JP2011211812A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit which has a generator, a voltage conversion unit for stepping up or down an input voltage, and a power storage unit, and is free from a decrease in energy efficiency of the power unit even if an output of the power unit is low.SOLUTION: The power unit has: a first power supply path for supplying output from the generator to a load via the voltage conversion unit; a second power supply path for supplying an output from the energy storage unit to the load without going through the voltage conversion unit; a current detection unit for detecting a consumption current of the load; and a control unit for switching between the first power supply path and the second power supply path. The control unit switches to the first power supply path when the current detection unit detects a consumption current where the conversion efficiency is not less than an intermediate value between the minimum and maximum values, and switches to a second power supply path when the current detection unit detects a consumption current where desired conversion efficiency is lower than the intermediate value.

Description

  The present invention relates to a power supply device having a generator, a voltage conversion unit that boosts or lowers an input voltage and outputs the same, and more particularly to improvement of energy efficiency of the power supply device.

    Secondary batteries such as lithium-ion secondary batteries are currently used as power sources for mobile devices such as mobile phones, but there is an inconvenience that the capacity is short and the usable time is short or the battery must be charged. is there. Therefore, when the input / output voltage from the rechargeable battery is output exceeding the allowable range, the load may not be driven or the load may be damaged. Therefore, a power supply system that supplies power from a fuel cell output to a load via a voltage converter is known. (For example, see Patent Document 1)

  In addition, since the power source for portable devices is required to be small, a small and highly efficient switching converter is often used for the voltage converter. FIG. 2 shows a schematic diagram of a voltage converter that is a switching converter that steps up or steps down an input voltage supplied from a generator to a predetermined output voltage.

  When the input voltage Vi from the generator 100 is higher than the output voltage Vo set in the voltage converter 103, the control circuit 208 sets the second changeover switch 204, which is a MOS-FET, in a non-conductive state. . Further, the control circuit 208 steps down and outputs the input voltage by causing the first changeover switch 201, which is a MOS-FET, to perform a switching operation so as to be in a conductive state and a non-conductive state within a predetermined period.

  When the input voltage Vi from the generator 100 is lower than the output voltage Vo set in the voltage conversion unit 103, the control circuit 208 sets the first changeover switch 201 in a conductive state. Further, the control circuit 208 boosts and outputs the input voltage by causing the second changeover switch 204 to perform a switching operation so as to be in a conductive state and a non-conductive state within a predetermined period.

  Whether the voltage conversion unit 103 steps up or down, the first changeover switch 201, the second changeover switch 204, the diode 202, and the diode 205 are switched when the conduction state of the first changeover switch 201 and the second changeover switch 204 is changed. A switching loss in which power is consumed occurs in the transition of the on / off state. Therefore, if the operating frequency of the voltage converter is increased, the number of times of switching per unit time increases, so that switching loss also increases. In addition, when the frequency is fixed and the current consumption of the load is small, that is, when the output of the voltage converter is small, the ratio of the switching loss to the output of the voltage converter is higher than when the output of the voltage converter is large. Therefore, the problem that the conversion efficiency of a voltage conversion part becomes low arises.

  Therefore, a method is known in which when the output of the voltage converter is small, the switching frequency is lowered and the ratio of switching loss per cycle is lowered to increase the conversion efficiency. (For example, see Patent Document 2)

JP-A-2005-123110 JP-A-10-215569

  However, in the conventional technology, when designing the voltage conversion unit, it is necessary to set the coefficients of the inductor and the capacitor so that the power can be stably supplied even in a low switching operation, which increases the size of the circuit. There is a problem.

  Therefore, the present invention has been made in view of the above points, and in a power supply device having a voltage conversion unit and a power storage unit that boosts or steps down an input voltage of a generator and outputs it, even when the current consumption of the load is small It is an object of the present invention to provide a small power supply device that eliminates a decrease in energy efficiency of the power supply device.

  In order to solve the above problems, a first feature of the present invention is that a first power supply path for supplying an output from a generator to a load via a voltage converter, and an output from the power storage unit as a voltage converter. A second power supply path that supplies power to the load without going through the power supply, a current detection unit that detects current consumption of the load, and a control unit that switches between the first power supply path and the second power supply path. The voltage conversion unit changes the conversion efficiency according to the current consumption, and the control unit detects the current consumption when the current detection unit is equal to or higher than the intermediate value between the minimum value and the maximum value. Switching to the first power supply path, and switching to the second power supply path when the current detection unit detects current consumption when the conversion efficiency is lower than the intermediate value between the lowest value and the highest value. Is the gist.

  According to such characteristics, the current consumption of the load, that is, the conversion efficiency characteristic with respect to the output current of the voltage converter is obtained in advance, and the current equal to or lower than the load current corresponding to the intermediate efficiency between the maximum value and the minimum value of the conversion efficiency When the current detection unit detects the power supply path, the power supply path to the load is the second power supply path that does not go through the voltage conversion section, so that power supply with low conversion efficiency of the voltage conversion section can be avoided. . The intermediate value may be set between 20% and 80% including the vicinity of the intermediate value between the lowest value and the highest value of the conversion efficiency. The conversion efficiency when switching the power supply path depends on the type of load to which the power supply is applied, the power capacity of the power storage unit used in the power supply, and the output distribution between the generator and the power storage unit. It is desirable to set as appropriate. In addition, it is desirable to provide hysteresis for setting the conversion efficiency when switching the power supply path. By providing the hysteresis at the time of switching, it is possible to suppress fluctuation of switching of the power supply path when the load fluctuation is fine movement and to supply stable power.

  The second feature of the present invention is that the voltage conversion unit boosts or decreases the voltage of the generator and supplies it to the load. The voltage conversion unit is an inductor that charges or discharges the output from the generator as energy. And a switching element that switches between a charge state in which energy is charged to the inductor and a discharge state in which energy is released to the load, and the switching element generates a switching loss that is a loss of energy when the energy release state is switched. The conversion efficiency is influenced by the switching loss value and the current consumption, and the control unit detects the second current when the current detection unit detects a current consumption equivalent to the power consumption below the switching loss value. The main point is to switch to the power supply path.

  According to this feature, the switching loss of the voltage converter is obtained in advance, and when the setting of the output voltage of the voltage converter is fixed and known, the current consumption of the load, that is, the output current of the voltage converter is detected. When the switching loss is larger than the current consumption of the load detected by the power unit, the power conversion path is a second power supply path that does not go through the voltage conversion section, so that the conversion efficiency of the voltage conversion section is low. Supply can be avoided. When the output voltage of the voltage conversion unit is variable, the power consumption of the load may be obtained by detecting the voltage and current supplied to the load using a voltage detection unit or the like. Further, hysteresis may be provided when switching the power supply path to the load. For example, a range may be given to the current consumption and the power consumption value of the load for switching the preset power supply path, and the power supply path may be switched when a current between the widths is detected. Also, after the power consumption of the load becomes larger than the switching loss obtained in advance by a predetermined amount, the power supply route is switched from the second power supply route to the first power supply route, and conversely the switching loss obtained in advance. The power supply path may be switched from the first power supply path to the second power supply path after the power consumption of the load is reduced by a predetermined amount. Here, the power consumption of the load that is smaller by the predetermined power is the minimum value of the current consumption value of the load having sufficiently good conversion efficiency. Set the power value of the hysteresis when switching the power supply path appropriately according to the type of load to which the power supply is applied, the power capacity of the power storage unit used in the power supply, and the output distribution between the generator and the power storage unit Is desirable. As a result, it is possible to suppress fluctuation in switching of the power supply path when the load fluctuation is fine, and to supply stable power.

  The third feature of the present invention is that the voltage conversion unit increases the conduction loss in proportion to the increase in current consumption, and the conversion efficiency decreases as the conduction loss increases. The power supply unit supplies power to the load from the first power supply path and the second power supply path when detecting a current consumption of 70% or more of the current consumption when the conversion efficiency reaches the maximum value. And

According to this feature, the conversion efficiency of the voltage conversion unit is low when the power consumption of the load is small, that is, the ratio of the switching loss that is converted to the output from the voltage conversion unit with a decrease in the output of the voltage conversion unit is high. On the contrary, as the output of the voltage converter increases, the ratio of the switching loss that is converted to the output from the voltage converter decreases, so that the conversion efficiency increases. However, as the output of the voltage converter increases, the current flowing in the voltage converter increases, the conduction loss Pl expressed by Pl = R · I ² increases, and the conversion efficiency of the voltage converter is the output from the voltage converter. Decreases with increasing. R is an electrical resistance in the voltage converter, and I is a current value in the voltage converter. Therefore, power is supplied to the load from both the first power supply path and the second power supply path when an output current of at least 70% of the output current value that takes the maximum value of the conversion efficiency of the voltage converter is detected. By doing so, power loss due to conduction loss can be reduced. Note that hysteresis may be provided when switching the power supply path to the load. For example, when the current consumption of the load detected by the current detector, that is, the output current of the voltage converter increases to 100% of the output current value that takes the maximum value of the conversion efficiency of the voltage converter, the power supply to the load is Performed from both of the first power supply path and the second power supply path, the output current of the voltage converter decreased, and the current value was 80% or less of the output current value at which the maximum value of the conversion efficiency of the voltage converter was obtained. Sometimes the second power supply path may be cut off and switched to the first power supply path. The current value for switching the power supply path to the load with hysteresis may be set to a current value of 70% or more of the output current value that takes the maximum value of the conversion efficiency of the voltage conversion unit. Set the power value of the hysteresis when switching the power supply path appropriately according to the type of load to which the power supply is applied, the power capacity of the power storage unit used in the power supply, and the output distribution between the generator and the power storage unit Is desirable. As a result, it is possible to suppress fluctuation of switching of the power supply path when the load fluctuation is fine, and to supply stable power.

The gist of the fourth feature of the present invention is that the generator is a fuel cell.
According to this feature, stable power supply can be performed.

  The fifth feature of the present invention is that the control unit detects one of the generator and the storage unit having a large remaining power capacity, and switches to the first power supply path when the remaining power capacity of the generator is large. The gist is to switch to the second power supply path when the remaining power of the power storage unit is large.

  According to this feature, it is possible to reliably and stably supply power to the load. In addition, when the remaining amount of fuel, etc. on the generator side cannot be detected or is uncertain, the remaining amount of each of the generator and the storage unit is 100%, or the remaining amount is equivalent May use the priority route as the second power supply route.

  According to the present invention, in the power supply device having the generator and the voltage conversion unit that outputs the voltage by stepping up or down the input voltage and the power storage unit, the reduction in the energy efficiency of the power supply device is eliminated even when the current consumption of the load is small. A small power supply device can be provided.

It is a schematic block diagram of the voltage converter which concerns on this invention. It is a schematic block diagram of the voltage converter used for a power supply device. It is a conceptual diagram of the conversion efficiency change in the current change and voltage change of a voltage converter. It is a conceptual diagram of the switching hysteresis of a 1st electric power supply path | route and a 2nd electric power supply path | route. It is a schematic block diagram of the example of a change of the voltage converter which concerns on this invention.

Next, the present invention will be described in detail based on the embodiments shown in the drawings.
(First embodiment)
FIG. 1 shows an example of a power supply device according to the first embodiment of the present invention.

  FIG. 1 shows a generator 100 that generates electric power, a voltage converter 103 that converts a voltage input from the generator 100 into a predetermined constant voltage, a load 112 that is supplied with electric power from the voltage converter 103, and charging and discharging are possible. A power storage unit 106, a voltage detection unit 104 that detects an output voltage of the voltage conversion unit 103, and a path that supplies power from the generator 100 to the load 112 via the voltage conversion unit 103 is defined as a first power supply path. A path for supplying power from 106 to the load 112 is a second power supply path, and the first switching unit 102 switches the electrical continuity state of the first power supply path, and the electrical continuity state of the second power supply path A second switching unit 109 for switching the current, a current detection unit 105 for detecting the current supplied to the load 112, a charge control unit 111 for controlling the charging of the power storage unit 106 using the power of the generator 100, Based on the detection value of the detecting section 104 and the current detecting section 105, indicating the configured power supply device 10 from the control unit 110 for controlling the first switching unit 102 and the second switching unit 109 and charge control unit 111.

(A) Switching efficiency and switching of current supply path of voltage converter when load fluctuation is small Using FIGS. 1 to 4, the switching efficiency of voltage converter and switching operation of current supply path when load fluctuation is small This will be specifically described.

  First, the conversion efficiency characteristic with respect to the consumption current of the load 112, that is, the output current of the voltage conversion unit 103 is obtained. When the current detection unit 105 detects a current equal to or lower than the load current corresponding to the intermediate efficiency between the maximum value and the minimum conversion efficiency, the control unit 110 shuts off the first switching unit 102 and performs the second switching. The unit 109 is turned on. As a result, the power supply path to the load 112 is changed to the second power supply path in which power is supplied from the power storage unit 106 without passing through the voltage conversion unit 103.

  In addition, when the current detection unit 105 detects a current larger than the load current corresponding to the intermediate efficiency between the maximum value and the minimum value of the conversion efficiency, the control unit 110 blocks the second switching unit 109, and One switching unit 102 is turned on. Thus, the power supply path to the load 112 is changed to the first power supply path for supplying power from the generator 100 via the voltage conversion unit 103.

  FIG. 4 shows the switching hysteresis between the first power supply path and the second power supply path. For example, when the current detection unit 105 detects an increase in current and switches from the second power supply path to the first supply path, the conversion efficiency is set to 50%. Next, the conversion efficiency when switching from the first power supply path to the second power supply path is set to 40%. The difference between the switching timings of the two switching methods is intended to reduce the flutter of excessive switching between the generator 100 that is the power supply source and the power storage unit 106. At this time, the conversion efficiency of 40% is assumed to be sufficient conversion efficiency. If the conversion efficiency setting that is the switching timing of the two switching methods is the same, the output of the electric conversion unit 105 detected by the current detection unit 105 fluctuates in the vicinity of the current corresponding to the conversion efficiency that is the switching timing. In some cases, the control unit 110 switches the first power supply path and the second power supply path in small increments. At this time, if the voltage values of the generator 100 and the power storage unit 106 are different, the load 112 may be damaged. In order to avoid this point, the timings of the two switching methods are made different to reduce the switching of extra power supply paths.

  The intermediate value may be set between 20% and 80% including the vicinity of the intermediate value between the lowest value and the highest value of the conversion efficiency. The conversion efficiency when switching the power supply path depends on the type of load to which the power supply is applied, the power capacity of the power storage unit used in the power supply, and the output distribution between the generator and the power storage unit. It is desirable to set as appropriate within the range that can be obtained.

Further, it is desirable that the hysteresis of the conversion efficiency as the switching timing is appropriately set within a range where sufficient conversion efficiency can be obtained.
In addition, it is desirable that the voltage values of the generator 100 and the power storage unit 106 are close to each other at the switching timing.

  Hereinafter, an example of the conversion efficiency of the voltage converter and switching of the current supply path will be described with reference to FIGS.

  A PEFC type fuel cell was prepared as the generator 100 for the load 112 having an average power consumption of 24 W (12 V · 2 A) and a pulse load of 42 W (about 3.5 msec). The fuel cell has a 12-series rated output of 27 W (8.4 V · 3.2 A). The capacity of the fuel tank is 48 Wh in terms of electric energy. In addition to PEFC, DMFC (direct methanol fuel cell) using methanol-oxygen as fuel, SOFC (solid oxide fuel cell), MCFC (molten carbonate fuel cell), PAFC (phosphoric acid type) A fuel cell) or the like. In addition to the fuel cell, a generator 100 such as a physical battery such as a solar battery can be used. In addition, the AC generator 100 can be used as the generator 100 through an inverter.

  A power storage unit 106 was prepared by connecting three lithium ion secondary batteries having a capacity of 300 mAh and a nominal voltage of 3.7 V in series. The capacity of power storage unit 106 is about 3.7 Wh as the amount of power in a fully charged state. The power storage unit 106 is charged by application of a voltage such as a rechargeable battery such as a lead storage battery, a nickel metal hydride secondary battery, or a lithium ion secondary battery, or a capacitor, a capacitor, or an electric double layer capacitor. A power storage unit that stores electrostatic energy and obtains electric capacity can be used. Depending on the operating voltage, minimum operating voltage, load characteristics, etc. of the load 112, an appropriate type of secondary battery or power storage unit is selected, and if necessary, the voltage supplied to the load 112 by connecting the secondary battery or power storage unit in series is selected. Can be adjusted.

A step-up circuit was manufactured using a step-up type switching regulator IC commercially available as the voltage conversion unit 103.
The switching of the power supply path is controlled by the control unit 110, and an 8-bit microcomputer is used for the control unit 110 in the present embodiment.

  The first switching unit 102 and the second switching unit 109 controlled by the control unit 110 use a P-type MOS-FET and connect the source terminal of the MOS-FET so as to come to the load 112 side. The connection with 110 is connected to the gate terminal of the MOS-FET through a drive circuit (not shown). Note that the switching unit is connected in series with the source and gate terminals of the two MOS-FETs in common so that current does not pass through each switching unit via the body diode of the MOS-FET. You may comprise.

  An example of the operation of the power supply device according to the first embodiment of the present invention will be described with reference to FIGS.

  The variation in the current consumption of the load 112 was small, and the conversion efficiency of the voltage conversion unit 103 when the load 112 was operating varied between 60% and 90%. The maximum value of the conversion efficiency of the voltage conversion unit 103 was about 90% when the current consumption of the load 112 was about 2A. Since the fluctuation of the consumption current of the load 112 is small and the conversion efficiency of the voltage conversion unit 103 during the operation of the load 112 fluctuates between 60% and 90%, the power supply to the load 112 is changed to the second power supply path. If the power of the power storage unit 106 with a small capacity is relied too much, the capacity of the power storage unit 106 will be lost immediately. Therefore, the efficiency when switching from the second power supply path to the first power supply path is 50%. did. At this time, the current consumption of the load 112 was about 20 mA.

  The conversion efficiency when switching from the first power supply path to the second power supply path was 40%.

  FIG. 3 shows a change in current in the voltage converter and a change in conversion efficiency due to a change in voltage. Regarding the conversion efficiency of the voltage conversion unit 103, when the output current is 2A, if the output current increases with a conversion efficiency of 90% as a boundary, the conduction loss increases, so the conversion efficiency decreases. Therefore, when the current detection value by the current detection unit 105 exceeds 2.2 A, that is, the consumption current of the load 112 detected by the current detection unit 105, that is, the output current of the voltage conversion unit 103 is the maximum conversion efficiency of the voltage conversion unit 103. When the value is 110% of the current value 2A, the switching unit is controlled so that the power supply to the load 112 becomes the first power supply path and the second power supply path. Conversely, when the current detection value by the current detection unit 105 is 2.0 A or less, that is, the current consumption of the load 112 detected by the current detection unit 105, that is, the output current of the voltage conversion unit 103 is the conversion efficiency of the voltage conversion unit 103. When the current value is 2% at the maximum value of 100%, the power supply to the load 112 is switched to the first power supply path.

In order to prevent fluctuations due to output switching when there is a pulse-like load, etc., in order not to switch the power supply path for temporary load fluctuations, conversion efficiency and load current power The power supply path is switched after a state that exceeds the threshold for switching the supply path and exceeds a predetermined time threshold is recognized. In this embodiment, in order to have a sufficient margin for the generation time of the pulse load, the switching is performed unless the state exceeding the conversion efficiency of 350 msec or more and the threshold value for switching the power supply path of the load current is maintained. I didn't do it. The holding time from when the conversion efficiency or load current power supply path switching threshold is exceeded to when the power supply path is switched depends on the pulse width of the pulse load, the size of the pulse load, and the frequency of occurrence of the pulse load. It is desirable to set appropriately according to the situation.
A program was created to perform the control as described above, and the program was written to the microcomputer.

(B) Switching loss and switching of current supply path The switching loss and switching operation of the current supply path will be specifically described with reference to FIG.

  First, the switching loss of the voltage conversion unit 103 is obtained, and the current consumption of the load 112, that is, the output current of the voltage conversion unit 103 is detected by the current detection unit 105. The output voltage is detected by the voltage detection unit 104, and the power consumption of the load 112 is obtained from the current consumption and the voltage consumption. When the switching loss is larger than the power consumption of the load 112, the voltage conversion unit 103 is connected to the power supply path. By setting the second power supply path not to be interposed, power supply with low conversion efficiency of the voltage conversion unit 103 can be avoided. In addition, when the switching loss current or the switching loss is smaller than the consumption current or the power consumption of the load 112, the control unit 110 blocks the second switching unit 109 and puts the first switching unit 102 into a conductive state. . Thus, the power supply path to the load 112 is changed to the first power supply path for supplying power from the generator 100 via the voltage conversion unit 103.

  Further, hysteresis may be provided when switching the power supply path to the load. For example, the power supply path is switched from the second power supply path to the first power supply path after the power consumption of the load becomes larger than the previously determined switching loss by a predetermined amount of power. The power supply path may be switched from the first power supply path to the second power supply path after the power consumption of the load is reduced by a predetermined amount. Here, the power consumption of the load that is smaller by the predetermined power is the minimum value of the current consumption value of the load having sufficiently good conversion efficiency. Set the power value of the hysteresis when switching the power supply path appropriately according to the type of load to which the power supply is applied, the power capacity of the power storage unit used in the power supply, and the output distribution between the generator and the power storage unit Is desirable. As a result, it is possible to suppress fluctuation in switching of the power supply path when the load fluctuation is fine, and to supply stable power.

  The switching loss of the voltage conversion unit 103 is a power loss during a state transition when a switching element such as a MOS-FET is turned on / off.

  At the time of turn-on, a loss of Pr = (Vin × I × Fsw × Trise) / 2 occurs, and at the time of turn-off, a loss of Pf = (Vin × I × Fsw × Tfall) / 2 occurs. It is an addition. Here, Vin is an input voltage, I is a current flowing through the switching element, Fsw is a switching frequency, Trise is a switching transition time at turn-on, and Tfall is a switching transition time at turn-off. For Trise and Tfall, values described in the data sheet of the switching element may be used, or measured values using an oscilloscope or the like may be used.

  Further, the switching loss may be obtained in advance, or each parameter may be detected every time the voltage conversion unit 103 is operated to obtain the switching loss.

  Hereinafter, an example of switching of the switching loss and the current supply path will be described with reference to FIGS. Note that the average power consumption of the load, the pulse load is 42 W, and the specific configurations of the generator 100 and the power storage unit 106 are the same as described in (A).

  In this embodiment, although there are load fluctuations, average Vin and I are set and the switching loss is obtained in advance. Since Vin was 8.4 V, I was 3.2 A, the switching frequency was 500 kHz, Trise was 15 nsec from the data sheet, and Tfall was 40 nsec from the data sheet, the switching loss value was stored in the control unit 110. When the switching loss is larger than the power supplied to the load 112 obtained from the switching loss value, the detection value of the voltage detection unit 104, and the detection value of the current detection unit 105, the power path that the control unit 110 supplies to the load 112 Is set to be the second power supply path, the conduction state of the first switching unit 102 and the second switching unit 109 is controlled.

  When the power supplied to the load 112 becomes 150% or less of the switching loss, the control unit 110 switches from the first power supply path to the second power supply path, and conversely, the power supplied to the load 112 is switched to the switching loss. A program was created and written to the control unit 110 so that the second power supply path was switched to the first power supply path when 70% or higher.

(C) Determination of priority route of power supply route The operation of setting the priority route of the power supply route will be specifically described with reference to FIG.

  The control unit 110 compares the remaining capacity of the generator 100 and the state of charge of the power storage unit 106, and is connected to the one with the higher remaining amount of energy or the higher remaining rate of energy. One of the first power supply path and the second power supply path is determined as a priority path for supplying power to the load at the initial startup of the power supply apparatus. It should be noted that the initial startup of the power supply device 10 includes both cases when the load starts to consume power or when the generator starts generating power.

  Hereinafter, an example of determining the priority route of the power supply route will be described with reference to FIG. Note that the average power consumption of the load, the pulse load is 42 W, and the specific configurations of the generator 100 and the power storage unit 106 are the same as described in (A).

  In this embodiment, a fuel cell is used as the generator 100. Since only about half of the fuel tank is prepared for the fuel cell, the capacity is about 24 Wh and the remaining rate is 50%. The power storage unit 106 was almost fully charged, had a capacity of 3.7 Wh, and the remaining rate (SOC: state of charge) was almost 100%. In the present embodiment, the higher energy remaining rate is set as the priority route for first supplying power to the load 112 such as at the time of start-up, so the second power supply route is the priority route here.

  When the remaining capacity of the fuel in the fuel cell and the state of charge of the power storage unit 106 are unclear, or when the control unit 110 determines that the remaining capacity of the fuel and the state of charge are equivalent, The control unit 110 may set a priority path for first supplying power to the load 112 as the second power supply path. After power is supplied from the second power supply path to the load 112 at the start of the power supply device 10, if the threshold value of the conversion efficiency for switching the power supply path or the threshold value of switching loss is exceeded, The control unit 110 performs switching control as described above.

  In addition, the control unit 110 detects that the fuel has been added to the fuel cell and the fuel tank has become full, or has detected that the fuel has been replaced with a new fuel cartridge, and the power supply device 10 is activated. The priority route for supplying power to the load 112 may be the first priority route.

  In addition, as shown in FIG. 5, when the output of the fuel cell is less than the rated output when power is supplied to the load 112 via the first power supply path, the control unit 110 performs charge control. As long as the output of the fuel cell does not exceed the rating, the unit 111 may be controlled to charge the power storage unit 106 with the output of the fuel cell via the charge control unit 111. However, when the conversion efficiency threshold for switching the power supply path or the threshold for switching loss is exceeded and the power supply path is switched, the control unit 110 operates the charge control unit 111. Is stopped and charging of the power storage unit 106 is stopped.

  In this way, in the power supply device 10 having the generator 100 and the voltage conversion unit 103103 that outputs the voltage by stepping up or down the input voltage and the power storage unit 106, the energy efficiency of the power supply device is reduced even when the output of the power supply device 10 is low. Thus, it is possible to provide the power supply apparatus 10 that can stably obtain power.

(D) Switching efficiency and switching of current supply path of voltage converter when load fluctuation is large Using FIG. 1, the switching efficiency of voltage converter and switching operation of current supply path when load fluctuation is large are concretely described. Explained.

  A PEFC-type fuel cell is prepared as the generator 100 for the load 112 with an average power consumption of the load 112 of 2.2 W (7.4 V, 0.3 A) and a pulse load of 18.5 W (about 2.0 msec). did. The fuel cell has a 5-series rated output of 2.5 W (3.5 V, 0.72 A).

  A power storage unit 106 was prepared by connecting two lithium ion secondary batteries having a capacity of 500 mAh and a nominal voltage of 3.7 V in series.

  A step-up circuit was manufactured using a step-up type switching regulator IC commercially available as the voltage conversion unit 103. The maximum value of the conversion efficiency was about 88% when the output current of the voltage conversion unit 103 was about 0.15 A. The efficiency when switching from the second power supply path to the first power supply path was 40%. The output current at this time was 10 mA or less.

Conversely, the conversion efficiency when switching from the first power supply path to the second power supply path was 30%.
The switching of the power supply path was controlled by the control unit 110 using an 8-bit microcomputer.

  Regarding the conversion efficiency of the voltage conversion unit 103, when the output current is 0.15 A, the conduction loss increases when the output current increases at the conversion efficiency of 88%. Therefore, when the current detection value by the current detection unit 105 exceeds 0.35 A, that is, the consumption current of the load 112 detected by the current detection unit 105, that is, the output current of the voltage conversion unit 103 is the maximum conversion efficiency of the voltage conversion unit 103. When the current value is 234% of the current value of 0.15 A, the switching unit is controlled so that the power supply to the load 112 becomes the first power supply path and the second power supply path. On the contrary, when the current detection value by the current detection unit 105 becomes 0.27 A or less, that is, the consumption current of the load 112 detected by the current detection unit 105, that is, the output current of the voltage conversion unit 103 is the conversion efficiency of the voltage conversion unit 103. The power supply to the load 112 is switched to the first power supply path when the current value is 180% of the current value of 0.15 A at the maximum value.

  When there is a pulse load, etc., temporary fluctuations in the load to suppress fluctuations due to output switching when temporarily crossing over the conversion efficiency and switching threshold of the load current power supply path On the other hand, although the power supply path is switched, the power supply path is maintained without returning to the previous state even after the load fluctuation is settled below the lower limit value of the power supply path switching. In the case of the load of the present embodiment, the load 112 that is longer than the pulse width time but continuously generates the pulse load is used. Therefore, when the pulse load occurs, the load 112 detected by the current detection unit 105 is detected. When the current consumption exceeds 0.35 A, the control unit 110 controls the switching unit so that the power supply to the load 112 becomes the first power supply path and the second power supply path. About 2.0 msec after detecting a current exceeding 35 A, the current consumption to the load 112 becomes 0.27 A or less, and the control unit 110 supplies power to the load 112 only in the first power supply path. However, the power supply to the load 112 is maintained using the first power supply path and the second power supply path. This is because a similar pulse load is generated again several hundred msec after the first pulse load, so that the occurrence of fluttering due to output switching is suppressed. Only after the state where the current consumption to the load 112 is 0.27 A or less continues for 1 second or longer, the control unit 110 starts the power supply to the load 112 from the state using the first power supply path and the second power supply path. Control is performed so that only the power supply path is used.

  A program was created to perform the control as described above, and the program was written to the microcomputer.

  In this way, in the power supply device 10 having the generator 100, the voltage conversion unit 103 that boosts or steps down the input voltage, and the power storage unit 106, even when the current consumption of the load 112 is small, the energy efficiency of the power supply device 10 Therefore, it is possible to provide a small power supply device 10 that eliminates the decrease in the above.

DESCRIPTION OF SYMBOLS 10: Power supply device 100: Generator 102: 1st switching part 103: Voltage conversion part 104: Voltage detection part 105: Current detection part 106: Power storage part 109: 2nd switching part 110: Control part 111: Charge control part 112: Load 201: First changeover switch 202: Diode 203: Inductor 204: Second changeover switch 205: Diode 206: Resistance voltage dividing circuit 207: Capacitor 208: Control circuit

Claims (5)

A first power supply path for supplying an output from the generator to a load via a voltage converter;
A second power supply path for supplying an output from the power storage unit to the load without passing through the voltage conversion unit;
A current detection unit for detecting current consumption of the load;
A controller that switches between the first power supply path and the second power supply path;
The voltage conversion unit changes conversion efficiency according to the consumption current,
The control unit switches to the first power supply path when the current detection unit detects the current consumption when the conversion efficiency is equal to or higher than an intermediate value between the lowest value and the highest value, and the current detection unit A power supply apparatus that switches to the second power supply path when detecting the consumption current when the current becomes lower than the intermediate value. The voltage conversion unit is configured to increase or decrease the voltage of the generator and supply the load to the load.
The voltage conversion unit includes: an inductor that charges or discharges the output from the generator as energy; and a switching element that switches between a charge state that charges the energy to the inductor and a discharge state that discharges the energy to the load. Have
The switching element has a switching loss that is a loss of the energy when switching the emission state of the energy.
The conversion efficiency is affected by the switching loss value and the current consumption,
2. The control unit according to claim 1, wherein the control unit switches to the second power supply path when the current detection unit detects the current consumption equivalent to the power consumption of the load that is lower than the switching loss value. The power supply described. In the voltage conversion unit, conduction loss increases in proportion to the consumption current,
The conversion efficiency decreases as the conduction loss increases.
The control unit is configured to detect the first power supply path and the second power supply when the current detection unit detects the current consumption that is 70% or more of the current consumption when the conversion efficiency reaches a maximum value. The power supply apparatus according to claim 1, wherein electric power is supplied from a path to the load.   The power generator according to any one of claims 1 to 3, wherein the generator is a fuel cell.   The control unit detects one of the generator and the power storage unit having a large remaining power capacity, and switches to the first power supply path when the remaining power capacity of the generator is large, and the power storage unit 5. The power supply device according to claim 1, wherein when the remaining power capacity of the power supply is large, the power supply device is switched to the second power supply path.

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