JP2006340517A - Power supply unit and power supply control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply unit capable of significantly utilizing power stored in a secondary battery. <P>SOLUTION: This power supply unit includes: the secondary battery ( secondary battery 30) for outputting DC power; a switching device (switching circuit 40f) for converting the DC power supplied from the secondary battery into AC power; a controller (reference voltage determination circuit 40c, triangular wave generation circuit 40d, reference voltage generation circuit 40e, PWM circuit 40g, compensation circuit 40h, subtraction circuit 40i) for controlling a voltage of the AC power outputted from the switching device so as to be a determined target value. The controller reduces a target value if the remaining level of the secondary battery is lower than a predetermined level. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply device and a power supply control method.

  For example, in a power supply device such as an uninterruptible power supply device, as shown in Patent Document 1, DC power stored in a secondary battery is converted into AC power by an inverter and supplied to a load when a commercial power supply fails. It is configured.

  FIG. 6 is a block diagram showing a configuration of a conventional power supply apparatus. As shown in this figure, the conventional power supply device includes a secondary battery 1a, a triangular wave generation circuit 1b, a reference voltage generation circuit 1c, a switching circuit 1d, a PWM (Pulse Width Modulation) circuit 1e, a compensation circuit 1f, a subtraction circuit 1g, It is comprised by the inductor 1h, the capacitor 1i, and the load 1j.

  Here, the secondary battery 1a is composed of, for example, a lead storage battery, and is normally charged by a commercial power source (not shown), and supplies DC power to the switching circuit 1d at the time of a power failure.

  The triangular wave generating circuit 1b generates a triangular wave for PWM and supplies it to the PWM circuit 1e. The reference voltage generation circuit 1c generates a reference voltage for determining the output voltage Vo and supplies it to the subtraction circuit 1g. The switching circuit 1d switches the DC power from the secondary battery 1a in accordance with the drive signal supplied from the PWM circuit 1e, converts it to AC power, and outputs it.

  The PWM circuit 1e compares the sine wave supplied from the compensation circuit 1f with the triangular wave output from the triangular wave generation circuit 1b, generates a switching signal corresponding to the magnitude, and supplies the switching signal to the switching circuit 1d. The compensation circuit 1f has a predetermined transfer function, and adjusts the output signal of the subtraction circuit 1g so that the control is properly performed. Inductor 1h and capacitor 1i constitute a low-pass filter, which attenuates the harmonic signal contained in the output signal from switching circuit 1d. The load 1j is, for example, a server computer or the like and is a target for supplying AC power.

  In the conventional power supply apparatus as described above, the following relationship (1) is established between the DC voltage Vd of the secondary battery 1a and the AC output voltage Vo. However, M is a modulation rate, Vs is the amplitude of the sine wave output from the compensation circuit 1f, and Vt is the amplitude of the triangular wave output from the triangular wave generation circuit 1b. Further, M = Vs / Vt.

  Vo∝M · Vd (Formula 1)

  Therefore, the AC output voltage Vo can be maintained at a constant voltage by controlling the modulation factor M with respect to the fluctuation of the DC voltage Vd.

  FIG. 7 is a diagram illustrating temporal changes in the triangular wave Vt, the sine wave Vs, and the output Vp of the switching circuit 1d. FIG. 7A shows a case where the modulation factor M ≦ 1. The horizontal axis indicates time, and the vertical axis indicates voltage. The upper diagram in FIG. 7A shows the sine wave Vs and the triangular wave Vt, and the lower diagram shows the output Vp of the switching circuit 1d. As shown in FIG. 7A, when the modulation factor M ≦ 1, the maximum amplitude of the triangular wave Vt ≧ the maximum amplitude of the sine wave Vs, and the output Vp of the switching circuit 1d depends on the amplitude of the sine wave Vs. It is a signal (PWM signal) whose pulse width increases or decreases.

  On the other hand, FIG. 7B shows a case where M> 1. In this case, the maximum amplitude of the triangular wave Vt <the maximum amplitude of the sine wave Vs. The output Vp of the switching circuit 1d maintains a high pulse state near the positive maximum value of the sine wave output, and maintains a low state near the negative maximum value. That is, the waveform of the output Vp is distorted in the vicinity thereof. In such a state, the output voltage Vo includes a low-order harmonic, and the influence on the load 1j cannot be ignored. Further, in this case, the switching circuit 1d continues to maintain the on or off state, and thus is out of control. As a result, for example, the voltage supplied to the load may deviate from the normal range. Further, when performing parallel operation by connecting a plurality of power supply devices shown in FIG. 6, it is assumed that load sharing is not appropriate when the control is lost.

  Therefore, the modulation factor M needs to be controlled in the range of M ≦ 1. For this reason, in the conventional power supply device, when the DC voltage Vd drops below a certain voltage, the operation of the device is stopped in order to avoid the above-mentioned problem due to the range of M> 1. is doing.

Japanese Patent Laid-Open No. 05-146099 (abstract, claim)

  By the way, if the control of the device is stopped when the DC voltage Vd drops below a certain level in this way, the operation is stopped with sufficient power remaining in the secondary battery. Therefore, there is a problem that the power of the secondary battery cannot be fully utilized.

  In addition, since the operation is stopped without fully using the power of the secondary battery, in order to ensure the operation time, it is necessary to use a secondary battery having a large capacity, which increases the cost. There is a problem that the size of the apparatus is increased.

  The present invention has been made based on the above circumstances, and an object of the present invention is to provide a power supply device and a power supply control method capable of fully utilizing the power stored in the secondary battery. Is.

  In order to achieve the above-described object, the power supply device of the present invention outputs a secondary battery that outputs DC power, conversion means that converts DC power supplied from the secondary battery into AC power, and output from the conversion means. Control means for controlling the voltage of the AC power to be a predetermined target value, and the control means decreases the target value when the remaining amount of the secondary battery becomes less than the predetermined amount. Like that.

  For this reason, the power supply device which can fully utilize the electric power stored in the secondary battery can be provided.

  In addition to the above-described invention, the power supply device according to another aspect of the invention may be configured such that when the remaining power of the secondary battery is equal to or greater than a predetermined amount, the control unit keeps the target value constant and falls below the predetermined amount. In order to reduce the target value. For this reason, when the remaining amount of power of the secondary battery is sufficient, AC power with a constant voltage can be output, and when the remaining amount is low, the voltage can be decreased to output without distortion. At the same time, the electric power stored in the secondary battery can be used effectively.

  Further, in addition to the above-described invention, the power supply device according to another aspect of the invention may convert the control unit when the remaining amount of power of the secondary battery is smaller than another predetermined amount that is smaller than the predetermined amount. The output of AC power from the means is stopped. For this reason, it is possible to prevent the output voltage from being distorted and to effectively use the power stored in the secondary battery.

  In addition to the above-described invention, the power supply device of another invention may be configured such that the control means sets the target value to the remaining amount of the secondary battery when the remaining amount of power of the secondary battery is less than a predetermined amount. It is made to decrease gradually according to. For this reason, by gradually decreasing the output voltage, it is possible to prevent the output voltage from being distorted and to effectively use the power stored in the secondary battery.

  In addition to the above-described invention, the power supply device of another invention may be configured such that the control means sets the target value to the remaining amount of the secondary battery when the remaining amount of power of the secondary battery is less than a predetermined amount. It is made to decrease in steps according to. For this reason, by decreasing the output voltage stepwise, it is possible to prevent the output voltage from being distorted and to effectively use the power stored in the secondary battery.

  In addition to the above-described invention, the power supply device according to another aspect of the invention may be configured such that when the remaining power of the secondary battery is less than a predetermined amount, the control unit rapidly increases the target value to a predetermined value. I try to decrease. For this reason, by rapidly decreasing the output voltage, it is possible to prevent the output voltage from being distorted and to effectively use the power stored in the secondary battery.

  Further, the power supply control method of the present invention converts the DC power supplied from the secondary battery into AC power, and controls so that the voltage of the AC power obtained by the conversion becomes a predetermined target value. When the remaining amount of power becomes less than a predetermined amount, the target value is decreased.

  For this reason, the power supply control method which can fully utilize the electric power stored in the secondary battery can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the power supply device and power supply control method which can fully utilize the electric power stored in the secondary battery can be provided.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration example of a power supply device according to an embodiment of the present invention. As shown in this figure, the power supply device according to the embodiment of the present invention includes a converter circuit 20, a secondary battery 30, an inverter circuit 40, and switches 50 and 60 as main components. A commercial power supply 10 is connected to the switch 50 and the converter circuit 20, and a load 70 is connected to the switches 50 and 60.

  Here, the commercial power source 10 is a power source that supplies AC power such as 100 V or 200 V, for example. Hereinafter, the AC voltage output from the commercial power supply 10 is referred to as Vac.

  The converter circuit 20 is a circuit that converts AC power supplied from the commercial power supply 10 into DC power, and includes, for example, a rectifier circuit.

  The secondary battery 30 is composed of, for example, a lead storage battery, and is charged with DC power output from the converter circuit 20 during normal times, and supplies DC power to the inverter circuit 40 during a power failure. Hereinafter, the DC voltage output from the secondary battery 30 is referred to as Vd.

  The inverter circuit 40 converts the DC power supplied from the secondary battery 30 into AC power and outputs the AC power. A detailed configuration example of the inverter circuit 40 will be described later with reference to FIG. In the following, the AC voltage output from the inverter circuit 40 is Vo.

  The switches 50 and 60 are controlled by a control circuit (not shown). Normally, the switch 50 is turned on, the switch 60 is turned off, and AC power from the commercial power supply 10 is supplied to the load 70. The At the time of a power failure, the switch 50 is turned off, the switch 60 is turned on, and AC power from the inverter circuit 50 is supplied to the load 70.

  The load 70 is configured by, for example, a server computer or the like, and is supplied with AC power from the commercial power supply 10 during normal times, and is supplied with AC power from the inverter circuit 40 during a power failure. As a result, the operation can be continued even during a power failure. In the following description, the AC voltage applied to the load 70 is Vl.

  FIG. 2 is a diagram showing a detailed configuration example of the inverter circuit 40 shown in FIG. As shown in this figure, the inverter circuit 40 includes input terminals 40a and 40b, a reference voltage determination circuit 40c, a triangular wave generation circuit 40d, a reference voltage generation circuit 40e, a switching circuit 40f, a PWM circuit 40g, a compensation circuit 40h, and a subtraction circuit 40i. The inductor 40j, the capacitor 40k, and the output terminals 40l and 40m are the main components.

  Here, the input terminals 40 a and 40 b are connected to the plus terminal and the minus terminal of the secondary battery 30, respectively, and are connected to the plus side output terminal and the minus side output terminal of the converter circuit 20, respectively.

  The reference voltage determination circuit 40c as a part of the control unit generates a reference voltage corresponding to the output voltage Vd of the secondary battery 30 when power supply from the secondary battery 30 is started in the event of a power failure. Level signal Vr0 is supplied to the reference voltage generation circuit 40e.

  FIG. 3A is a diagram for explaining the operation of the reference voltage determination circuit 40c. In this figure, the horizontal axis indicates the DC voltage Vd input to the reference voltage determination circuit 40c. The vertical axis represents the level signal Vr0 output from the reference voltage determination circuit 40c. As shown in this figure, when the voltage input to the reference voltage determination circuit 40c is equal to or higher than the first threshold E1 as a predetermined amount, the level of the output signal is “1” and constant. In addition, when the first threshold value E1 or less is reached, the level of the output signal decreases according to the input voltage. When the voltage falls below the second threshold value E2 as another predetermined amount, the control circuit (not shown) stops the operation of the switching circuit 40f and stops the supply of AC power.

  As the reference voltage determination circuit 40c, for example, the DC voltage Vd is A / D (Analog to Digital) converted and input as digital data. Then, a table indicating the correspondence relationship between the value of the digital data and the output signal may be prepared in advance, and a value corresponding to the input digital data may be output. In addition, the circuit can be configured as an analog circuit using an operational amplifier or the like, for example.

  The triangular wave generation circuit 40d generates a triangular wave for PWM (see FIG. 7) and supplies it to the PWM circuit 40g. In the following, the triangular wave is represented by Vt.

  The reference voltage generation circuit 40e generates and outputs a reference voltage Vr as a sine wave signal corresponding to the level signal Vr0 output from the reference voltage determination circuit 40c. Specifically, when the signal level of the level signal Vr0 is “1”, a reference voltage for outputting the rated voltage is output, and when the signal level is “0.9”, the rated voltage is output. A reference voltage for outputting 90% of the voltage is output.

  The switching circuit 40f as conversion means performs a switching operation in accordance with the drive signal supplied from the PWM circuit 40g, converts DC power to AC power, and outputs the AC power.

  The PWM circuit 40g as a part of the control means compares the triangular wave Vt output from the triangular wave generation circuit 40d with the sine wave Vs output from the compensation circuit 40h. For example, when the triangular wave Vt ≦ sine wave Vs, Outputs a high level signal, and outputs a low level signal when triangular wave Vt> sine wave Vs. The signal output from the PWM circuit 40g in this way is supplied as a drive signal to the switching circuit 40f.

  The compensation circuit 40h adjusts the characteristic of the control system to a desired characteristic by applying compensation having a predetermined transfer function to the output signal of the subtraction circuit 40i.

  The subtraction circuit 40i outputs the result of subtracting the output voltage Vo from the output Vr of the reference voltage generation circuit 40e to the compensation circuit 40h.

  The inductor 40j and the capacitor 40k constitute a low-pass filter, and the output voltage waveform becomes close to a sine wave by attenuating the harmonic component included in the PWM signal output from the switching circuit 40f. .

  The output terminals 40l and 40m are connected to the switch 60 and the load 70.

  Next, the operation of the above embodiment will be described.

  During normal operation, the switch 50 is turned on, and the switch 60 is turned off. Further, the operation of the inverter circuit 40 is stopped. As a result, AC power from the commercial power supply 10 is supplied to the load 70. At this time, since the converter circuit 20 is in an operating state, a part of the AC power supplied from the commercial power supply 10 is converted into DC power, and the secondary battery 30 is charged.

  In such an operating state, when a power failure occurs, the inverter circuit 40 starts operating. Specifically, the reference voltage determination circuit 40c receives the DC voltage Vd supplied from the secondary battery 30 and outputs a value corresponding to the table shown in FIG. In the present example, since the secondary battery 30 is unused and in a fully charged state, a value sufficiently larger than the first threshold value E1 is output as the DC voltage Vd. "1" is output from the circuit 40c.

  The reference voltage generation circuit 40e generates and outputs a reference voltage corresponding to the output signal Vr0 from the reference voltage determination circuit 40c. Specifically, when the output of the reference voltage determination circuit 40 c is “1”, a reference voltage (sine wave) corresponding to the rated voltage (for example, 100 V) of the commercial power supply 10 is output. When the output of the reference voltage determination circuit 40c is “0.9”, a reference voltage corresponding to a voltage of 90% of the rated voltage (for example, 90V) is output.

  The subtraction circuit 40i outputs a value obtained by subtracting the output voltage Vo from the reference voltage Vr from the reference voltage generation circuit 40e. The compensation circuit 40h performs compensation having a predetermined transfer function on the signal output from the subtraction circuit 40i, and outputs the obtained signal as a sine wave signal Vs.

  The PWM circuit 40g compares the triangular wave signal Vt output from the triangular wave generation circuit 40d with the sine wave signal Vs output from the compensation circuit 40h, and as shown in the upper diagram of FIG. 7A, the triangular wave Vt In the case of ≦ sine wave Vs, a high level signal is output, and in the case of triangular wave Vt> sine wave Vs, a low level signal is output.

  The switching circuit 40f switches the DC power output from the secondary battery 30 based on the drive signal supplied from the PWM circuit 40g. As a result, a PWM signal as shown in the lower part of FIG. 7A is output.

  The harmonic component of the PWM signal output from the switching circuit 40f is attenuated by a low-pass filter including the inductor 40j and the capacitor 40k. As a result, a signal close to a sine wave signal is output from the low-pass filter.

  The AC voltage Vo output from the low-pass filter is supplied to the subtraction circuit 40i, and a difference from the reference voltage Vr output from the reference voltage generation circuit 40e is calculated. Since the compensation circuit 40h and the PWM circuit 40g control the output voltage Vo so as to cancel the difference, as a result, the output voltage Vo becomes substantially equal to the rated voltage of the commercial power supply 10.

  When the output of AC power from the inverter circuit 40 is started, a control circuit (not shown) turns off the switch 50 and turns on the switch 60. As a result, AC power output from the inverter circuit 40 is supplied to the load 70. Since the time from when the commercial power supply 10 is cut off to when the power supply from the inverter circuit 40 is started is set to a sufficiently short time, the load 70 operates without causing a malfunction or the like. continue.

  When the power failure state continues, the supply of power from the secondary battery 30 continues. The secondary battery 30 has a capacity of current (electric power) that can be continuously output, for example, 40 Ah (a current of 40 amperes can be output continuously for one hour), and the remaining capacity of the electric power decreases. The output voltage decreases. For example, in the case of a lead-acid battery, the voltage per cell is 2 V when fully charged, for example, but decreases to, for example, about 1.6 V to 1.7 V when the remaining amount decreases. .

  As a result, for example, if the DC voltage Vd becomes equal to or lower than the first threshold value E1, the level signal Vr0 output from the reference voltage determination circuit 40c decreases in accordance with the DC voltage Vd. The first threshold value E1 is, for example, a voltage at which the modulation factor M is close to “1” (for example, a voltage at which M = 0.99).

  When the value of the level signal Vr0 from the reference voltage determination circuit 40c decreases from “1”, the reference voltage Vr output from the reference voltage generation circuit 40e also decreases according to the level signal. For example, when the value of the level signal Vr0 becomes “0.95”, the reference voltage Vr output from the reference voltage generation circuit 40e is also a value corresponding to the output voltage Vo of 95% of the rating. As a result, the output voltage Vo of the inverter circuit 40 is a voltage that is 95% of the rated voltage of the commercial power supply 10.

  When the DC voltage Vd is equal to or lower than the first threshold value E1 at which the modulation factor M is close to “1”, the output voltage Vo is distorted as shown in FIG. However, in the embodiment of the present invention, when the DC voltage Vd becomes equal to or lower than the first threshold value E1, the output voltage Vo is controlled so as to decrease according to the DC voltage Vd. For this reason, since the modulation factor M changes without becoming “1” or more, a distortion waveform is not output.

  By the way, as the quality of the commercial power source 10, about plus or minus 10% of the rated voltage is allowed. Therefore, the load 70 is also designed to operate normally even when the voltage of the commercial power supply fluctuates within the range. In the embodiment of the present invention, as shown in FIG. 3A, the output voltage Vo decreases to about 90% of the rating at maximum, but this is within an allowable range. For this reason, even if the remaining capacity of the secondary battery 30 decreases and the output voltage Vo of the inverter circuit 40 decreases, the load 70 can operate normally.

  When the power failure state continues further, the remaining amount of the secondary battery 30 decreases, and the DC voltage Vd becomes equal to or lower than E2, which is the second threshold value. Here, for example, E2 is set to the lowest voltage at which the secondary battery 30 is not overdischarged. Specifically, in the case of a lead storage battery, the voltage per cell is set to a voltage that is about 1.6 V (for example, in the case of a lead storage battery with an output of 12 V, 9.6 V (= 1.6 × 6 )). When the DC voltage Vd becomes equal to or lower than the second threshold value E2, a control circuit (not shown) detects this and stops the operation of the switching circuit 40f. As a result, the supply of AC power to the load 70 is stopped. Note that, when the DC voltage Vd becomes equal to or lower than the second threshold value E2, the secondary battery 30 can be prevented from being overdischarged by stopping the operation of the switching circuit 40f.

  FIG. 3B shows the relationship between the DC voltage Vd and the output voltage Vo. As shown in this figure, when the relationship between the DC voltage Vd and the first threshold value E1 is Vd ≧ E1, the output voltage Vo is the rated voltage Vn. When E2 <Vd <E1, the output voltage Vo decreases from the rated voltage Vn to Vn × 0.9 according to the DC voltage Vd. Furthermore, when Vd ≦ E2, the operation of the inverter circuit 40 is stopped, and the secondary battery 30 is prevented from being overdischarged.

  Conventionally, as shown in FIG. 4, when the modulation factor M reaches the first threshold value E1 that is substantially equal to “1”, the inverter circuit is stopped in order to prevent the distortion wave from being output. It was like that. For this reason, the inverter circuit is stopped in a state where the electric power stored in the secondary battery is not sufficiently used. On the other hand, in the embodiment of the present invention, since the operation can be continued up to the second threshold value E2, the electric power stored in the secondary battery 30 can be fully utilized.

  As described above, in the embodiment of the present invention, when the DC voltage Vd of the secondary battery 30 is equal to or lower than the first threshold value E1, the output voltage Vo is decreased according to the DC voltage Vd. I made it. For this reason, the range in which the output voltage Vo is not distorted can be expanded, and the power stored in the secondary battery 30 can be fully utilized.

  As a result, when the secondary battery 30 having the same capacity is used, the power supply time to the load 70 can be extended as compared with the conventional case. For example, when a lead storage battery is used as the secondary battery 30, the operation stop voltage, which is normally set to about 1.7 V, is reduced to around 1.6 V, which is overdischarged. %, The operating time can be extended. Further, in the case of the same power supply time, by reducing the capacity of the secondary battery 30, it is possible to reduce the manufacturing cost of the device and reduce the size of the entire device.

  Further, in the embodiment of the present invention, the range of the output voltage of the secondary battery 30 in which the distortion of the output voltage Vo does not occur, that is, the range where the control is reliably performed can be expanded. For this reason, when performing operation by connecting the power supply devices according to the embodiments of the present invention in parallel, it is possible to reliably perform the parallel operation in a wide range of the voltage of the secondary battery 30.

  Further, for example, when the power supply apparatus is set to a double rating (for example, 200 V and 220 V), generally, the range in which 220 V can operate without distortion is narrower than 200 V. However, if the embodiment of the present invention is applied, the range can be widened by operating at a reduced voltage.

  The above embodiment is merely an example, and there are various other modified embodiments. For example, in the above-described embodiment, the description has been given by taking as an example the power supply device of the constant commercial power supply system that normally supplies power from the commercial power supply 10 to the load 70 and charges the secondary battery 30. It is also possible to apply the present invention to a constant inverter type power supply device that always supplies the output from the power supply 70 to the load 70. In that case, during normal operation, the secondary battery 30 is charged by the output from the converter circuit 20 and power is supplied from the inverter circuit 40 to the load 70. Then, when a power failure occurs, the operation of the converter circuit 20 may be stopped and power supply from the inverter circuit 40 to the load 70 may be continuously performed.

  In the above embodiment, when the output voltage Vd of the secondary battery 30 is equal to or lower than the first threshold value E1, the output voltage Vo is linearly decreased according to the voltage of the secondary battery 30. I made it. However, in addition to this, for example, as shown in FIG. 5 (A), it may be decreased in a stepwise manner, or as shown in FIG. 5 (B), it may be decreased rapidly. As shown in FIG. 5B, when the voltage is rapidly decreased, the output voltage Vo is rapidly decreased. Therefore, a stress may be applied to the load 70. Therefore, it is preferable to decrease the voltage gently if possible.

  In the above embodiment, the case where a lead storage battery is used as the secondary battery 30 has been described as an example. However, other secondary batteries such as a nickel cadmium battery, a nickel hydride battery, and a lithium battery are used. It is also possible to use it. In some cases, a primary battery may be used.

  In the above embodiment, the first threshold value E1 is a voltage at which the modulation factor M is close to “1”, but may be a voltage other than this. For example, the voltage at which the modulation factor M becomes “0.9” may be used. Note that the second threshold value E2 needs to be set in a range in which the secondary battery 30 is not overdischarged in order to prevent the secondary battery 30 from being deteriorated.

  Further, in the above embodiment, the output voltage Vo at the second threshold value E2 is set to 90% of the rated voltage, but other than this, for example, it may be 95% or 85%. May be. It may be in a range where the load 70 operates normally.

  Further, the circuit configurations of the above embodiments are merely examples, and it goes without saying that the present invention is not limited only to such cases.

  The power supply device of the present invention can be used for an uninterruptible power supply device having a secondary battery.

It is a block diagram which shows the structural example of the power supply device which concerns on embodiment of this invention. It is a block diagram which shows the structural example of the inverter circuit shown in FIG. (A) is a figure which shows the input output characteristic of the reference voltage determination circuit shown in FIG. 2, (B) is a figure which shows the relationship between a DC voltage and an output voltage. It is a figure which shows the relationship between the DC voltage and output voltage of the conventional power supply device. FIGS. 3A and 3B are diagrams illustrating other input / output characteristics of the reference voltage determination circuit illustrated in FIG. 2, in which FIG. 2A illustrates a case where the output voltage decreases stepwise, and FIG. It is a structural example of the power supply device in the past. FIG. 7 is a diagram illustrating an operation of the conventional power supply device illustrated in FIG. 6, where (A) illustrates an operation when the modulation factor M ≦ 1, and (B) illustrates an operation when the modulation factor M> 1.

Explanation of symbols

  30 secondary battery, 40 inverter circuit, 40c reference voltage determination circuit (part of control means), 40d triangular wave generation circuit (part of control means), 40e reference voltage generation circuit (part of control means), 40f switching circuit (Power conversion means), 40g PWM circuit (part of control means), 40h compensation circuit (part of control circuit), 40i subtraction circuit (part of control circuit), 70 load

Claims (7)

A secondary battery that outputs DC power;
Conversion means for converting DC power supplied from the secondary battery into AC power;
Control means for controlling the voltage of the AC power output from the conversion means to be a predetermined target value,
The power supply apparatus according to claim 1, wherein the control unit decreases the target value when the remaining amount of the secondary battery is less than a predetermined amount.   The control means is configured to keep the target value constant when the remaining amount of power of the secondary battery is equal to or greater than the predetermined amount, and to decrease the target value when the remaining amount is equal to or less than the predetermined amount. The power supply device according to claim 1.   The control means stops output of AC power from the conversion means when the remaining amount of power of the secondary battery becomes smaller than another predetermined amount that is smaller than the predetermined amount. The power supply device according to claim 2.   The control means is configured to gradually decrease the target value in accordance with the remaining amount of the secondary battery when the remaining amount of power of the secondary battery is less than a predetermined amount. Item 1. The power supply device according to Item 1.   The control means reduces the target value stepwise in accordance with the remaining amount of the secondary battery when the remaining amount of power of the secondary battery is less than a predetermined amount. The power supply device according to claim 1.   2. The power supply device according to claim 1, wherein the control unit rapidly reduces the target value to a predetermined value when a remaining amount of power of the secondary battery becomes smaller than a predetermined amount. . Converts DC power supplied from the secondary battery into AC power,
Control the voltage of the AC power obtained by the conversion to a predetermined target value,
A power control method, wherein the target value is decreased when the remaining amount of power of the secondary battery is less than a predetermined amount.

Images