JP2001275352A - Forward resonance converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forward resonance converter, capable of both soft- switching and power factor improvement with a simple structure by reducing the required number of parts. SOLUTION: This resonant converter is formed by eliminating a feedback diode connected to a resonance inductance on input side, and a third winding (reset winding) of a transformer, based on the circuit structure of a conventional forward AC/DC resonance converter. This converter is provided with a transformer, having first and third windings of which one terminals are connected to each other and a second winding, a main switch connected between the other terminal of the first winding and a pole of a DC power source, an output diode connected to one terminal of the second winding, an output reactor and a capacitor connected in series between the output terminal of the output diode and the other terminal of the second winding, a circulating diode connected to the output terminal of the output diode from the other terminal of the second winding so as to be in the forward direction, and a resonance capacitor connected between one terminal of the first or third winding and the other pole of the DC power source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forward-type resonant converter, and more particularly, to a forward-type DC / DC and an A / D converter in which soft switching is realized by employing a resonance system.
It relates to a C / DC converter.

[0002]

2. Description of the Related Art Conventionally, various types of forward DC / DC and AC / DC converters have been proposed for realizing soft switching and reducing switching loss (for example, Japanese Patent Application Laid-Open No. H10-108458). Gazette, Japanese Patent Laid-Open No. 7-95767,
788, etc.).

If a conventionally proposed forward converter is used as it is for an AC / DC converter, it is difficult to improve the power factor, and it is difficult to achieve both soft switching and high power factor with a simple configuration. There was a problem.

As a solution to such a problem, a specific example in which a forward-type resonance converter is applied to an AC / DC converter is described in IEICE Technical Research Group (1992).
May 17, 2009) "Electronic Communication Energy Technology"
(IEICE Technical Report, Vol. 99, No. 54), pp. 35-40. The circuit is shown in FIG. This circuit configuration is based on a forward AC / DC converter, and its input side includes a resonance inductor LR and a capacitor CR.
Is additionally connected.

[0005] This forward-type resonant converter includes a transformer having first and third windings and a second winding each connected to one terminal, and one terminal of the first and third windings. A resonance inductor connected to one pole of the DC power supply and a resonance capacitor connected to the other pole of the DC power supply; a main switch connected between another terminal of the first winding and the other pole of the DC power supply; An output diode connected to one terminal of the second winding, an output reactor and a capacitor connected in series between an output terminal of the output diode and another terminal of the second winding; A return diode connected in a forward direction from a terminal to an output side terminal of the output diode; and a feedback diode connected in a forward direction from the other pole of the DC power supply to another terminal of the third winding. Comprising a chromatography de, the output diode, the main switch is configured by connecting to a polarity to conduct when conducting.

The main switch Q1 has a preset duty ratio D
Driven by When Q1 is on, the resonance capacitor C
R, the output reactor L, and the exciting inductance LM of the transformer TR cause current resonance, and the current flowing through the main switch Q1 rises from zero. On the other hand, when the main switch Q1 is turned off, the CR and LM and the resonance inductor LR resonate with each other, and the voltage between the terminals of the main switch Q1 rises from zero. As a result, in the discontinuous mode in which the current of the output reactor L has a cutoff period, soft switching is realized both when the main switch Q1 is on and when it is off.

In the continuous mode in which the current of the output reactor L is not interrupted, soft switching is realized when the main switch Q1 is turned off. However, when the main switch Q1 is turned on, the output current iL flowing through the output reactor L does not become zero. Also, the current flowing through the main switch Q1 does not become zero, and soft switching is not realized. However, in any case, as compared with a normal forward type AC / DC converter, the capacitor CR completely repeats charging and discharging every switching cycle, and a high power factor can be achieved because the charging current is supplied from the power supply ei. it can.

FIGS. 2 and 7 show the current and voltage waveforms, the operating state, and the generation period of each part of the circuit in FIG. 6 during the discontinuous mode operation. FIG. 2 shows the voltage and current waveform of each part with respect to the AC input voltage ei. FIG. 7 is an enlarged time axis (horizontal axis) of the waveform of FIG.
The waveform of each part with respect to the period TC is shown. Note that the magnitudes (vertical axis) of the AC current ii and the input current iLR are enlarged as compared with other waveforms so that the operation can be easily understood.

In the circuit of FIG. 6, two operation modes occur as shown in FIG. That is, the terminal voltage VCR (hereinafter, referred to as "input voltage") of the resonance capacitor CR is smaller than the output voltage (N1 / N2) v0 (hereinafter, referred to as "converted output voltage") converted to the primary side of the transformer TR. That is, the mode A in the case of (N1 / N2) v0> VCR is opposite to the mode A, and the mode B in the case of (N1 / N2) v0 <VCR.

In the mode A, since the input voltage VCR is lower than the reduced output voltage (N1 / N2) v0, energy is not transmitted from the input side to the output side, and the reactor (output) current iL does not flow. However, in this circuit, the inductor L
The input voltage VCR increases due to the resonance between R and the exciting inductance LM and the capacitor CR, and the period of the mode A becomes shorter than that of a normal forward AC / DC converter, so that the power factor increases.

On the other hand, in mode B, if the characteristics of the diode are ideal and the transformer TR is tightly coupled, the four operations shown in the waveform diagram of FIG. 7 and the equivalent circuit diagrams of FIGS. States a to d occur. The following states a to d
Will be described in detail.

In the state a, the main switch Q1 is turned on at time t1, and the diode D2 on the output side is turned on. As will be described later, the input voltage VCR is higher than the power supply voltage ei due to the resonance between the inductor LR and the capacitor CR, and the input current iL R does not flow because the full-wave rectifier diode REC is reverse-biased. The energy stored in the capacitor CR is transferred to the output side by current resonance between the exciting inductance LM and the parallel inductance of the output reactor L and the resonance capacitor CR.

At this time, the current iD _{1 of the} main switch Q1
Rises from zero, so that soft switching is realized. Note that the resonance frequency in this case is determined by the value of the capacitor C
It is necessary that the timing (time t2) at which the terminal voltage VCR becomes 0 after R has finished discharging is selected so as not to be later than the off timing (time t3) of the main switch Q1. This state a ends at the time t2 when the capacitor CR is discharged and its terminal voltage, that is, the input voltage VCR becomes zero (see FIG. 7).

In the state b, the main switch Q1 and the freewheeling diode D3 are turned on, and the output diode D2 is turned off. Since the exciting inductance LM is short-circuited by the transformer TR and the feedback diode DF, the exciting energy stored there is returned as the current i 電流. At this time, the capacitor CR is not charged, and the input voltage VCR holds 0.
Therefore, a current i LR starts to flow from the power supply νD via LR, and energy is stored in the resonance inductor LR. On the output side, the energy of the output reactor L is equal to the diode D3.
And energy is supplied to the load R. This state b ends at time t3 when the main switch Q1 is turned off (see FIG. 7).

In the state c, since the main switch Q1 is turned off at the time t3, the diode D2 is turned off, and the freewheeling diode D3 maintains the on state. Resonant inductor L
R and the parallel inductance of the exciting inductance LM and the capacitor CR cause voltage resonance, and the input voltage VCR
In addition, the terminal voltage VDS of the main switch Q1 rises from zero, and soft switching is realized.

The exciting energy stored in the transformer TR charges the capacitor CR via the tertiary winding N3 and the feedback diode DF. On the other hand, a current iLR also flows from the power supply νD via the inductor LR to charge the resonance capacitor CR. The output side is the same as the previous state b. This state c ends at time t4 when the current i3 passing through the diode DF becomes zero (see FIG. 7).

In a state d starting at time t4, the main switch Q1 and the diode D2 are off, and the diode D3 is on. The inductor LR and the capacitor CR resonate in series, and the capacitor CR is charged by the current iLR from the power supply νD. At time t5 when the charging is completed, the current iLR becomes 0, and the capacitor CR is charged to a voltage VCR higher than the power supply voltage νD. The resonance capacitor CR is then connected to the main switch Q
Until time t6 when 1 turns on (state a), the terminal voltage VCR is held.

At this time, the output side is the same as the states b and c, during which the (output) current i flowing through the output reactor L
L will be zero. This state d ends at time t6 when the main switch Q1 is turned on, and returns to state a (see FIG. 7).

As described above, according to the converter of FIG. 6, soft switching is performed both when the main switch Q1 is turned on (time t1) and when it is turned off (time t3). As shown in FIG. 7, the terminal voltage VCR of the resonance capacitor CR becomes zero at each switching cycle, and the input current iLR (that is, the power supply current ii) flows in each switching cycle in proportion to the power supply voltage VD. Power factor is realized.

The power factor of the above-mentioned resonant converter has a small dependence on the output current, a power factor of about 95% or more can be obtained even in a small output current region, and the higher the duty ratio D, the higher the power factor. I know it. On the other hand, in the conventional type, the dependency of the power factor on the output current and the duty ratio is larger than that of the resonant converter. That is, in the conventional type, the output current is large,
A power factor close to 98% can be obtained where the duty ratio is small, but 8% where the output current is small and the duty ratio D is large.
It tends to be as low as 3%.

[0021]

With the rapid expansion of applications and demands for devices using electronic circuits, there has been a demand for further miniaturization.

An object of the present invention is to provide a simple configuration in which the number of necessary components is reduced, to achieve both soft switching and power factor improvement, and to reduce the size without lowering the performance. It is another object of the present invention to provide a forward resonance converter that can also achieve the above.

[0023]

A forward type resonant converter according to the present invention has first and third windings each having one terminal connected to each other, and a second winding.
The other terminal of the winding is a transformer connected to one pole of the DC power supply; a main switch connected between the other terminal of the first winding and the other pole of the DC power supply; An output diode connected to one terminal, an output reactor and a capacitor connected in series between an output terminal of the output diode and the other terminal of the second winding, and an output diode connected to the other terminal of the second winding. And a resonant capacitor connected between the other terminal of the DC power supply and a first terminal of the first and third windings. The output diode is characterized in that it is connected to a polarity that conducts when the main switch conducts.

In this case, in the discontinuous mode (DCM) operation, soft switching is realized both when the main switch Q1 is turned on and off. On the other hand, in continuous mode (CCM) operation, soft switching is realized when the switch is off, but soft switching is not achieved when the switch is on. However, for the above reason, since the current ii flows in each switching cycle, the normal CCM forward AC /
The power factor is greatly improved as compared with the DC converter. Also,
If a saturable reactor is added in series to the second winding, soft switching is achieved even when the main switch is turned on.

[0025]

FIG. 1 is a circuit diagram showing an embodiment of a forward resonance converter according to the present invention. 6, the same reference numerals as those in FIG. 6 denote the same or equivalent parts.
As is clear from comparison with the circuit of FIG. 6, in this embodiment, the third winding of the forward resonance converter of FIG. 6 is omitted by omitting the resonance inductance LR inserted in series on the power supply side of the transformer. The reset winding (N3) is also used, and the feedback diode DF is omitted. In this embodiment, the same two operation modes as those shown in FIG. 2 occur. The operation is common to the circuit of FIG. 6 in many cases, so the common parts are omitted, and different parts will be mainly described below.

An operation mode B in which the primary-side converted output voltage of the transformer TR is larger than the terminal voltage of the resonance capacitor CR.
In (see FIG. 2), five operation states a to e shown in FIG. 3 occur. 4A to 4D show the operating states a to d.
Are equivalent circuits. In the following, for convenience of explanation, the number of turns of each winding of the transformer TR is equal, and N
Assume that 1 = N2 = N3.

In the state a, the main switch Q1 is turned on, and the output diode D2 is also turned on. Since the terminal voltage νCR of the resonance capacitor CR is higher than the input voltage νD and the full-wave rectifier diode REC is reverse-biased, the input current i3
(See FIG. 1) does not flow. The energy (charge) stored in the resonance capacitor CR is transferred to the output side through the transformer TR. At that time, the current iD1 of the main switch Q1 is
Since current resonates between the capacitor CR, the exciting inductance LM and the output inductor L and rises from zero, soft switching is realized. This state a ends when the terminal voltage νCR of the capacitor CR becomes equal to the reduced output voltage (N1 / N2) ν0 (t2) as shown in FIG.

In the state b, the main switch Q1 and the diode D2 maintain the ON state. The excitation energy of the excitation inductance LM and the energy of the output inductor L are equal to the power supply ν.
Reflux through D. At this time, since the current iL of the output inductor L is substantially constant, the terminal voltage νCR of the capacitor CR becomes substantially equal to the output voltage ν0. At the time point t2 when the state b is reached, the turns ratio of the transformer (N1 + N3) / N2
Changes from 1 to 2, the primary current corresponding to the current iL is iL / 2. As a result, the primary current iD1
Is iDi = i3 = iLM + iL / 2, and decreases stepwise at time t2 as shown in the waveform of FIG. This state b
Ends when the main switch Q1 is turned off.

In the state c, the main switch Q1 is turned off, and the exciting energy is fed back to the capacitor CR through the winding N3 to charge the capacitor CR. Further, the primary current corresponding to the current iL increases since N2 = N3 as compared with the state b, and the input current i3, that is, the capacitor current iCR becomes iLM + iL, and increases stepwise at time t3.
On the other hand, the voltage .nu.DS of the main switch Q1 rises from zero due to voltage resonance between the capacitor CR, the exciting inductance LM and the output inductor L, and soft switching is realized. In this state c, the voltage νN1 of the winding N1 becomes zero.
, D2 is turned off, and the process ends.

In state d, the main switch Q1 and the output diode D2 are both off, and the freewheeling diode D3 is on. The exciting energy stored in the transformer TR charges the capacitor CR while resonating between the exciting inductance LM and the resonance capacitor CR via the third winding N3, and the transformer TR is reset. When the excitation energy becomes 0, that is, when the currents of the excitation inductance LM and the resonance capacitor CR both become 0,
This state d ends.

During this time, on the load side, the energy of the output inductor L circulates through the freewheeling diode D3, and this energy becomes zero at time t41 before time t5 when the state d ends. Energy supply to the load R after this point is performed only from the output capacitor C.

Although the equivalent circuit in the state e is not shown in FIG. 4, all the switch elements are off, and the energy is continuously supplied from the output capacitor C to the load R. During this time, the voltage .nu.DS of the main switch Q1 is equal to the voltage .nu.CR of the resonance capacitor CR, and both maintain the peak voltage. This relationship is maintained at time t6 until the next time the main switch Q1 is turned on and the state a starts.

As can be seen from the above description, in order to realize the soft switching in this embodiment, the electric charge of the capacitor CR is discharged before the main switch Q1 is turned off.
The terminal voltage νCR must be equal to the reduced output voltage (N1 / N2) ν0. Therefore, the switch Q with respect to the switching cycle Tc of the main switch Q1 (see FIG. 3)
The minimum value Dmin of the duty ratio, which is the ratio of the ON periods of 1, is determined by the resonance cycle in the state a, as in the case of FIG. By the time the main switch Q1 is turned on, the current of the exciting inductance needs to be zero (that is, the reset of the transformer TR is completed). Decided.

It will be readily understood that the embodiment shown in FIG. 1 can realize a high power factor and a small distortion factor similarly to the case of FIG. 6 described above.

FIG. 5 is a diagram showing power factor characteristics of the forward type AC / DC resonant converter of the present invention and a conventional forward type AC / DC converter having no resonant inductor LR or capacitor CR. A) is a conventional type,
(B) is an experimental example showing the power factor characteristics of the converter of the present invention with respect to the output current, using the duty ratio D as a parameter.

The power factor of the resonant converter of the present invention has a small dependence on the output current, a power factor of about 95% or more can be obtained even in a small output current region, and the higher the duty ratio D, the higher the power factor. I understand. On the other hand, Japanese Unexamined Patent Publication No.
In the conventional type as disclosed in Japanese Patent Application Laid-Open Publication No. H10-115, the power factor has a large dependency on the output current and the duty ratio as compared with the resonant converter of the present invention. That is, in the conventional type, a power factor close to 98% can be obtained where the output current is large and the duty ratio is small, but it is as low as 83% when the output current is small and the duty ratio is large.

Although not shown, the distortion factor characteristic of the resonant converter according to the present invention also increases as the output current increases.
% From around 5% to around 5%, while in the conventional type the output current rises from around 70% to around 18%, confirming that the resonant converter has a lower distortion rate than the conventional type. Was. In the conventional type, the zero period during which the AC current ii (input current iLR) does not flow is long, whereas in the resonant converter of the present invention, since the zero period is short, the power factor is high and the distortion factor is small as described above. ing.

Although the embodiment of the present invention has been described as operating in the discontinuous mode, these circuits can also be operated in the continuous mode. In continuous mode,
When the main switch Q1 turns off, zero voltage switching is performed. When the main switch Q1 turns on,
Due to the continuity of the reactor current iL (it does not become 0 at the end of the state d), the drain current iD1 does not rise from zero, and soft switching is not realized. However, also in this case, the same operation state is basically repeated, and a high power factor is achieved.

As a countermeasure against this, in the circuit of FIG.
Oversaturating the output diode D2 in series with the connection point between the upper terminal of the freewheeling diode D3 and the output reactor L and closer to the winding N2 of the transformer TR than the connection point between the lower terminal of the freewheeling diode D3 and the output capacitor C. It is preferable to connect a reactor (not shown). If you do this,
At the moment when the main switch Q1 is turned on, the current flowing through the diode D2 is blocked to open the secondary winding N2, thereby realizing soft switching.

In the above description, an example of an AC / DC converter using a DC power supply in which an AC input is full-wave rectified has been described.
It is obvious that the present invention can be similarly applied to a converter and a DC / DC converter in which a backflow prevention diode is connected in series to the DC power supply.

[0041]

According to the present invention, a compact and high power factor is achieved as compared with the conventional forward converter, and current resonance occurs when the main switch Ql is turned on, voltage resonance occurs when the main switch Ql is turned off, and in the discontinuous operation mode. , Soft switching is realized both on and off. Therefore, both improvement of the power factor and reduction of the switching loss can be achieved. Also in the continuous operation mode, it is possible to achieve both the soft switching when the main switch is off and the improvement of the power factor. Furthermore, if a saturable reactor is inserted in series with the output diode on the secondary side of the transformer, soft switching can be realized even when the main switch is turned on.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is a diagram showing a current and a voltage waveform of each part of the circuit with respect to an AC input voltage ei during a discontinuous mode operation of the circuit of FIG.

3 is a diagram in which the time axis (horizontal axis) of the waveform in FIG. 2 is enlarged and shows the waveform of each unit with respect to one switching period TC.

FIG. 4 is a diagram showing an equivalent circuit of the circuit of FIG. 1 in states a to d of FIG. 3;

5 is a diagram showing the power factor characteristics of the embodiment circuit of FIG. 1 and a conventional forward type AC / DC converter that does not use resonance, using a duty ratio D as a parameter. FIG. (B) is an experimental example of one embodiment of the present invention.

FIG. 6 is a circuit diagram of an example of a conventional forward resonance converter.

FIG. 7 shows one cycle T of switching of the converter of FIG.
It is a figure which shows the waveform of each part with respect to C.

8 is a diagram showing an equivalent circuit of the circuit of FIG. 6 in states a to d of FIG. 7;

[Explanation of symbols]

C: output capacitor, CR: resonance capacitor, D2
... Output diode, D3 ... Reflux diode, L ... Output inductance, N1 to N3 ... First to third transformers
Winding, Q1 ... Main switch, TR ... Transformer

Claims (5)

[Claims] 1. A transformer having first and third windings each having one terminal connected to each other, and a second winding, and the other terminal of the third winding connected to one pole of a DC power supply. A main switch connected between the other terminal of the first winding and the other pole of the DC power supply; an output diode connected to one terminal of the second winding; and an output side of the output diode. An output reactor and a capacitor connected in series between a terminal and the other terminal of the second winding; and a free-wheeling diode connected in a forward direction from the other terminal of the second winding to an output terminal of the output diode. And a resonance capacitor connected between one terminal of the first and third windings and the other pole of the DC power supply, wherein the output diode has a polarity that conducts when the main switch conducts. Forward type connected to Vibration converter. 2. The forward resonant converter according to claim 1, further comprising a diode for preventing a current from flowing from the other terminal of said third winding to a power supply side. 3. A supersaturated reactor which is connected in parallel with said output diode to substantially block a current flowing through said output diode at the moment when said main switch is turned on. Forward type resonant converter. 4. A forward resonant converter according to claim 1, wherein said DC power supply is obtained by rectifying an AC power supply. 5. The forward-type resonant converter according to claim 2, wherein a diode for preventing a backflow of current rectifies an AC power to provide the DC power.