third winding43is connected between a connection point between the switching element S9and the switching element S10and a connection point between the switching element S11and the switching element S12.

The auxiliary capacitor33is connected between a lower-side parallel connection point among the switching arms31a,31band the intermediate capacitor32and a midway point of the third winding43. The midway point of the third winding43is connected to the positive electrode terminal of the auxiliary battery4. The lower-side parallel connection point among the switching arms31a,31band the intermediate capacitor32is connected to the negative electrode terminal of the auxiliary battery4. The midway point of the third winding43is a midway point of a conductor wire forming the third winding43. The midway point may be a center tap provided at the middle point of a conductor wire forming the third winding43. The auxiliary capacitor33is a third capacitor. The intermediate capacitor32is a fourth capacitor.

Diodes are respectively connected to the switching elements S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12such that anode terminals are respectively connected to the lower end sides of the switching elements S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12. Each of the switching elements S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12is made up of an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET).

Here, the operation of the power conversion apparatus1will be described.

The operation of the power conversion apparatus1is different between a case where electric power is supplied between the external power supply2and the main battery3in a state where the vehicle Ve is stopped (charger or AC feeder) and a case where electric power is supplied between the main battery3and the auxiliary battery4in a state where the vehicle Ve is traveling (auxiliary DC-DC converter).

Initially, the operation of the power conversion apparatus1in the case where electric power is supplied between the external power supply2and the main battery3in a state where the vehicle Ve is stopped will be described. When the power conversion apparatus1functions as a charger or an AC feeder, the external power supply2is connected to the PFC circuit11. For example, an external power supply2-side charging plug is connected to a charging port provided on the vehicle Ve. An input terminal of the power conversion apparatus1, that is, the alternating-current terminal of the PFC circuit11, is provided at the charging port.

When the main battery3is charged by using the external power supply2in a state where the vehicle Ve is stopped, the power conversion apparatus1keeps the relay14in a closed state and transfers electric power from the external power supply2to the second switching circuit20via the first switching circuit10and the transformer40.

In this case, the PFC circuit11controls the current flowing through the alternating-current terminal of the PFC circuit11through the switching operation such that the temporal waveform of current flowing through the alternating-current terminal is approximated to or brought into coincidence with the temporal waveform of alternating-current voltage output from the external power supply2. While the PFC circuit11performs the operation to improve the power factor, the PFC circuit11converts alternating-current power input from the external power supply2to direct-current power and outputs the direct-current power to the first bridge circuit13. The PFC circuit11steps up the voltage of electric power supplied from the external power supply2and outputs the electric power to the first bridge circuit13. In other words, a terminal voltage of the smoothing capacitor12is adjusted by the PFC circuit11. At this time, the power conversion apparatus1adjusts the output voltage of the PFC circuit11such that the output voltage is higher than a voltage peak value of the external power supply2. For example, the charging voltage of the main battery3is 350 V, and the charging voltage of the auxiliary battery4is 14.5 V. The output voltage of the PFC circuit11is adjusted to 400 V.

The first bridge circuit13outputs alternating-current voltage to the first winding41by performing switching over the direct-current voltage output from the PFC circuit11. In other words, the first bridge circuit13converts the direct-current power of the PFC circuit11to alternating-current power and supplies the alternating-current power to the first winding41. When electric power is transferred to the second switching circuit20via the transformer40, electric power is transferred to the second switching circuit20in accordance with a difference between the switching timing of the first bridge circuit13and the switching timing of the second bridge circuit22.

The second switching circuit20supplies the main battery3with electric power transferred from the first switching circuit10. In this case, the second bridge circuit22converts the alternating-current power transferred from the second winding42to direct-current power and supplies the direct-current power to the main battery3. At this time, the second switching circuit20is capable of outputting electric power to the main battery3and outputting electric power to a load circuit connected to the main battery3.

When the main battery3is charged with electric power from the external power supply2, the auxiliary battery4can be charged with electric power from the external power supply2. The power conversion apparatus1transfers electric power from the external power supply2to the third switching circuit30via the first switching circuit10and the transformer40.

When electric power is transferred to the third switching circuit30via the transformer40, electric power is transferred to the third switching circuit30in accordance with a difference between the switching timing of the first bridge circuit13and the switching timing of the third bridge circuit31.

The third switching circuit30supplies the auxiliary battery4with electric power transferred from the first switching circuit10. In this case, the third switching circuit30initially charges the intermediate capacitor32with electric power supplied from the first switching circuit10via the transformer40. Through the switching operation of the third bridge circuit31, electric power is output from the intermediate capacitor32to the auxiliary battery4via the midway point of the third winding43.

A terminal voltage of the intermediate capacitor32is adjusted by controlling a phase difference that is a delay of the phase of switching of the switching arms31a,31bof the third bridge circuit31with respect to the phase of switching of the switching arms13a,13bof the first bridge circuit13. The third bridge circuit31outputs alternating-current voltage to the third winding43by performing switching of voltage to the intermediate capacitor32. In the power conversion apparatus1, the switching arms13a,13b,22a,22b,31a,31bperform switching operation with the same duty ratio D. Therefore, through the switching operation of the third bridge circuit31, a voltage (1−D) times the terminal voltage of the intermediate capacitor32appears at both ends of each of the auxiliary battery4and the auxiliary capacitor33. In this way, the third bridge circuit31supplies electric power transferred from the first switching circuit10to the auxiliary battery4via the intermediate capacitor32. At this time, the third switching circuit30is capable of outputting electric power to the auxiliary battery4and outputting electric power to auxiliaries connected to the auxiliary battery4.

With this configuration, in the first switching circuit10and the third switching circuit30, the terminal voltage of the smoothing capacitor12is stepped down to the terminal voltage of the intermediate capacitor32, and the terminal voltage of the intermediate capacitor32is stepped down to the terminal voltage of the auxiliary battery4and the terminal voltage of the auxiliary capacitor33. Electric power stepped down in a stepwise manner in this way is supplied.

Next, the operation of the power conversion apparatus1in the case where electric power is supplied between the main battery3and the auxiliary battery4while the vehicle Ve is traveling will be described. When the power conversion apparatus1functions as an auxiliary DC-DC converter, the external power supply2is isolated from the PFC circuit11, and the PFC circuit11stops switching operation. When the main battery3supplies electric power to the auxiliary battery4while the vehicle Ve is traveling, the power conversion apparatus1keeps the relay14in an open state and transfers electric power from the main battery3to the third switching circuit30via the second switching circuit20and the transformer40.

In this case, the second bridge circuit22outputs alternating-current voltage to the second winding42by performing switching over direct-current voltage output from the main battery3. The second bridge circuit22converts direct-current power from the main battery3to alternating-current power and supplies the alternating-current power to the second winding42. When electric power is transferred to the third switching circuit30via the transformer40, electric power is transferred to the third switching circuit30in accordance with a difference between the switching timing of the second bridge circuit22and the switching timing of the third bridge circuit31.

The third switching circuit30supplies the auxiliary battery4with electric power transferred from the second switching circuit20. In this case, the third switching circuit30, as in the case during external charging, initially charges the intermediate capacitor32with electric power supplied from the second switching circuit20via the transformer40. Through the switching operation of the third bridge circuit31, electric power is output from the intermediate capacitor32to the auxiliary battery4via the midway point of the third winding43.

In this way, when the vehicle Ve is traveling, electric power is supplied from the main battery3to the auxiliary battery4in a state where the relay14is in an open state, and the auxiliary battery4is charged. If a short circuit occurs in the smoothing capacitor12of the first switching circuit10, a current path between the first winding41and the smoothing capacitor12is interrupted because the relay14is in an open state. Flow of a current to the first winding41due to a short circuit of the smoothing capacitor12is prevented by setting the relay14in an open state while the vehicle Ve is traveling. Therefore, while the vehicle Ve is traveling, an overcurrent in the main battery3-side second switching circuit20and the auxiliary battery4-side third switching circuit30is avoided by transfer of electric power from the first switching circuit10via the transformer40.

If a circuit does not include the relay14, the second switching circuit20and the first switching circuit10are driven such that the terminal voltage of the PFC-side smoothing capacitor12is kept at 400 V. Therefore, if a short circuit occurs in the smoothing capacitor12, a current flowing through the main battery3-side circuit and a current flowing through the auxiliary battery4-side circuit increase. In the case of, for example, 1000 W output, the value of current flowing through the main battery3-side circuit increases from 4 Aac to 50 Aac, and the value of current flowing through the auxiliary battery4-side circuit increases from 50 Aac to 180 Aac. A battery fuse can melt due to the increase in current. In contrast, in the power conversion apparatus1including the relay14, flow of an overcurrent to the second switching circuit20and the third switching circuit30via the transformer40is prevented.

As described above, according to the embodiment, when electric power is supplied from the main battery3to the auxiliary battery4, transfer of electric power from the first switching circuit10to the second switching circuit20and the third switching circuit30via the transformer40is prevented because the relay14is in an open state. Thus, when a short circuit occurs in the smoothing capacitor12of the first switching circuit10, flow of an overcurrent to the second switching circuit20and the third switching circuit30is prevented because the relay14is in an open state.

An installation location of the relay14is not limited to the above-described embodiment. As measures against a short circuit of the smoothing capacitor12, the relay14just needs to be provided in a power line between the smoothing capacitor12and the first winding41. As shown inFIG.2, first to sixth installation locations14A,14B,14C,14D,14E,14F may be used as an installation location of the relay14in this case.

The first installation location14A is a power line between the first winding41and a connection point between the switching elements S1, S2. The second installation location14B is a power line between the first winding41and a connection point between the switching elements S3, S4. The third installation location14C is a power line connecting the upper side of the switching arm13awith the upper side of the switching arm13b. The fourth installation location14D is a power line connecting the lower side of the switching arm13awith the lower side of the switching arm13b. The fifth installation location14E is a power line connecting the upper side of the switching arm13awith the upper side of the smoothing capacitor12. The sixth installation location14F is a power line connecting the upper side of the switching arm13bwith the upper side of the smoothing capacitor12.

As measures against a short circuit of the smoothing capacitor12, the relay14just needs to be provided in at least any one of the first to sixth installation locations14A,14B,14C,14D,14E,14F. In other words, the number of the relays14is not limited to one and may be installed at multiple installation locations.

A short circuit of the first switching circuit10is not limited to the smoothing capacitor12, and it is conceivable that a short circuit occurs even in the switching elements of the first bridge circuit13. As measures against a short circuit in the switching elements S1, S2, S3, S4of the first bridge circuit13, the relay14just needs to be provided in a power line between the first bridge circuit13and the first winding41. As shown inFIG.3, the first and second installation locations14A,14B may be used as an installation location of the relay14in this case.

As for measures against a short circuit of the switching elements of the first bridge circuit13, the relay14just needs to be provided in at least any one of the first and second installation locations14A,14B. In this case as well, the number of the relays14is not limited to one, and the relays14may be respectively installed in the first and second installation locations14A,14B.