JP2004129412A - Power storing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prolong the lifetime of a secondary battery having a suitable battery capacity by selecting the battery, and to reduce the environmental load. <P>SOLUTION: In the power storage device 13 having a secondary battery 5, which can be charged and discharged to a DC side of a power converter 4 connected between a system power source 2 of a power system for linking a distributed power source 1 and the load via a linkage transformer 8, the battery 5 is charged and discharged at a load leveling time to reduce a peak power; and a capacitor 9 is charged and discharged at a change-compensating operation time for suppressing the output change of the distributed power source 1, so that the capacitor 9 for complementing charging/discharging of the battery 5 is provided in parallel with the battery 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power storage device provided in an AC circuit including a commercial power supply or a self-powered facility and a load, and for suppressing load leveling due to charging and discharging of a secondary battery and suppressing power quality deterioration due to load fluctuation and output fluctuation of a distributed power supply. About.
[0002]
[Prior art]
For example, in a power system in which a distributed power supply such as a wind power generation system is connected to a system power supply, the wind power generator fluctuates every moment in accordance with natural conditions such as wind speed, such as a remote place or a remote island. In general, it is a small-sized, so-called weak power system having a diesel generator as a system power supply. In this type of weak power system, if load fluctuations such as wind power output appear frequently, the load fluctuations will have a large effect on the power system in voltage or frequency fluctuations. A power storage device is installed to suppress voltage or frequency fluctuations.
[0003]
FIG. 4 shows a circuit configuration of the power storage device 3 installed in the power system. This power storage device 3 is installed between a distributed power source 1 and a system power source 2 which are, for example, a wind power generation system, and the power storage device 3 is connected to a connection point A thereof via a connection transformer 8. Having a configuration. The power storage device 3 includes a power converter 4 and a secondary battery 5 such as a chargeable / dischargeable lead storage battery connected to the DC side thereof. In the figure, reference numerals 6 and 7 denote an instrument transformer (VT) and a current transformer (CT) provided on the system bus.
[0004]
The power converter 4 is a bidirectional AC / DC converter having a discharging function and a charging function. The converter operates to convert AC power from the system bus into DC and charge the secondary battery 5, and to charge the secondary battery 5. The control is switched to an inverter operation in which the converted DC power is converted to AC and supplied to the system bus.
[0005]
Therefore, in the power storage device 3, the output fluctuation of the distributed power source 1 described above is detected by the instrument transformer 6 and the current transformer 7, and the power converter of the power storage device 3 is configured to cancel the output fluctuation of the distributed power source 1. The secondary battery 5 is charged / discharged by operating the converter 4 in the converter operation or the inverter operation, and the output fluctuation of the distributed power source 1 is suppressed by exchanging the power with the power system by the converter operation or the inverter operation of the power converter 4. The power fluctuation compensation operation is performed so as to suppress the voltage or frequency fluctuation of the power system.
[0006]
The power fluctuation compensation operation in the power storage device 3 is performed not only for the output fluctuation of the distributed power supply 1 described above but also for a case based on a power pattern in a power consumer such as a general home or a factory.
[0007]
The daily power pattern of the power consumer has a characteristic such that the power peaks during a heavy load time period, for example, around 1 to 4 PM. Therefore, in the power storage device 3, the secondary battery 5 is charged by the converter operation of the power converter 4 at midnight and during a light load time period (for example, from 8:00 to 1:00 AM, from 5:00 to 10:00 PM), and the secondary battery is charged. 5 is discharged by the inverter operation of the power converter 4 during a heavy load time period (for example, around 1 PM to 4 PM), and the discharge power of the secondary battery 5 is supplied to the load. As described above, load leveling is realized by reducing the peak power by shifting the peak power of the discharge power of the secondary battery 5 (for example, see Patent Document 1).
[0008]
[Patent Document 1]
JP-A-2002-171669
[Problems to be solved by the invention]
By the way, in the above-described power storage device 3, the output of the distributed power source 1 fluctuates momentarily according to natural conditions such as wind speed and the like. In the power exchange with the power system, the power fluctuation compensation operation that suppresses the output fluctuation of the distributed power source 1 to suppress the voltage or frequency fluctuation of the power system at all times, and the power consumption based on the daily power pattern in the power consumer Regarding both load leveling in which the peak power is reduced by peak-shifting the discharge power of the secondary battery by the converter operation or inverter operation of the converter 4, the secondary battery 5 provided on the DC side of the power converter 4 Achieved by charging and discharging.
[0010]
However, in the above-described secondary battery 5, it is very difficult to make all of the battery capacity correspond to output fluctuations that appear in a short time, for example, on the order of seconds. At present, a secondary battery 5 having a large margin is selected as a response to fluctuations in a power system in which the power supply system is interconnected.
[0011]
In using the secondary battery 5, the state of charge (SOC) of the secondary battery 5 is set to, for example, about 60 to 70% so that a problem of overvoltage does not occur in the charge / discharge current corresponding to the output fluctuation. Therefore, it was difficult to use 100% of the battery capacity of the secondary battery 5 at the time of load leveling by peak shift. In addition, in order to maintain a state of charge (SOC) of 60 to 70% in the secondary battery 5, for example, a charge / discharge operation for preventing battery deterioration is required about once a week.
[0012]
Therefore, the present invention has been proposed in view of the above-mentioned problems, and its purpose is to select a secondary battery having an appropriate battery capacity, or to extend the life of the secondary battery. Accordingly, an object of the present invention is to provide a power storage device that can contribute to reduction of environmental load.
[0013]
[Means for Solving the Problems]
As a technical means for achieving the object, the present invention provides a chargeable / dischargeable secondary battery on the DC side of a power converter connected to an AC circuit including a commercial power supply or a self-propelled facility and a load. The power storage device is characterized in that a capacitor that complements the charging and discharging of the secondary battery is provided in parallel with the secondary battery.
[0014]
In the present invention, the charging and discharging of the secondary battery is complemented by the capacitor. As a complementing means, (1) the secondary battery is charged and discharged at the time of load leveling to reduce the peak power, and in the AC circuit, Charging and discharging the capacitor during a fluctuation compensation operation for suppressing load fluctuations and output fluctuations of the distributed power source; (2) in the charging region where the transition from constant current charging to constant voltage charging of the secondary battery is required, The capacitor may be started to charge in parallel with the charging of the battery.
[0015]
The load fluctuation in the AC circuit means a system voltage fluctuation caused by a variable load such as a large-capacity arc furnace connected to an electric power system, a railway load, a steel rolling load, and the like. The fluctuation means an output fluctuation that appears in a short time on the order of seconds in a wind power generation system, a solar power generation system, or the like.
[0016]
Thus, by using the secondary battery and the capacitor together, energy storage provided on the DC side of the power converter is shared between the secondary battery and the capacitor. The burden on the secondary battery can be reduced by the sharing of the secondary battery and the capacitor, and a secondary battery having a necessary minimum capacity can be selected.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a power storage device according to the present invention will be described in detail below. FIG. 1 shows a circuit configuration of a power storage device 13 installed in a power system as an AC circuit in which a wind power generation system is interconnected as a distributed power source 1 as a clean power supply source using natural energy, for example. The same parts as those in FIG. 4 are denoted by the same reference numerals. The distributed power source 1 is applicable to a solar power generation system and the like in addition to the wind power generation system.
[0018]
The power storage device 13 of this embodiment is installed between the distributed power source 1 and the system power source 2 which are, for example, a wind power generation system, and connects the power storage device 13 to the connection point A via the connection transformer 8. It has a schematic configuration connected. The power storage device 13 includes a power converter 4, a secondary battery 5 such as a lead storage battery connected to a DC side thereof, and a capacitor 9 connected in parallel to the secondary battery 5. It is desirable to use a relatively large-capacity electrolytic capacitor or electric double-layer capacitor as the capacitor 9 described above. In the figure, reference numerals 6 and 7 denote an instrument transformer (VT) and a current transformer (CT) provided on the system bus.
[0019]
The power converter 4 is a bidirectional AC / DC converter having a discharging function and a charging function. The converter operates to convert AC power from the system bus into DC and charge the secondary battery 5, and to charge the secondary battery 5. The control is switched to an inverter operation in which the converted DC power is converted to AC and supplied to the system bus.
[0020]
Here, FIG. 2 shows standard characteristics of an MSE type (JIS standard) lead storage battery specified by the guidelines of the Battery Association of Japan, and shows an example of general characteristics of a secondary battery. The standard characteristics exemplify the relationship of the capacity conversion time (hour) to the discharge time (minute) setting of the secondary battery 5 in terms of 10 HR capacity, and the minimum allowable voltage in the secondary battery 5 of the minimum unit (cell) 2V Are plotted for 1.6 to 1.9 V / cell (storage battery temperature 25 ° C.). The capacity of the secondary battery 5 is selected based on, for example, the standard characteristics shown in FIG.
[0021]
In this standard characteristic, the capacity conversion coefficient K corresponding to the discharge time of the secondary battery is determined for any of the allowable minimum voltages of 1.6 to 1.9 V / cell based on the required battery current and discharge time. Thus, the minimum capacity of the secondary battery 5 is selected by the product of the required battery current and the capacity conversion coefficient K.
[0022]
In the standard characteristics, there are a section in which the change of the capacity conversion coefficient K is gentle and a section in which the change is remarkable with respect to a change in the required discharge time. This reflects the characteristics of batteries having the same capacity (Ah). As the energizing time becomes shorter, the energizing current can be increased. However, the energizing current value has an upper limit, and in the rechargeable battery characteristics shown in FIG. Approaching).
[0023]
Therefore, in the power storage device 13, a capacitor 9 that complements charging and discharging of the secondary battery 5 is connected in parallel to the secondary battery 5 as an energy storage unit on the DC side of the power converter 4. Of the secondary battery 5 and the capacitor 9 that are components of the energy storage unit, the secondary battery 5 operates to reduce the peak power and level the load or supply the loss of the power converter 4. And the capacitor 9 performs a fluctuation compensation operation for suppressing the output fluctuation of the distributed power supply 1. Both the secondary battery 5 and the capacitor 9 have an internal impedance. By setting the impedance of the capacitor 9 low, the capacitor 9 preferentially responds to a short-term output fluctuation on the order of seconds.
[0024]
From the standard characteristics of the secondary battery 5 described above, consider the use of the secondary battery in the load leveling due to the peak shift and the fluctuation compensation operation for the output fluctuation of the distributed power supply. When the discharge time is as long as the order of time, the operation is performed to reduce the peak power by charging and discharging only the secondary battery 5 to level the load. The current limit of each charge / discharge determined by the above is handled only by the secondary battery 5, and the portion exceeding the current limit of each charge / discharge of the battery is subjected to the fluctuation compensation operation for the output fluctuation of the distributed power supply 1 by charging / discharging the capacitor 9. In this case, the secondary battery 5 is used in its full capacity within the allowable capacity range, and an appropriate secondary battery 5 having a minimum necessary capacity can be selected.
[0025]
In the power storage device 13, the output fluctuation of the distributed power source 1 is detected by the instrument transformer 6 and the current transformer 7, and the power converter 4 is converted into a converter based on the detected power amount (or power fluctuation amount). The secondary battery 5 and the capacitor 9 are charged and discharged by the operation or the inverter operation. For example, the output of the distributed power supply 1 installed at the terminal of the power system such as a remote area or a remote island is constantly changed according to natural conditions such as wind speed. Even if it fluctuates, by controlling the power converter 4 to cancel the output fluctuation of the distributed power supply 1 by charging and discharging the capacitor 9, the output fluctuation of the distributed power supply 1 is suppressed, and the voltage or frequency fluctuation of the power system is suppressed. Suppress.
[0026]
That is, the power storage device 13 charges the secondary battery 5 and the capacitor 9 by the converter operation of the power converter 4 when the output of the distributed power source 1 is large, and charges the secondary battery 5 when the output of the distributed power source 1 is small. In addition, the power stored in the capacitor 9 is discharged to the power system by the inverter operation of the power converter 4, and by exchanging the power with the power system by the operation of the power converter 4, the output fluctuation of the distributed power supply 1 is suppressed to suppress the power system. The power fluctuation compensation operation is performed so as to suppress the voltage or frequency fluctuation.
[0027]
In the above-described secondary battery 5, it is very difficult to make all of the battery capacity correspond to the output fluctuation appearing in a short time, for example, on the order of seconds. On the other hand, by supplementing the fluctuation compensation function by charging and discharging the capacitor 9, it is possible to select the secondary battery 5 having the minimum necessary and optimal capacity for the load.
[0028]
In addition, for example, regarding load leveling based on a daily power pattern in a power consumer such as a general household or a factory, the power storage device 13 uses the power storage device 13 at midnight and light load time periods (for example, 8:00 to 10:00 AM, 5:00 to 10:00 PM, and so on). The secondary battery 5 is charged by the converter operation of the power converter 4 around the time), and the charging power of the secondary battery 5 is changed by the inverter operation of the power converter 4 during the heavy load time period (for example, around 1 PM to 4 PM). It discharges, and supplies the discharge power of the secondary battery 5 to the load. In this way, load leveling is realized by reducing the peak power by shifting the discharge power of the secondary battery 5 to the peak.
[0029]
In such load leveling for reducing peak power based on the power pattern in the power consumer, when the fluctuation compensation function is exhibited by charging and discharging the secondary battery 5 by the present apparatus, the above-described short-term output fluctuation Is supplemented by the capacitor 9, the charging / discharging current corresponding to the output fluctuation causes an overvoltage problem, and there is no need to consider the battery capacity equivalent to fluctuation compensation. It is not necessary to keep the SOC) at about 60 to 70%, and it is close to the ideal to use the secondary battery 5 only for load leveling by peak shift, and to use the battery capacity of the secondary battery 5 at 100%. You can get closer. In addition, in the secondary battery 5 used only for the peak shift, in order to keep the state of charge (SOC) of 60 to 70%, for example, a charge / discharge operation for preventing the deterioration of the battery about once a week is also performed. It becomes unnecessary.
[0030]
As described above, in the power storage device 13, the above-described power fluctuation compensation operation for the output fluctuation of the distributed power source 1 is performed by the secondary battery 5 and the capacitor 9, and the load leveling during the day and night is performed based on the power demand of the load. , The secondary battery 5 having an appropriate battery capacity can be selected, the life of the secondary battery 5 can be extended, and the environmental load can be reduced.
[0031]
Here, in general, when charging a secondary battery 5 such as a lead storage battery, it is difficult to continuously charge the secondary battery 5 with the same current value as the rated discharge current due to the reaction speed with the electrolytic solution. Therefore, as shown in FIG. 3, when the rated discharge current is 1 C (A), charging starts at a constant current of, for example, about 0.1 C (A), and the charging amount of the secondary battery 5 is about 80%. When the state (SOC) is reached, the charging is shifted to the constant voltage charging, and the charging is completed when the battery is finally fully charged. In the characteristics of the charge amount of the secondary battery 5, the charge amount increases almost linearly up to 80%, but when the charge amount exceeds 80%, the charge amount efficiency decreases and the rate of increase of the charge amount decreases. Finally, it draws a gentle curve and finally reaches a fully charged state of 100%.
[0032]
In the power storage device 13 of this embodiment, in order to compensate for a decrease in the charging efficiency that occurs after the state of charge (SOC) of the secondary battery 5 of 80%, the state of charge of the secondary battery 5 starts after the state of charge of 80%. The capacitor 9 is charged (indicated by a broken line m in the figure). Although both the secondary battery 5 and the capacitor 9 have an internal impedance, by setting the impedance of the capacitor 9 low, the capacitor 9 preferentially responds during a transitional period during charging when switching from constant current charging to constant voltage charging. I do. When the charging is completed, the voltage of the capacitor 9 and the voltage of the secondary battery 5 are balanced over a time equivalent to the internal impedance × capacitor capacity, and the charging is finally completed.
[0033]
Note that the same operation is performed at the time of discharging, and the capacitor 9 transiently responds preferentially due to the difference between the internal impedance of the secondary battery 5 and the capacitor 9, and thereafter, the voltage takes a time corresponding to the internal impedance and the capacitor capacity. Head for equilibrium.
[0034]
【The invention's effect】
According to the present invention, in a power storage device provided with a chargeable / dischargeable secondary battery on the DC side of a power converter connected to an AC circuit including a commercial power supply or an autonomous facility and a load, the charging of the secondary battery is performed. By arranging the capacitor complementing the discharge in parallel with the secondary battery, energy storage provided on the DC side of the power converter is shared between the secondary battery and the capacitor. By sharing the rechargeable battery and the capacitor, the burden on the rechargeable battery can be reduced, and a rechargeable battery having the minimum necessary capacity can be selected. Can be achieved.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram showing an embodiment of a power storage device according to the present invention.
FIG. 2 is a characteristic diagram showing an example of standard characteristics of a lead storage battery.
FIG. 3 is a characteristic diagram showing charging characteristics of a secondary battery.
FIG. 4 is a circuit configuration diagram showing a conventional power storage device.
[Explanation of symbols]
1 distributed power source (wind generator)
2 System power supply 4 Power converter 5 Secondary battery 8 Interconnection transformer 9 Capacitor 13 Power storage device

Claims (3)

In a power storage device provided with a chargeable / dischargeable secondary battery on the DC side of a power converter connected to an AC circuit including a commercial power supply or a self-generating facility and a load, a capacitor for complementing the charge / discharge of the secondary battery A power storage device characterized in that a battery is provided in parallel with a secondary battery. Charging and discharging the secondary battery at the time of load leveling by reducing peak power, and charging and discharging the capacitor at the time of a fluctuation compensation operation for suppressing load fluctuation and output fluctuation of the distributed power supply in the AC circuit. The power storage device according to claim 1. 2. The power storage according to claim 1, wherein charging of the capacitor is started in parallel with the charging of the secondary battery in a charging area where a transition from constant current charging to constant voltage charging of the secondary battery is required. apparatus.

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