KR100199508B1 - A zero-crossing voltage/current circuit for full-bridge dc/dc converter - Google Patents

Abstract

The present invention is different from the prior art in that a full bridge that allows zero voltage / zero current switching is possible even for a switching element composed of a small number of carrier elements by only a passive element of the secondary side without using a separate saturated reactor or an active element The present invention relates to a circuit for switching between zero voltage and zero current of a DC / DC converter. The full bridge DC / A transformer (T) for inducing the current and voltage of the transformer to the secondary side and the tertiary side; Diodes (D1, D2, D3, D4) constituting a full bridge for allowing current to flow in one direction on the secondary side; An output filter on the secondary side (L _O, C _O), and the applied load (R _O); and the full-bridge rectifier (BD100) which is connected to the third winding of the transformer (T) rectifies the current as a component according to the invention ; A capacitor C100 connected between the output terminal of the rectifier BD100 and the ground; And a diode (D100) connected between the output terminal of the rectifier (BD100) and the output terminal of the secondary side, so that zero voltage / zero current switching is performed. Thus, the full bridge DC / The converter can be realized at a low cost by not including lossy parts such as a saturated reactor and expensive parts such as active elements, and is also widely used in a DC / DC converter of a large capacity high frequency switching It is an economical and useful invention.

Description

Circuit for zero voltage / zero current switching of full bridge DC / DC converters

The present invention relates to a circuit for zero voltage / zero current switching of a full-bridge DC / DC converter, and more particularly, To a circuit for zero voltage / zero current switching of a full bridge DC / DC converter capable of zero voltage / zero current switching even for a switching element composed of a small number of carrier elements using only passive elements.

In the switching operation of the power semiconductor device, since the voltage and current vary with a constant delay and slope depending on the device, the switch is short-circuited (hereinafter referred to as turn-on) or open (hereinafter referred to as turn-off ), The voltage and current are applied to the switch at the same time. Therefore, power loss of switching corresponding to the product of voltage and current occurs during this interval. Particularly, an element such as an insulated gate bipolar transistor (IGBT) or a gate turn off thyristor (GTO) has a structure in which, as shown in FIG. 6, The switching loss at the time of turn-off is very large because the current flows during a certain period (a period denoted by "L") even after the voltage is sufficiently applied to both ends of the switch.

Since the switching loss increases in proportion to the frequency at which the device is opened and closed, it is a factor limiting the maximum switching frequency of the device. Therefore, to reduce the switching losses of devices with these characteristics and enable high frequency switching, the zero voltage switching method as shown in Figure 7 (a) or the zero current switching method as shown in Figure 7 (b) should be used. In the zero-voltage switching, when the diode connected in anti-parallel with the switching element is turned on after the voltage across both ends of the switching element is turned on due to conduction by the return current, power loss due to switching is completely eliminated as shown in FIG. 7 (a) . However, when the switching element is turned off, the loss is not reduced because it is the same as in Hard-Switching of FIG. 6. If a snubber capacitor is connected to both ends of the switching element to eliminate this loss, as shown in FIG. 7 (b), the voltage increase rate decreases and the power loss during the current decrease period is reduced do.

In the zero current switching, as shown in (b) of FIG. 7, when the current flowing through the switching element is zero, the switching element is turned off. In this case, since the accumulated minority carriers forming the tail current have disappeared, The power loss caused by the power consumption is not generated. However, at the time of turn-on, there is generally a loss due to the reverse recovery time of the diode because it is the same as the hard switching of FIG. 6, but the diode is not recovered in the full bridge DC / DC converter. Do not. Therefore, it can be seen that the zero-current switching is slightly advantageous for zero-voltage switching in a full-bridge DC / DC converter.

At present, full-bridge DC / DC converters of zero voltage switching are widely used for large capacity high frequency switching applications. However, since a load range for zero voltage switching is narrow, a large snubber capacitor can not be connected in parallel with the switching device. ) Or a gate turn-off ring (GTO) in a high-frequency switching operation is difficult due to the switching loss.

In order to solve this problem, full bridge DC / DC converters in which the zero-voltage switching and the zero-current switching are mixed, such as the fifth aspect, in which high frequency switching is enabled also for a small number of carrier elements such as insulated gate bipolar transistors and gate turn- Have been proposed and used.

In the full bridge DC / DC converter of FIG. 5, the left legs S1 and S3 of the primary side perform the zero voltage switching and the right legs S2 and S4 perform the zero current switching in the wide load range, Frequency switching can be performed even for devices having a tail current characteristic at the time of turn-off such as a transistor or a gate turn-off thyristor. In the reflux mode, the secondary side current does not flow back through the primary side and the secondary side rectifying devices D1, D3 and D4 so that the conduction losses due to the primary side switching elements S1, S2, S3 and S4 and the transformer T are reduced.

However, the full bridge zero voltage / zero current DC / DC converters constructed as in the fifth aspect have respective problems, and the converter circuit shown in FIG. 5 (a) includes a saturated reactor SR on the primary side There is a problem that the additional power loss and the saturated reactor (SR) must be cooled,

the converter circuit shown in FIG. 6B has a problem that the cost is increased by including an active element in the secondary circuit, and a separate control circuit for controlling the active element is required.

the rectifier voltage Vrec of the secondary side is in a steady state due to the resonance between the leakage inductance of the transformer T and the capacitor in the auxiliary circuit part 10 although the converter circuit shown in Fig. The voltage stress of the rectifier diodes D1, D2, D3 and D4 is increased, and the power loss is increased due to the return current due to the resonance.

Accordingly, the present invention has been made to overcome the above problems, and it is an object of the present invention to provide a rectifier which does not use a lossy element such as a saturated reactor or an active element and which can reduce a power loss due to a high voltage stress or a return current The present invention provides a circuit for zero voltage / zero current switching of a bridge DC / DC converter,

Another object of the present invention is to provide a circuit for zero voltage / zero current switching of a full bridge DC / DC converter which prevents an excessive peak in current from occurring when current is charged in a capacitive element in a circuit according to the present invention .

FIG. 1 is a full bridge DC / DC converter equipped with an embodiment of a circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to the present invention,

FIG. 2 shows a configuration of various full bridge DC / DC converters equipped with an embodiment of a circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to the present invention,

Figure 3 shows an equivalent circuit according to each operating phase of the first phase circuit,

4 shows the current and voltage waveforms generated according to the respective operation steps of the first-degree circuit by extracting only the main portion,

FIG. 5 illustrates a full bridge DC / DC converter of conventional zero voltage / zero current switching,

FIG. 6 shows current and voltage waveforms during hard switching rather than zero voltage / zero current switching,

FIG. 7 shows current and voltage waveforms during zero voltage / zero current switching,

(a) is the current and voltage waveform at zero voltage switching,

(b) are the current and voltage waveforms at zero current switching.

DESCRIPTION OF THE REFERENCE NUMERALS

10: Conventional circuit for zero voltage / zero current switching

100: Embodiment of circuit according to the present invention BD100: Full bridge rectifier

BD100 ': Half bridge rectifier C1, C3: Snubber capacitor

C100: capacitor

D1, D2, D3, D4: Diodes constituting a rectifier

D100: Diode D101: Reflux diode

DS1, DS2, DS3, DS4: Diode I _C : Current flowing through the capacitor (C100)

I _O : Load current I _SW : Current flowing through the switch

I _P : Primary current L100: Coil

L _O , C _O : Output filter L _lk : Leakage inductance

R _O : Load

S1, S2, S3, S4: Switches that make up the full bridge

SR: Saturated reactor T: Transformer

V _C : Capacitor (C100) voltage at both ends V _GS : Switch control voltage

V _SW : voltage across switch V _ab : primary voltage

V _rec : secondary voltage

According to another aspect of the present invention, there is provided a full bridge DC / DC converter including a transformer, the zero-voltage / zero current switching circuit of the full bridge DC / DC converter including: Rectifying means connected to the two terminals for rectifying the current induced in the tertiary winding and outputting the rectified current to the output terminal; A passive capacitive element connected between the output terminal of the rectifying means and ground; And a first rectifying element connected and arranged in a direction in which a current of the rectifying means can flow between an output terminal of the rectifying means and a terminal to which a rectified current is outputted from the secondary side of the transformer And the rectifying means is implemented as a rectifier of a full bridge rectifier or a half bridge,

A circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to the present invention is characterized in that a circuit for zero voltage / zero current switching of a full bridge DC / DC converter is provided between the third winding of the transformer and the rectifying means, or between the connection point of the first rectifying element and the rectifying means And a passive inductive element connected between the output terminals.

When a circuit for switching the zero voltage / zero current of the full bridge DC / DC converter according to the present invention is installed on the secondary side, the full bridge DC / DC converter switches the zero voltage / do.

The switches on the leading leg and the lagging leg constituting the full bridge are alternately turned on and off according to the phase of the control voltage for opening and closing applied to the gate, Off of the switch on the forward leg is the same as in the conventional configuration. That is, when the switch is turned off, the switching loss is reduced by the snubber capacitors connected in parallel. The turn-on of the switch is controlled by the voltage charged in the passive capacitive element and the voltage charged in the snubber capacitor connected in parallel to the switch The switching diode is turned on by turning off the other switch on the same leg, thereby reducing the switching loss by completely supplying the current to the load instead of turning on the reverse diode while the voltage across the switch is zero. . The above-mentioned passive capacitive element is connected to the rectifier circuit connected to the third winding during a powering mode for supplying current to the load, A positive voltage is applied to the secondary side for a predetermined period while the charged voltage is started to be discharged through the first rectifying element while a reflux mode in which the power supplied from the power source is temporarily started. The voltage applied to the secondary side is applied in reverse to the direction in which the current flows in the primary leakage inductance through the transformer, thereby rapidly reducing the current flowing to the primary side. When the current flowing in the primary side rapidly decreases to zero, the corresponding switch on the ground leg is turned off at zero current.

Hereinafter, the configuration and operation of an embodiment of a circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to the present invention will be described with reference to the drawing of the attached full bridge DC / Will be described in detail.

FIG. 1 illustrates a full bridge DC / DC converter in which an embodiment of a circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to the present invention is implemented. , S4) for inducing the current and voltage on the primary side to the secondary side and the tertiary side according to the opening and closing operation of the primary side and the secondary side; Full bridge diodes (D1, D2, D3, D4) for allowing current to flow in one direction in the secondary side; The output filter is applied to the secondary side (L _O, C _O) and a load (R _O); and the full-bridge rectifier (BD100) which is connected to the third winding of the transformer (T) rectifies the current as a component according to the invention ; A capacitor C100 connected between the output terminal of the rectifier BD100 and the ground; And a diode D100 connected between the output terminal of the rectifier BD100 and the output terminal of the secondary side.

FIG. 4 shows only a main part of a waveform of a signal generated during the operation of the full bridge DC / DC converter configured as described above. The waveform of the signal indicates the operation of the full bridge DC / DC converter Respectively.

FIG. 3 shows an equivalent circuit of the DC / DC converter in the divided operation mode according to the signal waveform of FIG. 4.

In order to simplify the explanation of the operation of the full bridge DC / DC converter configured as described above, it is assumed that the inductor (L _O ) of the output filter is sufficiently large so that the load current (I _O ) Of the secondary winding is less than or equal to the root of the secondary winding.

Hereinafter, the process of performing the zero voltage and the zero current switching in the full bridge DC / DC converter configured as above will be described step by step with reference to waveforms according to the divided operation modes of FIG.

Mode 1 (M1)

The switches S1 and S2 on the primary side are conducted to transmit power from the input terminal to the output terminal, and this mode is referred to as a 'powering mode'. The capacitor C100 begins to charge by resonance with the leakage inductance in the tertiary winding of the transformer T. [ When the voltage to be charged is increased by twice the voltage obtained by multiplying the input power supply voltage V _S by the winding ratio N3 / N1 of the third winding, the resonance ends and a reverse voltage is applied to the diode in the rectifier BD100 The flow of current is cut off. Also, the voltage charged in the capacitor C100 is lower than the output voltage of the secondary winding because the tertiary winding is equal to or less than 1/2 of the secondary winding, and therefore, the voltage is not discharged to the load through the diode D100.

Mode 2 (M2)

Since the voltage charged in the capacitor C100 is not formed with a discharge loop, the charged voltage is maintained until a loop due to an external factor is formed.

Mode 3 (M3)

When the switch s1 is opened by a predetermined duty cycle, the snubber capacitor C1 starts to charge and the snubber capacitor C3 starts discharging due to the constantly flowing load current. The voltage of the snubber capacitor C1 increases linearly because the load current is constantly flowing, so that the primary side voltage V _ab of the transformer T decreases linearly. The value of the snubber capacitor C1 is sufficiently increased as in the conventional zero voltage switching so that the voltage across the switch S1 in the turned off period is maintained close to zero (see FIG. 7 (a)), It is possible to prevent the loss from occurring. At this time, the secondary side voltage (V _rec) is to be reduced at the same rate as the rate at which the reduced voltage (V _ab) of the primary winding, the voltage loss is then the secondary side voltage, the capacitor (C100 from the M2 stage ) Until it becomes equal to the voltage being held and charged

Mode 4 (M4)

Voltage (V _rec) on the secondary side when becomes equal to the voltage charged in the capacitance when emitter (C100) while decreasing the diode (D100) is the conduction voltage of the secondary side of the transformer (T) (V _rec) Discharges at a very slow rate from the voltage charged in the capacitor C100. On the other hand, the voltage discharged from the snubber capacitor C3 on the primary side is discharged at a high speed continuously by the current flowing in the leakage inductance on the primary side. Therefore, the primary voltage V _ab , The voltage gradually discharged from the capacitor C100 becomes lower than the voltage applied to the primary side. Thus, the voltage passed to the primary winding a voltage difference part than the primary voltage (V _ab) of the secondary-side voltage (V _rec) is applied in a direction opposite to the current (I _P) flowing in the leakage inductance of the primary winding of the primary winding The current is sharply reduced.

Since the current flowing through the inductor L _O of the output filter is constant, current is supplied from the capacitor C 100 on the secondary side through the diode D 100 by the amount of current decreasing on the primary side, The voltage of the capacitor C100 begins to decrease at a faster rate than that at the step M3 and the above process is performed until the voltage of the snubber capacitor C3 on the primary side becomes zero.

Mode 5 (M5)

When the voltage of the snubber capacitor C3 which is decreasing becomes zero, the diode DS3 connected in the reverse direction to the switch S3 becomes conductive, so that the voltage across the switch S3 becomes zero and the zero voltage switching is performed. This step is continued until the current I _P flowing in the primary side continues to decrease at a high speed by the voltage applied from the secondary side to the primary side and in the reverse direction until it becomes zero.

Mode 6 (M6)

Since the current I _{P on the} primary side is zero, the switch S2 is allowed to turn off at zero current. At this time, since there is no current supplied from the primary side, the capacitor C100 on the secondary side is supplied with the full load current, and this step proceeds until the voltage of the capacitor C100 is completely discharged and becomes zero.

Mode 7 (M7)

When the voltage of the capacitor C100 on the secondary side is completely discharged, the load current I _O flows through the full-bridge diode of the secondary side to reflux (D2-D4, D3-D1).

Mode 8 (M8)

Since the current is not flowing through the switch S2, the switch S4 is turned off in the zero current state, and the dead time is reached until the switch S4 is turned on to newly form a current loop.

Mode 9 (M9)

The switch S4 is turned on and the reflux mode is ended. The turn-on process of the switch S4 is also performed in the state of zero current since the current can not be abruptly changed due to the leakage inductance of the primary side. Since the current supply loop is formed through the switches S4 and S3 on the primary side, the current linearly increases, and this current is induced to the secondary side and rectified through the secondary side full bridge diodes D3-D4, Flow. The voltage _{Vrec on the} secondary side is maintained in the zero state until the current induced to the secondary side becomes larger than the load current that was being reflowed, and the voltage corresponding to the winding ratio N2 / N1 of the primary side voltage Value.

According to an embodiment of the full bridge DC / DC converter having the circuit for switching the zero voltage / zero current according to the present invention, the switches S1 and S3 of the forward leg are switched to zero voltage switching (M3: turn off, M5: turn on), and the ground leg switches S2 and S4 are switched to zero current switching (M8: turn off and M9: turn on)

FIG. 2 shows various full bridge DC / DC converters to which an embodiment of a circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to the present invention is applied, in which (a) (B) shows a configuration in which a half bridge rectifier is used for the secondary side and a full bridge rectifier is used for the tertiary side, and (c) (D) shows a rectifier structure similar to that shown in FIG. 2 (b), except that the rectifier (D100) and the rectifier (BD100) are connected in the secondary output direction from the ground to the rectifier And a coil L100 connected between the output terminal and the capacitor C100. As shown in FIG. 2, when the current is rectified by using the half bridge rectifier, the ground of the secondary side circuit and the circuit for the zero voltage / And are respectively connected to the neutral terminals of the secondary side and the tertiary side.

Each of the above-described embodiments differs from the rectifier for rectifying the current only in accordance with the wiring scheme, and the operation of the rectifier is the same as that of the embodiment of FIG. However, the reflux diode D101 included in (d) of FIG. 2 is a case where the half bridge rectifier is used in the secondary side as in FIGS. 2 (a) and 2 (b) M7), and the return current flows through the reflux diode D101 instead of flowing through the secondary winding, thereby reducing the conduction loss. The coil L100 is in the power ring mode Only the peak value of the voltage charged in the capacitor C100 is limited in the first mode M1 so that voltage stress is not applied to the capacitor C100. The coil L100 acting as described above may be connected in series between the third winding of the transformer T and the rectifier BD100 instead of being connected as shown in FIG. 2 (d).

The circuit for switching the zero voltage / zero current of the full bridge DC / DC converter according to the present invention constituted as described above does not include expensive parts such as a saturated reactor or an expensive element such as a saturated reactor, DC / DC converter of zero voltage / zero current switching can be implemented at a lower cost, and it is easy to increase the capacity, which is a very economical and useful invention which can be widely used in a large capacity high frequency DC / DC converter field .

Claims (4)

A full bridge DC / DC converter including a transformer, comprising: rectifying means connected to two terminals of a tertiary winding of the transformer to rectify a current induced in a tertiary winding and outputting the rectified current to an output terminal; A passive capacitive element connected between the output terminal of the rectifying means and ground; And a first rectifying element arranged and connected in a direction in which a current of the rectifying means can flow between an output terminal of the rectifying means and a terminal to which a current rectified at the secondary side of the transformer is outputted, Circuit for zero voltage / zero current switching of bridge DC / DC converters. 2. The transformer of claim 1, wherein the rectifying means is a full bridge rectifier comprising four diodes, wherein the first and second diodes are connected between the output terminal and two terminals of the tertiary winding of the transformer, And the third and fourth diodes are disposed between the ground and the two terminals of the tertiary winding of the transformer in such a direction that current can flow into the respective terminals, Circuit for zero voltage / zero current switching of a full bridge DC / DC converter. The transformer according to claim 1, wherein the rectifying means is a Harf Brldge rectifier composed of two diodes, the first and second diodes being connected to the output terminal and two non-neutral terminals of the tertiary winding of the transformer, And the neutral terminal of the third winding of the transformer is connected to the ground. The circuit for zero voltage / zero current switching of a full bridge DC / DC converter according to claim 1, wherein the neutral terminal of the third winding of the transformer is grounded. The apparatus according to claim 1, 2, or 3, further comprising: a passive inductive element connected between a connection point of the passive capacitive element and the first rectifying element and an output terminal of the rectifying means; Circuit for zero voltage / zero current switching of bridge DC / DC converters.