JP5829999B2 - Charger - Google Patents

Description

  The present invention relates to a charging device for charging a storage battery with electric power generated by a generator.

  The focus on renewable energy is increasing against the backdrop of reducing greenhouse gas emissions, rising fossil fuels, and nuclear accidents. Major renewable energy sources include sunlight, solar heat, wind power, hydropower, geothermal heat, biomass, and wave power.

  In general, electric power generated by renewable energy is used by charging a storage battery (see, for example, Patent Document 1). Power generation using renewable energy has the property that the power generation tends to become unstable due to temporal and environmental influences. For example, in solar power generation, the amount of power generation decreases or becomes zero when dark. In addition, power generation using renewable energy tends to be very small due to instability. By the way, if the storage battery is charged with a current out of the proper range, the life and reliability may be adversely affected. This tendency is particularly apparent in lead-acid batteries.

  When charging a lead storage battery with electric power generated by a low-power generator using renewable energy, control is generally performed in which a minute electric power is discarded without being charged.

JP 2010-81711 A

  However, it is uneconomical to throw away even very small electric power, which is electric power that should be charged.

  This invention is made | formed in view of such a condition, The objective is to provide the technique which charges efficiently the electric power generated with renewable energy, suppressing the burden to a storage battery.

  In order to solve the above problems, a charging device according to an aspect of the present invention is inserted into a capacitor that temporarily stores power generated by a generator using renewable energy, and a path between the capacitor and the storage battery. And a switch control circuit that turns on the switch when the voltage of the capacitor reaches an upper threshold voltage and turns off the switch when the voltage of the capacitor reaches the lower threshold voltage.

  According to this aspect, even if the generated power is weak, it is possible to charge the storage battery with a current within an appropriate charging range of the storage battery by temporarily storing it in the capacitor. Therefore, the generated power can be efficiently charged without waste while suppressing the burden on the storage battery.

  ADVANTAGE OF THE INVENTION According to this invention, the electric power generated with renewable energy can be charged efficiently, suppressing the burden on a storage battery.

It is a figure for demonstrating the charging device which should be compared with this invention. It is a figure for demonstrating the charging current in the case of charging a storage battery using the charging device of FIG. It is a figure for demonstrating the charging device which concerns on Embodiment 1 of this invention. FIG. 4 is a diagram for describing a configuration example of a switch control circuit of the charging device in FIG. 3. It is a figure which shows transition of the terminal voltage of the 2nd capacitor | condenser of FIG. It is a figure for demonstrating the charging current in the case of charging a storage battery using the charging device which concerns on Embodiment 1. FIG. It is a figure for demonstrating the charging device which concerns on Embodiment 2 of this invention.

  FIG. 1 is a diagram for explaining a charging device 20 to be compared with the present invention. The charging device 20 is a charging device for charging the storage battery 30 with the power generated by the generator 10 using renewable energy. In this specification, a low power generator is mainly assumed as the generator 10. Specifically, a generator that is strongly influenced by changes in the natural environment such as small-scale solar power generation, micro wind power generation, and micro hydro power generation and that has a small power generation amount P (W) is mainly assumed.

  In this specification, a lead storage battery is assumed as the storage battery 30. Lead storage batteries are less expensive than lithium ion storage batteries, nickel metal hydride storage batteries, and the like, and are widely used in applications where the installation space is small, although the energy density is inferior to lithium ion storage batteries. It is known that lead-acid batteries have an appropriate charging current range, and charging with a current outside the range leads to shortened battery life and reduced reliability.

  1, both ends of the generator 10 are connected to a positive input terminal and a negative input terminal of the charging device 20, respectively. The plus output terminal and minus output terminal of the charging device 20 are connected to the plus terminal and minus terminal of the storage battery 30, respectively.

  The charging device 20 includes a diode D1 and a first constant current circuit CI1. The diode D1 and the first constant current circuit CI1 are inserted in series in the positive path of the charging device 20. The diode D <b> 1 prevents a back flow from the storage battery 30 to the generator 10. Moreover, when the generator 10 is not a direct current generator like solar power generation but an alternating current generator like wind power generation, it also takes a rectifying action.

  The first constant current circuit CI1 controls to maintain the output current at a set constant current value. Here, control is performed so as to maintain the upper limit current value (hereinafter referred to as the appropriate upper limit current value) of the appropriate charging current range of the storage battery 30. There are various constant current circuits such as those using a regulator and those using a constant current diode, and any circuit can be used.

  The output current of the first constant current circuit CI1 is input to the storage battery 30. That is, constant current charging (CC charging) is performed.

  FIG. 2 is a diagram for explaining a charging current when charging the storage battery 30 using the charging device 20 of FIG. 1. The unchargeable area is an area where the generated voltage is less than the chargeable voltage (open voltage) of the storage battery 30, and the generated power in the unchargeable area is discarded without being charged.

  The improper charging area is an area where the generated voltage exceeds the chargeable voltage of the storage battery 30 but the generated current is less than the lower limit current value of the appropriate charging current range of the storage battery 30 (hereinafter referred to as the appropriate lower limit current value). . Although the storage battery 30 can be charged in the improper charging range, the life and reliability of the storage battery 30 are impaired. Therefore, if priority is given to the protection of the storage battery 30, charging should be stopped in the improper charging range.

  The appropriate charging area is an area in which the storage battery 30 is charged with a current in an appropriate charging current range of the storage battery 30. When a current exceeding the appropriate upper limit current value is output from the generator 10, the first constant current circuit CI1 limits the current to the appropriate upper limit current value. Therefore, even when the generated current exceeds the appropriate upper limit current value due to changes in the natural environment, no burden is generated on the storage battery 30.

  Since the output of the low-power generator using renewable energy is unstable in this way, a period during which a current outside the appropriate charging current range of the storage battery 30 is output occurs and a lot of energy loss occurs. Even if the generated power in the improper charging area is included in the charging target, the amount of charge corresponding to the area of the hatched area in FIG. 2 remains, and an energy loss corresponding to the area of the blank area occurs.

  FIG. 3 is a diagram for illustrating the charging device 20 according to Embodiment 1 of the present invention. The charging device 20 according to the first embodiment includes a diode D1, a first capacitor C1, a boost chopper 21, a first constant current circuit CI1, a second capacitor C2, a switch S1, a switch control circuit 22, and a second constant current circuit CI2. Including.

  The first capacitor C1 is connected between the positive path and the negative path of the charging device 20 at the subsequent stage of the diode D1. The first capacitor C1 temporarily stores the power generated by the generator 10.

  The step-up chopper 21 is provided at the subsequent stage of the first capacitor C <b> 1, and boosts the voltage of the first capacitor C <b> 1 to be higher than the chargeable voltage of the storage battery 30. As the step-up chopper 21, a general one using an inductor, a switch, and a diode can be used.

  The first constant current circuit CI1 is inserted in the plus path at the rear stage of the boost chopper 21. The first constant current circuit CI1 controls to maintain the output current at a set constant current value.

  The second capacitor C <b> 2 is connected between the positive path and the negative path of the charging device 20 at the subsequent stage of the boost chopper 21. The second capacitor C2 temporarily stores the electric power generated by the generator 10 that is input via the step-up chopper 21 and the first constant current circuit CI1.

  The switch S1 is inserted in the plus path downstream of the second capacitor C2. As the switch S1, a semiconductor switching element such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) or an IGBT (Insulated Gate Bipolar Transistor) or a relay can be used.

  The switch control circuit 22 performs on / off control of the switch S1 based on the voltage of the second capacitor C2. Specifically, the switch S1 is turned on when the voltage of the second capacitor C2 reaches the upper threshold voltage Vth1, and the switch S1 is turned off when the voltage of the second capacitor C2 reaches the lower threshold voltage Vth2.

  For example, the charge end voltage of the second capacitor C2 can be used as the upper threshold voltage Vth1. The lower limit threshold voltage Vth2 is set to a voltage at which the charging current to the storage battery 30 can maintain at least an appropriate lower limit current value.

  The second constant current circuit CI2 is inserted in the plus path downstream of the switch S1. The second constant current circuit CI2 controls to maintain the output current at a set constant current value. In the present embodiment, control is performed so as to maintain the appropriate upper limit current value. Note that another current limiting circuit (element) may be used instead of the constant current circuit. For example, a current limiting resistor for limiting the charging current to the storage battery 30 to an appropriate upper limit current value or less may be used. The charging current to the storage battery 30 is controlled by the switch control circuit 22 so as not to decrease below the appropriate lower limit current value. Therefore, even if a current limiting resistor that limits the upper limit of the charging current is used instead of the constant current circuit, the charging current can be kept within the appropriate charging current range.

  FIG. 4 is a diagram for explaining a configuration example of the switch control circuit 22 of the charging device 20 of FIG. The switch control circuit 22 includes a first comparator CP 1, a second comparator CP 2, and a latch circuit 23.

  The first comparator CP1 compares the terminal voltage of the second capacitor C2 with the upper threshold voltage Vth1, and outputs a signal of a significant level to the latch circuit 23 when the terminal voltage of the second capacitor C2 is equal to or higher than the upper threshold voltage Vth1. The second comparator CP2 compares the terminal voltage of the second capacitor C2 with the lower threshold voltage Vth2, and outputs a signal of a significant level to the latch circuit 23 when the terminal voltage of the second capacitor C2 is lower than or equal to the lower threshold voltage Vth2.

  The significance level may be a high level or a low level. The designer can choose arbitrarily.

  The latch circuit 23 switches the level of the control signal output to the switch S1 based on the output signals of the first comparator CP1 and the second comparator CP2. Specifically, when receiving a signal of a significant level from the first comparator CP1, the latch circuit 23 outputs a control signal for turning on the switch S1 (a high level signal when an n-channel MOSFET is used). Then, the output level is maintained until a significant level signal is received from the second comparator CP2.

  When the latch circuit 23 next receives a signal of a significant level from the second comparator CP2, the latch circuit 23 outputs a control signal for turning off the switch S1 (a low level signal when an n-channel MOSFET is used). That is, the output level is inverted with the reception of a significant level signal from the second comparator CP2 as a trigger. Then, the output level is maintained until a significant level signal is received from the first comparator CP1.

  When the latch circuit 23 next receives a signal of a significant level from the first comparator CP1, the latch circuit 23 outputs a control signal for turning on the switch S1. That is, the output level is inverted with the reception of a significant level signal from the first comparator CP1 as a trigger. Then, the output level is maintained until a significant level signal is received from the second comparator CP2.

  Those skilled in the art can easily generate a latch circuit that performs such a toggle operation by combining a plurality of logic gates.

  FIG. 5 is a diagram showing the transition of the terminal voltage of the second capacitor C2 of FIG. FIG. 5 is based on the premise that a minute electric power is being generated, that is, a minute current that is less than the appropriate lower limit current value is being output to the charging device 20.

  When the switch S1 is off, the second capacitor C2 is in a charged state, and its terminal voltage increases. When the terminal voltage of the second capacitor C2 reaches the upper threshold voltage Vth1, the switch S1 is turned on and the second capacitor C2 is discharged. As a result, the terminal voltage of the second capacitor C2 decreases, and when the terminal voltage of the capacitor C2 reaches the lower limit threshold voltage Vth2, the switch S1 is turned off. As a result, the second capacitor C2 is charged again.

  By repeating such a charge / discharge cycle, even if the generated current is a minute current that is less than the appropriate lower limit current value, the minute current is stored in the second capacitor C2, so that the storage battery can be used with a current that is equal to or greater than the appropriate lower limit current value. 30 can be charged.

  The charging time for the second capacitor C2 varies according to the amount of power generated by the generator 10. For example, when the power generation amount decreases, the charging time for the second capacitor C2 is extended (see the charging cycle t and the charging cycle t 'in FIG. 5). The charging time to the storage battery 30 (that is, the discharging time of the second capacitor C2) is basically constant, although it varies somewhat depending on the amount of power generation.

  Thus, by changing the charging cycle to the storage battery 30 according to the change in the amount of power generation, the current-time product of each charging cycle can be made constant, and the charging current to the storage battery 30 is prevented from falling below the appropriate lower limit current value. it can. The switch control circuit 22 changes the duty ratio of the switch S1 in accordance with the change in the amount of power generation in order to make the current-time product of each charging cycle constant. Specifically, when the power generation amount decreases, the duty ratio is lowered (narrows the ON width), and when the power generation amount increases, the duty ratio is increased (the ON width is widened).

  FIG. 6 is a diagram for describing a charging current when charging storage battery 30 using charging device 20 according to the first embodiment. Comparing FIG. 6 and FIG. 2, in FIG. 6, even when the generated voltage of the generator 10 is less than the chargeable voltage of the storage battery 30 and when the generated current is less than the appropriate lower limit current value, It turns out that it can charge with an electric current. That is, proper charging is possible over the entire range of the generated current value.

  FIG. 6 shows an example in which the storage battery 30 is CC charged with an appropriate upper limit current value. The constant current value for charging is not limited to the appropriate upper limit current value, and can be set to any value as long as the value is within the appropriate charging current range.

  Comparing FIG. 6 and FIG. 2, it can be seen that the area of the shaded region indicating the charge amount is larger in FIG. 6, and the charge amount is greatly improved. Further, in FIG. 6, there is no region that is charged at a value less than the appropriate lower limit current value, and it is possible to avoid that the life and reliability of the storage battery 30 are impaired by the charging current.

  As described above, according to the first embodiment, even if the power generated by the generator 10 is weak, the voltage can be boosted to a chargeable voltage of the storage battery 30 and the storage battery 30 can be charged with a current in an appropriate current range. The generated power is temporarily stored in the second capacitor C2. As a result, the generated power can be efficiently charged without waste, and the life and reliability of the storage battery 30 can be prevented from being impaired by the charging current. Further, since the switch control circuit 22 can be simply configured without using a microcomputer, an increase in cost can be suppressed.

  Such a charging system is suitable for a generator using renewable energy that includes a period in which the output is unstable and the output is weak. It is particularly suitable for micro-generators using sunlight, wind power, hydropower, etc.

  FIG. 7 is a diagram for illustrating a charging device 20 according to Embodiment 2 of the present invention. The charging device 20 according to the second embodiment has a configuration in which the first capacitor C1 and the boost chopper 21 are removed from the charging device 20 according to the first embodiment shown in FIG. A drive power supply is required to operate the boost chopper 21. In the case of a generator that generates many extremely weak power generation periods or non-power generation periods, the power consumed by the boost chopper 21 may be larger than the power stored in the first capacitor C1.

  In the case of such a generator 10, it is more efficient to throw away the generated power that does not satisfy the chargeable voltage of the storage battery 30 without using the boost chopper 21. The charging device 20 according to the second embodiment is suitable for such a type of generator 10. Similarly to the first embodiment, the charging device 20 according to the second embodiment also stores the generated power in the second capacitor C2 so that the storage battery 30 can be charged with a current in an appropriate current range. Therefore, the generated power can be efficiently charged without waste without burdening the storage battery 30.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  10 generator, 20 charging device, 30 storage battery, D1 diode, CI1 first constant current circuit, C1 first capacitor, C2 second capacitor, S1 switch, CI2 second constant current circuit, 21 step-up chopper, 22 switch control circuit, CP1 first comparator, CP2 second comparator, 23 latch circuit.

Claims (1)

A first capacitor for temporarily storing power generated by a generator using renewable energy;
A step-up chopper that boosts the voltage of the first capacitor to a chargeable voltage or higher of the lead-acid battery;
A first constant current circuit provided downstream of the boost chopper;
A second capacitor for temporarily storing the electric power generated by the generator, which is input through the boost chopper and the first constant current circuit;
A switch provided at a subsequent stage of the first constant current circuit and the second capacitor;
A second constant current circuit provided at a subsequent stage of the switch and outputting a constant current to the lead acid battery;
A switch control circuit that turns on the switch when the voltage of the second capacitor reaches an upper threshold voltage, and turns off the switch when the voltage of the second capacitor reaches the lower threshold voltage;
With
The switch control circuit includes:
A first comparator that outputs a signal of a significant level when the voltage of the second capacitor is equal to or higher than the upper threshold voltage;
A second comparator that outputs a signal of a significant level when the voltage of the second capacitor is equal to or lower than the lower threshold voltage;
A latch circuit that switches a level of a control signal output to the switch based on output signals of the first comparator and the second comparator;
Including
The upper threshold voltage is set to a charge end voltage of the second capacitor,
The lower limit threshold voltage is set to a voltage at which a charging current to the lead storage battery can maintain at least an appropriate lower limit current value .

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