JP7589126B2 - Power Conversion Equipment - Google Patents

Description

The present invention relates to a power conversion device.

In order to achieve energy conservation in railways, development of storage systems to be installed in electric cars is underway (see, for example, Patent Document 1).

JP 2016-226127 A

The volume of the energy storage systems installed in electric vehicles is limited due to the installation space, and it is desirable for them to be as light as possible due to fuel efficiency. When designing an energy storage system, it may be possible to make the entire system smaller and lighter by combining multiple types of energy storage devices with different power densities and energy densities, rather than using a single type of energy storage device.

However, by simply connecting multiple types of power storage devices, the charge and discharge current of each power storage device is passively determined, and the effect of using them in combination cannot be fully achieved. For this reason, when using multiple types of power storage devices in combination, it is necessary to actively control the charge and discharge current of each power storage device using a power conversion device in order to enhance the effect of using them in combination. However, the conventional idea of using a power conversion device was to prepare and connect both positive and negative terminals to each power storage device and control based on the overall voltage of each power storage device. Therefore, it was necessary to prepare a power conversion device with a large voltage rating that could be sufficiently controlled for each capacity of multiple types of power storage devices. As a result, a large power conversion device was required, and as a result, the entire system, including the heat sink of the power conversion device, became larger and the weight increased, and there was a possibility that the benefits of using multiple types of power storage devices in combination could not be obtained. In other words, it was counter to the desire to make the entire system smaller.

The problem that this invention aims to solve is to reduce the size and weight of a power conversion device that controls the charge and discharge currents of multiple types of power storage devices used in combination.

The first invention for solving the above problem is:
A power conversion device that is interposed between a first power storage device, a second power storage device, and a load circuit and exchanges power,
a first terminal to which the first power storage device is connected;
a second terminal to which the second power storage device is connected;
a load terminal to which the load circuit is connected;
Equipped with
The power conversion apparatus controls charging and discharging operations of the first power storage device and the second power storage device by controlling current flow between the first terminal, the second terminal, and the load terminal.

According to the first invention, it is possible to reduce the size and weight of a power conversion device that controls the charge and discharge currents of multiple types of power storage devices. The power conversion device controls the charging and discharging operations of each power storage device by controlling the current flow between each terminal. For example, the voltage between the first terminal and the second terminal is the voltage difference between the first power storage device and the second power storage device, and the voltage between the load terminal and the second terminal is the voltage difference between the load circuit and the second power storage device. Since this voltage difference becomes the input/output voltage of the power conversion device, it is possible to reduce the rated capacity, which is a guideline for the dimensions of the power conversion device. This allows the power conversion device to be reduced in size and weight.

The second invention is the first invention,
This is a power conversion device that controls the charging and discharging operations of the first power storage device and the second power storage device by controlling the flow of current between the primary side and the secondary side, with the voltage between the first terminal and the second terminal being a primary side voltage and the voltage between the load terminal and the second terminal being a secondary side voltage.

According to the second invention, the primary voltage of the power conversion device is the voltage difference between the first and second power storage devices, and the secondary voltage is the voltage difference between the load circuit and the second power storage device. Since these voltage differences become the input and output voltages of the power conversion device, the rated capacity, which is a guideline for the dimensions of the power conversion device, can be reduced. This allows the power conversion device to be made smaller and lighter.

The specific configuration of the power conversion device may be as follows:

As a third invention, in the first or second invention,
A current booster circuit (for example, the current booster circuit 41 of FIG. 2 ) is provided,
the first terminal is connected to a high-voltage side connection point of the current boost chopper circuit;
The second terminal is connected to a ground connection point of the current boost chopper circuit,
The load terminal is connected to a low-voltage side connection point of the current boost chopper circuit.
A power conversion device (for example, power conversion device 30A in FIG. 2) may be configured.

As a fourth invention, in the first or second invention,
The power supply includes two current booster circuits (for example, the current booster circuits 42a and 42b in FIG. 3) connected in parallel by connecting the low-voltage side connection points to each other and the ground connection points to each other,
the first terminal is connected to a high-voltage side connection point of one of the two current boost chopper circuits;
the second terminal is connected to the ground connection point of the two current reversible chopper circuits;
The load terminal is connected to a high-voltage side connection point of the other of the two current reversible chopper circuits.
A power conversion device (for example, power conversion device 30B in FIG. 3) may be configured.

As a fifth invention, in the first or second invention,
The power supply includes two current booster circuits (for example, the current booster circuits 43a and 43b in FIG. 4 ) connected in parallel by connecting the high-voltage side connection points to each other and the ground connection points to each other,
the first terminal is connected to a low-voltage side connection point of one of the two current boost chopper circuits;
the second terminal is connected to the ground connection point of the two current reversible chopper circuits;
the load terminal is connected to a low-voltage side connection point of the other of the two current boost chopper circuits;
A power conversion device (for example, power conversion device 30C in FIG. 4) may be configured.

As a sixth aspect of the present invention, in the first or second aspect of the present invention,
a reversible buck-boost chopper circuit having one side connection point connected to the first terminal, the other side connection point connected to the load terminal, and a ground connection point connected to the second terminal (e.g., the reversible buck-boost chopper circuit 44 in FIG. 5 );
A power conversion device including the above (for example, the power conversion device 30D in FIG. 5) may be configured.

As a seventh invention, in the first invention,
The present invention includes three current booster circuits (for example, the current booster circuits 45a to 45c in FIG. 6) connected in parallel by connecting high-voltage side connection points to each other and connecting ground connection points to each other,
the first terminal is connected to a low-voltage side connection point of a first current reversible chopper circuit among the three current reversible chopper circuits;
the second terminal is connected to a low-voltage side connection point of a second current boost chopper circuit among the three current boost chopper circuits;
the load terminal is connected to a low-voltage side connection point of a third current reversible chopper circuit among the three current reversible chopper circuits;
A power conversion device (for example, the power conversion device 30E in FIG. 6) may be configured.

An eighth aspect of the present invention is the method according to any one of the first to seventh aspects of the present invention,
The second power storage device has a higher power density and a lower energy density than the first power storage device.
It is a power conversion device.

According to the eighth invention, it is possible to achieve a reduction in size and weight in an energy storage system that uses different types of energy storage devices in combination and has a power conversion device that controls the charge/discharge current of each energy storage device.

1 shows an example of the configuration of a power storage system. 2 shows an example of a circuit configuration of a power conversion device according to a first embodiment. 13 shows an example of a circuit configuration of a power conversion device according to a second embodiment. 13 shows an example of a circuit configuration of a power conversion device according to a third embodiment. 13 shows an example of a circuit configuration of a power conversion device according to a fourth embodiment. 13 shows an example of a circuit configuration of a power conversion device according to a fifth embodiment. An example of current control when an electric vehicle is powered. An example of current control when an electric vehicle is powered. An example of current control when an electric vehicle is coasting or stopping. An example of current control when an electric vehicle is coasting or stopping. An example of current control when an electric vehicle is coasting or stopping. An example of current control during regeneration and charging of an electric vehicle. An example of current control during regeneration and charging of an electric vehicle. Circuit simulation results for current control during power running of electric vehicles. Circuit simulation results for a power conversion device during regeneration and charging of an electric vehicle. Circuit simulation results for a power conversion device during regeneration and charging of an electric vehicle. 1 shows an example of the configuration of a power storage system in which a power conversion device is used as the negative side circuit. 4 is a circuit configuration example when the power conversion device of the first embodiment is connected to the negative side. 13 is a circuit configuration example when the power conversion device of the second embodiment is connected to the negative side. 13 shows an example of a circuit configuration when a power conversion device according to a third embodiment is connected to a negative side. 13 shows an example of a circuit configuration when a power conversion device according to a fourth embodiment is connected to the negative side. 13 shows an example of a circuit configuration when a power conversion device according to a fifth embodiment is connected to the negative side.

Below, a preferred embodiment of the present invention will be described with reference to the drawings. Note that the forms to which the present invention can be applied are not limited to the following embodiments. In addition, in the description of the drawings, the same elements are given the same reference numerals.

[System configuration]
Fig. 1 is a diagram showing a configuration example of a power storage system 1 to which a power conversion device of the present embodiment is applied. The power storage system 1 of the present embodiment is mounted on a railway electric car and is used to store regenerative power, overhead line power, etc. and supply it as traction power, etc. As shown in Fig. 1, the power storage system 1 includes a first power storage device 10, a second power storage device 20, a power conversion device 30, and a control unit 60.

The first power storage device 10 and the second power storage device 20 are different types of power storage devices. In this embodiment, the first power storage device 10 is a power storage device that has a higher energy density but a lower power density than the second power storage device 20. For example, it is realized by a secondary battery or a fuel cell. Moreover, the second power storage device 20 is a power storage device that has a higher power density but a lower energy density than the first power storage device 10. For example, it is realized by an electric double layer capacitor.

The power conversion device 30 is a device that performs DC-DC power conversion, and is interposed between the first power storage device 10, the second power storage device 20, and the load circuit 100 to exchange power. The power conversion device 30 has three input/output terminals: a first terminal 31 to which the first power storage device 10 is connected, a second terminal 32 to which the second power storage device 20 is connected, and a load terminal 33 to which the load circuit 100 is connected. The load circuit 100 is a main circuit including a main motor, a static inverter (SIV: static inverter) for auxiliary equipment, a current collector such as a pantograph, etc.

The control unit 60 controls the charging and discharging operations of the first and second power storage devices 10 and 20 by controlling the current flow through each input/output terminal of the power conversion device 30. In other words, it controls the charging operation in which the output power of the load circuit 100 is converted to DC to charge the first and second power storage devices 10 and 20, and the discharging operation in which the discharged power of the first and second power storage devices 10 and 20 is converted to DC and supplied to the load circuit 100.

Here, the voltages and currents of the various parts of the power storage system 1 are defined as shown in Fig. 1. That is, the terminal voltages of the first power storage device 10 and the second power storage device 20 are "Vb1" and "Vb2", the output currents are "Ib1" and "Ib2", the voltage (load voltage) of the load circuit 100 is "VL", and the output current (load current) to the load circuit 100 is "IL". Then, the relationship between the current and energy input and output to the power conversion device 30 needs to satisfy the following formulas (1) and (2) when the power loss inside the power conversion device 30 is ignored.
Ib1+Ib2=IL...(1)
Vb1・Ib1+Vb2・Ib2=VL・IL...(2)

The power conversion device 30 can control (shunt control) the output currents Ib1 and Ib2 of the first power storage device 10 and the second power storage device 20. When the ratio (shunt ratio) of the current Ib1 to the current IL is "d", the currents Ib1 and Ib2 are expressed by the following equations (3) and (4).
Ib1=d・IL...(3)
Ib2=(1-d)・IL...(4)

By substituting the equations (3) and (4) into the equation (2), the following equation (5) regarding voltage is obtained.
VL=d・Vb1+(1-d)Vb2...(5)
It can be seen from this equation (5) that the load voltage VL is determined according to the terminal voltages Vb1, Vb2 of the first power storage device 10 and the second power storage device 20 and the shunt ratio d.

The current division ratio d can be any real number. When the current division ratio d is "0", the current Ib1 is "0", that is, a current flows only through the closed loop consisting of the second power storage device 20 and the load circuit 100 via the power conversion device 30. When the current division ratio d is "1", the current Ib2 is "0", that is, a current flows only through the closed loop consisting of the first power storage device 10 and the load circuit 100 via the power conversion device 30. When the current division ratio d is "greater than 1" or a "negative value", the output currents of the first power storage device 10 and the second power storage device 20 are of opposite polarity.

The control of the shunt ratio d (shunt control) is performed by the control unit 60. As described below, the power conversion device 30 is configured with a chopper circuit, and the shunt control is realized by the switching control (on/off control) of each switching element of this chopper circuit performed by the control unit 60.

Five specific examples of the power conversion device 30 are described below.

[First embodiment]
2 is a diagram showing a circuit configuration of the power conversion device 30A of the first embodiment. The power conversion device 30A of the first embodiment includes a current reversible chopper circuit 41. A high-voltage side connection point 51 of the current reversible chopper circuit 41 is connected to a first terminal 31 of the power conversion device 30A, a ground connection point 53 of the current reversible chopper circuit 41 is connected to a second terminal 32, and a low-voltage side connection point 52 of the current reversible chopper circuit 41 is connected to a load terminal 33. The power conversion device 30A also has an input/output capacitor C1 connected between the first terminal 31 and the second terminal 32, and an input/output capacitor C2 connected between the load terminal 33 and the second terminal 32.

In the power conversion device 30A, the difference voltage (= Vb1 - Vb2) between the voltage Vb1 applied to the first terminal 31 and the voltage Vb2 applied to the second terminal 32 is defined as the primary side voltage, and the difference voltage (= VL - Vb2) between the load voltage VL applied to the load terminal 33 and the voltage Vb2 applied to the second terminal 32 is defined as the secondary side voltage. The current reversible chopper circuit 41 can perform bidirectional DC conversion between the primary side voltage and the secondary side voltage. In other words, the bidirectional DC conversion by the current reversible chopper circuit 41 can perform DC conversion between the primary side and the secondary side, thereby controlling the charging and discharging operations of the first power storage device 10 and the second power storage device 20. The DC conversion by the current reversible chopper circuit 41 is realized by the switching control of the switching element by the control unit 60.

In addition, the shunt control of currents Ib1 and Ib2 (control of shunt ratio d) is performed by switching control of the switching elements. Therefore, in order to actively control the shunt, it is necessary to determine the voltages Vb1, Vb2, and VL of each input/output terminal of the power conversion device 30A so that the anti-parallel diode of each switching element is not always on. Therefore, the condition that the magnitude relationship that the voltages Vb1, Vb2, and VL must satisfy is Vb2<VL<Vb1.

[Second embodiment]
3 is a diagram showing a circuit configuration of a power converter 30B of the second embodiment. The power converter 30B includes two current reversible chopper circuits 42a and 42b. The two current reversible chopper circuits 42a and 42b are connected in parallel by sharing a reactor L and connecting the low-voltage side connection points 52 and the ground connection points 53 to each other. The high-voltage side connection point 51 of one of the current reversible chopper circuits 42a and 42b is connected to the first terminal 31 of the power converter 30B, the ground connection points 53 of the two current reversible chopper circuits 42a and 42b are connected to the second terminal 32, and the high-voltage side connection point 51 of the other of the two current reversible chopper circuits 42a and 42b is connected to the load terminal 33. The power conversion device 30B also has an input/output capacitor C1 connected between the first terminal 31 and the second terminal 32, and an input/output capacitor C2 connected between the load terminal 33 and the second terminal 32.

In the power conversion device 30B, the difference voltage (= Vb1 - Vb2) between the voltage Vb1 applied to the first terminal 31 and the voltage Vb2 applied to the second terminal 32 is the primary voltage, and the difference voltage (= VL - Vb2) between the load voltage VL applied to the load terminal 33 and the voltage Vb2 applied to the second terminal 32 is the secondary voltage. The current reversible chopper circuits 42a and 42b can perform bidirectional DC conversion between the primary and secondary voltages. In other words, the bidirectional DC conversion by the current reversible chopper circuits 42a and 42b can perform DC conversion between the primary and secondary sides, thereby controlling the charging and discharging operations of the first power storage device 10 and the second power storage device 20. The DC conversion by the current reversible chopper circuits 42a and 42b is realized by the switching control of the switching elements by the control unit 60.

In addition, the shunt control of currents Ib1 and Ib2 (control of shunt ratio d) is performed by switching control of the switching elements. Therefore, in order to actively control the shunt, it is necessary to determine the voltages Vb1, Vb2, and VL of each input/output terminal of the power conversion device 30B so that the anti-parallel diode of each switching element is not always on. Therefore, the magnitude relationship condition that the voltages Vb1, Vb2, and VL must satisfy is Vb2<VL and Vb2<Vb1.

[Third Example]
4 is a diagram showing a circuit configuration of a power conversion device 30C of the third embodiment. The power conversion device 30C includes two current reversible chopper circuits 43a and 43b. The two current reversible chopper circuits 43a and 43b are connected in parallel by connecting the high-voltage side connection points 51 and the ground connection points 53 to each other via a link capacitor Cm. The low-voltage side connection point 52 of one current reversible chopper circuit 43a of the two current reversible chopper circuits 43a and 43b is connected to the first terminal 31 of the power conversion device 30C, the ground connection points 53 of the two current reversible chopper circuits 43a and 43b are connected to the second terminal 32, and the low-voltage side connection point 52 of the other current reversible chopper circuit 43b of the two current reversible chopper circuits 43a and 43b is connected to the load terminal 33. The power conversion device 30C also has an input/output capacitor C1 connected between the first terminal 31 and the second terminal 32, and an input/output capacitor C2 connected between the load terminal 33 and the second terminal 32.

In the power conversion device 30C, the difference voltage (= Vb1 - Vb2) between the voltage Vb1 applied to the first terminal 31 and the voltage Vb2 applied to the second terminal 32 is the primary voltage, and the difference voltage (= VL - Vb2) between the load voltage VL applied to the load terminal 33 and the voltage Vb2 applied to the second terminal 32 is the secondary voltage. The current reversible chopper circuits 43a and 43b can perform bidirectional DC conversion between the primary and secondary voltages. In other words, the bidirectional DC conversion by the current reversible chopper circuits 43a and 43b can perform DC conversion between the primary and secondary sides, thereby controlling the charging and discharging operations of the first power storage device 10 and the second power storage device 20. The DC conversion by the current reversible chopper circuits 43a and 43b is realized by the switching control of the switching elements by the control unit 60.

In addition, the shunt control of currents Ib1 and Ib2 (control of shunt ratio d) is performed by switching control of the switching elements. Therefore, in order to actively control the shunt, it is necessary to determine the voltages Vb1, Vb2, and VL of each input/output terminal of power conversion device 30C so that the anti-parallel diode of each switching element is not always on. Therefore, the conditions that the voltages (terminal voltages) of each input/output terminal of power conversion device 30C must satisfy are Vb2<VL and Vb2<Vb1.

[Fourth embodiment]
5 is a diagram showing a circuit configuration of a power conversion device 30D of the fourth embodiment. The power conversion device 30D includes a reversible step-up/step-down chopper circuit 44. A first terminal 31 of the power conversion device 30D is connected to one side connection point 54 of the reversible step-up/step-down chopper circuit 44, a load terminal 33 is connected to the other side connection point 55 of the reversible step-up/step-down chopper circuit 44, and a second terminal 32 is connected to a ground connection point 56 of the reversible step-up/step-down chopper circuit 44. The power conversion device 30D also includes an input/output capacitor C1 connected between the first terminal 31 and the second terminal 32, and an input/output capacitor C2 connected between the load terminal 33 and the second terminal 32.

In the power conversion device 30D, the difference voltage (= Vb1 - Vb2) between the voltage Vb1 applied to the first terminal 31 and the voltage Vb2 applied to the second terminal 32 is taken as the primary side voltage, and the difference voltage (= VL - Vb2) between the load voltage VL applied to the load terminal 33 and the voltage Vb2 applied to the second terminal 32 is taken as the secondary side voltage. The current reversible step-up/step-down chopper circuit 44 can perform bidirectional DC conversion between the primary side voltage and the secondary side voltage. In other words, the bidirectional DC conversion by the current reversible step-up/step-down chopper circuit 44 can convert DC between the primary side and the secondary side, thereby controlling the charging and discharging operations of the first power storage device 10 and the second power storage device 20. The DC conversion by the current reversible step-up/step-down chopper circuit 44 is realized by the switching control of the switching element by the control unit 60.

In addition, the shunt control of currents Ib1 and Ib2 (control of shunt ratio d) is performed by switching control of the switching elements. Therefore, in order to actively control the shunt, it is necessary to determine the voltages Vb1, Vb2, and VL of each input/output terminal of the power conversion device 30D so that the anti-parallel diode of each switching element is not always on. Therefore, the condition that the magnitude relationship that the voltages Vb1, Vb2, and VL must satisfy is VL<Vb2<Vb1.

[Fifth Example]
6 is a diagram showing a circuit configuration of a power conversion device 30E of the fifth embodiment. The power conversion device 30E includes three current reversible chopper circuits 45a, 45b, and 45c. The current reversible chopper circuits 45a, 45b, and 45c are connected in parallel by connecting the high-voltage side connection points 51 to each other and the ground connection points 53 to each other via a link capacitor Cm. A low-voltage side connection point 52 of the first current reversible chopper circuit 45a of the three current reversible chopper circuits 45a, 45b, and 45c is connected to a first terminal 31 of the power conversion device 30E, a low-voltage side connection point 52 of the second current reversible chopper circuit 45b of the three current reversible chopper circuits 45a, 45b, and 45c is connected to a second terminal 32, and a low-voltage side connection point 52 of the third current reversible chopper circuit 45c of the three current reversible chopper circuits 45a, 45b, and 45c is connected to a load terminal 33. The power conversion device 30E also has an input/output capacitor C1 connected between the low-voltage side connection point 52 and the ground connection point 53 of the first current reversible chopper circuit 45a, an input/output capacitor C2 connected between the low-voltage side connection point 52 and the ground connection point 53 of the second current reversible chopper circuit 45b, and an input/output capacitor C3 connected between the low-voltage side connection point 52 and the ground connection point 53 of the third current reversible chopper circuit 45c.

In addition, the shunt control of currents Ib1 and Ib2 (control of shunt ratio d) is performed by switching control of the switching elements. Therefore, in order to actively control the shunt, it is necessary to determine the voltages Vb1, Vb2, and VL of the input/output terminals of the power conversion device 30E so that the anti-parallel diodes of each switching element are not always on. In the power conversion device 30E, the anti-parallel diodes of two switching elements are connected in opposite directions between the input/output terminals of the first terminal 31, the second terminal 32, and the load terminal 33. Therefore, the anti-parallel diodes are not always on. Therefore, there is no condition that the voltages Vb1, Vb2, and VL must satisfy.

[Example of control of power conversion device]
Next, a specific control example of the power conversion device 30 will be described. In each control example, the output voltages Vb1 and Vb2 of the first and second storage devices 10 and 20 are designed in advance, and the shunt ratio d is determined and controlled so that the output currents Ib1 and Ib2 of the first and second storage devices 10 and 20 are desired values. The output currents Ib1 and Ib2 are set to values that satisfy the current relational expression (1) according to the output current IL to the load circuit 100. The output currents Ib1 and Ib2 being "negative values" corresponds to the input current (charging current) to the first and second storage devices 10 and 20, and the output current IL being "negative value" corresponds to the input current from the load circuit 100. For simplicity, an ideal state in which there is no loss in the power conversion device 30 is assumed.

Figures 7 and 8 show an example of control in which the load circuit 100 consumes a current IL = 400 A when the electric vehicle is powered. In this case, the first power storage device 10 and the second power storage device 20 are discharged to output the current IL = 400 A consumed by the load circuit 100.

Figure 7 shows an example of control in which the second power storage device 20, which has a high power density, bears the entire current IL = 400 A consumed by the load circuit 100. In other words, the output current Ib1 of the first power storage device 10 is "0 A", the output current Ib2 of the second power storage device 20 is "400 A", and the current division ratio d is "0". Then, from the voltage relational equation (5), the load voltage VL is "1400 V". This control example of Figure 7 is suitable when it is necessary to supply a large amount of power to the load circuit 100. For example, this applies when an electric vehicle is accelerating or re-accelerating.

Figure 8 shows an example of control in which the current IL = 400 A consumed by the load circuit 100 is borne by both the first power storage device 10 and the second power storage device 20. In other words, the output current Ib1 of the first power storage device 10 is "100 A", the output current Ib2 of the second power storage device 20 is "300 A", and the current division ratio d is "0.25". Then, from the voltage relational expression (5), the load voltage VL is "1450 V". This control example of Figure 8 is suitable when it is necessary to continuously supply a large amount of power to the load circuit 100 following the control example of Figure 7. For example, this applies when the running speed of the electric vehicle is gradually increased, or when the electric vehicle is powered at a nearly constant speed.

Figures 9 to 11 show examples of control in which the load circuit 100 consumes a current IL = 20A when the electric vehicle is coasting or stopped. In this case, the current IL is assumed to be the current consumed by the auxiliary equipment. As in power running, both or one of the first and second power storage devices 10 and 20 are discharged to output the current IL = 20A consumed by the load circuit 100.

Figure 9 shows an example of control in which the first power storage device 10 is made to bear the entire current IL = 20A consumed by the load circuit 100. In other words, the output current Ib1 of the first power storage device 10 is set to "20A", the output current Ib2 of the second power storage device 20 is set to "0A", and the current division ratio d is "1". Then, from the voltage relational equation (5), the load voltage VL is "1600V". This control example of Figure 9 is suitable for the case where the second power storage device 20 is in a state where charging is not required (for example, in a fully charged state).

Figure 10 shows an example of control in which the first power storage device 10 is made to bear the entire current IL = 20A consumed by the load circuit 100 while charging the second power storage device 20. Specifically, the first power storage device 10, which has a surplus of stored energy, is discharged to output the discharge current to the load circuit 100, while also outputting a part of the discharge current to the second power storage device 20, which has a low remaining amount of stored energy, to charge the second power storage device 20. In other words, the output current Ib1 of the first power storage device 10 is "40A", the output current Ib2 of the second power storage device 20 is "-20A", and the current division ratio d is "2". Since the output current Ib2 is negative, it means that it is an input current (charging current) to the second power storage device 20. Then, from the voltage relational expression (5), the load voltage is "1800V".

The control example in FIG. 10 cannot be implemented in the power conversion device 30A of the first embodiment (see FIG. 2) or the power conversion device 30D of the fourth embodiment (see FIG. 5) because the voltage magnitude relationship is "Vb2<Vb1<VL."

Figure 11 shows a control example in which the second power storage device 20 is charged while the first power storage device 10 is made to bear the entire current IL = 20 A consumed by the load circuit 100, similar to the control example of Figure 10. However, it differs from the control example of Figure 10 in that the voltages Vb1, Vb2 of the first power storage device 10 and the second power storage device 20 are the same. In other words, the output current Ib1 is "60 A", the output current Ib2 is "-40 A", and the current division ratio d is "3". Since the output current Ib2 is negative, it means that it is an input current (charging current) to the second power storage device 20. And, from the voltage relational equation (5), the load voltage is "1600 V".

In this case, substituting Vb1=Vb2 into the voltage relational equation (5) gives VL=Vb1=Vb2. In other words, the load voltage VL is determined according to the output voltages Vb1, Vb2 of the first and second power storage devices 10 and 20, regardless of the current division ratio d. Therefore, even if the current division ratio d is changed to change (increase or decrease) the charging current (corresponding to the negative value of the output current Ib2) to the second power storage device 20, the load voltage VL does not change, and the degree of freedom of the current division ratio d is large.

The control example in FIG. 11 can be implemented only by the power conversion device 30E (see FIG. 6) of the fifth embodiment, which has no conditions on the voltage magnitude relationship, since the voltage magnitude relationship is "Vb2 = Vb1 = VL."

Figures 12 and 13 show examples of control in the case where a current IL = 400A is input from the load circuit 100 when an electric vehicle is decelerating and regenerating or charging from an overhead line, etc. In this case, the current IL = 400A input from the load circuit 100 is used to charge both or one of the first power storage device 10 and the second power storage device 20.

Figure 12 shows an example of control in which the entire input current IL = 400 A from the load circuit 100 is charged to the second power storage device 20. In other words, the output current Ib1 of the first power storage device 10 is "0 A", the output current Ib2 of the second power storage device 20 is "-400 A", and the shunt ratio d is "0". Since the output current Ib2 is negative, it means that it is an input current (charging current) to the second power storage device 20. Then, from the voltage relational equation (5), the load voltage VL is "1400 V". This control example of Figure 12 is suitable for a case in which the first power storage device 10 does not need to be charged (for example, it is fully charged).

Figure 13 shows an example of control in which the input current IL = 400 A from the load circuit 100 is shunted to charge both the first power storage device 10 and the second power storage device 20. In other words, the output current Ib1 of the first power storage device 10 is set to "-100 A", the output current Ib2 of the second power storage device 20 is set to "-300 A", and the shunt ratio d is "0.25". Since the output currents Ib1 and Ib2 are negative, this means that they are input currents (charging currents) to the first power storage device 10 and the second power storage device 20. Then, from the voltage relational equation (5), the load voltage VL is "1450 V".

[Example of circuit simulation of power conversion device]
Next, a description will be given of the results of a circuit simulation of the power conversion device 30. The simulation was performed under the condition that the output current IL to the load circuit 100 was fixed and the current division ratio d was changed for each of the following conditions: (1) when the electric vehicle is powered, (2) when it is coasting, and (3) when it is regenerating.

Figure 14 shows the results of a circuit simulation when the electric vehicle is powered, Figure 15 shows the results of a circuit simulation when the electric vehicle is coasting, and Figure 16 shows the results of a circuit simulation when the electric vehicle is regenerating. In all of Figures 14 to 16, the horizontal axis represents time, and graphs of voltages Vb1, Vb2, VL and currents Ib1, Ib2, IL are shown. However, to make the graphs easier to see, the output currents Ib1 and Ib2 are shown as graphs of values with inverted signs, "-Ib1, -Ib2". In addition, the voltage drop in the first and second power storage devices 10 and 20, and the voltage drop due to the parasitic resistance of each switching element of the power conversion device 30 are taken into consideration. For this reason, the values are slightly different from the ideal values.

Figure 14 shows the results of a circuit simulation when the electric vehicle is powered. In this simulation, the circuit configuration of the power conversion device 30 was the configuration of the first embodiment (see Figure 2). The current division control of the power conversion device 30 was performed assuming a transition from the control state shown in Figure 7 to the control state shown in Figure 8. In other words, the output voltage Vb1 of the first power storage device 10 was set to "approximately 1600 V", the output voltage Vb2 of the second power storage device 20 was set to "approximately 1400 V", and the current IL consumed by the load circuit 100 was set to "400 A". The current division ratio d was changed from "0", which corresponds to the control state of Figure 7, to "0.25", which corresponds to the control state of Figure 8.

In FIG. 14, the period from 0 to 0.02 seconds corresponds to the control state of FIG. 7 (diversion ratio d = 0), and the period from 0.03 to 0.06 seconds corresponds to the control state of FIG. 8 (diversion ratio d = 0.25). In the period when the diversion ratio d is "0", each switching element of the power conversion device 30 is fixed to on or off. Then, from the time "0.02 seconds" to 0.01 seconds, the diversion ratio d is linearly increased to "0.25", and switching control of each switching element of the power conversion device 30 is started. Then, the output current Ib1 of the first storage device 10 changes from "0 A" to "100 A", the output current Ib2 of the second storage device 20 changes from "400 A" to "300 A", and the load voltage VL changes from "approximately 1400 V" to "approximately 1450 V". The circuit simulation results in FIG. 14 show that the power conversion device 30 of this embodiment is capable of controlling the current split ratio during power running.

In addition, during the period when the current division ratio d is greater than "0", pulsation occurs in the voltage VL and the currents Ib1 and Ib2 due to the switching control (on/off control) of each switching element of the power conversion device 30.

Figure 15 shows the results of a circuit simulation when the electric vehicle is coasting. In this simulation, the circuit configuration of the power conversion device 30 was the configuration of the fifth embodiment (see Figure 6). The current division control of the power conversion device 30 was performed under the assumption that the output current IL to the load circuit 100 was evenly shared by the output currents Ib1 and Ib2 of the first and second storage devices 10 and 20 (current division ratio d is "0.5"; referred to as the "initial control state"), and was shifted to the control state shown in Figure 11. In other words, the output voltage Vb1 of the first storage device 10 and the output voltage Vb2 of the second storage device 20 were both set to "approximately 1600 V," and the current IL consumed by the load circuit 100 was set to "20 A." The current division ratio d was changed from "0.5" to "3," which corresponds to the control state of Figure 11.

In FIG. 15, the period from 0 to 0.02 seconds corresponds to the initial control state (diversion ratio d = 0.5), and the period from 0.03 to 0.06 seconds corresponds to the control state of FIG. 11 (diversion ratio d = 3). From the time 0.02 seconds, the diversion ratio d was increased linearly to 3 over 0.01 seconds, and switching control of each switching element of the power conversion device 30 was started. Then, the output current Ib1 of the first storage device 10 changed from 10 A to 60 A, and the output current Ib2 of the second storage device 20 changed from 10 A to -40 A (corresponding to the charging current). However, the load voltage VL remains at about 1600 V, although it is affected by the voltage drop described above. This is because, as explained in FIG. 11, Vb1 = Vb2, so the load voltage VL does not change even if the diversion ratio d changes. The circuit simulation results in FIG. 15 show that the power conversion device 30 of this embodiment is capable of controlling the current split ratio to change during coasting.

Note that pulsations occur in the voltage VL and the currents Ib1 and Ib2 due to the switching control (on/off control) of each switching element of the power conversion device 30.

Figure 16 shows the results of a circuit simulation during regeneration of an electric vehicle. In this simulation, the circuit configuration of the power conversion device 30 was the configuration of the first embodiment (see Figure 2). The simulation was performed assuming that the shunt control of the power conversion device 30 was shifted from the control state shown in Figure 12 to the control state shown in Figure 13. In other words, the output voltage Vb1 of the first power storage device 10 was set to "approximately 1600 V", the output voltage Vb2 of the second power storage device 20 was set to "approximately 1400 V", and the current IL input from the load circuit 100 was set to "400 A". The shunt ratio d was changed from "0", which corresponds to the control state of Figure 12, to "0.25", which corresponds to the control state of Figure 13.

In Figure 16, the period from "0 to 0.02 seconds" corresponds to the control state of Figure 12 (diversion ratio d = 0), and the period from "0.03 to 0.06 seconds" corresponds to the control state of Figure 13 (diversion ratio d = 0.25). During the period when the diversion ratio d is "0", each switching element of the power conversion device 30 is fixed to either on or off. Then, from the time "0.02 seconds" over a period of 0.01 seconds, the diversion ratio d is increased linearly to "0.25", and switching control (diversion control) of each switching element of the power conversion device 30 is started. As a result, the output current Ib1 of the first power storage device 10 changes from 0 A to -100 A (corresponding to the charging current), the output current Ib2 of the second power storage device 20 changes from -400 A (corresponding to the charging current) to -300 A (corresponding to the charging current), and the load voltage VL changes from approximately 1400 V to approximately 1450 V. From the circuit simulation results in FIG. 16, it can be seen that the power conversion device 30 of this embodiment is capable of controlling the current division ratio to change during regeneration.

In addition, during the period when the current division ratio d is greater than "0", pulsation occurs in the voltage VL and the currents Ib1 and Ib2 due to the switching control (on/off control) of each switching element of the power conversion device 30.

[Action and Effect]
In this way, according to the present embodiment, it is possible to reduce the size and weight of the power conversion device 30 that controls the charge and discharge currents of a plurality of types of power storage devices. This makes it possible to reduce the size and weight of the power storage system 1 that uses the first power storage device 10 and the second power storage device 20 of different types in combination and includes the power conversion device 30 that controls the charge and discharge currents of the power storage devices.

The power conversion device 30 controls the charging and discharging operations of each power storage device by controlling the flow of current between each input terminal. The primary voltage between the first terminal 31 and the second terminal 32 is the voltage difference (=Vb1-Vb2) between the voltage Vb1 of the first power storage device 10 and the voltage Vb2 of the second power storage device 20, and the secondary voltage between the load terminal 33 and the second terminal 32 is the voltage difference between the voltage VL of the load circuit 100 and the voltage of the second power storage device 20. Since these voltage differences are the input/output voltages of the power conversion device 30, it is possible to reduce the rated capacity, which is a guideline for the dimensions of the power conversion device. This allows the power conversion device 30 to be made smaller and lighter.

The power conversion device 30 is also configured with a chopper circuit, and each switching element of this chopper circuit is applied with the difference voltage between the voltages Vb1 and Vb2 or the difference voltage between the voltage Vb2 and the load voltage VL, rather than the voltages Vb1 and Vb2 of the first and second power storage devices 10 and 20 or the load voltage VL themselves. For this reason, small, low-loss elements with a low rated voltage can be used as switching elements. For these reasons, the power conversion device 30 can be made smaller and lighter.

Furthermore, the use of small, low-loss switching elements reduces losses in the power conversion device 30, contributing to energy savings and also leading to smaller, lighter heat sinks in the power conversion device 30, which also contributes to the miniaturization of the power conversion device 30.

[Modification]
Incidentally, the applicable embodiments of the present invention are not limited to the above-described embodiments, and can of course be modified as appropriate without departing from the spirit of the present invention.

For example, in the above embodiment, the power conversion device 30 is used as a positive side circuit connected to the positive side (positive electrode side) of the power storage device, but it may also be used as a negative side circuit connected to the negative side (negative electrode side) of the power storage device.

Figure 17 is a configuration example of a power storage system 1X using a power conversion device as a negative side circuit. In the power storage system 1X, the negative side of the first power storage device 10 is connected to the first terminal 31 of the power conversion device 30, the negative side of the second power storage device 20 is connected to the second terminal 32, and the negative side of the load circuit 100 is connected to the load terminal 33. The currents Ib1, Ib2, and IL input and output to the input/output terminals have values with the positive and negative reversed from those of the power conversion device 30 (see Figure 1) in the above-mentioned embodiment. In many electric vehicles, the negative side of the circuit is grounded, so using a power conversion device as a negative side circuit is advantageous in terms of insulation design because the ground potential of the power conversion device can be reduced.

The specific circuit configuration of the power conversion device 30X is basically a circuit configuration in which the arrangement of each element in the circuit configuration of the above-mentioned embodiments (first to fifth embodiments) is reversed upside down. Specifically, it is configured as shown in Figures 18 to 22. Figure 18 is a circuit configuration diagram of the circuit when the power conversion device 30A (see Figure 2) of the first embodiment is connected to the negative side, Figure 19 is a circuit configuration diagram of the circuit when the power conversion device 30B (see Figure 3) of the second embodiment is connected to the negative side, Figure 20 is a circuit configuration diagram of the circuit when the power conversion device 30C (see Figure 4) of the third embodiment is connected to the negative side, Figure 21 is a circuit configuration diagram of the circuit when the power conversion device 30D (see Figure 5) of the fourth embodiment is connected to the negative side, and Figure 22 is a circuit configuration diagram of the circuit when the power conversion device 30E (see Figure 6) of the fifth embodiment is connected to the negative side.

REFERENCE SIGNS LIST 1...Energy storage system 10...First energy storage device 20...Second energy storage device 30 (30A to 30E)...Power conversion device 31...First terminal 32...Second terminal 33...Load terminal 41, 42a, 42b, 43a, 43b, 45a, 45b, 45c...Current reversible chopper circuit 51...High voltage side connection point 52...Low voltage side connection point 53...Ground connection point 44...Current reversible step-up/step-down chopper circuit 54...One side connection point 55...Other side connection point 56...Ground connection point 60...Control unit 100...Load circuit

Claims (6)

A power conversion device that is interposed between a first power storage device, a second power storage device, and a load circuit and exchanges power,
a first terminal to which the first power storage device is connected;
a second terminal to which the second power storage device is connected;
a load terminal to which the load circuit is connected;
Equipped with
A power conversion device that controls charging and discharging operations of the first power storage device and the second power storage device by controlling the flow of current between the primary side and the secondary side, with the voltage between the first terminal and the second terminal being a primary side voltage and the voltage between the load terminal and the second terminal being a secondary side voltage. A power conversion device that is interposed between a first power storage device, a second power storage device, and a load circuit and exchanges power,
a first terminal to which the first power storage device is connected;
a second terminal to which the second power storage device is connected;
a load terminal to which the load circuit is connected;
A current boost chopper circuit;
Equipped with
the first terminal is connected to a high-voltage side connection point of the current boost chopper circuit;
The second terminal is connected to a ground connection point of the current boost chopper circuit,
the load terminal is connected to a low-voltage side connection point of the current boost chopper circuit;
A power conversion apparatus that controls charging and discharging operations of the first power storage device and the second power storage device by controlling current flow between the first terminal, the second terminal, and the load terminal. A power conversion device that is interposed between a first power storage device, a second power storage device, and a load circuit and exchanges power,
a first terminal to which the first power storage device is connected;
a second terminal to which the second power storage device is connected;
a load terminal to which the load circuit is connected;
Two current booster chopper circuits connected in parallel by connecting their low-voltage side connection points to each other and their ground connection points to each other;
Equipped with
the first terminal is connected to a high-voltage side connection point of one of the two current boost chopper circuits;
the second terminal is connected to the ground connection point of the two current reversible chopper circuits;
the load terminal is connected to a high-voltage side connection point of the other of the two current boost chopper circuits;
A power conversion apparatus that controls charging and discharging operations of the first power storage device and the second power storage device by controlling current flow between the first terminal, the second terminal, and the load terminal. A power conversion device that is interposed between a first power storage device, a second power storage device, and a load circuit and exchanges power,
a first terminal to which the first power storage device is connected;
a second terminal to which the second power storage device is connected;
a load terminal to which the load circuit is connected;
Two current booster chopper circuits connected in parallel by connecting high-voltage side connection points to each other and ground connection points to each other;
Equipped with
the first terminal is connected to a low-voltage side connection point of one of the two current boost chopper circuits;
the second terminal is connected to the ground connection point of the two current reversible chopper circuits;
the load terminal is connected to a low-voltage side connection point of the other of the two current boost chopper circuits;
A power conversion apparatus that controls charging and discharging operations of the first power storage device and the second power storage device by controlling current flow between the first terminal, the second terminal, and the load terminal. A power conversion device that is interposed between a first power storage device, a second power storage device, and a load circuit and exchanges power,
a first terminal to which the first power storage device is connected;
a second terminal to which the second power storage device is connected;
a load terminal to which the load circuit is connected;
a reversible step-up/step-down chopper circuit having a first connection point connected to the first terminal, a second connection point connected to the load terminal, and a ground connection point connected to the second terminal;
Equipped with
A power conversion apparatus that controls charging and discharging operations of the first power storage device and the second power storage device by controlling current flow between the first terminal, the second terminal, and the load terminal. The second power storage device has a higher power density and a lower energy density than the first power storage device.
The power conversion device according to any one of claims 1 to 5 .

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