Power converter

An LLC resonant converter in which a capacitor (Cr), an inductance (Lr), and a power line between the capacitor (Cr) and the inductance (Lr), which constitute a series resonance unit, are resin-encapsulated by a resin. Because the series resonance unit that is a high voltage portion is resin-encapsulated collectively, it is possible to shorten an insulation distance even in the case of higher voltages and frequencies, and to prevent an increase in size.

TECHNICAL FIELD

The present invention relates to an LLC resonant converter used in, for example, an on-board charger.

BACKGROUND ART

Conventionally, as a charger mounted on an electric vehicle (EV) or a plug-in hybrid vehicle (PHV) or the like, a configuration is known comprising an LLC resonant converter for converting power. A typical LLC resonant converter includes a transformer having a primary winding and a secondary winding, a resonant capacitor connected to the primary side of the transformer, a switching circuit for controlling the energization of the transformer and the resonant capacitor, a rectifying circuit connected to the secondary side of the transformer, and the like.

An LLC resonant converter proactively generates a leakage inductance due to a reduced coupling coefficient of the transformer, and utilizes this as a resonant inductance. That is, an LLC resonant converter has a resonant circuit constituted with a leakage inductance and a resonant capacitor of a transformer.

The LLC resonant converter is disclosed in, for example, Patent Literatures (hereinafter, referred to as “PTLs”) 1 and 2.

CITATION LIST

Patent Literatures

SUMMARY OF INVENTION

Technical Problem

When an LLC resonant converter is formed to include a series resonator constituted with a capacitor and an impedance, a high voltage is generated at the series resonator (LC series resonator).

On the other hand, in order to compactify an LLC resonant converter, it is desired to increase the resonant frequency (driving frequency).

Therefore, the series resonator (LC series resonator) is expected to be exposed to a high voltage and a high frequency.

Here, according to the insulation distance (creepage distance) defined in IEC60664-4 (JIS C 60664-4), the higher the voltage becomes and the higher the frequency becomes, the longer the required insulation distance becomes. As a result, designing an LLC resonant converter for a higher voltage and a higher frequency leads to increase in size of the LLC resonant converter.

The present invention has been made in consideration of the points described above; even when designed for a higher voltage and a higher frequency, an LLC resonant converter is provided with suppressing increase in size.

Solution to Problem

One aspect of the LLC resonant converter of the present invention is an LLC resonant converter including at least a series resonator constituted with a capacitor and an inductance, and the capacitor, the inductance, and a power line between the capacitor and the inductance, are resin-sealed.

Advantageous Effects of Invention

According to the present invention, even when designed for a higher voltage and a higher frequency, an LLC resonant converter can be provided with suppressing increase in size.

DESCRIPTION OF EMBODIMENTS

Embodiment

FIG. 1is a circuit diagram including LLC resonant converter100according to an embodiment of the present invention. The example shown inFIG. 1is an example using LLC resonant converter100of the present embodiment in an on-board charger.

InFIG. 1, LLC resonant converter100is connected to external power supply1via AC/DC converter2. External power supply1is a commercial power supply for supplying single-phase AC power of, for example, 60 Hz and 200V, and supplies an AC power to the input stage of AC/DC converter2.

AC/DC converter2converts an AC power inputted from external power supply1into a DC power, and supplies this to LLC resonant converter100. AC/DC converter2includes, for example, a rectifying circuit and a smoothing capacitor. Also, AC/DC converter2may be further provided with power factor improving circuitry or the like at the output stage. AC/DC converter2converts, for example, a 200V single-phase AC power inputted from external power source1into a 400V DC power.

LLC resonant converter100supplies a DC power obtained by AC/DC converter2to battery3while insulating external power supply1from battery3.

LLC resonant converter100has inverter101. Inverter101forms a transmission power having a predetermined driving frequency from a DC power inputted from AC/DC converter2, and outputs the transmission power to first and second nodes N1and N2.

Furthermore, LLC resonant converter100includes transformers (or power transmission coils) T1and T2, capacitor (or capacity element) Cr, and inductance (or inductance element) Lr. Primary winding T1of the transformer is electrically connected between first node N1and second node N2. Further, between first node N1and first wire T1, capacitor Cr and inductance Lr are connected in serial. Thus, a series resonator is constituted with capacitor Cr and inductance Lr.

Rectifier circuit102is connected to third and fourth nodes N3and N4provided at both ends of secondary winding T2of a transformer, and battery3to be charged is connected via rectifier circuit102.

With this configuration, LLC resonant converter100can supply a DC power obtained by AC/DC converter2to battery3while insulating external power supply1from battery3. Here, when LLC resonant converter100inputs a DC power of 400V from AC/DC converter2, the series resonator of LLC resonant converter100operates at a driving frequency of 0.35 MHz and a peak voltage of 2000V, for example.

Inverter101and rectifier circuit102can have a known configuration, and thus a description thereof is provided herein briefly. Inverter101is configured with a plurality of switching elements, and a driving power having a frequency corresponding to the switching of the switching element is outputted as a power transmitted to LLC resonant converter100. Rectifier circuit102is configured of a plurality of rectifying elements and smoothing capacitors.

FIGS. 2 to 4are a diagram showing a package configuration of LLC resonant converter100according to the present embodiment.FIG. 2is a perspective view of packaged LLC resonant converter100from a diagonally upward direction.FIG. 3is a perspective view in which case110is removed fromFIG. 2FIG. 4is a cross-sectional view showing an A-A′ cross-section ofFIG. 2.

LLC resonant converter100is formed with primary winding T1, secondary winding T2, bobbin120, upper core131, lower core132, printed circuit board140, partition plate150, and the like, which are accommodated in case110.

Case110is made of a metal. Case110may be made of, for example, a resin, however heat dissipation is improved by being made of a metal, resulting in being advantageous in terms of compactification.

Bobbin120is made of, for example, a synthetic resin material having insulating properties. Bobbin120has a winding portion (reference sign omitted) for winding primary winding T1and secondary winding T2. As can be seen inFIG. 4, bobbin120has, for example, a first winding portion (reference sign omitted) at a lower side around which primary winding T1is wound, and a second winding portion (not shown) at an upper side around which secondary winding T2is wound. The first winding portion and the second winding portion are separated by partition plate150. Primary winding T1and secondary winding T2are wound around the winding portion of bobbin120while being insulated by partition plate150. In an example ofFIG. 4, partition plate150extends from the inside to the outside of bobbin120so as to be interposed between lead wires161and162drawn out from primary winding T1and secondary winding T2, thereby providing insulation between lead wires161and162, as well.

Upper core131and lower core132are, for example, an EE core made of a magnetic material such as ferrite. Upper core131and lower core132are coupled to the bobbin120around which primary winding T1and secondary winding T2are wound, and form a magnetic path when primary winding T1and secondary winding T2are energized.

Lead wire161drawn out from primary winding T1and lead wire162drawn out from secondary winding T2are electrically connected to printed circuit board140disposed over an upper side of the transformer portion to be stacked on transformer portion. Here, in practice, there are two lead wires161of primary winding T1and two lead wires162of secondary winding T2, respectively, so that a total of four lead wires160(FIG. 3) are electrically connected to wiring patterns of printed circuit board140.

Lead wires160are connected by the wiring of printed circuit board140as follows. One of two lead wires161of primary winding T1is connected to first node N1via a capacitor Cr, and the other is connected to second node N2. One of two lead wires162of secondary winding T2is connected to third node N3, and the other is connected to fourth node N4.

Here, in the present embodiment, capacitor Cr comprises a plurality of capacitors provided in cascaded connection. As a capacitor, for example, a ceramic capacitor is used.

In addition to the above-described configuration, in LLC resonant converter100of the present embodiment, case110is filled with thermal curing resin200, as shown inFIG. 4. Resin200is poured into case110after the above-described components are disposed in case110.

Thus, capacitor Cr and inductance Lr (in this embodiment, primary winding T1functions as inductance Lr) which constitutes a serial resonator, and a power line between capacitor Cr and inductance Lr (lead wire160), are resin-sealed.

Here, in the present embodiment, primary winding (transformer) T1has a function which corresponds to that of inductance Lr. That is, primary winding (transformer) T1and inductance Lr are integrally formed. This enables compactification compared to when inductance Lr and a transformer are formed separately. Of course, inductance Lr may be formed separately from primary winding (transformer) T1. When inductance Lr and primary winding (transformer) T1are separately formed, primary winding (transformer) T1is excluded from a high-voltage portion, and thus primary winding (transformer) T1may not be resin-sealed. However, in consideration of easiness of the resin-sealing process, the transformer may also be resin-sealed.

As resin200for sealing, a resin having a high insulating property is used. Further, as resin200, a resin having high-voltage resistance is preferably used. Further, a resin having high thermal conductivity is preferably used. Further, in order to prevent breakage of upper core131, lower core132, and capacitor Cr during thermal curing, it is preferable to use a resin having a low shrinkage during thermal curing. As resin200, for example, a resin made of silicone, epoxy, urethane, or the like is used.

Here, when LLC resonant converter100is operated, a particularly high voltage is generated at the series resonator shown inFIG. 1. Therefore, it is necessary to increase the insulation distances. For example, in lead wires161of primary winding T1, the voltage becomes high at lead wire161that is connected to capacitor Cr, and thus it is necessary to increase the insulation distances, for example, between that lead wire161and case110, between that lead wire161and other lead wires, and between that lead wire161and cores131,132. Further, since a high voltage is generated at capacitor Cr, it is necessary to increase the insulation distance between capacitor Cr and an upper cover (not shown) of case110disposed over capacitor Cr. Also, it is necessary to increase the insulation distance between primary winding T1and core131. Higher driving frequency of LLC resonant converter100requires further increase in these isolation distances.

In the present embodiment, since capacitor Cr, inductance Lr (primary winding T1in the present embodiment), and the power line between capacitor Cr and inductance Lr (lead wire160) where a high voltage is generated, are resin-sealed, even when operated at a high voltage and a high frequency, the required insulation distances can be shortened. More specifically, the insulation distances can be shortened between lead wire161and case110, between high-voltage lead wire161and other lead wires, between high-voltage lead wire161and cores131,132, and between capacitor Cr and an upper cover of case110where a high voltage is generated. As a result, increase in size of an LLC resonant converter can be suppressed even when designed for a higher voltage and a higher frequency.

As described above, according to the present embodiment, by resin-sealing capacitor Cr, inductance Lr (primary winding T1, also functioning as inductance Lr in the present embodiment), and a power line (lead wire160) between capacitor Cr and inductance Lr that constitute a series resonator, increase in size of an LLC resonant converter can be suppressed even when designed for a higher voltage and a higher frequency.

The above-described embodiments are merely illustrative embodiments for implementing the present invention, and the technical scope of the present invention should not be construed as being limited by these embodiments. That is, the present invention can be embodied in various forms without departing from the gist or essential features thereof.

In the embodiments described above, all capacitors that constitute capacitor Cr are resin-sealed. However, only some of capacitors where a high voltage is generated may be resin-sealed, and the other capacitors may not be resin-sealed. Similarly, in the embodiment described above, an example where all lead wires (power lines)160are resin-sealed has been described, but only some of lead wires (power lines)160where a high voltage is generated may be resin-sealed, and other lead wires (power lines)160may not be resin-sealed.

In the above-described embodiment, an example of using an LLC resonant converter of the present invention in an on-board charger has been illustratively described, an LLC resonant converter of the present invention can be used in devices other than an on-board charger. For example, as shown inFIG. 5, an LCC resonant converter of the present invention can be provided between battery10and load30and used as a step-up DC-DC converter for boosting the voltage of battery10to be supplied to load30. Specifically, LLC resonant converter100ofFIG. 5inputs and boosts the power of battery10to output. For example, a voltage of battery10of about 200V is boosted to a voltage of about 500V by LLC resonant converter100. A power boosted by LLC resonant converter100is supplied to load30, such as a motor. Similarly, the inventive LLC resonant converter can also be used as a step-down DC-DC converter.

The disclosures of the specification, drawings and abstract contained in the Japanese Patent Application No. 2018-061917, filed on Mar. 28, 2018, are hereby incorporated by reference in their entirety.

INDUSTRIAL APPLICABILITY

An LLC resonant converter of the present invention has the effect of suppressing increase in size even when designed for a higher voltage and a higher frequency, and applicable to various DC-DC converters.

REFERENCE SIGNS LIST