Power device

A first direct-current power converter circuit increases an electrical potential difference between a positive electrical potential of a load and a positive electrical potential of a power source by a step-up operation, and a second direct-current power converter circuit increases an electrical potential difference between a negative electrical potential of the load and a negative electrical potential of the power source by a step-up operation. A control device controls switching operations of first and second switching devices included in the first direct-current power converter circuit based on a first duty. The control device controls switching operations of third and fourth switching devices included in the second direct-current power converter circuit based on a second duty. The control device controls a load voltage to be an arbitrary voltage, which is equal to or more than a source voltage.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a power device. Priority is claimed on Japanese Patent Application No. 2013-120150, filed Jun. 6, 2013, the content of which is incorporated herein by reference.

Description of Related Art

A DC-DC converter which includes two step-up converters connected in parallel has been known. An inductor included in the DC-DC converter is a magnetic-field cancellation type transformer (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2005-224058 and Japanese Unexamined Patent Application, First Publication No. 2006-149054).

A power converter circuit which includes more than three step-up converters connected in parallel has been known. The power converter circuit reduces a ripple current (for example, refer to Japanese Unexamined Patent Application, First Publication No. 2009-170620).

According to the DC-DC converter in the related art described above, when a step-up ratio (a transformer ratio), which is a ratio of an input voltage and an output voltage, is increased to equal to or more than two, the ripple current passed through the inductor is increased. Therefore, it is necessary to enlarge a device, and thereby the loss of circuit is increased.

Moreover, according to the power converter circuit in the related art described above, the number of the step-up converter connected in parallel is increased, and thereby the number of elements needed to configure the circuit is increased. Therefore, the circuit is enlarged.

The present invention provides a power device which can suppress increase of the number of elements needed to configure a circuit and reduce a ripple current when a step-up ratio (a transformer ratio) is increased.

SUMMARY OF THE INVENTION

(1) A power device according to one aspect of the present invention may include a power source, a load configured to be driven by power supplied from the power source, and a voltage control unit configured to control a voltage to be applied to the load. The voltage control unit may include a first reactor and a second reactor, a plurality of switches, a first capacitor and a second capacitor, and a first step-up circuit and a second step-up circuit. A positive electrode of the power source may be connected with a first node, a negative electrode of the power source may be connected with a second node. A first end of the first reactor may be connected with a third node and a second end of the first reactor may be connected with the first node. A first end of the second reactor may be connected with a fourth node and a second end of the second reactor may be connected with the second node. A first end of the first capacitor may be connected with a fifth node and a second end of the first capacitor may be connected with the second node. A first end of the second capacitor may be connected with a sixth node and a second end of the second capacitor may be connected with the first node. The switches may include a first switch, a second switch, a third switch, and a fourth switch. A first end of the first switch may be connected with the fifth node and a second end of the first switch may be connected with the third node. A first end of the second switch may be connected with the third node and a second end of the second switch may be connected with the second node. A first end of the third switch may be connected with the first node and a second end of the third switch may be connected with the fourth node. A first end of the fourth switch may be connected with the fourth node and a second end of the fourth switch may be connected with the sixth node. The first step-up circuit may include the first reactor, the first capacitor, and the first and second switches. The first step-up circuit may be connected with the power source. The second step-up circuit may include the second reactor, the second capacitor, and the third and fourth switches. The second step-up circuit may be connected with the power source. The voltage control unit may be configured to control the voltage applied to the load to be an arbitrary voltage, which is equal to or more than the voltage of the power source, based on a duty of ON and OFF switching operation of the switch.

(2) In the power device described in (1), the voltage control unit may be configured to perform a first switching operation and a second switching operation such that a phase shift is provided between the first and second switching operations. The first switching operation is that the first switch and the second switch of the first step-up circuit are inverted and alternative ON and OFF operations of each first and second switch are performed. The second switching operation is that the third switch and the fourth switch of the second step-up circuit are inverted and alternative ON and OFF operations of each third and fourth switch are performed.

(3) In the power device described in (1) or (2), the first reactor and the second reactor may be magnetically coupled.

(4) In the power device described in (3), the first reactor and the second reactor may be provided to perform a magnetic-field cancellation.

(5) In the power device described in any one of (1) to (4), the first and fourth switches may be configured to interrupt a conduction for charging the power source.

(6) In the power device described in (1), the voltage control unit may further include a third reactor and a fourth reactor, a third capacitor and a fourth capacitor, and a third step-up circuit and a fourth step-up circuit. A first end of the third reactor may be connected with a seventh node and a second end of the third reactor may be connected with the first node. A first end of the fourth reactor may be connected with an eighth node and a second end of the fourth reactor may be connected with the second node. A first end of the third capacitor may be connected with the fifth node and a second end of the third capacitor may be connected with the second node. A first end of the fourth capacitor may be connected with the sixth node and a second end of the fourth capacitor may be connected with the first node. The switches may further include a fifth switch, a sixth switch, a seventh switch, and an eighth switch. A first end of the fifth switch may be connected with the fifth node and a second end of the fifth switch may be connected with the seventh node. A first end of the sixth switch may be connected with the seventh node and a second end of the sixth switch may be connected with the second node. A first end of the seventh switch may be connected with the first node and a second end of the seventh switch may be connected with the eighth node. A first end of the eighth switch may be connected with the eighth node and a second end of the eighth switch may be connected with the sixth node. The third step-up circuit may include the third reactor, the third capacitor, and the fifth and sixth switches. The third step-up circuit may be connected with the power source. The fourth step-up circuit may include the fourth reactor, the fourth capacitor, and the seventh and eighth switches. The fourth step-up circuit may be connected with the power source.

(7) In the power device described in (6), the voltage control unit may be configured to perform first to fourth switching operations such that a phase shift is provided between the first and second switching operations and a phase shift is provided between the third and fourth switching operations. The first switching operation is that the first switch and the second switch of the first step-up circuit are inverted and alternative ON and OFF operations of each first and second switch are performed. The second switching operation is that the third switch and the fourth switch of the second step-up circuit are inverted and alternative ON and OFF operations of each third and fourth switch are performed. The third switching operation is that the fifth switch and the sixth switch of the third step-up circuit are inverted and alternative ON and OFF operations of each fifth and sixth switch are performed. The fourth switching operation is that the seventh switch and the eighth switch of the fourth step-up circuit are inverted and alternative ON and OFF operations of each seventh and eighth switch are performed.

(8) In the power device described in (7), the voltage control unit may be configured to perform the first to fourth switching operations such that a phase shift is provided between a pair of the first and second switching operations and a pair of the third and fourth switching operations.

(9) In the power device described in (7) or (8), the first reactor and the second reactor may be magnetically coupled, and the third reactor and the fourth reactor may be magnetically coupled.

(10) In the power device described in (9), the first reactor and the second reactor may be provided to perform a magnetic-field cancellation, and the third reactor and the fourth reactor may be provided to perform a magnetic-field cancellation.

(11) In the power device described in (6), the voltage control unit may be configured to perform first to fourth switching operations such that a phase shift is provided between the first and third switching operations and a phase shift is provided between the second and fourth switching operations. The first switching operation is that the first switch and the second switch of the first step-up circuit are inverted and alternative ON and OFF operations of each first and second switch are performed. The second switching operation is that the third switch and the fourth switch of the second step-up circuit are inverted and alternative ON and OFF operations of each third and fourth switch are performed. The third switching operation is that the fifth switch and the sixth switch of the third step-up circuit are inverted and alternative ON and OFF operations of each fifth and sixth switch are performed. The fourth switching operation is that the seventh switch and the eighth switch of the fourth step-up circuit are inverted and alternative ON and OFF operations of each seventh and eighth switch are performed.

(12) In the power device described in (11), the voltage control unit may be configured to perform the first to fourth switching operations such that a phase shift is provided between a pair of the first and third switching operations and a pair of the second and fourth switching operations.

(13) In the power device described in (11) or (12), the first reactor and the third reactor may be magnetically coupled, and the second reactor and the fourth reactor may be magnetically coupled.

(14) In the power device described in (13), the first reactor and the third reactor may be provided to perform a magnetic-field cancellation, and the second reactor and the fourth reactor may be provided to perform a magnetic-field cancellation.

(15) In the power device described in any one of (6) to (14), the first, fourth, fifth, and eighth switches may be configured to interrupt a conduction for charging the power source.

According to the power device of the aspect described in (1), the first step-up circuit increases the electrical potential difference between the positive electrical potential of the load and the positive electrical potential of the power source by the step-up operation, and the second step-up circuit increases the electrical potential difference between the negative electrical potential of the load and the negative electrical potential of the power source by the step-up operation. Thereby, for example, a duty needed to achieve a desired step-up ratio can be reduced in comparison with a device that a plurality of step-up converters are connected with a power source in parallel. Moreover, a ripple current can be reduced when a step-up ratio (a transformer ratio) is increased. Therefore, it is unnecessary to enlarge a device, and thereby an increase of loss of circuit is suppressed. Moreover, an increase of the number of elements needed to configure the circuit and an enlargement of the circuit can be suppressed, and the ripple current can be reduced in comparison with a device in which more than three step-up converters are connected with a power source in parallel. Moreover, the voltage resistance of the first and second capacitors can be reduced. Thereby, the entire circuit can be reduced in size.

Moreover, according to the power device described in (2), a ripple frequency of current flowing through each of the load, which includes the capacitors connected in parallel, and the power source can be more than a switching frequency. For example, even if the switching frequency is within an audible band, a frequency of noise caused by the ripple current, which is generated in the load and the power source, is changed into one outside the audible band. Thereby, the noise can be suppressed. In particular, based on the switching operation using an opposite phase, since the ripple of current based on the operation of the first step-up circuit and that of the second step-up circuit are superimposed in the opposite phase each other, the ripple of current flowing through each of the load and the power source can be reduced in comparison with a switching operation using a same phase.

Moreover, according to the power device described in (3), the frequency of each first and second reactor current can be more than the switching frequency. For example, by the opposite phase switching operation, the frequency of each first and second reactor current can be increased to the twice of the switching frequency, and a frequency of magnetostrictive noise generated in the first and second reactors can be increased to outside the audible band.

Moreover, according to the power device described in (4), a generation of magnetic saturation in the first and second reactors is suppressed. Thereby, each element can be reduced in size.

Moreover, according to the power device described in (5), even if the power source is a fuel cell or a power generator which is only capable of discharging power, an appropriate operation can be performed.

Moreover, according to the power device described in (6), the electrical power covered by each step-up circuit can be reduced.

Moreover, according to the power device described in (7) or (11), the ripple frequency of current flowing through each of the load, which includes the capacitors connected in parallel, and the power source can be more than the switching frequency. For example, even if the switching frequency is within the audible band, the frequency of noise caused by the ripple current, which is generated in the load and the power source, is changed into one outside the audible band. Thereby, the noise can be suppressed. In particular, based on the switching operation using an opposite phase, since the ripples of current based on the operations of the first to fourth step-up circuits are superimposed in the opposite phase each other, the ripple of current flowing through each of the load and the power source can be reduced in comparison with a switching operation using a same phase.

Moreover, according to the power device described in (8) or (12), the ripple frequency of current flowing through each of the load and the power source can be further increased.

Moreover, according to the power device described in (9) or (13), the ripple frequency of current flowing through each of the load, which includes the capacitors connected in parallel, and the power source can be more than the switching frequency. For example, by shifting a phase of a first pair of switching operations using an opposite phase from that of a second pair of switching operations using an opposite phase by 90°, the ripple frequency of current flowing through each of the load and the power source can be increased to the four times of the switching frequency. Therefore, the frequency of noise caused by the ripple current, which is generated in the load and the power source, can be increased to outside the audible band.

Moreover, according to the power device described in (10) or (14), a generation of magnetic saturation in the first to fourth reactors is suppressed. Thereby, each element can be reduced in size.

Moreover, according to the power device described in (15), even if the power source is a fuel cell or a power generator which is only capable of discharging power, an appropriate operation can be performed.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a power device according to an embodiment of the present invention will be described with reference to the attached drawings.

The power device according to the embodiment of the present invention provides a direct-current power to a load such as an inverter. The inverter controls a power mode and a regenerative mode of an electric motor which can produce, for example, a drive force to run a vehicle.

As illustrated inFIG. 1, a power device10according to the embodiment of the present invention includes a power source BT such as a battery, a first direct-current power converter circuit (REG1)11, a second direct-current power converter circuit (REG2)12, a load (LD)13, a capacitor (CA)14, and a control device15. The load13can drive using a direct-current power supplied from the first and second direct-current power converter circuits11and12, and supply a generated direct-current power to the first and second direct-current power converter circuits11and12. The capacitor (CA)14is connected with both ends of the load13.

The first direct-current power converter circuit (REG1)11is connected with the power source BT, and include first and second switching devices SW1and SW2such as IGBT (Insulated Gate Bipolar mode Transistor), which configure a first switch group, a first reactor L1, and a first capacitor CA1.

The second direct-current power converter circuit (REG2)12is connected with the power source BT, and include third and fourth switching devices SW3and SW4such as IGBT, which configure a second switch group, a second reactor L2, and a second capacitor CA2.

The power device10includes first to sixth nodes A to F.

A positive electrode of the power source BT is connected with the first node A, and a negative electrode of the power source BT is connected with the second node B. One end of the first reactor L1is connected with the third node C, and the other end of the first reactor L1is connected with the first node A. One end of the second reactor L2is connected with the fourth node D, and the other end of the second reactor L2is connected with the second node B.

A collector and an emitter of the first switching device SW1are connected with the fifth node E and the third node C, respectively. A collector and an emitter of the second switching device SW2are connected with the third node C and the second node B, respectively. A collector and an emitter of the third switching device SW3are connected with the first node A and the fourth node D, respectively. A collector and an emitter of the fourth switching device SW4are connected with the fourth node D and the sixth node F, respectively. Diodes D1to D4are connected between the emitter and collector of the switching devices SW1to SW4, respectively. The direction from the emitter to the collector of each switching device SW1to SW4is a forward direction of each diode D1to D4.

The first capacitor CA1is connected between the fifth node E and the second node B, and the second capacitor CA2is connected between the first node A and the sixth node F.

The first and second direct-current power converter circuits11and12are controlled based on pulse-width-modulated signals (PWM signals) output from the control device15and input into a gate of each switching device SW1to SW4so that the first and second direct-current power converter circuits11and12drive independently from each other.

In more detail, the first and second direct-current power converter circuits11and12are controlled so that a switching operation for at least one of a pair of the first and second switching devices SW1and SW2included in the first direct-current power converter circuit11and a pair of the third and fourth switching devices SW3and SW4included in the second direct-current power converter circuit12is performed. In this switching operation, close (ON) and open (OFF) of each switching device SW1to SW4are switched alternately.

In the first direct-current power converter circuit11, for example, as illustrated inFIG. 2A, when the first capacitor CA1is charged in a stopped state of the load13(in other words, a state where the load13do not perform a power consumption and a regeneration), the first switching device SW1is turned off and the second switching device SW2is turned on. Thereby, the first reactor L1is excited by flowing a circulating current via the power source BT, the first reactor L1, and the second switching device SW2in series, and a first reactor current I (L1) flowing through the first reactor L1is increased. On the other hand, by turning on the first switching device SW1and turning off the second switching device SW2, a current flows into the first capacitor CA1via the power source BT, the first reactor L1, and the first switching device SW1and the first diode D1.

In the first direct-current power converter circuit11, for example, as illustrated inFIG. 2B, when the first capacitor CA1is discharged in the stopped state of the load13, the first switching device SW1is turned on and the second switching device SW2is turned off. Thereby, a current flows via the first switching device SW1, the first reactor L1, and the power source BT in series. On the other hand, by turning off the first switching device SW1and turning on the second switching device SW2, a circulating current flows via the second switching device SW2and the second diode D2, the first reactor L1, and the power source BT.

In the second direct-current power converter circuit12, for example, as illustrated inFIG. 2A, when the second capacitor CA2is charged in the stopped state of the load13, the fourth switching device SW4is turned off and the third switching device SW3is turned on. Thereby, the second reactor L2is excited by flowing a circulating current via the power source BT, the third switching device SW3, and the second reactor L2in series, and a second reactor current I (L2) flowing through the second reactor L2is increased. On the other hand, by turning on the fourth switching device SW4and turning off the third switching device SW3, a current flows into the second capacitor CA2via the fourth switching device SW4and the fourth diode D4, the second reactor L2, and the power source BT.

In the second direct-current power converter circuit12, for example, as illustrated inFIG. 2B, when the second capacitor CA2is discharged in the stopped state of the load13, the fourth switching device SW4is turned on and the third switching device SW3is turned off Thereby, a current flows via the power source BT, the second reactor L2, and the fourth switching device SW4. On the other hand, by turning off the fourth switching device SW4and turning on the third switching device SW3, a circulating current flows via the second reactor L2, the third switching device SW3and the third diode D3, and the power source BT.

The control device15includes a load control unit21and a connection switching control unit22.

The load control unit21controls the operation of the load13. For example, if the load13includes an electric motor such as a three-phase brushless DC motor and an inverter to control the power mode and regenerative mode of the electric motor, the load control unit21controls a power conversion operation of the inverter. In more detail, when the electric motor is in the power mode, the load control unit21converts a direct-current power applied between both electrodes at the direct current side of the inverter into a three-phase alternating-current power, performs a commutation of a conduction for each phase of the electric motor sequentially, and thereby, each phase current, which is alternating-current, flows. On the other hand, when the electric motor is in the regenerative mode, the load control unit21converts the generated alternating-current power output from the electric motor into a direct-current power, while the load control unit21synchronizes based on a rotation angle of the electric motor.

The connection switching control unit22can drive the first and second direct-current power converter circuits11and12independently from each other by inputting signals (PWM signals) based on a pulse width modulation (PWM) into a gate of each switching device SW1to SW4. The connection switching control unit22controls the first and second direct-current power converter circuits11and12so that a switching operation for at least one of a pair of the first and second switching devices SW1and SW2included in the first direct-current power converter circuit11and a pair of the third and fourth switching devices SW3and SW4included in the second direct-current power converter circuit12is performed. Thereby, the connection switching control unit22controls a voltage V0applied to the load13(a load voltage) to be equal to or more than a voltage VB applied between terminals of the power source BT (a source voltage).

The connection switching control unit22controls a switching operation of the first switching device SW1and the second switching device SW2included in the first direct-current power converter circuit11based on a first duty DT1. In the switching operation, the first switching device SW1and the second switching device SW2are inverted and the alternative close and open (ON/OFF) switching operations of each switching device SW1and SW2are performed. As illustrated in the following equation (1), the first duty DT1is defined by ON time t(SW1) of the first switching device SW1and ON time t(SW2) of the second switching device SW2.

For example, when the first switching device SW1is turned on and the second switching device SW2is turned off, the first duty DT1is 0%. On the other hand, when the first switching device SW1is turned off and the second switching device SW2is turned on, the first duty DT1is 100%.

The connection switching control unit22can step up the source voltage VB based on the first duty DT1and output the step-up voltage from the first direct-current power converter circuit11. The connection switching control unit22controls output voltage V10of the first direct-current power converter circuit11(in other words, the voltage applied between the fifth node E and the second node B) based on the source voltage VB and the first duty DT1.

The connection switching control unit22controls a switching operation of the third switching device SW3and the fourth switching device SW4included in the second direct-current power converter circuit12based on a second duty DT2. In the switching operation, the third switching device SW3and the fourth switching device SW4are inverted and the alternative close and open (ON/OFF) switching operations of each switching device SW3and SW4are performed. As illustrated in the following equation (2), the second duty DT2is defined by ON time t(SW3) of the third switching device SW3and ON time t(SW4) of the fourth switching device SW4.

For example, when the fourth switching device SW4is turned on and the third switching device SW3is turned off, the second duty DT2is 0%. On the other hand, when the fourth switching device SW4is turned off and the third switching device SW3is turned on, the second duty DT2is 100%.

The connection switching control unit22can step up the source voltage VB based on the second duty DT2and output the step-up voltage from the second direct-current power converter circuit12. The connection switching control unit22controls output voltage V20of the second direct-current power converter circuit12(in other words, the voltage applied between the first node A and the sixth node F) based on the source voltage VB and the second duty DT2.

The power device10according to the embodiment of the present invention includes the constitution described above. Hereinafter, the operation of the power device10, in other words, the control operation of the connection switching control unit22will be described.

In a first control mode, the connection switching control unit22drives one of the first and second direct-current power converter circuits11and12at a once. Thereby, the connection switching control unit22can arbitrarily control the load voltage V0to be equal to or more than the source voltage VB.

For example, the connection switching control unit22makes the power source BT into a connecting condition with the load13by turning on the first and fourth switching devices SW1and SW4and turning off the second and third switching devices SW2and SW3.

The connection switching control unit22performs a switching operation, which gradually increases the first duty DT1from zero, while the power source BT is connected with the load13. Thereby, the output voltage V10of the first direct-current power converter circuit11is gradually increased above the source voltage VB by the back electromotive force of the first reactor L1. Thereby, the capacitor14is charged, and the load voltage V0is gradually increased based on the output voltage V10.

Moreover, the connection switching control unit22performs a switching operation, which gradually decreases the first duty DT1to zero. Thereby, an electrical charge charged in the capacitor14is supplied to the power source BT while the electrical charge is consumed in the load13. Thereby, the power source BT is charged, and the load voltage V0is gradually decreased based on the output voltage V10. When the first duty DT1reaches zero, the load voltage V0is equals the source voltage VB.

Similarly, the connection switching control unit22performs a switching operation, which gradually increases the second duty DT2from zero, while the power source BT is connected with the load13. Thereby, the output voltage V20of the second direct-current power converter circuit12is gradually increased above the source voltage VB by the back electromotive force of the second reactor L2. Thereby, the capacitor14is charged, and the load voltage V0is gradually increased based on the output voltage V20.

Moreover, the connection switching control unit22performs a switching operation, which gradually decreases the second duty DT2to zero. Thereby, an electrical charge charged in the capacitor14is supplied to the power source BT while the electrical charge is consumed in the load13. Thereby, the power source BT is charged, and the load voltage V0is gradually decreased based on the output voltage V20. When the second duty DT2reaches zero, the load voltage V0is equals the source voltage VB.

In a second control mode, the connection switching control unit22simultaneously drives the first and second direct-current power converter circuits11and12. The phase of the switching operation of the first direct-current power converter circuit11is the same as that of the second direct-current power converter circuit12. Thereby, the connection switching control unit22can control the load voltage V0to be equal to or more than the source voltage VB. In this case, a current flowing through the load13and the capacitor14, and the power source BT is generated by combining currents based on the mutual operations of the first and second direct-current power converter circuits11and12. For example, if the first duty DT1and the second duty DT2are the same each other, the load voltage V0is represented byFIG. 3and the following equation (3).

For example, the connection switching control unit22makes the power source BT into a connecting condition with the load13by turning on the first and fourth switching devices SW1and SW4and turning off the second and third switching devices SW2and SW3.

The connection switching control unit22performs a switching operation, which gradually increases the first and second duties DT1and DT2from zero, while the power source BT is connected with the load13. Thereby, the output voltage V10of the first direct-current power converter circuit11and the output voltage V20of the second direct-current power converter circuit12are gradually increased above the source voltage VB by the back electromotive force of the first reactor L1and the back electromotive force of the second reactor L2, respectively, and the electrical power is supplied to the load13and the capacitor14. Thereby, the capacitor14is charged, and the load voltage V0is gradually increased based on the first and second duties DT1and DT2.

Moreover, the connection switching control unit22performs a switching operation, which gradually decreases the first and second duties DT1and DT2to zero. Thereby, an electrical charge charged in the capacitor14is supplied to the power source BT while the electrical charge is consumed in the load13. Thereby, the power source BT is charged, and the load voltage V0is gradually decreased based on the first and second duties DT1and DT2. When the first and second duties DT1and DT2reach zero, the load voltage V0is equals the source voltage VB.

In a third control mode, the connection switching control unit22simultaneously drives the first and second direct-current power converter circuits11and12. The phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the second direct-current power converter circuit12(for example, as illustrated in (A) to (C) ofFIG. 4, an opposite phase where a phase shift is 180°). Thereby, the connection switching control unit22can control the load voltage V0to be equal to or more than the source voltage VB. Moreover, a ripple frequency of each current through the load13, the capacitor14, and the power source BT can be more than a switching frequency. For example, even if the switching frequency is within an audible band, the connection switching control unit22changes a frequency of noise caused by the ripple current, which is generated in the load13, the capacitor14, and the power source BT, into one outside the audible band. Thereby, the noise can be suppressed.

In particular, based on the switching operation using the opposite phase, since the ripple of current based on the operation of the first direct-current power converter circuit11and that of the second direct-current power converter circuit12are superimposed in the opposite phase each other, the ripples of current flowing through the load13, the capacitor14, and the power source BT can be reduced in comparison with the second control mode.

In a current waveform based on a time t illustrated in (A) to (C) ofFIG. 4, as illustrated inFIG. 1, a positive direction of a first reactor current I(L1) flowing through the first reactor L1is from the first node A to the third node C. A positive direction of a second reactor current I(L2) flowing through the second reactor L2is from the fourth node D to the second node B. A positive direction of a current I(BT) flowing through the power source BT is from the negative electrode to the positive electrode. A positive direction of a summed current I(LD) of currents flowing through the load13and the capacitor14is from the fifth node E to the sixth node F.

If the first and second reactors L1and L2are not magnetically coupled as illustrated in (A) to (C) ofFIG. 4in the third control mode described above, the frequency of each first and second reactor current I(L1) and I(L2) is the same as the switching frequency. On the other hand, if the first and second reactors L1and L2are magnetically coupled as illustrated in (A) to (C) ofFIG. 5, the frequency of each first and second reactor current I(L1) and I(L2) can be increased above the switching frequency.

Namely, in a fourth control mode, the connection switching control unit22simultaneously drives the first and second direct-current power converter circuits11and12in the condition that the first and second reactors L1and L2are magnetically coupled. The phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the second direct-current power converter circuit12(for example, as illustrated in (A) to (C) ofFIG. 5, an opposite phase where a phase shift is 180°).

The first and second reactors L1and L2are magnetically coupled by, for example, winding the first and second reactors L1and L2around a common core to share a magnetic path. Moreover, the first and second reactors L1and L2may be provided by, for example, winding the first and second reactors L1and L2around a common core to share a magnetic path in opposite directions each other (reverse phase). Each first reactor current I(L1) and second reactor current I(L2) flows so that magnetizations of the magnetic path are canceled.

For example, as illustrated in (A) to (C) ofFIG. 5, in the condition that the first and second reactors L1and L2are magnetically coupled, the connection switching control unit22increases the first reactor current I(L1) by turning on the second switching device SW2in the first direct-current power converter circuit11. Subsequently, by turning off the second switching device SW2, and by turning on the third switching device SW3in the condition that the first reactor current I(L1) is reduced, the second reactor current I(L2) is increased. Thereby, an inductive voltage caused by the magnetic coupling is generated in the first reactor L1so that the reduction of the first reactor current I(L1) is suppressed, and the condition of the first reactor current I(L1) is changed from the reduction to the increase, or the reduction of the first reactor current I(L1) is suppressed. Subsequently, by turning off the third switching device SW3, the second reactor current I(L2) is reduced, and the first reactor current I(L1) is reduced.

Moreover, the connection switching control unit22increases the second reactor current I(L2) by turning on the third switching device SW3in the second direct-current power converter circuit12. Subsequently, by turning off the third switching device SW3, and by turning on the second switching device SW2in the condition that the second reactor current I(L2) is reduced, the first reactor current I(L1) is increased. Thereby, an inductive voltage caused by the magnetic coupling is generated in the second reactor L2so that the reduction of the second reactor current I(L2) is suppressed, and the condition of the second reactor current I(L2) is changed from the reduction to the increase, or the reduction of the second reactor current I(L2) is suppressed. Subsequently, by turning off the second switching device SW2, the first reactor current I(L1) is reduced, and the second reactor current I(L2) is reduced.

Thereby, the connection switching control unit22increases the frequency of each first and second reactor current I(L1) and I(L2) to the twice of the switching frequency, and a frequency of magnetostrictive noise generated in the first and second reactors L1and L2can be increased to outside an audible band.

As described above, the power device10according to the embodiment of the present invention can easily control the load voltage V0to be arbitrary voltage, which is equal to or more than the source voltage VB, by controlling the first duty DT1and the second duty DT2. In other words, the first direct-current power converter circuit11increases the electrical potential difference between the positive electrical potential of the load13and the positive electrical potential of the power source BT by the step-up operation, and the second direct-current power converter circuit12increases the electrical potential difference between the negative electrical potential of the load13and the negative electrical potential of the power source BT by the step-up operation.

Moreover, by simultaneously driving the first and second direct-current power converter circuits11and12using the switching operation where the phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the second direct-current power converter circuit12, the ripple frequency of each current of the load13, the capacitor14, and the power source BT can be more than the switching frequency. Thereby, for example, even if the switching frequency is within an audible band, the connection switching control unit22changes a frequency of noise caused by the ripple current, which is generated in the load13, the capacitor14, and the power source BT, into a frequency outside the audible band. Thereby, the noise can be suppressed.

Moreover, in the condition that the first and second reactors L1and L2are magnetically coupled, by simultaneously driving the first and second direct-current power converter circuits11and12using the switching operation where the phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the second direct-current power converter circuit12, the frequency of each first and second reactor current I(L1) and I(L2) can be more than the switching frequency. For example, by the opposite phase switching operation, the frequency of each first and second reactor current I(L1) and I(L2) can be increased to the twice of the switching frequency, and a frequency of magnetostrictive noise generated in the first and second reactors L1and L2can be increased to outside an audible band.

Moreover, by providing the first and second reactors L1and L2to perform a magnetic cancellation, a generation of magnetic saturation in the first and second reactors L1and L2is suppressed. Thereby, each element can be reduced in size.

Moreover, for example, given a DC-DC converter100disclosed in Japanese Unexamined Patent Application, First Publication No. 2005-224058 as illustrated inFIG. 6is a comparative example, the power device10according to the embodiment of the present invention can reduce the first and second duties DT1and DT2needed to achieve a desired step-up ratio in comparison with the comparative example. Moreover, the ripple current can be reduced in a range that the step-up ratio is more than two. Moreover, the voltage resistance of each first and second capacitor CA1and CA2needed for the first and second direct-current power converter circuits11and12can be reduced. Thereby, the entire circuit can be reduced in size.

COMPARATIVE EXAMPLE

The DC-DC converter100of the comparative example illustrated inFIG. 6includes two step-up converters connected with a power source BT in parallel, and first to fifth nodes A to E.

A positive electrode of the power source BT is connected with the first node A, and a negative electrode of the power source BT is connected with the second node B. One end of the first reactor L1is connected with the third node C, and the other end of the first reactor L1is connected with the first node A. One end of the second reactor L2is connected with the fourth node D, and the other end of the second reactor L2is connected with the first node A.

A collector and an emitter of the first switching device SW1are connected with the fifth node E and the third node C, respectively. A collector and an emitter of the second switching device SW2are connected with the third node C and the second node B, respectively. A collector and an emitter of the third switching device SW3are connected with the fifth node E and the fourth node D, respectively. A collector and an emitter of the fourth switching device SW4are connected with the fourth node D and the second node B, respectively. Diodes D1to D4are connected between the emitter and collector of the switching devices SW1to SW4, respectively. The direction from the emitter to the collector of each switching device SW1to SW4is a forward direction of each diode D1to D4.

The first and second capacitors CA1and CA2are connected between the fifth node E and the second node B.

A variation of each current I(BT), I(L1), I(L2), and I(LD) is illustrated in (A) to (C) ofFIG. 7and (A) to (C) ofFIG. 8when control operations, which are similar to the third and fourth control mode of the power source10according to the embodiment of the present invention described above, are performed in the DC-DC converter100of the comparative example illustrated inFIG. 6. In (A) to (C) ofFIG. 7and (A) to (C) ofFIG. 8of the comparative example, step-up ratios, which are the same as those of (A) to (C) ofFIG. 4and (A) to (C) ofFIG. 5of the embodiment of the present invention described above, are set (for example, the step-up rations are 2.0, 2.5, and 3.0).

In a current waveform based on a time t illustrated in (A) to (C) ofFIG. 7and (A) to (C) ofFIG. 8, as illustrated inFIG. 6, a positive direction of the first reactor current I(L1) flowing through the first reactor L1is from the first node A to the third node C. A positive direction of the second reactor current I(L2) flowing through the second reactor L2is from the first node A to the fourth node D. A positive direction of the current I(BT) flowing through the power source BT is from the negative electrode to the positive electrode. A positive direction of the summed current I(LD) of currents flowing through the load13and the capacitor14is from the fifth node E to the second node B.

The load voltage V0in the embodiment of the present invention is represented by the equation (3) described above, while the load voltage V0in the comparative example is represented by the following equation (4). Thereby, as illustrated inFIG. 9, according to the embodiment of the present invention, the first and second duties DT1and DT2needed to achieve a desired step-up ratio can be reduced in comparison with the comparative example.

In the embodiment and the comparative example, when the step-up ratio is increased by increasing the first and second duties DT1and DT2, the ripple currents flowing through the first and second reactors L1and L2are changed so that the ripple currents have an increasing state. In particular, in the range that the first and second duties DT1and DT2are more than 0.5, the increase of the ripple current is remarkable. When the first and second duties DT1and DT2are more than 0.5, the step-up ratio in the comparative example is more than only two, while the step-up ratio in the embodiment is more than three. Therefore, as illustrated inFIG. 10, according to the embodiment of the present invention, the ripple current in the range that the step-up ratio is more than 2 can be reduced in comparison with the comparative example.

Furthermore, in the comparative example, the entire voltage of load voltage V0is applied to the first and second capacitors CA1and CA2. On the other hand, in the embodiment of the present invention, only the output voltages V10and V20are applied to the first and second capacitors CA1and CA2, respectively. Therefore, the voltage resistance needed for the first and second capacitor CA1and CA2can be reduced. Thereby, the entire circuit can be reduced in size.

As a power device10according to a variation illustrated inFIG. 11, the embodiment described above may further include seventh and eighth nodes G and H, a third direct-current power converter circuit (REG3)31, and a fourth direct-current power converter circuit (REG4)32.

The third direct-current power converter circuit (REG3)31is connected with a power source BT, and include fifth and sixth switching devices SW5and SW6such as IGBT (Insulated Gate Bipolar mode Transistor), which configure a third switch group, a third reactor L3, and a third capacitor CA3.

The fourth direct-current power converter circuit (REG4)32is connected with the power source BT, and include seventh and eighth switching devices SW7and SW8such as IGBT, which configure a fourth switch group, a fourth reactor L4, and a fourth capacitor CA4.

One end of the third reactor L3is connected with the first node A, and the other end of the third reactor L3is connected with the seventh node G One end of the fourth reactor L4is connected with the second node B, and the other end of the fourth reactor L4is connected with the eighth node H.

A collector and an emitter of the fifth switching device SW5are connected with the fifth node E and the seventh node G, respectively. A collector and an emitter of the sixth switching device SW6are connected with the seventh node G and the second node B, respectively. A collector and an emitter of the seventh switching device SW7are connected with the first node A and the eighth node H, respectively. A collector and an emitter of the eighth switching device SW8are connected with the eighth node H and the sixth node F, respectively. Diodes D5to D8are connected between the emitter and collector of the switching devices SW5to SW8, respectively. The direction from the emitter to the collector of each switching device SW5to SW8is a forward direction of each diode D5to D8.

The third capacitor CA3is connected between the fifth node E and the second node B, and the fourth capacitor CA4is connected between the first node A and the sixth node F.

In this variation, in a similar way to the first and second direct-current power converter circuits11and12, the third and fourth direct-current power converter circuits31and32are controlled based on pulse-width-modulated signals (PWM signals) output from a control device15and input into a gate of each switching device SW5to SW8so that the third and fourth direct-current power converter circuits31and32drive independently from each other.

In the third direct-current power converter circuit31, when the third capacitor CA3is charged in a stopped state of a load13(in other words, a power consumption and a regeneration are not performed), the fifth switching device SW5is turned off and the sixth switching device SW6is turned on. Thereby, the third reactor L3is excited by flowing a circulating current via the power source BT, the third reactor L3, and the sixth switching device SW6in series, and a third reactor current I(L3) flowing through the third reactor L3is increased. On the other hand, by turning on the fifth switching device SW5and turning off the sixth switching device SW6, a current flows into the third capacitor CA3via the power source BT, the third reactor L3, and the fifth switching device SW5and the fifth diode D5.

In the third direct-current power converter circuit31, when the third capacitor CA3is discharged in the stopped state of the load13, the fifth switching device SW5is turned on and the sixth switching device SW6is turned off. Thereby, a current flows via the fifth switching device SW5, the third reactor L3, and the power source BT in series. On the other hand, by turning off the fifth switching device SW5and turning on the sixth switching device SW6, a circulating current flows via the sixth switching device SW6and the sixth diode D6, the third reactor L3, and the power source BT in series.

In the fourth direct-current power converter circuit32, when the fourth capacitor CA4is charged in the stopped state of the load13, the eighth switching device SW8is turned off and the seventh switching device SW7is turned on. Thereby, the fourth reactor L4is excited by flowing a circulating current via the power source BT, the seventh switching device SW7, and the fourth reactor L4in series, and a fourth reactor current I(L4) flowing through the fourth reactor L4is increased. On the other hand, by turning on the eighth switching device SW8and turning off the seventh switching device SW7, a current flows into the fourth capacitor CA4via the eighth switching device SW8and the eighth diode D8, the fourth reactor L4, and the power source BT.

In the fourth direct-current power converter circuit32, when the fourth capacitor CA4is discharged in the stopped state of the load13, the eighth switching device SW8is turned on and the seventh switching device SW7is turned off. Thereby, a current flows via the power source BT, the fourth reactor L4, and the eighth switching device SW8in series. On the other hand, by turning off the eighth switching device SW8and turning on the seventh switching device SW7, a circulating current flows via the fourth reactor L4, the seventh switching device SW7and the seventh diode D7, and the power source BT in series.

According the variation, the electrical power covered by each direct-current power converter circuits11,12,31, and32can be reduced in comparison with the embodiment described above.

(First Control Mode of the Variation)

In a first control mode, when the connection switching control unit22according to the variation simultaneously drives the first to fourth direct-current power converter circuits11,12,31, and32, the phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the second direct-current power converter circuit12(for example, an opposite phase where a phase shift is 180°). Moreover, the connection switching control unit22drives the third and fourth direct-current power converter circuits31and32, where the phase of the switching operation of the third direct-current power converter circuit31is arbitrarily shifted from that of the fourth direct-current power converter circuit32(for example, an opposite phase where a phase shift is 180°). Thereby, the connection switching control unit22can control the load voltage V0to be equal to or more than the source voltage VB. Moreover, a ripple frequency of each current of the load13, the capacitor14, and the power source BT can be more than a switching frequency. For example, even if the switching frequency is within an audible band, the connection switching control unit22changes the frequency of noise caused by the ripple current, which is generated in the load13, the capacitor14, and the power source BT, into a frequency outside the audible band. Thereby, the noise can be suppressed.

In particular, according to the switching operation using the opposite phase, since the ripple of current based on the operation of the first direct-current power converter circuit11and that of the second direct-current power converter circuit12are superimposed in the opposite phase each other, and the ripple of current based on the operation of the third direct-current power converter circuit31and that of the fourth direct-current power converter circuit32are superimposed in the opposite phase each other, the ripple of current flowing through the load13, the capacitor14, and the power source BT can be reduced in comparison with the switching operation using the same phase.

(Second Control Mode of the Variation)

In relation to the first control mode of the variation described above, the connection switching control unit22in a second control mode drives the first to fourth direct-current power converter circuits11,12,31, and32, where the phase of the switching operation of a pair of the first and second direct-current power converter circuits11and12is arbitrarily shifted from that of a pair of the third and fourth direct-current power converter circuits31and32(for example, a phase where a phase shift is 90°). Thereby, the ripple frequency of each current of the load13, the capacitor14, and the power source BT can be increased.

(Third Control Mode of the Variation)

In the second control mode of the variation described above, if the first and second reactors L1and L2are magnetically coupled and the third and fourth reactors L3and L4are magnetically coupled, the frequency of each first to fourth reactor current I(L1) to I(L4) can be increased more than the switching frequency. Moreover, the first and second reactors L1and L2may be provided to perform a magnetic-field cancellation, and the third and fourth reactors L3and L4may be provided to perform a magnetic-field cancellation.

Namely, in a third control mode, the connection switching control unit22sets the first to fourth direct-current power converter circuits11,12,31, and32in a condition that the first and second reactors L1and L2are magnetically coupled and the third and fourth reactors L3and L4are magnetically coupled so that the phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the second direct-current power converter circuit12and that the phase of the switching operation of the third direct-current power converter circuit31is arbitrarily shifted from that of the fourth direct-current power converter circuit32. Moreover, the connection switching control unit22sets the first to fourth direct-current power converter circuits11,12,31, and32so that the phase of the switching operation of a pair of the first and second direct-current power converter circuits11and12is arbitrarily shifted from that of a pair of the third and fourth direct-current power converter circuits31and32.

In particular, the phase of the switching operation of the first direct-current power converter circuit11is opposite to that of the second direct-current power converter circuit12, the phase of the switching operation of the third direct-current power converter circuit31is opposite to that of the fourth direct-current power converter circuit32, and a phase shift of the switching operation of the pair of the first and second direct-current power converter circuits11and12and the switching operation of the pair of the third and fourth direct-current power converter circuits31and32is 90°. Thereby, the ripple frequency of each current of the load13, the capacitor14, and the power source BT can be increased to the four times of the switching frequency, and a frequency of noise caused by the ripple current, which is generated in the load13, the capacitor14, and the power source BT, can be increased to outside an audible band.

(Fourth Control Mode of the Variation)

In a fourth mode, when the connection switching control unit22according to the variation simultaneously drives the first to fourth direct-current power converter circuits11,12,31, and32, where the phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the third direct-current power converter circuit31(for example, an opposite phase where a phase shift is 180°). Moreover, the connection switching control unit22drives the second and fourth direct-current power converter circuits12and32, where the phase of the switching operation of the second direct-current power converter circuit12is arbitrarily shifted from that of the fourth direct-current power converter circuit32(for example, an opposite phase where a phase shift is 180°). Thereby, the connection switching control unit22can control the load voltage V0to be equal to or more than the source voltage VB. Moreover, a ripple frequency of each current of the load13, the capacitor14, and the power source BT can be more than a switching frequency. For example, even if the switching frequency is within an audible band, the connection switching control unit22changes the frequency of noise caused by the ripple current, which is generated in the load13, the capacitor14, and the power source BT, into a frequency outside the audible band. Thereby, the noise can be suppressed.

In particular, based on the switching operation using the opposite phase, since the ripple of current based on the operation of the first direct-current power converter circuit11and that of the third direct-current power converter circuit31are superimposed in the opposite phase each other, and the ripple of current based on the operation of the second direct-current power converter circuit12and that of the fourth direct-current power converter circuits32are superimposed in the opposite phase each other, the ripple of current flowing through the load13, the capacitor14, and the power source BT can be reduced in comparison with the switching operation using the same phase.

(Fifth Control Mode of the Variation)

In relation to the fourth control mode of the variation described above, in a fifth mode, the connection switching control unit22drives the first to fourth direct-current power converter circuits11,12,31and32, where the phase of the switching operation of the pair of the first and third direct-current power converter circuits11and31is arbitrarily shifted from that of the pair of the second and fourth direct-current power converter circuits12and32(for example, a phase shift is 90°). Thereby, a ripple frequency of each current of the load13, the capacitor14, and the power source BT can be increased.

(Sixth Control Mode of the Variation)

In the fifth control mode of the variation described above, if the first and third reactors L1and L3are magnetically coupled and the second and fourth reactors L2and L4are magnetically coupled, the frequency of each first to fourth reactor currents I(L1) to I(L4) can be increased more than a switching frequency. Moreover, the first and third reactors L1and L3may be provided to perform a magnetic-field cancellation, and the second and fourth reactors L2and L4may be provided to perform a magnetic-field cancellation.

Namely, in a sixth control mode, the connection switching control unit22sets the first to fourth direct-current power converter circuits11,12,31, and32in the condition that the first and third reactors L1and L3are magnetically coupled and the second and fourth reactors L2and L4are magnetically coupled so that the phase of the switching operation of the first direct-current power converter circuit11is arbitrarily shifted from that of the third direct-current power converter circuit31, and that the phase of the switching operation of the second direct-current power converter circuit12is arbitrarily shifted from that of the fourth direct-current power converter circuit32. Moreover, the connection switching control unit22sets the first to fourth direct-current power converter circuits11,12,31, and32so that the phase of the switching operation of the pair of the first and third direct-current power converter circuits11and31is arbitrarily shifted from that of the pair of the second and fourth direct-current power converter circuits12and32.

In particular, the phase of the switching operation of the first direct-current power converter circuit11is opposite to that of the third direct-current power converter circuit31, the phase of the switching operation of the second direct-current power converter circuit12is opposite to that of the fourth direct-current power converter circuit32, and a phase shift of the switching operation of the pair of the first and third direct-current power converter circuits11and31and the switching operation of the pair of the second and fourth direct-current power converter circuits12and32is 90°. Thereby, the ripple frequency of each current of the load13, the capacitor14, and the power source BT can be increased to the four times of the switching frequency, and a frequency of noise caused by the ripple current, which is generated in the load13, the capacitor14, and the power source BT, can be increased to outside an audible band.

The technical scope of the present invention is not limited to the embodiments described above, and includes variations where a variety of modifications are made in the embodiments described above without departing from the spirit or scope of the present invention. In other words, the embodiments described above are illustrative only, and modifications may be made accordingly in the embodiments.

For example, the power source BT is not limited to a dischargeable and chargeable battery. The power source13T may be a fuel cell or a power generator which is only capable of discharging power. In this case, the first and fourth switching devices SW1and SW4of the embodiment described above and the first, fourth, fifth, and eighth switching devices SW1, SW4, SW5, and SW8of the variation of the embodiment described above may be replaced with a diode (in other words, a switch which can be electrically conducted in a forward direction by applying a forward direction voltage) to interrupt the charge from the load13to the source power BT.