JP2011015485A - Electrical power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrical power system which keeps the state of a storage battery suitably by saving fuel without annexing a converter for charge/discharge control to the storage battery in an electrical power system where a fuel cell and a storage battery are combined.SOLUTION: This electrical power system supplies a load with power by connecting an accumulator and a fuel cell device each in parallel with the load. The accumulator is equipped with a secondary battery pack where one piece or plural pieces of secondary batteries are connected in series or in parallel. The fuel cell device is equipped with a fuel cells stack where a plurality of fuel battery cells are stacked, a DC/DC converter which converts power generated by the fuel cell stack and supplies it to the output of the fuel cell device, a voltage detector which detects the output voltage of the fuel cell device, a current detector which detects the output current of the fuel cell device, and an accumulator state determiner which determines the charge/discharge state of the accumulator from an output voltage value detected with the voltage detector and an output current value detected with the current detector and controls the output voltage of the DC/DC converter based on the determination results.

Description

  The present invention relates to a power supply system that is used for a backup power supply or the like and is configured by using a fuel cell and a storage battery in combination.

  A polymer electrolyte fuel cell (PEFC), which is a type of fuel cell, is a cell that obtains an electromotive force by electrochemically reacting a fuel gas mainly composed of hydrogen and an oxidant gas. In addition to cogeneration systems that use generated power and exhaust heat, PEFC is being considered for use in power systems that provide backup power supply to core industrial equipment such as communication infrastructure and data servers in the event of system power abnormalities such as power outages. . As another backup power source, a power supply system using a lead storage battery is used. Furthermore, it is conceivable to use a lead storage battery and a fuel cell in parallel.

JP 2004-112871 A

  The fuel cell consumes fuel and obtains electric power, so that it is important to save the fuel in order to perform an economical operation. In a power supply system in which a storage battery and a fuel cell are connected in parallel, the power entering and exiting the storage battery varies depending on the power balance of the fuel cell system, the storage battery, and the load. Since the storage battery loses when it is charged and discharged, fuel can be saved by performing an operation that does not charge the storage battery with the power generated by the fuel cell. Although there exists a method of avoiding charge of a storage battery by attaching the converter for charging / discharging control to a storage battery, there exists a subject which a loss generate | occur | produces with a converter. In addition, it is known that the storage battery has an influence on the life if the charge rate and the depth of discharge are not properly managed.

  In order to solve the above problems, the object of the present invention is to manage the state of the storage battery by the operation of the fuel cell device without attaching a converter for charge / discharge control to the storage battery in a backup power supply system using both the fuel cell and the storage battery. Thus, an object of the present invention is to provide a power supply system that can save fuel and can favorably maintain the state of a storage battery.

  In order to achieve the above object, a power supply system according to the present invention is a power supply system in which a power storage device and a fuel cell device are respectively connected in parallel to a load and supplies power to the load. A fuel cell stack comprising a plurality of secondary batteries connected in series or in parallel, wherein the fuel cell device is a fuel cell stack in which a plurality of fuel cells are stacked; DC / DC converter supplied to output of battery device, voltage detection means for detecting output voltage of fuel cell device, current detection means for detecting output current of fuel cell device, and voltage detection means The charge / discharge state of the power storage device is determined from the output voltage value and the output current value detected by the current detection means, and the output voltage of the DC / DC converter is controlled based on the determination result Power storage device state determination means.

  According to the present invention, in a power supply system using both a fuel cell and a storage battery, fuel can be saved and the state of the storage battery can be suitably maintained without adding a converter for charge / discharge control to the storage battery.

1 is a schematic configuration diagram showing a first embodiment of a power supply system according to the present invention. It is an operation | movement time chart of the power supply system of FIG. 4 is a graph showing output voltage-output current distribution characteristics for explaining charge / discharge determination of the power storage device of FIG. 1. FIG. 4 is a circuit diagram illustrating a calculation model of an output circuit for explaining the distribution characteristics of FIG. 3. It is a figure which shows the load fluctuation determination of electrical storage apparatus charging / discharging determination, (a) shows the example when the deviation of an output voltage-output current characteristic is small, (b) shows the example when the deviation of an output voltage-output current characteristic is large. FIG. It is a graph which shows the example of determination of the charge rate of an electrical storage apparatus in 2nd Embodiment of the power supply system which concerns on this invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.
(First embodiment)
FIG. 1 is a schematic diagram illustrating a configuration of a power supply system according to the first embodiment. As shown in FIG. 1, the power supply system includes a fuel cell module 1 that constitutes a fuel cell device, and a power storage device 4. The fuel cell module 1 and the power storage device 4 are connected in parallel to a load 7. It is a system that supplies power. In the present embodiment, the fuel cell module 1 and the power storage device 4 are connected to the load 7 together with the rectifier 5 that converts the AC power supplied from the system power supply 6 to obtain DC power, and are backed up when the system power supply 6 is stopped. Functions as a power source.

  The fuel cell module 1 includes a fuel cell stack 8, a DC / DC converter 9, and an auxiliary device 10 inside. Hydrogen fuel is supplied from the hydrogen cylinder 2 through the hydrogen pipe 3 to the fuel cell stack 8 of the fuel cell module 1. Part of the hydrogen fuel supplied from the hydrogen pipe 3 and the air around the fuel cell module 1 flows through the fuel cell stack 8 by the operation of the auxiliary device 10 and is consumed as an electromotive force of the fuel cell stack 8.

  The fuel cell stack 8 has a structure in which a plurality of fuel cells are stacked so as to be connected in series, and the positive and negative terminals of the outermost fuel cell are connected to the input of the DC / DC converter 9. The DC / DC converter 9 converts the electromotive force of the fuel cell stack 8 obtained from the input into DC power having a voltage controlled by a predetermined voltage command VO_ref. A diode for preventing backflow may be provided at the output of the DC / DC converter 9.

  The output of the DC / DC converter 9 is taken out as an output to the outside of the fuel cell module 1 and connected in parallel to the load 7, the DC output of the rectifier 5, and the power storage device 4. Here, the load 7 may be provided with a device that consumes DC power, such as a broadcasting / communication base station, a data server, or the like. The DC power transmission circuit connected to the output of the DC / DC converter 9 may be operated using DC 24V or DC 48V as a reference voltage. The rectifier 5 has a function of converting commercial AC100V or AC200V class AC power received from the system power supply 6 into DC power output, and stops output when the system power supply 6 is abnormal such as a power failure. The fuel cell module 1 and the power storage device 4 mainly perform a backup operation for continuing power supply to the load 7 when the system power supply 6 becomes abnormal and the output of the rectifier 5 stops.

  The fuel cell module 1 further includes a voltage detection means 11 for detecting the output voltage VO of the DC / DC converter 9, a current detection means 12 for detecting the output current IO of the DC / DC converter, and the output voltage VO and the output current IO. Power storage device state determination means 13 for determining the charge / discharge state of the power storage device 4 based on the above. The power storage device state determination unit 13 calculates a voltage command VO_ref for controlling the output voltage VO of the DC / DC converter 9 and transmits it to the DC / DC converter 9. The current detection means 12 may be configured using a current sensor using a Hall element or a shunt resistor. The power storage device state determination means 13 is preferably mounted on the fuel cell module 1 by means such as an electric circuit, a control program installed in a microcomputer or DSP on the electric circuit, and the like.

  FIG. 2 shows an example of a time chart regarding the operation of the fuel cell module 1. As shown in FIG. 2, the operation of the fuel cell module 1 is roughly classified into two modes, mode A and mode B. In the present embodiment, the fuel cell module 1 alternately repeats mode A and mode B, and the duration times of mode A and mode B are set.

  In mode A, the fuel cell module 1 stores the output voltage VO and the output current IO that respond to the fluctuations in the power storage device state determination means 13 while varying the voltage command VO_ref. In FIG. 2, voltage fluctuations in five stages are given. Since the DC / DC converter 9 performs control so that the output voltage VO coincides with VO_ref, the output voltage VO substantially coincides with the voltage command VO_ref.

  When the power storage device 4 is a secondary battery not provided with a converter for charge / discharge control as in the present embodiment, the output current IO shows a transient change in a predetermined jumping shape. This is due to the polarization voltage of the secondary battery, and the data stored in the power storage device state determination means 13 is preferably at the time when this transient change has converged. Therefore, the data of the output voltage VO and the output current IO after the predetermined delay time Td has elapsed after giving a predetermined change to the voltage command VO_ref is used for the power storage device state determination. When the power storage device 4 is composed of a lead storage battery, the delay time Td is preferably about 1 to 5 minutes. Regarding the measurement of the output voltage VO and the output current IO in the mode A, an operation for removing measurement noise may be performed by an analog filter or digital filter processing such as first-order lag or moving average. A time constant considering the convergence time may be selected.

  At the end of mode A, the power storage device state determination unit 13 determines the state of the power storage device 4 using the stored data of the output voltage VO and the output current IO, and obtains the optimum output voltage VB according to the determination result. The voltage command VO_ref is changed to a value equivalent to VB, and the mode is shifted to mode B. Next, in mode B, an operation with the voltage command VO_ref fixed to a value equivalent to VB is performed, and after the duration of mode B ends, the operation of mode A is resumed.

  Based on the distribution of the output voltage VO with respect to the output current IO, the power storage device state determination unit 13 determines the output voltage range in which the power storage device is in a discharge state, a charge state, and a boundary state between discharge and charge. Hereinafter, a method for determining the charge / discharge state will be described.

  FIG. 3 is a graph showing an example of output voltage-output current distribution characteristics used for determining the charge / discharge of the power storage device in the power storage device state determination means 13. In the mode A, for example, when the fluctuation of the voltage command VO_ref in five steps is given, five distributions of the output voltage VO-the output current IO are obtained as shown in FIG. In FIG. 3, the distribution relating to the voltage command VO_ref in five steps is displayed with five points. However, when recording is performed a plurality of times for each condition of the voltage command VO_ref, a set of a plurality of points including deviations is obtained. Five will be displayed. In such a case, for each set, the center of gravity, average value, maximum value, minimum value, median value, etc. of the distribution may be obtained and handled as representative points of each set.

  When the power consumption PL of the load 7 does not fluctuate greatly during the mode A, the distribution of the output voltage VO and the output current IO becomes two types of linear shapes with different slopes, as shown in FIG. Here, the output voltage VO at the intersection of the two straight lines is determined as the voltage VB.

FIG. 4 is a calculation model for explaining the distribution characteristics in which the distribution of the output voltage VO−the output current IO is two types of straight lines. The calculation model of FIG. 4, to simulate a power storage device 4 by the voltage source V2 and the internal resistance r _b, and the current consumption of the load 7 IL, the wiring resistance between the fuel cell module 1 and the power storage device 4 and R . Regarding this calculation model, the relationship of output voltage VO−output current IO can be expressed by the following Equation 1. In a general power supply system, the wiring resistance R is designed to be a sufficiently small value to reduce the loss. Therefore, if the consumption current IL of the load 7 and the voltage source V2 are substantially constant in Equation 1, the relationship between the output voltage VO and the output current IO. is generally becomes a linear distribution, the slope is determined by the internal resistance r _b of the power storage device 4.

一般に蓄電装置４に用いられる二次電池の内部抵抗ｒ_ｂは、充電時においては放電時よりも大きい値を示す。特に、充電率が８０％程度以上の高い状態での充電時は内部抵抗ｒ_ｂが大きく上昇する。従って、出力電圧ＶＯと出力電流ＩＯの関係は、内部抵抗ｒ_ｂの変化により、放電状態および充電状態とで傾きの異なる２種類の直線状の分布特性となり、２直線の交点電圧ＶＢよりも低い出力電圧ＶＯの範囲では放電状態、電圧ＶＢよりも高い出力電圧ＶＯの範囲では充電状態と判定できる。

Generally the internal resistance r _b of the rechargeable battery used in the power storage device 4, at the time of charge indicates a value greater than the time of discharge. In particular, the charging rate when charging at a high state of about 80% or more the internal resistance r _b is increased greatly. Therefore, the relationship the output voltage VO and the output current IO, a change in the internal resistance r _b, between the discharge state and charge state becomes two kinds of linear distribution characteristics of different slopes, less than two lines of intersection voltage VB It can be determined that the battery is discharged in the range of the output voltage VO, and the battery is charged in the range of the output voltage VO higher than the voltage VB.

  Here, the backup operation of the entire system using both the fuel cell module 1 and the power storage device 4 will be examined. Since the fuel cell module 1 generates power using hydrogen supplied from the hydrogen cylinder 2, it is necessary to save hydrogen consumption in order to save the trouble of replacing the consumed hydrogen cylinder 2. On the other hand, the power storage device 4 can be charged from the system power source 6 without using hydrogen in addition to the loss that occurs during charging and discharging, and therefore avoids the operation of charging the power storage device 4 with the generated power of the fuel cell module 1. This saves the hydrogen consumed. Therefore, in the power supply system, the power storage device state determination unit 13 determines the charge / discharge state of the power storage device 4 and maintains the voltage command VO_ref at the voltage VB or less in the operation mode B, thereby storing power with the generated power of the fuel cell module 1. The operation of charging the device 4 can be avoided, and the hydrogen consumption of the hydrogen cylinder 2 can be saved.

  Further, if a deviation appears in the distribution of output voltage VO−output current IO stored in mode A, the determination result calculated by the power storage device state determination means is affected, and therefore the output voltage VO and output current IO can be recorded as much as possible. Conditions that do not cause deviation are desirable. Examples of the conditions that cause the deviation include fluctuations in the polarization voltage of the power storage device 4 and the power PL of the load 7.

  Since the polarization voltage of power storage device 4 generally changes so as to finally converge as a transient change if there is no fluctuation in power PL of load 7, the duration of mode A is set to the polarization of the secondary battery constituting power storage device 4. By setting the time longer than the voltage equilibrium time constant, the influence of the polarization voltage can be minimized.

FIG. 5A and FIG. 5B are diagrams showing variation determination of the load 7 in the storage device charge / discharge determination. When fluctuation occurs in the power PL of the load 7, a deviation occurs in the distribution of the output voltage VO-the output current IO. Therefore, the average current I _AVE is obtained for the output current IO of each distribution, and when there is a distribution point that deviates from the upper and lower limit current threshold value I _AVE ± ΔI obtained by adding a predetermined deviation width ΔI, it is determined as the variation of the load 7. . In FIG. 5A, there is no distribution point exceeding the upper and lower limit current threshold value I _AVE ± ΔI, and it is determined that the deviation is small, and it is determined that there is no variation in the power PL of the load 7. In (b), since there are distribution points exceeding the upper and lower limit current threshold value I _AVE ± ΔI, it is considered that the deviation is large, and it is determined that the power PL of the load 7 has changed. In FIG. 5, the variation of the load 7 is determined by obtaining the deviation of the output current IO. However, the variation of the load 7 may be determined by obtaining the deviation of the output voltage VO.

  Here, when the variation of the load 7 is determined, the result of the determination of charge / discharge of the power storage device may be corrected. As the correction method, for example, when the fluctuation of the load 7 is determined, the power storage device charging / discharging determination in the mode A in which the fluctuation is determined is ignored, and the output voltage VB obtained before the previous mode A is based on the output voltage VB. If the operation of the next mode B is performed, the influence due to the fluctuation of the load 7 can be avoided. In addition, when it is determined that the load 7 has changed, or when it is determined that the load 7 that is constantly changing and the charge / discharge determination of the power storage device cannot be appropriately performed is connected, the determination result is displayed outside the fuel cell module 1. -You may provide the function to notify using means, such as communication.

  According to the power supply system of the present embodiment, the charge / discharge state (charge state, discharge state, or boundary state between charge and discharge) of the power storage device 4 is determined from the output voltage VO and the output current IO of the fuel cell module 1. By controlling the output voltage VO using the voltage command VO_ref to the DC / DC converter 9 based on the charge / discharge state of the power storage device 4, the consumption of hydrogen fuel is suppressed and the state of the storage battery is suitably maintained. be able to.

However, since the operation of mode A temporarily includes the operation of a voltage command VO_ref that is larger than the optimum output voltage VB, the power storage device 4 may be charged and a large amount of hydrogen may be consumed. Therefore, considering the hydrogen consumption in both modes as a whole, at least the duration of mode B is set longer than the duration of mode A so that the hydrogen saving effect in mode B offsets the extra hydrogen consumption in mode A By doing so, it becomes possible to increase the saving effect of hydrogen. For example, the duration of mode B is preferably set to be twice or more the duration of mode A.
(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  The basic components of the power supply system of this embodiment are almost the same as those of the power supply system of FIG. In the present embodiment, the power storage device state determination unit 13 has a function of determining the charging rate (SOC) of the power storage device 4 based on the distribution of the output power value VO with respect to the output current value IO.

  FIG. 6 is a diagram showing an example of the power storage device charging rate determination in the power storage device state determination means 13. The distribution of the output voltage VO-the output current IO is shown for the two charge rates S1 and S2 (S1> S2) of the secondary battery constituting the power storage device 4. According to the graph shown in FIG. 6, for example, the distribution of the output voltage VO-output current IO shifts to the right side as the charging rate increases, so that the output voltage VO-output current depends on the difference between the charging rates S1, S2. The distribution of IO is different. It is possible to estimate the charging rate by storing the relationship between the distribution of the output voltage VO−the output current IO and the charging rate in the power storage device state determination unit 13 in advance or by learning from the actual operation. It becomes possible.

  Secondary batteries, particularly lead-acid batteries, tend to affect the battery life as discharge progresses and the charge rate decreases. Therefore, it is possible to extend the lifetime of the power storage device 4 by determining the power storage device charge rate in the power storage device state determination means 13 and maintaining the power storage device 4 at an appropriate charge rate. Specifically, when the charge rate of power storage device 4 is lower than a preset charge rate (first charge rate threshold) during operation in mode B, the charge rate of power storage device 4 is the first charge. The fixed voltage (voltage command VO_ref) is set higher than the fixed voltage (voltage command VO_ref (normal voltage command)) when higher than the rate threshold. Thereby, the output of the fuel cell module 1 can be increased, the amount of discharge of the power storage device 4 can be relaxed, and the influence on the battery life can be prevented.

  When the charging rate of the power storage device 4 is sufficiently high, for example, when the charging rate is 90% or more, the load 7 can be backed up only by discharging the power storage device 4 even if the fuel cell module 1 does not generate power. is there. As described above, when it is determined that the charging rate is higher than the predetermined charging rate threshold (second charging rate threshold), the power generation operation of the fuel cell module 1 is paused in mode B to save hydrogen consumption. be able to.

  As described above, the present invention is not limited to the above-described embodiments, and various other ones are assumed.

  DESCRIPTION OF SYMBOLS 1 ... Fuel cell module 4 ... Power storage device 5 ... Rectifier 7 ... Load 8 ... Fuel cell stack 9 ... DC / DC converter 11 ... Voltage detection means 12 ... Current detection means 13 ... Power storage device state determination means

Claims (11)

A power supply system for connecting a power storage device and a fuel cell device in parallel to a load, respectively, and supplying power to the load,
The power storage device includes a secondary battery group in which one or a plurality of secondary batteries are connected in series or in parallel,
The fuel cell device includes a fuel cell stack in which a plurality of fuel cells are stacked, a DC / DC converter that converts the generated power of the fuel cell stack and supplies it to the output of the fuel cell device, and the output of the fuel cell device Voltage storage means for detecting voltage, current detection means for detecting output current of the fuel cell device, output voltage value detected by the voltage detection means, and output current value detected by the current detection means, the power storage device A power supply system comprising: a power storage device state determination unit that determines a charge / discharge state of the battery and controls an output voltage of the DC / DC converter based on the determination result. The power supply system according to claim 1, wherein the fuel cell device includes:
The output voltage of the fuel cell device is varied within a predetermined range by the operation of the DC / DC converter, and the distribution of the output voltage value and the output current value responding to the variation is output to the power storage device state determination means. Recording operation mode A;
The charge / discharge state of the power storage device is determined from the distribution recorded in the operation mode A, and the output voltage of the fuel cell device is one of the operation mode B that outputs a predetermined fixed voltage corresponding to the power storage device state. A power supply system that is operated in a mode.   The power supply system according to claim 2, wherein the duration of the operation mode A is set to a time longer than an equilibrium time constant of the polarization voltage of the secondary battery.   4. The power supply system according to claim 2, wherein the operation mode A and the operation mode B are alternately repeated, and the duration of the operation mode B is set to be longer than the duration of the operation mode A. 5. A power system characterized by setting.   5. The power supply system according to claim 2, wherein the power storage device state determination unit includes a deviation of an output current value with respect to a predetermined output voltage value in the operation mode A or an output voltage value with respect to an output current value. The power supply system is characterized in that a change in the load is determined based on a deviation of the load.   6. The power supply system according to claim 5, wherein the power storage device state determination unit corrects the charge / discharge state determination of the power storage device based on the determination result of the load fluctuation.   7. The power supply system according to claim 1, wherein the power storage device state determination unit is configured to determine whether the power storage device is in a discharged state, a charged state, or a charge state based on a distribution of the output voltage value with respect to the output current value. A power supply system that determines a range of an output voltage that is a boundary state between discharging and charging.   8. The power supply system according to claim 7, wherein the fixed voltage in the operation mode B is set to a range of the output voltage that is in a discharge state.   9. The power supply system according to claim 1, wherein the power storage device state determination unit determines a charging rate of the power storage device based on a distribution of output voltage values with respect to the output current value. A featured power supply system.   10. The power supply system according to claim 9, wherein when the charging rate is lower than a predetermined first charging rate threshold, the fixed voltage in the operation mode B is set so that the charging rate is higher than the first charging rate threshold. A power supply system that is set higher than a fixed voltage when high.   11. The power supply system according to claim 9, wherein when the power storage device state determination unit determines that the charging rate is higher than a predetermined second charging rate threshold, the fuel cell device is configured to operate in the operation mode. A power supply system that stops a power generation operation at the start of B and starts a power generation operation at the end of the operation mode B.

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