WO2018155442A1 - Dc power supply system - Google Patents

Abstract

In order to provide a DC power supply system capable of preventing system shutdown even when the power consumption of a DC load abruptly falls, the DC power supply system is provided with: a DC bus line 5 to which a DC load 6 can be connected; a power generation device 1 for supplying power to the DC bus line 5; a secondary battery 3 capable of supplying power to the DC bus line 5; and a control unit 7 for controlling the charging and discharging of the secondary battery 3. The control unit 7 performs control so that a charging current value does not exceed a first value until the charging amount of the secondary battery 3 reaches a predetermined set charging value that is lower than a predetermined charging allowable upper limit value, and performs control so that the charging current value is set to a second value lower than the first value when the charging amount exceeds the set charging value.

Description

DC power supply system

This invention relates to a DC power supply system.

Conventionally, power supply systems combining solar cells and storage batteries have been provided. In such a power feeding system, various devices have been made in order to prevent overcharge and overdischarge in the storage battery.

For example, in Patent Document 1, the voltage of the unit cell of the storage battery pack and the series voltage of the storage battery pack in the power storage unit are compared with the upper limit value and the lower limit value, respectively, and if the upper limit value is exceeded, the charging process of the power storage unit is stopped However, when the value is less than the lower limit, the discharging process of the power storage unit is stopped.

JP 2014-195401 A

However, in the method of Patent Document 1, the power consumption of the DC load is suddenly reduced and the charging process of the power storage unit is stopped in a state where the power generation amount of the solar cell and the power supplied from the power system are maintained. In some cases, there was a problem that the system could be stopped.

The present invention has been made to solve the above-described problem, and provides a DC power feeding system that can prevent a system from being stopped even when the power consumption of a DC load suddenly decreases. Objective.

A first aspect of the present invention includes a DC bus line to which a DC load can be connected, a power generator for supplying power to the DC bus line, a secondary battery capable of supplying power to the DC bus line, A controller that controls charging / discharging of the secondary battery, and the controller charges until the charge amount of the secondary battery reaches a predetermined charge set value lower than a predetermined charge allowable upper limit value. The current value is controlled so as not to exceed the first value, and when the charge amount exceeds the charge setting value, the charge current value is set to a second value lower than the first value. It is characterized by controlling.

According to the present invention, it is possible to prevent the system from being stopped even when the power consumption of the DC load suddenly decreases.

It is a figure showing a schematic structure of a direct-current power supply system of a 1st embodiment concerning the present invention. It is a figure explaining operation | movement of the steady state in a DC power supply system. It is a figure explaining operation | movement when the power consumption of DC load reduces in a DC power supply system. It is a figure which shows the charging current limiting value according to SOC (State | of | Charge: Charge rate) in a direct current power supply system. It is a flowchart which shows control of the charging current limit value according to SOC in a DC power supply system. It is a flowchart which shows control of the charging current limit value according to SOC in the DC power supply system of 2nd Embodiment which concerns on this invention.

(First embodiment)
Hereinafter, a DC power supply system according to a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of a DC power supply system 100 according to the present embodiment. As shown in FIG. 1, the DC power supply system 100 includes a solar cell 1, a PV converter 2, a lithium ion battery 3, a bidirectional DC-DC converter 4, an HVDC bus 5, and a DC load 6. Yes. The DC power supply system 100 is connected between the control unit 7, the bidirectional DC-AC converter 8, the CAN bus 9, the power system 10, and the bidirectional DC-AC converter 8 and the power system 10. AC load 11 is provided.

As the solar cell 1 as the power generation device, for example, a silicon-based solar cell or a compound semiconductor-based CIS solar cell composed of copper (Cu), indium (I), selenium (Se), or the like is used.

The PV (Photovoltaic) converter 2 performs maximum power point tracking (MPPT: Maximum に 対 し て Power Point Tracking) control on the output power of the solar cell 1 and supplies power to the HVDC bus 5.

The lithium ion battery 3 as a secondary battery is a rechargeable storage battery. As the secondary battery, in addition to the lithium ion battery 3, another type of storage battery such as a sodium-sulfur battery may be used.

The bidirectional DC-DC converter 4 is connected to the lithium ion battery 3 and the HVDC bus 5, converts the voltage value of the output voltage of the lithium ion battery 3 into a predetermined voltage value, and supplies it to the HVDC bus 5. Further, the voltage value of the voltage supplied via the HVDC bus 5 is converted into a predetermined voltage value and supplied to the lithium ion battery 3.

The HVDC bus 5 as a DC bus line is a bus for high-voltage DC power supply (HVDC: High-Voltage Direct Current), and includes a PV converter 2, a bidirectional DC-DC converter 4, a DC load 6, and a bidirectional DC- Connected to the AC converter 8.

The direct current load 6 is a device capable of direct current drive connected to the HVDC bus 5, and examples thereof include a refrigerator and an air conditioner.

The control unit 7 includes, for example, a CPU, a ROM, a RAM, and the like. The control unit 7 is connected to the PV converter 2, the bidirectional DC-DC converter 4, and the bidirectional DC-AC converter 8 through the CAN bus 9, and controls these converters.

The bidirectional DC-AC converter 8 as a DC-AC converter is connected to the power system 10 and the HVDC bus 5, converts the AC voltage supplied from the power system 10 into a DC voltage, and supplies the DC voltage to the HVDC bus 5. The bidirectional DC-AC converter 8 converts the DC voltage supplied to the HVDC bus 5 into an AC voltage and supplies the AC voltage to the AC load 11 or reversely flows to the power system 10.

A CAN (Controller Area Network) bus 9 is connected to the PV converter 2, the bidirectional DC-DC converter 4, the control unit 7, and the bidirectional DC-AC converter 8, and is used as a transmission path for signals such as control signals.

Electric power system 10 is supplied with a commercial AC voltage such as 200V. In addition, the DC voltage of the solar cell 1 supplied via the HVDC bus 5 can be converted into an AC voltage by the bidirectional DC-AC converter 8 and flown back to the power system 10.

As described above, the DC power supply system 100 according to the present embodiment supplies the internal current and voltage with DC, so that a switch such as a relay is not necessary, and the switching of the power supply path is necessary. The power supply route can be switched seamlessly.

Next, the operation of the DC power supply system 100 of the present embodiment as described above will be described with reference to the accompanying drawings. FIG. 2 is a diagram for explaining the steady-state operation in the DC power supply system 100. FIG. 3 is a diagram for explaining the operation when the power consumption of the DC load 6 is reduced in the DC power supply system 100. FIG. 4 is a diagram illustrating a charging current limit value according to SOC (State of charge) in the DC power supply system 100. FIG. 5 is a flowchart showing the control of the charging current limit value according to the SOC in DC power supply system 100.

In the DC power supply system 100 of the present embodiment, a generated power sensor (not shown) is provided in the connection path between the output stage of the PV converter 2 and the HVDC bus 5, and the control unit 7 controls the solar cell 1. It is possible to detect the amount of generated power. A power sensor (not shown) is provided in the connection path between the input / output stage of the bidirectional DC-DC converter 4 and the HVDC bus 5, and the controller 7 controls the discharge power amount of the lithium ion battery 3. It is possible to detect the amount of charged power and the SOC. Further, a power sensor (not shown) is provided in the connection path between the input stage of the DC load 6 and the HVDC bus 5, and the control unit 7 can detect the power consumption of the DC load. ing. Further, a power sensor (not shown) is provided in the connection path between the input / output stage of the bidirectional DC-AC converter 8 and the HVDC bus 5, and the amount of power supplied to the power system 10 by the control unit 7. In addition, the amount of power supplied from the power system 10 can be detected. In the following description, the AC load 11 connected between the bidirectional DC-AC converter 8 and the power system 10 is omitted because it is not connected in order to simplify the description.

(Steady state operation)
First, the steady state operation of the DC power supply system 100 will be described. When the control unit 7 compares the power generation amount of the solar cell 1 with the power consumption amount of the DC load 6 and determines that the power generation amount is lower than the power consumption amount, the control unit 7 generates the power generation power of the solar cell 1. Is supplied to the DC load 6, and power is supplied from the power system 10 to the DC load 6 as a shortage. Specifically, the control unit 7 brings the bidirectional DC-DC converter 4 into an inactive state and the bidirectional DC-AC converter 8 into an active state. Then, the control unit 7 controls the bidirectional DC-AC converter 8 so as to supply the insufficient power to the DC load 6.

In the example shown in FIG. 2, the power generation amount of the solar cell 1 is 7 kW, and the power consumption amount of the DC load 6 is 10 kW. Therefore, the control unit 7 supplies 7 kW, which is the power generation amount of the solar cell 1, to the DC load 6. Supply the shortage of 3 kW from the power system 10 side. In this case, charging of the lithium ion battery 3 and discharging from the lithium ion battery 3 are not performed.

(Operation when the power consumption of the DC load 6 is reduced)
During the operation in the steady state as described above, the power consumption of the DC load 6 may suddenly decrease for some reason. In this case, the control unit 7 determines that the power generation amount exceeds the power consumption amount, and out of the power generation amount of the solar cell 1, the power corresponding to the power consumption amount of the DC load 6 is converted to DC. Supply to load 6. Further, the control unit 7 supplies surplus power to the lithium ion battery 3 to charge the lithium ion battery 3. Specifically, the control unit 7 sets the bidirectional DC-DC converter 4 to an active state and sets the bidirectional DC-AC converter 8 to an inactive state.

In the example shown in FIG. 3, the power consumption of the DC load 6 is reduced to 5 kW from the case shown in FIG. 2, and the power generation amount of the solar cell 1 is 7 kW. It is judged that it is over. The control unit 7 supplies 5 kW to the DC load 6 out of 7 kW of the generated power amount of the solar cell 1 and supplies 3 kW of surplus power to the lithium ion battery 3 via the bidirectional DC-DC converter 4. .

(Operation when charging the lithium ion battery 3)
Next, an operation when the lithium ion battery 3 is charged under the control of the control unit 7 will be described. FIG. 4 is a diagram illustrating a charging current limit value according to the SOC in the DC power supply system 100. FIG. 5 is a flowchart showing the control of the charging current limit value according to the SOC in DC power supply system 100.

In the present embodiment, control for changing the charging current limit value is performed in accordance with the SOC of the lithium ion battery 3. The charge current limit value is also called a C (Capacity) rate, and represents a relative ratio of the charge current value to the capacity of the lithium ion battery 3. For example, the charge current limit value of 1 [C] refers to a current value at which a certain capacity cell is charged with a constant current and charging ends in one hour. For example, when the rated capacity of the lithium ion battery 3 is 40 Ah, the charge of 1 [C] represents the charge with a charge current value of 40 A. In addition, charging of 0.5 [C], 0.3 [C], and 0.1 [C] represents charging with charging current values of 20A, 12A, and 4A, respectively.

As shown in FIG. 4, in this embodiment, when the SOC is 20% to 70%, the charging current limit value is set to 1 [C]. When the SOC is 75%, 80%, and 85%, the charging current limit values are set to 0.5 [C], 0.3 [C], and 0.1 [C], respectively. . When the SOC reaches 90%, the charging current limit value is set to 0 [C].

In the present embodiment, the charge amount when the SOC is 90% is set as the charge allowable upper limit value. When the SOC reaches 90%, the charge current limit value is set to 0 [C] and the charge is stopped. ing. In this embodiment, the charge amount when the SOC is 75% is set as the charge set value, and the charge current value is set to the first value until the charge amount reaches a charge set value lower than the charge allowable upper limit value. Control not to exceed. As an example, the first value is the charging current value when the charging current limit value is 1 [C]. Furthermore, in the present embodiment, when the charge amount exceeds the charge set value, that is, when the SOC exceeds 75%, the charge current value is set to the second value lower than the first value. Control. As an example, the second value is a charging current value when the charging current limit value is 0.5 [C], 0.3 [C], and 0.1 [C].

As shown in FIG. 5, the control unit 7 first determines whether or not the charge amount of the lithium ion battery 3 has reached the charge setting value based on whether the SOC is 75% or more (S10). When the SOC is less than 75% (S10: NO), the control unit 7 sets the charging current limit value to 1 [C] (S11). That is, the control unit 7 sets the charging current limit value to 1 so that the charging current value does not exceed the first value until the SOC reaches 75% of the charging setting value lower than 90% of the allowable charging upper limit value. Set to [C] to charge.

When the SOC is 75% or more and less than 80% (S10: YES, S12: NO, S13: NO, S15: NO), the control unit 7 sets the charging current limit value to 0.5 [C]. (S17). When the SOC is 80% or more and less than 85% (S10: YES, S12: NO, S13: NO, S15: YES), the control unit 7 sets the charging current limit value to 0.3 [C] ( S16). When the SOC is 85% or more and less than 90% (S10: YES, S12: NO, S13: YES), the control unit 7 sets the charging current limit value to 0.1 [C] (S14). That is, when the charge amount exceeds 75% of the charge setting value, the control unit 7 sets the charge current limit value to 0. 0 so that the charge current value becomes the second value lower than the first value. Charging is performed by setting 5 [C], 0.3 [C], or 0.1 [C].

Furthermore, when the SOC reaches 90% (S10: YES, S12: YES), the control unit 7 sets the charging current limit value to 0 [C] and stops charging (S18).

As described above, according to the present embodiment, when the charge amount of the lithium ion battery 3 exceeds 75% of the charge setting value, the charge amount does not immediately reach 90% of the charge allowable upper limit value. The charging current value is set lower than the charging current value when the charging amount is less than 75% of the charging set value. As a result, even if the SOC exceeds 75%, the amount of charge to the lithium ion battery 3 has a margin until it is fully charged. Electric power can be absorbed by charging the lithium ion battery 3. Therefore, even when the power consumption of the DC load 6 suddenly decreases, an overvoltage protection function is activated due to a rapid rise in the HVDC bus voltage, preventing the system from shutting down and providing a DC power supply system that is easy to continue operation. be able to.

Further, in the present embodiment, the charging current value is gradually reduced as the charging amount approaches 90% of the allowable charging upper limit value. Therefore, even if the SOC of the lithium ion battery 3 exceeds 75%, the charging current value is fully satisfied. The period until charging can be extended.
The first value and the second value are values that depend on the charge / discharge characteristics of the lithium ion battery and the battery capacity, and some of the lithium ion batteries in practical use can be charged at about 10 C. The values are not limited to those shown in this embodiment, and can be set as appropriate.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is a flowchart showing the control of the charging current limit value according to the SOC in the DC power supply system 100 according to the second embodiment.

In the first embodiment, an example in which charging of the lithium ion battery 3 is stopped by setting the charging current limit value to 0 when the charging amount reaches 90% of the allowable charging upper limit value has been described. However, in the present embodiment, even if the charge amount has reached 90% of the charge allowable upper limit value, if the voltage value of the HVDC bus 5 exceeds the threshold value within a predetermined time, the lithium ion battery 3 is turned off. Allow current to flow.

As shown in FIG. 6, the control until the amount of charge reaches 90% of the allowable charging upper limit is the same as the control in the first embodiment shown in FIG. As shown in FIG. 6, when the control unit 7 in the present embodiment determines that the charge amount has reached 90% of the charge allowable upper limit value (S12: YES), the voltage value of the HVDC bus 5 increases beyond the threshold value. It is determined whether or not (S20). Whether or not the voltage value of the HVDC bus 5 has exceeded the threshold value is detected by, for example, providing a voltage detection circuit for monitoring the HVDC bus voltage using a voltage dividing resistor or the like, and comparing it with the threshold value. Judgment is possible.

When the control unit 7 determines that the voltage value of the HVDC bus 5 has exceeded the threshold value (S20: YES), the control unit 7 permits the current to flow to the lithium ion battery 3. Next, the control unit 7 determines whether or not the voltage increase of the HVDC bus 5 has continued for a predetermined time or more, that is, whether or not the voltage increase has stopped within a predetermined time (S22). If the voltage rise is transient (the voltage rise has stopped within a predetermined time) (S22: NO), permission of charging is continued. However, when it is determined that the voltage value of the HVDC bus 5 has not increased beyond the threshold (S20: NO), or when it is determined that the voltage increase is not transient (continues for a predetermined time or more) (S22: YES) ), The charging current limit value is set to 0 [C] (S23), and control is performed so that no current flows to the lithium ion battery 3.

"The" predetermined time "in this case is in milliseconds, for example within 1 second. Assuming that the charging capacity of the lithium ion battery 3 is 40 Ah, even if it is charged at 10 C, the capacity is only affected by about 0.1 Ah in 1 second, which is an increase of about 0.25% when converted to SOC. Therefore, the life of the lithium ion battery is not substantially affected.

As described above, according to the present embodiment, even when the charge amount of the lithium ion battery 3 has reached 90% of the charge allowable upper limit value, the voltage value of the HVDC bus 5 has risen transiently beyond the threshold value. The current is allowed to flow to the lithium ion battery 3. Therefore, even when the DC load 6 suddenly changes to a light load and the power consumption decreases transiently, it is possible to prevent the system from stopping and provide a DC power supply system that is easy to continue operation.

The present invention can be used for a DC power supply system in which a solar battery and a storage battery are combined.

DESCRIPTION OF SYMBOLS 1 Solar cell 3 Lithium ion battery 6 DC load 7 Control part 10 Electric power system 100 DC power supply system

Claims (3)

A DC bus line to which a DC load can be connected;
A power generator for supplying power to the DC bus line;
A secondary battery capable of supplying power to the DC bus line;
A controller that controls charging and discharging of the secondary battery,
The control unit performs control so that a charging current value does not exceed a first value until a charge amount of the secondary battery reaches a predetermined charge setting value lower than a predetermined charge allowable upper limit value, and the charge When the amount exceeds the charging set value, the charging current value is controlled to be a second value lower than the first value.
DC power supply system characterized by this. When the voltage value of the DC bus line rises above a threshold value and the voltage rise falls within a predetermined time, the control unit determines whether the charge amount of the secondary battery has reached the charge allowable upper limit value. Allowing current to flow to the secondary battery,
The DC power supply system according to claim 1, wherein The control unit includes a plurality of values as the second value, and when the charge amount exceeds the charge setting value, the second value is lowered stepwise.
The DC power feeding system according to claim 1 or 2, wherein

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