JP7272897B2 - Charge/discharge control device and battery and DC power supply system equipped with the same - Google Patents

Description

The present invention relates to a charge/discharge control device for controlling charge/discharge of a battery connected to a DC bus.

At least a DC power supply and a load device are connected to the DC bus. DC power sources include, for example, those based on natural energy power generation and those based on linkage with a system power supply. The voltage of the DC bus fluctuates within a range in which the load device can operate normally. Therefore, when a battery is further connected to the DC bus as a DC power supply, it is necessary to detect the level relationship between the DC bus and the voltage of the battery, and switch between charging and discharging of the battery accordingly. Patent documents 1, 2, etc. are known as conventional techniques for controlling charging and discharging of a battery connected to a DC bus.

JP 2019-30104 A Japanese Patent Application Laid-Open No. 2019-30110

When charging/discharging a battery, the difference between the voltage at which the battery is charged and the voltage at which the battery is discharged is relatively large, which causes problems such as overcharging and undercharging, and charging current flowing in from undesired points. For example, when 20 12V lead-acid batteries in which 6 cells with a rated voltage of 2V are connected in series are connected in series, there is a difference of 80V or more between a full charge voltage of 276V and a discharge end voltage of 192V. Since this voltage range overlaps with the voltage fluctuation range of the DC bus, the charging/discharging state of the battery is greatly affected by the voltage fluctuation of the DC bus.

In addition, it is preferable to use only power from the natural energy power generation device for charging the battery, that is, not to use power from the grid power supply. However, when the system voltage is output to the DC bus, if the battery voltage is also low, the battery will be charged by the system power supply. Further, when the battery voltage is boosted by a booster circuit and discharged, a phenomenon may occur in which the power output by the battery returns and charges itself depending on the circuit loop.

In view of the above-described current situation, the present invention provides a charge/discharge control device for a battery connected to a DC bus, in which the battery is charged only from the natural energy power generation device and the battery is charged from the system power supply and the battery is self-charged. The object is to control the charging and discharging of the battery in such a way that it is blocked. Another object of the present invention is to provide a battery and a DC power supply system having such a charge/discharge control device.

In order to achieve the above objects, the present invention provides the following configurations.
- An aspect of the present invention includes a battery, a natural energy power generation device set to a maximum output voltage higher than the full charge voltage of the battery, and a grid connection device capable of outputting a system voltage lower than the full charge voltage of the battery. , a charge and discharge control device connected between a DC bus to which a load device is connected and the battery, and for controlling charge and discharge of the battery,
a charging unit capable of charging the battery from the DC bus only when the bus voltage of the DC bus exceeds a charging start voltage equal to or higher than a full charge voltage of the battery;
a boosting discharge unit that boosts the battery voltage of the battery to a boosted discharge voltage that is lower than the full charge voltage and higher than the system voltage of the grid connection device, and enables discharge from the battery to the DC bus with the boosted discharge voltage; ,
and a normal discharge section that enables discharging to the DC bus with the battery voltage when the battery voltage of the battery is between the boosted discharge voltage and the full charge voltage.
- In the above aspect, the charging unit is
a detection unit that detects whether the bus voltage exceeds the charging start voltage;
Based on the detection result of the detection unit, when the bus voltage exceeds the charge start voltage, the DC bus and the battery are connected, and when the bus voltage is equal to or lower than the charge start voltage, the DC bus and the battery are connected. It is preferable to have a switch section that cuts off the
In the above aspect, the boosting discharge unit includes a boosting circuit that boosts the battery voltage to the boosting discharge voltage, and a first booster circuit that conducts discharge current from the battery to the DC bus and blocks current in the opposite direction. It is preferred to have a rectifying element.
- In the above aspect, it is preferable that the normal discharge section includes a second rectifying element that conducts discharge current from the battery to the DC bus and blocks current in the opposite direction.
- Another aspect of the present invention is a battery including any of the charge/discharge control devices described above.
- Yet another aspect of the present invention is a battery comprising any one of the charge and discharge control devices described above, a natural energy power generation device set to a maximum output voltage higher than the full charge voltage of the battery, and a full charge of the battery. A DC power supply system in which a grid connection device capable of outputting a grid voltage lower than a charging voltage and a load device are connected to a DC bus.

According to the present invention, in a charge/discharge control device for a battery connected to a DC bus, the battery is charged only from the natural energy power generation device, and charging to the battery from the grid power supply and self-charging of the battery are prevented. Controlling the charging and discharging of the battery is achieved. Further, the present invention realizes a battery provided with such a charge/discharge control device.

FIG. 1 shows a schematic configuration of an example of a charge/discharge control device according to an embodiment of the present invention. FIG. 2 is a diagram for explaining the charge/discharge state of the battery by the charge/discharge control device of FIG. FIG. 3 shows operation during charging in mode A of FIG. FIG. 4 shows the operation during discharge in mode B of FIG. FIG. 5 shows operation during discharge in mode C of FIG.

Embodiments of the invention will now be described with reference to the drawings, which are exemplary. A battery to which the present invention is applied is, for example, a lead-acid battery in which six cells of about 2V per cell are connected in series to obtain an output voltage of 12V. Furthermore, it includes a battery in which a plurality of such 12V lead-acid batteries are further connected in series or in parallel. However, the present invention is also applicable to batteries other than such lead-acid batteries. Also, the battery voltage range of the battery to which the present invention is applied and the voltage range of the DC bus to which the battery is connected are not limited to specific ranges. Numerical values shown in the following embodiments are all examples.

(1) Circuit Configuration FIG. 1 schematically shows an example of the circuit configuration of a charge/discharge control device 1 according to an embodiment of the present invention. FIG. 1 schematically shows an overall DC power supply system to which a charge/discharge control device 1 of the present invention is connected. In the illustrated example, the DC power supply system includes a DC bus, a battery B, a grid connection device 40 , a natural energy power generation device 50 and a load device 60 .

A DC bus is represented by a high potential line LH and a low potential line LL. When the potential of the low potential line LL is taken as a reference potential (zero potential), the voltage of the high potential line LH (hereinafter referred to as "bus voltage") is denoted by Vdc.The high potential line LH and the low potential line LL of the DC bus. In between, are connected in parallel respectively a grid connection device 40, a natural energy generator 50, and a load device 60. In such a DC power supply system, the bus voltage Vdc is within a range in which the load device 60 can operate normally. configured to vary.

The natural energy power generation device 50 is, for example, a wind power generation device, a solar power generation device, or the like, and may include a plurality of power generation devices of different types, but is schematically shown here as one concept. The output voltage of the natural energy power generation device 50 (referred to as "natural energy power generation voltage") is indicated by Vg. The natural energy power generation voltage fluctuates depending on power generation conditions.

Furthermore, each generator has a maximum output voltage. For example, if the maximum voltage of the wind power generator is set to 300 V, the wind power generator should output to the bus when its output voltage Vg is 300 V or less and the bus voltage Vdc is lower than the output voltage Vg. can be done. Further, for example, when the maximum voltage of the photovoltaic power generation device is set to 280 V, the photovoltaic power generation device operates when the output voltage Vg is 280 V or less and the bus voltage Vdc is lower than the output voltage Vg. can be output.

The output voltage (referred to as "system voltage") of the system interconnection device 40 is indicated by Vs. The system interconnection device 40 converts the AC voltage of the system power supply into a DC voltage and outputs the DC voltage to the bus. The system voltage Vs is a constant value that does not substantially fluctuate. The system interconnection device 40 can output to the bus when the bus voltage Vdc is lower than the system voltage Vs.

The battery B, with the charging/discharging control device 1 interposed therebetween, is substantially connected in parallel to the grid connection device 40 , the natural energy power generation device 50 , and the load device 60 . The battery B has terminals of a positive electrode p and a negative electrode n, and the negative electrode n is connected to the low potential line LL. The voltage of the positive electrode p with the negative electrode n as a reference potential is referred to as a battery voltage Vb. Battery voltage Vb fluctuates as battery B is charged and discharged.

The charge/discharge control device 1 is arranged between the high potential line HL of the DC bus and the positive electrode p of the battery B as a preferred example. When the battery B is discharged, a discharge current flows from the positive electrode p to the high potential line HL through the charge/discharge control device 1, and when the battery B is charged, the high potential line H flows through the charge/discharge control device 1 to the positive electrode of the battery B. A charging current flows to p.

The charge/discharge control device 1 has a charging section 10, a normal discharging section 20, and a boosting discharging section 30 as main functional components. These functional components 10, 20, and 30 all have a common terminal connected to the positive electrode p of the battery B. As shown in FIG.

Charging unit 10 further includes two external terminals 11 and 12 connected to high potential line HL of the DC bus, detection unit 13 , switch unit 14 , and charging circuit 15 . The external terminal 11 is an input terminal of the detection section 13 , and the external terminal 12 is an input terminal of the switch section 14 .

Detector 13 detects bus voltage Vdc. Further, the detection unit 13 compares the detected bus voltage Vdc with a reference voltage and determines whether or not it exceeds the reference voltage. The reference voltage is a predetermined voltage set equal to or higher than the full charge voltage of battery B (hereinafter referred to as "charging start voltage"). Furthermore, when the bus voltage Vdc exceeds the charging start voltage, the detection unit 13 sends a control signal instructing the switch unit 14 to conduct the current path. On the other hand, when the bus voltage Vdc is equal to or lower than the charging start voltage, a control signal is sent to the switch section 14 to instruct it to cut off the current path. The detection unit 13 can be implemented using, for example, a comparator IC or the like.

The switch unit 14 connects or disconnects the DC bus and the charging circuit 15 according to the instruction from the detection unit 13 . When the switch section 14 is conducting, a charging current based on the bus voltage Vdc flows through the charging circuit 15 to charge the battery B. As an example, the charging circuit 15 is configured here by a reactor for preventing a rush current to the battery B and allowing a constant current to flow. Thus, according to the present invention, the charging circuit 15 can have a very simple configuration. When the switch section 14 is cut off, the battery B is not charged. The switching elements of the switching section 14 can be implemented by semiconductor switching elements or mechanical switches. The detection unit 13 and switch unit 14 can also be implemented using a DSP (Digital Signal Processor).

The normal discharge section 20 functions when the battery B can be discharged directly to the DC bus with its battery voltage Vb. Operating conditions of the normal discharge unit 20 will be described in detail later with reference to FIG.

The normal discharge section 20 has an external terminal 21 connected to the high potential line HL of the DC bus and a diode 22 . The diode 22 has an anode connected to the positive electrode p of the battery B and a cathode connected to the external terminal 21, that is, the DC bus. Diode 22 can conduct discharge current from battery B to the DC bus and block current in the opposite direction. Diode 22 is an example of a rectifying element and can be replaced with a rectifying circuit and rectifying element having similar functions.

The step-up discharge section 30 has an external terminal 31 connected to the high potential line HL of the DC bus, a step-up circuit, and a diode 35 .

The boost circuit of the boost discharge unit 30 has a function of boosting the battery voltage Vb to a predetermined voltage lower than the full charge voltage of the battery and higher than the system voltage Vs of the system interconnection device 40 (hereinafter referred to as "boost discharge voltage"). have. The booster circuit boosts the battery voltage Vb to the boosted discharge voltage when the battery voltage Vb is lower than the boosted discharge voltage. Further, even if the battery voltage Vb is higher than the boosted discharge voltage, it is not necessary to stop driving the booster circuit. In that case, the current is simply not output from the booster circuit. The operating conditions of the boosting discharge unit 30 will also be described in detail with reference to FIG. 2, which will be described later.

The booster circuit is here, as an example, a boost chopper circuit that is a type of non-insulated switching power supply configured by a reactor 32 , a switching element 33 , and a PWM (Pulse Width Modulation) signal generator 34 . A control circuit (not shown) detects the current battery voltage Vb and adjusts the duty ratio of the PWM signal according to the detected battery voltage Vb, thereby boosting the battery voltage Vb to a constant boost discharge voltage. Such control circuits are well known.

When switching element 33 is turned on by the PWM signal, current flows through reactor 32 and switching element 33 due to battery voltage Vb, and magnetic energy is accumulated in the core of reactor 32 . When the switching element 33 is turned off by the PWM signal, the back electromotive force generated in the reactor 32 reaches a boosted discharge voltage, and a discharge current can flow through the diode 35 to the DC bus.

The diode 35 has an anode connected to a connection point between the reactor 32 and the switching element 33, and a cathode connected to the external terminal 31, that is, the DC bus. Diode 35 can conduct discharge current from battery B to the DC bus and block current in the opposite direction. Diode 35 is an example of a rectifying element, and can be replaced with a rectifying circuit and a rectifying element having similar functions.

(2) Circuit Operation The operation of the charge/discharge control device 1 shown in FIG. 1 will be described with reference to the graph of FIG. 2 and FIGS. The charge/discharge control device 1 has a plurality of operation modes determined by varying operating conditions. The operating condition parameters include at least the current bus voltage Vdc, the current battery voltage Vb, the relationship between the bus voltage Vdc and the charge start voltage, and the relationship between the battery voltage Vb and the boosted discharge voltage. The operation mode of the charge/discharge control device 1 is determined by those parameters.

The graph of FIG. 2 schematically represents the operating conditions and operation modes of the charge/discharge control device 1. As shown in FIG. The horizontal axis indicates the battery voltage Vb, and the vertical axis indicates the bus voltage Vdc. The horizontal and vertical scales are the same. Therefore, in the graph of FIG. 2, the battery voltage Vb is higher than the bus voltage Vdc in the region below the dotted line L1 (Vb>Vdc), and the bus voltage Vdc is higher than the battery voltage Vb in the region above the line L1 (Vdc >Vb). The operation of the charge/discharge control device 1 will be described below with reference to the symbols in FIG.

The variation range of the battery voltage Vb is normally from the full charge voltage Vb1, which is the maximum voltage, to the discharge end voltage Vb3, which is the minimum voltage. Here, as an example, the full charge voltage Vb1 is 276V, and the discharge end voltage Vb3 is 192V. This is an example of a battery configured by connecting twenty 12V lead-acid batteries (six cells with a rated voltage of 2V connected).

The boosted discharge voltage Vb2 in the boosted discharge unit 30 of FIG. It is sufficient to set the boosted discharge voltage Vb2 slightly higher than the system voltage Vs in order to realize the operation of the present invention. Here, as an example, the system voltage Vs is 269V, and the boosted discharge voltage Vb2 is set to 270V.

The maximum voltage in the fluctuation range of the bus voltage Vdc is the maximum voltage Vg1 set for the natural energy power generation voltage. Here, as an example, the maximum voltage Vg1 is set to 300V. Here, as an example, the minimum voltage in the fluctuation range of the bus voltage Vdc is slightly lower than the system voltage Vs.

Charging start voltage Vg2 of bus voltage Vdc detected by charging unit 10 in FIG. 1 is set equal to or higher than full charge voltage Vb1 of battery B. As shown in FIG. When the charging start voltage Vg2 is set higher than the full charge voltage Vb1, it is sufficient if it is slightly higher. Here, as an example, when the full charge voltage Vb1 is 276V, the charging start voltage Vg2 is set to 277V.

Under the operating conditions as described above, the charge/discharge control device 1 has three main operation modes, A mode, B mode, and C mode, shown in FIG.

<A mode: charging area>
In FIG. 2, the charging region A is a region where the A mode operation is performed, and the charging operation in which the battery B is charged by the bus voltage Vdc is performed in this region. Battery B is charged only in A mode. A mode operating condition is that the bus voltage Vdc is equal to or higher than the charging start voltage Vg2. The A mode operation is performed by the charging unit 10 of the charge/discharge control device 1, and is preferentially executed regardless of the value of the battery voltage Vb.

Since charge start voltage Vg2 is equal to or higher than full charge voltage Vb1, which is the maximum voltage of battery B, battery B is always charged in A mode. In addition, since the charging start voltage Vg2 is naturally higher than the system voltage Vs, it is impossible for the battery B to be charged by the system voltage Vs in the A mode, and the battery B is always charged only by the natural energy generated voltage Vg. It will happen.

FIG. 3 schematically shows the A-mode current flow in the circuit of FIG. In this case, the charging current is output from the natural energy power generation device 50 to the DC bus, and flows from the external terminal 12 of the charging section 10 of the charge/discharge control device 1 to the battery B through the switch section 14 and the charging circuit 15 .

<B mode: normal discharge area>
In FIG. 2, normal discharge region B is a region where B mode operation is performed, and discharge is performed in this region by normal discharge section 20 of charge/discharge control device 1 of FIG. The operating condition of the B mode is that the battery voltage Vb is between the boosted discharge voltage Vb2 and the full charge voltage Vb1. However, the bus voltage Vdc must be lower than the battery voltage Vb (area below line L1 in FIG. 2).

Note that the boost discharge unit 30 of the charge/discharge control device 1 cannot output a voltage equal to or higher than the boost discharge voltage Vb2, and therefore cannot output a discharge current in the B mode. Therefore, when the battery voltage Vb is between the boosted discharge voltage Vb2 and the full charge voltage Vb1, the normal discharge section 20 preferentially causes the discharge current to flow to the boosted discharge section 30 .

FIG. 4 schematically shows the B-mode current flow in the circuit of FIG. In this case, the discharge current is output from the battery B through the normal discharge section 20 of the charge/discharge control device 1 to the DC bus, and then flows to the load device 60 .

<C mode: boost discharge region>
In FIG. 2, a boost discharge region C is a region where C mode operation is performed, and discharge is performed in this region by the boost discharge section 30 of the charge/discharge control device 1 of FIG. The operating condition of the C mode is that the battery voltage Vb is equal to or lower than the boosted discharge voltage Vb2. Therefore, in the C mode, the booster circuit boosts the battery voltage Vb to the boosted discharge voltage Vb2, and the boosted discharge voltage Vb2 causes a discharge current to flow through the DC bus.

If the battery voltage Vb is not boosted, output from the system voltage Vs to the DC bus preferentially occurs in a range where the battery voltage Vb is lower than the system voltage Vs. Since the battery voltage Vb at all the coordinate points in the boosted discharge area C is boosted to the boosted discharge voltage Vb2, the discharge from the battery B is prioritized over the system interconnection device 40. FIG.

FIG. 5 schematically shows the C-mode current flow in the circuit of FIG. In this case, the discharge current is output from the battery B to the DC bus through the boost discharge unit 30 of the charge/discharge control device 1 and then flows to the load device 60 .

Note that the transition between the B mode and the C mode is performed naturally depending on the battery voltage Vb without switching control. This also simplifies the configuration of the charge/discharge control device 1 . In addition, since there is no possibility that battery B will be charged during boost discharge of battery B in C mode (because charging is performed only in charging region A), monitoring and control for suppressing self-charging are also unnecessary. is.

The specific configurations of the embodiments of the present invention described above are not limited to the illustrated examples, and various modifications are possible within the scope of the gist of the present invention.

1 charge/discharge control device 10 charging unit 11, 12 external terminal 13 detection unit 14 switch unit 15 charging circuit 20 normal discharge unit 21 external terminal 22 diode 30 boost discharge unit 31 external terminal 32 reactor 33 switching element 34 PWM signal generation unit 35 diode 40 grid connection device 50 natural energy generator 60 load device H high potential line L low potential line

Claims (6)

A battery, a natural energy power generation device set to a maximum output voltage higher than the full charge voltage of the battery, a grid connection device capable of outputting a grid voltage lower than the full charge voltage of the battery, and a load device are connected. A charge/discharge control device connected between the DC bus and the battery, and controlling charge/discharge of the battery,
a charging unit capable of charging the battery from the DC bus only when the bus voltage of the DC bus exceeds a charging start voltage equal to or higher than a full charge voltage of the battery;
a boosting discharge unit that boosts the battery voltage of the battery to a boosted discharge voltage that is lower than the full charge voltage and higher than the system voltage of the grid connection device, and enables discharge from the battery to the DC bus with the boosted discharge voltage; ,
and a normal discharge unit that enables discharge to the DC bus by the battery voltage when the battery voltage of the battery is between the boosted discharge voltage and the full charge voltage. Control device. the charging unit
a detection unit that detects whether the bus voltage exceeds the charging start voltage;
Based on the detection result of the detection unit, when the bus voltage exceeds the charge start voltage, the DC bus and the battery are connected, and when the bus voltage is equal to or lower than the charge start voltage, the DC bus and the battery are connected. 2. The battery charging/discharging control device according to claim 1, further comprising a switch section for shutting off the charging and discharging of the battery. The step-up discharge unit includes a step-up circuit for stepping up the battery voltage to the step-up discharge voltage, and a first rectifying element for conducting discharge current from the battery to the DC bus and blocking current in the opposite direction. 3. The battery charging/discharging control device according to claim 1 or 2, characterized in that: 4. The normal discharge section according to any one of claims 1 to 3, wherein the normal discharge section comprises a second rectifying element that conducts discharge current from the battery to the DC bus and blocks current in the opposite direction. battery charge/discharge control device. A battery comprising the battery charge/discharge control device according to any one of claims 1 to 4. A battery comprising the battery charge/discharge control device according to any one of claims 1 to 4, a natural energy power generation device set to a maximum output voltage higher than the full charge voltage of the battery, and the battery full A DC power supply system in which a grid connection device capable of outputting a grid voltage lower than a charging voltage and a load device are connected to a DC bus.

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