Power supply system and method for controlling power supply system

0001The present invention relates to a power supply system according to the preamble of independent claim 1, and a method for controlling a power supply system according to the preamble of independent claim 6. Such a power supply system and such a method for controlling a power supply system can be taken from the prior art document <patcit id="pcit0001" dnum="US2002172847A1"><text>US 2002/172847 A1</text></patcit>. In particular, prior art document <patcit id="pcit0002" dnum="US2002172847A1"><text>US2002/172847 A1</text></patcit> discloses a fuel cell power supply with a fuel cell and a capacitor which are connected parallel to each other, and controls the amount of a reacting gas supplied to the fuel gas based on a target supply current. A capacitor open voltage calculator calculates an open voltage of the capacitor from a detected current of the capacitor, an output voltage of the fuel cell, and an internal resistance of the capacitor. A corrective quantity calculator calculates a corrective quantity for a target supply current based on the open voltage of the capacitor, the output voltage of the fuel cell, and the target supply current, so as to prevent an air compressor from operating excessively and also prevent the fuel cell from suffering a gas shortage, depending on current-voltage characteristic data of the fuel cell and current-voltage characteristic data of the capacitor.

0002Recently, a hybrid power supply system in which a storage cell is connected in parallel with a fuel cell as a power generating device such that both the fuel cell and the storage cell supply electric power to a load has been developed. It is considered that such a power supply system compensates for the lack of electric power generated by the fuel cell for power consumption in the load due to response characteristics (or response delay) of the electric power by output power from the storage cell (Patent Literature 1).

CITATION LIST

PATENT LITERATURE

0003Patent Literature 1: <patcit id="pcit0003" dnum="JP2003235162A"><text>Japanese Patent Application Publication No. 2003-235162</text></patcit>

0004However, the above-mentioned conventional power supply system does not take into account transient response characteristics of the output power from the storage cell, and thus has the problem of being incapable of accurately compensating for the output power. For example, when the electric power generated by the fuel cell is insufficient for the power consumption by the load, even if an attempt is made to compensate for the generated power by the output power from the storage cell, sufficient output power cannot be obtained depending on the transient response characteristics of the output power from the storage cell, which in turn leads to the problem of causing an excessive or insufficient amount of electric power supplied to the load.

0005Therefore, the present invention has been proposed in view of the above-mentioned circumstances. An object of the present invention is to provide a power supply system and a method for controlling a power supply system, capable of accurately compensating for output power to a load.

0006According to the present invention said object is solved by a power supply system having the features of independent claim 1. Preferred embodiments are laid down in the dependent claims. Moreover, said object is also solved by a method for controlling a power supply system having the features of independent claim 6.

0007In order to solve the foregoing problem, the present invention provides a power supply system including a storage cell connected in parallel with a power generating device. The power supply system obtains electric power being currently consumed by a load, as a power-supply target value, and detects a generated-power value of electric power generated by the power generating device with respect to the power-supply target value. Then, the power supply system calculates a deviation of the generated-power value from the power-supply target value and determines an amount of power compensation to be supplied to the load from the storage cell, and determines current transient response characteristics of the storage cell, and performs control so that output power from the storage cell becomes equal to the amount of power compensation based on the current transient response characteristics.

BRIEF DESCRIPTION OF DRAWINGS

0008<ul id="ul0001" list-style="none" compact="compact"><li>[<figref idref="f0001">Fig. 1] Fig. 1</figref> is a block diagram illustrating a configuration of a power supply system according to one embodiment to which the present invention is applied.</li><li>[<figref idref="f0001">Fig. 2] Fig. 2</figref> is a block diagram illustrating a configuration of a power control device of the power supply system according to one embodiment to which the present invention is applied.</li><li>[<figref idref="f0002">Fig. 3] Fig. 3</figref> is a flowchart illustrating a procedure for power control operation by the power control device of the power supply system according to one embodiment to which the present invention is applied.</li><li>[<figref idref="f0003">Fig. 4] Fig. 4</figref> is a graph illustrating power generation characteristics of a fuel cell with respect to a power-supply target value, stored by the power control device of the power supply system according to one embodiment to which the present invention is applied.</li><li>[<figref idref="f0004">Fig. 5] Fig. 5</figref> is a graph illustrating a change over time in internal resistance of a storage cell, stored by the power control device of the power supply system according to one embodiment to which the present invention is applied.</li><li>[<figref idref="f0004">Fig. 6] Fig. 6</figref> is a graph of assistance in explaining advantageous effects of the power control operation by the power control device of the power supply system according to one embodiment to which the present invention is applied.</li><li>[<figref idref="f0005">Fig. 7] Fig. 7</figref> is a graph illustrating a relationship between a voltage value to increase an output current by 1 A in the storage cell and the internal resistance.</li><li>[<figref idref="f0005">Fig. 8] Fig. 8</figref> is a graph of assistance in explaining advantageous effects of the power control operation by the power control device of the power supply system according to one embodiment to which the present invention is applied.</li></ul>

DESCRIPTION OF EMBODIMENTS

0009Description will be given below with reference to the drawings with regard to one embodiment to which the present invention is applied.

[Configuration of Power Supply System]

0010<figref idref="f0001">Fig. 1</figref> is a block diagram illustrating a configuration of a power supply system according to the embodiment. As illustrated in <figref idref="f0001">Fig. 1</figref>, a power supply system 1 according to the embodiment includes a fuel cell 2 to act as a power generating device to supply electric power, a fuel cell control device 3 to control power generation by the fuel cell 2, a DCDC converter 4 to convert the electric power generated by the fuel cell 2 into electric power required by a load, a converter control unit 5 to control output power from the DCDC converter 4, a storage cell 6 to compensate for the electric power if the electric power generated by the fuel cell 2 is excessive or insufficient for power consumption by the load, a battery controller 7 to control operation of the storage cell 6, a DCDC converter 8 to control charging and discharging for the storage cell 6, a power control device 9 to control output power from the DCDC converter 8, a DCAC converter 10 to convert DC power supplied by the fuel cell 2 and the storage cell 6 into AC power, and a power-supply target value calculation unit 11 to calculate and output a power-supply target value.

0011Here, the power supply system 1 according to the embodiment is a system in which the fuel cell 2 as the power generating device and the storage cell 6 are connected in parallel to supply electric power to the load, and compensates for insufficient power by output power from the storage cell 6 if the electric power generated by the fuel cell 2 is insufficient for power consumption by the load.

0012The fuel cell 2 is a power generating device in which supply of oxygen and a fuel (e.g. hydrogen gas or modified gas) is controlled and electric power is generated, based on a command from the fuel cell control device 3.

0013The fuel cell control device 3 controls the oxygen and the fuel (e.g. the hydrogen gas or the reformed gas) supplied to the fuel cell 2 so that the electric power generated by the fuel cell 2 reaches a power-supply target value inputted from the converter control unit 5.

0014The DCDC converter 4 converts the electric power generated by the fuel cell 2 so as to become equal to a power-supply target value, and outputs the electric power to DCAC converter 10.

0015The converter control unit 5 performs control so that the output power from the DCDC converter 4 reaches the power-supply target value, and calculates input power for the output power from the DCDC converter 4 to satisfy the power-supply target value, and outputs the calculated power as the power-supply target value to the fuel cell control device 3.

0016The storage cell 6 is a secondary cell capable of charging and discharging, such for example as a lithium ion cell, and the storage cell 6 is discharged to supply electric power to the load and is charged with excessive power.

0017The battery controller 7 detects a terminal voltage and an electric current of the storage cell 6 and calculates internal resistance, and detects a value of a temperature sensor provided in the storage cell 6 and outputs these values to the power control device 9.

0018The DCDC converter 8 converts the electric power of the storage cell 6 and outputs the converted power as the insufficient power when the electric power generated by the fuel cell 2 is insufficient for power consumption by the load. Also, the DCDC converter 8 inputs excessive power of the electric power generated by the fuel cell 2 to the storage cell 6 and charges the storage cell 6.

0019The power control device 9 calculates output power from the DCDC converter 8, based on the internal resistance and temperature of the storage cell 6 inputted from the battery controller 7, the power-supply target value inputted from the power-supply target value calculation unit 11, and the terminal voltage and current of the DCDC converter 4, and output a discharging or charging command to the DCDC converter 8 to control the DCDC converter 8. Specifically, the power control device 9 calculates an amount of power compensation by subtracting the output power of the DCDC converter 4 from the power-supply target value, and controls the DCDC converter 8 so that the output power of the DCDC converter 8 becomes equal to the amount of power compensation.

0020The DCAC converter 10 converts the DC power supplied by the fuel cell 2 and the storage cell 6 into AC power of a predetermined voltage (for example, 100 V) as an operating voltage of the load, and outputs the AC power to the load.

0021The power-supply target value calculation unit 11 calculates electric power required to maintain the voltage of the AC power to be output to the load at the predetermined voltage, as the power-supply target value, and outputs the power-supply target value to the converter control unit 5 and the power control device 9.

0022In the embodiment, the load is configured as an AC load to be operated by the AC power, and thus, the DCAC converter 10 which converts the DC power supplied by the fuel cell 2 and the storage cell 6 into the AC power and outputs the AC power is used; however, the present invention is not so limited. For example, if the load is configured as a DC load to be operated by DC power, a DCDC converter is used in place of the DCAC converter 10.

0023Next, a configuration of the power control device 9 according to the embodiment will be described with reference to <figref idref="f0001">Fig. 2</figref>. As illustrated in <figref idref="f0001">Fig. 2</figref>, the power control device 9 of the power supply system 1 according to the embodiment includes a power-supply target value obtaining unit 21 configured to obtain electric power being currently consumed by the load, as a power-supply target value, a generated-power detection unit 22 configured to detect a generated-power value of electric power generated by the fuel cell 2 with respect to the power-supply target value, a power compensation amount calculation unit 23 configured to calculate a deviation of the generated-power value from the power-supply target value and thereby determine the amount of power compensation to be supplied to the load from the storage cell 6, and an output power control unit 24 configured to determine current transient response characteristics of the storage cell 6, and perform control so that output power from the storage cell 6 becomes equal to the amount of power compensation, based on the current transient response characteristics.

0024Here, the power control device 9 is configured with a general-purpose electronic circuit including a microcomputer, a microprocessor and a CPU (central processing unit), and a peripheral device. A specific program is executed to allow the power control device 9 to operate as the power-supply target value obtaining unit 21, the generated-power detection unit 22, the power compensation amount calculation unit 23 and the output power control unit 24.

0025The power-supply target value obtaining unit 21 receives and obtains the power-supply target value calculated and outputted by the power-supply target value calculation unit 11.

0026The generated-power detection unit 22 calculates the output power from the DCDC converter 4, based on the voltage and current output from the DCDC converter 4, and detects the output power as the generated-power value of the fuel cell 2. Also, the generated-power detection unit 22 may prestore power generation characteristics of the fuel cell 2 with respect to the power-supply target value, and, in this case, the generated-power value is detected according to the power-supply target value.

0027The power compensation amount calculation unit 23 calculates the deviation by subtracting the generated-power value from the power-supply target value, and determines the deviation as the amount of power compensation by the storage cell 6.

0028The output power control unit 24 obtains the internal resistance of the storage cell 6 output by the battery controller 7, and calculates the current transient response characteristics of the storage cell 6, based on the internal resistance. Then, the DCDC converter 8 is controlled by changing control gain so that the output power from the storage cell 6 reaches the amount of power compensation, based on the current transient response characteristics. Also, the output power control unit 24 may prestore a change over time in the internal resistance of the storage cell 6, and, in this case, the change over time in the internal resistance since the time of initialization is added to the internal resistance at the time of the initialization according to a period of time elapsed since the initialization (or since the time at which the storage cell 6 is installed in the system) thereby to determine the internal resistance of the storage cell 6.

[Procedure for Power Control Operation of Storage Cell]

0029Next, description will be given with reference to a flowchart of <figref idref="f0002">Fig. 3</figref> with regard to a procedure for power control operation by the power control device 9 of the power supply system 1 according to the embodiment.

0030As illustrated in <figref idref="f0002">Fig. 3</figref>, first, at step S101, the power-supply target value obtaining unit 21 obtains the power-supply target value output by the power-supply target value calculation unit 11, and recognizes electric power being currently consumed by the load.

0031Then, at step S102, the generated-power detection unit 22 obtains a voltage value and a current value output by the DCDC converter 4, and detects the generated-power value of the fuel cell 2, based on the voltage value and the current value. Also, the generated-power detection unit 22 may prestore the power generation characteristics of the fuel cell 2 with respect to the power-supply target value, as illustrated in <figref idref="f0003">Fig. 4</figref>. In this case, the generated-power detection unit 22 determines the generated-power value according to the power-supply target value, and thus, feed forward control can be performed to thus enable achieving accuracy of processing and an improvement in processing speed.

0032Then, at step S103, the power compensation amount calculation unit 23 determines whether or not the power-supply target value is equal to the generated-power value. If the power-supply target value is equal to the generated-power value, power supply from the storage cell 6 is unnecessary, and thus, the power control operation according to the embodiment comes to an end.

0033Meanwhile, if at step S103 the power-supply target value is not equal to the generated-power value, the processing goes to step S104, and the power compensation amount calculation unit 23 determines whether or not the electric power generated by the fuel cell 2 is insufficient (or the power-supply target value exceeds the generated-power value). Then, if the electric power generated by the fuel cell 2 is insufficient (or the power-supply target value exceeds the generated-power value), the processing goes to step S105A, and the power compensation amount calculation unit 23 subtracts the generated-power value from the power-supply target value to calculate the deviation and determines the deviation as the amount of power compensation by the storage cell 6.

0034Then, at step S106A, the output power control unit 24 obtains the present voltage value and current value of the storage cell 6 output by the DCDC converter 8, and, at step S 107A, obtains the internal resistance of the storage cell 6 from the battery controller 7.

0035Here, the internal resistance of the storage cell 6 may be always obtained in real time from the battery controller 7, or may be obtained only at the time of start of the system. If the internal resistance of the storage cell 6 is obtained only at the time of start of the system, at step S108A, the output power control unit 24 obtains the temperature of the storage cell 6 from the battery controller 7, and always corrects the value of the internal resistance according to the obtained temperature of the storage cell 6.

0036Further, as illustrated in <figref idref="f0004">Fig. 5</figref>, the output power control unit 24 may prestore the change over time in the internal resistance of the storage cell 6 and determine the internal resistance of the storage cell 6 according to the period of time elapsed since the initialization. This enables easily obtaining the value of the internal resistance even without performing sequential calculation, and thus enables reducing the time required for the processing.

0037When the value of the internal resistance is thus obtained, at step S 109A, the output power control unit 24 calculates the current transient response characteristics of the storage cell 6 based on the internal resistance. The transient response characteristics can be determined by solving a voltage equation of LCR circuit represented as Equation (1). <maths id="math0001" num="(1)"><math display="block"><mfrac><mn>2</mn><mi>C</mi></mfrac><mstyle displaystyle="true"><mrow><msubsup><mo>∫</mo><mn>0</mn><mi>t</mi></msubsup><mi mathvariant="italic">idt</mi></mrow></mstyle><mo>+</mo><mi>L</mi><mfrac><mi mathvariant="italic">di</mi><mi mathvariant="italic">dt</mi></mfrac><mo>+</mo><mi mathvariant="italic">iR</mi><mo>=</mo><msub><mi>V</mi><mn>0</mn></msub></math><img file="EP2887487B1_D0001.tif" /></maths>

0038Here, when the voltage equation represented as Equation (1) is solved, the transient response characteristics are represented as Equations (2) and (3): <maths id="math0002" num="(2)"><math display="block"><mi>i</mi><mfenced><mi>t</mi></mfenced><mo>=</mo><mfrac><msub><mi>v</mi><mn>0</mn></msub><mi mathvariant="italic">ωL</mi></mfrac><msup><mi>e</mi><mrow><mo>−</mo><mi mathvariant="italic">Rt</mi><mo>/</mo><mn>2</mn><mi>L</mi></mrow></msup><mi mathvariant="italic">sinωt</mi></math><img file="EP2887487B1_D0002.tif" /></maths><maths id="math0003" num="(3)"><math display="block"><mi>ω</mi><mo>=</mo><msup><mfenced open="[" close="]"><mfrac><mn>1</mn><mi mathvariant="italic">LC</mi></mfrac><mo>−</mo><msup><mfenced><mfrac><mi>R</mi><mrow><mn>2</mn><mi>L</mi></mrow></mfrac></mfenced><mn>2</mn></msup></mfenced><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msup></math><img file="EP2887487B1_D0003.tif" /></maths> where i(t) denotes an output current indicating the transient response characteristics of the storage cell 6; V₀ denotes a voltage value of a current response component of the terminal voltage of the storage cell 6 (or equivalently, a voltage value which varies according to the current, and a voltage value obtained by subtracting a no-load voltage from the terminal voltage); L denotes an inductance component inherent in the system; C denotes a capacitance component inherent in the system; and R denotes the internal resistance of the storage cell 6. Since L and C are constants, the transient response characteristics are determined by setting the internal resistance R.

0039Here, if the transient response characteristics are set using the internal resistance at the time of the initialization and are not corrected, an increase in the internal resistance due to the change over time causes a deterioration in the transient response characteristics and thus makes it impossible for the electric power of the storage cell 6 to accurately compensate for necessary electric power. However, in the embodiment, the current transient response characteristics are calculated based on the current internal resistance, and thus, even if the change over time causes a change in the transient response characteristics, the output power to the load can be accurately compensated.

0040When the current transient response characteristics are thus calculated, at step S110A, the output power control unit 24 calculates control gain capable of achieving the amount of power compensation, and, at step S111A, outputs a discharging command based on the control gain thereby to control the DCDC converter 8.

0041Thereby, if the electric power generated by the fuel cell 2 is insufficient for the power consumption by the load, the sufficient power is discharged by the storage cell 6, and the power control operation according to the embodiment comes to an end.

0042Meanwhile, if at step S104 the electric power generated by the fuel cell 2 is not insufficient (or the power-supply target value is less than the generated-power value), in other words, if the electric power generated by the fuel cell 2 is excessive, steps S105B to S110B perform the same processing as steps S105A to S110A. Then, at step S111B, a charging command is output to control the DCDC converter 8, and thereby, if the electric power generated by the fuel cell 2 is excessive for the power consumption by the load, the excessive power is charged into the storage cell 6, and the power control operation according to the embodiment comes to an end.

[Advantageous Effects of Embodiment]

0043By performing the above-mentioned processing, the power control device 9 of the power supply system 1 according to the embodiment enables the discharging of the storage cell 6 to compensate for the insufficiency of the electric power generated by the fuel cell 2, when the power-supply target value changes sharply at time t₀ as illustrated in <figref idref="f0004">Fig. 6</figref>. Also, if after time t₁ the electric power generated by the fuel cell 2 exceeds the power-supply target value, the excessive power can be charged into the storage cell 6.

0044Further, the power control device 9 of the power supply system 1 according to the embodiment determines the current transient response characteristics of the storage cell 6 and performs control so that the output power from the storage cell 6 reaches the amount of power compensation based on the current transient response characteristics. Thereby, even if the transient response characteristics of the storage cell 6 change due to the change over time or the like, the output power to the load can be accurately compensated.

0045For example, a relationship between the voltage value and the internal resistance to increase the output current by 1 A in the storage cell 6 is as illustrated in <figref idref="f0005">Fig. 7</figref>. Specifically, an increase in the value of the internal resistance from 160 mΩ to 320 mΩ causes an increase in a voltage required to increase the output current from the storage cell 6 by 1 A (or a voltage to be increased) from 0.17 V to 0.33 V. In other words, output power required for the storage cell 6 to increase the output current by 1 A increases from 0.17 W to 0.33 W.

0046This will be described below in terms of the transient response characteristics. If the amount of power compensation is C [w] as illustrated in <figref idref="f0005">Fig. 8</figref>, when the internal resistance is 160 mΩ, the transient response characteristics of the storage cell 6 obtained by multiplying i(t) in Equation (2) by V₀ are K1. In this case, at the time t₀, an increase in the transient response characteristics to the amount of power compensation C [w] requires 0.17 W.

0047Meanwhile, when the storage cell 6 undergoes the change over time and hence the deterioration and thus the internal resistance reaches 320 mΩ, the transient response characteristics become K2, and, at the time t₀, an increase in the transient response characteristics to the amount of power compensation C [w] requires 0.33 W.

0048For example, when the transient response characteristics are set with the internal resistance remaining as it is at the time of the initialization, even though the transient response characteristics actually decrease from K1 to K2 due to the change over time, consideration is not given to this decrease, and therefore, the output power from the storage cell 6 cannot become accurately equal to the amount of power compensation.

0049On the other hand, even if when the internal resistance undergoes the change over time and hence the deterioration, the power control device 9 of the power supply system 1 according to the embodiment calculates the current transient response characteristics K2, and controls the output power from the storage cell 6 based on the current transient response characteristics K2. Therefore, even if the transient response characteristics of the storage cell 6 change due to the change over time or the like, the output power to the load can be accurately compensated.

0050In particular, according to the power control device 9 of the power supply system 1 according to the embodiment, the current transient response characteristics are calculated based on the internal resistance of the storage cell 6, and thus, the value of the internal resistance generally measured in the storage cell is utilized to enable easy calculation of the current transient response characteristics.

0051Also, the power control device 9 of the power supply system 1 according to the embodiment stores the change over time in the internal resistance of the storage cell 6, and determines the internal resistance of the storage cell 6 according to the period of time elapsed since the initialization. This enables easily obtaining the value of the internal resistance even without performing sequential calculation, and thus enables reducing the time required for the processing.

0052Further, the power control device 9 of the power supply system 1 according to the embodiment stores the power generation characteristics of the fuel cell 2 with respect to the power-supply target value, and determines the generated-power value according to the power-supply target value. Thereby, the stored power generation characteristics of the fuel cell 2 are utilized to perform the feed forward control, which in turn enables achieving the accuracy of the processing and the improvement in the processing speed.

0053Also, according to the power control device 9 of the power supply system 1 according to the embodiment, the control gain is changed according to the current transient response characteristics of the storage cell 6, and thus, the output power from the storage cell 6 can quickly become equal to the amount of power compensation.

INDUSTRIAL APPLICABILITY

0054According to the power supply system and the method for controlling the power supply system according to one aspect of the present invention, the current transient response characteristics of the storage cell are determined, and control is performed so that the output power from the storage cell reaches the amount of power compensation, based on the transient response characteristics, and thus, the output power to the load can be accurately compensated for. Therefore, the power supply system and the method for controlling the power supply system according to the aspect of the present invention have industrial applicability.

REFERENCE SIGNS LIST

0055<dl id="dl0001"><dt>1</dt><dd>power supply system</dd><dt>2</dt><dd>fuel cell</dd><dt>3</dt><dd>fuel cell control device</dd><dt>4</dt><dd>DCDC converter</dd><dt>5</dt><dd>converter control unit</dd></dl>