Power conversion device

Abstract

This power conversion device comprises: a first isolation transformer that includes a first primary winding and a first secondary winding; a primary-side bridge circuit to which first DC power is input; a secondary-side bridge circuit that outputs second DC power; a second isolation transformer that is provided between the first isolation transformer, and the primary-side bridge circuit or the secondary-side bridge circuit, and includes a second primary winding and a second secondary winding; a pair of connection lines that respectively connect both ends of the second primary winding and both ends of the second secondary winding; a pair of first switches that are respectively connected to both ends of the second primary winding; and a pair of second switches that are provided on the connection lines.

Description

Power conversion device

[0001] The present invention relates to a power conversion device.

[0002] Conventionally, a power conversion device that converts DC power into another DC power by performing voltage conversion using a transformer is known. For example, in Patent Document 1, a pair of input terminals and a pair of output terminals are insulated via an insulating transformer, and the voltage between the pair of input terminals is converted into a voltage having another value using the insulating transformer and output from the pair of output terminals. In an isolation type converter, there are provided smoothing means for smoothing the output current on the secondary side of the insulating transformer, a voltage regulating transformer in which a secondary coil is connected in series to the primary coil of the insulating transformer, and a voltage applied to the primary side of the insulating transformer and equal to the total magnitude of the voltage applied to the primary coil of the insulating transformer and the secondary coil of the voltage regulating transformer is applied to the primary coil of the voltage regulating transformer.

[0003] Japanese Patent Application Laid-Open No. 2011-4532 [[ID=1"0]]

[0004] In a conventional power conversion device represented by the isolation type converter of Patent Document 1, the relationship between the input voltage and the output voltage is determined according to the turns ratio of the insulating transformer. The larger the turns ratio of the insulating transformer, the higher the power conversion efficiency can be increased within a wide range of input voltages, but the range of the output voltage obtained with respect to the input voltage becomes narrower. Conversely, the smaller the turns ratio of the insulating transformer, the wider the range of the output voltage obtained with respect to the input voltage, but there is a risk that the power conversion efficiency at a frequently used voltage may decrease. Therefore, it is difficult for a conventional power conversion device to perform power conversion with high efficiency over a wide range of input voltages.

[0005] The present invention has been made in view of the above problems, and a main object thereof is to realize a power conversion device capable of performing power conversion with high efficiency over a wide range of input voltages.

[0006] The power conversion device according to the present invention comprises: a first isolation transformer having a first primary winding and a first secondary winding; a primary bridge circuit to which a first DC power is input; a secondary bridge circuit to which a second DC power is output; a second isolation transformer provided between the first isolation transformer and the primary bridge circuit or the secondary bridge circuit, having a second primary winding and a second secondary winding; a pair of connecting wires connecting both ends of the second primary winding and both ends of the second secondary winding, respectively; a pair of first switches connected to both ends of the second primary winding, respectively; and a pair of second switches provided on the connecting wires.

[0007] According to the present invention, a power conversion device capable of highly efficient power conversion over a wide input voltage range can be realized.

[0008] This is a diagram showing the configuration of a power conversion device according to the first embodiment of the present invention. This is a flowchart showing the processing flow performed by the control unit. This is a diagram showing the configuration of a power conversion device according to the second embodiment of the present invention.

[0009] (First Embodiment) Figure 1 is a diagram showing the configuration of a power converter according to the first embodiment of the present invention. The power converter 100 shown in Figure 1 is connected between a DC power source 1 and a storage battery 2, and performs power conversion when charging the storage battery 2 using DC power supplied from the DC power source 1. The power converter 100 is used, for example, mounted on a vehicle.

[0010] DC power supply 1 is a power supply device capable of supplying multiple types of DC power with different voltages (for example, 400V and 800V). Examples of DC power supply 1 include a rapid charger for vehicles and an on-board high-voltage battery composed of multiple lithium-ion batteries.

[0011] The battery 2 is a rechargeable and dischargeable energy storage device. For example, an in-vehicle low-voltage battery consisting of a lead-acid battery or a lithium-ion battery can be used as the battery 2. In this embodiment, the voltage V2 of the battery 2 is lower than the voltage V1 of the DC power supply 1.

[0012] The power converter 100 comprises a primary bridge circuit 101, a secondary bridge circuit 102, a voltage sensor 103, and a control unit 104. A first isolation transformer Tr1 and a second isolation transformer Tr2 are provided between the primary bridge circuit 101 and the secondary bridge circuit 102. In the following, the first isolation transformer Tr1 and the second isolation transformer Tr2 may be collectively referred to as the "transformer circuit."

[0013] The primary bridge circuit 101 receives DC power supplied from the DC power supply 1. The primary bridge circuit 101 is composed of a combination of multiple (for example, four) semiconductor switching elements, and by operating these semiconductor switching elements at predetermined timings, it converts the DC power from the DC power supply 1 into AC power. The AC power converted by the primary bridge circuit 101 is output to the transformer circuit.

[0014] The transformer circuit converts the AC power output from the primary bridge circuit 101 into AC power of a different voltage and outputs it to the secondary bridge circuit 102. Specifically, it converts the AC power input from the primary bridge circuit 101 into AC power of a lower voltage and outputs it to the secondary bridge circuit 102. In this case, the transformer circuit may use both the first isolation transformer Tr1 and the second isolation transformer Tr2 to perform the power conversion, or it may use only the first isolation transformer Tr1 to perform the power conversion. Details of these will be described later.

[0015] The secondary bridge circuit 102 is an active ridge rectifier that is composed of a combination of multiple (for example, four) semiconductor switching elements, and converts the AC power output from the transformer circuit into DC power by operating each of these semiconductor switching elements at predetermined timings. The DC power converted by the secondary bridge circuit 102 is output to the storage battery 2 and used to charge the storage battery 2.

[0016] The voltage sensor 103 detects the voltage V1 of the DC power input to the primary bridge circuit 101 and transmits a voltage signal indicating that voltage value to the control unit 104.

[0017] The control unit 104 generates control signals P1 and P2 to control the semiconductor switching elements of the primary bridge circuit 101 and the secondary bridge circuit 102 based on the voltage signal transmitted from the voltage sensor 103, and transmits them to the primary bridge circuit 101 and the secondary bridge circuit 102, respectively. At this time, the voltage V2 of the storage battery 2 may be detected, and the detection result may be used to generate the control signals P1 and P2. The control unit 104 also generates switching signals to control the switching state of the switches SW1a, SW1b, SW2a, and SW2b provided in the transformer circuit, as described later, and transmits them to each of these switching elements, respectively. The control unit 104 is configured by combining, for example, a microcomputer and a signal generation circuit that generates control signals P1 and P2 and switching signals in response to signals from the microcomputer.

[0018] Next, the details of the transformer circuit will be explained below.

[0019] In the transformer circuit, the first isolation transformer Tr1 has a primary winding N1a and a secondary winding N1b. The primary winding N1a is connected to the second isolation transformer Tr2, and the secondary winding N1b is connected to the secondary bridge circuit 102.

[0020] The second isolation transformer Tr2 has a primary winding N2a and a secondary winding N2b, and is installed between the first isolation transformer Tr1 and the primary bridge circuit 101. The primary winding N2a is connected to the primary bridge circuit 101 via switches SW1a and SW1b, and the secondary winding N2b is connected to the primary winding N1a of the first isolation transformer Tr1.

[0021] The turns ratio between the primary winding N1a and the secondary winding N1b in the first isolation transformer Tr1 (hereinafter referred to as the "first turns ratio"), and the turns ratio between the primary winding N2a and the secondary winding N2b in the second isolation transformer Tr2 (hereinafter referred to as the "second turns ratio") are determined according to the input-output voltage ratio of the power converter 100, that is, the voltage ratio between the voltage V1 of the DC power supply 1 and the voltage V2 of the storage battery 2. Here, it is preferable that the first turns ratio and the second turns ratio are different values, and it is even more preferable that the second turns ratio is smaller than the first turns ratio. The reason for this will be explained later.

[0022] In the second isolation transformer Tr2, a pair of connecting wires L1a and L1b are provided between both ends of the primary winding N2a and the primary bridge circuit 101. Additionally, a pair of connecting wires L2a and L2b are provided between both ends of the primary winding N2a and the secondary winding N2b. The connecting wires L2a and L2b connect the primary bridge circuit 101 and the primary winding N1a of the first isolation transformer Tr1, respectively, without passing through the second isolation transformer Tr2.

[0023] A pair of switches SW1a and SW1b are provided on the connecting lines L1a and L1b, respectively. That is, a pair of switches SW1a and SW1b are connected to both ends of the primary winding N2a of the second isolation transformer Tr2. Switches SW1a and SW1b operate in response to switching signals from the control unit 104, respectively, to switch the connection state between the primary bridge circuit 101 and the second isolation transformer Tr2.

[0024] A pair of switches, SW2a and SW2b, are provided on the connecting lines L2a and L2b, respectively. Switches SW2a and SW2b operate in response to switching signals from the control unit 104, respectively, to switch the connection state between the primary bridge circuit 101 and the first isolation transformer Tr1 via the connecting lines L2a and L2b.

[0025] When the input / output voltage ratio of the power converter 100 is large, the control unit 104 outputs switching signals to switches SW1a and SW1b to the ON state and switches SW2a and SW2b to the OFF state, respectively. As a result, in the power converter 100, switches SW1a, SW1b, SW2a, and SW2b are controlled to the switching states shown in Figure 1(a).

[0026] In the switching state shown in Figure 1(a), the AC power output from the primary bridge circuit 101 is input to the primary winding N2a of the second isolation transformer Tr2. When the AC power from the primary bridge circuit 101 is input to the primary winding N2a of the second isolation transformer Tr2, the secondary winding N2b converts this into AC power with a voltage corresponding to the second turns ratio and outputs it to the primary winding N1a of the first isolation transformer Tr1. When the AC power from the second isolation transformer Tr2 is input to the primary winding N1a of the first isolation transformer Tr1, the secondary winding N1b converts this into AC power with a voltage corresponding to the first turns ratio and outputs it to the secondary bridge circuit 102.

[0027] In the switching state shown in Figure 1(a), the power converter 100 performs the operations described above. This allows the DC power supplied from the DC power source 1 to be converted into power at a voltage ratio obtained by multiplying the first turns ratio by the second turns ratio, and output to the storage battery 2.

[0028] When the input-output voltage ratio of the power converter 100 is small, the control unit 104 outputs switching signals to switches SW1a and SW1b to the off state and switches SW2a and SW2b to the on state, respectively. As a result, in the power converter 100, switches SW1a, SW1b, SW2a, and SW2b are controlled to the switching states shown in Figure 1(b).

[0029] In the switching state shown in Figure 1(b), the AC power output from the primary bridge circuit 101 is directly input to the primary winding N1a of the first isolation transformer Tr1 without passing through the second isolation transformer Tr2. When the AC power from the primary bridge circuit 101 is input to the primary winding N1a of the first isolation transformer Tr1, the secondary winding N1b converts this into AC power with a voltage corresponding to the first turns ratio and outputs it to the secondary bridge circuit 102.

[0030] In the switching state shown in Figure 1(b), the power converter 100 performs the operations described above. This allows the DC power supplied from the DC power source 1 to be converted into power at a voltage ratio corresponding to the first turns ratio and output to the storage battery 2.

[0031] Here, the second turns ratio of the second isolation transformer Tr2 is set to be smaller than the first turns ratio of the first isolation transformer Tr1. Specifically, for example, if the first turns ratio is set to a value of about 10:1, the second turns ratio is set to a value of about 2:1 to 3:1. In this way, the second isolation transformer Tr2, which has a smaller turns ratio, can be placed on the upstream side (primary bridge circuit 101 side), making it possible to miniaturize the second isolation transformer Tr2. In addition, the current flowing through the first isolation transformer Tr1 can be reduced, enabling more efficient power conversion operation.

[0032] Furthermore, the primary winding N2a and secondary winding N2b of the second isolation transformer Tr2 can also be constructed, for example, using substrate patterns formed on a circuit board. This makes it possible to realize a smaller and lower-cost second isolation transformer Tr2. In this case, by forming the primary winding N2a and secondary winding N2b on the same circuit board as the connecting wires L1a, L1b and L2a, L2b, it is possible to further miniaturize and reduce the cost of the transformer circuit including the second isolation transformer Tr2.

[0033] Figure 2 is a flowchart showing the processing flow performed by the control unit 104. The control unit 104 performs the processing shown in the flowchart of Figure 2 at predetermined intervals by executing a predetermined program, for example, while the power converter 100 is operating.

[0034] In step S10, the value of the input voltage V1 of the primary bridge circuit 101 is obtained based on the voltage signal transmitted from the voltage sensor 103.

[0035] In step S20, it is determined whether the input voltage V1 obtained in step S10 is equal to or greater than a predetermined value. For example, based on the first turns ratio of the first isolation transformer Tr1, a range of input voltage V1 is predetermined such that the output voltage of the power converter 100 is within an appropriate range as the voltage V2 of the storage battery 2 when power conversion is performed using only the first isolation transformer Tr1. The upper limit of this voltage range is set as the determination threshold in step S20. The obtained input voltage V1 is then compared with the above determination threshold. If the input voltage V1 is equal to or greater than the determination threshold, it is determined that the input voltage V1 is equal to or greater than the predetermined value, and the process proceeds to step S30. On the other hand, if the input voltage V1 is less than the determination threshold, it is determined that the input voltage V1 is not equal to or greater than the predetermined value, and the process proceeds to step S40.

[0036] In step S30, each switch in the transformer circuit is switched to the side connected to the second isolation transformer Tr2. Here, as shown in Figure 1(a), switches SW1a and SW1b are switched to the ON state, and switches SW2a and SW2b are switched to the OFF state. This ensures that the AC power output from the primary bridge circuit 101 in response to the input voltage V1 is input to the primary winding N2a of the second isolation transformer Tr2.

[0037] In step S40, each switch in the transformer circuit is switched to the disconnect side of the second isolation transformer Tr2. Here, as shown in Figure 1(b), switches SW1a and SW1b are switched to the off state, and switches SW2a and SW2b are switched to the on state. This ensures that the AC power output from the primary bridge circuit 101 in response to the input voltage V1 is input to the primary winding N1a of the first isolation transformer Tr1.

[0038] After step S30 or S40 is performed, in step S50, control signals P1 and P2 are transmitted to the primary bridge circuit 101 and the secondary bridge circuit 102, respectively, and these bridge circuits are controlled. As a result, the power converter 100 performs power conversion on the input voltage V1 from the DC power supply 1 according to the switching state of each switch performed in step S30 or S40, and outputs the converted voltage V2 to the storage battery 2. After the processing in step S50 is completed, the control unit 104 terminates the process shown in the flowchart of Figure 2.

[0039] According to the first embodiment of the present invention described above, the following effects are achieved.

[0040] (1) The power converter 100 comprises a first isolation transformer Tr1 having a primary winding N1a and a secondary winding N1b, a primary bridge circuit 101 to which DC power from a DC power source 1 is input, a secondary bridge circuit 102 to which DC power is output to a storage battery 2, a second isolation transformer Tr2 provided between the first isolation transformer Tr1 and the primary bridge circuit 101 and having a primary winding N2a and a secondary winding N2b, a pair of connecting wires L2a and L2b connecting both ends of the primary winding N2a and both ends of the secondary winding N2b, respectively, a pair of switches SW1a and SW1b connected to both ends of the primary winding N2a, respectively, and a pair of switches SW2a and SW2b provided on the connecting wires L2a and L2b. In this manner, in a transformer circuit consisting of a first isolation transformer Tr1 and a second isolation transformer Tr2, it is possible to arbitrarily switch between performing power conversion using both the first isolation transformer Tr1 and the second isolation transformer Tr2, and performing power conversion using only the first isolation transformer Tr1. Therefore, a power conversion device 100 capable of highly efficient power conversion over a wide input voltage range can be realized.

[0041] (2) Preferably, the turns ratio of the primary winding N2a to the secondary winding N2b is different from the turns ratio of the primary winding N1a to the secondary winding N1b. Specifically, it is preferable that the turns ratio of the primary winding N2a to the secondary winding N2b is smaller than the turns ratio of the primary winding N1a to the secondary winding N1b. In this way, the second isolation transformer Tr2 can be made smaller and the current flowing through the first isolation transformer Tr1 can be reduced, thereby achieving more efficient power conversion operation.

[0042] (3) The primary winding N2a and the secondary winding N2b may be constructed using substrate patterns formed on the circuit board. This makes it possible to realize a smaller and lower-cost second isolation transformer Tr2.

[0043] (4) The second isolation transformer Tr2 is provided between the first isolation transformer Tr1 and the primary bridge circuit 101. When switches SW1a and SW1b are switched to the ON state and switches SW2a and SW2b are switched to the OFF state (Figure 1(a)), the AC power output from the primary bridge circuit 101 is input to the primary winding N2a of the second isolation transformer Tr2, and when AC power is input to the primary winding N2a, the secondary winding N2b outputs AC power with a different voltage from this AC power to the primary winding N1a of the first isolation transformer Tr1. When AC power is input to the primary winding N1a of the first isolation transformer Tr1, the secondary winding N1b outputs AC power with a different voltage from this AC power to the secondary bridge circuit 102. The secondary bridge circuit 102 converts the AC power output from the first isolation transformer Tr1 into DC power and outputs it. On the other hand, when switches SW1a and SW1b are switched to the off state and switches SW2a and SW2b are switched to the on state (Figure 1(b)), the primary winding N1a of the first isolation transformer Tr1 receives AC power output from the primary bridge circuit 101, and when AC power is input to the primary winding N1a, the secondary winding N1b outputs AC power with a different voltage to the secondary bridge circuit 102. The secondary bridge circuit 102 converts the AC power output from the first isolation transformer Tr1 into DC power and outputs it. In this way, by switching the switches SW1a, SW1b, SW2a, and SW2b, it is possible to realize both a case where power conversion is performed using both the first isolation transformer Tr1 and the second isolation transformer Tr2, and a case where power conversion is performed using only the first isolation transformer Tr1.

[0044] (5) The power conversion device 100 includes a primary-side bridge circuit 101, a secondary-side bridge circuit 102, and a control unit 104 that controls switches SW1a, SW1b and switches SW2a, SW2b respectively. When the voltage V1 of the DC power input from the DC power supply 1 is greater than or equal to a predetermined value (step S20: Yes), the control unit 104 switches the switches SW1a, SW1b to the on state and the switches SW2a, SW2b to the off state respectively (step S30). Also, when the voltage V1 of the DC power input from the DC power supply 1 is less than the predetermined value (step S20), the control unit 104 switches the switches SW1a, SW1b to the off state and the switches SW2a, SW2b to the on state respectively (step S40). By doing so, the switching operations of the switches SW1a, SW1b, SW2a, and SW2b can be appropriately performed according to the voltage V1 of the DC power input from the DC power supply 1.

[0045] (Second Embodiment) FIG. 3 is a diagram showing the configuration of a power conversion device according to the second embodiment of the present invention. The power conversion device 100a shown in FIG. 3 is connected between the DC power supply 1 and the storage battery 2, and performs power conversion when charging the storage battery 2 using the DC power supplied from the DC power supply 1, similar to the power conversion device 100 of FIG. 1 described in the first embodiment. The power conversion device 100a is used, for example, when mounted on a vehicle.

[0046] In the first embodiment, an example of the power conversion device 100 in which the second isolation transformer Tr2 is provided between the first isolation transformer Tr1 and the primary-side bridge circuit 101 has been described. On the other hand, in the power conversion device 100a of the present embodiment, as shown in FIG. 3, the second isolation transformer Tr2 is provided between the first isolation transformer Tr1 and the secondary-side bridge circuit 102. Along with this, the connection lines L1a, L1b are provided between both ends of the primary winding N2a and both ends of the secondary winding N1b of the first isolation transformer Tr1 respectively. The connection lines L2a, L2b are provided between both ends of the primary winding N2a and both ends of the secondary winding N2b, similar to the power conversion device 100 in the first embodiment.

[0047] In the power conversion device 100a of the present embodiment as well, the control unit 104 performs the processes shown in the flowchart of FIG. 2 at a predetermined period. As a result, in the power conversion device 100a, the switches SW1a, SW1b, SW2a, and SW2b are each controlled to a switching state as shown in FIG. 3(a) or FIG. 3(b). Therefore, similar to the first embodiment, in the transformer circuit including the first insulation transformer Tr1 and the second insulation transformer Tr2, it is possible to arbitrarily switch between the case of performing power conversion using both the first insulation transformer Tr1 and the second insulation transformer Tr2 and the case of performing power conversion using only the first insulation transformer Tr1. As a result, it is possible to realize a power conversion device 100a capable of performing power conversion with high efficiency over a wide input voltage range.

[0048] Note that the present invention is not limited to the above-described embodiments, and includes various modifications. For example, each of the above embodiments has been described in detail for easy understanding of the present invention, and is not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

[0049] The present invention is not limited to the above-described embodiments, and various changes can be made without departing from the spirit of the present invention.

[0050] 1: DC power supply, 2: storage battery, 100, 100a: power conversion device, 101: primary side bridge circuit, 102: secondary side bridge circuit, 103: voltage sensor, 104: control unit, Tr1: first insulation transformer, N1a: primary winding, N1b: secondary winding, Tr2: second insulation transformer, N2a: primary winding, N2b: secondary winding, L1a, L1b, L2a, L2b: connection lines, SW1a, SW1b, SW2a, SW2b: switches

Claims

1. A power conversion device comprising: a first isolation transformer having a first primary winding and a first secondary winding; a primary bridge circuit to which a first DC power is input; a secondary bridge circuit to which a second DC power is output; a second isolation transformer provided between the first isolation transformer and the primary bridge circuit or the secondary bridge circuit, having a second primary winding and a second secondary winding; a pair of connecting wires connecting both ends of the second primary winding and both ends of the second secondary winding, respectively; a pair of first switches connected to both ends of the second primary winding, respectively; and a pair of second switches provided on the connecting wires.

2. A power conversion device according to claim 1, wherein the turns ratio of the second primary winding to the second secondary winding is different from the turns ratio of the first primary winding to the first secondary winding.

3. A power conversion device according to claim 2, wherein the turns ratio of the second primary winding to the second secondary winding is smaller than the turns ratio of the first primary winding to the first secondary winding.

4. A power conversion device according to claim 1, wherein the second primary winding and the second secondary winding are each configured using a substrate pattern formed on a circuit board.

5. In the power conversion device according to claim 1, the second isolation transformer is provided between the first isolation transformer and the primary bridge circuit, and when the first switch is switched to the ON state and the second switch is switched to the OFF state, the first AC power output from the primary bridge circuit is input to the second primary winding, and when the first AC power is input to the second primary winding, the second secondary winding outputs a second AC power to the first primary winding having a different voltage from the first AC power, and when the second AC power is input to the first primary winding, the first secondary winding outputs a third AC power to the secondary bridge circuit having a different voltage from the second AC power, and the secondary bridge circuit converts the third AC power to the second DC power and outputs it, and when the first switch is switched to the OFF state and the second switch is switched to the ON state, the first AC power output from the primary bridge circuit is input to the first primary winding, The first secondary winding outputs a fourth AC power, which has a different voltage from the first AC power, to the secondary bridge circuit when the first AC power is input to the first primary winding, and the secondary bridge circuit converts the fourth AC power to the second DC power and outputs it, making it a power conversion device.

6. A power conversion device according to claim 1, comprising a control unit that controls the primary bridge circuit, the secondary bridge circuit, the first switch, and the second switch, wherein the control unit switches the first switch to the ON state and the second switch to the OFF state when the voltage of the first DC power is equal to or greater than a predetermined value.

7. A power conversion device according to claim 6, wherein the control unit switches the first switch to the off state and the second switch to the on state when the voltage of the first DC power is less than the predetermined value.

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