JP3709619B2

JP3709619B2 - Cascade control device

Info

Publication number: JP3709619B2
Application number: JP24323496A
Authority: JP
Inventors: 良久高塚
Original assignee: 石川島播磨重工業株式会社
Priority date: 1996-09-13
Filing date: 1996-09-13
Publication date: 2005-10-26
Anticipated expiration: 2016-09-13
Also published as: JPH1091204A

Description

【０００１】
【発明の属する技術分野】
本発明は、カスケード式制御装置に関するものである。より詳しくは、自動手動切換器をなくすと共に、応答遅れを減少させ得るようにしたカスケード式制御装置に関するものである。
【０００２】
【従来の技術】
二つの制御対象を扱うようにした制御装置は、従来より存在する。
【０００３】
これらのうち、制御対象に主制御対象と従制御対象の別があり、従制御対象を制御することによって間接的に主制御対象を制御するようにしたものをカスケード式の制御装置という。
【０００４】
このようなカスケード式制御装置の一例として、ボイラの蒸気圧力を制御する場合を、図２を用いて説明する。
【０００５】
図中、１はボイラ本体、２はボイラ本体１で発生された蒸気を貯めるための蒸気ドラム、３は蒸気ドラム２に接続された蒸気系統、４は蒸気系統３の途中に設けられた過熱器である。又、５はボイラ本体１に取付けられたバーナ、６はバーナ５へ燃料を送る燃料系統、７は燃料系統６に設けられた燃料流量調整弁などの従制御対象用操作器、８はバーナ５の使用本数を切換えるための開閉弁である。
【０００６】
そして、蒸気系統３における過熱器４の出側に、蒸気圧力計などの主側検出器９を取付け、且つ、燃料系統６の燃料流量調整弁などの従制御対象用操作器７入側に燃料流量計などの従側検出器１０を取付ける。
【０００７】
次いで、蒸気圧力計などの主側検出器９で検出した蒸気圧力などの主側検出信号１１と、設定器１２に設定した設定蒸気圧力などの主側設定信号１３との偏差を取り、蒸気圧力偏差などの主側偏差信号１４を出力する減算器１５を設け、減算器１５が出力した主側偏差信号１４を基に比例積分制御を行って燃料流量制御信号などの従制御用信号１６を出力する主側比例積分制御器１７を設け、主制御系統１８を構成する。
【０００８】
そして、主側比例積分制御器１７が出力した従制御用信号１６と、燃料流量計などの従側検出器１０で検出した燃料流量などの従側検出信号１９との偏差を取り、燃料流量偏差などの従側偏差信号２０を出力する減算器２１を設け、減算器２１が出力した従側偏差信号２０を基に比例積分制御を行って流量調整弁開度調整信号などの従側制御信号２２を出力する従側比例積分制御器２３を設け、従制御系統２４を構成する。
【０００９】
この際、従側比例積分制御器２３に、最大開度制限信号発生器２５からの最大開度制限信号２６及び最小開度制限信号発生器２７からの最小開度制限信号２８と、前記流量調整弁開度調整信号などの従側制御信号２２とをそれぞれ比較して、従側制御信号２２が最大開度制限信号２６を上回った場合に最大開度制限信号２６を出力し、且つ、従側制御信号２２が最小開度制限信号２８を下回った場合に最小開度制限信号２８を出力するリミッタ２９を取付ける。
【００１０】
更に、主側比例積分制御器１７からの従制御用信号１６が、従制御系統２４へ送られるようにして燃料流量調整弁などの従制御対象用操作器７の制御を自動的に行わせるようにするか、或いは、従制御用信号１６を手動設定信号として従制御系統２４が手動設定によって動作させるようにするかのどちらかを選択するための自動手動切換器３０を設ける。
【００１１】
かかる構成によれば、以下の作動が得られる。
【００１２】
先ず、燃料系統６を介してバーナ５へ燃料を送り、ボイラ本体１内で燃料を燃焼させる。そして、燃焼によって発生した燃焼ガスにより、ボイラ本体１内に通されるボイラ水を加熱して蒸気を発生させ、発生した蒸気を蒸気ドラム２に貯め、蒸気ドラム２から蒸気系統３を介して、図示しない蒸気タービンへ蒸気を送り、蒸気タービンを回して発電を行わせる。尚、蒸気系統３には、過熱器４が設けられ、蒸気タービンへ送られる途中、蒸気は、過熱器４によって過熱されることになる。
【００１３】
そして、燃料系統６に設けられた燃料流量調整弁などの従制御対象用操作器７の開度を制御することにより、バーナ５における燃料の燃焼量が変り、結果として、蒸気系統３を流れる蒸気圧力が制御されることとなる。
【００１４】
そのために、蒸気系統３における過熱器４の出側に、蒸気圧力計などの主側検出器９を取付け、且つ、燃料系統６の燃料流量調整弁などの従制御対象用操作器７入側に燃料流量計などの従側検出器１０を取付けて、蒸気圧力計などの主側検出器９で蒸気圧力などの主側検出信号１１を検出し、減算器１５で、予め設定器１２に設定しておいた設定蒸気圧力などの主側設定信号１３と、前記蒸気圧力などの主側検出信号１１とを比較して両者の偏差を取り、減算器１５が出力した蒸気圧力偏差などの主側偏差信号１４を基に、主側比例積分制御器１７が比例積分制御を行い、燃料流量制御信号などの従制御用信号１６を出力する。
【００１５】
そして、燃料流量計などの従側検出器１０で燃料流量などの従側検出信号１９を検出し、減算器２１で、主側比例積分制御器１７が出力した従制御用信号１６と、前記燃料流量などの従側検出信号１９とを比較して両者の偏差を取り、減算器２１が出力した燃料流量偏差などの従側偏差信号２０を基に、従側比例積分制御器２３が比例積分制御を行い、流量調整弁開度調整信号などの従側制御信号２２を出力して、蒸気系統３における蒸気圧力が設定器１２に設定しておいた設定蒸気圧力と等しい一定の値となるよう、燃料流量調整弁などの従制御対象用操作器７の開度を制御する。
【００１６】
この際、従側比例積分制御器２３に、リミッタ２９を取付け、最大開度制限信号発生器２５からの最大開度制限信号２６及び最小開度制限信号発生器２７からの最小開度制限信号２８と、流量調整弁開度調整信号などの従側制御信号２２とをそれぞれ比較して、従側制御信号２２が最大開度制限信号２６を上回った場合に最大開度制限信号２６を出力させ、且つ、従側制御信号２２が最小開度制限信号２８を下回った場合に最小開度制限信号２８を出力させて従側制御信号２２を制限させるようにする。
【００１７】
そして、従側比例積分制御器２３のリミッタ２９が作動した場合、一旦、自動手動切換器３０を手操作で手動側へ切換えるようにして、主側比例積分制御器１７からの従制御用信号１６が、手動設定信号に切換えられる。そして、減算器１５が出力した蒸気圧力偏差などの主側偏差信号１４の正負が完全に逆転するのを待って、自動手動切換器３０を手操作で自動側へ切換えることにより、リミッタ２９を解除させると共に、制御を復帰させるようにする。
【００１８】
【発明が解決しようとする課題】
しかしながら、上記従来のカスケード式制御装置には、以下のような問題があった。
【００１９】
即ち、従側比例積分制御器２３にリミッタ２９を取付けて、燃料流量調整弁などの従制御対象用操作器７の開度を制限させるようにしており、リミッタ２９が作動した場合、自動手動切換器３０を、一旦、手操作で手動側へ切換えて、従制御用信号１６は手動設定信号に切換えられるので、自動手動切換器３０を操作するための手間が掛ると共に、一旦手動側へ切換えてしまうと、自動的に自動手動切換器３０を自動側へ切換えさせることができない。
【００２０】
又、自動手動切換器３０を手操作で自動側へ切換えるタイミングは、減算器１５が出力した蒸気圧力偏差などの主側偏差信号１４の正負が完全に逆転してからとしていたので、応答遅れが生じるのを避けられない。
【００２１】
本発明は、上述の実情に鑑み、自動手動切換器をなくすと共に、応答遅れを減少させ得るようにしたカスケード式制御装置を提供することを目的とするものである。
【００２２】
【課題を解決するための手段】
本発明は、主側検出器３９で検出した主側検出信号４１及び設定器４２に設定した主側設定信号４３の偏差である主側偏差信号４４に基づいて従制御用信号４６を出力する主側比例積分制御部４７と、従制御用信号４６及び従側検出器４０で検出した従側検出信号５９の偏差である従側偏差信号６０に基づいて従制御対象用操作器３７へ従側制御信号６２を出力することにより間接的に主制御対象を制御させるリミッタ６９付きの従側比例積分制御器６３とを備えたカスケード式制御装置において、
主側比例積分制御部４７を、前記主側偏差信号４４及び信号発生器５１が発生するホールド信号５２のどちらかを出力する切換リレー５３と、切換リレー５３を通ってきた主側偏差信号４４及びホールド信号５２のどちらかに基づき積分制御を行い積分制御信号５６を出力する積分制御器５４と、前記主側偏差信号４４に基づき比例制御を行い比例制御信号５７を出力する比例制御器５５と、前記積分制御信号５６及び比例制御信号５７を加算して前記従制御用信号４６を出力する加算器５８とで構成し、
従側比例積分制御器６３のリミッタ６９に対し、リミッタ６９が作動した時に、主側偏差信号４４側からホールド信号５２側へ出力を切換えさせる切換信号４９，５０を切換リレー５３へ送るモニタスイッチ７０，７１を設け、切換リレー５３によりホールド信号５２へ切換えた際には、積分制御器５４の積分動作を停止し、比例制御器５５の側で、主側偏差信号４４に基づき比例制御器５５で比例制御を行い、比例制御器５５からの比例制御信号５７をそのまま従制御用信号４６として出力し、
主側偏差信号４４が増加から減少に転じた時、又は、主側偏差信号４４が減少から増加に転じた時には、加算器５８の出力信号が変化して従側偏差信号６０、従側制御信号６２の値が変り、リミッタ６９を自動的に解除するように構成されたことを特徴とするカスケード式制御装置にかかるものである。
【００２３】
上記手段によれば、以下のような作用が得られる。
【００２４】
主側検出器３９で検出した主側検出信号４１と、予め設定器４２に設定しておいた主側設定信号４３との偏差である主側偏差信号４４を基に、主側比例積分制御部４７が比例積分制御を行い、従制御用信号４６を出力し、従側検出器４０で検出した従側検出信号５９と、主側比例積分制御部４７が出力した従制御用信号４６との偏差である従側偏差信号６０を基に、従側比例積分制御器６３が比例積分制御を行い、従側制御信号６２を出力して、主制御対象が設定器４２に設定しておいた主側設定信号４３と等しい一定の値となるよう、従制御対象用操作器３７を制御する。
【００２５】
この際、従側比例積分制御器６３に、リミッタ６９を取付け、従側制御信号６２を制限させるようにする。
【００２６】
そして、従側比例積分制御器６３のリミッタ６９が作動した場合、本発明では、以下のようにして、リミッタ６９を自動的に解除させる。
【００２７】
即ち、上記主側比例積分制御部４７による比例積分制御を、積分制御器５４による積分制御と比例制御器５５による比例制御とに分けて、先ず通常時は、従側比例積分制御器６３のリミッタ６９部分に取付けたモニタスイッチ７０，７１からの切換信号４９，５０により、切換リレー５３に、前記主側偏差信号４４を出力させ、切換リレー５３を通ってきた主側偏差信号４４に基づき積分制御器５４が積分制御を行う一方で、前記主側偏差信号４４に基づき比例制御器５５が比例制御を行い、加算器５８が、積分制御器５４からの積分制御信号５６及び比例制御器５５からの比例制御信号５７を加算して前記従制御用信号４６を出力するようになっている。
【００２８】
そして、リミッタ６９が作動すると、従側比例積分制御器６３のリミッタ６９部分に取付けたモニタスイッチ７０，７１が切換信号４９，５０を発生し、モニタスイッチ７０，７１からの切換信号４９，５０により、切換リレー５３に、信号発生器５１が発生するホールド信号５２を出力させ、切換リレー５３を通ってきたホールド信号５２に基づき積分制御器５４の積分動作は停止し、結果として、積分制御をホールドさせてしまう。すると、比例制御器５５の側はホールドされていないので、前記主側偏差信号４４に基づき比例制御器５５が比例制御を行い、加算器５８は、比例制御器５５からの比例制御信号５７とホールドされた積分制御器５４の出力を加算した信号をそのまま従制御用信号４６として出力することになる。
【００２９】
比例制御は主側偏差信号４４の増減の傾向をモニターしていることと同じ意義となるので、主側偏差信号４４が増加から減少に転じた時、又は、主側偏差信号４４が減少から増加に転じた時に、加算器５８の出力信号が変化し、その結果従側偏差信号６０の値が変って、従側比例積分制御器６３が出力する従側制御信号６２の値が変り、リミッタ６９が自動的に解除されることになる。
【００３０】
これにより、リミッタ６９の解除のために従来のような自動手動切換器を設ける必要がなくなり、自動手動切換器を手操作する手間も省略することができるようになる。
【００３１】
又、従来よりも早い時点でリミッタ６９を解除させることができるので、応答遅れを大幅に減少させることが可能となる。
【００３２】
【発明の実施の形態】
以下、本発明の実施の形態を、図示例と共に説明する。
【００３３】
図１は、本発明の実施の形態の一例である。
【００３４】
図中、３１はボイラ本体、３２はボイラ本体３１で発生された蒸気を貯めるための蒸気ドラム、３３は蒸気ドラム３２に接続された蒸気系統、３４は蒸気系統３３の途中に設けられた過熱器である。又、３５はボイラ本体３１に取付けられたバーナ、３６はバーナ３５へ燃料を送る燃料系統、３７は燃料系統３６に設けられた燃料流量調整弁などの従制御対象用操作器、３８はバーナ３５の使用本数を切換えるための開閉弁である。
【００３５】
そして、蒸気系統３３における過熱器３４の出側に、蒸気圧力計などの主側検出器３９を取付け、且つ、燃料系統３６の燃料流量調整弁などの従制御対象用操作器３７入側に燃料流量計などの従側検出器４０を取付ける。
【００３６】
次いで、蒸気圧力計などの主側検出器３９で検出した蒸気圧力などの主側検出信号４１と、設定器４２に設定した設定蒸気圧力などの主側設定信号４３との偏差を取り、蒸気圧力偏差などの主側偏差信号４４を出力する減算器４５を設け、減算器４５が出力した主側偏差信号４４を基に燃料流量制御信号などの従制御用信号４６を出力する主側比例積分制御部４７を設け、主制御系統４８を構成する。
【００３７】
上記主側比例積分制御部４７は、後述する切換信号４９，５０によって、前記減算器４５が出力した主側偏差信号４４及び信号発生器５１が発生するホールド信号５２のどちらかを出力する切換リレー５３と、切換リレー５３を通ってきた主側偏差信号４４及びホールド信号５２のどちらかに基づき積分制御を行う積分制御器５４と、前記減算器４５が出力した主側偏差信号４４に基づき比例制御を行う比例制御器５５と、積分制御器５４が出力する積分制御信号５６及び比例制御器５５が出力する比例制御信号５７を加算して前記従制御用信号４６を出力する加算器５８とで構成されている。
【００３８】
そして、主側比例積分制御部４７が出力した従制御用信号４６と、燃料流量計などの従側検出器４０で検出した燃料流量などの従側検出信号５９との偏差を取り、燃料流量偏差などの従側偏差信号６０を出力する減算器６１を設け、減算器６１が出力した従側偏差信号６０を基に流量調整弁開度調整信号などの従側制御信号６２を出力する従側比例積分制御器６３を設け、従制御系統６４を構成する。
【００３９】
この際、従側比例積分制御器６３に、最大開度制限信号発生器６５からの最大開度制限信号６６及び最小開度制限信号発生器６７からの最小開度制限信号６８と、前記流量調整弁開度調整信号などの従側制御信号６２とをそれぞれ比較して、従側制御信号６２が最大開度制限信号６６を上回った場合に最大開度制限信号６６を出力し、且つ、従側制御信号６２が最小開度制限信号６８を下回った場合に最小開度制限信号６８を出力するリミッタ６９を取付ける。
【００４０】
加えて、最大開度制限信号発生器６５からの最大開度制限信号６６と、流量調整弁開度調整信号などの従側制御信号６２とを比較して、従側制御信号６２が最大開度制限信号６６を上回った場合に前記切換リレー５３をａ側へ切換え、従側制御信号６２が最大開度制限信号６６を下回った場合に前記切換リレー５３をｂ側へ切換えるための前記切換信号４９を前記切換リレー５３へ出力するモニタスイッチ７０を取付ける。
【００４１】
同様に、最小開度制限信号発生器６７からの最小開度制限信号６８と、流量調整弁開度調整信号などの従側制御信号６２とを比較して、従側制御信号６２が最小開度制限信号６８を下回った場合に前記切換リレー５３をａ側へ切換え、従側制御信号６２が最小開度制限信号６８を上回った場合に前記切換リレー５３をｂ側へ切換えるための前記切換信号５０を前記切換リレー５３へ出力するモニタスイッチ７１を取付ける。
【００４２】
次に、作動について説明する。
【００４３】
先ず、燃料系統３６を介してバーナ３５へ燃料を送り、ボイラ本体３１内で燃料を燃焼させる。そして、燃焼によって発生した燃焼ガスにより、ボイラ本体３１内に通されるボイラ水を加熱して蒸気を発生させ、発生した蒸気を蒸気ドラム３２に貯め、蒸気ドラム３２から蒸気系統３３を介して、図示しない蒸気タービンへ蒸気を送り、蒸気タービンを回させて発電を行わせる。尚、蒸気系統３３には、過熱器３４が設けられ、蒸気タービンへ送られる蒸気は、途中、過熱器３４によって加熱されることになる。
【００４４】
そして、燃料系統３６に設けられた燃料流量調整弁などの従制御対象用操作器３７の開度を制御することにより、バーナ３５における燃料の燃焼量が変り、結果として、蒸気系統３３を流れる蒸気圧力が制御されることとなる。
【００４５】
そのために、蒸気系統３３における過熱器３４の出側に、蒸気圧力計などの主側検出器３９を取付け、且つ、燃料系統３６の燃料流量調整弁などの従制御対象用操作器３７入側に燃料流量計などの従側検出器４０を取付けて、蒸気圧力計などの主側検出器３９で蒸気圧力などの主側検出信号４１を検出し、減算器４５で、予め設定器４２に設定しておいた設定蒸気圧力などの主側設定信号４３と、前記蒸気圧力などの主側検出信号４１とを比較して両者の偏差を取り、減算器４５が出力した蒸気圧力偏差などの主側偏差信号４４を基に、主側比例積分制御部４７が比例積分制御（Ｋ＋Ｋ／Ｔ∫ｄｔここで、Ｋはゲイン、Ｔは積分時間である）を行い、燃料流量制御信号などの従制御用信号４６を出力する。
【００４６】
そして、燃料流量計などの従側検出器４０で燃料流量などの従側検出信号５９を検出し、減算器６１で、主側比例積分制御部４７が出力した従制御用信号４６と、前記燃料流量などの従側検出信号５９とを比較して両者の偏差を取り、減算器６１が出力した燃料流量偏差などの従側偏差信号６０を基に、従側比例積分制御器６３が比例積分制御を行い、流量調整弁開度調整信号などの従側制御信号６２を出力して、蒸気系統３３における蒸気圧力が設定器４２に設定しておいた設定蒸気圧力と等しい一定の値となるよう、燃料流量調整弁などの従制御対象用操作器３７の開度を制御する。
【００４７】
この際、従側比例積分制御器６３に、リミッタ６９を取付け、最大開度制限信号発生器６５からの最大開度制限信号６６及び最小開度制限信号発生器６７からの最小開度制限信号６８と、流量調整弁開度調整信号などの従側制御信号６２とをそれぞれ比較して、従側制御信号６２が最大開度制限信号６６を上回った場合に最大開度制限信号６６を出力させ、且つ、従側制御信号６２が最小開度制限信号６８を下回った場合に最小開度制限信号６８を出力させて従側制御信号６２を制限させるようにする。
【００４８】
そして、従側比例積分制御器６３のリミッタ６９が作動した場合、本発明では、以下のようにして、リミッタ６９を自動的に解除させるようにしている。
【００４９】
即ち、上記主側比例積分制御部４７による比例積分制御（Ｋ＋Ｋ／Ｔ∫ｄｔ）を、積分制御器５４による積分制御（Ｋ／Ｔ∫ｄｔ）と比例制御器５５による比例制御（Ｋ）とに分けて、先ず通常時は、従側比例積分制御器６３のリミッタ６９部分に取付けたモニタスイッチ７０，７１からの切換信号４９，５０により、切換リレー５３に、前記減算器４５が出力した主側偏差信号４４を出力させ、切換リレー５３を通ってきた主側偏差信号４４に基づき積分制御器５４が積分制御を行う一方で、前記減算器４５が出力した主側偏差信号４４に基づき比例制御器５５が比例制御を行い、加算器５８が、積分制御器５４からの積分制御信号５６及び比例制御器５５からの比例制御信号５７を加算して前記従制御用信号４６を出力するようになっている。
【００５０】
そして、リミッタ６９が作動すると、従側比例積分制御器６３のリミッタ６９部分に取付けたモニタスイッチ７０，７１のうちのどちらかが切換信号４９，５０を発生し、モニタスイッチ７０，７１からの切換信号４９，５０により、切換リレー５３に、信号発生器５１が発生するホールド信号５２を出力させ、切換リレー５３を通ってきたホールド信号５２に基づき積分制御器５４は動作を停止し、結果として、積分制御をホールドさせてしまう。比例制御器５５の側はホールドされていないので、前記減算器４５が出力した主側偏差信号４４に基づき比例制御器５５が比例制御を行い、加算器５８が、比例制御器５５からの比例制御信号５７をそのまま従制御用信号４６として出力することになる。
【００５１】
比例制御は主側偏差信号４４の値にＫを掛けるだけの制御であるため、主側偏差信号４４の増減の傾向をモニターしていることと同じ意義となるので、最大制限開度でリミッタ６９が作動した場合には、主側偏差信号４４が増加から減少に転じた時に、又、最小制限開度でリミッタ６９が作動した場合には、主側偏差信号４４が減少から増加に転じた時に、減算器６１が出力する燃料流量偏差などの従側偏差信号６０の値が変って、従側比例積分制御器６３が出力する流量調整弁開度調整信号などの従側制御信号６２の値が変りリミッタ６９が自動的に解除されることになる。
【００５２】
これにより、リミッタ６９の解除のために図２のような自動手動切換器３０を設ける必要がなくなり、自動手動切換器３０を手操作する手間も省略することができるようになる。
【００５３】
更に、図２に示すように自動手動切換器３０を設けた場合、自動手動切換器３０を手操作してリミッタ６９を解除するタイミングは、最大開度でリミッタ６９が作動した場合には、主側偏差信号４４が増加から減少に転じ、更に、主側偏差信号４４が０となり、主側偏差信号４４の値正負が逆転した後であり、又、最小開度でリミッタ６９が作動した場合には、主側偏差信号４４が減少から増加に転じ、更に、主側偏差信号４４が０となり、主側偏差信号４４の値正負が逆転した後であるため、かなりの応答遅れが生じていたが、本発明では、それよりも早い時点でリミッタ６９を解除させることができるので、応答遅れを大幅に減少させることが可能となる。
【００５４】
尚、本発明は、上述の実施の形態にのみ限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々変更を加え得ることは勿論である。
【００５５】
【発明の効果】
以上説明したように、本発明のカスケード式制御装置によれば、自動手動切換器をなくすと共に、応答遅れを減少させることができるという優れた効果を奏し得る。
【図面の簡単な説明】
【図１】本発明の実施の形態の一例の概略制御系統図である。
【図２】従来例の概略制御系統図である。
【符号の説明】
３７従制御対象用操作器
３９主側検出器
４０従側検出器
４１主側検出信号
４２設定器
４３主側設定信号
４４主側偏差信号
４６従制御用信号
４７主側比例積分制御部
４９，５０切換信号
５１信号発生器
５２ホールド信号
５３切換リレー
５４積分制御器
５５比例制御器
５６積分制御信号
５７比例制御信号
５８加算器
５９従側検出信号
６０従側偏差信号
６２従側制御信号
６３従側比例積分制御器
６９リミッタ
７０，７１モニタスイッチ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cascade control device. More specifically, the present invention relates to a cascade control device that eliminates an automatic manual switching device and can reduce response delay.
[0002]
[Prior art]
Conventionally, there has been a control device that handles two control objects.
[0003]
Among these, there are two types of control objects, the main control object and the sub control object, and the main control object that is indirectly controlled by controlling the sub control object is called a cascade control device.
[0004]
As an example of such a cascade control device, a case where the steam pressure of a boiler is controlled will be described with reference to FIG.
[0005]
In the figure, 1 is a boiler body, 2 is a steam drum for storing steam generated in the boiler body 1, 3 is a steam system connected to the steam drum 2, and 4 is a superheater provided in the middle of the steam system 3. It is. Further, 5 is a burner attached to the boiler body 1, 6 is a fuel system for sending fuel to the burner 5, 7 is a control device for a slave control target such as a fuel flow rate adjusting valve provided in the fuel system 6, and 8 is a burner 5 It is an on-off valve for switching the number of used.
[0006]
Then, a main detector 9 such as a steam pressure gauge is attached to the outlet side of the superheater 4 in the steam system 3, and fuel is supplied to the input side of the slave control target operating device 7 such as a fuel flow rate adjusting valve of the fuel system 6. A slave detector 10 such as a flow meter is installed.
[0007]
Next, a deviation between the main side detection signal 11 such as the steam pressure detected by the main side detector 9 such as a steam pressure gauge and the main side setting signal 13 such as the set steam pressure set in the setting device 12 is taken to determine the steam pressure. A subtractor 15 that outputs a main-side deviation signal 14 such as a deviation is provided, and a proportional-integral control is performed based on the main-side deviation signal 14 output from the subtractor 15 to output a sub-control signal 16 such as a fuel flow rate control signal. The main proportional integral controller 17 is provided, and the main control system 18 is configured.
[0008]
Then, a deviation between the slave control signal 16 output from the primary proportional integral controller 17 and the slave detection signal 19 such as the fuel flow rate detected by the slave detector 10 such as a fuel flow meter is taken to obtain a fuel flow deviation. The subtractor 21 for outputting the subordinate deviation signal 20 is provided, and the proportional control is performed on the basis of the subordinate deviation signal 20 output from the subtractor 21 to perform the subordinate control signal 22 such as a flow rate adjustment valve opening degree adjustment signal. Is provided, and a slave control system 24 is configured.
[0009]
At this time, the secondary proportional integral controller 23 has the maximum opening restriction signal 26 from the maximum opening restriction signal generator 25 and the minimum opening restriction signal 28 from the minimum opening restriction signal generator 27, and the flow rate adjustment. The slave side control signal 22 such as a valve opening degree adjustment signal is respectively compared, and when the slave side control signal 22 exceeds the maximum opening degree limit signal 26, the maximum opening degree limit signal 26 is output, and the slave side A limiter 29 that outputs a minimum opening restriction signal 28 when the control signal 22 falls below the minimum opening restriction signal 28 is attached.
[0010]
Further, the slave control signal 16 from the primary proportional integral controller 17 is sent to the slave control system 24 so that the slave control target operating device 7 such as a fuel flow rate adjusting valve is automatically controlled. Alternatively, an automatic manual switch 30 is provided for selecting whether the slave control system 24 is operated by manual setting using the slave control signal 16 as a manual setting signal.
[0011]
According to this configuration, the following operation can be obtained.
[0012]
First, fuel is sent to the burner 5 through the fuel system 6 to burn the fuel in the boiler body 1. Then, the combustion gas generated by the combustion heats the boiler water passed through the boiler body 1 to generate steam, stores the generated steam in the steam drum 2, and from the steam drum 2 through the steam system 3, Steam is sent to a steam turbine (not shown), and the steam turbine is rotated to generate power. The steam system 3 is provided with a superheater 4, and the steam is superheated by the superheater 4 while being sent to the steam turbine.
[0013]
The amount of fuel burned in the burner 5 is changed by controlling the opening degree of the sub-control target operating unit 7 such as a fuel flow rate adjusting valve provided in the fuel system 6. As a result, the steam flowing through the steam system 3 is changed. The pressure will be controlled.
[0014]
For this purpose, a main detector 9 such as a steam pressure gauge is attached to the outlet side of the superheater 4 in the steam system 3, and the slave control target operation device 7 such as a fuel flow rate adjustment valve of the fuel system 6 is input to the inlet side. A slave side detector 10 such as a fuel flow meter is attached, a main side detector 9 such as a steam pressure gauge detects a main side detection signal 11 such as a steam pressure, and a subtractor 15 presets the setting unit 12. The main side setting signal 13 such as the set steam pressure and the main side detection signal 11 such as the steam pressure are compared to obtain a deviation between them, and a main side deviation such as a steam pressure deviation output from the subtractor 15 is obtained. Based on the signal 14, the main-side proportional-integral controller 17 performs proportional-integral control and outputs a sub-control signal 16 such as a fuel flow rate control signal.
[0015]
Then, a slave detection signal 19 such as a fuel flow rate is detected by the slave detector 10 such as a fuel flow meter, the slave control signal 16 output from the master proportional integral controller 17 is detected by the subtractor 21, and the fuel. The slave side detection signal 19 such as the flow rate is compared to take a deviation between the two, and the slave side proportional integration controller 23 controls the proportional integral control based on the slave side deviation signal 20 such as the fuel flow rate deviation output from the subtractor 21. To output a slave side control signal 22 such as a flow rate adjustment valve opening adjustment signal so that the steam pressure in the steam system 3 becomes a constant value equal to the set steam pressure set in the setting device 12. The opening degree of the operation device for slave control 7 such as a fuel flow rate adjusting valve is controlled.
[0016]
At this time, a limiter 29 is attached to the secondary proportional integration controller 23, and a maximum opening restriction signal 26 from the maximum opening restriction signal generator 25 and a minimum opening restriction signal 28 from the minimum opening restriction signal generator 27. And the secondary control signal 22 such as the flow rate adjustment valve opening adjustment signal, respectively, and when the secondary control signal 22 exceeds the maximum opening restriction signal 26, the maximum opening restriction signal 26 is output. When the slave control signal 22 falls below the minimum opening restriction signal 28, the minimum opening restriction signal 28 is output to restrict the slave control signal 22.
[0017]
When the limiter 29 of the secondary proportional integration controller 23 is activated, the automatic manual switching device 30 is once manually switched to the manual side so that the slave control signal 16 from the primary proportional integration controller 17 is switched. Is switched to the manual setting signal. Then, after the sign of the main side deviation signal 14 such as the steam pressure deviation outputted from the subtractor 15 is completely reversed, the limiter 29 is released by manually switching the automatic manual switching unit 30 to the automatic side. And return control.
[0018]
[Problems to be solved by the invention]
However, the conventional cascade control device has the following problems.
[0019]
In other words, a limiter 29 is attached to the secondary proportional integration controller 23 to limit the opening degree of the slave control target operating unit 7 such as a fuel flow rate adjusting valve. When the limiter 29 is activated, automatic manual switching is performed. Since the secondary control signal 16 is switched to the manual setting signal by manually switching the device 30 to the manual side, it takes time to operate the automatic manual switching device 30, and once it is switched to the manual side. If this happens, the automatic manual switching device 30 cannot be automatically switched to the automatic side.
[0020]
Also, the timing for manually switching the automatic manual changer 30 to the automatic side is that the main side deviation signal 14 such as the steam pressure deviation output from the subtractor 15 is completely reversed, so that there is a response delay. Inevitable.
[0021]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a cascade control device that eliminates an automatic manual switching device and can reduce response delay.
[0022]
[Means for Solving the Problems]
The present invention outputs a slave control signal 46 based on a master side detection signal 41 detected by the master side detector 39 and a master side deviation signal 44 which is a deviation between the master side setting signal 43 set in the setting device 42. Based on the side proportional integration control unit 47, the slave control signal 46 and the slave side deviation signal 60 which is the deviation of the slave side detection signal 59 detected by the slave side detector 40, the slave side control unit 37 is controlled to the slave side. In a cascade control device including a slave proportional integration controller 63 with a limiter 69 that indirectly controls a main control target by outputting a signal 62,
The main-side proportional-plus-integral control unit 47 outputs a switching relay 53 that outputs either the main-side deviation signal 44 or the hold signal 52 generated by the signal generator 51, and the main-side deviation signal 44 that has passed through the switching relay 53 and An integration controller 54 that performs integral control based on one of the hold signals 52 and outputs an integral control signal 56; a proportional controller 55 that performs proportional control based on the main-side deviation signal 44 and outputs a proportional control signal 57; An adder 58 that adds the integral control signal 56 and the proportional control signal 57 and outputs the slave control signal 46;
A monitor switch 70 for sending switching signals 49 and 50 for switching the output from the main deviation signal 44 side to the hold signal 52 side when the limiter 69 is operated with respect to the limiter 69 of the slave proportional integration controller 63. 71, and when switching to the hold signal 52 by the switching relay 53, the integration operation of the integration controller 54 is stopped, and the proportional controller 55 based on the main side deviation signal 44 is stopped on the proportional controller 55 side. Proportional control is performed, and the proportional control signal 57 from the proportional controller 55 is output as the slave control signal 46 as it is.
When the main-side deviation signal 44 changes from increasing to decreasing, or when the main-side deviation signal 44 changes from decreasing to increasing, the output signal of the adder 58 changes to change the slave-side deviation signal 60 and the slave-side control signal. This is a cascade type control device characterized in that the value of 62 changes and the limiter 69 is automatically released .
[0023]
According to the above means, the following operation can be obtained.
[0024]
Based on a main-side deviation signal 44 that is a deviation between the main-side detection signal 41 detected by the main-side detector 39 and the main-side setting signal 43 set in advance in the setting device 42, a main-side proportional integration control unit 47 performs proportional-integral control and outputs a slave control signal 46, and a deviation between the slave-side detection signal 59 detected by the slave-side detector 40 and the slave-control signal 46 output by the master-side proportional-plus-integral control unit 47. On the basis of the slave deviation signal 60, the slave proportional integral controller 63 performs proportional integral control, outputs a slave control signal 62, and the master control target set in the setter 42 is the master side. The slave control target operation device 37 is controlled so as to have a constant value equal to the setting signal 43.
[0025]
At this time, a limiter 69 is attached to the secondary proportional integration controller 63 to limit the secondary control signal 62.
[0026]
When the limiter 69 of the secondary proportional integration controller 63 is activated, the limiter 69 is automatically released as follows in the present invention.
[0027]
That is, the proportional integral control by the main proportional integral control unit 47 is divided into integral control by the integral controller 54 and proportional control by the proportional controller 55. First, in the normal time, the limiter of the slave proportional integral controller 63 is first. The main side deviation signal 44 is output to the switching relay 53 by switching signals 49 and 50 from the monitor switches 70 and 71 attached to the 69 portion, and the integration control is performed based on the main side deviation signal 44 that has passed through the switching relay 53. While the controller 54 performs integral control, the proportional controller 55 performs proportional control based on the main-side deviation signal 44, and the adder 58 includes the integral control signal 56 from the integral controller 54 and the proportional controller 55. The slave control signal 46 is output by adding the proportional control signal 57.
[0028]
When the limiter 69 is activated, the monitor switches 70 and 71 attached to the limiter 69 portion of the slave proportional integration controller 63 generate switching signals 49 and 50, and the switching signals 49 and 50 from the monitor switches 70 and 71 are used. The switching relay 53 outputs a hold signal 52 generated by the signal generator 51, and the integration operation of the integration controller 54 is stopped based on the hold signal 52 that has passed through the switching relay 53, and as a result, the integration control is held. I will let you. Then, since the proportional controller 55 side is not held, the proportional controller 55 performs proportional control based on the main deviation signal 44, and the adder 58 holds the proportional control signal 57 from the proportional controller 55 and the hold. a signal obtained by adding the output of the integral controller 54 will output as従制patronage signal 46 remains fully.
[0029]
Proportional control has the same meaning as monitoring the increase / decrease tendency of the main side deviation signal 44. Therefore, when the main side deviation signal 44 changes from increasing to decreasing, or the main side deviation signal 44 increases from decreasing. The output signal of the adder 58 changes, and as a result, the value of the slave deviation signal 60 changes, the value of the slave control signal 62 output from the slave proportional integral controller 63 changes, and the limiter 69 changes. Will be automatically canceled.
[0030]
As a result, it is not necessary to provide a conventional automatic manual switching device for releasing the limiter 69, and it is possible to eliminate the trouble of manually operating the automatic manual switching device.
[0031]
In addition, since the limiter 69 can be released at an earlier point than before, the response delay can be greatly reduced.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0033]
FIG. 1 is an example of an embodiment of the present invention.
[0034]
In the figure, 31 is a boiler body, 32 is a steam drum for storing steam generated in the boiler body 31, 33 is a steam system connected to the steam drum 32, and 34 is a superheater provided in the middle of the steam system 33. It is. Also, 35 is a burner attached to the boiler body 31, 36 is a fuel system for sending fuel to the burner 35, 37 is a slave control target operating device such as a fuel flow rate adjusting valve provided in the fuel system 36, and 38 is a burner 35. It is an on-off valve for switching the number of used.
[0035]
A main detector 39 such as a steam pressure gauge is attached to the outlet side of the superheater 34 in the steam system 33, and the fuel is supplied to the inlet side of the slave control target operating device 37 such as a fuel flow rate adjusting valve of the fuel system 36. Install the secondary detector 40 such as a flow meter.
[0036]
Next, a deviation between the main-side detection signal 41 such as the steam pressure detected by the main-side detector 39 such as a steam pressure gauge and the main-side setting signal 43 such as the set steam pressure set in the setting device 42 is taken to determine the steam pressure. A subtractor 45 that outputs a main side deviation signal 44 such as a deviation is provided, and a main side proportional integral control that outputs a sub control signal 46 such as a fuel flow rate control signal based on the main side deviation signal 44 output from the subtractor 45. A unit 47 is provided to constitute the main control system 48.
[0037]
The main proportional integral control unit 47 outputs either a main deviation signal 44 output from the subtractor 45 or a hold signal 52 generated by the signal generator 51 in response to switching signals 49 and 50 described later. 53, an integration controller 54 that performs integration control based on either the main-side deviation signal 44 or the hold signal 52 that has passed through the switching relay 53, and proportional control based on the main-side deviation signal 44 that is output from the subtractor 45. And an adder 58 that adds the integral control signal 56 output from the integral controller 54 and the proportional control signal 57 output from the proportional controller 55 and outputs the slave control signal 46. Has been.
[0038]
Then, a deviation between the slave control signal 46 output by the primary proportional integral control unit 47 and the slave detection signal 59 such as the fuel flow rate detected by the slave detector 40 such as a fuel flow meter is taken to obtain a fuel flow deviation. A subtractor 61 that outputs a slave side deviation signal 60 such as a slave side proportional signal that outputs a slave side control signal 62 such as a flow rate adjustment valve opening degree adjustment signal based on the slave side deviation signal 60 output by the subtractor 61 is provided. An integration controller 63 is provided to constitute a sub control system 64.
[0039]
At this time, the secondary proportional integral controller 63 has a maximum opening restriction signal 66 from a maximum opening restriction signal generator 65 and a minimum opening restriction signal 68 from a minimum opening restriction signal generator 67, and the flow rate adjustment. The slave side control signal 62 such as a valve opening degree adjustment signal is compared with each other, and when the slave side control signal 62 exceeds the maximum opening degree limit signal 66, the maximum opening degree limit signal 66 is output, and the slave side A limiter 69 that outputs a minimum opening restriction signal 68 when the control signal 62 falls below the minimum opening restriction signal 68 is attached.
[0040]
In addition, the maximum opening restriction signal 66 from the maximum opening restriction signal generator 65 is compared with the slave control signal 62 such as the flow rate adjustment valve opening adjustment signal, so that the slave control signal 62 has the maximum opening. When the limit signal 66 is exceeded, the switching relay 53 is switched to the a side, and when the slave control signal 62 is below the maximum opening limit signal 66, the switching signal 49 for switching the switching relay 53 to the b side. Is attached to the switching relay 53.
[0041]
Similarly, the minimum opening restriction signal 68 from the minimum opening restriction signal generator 67 is compared with the slave control signal 62 such as the flow rate adjustment valve opening adjustment signal, so that the slave control signal 62 is the minimum opening. The switching signal 53 for switching the switching relay 53 to the b side when the subordinate control signal 62 exceeds the minimum opening degree limiting signal 68 when the subordinate control signal 62 exceeds the minimum opening degree limiting signal 68 when the limiting signal 68 falls below. Is attached to the switching relay 53.
[0042]
Next, the operation will be described.
[0043]
First, the fuel is sent to the burner 35 through the fuel system 36, and the fuel is burned in the boiler body 31. And by the combustion gas generated by the combustion, the boiler water passed through the boiler body 31 is heated to generate steam, the generated steam is stored in the steam drum 32, and from the steam drum 32 through the steam system 33, Steam is sent to a steam turbine (not shown), and the steam turbine is rotated to generate power. The steam system 33 is provided with a superheater 34, and the steam sent to the steam turbine is heated by the superheater 34 in the middle.
[0044]
The amount of fuel burned in the burner 35 is changed by controlling the degree of opening of the slave control target operating device 37 such as a fuel flow rate adjusting valve provided in the fuel system 36. As a result, the steam flowing through the steam system 33 is changed. The pressure will be controlled.
[0045]
For this purpose, a main-side detector 39 such as a steam pressure gauge is attached to the outlet side of the superheater 34 in the steam system 33, and the sub-control target operation unit 37 such as a fuel flow rate adjustment valve of the fuel system 36 is input to the inlet side. A slave side detector 40 such as a fuel flow meter is attached, a main side detection signal 41 such as a steam pressure is detected by a main side detector 39 such as a steam pressure gauge, and a subtractor 45 sets in advance to a setting device 42. The main side setting signal 43 such as the set steam pressure and the main side detection signal 41 such as the steam pressure are compared to obtain a deviation between them, and a main side deviation such as a steam pressure deviation output from the subtractor 45. Based on the signal 44, the main proportional integral control unit 47 performs proportional integral control (K + K / T∫dt, where K is a gain and T is an integral time), and a sub control signal such as a fuel flow rate control signal. 46 is output.
[0046]
Then, a slave detection signal 59 such as a fuel flow rate is detected by a slave detector 40 such as a fuel flow meter, and a slave control signal 46 output from the master proportional integral control unit 47 is output by the subtractor 61, and the fuel. The slave side detection signal 59 such as the flow rate is compared to take the difference between the two, and based on the slave side deviation signal 60 such as the fuel flow rate deviation output from the subtractor 61, the slave side proportional integration controller 63 controls the proportional integral control. And a slave control signal 62 such as a flow rate adjustment valve opening adjustment signal is output so that the steam pressure in the steam system 33 becomes a constant value equal to the set steam pressure set in the setting device 42. It controls the opening degree of the slave control target operating device 37 such as a fuel flow rate adjusting valve.
[0047]
At this time, a limiter 69 is attached to the slave proportional integral controller 63, and a maximum opening restriction signal 66 from the maximum opening restriction signal generator 65 and a minimum opening restriction signal 68 from the minimum opening restriction signal generator 67. And the secondary control signal 62 such as the flow rate adjustment valve opening adjustment signal, respectively, and when the secondary control signal 62 exceeds the maximum opening restriction signal 66, the maximum opening restriction signal 66 is output. When the slave control signal 62 falls below the minimum opening restriction signal 68, the minimum opening restriction signal 68 is output to restrict the slave control signal 62.
[0048]
When the limiter 69 of the secondary proportional integration controller 63 is activated, the limiter 69 is automatically released as follows in the present invention.
[0049]
That is, the proportional integral control (K + K / T∫dt) by the main proportional integral control unit 47 is changed into the integral control (K / T∫dt) by the integral controller 54 and the proportional control (K) by the proportional controller 55. First, in the normal state, the main side output from the subtractor 45 to the changeover relay 53 by the changeover signals 49 and 50 from the monitor switches 70 and 71 attached to the limiter 69 portion of the secondary proportional integration controller 63. A deviation signal 44 is output, and the integration controller 54 performs integration control based on the main side deviation signal 44 that has passed through the switching relay 53, while the proportional controller based on the main side deviation signal 44 output from the subtractor 45. 55 performs proportional control, and an adder 58 adds the integral control signal 56 from the integral controller 54 and the proportional control signal 57 from the proportional controller 55 and outputs the slave control signal 46. That.
[0050]
When the limiter 69 is activated, one of the monitor switches 70 and 71 attached to the limiter 69 portion of the slave proportional integration controller 63 generates a switching signal 49 and 50, and the switching from the monitor switches 70 and 71 is performed. The signals 49 and 50 cause the switching relay 53 to output the hold signal 52 generated by the signal generator 51, and the integration controller 54 stops operating based on the hold signal 52 that has passed through the switching relay 53. As a result, The integration control is held. Since the proportional controller 55 side is not held, the proportional controller 55 performs proportional control based on the main deviation signal 44 output from the subtractor 45, and the adder 58 performs proportional control from the proportional controller 55. The signal 57 is output as the slave control signal 46 as it is.
[0051]
Since the proportional control is a control that simply multiplies the value of the main deviation signal 44 by K, it has the same significance as monitoring the increase / decrease tendency of the main deviation signal 44. When the main side deviation signal 44 changes from increase to decrease, and when the limiter 69 operates at the minimum limit opening degree, the main side deviation signal 44 changes from decrease to increase. The value of the slave side deviation signal 60 such as the fuel flow rate deviation output from the subtractor 61 changes, and the value of the slave side control signal 62 such as the flow rate adjustment valve opening adjustment signal output from the slave proportional integral controller 63 changes. The change limiter 69 is automatically released.
[0052]
Thereby, it is not necessary to provide the automatic manual switching device 30 as shown in FIG. 2 for releasing the limiter 69, and it is possible to eliminate the trouble of manually operating the automatic manual switching device 30.
[0053]
Further, when the automatic manual changer 30 is provided as shown in FIG. 2, the timing for releasing the limiter 69 by manually operating the automatic manual changer 30 is the main timing when the limiter 69 is operated at the maximum opening. The side deviation signal 44 changes from increasing to decreasing, and further after the main side deviation signal 44 becomes 0, the value of the main side deviation signal 44 is reversed, and when the limiter 69 is operated at the minimum opening. The main-side deviation signal 44 has changed from decreasing to increasing, and the main-side deviation signal 44 has become 0, and the value of the main-side deviation signal 44 has been reversed. In the present invention, since the limiter 69 can be released at an earlier time point, the response delay can be greatly reduced.
[0054]
It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.
[0055]
【The invention's effect】
As described above, according to the cascade control device of the present invention, it is possible to achieve an excellent effect of eliminating the automatic manual switching device and reducing the response delay.
[Brief description of the drawings]
FIG. 1 is a schematic control system diagram of an example of an embodiment of the present invention.
FIG. 2 is a schematic control system diagram of a conventional example.
[Explanation of symbols]
37 Subordinate control target operating device 39 Main side detector 40 Subordinate detector 41 Main side detection signal 42 Setter 43 Main side setting signal 44 Main side deviation signal 46 Sub control signal 47 Main side proportional integral control units 49, 50 Switching signal 51 signal generator 52 hold signal 53 switching relay 54 integral controller 55 proportional controller 56 integral control signal 57 proportional control signal 58 adder 59 slave detection signal 60 slave deviation signal 62 slave control signal 63 slave proportional Integration controller 69 Limiter 70, 71 Monitor switch

Claims

Based on a main side deviation signal (44) that is a deviation between the main side detection signal (41) detected by the main side detector (39) and the main side setting signal (43) set in the setting unit (42). A slave side deviation which is a deviation of the slave side detection signal (59) detected by the slave side control signal (46) and the slave side detector (40), the master side proportional integration control unit (47) which outputs the signal (46). A slave proportional control unit with a limiter (69) that indirectly controls the master control object by outputting the slave control signal (62) to the slave control object operating device (37) based on the signal (60). (63)
The main-side proportional-plus-integral control unit (47) includes a switching relay (53) that outputs either the main-side deviation signal (44) or a hold signal (52) generated by the signal generator (51), and a switching relay ( 53) an integration controller (54) that performs integration control based on either the main-side deviation signal (44) or the hold signal (52) that has passed through and outputs an integration control signal (56), and the main-side deviation signal The proportional controller (55) that performs proportional control based on (44) and outputs a proportional control signal (57), and adds the integral control signal (56) and the proportional control signal (57) to add the slave control signal (57). 46) and an adder (58) for outputting,
A switching signal (49) for switching the output from the main deviation signal (44) side to the hold signal (52) side when the limiter (69) is operated with respect to the limiter (69) of the slave proportional integration controller (63). ) (50) is sent to the switching relay (53), and monitor switches (70) (71) are provided . When the switching relay (53) switches to the hold signal (52), the integration controller (54) performs the integration operation. The proportional controller (55) performs proportional control by the proportional controller (55) based on the main side deviation signal (44), and the proportional control signal (57) from the proportional controller (55) is Output as it is as a slave control signal (46),
When the main-side deviation signal (44) changes from increase to decrease, or when the main-side deviation signal (44) changes from decrease to increase, the output signal of the adder (58) changes and the slave-side deviation signal (60) A cascade type control device configured to automatically release the limiter (69) when the value of the slave control signal (62) changes .

The cascade control device according to claim 1, wherein the main control target is a steam pressure of the boiler, and the sub control target is a fuel flow rate of the boiler.