Power supply device operating switching elements of first and second switching legs to charge first and second capacitors to a voltage higher than a voltage crest value of an AC power supply and method of operating the power supply device

The present application claims priority from Japanese Patent Application JP 2013-155317 filed on Jul. 26, 2013, the content of which is hereby incorporated by reference into this application.

The present invention relates to a power supply device which converts power between direct current and alternating current and a method of operating the device.

In recent years, as awareness of global environment conservation increases, systems having a direct-current power supply such as a storage cell, a solar cell or a fuel cell are being developed. Those systems need a power supply device for converting direct-current (DC) power generated by a storage cell, a solar cell, a fuel cell, or the like to an alternating-current (AC) power and supplying the AC power to a load or a commercial power supply. In the case of charging a storage cell from a commercial power supply, it is necessary to convert the AC power of the commercial power supply to DC power and supply the DC power to the storage cell.

Japanese Unexamined Patent Application Publication No. 2002-78350 (Document 1) discloses a single-phase three-wire AC/DC bidirectional converter. The converter realizes charging of a cell from a single-phase three-wire AC power supply and power regeneration to the single-phase three-wire AC power supply by discharging the cell in a single circuit, aiming to realize smaller size and lower cost.

Japanese Unexamined Patent Application Publication No. 2008-289211 (Document 2) and Japanese Unexamined Patent Application Publication No. 9-140157 (Document 3) also disclose inverters adapted to a single-phase three-wire system.

In the case of performing backup of an AC load at the time of interruption of power supply of a commercial power system by using any of the power supply devices, which output a single-phase three-wire AC voltage, disclosed in Documents 1 to 3, the power supply device has to be in a standby state in which DC voltage is always supplied to the power supply device to promptly output the single-phase three-wire AC voltage from the power supply device.

However, two capacitors are connected in series between DC lines, which are DC input terminals, of each of those power supply devices and, generally, leakage current flows in the capacitors. In some cases, an auxiliary power supply for control is connected between the DC lines. Therefore, when the power supply device stands by in a state where DC voltage is supplied, DC power is consumed. In the case where the DC power supply is a battery, there is a problem that the battery gradually discharges.

There is a case that leakage current values vary among parts due to individual variability in two capacitors connected in series between DC lines. The voltages in the capacitors have to be balanced to some extent to maintain both of two capacitors connected in series in a charged state in order to promptly output a single-phase three-wire AC voltage. However, there is a problem that a loss will be large when a circuit for balancing voltages is provided and operated.

An object of the present invention is to provide a power supply device which has a small loss in a standby state when backup of an AC load is performed by outputting a single-phase three-wire AC voltage, and to provide a method of operating the device.

To achieve the object, a power supply device of the present invention comprises a first switching leg in which a series circuit of a first switching element and a second switching element is connected between DC terminals; a second switching leg in which a series circuit of a third switching element and a fourth switching element is connected between the DC terminals; a first capacitor leg in which a series circuit of a first capacitor and a second capacitor is connected between the DC terminals; a second capacitor leg in which a series circuit of a third capacitor and a fourth capacitor is connected between AC terminals and in which a connection point of the third and fourth capacitors and a connection point of the first and second capacitors are connected by a neutral point connection line; a first inductor connected between a connection point of the first and second switching elements and one of the AC terminals; a second inductor connected between a connection point of the third and fourth switching elements and another of the AC terminals; a controller configured to control the first to fourth switching elements; an AC power supply connected to the AC terminals and the connection point of the third and fourth capacitors, in parallel to the second capacitor leg; and a DC power supply connected between the DC terminals, wherein the controller is configured to operate the switching elements of the first and second switching legs so as to charge the first and second capacitors to a voltage higher than a voltage crest value of the AC power supply by using power of the AC power supply.

To achieve the object, in a method of operating a power supply device of the present invention, the device comprises a first switching leg in which a series circuit of a first switching element and a second switching element is connected between DC terminals; a second switching leg in which a series circuit of a third switching element and a fourth switching element is connected between the DC terminals; a first capacitor leg in which a series circuit of a first capacitor and a second capacitor is connected between the DC terminals; a second capacitor leg in which a series circuit of a third capacitor and a fourth capacitor is connected between AC terminals and in which a connection point of the third and fourth capacitors and a connection point of the first and second capacitors are connected by a neutral point connection line; a first inductor connected between a connection point of the first and second switching elements and one of the AC terminals; a second inductor connected between a connection point of the third and fourth switching elements and another of the AC terminals; a controller configured to control the first to fourth switching elements; an AC power supply and a load connected to the AC terminals and the connection point of the third and fourth capacitors, the AC power supply and the load in parallel to each other; and a DC power supply connected between the DC terminals, and the method comprises a step of operating the switching elements of the first and second switching legs by the controller in a normal operation state of supplying power from the AC power supply to the load, so as to charge the first and second capacitors to a voltage higher than a voltage crest value of the AC power supply by using power of the AC power supply.

According to the invention, a power supply device in which a loss in a standby state is small and which performs backup of an AC load by outputting a single-phase three-wire AC voltage and a method of operating the device can be provided.

FIG. 1 is a circuit configuration diagram of a power supply device of an embodiment of the present invention;

FIG. 2 is a diagram illustrating circuit operation in a battery charge mode (B);

FIG. 3 is a diagram illustrating circuit operation in positive half-wave in a capacitor charge mode (C);

FIG. 4 is a diagram illustrating circuit operation in negative half-wave in the capacitor charge mode (C);

FIG. 5 is a diagram illustrating signals in parts changing with time in the capacitor charge mode (C);

FIG. 6 is a diagram illustrating an example of a circuit configuration of a controller in the capacitor charge mode (C);

FIG. 7 is a diagram illustrating an example of a circuit configuration of the controller in a battery power supply mode (D) at a time of power interruption of alternating-current power supply 2 ; and

FIG. 8 is a diagram illustrating signals in parts changing with time in another operation in the capacitor charge mode (C).

Hereinafter, embodiments of the present invention will be described specifically with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a power supply device according to an embodiment of the present invention. In a power supply device 100 , power is transmitted and received between direct-current (DC) lines connected to direct-current (DC) terminals 14 and 15 and alternating-current (AC) lines connected to alternating-current (AC) terminals 11 to 13 . To the DC terminals 14 and 15 , a battery 7 is connected via a converter 8 , and a solar cell 9 is connected via a converter 10 . To the AC terminals 11 to 13 , an alternating-current (AC) power supply 2 is connected via a relay contact RY 1 , and alternating-current (AC) loads 3 to 5 are connected via a relay contact RY 2 .

The AC power supply 2 is of a single-phase three-wire system and can supply 100V in two systems and 200V in one system. A voltage approximately 85V to 132V is widely used as the voltage of the 100V system, and a voltage approximately 170V to 265V is widely used as the voltage of the 200V system. In the embodiment, it is assumed that a load of the 100V system is used for the AC loads 3 and 4 , and a load of the 200V system is used for the AC load 5 .

The power supply device 100 includes a first switching leg in which switching elements Q 1 and Q 2 are connected in series at a node Nd 1 , a second switching leg in which switching elements Q 3 and Q 4 are connected in series at a node Nd 2 , a first capacitor leg in which capacitors C 1 and C 2 are connected in series at a node Nd 3 , a second capacitor leg in which capacitors C 3 and C 4 are connected in series at a node Nd 4 , and a third switching leg in which switching elements Q 5 and Q 6 are connected in series at a node Nd 5 .

The first to third switching legs and the first capacitor leg are connected in parallel to each other. The negative electrode of the capacitor C 1 and the positive electrode of the capacitor C 2 are connected to each other. An inductor L 1 is connected between one end (capacitor C 3 ) of the second capacitor leg and the node Nd 1 . An inductor L 2 is connected between the other end (capacitor C 4 ) of the second capacitor leg and the node Nd 2 . An inductor L 3 is connected between the nodes Nd 3 and Nd 5 . The nodes Nd 3 and Nd 4 are connected to each other by a neutral point connection line LN.

Diodes D 1 to D 6 are connected to the switching elements Q 1 to Q 6 , respectively, in inverse-parallel connection.

However, the diodes D 1 to D 6 can be omitted if MOSFETs are used as the switching elements Q 1 to Q 6 because parasite diodes of the MOSFETs can be used.

The positive electrode of the capacitor C 1 is connected to the DC terminal 14 , and the negative electrode of the capacitor C 2 is connected to the DC terminal 15 . A voltage V 1 of the capacitor C 1 is defined with the positive electrode of the capacitor C 1 positive, and a voltage V 2 of the capacitor C 2 is defined with the positive electrode of the capacitor C 2 positive.

A connection point of the inductor L 1 and the capacitor C 3 is set as the AC terminal 11 . A connection point of the inductor L 2 and the capacitor C 4 is set as the AC terminal 12 . A connection point of the capacitors C 3 and C 4 is set as the AC terminal 13 . An a-phase is defined between the AC terminals 11 and 13 , that is, both ends of the capacitor C 3 . A b-phase is defined between the AC terminals 13 and 12 , that is, both ends of the capacitor C 4 . An ab-phase is defined between the alternating-current terminals 11 and 12 , that is, both ends of the second capacitor leg. A voltage of the AC terminal 11 for the AC terminal 13 is defined as an a-phase voltage Va. A voltage of the AC terminal 13 for the AC terminal 12 is defined as a b-phase voltage Vb. A voltage of the AC terminal 11 for the AC terminal 12 is defined as an ab-phase voltage Vab. The a-phase voltage Va, the b-phase voltage Vb, and the ab-phase voltage Vab are collectively called phase voltages.

The direction of current In of the neutral point connection line LN is defined as positive flowing from the node Nd 3 to the node Nd 4 . The direction of current Ia of the inductor L 1 is defined as positive flowing from the AC terminal 11 to the inductor L 1 . The direction of current Ib of the inductor L 2 is defined as positive flowing from the inductor L 2 to the AC terminal 12 .

The battery 7 is connected in parallel to the first capacitor leg via the converter 8 . The solar cell 9 is connected in parallel to the first capacitor leg via the converter 10 . The AC power supply 2 is connected to the AC terminals 11 to 13 via the relay contact RY 1 so that the AC terminal 13 is connected to the neutral line of the single-phase three-wire system. The AC loads 3 , 4 , and 5 are connected to the a-phase, the b-phase, and the ab-phase, respectively, via the relay contact RY 2 .

The switching operation of the switching elements Q 1 to Q 6 and the relay contacts RY 1 and RY 2 are controlled by a controller 1 . An auxiliary power supply 6 for supplying power to the controller 1 is connected between the DC terminals 14 and 15 .

The capacitors C 1 and C 2 divide the voltage between the DC terminals 14 and 15 , and an intermediate voltage of the voltage between the DC terminals 14 and 15 is generated at Nd 3 . The switching elements Q 5 and Q 6 and the inductor L 3 make the voltage sharing of the capacitors C 1 and C 2 balanced by controlling the switching elements Q 5 and Q 6 . In the embodiment, the converters 8 and 10 are connected in parallel to the first capacitor leg as DC power supplies. The converters 8 and 10 may be connected in parallel to one or both of the capacitors C 1 and C 2 .

The power supply device 100 in FIG. 1 , configured as described above, is operated as follows. In the operation, four modes below are performed: a commercial power supply mode (A) of supplying power from the AC power supply 2 to the AC loads 3 to 5 , a battery charge mode (B) when the battery 7 is not in a full charge state in the commercial power supply mode, a capacitor charge mode (C) after completion of charging the battery in the commercial power supply mode, and a battery power supply mode (D) at a time of power interruption of AC power supply 2 . Having performed the four modes, the operation returns to the commercial power supply mode (A) after the AC power supply 2 recovers.

The present invention has a feature that, in the series of processes, the capacitor charge mode after completion of charging the battery is performed in the commercial power supply mode. In the following, the processes will be sequentially described in accordance with the operation procedure.

[Commercial Power Supply Mode (A)]

In the commercial power supply mode, the relay contacts RY 1 and RY 2 are set to the on-state, and power of the AC power supply 2 is supplied to the alternating-current loads 3 to 5 in FIG. 1 .

[Battery Charge Mode (B) when Battery 7 is not in Full Charge State in Commercial Power Supply Mode]

When the battery 7 is not in the full charge state in the commercial power supply mode, the power of the AC power supply 2 is converted into direct current, the direct current is output to the DC terminals 14 and 15 , and the converter 8 is operated to charge the battery 7 . In this case, the power supply of the battery 7 is the capacitors C 1 and C 2 . Consequently, the charging operation of charging the capacitors C 1 and C 2 from the AC power supply 2 will be described. In the charging operation, the capacitors C 1 and C 2 are charged by using AC100/200V as inputs.

With reference to FIG. 2 , the charging operation of supplying power from the capacitors C 3 and C 4 to the capacitors C 1 and C 2 , receiving AC100V from both the a-phase and the b-phase, and receiving AC200V from the ab-phase will be described. In the description below, only a half cycle in which the AC voltage is positive will be described.

In this charging operation, the switching elements Q 1 to Q 4 will be operated as follows. In the switching operation, a mode B 1 and a mode B 2 are alternately executed. In the mode B 1 , the switching element Q 2 on the negative terminal side of a first switching leg SL 1 and the switching element Q 3 on the positive terminal side of a second switching leg SL 2 are set to the on-state, and the others are set to the off-state. In the mode B 2 , the switching element Q 1 on the positive terminal side of the first switching leg SL 1 and the switching element Q 4 on the negative terminal side of the second switching leg SL 2 are set to the on-state, and the others are set to the off-state. The left part in FIG. 2 illustrates the circuit configuration, the current directions, and so on in the mode B 1 , and the right part in FIG. 2 illustrates the circuit configuration, the current directions, and so on in the mode B 2 .

In the mode B 1 , the switching element Q 2 is in the on-state, and the voltage of the capacitor C 3 is applied to the inductor L 1 via the capacitor C 2 . In addition, the switching element Q 3 is in the on-state, and the voltage of the capacitor C 4 is applied to the inductor L 2 via the capacitor C 1 . The energy of the capacitors C 3 and C 4 is accumulated in the inductors L 1 and L 2 .

When the switching element Q 2 is turned off in the mode B 2 , the current in the inductor L 1 flowing in the switching element Q 2 changes to flow into the diode D 1 and is supplied to the capacitor C 1 . At this time, the switching element Q 1 is turned on. When the switching element Q 3 is turned off, the current in the inductor L 2 flowing in the switching element Q 3 changes to flow into the diode D 4 and is supplied to the capacitor C 2 . At this time, the switching element Q 4 is turned on. The currents in the inductors L 1 and L 2 decrease with time.

By continuous execution of the switching operation between the modes B 1 and B 2 , power is supplied from the capacitors C 3 and C 4 to the capacitors C 1 and C 2 . The operation of operating the converter 8 to charge the battery 7 will not be described here. At this time, AC100V is applied to both of the a-phase and the b-phase, and AC200V is applied to the ab-phase.

[Capacitor Charge Mode (C) after Completion of Charging Battery in Commercial Power Supply Mode]

After completion of charging the battery 7 , the capacitors C 1 and C 2 are charged by using the power of the AC power supply 2 in preparation for interruption of power supply of the AC power supply 2 and the like. This charge mode is performed so that the device can promptly shift to the battery power supply mode immediately after the interruption of the AC power supply 2 .

To prevent the AC loads 3 to 5 from interruption of power supply, AC voltage has to be promptly output from the power supply device 100 at the time of switching from the commercial power supply mode to the battery power supply mode. However, the power supply device 100 can output only voltage equal to or less than the voltages of the capacitors C 1 and C 2 as the a-phase voltage Va and the b-phase voltage Vb. Therefore, the capacitors C 1 and C 2 need to be charged to voltages higher than crest values of the a-phase voltage Va and the b-phase voltage Vb, which are output, at the standby time of the commercial power supply mode. This state corresponds to the capacitor charge mode (C). The present invention is mainly characterized by the capacitor charge mode (C).

The battery 7 can be used as a power supply for charging the capacitors C 1 and C 2 to voltages higher than the crest values of the a-phase voltage Va and the b-phase voltage Vb, which are output. However, there is leakage current of the capacitors C 1 and C 2 and power is consumed by the auxiliary power supply 6 . Consequently, the battery 7 gradually discharges when the device stands by while charging the capacitors C 1 and C 2 from the battery 7 via the converter 8 .

In a case where leakage current values in the capacitors C 1 and C 2 are different from each other due to individual variability, the voltages may be unbalanced between the capacitors. When the switching elements Q 5 and Q 6 are operated to balance the voltages, a loss will be large although the power necessary to charge the capacitors C 1 and C 2 while the device is on standby is relatively small.

In the power supply device 100 of the embodiment, at the time of standby in the commercial power supply mode, the capacitors C 1 and C 2 are charged to voltages higher than the crest values of the a-phase voltage Va and the b-phase voltage Vb by using the power of the AC power supply 2 . Consequently, the charge state of the capacitors C 1 and C 2 is maintained without discharging the battery 7 , and backup of the AC loads 3 to 5 can be performed by promptly outputting AC voltage in a case of abnormality in the system such as blackout.

Further, in the power supply device 100 , charging of the capacitors C 1 and C 2 is performed while only the switching elements Q 1 and Q 2 are operated among the switching elements Q 1 to Q 6 with the switching elements Q 3 to Q 6 stopped, and the voltages of the capacitors C 1 and C 2 are balanced. Consequently, the number of switching elements for performing switching operation is small as two, and it is unnecessary to operate the switching elements Q 5 and Q 6 for balancing the voltages of the capacitors C 1 and C 2 , so that a switching loss and iron loss of the inductor L 3 can be reduced.

Hereinafter, operation will be described in which, by controlling the switching elements Q 1 and Q 2 , power is supplied from the a-phase of the AC power supply 2 connected to both ends of the capacitor C 3 and charging of the capacitors C 1 and C 2 is performed with the voltages of the capacitors C 1 and C 2 balanced. In a case of supplying power from the b-phase of the AC power supply 2 connected to both ends of the capacitor C 4 , the switching elements Q 3 and Q 4 will be controlled. In this case, the switching elements Q 3 to Q 6 are fixed in the off-state.

In the capacitor charge mode (C), different operations are performed in a half cycle in which the voltage of the AC power supply 2 is positive in the alternating current and a half cycle in which the voltage of the AC power supply 2 is negative. The operations will be described with reference to FIGS. 3 and 4 .

With reference to FIG. 3 , a circuit operation will be described in the half cycle in which the voltage of the AC power supply 2 is positive in the alternating current, that is, in a period in which the a-phase voltage Va is positive. In FIGS. 3 , C 11 and C 12 indicate circuit operations in a lower-arm conduction mode C 11 and an upper-arm conduction mode C 12 , respectively. Although the operations are executed by using the first switching leg (switching elements Q 1 and Q 2 ), they may be executed by using the second switching leg (switching elements Q 3 and Q 4 ). In a case of using the second switching leg (switching elements Q 3 and Q 4 ), an operation of supplying power from the b-phase is performed.

[Lower-Arm Conduction Mode C 11 ]

The switching element Q 2 is in the on-state and the switching element Q 1 is in the off-state in the first switching leg, and the second switching leg (switching elements Q 3 and Q 4 ) is in the off-state. In this case, a circuit including capacitor C 3 , inductor L 1 , switching element Q 2 , capacitor C 2 , neutral point connection line LN, and capacitor C 3 in this order is formed. The a-phase voltage Va is applied to the inductor L 1 via the capacitor C 2 , and the current Ia of the inductor L 1 increases.

[Upper-Arm Conduction Mode C 12 ]

The switching element Q 1 is in the on-state and the switching element Q 2 is in the off-state in the first switching leg, and the second switching leg (switching elements Q 3 and Q 4 ) is in the off-state. In this case, a circuit including capacitor C 3 , inductor L 1 , switching element Q 1 , capacitor C 1 , neutral point connection line LN, and capacitor C 3 in this order is formed. In a transient state of forming the circuit, when the switching element Q 2 is turned off, the current of the inductor L 1 flowing in the switching element Q 2 changes to flow in the diode D 1 parallel to the switching element Q 1 and flows in the capacitor C 1 . At this time, the switching element Q 1 is turned on. The current Ia in the inductor L 1 decreases.

After that, the switching element Q 1 is turned off and the switching element Q 2 is turned on, thereby returning to the mode C 11 . Switching between the modes C 11 and C 12 is repeatedly executed by an output of the controller 1 . In the controller 1 , a firing time point and a firing period of the switching elements Q 1 and Q 2 are controlled by a voltage instruction signal and PWM control using, for example, a triangular wave.

With reference to FIG. 4 , a circuit operation will be described in the half cycle in which the voltage of the AC power supply 2 is negative in the alternating current, that is, in a period in which the a-phase voltage Va is negative. In FIGS. 4 , C 21 and C 22 indicate circuit operations in an upper-arm conduction mode C 21 and a lower-arm conduction mode C 22 , respectively. Although the operations are executed by using the first switching leg (switching elements Q 1 and Q 2 ), they may be executed by using the second switching leg (switching elements Q 3 and Q 4 ). In a case of using the second switching leg (switching elements Q 3 and Q 4 ), an operation of supplying power from the b-phase is performed.

[Upper-Arm Conduction Mode C 21 ]

The switching element Q 1 is in the on-state and the switching element Q 2 is in the off-state in the first switching leg, and the second switching leg (switching elements Q 3 and Q 4 ) is in the off-state. In this case, a circuit including capacitor C 3 , neutral point connection line LN, capacitor C 1 , switching element Q 1 , inductor L 1 , and capacitor C 3 in this order is formed. The a-phase voltage Va is applied to the inductor L 1 via the capacitor C 1 , and the current Ia of the inductor L 1 increases in the negative direction.

[Lower-Arm Conduction Mode C 22 ]

The switching element Q 2 is in the on-state and the switching element Q 1 is in the off-state in the first switching leg, and the second switching leg (switching elements Q 3 and Q 4 ) is in the off-state. In this case, a circuit including capacitor C 3 , neutral point connection line LN, capacitor C 2 , switching element Q 2 , inductor L 1 , and capacitor C 3 in this order is formed. In a transient state of forming the circuit, when the switching element Q 1 is turned off, the current of the inductor L 1 flowing in the switching element Q 1 changes to flow in the diode D 2 parallel to the switching element Q 2 and flows in the capacitor C 2 . At this time, the switching element Q 2 is turned on. The current Ia in the inductor L 1 decreases in the positive direction.

After that, the switching element Q 2 is turned off and the switching element Q 1 is turned on, thereby returning to the mode C 21 . Switching between the modes C 21 and C 22 is repeatedly executed by an output of the controller 1 .

In the above-described operation, the current In of the neutral point connection line LN is equal to the current Ia of the inductor L 1 because the second switching leg (switching elements Q 3 and Q 4 ) is fixed in the off-state and the current Ib of the inductor L 2 does not flow. According to the above-described control, it is possible to control the current value when the current In of the neutral point connection line LN flows in the positive direction by adjusting the ratio between the length of the period of the mode C 11 and the length of the period of the mode C 12 , and to control the current value when the current In of the neutral point connection line LN flows in the negative direction by adjusting the ratio between the length of the period of the mode C 21 and the length of the period of the mode C 22 .

FIG. 5 illustrates signals in parts changing with time in the capacitor charge mode (C). FIG. 5 illustrates, as an example, time change of the AC terminal voltages Va and Vb, the respective currents Ia and Ib of the inductors L 1 and L 2 , the current In of the neutral point connection line LN, and the respective voltages V 1 and V 2 of the capacitors C 1 and C 2 . It is assumed that the voltages V 1 and V 2 of the capacitors C 1 and C 2 have different voltage values with each other in a state before time t 1 . It is also assumed that repetitive control of the modes C 11 and C 12 is executed in the period of the positive half wave of the AC terminal voltages Va and Vb, and repetitive control of the modes C 21 and C 22 is executed in the period of the negative half wave of the AC terminal voltages Va and Vb.

With reference to FIG. 5 , the operation sequence of the power supply device of the embodiment will be described. When the phase of the a-phase voltage Va and that of the current Ia of the inductor L 1 is close to each other, power is supplied from the a-phase of the AC power supply 2 . Consequently, the current In of the neutral point connection line LN is equal to the current Ia of the inductor L 1 because only the switching elements Q 1 and Q 2 are operated and the switching elements Q 3 and Q 4 are fixed in the off-state.

If the voltage V 1 of the capacitor C 1 is lower than the voltage V 2 of the capacitor C 2 in the above-described state (the state before time t 1 ), the positive crest value Inp of the current In of the neutral point connection line LN is made larger than the negative crest value Inn after the time t 1 , increasing the amount of the charge current of the capacitor C 1 . On the other hand, if the voltage V 2 of the capacitor C 2 is lower than the voltage V 1 of the capacitor C 1 , the negative crest value Inn of the current In of the neutral point connection line LN is made larger than the positive crest value Inp, increasing the amount of the charge current of the capacitor C 2 . By this voltage balance control, the difference between the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 is decreased, and the voltages V 1 and V 2 of the capacitors can be balanced.

In FIG. 5 , the voltage V 1 of the capacitor C 1 is lower than the voltage V 2 of the capacitor C 2 . By making the voltage balance control effective at time t 1 , the positive crest value of the current In of the neutral point control line LN is larger than the negative crest value, and the difference between the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 decreases.

In FIG. 5 , there is a case in reality that ripples overlap in the current Ia of the inductor L 1 , the current In of the neutral point connection line LN, the voltage V 1 of the capacitor C 1 , and the voltage V 2 of the capacitor C 2 . In addition, there is a case in reality that a period occurs in which the direction of the a-phase voltage Va and the current Ia of the inductor L 1 is opposite to each other due to a control delay or the like, although the controller 1 has a power factor improvement control function.

In the embodiment, the battery 7 is connected between the DC terminals 14 and 15 via the converter 8 . In the present invention, a battery can be directly connected between the DC terminals 14 and 15 and charged with relatively small current.

FIG. 6 illustrates an example of a circuit configuration of the controller 1 in the capacitor charge mode (C). In this embodiment, the controller 1 has a function to perform the balance control of the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 and to maintain the voltages V 1 and V 2 at the AC voltage Va or higher. The function can be realized also by circuit configurations other than the illustrated circuit configuration, which is illustrated just for an example. The controller 1 in the capacitor charge mode (C) includes a voltage control unit 21 , a power-factor improvement control unit 22 , a balance control unit 23 , and a current control unit 24 , for example.

The voltage control unit 21 supplies a control signal Iref 1 so that the total voltage (V 1 +V 2 ) of the capacitors C 1 and C 2 is equal to a target voltage Vref. That is, if the total voltage (V 1 +V 2 ) is lower than the target voltage Vref, the control signal Iref 1 is increased. If the total voltage (V 1 +V 2 ) is higher than the target voltage Vref, the control signal Iref 1 is decreased. In the present invention, the target voltage Vref is set to a voltage higher than the total voltage of the crest value of the AC voltage Va and the crest value of the AC voltage Vb. Consequently, power supply from the power supply device 100 can be promptly realized immediately after interruption of a commercial power supply.

The power-factor improvement control unit 22 generates a sine-wave shaped control signal Iref 2 having an amplitude proportional to that of the control signal Iref 1 and a phase equal to that of the AC voltage Va.

The balance control unit 23 generates a target current Iref 3 having the positive crest value Inp higher than the negative crest value Inn if V 1 is lower than V 2 and generates a target current Iref 3 having the negative crest value Inn higher than the positive crest value Inp if V 2 is lower than V 1 , so that the capacitor voltages V 1 and V 2 are equal to each other.

The current control unit 24 increases a firing signal “duty” if the current Ia of the inductor L 1 is smaller than the target current Iref 3 and decreases the firing signal “duty” if the current Ia of the inductor L 1 is larger than the target current Iref 3 , so that the current Ia of the inductor L 1 is equal to the target current Iref 3 .

In the period in which the AC voltage Va is positive, the period of the mode C 11 is increased and the period of the mode C 12 is decreased by increasing the firing signal “duty.” In the period in which the AC voltage Va is negative, the period of the mode C 22 is increased and the period of the mode C 21 is decreased by increasing the firing signal “duty.”

[Battery Power Supply Mode (D) at a Time of Power Interruption of AC Power Supply 2 ]

When a system abnormality such as power supply interruption of the AC power supply 2 is detected, the relay contact RY 1 is turned off to shift to the battery power supply mode. The DC power supplied to the DC terminals 14 and 15 is converted to alternating current, and the alternating current is supplied to the AC loads 3 to 5 . An operation of outputting AC100V/AC200V will be described as a discharging operation with reference to FIG. 7 . Specifically, a discharging operation will be described in which power is supplied from the capacitors C 1 and C 2 to the capacitors C 3 and C 4 , AC 100V is output to both of the a-phase and the b-phase, and, accordingly, AC200V is output to the ab-phase. Only a case of the positive half cycle of the AC voltage will be described here.

In this discharging operation, the switching elements Q 1 to Q 4 are operated as follows. In the switching operation, a mode D 1 and a mode D 2 are alternately executed. In the mode D 1 , the switching element Q 1 on the positive terminal side of the first switching leg SL 1 and the switching element Q 4 on the negative terminal side of the second switching leg SL 2 are set to the on-state, and the others are set to the off-state. In the mode D 2 , the switching element Q 2 on the negative terminal side of the first switching leg SL 1 and the switching element Q 3 on the positive terminal side of the second switching leg SL 2 are set to the on-state, and the others are set to the off-state. The left part in FIG. 7 illustrates the circuit configuration, the current directions, and so on in the mode D 1 , and the right part in FIG. 7 illustrates the circuit configuration, the current directions, and so on in the mode D 2 .

In the mode D 1 , the switching element Q 1 is in the on-state, and the voltage of the capacitor C 1 is applied to the inductor L 1 and the capacitor C 3 . In addition, the switching element Q 4 is in the on-state, and the voltage of the capacitor C 2 is applied to the inductor L 2 and the capacitor C 4 . The currents in the inductors L 1 and L 2 increase with time and are supplied to the capacitors C 3 and C 4 .

When the mode D 1 shifts to the mode D 2 and the switching element Q 1 is turned off, the current in the inductor L 1 flowing in the switching element Q 1 changes to flow into the diode D 2 and returns via the capacitor C 2 . At this time, the switching element Q 2 is turned on.

When the switching element Q 4 is turned off, the current in the inductor L 2 flowing in the switching element Q 4 changes to flow into the diode D 3 and returns via the capacitor C 1 . At this time, the switching element Q 3 is turned on. The currents in the inductors L 1 and L 2 decrease with time and are supplied to the capacitors C 3 and C 4 .

Subsequently, the switching elements Q 2 and Q 3 are turned off and the switching element Q 1 and Q 4 are turned on, thereby returning to the mode D 1 .

By continuous execution of the switching operation between the modes D 1 and D 2 , power is supplied from the capacitors C 1 and C 2 to the capacitors C 3 and C 4 , AC100V is output to both of the a-phase and the b-phase and, therefore, AC200V can be output to the ab-phase.

With the circuit configuration in FIG. 1 , the following operation modes can be used and optionally executed as necessary besides the above-described operation. In this case, the operation modes can be grasped as two modes (DC-AC mode and AC-DC mode) according to the power conversion directions. Further, the DC-AC mode can be divided to a DC-AC mode 1 and a DC-AC mode 2 depending on circuits on the AC side to which power is supplied.

The DC-AC mode 1 of the DC-AC mode is a mode to convert DC power supplied between the DC terminals 14 and 15 to AC power and supply the AC power to the AC power supply 2 . In the DC-AC mode 1 , the relay contact RY 1 is set to the on-state, the switching elements Q 1 and Q 2 are controlled to pass the current Ia to the inductor L 1 , and the switching elements Q 3 and Q 4 are controlled to pass the current Ib to the inductor L 2 .

The DC-AC mode 2 of the DC-AC mode is a mode to convert DC power supplied between the DC terminals 14 and 15 to AC power and supply the AC power to the AC loads 3 to 5 . In the DC-AC mode 2 , the relay contact RY 1 is set to the off-state, the relay contact RY 2 is set to the on-state, the switching elements Q 1 and Q 2 are controlled to generate the a-phase voltage Va, and the switching elements Q 3 and Q 4 are controlled to generate the b-phase voltage Vb.

The AC-DC mode is a mode to convert the power of the AC power supply 2 supplied to the AC terminals 11 to 13 to DC power and output the DC power to the DC terminals 14 and 15 . In the AC-DC mode, the relay contact RY 1 is set to the on-state, the switching elements Q 1 and Q 2 are controlled to pass the current Ia to the inductor L 1 , the switching elements Q 3 and Q 4 are controlled to pass the current Ib to the inductor L 2 , and the current supplied from the AC power supply 2 is controlled to be in a sine wave shape to increase the power factor. The controller 1 has this power-factor improvement control function.

In the present invention, operation can be performed as illustrated in FIG. 8 without changing the configuration of the power supply device 100 as illustrated in FIG. 1 . FIG. 8 illustrates signals changing with time of the AC terminal voltages Va and Vb, the respective currents Ia and Ib of the inductors L 1 and L 2 , the current In of the neutral point connection line LN, and the respective voltages V 1 and V 2 of the capacitors C 1 and C 2 .

In an operation sequence illustrated in FIG. 8 , intermittent control is performed with repetition of starts and stops, thereby providing a pause period to further decrease the loss in the capacitor charge mode (C). If both of the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 are equal to or larger than a threshold value Vth 1 , the switching operation is stopped. If at least one of the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 is equal to or less than a threshold value Vth 2 , the switching operation is restarted.

In FIG. 8 , the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 decrease gradually in the period T 1 due to power consumption by the auxiliary power supply 6 and leakage current of the capacitors C 1 and C 2 . If the electrostatic capacitance of the capacitor C 1 is smaller than that of the capacitor C 2 or if the leakage current of the capacitor C 1 is larger than that of the capacitor C 2 , the voltage V 1 of the capacitor C 1 decreases faster than the voltage V 2 of the capacitor C 2 .

When the voltage V 1 of the capacitor C 1 reaches the threshold value Vth 2 , the switching operation is restarted and the state enters in the period T 2 . The capacitors C 1 and C 2 are charged, and the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 rise. At this time, as the operation sequence illustrated in FIG. 5 , the positive crest value of the current In of the neutral point connection line LN is larger than the negative crest value to decrease the difference between the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 because the voltage V 1 of the capacitor C 1 is lower than the voltage V 2 of the capacitor C 2 .

When both of the voltage V 1 of the capacitor C 1 and the voltage V 2 of the capacitor C 2 are equal to or larger than the threshold value Vth 1 , the switching operation is stopped, thereby returning to the state in the period T 1 .

The embodiments of the present invention have been described above. In the embodiments, the capacitors C 1 and C 2 are charged while the device is on standby to promptly output AC voltage. The operating method of the present invention can be applied to a case of charging the battery 7 with relatively small current, obtaining a merit to reduce a loss by stopping the switching elements Q 5 and Q 6 . As described above, the present invention can be widely applied to power supply devices of converting power bidirectionally between the single-phase three-wire AC line and the DC line.