JP3804276B2

JP3804276B2 - Solar power system

Info

Publication number: JP3804276B2
Application number: JP18510498A
Authority: JP
Inventors: 潔後藤; 洋一国本; 博昭小新; 忠吉向井; 弘忠東浜; 裕明湯浅
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 1998-06-30
Filing date: 1998-06-30
Publication date: 2006-08-02
Anticipated expiration: 2018-06-30
Also published as: JP2000023370A

Description

【０００１】
【発明の属する技術分野】
本発明は、太陽電池を電源とし、太陽電池の直流電圧を交流電圧に変換して供給する太陽光発電システムに関するものである。
【０００２】
【従来の技術】
従来より、太陽電池からなる直流電源を用いた数ｋＷ程度の小容量の分散電源を備え、分散電源と商用電力系統とを連系して、負荷に電力を供給する太陽光発電システムが提供されている（例えば特開平９−２８５０１５号公報参照）。
【０００３】
従来の太陽光発電システムは、図５に示すように、多数の太陽電池セルを配列してパネル状とし、太陽エネルギーを直流電圧に直接変換する太陽電池１と、太陽電池１の直流電力を交流電力に変換し、解列開閉器１４を介して商用電力系統３と連系し配電線に接続された各種家電製品などの負荷４に電力供給する分散電源２とを備えている。
【０００４】
分散電源２では、太陽電池１の出力電圧を昇圧回路５が所定の直流電圧に昇圧し、昇圧回路５の直流電圧をインバータ回路６が交流電圧に変換した後、フィルタ回路７がインバータ回路６の出力電圧を略正弦波状の交流電圧に変換し、解列開閉器１４を介して負荷４に供給する。分散電源２には、昇圧回路５およびインバータ回路６の出力電圧や、解列開閉器１４のオン・オフを制御する制御回路８と、直流電路２１の地絡を検出する地絡検出回路９とが設けられており、地絡検出回路９が直流電路２１の地絡を検出すると、制御回路８は地絡検出回路９の検出信号に基づいて昇圧回路５およびインバータ回路６の出力を停止させるとともに、解列開閉器１４をオフする。
【０００５】
ここで、地絡検出回路９は、磁性材料より形成された検出コア１１の貫通孔１２内に太陽電池１と昇圧回路５との間を接続する直流電路２１が挿通された電流センサとしての零相変流器１０の出力から直流電路２１の地絡を検出する。例えば、負極側の直流電路２１が地絡すると、太陽電池１→昇圧回路５→インバータ回路６のスイッチング素子６１（又は６２）→フィルタ回路７のインダクタＬ１（又はＬ２）→解列開閉器１４→商用電力系統３→地絡抵抗Ｒｇ→太陽電池１の経路（図５中に実線および破線の矢印で示す）で地絡電流Ｉｒが流れ、正極側の直流電路２１に流れる電流と負極側の直流電路２１に流れる電流との間に地絡電流Ｉｒの分だけ差が発生するから、この電流の差に応じた出力が検出コア１１に巻回された二次巻線（図示せず）に発生する。而して、地絡検出回路９は零相変流器１０の出力と所定の判定値との大小関係を比較し、零相変流器１０の出力が判定値よりも大きくなると、直流電路２１の地絡が発生したと判断して、制御回路８に検出信号を出力する。
【０００６】
【発明が解決しようとする課題】
上記構成の太陽光発電システムでは、地絡検出回路９が、直流電路２１の絶縁性能の劣化などによって流れる比較的電流値の小さい地絡電流Ｉｒを検出して、検出信号を発生できるように、地絡検出回路９の判定値は小さい値に設定されている。しかしながら、事故などによって直流電路２１が地絡し、直流電路２１に比較的大きな電流値の地絡電流Ｉｒが流れると、零相変流器１０の検出コア１１が着磁されて、検出コア１１に残留磁気が残るため、零相変流器１０の出力がオフセットして、地絡検出回路９が地絡を検出するときの検出レベルが変動するという問題があり、地絡検出回路９が誤動作する虞があった。
【０００７】
本発明は上記問題点に鑑みて為されたものであり、その目的とするところは、直流電路の地絡を検出する地絡検出回路の誤動作を無くした太陽光発電システムを提供することにある。
【０００８】
【課題を解決するための手段】
上記目的を達成するために、請求項１の発明では、太陽電池の直流電圧を所定の交流電圧に変換する電力変換手段を具備し解列開閉器を介して商用電力系統と連系し負荷に電力を供給する分散電源を備えた太陽光発電システムにおいて、分散電源に、磁性材料からなる検出コアの貫通孔内に直流電路が挿通された電流センサと、検出コアに巻回された巻線の出力から直流電路に流れる地絡電流を検出する地絡検出回路と、地絡検出回路が地絡電流を検出すると解列開閉器を開極させる制御回路と、少なくとも地絡電流検出後に制御回路が解列開閉器を再投入する際に検出コアを消磁する消磁回路とを設け、前記消磁回路が、太陽電池の出力電圧により充電される第１のコンデンサと、検出コアの貫通孔に挿通される直流電路に第１のコンデンサを介して接続される第１のインダクタとを備え、第１のコンデンサに蓄積された電荷を第１のインダクタを介して直流電路に放出することにより、直流電路に減衰振動電流を流して検出コアを消磁することを特徴とし、例えば直流電路が地絡し直流電路に比較的大きな地絡電流が流れて、検出コアが着磁したとしても、地絡電流検出後の解列開閉器の再投入時に消磁回路が検出コアの貫通孔に挿通された直流電路に減衰振動電流を流すことによって、検出コアの残留磁気を消磁することができ、地絡検出回路の検出レベルを一定に保つことができる。
【００１１】
請求項２の発明では、請求項１の発明において、電力変換手段は太陽電池の直流電圧を所定の電圧値に昇圧する昇圧回路を備え、昇圧回路は、太陽電池の直流出力端間に接続された第２のインダクタおよび第２のスイッチング素子の直列回路と、第２のインダクタ及び第２のスイッチング素子の接続点にアノードが接続されたダイオードと、ダイオードを介して第２のスイッチング素子の両端間に接続された平滑用の第２のコンデンサとから構成され、第２のインダクタが減衰振動電流を流すための第１のインダクタを兼用することを特徴とし、昇圧回路を構成する第２のインダクタが減衰振動電流を流すための第１のインダクタを兼用しているので、部品点数を減らして、分散電源の小型化を図ることができる。
【００１２】
【発明の実施の形態】
本発明の実施の形態を図面を参照して説明する。
（実施形態１）
本実施形態の太陽光発電システムは、図１に示すように、多数の太陽電池パネルを配列してパネル状とし、太陽エネルギーを直流電圧に直接変換する太陽電池１と、太陽電池１の直流電力を交流電力に変換し、解列開閉器１４を介して商用電力系統３と連系し配電線に接続された各種家電製品などの負荷４に電力供給する分散電源２とから構成される。
【００１３】
分散電源２は、太陽電池１の出力電圧を所定の直流電圧に昇圧する昇圧回路５と、第１のスイッチング素子たる４個のＩＧＢＴ６１〜６４をブリッジ接続して構成され、昇圧回路５の出力電圧をＩＧＢＴ６１〜６４でスイッチングすることにより交流電圧に変換するインバータ回路６と、インダクタＬ１，Ｌ２およびコンデンサＣ１，Ｃ２からなりインバータ回路６の出力電圧を平滑して略正弦波状の交流電圧を出力するフィルタ回路７と、昇圧回路５およびインバータ回路６の出力を制御する例えば１チップのマイクロコンピュータから構成される制御回路８と、磁性材料からなる検出コア１１の貫通孔１２内に太陽電池１と昇圧回路５との間を接続する直流電路２１が挿通された電流センサたる零相変流器１０と、検出コア１１に巻回された二次巻線（図示せず）の出力から直流電路２１の地絡を検出する地絡検出回路９と、制御回路８の出力信号に応じてオン・オフし、分散電源２から負荷４への電力供給をオン・オフする解列開閉器１４とで構成される。ここに、昇圧回路５およびインバータ回路６から電力変換手段が構成される。なお図示は省略するが、インバータ回路６と商用電力系統３との間には系統保護のため解列開閉器１４とは別に手動復帰型のブレーカを設けられ、単相３線式の商用電力系統３と負荷４との間には負荷４を保護するために主幹開閉器や分岐開閉器が設けられている。
【００１４】
昇圧回路５は、太陽電池１の出力端子間に接続された第２のインダクタ５１および第２のスイッチング素子たるＩＧＢＴ５２の直列回路と、第２のインダクタ５１およびＩＧＢＴ５２の接続点にアノードが接続されたダイオード５３と、ＩＧＢＴ５２の両端間にダイオード５３を介して接続される第２のコンデンサ５４と、ＩＧＢＴ５２に逆並列接続されたダイオード５５とで構成される一石式の昇圧チョッパ回路からなる。
【００１５】
インバータ回路６は、ＩＧＢＴ６１，６３の直列回路と、ＩＧＢＴ６２，６４の直列回路とを第２のコンデンサ５４と並列に接続し、各ＩＧＢＴ６１〜６４とそれぞれ逆並列にダイオード６５〜６８を接続して構成され、これら４個のＩＧＢＴ６１〜６４を用いて昇圧回路５の直流電圧をスイッチングすることにより、昇圧回路５の直流電圧を交流電圧に変換して出力する。ＩＧＢＴ６２，６４の接続点と、ＩＧＢＴ６１，６３の接続点とは、それぞれ、フィルタ回路７のインダクタＬ１，Ｌ２を介して、解列開閉器１４の電圧線側の接点に接続され、解列開閉器１４の電圧線側の接点と接地線側の接点との間はフィルタ回路７のコンデンサＣ１，Ｃ２を介して接続されており、インバータ回路６の出力波形はフィルタ回路７によって平滑されて略正弦波状の波形となり、解列開閉器１４を介して負荷４に供給される。
【００１６】
ところで、太陽電池１の出力電圧は日射量に応じて絶えず変化し、例えば０Ｖから３００Ｖまで変化する。制御回路８は太陽電池１の出力電圧をモニタしており、夜間や光量不足などで太陽電池１の出力電圧が例えば１５０Ｖ未満の場合は解列開閉器１４をオフして、分散電源２を商用電力系統３と切り離す。一方、太陽電池１の出力電圧が例えば１５０Ｖ以上の場合は、昇圧回路５が太陽電池１の出力電圧をＩＧＢＴ５２によりスイッチングして、太陽電池１の出力電圧を商用電源の実効値電圧の略１．４倍に相当する直流電圧（例えば１００Ｖ単相三線式の場合は１４０×２＝２８０Ｖ）まで昇圧して、インバータ回路６に出力する。ここで、ＩＧＢＴ５２は制御回路８から制御電極（ゲート）に入力される制御信号によってオン・オフされる。制御回路８は昇圧回路５の出力電圧を図示しない検出手段により検出しており、昇圧回路５の出力電圧に応じて例えばＩＧＢＴ５２のオンデューティを変化させ、昇圧回路５の出力を略一定に制御する。
【００１７】
また、制御回路８はＩＧＢＴ６１〜６４の制御電極（ゲート）に制御信号を夫々出力し、昇圧回路５の直流電圧を略正弦波状の交流電圧に変換して商用電力系統３に出力させる。図２（ａ）〜（ｃ）に示すように、制御回路８では、基準となる三角波状の基準発振信号Ｖｓと、基準発振信号Ｖｓに比べて周波数の低い正弦波状の指令信号Ｖｅとの大小関係を比較し、指令信号Ｖｅの電圧値に比べて基準発振信号Ｖｓの電圧値が高い期間のみ信号レベルがハイになるパルス信号Ｓ１と、指令信号Ｖｅの電圧値に比べて基準発振信号Ｖｓの電圧値が低い期間のみ信号レベルがハイになるパルス信号Ｓ２とを発生する。
【００１８】
而して、制御回路８は、ブリッジ接続されたＩＧＢＴ６１〜６４の内で対角に配置されたＩＧＢＴ６１，６４にパルス信号Ｓ１を出力するとともに、残りのＩＧＢＴ６２，６３にパルス信号Ｓ２を出力して、一対のＩＧＢＴ６１，６４と他の一対のＩＧＢＴ６２，６３とを交互にオン・オフし、昇圧回路５の直流電圧を交流電圧に変換する。ここに、制御回路８はパルス信号Ｓ１，Ｓ２のパルス幅を変調してＰＷＭ制御を行うことにより、一対のＩＧＢＴ６１，６４のオン期間と、他の一対のＩＧＢＴ６２，６３のオン期間とを変化させ、インバータ回路６の出力を制御する。なお、制御回路８はフィルタ回路７の出力電圧の位相が商用電力系統３の電圧位相に略一致するようにインバータ回路６の出力を制御している。
【００１９】
また、分散電源２では、地絡検出回路９が直流電路２１の地絡を検出すると、制御回路８が地絡検出回路９の検出信号に基づいて昇圧回路５およびインバータ回路６の出力を停止するとともに、解列開閉器１４をオフして、分散電源２の連系を停止する。例えば直流電路２１の負極側が地絡すると、太陽電池１→昇圧回路５→ＩＧＢＴ６１（又は６２）→インダクタＬ１（又はＬ２）→解列開閉器１４→商用電力系統３→地絡抵抗Ｒｇ→太陽電池１の経路（図１中に実線および破線の矢印で示す）で地絡電流Ｉｒが流れ、正極側の直流電路２１に流れる電流と負極側の直流電路２１に流れる電流との間に地絡電流Ｉｒの分だけ差が発生するから、この電流の差に応じた出力が検出コア１１に巻回された二次巻線に発生する。而して、地絡検出回路９は零相変流器１０の出力と所定の判定値との大小関係を比較し、零相変流器１０の出力が判定値よりも大きくなると、直流電路２１の地絡が発生したと判断して、制御回路８に地絡の検出信号を出力する。そして、地絡検出回路９が地絡を検出すると、制御回路８は地絡検出回路９の検出信号に基づいて昇圧回路５およびインバータ回路６の出力を停止させるとともに、解列開閉器１４をオフして、商用電力系統３と系統を分離する。
【００２０】
ところで、直流電路２１が地絡すると、比較的大きな地絡電流Ｉｒが直流電路２１に流れるため、この地絡電流Ｉｒによって零相変流器１０の検出コア１１が着磁し、検出コア１１の残留磁気によって地絡検出回路９の検出レベルが変化してしまう。そこで、本実施形態の太陽光発電システムでは、検出コア１１の残留磁気を消磁するための消磁回路１５を設けている。
【００２１】
消磁回路１５は、負極側の直流電路２１における検出コア１１に対して太陽電池１側の部位に一端が接続された第１のインダクタ１９と、第１のインダクタ１９の他端に一端が接続された第１のコンデンサ１８と、第１のコンデンサ１８の他端に一端が接続された抵抗１７と、正極側又は負極側の直流電路２１における検出コア１１に対して昇圧回路５側の部位と抵抗１７の他端との間をそれぞれ接続するスイッチ１６ａ，１６ｂとから構成される。スイッチ１６ａ，１６ｂは制御回路８によってそれぞれオン・オフされ、制御回路８がスイッチ１６ａをオンすると、第１のコンデンサ１８が太陽電池１の出力電圧によって充電される。そして、地絡検出後に制御回路８が昇圧回路５およびインバータ回路６を再起動するとともに解列開閉器１４を再投入する際に、制御回路８がスイッチ１６ｂをオンし、第１のコンデンサ１８に蓄積された電荷を第１のインダクタ１９を介して放出し、検出コア１１の貫通孔１２に挿通された直流電路２１に減衰振動電流を流しており、この減衰振動電流によって検出コア１１の残留磁気を消磁した後、地絡検出回路９は地絡の検出を行う。
【００２２】
このように、零相変流器１０を用いて直流電路２１の地絡を検出する際に、地絡電流によって検出コア１１が着磁し、検出コア１１に残留磁気が発生して、地絡検出回路９の検出レベルが変化したとしても、地絡電流検出後に制御回路８が分散電源２を再起動する際に、消磁回路１５が検出コア１１の残留磁気を消磁しているので、地絡検出回路９の検出レベルを一定に保つことができ、地絡検出回路９の誤動作を無くすことができる。また、制御回路８が分散電源２を初めて起動する際に、制御回路８が消磁回路１５を用いて検出コア１１を消磁するようにしても良く、分散電源２を初めて起動する際、および、再起動する際に消磁回路１５が検出コア１１を消磁して、検出コア１１の残留磁気を取り除くことにより、地絡検出回路９の検出レベルを一定に保ち、地絡検出回路９の誤検出を防止することができる。
（参考例）
参考例の太陽光発電システムの回路図を図３に示す。なお、基本的な構成は実施形態１と同様であるので、同一の構成要素には同一の符号を付して、その説明を省略する。
【００２３】
実施形態１では消磁回路１５が直流電路２１に減衰振動電流を流すことによって検出コア１１の残留磁気を消磁しているが、本参考例では消磁回路１５が制御回路８の制御信号に基づいて検出コア１１に巻回された検出用の二次巻線（図示せず）に減衰振動電流を流すことにより、検出コア１１の残留磁気を消磁している。尚、消磁回路１５は、検出用の二次巻線とは別に検出コア１１に巻回された二次巻線（図示せず）に減衰振動電流を流すようにしても良い。
【００２４】
このように、消磁回路１５は検出コア１１に巻回された二次巻線に減衰振動電流を流しており、この二次巻線に減衰振動電流を流すことによって、実施形態１と同様、検出コア１１の残留磁気を消磁することができる。而して、地絡電流検出時に検出コア１１が地絡電流によって着磁し、地絡検出回路９の検出レベルが変化したとしても、地絡電流検出後に制御回路８が昇圧回路５およびインバータ回路６を再起動するとともに解列開閉器１４を再投入する際に、制御回路８が消磁回路１５を用いて検出コア１１の残留磁気を消磁しているので、地絡検出回路９の検出レベルを一定に保つことができ、地絡検出回路９の誤動作を無くすことができる。
（実施形態２）
本実施形態の太陽光発電システムの回路図を図４に示す。なお、基本的な構成は実施形態１と同様であるので、同一の構成要素には同一の符号を付して、その説明を省略する。
【００２５】
本実施形態では、第２のインダクタ５１およびＩＧＢＴ５２の接続点に一端が接続された抵抗１７と、抵抗１７の他端に一端が接続された第１のコンデンサ１８と、負極側の直流電路２１における検出コア１１に対して太陽電池１側の部位と第１のコンデンサ１８の他端とを接続するスイッチ１６ｃと、正極側の直流電路２１における検出コア１１に対して太陽電池１側の部位と第１のコンデンサ１８の他端とを接続するスイッチ１６ｄとで消磁回路１５が構成され、スイッチ１６ｃ，１６ｄは制御回路８によってオン・オフされる。ここで、制御回路８の出力信号によってスイッチ１６ｃがオンすると、太陽電池１の出力電圧によって第１のコンデンサ１８が充電される。そして、地絡電流検出後に制御回路８が昇圧回路５およびインバータ回路６を再起動するとともに、解列開閉器１４を再投入する際に、制御回路８がスイッチ１６ｄをオンすると、第１のコンデンサ１８に蓄積された電荷が抵抗１７および第２のインダクタ５１を介して放出され、検出コア１１の貫通孔１２内に挿通された直流電路２１に減衰振動電流が流れて、検出コア１１の残留磁気が消磁される。
【００２６】
このように、本実施形態では昇圧回路５を構成する第２のインダクタ５１が、第１のコンデンサ１８に蓄積された電荷を放出して減衰振動電流を流す第１のインダクタに兼用されているので、構成部品の数を減らすことができ、分散電源２の小型化を図ることができる。
【００２７】
【発明の効果】
上述のように、請求項１の発明は、太陽電池の直流電圧を所定の交流電圧に変換する電力変換手段を具備し解列開閉器を介して商用電力系統と連系し負荷に電力を供給する分散電源を備えた太陽光発電システムにおいて、分散電源に、磁性材料からなる検出コアの貫通孔内に直流電路が挿通された電流センサと、検出コアに巻回された巻線の出力から直流電路に流れる地絡電流を検出する地絡検出回路と、地絡検出回路が地絡電流を検出すると解列開閉器を開極させる制御回路と、少なくとも地絡電流検出後に制御回路が解列開閉器を再投入する際に検出コアを消磁する消磁回路とを設け、前記消磁回路が、太陽電池の出力電圧により充電される第１のコンデンサと、検出コアの貫通孔に挿通される直流電路に第１のコンデンサを介して接続される第１のインダクタとを備え、第１のコンデンサに蓄積された電荷を第１のインダクタを介して直流電路に放出することにより、直流電路に減衰振動電流を流して検出コアを消磁することを特徴とし、例えば直流電路が地絡し直流電路に比較的大きな地絡電流が流れて、検出コアが着磁したとしても、地絡電流検出後の解列開閉器の再投入時に消磁回路が検出コアの貫通孔に挿通された直流電路に減衰振動電流を流すことによって、検出コアの残留磁気を消磁することができ、地絡検出回路の検出レベルを一定に保ち、地絡検出回路の誤動作を防止できるという効果がある。
【００３０】
請求項２の発明は、請求項１の発明において、電力変換手段は太陽電池の直流電圧を所定の電圧値に昇圧する昇圧回路を備え、昇圧回路は、太陽電池の直流出力端間に接続された第２のインダクタおよび第２のスイッチング素子の直列回路と、第２のインダクタ及び第２のスイッチング素子の接続点にアノードが接続されたダイオードと、ダイオードを介して第２のスイッチング素子の両端間に接続された平滑用の第２のコンデンサとから構成され、第２のインダクタが減衰振動電流を流すための第１のインダクタを兼用することを特徴とし、昇圧回路を構成する第２のインダクタが減衰振動電流を流すための第１のインダクタを兼用しているので、部品点数を減らして、分散電源の小型化を図ることができるという効果がある。
【図面の簡単な説明】
【図１】実施形態１の太陽光発電システムを示す回路図である。
【図２】（ａ）〜（ｃ）は同上の動作を説明する説明図である。
【図３】参考例の太陽光発電システムを示す回路図である。
【図４】実施形態２の太陽光発電システムを示す回路図である。
【図５】従来の太陽光発電システムを示す回路図である。
【符号の説明】
１太陽電池
２分散電源
３商用電力系統
４負荷
８制御回路
９地絡検出回路
１０零相変流器
１１検出コア
１２貫通孔
１５消磁回路
２１直流電路[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a solar power generation system that uses a solar cell as a power source and converts a DC voltage of the solar cell into an AC voltage and supplies the AC voltage.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a photovoltaic power generation system that includes a distributed power source with a small capacity of about several kW using a direct current power source composed of a solar cell, and supplies power to a load by connecting the distributed power source and a commercial power system is provided. (See, for example, JP-A-9-285015).
[0003]
As shown in FIG. 5, the conventional solar power generation system arranges a large number of solar cells into a panel shape, and converts the solar energy 1 directly into a DC voltage, and the DC power of the solar cell 1 is AC. A distributed power source 2 that converts power into electric power and supplies power to a load 4 such as various home appliances connected to a distribution line via a disconnecting switch 14 and connected to a commercial power system 3 is provided.
[0004]
In the distributed power supply 2, the booster circuit 5 boosts the output voltage of the solar cell 1 to a predetermined DC voltage, the inverter circuit 6 converts the DC voltage of the booster circuit 5 into an AC voltage, and then the filter circuit 7 is connected to the inverter circuit 6. The output voltage is converted into a substantially sinusoidal AC voltage and supplied to the load 4 via the disconnection switch 14. The distributed power source 2 includes a control circuit 8 that controls the output voltage of the booster circuit 5 and the inverter circuit 6 and the on / off of the disconnect switch 14, and a ground fault detection circuit 9 that detects a ground fault of the DC circuit 21. When the ground fault detection circuit 9 detects the ground fault of the DC circuit 21, the control circuit 8 stops the output of the booster circuit 5 and the inverter circuit 6 based on the detection signal of the ground fault detection circuit 9. Then, the disconnection switch 14 is turned off.
[0005]
Here, the ground fault detection circuit 9 is a zero as a current sensor in which a DC circuit 21 connecting the solar cell 1 and the booster circuit 5 is inserted in the through hole 12 of the detection core 11 made of a magnetic material. The ground fault of the DC circuit 21 is detected from the output of the phase current transformer 10. For example, when the DC circuit 21 on the negative electrode side is grounded, the solar cell 1 → the booster circuit 5 → the switching element 61 (or 62) of the inverter circuit 6 → the inductor L1 (or L2) of the filter circuit 7 → the disconnect switch 14 → The ground fault current Ir flows along the path of the commercial power system 3 → the ground fault resistance Rg → the solar cell 1 (indicated by solid and broken arrows in FIG. 5), and the current flowing in the positive side DC circuit 21 and the negative side DC Since there is a difference between the current flowing in the electric circuit 21 by the amount of the ground fault current Ir, an output corresponding to this current difference is generated in a secondary winding (not shown) wound around the detection core 11. To do. Thus, the ground fault detection circuit 9 compares the magnitude relationship between the output of the zero-phase current transformer 10 and a predetermined judgment value. When the output of the zero-phase current transformer 10 becomes larger than the judgment value, the DC circuit 21 And a detection signal is output to the control circuit 8.
[0006]
[Problems to be solved by the invention]
In the photovoltaic power generation system having the above configuration, the ground fault detection circuit 9 can detect the ground fault current Ir having a relatively small current value that flows due to deterioration of the insulation performance of the DC electric circuit 21 and the like, and can generate a detection signal. The determination value of the ground fault detection circuit 9 is set to a small value. However, when the DC circuit 21 is grounded due to an accident or the like and a ground fault current Ir having a relatively large current value flows through the DC circuit 21, the detection core 11 of the zero-phase current transformer 10 is magnetized, and the detection core 11. Since the residual magnetism remains, the output of the zero-phase current transformer 10 is offset, and there is a problem that the detection level when the ground fault detection circuit 9 detects the ground fault varies, and the ground fault detection circuit 9 malfunctions. There was a fear.
[0007]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a solar power generation system that eliminates malfunction of a ground fault detection circuit that detects a ground fault of a DC circuit. .
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided a power conversion means for converting a DC voltage of a solar cell into a predetermined AC voltage, which is connected to a commercial power system via a disconnect switch and connected to a load. In a photovoltaic power generation system equipped with a distributed power source for supplying power, a distributed power source includes a current sensor in which a DC circuit is inserted into a through hole of a detection core made of a magnetic material, and a winding wound around the detection core. A ground fault detection circuit for detecting a ground fault current flowing from the output to the DC circuit, a control circuit for opening the disconnecting switch when the ground fault detection circuit detects the ground fault current, and a control circuit at least after detecting the ground fault current A demagnetizing circuit for demagnetizing the detection core when the disconnecting switch is turned on again , and the demagnetization circuit is inserted into the first capacitor charged by the output voltage of the solar cell and the through hole of the detection core. The first condenser in the DC circuit A first inductor connected via the first inductor, and discharging the charge accumulated in the first capacitor to the DC circuit via the first inductor, thereby causing a damped oscillation current to flow through the DC circuit and detecting core and wherein the degaussing, for example direct current path is relatively large ground fault current flows through the ground fault and a DC path, even detecting core is magnetized, repopulation disconnection switch after ground fault current detection Sometimes, the demagnetization circuit can demagnetize the residual magnetism of the detection core by flowing a damped oscillating current through a DC circuit that is inserted into the through hole of the detection core, and the detection level of the ground fault detection circuit can be kept constant. .
[0011]
In the invention of claim 2, in the invention of claim 1 , the power conversion means includes a booster circuit that boosts the DC voltage of the solar cell to a predetermined voltage value, and the booster circuit is connected between the DC output terminals of the solar cell. A series circuit of the second inductor and the second switching element, a diode having an anode connected to a connection point of the second inductor and the second switching element, and both ends of the second switching element via the diode And a second capacitor for smoothing, wherein the second inductor also serves as the first inductor for flowing the damped oscillation current, and the second inductor constituting the booster circuit includes: Since the first inductor for flowing the damped oscillating current is also used, the number of components can be reduced and the distributed power supply can be downsized.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
As shown in FIG. 1, the solar power generation system of the present embodiment has a solar cell 1 that directly converts solar energy into a DC voltage by arranging a large number of solar cell panels into a panel shape, and the DC power of the solar cell 1. Is distributed to the commercial power system 3 through the disconnect switch 14 and supplied to the load 4 such as various home appliances connected to the distribution line.
[0013]
The distributed power source 2 is configured by bridge-connecting a booster circuit 5 that boosts the output voltage of the solar cell 1 to a predetermined DC voltage and four IGBTs 61 to 64 that are first switching elements, and the output voltage of the booster circuit 5 And an inverter circuit 6 for converting to AC voltage by switching with IGBTs 61 to 64, and a filter comprising inductors L1 and L2 and capacitors C1 and C2 for smoothing the output voltage of the inverter circuit 6 and outputting a substantially sinusoidal AC voltage A control circuit 8 composed of, for example, a one-chip microcomputer for controlling the output of the circuit 7, the booster circuit 5 and the inverter circuit 6, and the solar cell 1 and the booster circuit in the through hole 12 of the detection core 11 made of a magnetic material. 5 is wound around a detection core 11 and a zero-phase current transformer 10 which is a current sensor through which a DC electric path 21 is connected. The ground fault detection circuit 9 detects a ground fault of the DC circuit 21 from the output of the secondary winding (not shown), and is turned on / off according to the output signal of the control circuit 8, from the distributed power source 2 to the load 4. It is comprised with the disconnection switch 14 which turns on and off the electric power supply of. Here, the booster circuit 5 and the inverter circuit 6 constitute power conversion means. Although illustration is omitted, a manual return type breaker is provided between the inverter circuit 6 and the commercial power system 3 in order to protect the system, in addition to the disconnect switch 14, and a single-phase three-wire commercial power system. A main switch and a branch switch are provided between 3 and the load 4 to protect the load 4.
[0014]
The booster circuit 5 has an anode connected to a connection point between the second inductor 51 and the IGBT 52 as the second switching element connected between the output terminals of the solar cell 1 and the second inductor 51 and the IGBT 52. The booster chopper circuit is a monolithic type composed of a diode 53, a second capacitor 54 connected between both ends of the IGBT 52 via the diode 53, and a diode 55 connected in reverse parallel to the IGBT 52.
[0015]
The inverter circuit 6 is configured by connecting a series circuit of IGBTs 61 and 63 and a series circuit of IGBTs 62 and 64 in parallel with the second capacitor 54 and connecting diodes 65 to 68 in antiparallel with the IGBTs 61 to 64, respectively. Then, by switching the DC voltage of the booster circuit 5 using these four IGBTs 61 to 64, the DC voltage of the booster circuit 5 is converted into an AC voltage and output. The connection point of the IGBTs 62 and 64 and the connection point of the IGBTs 61 and 63 are connected to the contact on the voltage line side of the disconnection switch 14 via the inductors L1 and L2 of the filter circuit 7, respectively. 14 is connected to the contact on the voltage line side and the contact on the ground line side via capacitors C1 and C2 of the filter circuit 7. The output waveform of the inverter circuit 6 is smoothed by the filter circuit 7 and is substantially sinusoidal. And is supplied to the load 4 through the disconnection switch 14.
[0016]
By the way, the output voltage of the solar cell 1 constantly changes according to the amount of solar radiation, for example, changes from 0V to 300V. The control circuit 8 monitors the output voltage of the solar cell 1. When the output voltage of the solar cell 1 is less than 150 V, for example, at night or when the amount of light is insufficient, the disconnect switch 14 is turned off and the distributed power source 2 is used as a commercial power source. Disconnect from power system 3. On the other hand, when the output voltage of the solar cell 1 is, for example, 150 V or more, the booster circuit 5 switches the output voltage of the solar cell 1 by the IGBT 52, and the output voltage of the solar cell 1 is approximately 1. The voltage is boosted to a DC voltage equivalent to four times (for example, 140 × 2 = 280 V in the case of a 100 V single-phase three-wire system) and output to the inverter circuit 6. Here, the IGBT 52 is turned on / off by a control signal input from the control circuit 8 to the control electrode (gate). The control circuit 8 detects the output voltage of the booster circuit 5 by detection means (not shown), and changes the on-duty of the IGBT 52, for example, in accordance with the output voltage of the booster circuit 5, thereby controlling the output of the booster circuit 5 to be substantially constant. .
[0017]
The control circuit 8 outputs control signals to the control electrodes (gates) of the IGBTs 61 to 64, respectively, converts the DC voltage of the booster circuit 5 into a substantially sinusoidal AC voltage, and outputs it to the commercial power system 3. As shown in FIGS. 2A to 2C, in the control circuit 8, the magnitude of the reference triangular wave reference oscillation signal Vs and the sine wave command signal Ve having a frequency lower than that of the reference oscillation signal Vs is large. The relationship is compared, and the pulse signal S1 whose signal level is high only during the period when the voltage value of the reference oscillation signal Vs is higher than the voltage value of the command signal Ve and the reference oscillation signal Vs compared to the voltage value of the command signal Ve. A pulse signal S2 whose signal level is high only during a period when the voltage value is low is generated.
[0018]
Thus, the control circuit 8 outputs the pulse signal S1 to the IGBTs 61 and 64 diagonally arranged among the bridge-connected IGBTs 61 to 64, and outputs the pulse signal S2 to the remaining IGBTs 62 and 63. The pair of IGBTs 61 and 64 and the other pair of IGBTs 62 and 63 are alternately turned on / off to convert the DC voltage of the booster circuit 5 into an AC voltage. Here, the control circuit 8 performs PWM control by modulating the pulse widths of the pulse signals S1 and S2, thereby changing the on period of the pair of IGBTs 61 and 64 and the on period of the other pair of IGBTs 62 and 63. The output of the inverter circuit 6 is controlled. The control circuit 8 controls the output of the inverter circuit 6 so that the phase of the output voltage of the filter circuit 7 substantially matches the voltage phase of the commercial power system 3.
[0019]
In the distributed power supply 2, when the ground fault detection circuit 9 detects a ground fault of the DC circuit 21, the control circuit 8 stops the output of the booster circuit 5 and the inverter circuit 6 based on the detection signal of the ground fault detection circuit 9. At the same time, the disconnection switch 14 is turned off, and the interconnection of the distributed power supply 2 is stopped. For example, when the negative electrode side of the DC circuit 21 is grounded, the solar cell 1 → the booster circuit 5 → the IGBT 61 (or 62) → the inductor L1 (or L2) → the disconnect switch 14 → the commercial power system 3 → the ground resistance Rg → the solar cell. The ground fault current Ir flows through a single path (indicated by solid and broken arrows in FIG. 1), and the ground fault current is between the current flowing in the positive-side DC circuit 21 and the current flowing in the negative-side DC circuit 21. Since a difference is generated by Ir, an output corresponding to the current difference is generated in the secondary winding wound around the detection core 11. Thus, the ground fault detection circuit 9 compares the magnitude relationship between the output of the zero-phase current transformer 10 and a predetermined judgment value. When the output of the zero-phase current transformer 10 becomes larger than the judgment value, the DC circuit 21 The ground fault detection signal is output to the control circuit 8. When the ground fault detection circuit 9 detects a ground fault, the control circuit 8 stops the outputs of the booster circuit 5 and the inverter circuit 6 based on the detection signal of the ground fault detection circuit 9 and turns off the disconnection switch 14. Then, the commercial power system 3 and the system are separated.
[0020]
By the way, when the DC circuit 21 is grounded, a relatively large ground fault current Ir flows through the DC circuit 21, so that the detection core 11 of the zero-phase current transformer 10 is magnetized by this ground fault current Ir. The detection level of the ground fault detection circuit 9 changes due to the residual magnetism. Therefore, in the photovoltaic power generation system of the present embodiment, a degaussing circuit 15 for demagnetizing the residual magnetism of the detection core 11 is provided.
[0021]
The degaussing circuit 15 has one end connected to a part on the solar cell 1 side with respect to the detection core 11 in the DC circuit 21 on the negative electrode side, and one end connected to the other end of the first inductor 19. The first capacitor 18, the resistor 17 having one end connected to the other end of the first capacitor 18, the portion on the booster circuit 5 side and the resistance with respect to the detection core 11 in the DC circuit 21 on the positive electrode side or the negative electrode side 17 is composed of switches 16a and 16b that connect the other end of 17 respectively. The switches 16a and 16b are turned on and off by the control circuit 8, respectively. When the control circuit 8 turns on the switch 16a, the first capacitor 18 is charged by the output voltage of the solar cell 1. Then, when the control circuit 8 restarts the booster circuit 5 and the inverter circuit 6 and detects the disconnection switch 14 again after the ground fault is detected, the control circuit 8 turns on the switch 16b and turns on the first capacitor 18. The accumulated electric charge is discharged through the first inductor 19, and a damped oscillating current is caused to flow through the DC circuit 21 inserted through the through hole 12 of the detection core 11, and the residual magnetism of the detection core 11 is caused by this damped oscillating current. Is demagnetized, the ground fault detection circuit 9 detects the ground fault.
[0022]
Thus, when the ground fault of the DC circuit 21 is detected using the zero-phase current transformer 10, the detection core 11 is magnetized by the ground fault current, and the residual magnetism is generated in the detection core 11, and the ground fault is generated. Even if the detection level of the detection circuit 9 changes, when the control circuit 8 restarts the distributed power supply 2 after detecting the ground fault current, the demagnetization circuit 15 demagnetizes the residual magnetism of the detection core 11. The detection level of the detection circuit 9 can be kept constant, and malfunction of the ground fault detection circuit 9 can be eliminated. Further, when the control circuit 8 starts up the distributed power source 2 for the first time, the control circuit 8 may use the degaussing circuit 15 to demagnetize the detection core 11, and when the distributed power source 2 is started up for the first time, The degaussing circuit 15 demagnetizes the detection core 11 when starting up, and the residual magnetism of the detection core 11 is removed, so that the detection level of the ground fault detection circuit 9 is kept constant and erroneous detection of the ground fault detection circuit 9 is prevented. can do.
(Reference example)
A circuit diagram of a photovoltaic power generation system of a reference example is shown in FIG. Since the basic configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals and the description thereof is omitted.
[0023]
In the first embodiment, the demagnetization circuit 15 demagnetizes the residual magnetism of the detection core 11 by causing a damped oscillation current to flow in the DC circuit 21. However, in this reference example , the demagnetization circuit 15 detects based on the control signal of the control circuit 8. The residual magnetism of the detection core 11 is demagnetized by passing a damped oscillation current through a secondary winding for detection (not shown) wound around the core 11. Note that the degaussing circuit 15 may cause a damped oscillation current to flow in a secondary winding (not shown) wound around the detection core 11 separately from the secondary winding for detection.
[0024]
In this way, the degaussing circuit 15 passes a damped oscillating current through the secondary winding wound around the detection core 11. By passing the damped oscillating current through the secondary winding, the demagnetizing circuit 15 detects the same as in the first embodiment. The residual magnetism of the core 11 can be demagnetized. Thus, even when the detection core 11 is magnetized by the ground fault current when the ground fault current is detected and the detection level of the ground fault detection circuit 9 is changed, the control circuit 8 causes the booster circuit 5 and the inverter circuit after the ground fault current is detected. 6 and when the disconnect switch 14 is turned on again, the control circuit 8 uses the demagnetization circuit 15 to demagnetize the residual magnetism of the detection core 11, so that the detection level of the ground fault detection circuit 9 is set. It can be kept constant, and malfunction of the ground fault detection circuit 9 can be eliminated.
(Embodiment 2)
A circuit diagram of the photovoltaic power generation system of the present embodiment is shown in FIG. Since the basic configuration is the same as that of the first embodiment, the same components are denoted by the same reference numerals and the description thereof is omitted.
[0025]
In the present embodiment, in the resistor 17 having one end connected to the connection point of the second inductor 51 and the IGBT 52, the first capacitor 18 having one end connected to the other end of the resistor 17, and the DC circuit 21 on the negative electrode side A switch 16c that connects the part on the solar cell 1 side to the detection core 11 and the other end of the first capacitor 18, and a part on the solar cell 1 side relative to the detection core 11 in the DC circuit 21 on the positive electrode side. A demagnetizing circuit 15 is configured by a switch 16 d connecting the other end of one capacitor 18, and the switches 16 c and 16 d are turned on and off by the control circuit 8. Here, when the switch 16 c is turned on by the output signal of the control circuit 8, the first capacitor 18 is charged by the output voltage of the solar cell 1. Then, after the ground fault current is detected, the control circuit 8 restarts the booster circuit 5 and the inverter circuit 6, and when the control circuit 8 turns on the switch 16d when the disconnecting switch 14 is turned on again, the first capacitor 18 is discharged through the resistor 17 and the second inductor 51, and a damped oscillating current flows through the DC circuit 21 inserted into the through hole 12 of the detection core 11, thereby causing the residual magnetism of the detection core 11 to remain. Is demagnetized.
[0026]
Thus, in the present embodiment, the second inductor 51 constituting the booster circuit 5 is also used as the first inductor that discharges the electric charge accumulated in the first capacitor 18 and flows the damped oscillation current. Thus, the number of components can be reduced, and the size of the distributed power source 2 can be reduced.
[0027]
【The invention's effect】
As described above, the invention of claim 1 includes power conversion means for converting a DC voltage of a solar cell into a predetermined AC voltage, and is connected to a commercial power system via a disconnect switch to supply power to a load. In a photovoltaic power generation system equipped with a distributed power source, a direct current is output from the output of a current sensor in which a DC circuit is inserted into a through hole of a detection core made of a magnetic material and a winding wound around the detection core. A ground fault detection circuit that detects a ground fault current flowing in the electric circuit, a control circuit that opens the disconnect switch when the ground fault detection circuit detects a ground fault current, and a control circuit that opens and closes at least after detecting the ground fault current A demagnetizing circuit that demagnetizes the detection core when the detector is turned on again , and the demagnetization circuit is connected to a first capacitor that is charged by the output voltage of the solar cell and a DC circuit that is inserted through the through hole of the detection core. Connected via first capacitor And a first inductor, by releasing the charge accumulated in the first capacitor to the DC path through the first inductor, to demagnetize the detecting core by passing a damped oscillation current to a direct current path For example, even if a DC circuit is grounded and a relatively large grounding current flows in the DC circuit and the detection core is magnetized, the degaussing circuit detects when the disconnecting switch is turned on again after detecting the grounding current By passing a damped oscillating current through a DC circuit inserted through the core's through hole, the residual magnetism of the detection core can be demagnetized, the detection level of the ground fault detection circuit is kept constant, and malfunctions of the ground fault detection circuit are prevented. There is an effect that it can be prevented.
[0030]
According to a second aspect of the present invention, in the first aspect of the invention, the power conversion means includes a booster circuit that boosts the DC voltage of the solar cell to a predetermined voltage value, and the booster circuit is connected between the DC output terminals of the solar cell. A series circuit of the second inductor and the second switching element, a diode having an anode connected to a connection point of the second inductor and the second switching element, and both ends of the second switching element via the diode And a second capacitor for smoothing, wherein the second inductor also serves as the first inductor for flowing the damped oscillation current, and the second inductor constituting the booster circuit includes: Since the first inductor for passing the damped oscillation current is also used, there is an effect that the number of parts can be reduced and the distributed power supply can be miniaturized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a photovoltaic power generation system according to a first embodiment.
FIGS. 2A to 2C are explanatory diagrams for explaining the operation described above. FIG.
FIG. 3 is a circuit diagram showing a photovoltaic power generation system of a reference example .
FIG. 4 is a circuit diagram showing a photovoltaic power generation system according to a second embodiment.
FIG. 5 is a circuit diagram showing a conventional photovoltaic power generation system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Solar cell 2 Distributed power supply 3 Commercial power system 4 Load 8 Control circuit 9 Ground fault detection circuit 10 Zero phase current transformer 11 Detection core 12 Through-hole 15 Demagnetization circuit 21 DC electric circuit

Claims

In a solar power generation system including a distributed power source that includes a power conversion unit that converts a DC voltage of a solar cell into a predetermined AC voltage and that supplies power to a load connected to a commercial power system via a disconnect switch. A ground fault detection that detects a ground fault current that flows in the DC circuit from the output of the winding wound around the detection core and the current sensor in which the DC circuit is inserted into the through hole of the detection core made of magnetic material. A circuit, a control circuit that opens the disconnect switch when the ground fault detection circuit detects a ground fault current, and at least the control circuit demagnetizes the detection core when the control circuit is turned on again after detecting the ground fault current A demagnetizing circuit is provided , and the demagnetizing circuit is connected to the first capacitor charged by the output voltage of the solar cell, and the first capacitor connected to the direct current circuit inserted through the through hole of the detection core via the first capacitor. Inductor and By releasing the charge accumulated in the first capacitor to the DC path through the first inductor, photovoltaic system characterized by demagnetizing the detecting core by passing a damped oscillation current to a direct current path.

The power conversion means includes a booster circuit that boosts the DC voltage of the solar battery to a predetermined voltage value. The booster circuit is a series circuit of a second inductor and a second switching element connected between the DC output terminals of the solar battery. And a diode having an anode connected to a connection point between the second inductor and the second switching element, and a second capacitor for smoothing connected between both ends of the second switching element via the diode. The solar power generation system according to claim 1, wherein the second inductor also serves as the first inductor for flowing the damped oscillation current .