JPH0759348A - Parallel connecting device for dc-dc converter - Google Patents

Abstract

PURPOSE:To simplify the constitution of a parallel connecting device for DC-DC converters for the reduction of cost and the improvement of efficiency. CONSTITUTION:A first and a second DC-DC converters 1, 2 are connected in parallel. The average value of output of PWM pulse generating circuits 16a, 16b is obtained using average signal generating circuits 41a, 41b. The output of the average signal generating circuits 41a, 41b is input to comparators 27a, 27b. The average signals have a value corresponding to the output current of the DC-DC converters 1, 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a DC-DC converter or D.
The present invention relates to a parallel connection device for a C-DC converter.

[0002]

2. Description of the Related Art A conventional DC-DC converter parallel connection device is, for example, a flyback type first parallel connection device as shown in FIG.
And the second DC-DC converters 1 and 2 are connected in parallel between the common DC power supply 3 and the common output terminals 4 and 5.

The first DC-DC converter 1 includes first and second DC power supply terminals 6a and 7 connected to a DC power supply 3.
a and a series circuit of a primary winding 9a of a transformer 8a connected between them and a switch element 10a composed of a field effect transistor. Output terminals 14a and 15a are provided on the secondary winding 11a of the transformer 8a via a rectifying / smoothing circuit including a diode 12a and a smoothing capacitor 13a.
Are connected. The output terminals 14a and 15a of the first DC-DC converter 1 are common output terminals (load terminals).
4 and 5 are connected.

The control circuit for ON / OFF controlling the switch element 10a with a PWM pulse includes an output voltage detecting error amplifier 17 in addition to the well-known PWM pulse forming circuit 16a.
a, a reference voltage source 18a, a light emitting diode 19a, and a phototransistor 20a, and a voltage control unit including a CT transformer, a current detector 21a, and a diode 2
2a, 23a, resistors 24a, 25a, capacitor 26
a, comparator (comparator) 27a, resistors 28a, 29
a and diodes 30a and 31a.

One input terminal of the error amplifier 17a is connected to the output terminal 14a, and the other input terminal is connected to the reference voltage source 1.
8a. The light emitting diode 19a is connected between the output terminal 14a and the output terminal of the error amplifier 17a via an OR gate diode 31a. Phototransistor 20 optically coupled to light emitting diode 19a
a is connected to the PWM pulse forming circuit 16a. P
The WM pulse forming circuit 16a is controlled by the phototransistor 20a to generate a PWM pulse (ON / OFF control signal) having various pulse widths and sends it to the control terminal (gate) of the switch element 10a.

The current detector 21a detects the current flowing through the switch element 10a as the output current of the DC-DC converter 1 in order to control the current balance in parallel operation. The diodes 22a and 23a, the resistors 24a and 25a, and the capacitor 26a connected to the output stage of the current detector 21a function as a smoothing circuit and generate a voltage corresponding to the detected current. The upper end of the capacitor 26a is connected to one input terminal of the comparator 27a, and the lower end thereof is DC-
Since it is connected to the ground output terminal 15a of the DC converter 1, the current detection signal is input to one input terminal of the comparator 27a. A resistor 28a is connected between one input terminal and the other input terminal of the comparator 27a, and a resistor 29a is connected between the other input terminal of the comparator 27a and the reference voltage source 18a.
The reference voltage source 18a and the resistors 28a and 29a function as a reference signal generating means of the comparator 27a. The output terminal of the comparator 27a is an OR gate diode 3
It is connected to the cathode of the light emitting diode 19a through 0a. The other input terminal of the comparator 27a is connected to the balance control terminal 32a for parallel operation.

The second DC-DC converter 2 is constructed exactly the same as the first DC-DC converter 1 as shown in FIG. Therefore, the same reference numerals are given to common portions in the first and second DC-DC converters 1 and 2, and the first and second comparators 1 and 2 are distinguished by the subscripts a and b. Further, the description of the second DC-DC converter 2 is omitted.

First and second DC-DC converters 1,
In order to operate the two in parallel, as shown in FIG.
The first and second power supply terminals 6b, 7 of the DC converter 2
b is connected to a common DC power source 3, and output terminals 14b, 1
5b is connected to the common output terminals 4 and 5. Also,
The balance control terminals 32a and 32b are connected to each other.

The PWM pulse forming circuit 16 of FIGS. 1 and 2
As shown in principle in FIG. 3, a and 16b are well-known circuits including a triangular wave generating circuit 33, a comparator 34, and a resistor 35. One input terminal of the comparator 34 is connected to the triangular wave generating circuit 33, and the other input terminal of the comparator 34 is a resistor 3
5 and the phototransistor 20a or 20b are connected to a voltage dividing point. Since the series circuit of the resistor 35 and the phototransistor 20a or 20b is connected between the power supply terminal 36 and the ground, the phototransistor 20a or 20b is connected.
The detection voltage corresponding to the change in the resistance value of is input to the comparator 34, a PWM pulse is formed based on the comparison with the triangular wave, and the PWM pulse is supplied to the switch element 10a or 10b.

[0010]

[Operation] First, the basic operation of the first DC-DC converter 1 will be described. The switch element 10a interrupts the DC voltage. As a result, a DC voltage is intermittently applied to the primary winding 9a, a voltage corresponding to the DC voltage is obtained in the secondary winding 11a, and is rectified and smoothed by the diode 12a and the capacitor 13a to become a DC output voltage. The output voltage is compared with the reference voltage by the error amplifier (op amp) 17a, an output corresponding to the difference between the two is generated, and the light emitting diode 19a emits light in response to this, the resistance value of the phototransistor 20a changes, and the output The width of the PWM pulse changes so as to keep the voltage constant. The second DC-DC converter 2 is also the first
The DC-DC converter 1 operates in exactly the same manner.

When the second DC-DC converter 2 is not connected in parallel to the first DC-DC converter 1, that is, when operating independently, the reference voltage of the second DC-DC converter 2 is applied to the balance control terminal 32a. Since the voltage based on the source 18b is not applied, there is no component that cancels the voltage of the reference voltage source 18a of the first DC-DC converter 1, and the positive input terminal of the comparator 27a has a higher voltage than the voltage of the capacitor 26a from the reference voltage source 18a. Also, the reference signal having a high voltage is input, the output of the comparator 27a is kept in the high level state, and the diode 30a is kept in the off state.
As a result, the islanding operation is performed regardless of the comparator 27a.

As shown in FIG. 1, the first and second DC-
When the DC converters 1 and 2 are connected in parallel, a balance control operation is performed to make the voltages of the capacitors 26a and 26b corresponding to the current values detected by the first and second current detectors 21a and 21b equal to each other. Now the first
Assuming that the currents flowing through the second switch elements 10a and 10b are the same, the voltages of the capacitors 26a and 26b are also the same, and no current flows between the capacitors 26a and 26b. In addition, the comparators 27a and 27b
The output of is kept high.

Due to the imbalance of the currents of the switch elements 10a and 10b, the voltage of the capacitor 26a of the first DC-DC converter 1 is changed to the second DC-DC converter 2.
When it becomes higher than the voltage of the capacitor 26b, the first capacitor 26a, the resistor 28a, the balance control terminals 32a and 32b, the resistor 28b, and the second capacitor 2a.
An electric current flows in the circuit composed of 6b. At this time, a current flows in the first resistor 28a in a direction opposite to that in the single operation, and a current flows in the second resistor 28b in the same direction as in the single operation. Since the reference signal in the first comparator 27a becomes lower than the voltage (detection voltage) of the capacitor 26a, the output of the first comparator 27a becomes low level. The output of the second comparator 27b is maintained at the high level as in the balance. First comparator 2
When the output of 7a goes low, diode 30a turns on and the current of light emitting diode 19a flows through it. As a result, the amount of light emitted from the light emitting diode 19a increases and the same state as when the output voltage rises is reached, and the first PWM pulse forming circuit 16a narrows the width of the PWM pulse. As a result, the output voltage of the first DC-DC converter 1 decreases, this output current also decreases, and the currents of the switch elements 10a and 10b are balanced.

[0014]

In the parallel connection state configured as shown in FIG. 1, current detectors 21a and 21b composed of CT transformers are necessary for balancing the currents, which inevitably results in cost of the device. Led to a rise. Also, CT
There is a method in which a current detection resistor is connected in series to the switch elements 10a and 10b instead of the current detectors 21a and 21b of the transformer or in series to the output lines of the capacitors 13a and 13b of the rectifying and smoothing circuit. In addition to the current detection resistor, an operational amplifier for current detection is required, which not only increases the cost but also lowers the efficiency due to the power loss due to the current detection resistor.

Therefore, an object of the present invention is to provide a parallel connection device of a DC-DC converter (DC-DC converter) capable of achieving control of current balance by a simple circuit.

[0016]

The present invention for achieving the above object comprises a series circuit of a primary winding of a transformer and a switch element connected between one end and the other end of a DC power source, and A rectifying / smoothing circuit connected to the primary winding or the secondary winding of the transformer, and a control circuit for controlling ON / OFF of the switch element so as to keep the output voltage of the rectifying / smoothing circuit constant. In a device in which at least first and second DC-DC converters are connected in parallel, the first
And the control circuits of the second DC / DC converters are associated with each other, and the first and the first and second DC / DC converters are substantially balanced to balance the currents flowing through the switch elements of the first and second DC / DC converters. The present invention relates to a DC-DC converter parallel connection device in which the control circuit is configured so that the ON / OFF control signals of the switching elements of the DC-DC converter of No. 2 are substantially the same. As described in claim 2, it is desirable to control the current balance based on the average value signal of the ON / OFF control signals of the first and second DC-DC converters.

[0017]

According to the present invention, control for balancing the currents of the switch elements during parallel operation can be executed without depending on the output of the current detector. Therefore, the circuit configuration is simplified and the power loss is reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a parallel connection device for a DC-DC converter according to an embodiment of the present invention will be described with reference to FIGS. However, in FIG. 4, portions common to FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof will be omitted.

As is clear from the comparison between FIGS. 1 and 2 and FIG. 4, the circuit of FIG.
It does not have the equivalent of a and 21b. Instead, smoothing circuits, that is, average value signal forming circuits 41a and 41b are connected to the output lines of the PWM pulse forming circuits 16a and 16b. The average value signal forming circuits 41a and 41b include resistors 43a, 43b, 44a and 44b and a capacitor 45a,
45b, and the capacitor 26a of FIG. 1 and FIG.
An average value signal (average voltage) containing the same information as 26b is generated. That is, the average value signal forming circuits 41a and 41b are
When the width of the PWM pulse is wide as shown in the first half of FIG. 5, a high level average value voltage as shown by the dotted line is output,
When the width of the PWM pulse is narrow as shown in the latter half of FIG. 5, a low level average value voltage is output as shown by the dotted line. In order to configure the average value signal forming circuits 41a and 41b, a series circuit of resistors 43a and 43b and resistors 44a and 44b is connected between the output lines of the PWM pulse forming circuits 16a and 16b and the ground, and the resistors 44a and Capacitors 45a and 45b are connected in parallel with 44b. The output lines of the average value signal forming circuits 41a and 41b are connected to the negative input terminals of the comparators 27a and 27b. The output terminals of the comparators 27a and 27b are OR
It is connected to the input terminals of the PWM pulse forming circuits 16a and 16b via the gate diodes 46a and 46b. An OR is provided between the phototransistors 20a and 20b and the input terminals of the PWM pulse forming circuits 16a and 16b.
The gate diodes 47a and 47b are connected.
Other configurations in FIG. 4 are the same as those in FIGS. 1 and 2.

[0020]

[Operation] The basic operation of the parallel connection device of FIG. 4 is the same as that of FIG. That is, in the case of an independent operation, the balance control terminal 32
Since the connection between a and 32b is released, the reference signal becomes a high level, and the outputs of the comparators 27a and 27b are shown in FIG.
And becomes high level as in FIG. 2, and the diode 46a,
46b is turned off, the PWM pulse forming circuits 16a, 1
6b operates independently of the comparators 27a and 27b. The voltage applied to the comparators 27a and 27b from the reference voltage sources 18a and 18b during the isolated operation is higher than the output voltage of the average value signal forming circuits 41a and 41b.

Since the voltages of the capacitors 45a and 45b in FIG. 4 change in accordance with the currents of the switch elements 10a and 10b like the voltages of the capacitors 26a and 26b in FIGS. 1 and 2, the capacitors are balanced when the currents are balanced. Since the voltages of 45a and 45b become the same, the comparator 27
The outputs of a and 27b are kept at a high level. First DC-
Assuming that the current of the switch element 10a of the DC converter 1 becomes larger than that of the second DC-DC converter 2, for example, the capacitor 45 is similar to the case of FIG.
A current flows through the circuit of a, the resistor 28a, the terminals 32a and 32b, the resistor 28b, and the capacitor 45b. Resistance 28 at this time
As in the case of FIG. 1, the current flowing through a is in the opposite direction to that during islanding, so the reference signal of the first comparator 27a becomes lower than the voltage of the capacitor 45a, and the output of the comparator 27a becomes low level. The diode 46b is turned on, the input voltage of the PWM pulse forming circuit 16a is lowered, the width of the PWM pulse is narrowed, the output voltage is lowered, and the output current is also reduced. In the second PWM pulse forming circuit 16b, the pulse width correcting operation does not occur,
The output pulse widths of the second PWM pulse forming circuits 16a and 16b approach the same, and the output voltage and the current are balanced.

In the flyback type DC-DC converter, when the transformers as chokes of the same plurality of converters are used in the discontinuous mode, the output currents are the same as long as they are used with the same ON width of the same frequency. This is because the change current ΔI when the same voltage E is applied to the same inductance L for the same time T is ΔI = E · T / L,
The changing current is the same. Since the change current here is proportional to the output current, it can be seen that if the change currents are equal, the output currents are also equal and the output currents are balanced. Therefore, the current detecting means, which has been conventionally required, becomes unnecessary, and balanced operation becomes possible.

As is clear from the above, since the device of FIG. 4 does not have a current detector, it does not cause an increase in cost and a decrease in efficiency.

[0024]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) The output current can be substantially balanced even when the DC-DC converters 1 and 2 are configured as forward converters. (2) The PWM pulse forming circuits 16a and 16b can be variously modified. (3) The light-emitting diodes 19a and 19b and the phototransistors 20a and 20b may be directly connected without using a photocoupler. (4) A voltage dividing resistor for detecting the output voltage can be provided at the input stage of the error amplifiers 17a and 17b. (5) In FIG. 4, the outputs of the comparators 27a and 27b can be given to the preceding stage of the light emitting diodes 19a and 19b as in the case of FIG. (6) Without connecting a rectifying / smoothing circuit to the secondary windings 11a and 11b, it is possible to provide a step-up or step-down tap on the primary windings 9a and 9b and connect them here.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a parallel connection device for a conventional DC-DC converter.

FIG. 2 is a circuit diagram showing in detail the second DC-DC converter of FIG.

FIG. 3 is a block diagram showing the PWM pulse forming circuit of FIGS. 1 and 2.

FIG. 4 is a circuit diagram showing a parallel connection device for a DC-DC converter according to an embodiment of the present invention.

5 is a waveform chart showing the relationship between the change in the pulse width of the PWM pulse and the output of the average value signal forming circuit in the circuit of FIG.

[Explanation of symbols]

 1, 2 First and second DC-DC converters 41a, 41b Average value signal forming circuit

Claims (2)

[Claims] 1. A series circuit of a primary winding of a transformer and a switch element connected between one end and the other end of a DC power supply,
A rectifying / smoothing circuit connected to the primary winding or the secondary winding of the transformer, and a control circuit for controlling ON / OFF of the switching element so as to keep the output voltage of the rectifying / smoothing circuit constant. In a device having at least first and second DC-DC converters connected in parallel, the control circuits of the first and second DC-DC converters are associated with each other, and the first and second The ON / OFF control signals of the switch elements of the first and second DC-DC converters are substantially the same so as to substantially balance the currents flowing through the switch elements of the DC-DC converter. A parallel connection device for a DC-DC converter, wherein a control circuit is configured. 2. The control circuit of the first and second DC-DC converters is a PWM for controlling the switch element.
PWM pulse forming circuit for forming a pulse, and the PWM
An average value signal forming circuit for forming a signal indicating the average value of the pulse train, a reference signal generating means, and a comparison output of the output of the average value signal forming circuit and the reference signal of the reference signal generating means. Respectively, the reference signal generating means of the first and second DC-DC converters are associated with each other, and the output of the comparison circuit is the first
2. The DC / DC converter parallel connection device according to claim 1, wherein the PWM pulse forming circuit operates so as to balance the control signals of the switching elements of the second DC / DC converter.