KR100732612B1 - High efficiency dc-dc converter for hybrid car - Google Patents

Abstract

A high efficiency step-down type DC-DC converter for a hybrid car is provided to obtain a high efficiency of the converter by allowing a current-doubler rectifier circuit to use a synchronous rectifier by using a self excited method employing an auxiliary winding. A high efficiency step-down type DC-DC converter for a hybrid car includes an active clamp circuit unit(110), a main switch(S1), a current-doubler circuit unit(210'), and a transformer(T). The active clamp circuit unit(110) includes one switch and one condenser and is included at a primary side. The main switch(S1) is included in the primary side and is complementarily driven with a clamp switch of the active clamp circuit unit(110). The main switch(S1) performs zero voltage switching by leakage inductance of the transformer(T) and filter inductance included in a secondary side. The current-doubler circuit unit(210') is coupled to two diodes or two synchronous rectifying switches by a coupling inductor. The transformer(T) connects the primary side to the secondary side to perform electric insulation and has a turn ratio of the leakage inductance characteristic larger than 4:1.

Description

High efficiency step-down DC-DC converter for hybrid vehicles {High efficiency dc-dc converter for hybrid car}

1 is a block diagram of a phase-shifted full-bridge step-down DC-DC converter according to the prior art.

Figure 2 is a circuit diagram of a dc-dc converter circuit in accordance with the present invention.

Figure 3 is a schematic diagram of a dc-dc converter circuit of another embodiment according to the present invention.

4 is a timing diagram for explaining the operation of the dc-dc converter according to the present invention.

<Description of the symbols for the main parts of the drawings>

100 ... primary switching circuit

110 ... active clamp circuit

210 ... current-doubler rectifier circuit section

The present invention relates to a high efficiency step-down DC-DC (dc-dc) converter for a hybrid vehicle, and more particularly, a 1 kW class high efficiency step-down dc-dc converter for a hybrid vehicle having characteristics of input high voltage and output low voltage. On the primary side, an active-clamp circuit with two switches with zero voltage switching by the leakage inductance of the transformer is provided, and a current-doubler rectifier with a loose coupling to reduce the output voltage ripple on the secondary side. Dc-dc, which allows the current-doubler rectifier circuit to use a synchronous rectifier to reduce the conduction loss, thereby simplifying the control scheme of the dc-dc converter and achieving the converter's high efficiency. It is about a converter.

As is well known to those skilled in the art, for example, a 1 kW hybrid automotive step-down dc-dc converter is mainly a phase-shifted full-bridge step-down type of FIG. 1 for high efficiency. The dc-dc converter is mainly used.

The phase-transition full-bridge step-down dc-dc converter shown in FIG. 1 has zero-zero switching such that all the switches S ₁₁ , S ₂₂ , S ₃₃ , and S ₄₄ on the primary side minimize switching losses. voltage switching). However, this phase-transition full-bridge step-down dc-dc converter is a method for reducing the conduction loss of the secondary-side diode because the control method through the phase transition is complicated and there is no voltage induced in the secondary winding due to the control characteristics. The use of an synchronous rectifier has the disadvantage of being difficult. In addition, the inductor added in series with the transformer T1 such that the primary side switch performs zero voltage switching has a problem of reducing overall power efficiency and increasing noise of the converter due to parasitic resonance.

Therefore, the technical problem to be achieved by the present invention, for example, in the 1kW high-efficiency step-down type dc-dc converter for a hybrid vehicle, the zero voltage switching by the leakage inductance of the transformer and the inductance of the current-doubler on the primary side Combined current-double implemented in one core using loose coupling method to reduce output voltage ripple and reduce the number of conventional filter inductors on the secondary side. By providing a current-doubler rectifier circuit and allowing the current-doubler rectifier circuit to use a synchronous rectifier to reduce the conduction loss, simplifying the control method of the dc-dc converter and improving efficiency at a small size. To provide a dc-dc converter that can have. Here, the small size means that the number of inductors is reduced by implementing two windings in one core at a time.

The present invention, in order to achieve the above technical problem, a DC-DC converter, comprising: an active-clamp circuit unit included on the primary side and having one switch and one capacitor; A main switch included in the primary side and driven complementarily with the clamp switch of the active-clamp circuit portion, and configured to perform zero voltage switching by a leakage inductance of the transformer and a filter inductance included in the secondary side; A current-doubler circuit portion implemented by two diodes or two synchronous rectification switches and a coupling coupling inductor; And a transformer connecting the primary side and the secondary side and performing electrical insulation, and having a turn ratio of leakage inductance characteristic of 4: 1 or more.
Advantageously, said switch and capacitor of said active-clamp circuitry not only provide a path through which energy stored in the leakage inductance of said transformer can be transferred and recycled, but also a parasitic capacitor of said switch by energy stored in said leakage inductance. Zero voltage switching can be provided by discharging the voltage applied to the.
Preferably, the zero voltage switching is performed using the leakage inductance generated by the transformer itself. The zero voltage switching condition may be implemented by designing the energy stored in the leakage inductance before turning on to be larger than the energy stored in the parasitic capacitor of the switch. The leakage inductance may be different according to the turn ratio and winding method of the transformer. However, in the present invention, in the case of the input high voltage and the output low pressure, the turn ratio is very large, so that a large leakage inductance can be easily realized.
Advantageously, said current-doubler circuit portion comprises a MOSFET, said MOSFET comprising a parasitic capacitor and a body diode between a drain and a source.
Preferably, the coupling inductor provided in the current-doubler circuit unit is implemented by one single core (EE or EI core) coupling and an air gap for preventing core saturation.
Advantageously, said switches and capacitors in said active-clamp circuitry provide a path through which energy stored in the leakage inductance of said transformer can be transferred and recycled, as well as leakage greater than the energy stored in the parasitic capacitor of the switch. Zero-voltage switching can be achieved by implementing inductance.
Preferably, the primary side and the secondary side are electrically insulated by the transformer and have a characteristic of leakage inductance sufficient to provide zero voltage switching by a high turn ratio.

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In addition, the present invention, in order to achieve another technical problem, a DC-DC converter, comprising: an active-clamp circuit unit included on the primary side and having one switch and one capacitor; A main switch included on the primary side and driven complementarily with a switch of the active-clamp circuit unit to perform zero voltage switching by a leakage inductance of a transformer; A secondary current coupled double-circuit circuit unit having two diodes and a low coupling degree, and implementing two inductors in one core; And a transformer connecting the primary side and the secondary side and having a high turn ratio and having a large leakage inductance characteristic.
Preferably, the two transistors are MOSFETs having the characteristics of body diodes and parasitic capacitors connected in parallel between the drain and the source.

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Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the dc-dc converter according to the present invention. In the following description of the present invention, when it is determined that detailed descriptions of related well-known technologies or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of a user or an operator. Therefore, the definition should be made based on the contents throughout the specification.

In the following description, when the member according to the prior art and the member according to the present invention are the same, the same reference numerals used in the prior art are used as they are, and detailed description thereof will be omitted.

Figure 2 is a schematic diagram of a dc-dc converter circuit according to the present invention, Figure 3 is a schematic diagram of a dc-dc converter circuit of another embodiment according to the present invention, Figure 4 shows the operation of the dc-dc converter according to the present invention It is a timing diagram for demonstrating. Figure 5a, b is a view showing a coupled current-doubler winding method according to the present invention, Figure 6 is a prototype picture actually produced according to the present invention, Figures 7a, b is an actual measurement waveform diagram according to the present invention to be.

2 and 3, the present invention uses an active-clamp circuit on the primary side as part of solving the problems of the prior art. The active-clamp circuit unit 110 composed of one switch S ₂ and one capacitor C _c operates when the main switch S ₁ is erased to store the leakage inductance or the magnetizing inductance. It is possible to improve the power conversion efficiency by preventing overvoltage of the switching element due to energy and recycling the energy.

In addition, the active-clamp circuit 110 has a simple control scheme and a structure in which a voltage can always be generated in the secondary winding, thereby making it possible to make a driving waveform of a synchronous rectifier by using a simple auxiliary winding. The rectifier circuit 210 of the secondary side as shown in FIG. 2 is a current-doubler rectifier, and the rectifier has a small output voltage ripple due to the effect of canceling the current ripple of the two inductors. It has In addition, as shown in FIG. 5, by implementing a loose coupling winding method on one EE core or EI core, the filter inductor may be reduced and power density may be increased. Here, the loose coupling winding refers to the winding structure, and when the winding is usually wound as close to the winding as close as possible for a high coupling, in the present invention, as shown in Figure 5 the winding in the EE core or EI core It refers to a structure that is wound as far as possible so that there is no interference between windings. Therefore, such a loose binding winding will result in a low binding degree, which will be apparent to those skilled in the art.

Looking at the active-clamp dc-dc converter using a current-doubler according to the present invention in more detail as follows.

2 is an active-clamp dc-dc converter using a current-doubler. The primary side has a switching circuit section including an active-clamp circuit section 110 composed of an auxiliary switch S ₂ and a capacitor C _c providing a path through which energy stored in the leakage inductance of the transformer T can be transferred and recycled ( 100), the secondary side is a current-doubler rectifier 210 comprising diodes D ₁ , D ₂ and inductors L ₁ , L ₂ . Both inductors (L ₁ , L ₂ ) are implemented on one core with low coupling and are wound at a large rate due to the input high-output low-voltage relationship, so that the primary side through a transformer (T) characterized by large leakage inductance The secondary side and the secondary side are electrically insulated, and the output voltage V _o is adjusted by adjusting the duty ratio of the main switch S1 by receiving the feedback of the output voltage V _o . The two switches (S ₁ , S ₂ ), preferably implemented with MOSFETs featuring body diodes and parasitic capacitors between the drain and the source, have a short dead time, a period of time in which all are erased, and a given switching frequency. driven asymmetrically under a switching frequency. When the main switch (S ₁ ) conducts, the current of the main switch (S ₁ ) flows from negative to positive due to the leakage inductance of the transformer (T), that is, zero voltage switching, and charges the inductor (L ₂ ) of the secondary rectifier. To deliver energy to the secondary side. In this process, the current flowing in the main switch (S ₁ ) and diode (D ₁ ) flows in a form similar to the square waveform, which minimizes the peak current of the switch and diode and reduces the conduction loss. Zero voltage switching reduces switching losses of the switch due to high speed switching and improves power conversion efficiency. When the main switch (S ₁ ) is erased, the auxiliary switch (S ₂ ) becomes conductive and the current of the auxiliary switch (S ₂ ) flows from negative to positive by the current flowing through the magnetizing inductance and the leakage inductance of the transformer (T). Voltage switching is performed, and the inductor (L ₁ ) of the secondary rectifier is charged to transfer energy to the secondary side. The current flowing through the leakage inductance while the auxiliary switch S ₂ conducts charges and discharges the capacitor C _c , and in this process, the energy stored in the leakage inductance is recycled.

3 is a circuit diagram of another embodiment of a dc-dc converter according to the present invention, in which two diodes D ₁ and D _{2 of} FIG. ₂ are replaced with two MOSFETs Q ₁ and Q ₂ . When the diode D ₁ of FIG. 2 conducts, the MOSFET Q ₁ of FIG. 3 conducts, and likewise, the MOSFET Q ₂ conducts when the diode D ₂ conducts. Therefore, the current and voltage waveforms of all the devices of FIG. 3 are the same as those of FIG. 2. For example, in the dc-dc converter for a 1 kW hybrid vehicle, the output current is very large, so the current flowing in the secondary rectifier is very large. In the circuit of FIG. 2, the conduction loss due to the forward voltage drop of the diode is reduced. very big. The circuit using the synchronous rectifier to reduce this loss is the circuit of FIG.

The voltage across the very small on-resistance of the synchronous rectifier MOSFETs Q ₁ and Q ₂ of FIG. 3 is less than the forward drop voltage across diodes D ₁ and D _{2 of} FIG. Power loss is reduced. Unlike the conventional phase-transition full-bridge circuit shown in FIG. 1, the circuit of the dc-dc converter of the present invention can simply implement the drive signal of the synchronous rectifier by using the auxiliary winding of the transformer T.
5 is a diagram illustrating a core structure and a winding method of a current-doubler according to the present invention. FIG. 5A shows an air-gap to prevent core saturation due to high DC current and reflow by loose winding due to the center lag by winding the windings for each inductor to the outer leg of the EI-shaped ferrite core. It is an implementation. Figure 5b is a current-doubler implemented in the same manner as Figure 4a in the EE-shaped ferrite core. The structure is simple and the winding method is not difficult.

Figure 4 is a waveform diagram showing the operation of the main part in the circuit of the dc-dc converter according to the present invention.

Each waveform shown in FIG. 4 is a drive signal (V _gs1 , V _gs2 ) and a switch current (i _s1 , i _s2 ) of the switches S ₁ and S ₂ when the ratio is D in one period T _s . And diode currents i _d1 , i _d2 . The main switch S ₁ becomes conductive by the gate signal V _gs1 of the main switch when the current i _s1 is negative, that is, when the voltage between the drain and the source of the main switch is zero voltage. And the shape of the current is a square wave, and the conduction loss is small. The auxiliary switch S ₂ not only performs zero voltage switching but also a very small current loss due to a very small current i _s2 . The currents i _d1 , i _d2 of the diodes D ₁ , D ₂ of the secondary rectifier are square wave-shaped due to the use of inductors L ₁ , L ₂ of the rectifier and two diode currents i _d1 , i _d2 . Due to the effect of canceling the output capacitor (C _o ) has a relatively small output voltage ripple is very small and the overall power efficiency is very high.
6 is a photograph showing a prototype (proto-type) according to an embodiment of the present invention. As an example, the conventional phase-transition full-bridge dc-dc converter has an efficiency of about 89% at an input voltage of 200 V and an output voltage of 14 V, but a step-down active-clamp dc-dc using a current-doubler synchronous rectifier according to the present invention is used. The converter is around 94.5% and features a more simplified power circuit.
7 is a waveform diagram of actual measured current and voltage according to an embodiment of the present invention. It can be seen that it is similar to the timing diagram shown in FIG.
Main parameters properly tuned according to an embodiment of the present invention are shown as examples below.
Component Display value Input voltage Vd DC 200 ~ 300V Output voltage Vo DC 14V Rated load Po, max 1 kW Switching frequency fs 100 kHz Primary Turns Np 24turns Secondary Turns Ns 4turns Auxiliary winding turns Na1, Na2 1turn Magnetization inductance Lm 300 uH Leakage Inductance Llk 5 uH Clamp capacitor Cc 1 uF Input capacitor Ci 560 uF Output capacitor Co 6800 X 2 uF Current-doubler L1, L2 8.1 u part Display name Main switch S1 20N60C3 X 2 Auxiliary switch S2 20N60C3 Synchronous Rectification Switch Q1, Q2 IRF3808 X 3 Transformer T EER4242 Driving chip MIC4427 PWM chip KA7552

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In the dc-dc converter according to the present invention as described above, the primary side is provided with an active-clamp circuit having two switches for zero voltage switching using the leakage inductance of the transformer, the secondary side to reduce the output voltage ripple By implementing two filter inductors in one core using a loose winding method, a combined current-doubler rectifier circuit with reduced inductor component is provided, and simply using an auxiliary winding in the transformer to reduce the conduction loss. The self-contained approach allows the current-doubler rectifier circuit to use a synchronous rectifier, thereby simplifying the control scheme of the dc-dc converter and providing the advantage of achieving high efficiency of the converter. In addition, in a preferred embodiment having the characteristics of input high voltage and output low voltage, a transformer having a leakage inductance characteristic larger than the energy stored in the parasitic capacitor of the switch can be realized by the turn ratio between the high input winding and the output winding. No additional inductance is needed.

Although a preferred embodiment of the present invention has been described in detail above, those skilled in the art to which the present invention pertains may make various changes without departing from the spirit and scope of the invention as defined in the appended claims. It will be appreciated that modifications or variations may be made. Therefore, changes in the future embodiments of the present invention will not be able to escape the technology of the present invention.

Claims (6)

In a DC-DC converter for a hybrid vehicle, An active-clamp circuit portion included on the primary side and having one switch and one capacitor; A main switch included in the primary side and driven complementarily with the clamp switch of the active-clamp circuit portion, and configured to perform zero voltage switching by a leakage inductance of the transformer and a filter inductance included in the secondary side; A current-doubler circuit portion implemented by two diodes or two synchronous rectification switches and a coupling coupling inductor; And And a transformer connecting the primary side and the secondary side to perform electrical insulation and having a turn ratio of leakage inductance characteristic of 4: 1 or more. The switch of claim 1, wherein the switch and the capacitor of the active-clamp circuitry provide a path through which the energy stored in the leakage inductance of the transformer can be transferred and recycled, as well as the switching of the switch by the energy stored in the leakage inductance. DC-DC converter, characterized in that for providing a zero voltage switching by discharging the voltage applied to the parasitic capacitor. The method according to claim 1 or 2, DC-DC converter, characterized in that the zero voltage switching using the leakage inductance generated by the transformer itself. delete The method of claim 1, And the current-doubler circuit portion comprises a MOSFET, wherein the MOSFET comprises a parasitic capacitor and a body diode between the drain and the source. The method of claim 1, The coupling inductor provided in the current-doubler circuit portion is DC-DC converter, characterized in that implemented by the air-gap (gap) for preventing the single core coupling and core saturation (saturation).

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