JP2000333455A - Bidirectional DC-DC converter - Google Patents

Abstract

(57) [Summary] [Problem] High-efficiency bidirectional DC-DC capable of energy regeneration
Provide a converter. A bidirectional DC-DC converter provided between a battery (1) and a load (7), comprising: a first series circuit of a primary winding (3) and a first FET (4) connected in parallel to the battery (1); A second series circuit of the secondary winding 5 of the transformer 2 and the second FET 6, which is connected in parallel to the load 7 so that a voltage having an opposite phase to the primary winding 3 of the transformer 2 is induced; To the load 7 and regenerate the energy stored in the capacitor 8 connected in parallel with the load 7 to the battery 1 so that the first FET 4 and the second F
Control means 9, 9a and 9b for controlling each gate of ET6 are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC converter, and more particularly, to a high-efficiency bidirectional D-type converter capable of regenerating energy.
It relates to a C-DC converter.

[0002]

2. Description of the Related Art A DC-DC converter is usually used in a DC power supply circuit when a voltage different from the DC power supply voltage is required. FIG. 5 is a diagram showing an example of a DC power supply circuit using a flyback type DC-DC converter according to the related art. Transformer 2 for power supply of battery 1
The series circuit of the primary winding 3 and the FET 4 is connected in parallel, and the series circuit of the diode 11 and the load 7 is connected in parallel to the secondary winding 5 of the transformer 2. Load 7
Is connected in parallel with a capacitor 8. Secondary winding 5
Is connected to the load 7 such that a voltage having a phase opposite to that of the primary winding 3 is induced. FET4 is an n-channel MO
The S type is used, and the source of the FET 4 is connected to the ground terminal of the battery 1 and one end of the secondary winding 5.
The drain of T4 is connected to one end of the primary winding 3.
The other end of the primary winding 3 is connected to the positive potential terminal of the battery 1, and the other end of the secondary winding 5 is connected to the anode of the diode 11.

[0005] A rectangular wave signal for turning on and off the FET 4 at a predetermined cycle is input from the control circuit 19 to the gate of the FET 4. The control circuit 19 is connected to a voltage detector 19a for detecting a voltage across the load and a current detector 19b for detecting a current flowing through the FET 4. The control circuit 19 controls the load 7 in response to signals from these detectors. The signal to the gate of the FET 4 is controlled so that the voltage between both ends becomes constant.

However, the DC power supply circuit according to the prior art shown in FIG. 5 has a problem that the energy is consumed by the backflow preventing diode 11 and the efficiency is low as shown in the following formula. PDi = IF × VF Here, PDi indicates a forward voltage loss due to the diode 11, IF indicates a forward junction current, and VF indicates a forward junction voltage.

Further, the DC power supply circuit has a circuit configuration in which the energy stored in the capacitor 8 cannot be regenerated to the battery 1. In order to reduce the forward voltage loss due to the diode 11, a rectifying diode is
There is known a synchronous rectifier circuit that is replaced with an SFET. However, since the on / off of the MOSFET is controlled by the voltage generated in the inductance L (secondary winding) on the secondary side of the transformer, the gate capacitance C and LC resonance occur to lower the circuit efficiency. For this reason, a series resistor is connected to the gate to prevent LC resonance, but switching of the MOSFET is delayed and circuit efficiency is reduced.

A DC-DC converter disclosed in Japanese Patent Application Laid-Open No. 6-98540 is a MOSFET having a high circuit efficiency.
This realizes a synchronous rectifier circuit.

[0007]

However, the DC-DC converter disclosed in JP-A-6-98540 does not consider a circuit for regenerating excess energy on the load side to the power supply side. Therefore, the present invention solves the above-mentioned problem, and realizes a high-efficiency bidirectional D capable of energy regeneration.
It is an object to provide a C-DC converter.

[0008]

A bidirectional DC-DC converter according to the present invention that solves the above-mentioned problems includes a DC power supply,
Bidirectional DC provided between a load including a capacitor
A DC converter, wherein a first series circuit of a primary winding of a transformer and a first FET, which is connected in parallel to the DC power supply, and a voltage having a phase opposite to that of the primary winding of the transformer is induced; A second series circuit of a secondary winding of the transformer and a second FET, which is connected in parallel to the load, supplies energy of the DC power supply to the load, and supplies energy stored in the capacitor to the DC power supply. Control means for controlling the gates of the first FET and the second FET so as to regenerate the current.

By the above control means, the second FET is turned off, the first FET is turned on, and then the first FET is turned off and the second FET is turned on, whereby the energy supplied from the DC power supply and temporarily stored in the primary winding is obtained. By supplying power to the load, turning on the second FET, and then turning off the second FET and turning on the first FET, energy supplied from the capacitor and temporarily stored in the secondary winding is regenerated to the DC power supply. As a result, a bidirectional DC-DC converter is realized, and high efficiency power transmission with little loss is realized because the forward voltage drops of the first FET and the second FET are low.

[0010] In the bidirectional DC-DC converter according to the present invention, the control means controls the voltage of the capacitor to a predetermined voltage.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a first embodiment of a DC power supply circuit using a DC-DC converter of the present invention. In the drawings, the same components are denoted by the same reference numerals. A series circuit of a primary winding 3 of a transformer 2 and an FET 4 is connected in parallel to a power source of a battery 1. A series circuit of the secondary winding 5 of the transformer 2 and the FET 6 is provided symmetrically with the series circuit, and a load 7 and a capacitor 8 are connected in parallel to the series circuit.
The connection of the secondary winding 5 to the load 7 is performed such that a voltage having a phase opposite to that of the primary winding 3 is induced. FET4 and F
ET6 uses n-channel MOS type, FET
The sources of FET 4 and FET 6 are connected to the ground terminal of battery 1, and the drain of FET 4 is connected to one end of primary winding 3. The other end of the primary winding 3 is connected to a positive potential terminal of the battery 1. The drain of the FET 6 is connected to one end of the secondary winding 5. The other end of the secondary winding 5 is connected to the positive potential side of the capacitor 8. As will be described later, a rectangular wave signal for turning on and off the FET 4 and the FET 6 is input to the gates of the FET 4 and the FET 6 from the control circuit 9 at a predetermined cycle, as described later. The control circuit 9 includes a voltage detector 9a for detecting a voltage across the load, an FET 4 and an FET 4.
A current detector 9b for detecting each current flowing through the FET 6 is connected to the FET 4 and the FE so that the voltage between both ends of the load 7 becomes constant in accordance with the signals from these detectors.
Controls the signal to the gate of T6.

When the DC power supply circuit shown in FIG. 1 is used in a vehicle, an air conditioner is used as the load of the battery 1 and a starter motor is used as the load 7 of the capacitor 8. As described above, the DC power supply circuit according to the present invention shown in FIG. 1 uses FET4 and FET6 instead of the diode for backflow prevention. Therefore, the forward voltage loss of the built-in diodes of the FET 4 and the FET 6 is much smaller than the forward voltage loss of the normally used diode.
The power transmission efficiency of the converter is improved. This built-in diode is also called a body diode.

FIG. 2 is a diagram showing a second embodiment of a DC power supply circuit using the DC-DC converter of the present invention. FIG.
The first embodiment shown in FIG. 11 is different from the first embodiment in that external diodes 12 and 1 are connected between the sources and drains of FET4 and FET6.
3 is connected only to each other. The switching speed of the external diodes 12 and 13 is higher than that of the built-in diodes of the FETs 4 and 6, and the DC-
The responsiveness of the DC converter during power transmission is improved.

Next, the operation of the DC power supply circuit according to the present invention shown in FIGS. 2 and 3 will be described. FIG. 3 shows FIGS. 2 and 3
5 is a time chart of a gate signal to each FET shown in FIG. The gate signals φ1 and φ2 are supplied to the load 7 by the control means including the control circuit 9, the voltage detector 9a and the current detector 9b, and the energy stored in the capacitor 8 is regenerated to the battery 1. To the gates of FET4 and FET6. FIG.
In the graph, the horizontal axis represents time, the vertical axis represents the voltage applied between the source and the gate of the FET 4 in the upper part, and the voltage applied between the source and the gate of the FET 6 in the lower part. Gate signal φ
1, φ2 has a period of about 10 to 50 KHz.

In the first mode in which power is transmitted from the battery 1 to the load 7, a voltage is applied between the source and the gate of the FET 4 at times t0 to t1 and t10 to t11 between the source and the gate of the FET 4, and the voltage between the source and the gate of the FET 6 is Has a predetermined cycle,
A voltage is applied between times t1 and t2 and between t11 and t11. Therefore, the FET 4 is turned on every predetermined period, and the FET 6 is turned on immediately after the FET 4 is switched from on to off.

As described above, when power is transmitted from the battery 1 to the load 7 in the first mode, the control circuit 9 controls the F
ET4 and FET6 are switched. In the switching operation of FET4, FET4 is turned on and FET6 is turned on.
Is off, energy is stored in the primary winding 3 and FE
When T4 is off and FET 6 is on, the energy stored in the primary winding 3 is charged in the capacitor 8, and at this time F
A charging current flows through the built-in diodes of ET4 and FET6.

In the second mode in which the battery 8 is regenerated from the capacitor 8, the time between the source and the gate of the FET 6 is set at a predetermined cycle from time t 100 to t 101, t 110 to t 1.
11, a voltage is applied between the source and the gate of the FET 4 at a predetermined cycle at times t101 to t102 and t111.
The voltage is applied between t112. Therefore, FET
6 turns on at predetermined intervals, and FET4 turns on immediately after FET6 switches from on to off.

As described above, when the battery 8 is regenerated from the capacitor 8 in the second mode, the control circuit 9 switches the FETs 4 and 6. FE
In the switching operation of T6, FET6 is turned on and F6 is turned on.
When the ET 4 is off, energy is stored in the secondary winding 5, the FET 6 is off, and when the FET 4 is on, the energy stored in the secondary winding 5 is regenerated to the battery 1. A charging current flows through the built-in diode.

The step-up / step-down of the voltage from the battery 1 to the capacitor 8 is determined not only by the turns ratio of the primary winding 3 and the secondary winding 5 of the transformer 2 but also by the FETs 4 and F
It is also determined by the duty ratio of the gate signal of ET6. The larger the duty ratio, that is, the longer the on-time of the gate signals of the FET 4 and the FET 6, the larger the voltage of the capacitor 8 becomes. When the detected voltage is higher than the predetermined voltage, the control circuit 9 controls the F so that the voltage of the capacitor 8 becomes a predetermined voltage.
The switching of ET4 and FET6 is stopped.

The current detection circuit 9b detects the current flowing through the FET 4, and the control circuit 9 controls the FE when the detected current is larger than a predetermined current so that an excessive current is not supplied to the load 7.
The switching of T4 and FET6 is stopped. Also,
The duty ratio may be feedback-controlled so as to obtain a predetermined current. The first mode and the second mode are:
When the voltage of the capacitor 8 detected by the voltage detector 9a is within a predetermined voltage, the mode is switched to the first mode, and when the voltage exceeds the predetermined voltage, the mode is switched to the second mode. That is, the capacitor 8
Is fully charged, the mode is switched from the first mode to the second mode, and regeneration from the capacitor 8 to the battery 1 is performed.

Next, another embodiment of the present invention will be described. FIG. 4 is a diagram showing a third embodiment of a DC power supply circuit using the DC-DC converter of the present invention. The first embodiment shown in FIG. 1 is different from the first embodiment in that the FET 14 is disposed between the positive potential terminal of the battery 1 and the first winding 3, the FET 15 is disposed between the second winding and the load, and External diodes 16 and 17 are connected between the sources and drains of the FETs 14 and 15, respectively.
FET4 and FET6 at the gates of FET4 and FET15
The only difference is that a boosting means 18 for sending a signal synchronized with a signal to the gate of the first stage is provided.

When transmitting power from the battery 1 to the load 7,
By the control means comprising the control circuit 9, the voltage detector 9a and the current detector 9b and the boosting means 18, the FET 14 is turned on, the FET 15 is turned off, the FET 6 is turned on,
4 is switched. In the switching operation of the FET 4, when the FET 4 is on, energy is stored in the primary winding 3, and when the FET 4 is off, the energy stored in the primary winding 3 is charged in the capacitor 8. This FE
When T4 is off, a charging current flows through the built-in diodes of FET4 and FET6.

When the battery 1 is regenerated from the capacitor 8, the control circuit 9, the voltage detector 9a and the current detector 9
b, and the boosting means 18
14 off, FET15 on, FET4 on,
The FET 6 is switched. In the switching operation of the FET 6, energy is stored in the secondary winding 5 when the FET 6 is on, and energy is stored in the secondary winding 5 when the FET 6 is off.
Is stored in the battery 1. When the FET 6 is off, a charging current flows through the built-in diodes of the FET 4 and the FET 6.

[0024]

As described above, according to the present invention, a high-efficiency bidirectional DC-DC converter capable of regenerating energy can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a DC power supply circuit using a DC-DC converter of the present invention.

FIG. 2 is a diagram showing a second embodiment of a DC power supply circuit using the DC-DC converter of the present invention.

FIG. 3 is a time chart of a gate signal to each FET shown in FIGS. 2 and 3;

FIG. 4 is a diagram showing a third embodiment of a DC power supply circuit using the DC-DC converter of the present invention.

FIG. 5 is a diagram illustrating an example of a DC power supply circuit using a flyback type DC-DC converter according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Battery (DC power supply) 2 ... Transformer 3 ... 1st winding 4, 6, 14, 15 ... FET 5 ... 2nd winding 7 ... Load 8 ... Capacitor 9 ... Control circuit 11, 12, 13, 16, 17 …diode

Claims (2)

[Claims] 1. A DC power supply, a load including a capacitor,
A first series circuit of a primary winding of a transformer and a first FET, which is connected in parallel to the DC power supply, and has a phase opposite to that of the primary winding of the transformer. A second series circuit of a secondary winding of the transformer and a second FET, connected in parallel to the load so that a voltage is induced, supplying energy of the DC power supply to the load, and A bidirectional DC-DC converter, comprising: control means for controlling each gate of the first FET and the second FET so as to regenerate stored energy to the DC power supply. 2. The bidirectional DC according to claim 1, wherein said control means controls the voltage of said capacitor to a predetermined voltage.
-DC converter.