JP6795082B2 - DC power supply system - Google Patents

Description

The present invention relates to a DC power supply system.

Conventionally, a power supply system that combines a solar cell and a storage battery has been provided. In such a power supply system, various measures have been taken to prevent overcharging and overdischarging of the storage battery.

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

Japanese Unexamined Patent Publication No. 2014-195401

However, in the method of Patent Document 1, the power consumption of the DC load suddenly decreases and the charging process of the power storage unit is stopped while the power generation amount of the solar cell and the power supply 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 problems, and to provide a DC power supply system capable of preventing a system outage even when the power consumption of a DC load suddenly drops. The purpose.

The first aspect of the present invention includes a DC bus line to which a DC load can be connected, a power generation device for supplying power to the DC bus line, and a secondary battery capable of supplying power to the DC bus line. The control unit includes a control unit that controls charging / discharging of the secondary battery, and the control unit charges the secondary battery until the charge amount reaches a predetermined charge setting 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 set 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 stopping even when the power consumption of the DC load suddenly drops.

It is a figure which shows the schematic structure of the DC power supply system of 1st Embodiment which concerns on this invention. It is a figure explaining the operation of the steady state in a DC power supply system. It is a figure explaining the operation when the power consumption of a DC load is reduced in a DC power supply system. It is a figure which shows the charge current limit value according to SOC (State of Charge: charge rate) in a DC power supply system. It is a flowchart which shows the control of the charge current limit value according to SOC in a DC power supply system. It is a flowchart which shows the control of the charge current limit value according to SOC in the DC power supply system of 2nd Embodiment which concerns on this invention.

(First Embodiment)
Hereinafter, the DC power supply system according to the first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing 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 battery 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. There is. Further, 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, the bidirectional DC-AC converter 8 and the power system 10. It has an AC load 11.

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

The PV (Photovoltaic) converter 2 performs maximum power point tracking (MPPT) control with respect to 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 storage battery that can be charged and discharged. 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 the voltage value 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 direct current power supply (HVDC: High-Voltage Direct Current), and is a PV converter 2, a bidirectional DC-DC converter 4, a DC load 6, and a bidirectional DC-. It is connected to the AC converter 8.

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

The control unit 7 is composed of, 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 via 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 AC voltage to the HVDC bus 5. Further, the bidirectional DC-AC converter 8 converts the DC voltage supplied to the HVDC bus 5 into an AC voltage and supplies it to the AC load 11 or reverse power flows to the power system 10.

The CAN (Control Area Network) bus 9 is connected to a PV converter 2, a bidirectional DC-DC converter 4, a control unit 7, and a bidirectional DC-AC converter 8 and is used as a signal transmission path for a control signal or the like.

A commercial AC voltage such as 200V is supplied to the power system 10. Further, it is also possible to convert the DC voltage of the solar cell 1 supplied via the HVDC bus 5 into an AC voltage by the bidirectional DC-AC converter 8 and reverse power flow to the power system 10.

As described above, in the DC power supply system 100 of the present embodiment, since the internal current and voltage are supplied by direct current, a switch such as a relay is unnecessary, and when it is necessary to switch the power supply path, a break occurs. It is possible to seamlessly switch the power supply route.

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

In the DC power supply system 100 of the present embodiment, a power generation 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 solar cell 1 is provided by the control unit 7. It is possible to detect the amount of power generated by the system. Further, 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 control unit 7 determines the amount of discharge power of the lithium ion battery 3. It is possible to detect the amount of charging 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. And it is possible to detect the amount of power supplied from the power system 10. In the following description, the AC load 11 connected between the bidirectional DC-AC converter 8 and the power system 10 will be omitted as if they were not connected for the sake of simplicity.

(Steady state operation)
First, the steady state operation in the DC power supply system 100 will be described. The control unit 7 compares the electric energy generated by the solar cell 1 with the electric energy consumed by the DC load 6, and if it is determined that the electric energy generated is less than the electric energy consumed, the electric energy generated by 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 puts the bidirectional DC-DC converter 4 in the inactive state and the bidirectional DC-AC converter 8 in the 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, since 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, the control unit 7 changes the power generation amount of the solar cell 1 from 7 kW to the DC load 6. It is supplied, and the shortage of 3 kW is supplied from the power system 10 side. In this case, the lithium ion battery 3 is not charged and the lithium ion battery 3 is not discharged.

(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 amount of generated power exceeds the amount of power consumption, and uses the amount of power generated by the solar cell 1 corresponding to the amount of power consumed by the DC load 6 as direct current. Supply to load 6. Further, the control unit 7 supplies surplus electric power to the lithium ion battery 3 to charge the lithium ion battery 3. Specifically, the control unit 7 activates the bidirectional DC-DC converter 4 and deactivates the bidirectional DC-AC converter 8.

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. Therefore, the power generation amount of the control unit 7 is the power consumption amount. It is judged that it exceeds. The control unit 7 supplies 5 kW of the 7 kW of power generated by the solar cell 1 to the DC load 6, 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, the 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 showing a charging current limit value according to the SOC in the DC power supply system 100. FIG. 5 is a flowchart showing control of the charging current limit value according to the SOC in the DC power supply system 100.

In the present embodiment, control is performed to change the charging current limit value according to the SOC of the lithium ion battery 3. The charging current limit value is also called a C (Capacity) rate and represents a relative ratio of the charging current value to the capacity of the lithium ion battery 3. For example, the charging current limit value of 1 [C] means a current value at which a cell having a certain capacity is charged with a constant current and charging is completed in 1 hour. For example, when the rated capacity of the lithium ion battery 3 is 40 Ah, charging of 1 [C] means charging with a charging current value of 40 A. Further, 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 the present 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. .. Then, 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 allowable upper limit value for charging, and when the SOC reaches 90%, the charging current limit value is set to 0 [C] and charging is stopped. ing. Further, in the present embodiment, the charge amount when the SOC is 75% is set as the charge setting value, and the charge current value is set to the first value until the charge amount reaches the charge set value lower than the charge allowable upper limit value. Control so that it does not exceed. As an example, the first value is the charging current value when the charging current limit value is 1 [C]. Further, 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 a second value lower than the first value. Control. As an example, the second value is the charging current value when the charging current limit value is 0.5 [C], 0.3 [C], and 0.1 [C], respectively.

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 set value depending 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 charging allowable upper limit value. Set to [C] to charge.

Further, 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 set value, the control unit 7 sets the charge current limit value to 0 so that the charge current value becomes a second value lower than the first value. Charging is performed by setting the value to 5 [C], 0.3 [C], or 0.1 [C].

Further, 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 set value, the charge amount does not immediately reach 90% of the charge allowable upper limit value. , The charging current value is made lower than the charging current value when the charge amount is less than 75% of the charge set value. As a result, the amount of charge to the lithium-ion battery 3 is surplus when the power consumption of the DC load 6 suddenly decreases because there is a margin before the battery is fully charged even if the SOC exceeds 75%. Electric power can be absorbed by charging the lithium-ion battery 3. Therefore, even if the power consumption of the DC load 6 suddenly decreases, the HVDC bus voltage suddenly rises and the overvoltage protection function works to prevent the system from stopping, providing a DC power supply system that facilitates continuous 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 upper limit value of charging, so that even if the SOC of the lithium ion battery 3 exceeds 75%, it is fully satisfied. The period until charging can be extended.
The first value and the second value depend on the charge / discharge characteristics and the battery capacity of the lithium ion battery, and some of the lithium ion batteries in practical use can be charged at about 10 C. , Not limited to the values shown in this example, it 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 the charging current limit value is set to 0 and the charging of the lithium ion battery 3 is stopped when the charge amount reaches 90% of the charge allowable upper limit value has been described. However, in the present embodiment, even if the charge amount reaches 90% of the charge allowable upper limit value, when the voltage value of the HVDC bus 5 exceeds the threshold value within a predetermined time, the lithium ion battery 3 is charged. Allow current to flow.

As shown in FIG. 6, the control until the charge amount reaches 90% of the allowable upper limit value of charge is the same as the control in the first embodiment shown in FIG. 5, and therefore the duplicate description will be omitted. As shown in FIG. 6, when the control unit 7 in the present embodiment determines that the charge amount has reached 90% of the allowable upper limit value of charge (S12: YES), the voltage value of the HVDC bus 5 rises beyond the threshold value. It is determined whether or not it has been done (S20). Whether or not the voltage value of the HVDC bus 5 has risen beyond 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 with the threshold value. It is possible to judge.

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

The "predetermined time" at this time is in milliseconds, for example, within 1 second. Assuming that the charge 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. This has virtually no effect on the life of the lithium-ion battery.

As described above, according to the present embodiment, even if the charge amount of the lithium ion battery 3 reaches 90% of the allowable upper limit value of charging, when the voltage value of the HVDC bus 5 transiently rises beyond the threshold value. Allows current to flow through the lithium-ion battery 3. Therefore, even when the DC load 6 suddenly changes to a light load and the power consumption is transiently significantly reduced, it is possible to prevent the system from stopping and provide a DC power supply system that facilitates continuous operation.

The present invention can be used in a DC power supply system that combines a solar cell and a storage battery.

1 Solar cell 3 Lithium-ion battery 6 DC load 7 Control unit 10 Power system 100 DC power supply system

Claims (2)

A DC bus line that can connect a DC load,
A power generation device for supplying electric power to the DC bus line,
A secondary battery that can supply power to the DC bus line,
A control unit that controls charging / discharging of the secondary battery is provided.
The control unit controls the charging current value so as not to exceed the first value until the charge amount of the secondary battery reaches a predetermined charge set value lower than the predetermined charge allowable upper limit value, and the charge is performed. When the amount exceeds the charge set value, the charge current value is controlled to be a second value lower than the first value, and the charge current value is controlled to be a second value .
When the voltage value of the DC bus line rises beyond the threshold value, if the voltage rise is within a predetermined time, even if the charge amount of the secondary battery reaches the charge allowable upper limit value, the secondary battery Allows the current to flow to the secondary battery, and controls the current flowing to the secondary battery to become zero after a lapse of a predetermined time .
A DC power supply system characterized by this. The control unit includes a plurality of values as the second value, and when the charge amount exceeds the charge set value, the second value is gradually lowered .
The DC power supply system according to claim 1.

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