JP2004153957A - Power conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power conversion apparatus capable of preventing the occurrence of an excess current by quickly responding if an abnormality occurs in a grid to abruptly change a grid voltage, and suppressing the output of an unbalance component or a harmonic component in a normal time. <P>SOLUTION: Filters 15 and 16 input a detection voltage of the grid through a three-phase/dq axes converter 5. A grid abnormality determination means 17 inputs one of the outputs of the three-phase/dq axes converter 5, and outputs a time constant switching command to the filters 15 and 16 when the change rate exceeds a prescribed value. The filters 15 and 16 switch a response time constant to a long value in a normal time or to a short value at grid abnormality under the time constant switching command. <P>COPYRIGHT: (C)2004,JPO

Description

【００２４】
上記の変換操作を（１）〜（３）式について行えば（５），（６）式となる。
【００２５】
Ｌ・（ｄＩｄ／ｄｔ）＝Ｖｃｄ−Ｖｓｄ−ωＬＩｑ （５）
Ｌ・（ｄＩｑ／ｄｔ）＝Ｖｃｑ−Ｖｓｑ＋ωＬＩｄ （６）
ここで、Ｖｃｄ，Ｖｃｑはインバータ１の発生電圧を２軸に変換した量、Ｖｓｄ，Ｖｓｑは系統電圧を２軸に変換した量、Ｉｄ，Ｉｑはインバータ１の電流を２軸に変換した量、ωは系統電圧の角周波数である。
【００２６】
更に、インバータ１の出力電圧を下記（７），（８）式に基づいて決める。
【００２７】
Ｖｃｄ＝Ｖｓｄ＋ωＬＩｑ＋Ｕｃｄ （７）
Ｖｃｑ＝Ｖｓｑ−ωＬＩｄ＋Ｕｃｑ （８）
（７），（８）式を（５），（６）式に代入すると、（９），（１０）式となる。
【００２８】
Ｌ・（ｄＩｄ／ｄｔ）＝Ｕｃｄ （９）
Ｌ・（ｄＩｑ／ｄｔ）＝Ｕｃｑ （１０）
上記（９），（１０）式から、Ｉｄを制御するにはＵｃｄを、Ｉｑを制御するにはＵｃｑを制御すればよいことが分かる。したがって、インバータ１の各相の出力電圧は、Ｕｃｄ，Ｕｃｑの操作量に基づいて（７），（８）式から得られるＶｃｄ，Ｖｃｑを三相に逆変換することで求められる。その逆変換は、下記（１１）式で表せる。
【００２９】
【数２】

【００３０】
次に、図１を参照して具体的に説明する。電圧位相検出器４では、系統電源３から検出した三相検出電圧Ｖｓａ，Ｖｓｂ，Ｖｓｃに基づいて、系統電圧の位相を求めてサイン波（以下、ｓｉｎωｔと記す）とコサイン波（以下、ｃｏｓωｔと記す）の信号を発生する。三相／ｄｑ軸変換器６は、インバータ１の三相出力電流Ｉａ，Ｉｂ，Ｉｃを入力して、電圧位相検出器４から出力されるｓｉｎωｔ信号とｃｏｓωｔ信号から、ｄ軸電流Ｉｄとｑ軸電流Ｉｑを出力する。
【００３１】
ｄ軸電流Ｉｄは、減算器１１においてｄ軸電流設定値Ｉｄ’と比較され、その偏差がｄ軸電流制御回路７に入力される。ｄ軸電流制御回路７は、前記偏差が０になるような信号を出力する。このｄ軸電流制御回路７の出力Ｕｄｃとフィルタ１５の出力Ｖｓｄ２は、加算器１３において加算され、ｄ軸電圧設定値Ｖｃｄとしてｄｑ軸／三相変換器９に入力される。
【００３２】
同様に、ｑ軸電流Ｉｑは、減算器１２においてｑ軸電流設定値Ｉｑ’と比較され、その偏差がｑ軸電流制御回路８に入力される。ｑ軸電流制御回路８は、前記偏差が０になるような信号を出力する。このｑ軸電流制御回路８の出力Ｕｃｑとフィルタ１６の出力Ｖｓｑ２は、加算器１４において加算され、ｑ軸電圧設定値Ｖｃｑとしてｄｑ軸／三相変換器９に入力される。
【００３３】
ｄｑ軸／三相変換器９は、入力したｄ軸電圧設定値Ｖｃｄとｑ軸電圧設定値Ｖｃｑとを逆変換することによって三相電圧指令値Ｖｃａ’，Ｖｃｂ’，Ｖｃｃ’を得て、これらをパルス幅変調回路１０に出力する。パルス幅変調回路１０は、インバータの三相出力電圧Ｖｃａ，Ｖｃｂ，Ｖｃｃが三相電圧指令値Ｖｃａ’，Ｖｃｂ’，Ｖｃｃ’と等しくなるようにインバータ１を制御する。
【００３４】
次に、本実施例の特徴動作を図１を参照して説明する。三相／ｄｑ軸変換器５は、系統から三相電圧Ｖｓａ，Ｖｓｂ，Ｖｓｃを入力して、ｄ軸電圧Ｖｓｄ１とｑ軸電圧Ｖｓｑ１に変換する。フィルタ１５は、ｄ軸電圧Ｖｓｄ１を入力してｄ軸電圧Ｖｓｄ２として出力する。ここで、２軸変換された電圧は、正相電圧が直流、逆相電圧が２倍調波、高調波電圧が高調波成分となるため、低域フィルタを用いることにより、ｄ軸電圧Ｖｓｄ２は正相電圧成分のみとなる。同様に、フィルタ１６は、ｑ軸電圧Ｖｓｑ１を入力して系統電圧の正相分のみであるｑ軸電圧Ｖｓｑ２を出力する。
【００３５】
系統異常判定手段１７は、三相／ｄｑ変換器５の出力であるｄ軸電圧Ｖｓｄ１を入力する。ｄ軸電圧Ｖｓｄ１は、通常、系統電圧の正相分振幅値に相当する。系統異常判定手段１７は、ｄ軸電圧Ｖｓｄ１の変化率の絶対値｜ΔＶｓｄ１｜を演算して、所定の設定値ΔＶｍａｘと比較する。Ｖｓｄ１の変化率の絶対値｜ΔＶｓｄ１｜が、設定値ΔＶｍａｘより大きい場合は、系統異常発生と判断して、フィルタ１５，１６に対してそれらの時定数τｖを長い状態τｖ１から短い状態τｖ２に切り換える指令を出力する。この指令はＶｓｄ１の変化率の絶対値｜ΔＶｓｄ１｜が設定値ΔＶｍａｘより小さくなる状態が、設定された系統異常継続想定時間ｔ１を超過するまで継続される。言い換えると、系統電圧振幅の変化率｜ΔＶｓｄ１｜が、しきい値ΔＶｍａｘ以内に戻った状態が所定時間ｔ１だけ継続したことによって、系統異常の収束と判定している。
【００３６】
フィルタ時定数の具体例は、通常時にτｖ１＝２［ｍｓ］、系統異常時はτｖ２＝０．１［ｍｓ］である。フィルタ１５，１６は、（１２）式で表される機能を持つ構成とすることが望ましい。すなわち、ｉ回目のサンプリング時のフィルタ出力値Ｙ_ｉは、入力値Ｘ_ｉ、係数ａ、前回（ｉ―１）の出力値Ｙ_{ｉ ― １}の下で、
Ｙ_ｉ＝ａＸ_ｉ＋（１−ａ）Ｙ_{ｉ ― １} （１２）
となる特性を持つことである。このようにすれば、フィルタの時定数τｖが、τｖ＝τｖ１＝２［ｍｓ］からτｖ＝τｖ２＝０．１［ｍｓ］に短くなるときは、０．１［ｍｓ］の短時間に変化する。一方、τｖ２＝０．１［ｍｓ］からτｖ１＝２［ｍｓ］へと長くなるときは、２［ｍｓ］をかけて連続的に変化する。
【００３７】
また、系統異常継続想定時間ｔ１は、例えばｔ１＝２００［ｍｓ］である。検出電圧振幅の変化率ΔＶｓｄ１は、離散制御において検出電圧振幅の前回取込み値と今回取込み値の差分である。取込み周期は約１００［μｓ］、しきい値ΔＶｍａｘは、０．０３［ｐｕ］／１００［μｓ］としている。
【００３８】
系統電圧の急変がない場合は、系統異常判定手段１７において、電圧Ｖｓｄ１の変化率は小さくなっているため、判定手段１７はフィルタ１５及び１６に対して時定数切り換え指令を出力しない。これにより、フィルタ１５及び１６は、時定数が長い状態τｖ＝τｖ１（≧τｖ２）に保たれ、フィルタ出力Ｖｓｄ２，Ｖｓｑ２は、系統の検出電圧Ｖｓｄ１，Ｖｓｑ１に含まれる逆相分や高調波分は充分に除去された状態となる。
【００３９】
一方、系統電圧において、電圧の急変があった場合は、系統異常判定手段１７において、電圧Ｖｓｄ１の変化率は一定値よりも大きくなり、判定手段１７はフィルタ１５及び１６に対して時定数切り換え指令を直ちに出力する。例えば、サンプリングタイム１００［μｓ］とすれば、前回と今回のサンプリング電圧値そのものの偏差により、１００［μｓ］強で電圧の急変を検出できる。これにより、フィルタ１５及び１６は、直ちに短い時定数状態τｖ＝τｖ２（≦τｖ１）に切り換わり、フィルタ出力Ｖｓｄ２，Ｖｓｑ２は、系統の検出電圧Ｖｓｄ１，Ｖｓｑ１に含まれる逆相分や高調波分がほぼそのまま伝わる状態となる。
【００４０】
これにより、系統が定常状態では、系統異常判定手段１７における電圧Ｖｓｄ１の変化率が一定値以下であり、長い時定数のフィルタ１５，１６を通して系統電圧正相分が得られる。したがって、逆相電圧や高調波成分の影響をなくすことができ、きれいな波形でインバータ１を動作させることができる。
【００４１】
一方、系統異常で電圧急変が発生した場合には、系統異常判定手段１７における電圧Ｖｓｄ１の変化率が一定値を超え、フィルタ１５，１６の時定数切り換え指令が出力される。このため、短い時定数であるフィルタ１５，１６を通した制御に高速に切り換えられ、系統の瞬時電圧に高速に追従して応答できる。
【００４２】
したがって、本実施例の電力変換装置は、定常時における波形改善と異常時等における応答改善との双方を実現することができる。
【００４３】
図２は、本発明の第２の実施例による電力変換装置を示すブロック図である。なお、図１に示す第１の実施例の構成要素と同一のものには同一符号を付して説明を省略する。第１の実施例と異なる構成は、系統異常判定手段１７の入力信号がｄ軸電圧Ｖｓｄ１ではなく、ｑ軸電圧Ｖｓｑ１であることである。ｑ軸電圧Ｖｓｑ１は、通常時において系統電圧の位相に相当する。ｑ軸電圧Ｖｓｑ１が変動する状態は系統電圧位相が変動しており、系統異常状態にあることを意味する。
【００４４】
本実施例は、第１の実施例に比べ、系統異常判定手段１７の入力信号が異なるのみであり、入力信号の取扱いは第１の実施例と全く同一である。したがって、本実施例の電力変換装置は、第１の実施例の電力変換装置と全く同様に、定常時における波形改善と異常時等における応答改善との双方を実現することができる。
【００４５】
図３は、本発明の第１及び第２の実施例による系統電圧波形の挙動例である。２線地絡系統異常におけるｄ軸電圧Ｖｓｄ１、ｑ軸電圧Ｖｓｑ１の解析波形と、フィルタ時定数切り換えにより算出されたｄ軸電圧Ｖｓｄ２、ｑ軸電圧Ｖｓｑ２の解析波形である。フィルタを通過する前の信号である電圧Ｖｓｄ１とＶｓｑ１に注目すると、通常時はＶｓｄ１＝１［ｐｕ］、Ｖｓｑ１＝０［ｐｕ］付近で細かく振動しており、系統異常時にＶｓｄ１、Ｖｓｑ１が大きく変動していることが正相電圧軌跡から理解できる。フィルタを通過した後の信号であるＶｓｄ２（Ｖｓｑ２も同じ）に注目すると、通常時はＶｓｄ２＝１［ｐｕ］（Ｖｓｑ２＝０［ｐｕ］）付近でほぼ一定値になっている。また、系統異常時はＶｓｄ１（Ｖｓｑ１）とほぼ同じ挙動をしていることが正相電圧軌跡から理解できる。
【００４６】
これらの実施例の電力変換装置においては、系統電圧が定常状態であるときには、系統異常判定手段１７における系統の検出電圧振幅または検出電圧位相の変化率が所定の値よりも小さい。したがって、フィルタの時定数は長い状態となり、そのフィルタの出力を用いてインバータを制御する。これにより、電力変換装置は、インバータの出力において逆相電圧や高調波成分を減少させることができる。
【００４７】
更に、これらの実施例の電力変換装置は、系統異常によって電圧急変が発生した場合には、系統異常判定手段における系統の検出電圧振幅または検出電圧位相の変化率が所定の値よりも大きくなる。したがって、フィルタの時定数は短い状態となり、系統の検出電圧にほぼ追従した信号を用いてインバータを制御する。判定手段の入力信号として、フィルタを通過した信号を使用せず生の信号のみを使用しているため、フィルタによる検出遅れ、例えば１０［ｍｓ］がなく、約１００分の１である１００［μｓ］で判定が可能である。また、フィルタ出力と生信号を切り換えるのではなく、フィルタの時定数を切り換えるため、（１２）式で述べたように、フィルタ内部の積分成分が寄与して出力電圧補正信号が不連続に急変することがない。これにより、本電力変換装置は、電圧急変に対して安定して高速に応答することができる。
【００４８】
系統異常解析結果から、所定値以上の系統の検出電圧振幅又は位相の変化率が観測されるのは、系統異常発生直後と系統異常除去直後、再閉路直後が主である。それ以外の期間では前記変化率が所定の値より小さくなる状態が継続することが確認されている。前記変化率が所定の値より小さくなっていても系統異常が継続しているわけで、この期間にフィルタ時定数を短い状態から長い状態に戻すと電圧急変に対して高速に応答できず過電流を招いてしまう。一方、系統異常発生から異常除去を経由して高速再閉路までの時間は、電力事業者毎に一定の管理値内で実施されている。この管理値より若干長い時間を系統異常継続想定時間に設定する。これらの実施例の電力変換装置では、前記変化率が所定の値より小さくなる状態が、系統異常想定継続時間を超えて継続した場合に、フィルタの時定数を短い状態から長い状態に切り換えて、そのフィルタの出力を用いてインバータを制御する。充分な確認時限を持たせているため系統の検出電圧の変動が無い状況での切り換えが確保される。
【００４９】
なお、系統異常の様相によっては、中速再閉路、低速再閉路が選択される場合もあるが、この場合は、欠相検出、不足電圧検出により母線が遮断されるため、本発明でも対応できない領域となる。
【００５０】
【発明の効果】
本発明によれば、定常時においては、不平衡成分や高調波成分の出力を抑制するとともに、系統異常により系統電圧が急変した場合には、高速に応答して過電流の発生を防止し得る電力変換装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施例による電力変換装置を示すブロック図である。
【図２】本発明の第２の実施例による電力変換装置を示すブロック図である。
【図３】本発明の第１及び第２の実施例による系統電圧の挙動例を示す波形図である。
【符号の説明】
１…インバータ、２…誘導性インピーダンス、３…系統電源、４…電圧位相検出器、５，６…三相／ｄｑ軸変換器、７…ｄ軸電流制御回路、８…ｑ軸電流制御回路、９…ｄｑ軸／三相変換器、１０…パルス幅変調回路、１１，１２…減算器、１３，１４…加算器、１５，１６…フィルタ、１７…系統異常判定手段、１８…ＮａＳ電池。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power converter used in parallel with a power system, and more particularly to a power converter suitable for use in a power storage system and a reactive power compensator that stabilizes supply of system power.
[0002]
[Prior art]
As a power conversion device used for such a purpose, there are a power storage system in which a sodium-sulfur (NaS) battery and an inverter are combined, a reactive power compensator (SVC: Static Var Compensator), and the like. In these systems, an inverter is connected in parallel to the system via an inductive impedance. For example, in the power storage system, the inverter is controlled so that the NaS battery is charged with surplus power and the insufficient power is supplemented by discharging from the NaS battery. A reference current command is determined based on this power control system, and a voltage control circuit generates a voltage control signal so that the output current of the inverter matches the reference current. Further, there has been known an apparatus which corrects an output of an inverter by adding a detected voltage of a system to a voltage control signal, and immediately responds to a change in the system voltage when the change occurs. However, in the above-described power converter, power is supplied to the system following the system voltage. Therefore, if the system voltage includes an unbalanced component or a harmonic component, an unnecessary operation is performed on the component. Will do. For this reason, there has been a problem that the unbalance of the output voltage and the generated harmonics increase in the power converter in the steady state. As means for solving this, Patent Document 1 includes a filter that uses a system detection voltage as an input signal, and a switch that outputs one of an output signal of the filter and a system detection voltage signal. . Then, when the difference between the detection voltage signal and the filter output signal is larger than a predetermined value, a technique for switching the output of the switch to the detection voltage of the system voltage has been proposed.
[0003]
[Patent Document 1]
JP-A-07-123726 (whole)
[0004]
[Problems to be solved by the invention]
In Patent Literature 1, an output signal of a filter is used as an input of a detection circuit. Therefore, in principle, a certain detection delay occurs from occurrence of a system abnormality to detection of the phenomenon. For this reason, high-speed response to a sudden voltage change in the system is insufficient.
[0005]
An object of the present invention is to suppress the output of unbalanced components and harmonic components in a steady state, and to prevent the occurrence of overcurrent by responding quickly when the system voltage suddenly changes due to a system abnormality. An object of the present invention is to provide a power conversion device.
[0006]
The inventor analyzed the system abnormal waveform and found that immediately after the system abnormality occurred, the amplitude and phase of the detected voltage of the system suddenly changed, and the output voltage signal of the power converter was quickly corrected when the detected voltage of the system suddenly changed. It was found that if not possible, overcurrent would occur.
[0007]
Another object of the present invention is to correct the output voltage signal of the power converter at a high speed when the detected voltage of the system changes suddenly, and to suppress the occurrence of overcurrent.
[0008]
Further, according to the above analysis, it was found that the voltage signal of the system fluctuated drastically during the system abnormal period, and a divergence from the filter output signal was periodically observed. Then, when it is determined that the system abnormality has converged by mistake before the reclosing, and the voltage signal is switched to the output signal of the filter, the output voltage correction signal may suddenly change discontinuously and an overcurrent may occur. I found it to be.
[0009]
Still another object of the present invention is to accurately determine the timing of system abnormality convergence and suppress discontinuous sudden change of the output voltage correction signal and occurrence of overcurrent based on the discontinuous sudden change.
[0010]
[Means for Solving the Problems]
A feature of the present invention is that in a power conversion device configured to correct a voltage control signal in accordance with a detected voltage of a system, a low-pass filter having a variable time constant using a detected voltage of the system as an input signal before the correction signal. A filter, a system abnormality determining means for determining a system abnormality, and switching the time constant of the filter to a shorter state than before until the system abnormality determining means determines that the system abnormality has occurred. A time-constant switching means is provided for continuously returning the time constant of the filter to the previous long time-constant state in response to the determination of the convergence of the system abnormality.
[0011]
The term “continuous” as used herein is not necessarily limited to the case where the whole is continuous, but may be multi-stepped or may have a discontinuous portion in part. The point is to distinguish it from the one in which the time constant is switched at once in a step-like manner.
[0012]
As described above, by continuously returning the time constant of the filter to the long time constant state, occurrence of an overcurrent due to a sudden change in the voltage correction signal is prevented.
[0013]
According to another feature of the present invention, there is provided a means for determining a system abnormality in response to a change rate of a detected voltage amplitude or a phase of a system exceeding a threshold value, and the system abnormality determining means determines whether or not the system is abnormal. When the determination is made, the time constant of the filter is shorter than the other period or a means for taking in the detection voltage of the system as a correction signal without passing through the filter is provided.
[0014]
As described above, since the system abnormality is determined directly when the rate of change in the amplitude or phase of the detection voltage itself of the system exceeds the threshold value without passing through a filter, high-speed response to a sudden change in system voltage is achieved. To improve.
[0015]
Still another feature of the present invention is that a system abnormality is determined in response to a change rate of a detected voltage amplitude or a phase of a system exceeding a threshold, and the change rate falls below the threshold and the system is changed. The convergence of the system abnormality is determined in accordance with the lapse of a predetermined time after the abnormality determination.
[0016]
As described above, the system abnormality is directly determined without passing through the filter in accordance with the change rate of the amplitude or phase of the system detection voltage itself exceeding the threshold value, and the system abnormality convergence is determined for a predetermined time. The occurrence of overcurrent is prevented by introducing the element of (1).
[0017]
Other objects and features of the present invention will become apparent from the following description of embodiments.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
FIG. 1 is a block diagram showing a power converter according to a first embodiment of the present invention. The inverter 1 is connected in parallel to a system having a system power supply 3 via an inductive impedance 2. As the inductive impedance 2, a transformer for a converter or an AC reactor is generally used. In the power storage system, reference numeral 18 denotes a NaS battery.
[0020]
The voltage control circuit includes a voltage phase detector 4, three-phase / dq-axis converters 5, 6, a d-axis current control circuit 7, a q-axis current control circuit 8, a dq-axis / three-phase converter 9, a pulse width modulation circuit 10. , And subtracters 11 and 12 and adders 13 and 14. Voltage control signals Ucd and Ucq are generated in accordance with the difference between the output currents Ia to Ic of the inverter 1 and the d-axis and q-axis current set values Id ′ and Iq ′, which are reference currents. And controlling the output voltage of the inverter. Further, the voltage control circuit corrects the voltage control signals Ucd and Ucq according to system detection voltages Vsa to Vsc to obtain Vcd and Vcq. At this time, the filters 15 and 16 are receiving the system detection voltage via the three-phase / dq-axis converter 5. The system abnormality determination unit 17 outputs a system abnormality occurrence flag τv, and the filters 15 and 16 switch the response time constant to a short state when a system abnormality occurs, and switch the response time constant to a long state otherwise.
[0021]
Next, the operation of the present embodiment will be described. First, an outline of the basic operation of the present embodiment will be described. The voltages of the respective phases output from the inverter 1 are Vca, Vcb, and Vcc, the voltages of the respective phases of the system are Vsa, Vsb, and Vsc, and the currents flowing through the respective phases of the system are Ia, Ib, and Ic. Assuming that the inductance of the inductive impedance 2 is L and the resistance is ignored, the following equations (1) to (3) are established between the above-mentioned quantities.
[0022]
L · (dIa / dt) = Vca−Vsa (1)
L · (dIb / dt) = Vcb−Vsb (2)
L · (dIc / dt) = Vcc−Vsc (3)
Here, a conversion operation to the dq2 axis is performed. For conversion to the dq2 axis, for example, a conversion operation is performed on the output voltage of the inverter 1 using the following equation (4). The same applies to other quantities.
[0023]
(Equation 1)

[0024]
If the above conversion operation is performed for equations (1) to (3), equations (5) and (6) are obtained.
[0025]
L · (dId / dt) = Vcd−Vsd−ωLIq (5)
L · (dIq / dt) = Vcq−Vsq + ωLId (6)
Here, Vcd and Vcq are amounts obtained by converting the voltage generated by the inverter 1 into two axes, Vsd and Vsq are amounts obtained by converting the system voltage into two axes, Id and Iq are amounts obtained by converting the current of the inverter 1 into two axes, ω is the angular frequency of the system voltage.
[0026]
Further, the output voltage of the inverter 1 is determined based on the following equations (7) and (8).
[0027]
Vcd = Vsd + ωLIq + Ucd (7)
Vcq = Vsq−ωLId + Ucq (8)
Substituting equations (7) and (8) into equations (5) and (6) yields equations (9) and (10).
[0028]
L · (dId / dt) = Ucd (9)
L · (dIq / dt) = Ucq (10)
From the above equations (9) and (10), it can be seen that Ucd should be controlled to control Id, and Ucq should be controlled to control Iq. Therefore, the output voltage of each phase of the inverter 1 is obtained by inversely converting Vcd and Vcq obtained from the equations (7) and (8) into three phases based on the manipulated variables of Ucd and Ucq. The inverse transformation can be expressed by the following equation (11).
[0029]
(Equation 2)

[0030]
Next, a specific description will be given with reference to FIG. The voltage phase detector 4 determines the phase of the system voltage based on the three-phase detection voltages Vsa, Vsb, and Vsc detected from the system power supply 3 to obtain a sine wave (hereinafter, referred to as sinωt) and a cosine wave (hereinafter, cosωt). ) Is generated. The three-phase / dq-axis converter 6 receives the three-phase output currents Ia, Ib, and Ic of the inverter 1 and obtains the d-axis current Id and the q-axis current from the sinωt signal and the cosωt signal output from the voltage phase detector 4. The current Iq is output.
[0031]
The d-axis current Id is compared with the d-axis current set value Id ′ in the subtractor 11, and the deviation is input to the d-axis current control circuit 7. The d-axis current control circuit 7 outputs a signal such that the deviation becomes zero. The output Udc of the d-axis current control circuit 7 and the output Vsd2 of the filter 15 are added in the adder 13 and input to the dq-axis / three-phase converter 9 as a d-axis voltage set value Vcd.
[0032]
Similarly, the q-axis current Iq is compared with the q-axis current set value Iq ′ in the subtractor 12, and the deviation is input to the q-axis current control circuit 8. The q-axis current control circuit 8 outputs a signal such that the deviation becomes zero. The output Ucq of the q-axis current control circuit 8 and the output Vsq2 of the filter 16 are added in the adder 14 and input to the dq-axis / three-phase converter 9 as a q-axis voltage set value Vcq.
[0033]
The dq-axis / three-phase converter 9 obtains three-phase voltage command values Vca ′, Vcb ′, and Vcc ′ by inversely converting the input d-axis voltage set value Vcd and q-axis voltage set value Vcq. Is output to the pulse width modulation circuit 10. The pulse width modulation circuit 10 controls the inverter 1 so that the three-phase output voltages Vca, Vcb, Vcc of the inverter become equal to the three-phase voltage command values Vca ′, Vcb ′, Vcc ′.
[0034]
Next, the characteristic operation of the present embodiment will be described with reference to FIG. The three-phase / dq-axis converter 5 receives three-phase voltages Vsa, Vsb, and Vsc from the system and converts them into a d-axis voltage Vsd1 and a q-axis voltage Vsq1. The filter 15 receives the d-axis voltage Vsd1 and outputs it as a d-axis voltage Vsd2. Here, the biaxially converted voltage is such that the positive-phase voltage is DC, the negative-phase voltage is a second harmonic, and the harmonic voltage is a harmonic component. Therefore, by using a low-pass filter, the d-axis voltage Vsd2 becomes Only the positive phase voltage component is provided. Similarly, the filter 16 receives the q-axis voltage Vsq1 and outputs a q-axis voltage Vsq2 that is only the positive-phase component of the system voltage.
[0035]
The system abnormality determination unit 17 receives the d-axis voltage Vsd1 output from the three-phase / dq converter 5. The d-axis voltage Vsd1 usually corresponds to the positive phase amplitude value of the system voltage. The system abnormality determination means 17 calculates the absolute value | ΔVsd1 | of the rate of change of the d-axis voltage Vsd1 and compares it with a predetermined set value ΔVmax. If the absolute value | ΔVsd1 | of the rate of change of Vsd1 is larger than the set value ΔVmax, it is determined that a system abnormality has occurred, and the time constants τv of the filters 15 and 16 are switched from the long state τv1 to the short state τv2. Output command. This command is continued until the absolute value | ΔVsd1 | of the rate of change of Vsd1 becomes smaller than the set value ΔVmax until the set system abnormality continuation expected time t1 is exceeded. In other words, when the rate of change | ΔVsd1 | of the system voltage amplitude returns within the threshold value ΔVmax for a predetermined time t1, it is determined that the system abnormality has converged.
[0036]
A specific example of the filter time constant is τv1 = 2 [ms] in a normal state, and τv2 = 0.1 [ms] in a system abnormality. It is desirable that the filters 15 and 16 have a configuration having a function represented by the expression (12). That is, the filter output value _{Y i} of the time of sampling of the i-th, the input value _{X i,} coefficients a, the output value _{Y i} of the previous (i-1) _- Under _{1,
Y i = aX i + (1} -a) Y i - 1 (12)
It has the following characteristics. In this way, when the time constant τv of the filter becomes shorter from τv = τv1 = 2 [ms] to τv = τv2 = 0.1 [ms], it changes in a short time of 0.1 [ms]. . On the other hand, when it becomes longer from τv2 = 0.1 [ms] to τv1 = 2 [ms], it changes continuously over 2 [ms].
[0037]
The system abnormality continuation assumed time t1 is, for example, t1 = 200 [ms]. The change rate ΔVsd1 of the detected voltage amplitude is a difference between the previously obtained value and the currently obtained value of the detected voltage amplitude in the discrete control. The fetch cycle is about 100 [μs], and the threshold value ΔVmax is 0.03 [pu] / 100 [μs].
[0038]
When there is no sudden change in the system voltage, the change rate of the voltage Vsd1 in the system abnormality judgment unit 17 is small, so that the judgment unit 17 does not output a time constant switching command to the filters 15 and 16. As a result, the filters 15 and 16 are kept in a state in which the time constant is long τv = τv1 (≧ τv2), and the filter outputs Vsd2 and Vsq2 have the opposite phase components and harmonic components included in the system detection voltages Vsd1 and Vsq1. It will be in a state of being sufficiently removed.
[0039]
On the other hand, when there is a sudden change in the system voltage, the change rate of the voltage Vsd1 becomes larger than a fixed value in the system abnormality judging unit 17, and the judging unit 17 instructs the filters 15 and 16 to switch the time constant. Is output immediately. For example, if the sampling time is 100 [μs], a sudden change in the voltage can be detected at a little over 100 [μs] due to the difference between the previous and current sampling voltage values. As a result, the filters 15 and 16 immediately switch to the short time constant state τv = τv2 (≦ τv1), and the filter outputs Vsd2 and Vsq2 have the negative phase components and harmonic components included in the system detection voltages Vsd1 and Vsq1. It will be transmitted almost as it is.
[0040]
Accordingly, when the system is in a steady state, the rate of change of the voltage Vsd1 in the system abnormality determination means 17 is equal to or less than a certain value, and the system voltage positive phase component is obtained through the filters 15 and 16 having long time constants. Therefore, the influence of the negative phase voltage and the harmonic component can be eliminated, and the inverter 1 can be operated with a clean waveform.
[0041]
On the other hand, when a sudden change in voltage occurs due to a system abnormality, the rate of change of the voltage Vsd1 in the system abnormality determination means 17 exceeds a certain value, and a time constant switching command for the filters 15 and 16 is output. Therefore, the control is quickly switched to the control through the filters 15 and 16 having a short time constant, and the response can be made to follow the instantaneous voltage of the system at a high speed.
[0042]
Therefore, the power conversion device according to the present embodiment can achieve both a waveform improvement in a steady state and a response improvement in an abnormal state.
[0043]
FIG. 2 is a block diagram showing a power converter according to a second embodiment of the present invention. The same components as those of the first embodiment shown in FIG. The configuration different from the first embodiment is that the input signal of the system abnormality determination means 17 is not the d-axis voltage Vsd1 but the q-axis voltage Vsq1. The q-axis voltage Vsq1 normally corresponds to the phase of the system voltage. A state in which the q-axis voltage Vsq1 fluctuates means that the system voltage phase has fluctuated and is in a system abnormal state.
[0044]
This embodiment is different from the first embodiment only in the input signal of the system abnormality judging means 17, and the handling of the input signal is exactly the same as the first embodiment. Therefore, the power converter of the present embodiment can realize both the improvement of the waveform at the time of steady state and the improvement of the response at the time of abnormality or the like, just like the power converter of the first embodiment.
[0045]
FIG. 3 is an example of the behavior of the system voltage waveform according to the first and second embodiments of the present invention. 5 shows an analysis waveform of a d-axis voltage Vsd1 and an analysis waveform of a q-axis voltage Vsq1 in a two-line ground fault system abnormality, and an analysis waveform of a d-axis voltage Vsd2 and a q-axis voltage Vsq2 calculated by switching a filter time constant. Paying attention to the voltages Vsd1 and Vsq1, which are signals before passing through the filter, they normally vibrate finely near Vsd1 = 1 [pu] and Vsq1 = 0 [pu], and Vsd1 and Vsq1 fluctuate greatly when the system is abnormal. Can be understood from the positive-sequence voltage locus. Focusing on Vsd2 (also Vsq2), which is a signal after passing through the filter, it is almost constant at around Vsd2 = 1 [pu] (Vsq2 = 0 [pu]) in normal times. Also, it can be understood from the positive-phase voltage locus that the behavior is almost the same as Vsd1 (Vsq1) when the system is abnormal.
[0046]
In the power converters of these embodiments, when the system voltage is in a steady state, the change rate of the detected voltage amplitude or detected voltage phase of the system in the system abnormality determination means 17 is smaller than a predetermined value. Therefore, the time constant of the filter becomes long, and the inverter is controlled using the output of the filter. Thereby, the power converter can reduce the negative-phase voltage and the harmonic component in the output of the inverter.
[0047]
Furthermore, in the power converters of these embodiments, when a sudden change in voltage occurs due to a system abnormality, the change rate of the detected voltage amplitude or detected voltage phase of the system in the system abnormality determination means becomes larger than a predetermined value. Therefore, the time constant of the filter is short, and the inverter is controlled using a signal substantially following the detected voltage of the system. Since only the raw signal is used as the input signal of the determination means without using the signal passed through the filter, there is no detection delay by the filter, for example, 10 [ms], and is 100 [μs], which is about 1/100. ] Can be used for the determination. Further, since the time constant of the filter is switched instead of switching between the filter output and the raw signal, as described in the equation (12), the integrated component inside the filter contributes and the output voltage correction signal suddenly changes discontinuously. Nothing. Thereby, the present power converter can respond stably and rapidly to a sudden change in voltage.
[0048]
The change rate of the detected voltage amplitude or phase of a system having a predetermined value or more is observed from the system abnormality analysis result mainly immediately after the occurrence of the system abnormality, immediately after the system abnormality is removed, and immediately after the reclosing. It has been confirmed that the state in which the rate of change is smaller than a predetermined value continues during other periods. Even if the rate of change is smaller than a predetermined value, the system abnormality continues, and if the filter time constant is returned from a short state to a long state during this period, it is not possible to quickly respond to a sudden change in voltage, resulting in an overcurrent. Will be invited. On the other hand, the time from the occurrence of a system abnormality to the high-speed reclosing via the abnormality elimination is implemented within a certain management value for each electric power company. A time slightly longer than this management value is set as the system abnormality continuation estimated time. In the power converters of these embodiments, when the state in which the change rate is smaller than a predetermined value continues beyond the system abnormality assumed continuation time, the time constant of the filter is switched from a short state to a long state, The inverter is controlled using the output of the filter. Since there is a sufficient confirmation time limit, switching in a situation where there is no change in the detection voltage of the system is ensured.
[0049]
Depending on the state of the system abnormality, the medium-speed reclosing circuit and the low-speed reclosing circuit may be selected. In this case, the bus is cut off by the detection of the open phase and the detection of the undervoltage. Area.
[0050]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the output of an unbalanced component and a harmonic component can be suppressed at the time of a steady state, and when a system voltage changes suddenly by a system abnormality, it can respond quickly and can prevent generation | occurrence | production of overcurrent. A power converter can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a power converter according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a power converter according to a second embodiment of the present invention.
FIG. 3 is a waveform chart showing a behavior example of a system voltage according to the first and second embodiments of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Inverter, 2 ... Inductive impedance, 3 ... System power supply, 4 ... Voltage phase detector, 5, 6 ... Three-phase / dq-axis converter, 7 ... d-axis current control circuit, 8 ... q-axis current control circuit, 9: dq axis / three-phase converter, 10: pulse width modulation circuit, 11, 12: subtractor, 13, 14: adder, 15, 16: filter, 17: system abnormality determination means, 18: NaS battery.

Claims (7)

An inverter connected in parallel to the system via an inductive impedance, and a voltage control signal generated according to a difference between an output current of the inverter and a reference current, and an output voltage of the inverter is controlled according to the voltage control signal. A power control device having a voltage control circuit and correcting the voltage control signal in accordance with the detection voltage of the system, wherein the time constant variable is inserted at a stage preceding the correction signal and the detection voltage of the system is used as an input signal. A low-pass filter, system abnormality determining means for determining an abnormality in the system, and switching the time constant of the filter to a state shorter than before in response to the system abnormality determining means determining an abnormality in the system. In addition, in response to the system abnormality determination means determining the convergence of the system abnormality, the time constant of the filter is continuously returned to the previous long time constant state. Power conversion apparatus characterized by comprising a switching means. An inverter connected in parallel to the system via an inductive impedance, and a voltage control signal generated according to a difference between an output current of the inverter and a reference current, and an output voltage of the inverter is controlled according to the voltage control signal. In a power converter including a voltage control circuit and a low-pass filter inserted so as to correct the voltage control signal and having a detection voltage of the system as an input signal, a change rate of a detected voltage amplitude or a phase of the system. Means for determining a system abnormality according to exceeding the threshold value, and when the system abnormality determination means has determined an abnormality in the system, the time constant of the filter is shorter than other periods or the A power converter comprising: means for taking in the detected voltage of the system as a correction signal without using a filter. An inverter connected in parallel to the system via an inductive impedance, and a voltage control signal generated according to a difference between an output current of the inverter and a reference current, and an output voltage of the inverter is controlled according to the voltage control signal. A power conversion device having a voltage control circuit and correcting the voltage control signal in accordance with a detection voltage of a system, a low-pass filter having a detection voltage of the system as an input signal at a stage preceding the correction signal, It is determined that the system is abnormal when the rate of change of the detected voltage amplitude or phase of the system exceeds a threshold, and when a predetermined time elapses after the rate of change falls below the threshold and the system abnormality is determined. System abnormality determining means for determining the convergence of the system abnormality based on the time constant of the filter during the period when the determination means determines that the system is abnormal. Power conversion apparatus characterized by comprising means for capturing a correction signal to detect a voltage of the system without going through. An inverter connected in parallel to the system via an inductive impedance, and a voltage control signal generated according to a difference between an output current of the inverter and a reference current, and an output voltage of the inverter is controlled according to the voltage control signal. A power conversion device having a voltage control circuit and correcting the voltage control signal in accordance with a detection voltage of a system, a low-pass filter having a detection voltage of the system as an input signal at a stage preceding the correction signal, When the change rate of the detected voltage amplitude of the system exceeds the threshold value, it is determined that the system is abnormal, and when the change rate falls below the threshold value and a predetermined time has elapsed after the determination of the system abnormality, the system is determined to be abnormal. A system abnormality determining means for determining convergence of the abnormality; and a state in which the time constant of the filter is short during a period in which the determination means determines that the system is abnormal, and a long time constant during other periods. Power conversion apparatus characterized by comprising a means for switching. 5. The system according to claim 4, wherein the system abnormality determination unit includes a unit configured to convert the three-phase voltage of the system into a dq axis, and a unit configured to compare a change rate of the d-axis voltage obtained by the conversion with a predetermined value. A power converter characterized by the above-mentioned. An inverter connected in parallel to the system via an inductive impedance, and a voltage control signal generated according to a difference between an output current of the inverter and a reference current, and an output voltage of the inverter is controlled according to the voltage control signal. A power conversion device having a voltage control circuit and correcting the voltage control signal according to a detection voltage of a system, wherein a low-pass filter that uses the detection voltage of the system as an input signal at a stage preceding the correction signal; When the rate of change of the detected voltage phase of the system exceeds a threshold, it is determined that the system is abnormal, and when the rate of change falls below the threshold and a predetermined time has elapsed after the determination of the system abnormality, the system is determined to be abnormal. A system abnormality determining means for determining convergence of the abnormality; and a state in which the time constant of the filter is short during a period in which the determination means determines that the system is abnormal, and a long time constant during other periods. Power conversion apparatus characterized by comprising a means for switching. 7. The system according to claim 6, wherein the system abnormality determination unit includes a unit configured to convert the three-phase voltage of the system into dq axes, and a unit configured to compare a change rate of the q-axis voltage obtained by the conversion with a predetermined value. A power converter characterized by the above-mentioned.

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