KR20160066754A - Improved ZVS active clamp forward converter - Google Patents

Abstract

Disclosed is an improved zero voltage switching active clamp forward converter capable of improving the efficiency through zero voltage switching in an entire load range. According to an embodiment, the improved zero voltage switching active clamp forward converter comprises: a clamping switch unit alternately switching an input power after clamping the same; a first winding unit receiving the switched power from the clamping switch unit; and a voltage transforming unit, having a second winding unit, for transforming a voltage level of the switched power by forming a predetermined winding ratio by being electromagnetically combined to the first winding unit; and a rectifier unit for rectifying the transformed voltage and outputting the same. The voltage transforming unit comprises a core unit, a first bobbin and a second bobbin which are penetrated and supported by the core unit. The first wire is winding around the first bobbin to form a first winding unit, while a second wire is winding around the second bobbin to form a second winding unit. Here, the first winding unit and the second winding unit are apart from each other to a certain distance.

Description

Improved ZVS active clamp forward converter Abstract:

The present invention relates to an improved zero voltage switch active clamp forward converter, and more particularly to an improved zero voltage switch active clamp forward converter capable of improving efficiency through zero voltage switching in a full load region.

In general, a hybrid electric vehicle driven by an engine and a motor and a motor driven by an electric motor require high voltage and current to drive a motor, and a hybrid control unit (HPCU), which is a power control unit, is required. The HPCU consists of power supply products such as LDC (Low Voltage DC-DC Converter), Inverter, and HCU (Hybrid Control Unit).

 The dual LDC consists of a control unit that controls the power unit and the power unit to convert the high input voltage received from the lithium ion battery to low voltage to supply electric energy to the automotive electrical equipment.

The power unit is composed of a power board, a transformer, an output board and the like, and the control unit is composed of a control board.

 Power boards have a variety of circuits that can be used depending on the output capacitance of the LDC. For small LDCs, active clamp forward converters are suitable.

 On the other hand, when a high voltage of a square wave shape which varies with time as shown in FIG. 1 is applied to the primary side of the transformer through the power board, a current flows through the primary side coil and a magnetic flux is generated inside the core.

At this time, the magnetic flux passes through the secondary coil to generate the induced electromotive force. Through this principle, the energy of the primary is transmitted to the secondary. The user can adjust the turn ratio of the primary side and secondary side coils and the time the voltage is applied to the primary side so as to increase and decrease the pressure.

 At this time, it is the switch (MOSFET) that controls the time (Duty ratio, 0 <D <1) during which the input voltage is applied to the transformer. The duty should be increased as the input voltage is lower, the desired output voltage is greater, or the output current is greater.

 In the case of an ideal switch, the product of the voltage applied to the switch and the current flowing through the switch at the instant the switch is turned on and off is always zero, as shown in FIG. For an active clamp forward converter, the switching loss occurring when the switch is turned on (zero voltage switching) by resonance of the parasitic components present in the circuit under light load conditions (leakage inductance of the transformer, MOSFET output capacitance) is close to zero.

In the case of a general MOSFET, the parasitic component of the peripheral circuit and the delay of the switch itself cause a product of voltage and current at the moment of switching, which is represented by the power consumption as shown in FIG. 3 (P = VI, W = Pt). This is called switching loss. In the case of an active clamp forward converter, in contrast to a normal full bridge type circuit, a large switching loss occurs when the load is large. Generally, the switch operates at 100kHz, the loss is too large to generate a large amount of heat, and if the heat is not properly discharged, the switch may be burned out, and the operation of the entire LDC may be stopped.

 Also, as shown in FIG. 4, when the duty ratio is large due to a wide input voltage range, a wide output voltage range, and a wide output current range, the transformer is saturated due to insufficient reset time of the transformer, A high instantaneous voltage may be applied and the circuit may be damaged.

To prevent this, the turn ratio of the transformer is adjusted. Increasing the number of turn of 2 cutoff can reduce this risk. However, if two copper wires are used as a conventional copper plate, the two copper plates must be fastened with bolts and nuts, which increases the space occupied by the transformer and the number of parts used.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved zero voltage switch active clamp forward converter capable of improving efficiency through zero voltage switching in a full load region.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided an improved zero voltage switch active clamp forward converter including: a clamping switch unit for clamping an input power supply for alternating switching; A transformer unit having a first winding unit for receiving a switched power source from the clamping switch and a second winding unit for electromagnetic coupling with the first winding unit to form a predetermined winding ratio to transform the voltage level of the switched power source, ; And a rectification section for rectifying and outputting the transformed voltage from the transforming section.

Wherein the transforming portion includes a core portion and first and second bobbins penetrated and supported by the core portion, wherein the first bobbin is wound around a first wire to form a first winding portion, And the wire is wound to form a second winding portion, wherein the first winding portion and the second winding portion are separated by a predetermined distance.

The first wire and the second wire may be made of different materials.

And the second wire has a flexural characteristic.

The second wire is a coaxial coil.

Further, in the second winding portion, the second wire is wound in a layered structure.

 Further, in the second winding portion, the moving coil is wound in a layered structure.

 In addition, the first wire is a Litz wire.

As described above, according to the present invention, a leakage inductance is higher than that of a transformer used in a conventional LDC, and the secondary side wire is replaced with a copper coin instead of a copper plate used for a small capacity to facilitate a rise in the secondary side turn ratio Do.

Further, the bolts and nuts for space and copper plate fastening can be omitted as compared with the conventional ones. This is advantageous in reducing switching losses occurring in active clamp forward converters, even in light loads as well as in heavy loads.

1 is a diagram showing a square-wave-shaped input power source which varies with time;
Figure 2 shows the voltage applied to the switch and the current flowing through the switch at the moment the switch is turned on and off in the case of an ideal switch.
3 is a diagram showing a voltage applied to a switch at the moment of switching by a parasitic component of a peripheral circuit and a delay of the switch itself in a general MOSFET and a current flowing through the switch.
FIG. 4 is a diagram for explaining an example in which a wide input voltage range, a range of an output voltage, and a large duty ratio are generated by a wide output current region.
5 is a schematic circuit diagram of an active clamp forward converter according to an embodiment of the present invention;
6 is a sectional view showing a winding structure of a transformer according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. And is provided to fully convey the scope of the invention to those skilled in the art, and the present invention is defined by the claims. It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. It is noted that " comprises, " or "comprising," as used herein, means the presence or absence of one or more other components, steps, operations, and / Do not exclude the addition.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout. In the drawings, like reference numerals are used to denote like elements, and in the description of the present invention, In the following description, a detailed description of the present invention will be omitted.

5 is a schematic circuit diagram of an active clamp forward converter according to an embodiment of the present invention.

5, the active clamp forward converter 100 according to the embodiment of the present invention may include a clamp switch 110, a transformer 120, and a rectifier 130.

The clamp switching unit 110 may alternately switch the input power Vin by clamping it. To this end, the clamp switching unit 110 may include a clamp capacitor Cc, a first switch QA, and a second switch Qm.

One end of the clamp capacitor Cc may be connected to the input power supply Vin and the other end of the clamp capacitor Cc may be connected to one end of the first switch QA. The first switch QA may be electrically connected between the other end of the clamp capacitor Cc and the transforming unit 120 and the second switch Qm may be electrically connected between the transforming unit 120 and the ground.

The clamp capacitor Cc can clamp the input power supply Vin and transmit the clamped power supply Vin to the first switch QA and the first switch QA and the second switch Qm are alternately switched to switch the clamped power supply Vc And transmit it to the transforming unit 120.

The transforming unit 120 may transform the voltage level of the power source switched by the switching unit 110 and output the converted voltage level through a preset winding ratio. To this end, the transforming unit 120 includes a first winding unit Np for receiving a switched power source, and a pre-set winding to form the first winding unit Np and the winding ratio, And a second winding section Ns for outputting the second winding section Ns.

One end of the first winding section Np may be connected to one end of the clamp capacitor Cc and the other end of the first winding section Np may be connected to the other end of the first switch QA. In addition, the first winding portion Np may include a leakage inductance component Lk and a magnetizing inductance component Lm.

The rectifying unit 130 rectifies the transformed power from the second winding Ns of the transforming unit 120 and outputs the rectified power.

For this purpose, the rectifying part 130 may include first and second diodes D1 and D2, an output inductor Lo and an output capacitor Co.

The anode of the first diode D1 may be connected to one end of the first second winding section Ns1 to rectify the transformed power from the first second winding section Ns1.

The anode of the second diode D2 is connected to the other end of the second winding Ns2 to rectify the transformed power from the second winding Ns2.

One end of the output inductor Lo may be connected to the cathode of the first and second diodes D1 and D2 and the other end of the output inductor Lo may be connected to the output capacitor Co. One end of the output capacitor Co may be connected to the other end of the output inductor Lo and the output inductor Lo and the output capacitor Co may stabilize the rectified power from the first and second diodes D1 and D2 So that the output power Vo can be transmitted to the load R.

On the other hand, in order to obtain zero voltage switching to reduce switching loss, it is necessary to satisfy the condition that various items such as the current flowing in the circuit, the input voltage, and the voltage across the switch are generated immediately before the switch is turned on. The results are summarized in the following equations (1) and (2).

[Equation 1]

Where, L _k is the first coil portion leakage inductance, L _m is the first coil portion magnetizing inductance component, I _{L _ max} is the maximum leakage current, C _oss is the parasitic capacitance components of the second switch (Qm), V _DS1 is Quot; means a voltage across both ends of the second switch Qm.

&Quot; (2) &quot;

Equation (1) is a condition for performing zero voltage switching in a region under a specific load. Where, L _k is the first coil portion leakage inductance component, I _{L _ max} is the maximum leakage current, C _oss is the parasitic capacitance components of the second switch (Qm), V _DS1 is the voltage across the second switch (Qm) it means.

Since the leakage inductance and magnetizing inductance, which are parasitic components of the transformer, contribute to zero voltage switching, zero voltage switching can be obtained below a certain load. The reference of a particular load means that the current of the two blocking output inductor falls below zero within one period, which can be determined by the following equation (3).

&Quot; (3) &quot;

In this case, I _o is the current flowing through the output inductor, Lo is the inductance component of the output inductor, DT is the clamping time, Ns is the winding of the second winding, Np is the winding of the first winding, Vin is the input voltage, Vo is the output Voltage.

However, when Equation (3) is not satisfied, zero voltage switching becomes difficult to obtain because the magnetizing inductance component (Lm) does not affect the zero voltage switching as in Equation (2).

Therefore, in order to obtain zero voltage switching in the full load region, it is necessary to increase the leakage inductance component, and the zero voltage switch active clamp forward converter according to the embodiment of the present invention provides a measure for increasing the leakage inductance component .

6 is a cross-sectional view illustrating a winding structure of a transformer according to an embodiment of the present invention.

5 and 6, the transformer 120 according to the embodiment of the present invention includes a first winding part 120_1 for receiving switched power from the clamping switch part 110, And a second winding part 120_2 which is electromagnetically coupled with the first winding part 120_1 to transform the voltage level of the switched power source by forming a preset winding ratio.

The first wire portion 120_1 includes a core portion and a first bobbin 121 penetrated and supported by the core portion. The first wire 123 is connected to the first bobbin 121, Is wound.

The second winding part 120_2 is disposed opposite to the first winding part 120_1 and is composed of a core part (not shown) and a second bobbin 122 penetrated and supported by the core part, The second wire (124) is wound around the bobbin (122).

In the embodiment of the present invention, the first winding part 120_1 and the second winding part 120_2 are spaced apart from each other by a predetermined distance d. Conventional transformers are manufactured by winding a 1-cut or 2-cut wire on a bobbin, then winding 2-cut or 1-cut wire on it. In this case, since there is no gap between one blocking wire and two blocking wires, the leakage inductance component becomes very small, making it difficult to obtain zero voltage switching in the full load region.

In the embodiment of the present invention, the first wire 123 is wound on the first bobbin 121 to form the first wire portion 120_1, and the second wire 124 is separately provided on the second bobbin 122 By forming the second winding portion 120_2 by winding, a gap can be provided between the first wire 123 and the second wire 124. [ Thus, the leakage inductance component is increased and zero voltage switching is possible in the full load region even without the insertion of an additional inductor for a zero voltage switch.

The first wire 123 and the second wire 124 may be made of different materials. For example, the first wire 123 may be a Litz wire material, and the second wire 124 may be an angular coil material.

 In the case of the angle coil, since it has a bending characteristic, it is easy to wind on the second bobbin 122 and it is not necessary to fasten the bolt and the nut differently from the conventional method even when the number of turns is increased. Therefore, . &Lt; / RTI &gt;

The second wire 124 may be wound on the second bobbin 122 in a layered structure.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the scope of the claims and their equivalents shall be construed as being included within the scope of the present invention.

Claims (7)

A clamping switch unit for alternately switching the input power source; A transformer unit having a first winding unit for receiving a switched power source from the clamping switch and a second winding unit for electromagnetic coupling with the first winding unit to form a predetermined winding ratio to transform the voltage level of the switched power source, ; And a rectification section for rectifying and outputting a transformed voltage from the transforming section, the active clamp forward converter comprising:
Wherein the transforming portion includes a core portion and first and second bobbins penetrated and supported by the core portion, wherein the first bobbin is wound around a first wire to form the first winding portion, Wherein the first winding portion and the second winding portion are separated from each other by a predetermined distance, wherein the first winding portion and the second winding portion are separated by a predetermined distance.
The method according to claim 1,
Wherein the first wire and the second wire are of different materials. &Lt; Desc / Clms Page number 20 &gt;
The method according to claim 1,
Wherein the second wire has a flexural characteristic. &Lt; Desc / Clms Page number 15 &gt;
The method according to claim 1,
Wherein the second wire is a coaxial coil. &Lt; Desc / Clms Page number 15 &gt;
The method according to claim 1,
Wherein the second wire in the second winding portion is wound in a layered structure. &Lt; Desc / Clms Page number 13 &gt;
5. The method of claim 4,
And wherein in the second winding portion the coiling coil is wound in a layered configuration.
The method according to claim 1,
Wherein the first wire is a Litz wire. &Lt; RTI ID = 0.0 &gt; 31. &lt; / RTI &gt;

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