KR20060055415A - Three level dc-dc converter using zero voltage and zero current switching - Google Patents

Abstract

The present invention relates to a three-level DC-DC converter using zero voltage-zero current switching. In the three-level DC-DC converter according to the present invention, two switch assemblies composed of two switches of four switches in which an anti-parallel diode and a capacitor are connected in parallel are connected in parallel to the transformer primary side, respectively, Two-level, three-level DC-DC converters connected to the first and second rectifier diodes and providing current to the load through smooth inductors connected to the first and second rectifier diodes, respectively. A coupling inductor coupled to each other, an auxiliary capacitor connected between the contact of the smoothing inductor and the first auxiliary diode and one end of the coupling inductor, a second auxiliary diode connected between the contact of the smoothing inductor and the load and the other end of the coupling inductor, coupling A first auxiliary diode connected between the inductor and the auxiliary capacitor's contact and ground, and a smoothing with the first diode And a freewheeling diode that is connected between the emitter junction and ground. According to the present invention, not only high efficiency can be achieved by reducing conduction loss, but also low cost can be realized because no expensive devices such as active devices are included.

Zero voltage switching, zero current switching, converter

Description

Three Level DC-DC converter using Zero Voltage and Zero Current Switching

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to

1 is a circuit diagram of a three-level DC-DC converter using conventional zero voltage switching.

2 is a circuit diagram of a three-level DC-DC converter using conventional zero voltage-zero current switching.

3 is a circuit diagram of a three-level DC-DC converter using zero voltage-zero current switching according to an embodiment of the present invention.

4 is a waveform diagram of a major part of the converter in accordance with an embodiment of the invention.

5A to 5F are circuit diagrams illustrating an operating state of a converter according to an embodiment of the present invention.

6 and 7 show voltage and current waveforms of the transformer primary side of the converter shown in FIGS. 1 and 2, respectively.

8 is a view showing the voltage and current waveform of the transformer primary side of the converter according to an embodiment of the present invention.

9 and 10 illustrate auxiliary capacitor voltage and current waveforms of the converter shown in FIG. 2 and the converter according to the embodiment of the present invention, respectively.

11 is a graph comparing the efficiency of the converter shown in Figures 1 and 2 and the efficiency of the converter according to an embodiment of the present invention.

The present invention relates to a DC-DC converter, and more particularly, to a three-level DC-DC converter using zero voltage-zero current switching.

A converter is a device that boosts or depresses a certain input voltage and outputs it as a desired voltage. Today, each component constituting various electronic devices requires a DC voltage, but the requirements are very different. Is in charge of.

The DC-DC converter converting the input DC power of the converter into a different level of DC power has recently realized a high efficiency and high power density power supply device by controlling the flow of power by using a switching operation of the power semiconductor device. It was made.

However, in the switching operation of the power semiconductor device, since the voltage and the current change with a constant delay and slope according to the device, when the switch is turned on or off, a section in which the voltage and the current are simultaneously applied to the switch occurs. During this period, the power loss of the switching, which is the product of voltage and current, occurs. In particular, devices such as Insulated Gate Bipolar Transistors (IGBTs) have a voltage across the switch at turn-off. Even after being sufficiently applied, the tail current flows for a period of time, resulting in switching losses at turn-off. In addition, the switching loss increases in proportion to the frequency at which the device is opened and closed, thereby limiting the maximum switching frequency of the device. Accordingly, a zero voltage switching scheme for switching in a zero voltage state to reduce switching loss of a power semiconductor device and to switch high frequency has been proposed.

1 is a circuit diagram of a three level DC-DC converter using conventional zero voltage switching. Referring to FIG. 1, a converter is connected to a transformer Tr, a primary side of the transformer Tr, and a three level switch stage 10 including switches S1, S2, S3, and S4, and the transformer Tr. It is connected to the secondary side of the output terminal 30 including the rectifying elements (Dr1, Dr2) and the auxiliary circuit (20).

The three-level switch stage 10 includes an anti-parallel diode connected between emitters and collectors of four switches S1, S2, S3, and S4 made of IGBTs and four switches S1, S2, S3, and S4, respectively. D1, D2, D3, D4) and charging / discharging capacitors (C1, C2, C3, C4), and flying capacitors (Css) connected between the collector of S2 and the emitter of S3 to balance the voltage levels output by the switch. In addition, the flying capacitors Css are connected to each other in series and have diodes Dc1 and Dc2 connected in parallel, and capacitors Cin1 and Cin2 connected in parallel to the input power source Vin to divide the input power supply Vin. .

The output terminal 30 is connected to two taps on the secondary side of the transformer Tr, respectively, and rectifies the currents induced by the transformer Tr, respectively, rectifiers Dr1 and Dr2 and auxiliary devices connected to the rectifiers Dr1 and Dr2. Circuit 20. The auxiliary circuit 20 is connected between the output terminal of the rectifying elements Dr1 and Dr2 and ground to smooth the current rectified by the rectifying elements Dr1 and Dr2 to supply power to the load R _L. A smoothing filter comprising a utilization inductor Lo and a smoothing capacitor Co, and a reflux diode Dw connected to the rectifying elements Dr1 and Dr2 and the smoothing filter in parallel to reflux the current of the output terminal 30. It includes.

Referring to the operation of the conventional DC-DC converter configured as described above are as follows.

The switch control unit (not shown) controls the on / off operation of the switches S1, S2, S3, and S4 of the three-level switch stage 10 to operate the switches S1, S2, S3, and S4 in three modes. [(1) S1 and S2: turn-on, S3 and S4: turn-off (2) S2 and S3: turn-on, S1 and S4: turn-off (3) S3 and S4: turn-on, S1 and S2: turn off]. When the switch is operated by the switch control unit (not shown) in three modes as described above to apply current to the primary side of the transformer Tr, the current is increased or decreased at a constant rate by the transformer to the secondary side. . The induced current is rectified by the rectifier elements Dr1 and Dr2, and the ripple is removed through the smoothing filter so that a DC voltage is output to the load.

In the zero voltage switching, the diodes D1, D2, D3, and D4 connected in parallel with the switches S1, S2, S3, and S4 are conducted by current, so that the voltage across the switches S1, S2, S3, and S4 is zero. It turns on after being turned on. However, no loss occurs when the switch is turned on, but loss may occur when the switch is turned off. Therefore, as shown in FIG. 1, the capacitors C1, C2, C3, and C4 are connected to both ends of the switch to decrease the voltage increase rate, thereby reducing the loss when the switch is turned off.

However, in the conventional converter using zero voltage switching, the current is returned to the primary side by the energy of the leakage inductance L1k at the primary side of the transformer Tr and the energy reflected to the primary side by the output smoothing inductor Lo, thereby converting the current to the primary side. There is a problem of increasing the conductive loss.

In order to solve this problem, a zero voltage and zero current switching method has been proposed.

2 is a circuit diagram of a three level DC-DC converter using conventional zero voltage-zero current switching. Referring to FIG. 2, the converter shown in FIG. 2 includes a first capacitor Ca and a first capacitor between the flyback diode Dw and the smoothing filters Lo and Co in the auxiliary circuit 20 of the converter shown in FIG. 1. And a parallel circuit composed of second diodes Dh and Dc. The second diode Dc is disposed between the contact between the auxiliary capacitor Ca and the first diode Dh and the contact between the smoothing inductor Lo and the smoothing capacitor Co.

The auxiliary capacitor Ca turns the switch under zero current conditions by reducing the conduction loss of the converter by refluxing the current to the secondary side of the transformer through resonance with the smoothing inductor Lo, while preventing current from flowing through the primary side of the transformer. Switch-on reduces switching losses.

However, in the conventional zero-voltage, zero-current three-level DC-DC converter (see FIG. 2) described above, the soft switching operation area is not secured stably, and there is a reverse recovery loss of the secondary rectifier. Due to this, there is a problem of loss of conduction and transformer loss of the main circuit elements.

It is an object of the present invention to improve a conventional three-level DC-DC converter using zero voltage-zero current switching to provide a DC-DC converter having a high density and high efficiency at a low cost.

In order to achieve the above object, in a three-level DC-DC converter according to an aspect of the present invention, two switch assemblies composed of two switches among four semiconductor switches in which an anti-parallel diode and a capacitor are connected in parallel, respectively, have a transformer primary side. Are connected in parallel to each other, and the first and second rectifier diodes are respectively connected to the two tabs of the secondary side of the transformer, and a smoothing auxiliary circuit is provided between the first and second rectifier diodes and the load.

In this case, the smoothing auxiliary circuit may include: a smoothing filter for smoothing the voltage signal rectified by the first and second rectifying diodes; A coupling inductor (composed of the smoothing inductor and the smoothing capacitor) magnetically coupled to the smoothing inductor; An auxiliary capacitor coupled to the leakage inductor of the transformer primary side and the coupling inductor to cause resonance; It includes a reflux diode for refluxing the current to the load side during the discharge of the auxiliary capacitor.

The converter further includes a first auxiliary diode between the auxiliary capacitor and ground, and a second auxiliary diode between the coupling inductor and the smoothing capacitor.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

3 is a circuit diagram of a three-level DC-DC converter using zero voltage-zero current switching according to the present invention.

Referring to FIG. 3, the converter of the present invention includes a primary input terminal 10 and a secondary output terminal 30 that are magnetically coupled through a transformer Tr.

The primary input terminal 10 includes a three level switch stage consisting of four semiconductor switching elements S1, S2, S3, and S4, an input power supply Vin for supplying electrical energy to the primary coil of the transformer Tr, and And a divided capacitor Cin1 and Cin2 coupled in parallel between the input power Vin and the three-level switch stage to divide the input power Vin, and between the collector of the switching element S2 and the emitter of the switching element S3. It includes flying capacitors (Css) and diodes (Dc1, Dc2) coupled in parallel to each other at.

In addition, the three-level switch stage has four switching elements (S1, S2, S3, S4) made of IGBT, and inversely connected between emitters and collectors of the four switching elements (S1, S2, S3, S4). It consists of the parallel diodes D1, D2, D3, D4 and charge / discharge capacitors C1, C2, C3, C4.

The secondary output terminal 30 is connected to two taps of the secondary coil of the transformer Tr, respectively, to rectify currents induced in the secondary side Dr1 and Dr2 and the rectifying elements Dr1 and Dr2. Auxiliary circuit 20 for transmitting the rectified DC voltage to the load (R _L ).

The auxiliary circuit 20 again smoothes the current rectified by the rectifying elements Dr1 and Dr2 to remove the ripple, and then supplies an output terminal and ground of the rectifying elements Dr1 and Dr2 to supply the load R _L. A smoothing filter connected therebetween, and a reflux diode Dw connected in parallel between the rectifying elements Dr1 and Dr2 and the smoothing filter to reflux the current of the output terminal 30.

In addition, the smoothing filter includes an auxiliary capacitor Ca, a smooth coupling inductor Lc1 and Lc2, a smoothing capacitor Co, and first and second auxiliary diodes Da1 and Da2. The primary coupling inductor Lc1 and the smoothing capacitor Co are connected in parallel to each other, and are composed of an auxiliary capacitor Ca, a secondary coupling inductor Lc2, and first and second auxiliary diodes Da1 and Da2. The branch line is also connected in parallel with the primary coupling inductor Lc1 and the smoothing capacitor Co. In particular, the branch line where the secondary side coupling inductor Lc2 and the second auxiliary diode Da2 are configured in series includes a contact point between the auxiliary capacitor Ca and the first auxiliary diode Da1 and the primary coupling inductor ( It is arranged between the contacts between Lc1) and the smoothing capacitor Co.

That is, the DC / DC converter according to the present invention, unlike the conventional DC / DC converter is characterized in that it further comprises a coupling inductor (Lc1, Lc2) for smoothing in the secondary output terminal. Therefore, the converter of the present invention exhibits high-density and high-efficiency characteristics compared to conventional converters by mutual resonance between the leakage inductor L1k on the primary side, the auxiliary capacitor Ca on the secondary side, and the coupling inductor Lc2 on the secondary side. Can be implemented.

Referring to Figures 4 and 5 the operation of the converter according to the present invention configured as described above is as follows.

(1) Mode 1 (t ₀ <t <t ₁ ): As shown in FIG. 5A, as switching elements S1 and S2 are turned on, input power is transferred to the output side, and the secondary capacitor Ca of the secondary side is provided. Is charged through the coupling inductor Lc2 and the second auxiliary diode Da2. The auxiliary capacitor Ca causes resonance with the leakage inductor L1k on the primary side and the coupling inductor Lc2 on the secondary side, so that the conductive loss can be reduced. At the end of this mode, the auxiliary capacitor Ca is charged to its maximum value, so that no current flows into the auxiliary capacitor Ca. The voltage V _Ca and the current I _Ca of the auxiliary capacitor Ca are shown in Equation 1 below.

Where Vs is the transformer secondary voltage, ω _{s is the} angular frequency, n is the winding ratio of the transformer (N ₁ / N ₂ ), Vo is the voltage across the smoothing capacitor Co, Ca is the auxiliary capacitance, and L _{1k is the} leakage inductance.

(2) Mode 2 (t ₁ <t <t ₂ ): As shown in FIG. 5B, when switch S1 is turned off, the primary side current of the transformer attempts to maintain continuous flow by the primary side inductance of the transformer. . Therefore, since switch C1 of switch S1 and C4 of switch S4 are charged, and the built-in diode D4 of switch S4 is conducted, switch S4 is in a zero voltage switching state. At this time, the primary voltage V _ab of the transformer Tr is as follows.

Where n is the winding ratio of the transformer (N ₁ / N ₂ ), Io is the output current, C1 is the parasitic capacitance of switch S1, and C4 is the parasitic capacitance of switch S4.

On the other hand, when looking at the current on the secondary side of the transformer, since the voltage on the secondary side of the transformer is still greater than the voltage charged in the auxiliary capacitor Ca, the first auxiliary diode Da1 on the secondary side of the transformer Tr is turned off. It is maintained and no current flows through the auxiliary capacitor Ca. On the other hand, current flows through the coupling inductor Lc1, the load R _L , and the freewheeling diode Dw.

(3) Mode 3 (t ₂ <t <t ₃ ): As shown in Fig. 5C, the switch S4 is turned on in the zero voltage switching condition, and the current flowing to the transformer primary side is continuously continued through the voltage divider capacitor Dc1. Keep the flow Since the power transmitted from the primary side to the secondary side of the transformer is reduced, the charging energy of the auxiliary capacitor Ca on the secondary side is discharged through the first auxiliary diode Da1. At the end of this mode, the primary side current is nearly zero.

(4) Mode 4 (t ₃ <t <t ₄ ): As shown in Fig. 5D, the current on the transformer primary side reduced in mode 3 becomes zero. However, on the secondary side, in order to supply a constant load current, the secondary capacitor Ca on the secondary side is supplied with a load current through the first auxiliary diode Da1 until the voltage becomes zero and at the same time, coupling inductor (Lc1) supplies a load current through a freewheeling diode (Dw). At this time, the voltage Vca at both ends of the auxiliary capacitor Ca is as follows.

(Where, Io: output current, Ca: auxiliary capacitance, V _β : transformer secondary side voltage at time t ₃ of mode 3)

(5) Mode 5 (t ₄ <t <t ₅ ): As shown in FIG. 5E, since no current flows in the transformer primary side, the switch S2 is turned off in the zero current condition. On the secondary side of the transformer, the auxiliary capacitor Ca is completely discharged, and the load current is refluxed via the coupling inductor Lc1 and the freewheeling diode Dw.

(6) Mode 6 (t ₅ <t <t ₆ ): As shown in Fig. 5F, the switch S3 is turned on in the zero current switching condition, and the current on the primary side is suddenly caused by the leakage inductance L1k. Does not increase. Therefore, the current on the primary side increases linearly and current is induced on the secondary side by the current on the primary side, thereby ending the reflux mode on the secondary side.

Referring to FIG. 4, when the mode 6 ends, the above-described steps are repeated in the state where S3 and S4 are turned on. The converter according to the present invention outputs the DC power supply rectified to a predetermined level as shown in FIG. 4 through the above operation.

In addition, the present inventors fabricated and tested a three-level DC-DC converter using 50 kV, 1 kV zero-voltage-current switching.

6 and 7 show the voltage V _ab and current I _p waveforms of the transformer primary side of the converter shown in FIGS. 1 and 2, respectively, and FIG. 8 shows the converter according to the embodiment of the present invention. The voltage and current waveforms of the transformer primary side are shown.

6 to 8, in contrast to the conventional converter shown in FIGS. 1 and 2, in which resonance occurs only in a partial section, the converter according to the present invention generates resonance over an entire area for transmitting energy through a transformer. Because it was confirmed that the efficiency was improved.

9 and 10 illustrate the voltage V _Ca and current I _Ca waveforms of the converter shown in FIG. 2 and the auxiliary capacitor of the converter according to the embodiment of the present invention, respectively. Referring to the drawings, in the conventional converter shown in FIG. 2, the voltage of the auxiliary capacitor Ca is clamped, and the charging and discharging of the auxiliary capacitor Ca is performed only in some sections. Since the charging and discharging of the auxiliary capacitor Ca is performed, it can be confirmed that more energy can be transferred to the load side.

FIG. 11 is a graph comparing the efficiency of the converter shown in FIGS. 1 and 2 with the efficiency of the converter according to the embodiment of the present invention. Referring to the drawings, the converter according to the present invention has excellent efficiency over the entire load region compared to the conventional converter.

The technical problem of the present invention is achieved by the above technical configuration, and although the present invention has been described by the limited embodiments and the drawings, the present invention is not limited by this and the general knowledge in the technical field to which the present invention belongs. It is apparent that various modifications and variations can be made by those skilled in the art within the scope of the technical spirit of the present invention and the claims to be described below.

The three-level DC-DC converter using zero voltage-zero current switching according to the present invention can achieve high efficiency by reducing conduction loss and can be implemented at low cost because it does not include expensive devices such as active devices.

Claims (3)

Two switch assemblies consisting of two of the four semiconductor switches in which the anti-parallel diode and the capacitor are connected in parallel are respectively connected in parallel to the transformer primary side, and the two taps of the transformer secondary side are respectively the first and second In a three-level DC-DC converter having a rectifying diode connected, and comprising a smoothing auxiliary circuit between the first and second rectifying diodes and the load, the smoothing auxiliary circuit is A smoothing filter for smoothing the voltage signal rectified by the first and second rectifying diodes; (This smoothing filter consists of a smoothing inductor and a smoothing capacitor) A coupling inductor magnetically coupled to the smoothing inductor; An auxiliary capacitor coupled to the leakage inductor of the transformer primary side and the coupling inductor to cause resonance; And a reflux diode for refluxing the current to the load side when the auxiliary capacitor is discharged. The method of claim 1, And a first auxiliary diode between the auxiliary capacitor and the ground. The method of claim 2, And a second auxiliary diode between the coupling inductor and the smoothing capacitor.

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