JPH11187654A - Dc-to-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a specified output voltage, even if the duty ratio with an inverter is not made so small by having a voltage through the switching of a connection switching circuit annexed to a rectifying circuit, when the input voltage becomes larger than a specified value. SOLUTION: A connection switching circuit 18 and inductances 23 and 24 for smoothing are annexed to a rectifying circuit 10 which lies on the output side of a transformer 9. When the fluctuating input voltage is lower than a certain specified value, the connection switching circuit 18 is turned on (transistors 21 and 22 are on), and when that it is above the specified value, it is controlled by a controller 17 so that it is turned off. When the connection switching circuit 18 is turned off, the voltage coming out as output is halved, so that even if the input voltage becomes large, it obviates the need for making the duty ratio very small even if the input voltage becomes large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D (Digital-to-Digital) circuit in which the loss in a transformer is reduced even when the input voltage fluctuates greatly.
It relates to a C-DC converter.

[0002]

2. Description of the Related Art FIG. 7 is a diagram showing a first conventional example of a DC-DC converter. In FIG. 7, 1 is an input AC power supply, 2 is a rectifying circuit, 6 is a smoothing capacitor, 8 is an inverter, 9 is a transformer, 10 is a rectifying circuit, 11 is a smoothing inductance, 12 is a smoothing capacitor, and 13 and 14 are Reference numeral 15 denotes a current detector, 16 denotes a load, and 17 denotes a controller.

The AC of an input AC power supply 1 is rectified by a rectifier circuit 2 and applied to an inverter 8. The inverter 8 is controlled by a signal from the controller 17, converts an applied direct current into an alternating current, and sends the alternating current to the transformer 9. Transformer 9
Has the function of insulating the input side and the output side in addition to the voltage transforming action. The output of the transformer 9 is rectified by a rectifier circuit 10, smoothed by a smoothing inductance 11 and a smoothing capacitor 12, and supplied to a load 16. The resistors 13 and 14 are voltage-dividing resistors for detecting an output voltage, divide the smoothed DC voltage,
Tell The current detector 15 is for detecting an output current, and a detection signal is also transmitted to the controller 17.

The current detection by the current detector 15 is performed to monitor the output current so as not to exceed a predetermined value. If the predetermined value is reached, the control signal from the controller 17 to the inverter 8 is adjusted,
It is prevented from increasing any further. The detection of the output voltage by the resistors 13 and 14 is performed to control the output voltage to a predetermined value. The detection voltage is the controller 1
The control signal is compared with the set value in 7, and a control signal to the inverter 8 is generated based on the comparison result. The control signal to the inverter is the period of the alternating current generated as output (this is
It is expressed by a ratio (duty ratio) indicating how long the switching element is turned on among the lengths determined by the output frequency. Therefore, when the output voltage is higher than a predetermined value, the ratio of the time during which the switching element of the inverter 8 is on is shortened (duty ratio is reduced), and when the output voltage is lower than the predetermined value, the ratio of the on time is increased (duty ratio). The control signal is adjusted so that

FIG. 5 is a diagram for explaining the relationship between the input voltage of the inverter and the duty ratio. This figure shows how to change the duty ratio when the input voltage fluctuates while trying to obtain a constant voltage as the output voltage. The vertical axis represents the fluctuating input voltage, and the horizontal axis represents the duty ratio. Curve A is a curve representing the relationship between the input voltage and the duty ratio.
B and C are points on the curve. V _A , V _B , V
_C, respectively points A, B, the input voltage in the case of C, D _A, D _B, D _C, respectively points A, B, a duty ratio in the case of C.

Here, the output voltage to be obtained is V
_C is a rectified voltage. Therefore, the duty ratio D _C when the input voltage is V _C is set to 100% (see the case of point C in FIG. 5). When the input voltage of the inverter is higher than V _C , the output voltage is increased if the ON time (duty ratio) of the switching element of the inverter remains the same (100%) as that of V _C. Thus, as the input voltage is higher than V _C, the duty ratio is gradually decreased.

FIG. 6 is a diagram showing the switching time when the duty ratio is different in the inverter. FIG.
6A, 6B, and 6C are diagrams showing switching at points A, B, and C in FIG. 5, respectively. T represents a half cycle of AC, and T _ON represents a time during which the switching element is on in the half cycle. Therefore, T _ON /
T is the duty ratio.

FIG. 6 (C) shows switching when the input voltage is V _C , in which case it is turned on for the entire period of T (T = T _ON, duty ratio D _C = 100).
%). Although FIG. 6 (B) is a switching when the input voltage is V _B, since V _B is greater than V _C, the duty ratio D _B is smaller than D _C, the on-time is shortened. Although FIG. 6 (A) is a switching when the input voltage is V _A, since the V _A further is greater than V _B, the duty ratio D
_A is still smaller than D _B, on-time is further shortened.

Returning to FIG. 7, current flows in the forward and reverse directions through the transformer 9 in the DC-DC converter for a time determined by the duty ratio as shown in FIG. It is known that the efficiency of the transformer becomes worse as the duty ratio becomes smaller. If the input voltage does not fluctuate much, the winding ratio of the transformer is determined based on the voltage ratio with the desired output voltage, and the duty ratio can be controlled at a value close to 100%. Therefore, in such a case, the efficiency of the transformer can be increased.

However, when the input voltage fluctuates greatly, such measures cannot be taken. Therefore, the efficiency of the transformer is inevitably reduced. Therefore, in such a case, a circuit in which a voltage converting circuit (a booster circuit or a step-down circuit) is inserted before or after the transformer to improve the efficiency of the transformer is considered. Next, it is shown.

FIG. 8 is a diagram showing a second conventional example of a DC-DC converter. Reference numerals correspond to those in FIG. 7, 3 is a current detector, 4 and 5 are resistors, and 7 is a step-down circuit. The current detector 3 is for detecting an input current, and the resistors 4 and 5 are voltage dividing resistors for detecting an input voltage. When the current detector 3 detects that the input current has become excessive, the controller 17 takes measures to protect the DC-DC converter from overcurrent (for example, stop the control signal to the inverter 8).

The detection of the input voltage by the resistors 4 and 5 is performed to determine whether or not the step-down circuit 7 performs the step-down operation. Whether to perform the step-down operation is instructed by a signal from the controller 17. When the input voltage is large, the step-down circuit 7 performs a step-down operation. Then, the duty ratio of the inverter 8 becomes larger than when the voltage is not reduced, and the efficiency of the transformer 9 is much better than when the voltage is not reduced.

As a conventional document relating to a DC-DC converter, there is, for example, Japanese Patent Application Laid-Open No. 4-368644.

[0014]

In a DC-DC converter in which a step-down circuit or the like is inserted to maintain a high duty ratio to increase the efficiency of a transformer, the circuit scale is increased by the amount of the inserted circuit. In addition, there is a problem that the cost increases. An object of the present invention is to solve such a problem.

[0015]

According to the present invention, there is provided an inverter for converting a fluctuating input voltage into an alternating current by controlling a duty ratio, a transformer for transforming the alternating current, and a transformer for transforming the alternating current. A rectifying circuit for rectifying, a smoothing circuit for smoothing the rectified voltage to a DC output voltage, voltage detecting means for detecting the DC output voltage, and detection from the voltage detecting means for setting the DC output voltage to a constant value In a DC-DC converter comprising a controller for controlling a duty ratio of the inverter based on a value, an input voltage detecting means for detecting an input voltage and inputting a detection signal to the controller, and an anti-parallel transistor and diode. It consists of two connected bodies connected in series, and is connected between the output sides of two diodes adjacent to one DC output side terminal of the rectifier circuit. A connection switching circuit, one ends on the output side of the two diodes is connected to an inductance for smoothing the other end of which is connected to the output terminal collectively comprises,
The controller is controlled to turn on the transistor when the input voltage is lower than a predetermined value, and to turn off the transistor when the input voltage is higher than the predetermined value.

Such a DC-DC converter is used for obtaining a constant DC output voltage by using a voltage generated by a generator driven by an internal combustion engine of a vehicle as an input voltage. It is suitable as a converter.

(Summary of operation to be solved) In a DC-DC converter for obtaining a constant output voltage from a fluctuating input voltage, the duty ratio of the inverter is controlled, and the obtained AC is transformed by a transformer. Rectified and smoothed. Generally, the loss in the transformer increases as the duty ratio in the inverter decreases. According to the present invention, when the input voltage becomes larger than the predetermined value, the output voltage is reduced to one half by switching the connection switching circuit attached to the rectifier circuit. Therefore, the duty ratio of the inverter is not reduced so much. Thus, a predetermined output voltage is obtained. for that reason,
The efficiency of the transformer is improved as compared with the case where it is not reduced to half as described above.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a D according to the present invention.
It is a figure showing a C-DC converter. Reference numerals correspond to those in FIG. 8, 10A, 10B, 10C, and 10D are diodes that constitute the rectifier circuit 10, 18 is a connection switching circuit,
9 and 20 are diodes, 21 and 22 are transistors, 2
Numerals 3 and 24 are smoothing inductances. The smoothing inductances 23 and 24 have the same inductance value L. The same reference numerals as those in FIG. 8 perform the same operation, and thus the description thereof will be omitted.

The configuration differs from the conventional example of FIG. 8 in that the step-down circuit 7 is eliminated and a connection switching circuit 18 is provided instead. The smoothing inductances 23 and 24 correspond to the conventional smoothing inductance 11,
It is not purely new. However, only two connection switching circuits 18 are provided in correspondence with the new installation.

The configuration of the connection switching circuit 18 is such that two antiparallel connected bodies of a transistor and a diode are connected in series. The connection switching circuit 18 is connected to a diode (10A, 10A) adjacent to one DC output terminal of the rectifier circuit 10.
10C). One end of each of the smoothing inductances 23 and 24 is connected to the output side of the diode (10A, 10C), and the other end of each of the smoothing inductances 23 and 24 is collectively connected to the output terminal.

Switching by the connection switching circuit 18 is controlled by a control signal from the controller 17 so that the transistors 21 and
This is performed by turning on or off the switch 22. FIG.
FIG. 4 is a diagram for explaining circuits around the rectifier circuit 10 when switching is performed by the connection switching circuit 18. Fig. 2 (a)
When the transistors 21 and 22 are turned on,
FIG. 2B shows the state when the transistors 21 and 22 are turned off, and FIG. 2C rewrites the circuit shown in FIG.

First, the circuit shown in FIG. In the circuit of FIG. 1, in a half-wave in which the diode 10A is turned on, the transistor 21 is turned on and the diode 10A is turned on.
A current flows through a path of A → transistor 21 → diode 20 → smoothing inductance 24. Conversely, in a half-wave when the diode 10C is turned on, the transistor 22 is turned on, and a current flows through the path of the diode 10C → the transistor 22 → the diode 19 → the smoothing inductance 23. Since the inductance values of the smoothing inductances 23 and 24 are the same (L), the circuit at this time ends up with a rectifier circuit 10 as shown in FIG.
May be considered to be connected to one smoothing inductance 23 (or 24). Therefore, when the input voltage V _i, the output terminal O _1, O _2, appears the rectified voltage V _I.

Next, a circuit when the transistors 21 and 22 are turned off will be described with reference to FIG. The connection point between the smoothing inductances 23 and 24 is M, and the connection point between the diodes 10B and 10D is N. The connection point M is connected to the smoothing inductance 23 having the same inductance value L,
Sandwiched 24, as can be seen from the fact that a midpoint of the circuit configuration of the vertical symmetry, when the input voltage V _i of the AC to the circuit is applied, the voltage at node M is the half 1 rectified voltage. That is, a voltage of V _I / 2 appears between the output terminals O ₁ and O ₂ . As the voltage is reduced to half, circuit elements such as diodes can be made to have a low withstand voltage, and the cost can be reduced.

In the present invention, the connection switching circuit 18 as described above is used.
Is inserted so that the efficiency of the transformer 9 does not deteriorate even when the input voltage increases. Next, the switching control of the connection switching circuit 18 for explaining this fact will be described first. . If the input voltage is equal to or lower than a predetermined value, the transistors 21 and 22 are turned on (see FIG. 2).
(A) circuit). If the input voltage is higher than a predetermined value, the transistors 21 and 22 are turned off (FIG. 2B).
(C) circuit). This switching control is performed by the control signal from the controller 17 as described above.

By performing such switching control, it is not necessary to set the duty ratio of the inverter 8 to a very small value even when the input voltage becomes larger than the predetermined value. This will be described with reference to FIG. FIG. 3 is a diagram illustrating the duty ratio of the inverter according to the present invention. Vertical axis,
The horizontal axis and reference numerals correspond to those in FIG. V ₁ , V
₂ and V ₃ are input voltages, and D _M is a duty ratio when the input voltage is V ₂ . V ₁ is an input voltage at which a predetermined output voltage can be obtained with the duty ratio of the inverter 8 being 100%. V ₃ is the maximum input voltage is assumed. V ₂ is a voltage between V ₁ and V _3,
The voltage is twice the voltage of V ₁ , and switching control by the connection switching circuit 18 is performed at the voltage. That is, when the input voltage becomes V ₂ or more, the circuit shown in FIG.
And multiplying circuit), FIG. 2 when the input voltage becomes smaller than V ₂
The switching control is performed with a certain degree of hysteresis so that the circuit (a) is a circuit (single output circuit) (however, hunting does not actually occur.
The circuit of Figure 2 when raised to V ₂ + alpha (ii) exceeds the V _2, when reduced to V _2-.alpha. below the V ₂ 2 (b)
Circuit. ).

In such a case, as shown in FIG. 3, when the input voltage is in the range of V _{1 to} V ₂ , the relationship between the input voltage and the duty ratio is as shown by a curve A. This is the same as the conventional one. The duty ratio in this case only changes in a range larger than D _M , and does not become a very small value close to 0%. Therefore, the efficiency of the transformer 9 does not deteriorate.

Next, when the input voltage is in the range of V _{2 to} V ₃ ,
The relationship between the input voltage and the duty ratio is as shown by a curve B. That is, when the input voltage is V ₂ , the duty ratio is 100
%, And the duty ratio is gradually decreased as the input voltage increases. The reason why such a relationship may be satisfied is that the alternating current generated by the conversion by the inverter 8 passes through the transformer 9 and then returns to the state shown in FIG.
This is because it is halved by the circuit (b). That is, the inverter 8 may generate a double voltage alternating current.

If the duty ratio is not reduced to one half after passing through the transformer 9, the duty ratio control in the inverter 8 must be performed as shown by the dotted curve a-1 in FIG. Then, when the input voltage becomes close to V ₃ , the duty ratio must be set to a value close to 0%, but the efficiency of the transformer 9 becomes very poor. In the present invention, by switching as shown in FIG.
It is avoided. Note that the magnitude of the input voltage is
5, the controller 17 makes a determination based on the detected value, and sends a switching signal to the connection switching circuit 18.

As described above, the DC-DC converter of the present invention can operate the transformer 9 in an efficient state even when the input voltage fluctuates greatly.
An example suitable for using such a DC-DC converter will be described below. FIG. 4 is a diagram showing an example of use of the DC-DC converter of the present invention. In FIG. 4, 31 is a pulley, 32 is an engine, 33 is an intake pipe, 34 is an exhaust pipe,
35 is a turbocharger, 36 is a compressor blade, 37 is a rotor, 38 is a stator, 39 is a turbocharger rotating electric machine, 40 is a turbine blade, 41 is a belt, 42 is a pulley, 43 is a vehicle generator, 44 is a controller, 45 is a power unit, 46 is a DC-DC converter,
47 is a battery and 48 is a load.

The vehicle generator 43 is a vehicle-mounted generator driven by the engine 32 via the pulley 31, the belt 41, and the pulley 42. The turbocharger 35 is
The exhaust gas from the exhaust pipe 34 causes the turbine blade 40
Is rotated, and the compressor blade 36 is rotated by using the rotational force to take in external air into the intake pipe 33. The turbocharger rotating electric machine 39 is a rotating electric machine incorporated in the turbocharger 35, and a rotor 37 is attached to a rotating shaft of the turbocharger 35, and a stator 38 is attached in a housing of the turbocharger 35. An electromotive force is induced in the stator 38 by the rotation of the rotor 37, and the generated voltage is taken out to the outside.

The generated voltage from the vehicle generator 43 and the turbocharger rotating electric machine 39 is introduced to the power section 45. The power unit 45 has a built-in DC-DC converter 46 and converts the voltage into a voltage required by the vehicle. The conversion control is performed by the controller 44. The converted voltage is supplied to a battery 47, an electric load 48 in the vehicle, and the like. The rotation speed of the vehicle generator 43 greatly varies depending on the condition of the engine rotation speed. In particular, in the present embodiment, the speed is increased at a high speed (3 to 5 times) in consideration of supplying a voltage to the turbocharger rotating electric machine 39 at the time of starting, so that the generated voltage from the vehicle generator 43 greatly fluctuates. I do.
Therefore, it is suitable to use the DC-DC converter of the present invention as the DC-DC converter 46 built in the power unit 45. That is, even if the input voltage fluctuates greatly, the duty ratio can be used without making the duty ratio too small, so that the loss in the transformer can be reduced.

[0032]

As described above, according to the DC-DC converter of the present invention, the following effects can be obtained. (Effect of Claim 1) When the input voltage becomes larger than a predetermined value, the voltage is reduced to one half by switching the connection switching circuit provided in the rectifier circuit, so that the duty ratio in the inverter is so small. Without this, a predetermined output voltage can be obtained. For this reason, the loss in the transformer is reduced and the efficiency is improved as compared with the conventional one in which switching by the connection switching circuit is not performed. In addition,
Since a step-down circuit or the like becomes unnecessary, the circuit scale is reduced and the cost is reduced. Further, as the voltage is reduced to half, circuit elements such as diodes can be reduced in withstand voltage, and the cost is reduced in this aspect as well.

(Effect of the Second Invention) A DC-DC converter for obtaining a constant DC voltage by using a power generation voltage of a vehicle generator or a turbocharger rotating electric machine as an input has a constant DC voltage even if the input voltage greatly varies. It is demanded that the DC-DC converter of the present invention satisfies these conditions, and that the DC-DC converter of the present invention satisfies those conditions. It is suitable for.

[Brief description of the drawings]

FIG. 1 is a diagram showing a DC-DC converter according to the present invention.

FIG. 2 is a diagram illustrating circuits around a rectifier circuit when switching is performed by a connection switching circuit 18.

FIG. 3 is a diagram illustrating a duty ratio of an inverter according to the present invention.

FIG. 4 is a diagram showing an example of use of the DC-DC converter of the present invention.

FIG. 5 is a diagram for explaining a relationship between an input voltage and a duty ratio in an inverter.

FIG. 6 is a diagram showing switching when the duty ratio is different in the inverter.

FIG. 7 is a diagram showing a first conventional example of a DC-DC converter.

FIG. 8 is a diagram showing a second conventional example of a DC-DC converter.

[Explanation of symbols]

1: input AC power supply, 2: rectifier circuit, 3: current detector,
4, 5: resistor, 6: smoothing capacitor, 7: step-down circuit,
8 inverter, 9 transformer, 10 rectifier circuit, 10
A, 10B, 10C, 10D: diode, 11: smoothing inductance, 12: smoothing capacitor, 13, 1
4 ... resistance, 15 ... current detector, 16 ... load, 17 ... controller, 18 ... connection switching circuit, 19, 20 ... diode, 21, 22 ... transistor, 23, 24 ... smoothing inductance, 31 ... pulley, 32 ... Engine, 33 ...
Intake pipe, 34 ... exhaust pipe, 35 ... turbocharger, 36
... compressor blade, 37 ... rotor, 38 ... stator, 39 ... turbocharger rotating electric machine, 40 ... turbine blade, 41 ... belt, 42 ... pulley, 43 ... vehicle generator, 44 ... controller, 45 ... power section, 46 … D
C-DC converter, 47 ... battery, 48 ... load, V
_A, V _B, V _C ... input _{voltage, D A, D B, D} C, D M ...
Duty ratio

Claims (2)

[Claims] An inverter for converting a fluctuating input voltage into an alternating current by controlling a duty ratio, an transformer for transforming the alternating current, a rectifying circuit for rectifying the transformed alternating current, and a DC output voltage for smoothing the rectified voltage. A smoothing circuit, voltage detection means for detecting the DC output voltage, and a controller for controlling the duty ratio of the inverter based on a detection value from the voltage detection means to make the DC output voltage a constant value. A DC-DC converter comprising: an input voltage detecting means for detecting an input voltage and inputting a detection signal to the controller; and an anti-parallel connected body of two transistors and a diode connected in series. A connection switching circuit connected between the output sides of two diodes adjacent to one DC output side terminal of the circuit; One end is connected, and the other end is collectively connected to an output terminal. The input terminal is turned on when the input voltage is lower than a predetermined value, and the input voltage is higher than the predetermined value. A DC-DC converter, wherein the controller controls the transistor to be turned off at one time. 2. The DC-DC converter according to claim 1, wherein a generated voltage from a generator driven by an internal combustion engine of the vehicle is used as an input voltage.