Bidirectional DC/DC converter, and bidirectional power converter

In a discharging operation of a vehicle storage battery, a controller switches between a full-wave rectification operation of full-wave rectify a voltage across a second winding while maintaining a second short circuit in an open state, and a full-wave voltage doubling rectification operation of full-wave voltage doubling rectify a voltage across second winding while maintaining second short circuit in a closed state, based on magnitude relationship between DC voltage across first terminals and DC voltage across second terminals. In a charging operation, controller switches between a full-wave rectification operation of full-wave rectify a voltage across a first winding while maintaining a first short circuit in an open state, and a full-wave voltage doubling rectification operation of full-wave voltage doubling rectify a voltage across first winding while maintaining first short circuit in a closed state, based on magnitude relationship between DC voltage across first terminals and DC voltage across second terminals.

TECHNICAL FIELD

The invention relates generally to bidirectional DC/DC converters and bidirectional power converters and, more particularly, to a bidirectional DC/DC converter operating together with a bidirectional DC/AC inverter which is connected to a commercial power system and performs a linkage operation, and a bidirectional power converter including the bidirectional DC/DC converter.

BACKGROUND ART

In recent years, electric drive vehicles such as an electric vehicle (EV), a plug-in hybrid electric vehicle (PHEV) and the like become popular. Also, various kinds of power conditioners for a V2H (Vehicle to Home) system have been proposed for the purpose of using a vehicle storage battery equipped on the electric drive vehicle as a household power supply.

The power conditioner is generally constituted by a bidirectional DC/AC inverter (hereinafter, referred to as a bidirectional inverter) which is connected to the commercial power system and performs the linkage operation, and a bidirectional DC/DC converter to be connected to the vehicle storage battery equipped on the electric drive vehicle. The bidirectional DC/DC converter is required to have a function of electric power conversion from a battery voltage of the vehicle storage battery into a DC voltage required as an input of the bidirectional inverter, and a function of conversion from a DC voltage output from the bidirectional inverter into a charge voltage of the vehicle storage battery.

Conventionally, the bidirectional DC/DC converter includes a first conversion circuit including switching elements connected in a half-bridge manner and a voltage doubler rectifier circuit, and a second conversion circuit including switching elements connected in a full bridge manner. Power transfer between the first conversion circuit and the second conversion circuit is performed through a transformer, and the first conversion circuit and the second conversion circuit are electrically insulated by the transformer (for example, refer to JP 2011-120370 A).

The power conditioner for the V2H system is to be connected between the commercial power system and the electric drive vehicle, and controls charging and discharging operations between the vehicle storage battery and the commercial power system. The power conditioner is generally constituted by the bidirectional inverter which is to be connected to the commercial power system and performs the linkage operation, and the bidirectional DC/DC converter to be connected to the vehicle storage battery equipped on the electric drive vehicle.

The bidirectional DC/DC converter is required to have a function of performing electric power conversion from various battery voltages (DC150V to 450V) of the vehicle storage batteries into the DC voltages required as input of the bidirectional inverters in accordance with the battery voltage of a connected vehicle storage battery to be discharged. If a specification of an AC output of the bidirectional inverter is AC200V, the DC voltage required as an input of the bidirectional inverter is about DC300V to 400V. Also, if the specification of the AC output of the bidirectional inverter is AC 100V, the DC voltage required as an input of the bidirectional inverter is about DC 150V to 200V.

A voltage of the commercial power system to be connected to the bidirectional inverter is AC200V or AC100V. Accordingly, the bidirectional DC/DC converter is also required, for a charging operation of the vehicle storage battery, to have a function of performing electric power conversion from a DC voltage output from the bidirectional inverter connected to the commercial power system of AC200V or AC100V into any of the charge voltages of the vehicle storage batteries.

Accordingly, the bidirectional DC/DC converter is required to have a wide input voltage range and a wide output voltage range so as to be used for the various battery voltages of the vehicle storage batteries and various system voltages of the commercial power supplies. That is, such a bidirectional DC/DC converter is required that has a function of bidirectionally boosting and stepping down voltages in accordance with voltages selected from a wide range of battery voltages of vehicle storage batteries and a wide range of system voltages of commercial power supplies.

DISCLOSURE OF THE INVENTION

The invention is achieved in view of the above circumstances, and an object thereof is to provide a bidirectional DC/DC converter, which can bidirectionally boost and step down voltages with respect to wide ranges of an input voltage and an output voltage, and a bidirectional power converter.

A bidirectional DC/DC converter according to an aspect of the invention is configured to perform bidirectional voltage conversion in which an operation is switched between a first operation of outputting a second DC voltage resulting from DC/DC conversion of a first DC voltage received through first terminals, through second terminals, and a second operation of outputting a fourth DC voltage resulting from DC/DC conversion of a third DC voltage received through the second terminals, through the first terminals. The bidirectional DC/DC converter includes: a first switching circuit constituted by a series circuit of first and second switching elements connected between the first terminals and a series circuit of third and fourth switching elements connected between the first terminals; a first winding of a transformer connected between a connection point of the first and second switching elements and a connection point of the third and fourth switching elements; a second switching circuit constituted by a series circuit of fifth and sixth switching elements connected between the second terminals and a series circuit of seventh and eighth switching elements connected between the second terminals; a second winding of the transformer connected between a connection point of the fifth and sixth switching elements and a connection point of the seventh and eighth switching elements; first to eighth rectifying elements that are respectively connected in parallel to the first to eighth switching elements so that the first to eighth rectifying elements are reversely biased when receiving an input DC voltage; a series circuit of first and second capacitors connected between the first terminals; a series circuit of third and fourth capacitors connected between the second terminals; a first short circuit having a closed state of making electrical conduction between the connection point of the third and fourth switching elements and a connection point of the first and second capacitors and an open state of breaking the electrical conduction between the connection point of the third and fourth switching elements and the connection point of the first and second capacitors; a second short circuit having a closed state of making electrical conduction between the connection point of the seventh and eighth switching elements and a connection point of the third and fourth capacitors and an open state of breaking the electrical conduction between the connection point of the seventh and eighth switching elements and the connection point of the third and fourth capacitors; and a controller configured to perform drive controls of the first to eighth switching elements and open/close controls of the first and second short circuits. The controller is configured: in the first operation, to switch an operation between a full-wave rectification operation of applying a full-wave rectification voltage, resulting from full-wave rectification of a voltage across the second winding, to the series circuit of the third and fourth capacitors while maintaining the second short circuit in the open state, and a full-wave voltage doubling rectification operation of applying a voltage across the second winding alternately to the third capacitor and the fourth capacitor while maintaining the second short circuit in the closed state, on a basis of magnitude relationship between the first DC voltage received through the first terminals and the second DC voltage output through the second terminals; and in the second operation, to switch an operation between a full-wave rectification operation of applying a full-wave rectification voltage, resulting from full-wave rectification of a voltage across the first winding, to the series circuit of the first and second capacitors while maintaining the first short circuit in the open state, and a full-wave voltage doubling rectification operation of applying a voltage across the first winding alternately to the first capacitor and the second capacitor while maintaining the first short circuit in the closed state, on a basis of magnitude relationship between the fourth DC voltage output through the first terminals and the third DC voltage received through the second terminals.

A bidirectional power converter according to an aspect of the invention includes: the bidirectional DC/DC converter according to an aspect of the invention configured to perform bidirectional voltage conversion in which the operation is switched between the first operation of outputting the second DC voltage resulting from DC/DC conversion of the first DC voltage received through the first terminals, through the second terminals, and the second operation of outputting the fourth DC voltage resulting from DC/DC conversion of the third DC voltage received through the second terminals, through the first terminals; and a bidirectional inverter configured to convert the second DC voltage across the second terminals into an AC voltage and output the resultant AC voltage in accordance with the first operation, and to convert an AC voltage into the third DC voltage to apply the third DC voltage between the second terminals in accordance with the second operation.

DESCRIPTION OF EMBODIMENTS

FIG. 2shows a block diagram of a bidirectional power converter (power conditioner). The bidirectional power converter includes a bidirectional DC/DC converter1, a bidirectional inverter2and a capacitor3.

Regarding the bidirectional DC/DC converter1, a vehicle storage battery4of an electric drive vehicle is connected between terminals T11and T12(first terminals), and the capacitor3is connected between terminals T21and T22(second terminals). Regarding the bidirectional inverter2, the capacitor3is connected between terminals T31and T32, and a commercial power system in which a commercial power is supplied from a commercial power supply5is connected between terminals T41and T42.

In a discharging operation of the vehicle storage battery4(a first operation), the bidirectional DC/DC converter1converts a battery voltage of the vehicle storage battery4input through the terminals T11and T12into a desired DC voltage, and outputs the resultant DC voltage through the terminals T21and T22. The DC voltage output through the terminals T21and T22is smoothed by the capacitor3and then, the resultant DC voltage is applied across the terminals T31and T32of the bidirectional inverter2. The bidirectional inverter2converts the DC voltage input through the terminals T31and T32into an AC voltage compatible to the commercial power system, and outputs the resultant AC voltage through the terminals T41and T42.

In a charging operation of the vehicle storage battery4(a second operation), the bidirectional inverter2converts a commercial voltage (AC voltage) input through the terminals T41and T42into a DC voltage, and outputs the resultant DC voltage through the terminals T31and T32. The DC voltage output through the terminals T31and T32is smoothed by the capacitor3and then, the resultant DC voltage is applied across the terminals T21and T22of the bidirectional DC/DC converter1. The bidirectional DC/DC converter1converts the DC voltage input through the terminals T21and T22into a charge voltage, and outputs the resultant voltage through the terminals T11and T12to charge the vehicle storage battery4.

FIG. 1shows a circuit configuration of the bidirectional DC/DC converter1. The bidirectional DC/DC converter1includes switching circuits11and12, a transformer Tr1, diodes D1to D8, capacitors C1to C4, short circuits13and14, and a controller15, as main elements.

The switching circuit11(a first switching circuit) includes a parallel circuit of switching elements Q1and Q2connected in series, and switching elements Q3and Q4connected in series. The parallel circuit is connected between the terminals T11and T12. The switching elements Q1and Q4are positioned diagonally in a full-bridge, and the switching elements Q2and Q3are positioned diagonally in the full-bridge. Each of the switching elements Q1to Q4is constituted by a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) element. The switching elements Q1to Q4may be constituted by an IGBT (Insulated Gate Bipolar Transistor) element and the like, besides the MOSFET element. The switching elements Q1to Q4respectively correspond to first to fourth switching elements of an aspect of the present invention.

The diodes D1to D4(first to fourth rectifying elements) are respectively connected in inverse parallel to the switching elements Q1to Q4.

A first winding N1of the transformer Tr1is connected between a connection point of the switching elements Q1and Q2and a connection point of the switching elements Q3and Q4.

A series circuit of the capacitors C1and C2(first and second capacitors) is connected between the terminals T11and T12. Capacitances of the capacitors C1and C2are the same.

The short circuit13(a first short circuit) is provided between the connection point of the switching elements Q3and Q4and a connection point of the capacitors C1and C2to have a closed state of making electrical conduction and an open state of breaking the electrical conduction between two connection points. The short circuit13is constituted by a series circuit of switching elements Q11and Q12connected between the connection point of the switching elements Q3and Q4and the connection point of the capacitors C1and C2, and diodes D11and D12respectively connected in inverse parallel to the switching elements Q11and Q12. Each of the switching elements Q11and Q12is constituted by the MOSFET element, the IGBT element and the like.

The switching circuit12(a second switching circuit) includes a parallel circuit of switching elements Q5and Q6connected in series, and switching elements Q7and Q8connected in series. The parallel circuit is connected between the terminals T21and T22. The switching elements Q5and Q8are positioned diagonally in a full-bridge, and the switching elements Q6and Q7are positioned diagonally in the full-bridge. Each of the switching elements Q5to Q8is constituted by the MOSFET element, the IGBT element and the like. The switching elements Q5to Q8respectively correspond to fifth to eighth switching elements of an aspect of the present invention.

The diodes D5to D8(fifth to eighth rectifying elements) are respectively connected in inverse parallel to the switching elements Q5to Q8.

A series circuit of a second winding N2of the transformer Tr1and an inductor L1is connected between a connection point of the switching elements Q5and Q6and a connection point of the switching elements Q7and Q8.

A series circuit of the capacitors C3and C4(third and fourth capacitors) is connected between the terminals T21and T22. Capacitances of the capacitors C3and C4are the same.

The short circuit14(a second short circuit) is provided between the connection point of the switching elements Q7and Q8and a connection point of the capacitors C3and C4to have a closed state of making electrical conduction and an open state of breaking the electrical conduction between two connection points. The short circuit14is constituted by a series circuit of switching elements Q13and Q14connected between the connection point of the switching elements Q7and Q8and the connection point of the capacitors C3and C4, and diodes D13and D14respectively connected in inverse parallel to the switching elements Q13and Q14. Each of the switching elements Q13and Q14is constituted by the MOSFET element, the IGBT element and the like.

The controller15controls switching operations of the switching circuits11and12by controlling ON/OFF drives of the switching elements Q1to Q8on a basis of a voltage V1between the terminals T11and T12, a voltage V2between the terminals T21and T22and a charge or discharge current of the vehicle storage battery4. The controller15also controls open and close operations of the short circuits13and14by controlling ON/OFF drives of the switching elements Q11to Q14. Note that inFIG. 1, control lines between the controller15and each of the switching elements Q1to Q8and the switching elements Q11to Q14, a detector for the voltage V1and the voltage V2, and a detector for the charge and discharge currents of the vehicle storage battery4are omitted.

According to the present embodiment, the controller15switches an operation between a full-wave rectification operation and a full-wave voltage doubling rectification operation by switching the closed state of making electrical conduction and the open state of breaking the electrical conduction, of the short circuits13and14, on a basis of magnitude relationship between a DC voltage across the terminals T11and T12and a DC voltage across the terminals T21and T22.

Hereinafter, an operation of the bidirectional DC/DC converter1will be described.

Charge voltage and discharge voltage of the vehicle storage battery4(the voltage V1across the terminals T11and T12) vary within a range of DC150V to 450V depending on specifications and states of the vehicle storage battery4. A system voltage of the commercial power supply5is assumed to be AC200V, and a voltage across the capacitor3is assumed to be DC320V. In this case, a ratio in the number of turns of the windings N1, N2of the transformer is set that the number of turns of the first winding N1: the number of turns of the second winding N2is 3:4.

First explained is an operation for charging the vehicle storage battery4in a case where the charge voltage of the vehicle storage battery4is DC150V, with reference to waveform diagrams inFIGS. 3A to 3G. A voltage output from the bidirectional inverter2through the terminal T31and T32is DC320V. The bidirectional DC/DC converter1steps down a voltage V2across the terminals T21and T22of DC320V (an input voltage) to a voltage V1across the terminals T11and T12of DC150V (an output voltage).

In the charging operation of the vehicle storage battery4with a charge voltage of DC150V, as shown inFIGS. 3A to 3D, the controller15controls the switching operations of the switching elements Q5to Q8to perform a full bridge operation. In the full bridge operation of the switching circuit12, the switching elements Q13and Q14are maintained in OFF states by the controller15.

Duty cycles of the switching elements Q5and Q6are controlled to be approximately 50%, and ON/OFF states of the switching elements Q5and Q6are mutually inverted. That is, while the switching element Q5is in an ON state, the switching element Q6is in an OFF state. Also, while the switching element Q5is in an OFF state, the switching element Q6is in an ON state. A dead time in which the switching elements Q5and Q6are both in OFF states is provided when the ON/OFF states of the switching elements Q5and Q6are mutually inverted (not shown inFIGS. 3A and 3B).

Duty cycles of the switching elements Q7and Q8are controlled to be approximately 50%, and ON/OFF states of the switching elements Q7and Q8are mutually inverted. That is, while the switching element Q7is in an ON state, the switching element Q8is in an OFF state. Also, while the switching element Q7is in an OFF state, the switching element Q8is in an ON state. A dead time in which the switching elements Q7and Q8are both in OFF states is provided when the ON/OFF states of the switching elements Q7and Q8are mutually inverted (not shown inFIGS. 3C and 3D).

FIG. 3Eshows a waveform of a voltage Vn2of the second winding N2of the transformer Tr1, andFIG. 3Fshows a waveform of a voltage Vn1of the first winding N1of the transformer Tr1. In a period in which the switching elements Q5and Q8are both in the ON states and the switching elements Q6and Q7are both in the OFF states, a voltage Vn2of 320V is applied across the second winding N2of the transformer Tr1. In this period, a stepped down voltage Vn1of 240V in accordance with a ratio in the number of turns of the transformer Tr1is generated across the first winding N1of the transformer Tr1. In a period in which the switching elements Q6and Q7are both in ON states and the switching elements Q5and Q8are both in OFF states, a voltage Vn2of −320V is applied across the second winding N2of the transformer Tr1. In this period, a stepped down voltage Vn1of −240V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the first winding N1of the transformer Tr1. That is, a voltage of which peak voltage is 240V, having a shape of a substantially trapezoidal shape and a voltage of which peak voltage is −240V, having a shape of a substantially trapezoidal shape are alternately generated across the first winding N1.

The controller15keeps the switching elements Q1to Q4and the switching elements Q11and Q12in OFF states, and thus the resultant voltage Vn1is full-wave rectified by the diodes D1to D4. The resultant full-wave rectified voltage by the diodes D1to D4is applied across both ends of the series circuit of the capacitors C1and C2, and then is smoothed. The voltage across both ends of the series circuit of the capacitors C1and C2as a voltage V1shown inFIG. 3Gis output through the terminals T11and T12. Note that, the switching elements Q1to Q4may perform a full-wave rectification operation in accordance with a synchronous rectification operating together with ON/OFF operations of the switching elements Q5to Q8.

Hereinafter, a period during which the switching elements Q5and Q8are in the ON states and also the switching elements Q6and Q7are in the OFF states is referred to as a period T1. Also, a period during which the switching elements Q6and Q7are in the ON states and also the switching elements Q5and Q8are in the OFF states is referred to as a period T2. These two periods T1and T2correspond to supply periods of energy from the second winding N2to the first winding N1. Periods other than the two periods T1and T2(periods T3and T4inFIG. 3) correspond to stop periods of energy from the second winding N2to the first winding N1. The controller15controls the voltage V1which is output through the terminals T11and T12by adjusting a ratio of the supply periods of energy [T1+T2] and the stop periods of energy [T3+T4]. Specifically, the controller15performs a phase shift operation of changing a phase when the states of the switching elements Q5and Q6are inverted and a phase when the states of the switching elements Q7and Q8are inverted, for adjusting the ratio of the supply periods of energy and the stop periods of energy.

According to the present embodiment, in a case where a phase difference between an ON period of the switching element Q5and an ON period of the switching element Q8is 0 degree and also a phase difference between an ON period of the switching element Q6and an ON period of the switching element Q7is 0 degree, a voltage V1of DC240V is output through the terminals T11and T12. In a case where the phase difference between the ON period of the switching element Q5and the ON period of the switching element Q8is 180 degrees and also the phase difference between the ON period of the switching element Q6and the ON period of the switching element Q7is 180 degrees, a voltage V1output through the terminals T11and T12is approximately 0V. The controller15controls ON/OFF states of the switching elements Q5to Q8so that the voltage V1which is output through the terminals T11and T12equals to DC150V.

Next explained is an operation for discharging the vehicle storage battery4in a case where the discharge voltage of the vehicle storage battery4is DC 150V, with reference to waveform diagrams inFIGS. 4A to 4G. The bidirectional DC/DC converter1boosts (steps up) a voltage V1across the terminals T11and T12of DC150V (an input voltage) to a voltage V2across the terminals T21and T22of DC320V (an output voltage).

In the discharging operation of the vehicle storage battery4with a discharge voltage of DC 150V, as shown inFIGS. 4A to 4D, the controller15controls the switching operations of the switching elements Q1to Q4to perform a full bridge operation. In the full bridge operation of the switching circuit11, the switching elements Q11and Q12are maintained in OFF states by the controller15.

Duty cycles of the switching elements Q1and Q2are controlled to be approximately 50%, and ON/OFF states of the switching elements Q1and Q2are mutually inverted. That is, while the switching element Q1is in an ON state, the switching element Q2is in an OFF state. Also, while the switching element Q1is in an OFF state, the switching element Q2is in an ON state. A dead time in which the switching elements Q1and Q2are both in OFF states is provided when the ON/OFF states of the switching elements Q1and Q2are mutually inverted (not shown inFIGS. 4A and 4B).

Duty cycles of the switching elements Q3and Q4are controlled to be approximately 50%, and ON/OFF states of the switching elements Q3and Q4are mutually inverted. That is, while the switching element Q3is in an ON state, the switching element Q4is in an OFF state. Also, while the switching element Q3is in an OFF state, the switching element Q4is in an ON state. A dead time in which the switching elements Q3and Q4are both in OFF states is provided when the ON/OFF states of the switching elements Q3and Q4are mutually inverted (not shown inFIGS. 4C and 4D).

FIG. 4Eshows the waveform of the voltage Vn1of the first winding N1of the transformer Tr1, andFIG. 4Fshows the waveform of the voltage Vn2of the second winding N2of the transformer Tr1. In a period in which the switching elements Q1and Q4are both in ON states and the switching elements Q2and Q3are both in OFF states, a voltage Vn1of 150V is applied across the first winding N1of the transformer Tr1. In this period, a stepped up voltage Vn2of 200V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the second winding N2of the transformer Tr1. In a period in which the switching elements Q2and Q3are both in ON states and the switching elements Q1and Q4are both in OFF states, a voltage Vn1of −150V is applied across the first winding N1of the transformer Tr1. In this period, a stepped up voltage Vn2of −200V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the second winding N2of the transformer Tr1. That is, a voltage of which peak voltage is 200V, having a shape of a substantially trapezoidal shape and a voltage of which peak voltage is −200V, having a shape of a substantially trapezoidal shape are alternately generated across the second winding N2.

The controller15keeps the switching elements Q5to Q8in OFF states and also keeps the switching elements Q13and Q14in ON states. As a result, a full-wave voltage doubling rectification is performed in which a period when a voltage across the second winding N2is applied to the capacitor C3through the inductor L1and a period when the voltage across the second winding N2is applied to the capacitor C4through the inductor L1alternate every half cycle, and then the resultant voltage is smoothed by the capacitors C3and C4. The voltage across both ends of the series circuit of the capacitors C3and C4as a voltage V2shown inFIG. 4Gis output through the terminals T21and T22.

Hereinafter, a period during which the switching elements Q1and Q4are in the ON states and also the switching elements Q2and Q3are in the OFF states is referred to as a period T11. Also, a period during which the switching elements Q2and Q3are in the ON states and also the switching elements Q1and Q4are in the OFF states is referred to as a period T12. These two periods T11and T12corresponds to supply periods of energy from the first winding N1to the second winding N2. The voltage Vn2is applied to the capacitor C3during the period T11and is applied to the capacitor C4during the period T12. Periods other than the two periods T11and T12(periods T13and T14inFIG. 4) corresponds to stop periods of energy from the first winding N1to the second winding N2. The controller15controls the voltage V2which is output through the terminals T21and T22by adjusting a ratio of the supply periods of energy [T11+T12] and the stop periods of energy [T13+T14]. Specifically, the controller15performs a phase shift operation of changing a phase when the states of the switching elements Q1and Q2are inverted and a phase when the states of the switching elements Q3and Q4are inverted, for adjusting the ratio of the supply periods of energy and the stop periods of energy.

According to the present embodiment, in a case where a phase difference between an ON period of the switching element Q1and an ON period of the switching element Q4is 0 degree and also a phase difference between an ON period of the switching element Q2and an ON period of the switching element Q3is 0 degree, a voltage V2of DC400V is output through the terminals T21and T22. In a case where the phase difference between the ON period of the switching element Q1and the ON period of the switching element Q4is 180 degrees and also the phase difference between the ON period of the switching element Q2and the ON period of the switching element Q3is 180 degrees, a voltage V2which is output through the terminals T21and T22is approximately 0V. The controller15controls ON/OFF states of the switching elements Q1to Q4so that the voltage V2which is output through the terminals T21and T22equals to DC320V (the capacitor C3: DC160V, the capacitor C4: DC160V).

Next explained is an operation for charging a vehicle storage battery4in a case where the charge voltage of the vehicle storage battery4is DC450V. The bidirectional DC/DC converter1steps up a voltage V2across the terminals T21and T22of DC320V (an input voltage) to a voltage V1across the terminals T11and T12of DC450V (an output voltage).

In the charging operation of the vehicle storage battery4with a charge voltage of DC450V, the controller15controls the switching elements Q5to Q8to perform a full bridge operation (refer toFIGS. 3A to 3D). In the full bridge operation of the switching circuit12, the switching elements Q13and Q14are maintained in OFF states by the controller15.

In a period in which the switching elements Q5and Q8are both in the ON states and the switching elements Q6and Q7are both in the OFF states, a voltage Vn2of 320V is applied across the second winding N2of the transformer Tr1. In this period, a stepped down voltage Vn1of 240V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the first winding N1of the transformer Tr1. In a period in which the switching elements Q6and Q7are both in the ON states and the switching elements Q5and Q8are both in the OFF states, a voltage Vn2of −320V is applied across the second winding N2of the transformer Tr1. In this period, a stepped down voltage Vn1of −240V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the first winding N1of the transformer Tr1. That is, a voltage of which peak voltage is 240V, having a shape of a substantially trapezoidal shape and a voltage of which peak voltage is −240V, having a shape of a substantially trapezoidal shape are alternately generated across the first winding N1(refer toFIGS. 3E and 3F).

The controller15keeps the switching elements Q1to Q4in the OFF states and keeps the switching elements Q11and Q12in the ON states. As a result, a full-wave voltage doubling rectification is performed in which a period when a voltage across the first winding N1is applied to the capacitor C1and a period when the voltage across the first winding N1is applied to the capacitor C2alternate every half cycle, and then the resultant voltage is smoothed by the capacitors C1and C2. The voltage across both ends of the series circuit of the capacitors C1and C2as a voltage V1is output through the terminals T11and T12.

The controller15controls the ON/OFF states of the switching elements Q5to Q8so that the voltage V1which is output through the terminals T11and T12equals to DC450V (the capacitor C1: DC225V, the capacitor C2: DC225V). Specifically, the controller15performs the phase shift operation of changing a phase when the states of the switching elements Q5and Q6are inverted and a phase when the states of the switching elements Q7and Q8are inverted, for adjusting the ratio of the supply periods of energy and the stop periods of energy.

Next explained is an operation for discharging the vehicle storage battery4in a case where the discharge voltage of the vehicle storage battery4is DC450V. The bidirectional DC/DC converter1steps down a voltage V1across the terminals T11and T12of DC450V (an input voltage) to a voltage V2across the terminals T21and T22of DC320V (an output voltage).

In the discharging operation of the vehicle storage battery4with the discharge voltage of DC450V, the controller15controls the switching elements Q1to Q4to perform a full bridge operation (refer toFIGS. 4A to 4D). In the full bridge operation of the switching circuit11, the switching elements Q11and Q12are maintained in the OFF states by the controller15.

In a period in which the switching elements Q1and Q4are both in the ON states and the switching elements Q2and Q3are both in the OFF states, a voltage Vn1of 450V is applied across the first winding N1of the transformer Tr1. In this period, a stepped up voltage Vn2of 600V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the second winding N2of the transformer Tr1. In a period in which the switching elements Q2and Q3are both in the ON states and the switching elements Q1and Q4are both in the OFF states, a voltage Vn1of −450V is applied across the first winding N1of the transformer Tr1. In this period, a stepped up voltage Vn2of −600V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the second winding N2of the transformer Tr1. That is, a voltage of which peak voltage is 600V, having a shape of a substantially trapezoidal shape and a voltage of which peak voltage is −600V, having a shape of a substantially trapezoidal shape are alternately generated across the second winding N2.

The controller15keeps the switching elements Q5to Q8and the switching elements Q13and Q14in the OFF states, and thus the resultant voltage Vn2is full-wave rectified by the diodes D5to D8. The resultant full-wave rectified voltage by the diodes D5to D8is applied across the both ends of the series circuit of the capacitors C3and C4, and then is smoothed. The voltage across the both ends of the series circuit of the capacitors C3and C4as a voltage V2is output through the terminals T21and T22. Note that, the switching elements Q5to Q8may be controlled to perform a full-wave rectification operation in accordance with a synchronous rectification of operating together with ON/OFF operations of the switching elements Q1to Q4.

The controller15controls the ON/OFF states of the switching elements Q1to Q4so that the voltage V2which is output through the terminals T21and T22equals to DC320V. Specifically, the controller15performs the phase shift operation of changing a phase when the states of the switching elements Q1and Q2are inverted and a phase when the states of the switching elements Q3and Q4are inverted, for adjusting the ratio of the supply periods of energy and the stop periods of energy.

As described above, the controller15switches the operation between the full-wave rectification operation and the full-wave voltage doubling rectification operation on the basis of magnitude relationship between the DC voltage across the terminals T11and T12and the DC voltage across the terminals T21and T22. Accordingly, the bidirectional DC/DC converter1has wider available ranges of an input voltage and an output voltage. As a result, it is possible to perform the boost and step down operations bidirectionally within the widened ranges of the input voltage and the output voltage.

The controller15may be configured to switch operations of the switching circuits11and12between a full bridge operation and a half bridge operation on the basis of magnitude relationship between the DC voltage across the terminals T11and T12and the DC voltage across the terminals T21and T22. In this case, the ranges of the input voltage and the output voltage of the bidirectional DC/DC converter1can be further widened.

For example, in a case where the discharge voltage of the vehicle storage battery4is DC450V, the bidirectional DC/DC converter1may step down a voltage V1across the terminals T11and T12of DC450V (the input voltage) to a voltage V2across the terminals T21and T22of DC320V (the output voltage).

In the discharging operation of the vehicle storage battery4with a discharge voltage of DC450V, the controller15keeps the switching elements Q3and Q4in the OFF states and keeps the switching elements Q11and Q12in the ON states. The controller15controls the duty cycle of the switching element Q1to equal to or less than 50%, and controls the duty cycle of the switching element Q2to a value same as that of the switching element Q1. Also, the controller15controls the switching operation of the switching elements Q1and Q2so that a phase of an ON state of the switching element Q1and a phase of an ON state of the switching element Q2differ from each other by 180 degrees. That is, the controller15controls the switching circuit11in accordance with a half bridge operation.

In a period in which the switching element Q1is in the ON state and the switching element Q2is in the OFF state, a voltage Vn1of 225V (a half of 450V) is applied across the first winding N1of the transformer Tr1. In this period, a stepped up voltage Vn2of 300V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the second winding N2of the transformer Tr1. In a period in which the switching element Q2is in the ON state and the switching element Q1is in the OFF state, a voltage Vn1of −225V is applied across the first winding N1of the transformer Tr1. In this period, a stepped up voltage Vn2of −300V in accordance with the ratio in the number of turns of the transformer Tr1is generated across the second winding N2of the transformer Tr1. That is, a voltage of which peak voltage is 300V, having a shape of a substantially trapezoidal shape and a voltage of which peak voltage is −300V, having a shape of a substantially trapezoidal shape are alternately generated across the second winding N2.

The controller15keeps the switching elements Q5to Q8in the OFF states and keeps the switching elements Q13and Q14in the ON states. As a result, the full-wave voltage doubling rectification is performed in which a period when a voltage across the second winding N2is applied to the capacitor C3and a period when the voltage across the second winding N2is applied to the capacitor C4alternate every half cycle, and then the resultant voltage is smoothed by the capacitors C3and C4. The voltage across the both ends of the series circuit of the capacitors C3and C4as the voltage V1is output through the terminals T11and T12. Note that, the switching elements Q5and Q6may be controlled to perform a synchronous rectification by operating together with ON/OFF operations of the switching elements Q1and Q2.

The controller15controls ON/OFF states of the switching elements Q1and Q2so that the voltage V2which is output through the terminals T21and T22equals to DC320V (the capacitor C3: DC160V, the capacitor C4: DC160V). Specifically, the controller15controls the duty cycle of the switching elements Q1and Q2for adjusting the ratio of the supply periods of energy and the stop periods of energy.

Also, in the charging operation of the vehicle storage battery4, the controller15may switch an operation of the switching circuit12between a full bridge operation and a half bridge operation on the basis of magnitude relationship between the DC voltage across the terminals T11and T12and the DC voltage across the terminals T21and T22.

The present invention has been described with reference to certain preferred embodiments. However, the invention is not limited to the embodiments, and numerous modifications and variations can be made without departing from the true spirit and scope of this invention.

The bidirectional DC/DC converter1described above is configured to perform bidirectional voltage conversion in which an operation is switched between a first operation and a second operation. The first operation is the operation of outputting a DC voltage (a second DC voltage) resulting from DC/DC conversion of a DC voltage (a first DC voltage) received through first terminals (terminals T11and T12), through second terminals (terminals T21and T22). The second operation is the operation of outputting a DC voltage (a fourth DC voltage) resulting from DC/DC conversion of a DC voltage (a third DC voltage) received through the second terminals, through the first terminals. The bidirectional DC/DC converter1includes a first switching circuit11. The first switching circuit11is constituted by a series circuit of a first switching element Q1and a second switching element Q2connected between the first terminals and a series circuit of a third switching element Q3and a fourth switching element Q4connected between the first terminals. The bidirectional DC/DC converter1further includes a first winding N1of a transformer Tr1connected between a connection point of the first switching element Q1and the second switching element Q2and a connection point of the third switching element Q3and the fourth switching element Q4. The bidirectional DC/DC converter1further includes a second switching circuit12. The second switching circuit12is constituted by a series circuit of a fifth switching element Q5and a sixth switching element Q6connected between the second terminals and a series circuit of a seventh switching element Q7and an eighth switching element Q8connected between the second terminals. The bidirectional DC/DC converter1further includes a second winding N2of the transformer Tr1connected between a connection point of the fifth switching element Q5and the sixth switching element Q6and a connection point of the seventh switching element Q7and the eighth switching element Q8. The bidirectional DC/DC converter1further includes first to eighth rectifying elements D1to D8that are respectively connected in parallel to the first to eighth switching elements Q1to Q8so that the first to eighth rectifying elements D1to D8are reversely biased when receiving an input DC voltage. The bidirectional DC/DC converter1further includes a series circuit of a first capacitor C1and a second capacitor C2connected between the first terminals, and a series circuit of a third capacitor C3and a fourth capacitor C4connected between the second terminals. The bidirectional DC/DC converter1further includes a first short circuit13having a closed state of making electrical conduction between the connection point of the third switching element Q3and the fourth switching element Q4and a connection point of the first capacitor C1and the second capacitor C2and an open state of breaking the electrical conduction between the connection point of the third switching element Q3and the fourth switching element Q4and the connection point of the first capacitor C1and the second capacitor C2. The bidirectional DC/DC converter1further includes a second short circuit14having a closed state of making electrical conduction between the connection point of the seventh switching element Q7and the eighth switching element Q8and a connection point of the third capacitor C3and the fourth capacitor C4and an open state of breaking the electrical conduction between the connection point of the seventh switching element Q7and the eighth switching element Q8and the connection point of the third capacitor C3and the fourth capacitor C4. The bidirectional DC/DC converter1further includes a controller15configured to perform drive controls of the first to eighth switching elements Q1to Q8and open/close controls of the first short circuit13and the second short circuit14.

The controller15is configured, in the first operation, to switch an operation between a full-wave rectification operation and a full-wave voltage doubling rectification operation on a basis of magnitude relationship between the DC voltage (the first DC voltage) received through the first terminals and the DC voltage (the second DC voltage) output through the second terminals. The full-wave rectification operation in the first operation is the operation of applying a full-wave rectification voltage, resulting from full-wave rectification of a voltage across the second winding N2, to the series circuit of the third capacitor C3and the fourth capacitor C4while maintaining the second short circuit14in the open state. The full-wave voltage doubling rectification operation in the first operation is the operation of applying a voltage across the second winding N2alternately to the third capacitor C3and the fourth capacitor C4while maintaining the second short circuit14in the closed state.

Further, the controller15is configured, in the second operation, to switch an operation between a full-wave rectification operation and a full-wave voltage doubling rectification operation on a basis of magnitude relationship between the DC voltage (the fourth DC voltage) output through the first terminals and the DC voltage (the third DC voltage) received through the second terminals. The full-wave rectification operation in the second operation is the operation of applying a full-wave rectification voltage, resulting from full-wave rectification of a voltage across the first winding N1, to the series circuit of the first capacitor C1and the second capacitor C2while maintaining the first short circuit13in the open state. The full-wave voltage doubling rectification operation in the second operation is the operation of applying a voltage across the first winding N1alternately to the first capacitor C1and the second capacitor C2while maintaining the first short circuit13in the closed state.

According to the configuration, the bidirectional DC/DC converter1according to an aspect of the present invention switches the operation between the full-wave rectification operation and the full-wave voltage doubling rectification operation on the basis of magnitude relationship between the DC voltage (the first or fourth DC voltage) across the first terminals and the DC voltage (the second or third DC voltage) across the second terminals. Accordingly, the bidirectional DC/DC converter has wider available ranges of an input voltage and an output voltage. As a result, it is possible to perform the boost and step down operations bidirectionally within the widened ranges of the input voltage and the output voltage.

Preferably, the controller15is configured, in the first operation, to switch, on a basis of magnitude relationship between the DC voltage (the first DC voltage) of the first terminals and the DC voltage (the second DC voltage) of the second terminals, an operation between a full bridge operation and a half bridge operation. The full bridge operation for switching control is performed as follows while maintaining the first short circuit13in the open state. The full bridge operation includes switching controls of: the first switching element Q1and the second switching element Q2so that ON/OFF states of the first switching element Q1and the second switching element Q2are mutually inverted; and further the third switching element Q3and the fourth switching element Q4so that ON/OFF states of the third switching element Q3and the fourth switching element Q4are mutually inverted. The half bridge operation is performed as follows while maintaining the first short circuit13in the closed state. The half bridge operation includes: setting a duty cycle of the first switching element Q1to equal to or less than 50%; setting a duty cycle of the second switching element Q2to a value same as that of the first switching element Q1; controlling switching of the first switching element Q1and the second switching element Q2so that a phase difference between an ON state of the first switching element Q1and an ON state of the second switching element Q2is 180 degrees; and maintaining the third switching element Q3and the fourth switching element Q4in OFF states.

According to the configuration, in the first operation, the bidirectional DC/DC converter1switches, on the basis of magnitude relationship between the DC voltage (the first DC voltage) of the first terminals and the DC voltage (the second DC voltage) of the second terminals, the operation between the full bridge operation and the half bridge operation. Accordingly, both ranges of the input voltage and the output voltage of the bidirectional DC/DC converter1can be further widened.

Preferably, the controller15is configured, in the second operation, to switch, on a basis of magnitude relationship between the DC voltage (the fourth DC voltage) of the first terminals and the DC voltage (the third DC voltage) of the second terminals, an operation between a full bridge operation and a half bridge operation. The full bridge operation for switching control is performed as follows while maintaining the second short circuit14in the open state. The full bridge operation includes switching controls of: the fifth switching element Q5and the sixth switching element Q6so that ON/OFF states of the fifth switching element Q5and the sixth switching element Q6are mutually inverted; and further the seventh switching element Q7and the eighth switching element Q8so that ON/OFF states of the seventh switching element Q7and the eighth switching element Q8are mutually inverted. The half bridge operation is performed as follows while maintaining the second short circuit14in the closed state. The half bridge operation includes: setting a duty cycle of the fifth switching element Q5to equal to or less than 50%; setting a duty cycle of the sixth switching element Q6to a value same as that of the fifth switching element Q5; controlling switching of the fifth switching element Q5and the sixth switching element Q6so that a phase difference between an ON state of the fifth switching element Q5and an ON state of the sixth switching element Q6is 180 degrees; and maintaining the seventh switching element Q7and the eighth switching element Q8in OFF states.

According to the configuration, in the second operation, the bidirectional DC/DC converter1switches, on the basis of magnitude relationship between the DC voltage (the fourth DC voltage) of the first terminals and the DC voltage (the third DC voltage) of the second terminals, the operation between the full bridge operation and the half bridge operation. Accordingly, both ranges of the input voltage and the output voltage of the bidirectional DC/DC converter1can be further widened.

A bidirectional power converter includes the bidirectional DC/DC converter1according to an aspect of the present invention and a bidirectional inverter2. The bidirectional DC/DC converter1performs bidirectional voltage conversion in which the operation is switched between the first operation and the second operation. The first operation is for outputting the DC voltage (the second DC voltage) resulting from DC/DC conversion of the DC voltage (the first DC voltage) received through the first terminals (the terminals T11and T12), through the second terminals (the terminals T21and T22). The second operation is for outputting the DC voltage (the fourth DC voltage) resulting from DC/DC conversion of the DC voltage (the third DC voltage) received through the second terminals, through the first terminals. The bidirectional inverter2is configured: to convert the DC voltage (the second DC voltage) across the second terminals into an AC voltage and output the resultant AC voltage in accordance with the first operation; and to convert an AC voltage into the DC voltage (the third DC voltage) to apply the DC voltage (the third DC voltage) between the second terminals in accordance with the second operation.

According to the configuration, the bidirectional power converter according to an aspect of the present invention switches the operation between the full-wave rectification operation and the full-wave voltage doubling rectification operation on the basis of magnitude relationship between the DC voltage (the first or fourth DC voltages) across the first terminals and the DC voltage (the second or third DC voltages) across the second terminals. Accordingly, the bidirectional DC/DC converter1has wider available ranges of the input voltage and the output voltage. As a result, it is possible to perform the boost and step down operations bidirectionally within the widened ranges of the input voltage and the output voltage.