JP5004260B2 - Outer iron type power transformer and power converter using the same - Google Patents

Description

【００３３】
なお、本実施例では、パワートランス２０の偏磁の一因である主スイッチ２、３、４、および５のオン期間のバラツキを抑制するため、これら４つの主スイッチにはパワーＭＯＳ−ＦＥＴを用い、ターンオフタイムのバラツキを抑えるためターンオフ時のゲート電流波高値を大きくしてターンオフ時間を極力短くしている。
【００３４】
また、図７の回路において、帰還ダイオード６、７、８および９はパワートランス２０の励磁エネルギーを入力直流電源１に回生することによりコンバータの高効率化を図るとともに同パワートランス２０の偏磁を抑制する機能を有する。
さらに、直流電流を阻止するコンデンサ１０も、直流電流成分が前記パワートランス２０の１次巻線２１に流入することを防止できるため、同パワートランス２０の偏磁を抑制する機能を有する。
【００３５】
パワートランス２０には表２に示す磁心を用いた。表２において、磁心イから磁心トは、いずれも単ロール法で製造されたＦｅを主成分とする非晶質軟磁性合金薄帯を用いて所定の寸法の巻磁心を構成した後、無磁場の窒素雰囲気中で熱処理することにより得られた、結晶粒径５０ｎｍ以下の微細な結晶粒がその組織の体積全体の５０％以上を占めるノーカットのナノ結晶軟磁性合金薄帯巻磁心である。非晶質軟磁性合金薄帯の幅は２０ｍｍ、厚みは１８〜２０μｍのものを用いた。
【００３６】
表２の磁心イから磁心トは、いずれもその寸法が図１に示される磁心２ヶを用いて構成されている。ただし各磁心は、幅３２ｍｍ、高さ５１ｍｍ、奥行き１４ｍｍのプラスチック製絶縁ケースに挿入し、応力がかからないように磁心とケースを接着剤により固定し、同プラスチック製絶縁ケースでふたをすることにより構成されたものを用いた。図２に使用した外鉄型磁心のケース詰め後の形状と寸法を示す。磁心の有効断面積は７５ｍｍ^２、平均磁路長は１３０ｍｍですべて同一である。
【００３７】
【表２】

【００３８】
パワートランス２０の巻線仕様を表３に示す。表３において、本発明Ａから本発明Ｄ、および比較例ｏから比較例ｑのパワートランス２０の構成を図３に示す。図３は、本発明Ａから本発明Ｄ、および比較例ｏから比較例ｑのパワートランス２０の断面図である。
同図において、５０はケースを含む磁心、白抜きの円５１および縦縞の円５２は図７の１次巻線２１、網掛けの円５３および横縞の円５４は各々図７の２次巻線２２と２３に相当する。
【００３９】
２次巻線５３および５４は各々０.２３φのポリウレタン絶縁被覆電線１４本で構成したリッツ線を磁心５０にバイファイラ巻した。
一方、１次巻線は、１.０φの３層絶縁被覆電線を２本パラで３２ターンをケースを含む磁心５０に巻いた巻線５１と１.０φの３層絶縁被覆電線を２本パラで３２ターンを磁心５０に巻いた巻線５２で、前記２次巻線５３および５４を挟み込むと同時に、前記巻線５１と巻線５２をパラ接続することで４本パラで３２ターンの１次巻線２１を構成し、所謂サンドイッチ巻構成としている。
【００４０】
表３において、参考例Ｅから参考例Ｈ、および比較例ｒから比較例ｔのパワートランス２０の構成を図４に示す。図４は、本発明Ｅから本発明Ｈ、および比較例ｒから比較例ｔのパワートランス２０の断面図である。同図において、５０はケースを含む磁心、白抜きの円６１は図７の１次巻線２１、網掛けの円６２および横縞の円６３は各々図７の２次巻線２２と２３に相当する。
【００４１】
１次巻線６１は、１.０φの３層絶縁被覆電線を４本パラで磁心５０に３２ターン巻いた。一方、２次巻線６２および６３は、０.２３φのポリウレタン絶縁被覆電線を１４０本用い構成したリッツ線を、各々磁心５０にバイファイラ巻した。
【００４２】
表３において、比較例ａから比較例ｇのパワートランス２０の構成を図５に示す。図５は、比較例ａから比較例ｇのパワートランス２０の断面図である。
同図において、５０はケースを含む磁心、白抜きの円５１と縦縞の円５２は図７の１次巻線２１、網掛けの円５３および横縞の円５４は各々図７の２次巻線２２と２３に相当する。
【００４３】
【表３】

【００４４】
２次巻線６２および６３は、０.２３φのポリウレタン絶縁被覆電線を１４０本用い構成したリッツ線を、各々磁心５０に整列巻した。
一方、１次巻線は、１.０φの３層絶縁被覆電線を２本パラで３２ターンをケースを含む磁心５０に巻いた巻線５１と１.０φの３層絶縁被覆電線を２本パラで３２ターンを磁心５０に巻いた巻線５２で、前記２次巻線５３および５４をサンドイッチ状に挟み込むと同時に、前記巻線５１と巻線５２をパラ接続することにより４本パラで３２ターンの１次巻線２１を構成している。
【００４５】
表３において、比較例ｈから比較例ｎのパワートランス２０の構成を図６に示す。図６は、比較例ｈから比較例ｎのパワートランス２０の断面図である。
同図において、５０はケースを含む磁心、白抜きの円６１は図７の１次巻線２１、網掛けの円６２および横縞の円６３は各々図７の２次巻線２２と２３に相当する。
【００４６】
１次巻線６１は、１.０φの３層絶縁被覆電線を４本パラで磁心５０に３２ターン巻いた。一方、２次巻線６２および６３は、各々０.２３φのポリウレタン絶縁被覆電線を１４０本用いて構成したリッツ線を磁心５０に整列巻した。
【００４７】
表４に、表３に示す２８種類のパワートランス２０の周波数２０ｋＨｚにおける１次巻線と２次巻線間の各結合係数ｋ1、ｋ2、前記回路構成が図７、仕様が表１のフルブリッジ型ＤＣ−ＤＣコンバータに実装したときの同パワートランス２０の偏磁の有無、動作時の磁束密度の変化量ΔＢおよび温度上昇ΔＴを示す。
なお、前記結合係数ｋ1とｋ2は、１次巻線２１のインダクタンスをＬp、および各２次巻線２２と２３の各々1つのみを短絡して前記１次巻線側から測定した周波数２０ｋＨｚにおけるリーケージ・インダクタンスＬl1とＬl2から、それぞれ次式によって求めることができる。
ｋ1＝（１−（Ｌl1／Ｌp））^0.5 (1)
ｋ2＝（１−（Ｌl2／Ｌp））^0.5 (2)
【００４８】
偏磁については、表１の仕様の範囲において、負荷を２から２５Ａに急変させても偏磁によるパワートランスの飽和が生じない場合を○、負荷を２から２５Ａに急変させたときもしくは入力電圧定常動作のいずれかにおいて偏磁によりパワートランスが飽和した場合を×とした。
また、動作時の磁束密度の変化量ΔＢおよび温度上昇ΔＴは、周囲温度２５℃において入力電圧２００Ｖ、出力電圧４８Ｖ、負荷電流２５Ａの入出力条件のもとで連続通電してパワートランスの温度が飽和した時点で測定した結果である。
【００４９】
表４からわかるように、２０ｋＨｚ、磁化力の波高値０.０５Ａ／ｍのときの透磁率が１０,０００を超え９０，０００以下となる同形状のノーカットのナノ結晶軟磁性合金薄帯巻磁心を２ヶ用い、結合係数ｋ1およびｋ2がいづれも０.９９９７以上である本発明Ａから本発明Ｈのパワートランスによれば、偏磁を実用上問題のないレベルに押さえることができるとともに、その温度上昇ΔＴも実用上支障のない許容値である６０℃以下に押さえることができた。
なお、ここで温度上昇ΔＴの許容値は、表１の動作時の周囲温度の上限である４０℃に動作時のＤＣ−ＤＣコンバータケース内部の温度上昇想定上限値２０℃を足した６０℃をＥ種絶縁の許容温度である１２０℃から差し引いて６０℃以下とした。
【００５０】
結合係数ｋ1またはｋ2が０.９９９７未満の比較例ａから比較例ｏおよび比較例ｒでは、入力電圧定常動作でも偏磁によりパワートランスが飽和した。また、比較例ｑおよび比較例ｔでは、本発明Ｃおよび本発明Ｇと同程度の透磁率、結合係数であるにもかかわらず、角形比Ｂｒ／Ｂｓが０.７３と大きいため、入力電圧定常動作でも偏磁によりパワートランスが飽和した。この結果より角形比Ｂｒ／Ｂｓは０．７以下であることが好ましいことが分かった。
【００５１】
【表４】

【００５２】
比較例ｐおよび比較例ｓは、結合係数ｋ1とｋ2とも０.９９９８以上あり、温度上昇ΔＴも許容値以下であるが、２０ｋＨｚ、磁化力の波高値が０.０５Ａ／ｍで測定したときの透磁率が９０,０００を超えるために、負荷急変時に偏磁の影響によってパワートランスが飽和した。
【００５３】
以上のように、２０ｋＨｚ、磁化力の波高値０．０５Ａ／ｍのときの透磁率が１０，０００を超え９０，０００以下のノーカットのナノ結晶軟磁性合金薄帯巻磁心を用い、結合係数ｋ１およびｋ２がいずれも０．９９９７以上である本発明Ａから参考例Ｈのパワートランスによれば、偏磁を実用上問題のないレベルに押さえることができるとともに、その温度上昇ΔＴも実用上支障のない許容値である６０℃以下に押さえることができる。また、この時の動作磁束密度波高値ΔＢ／２は、パワートランス動作時の温度における飽和磁束密度Ｂｓの８０％に相当し、ナノ結晶軟磁性合金薄帯巻磁心のもつ高飽和磁束密度を有効に活用することができるため、信頼性が高く、高効率なパワートランスが得られるとともに、高効率、高信頼性の電力変換装置を実現できることがわかる。
【００５４】
次に、本発明Ａから参考例Ｈおよび比較例ａからｔを用いて、回路構成が図７の仕様を出力電圧を５３Ｖ、負荷電流を２〜２３Ａに変更することにより動作磁束密度ΔＢを２．０６Ｔとしたときのフルブリッジ型ＤＣ−ＤＣコンバータのパワートランス２０、および同フルブリッジ型ＤＣ−ＤＣコンバータの性能について検討したところ、１次巻線が２次巻線を挟み込むサンドイッチ構造とすることにより、結合係数がいずれも０．９９９８以上となる前記本発明Ａから本発明Ｄでは偏磁は確認されず、温度上昇ΔＴも６０℃以下となった。しかし結合係数がいずれも０．９９９８以下または片方の結合係数が０．９９９８以下となるパワートランスでは偏磁が確認された。
【００５５】
以上のように、２０ｋＨｚ、磁化力の波高値０.０５Ａ／ｍのときの透磁率が１０,０００を超え９０，０００以下、かつ角形比Ｂｒ／Ｂｓが０．７以下のノーカットのナノ結晶軟磁性合金薄帯巻磁心を用い、結合係数ｋ1およびｋ2がいずれも０.９９９８以上である本発明Ａから本発明Ｄのパワートランスによれば、さらに動作磁束密度を大きく設定できるためパワートランスをより小型化できることが分かった。
【００５６】
前記、巻線構造および透磁率の違いによる結合係数と角形比Ｂｒ／Ｂｓの値から、磁心にＣｏ基アモルファスを用い、同方法による偏磁の有無を確認したところ、前記ナノ結晶軟磁性合金薄帯巻磁心を用いたときと同様の結果が得られた。
【００５７】
なお、前記実施例で用いた磁心は、図２より磁心のケース詰め後の中足の幅Ｗが１８ｍｍ、奥行きがＤ１４ｍｍであり、その比Ｄ／Ｗは０.８８であった。この値が大きくなるように磁心および磁心を収納するケースを選定することにより、図３および図４に示す巻線構造のパワートランスにおいては結合係数が高くなることが分かった。しかしあまりＤ／Ｗの値を大きくしすぎると、パワートランスを自然空冷で使用する際には、熱がパワートランス内側こもるため好ましくないが、強制空冷用の冷却ファンにより、パワートランス内側の熱を吹き出す方法を用いることにより問題は解決する。
【００５８】
さらに、回路構成が図７、仕様が表１で与えられるＤＣ−ＤＣコンバータについて、その駆動周波数を変えたときに、本発明によるノーカットのナノ結晶軟磁性合金薄帯巻磁心を用いたパワートランス、Ｍｎ−Ｚｎフェライト磁心を用いたパワートランス、およびＦｅ基アモルファス軟磁性合金薄帯巻磁心を用いたパワートランスについて、温度上昇ΔＴが６０℃以下で、偏磁による異常動作を生じない条件を満足する製品サイズを比較検討した。その結果、Ｆｅ基アモルファス軟磁性合金薄帯巻磁心を用いたパワートランスは駆動周波数が５ｋＨｚ未満で最も小型化でき、Ｍｎ−Ｚｎフェライト磁心を用いたパワートランスは駆動周波数１５０ｋＨｚを超える場合に最も小型化できた。これらに対し、本発明によるノーカットのナノ結晶軟磁性合金薄帯巻磁心を用いたパワートランスは駆動周波数が５ｋＨｚ以上１５０ｋＨｚ以下の範囲で最も小型化できることもわかった。
【００５９】
なお、前記実施例においては、磁心形状を長方形として、また寸法を図１および図２にて例示したが、本考案はこれに限らずレーストラック形、円形等どのような形状および寸法のものを用いても良い。また、前記実施例では、巻き磁心と磁心ケースからなる磁心を２ヶ用いて例示したが、磁心ケースが２ヶ以上の磁心を挿入できる構造のものを用いても良いことは勿論である。
【００６０】
【発明の効果】
以上説明したように、本発明によれば、特に複雑な偏磁抑制回路を設けることなしに実用上障害となる偏磁の発生を抑制し得るとともにノーカットのナノ結晶軟磁性合金薄帯巻磁心を用いた場合には、磁心のもつ高飽和磁束密度、高透磁率を有効に活用でき、小型で温度上昇が小さく高効率のパワートランス２０、およびこれを用いた高効率で信頼性の高い電力変換装置が得られる。さらに、磁心を外鉄型とすることにより、磁心そのものを直接冷却することができるため、冷却効率も改善されることになる。
なお、前記実施例では、パワートランスを用いた代表的な電力変換装置としてフルブリッジ型ＤＣ−ＤＣコンバータへの応用例について詳細に説明したが、本発明はハーフブリッジ型コンバータを始めとするセンタータップを持たない１次巻線と、少なくとも1組以上のセンタータップ付き２次巻線を設けたパワートランス２０全般、またプッシュプル型コンバータを始めとする少なくとも1組以上のセンタータップ付き１次巻線と、少なくとも1組以上のセンタータップ付き２次巻線を設けたパワートランス２０全般、および同パワートランス２０を用いた電力変換装置全般に適用され、同様に有効な効果を発揮し、その効果は極めて大きい。
【図面の簡単な説明】
【図１】本発明の実施例で使用した磁心の形状と寸法を示した図。
【図２】本発明の実施例で使用した外鉄型磁心のケース詰め後の寸法を示した図。
【図３】本発明による、パワートランス２０の１実施例の巻線構造断面の概念図。
【図４】参考例による、パワートランス２０の１実施例の巻線構造断面の概念図。
【図５】比較例であるパワートランスの巻線構造断面の概念図。
【図６】比較例であるパワートランスの巻線構造断面の概念図。
【図７】フルブリッジ型ＤＣ−ＤＣコンバータの回路構成ブロック図。
【図８】図７のフルブリッジ型ＤＣ−ＤＣコンバータにおけるパワートランス２０の１次巻線２１の端子電圧概念図。
【図９】偏磁がない場合の図７のフルブリッジ型ＤＣ−ＤＣコンバータのパワートランス２０の動作Ｂ−Ｈループ概念図。
【図１０】偏磁により磁心が飽和したときの図７のフルブリッジ型ＤＣ−ＤＣコンバータのパワートランス２０の動作Ｂ−Ｈループ概念図。[0001]
[Industrial application fields]
The present invention relates to a small and high-efficiency power transformer using a soft magnetic alloy ribbon core having a relatively high relative initial permeability and a power converter using the power transformer.
[0002]
[Prior art]
A full-bridge DC-DC converter shown in FIG. 7 is used as one of the insulated power converters using a power transformer. In FIG. 7, 1 is an input DC power source, 2, 3, 4 and 5 are main switches, 6, 7, 8 and 9 are feedback diodes, 10 is a capacitor for blocking DC current, and 20 has no center tap. A power transformer provided with a primary winding and a secondary winding for full-wave rectification output, 21 is a primary winding of the power transformer 20, 22 and 23 are secondary for full-wave rectification output of the power transformer 20. Winding, 31 and 32 are output rectifier diodes, 33 is an output smoothing choke coil, 34 is an output smoothing capacitor, 35 and 36 are output terminals, and 37 is a load.
[0003]
In the full-bridge type DC-DC converter of FIG. 7, the main switches 2 and 3 and 4 and 5 are each set as one set of switches, and these two sets of switches are alternately switched. A voltage such as v21 in FIG. 8 is applied to the secondary winding 21 via the capacitor 10. From the secondary windings 22 and 23 for full-wave rectification output of the power transformer 20, output rectifier diodes 31 and 32, Electric power is supplied to the load 37 via the smoothing choke coil 33 and the smoothing capacitor 34. In FIG. 8, the period in which the main switches 2 and 3 are on is Ton23, the period in which the main switches 4 and 5 are on is Ton45, and Tp is the period.
(Ton23 + Ton45) / Tp is the on-duty ratio Don, and in order to keep the output voltage Vo constant with respect to fluctuations in the voltage E of the input DC power supply 1 and fluctuations in the load 37, PWM is controlled by changing Tn and changing Don. Control (pulse width modulation control) is generally used. The driving frequency f of the power transformer 20 is given by 1 / Tp.
[0004]
An operation BH loop conceptual diagram of the power transformer 20 in this converter is shown in FIG. The direction of the magnetic field generated in the power transformer 20 when current flows from the black circle side of the primary winding 21 of the power transformer 20 shown in FIG. 7 is set to the positive side of the H axis in FIG. Therefore, in the period Ton23 in which the main switches 2 and 3 are on, the magnetic flux density of the power transformer 20 changes by 2 Bm from the point a to the point b in FIG. 9, and in the period Ton45 in which the main switches 4 and 5 are on. The magnetic flux density of the power transformer 20 changes by -2 Bm from point b to point a in FIG. That is, the power transformer 20 in the converter operates to draw a symmetric minor loop with respect to the origin of the BH loop.
[0005]
In the power transformer 20 in this converter, downsizing and low loss are important issues. As a general technique for reducing the size of the power transformer 20, the drive frequency is increased. However, an extremely high frequency without considering the high frequency characteristics of elements such as the magnetic core used in the power transformer 20, the main switches 2, 3, 4 and 5, the feedback diodes 6, 7, 8 and 9, or the output rectifier diodes 31 and 32. Not only increases the loss of these elements, but also increases the loss of the power transformer 20, causing a decrease in converter efficiency and a decrease in reliability due to an excessive temperature rise.
[0006]
For the power transformer 20 in this converter, it is generally necessary to select a magnetic core that can be miniaturized and has a low loss at a driving frequency selected in consideration of the high-frequency characteristics of the main switches 2, 3, 4, and 5.
[0007]
For example, when the output power is relatively small up to about several kW, the main switch is usually2, 3,Power MOS-FETs are selected for 4 and 5, and the drive frequency is selected to be about 50 kHz or more. In this case, for the magnetic core of the power transformer 20, conventionally, an Mn—Zn ferrite core having a small magnetic core loss at several hundred kHz or more, although the saturation magnetic flux density Bs at room temperature is as small as about 0.5T. It was.
[0008]
On the other hand, in the region where the output power exceeds several kW, the IGBT is generally selected for the main switches 2, 3, 4 and 5, and the drive frequency is selected from several kHz to about 20 kHz.
In this case, Sakakibara, Saito, Kamo, Toyota, Yamauchi, Yoshizawa: “Inverter Transformer Using Ultrafine Crystal Alloy for Iron Core”, IEEJ Technical Report, MAG-90-194, December 6, 1990 ( Hereinafter, the magnetic core of the power transformer 20 has a saturation magnetic flux density of 1T or more, which is more than twice that of the Mn-Zn ferrite magnetic core, and a magnetic core loss at 20 kHz. A small Fe-based nanocrystalline soft magnetic alloy containing Fe as a main component as described in JP-A-63-302504 and having fine crystal grains having a crystal grain size of 50 nm or less account for 50% or more of the entire volume of the structure It is known that the ribbon magnetic core is excellent.
[0009]
In the Fe-based nanocrystalline soft magnetic alloy ribbon core, the above-mentioned document 1, or Fukunaga, Koga, Eguchi, Ota, Kakehashi: “Magnetic properties of gap-cut cores using iron-based magnetic ribbons; The wound magnetic core is formed by resin impregnation treatment or surface fixing treatment as described in the meeting material, MAG-89-203, December 1, 1989 (hereinafter referred to as Reference 2). It is known that the core loss increases remarkably when resin or varnish penetrates between layers of the nanocrystalline soft magnetic alloy ribbon and stress is applied to the nanocrystalline soft magnetic alloy ribbon.
[0010]
By the way, in the magnetic core for the power transformer 20, a cut magnetic core is widely used to facilitate the winding work. In order to cut the nanocrystalline soft magnetic alloy ribbon core, the core is impregnated with an impregnation material such as an epoxy adhesive, and the layers of the nanocrystalline soft magnetic alloy ribbon constituting the wound core are separated. After fixing with the impregnating material, it is necessary to cut with a rotating grindstone or the like. In addition, from the viewpoint of reducing the magnetic core loss, the end face is also mirror-polished after cutting. However, the magnetic core cut from the nanocrystalline soft magnetic alloy ribbon core using such a method has a complicated manufacturing process as described above, and as described in the literature 1 and literature 2, There is also a problem that the magnetic core loss is remarkably increased.
[0011]
For this reason, Yoshizawa, Mori, Arakawa, Yamauchi: "High-frequency magnetic properties of Fe-Cu-Nb-Si-B-based nanocrystalline alloys to reduce the core loss of cores cut using nanocrystalline soft magnetic alloy ribbons. As described in the Institute of Electrical Engineers of Japan, MAG-94-202, November 22, 1994 (hereinafter referred to as Reference 3), the saturation magnetostriction constant λs is 10^-6It is effective to use the following small nanocrystalline soft magnetic alloy ribbon and perform interlayer insulation treatment with the surface of the ribbon covered with ceramics. However, in the case of a magnetic core with an interlayer insulation treatment coated with the ceramic, the hardness of the ceramic insulating layer is high, so there is a problem that the man-hour for cutting increases significantly, and normal nanocrystalline soft magnetism without impregnation or cutting This is about 1.4 times the core loss of the alloy ribbon magnetic core.
[0012]
For this reason, in order to effectively utilize the low core loss that is characteristic of nanocrystalline soft magnetic alloy ribbon cores, the nanocrystalline soft magnetic alloy ribbon that constitutes the core is configured so that stress is not applied as much as possible. There is a need to. As a nanocrystalline soft magnetic alloy ribbon core with such a configuration, the uncut core is housed in an insulating case such as plastic or ceramic using silicon grease or gel-like silicon rubber as a cushioning material. In general, those in which it is difficult for the stress to be directly applied to the wound magnetic core are used.
[0013]
[Problems to be solved by the invention]
Like the full bridge type DC-DC converter of FIG. 7, the power converter device which operates to draw a BH minor loop in which the magnetic flux density of the power transformer 20 is symmetrical with respect to the origin of the BH loop as shown in FIG. In the power transformer 20, the BH minor loop at the time of operation is asymmetrical with respect to the origin of the BH loop as shown in FIG. It is very important to suppress the increase and to ensure the safe operation of the main switches 2, 3, 4 and 5.
[0014]
As is well known, the magnetic bias of the power transformer 20 is mainly caused by variations in the electrical characteristics of the main switches 2, 3, 4 and 5, and the excitation current has a certain value depending on the circuit impedance. Equilibrate at. However, when the bias of the power transformer 20 is large, the BH minor loop during operation reaches one saturation region as shown in FIG. 10, and the excitation current increases remarkably, so that the main switches 2, 3, 4, and An excessive current flowed between the five main electrodes, and the main switches 2, 3, 4 and 5 could be destroyed. In particular, sudden changes in voltage or load on the input DC power supply 137When the power transformer 20 suddenly changes, the amount of change ΔB in the magnetic flux density during the operation of the power transformer 20 becomes transiently large, so that the amount of increase in the excitation current due to the bias is also large, and the main switches 2, 3, 4 and 5 are destroyed. The risk was high.
[0015]
When an overcurrent protection circuit with a high response speed that suppresses overcurrent flowing between the main electrodes of the main switches 2, 3, 4, and 5 is provided, the main switches 2, 3, It is possible to suppress an excessive current from flowing through 4 and 5, and to prevent these main switches from being destroyed. However, when the overcurrent protection circuit operates, there is a problem that it is impossible to ensure the constant voltage accuracy of the output voltage because sufficient power cannot be supplied to the output side.
[0016]
As the most general technique for preventing the magnetism of the power transformer 20, a magnetic core having a small magnetic permeability is adopted for the power transformer 20, and the operating magnetic flux density peak value Bm of the magnetic core is used as the saturation magnetic flux of the magnetic core. Selection is made so as to be a sufficiently small value with respect to the density Bs. As a method for obtaining a magnetic core having a low magnetic permeability, the simplest method is to provide a gap in the cut magnetic core to reduce its effective relative magnetic permeability. According to this method, there is also an advantage that the effective relative magnetic permeability of the magnetic core can be arbitrarily selected by adjusting the gap width.
[0017]
However, in the case of a nanocrystalline soft magnetic alloy ribbon core, a method for reducing the effective relative permeability by providing a gap as described above is also described in the literature 1 to literature 3, By using a cut magnetic core and providing a gap, the core loss greatly increases, so that the characteristic of low core loss, which is the greatest advantage when used in the power transformer 20, is impaired, and the leakage magnetic flux generated in the gap portion. There was a problem that the copper loss increased due to the influence of.
[0018]
In a nanocrystalline soft magnetic alloy ribbon core, a method for reducing the relative permeability without providing a gap is to heat-treat while applying a magnetic field in the ribbon width direction (winding core height direction) of the winding core. There are a technique and a technique of applying stress to the nanocrystalline soft magnetic alloy ribbon forming the wound magnetic core. However, there are many problems in efficiently producing a magnetic core while suppressing variations in magnetic characteristics represented by relative permeability and magnetic core loss by these methods.
[0019]
That is, in the case of the former method, a nanocrystalline soft magnetic alloy ribbon core excellent in soft magnetic properties is obtained from a wound magnetic core formed using an amorphous soft magnetic alloy capable of forming a nanocrystalline soft magnetic alloy ribbon. Fluctuations at around 5 to tens of degrees Celsius, the optimum heat treatment temperature required30 ℃It must be kept to a certain extent, it must be performed in an inert gas atmosphere such as nitrogen to avoid oxidation during the heat treatment of the wound core, and about 100 kA / m in the direction of the ribbon width of the wound core There is a problem that the configuration and process of the heat treatment apparatus become complicated due to the restriction that the above-mentioned magnetization must be applied.
[0020]
On the other hand, the latter method of applying stress has a problem in that the magnetic core loss is significantly increased as described in the above-mentioned documents 1 and 2.
[0021]
Therefore, like the full-bridge type DC-DC converter of FIG. 7, the magnetic flux density of the power transformer 20 operates to draw a BH minor loop that is symmetric with respect to the origin of the BH loop as shown in FIG. In order to use the nanocrystalline soft magnetic alloy ribbon core for the power transformer 20 of the power converter and to exhibit the feature of low core loss, the power transformer is saturated due to extreme demagnetization and the main switch is destroyed. 2 sets formed by the main switches 2, 3, 4, and 5 in order to detect the amount of magnetic bias of the power transformer 20 and correct itofIt has been necessary to take measures such as adding a demagnetization suppression circuit capable of independently controlling the ON period of each switch.
[0022]
In the above description, the problem of the power transformer 20 using the nanocrystalline soft magnetic alloy ribbon magnetic core and the power converter using the same has been described by taking a full-bridge type DC-DC converter as an example. A half-bridge converter with a soft magnetic alloy ribbon core having a primary winding without a center tap and at least one set of secondary windings for full-wave rectification output, and at least one set of centers Power transformer 20 of other power converters such as a push-pull converter having a primary winding having a tap and at least one set of secondary windings for full-wave rectification output, and power using the same The conversion device has the same problem. The same problem occurs when a Co-based amorphous ribbon is used for the magnetic core.
[0023]
The object of the present invention is to prevent the occurrence of a practically disturbing level of demagnetization, which has been difficult to achieve with the prior art, and uses a small uncut ribbon core with a low core loss. An object of the present invention is to provide a type power transformer 20 and a highly efficient and reliable power conversion device using the same.
[0024]
[Means for Solving the Problems]
  In the present invention, the magnetic core material is composed of a nanocrystalline soft magnetic alloy ribbon wound core in which fine crystal grains mainly composed of Fe and having a crystal grain size of 50 nm or less occupy 50% or more of the entire volume of the structure. The squareness ratio Br / Bs, which is the ratio of the residual magnetic flux density Br to the saturation magnetic flux density Bs in the DC magnetic characteristics measured at a peak value of 800 A / m, is 0.7 or less, and the peak value of the magnetizing force is 0.05 A / m. An uncut outer core type magnetic core is formed by using at least two winding cores having an AC ratio initial permeability μri of 10,000 or more and 90,000 or less at a frequency of 20 kHz and centered on the center leg of the outer iron core. A primary winding having no tap, or a primary winding having at least one set of center taps wound with a bifilar, and at least one set of center taps wound with a bifilar Each of the secondary windings for full-wave rectification, which is a sandwich structure in which the primary winding sandwiches the secondary winding. Both of the two coupling coefficients at 20 kHz are 0.9998 or more.Can suppress the occurrence of bias.This is an outer iron type power transformer.
[0025]
With such a configuration, the power transformer 20 using the uncut ribbon core with high magnetic permeability and low magnetic core loss is used as a power converter such as a push-pull converter, a full bridge converter, and a half bridge converter. It is preferable that magnetic saturation due to magnetic bias, which has been a problem when used, can be prevented without adding a complicated magnetic bias suppression circuit.
[0026]
  In the power transformer 20, the secondary winding for full-wave rectification output, which is the main output, is bifilar wound around the ribbon magnetic core, and the secondary winding is wound around the ribbon magnetic core. Sandwiched by a primary windingForThe coupling coefficient can be reduced by reducing the leakage inductance between the primary winding and its secondary output secondary winding for full-wave rectification output.The highTherefore, it is possible to further reduce the increase in the excitation current due to the demagnetization and to suppress the increase in the copper loss due to the influence of the leakage magnetic flux. In addition, since the operating magnetic flux density can be set larger, the power transformer 20 can be reduced in size and efficiency, which is preferable.
[0028]
In the power transformer, the magnetic core is composed of a nanocrystalline soft magnetic alloy ribbon wound core in which fine crystal grains having a crystal grain size of 50 nm or less mainly composed of Fe occupy 50% or more of the entire volume of the structure. If the drive frequency is selected in the range of 5 kHz or more and 150 kHz or less, it is preferable because the size and efficiency can be further reduced as compared with the conventional power transformer.
[0029]
The power converter using the outer iron type power transformer 20 according to the present invention can be reduced in size and efficiency as compared with the conventional power converter, and the excitation current due to the bias of the power transformer with a simple circuit configuration. Therefore, the main switch can be safely operated and the reliability is improved.
[0030]
【Example】
Examples of the present invention will be described in detail below.
Example 1
The performance of the power transformer 20 of the full bridge type DC-DC converter whose circuit configuration is shown in FIG. 7 and whose specification is given in Table 1 and whose switching frequency f is 20 kHz was examined.
[0031]
In FIG. 7, 1 is an input DC power source, 2, 3, 4 and 5 are main switches, 6, 7, 8 and 9 are feedback diodes, 10 is a capacitor for blocking DC current, and 20 has no center tap. A power transformer provided with a primary winding and a secondary winding for full-wave rectification output, 21 is a primary winding of the power transformer 20, 22 and 23 are secondary for full-wave rectification output of the power transformer 20. Winding, 31 and 32 are output rectifier diodes, 33 is an output smoothing choke coil, 34 is an output smoothing capacitor, 35 and 36 are output terminals, and 37 is a load.
[0032]
[Table 1]

[0033]
In this embodiment, in order to suppress variations in the ON period of the main switches 2, 3, 4, and 5 that are a cause of the bias of the power transformer 20, a power MOS-FET is provided for these four main switches. In order to suppress variation in turn-off time, the gate current peak value at turn-off is increased to shorten the turn-off time as much as possible.
[0034]
In the circuit of FIG. 7, the feedback diodes 6, 7, 8 and 9 improve the converter efficiency by regenerating the excitation energy of the power transformer 20 to the input DC power supply 1, and also demagnetize the power transformer 20. It has a function to suppress.
Further, the capacitor 10 for blocking the direct current can also prevent the direct current component from flowing into the primary winding 21 of the power transformer 20 and thus has a function of suppressing the magnetization of the power transformer 20.
[0035]
A magnetic core shown in Table 2 was used for the power transformer 20. In Table 2, each of the magnetic cores A to G is composed of an amorphous soft magnetic alloy ribbon mainly composed of Fe manufactured by a single roll method, and then a magnetic core without a predetermined size is formed. This is an uncut nanocrystalline soft magnetic alloy ribbon core in which fine crystal grains having a crystal grain size of 50 nm or less occupy 50% or more of the entire volume of the structure obtained by heat treatment in a nitrogen atmosphere. An amorphous soft magnetic alloy ribbon having a width of 20 mm and a thickness of 18 to 20 μm was used.
[0036]
Each of the magnetic cores A to G in Table 2 is constructed using two magnetic cores whose dimensions are shown in FIG. However, each magnetic core is configured by inserting it into a plastic insulating case with a width of 32 mm, a height of 51 mm, and a depth of 14 mm, fixing the magnetic core and the case with an adhesive so that no stress is applied, and closing the lid with the plastic insulating case. What was done was used. FIG. 2 shows the shape and dimensions of the outer iron core used after packing the case. The effective cross-sectional area of the magnetic core is 75mm²The average magnetic path length is 130 mm and they are all the same.
[0037]
[Table 2]

[0038]
Table 3 shows the winding specifications of the power transformer 20. In Table 3, the structure of the power transformer 20 of this invention A to this invention D and comparative example o to comparative example q is shown in FIG. FIG. 3 is a cross-sectional view of the power transformer 20 of the present invention A to the present invention D and the comparative example o to the comparative example q.
In the figure, 50 is a magnetic core including a case, white circle 51 and vertical stripe circle 52 are primary winding 21 of FIG. 7, shaded circle 53 and horizontal stripe circle 54 are secondary windings of FIG. It corresponds to 22 and 23.
[0039]
The secondary windings 53 and 54 were bifilar wound around a magnetic core 50 of litz wire composed of 14 0.23φ polyurethane insulation coated electric wires.
On the other hand, the primary winding is composed of two windings of 1.0φ three-layer insulation-coated electric wires and 32 turns of 32 turns around a magnetic core 50 including a case and two 1.0-φ three-layer insulation-coated electric wires.soA winding 52 having 32 turns wound around a magnetic core 50 sandwiches the secondary windings 53 and 54, and at the same time, the winding 51 and the winding 52 are connected in parallel to form a primary winding of 32 turns in four lines. The wire 21 is configured as a so-called sandwich winding configuration.
[0040]
  In Table 3,Reference exampleFrom EReference exampleFIG. 4 shows the configuration of the power transformer 20 of H and Comparative Examples r to t. FIG. 4 is a cross-sectional view of the power transformer 20 from the present invention E to the present invention H and from the comparative example r to the comparative example t. In the drawing, 50 is a magnetic core including a case, white circle 61 is primary winding 21 in FIG. 7, shaded circle 62 and horizontal stripe circle 63 are equivalent to secondary windings 22 and 23 in FIG. 7, respectively. To do.
[0041]
As the primary winding 61, a 1.0φ three-layer insulation-coated electric wire was wound around the magnetic core 50 for 32 turns with four parallel wires. On the other hand, the secondary windings 62 and 63 were bifilar wound around the magnetic core 50 with litz wires constructed using 140 0.23φ polyurethane insulation-coated wires.
[0042]
In Table 3, the structure of the power transformer 20 of the comparative example a to the comparative example g is shown in FIG. FIG. 5 is a cross-sectional view of the power transformer 20 of Comparative Examples a to g.
In the figure, 50 is a magnetic core including a case, white circle 51 and vertical stripe circle 52 are primary winding 21 in FIG. 7, shaded circle 53 and horizontal stripe circle 54 are secondary windings in FIG. It corresponds to 22 and 23.
[0043]
[Table 3]

[0044]
As the secondary windings 62 and 63, litz wires formed by using 140 0.23 φ polyurethane insulation-coated electric wires were wound around the magnetic core 50.
On the other hand, the primary winding is composed of two windings of 1.0φ three-layer insulation-coated electric wires and 32 turns of 32 turns around a magnetic core 50 including a case and two 1.0-φ three-layer insulation-coated electric wires.soThe secondary windings 53 and 54 are sandwiched between the windings 52 wound around the magnetic core 50 in 32 sandwiches, and at the same time, the windings 51 and 52 are connected in parallel, so that 32 turns of 4 turns can be achieved. A primary winding 21 is configured.
[0045]
In Table 3, a comparative examplehComparison examplenThe configuration of the power transformer 20 is shown in FIG. FIG. 6 shows a comparative example.hComparison examplenIt is sectional drawing of the power transformer 20 of.
In the drawing, 50 is a magnetic core including a case, white circle 61 is primary winding 21 in FIG. 7, shaded circle 62 and horizontal stripe circle 63 are equivalent to secondary windings 22 and 23 in FIG. 7, respectively. To do.
[0046]
As the primary winding 61, a 1.0φ three-layer insulation-coated electric wire was wound around the magnetic core 50 for 32 turns with four parallel wires. On the other hand, the secondary windings 62 and 63 were formed by aligning and winding the Litz wire formed by using 140 0.23φ polyurethane insulation-coated electric wires around the magnetic core 50.
[0047]
Table 4 shows in Table 3.28When the coupling coefficient k1, k2 between the primary winding and the secondary winding at a frequency of 20 kHz of the type of power transformer 20 is mounted on the full-bridge type DC-DC converter shown in FIG. The presence / absence of demagnetization of the power transformer 20, the amount ΔB of change in magnetic flux density during operation, and the temperature rise ΔT are shown.
It should be noted that the coupling coefficients k1 and k2 are at a frequency of 20 kHz measured from the primary winding side by short-circuiting only one of the secondary windings 22 and 23 with the inductance of the primary winding 21 being Lp. The leakage inductances Ll1 and Ll2 can be obtained by the following equations, respectively.
k1 = (1- (Ll1 / Lp))^0.5              (1)
k2 = (1- (Ll2 / Lp))^0.5              (2)
[0048]
As for the bias, ○ within the range of specifications in Table 1, when the load is suddenly changed from 2 to 25A, the power transformer is not saturated due to the bias, and when the load is suddenly changed from 2 to 25A or the input voltage The case where the power transformer was saturated due to the magnetic bias in any of the steady operations was marked with x.
The amount of change ΔB in magnetic flux density during operation and the temperature rise ΔT are energized continuously under an input / output condition of an input voltage of 200 V, an output voltage of 48 V, and a load current of 25 A at an ambient temperature of 25 ° C.Power transformer temperatureIt is the result measured when is saturated.
[0049]
As can be seen from Table 4, the uncut nanocrystalline soft magnetic alloy ribbon core of the same shape having a magnetic permeability exceeding 10,000 and not exceeding 90,000 at 20 kHz and a peak value of the magnetizing force of 0.05 A / m According to the power transformers of the present invention A to present invention H in which the coupling coefficients k1 and k2 are both 0.9997 or more, it is possible to suppress the demagnetization to a level with no practical problem, The temperature rise ΔT could be suppressed to 60 ° C. or less, which is an allowable value that does not hinder practical use.
Here, the allowable value of the temperature rise ΔT is 40 ° C., which is the upper limit of the ambient temperature during operation shown in Table 1.In60 ° C., which is the upper limit 20 ° C. of the temperature rise inside the DC-DC converter case during operation, was subtracted from 120 ° C., which is the allowable temperature for class E insulation, to 60 ° C. or less.
[0050]
Coupling coefficient k1OrIn Comparative Example a to Comparative Example o and Comparative Example r in which k2 is less than 0.9997, the power transformer was saturated due to the bias magnetism even in the steady operation of the input voltage. In Comparative Example q and Comparative Example t, the squareness ratio Br / Bs is as large as 0.73 in spite of the same magnetic permeability and coupling coefficient as in the present invention C and present invention G. Even in operation, the power transformer was saturated due to bias. From this result, it was found that the squareness ratio Br / Bs is preferably 0.7 or less.
[0051]
[Table 4]

[0052]
In Comparative Example p and Comparative Example s, both of the coupling coefficients k1 and k2 are 0.9998 or more, and the temperature rise ΔT is also less than the allowable value, but when measured at 20 kHz and the peak value of the magnetizing force is 0.05 A / m. Since the magnetic permeability exceeds 90,000, the power transformer is saturated due to the influence of the demagnetization when the load suddenly changes.did.
[0053]
  As described above, an uncut nanocrystalline soft magnetic alloy ribbon core having a magnetic permeability of more than 10,000 and not more than 90,000 at 20 kHz and a peak value of the magnetizing force of 0.05 A / m is used, and the coupling coefficient k1 And from the present invention A in which k2 is both 0.9997 or moreReference exampleAccording to the H power transformer, it is possible to suppress the demagnetization to a level having no practical problem, and also to suppress the temperature rise ΔT to 60 ° C. or less, which is a practically acceptable allowable value. Further, the operating magnetic flux density peak value ΔB / 2 at this time corresponds to 80% of the saturation magnetic flux density Bs at the temperature when the power transformer operates, and the high saturation magnetic flux density of the nanocrystalline soft magnetic alloy ribbon core is effective. Therefore, it can be seen that a highly reliable and highly efficient power transformer can be obtained and a highly efficient and highly reliable power converter can be realized.
[0054]
  Next, from the present invention AReference exampleA full-bridge type using H and Comparative Examples a to t when the circuit configuration is changed from the specification of FIG. 7 to an output voltage of 53 V and a load current of 2 to 23 A so that the operating magnetic flux density ΔB is 2.06 T. When the performance of the power transformer 20 of the DC-DC converter and the performance of the full-bridge type DC-DC converter were examined, a sandwich structure in which the primary winding sandwiches the secondary winding so that the coupling coefficient is 0. In the present invention A to present invention D of 9998 or more, no magnetization was confirmed, and the temperature rise ΔT was also 60 ° C. or less. However, in the power transformer in which the coupling coefficient is 0.9998 or less or one of the coupling coefficients is 0.9998 or less, demagnetization was confirmed.
[0055]
As described above, the magnetic permeability exceeds 10,000 and is not more than 90,000 at 20 kHz and the peak value of the magnetizing force is 0.05 A / m.And the squareness ratio Br / Bs is 0.7 or less.According to the power transformers of the invention A to the invention D, in which the uncut nanocrystalline soft magnetic alloy thin ribbon core is used and the coupling coefficients k1 and k2 are both 0.9998 or more, the operating magnetic flux density is further increased. As a result, it was found that the power transformer can be made smaller.
[0056]
Coupling coefficient due to difference in winding structure and magnetic permeabilityAnd squareness ratio Br / BsFrom this value, when a Co-based amorphous was used for the magnetic core and the presence or absence of demagnetization by the same method was confirmed, the same result as that obtained when the nanocrystalline soft magnetic alloy ribbon core was used was obtained.
[0057]
The magnetic core used in the above embodiment had a width W of 18 mm and a depth of D14 mm after packing the case of the magnetic core as shown in FIG. 2, and the ratio D / W was 0.88. It has been found that the coupling coefficient is increased in the power transformer having the winding structure shown in FIG. 3 and FIG. 4 by selecting the magnetic core and the case storing the magnetic core so that this value is increased. However, if the value of D / W is too large, it is not preferable because the heat is trapped inside the power transformer when the power transformer is used in natural air cooling, but the heat inside the power transformer is reduced by the cooling fan for forced air cooling. The problem is solved by using the blowing method.
[0058]
Furthermore, for a DC-DC converter whose circuit configuration is given in FIG. 7 and whose specifications are given in Table 1, when the drive frequency is changed, a power transformer using the uncut nanocrystalline soft magnetic alloy ribbon core according to the present invention, For power transformers using Mn—Zn ferrite cores and power transformers using Fe-based amorphous soft magnetic alloy ribbon cores, the temperature rise ΔT is 60 ° C. or less, and the conditions that do not cause abnormal operation due to demagnetization are satisfied. Product size was compared. As a result, the power transformer using the Fe-based amorphous soft magnetic alloy ribbon core can be most compact when the driving frequency is less than 5 kHz, and the power transformer using the Mn-Zn ferrite core is most compact when the driving frequency exceeds 150 kHz. I was able to. On the other hand, it was also found that the power transformer using the uncut nanocrystalline soft magnetic alloy ribbon core according to the present invention can be miniaturized most when the driving frequency is in the range of 5 kHz to 150 kHz.
[0059]
In the above embodiment, the magnetic core shape is rectangular and the dimensions are illustrated in FIGS. 1 and 2, but the present invention is not limited to this.Race track shape, round shape, etc.Any shape and size can be used.Yes.Moreover, in the said Example, although illustrated using two magnetic cores which consist of a wound magnetic core and a magnetic core case, of course, the thing of the structure where a magnetic core case can insert two or more magnetic cores may be used.
[0060]
【The invention's effect】
As described above, according to the present invention, an uncut nanocrystalline soft magnetic alloy ribbon core can be formed while suppressing the occurrence of practically obstructed demagnetization without providing a complicated demagnetization suppression circuit. When used, the high saturation magnetic flux density and high magnetic permeability of the magnetic core can be effectively used, and the power transformer 20 is small, has a small temperature rise and is highly efficient, and the power conversion using this is highly efficient and highly reliable. A device is obtained. Furthermore, since the magnetic core itself can be directly cooled by using the outer core type as the magnetic core, the cooling efficiency is also improved.
In the above-described embodiment, the application example to the full-bridge type DC-DC converter is described in detail as a typical power conversion device using a power transformer. However, the present invention is a center tap including a half-bridge type converter. Power transformer 20 in general, which has a primary winding with no center and at least one pair of secondary windings with a center tap, and at least one primary winding with a center tap including a push-pull converter Applied to all power transformers 20 provided with at least one set of secondary windings with a center tap, and power converters using the power transformers 20 in the same way, exhibiting effective effects in the same way. Very large.
[Brief description of the drawings]
FIG. 1 is a diagram showing the shape and dimensions of a magnetic core used in an embodiment of the present invention.
FIG. 2 is a view showing dimensions after packing a case of an outer iron type magnetic core used in an example of the present invention.
FIG. 3 is a conceptual diagram of a winding structure cross-section of one embodiment of a power transformer 20 according to the present invention.
[Fig. 4]Reference exampleThe conceptual diagram of the coil | winding structure cross section of one Example of the power transformer 20 by FIG.
FIG. 5 is a conceptual diagram of a cross section of a winding structure of a power transformer as a comparative example.
FIG. 6 is a conceptual diagram of a cross section of a winding structure of a power transformer as a comparative example.
FIG. 7 is a block diagram of a circuit configuration of a full bridge type DC-DC converter.
8 is a conceptual diagram of a terminal voltage of a primary winding 21 of a power transformer 20 in the full bridge type DC-DC converter of FIG.
9 is a conceptual diagram of an operation BH loop of the power transformer 20 of the full bridge type DC-DC converter of FIG. 7 when there is no bias.
10 is a conceptual diagram of an operation BH loop of the power transformer 20 of the full bridge type DC-DC converter of FIG. 7 when the magnetic core is saturated due to the demagnetization.

Claims (1)

The magnetic core material is composed of a nanocrystalline soft magnetic alloy ribbon wound core in which fine crystal grains mainly composed of Fe and having a crystal grain size of 50 nm or less occupy 50% or more of the entire volume of the structure. The squareness ratio Br / Bs, which is the ratio of the residual magnetic flux density Br to the saturation magnetic flux density Bs in the DC magnetic characteristics measured as 800 A / m, is 0.7 or less, the peak value of the magnetizing force is 0.05 A / m, and the frequency is 20 kHz. An uncut outer iron core is formed by using at least two wound cores having an AC ratio initial permeability μri of 10,000 or more and 90,000 or less, and the center leg of the outer iron core does not have a center tap. A primary winding or a primary winding having at least one set of center taps wound with a bifilar and a full wave having at least one set of center taps wound with a bifilar A sandwich structure in which a secondary winding is applied and the primary winding sandwiches the secondary winding, and the primary winding and its main output, each secondary winding for full-wave rectification, at 2 kHz one der coupling coefficient are both 0.9998 or more is, shell-type power transformer, wherein the resulting Rukoto suppressing the occurrence of magnetic bias.

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