JP4287031B2

JP4287031B2 - Method and apparatus for controlling self-excited DC power transmission system

Info

Publication number: JP4287031B2
Application number: JP2000218757A
Authority: JP
Inventors: 裕成川添; 博雄小西; 均三ッ間; 隆文前田; 俊輔田中
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2000-07-14
Filing date: 2000-07-14
Publication date: 2009-07-01
Anticipated expiration: 2020-07-14
Also published as: JP2002034159A

Description

【０００１】
【発明の属する技術分野】
本発明は直流送電設備に関し、特に自励式変換器を用いた直流送電設備に関する。
【０００２】
【従来の技術】
直流送電設備は交流電力を順変換器で直流電力に変換して送電し、送電された直流電力を逆変換器で再び交流電力に変換して電力を供給するシステムである。電力系統においては、該設備の導入によって迅速な潮流制御ができること、周波数の異なる系統間の連系が行えること、長距離送電において交流送電よりロスが少なく送電できる等のメリットがある。また、ＩＧＢＴ等の自己消弧機能を持つ素子で構成される自励式変換器を用いた直流送電設備は、素子の制約等により送電容量は小さいが，弱小交流系統や無電源系統にも安定に送電でき、かつ有効電力と無効電力を独立して制御できるなど運転性能の面で優れている。
【０００３】
自励式変換器を用いた直流送電設備の制御方法としては、特許第２８５６７４３号、第２７３６１０２号、第２６３５７１２５号、第２６３５６６０号、特開平０９−１１７０５６に記載されているように、一つの変換器で直流電圧を一定に制御し、他の変換器で有効電力を制御して電力供給を行う方法が知られている。また、自励式変換器は、前述したように無効電力も同時に独立して制御できることから、各変換器において直接、無効電力を制御したり、あるいは間接的に交流電圧を一定に制御する方法が知られている。この制御方法は、各変換器が電源のある交流系統に接続されていることが前提条件となっており、変換器はそれぞれの交流系統の位相を検出し、これに同期して運転される。
【０００４】
【発明が解決しようとする課題】
直流送電による離島等の遠隔地需要家への電力供給を想定すると、逆変換器側に既存のディーゼル発電機等の電源設備が接続される場合に加え、これらの電源設備が無い（無電源系統の）場合でも直流単独で送電を行えることが望ましい。従来の制御方法は、逆変換器側に電源設備が接続されている場合にのみ有効な手段で、この場合、負荷に供給される電力は、電源設備と変換器の協調によって需給のバランスが保たれている。
【０００５】
しかしながら、無電源系統へ直流単独送電を行う場合は、負荷の大きさや力率に応じた電力をすべて変換器から供給しなければならず、従来の制御方法で負荷の変動に合わせて変換器の電力設定を行うことは難しい。また、無電源系統では同期する基準位相がないために、変換器は自ら基準位相を決めて負荷へ電力を供給しなければならない。
【０００６】
本発明の目的は、従来技術の問題点に鑑み、無電源系統への安定な直流単独送電を可能にし、かつ既存のディーゼル発電機等から電力供給を受ける電源系統との同期併入など、離島等の遠隔地側系統条件に適応した自励式直流送電設備の制御方式を提供することにある。
【０００７】
【課題を解決するための手段】
上記目的を達成するために、本発明では以下のような自励式変換器を用いた直流送電設備の制御装置を提供する。
【０００８】
即ち、交流電力を直流電力に変換するための順変換器と直流電力を交流電力に変換するための逆変換器が自励式変換器で構成される自励式直流送電システムの制御装置において、順変換器側には直流電圧を制御する回路と、逆変換器側には直流単独送電を検出する回路、制御回路を切り替える選択回路及び直流単独送電時に交流電圧を制御する回路（実施例では、ＡＶＲ‐ｄ，ｑ）を設けている。
【０００９】
また、前記逆変換器には、逆変換器側の交流系統の電圧位相を求める回路、該電圧位相を固定位相に切り換える回路、交流電圧を２軸変換する回路、交流電流を２軸変換する回路、２軸の制御出力信号（実施例では、Ｖｄ２１＊，Ｖｑ２１＊）を２相変換する回路を備え、交流電圧は前記電圧位相を使って２軸に変換し、交流電流は前記直流単独送電の検出により電圧位相を固定位相に切換え、該固定位相を用いて２軸に変換し、前記制御出力信号は前記固定位相を用いて２相に逆変換する。
【００１０】
これにより、順変換器で直流系統の電圧を一定に制御し、逆変換器で直流単独送電を検出信号として制御を交流電圧制御に切換え、逆変換器側交流系統の電圧を一定に制御する。
【００１１】
また、本発明は、逆変換器側には併入準備の信号を検出する回路、電源系統側併入点の電圧位相を求める回路、直流単独送電系統側併入点の電圧位相を求める回路、併入点の位相を同期させる回路、電圧位相が同期したことを検出する回路を設けている。これにより、直流単独送電系統に電源系統が併入される場合、併入準備の信号を検出して直流単独送電系統の電圧位相を電源系統の電圧位相と同期させ、同期を検出して電源系統に併入する。
【００１２】
また、直流単独送電を行う場合で、過負荷時には、変換器に流れる電流が制限値を越えないように抑制する。また、起動方法で、先に順変換器を起動して直流電圧を一定に制御し、その後、逆変換器を起動して交流電圧制御の指令値を緩やかに変更しながら交流電圧を制御し、該交流電圧を徐々に立ち上げて起動する。
【００１３】
以上により、無電源系統への安定な直流単独送電や既存のディーゼル発電機等から電力供給を受ける電源系統とのスムーズな同期併入が可能となり、離島送電等の遠隔地電力供給に適応した自励式直流送電設備が提供できる。
【００１４】
【発明の実施の形態】
本発明の一実施の形態の自励式直流送電設備を説明する。図１は一実施例による自励式直流送電システムの構成を示す。本システムは交流系統１４の交流電力を交流母線１３、変換用変圧器１２を介して順変換器１でスイッチングすることにより、直流電力に変換し、変換した直流電力を直流送電線３０ａ，３０ｂ、直流コンデンサ１１，１２を使って逆変換器側へ送電し、逆変換器２でスイッチングすることで再び交流電力に変換し、変換用変圧器２２、交流母線２３を介して負荷２４に交流電力を供給する。また、交流系統４３は、ディーゼル発電機などから交流電力を供給される側の系統であり、遮断器４１を介して併入される。
【００１５】
順変換器１及び逆変換器２の各々には、自励式変換器を構成する自己消弧型素子とダイオードをひとつのみ示しているが、実際には、３相分ブリッジ回路としてそれぞれ６個ずつを配置する。各自己消弧型素子には、制御パルスを入力するための制御装置１００と２００が接続される。
【００１６】
制御装置１００では、直流系統の電圧を一定に保つ直流電圧制御回路１０２ａと無効電力制御回路１０２ｂの出力に基づいて変換器制御部１０５で制御パルスが作られ、直流系統の電圧と順変換器側の無効電力を一定に制御する。
【００１７】
一方、制御装置２００は、有効電力制御回路２０２ａと無効電力制御回路２０２ｂ、ｄ軸電圧制御回路２０１ａとｑ軸電圧制御回路２０１ｂ、選択回路２０３ａ，２０３ｂ、直流単独送電検出回路２０４、変換器制御部２０５を備える。例えば、落雷事故等による区間切離しや保守点検作業等を行うための手動切離しによって遮断器４１が開放された場合は、自動的に直流単独送電検出回路２０４がリレー装置４２から遮断器４１の開放信号を受け、直流単独送電検出信号Ｓｄｃをオンとし、選択回路２０３ａ，２０３ｂで有効電力制御回路２０２ａをｄ軸電圧制御回路２０１ａに、無効電力制御回路２０２ｂをｑ軸電圧制御回路２０１ｂに切換え、２つの出力に基づいて変換器制御部２０５で制御パルスが作られ、逆変換器側の交流電圧を一定に制御する。
【００１８】
本実施例の直流単独送電に切換わる場合の座標変換の方法を説明する。図２は逆変換器側制御装置２００の詳細ブロック図を示す。まず、座標変換に必要な位相を求めるために、逆変換器側の３相交流電圧Ｖａ２１，Ｖｂ２１，Ｖｃ２１を制御装置に取り込み、２相変換回路２０１ｃで数１を用い、２相の交流電圧Ｖα２１，Ｖβ２１に変換する。
【００１９】
【数１】

【００２０】
ベクトル演算回路２０６ａで、２相の交流電圧Ｖα２１，Ｖβ２１と基準位相回路２０６ｃの装置内部で任意に作られる基準位相ｃｏｓωｔ，ｓｉｎωｔから、数２，３，４，５を用いて基準位相に対する電圧位相の実軸、虚軸のベクトル量Ｖ２１ＲＬ，Ｖ２１ＩＭを求める。なお、数式２，３のｍは、基本波一周期のサンプリング回数、ｉは、各サンプリングデータの番号を表す。
【００２１】
【数２】

【００２２】
【数３】

【００２３】
【数４】

【００２４】
【数５】

【００２５】
位相演算回路２０６ｄで、実軸、虚軸のベクトル量Ｖ２１ＲＬ，Ｖ２１ＩＭと基準位相ｃｏｓωｔ，ｓｉｎωｔから、数６，７を用いて電圧位相Ｃｏｓ２１，Ｓｉｎ２１が求まる。また、固定位相Ｃｏｓ２１Ｌ，Ｓｉｎ２１Ｌは、固定位相切換え回路２０６ｂで直流単独送電検出信号Ｓｄｃがオン、即ち、図１の交流系統４３が切離された時に入力のＶ２１ＲＬ，Ｖ２１ＩＭの値が保持され、固定される。逆に、Ｓｄｃがオフの時は、電圧位相Ｃｏｓ２１，Ｓｉｎ２１と同じ信号が出力される。
【００２６】
【数６】

【００２７】
【数７】

【００２８】
次に、２軸変換回路２０１ｄで、２相交流電圧Ｖα２１，Ｖβ２１と電圧位相Ｃｏｓ２１，Ｓｉｎ２１から数８を用いて、ｄ軸、ｑ軸電圧制御回路２０１ａ，２０１ｂのフィードバックとなる２軸の電圧成分Ｖｄ２１，Ｖｑ２１を求める。
【００２９】
【数８】

【００３０】
ｄ軸、ｑ軸電圧制御回路２０１ａ，２０１ｂは、２軸の電圧成分Ｖｄ２１，Ｖｑ２１が設定値Ｖｄｒｅｆ，Ｖｑｒｅｆとそれぞれ一致するように、ｄ軸、ｑ軸電流制御回路２０５ａ，２０５ｂに指令を出す。なお、有効電力制御回路２０２ａと無効電力制御回路２０２ｂ、選択回路２０３ａ，２０３ｂについては、既に切換え方法を説明してある。
【００３１】
図２上部の２０５ａ〜ｈは、変換器制御部２０５の詳細ブロックである。逆変換器側の３相交流電流Ｉａ２１，Ｉｂ２１，Ｉｃ２１を制御装置に取り込み、２相変換回路２０５ｃで数９を用いてＩα２１，Ｉβ２１に変換する。
【００３２】
【数９】

【００３３】
ｄ軸、ｑ軸電流制御回路２０５ａ，２０５ｂのフィードバックとなる２軸の電流成分Ｉｄ２１，Ｉｑ２１を、２軸変換回路２０５ｄで２相交流電流Ｉα２１，Ｉβ２１と固定位相Ｃｏｓ２１Ｌ，Ｓｉｎ２１Ｌから数１０を用いて求める。
【００３４】
【数１０】

【００３５】
ｄ軸、ｑ軸電流制御回路２０５ａ，２０５ｂは、ｄ軸、ｑ軸電圧制御回路２０１ａ，２０１ｂの指令値と２軸の電流成分Ｉｄ２１，Ｉｑ２１が一致するように動作する。また、この出力とＩｄ２１，Ｉｑ２１と変換用変圧器のリアクタンス分ＩＸを掛け算した値、および２軸の電圧成分Ｖｄ２１，Ｖｑ２１を、それぞれｄｑ軸に分けて加減算し、非干渉電流制御系の出力としてｄｑ軸の操作量Ｖｄ２１＊，Ｖｑ２１＊を得る。
【００３６】
Ｖｄ２１＊，Ｖｑ２１＊は，２相逆変換回路２０５ｅで前記の固定位相Ｃｏｓ２１Ｌ，Ｓｉｎ２１Ｌを用いて数１１により、２相の操作量Ｖα２１＊，Ｖβ２１＊に変換される。
【００３７】
【数１１】

【００３８】
さらに３相逆変換回路２０５ｆで数１２を用いて、３相の操作量Ｖａ２１＊，Ｖｂ２１＊，Ｖｃ２１＊に変換される。
【００３９】
【数１２】

【００４０】
最後に、ＰＷＭ制御回路２０５ｇで３相の操作量Ｖａ２１＊，Ｖｂ２１＊、Ｖｃ２１＊と三角波発生回路２０５ｈの三角波を用いて制御パルスが作られ、図１の逆変換器２の各自己消弧型素子にスイッチングを行うためのオン／オフ信号が導かれる。
【００４１】
これによれば、逆変換器側交流系統の電源が切り離されて直流単独送電となる場合に、逆変換器で直流単独送電を検出して制御を交流電圧制御に切換え、逆変換器側の交流電圧系統の電圧を一定に制御できる。
【００４２】
次に、本実施例の電源系統併入時の動作を説明する。図３は電源系統併入時の構成と機能を示す。交流系統４３が遮断器４１の開放により切離されていて、逆変換器２が単独で交流送電線２５を介して負荷２４に電力供給している状態で、遮断器４１を投入して交流系統４３を併入する時の動作を考える。この場合、併入点の位相（例えば、電圧Ｖａ４１とＶａ２２の位相）がずれていると併入時にお互いの系統に変動が生じるため、両者の位相を同期させてから遮断器４１を投入することが必要である。以下にその一実施例を示す。
【００４３】
図３で、２０１ｃ，２０６ａ，２０６ｂ，２０６ｃ，２０６ｄは図２と同様のブロックであり、逆変換器２が動作するための電圧位相Ｃｏｓ２１，Ｓｉｎ２１と、固定位相Ｃｏｓ２１Ｌ，Ｓｉｎ２１Ｌを求める。併入点の位相を同期させるためには、まず、負荷２４側の３相の交流電圧Ｖａ２２，Ｖｂ２２，Ｖｃ２２を取り込み、２相変換回路２０７ｃ、ベクトル演算回路２０７ａ、位相演算回路２０７ｄで、負荷２４側併入点の電圧位相Ｃｏｓ２２，Ｓｉｎ２２を求める。
【００４４】
次に、交流系統４３側の３相の交流電圧Ｖａ４１，Ｖｂ４１，Ｖｃ４１を取り込み、２相変換回路２０８ｃ、ベクトル演算回路２０８ａで負荷２４側の併入点の電圧位相に対する交流系統４３側併入点の電圧の実軸、虚軸のベクトル量Ｖ４１ＲＬ，Ｖ４１ＩＭを求め、最後に、併入準備信号Ｓ１を受けて同期処理回路２０８ｂで変換器２の基準位相回路２０６ｃのθを変えて、負荷２４側併入点の位相を交流系統４３側連系点の位相に同期させる。
【００４５】
図４、図５に同期処理回路２０８ｂの動作を説明するベクトル図とフローチャートを示す。変換用変圧器２２出口の電圧をＶ２１、負荷２４側連系点の電圧をＶ２２、交流系統４３側併入点の電圧をＶ４１、Ｖ４１の実軸と虚軸成分をＶ４１ＲＬとＶ４１ＩＭ、Ｖ２２とＶ４１の位相差をθとする。
【００４６】
まず、ステップ３０１で併入準備信号Ｓ１によって系統併入するかどうか判定し、Ｙｅｓならば、ステップ３０２，３０３，３０４で、虚軸成分Ｖ４１ＩＭの符号から積分入力値Δθの符号を決定し、ステップ３０５でΔθを積分して負荷側併入点の電圧Ｖ２２の最短方向に回転させる。ステップ３０６，３０７では、θが３６０゜を超えると０゜にリセットすることで、積分値θのオーバーフローを防止している。
【００４７】
最後に、ステップ３０８で前記の実軸成分Ｖ４１ＲＬが１、もしくは１近傍になったことで同期完了と判定し、同期完了信号Ｓ２をリレー装置４２に伝送することで遮断器４１が動作して交流系統４３が併入される。また、これによって直流単独送電検出信号Ｓｄｃがオフとなり、図１において制御回路が有効電力制御回路２０２ａと無効電力制御回路２０２ｂに、図２において検出位相がすべて電圧位相に切換わる。
【００４８】
次に、本発明の変換器の過電流抑制について説明する。図６は過電流抑制のための機能ブロック図である。直流単独送電時において、過負荷時や系統事故時の変換器に流れる過電流を抑制するため、ｄ軸電圧制御回路２０１ａとｑ軸電圧制御回路２０１ｂに±Ｖｄｌｍｔと±Ｖｑｌｍｔの値を持つリミッタを設ける。図７は制御特性を示す図である。常時は交流電圧が一定となるように制御する。Ｖａｃｒｅｆは、例えば、定格電圧となるように、図６のＶｄｒｅｆ＝１.０ＰＵ、Ｖｑｒｅｆ＝０.０に設定する。
【００４９】
過負荷などによって変換器の電流が制限値を超えそうな場合は、電流リミッタ制御を行って過電流による変換器停止を防止し、負荷遮断等によって交流電圧の低下を回復させる。これにより全域の停電は免れる。Ｉａｃｌｍｔは、例えば、変換器の過電流レベル１.５ＰＵとすると、これを超えないようにＶｄｌｍｔ＝Ｖｑｌｍｔ＝１.２に設定する。
【００５０】
次に、本発明の起動時の制御方法を説明する。図８に逆変換器の起動特性を示す。順変換器が直流電圧一定制御で起動している状態で、無電源系統で逆変換器を時刻Ｔ１の時点で起動し、例えば、ｄ軸電圧制御２０１ａの設定値Ｖｄｒｅｆを時刻Ｔ２までランプ状に緩やかに上昇させ、逆変換器側の交流電圧Ｖａ２１，Ｖｂ２１，Ｖｃ２１を徐々に立ち上げる。これにより、起動直後の過電圧が抑制され、変換器を安定に無電源起動できる。
【００５１】
以上により、本実施例該直流送電設備は、無電源系統においても安定に直流単独で送電でき、また、既存のディーゼル発電機等から電力供給を受ける電源系統にもスムーズに併入できる。
【００５２】
【発明の効果】
本発明によれば、無電源系統への安定な直流単独送電が可能である。また、既存のディーゼル発電機等から電力供給を受ける電源系統とのスムーズな同期併入が可能であり、離島送電等の遠隔地電力供給に適応した自励式直流送電設備を提供することができる。
【図面の簡単な説明】
【図１】本発明の一実施例による自励式直流送電設備の構成を示すブロック図。
【図２】逆変換器側制御装置２００の詳細ブロック図。
【図３】電源系統併入時の動作を説明するブロック図。
【図４】図３の同期処理回路２０８ｂの動作を説明するベクトル図。
【図５】図３の同期処理回路２０８ｂの動作を説明するフローチャート。
【図６】逆変換器に流れる電流を抑制する一実施例のブロック図。
【図７】図６の制御特性を説明する図。
【図８】本発明の起動時の制御方法を説明する図。
【符号の説明】
１…順変換器、２…逆変換器、１１，２１…直流コンデンサ、１２，２２…変換用変圧器、１４，４３…交流系統、２４…負荷、２５…交流送電線、３０ａ，３０ｂ…直流送電線、４１…遮断器、４２…リレー装置、１００…順変換器の制御装置、２００…逆変換器の制御装置、１０２ａ…直流電圧制御回路、２０２ａ…有効電力制御回路、１０２ｂ，２０２ｂ…無効電力制御回路、１０５，２０５…変換器制御部、２０１ａ…ｄ軸電圧制御回路、２０１ｂ…ｑ軸電圧制御回路、２０３ａ，２０３ｂ…選択回路、２０４…直流単独送電検出回路、２０５ａ…ｄ軸電流制御回路、２０５ｂ…ｑ軸電流制御回路、２０１ｃ，２０５ｃ，２０７ｃ，２０８ｃ…２相変換回路、２０１ｄ，２０５ｄ…２軸変換回路、２０５ｅ…２相逆変換回路、２０５ｆ…３相逆変換回路、２０５ｇ…ＰＷＭ制御回路、２０６ａ，２０７ａ，２０８ａ…ベクトル演算回路、２０６ｂ…固定位相切換え回路、２０６ｃ…基準位相回路、２０６ｄ，２０７ｄ…位相演算回路、２０８ｂ…同期処理回路。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a DC power transmission facility, and more particularly to a DC power transmission facility using a self-excited converter.
[0002]
[Prior art]
The DC power transmission equipment is a system for supplying AC power by converting AC power to DC power using a forward converter and converting the transmitted DC power into AC power using an inverse converter. In the electric power system, there are merits such as quick power flow control by introduction of the equipment, interconnection between systems having different frequencies, and transmission with less loss than AC power transmission in long-distance power transmission. In addition, DC transmission equipment using self-excited converters composed of elements with a self-extinguishing function, such as IGBTs, has a small transmission capacity due to element restrictions, etc., but is stable even in weak AC systems and non-powered systems It is excellent in terms of driving performance because it can transmit power and control active power and reactive power independently.
[0003]
As a method for controlling a DC power transmission facility using a self-excited converter, as described in Japanese Patent Nos. 2856743, 2736102, 26357125, 2635660, and Japanese Patent Laid-Open No. 09-1117056, one converter A method is known in which the DC voltage is controlled to be constant and the active power is controlled by another converter to supply power. In addition, since the self-excited converter can also control the reactive power simultaneously and independently as described above, there is a known method of controlling the reactive power directly or indirectly controlling the AC voltage constant in each converter. It has been. This control method is based on the precondition that each converter is connected to an AC system with a power source, and the converter detects the phase of each AC system and is operated in synchronization therewith.
[0004]
[Problems to be solved by the invention]
Assuming power supply to remote customers such as remote islands by DC power transmission, there is no such power supply equipment in addition to the case where the existing power equipment such as diesel generators is connected to the reverse converter side. )), It is desirable to be able to transmit power by DC alone. The conventional control method is effective only when the power supply equipment is connected to the inverter side. In this case, the power supplied to the load is balanced between supply and demand by the cooperation of the power supply equipment and the converter. I'm leaning.
[0005]
However, when direct DC power transmission is performed to a non-power supply system, all the power corresponding to the size and power factor of the load must be supplied from the converter. It is difficult to set the power. In addition, since there is no reference phase that is synchronized in the non-power supply system, the converter must determine the reference phase by itself and supply power to the load.
[0006]
In view of the problems of the prior art, the object of the present invention is to enable stable direct current transmission to a non-power supply system and to synchronize with a power supply system that receives power supply from an existing diesel generator, etc. It is to provide a control system for a self-excited DC power transmission facility adapted to the remote ground system conditions such as the above.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a control device for DC power transmission equipment using the following self-excited converter.
[0008]
That is, in a control device for a self-excited DC power transmission system in which a forward converter for converting AC power into DC power and an inverse converter for converting DC power into AC power are self-excited converters, A circuit for controlling the DC voltage on the converter side, a circuit for detecting DC single power transmission on the inverter side, a selection circuit for switching the control circuit, and a circuit for controlling the AC voltage during single DC power transmission (in the embodiment, AVR- d, q).
[0009]
Further, the inverse converter includes a circuit for obtaining the voltage phase of the AC system on the inverter side, a circuit for switching the voltage phase to a fixed phase, a circuit for converting AC voltage into two axes, and a circuit for converting AC current into two axes A two-axis control output signal (in the embodiment, Vd21 *, Vq21 *) is provided with a circuit for two-phase conversion, the AC voltage is converted into two axes using the voltage phase, and the AC current is the DC single power transmission The voltage phase is switched to a fixed phase by detection and converted into two axes using the fixed phase, and the control output signal is converted back to two phases using the fixed phase.
[0010]
Thereby, the voltage of the DC system is controlled to be constant by the forward converter, and the control is switched to AC voltage control by using the DC single transmission as a detection signal by the reverse converter, and the voltage of the AC system on the reverse converter side is controlled to be constant.
[0011]
Further, the present invention provides a circuit for detecting a signal for preparation for insertion on the inverse converter side, a circuit for obtaining a voltage phase at a power system side insertion point, a circuit for obtaining a voltage phase at a direct current transmission system side insertion point, A circuit for synchronizing the phase of the insertion point and a circuit for detecting that the voltage phase is synchronized are provided. As a result, when the power supply system is inserted into the single DC power transmission system, the signal for preparing the insertion is detected, the voltage phase of the single DC power transmission system is synchronized with the voltage phase of the power supply system, and the synchronization is detected to detect the power supply system. To enter.
[0012]
In addition, when direct DC power transmission is performed, during overload, the current flowing through the converter is suppressed so as not to exceed the limit value. Also, in the activation method, the forward converter is activated first to control the DC voltage constant, and then the inverse converter is activated to control the AC voltage while gradually changing the AC voltage control command value. The AC voltage is gradually raised to start up.
[0013]
As a result, stable direct current transmission to a non-power supply system and smooth synchronization with a power supply system that receives power supply from an existing diesel generator, etc. are possible, and self-adaptation suitable for remote power supply such as remote island power transmission. Excited DC power transmission equipment can be provided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A self-excited direct current power transmission facility according to an embodiment of the present invention will be described. FIG. 1 shows a configuration of a self-excited DC power transmission system according to an embodiment. This system converts the alternating current power of the alternating current system 14 into direct current power by switching with the forward converter 1 via the alternating current bus 13 and the conversion transformer 12, and converts the converted direct current power to the direct

current transmission lines

30a, 30b, Power is transmitted to the reverse converter side using the

DC capacitors

11 and 12, and is converted into AC power again by switching with the reverse converter 2, and AC power is supplied to the load 24 through the conversion transformer 22 and the AC bus 23. Supply. The AC system 43 is a system that is supplied with AC power from a diesel generator or the like, and is inserted through the circuit breaker 41.
[0015]
Each of the forward converter 1 and the inverse converter 2 shows only one self-extinguishing element and a diode constituting the self-excited converter. Place.

Control devices

100 and 200 for inputting control pulses are connected to each self-extinguishing element.
[0016]
In the control device 100, a control pulse is generated by the converter control unit 105 based on the outputs of the DC voltage control circuit 102a and the reactive power control circuit 102b that keep the DC system voltage constant, and the DC system voltage and the forward converter side The reactive power of is controlled to be constant.
[0017]
On the other hand, the control device 200 includes an active power control circuit 202a and a reactive power control circuit 202b, a d-axis voltage control circuit 201a and a q-axis voltage control circuit 201b,

selection circuits

203a and 203b, a single DC power transmission detection circuit 204, a converter control unit. 205. For example, when the circuit breaker 41 is opened by manual disconnection for performing section disconnection or maintenance / inspection work due to a lightning strike or the like, the DC single power transmission detection circuit 204 automatically outputs an open signal of the circuit breaker 41 from the relay device 42. In response, the DC single power transmission detection signal Sdc is turned on, the

selection circuits

203a and 203b switch the active power control circuit 202a to the d-axis voltage control circuit 201a, and the reactive power control circuit 202b to the q-axis voltage control circuit 201b. Based on the output, a control pulse is generated by the converter control unit 205, and the AC voltage on the inverse converter side is controlled to be constant.
[0018]
A method of coordinate conversion when switching to direct current power transmission according to the present embodiment will be described. FIG. 2 shows a detailed block diagram of the inverse converter side control device 200. First, in order to obtain the phase necessary for coordinate conversion, the three-phase AC voltages Va21, Vb21, and Vc21 on the inverse converter side are taken into the control device, and the two-phase AC voltage Vα21 is used using Equation 1 in the two-phase conversion circuit 201c. , Vβ21.
[0019]
[Expression 1]

[0020]
The voltage phase with respect to the reference phase is calculated from the two-phase AC voltages Vα21, Vβ21 and the reference phase cosωt, sinωt arbitrarily generated in the apparatus of the reference phase circuit 206c by the vector arithmetic circuit

206a using Equations

2, 3, 4, and 5. The vector quantities V21RL and V21IM of the real and imaginary axes are obtained. In Equations 2 and 3, m represents the number of samplings in one period of the fundamental wave, and i represents the number of each sampling data.
[0021]
[Expression 2]

[0022]
[Equation 3]

[0023]
[Expression 4]

[0024]
[Equation 5]

[0025]
In the phase calculation circuit 206d, the voltage phases Cos21 and Sin21 are obtained from the real and imaginary vector quantities V21RL and V21IM and the reference phases cosωt and

sinωt using Equations

6 and 7. Also, the fixed phases Cos21L and Sin21L hold the values of the input V21RL and V21IM when the DC single transmission detection signal Sdc is turned on by the fixed phase switching circuit 206b, that is, when the AC system 43 in FIG. 1 is disconnected. Is done. Conversely, when Sdc is off, the same signals as the voltage phases Cos21 and Sin21 are output.
[0026]
[Formula 6]

[0027]
[Expression 7]

[0028]
Next, in the biaxial conversion circuit 201d, the biaxial voltage components that serve as feedback of the d-axis and q-axis

voltage control circuits

201a and 201b by using the two-phase AC voltages Vα21 and Vβ21 and the voltage phases Cos21 and Sin21 from Equation 8. Vd21 and Vq21 are obtained.
[0029]
[Equation 8]

[0030]
The d-axis and q-axis

voltage control circuits

201a and 201b issue commands to the d-axis and q-axis

current control circuits

205a and 205b so that the two-axis voltage components Vd21 and Vq21 coincide with the set values Vdref and Vqref, respectively. Note that the switching method has already been described for the active power control circuit 202a, the reactive power control circuit 202b, and the

selection circuits

203a and 203b.
[0031]
205a to h in the upper part of FIG. 2 are detailed blocks of the converter control unit 205. The three-phase AC currents Ia21, Ib21, and Ic21 on the reverse converter side are taken into the control device and converted into Iα21 and Iβ21 by using the equation 9 in the two-phase conversion circuit 205c.
[0032]
[Equation 9]

[0033]
Two-axis current components Id21 and Iq21 serving as feedback of the d-axis and q-axis

current control circuits

205a and 205b are converted into two-axis alternating currents Iα21 and Iβ21 and fixed phases Cos21L and Sin21L using the formula 10 by the two-axis conversion circuit 205d. Ask.
[0034]
[Expression 10]

[0035]
The d-axis and q-axis

current control circuits

205a and 205b operate so that the command values of the d-axis and q-axis

voltage control circuits

201a and 201b coincide with the two-axis current components Id21 and Iq21. Also, this output, Id21, Iq21, the value obtained by multiplying the reactance component IX of the conversion transformer, and the biaxial voltage components Vd21, Vq21 are added and subtracted separately for the dq axis, and output as a non-interference current control system output. Operation amounts Vd21 * and Vq21 * of the dq axis are obtained.
[0036]
Vd21 * and Vq21 * are converted into two-phase manipulated variables Vα21 * and Vβ21 * by Equation 11 using the fixed phases Cos21L and Sin21L in the two-phase inverse conversion circuit 205e.
[0037]
[Expression 11]

[0038]
Further, the three-phase inverse conversion circuit 205f uses Equation 12 to convert the three-phase manipulated variables Va21 *, Vb21 *, and Vc21 *.
[0039]
[Expression 12]

[0040]
Finally, control pulses are generated by the PWM control circuit 205g using the three-phase manipulated variables Va21 *, Vb21 *, Vc21 * and the triangular wave of the triangular wave generating circuit 205h, and each self-extinguishing type of the inverse converter 2 in FIG. An on / off signal for switching to the element is introduced.
[0041]
According to this, when the power source of the AC system on the reverse converter side is disconnected and direct DC power transmission is performed, the DC power transmission is detected by the reverse converter and the control is switched to AC voltage control. The voltage of the voltage system can be controlled to be constant.
[0042]
Next, the operation when the power supply system is incorporated in this embodiment will be described. FIG. 3 shows the configuration and function when the power supply system is incorporated. The AC system 43 is disconnected by opening the circuit breaker 41, and the inverter 2 is turned on to supply power to the load 24 via the AC power transmission line 25 alone. Consider the operation when 43 is inserted. In this case, if the phase at the insertion point (for example, the phase between the voltages Va41 and Va22) is shifted, the two systems will fluctuate at the time of insertion, so the circuit breaker 41 should be turned on after both phases are synchronized. is required. One example is shown below.
[0043]
In FIG. 3, 201c, 206a, 206b, 206c, and 206d are the same blocks as in FIG. 2, and the voltage phases Cos21 and Sin21 and the fixed phases Cos21L and Sin21L for operating the inverse converter 2 are obtained. In order to synchronize the phase of the insertion point, first, the three-phase AC voltages Va22, Vb22, and Vc22 on the load 24 side are taken in, and the load 24 is transferred by the two-phase conversion circuit 207c, the vector calculation circuit 207a, and the phase calculation circuit 207d. The voltage phases Cos22 and Sin22 at the side entry points are obtained.
[0044]
Next, the three-phase AC voltages Va41, Vb41, and Vc41 on the AC system 43 side are taken in, and the AC system 43 side insertion point with respect to the voltage phase of the insertion point on the load 24 side in the two-phase conversion circuit 208c and the vector calculation circuit 208a. The vector amounts V41RL and V41IM of the real axis and the imaginary axis of the voltage are obtained, and finally the θ of the reference phase circuit 206c of the converter 2 is changed by the synchronization processing circuit 208b in response to the insertion preparation signal S1, and the load 24 side The phase of the insertion point is synchronized with the phase of the AC system 43 side interconnection point.
[0045]
4 and 5 show a vector diagram and a flowchart for explaining the operation of the synchronization processing circuit 208b. The voltage at the outlet of the conversion transformer 22 is V21, the voltage at the load 24 side connection point is V22, the voltage at the AC system 43 side insertion point is V41, the real and imaginary axis components of V41 are V41RL and V41IM, and V22 and V41. Let θ be the phase difference.
[0046]
First, in step 301, it is determined whether or not the system is to be merged based on the merge preparation signal S1, and if Yes, in

steps

302, 303, and 304, the sign of the integral input value Δθ is determined from the sign of the imaginary axis component V41IM. At 305, Δθ is integrated and rotated in the shortest direction of the voltage V22 at the load side insertion point. At

steps

306 and 307, when θ exceeds 360 °, the integral value θ is prevented from overflowing by being reset to 0 °.
[0047]
Finally, in step 308, it is determined that the real axis component V41RL is 1 or close to 1 so that the synchronization is completed, and the circuit breaker 41 is operated by transmitting the synchronization completion signal S2 to the relay device 42. System 43 is inserted. In addition, the DC single power transmission detection signal Sdc is turned off, and the control circuit is switched to the active power control circuit 202a and the reactive power control circuit 202b in FIG. 1, and all the detection phases are switched to the voltage phase in FIG.
[0048]
Next, overcurrent suppression of the converter of the present invention will be described. FIG. 6 is a functional block diagram for overcurrent suppression. In order to suppress the overcurrent flowing through the converter during overload or system fault during direct current DC power transmission, limiters having values of ± Vdlmt and ± Vqlmt are applied to the d-axis voltage control circuit 201a and the q-axis voltage control circuit 201b. Provide. FIG. 7 is a diagram showing control characteristics. Control is always performed so that the AC voltage is constant. For example, Vacref is set to Vdref = 1.0PU and Vqref = 0.0 in FIG.
[0049]
When the converter current is likely to exceed the limit value due to overload or the like, current limiter control is performed to prevent the converter from being stopped due to overcurrent, and the AC voltage drop is recovered by interrupting the load or the like. This avoids power outages throughout the area. Iaclmt is set to Vdlmt = Vqlmt = 1.2 so as not to exceed, for example, when the overcurrent level of the converter is 1.5 PU.
[0050]
Next, the control method at the start of the present invention will be described. FIG. 8 shows the starting characteristics of the inverse converter. In a state where the forward converter is activated by DC voltage constant control, the inverse converter is activated at the time T1 in the non-power supply system, and for example, the set value Vdref of the d-axis voltage control 201a is ramped until the time T2. The AC voltage Va21, Vb21, Vc21 on the inverse converter side is gradually raised by gradually increasing the voltage. Thereby, the overvoltage immediately after starting is suppressed and a converter can be stably started without a power source.
[0051]
As described above, this embodiment of the DC power transmission equipment can stably transmit DC alone even in a non-power supply system, and can be smoothly inserted into a power supply system that receives power supply from an existing diesel generator or the like.
[0052]
【The invention's effect】
According to the present invention, stable single DC power transmission to a non-power supply system is possible. In addition, it can be smoothly synchronized with a power supply system that receives power from an existing diesel generator or the like, and a self-excited direct current power transmission facility adapted to remote power supply such as remote island power transmission can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a self-excited DC power transmission facility according to an embodiment of the present invention.
FIG. 2 is a detailed block diagram of an inverse converter side control device 200;
FIG. 3 is a block diagram for explaining an operation when a power supply system is installed.
4 is a vector diagram for explaining the operation of the synchronization processing circuit 208b of FIG. 3;
FIG. 5 is a flowchart for explaining the operation of the synchronization processing circuit 208b of FIG. 3;
FIG. 6 is a block diagram of an embodiment that suppresses the current flowing through the inverter.
7 is a diagram for explaining the control characteristics of FIG. 6;
FIG. 8 is a diagram for explaining a control method at the start of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Forward converter, 2 ... Reverse converter, 11, 21 ... DC capacitor, 12, 22 ... Conversion transformer, 14, 43 ... AC system, 24 ... Load, 25 ... AC power transmission line, 30a, 30b ... DC Power transmission line, 41 ... circuit breaker, 42 ... relay device, 100 ... control device for forward converter, 200 ... control device for reverse converter, 102a ... DC voltage control circuit, 202a ... active power control circuit, 102b, 202b ... invalid Power control circuit, 105, 205 ... converter control unit, 201a ... d-axis voltage control circuit, 201b ... q-axis voltage control circuit, 203a, 203b ... selection circuit, 204 ... DC single power transmission detection circuit, 205a ... d-axis current control Circuit 205b... Q-axis current control circuit 201c 205205 207c 208c two-phase conversion circuit 201d 205d two-axis conversion circuit 205e two-phase inverse conversion circuit 205 ... 3-phase inverse conversion circuit, 205g ... PWM control circuit, 206a, 207a, 208a ... vector computing circuit, 206 b ... fixed phase switching circuit, 206c ... reference phase circuit, 206d, 207d ... phase arithmetic circuit, 208b ... synchronization processing circuit.

Claims

In a control device for a self-excited DC power transmission system in which a forward converter for converting AC power into DC power and an inverse converter for converting DC power into AC power are self-excited converters,
When the forward converter controls the voltage of the DC system to be constant, and the inverse converter detects the case where the power source of the AC system on the reverse converter side is disconnected and becomes direct current DC transmission, the voltage of the AC system on the reverse converter side is detected. Is controlled to be constant ,
The inverse converter includes a circuit for obtaining the voltage phase of the AC system on the inverse converter side, a circuit for switching the voltage phase to a fixed phase, a circuit for converting AC voltage into two axes, a circuit for converting AC current into two axes, A circuit for converting the control output signal of the shaft into two phases is converted, the AC voltage is converted into two axes using the voltage phase, and the AC current is switched to a fixed phase by detecting the DC single power transmission. A control device for a DC power transmission system , wherein the control output signal is converted back into two phases using the fixed phase .