JPH10232720A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform charging with high efficiency without considerably changing basic configuration concerning a power supply circuit which generates DC power by performing voltage transformation and has a drooping function. SOLUTION: Concerning the power supply circuit provided with a voltage transforming means 12 for generating the DC power of desired voltage by performing the processing of voltage transformation to input power supplied from the outside and for supplying that DC power to a load 11 and a voltage characteristic setting means 13 for monitoring a load current, providing the deviation of load current corresponding to a predetermined maximum load current and setting the voltage characteristic of voltage transforming means 12 to drooping characteristics to decrease a load voltage corresponding to that deviation when the deviation is positive, a voltage characteristic changing means 14 is provided for monitoring the load voltage and subtracting a value, which is applied by a decrease function for the deviation of load voltage corresponding to a desired voltage, from the deviation provided by the voltage characteristic setting means 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit that generates DC power by performing voltage conversion and has a drooping function.

[0002]

2. Description of the Related Art In order to charge a storage battery efficiently, a large amount of electric power is required at the start of charging, which is proportional to the remaining amount indicating the energy stored in the storage battery. It is difficult to predict the remaining amount. Also,
It is uneconomical to make the capacity of the power supply circuit large enough to withstand the maximum capacity that the storage battery can have.

Therefore, the power supply circuit is provided with a drooping function for performing constant voltage charging and rapidly suppressing the output voltage value when the output current takes a value larger than a value adapted to the capacity of the power supply circuit. FIG. 4 is a diagram illustrating a configuration example of a conventional power supply circuit. In the figure, an input of a voltage conversion circuit 41 is connected to a terminal of a battery 42 as a power source. The output of the voltage conversion circuit 41 (hereinafter referred to as “unbalanced output” for simplicity) is a load 43 and the load 43
And a resistor 44 connected in series. One of the terminals of the resistor 44, which is directly connected to the voltage conversion circuit 41, is connected to the inverting input of the differential amplifier 46 via the resistor 45, and the other terminal of the resistor 44 is connected to the resistor 47.
To the non-inverting input of the differential amplifier 46. The output of the differential amplifier 46 is connected to the non-inverting input of the differential amplifier 48, and the output of the differential amplifier 48 is
Is connected to the control input. The inverting input of the differential amplifier 48 is connected to the anode of a reference voltage source 49, and the cathode of the reference voltage source 49 is grounded.

[0004] Since the configuration of the voltage conversion circuit 41 is known, a detailed description thereof will be omitted. In the conventional example having such a configuration, the voltage conversion circuit 41 performs the PWM control according to the voltage value applied to the control terminal, and converts the DC power provided by the battery 42 into a DC power of a voltage adapted to the load 43. I do. On the other hand, the resistors 44, 45, 47 and the differential amplifier 46 convert the value of the load current I flowing through the load 43 into a voltage. The differential amplifier 48 obtains a difference between the voltage and a reference voltage VREF1 provided from a reference voltage source 49.

When the difference obtained in this way is a negative number, the voltage conversion circuit 41 sets the DC power supplied to the load 43 to a value proportional to the value of the difference, thereby setting the load voltage V When the stabilization is performed (hereinafter, the state in which the voltage conversion circuit 41 performs such an operation is referred to as “constant voltage mode”) and the difference is a positive number, the voltage conversion circuit 41 The drooping function is realized by setting the value of the difference to a value that monotonously decreases (hereinafter, the state in which the voltage conversion circuit 41 performs such an operation is referred to as “constant current mode”).

That is, during a period when the load 43 is light and the load current I is lower than the value Im set as the reference voltage VREF1 (FIG. 5 (1)), the voltage conversion circuit 41 is in the constant voltage mode. The voltage V is maintained at a constant value Vm (hereinafter, such a voltage characteristic (FIG. 5A) is referred to as a "constant voltage state"). In addition, during a period when the load 43 is heavy such that the load current I exceeds the value Im (FIG. 5B), the voltage conversion circuit 41 shifts to the constant current mode. The voltage V sharply decreases (hereinafter, such a characteristic (FIG. 5B) is referred to as “constant current state”).

In the following, the points where the load voltage and the load current are Vm and Im in FIG.
(C)) is called a "transition point". Generally, the product of these values (Vm * Im) is set to the maximum power allowed for the capacity of the voltage conversion circuit 41.

[0008]

In such a conventional example, when a storage battery is connected as the load 43, the voltage conversion circuit 41 charges the storage battery based on the voltage characteristics shown in FIG. Generally, during such a charging period, the load current I changes together with the capacity of the storage battery (the resistance value of the load 43). Therefore, the period corresponding to the transition point (FIG. 5C) is realized. short. That is, the maximum power that the voltage conversion circuit 41 can output is not effectively used, and the charging efficiency is low.

The power (V *) supplied to the load 43
It is technically possible to keep the output power at a large value by feeding back I) to the voltage conversion circuit 41. However, since a multiplier is required to generate an electric signal indicating the power, the cost is reduced. It is expensive and unrealistic. An object of the present invention is to provide a power supply circuit that performs high-efficiency charging without significantly changing the configuration of the power supply circuit having the above-described drooping characteristics.

[0010]

FIG. 1 is a block diagram showing the principle of the first aspect of the present invention. According to the first aspect of the present invention, a voltage conversion unit 12 generates a DC power of a desired voltage by performing a voltage conversion process on input power supplied from the outside, and supplies the DC power to a load 11. The load current is monitored, and a deviation of the load current from a predetermined maximum load current is obtained. When the deviation is positive, the voltage characteristic of the voltage conversion means 12 is changed according to the deviation. Voltage characteristic setting means 13 for setting characteristics
And a voltage characteristic changing means for monitoring a load voltage and subtracting a value given by a decreasing function of a deviation of the load voltage from a desired voltage from a deviation obtained by the voltage characteristic setting means. It is characterized by the following.

According to a second aspect of the present invention, in the power supply circuit according to the first aspect, the voltage characteristic changing means compares the load current with a critical current set to be larger than the maximum load current. The method is characterized in that it includes means for stopping the subtraction operation when it is larger than the latter. According to a third aspect of the present invention, in the power supply circuit according to the first or second aspect, the rate of change of the decreasing function applied to the voltage characteristic changing means is such that the voltage conversion means alone has a drooping characteristic. Is a value G given by the equation of G = − (μ + 1) / μ with respect to the change rate μ of the load voltage indicated by.

(Operation) In the power supply circuit according to the first aspect of the present invention, the voltage conversion means 12 generates DC power of a desired voltage by performing voltage conversion. The voltage characteristic setting means 13 obtains a deviation of the load current from the maximum load current, and when the deviation is positive, sets the voltage characteristic of the voltage conversion means 12 to a droop characteristic in which the load voltage decreases in accordance with the deviation. Set to. That is, the load voltage is maintained at a desired value when the load current is smaller than the maximum load current, and sharply decreases according to the load current when the load current is larger than the maximum load current.

However, the voltage characteristic changing means 14 subtracts the value given by the decreasing function of the deviation of the load voltage from the desired voltage from the deviation obtained by the voltage characteristic setting means 13,
In the overload state, the amount of load current deviation obtained by the voltage characteristic setting means 13 is updated to be small. That is, the degree of the decrease in the load voltage that the voltage conversion unit 12 exhibits under the above-described drooping mode is reduced. Further, since the voltage characteristic changing means 14 is realized by a circuit having a simple configuration having a linear input / output characteristic, by appropriately setting the above-described decreasing function, the magnitude of the rate of change of the load voltage can be reduced at a low cost and reliably. Can be changed to a desired small value.

In the power supply circuit according to the second aspect of the present invention, in the power supply circuit according to the first aspect, the voltage characteristic changing means compares the load current with a critical current set to be larger than the maximum load current. When the former is larger than the latter, the operation of subtracting the value from the deviation is stopped. That is, when the value of the load current exceeds the critical current, the voltage converting means 12 operates under the voltage characteristic setting means 13 without any hindrance by the voltage characteristic changing means 14,
A drooping characteristic can be obtained in the same manner as in the conventional example.

Further, by appropriately setting the value of the critical current to a value larger than the maximum load current, the load 1
An upper limit can be set for the load current flowing through the load 11 regardless of the weight of the load. In the power supply circuit according to the third aspect of the present invention, in the power supply circuit according to the first or second aspect, the rate of change of the decreasing function applied to the voltage characteristic changing means 14 is such that the voltage conversion means 12 alone has With respect to the change rate μ of the load voltage shown under the drooping characteristic, G = − (μ +
1) A value G given by the formula of / μ. According to this equation, the rate of change of the load current with respect to the load voltage indicated by the voltage conversion circuit 12 is 1 / k (1 / k = 1 / μ + G) under the operation of both the voltage characteristic setting means 13 and the voltage characteristic changing means 14. Is given by 1 / k = -1. Therefore, when the value of the load current is equal to or more than the maximum load current and less than the critical current, the power supplied to the load 11 is kept constant.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG.
FIG. 3 is a diagram showing a configuration of an embodiment corresponding to the invention described in FIG. In the figure, components having the same functions and configurations as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted here.

The difference between the present embodiment and the conventional example shown in FIG. 4 is that a resistor 21 is added between a differential amplifier 48 and a reference voltage source 49, and the resistor 21 and the differential amplifier The point is that the voltage dividing circuit 22, the inverting amplifier circuit 23, and the diode 24 connected in the reverse direction are connected in series between the connection point of the load 48 and the connection point of the load 43 and the voltage conversion circuit 41.

The voltage dividing circuit 22 includes resistors 22a and 22b connected in series. In the inverting amplifier circuit 23, the output of the voltage dividing circuit 22 is connected to the inverting input of the operational amplifier 23b and one terminal of the resistor 23c via the resistor 23a, and the output of the operational amplifier 23b is connected to the resistor 23c.
And the anode of the diode 24. The non-inverting input of the operational amplifier 23b is connected to the reference voltage source 23
Grounded via d.

The correspondence between the present embodiment and the block diagram shown in FIG. 1 is as follows. The load 43 corresponds to the load 11, the voltage conversion circuit 41 corresponds to the voltage conversion means 12, and the resistors 44, 45,. 47, the differential amplifiers 46 and 48, and the reference voltage source 49 correspond to the voltage characteristic setting means 13, and include a voltage dividing circuit 22, an inverting amplifier circuit 23, a diode 24, and a resistor 21.
Corresponds to the voltage characteristic changing means 14.

In the following, the resistors 22a, 22b,
Regarding the resistance values of 23a and 23c, the corresponding reference numerals are attached to the letter “R”. FIG. 3 is a diagram illustrating the operation of the present embodiment. Hereinafter, the operation of the present embodiment will be described with reference to FIGS. When the load 43 is light, the constant voltage state (FIG. 3A) is secured under the stabilization of the voltage performed inside the voltage conversion circuit 41 as in the conventional example. Thus, when the voltage conversion circuit 41 is in the constant voltage mode (FIG. 3A), the mutual gain G (= −R22b / (R22b) between the voltage dividing circuit 22 and the inverting amplifier circuit 23 is obtained.
+ R22a) * R23c / R23a) and reference voltage source 4
Since the diode 24 is biased in the forward direction between the reference voltages VREF1 and VREF2 given by 9 and 23d, the inequality VREF1> G * Vm + VREF2 (1) holds.

A DC voltage Vd expressed by the following equation is applied to the inverting input of the differential amplifier 48: Vd = VREF1 + G * Vm + VREF2 (2) Hereinafter, for the sake of simplicity, when the voltage conversion circuit 41 is in the constant voltage mode, the voltage Vd applied to the inverting input of the differential amplifier 48 becomes the same reference voltage VREF1 as the conventional example (that is, the voltage conversion). The circuit 41 operates under the same conditions as in the conventional example.) Therefore, it is assumed that VREF2 + G * Vm = 0 (3) holds.

When the load 43 becomes heavy and the voltage conversion circuit 41 shifts to the constant current mode (FIG. 3 (2)), the voltage Vin applied to the control terminal of the voltage conversion circuit 41 With respect to the current I, the gain g of the differential amplifier 46, and the load voltage V, the value is expressed by the following equation: Vin = (g * I−VREF1) − (G * V + VREF2) (4)

Here, the voltage conversion circuit 41 is arranged as shown in FIG.
As shown in (1), when the mode is the constant current mode, a response that can be regarded as linear is performed, and it is recognized that the load current I increases as the voltage Vin increases, and the value of the load voltage V is set to a small value. However, this voltage Vin changes according to the load voltage V.
That is, since the voltage conversion circuit 41 recognizes that even if the load current I increases, the increase is smaller than the actual value, the rate of change of the load voltage V with respect to the load current I is set smaller than in the conventional example (FIG. 3 (b)).

Further, when the load 43 becomes heavy and the potential of the output of the inverting amplifier circuit 23 becomes higher than the reference voltage REF1 given from the reference voltage source 49, the diode 24 moves to the cutoff region and the differential amplifier Since the connection between the inverting input 48 and the inverting amplifier 23 is cut off, a constant current state is realized in the same manner as in the conventional example (FIG. 3 (c)). Less than,
Based on the qualitative operation described above, the gain G and the reference voltage VRE are set to obtain desired voltage characteristics.
F1 and VREF2 will be described.

When the voltage conversion circuit 41 is in the constant current mode, the load current pressure V supplied to the load 43 in response to the voltage Vin is given by the following equation: V = μ * ((gI−VREF1) − (G * V + VREF2)) Approximately given by equation (4). Therefore, the rate of change k of the load current I with respect to the load voltage V is given by the following equation: k = (1 + μG) / (μ * g) (5), for example, (1 + μG) / (μ * g) = -1 (6) In this case, the power supplied to the load 43 is constant regardless of the load current I.

When the diode 24 starts to be reverse-biased, the following equation is established: VREF1 = VREF2 + G * V (7), so that the time when the droop function is realized (FIG. 3)
With respect to the value Vo that the load voltage V should take in (d)), the following equation holds: VREF1 = VREF2 + G * Vo (8)

That is, gain G, reference voltages VREF1, VRE
Since F2 is obtained as the root of the simultaneous equations consisting of the above equations (3), (5), and (8), a voltage dividing circuit 22, an inverting amplifier circuit 23, a diode 24, and a resistor 21 are added to the conventional example. A desired voltage characteristic is realized by a simple and inexpensive circuit. In particular, when the above equation (6) holds, the state in which the power supplied from the voltage conversion circuit 41 to the load 43 is constant and maximized is smaller than that of the conventional example (only the transition point shown in FIG. 5C). Is set widely.

Further, when the load 43 is an overdischarged storage battery, the electric power supplied to the storage battery in the initial stage of charging is long over a long period of time until the voltage conversion circuit 41 shifts to the constant voltage mode. Is the largest value.
That is, the maximum power that the voltage conversion circuit 41 can supply to the load 43 is effectively used, so that the charging efficiency is improved.

In the above-described embodiment, the diode 24 is disposed downstream of the inverting amplifier circuit 23. However, if the load 43 does not become heavy enough to apply the droop function, the diode 24 is It does not need to be arranged.
In the above-described embodiment, the load voltage is stabilized by the voltage conversion circuit 41 in the constant voltage mode.
If the load voltage V is applied to the load 43 with desired accuracy, the stabilization may not be performed.

Further, in the above-described embodiment, the voltage dividing circuit 22 is arranged at the preceding stage of the inverting amplifier circuit 23. However, if the load voltage V is inverted and amplified at a desired amplification factor in the inverting amplifier circuit 23, the voltage dividing circuit 22 is provided. The voltage dividing circuit 22 may not be provided. In the above-described embodiment, the voltage conversion circuit 4
1 performs voltage conversion based on the PWM control method, but any method may be used as long as desired voltage characteristics can be obtained.

Further, in the above-described embodiment, the battery 42 is applied as a power source, but any power source may be applied as long as power suitable for the operation of the voltage conversion circuit 41 is provided. In the above-described embodiment, the operational amplifier 23b is provided. However, when the voltage to be input to the control terminal of the voltage conversion circuit is smaller than the load voltage, an attenuator is used instead of the operational amplifier 23b. A circuit composed of passive elements such as a voltage divider may be arranged.

Further, in the above-described embodiment, the drooping characteristic is set as the input / output characteristic of the voltage conversion circuit 41. However, if the load voltage monotonously decreases with respect to the load current, any characteristic is obtained. It may be set.

[0033]

As described above, according to the first aspect of the present invention, the magnitude of the rate of change of the load voltage with respect to the load current can be changed to a desired small value at low cost and reliably.

Further, according to the second aspect of the present invention, an upper limit value can be set for the load current flowing through the load regardless of the weight of the load. According to the third aspect of the invention, when the value of the load current is equal to or larger than the maximum load current and smaller than the critical current, the power supplied to the load is kept constant. Therefore, in the power supply system to which these inventions are applied, the unique maximum available power of the power supply circuit is effectively used in a state where the load fluctuates. Furthermore, safety is ensured by setting the upper limit of the load current to an appropriate value adapted to the characteristics of the power supply path and the like.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the invention according to claim 1;

FIG. 2 is a diagram showing a configuration of an embodiment corresponding to the inventions of claims 1 to 3;

FIG. 3 is a diagram for explaining the operation of the embodiment according to the first to third aspects of the present invention;

FIG. 4 is a diagram illustrating a configuration example of a conventional power supply circuit.

FIG. 5 is a diagram illustrating the operation of a conventional power supply circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Load 12 Voltage conversion means 13 Voltage characteristic setting means 14 Voltage characteristic changing means 21,22a, 22b, 23a, 23c, 44,45,
47 resistor 23b operational amplifier 23d, 49 reference voltage source 24 diode 41 voltage conversion circuit 42 battery 43 load 46, 48 differential amplifier

Claims (3)

[Claims] A voltage conversion means for generating a DC power of a desired voltage by applying a voltage conversion process to input power supplied from the outside, supplying the DC power to a load, and monitoring a load current; A deviation of the load current from the predetermined maximum load current is obtained, and when the deviation is positive, the voltage characteristic of the voltage conversion means is set to a drooping characteristic in which the load voltage decreases according to the deviation. A voltage characteristic changing means for monitoring a load voltage and subtracting a value given by a decreasing function of a deviation of the load voltage from the desired voltage from a deviation obtained by the voltage characteristic setting means. A power supply circuit comprising: 2. The power supply circuit according to claim 1, wherein the voltage characteristic changing means compares the load current with a critical current set to be larger than the maximum load current, and decreases when the former is larger than the latter. A power supply circuit comprising means for stopping the power supply. 3. The power supply circuit according to claim 1, wherein the rate of change of the decreasing function applied to the voltage characteristic changing means is a change in the load voltage which the voltage converting means alone exhibits under the drooping characteristic. A power supply circuit, wherein a value G is given by an equation of G = − (μ + 1) / μ with respect to a rate μ.