JP2019169690A - Transformer and LLC resonant circuit using the same - Google Patents

Abstract

To provide a transformer in which leakage flux interlinking with winding is reduced significantly.SOLUTION: A transformer 3 includes a first coil having a primary main winding 31m and a secondary main winding 32m, and a second coil having a primary annex winding 31r connected with the primary main winding 31m and a second coil having a secondary annex winding 32r connected with the secondary main winding 32m. The primary main winding 31m and the secondary main winding 32m are magnetically coupled with the same polarity, and the primary annex winding 31r and the secondary annex winding 32r are magnetically coupled while inverting the polarities from each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an insulating transformer and an LLC resonant circuit using the transformer.

  Like a power generation device using natural energy such as solar power generation, the input voltage input to the LLC resonant circuit may greatly touch a high voltage from a low voltage due to environmental factors. Moreover, there is a possibility that the load state may vary greatly. For example, when it is assumed that the load is installed in a consumer, there is a possibility of a wide change from a light load state that hardly consumes power to a heavy load state that consumes a large amount of power.

  Patent Document 1 discloses a technique for shifting to a burst oscillation in which a switching frequency of a switching element is intermittent at a predetermined interval at light load.

JP 2010-263701 A

  However, in the conventional technique such as Patent Document 1, it may be difficult to control to a desired output voltage even at a high input voltage and a light load while ensuring a low input voltage and a prescribed output power.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a transformer capable of controlling an output voltage against a wide range of input voltage fluctuations and load fluctuations.

  A transformer according to an aspect of the present invention includes a primary winding and a secondary winding, and the primary winding and the secondary winding are magnetically coupled with their polarities aligned with each other. A primary auxiliary winding connected to the primary winding and a secondary auxiliary winding connected to the secondary winding, the primary auxiliary winding and the secondary auxiliary winding; Comprises a second coil that is magnetically coupled in a state in which the polarities of each other are reversed.

  The inventor reduces the apparent coupling coefficient between the primary winding and the secondary winding when the first coil and the second coil are combined by using the configuration as described above. I found what I could do. This means that the apparent leakage inductance of the transformer can be increased, so that the leakage inductance required to obtain the same characteristics can be reduced. Therefore, it becomes easy to take a specified load at a low input voltage, and as a result, control performance at a high input voltage and a light load is improved.

  According to the present invention, it is possible to provide a transformer capable of controlling an output voltage against a wide range of input voltage fluctuations and load fluctuations.

It is a circuit diagram which shows the structural example of a LLC resonant circuit. It is an equivalent circuit diagram which shows the structural example of a transformer. It is a figure which shows the relationship between the switching frequency of an LLC resonant circuit, and an output voltage. It is a figure which shows the relationship between the switching frequency of an LLC resonant circuit, and an output voltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

  The transformer according to the present embodiment and the LLC resonant circuit using the transformer are, for example, a power conditioner that converts the generated power of the photovoltaic power generation apparatus and is connected to a commercial power supply system or supplied to a load. used.

  In the transformer according to the present disclosure, (1) the first coil for forming the excitation inductance and the second coil for forming the leakage inductance are physically separated, and (2) the first The coil is magnetically coupled with the primary and secondary windings aligned in polarity, while the second coil is magnetic with the primary and secondary windings reversed in polarity. It is characterized by being connected to.

  This will be specifically described below.

-Configuration of power converter-
As shown in FIG. 1, the power conversion device A includes an LLC resonance circuit 1 and a control circuit 4 that controls the operation of the LLC resonance circuit 1. In the present embodiment, the LLC resonance circuit refers to a resonance circuit that utilizes the leakage inductance and excitation inductance of the transformer and the resonance of the capacitor.

  The LLC resonant circuit 1 receives a power supply voltage Vi at an input terminal IN, converts it to alternating current and outputs it, and converts the output of the resonant part 10 into a predetermined output voltage Vo and outputs it from the output terminal OUT. Part 20. In the following description, when the input terminal IN is described separately on the positive electrode side and the negative electrode side, it may be described with reference numerals INP and INM. Similarly, when the output terminal OUT is described separately on the positive electrode side and the negative electrode side, it may be described with OUTP and OUTM, respectively.

  The resonance unit 10 includes a switching unit 11, resonance capacitors C <b> 11 and C <b> 12, and a transformer 3.

  The switching unit 11 includes first and second switching elements Q11 and Q12 provided in series between a positive input terminal INP and a negative input terminal INM. FIG. 1 shows an example in which N-type MOS-FETs are used as the first and second switching elements Q11 and Q12. Further, FIG. 1 also shows a parasitic diode formed in parallel with the MOS-FET. In the parasitic diode, a current from the source to the drain of the MOS-FET passes through the parasitic diode. Note that the configuration of the switching unit 11 is not limited to the configuration of FIG. 1, and other switching circuits having the same function may be applied. For example, a high-speed diode element may be externally attached to the MOS-FET so as to be connected in parallel with the parasitic diode.

  The resonance capacitors C11 and C12 include a current resonance capacitor (hereinafter referred to as a first resonance capacitor C11) and a voltage resonance capacitor (hereinafter referred to as a second resonance capacitor C12). The second resonance capacitor C12 is connected in parallel to the first switching element Q11. Similarly, a series circuit of the first resonance capacitor C11 and the primary winding 31 of the transformer 3 is connected in parallel to the first switching element Q11.

  Although details will be described later, the primary winding 31 of the transformer 3 includes a primary body winding 31m and a primary auxiliary winding 31r, and both windings are connected in series. The positive input terminal INP is connected to one end (for example, the winding start end) of the primary auxiliary winding 31r via the first resonance capacitor C11. The other end (for example, winding end) of the primary accessory winding 31r and one end (for example, winding start end) of the primary body winding 31m are connected, and the other end (for example, winding end) of the primary body winding 31m is connected. ) Is connected to the negative input terminal INM via the second switching element Q12. Thus, a closed loop circuit is formed by the first switching element Q11, the first resonance capacitor C11, and the primary winding 31 (the primary body winding 31m and the primary auxiliary winding 31r) of the transformer 3. In FIG. 1, a black circle is attached to the winding start side of each winding of the transformer 3.

  In the present disclosure, the term “connection” includes all electrical connections. In other words, the “connection” is not limited to a direct connection, but includes a concept including an electrical connection via, for example, a resistance element or a semiconductor element.

  The transformer 3 includes a coil body 3M as a first coil for forming an excitation inductance and an attached coil 3R as a second coil for forming a leakage inductance.

  The coil body 3M has a primary body winding 31m and a secondary body winding 32m. Both windings 31m and 32m are arranged such that their polarities are the same and the coupling coefficient k indicating the degree of coupling is high. Specifically, the coupling coefficient km between the primary body winding 31m and the secondary body winding 32m is, for example, 0.9 or more and 1 or less, more preferably 0.97 or more and 1 or less.

  The coupling coefficient km = 1 indicates a state where there is no leakage magnetic flux. The same applies to a coupling coefficient kr between a primary auxiliary winding 31r and a secondary auxiliary winding 32r, which will be described later.

  Thus, by increasing the coupling coefficient km between the primary body winding 31m and the secondary body winding 32m, the magnetic flux linked to the primary body winding 31m and the secondary body winding 32m is reduced. Therefore, the heat generation of the coil main body 3M can be suppressed, and consequently the effect of suppressing the heat generation of the transformer 3 can be obtained.

  The winding structure of the coil body 3M is preferably a structure having a high coupling coefficient k, but the specific structure is not particularly limited. Generally, in order to increase the coupling coefficient k, it is preferable that the distance between the primary winding and the secondary winding of the coil is short. For example, a conventionally known so-called sandwich winding structure can be applied to this embodiment. The sandwich winding structure is a winding layer formed by one winding (for example, the primary body winding 31m) and the other winding (for example, the secondary body winding 32m) between the winding layers. In this structure, the formed winding layer is sandwiched. By doing so, the distance between the primary body winding 31m and the secondary body winding 32m is reduced in both the vertical direction and the radial direction, and as a result, the coupling coefficient k is increased.

  When the coupling coefficient k between the primary winding 31 and the secondary winding 32 is increased, the leakage inductance resulting from the mutual relationship between the primary winding 31 and the secondary winding 32 is reduced accordingly. Therefore, in this embodiment, a separation structure that generates leakage inductance with a separate coil (attached coil 3R) is employed. In addition, as long as the coil main body 3M and the attached coil 3R are magnetically separated, the specific configuration is not particularly limited. For example, the coil body 3M and the attached coil 3R may be mounted on different legs of the same core, or may be mounted on separate cores that are physically separated from each other.

  The attached coil 3R has a primary attached winding 31r and a secondary attached winding 32r. Both windings 31r and 32r are arranged so that their polarities are opposite to each other and the coupling coefficient kr indicating the degree of mutual coupling is high. Specifically, the coupling coefficient kr between the primary auxiliary winding 31r and the secondary auxiliary winding 32r is, for example, 0.9 or more and 1 or less, more preferably 0.97 or more and 1 or less. Thereby, the heat generation of the attached coil 3R can be suppressed, and as a result, the effect of suppressing the heat generation of the transformer 3 can be obtained.

  The conversion unit 20 is a circuit that converts the voltage output from the resonance unit 10 into a predetermined output voltage Vo and outputs the voltage to the load RL or the like. The converter 20 has a configuration in which the diode D22, the second capacitor C21, and the secondary winding 32 of the transformer 3 are connected in series between the positive output terminal OUTP and the negative output terminal OUTM. As described above, the secondary winding 32 of the transformer 3 includes the secondary main body winding 32m and the secondary auxiliary winding 32r, and both the windings 32m and 32r are connected in series.

  Specifically, in the converter 20, the positive output terminal OUTP is connected to one end (for example, the winding end) of the secondary auxiliary winding 32r via the diode D22 and the second capacitor C21. The other end (for example, the winding start end) of the secondary accessory winding 32r is connected to one end (for example, the winding start end) of the secondary body winding 32m, and the other end (for example, the winding end) of the secondary body winding 32m. ) Is connected to the negative output terminal OUTM. The diode D22 is connected in the forward direction from one end of the secondary auxiliary winding 32r toward the positive output terminal OUTP.

  As described above, the present embodiment is characterized in that the primary auxiliary winding 31r and the secondary auxiliary winding 32r are magnetically coupled so that their polarities are opposite to each other. That is, when the winding start end of the primary auxiliary winding 31r is connected to the positive input terminal, the winding end of the secondary auxiliary winding 32r is connected to the positive output terminal OUTP. On the other hand, since the primary body winding 31m and the secondary body winding 32m are arranged so that the polarities thereof coincide with each other, the winding end of the primary body winding 31m is connected to the input terminal on the negative electrode side. In this case, the winding terminal of the secondary main body winding 32m is connected to the negative output terminal OUTM. The connection method of the transformer 3 is not limited to the configuration example of FIG. For example, the winding start end and winding end may be reversed for all windings of the transformer 3, and the same effect can be obtained.

  The converter 20 further includes a rectifier diode D21 connected between the intermediate node N21 between the second capacitor C21 and the diode D22 and the negative output terminal OUTM. The rectifier diode D21 is connected in a direction opposite to the direction from the intermediate node N21 toward the negative output terminal OUTM. An output capacitor C22 is connected between the output terminals OUT.

  The control circuit 4 controls the operation of the entire power conversion apparatus A, and can be realized by, for example, an IC (Integrated Circuit). The control circuit 4 operates, for example, according to a program or sequence registered in advance in the own device. More specifically, the control circuit 4 outputs, for example, control signals Vg11 and Vg12 for on / off control of the first and second switching elements Q11 and 12 of the switching unit 11, respectively.

  By adopting the above configuration, the inventor can reduce the coupling coefficient k of the transformer 3 as compared with the transformer having the conventional configuration as shown in Patent Document 1, that is, substantially It has been found that the leakage inductance can be increased. This means that the value of the leakage inductance necessary for obtaining the same coupling coefficient k can be reduced.

  As a result, it is possible to improve the control performance at the time of a high input voltage and a light load when designed so that a prescribed load can be easily taken at a low input voltage. Specifically, for example, an increase in output voltage at high input voltage and light load can be suppressed, and output power at the time of burst oscillation can be kept low. Then, the output voltage can be controlled in a wide range from a low input voltage and a specified load to a high input voltage and a light load.

  In the following, a theoretical explanation will be given regarding the point that the above coupling coefficient can be reduced, that is, the apparent leakage inductance can be increased.

  First, as shown in FIG. 2A, the self-inductance (corresponding to leakage inductance) of the primary auxiliary winding 31r is Lr, and the self-inductance (corresponding to leakage inductance) of the secondary auxiliary winding 32r is Lrs. Let Mr be the mutual inductance of the secondary attached winding 31r and the secondary attached winding 32r. In this case, the voltage Vr1 across the primary auxiliary winding 31r and the voltage Vr2 across the secondary auxiliary winding 32r, the primary current I1 flowing through the primary winding 31, and the secondary winding 32 flow. The relationship with the secondary current I2 is expressed by the following formula (1).

  Similarly, the self-inductance (corresponding to excitation inductance) of the primary body winding 31m is Lm, and the self-inductance (corresponding to excitation inductance) of the secondary body winding 32m is Lms. Let Mm be the mutual inductance with the winding 32m. In this case, the voltage Vm1 across the primary body winding 31m and the voltage Vm2 across the secondary body winding 32m, the primary current I1 flowing through the primary winding 31, and the secondary winding 32 flow through. The relationship with the secondary current is as shown in the following equation (2).

  2 (b) is an equivalent circuit of FIG. 2 (a). In FIG. 2 (a), the self-inductance of the attached coil 3R and the coil body 3M in each of the primary winding 31 and the secondary winding 32 are shown. Is added to the self-inductance. That is, the inductance Lp of the primary winding 31, the inductance Ls of the secondary winding 32, and the mutual inductance M between the primary winding 31 and the secondary winding 32 are expressed by the following formula (3).

  In FIG. 2B, the voltage Vp between both ends of the primary winding 31 and the voltage between both ends of the secondary winding 32 are expressed by the following equation (4).

  Substituting the results of equations (1) and (2) into equation (4) yields equation (5) below.

  Also, between the self-inductance of the primary auxiliary winding 31r and the secondary auxiliary winding 32r and the mutual inductance Mr, and between the primary body winding 31m and the secondary main body winding 32m and the mutual inductance Mm. Has the relationship of the following formula (6).

  Therefore, substituting equation (6) into the equation of mutual inductance M in equation (3) yields equation (7) below.

  Then, the coupling coefficient k in the transformer 3 in FIG. 2B can be expressed as the following formula (8).

  Here, as described above, the coupling coefficient km between the primary main body winding 31m and the secondary main body winding 32m and the coupling coefficient kr between the primary auxiliary winding 31r and the secondary auxiliary winding 32r are increased. It is preferable to design to. Therefore,

  Assuming that, the coupling coefficient k in the above equation (8) is approximated as in the following equation (10).

  On the other hand, although a detailed calculation process is omitted, the coupling coefficient in a conventional transformer for an LLC resonant circuit such as Patent Document 1 can be expressed as the following Expression (11).

  Here, when the formula (10) is compared with the formula (11), the apparent coupling coefficient k between the primary winding 31 and the secondary winding 32 in the equivalent circuit is obtained by using the configuration of the present embodiment. Can be small. That is, the apparent leakage inductance of the transformer 3 can be increased. In other words, when configuring a circuit for obtaining equivalent characteristics, the leakage inductance can be designed to be small.

  FIG. 3 is a graph showing the relationship between the switching frequency and the output voltage for (1) the LLC resonant circuit of the present embodiment and (2) a general LLC resonant circuit. FIG. 4 is a graph obtained by extracting and plotting the characteristics (circles) of “low input voltage and heavy load” in FIG.

  In FIG. 3, the characteristic of “(1) LLC resonant circuit of this embodiment” is indicated by a solid line, and the characteristic of “(2) a general LLC resonant circuit” is indicated by a broken line. In FIG. 3, the characteristics plotted in a circle are “low input voltage and specified load”, and the characteristics plotted in a triangle are “high input voltage and light load”. As can be seen from FIG. 3, when the input voltage increases and the load decreases, the characteristic curve moves upward.

  By adopting the configuration of the present embodiment, as shown in FIG. 4, when viewed at the same switching frequency at “low input voltage and specified load”, the output voltage increases in the low range and is output in the high range. The voltage is low. That is, it is possible to easily take a specified load (output voltage) at a low input voltage. Further, as shown in FIG. 3, even in the case of “high input voltage and light load”, the overall characteristic curve moves upward as compared with “low input voltage and specified load”, that is, the output voltage increases. However, with the configuration of the present embodiment, an increase in the output voltage in the operation region (particularly on the high frequency side) can be suppressed. Thereby, the control performance at “high input voltage and light load” is improved. Specifically, according to the present embodiment, for example, output during burst oscillation can be suppressed, so that generation of noise can be suppressed, and deterioration of EMI and malfunction of the control system can be avoided. Further, failure due to destruction of the switching element can be avoided.

  Further, in the conventional transformer as in Patent Document 1, since the leakage inductance is determined by the mounting position of the winding, the design freedom of the leakage inductance is extremely low. The degree is greatly improved.

  In this embodiment, the coupling coefficient km between the primary main body winding 31m and the secondary main body winding 32m and the coupling coefficient kr between the primary auxiliary winding 31r and the secondary auxiliary winding 32r are set high. . Thereby, the heat generation of the coil main body 3M and the attached coil 3R can be suppressed, and as a result, the heat generation of the transformer 3 can be suppressed.

  The preferred embodiments of the present invention and the modifications thereof have been described above, but the technology according to the present disclosure is not limited thereto, and can be applied to embodiments that have been appropriately changed, replaced, and the like. Moreover, it is also possible to combine the components described in the above embodiment and the components described below to form a new embodiment.

  For example, in the above embodiment, the coupling coefficient km between the primary body winding 31m and the secondary body winding 32m is 0.9 or more and 1 or less. However, the present invention is not limited to this, and the coupling coefficient km is 0. It may be less than 9. However, the effect of suppressing the heat generation of the coil body 3M and the effect of increasing the apparent leakage inductance of the transformer 3 can be more remarkable when the coupling coefficient km is higher. The same applies to the coupling coefficient kr between the primary auxiliary winding 31r and the secondary auxiliary winding 32r, and the coupling coefficient kr may be less than 0.9. Further, the values of the coupling coefficient km and the coupling coefficient kr may be different from each other.

  Since the transformer according to the present invention can greatly reduce the heat generation of the transformer, it is extremely useful as a transformer for use in, for example, electrical equipment, power equipment, power converters, and the like used in homes and offices.

1 LLC resonant circuit 3 transformer 3M coil body (first coil)
31m Primary body winding (primary winding)
32m Secondary body winding (secondary winding)
3R Attached coil (second coil)
31r Primary accessory winding 32r Secondary accessory winding 11 Switching unit 20 Conversion unit C11, C12 Resonant capacitor

Claims (5)

A first coil having a primary winding and a secondary winding, wherein the primary winding and the secondary winding are magnetically coupled with their polarities aligned with each other;
A primary auxiliary winding connected to the primary winding and a secondary auxiliary winding connected to the secondary winding, wherein the primary auxiliary winding and the secondary auxiliary winding are mutually A transformer comprising: a second coil that is magnetically coupled with the polarity reversed. The transformer according to claim 1,
A coupling coefficient between the primary winding and the secondary winding is 0.9 or more and 1.0 or less. The transformer according to claim 2,
A coupling coefficient between the primary auxiliary winding and the secondary auxiliary winding is 0.9 or more and 1.0 or less. The transformer according to claim 1,
The transformer, wherein the first coil and the second coil are mounted on different cores. 5. The transformer according to claim 1, a switching unit, and a resonant capacitor, wherein the switching unit receives a DC input voltage, and an output of the switching unit is passed through the resonant capacitor. A resonating unit that is applied to the primary winding and the primary auxiliary winding of the transformer to resonate;
An LLC resonance circuit comprising: a conversion unit that converts an output voltage obtained from a secondary winding and a secondary auxiliary winding of the transformer into a predetermined DC output voltage and outputs the voltage.

Images