JP5089834B2 - X-ray generator and X-ray CT apparatus using the same - Google Patents

Description

ここで，Cp ：一次側に換算した二次巻線の浮遊容量(F)，eo：真空の誘電率(F/m)，ee：油浸紙の比誘電率，r2：二次巻線の平均半径(m)，h2：一次，二次巻線の高さ(m)，n：高電圧トランスの巻数比，d：二次巻線の層間距離(m)，mLayer：二次巻線の層数，m2nd：一脚当たりの二次巻線の分割数，mLeg：脚数である。 200Vの交流電源からCT装置用に140kVの高電圧を得ようとすると，Ｘ線発生装置が電力を取り込むときの交流電圧の電圧降下を見込むと，インバータの入力電圧は360V程度しか見込むことができず，そのため巻数比は490ほどが必要になる。
【００４３】
この場合，例えば，(1)式で求められる一次側に換算した二次巻線の浮遊容量は，Cpは2.5μF程度である。このとき，一次巻線に流れる電流は，Ｘ線管に流れる管電流が小さい場合であっても100〜200Aにも達し，管電流が大きい場合にも常に有効な電力にこの二次巻線の浮遊容量に流れる無効電流が重畳されることになる。
【００４４】
この無効電流によってインバータや高圧変圧器で損失による熱が発生するため，高速スキャンＸ線ＣＴ装置用Ｘ線発生装置に必要な十分な管電流を出力できないばかりか，発生した熱の放散のために，冷却フィンや冷却用ファンを設けるなどの処置が必要となり、装置が大型化してしまう。
【００４５】
これに対して，図１で示した本発明の実施例では，ソフトスイッチングインバータ５の直流入力側に昇圧型高力率AC/DCコンバータを備えているために，この直流電圧を例えば600V〜800V程度まの高めることができ，高電圧変圧器６の巻数比が小さくても，たとえばn=180〜200でも十分な高電圧出力を得ることができるようになる。
【００４６】
この場合，高電圧変圧器６の一次巻線電流と，インバータに流れる電流は，巻数比が従来の490に比べて１／５〜１／４程度に低減し，高電圧変圧器６一次巻線の銅損と，ソフトスイッチングインバータ５の導通損失，特に管電流が小さいとき大幅に低減可能である。昇圧機能を持たない従来のダイオード式コンバータに対して，昇圧機能をもった本コンバータを用いることは，上述のようにＸ線発生装置の損失を低減するために非常に有効である。昇圧型AC/DCコンバータは単相交流電源用，３相交流電源用それぞれにいくつかの方式があるが，本実施例の趣旨は，昇圧機能があることと高力率であることが必要用件であって，その回路方式，制御方式には限定されない。
【００４７】
次に、ソフトスイッチング5について説明する。従来のインバータはこのインバータのスイッチング素子に電圧が印加されている状態でスイッチングするために大きなスイッチング損失を発生させるものであったが、図１に示した本実施例に用いたインバータは、スイッチング損失をほぼゼロにできるソフトスイッチングインバータである。
【００４８】
ソフトスイッチングインバータとは，インダクタやコンデンサを応用してインバータを構成するスイッチング素子のスイッチングによって発生する損失をほぼゼロにするものである。種々のソフトスイッチングインバータが提案されており、例えば，特開平6-22551号に開示されているものがある。図２は上記広報に開示されているソフトスイッチングインバータの一例を説明する図である。
【００４９】
図２において、301は直流電源，311〜314は直流電源301に接続されたコンデンサで，311と312，313と314はそれぞれ直列に接続され接続点が直流電源301の中間の電位を持つようになっている。321〜324は直流電源に接続されH型に構成された電力用半導体スイッチング素子，ここでは逆並列ダイオードオートが内蔵されているIGBT（絶縁ゲート型バイポーラトランジスタ）で表記している。この４つの半導体スイッチ321〜324で一つのインバータを構成している。302はインバータを構成するIGBT321〜324に接続された負荷で，図１に示した第一の実施例では高電圧変圧器の一次巻線以降（Ｘ線管まで）に相当する。341と342は，それぞれIGBT 321と322の接続点，323と324の接続点と前記コンデンサ311と312の接続点，313と314の接続点の間に接続されたインダクタである。331〜334はそれぞれIGBT 321〜324に並列に接続されたコンデンサである。
【００５０】
図３は図２で示したソフトスイッチングインバータの動作を示すタイムチャートである。IGBT 321と322，IGBT 323と324は，図３(a)〜(d)で示した駆動信号に従い，デューティ50%でれぞれ交互にオンオフ動作を繰り返す。そのうえでIGBT 321に対してIGBT 324が位相差φだけ遅れて動作することにより，負荷302に電圧を出力する時間を図３(e)のように制御して結果的に図１で示したＸ線管へ供給する直流高電圧（以下，管電圧という）を制御することができる。
【００５１】
また，同時に，IGBT 321〜324のスイッチング動作によってインダクタ341と342には図３(f)(g)のような三角波の電流が流れる。IGBT 321〜324には，インダクタ341，342がない場合には図３(h)〜(k)で細線で示した電流が流れるが，これらインダクタのために実際には太線で示した電流波形となる。
【００５２】
図３(h)〜(k)で示した電流は必ずマイナス方向の状態でスイッチがターンオンし，プラス方向のときオフする。マイナス方向に電流が流れているときはIGBTに内蔵されている逆並列ダイオートが導通している状態，すなわち，IGBTの電圧がほぼゼロの状態を意味し，この状態でIGBTがターンオンしてもスイッチング損失は発生しない。また，IGBTがターンオフするときは直ちにIGBTの電流がゼロになるものの，IGBTに並列に接続されたコンデンサ311〜314によって，IGBT両端の電圧上昇が遅れ，やはりスイッチング損失は生じない。
【００５３】
このように，インダクタ341，342，及び，コンデンサ331〜334を設けることによって，インバータにはスイッチング損失が生じない，ソフトスイッチングインバータを構成することができる。
【００５４】
図１に示した本発明の第一の実施例では，インダクタ21と，図１に図示省略したが図２のコンデンサ331〜334とでソフトスイッチングインバータを実現することを表している。
【００５５】
なお，図２で示したソフトスイッチングインバータでは，図３に示したように，左側のIGBT 321，322がもともとダイオードに電流が流れた状態でターンオンする性質があり，このような場合には左型のインダクタ341は省略することができる。
【００５６】
ソフトスイッチングインバータには図２で示した回路以外にも種々の回路方式が考えられる。たとえば，インダクタ341，342に流れる電流を抑制し，これらインダクタに流れる電流によって生じる損失を低減するために，インダクタに直列にスイッチを挿入することもできる。
【００５７】
これらに本発明は，昇圧型高力率AC/DCコンバータを高電圧で動作させる場合に，その高電圧動作化によってインバータ部分で増加するスイッチング損失を低減しようとするもので，その趣旨でソフトスイッチングインバータを用いるために，その回路方式を限定するものではない。
【００５８】
また，図１では，昇圧型高力率AC/DCコンバータで高電圧化された直流電圧を陽極駆動回路に接続して，Ｘ線管の陽極を駆動している。これは，昇圧型スタータの電圧として十分な高電圧を作り出せることを利用したもので，この構成も，別に高電圧の直流電源を設ける必要がなく，Ｘ線発生装置全体を小型化するのに役立っている。この陽極駆動回路の構成と動作は，特開2000-150193号等に詳述されているので，ここでは詳しい説明を省略する。
【００５９】
【発明の効果】
以上、本発明による効果を列記すれば以下のようになる。
【００６０】
（1）Ｘ線高電圧装置の効率向上により、スキャン時間の高速化によるＸ線管に流す電流の大電流化及びこの大電流で長時間のら旋スキャンに対応できる大出力のＸ線高電圧装 置を提供できる。
【００６１】
（2）上記Ｘ線高電圧装置の効率向上により、商用電源から該Ｘ線高電圧装置への電力を供給するスリップリングとブラシから成る電力伝達機構に流れる電流が低減し、該電力伝達機構の保守工数の低減と高信頼性、高画質のＸ線ＣＴ装置を提供できる。
【００６２】
（3）上記Ｘ線高電圧装置とＸ線管の陽極回転駆動回路を小型、軽量化して、これらをスキャナ回転盤に搭載できるようにしたので、スキャナ、テーブル及び画像処理ユニットを内蔵した操作卓の３つのユニットの構成となり、設置スペースの小さいＸ線ＣＴ装置を提供できる。
【図面の簡単な説明】
【図１】本発明の実施例を示す図。
【図２】ソフトスイッチングインバータの一例を示す図。
【図３】ソフトスイッチングインバータのタイミングチャートを示す図。
【符号の説明】
１…交流電源、111a，111b，111c，111d…スリップリング、102a，102b，102c，102d…ブラシ、31a，31b，31c，22，23，311，312，313，314，331，332，333，334…コンデンサ、21，32a，32b，32c，341，342…インダクタ、４…昇圧型高力率AC/DCコンバータ、５…ソフトスイッチングインバータ、６…高電圧変圧器、７…高電圧整流器、８…平滑コンデンサ、10…Ｘ線管、11…コンバータ制御回路、12…インバータ制御回路、80…Ｘ線発生装置、107…Ｘ線検出部、108…スキャナの回転部、109…被検体、110…画像表示装置、112…画像処理装置、116…検出器、117…アンプ、301…直流電源、321，322，323，324…絶縁ゲート型バイポーラトランシスタ（IGBT）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray generation apparatus and an X-ray computed tomography apparatus (hereinafter referred to as an X-ray CT apparatus), and more particularly, to improve the efficiency of the X-ray generation apparatus and to mount the X-ray generation apparatus. The present invention relates to an X-ray generator and an X-ray CT apparatus suitable for reducing maintenance man-hours, improving reliability, and reducing installation space.
[0002]
[Prior art]
The X-ray CT apparatus irradiates a subject with a fan-shaped X-ray beam from an X-ray tube, detects X-rays transmitted through the subject with an X-ray detector disposed at a position facing the X-ray tube, The detected data is image-processed to obtain a tomographic image of the subject.
[0003]
The X-ray detector is composed of hundreds of detection element groups arranged in an arc shape, and is arranged to face the X-ray tube with the subject interposed therebetween, corresponding to the number of detector elements. A plurality of radially distributed X-ray passages are formed, and the transmitted X-rays of the subject are detected at every predetermined angle when the X-ray tube and the detector are integrally rotated 360 degrees around the subject.
[0004]
In recent years, this X-ray CT apparatus has features such as “a wide range of scanning is possible in a short time” and “continuous data in the body axis direction can be obtained, thereby enabling generation of a three-dimensional image”. Rotational CT called helical scan or spiral scan has spread rapidly.
[0005]
In this CT, the time taken for multi-layer imaging from a wide range is greatly reduced by actively moving the imaging position during imaging, and three-dimensional CT imaging is possible.
[0006]
In other words, in this case, the rotation CT is a method in which the fixed scanner body performs continuous rotation scanning, and at the same time, the bed is continuously moved in the body axis direction, so that the X-ray tube is rotated relative to the subject. It is. In this way, the spiral scan changes the shooting position in parallel with the continuous rotation scan during shooting, so that the overall shooting time is shortened. Further, since continuous scanning is also performed in the body axis direction during photographing, three-dimensional data is collected.
[0007]
In order to realize this spiral scan, it is necessary to continuously rotate the scanner turntable. To that end, means for continuously supplying power to the X-ray tube mounted on the scanner turntable is required. Become. As this means, a power transmission mechanism comprising a slip ring and a brush is used, and a high voltage (hereinafter referred to as a tube voltage) is applied to the X-ray tube together with the X-ray tube on the scanner rotating disk. The high voltage generator for mounting is supplied, and the high voltage generator is supplied with electric power for generating required X-rays from the X-ray tube via the power transmission mechanism.
[0008]
Thus, since the high voltage generator is mounted on the scanner turntable and rotated at a high speed, it is desirable that the weight be as light as possible. For this reason, an inverter type X-ray high voltage apparatus that can reduce the size and weight of the high voltage transformer of the high voltage generator and reduce the pulsation of the tube voltage is used for the X-ray high voltage apparatus.
[0009]
This inverter type X-ray high voltage device converts a commercial AC power source into a DC voltage with a converter circuit, converts this DC voltage into an AC voltage with a frequency higher than the commercial power source frequency with an inverter circuit, The AC voltage is boosted by a high voltage transformer, the boosted AC high voltage is rectified to a DC high voltage by a high voltage rectifier, and the DC high voltage is applied to an X-ray tube to generate X-rays. The scanner turntable is equipped with a circuit after the high voltage transformer, that is, a high voltage generator, and the output of the inverter circuit is transferred to the high voltage transformer by the power transmission mechanism comprising the slip ring and the brush. It is configured to supply the required power.
[0010]
In order to reduce the size of the high voltage transformer and reduce the pulsation of the tube voltage waveform, the frequency of the inverter circuit is increased to 20 kHz or higher.
[0011]
[Problems to be solved by the invention]
As described above, in the spiral CT, the X-ray tube performs a spiral motion relative to the subject by moving the bed continuously in the body axis direction while the fixed scanner body performs a continuous rotational scan. Therefore, the continuous rotation scan time becomes long. Furthermore, in recent years, there is no motion artifact, and the scan time tends to be faster in order to enable diagnosis of the heart, and one scan time of 0.5 seconds or less has been demanded. .
[0012]
Thus, the high-speed rotation type X-ray CT apparatus of 0.5 seconds at the shortest must increase the X-ray output per short time in inverse proportion to the rotation time as compared with a low-speed apparatus. In other words, in order to obtain a good tomographic image with less granular noise, a large amount of X-ray dose is applied to the current flowing between the anode and cathode of the X-ray tube (hereinafter referred to as tube current) in inverse proportion to the scanner rotation speed. To generate X-rays to the subject, and the tube current is higher than that of the conventional one.
[0013]
Therefore, the X-ray tube needs to have a large capacity due to the increase in the tube current due to the increase in the scanning time and the increase in the imaging time due to the spiral scanning, and the inverter type X that supplies power to the X-ray tube High-voltage line voltage devices have become necessary. Specifically, an X-ray high voltage device that can output 60 kW continuously for 1 minute or longer is required. However, as the tube current increases, the current flowing through the power transmission mechanism consisting of the slip ring and the brush naturally increases, and the slip ring of the power transmission mechanism supplies a high current to the brush at high speed while sliding. Due to the nature of this, the contact surface between the two tends to generate heat, and roughening and seizure are likely to occur. For this reason, maintenance such as periodically polishing the surface of the slip ring or replacing the brush is necessary, and it is difficult to maintain reliability.
[0014]
On the other hand, in order to reduce the installation space, it is desired that the number of units of the X-ray CT apparatus is composed of only three units of a scanner, a table, and an operation console incorporating an image processing unit. In order to meet this demand, it is necessary to reduce the size and weight of the high-power X-ray high-voltage device described above so that it can be mounted on the scanner rotating section. However, increasing the output of the X-ray high voltage device increases the loss, which is difficult with the conventional technology. That is, it is necessary to make the X-ray high voltage device highly efficient. Normally, an inverter is composed of a power semiconductor switching element. This switching element causes a switching loss due to an overlap of voltage and current of the switching element during the turn-on operation and the turn-off operation. , Conduction loss occurs according to the product of the flowing current and the on-time voltage.
[0015]
Among these, when the inverter is operated with a DC input voltage of about 200V to 450V obtained by rectifying a commercial 200V or 400V AC power supply voltage, the switching loss is in a certain range, which is a big problem. However, in order to operate the entire X-ray generator efficiently, the DC input voltage of the inverter must be increased to reduce the current flowing through the circuit. For this purpose, it is necessary to increase the DC input voltage to about 600V to 800V. When the inverter is operated at such a high voltage, the switching loss in the semiconductor switching element constituting the inverter is reduced to the operating voltage. Therefore, there is a need to suppress this switching loss by special measures.
[0016]
In addition, the X-ray generator consisting of a converter, inverter, high-voltage transformer, high-voltage rectifier, and X-ray tube mounted on the rotating part has a centrifugal force of 6 to 15 times the gravity due to the rotation of the scanner rotating part. Receive. X-ray generators operating under such harsh conditions are designed to be small and lightweight so as to have sufficient mechanical strength. However, as described above, the conventional technology has a higher rotational speed. It is difficult to achieve higher output that is inversely proportional to the rotation time. In addition, a rotary drive type anode is employed for the anode of the X-ray tube in order to efficiently dissipate heat generated on the anode by radiation. In this anode drive, an induction motor type stator coil and a rotor that is driven at high speed integrally with the anode in a vacuum of an X-ray tube are arranged at a predetermined distance in order to obtain a dielectric strength. The driving efficiency is low, and the voltage supplied to the stator coil usually requires a high voltage of 500V to 850V. However, in the conventional X-ray CT apparatus, a step-up transformer is provided before supplying a driving voltage to the stator coil or a high-voltage DC power supply in order to operate with a 200V AC power supply. This is also one of the factors that hinders the reduction in size and weight.
[0017]
Therefore, the present invention provides
(1) Increase the efficiency of the X-ray high-voltage device, increase the current flowing through the X-ray tube by increasing the scan time, and the high output X-ray that can handle long-time spiral scanning with this large current Provide high voltage equipment.
[0018]
(2) By increasing the efficiency of the X-ray high-voltage device, the current flowing to the power transmission mechanism consisting of a slip ring and a brush that supplies power from a commercial power source to the X-ray high-voltage device is reduced. The number of maintenance man-hours for the mechanism is reduced, and the reliability of the X-ray CT apparatus is improved.
[0019]
(3) To provide an X-ray CT apparatus capable of reducing the installation space by mounting these on the scanner turntable by reducing the size and weight of the X-ray high voltage apparatus and the anode rotation drive circuit of the X-ray tube. For the purpose.
[0020]
[Means for Solving the Problems]
The above problems are solved based on the following.
First, in order to increase the efficiency of the X-ray high voltage apparatus, it is necessary to reduce the loss of each circuit constituting the X-ray high voltage apparatus. For this purpose, it is effective to reduce the current flowing through the circuit and the switching loss of the power semiconductor switching element.
[0021]
Therefore, in order to reduce the current flowing through the circuit, the phase of the voltage and the current flowing through the commercial AC power supply are matched to improve the power factor and reduce the reactive current. For this purpose, an AC / DC converter (converter) that converts commercial power into DC power is controlled by using a converter circuit of pulse width modulation control, and the phase of current and voltage flowing through the AC power is matched.
[0022]
Next, in order to reduce the current after the inverter circuit that inputs the output of the converter circuit converted to DC and converts it to AC again, the voltage input to the inverter circuit is increased.
[0023]
That is, the converter circuit employs a circuit system having a boosting function for increasing the voltage, and reduces the current flowing through the inverter circuit operating at a frequency much higher than the commercial power supply frequency. In order to reduce the switching loss, a so-called soft switching technique is used in which the voltage applied to the switching element of the inverter circuit is made zero and the switching element is turned on and off.
[0024]
As described above, the converter uses a pulse width modulation control type converter having a high power factor and a voltage boosting function, and the inverter is a software having a zero voltage turn-on and turn-off function capable of reducing switching loss. A switching inverter is used.
[0025]
Next, in order to reduce the current flowing through the power transmission mechanism composed of the slip ring and the brush, the converter and the inverter are used, and a power transmission mechanism is provided between the AC power source and the converter. If AC power is supplied to the converter, the current flowing through the slip ring and the brush is reduced, thereby suppressing the heat generation at the contact surface between them, and it becomes difficult to cause roughening and seizure, so the surface of the slip ring is polished. Or by replacing the brush, and so on.
[0026]
And by making the above X-ray high voltage devices highly efficient and using the output voltage of the converter as a DC power source for the anode rotation drive circuit of the X-ray tube, these devices can be made smaller and lighter, making them a scanner turntable. As a result, the X-ray CT apparatus can be configured with only three units including a scanner, a table, and an operation console incorporating an image processing unit, and the installation space of the X-ray CT apparatus can be reduced.
[0027]
Based on the above, the above object is achieved by the following.
[0028]
(1) AC power supply La A converter that converts the supplied AC voltage into a DC voltage, and a DC voltage connected to this converter Exchange An inverter that converts current, a high voltage transformer that is connected to the inverter and boosts the output AC voltage, and a rectifier that is connected to the high voltage transformer and converts the output voltage of the high voltage transformer to DC, The converter comprises an X-ray tube connected to the rectifying means, and the converter includes a full-wave rectifier circuit composed of a switch capable of self-extinguishing, and an AC input of the full-wave rectifier circuit End and Said Between AC power supply Inductor connected to ,Previous The phase of the phase current and phase voltage of the AC power supply are matched, and the output voltage of the full-wave rectifier circuit The Match target voltage Let As The self-extinguishing switch A converter control circuit for controlling, the inverter, A semiconductor switching element; Zero voltage switching means for turning on and off the switching element by setting the voltage of the semiconductor switching element to substantially zero When The switching element of the inverter according to the setting signal of the voltage applied to the X-ray tube and the current flowing through the X-ray tube The Turn on as well as Turn off Make Means to control timing Possess It consists of
[0029]
(2) above Zero voltage switching means has inductor and capacitor .
[0030]
(3) The output voltage of the converter is converted into alternating current by a second inverter, and the output of the second inverter is input to the anode driving means of the X-ray tube.
[0031]
(4) an X-ray tube, an X-ray detector that detects a transmitted X-ray dose distribution emitted from the X-ray tube and transmitted through the subject, and amplifies the detection signal; the X-ray tube and the X-ray detector; Rotating the scanner around the subject, an image processing apparatus that processes an output signal from the X-ray detection unit of the scanner rotating unit, and reconstructs a tomographic image of the diagnostic part, and this image processing In an X-ray CT apparatus having an image display device for displaying a tomographic image by inputting an output signal from the device, the scanner rotation unit includes the X described in (1), (2), and (3). Equipped with a line generator.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows, as an embodiment of the present invention, a power transmission mechanism composed of a slip ring and a brush that feeds AC power of an AC power source via an AC power source, a pulse width modulation control type AC / AC with a booster and a high power factor function. X consisting of DC converter (hereinafter referred to as step-up type high power factor AC-DC converter), inverter with zero voltage turn-on / turn-off means (hereinafter referred to as soft switching inverter), high-voltage transformer, X-ray tube, etc. It is a figure which shows the structure of the X-ray CT apparatus which mounted the line generator in the scanner rotation part.
[0033]
In FIG. 1, 1 is an AC power source, 102a, 102b, and 102c are connected to the AC power source 1 and brushes for transmitting this AC voltage to the rotating portion 108 of the scanner, 111a, 111b, and 111c are the brushes 102a, 102b, The brush 102a, 102b, 102c and the slip ring 111a, 111b, 111c constitute a power transmission mechanism that is a slip ring that rotates together with the scanner rotating unit 108 while being in contact with 102c. 31a to 31c are connected to each AC phase supplied from the slip ring 2, and capacitors for preventing high-frequency voltage pulsation from being transmitted to the AC power supply side. 32a to 32c are inserted in series to each AC phase. The inductor 4 is a step-up type high power factor AC / DC converter connected to the inductors 32a to 32c, and 5 is a soft switching inverter that converts the output DC voltage of the AC / DC converter into high frequency alternating current. Is connected to an auxiliary reactor 21 and capacitors 22, 23, which are connected to the DC side of the AC / DC converter 4, respectively. 6 is a high voltage transformer connected to the soft switching inverter to boost the high frequency AC voltage, 7 is a high voltage rectifier connected to the high voltage transformer 6 and converts the AC high voltage into a DC high voltage, and 8 is a high voltage. A capacitor connected to the rectifier 7 for smoothing the DC high voltage (including parasitic capacitance existing in a high voltage cable not shown), 10 is connected to the capacitor 8 and is supplied with X-rays from the supplied DC high voltage. X-ray tube generated.
[0034]
11 is a converter control circuit for controlling the AC / DC converter while detecting the current supplied to the step-up type high power factor AC / DC converter 4 via the slip ring 2 and the DC output voltage of the converter 4, This is an inverter control circuit that controls the soft switching inverter 5 so that a high DC voltage supplied to the X-ray tube 10 is input and becomes a desired voltage.
[0035]
14 is an anode drive circuit that is connected to the output side of the step-up type high power factor AC / DC converter, generates an alternating current of about 50 Hz to 200 Hz from this DC voltage, and rotationally drives the anode of the X-ray tube 10. It has the same structure and function as a normal induction motor inverter.
[0036]
Thus, the X-ray generator 80 is configured.
X-rays radiated from the X-ray tube 10 pass through the subject 109, are detected by the detector 116 that constitutes the X-ray detector 107, and are further amplified by the amplifier 117. 111d is a slip ring mounted on the rotating part 108 of the scanner, 102d is a brush that transmits an X-ray detection signal output from the amplifier 117 while contacting the slip ring 111d, and 112 is an X-ray detection signal transmitted from the brush. An image processing apparatus 110 that generates a tomographic image from the image processing apparatus 110 is an image display apparatus that is connected to the image processing apparatus 112 and displays the generated tomographic image.
[0037]
Next, the operation of the X-ray CT apparatus configured as described above will be described.
First, the X-ray generator 80 will be described.
[0038]
In the step-up type high power factor AC-DC converter 4, the input current to the slip ring 2 is a sine wave by the converter control circuit 11, and the power factor is made to coincide with the voltage input to the slip ring 2. The phase of the input current is controlled to be approximately 1. Furthermore, it is possible to have a boosting function that makes the DC output voltage higher than the peak value of the AC input voltage. Since the configuration and operation of an AC / DC converter having these functions are disclosed in Japanese Patent Laid-Open No. 7-50200, details are omitted.
[0039]
When such a high power factor AC / DC converter capable of receiving power at a high power factor is applied to the X-ray generator, the current flowing through the slip ring 2 can be minimized. That is, when a conventional full-bridge three-phase full-wave rectifier diode rectifier circuit is used, the ratio of effective power and apparent power input from the AC power source to the rectifier circuit, that is, the power factor is about 0.4 to 0.6. On the other hand, the AC / DC converter 4 used in the present invention connects inductors 32a to 32c between the AC power source output from the slip ring 2 and the converter 4, and these inductors and the converter DC output. A self-quenching switching element, for example, an insulated gate bipolar transistor (hereinafter abbreviated as IGBT) is connected between each of the positive side and the negative side of the full-bridge three-phase full-wave rectifier circuit, A diode is connected to each of these self-extinguishing switching elements in antiparallel to form a converter. The converter control circuit 11 is controlled so that the phase current and the phase voltage input to the converter are detected, the phases are matched, and the output voltage of the converter becomes a predetermined voltage. Therefore, in the case of the high power factor AC / DC converter capable of taking in power with a power factor of 1, the input current may be about 1 / 2.5-1 to 1.67 compared with the conventional diode rectifier circuit. Accordingly, the current flowing through the slip ring and the brush can be reduced, and heat generation due to power loss generated at the contact surface can be reduced, and a highly reliable X-ray generator can be configured. Furthermore, there is an effect that the capacity of the AC power source may be 60 to 70% of the conventional capacity.
[0040]
Furthermore, since the step-up type high power factor AC / DC converter 4 shown in FIG. 1 has a step-up function for making the DC output voltage higher than the peak value of the AC input voltage, the step-up type AC / DC converter 4 It is possible to operate the soft switching inverter 5 connected to the output side of the transformer at a high voltage, and to effectively reduce the stray capacitance of the secondary winding of the transformer 6 as seen from the primary side. It is possible to reduce the current generated in the soft switching inverter 5 and the primary winding current of the high voltage transformer 6 and to significantly reduce the loss generated in these circuits.
[0041]
The stray capacitance Cp of the secondary winding as seen from the primary winding side is “Hiroshi Takano, Takanobu Hatakeyama, Ikuo Nakaoka:“ Application of Transformer Resonance Type Large Capacity DC-DC Converter to Medical X-ray High Voltage Device ”, IEEJ It is known that it is proportional to the square of the turns ratio, as described in the Journal of Industrial Applications, Vol.117-D, No.2, pp. 133-141 (1997-2).
[0042]
[Expression 1]

Where Cp: stray capacitance (F) of secondary winding converted to primary side, eo: dielectric constant of vacuum (F / m), ee: relative permittivity of oil-impregnated paper, r2: secondary winding Average radius (m), h2: Primary and secondary winding height (m), n: High voltage transformer turns ratio, d: Secondary winding interlayer distance (m), mLayer: Secondary winding Number of layers, m2nd: number of secondary windings divided per leg, mLeg: number of legs. When trying to obtain a high voltage of 140kV for a CT device from a 200V AC power supply, the input voltage of the inverter can only be expected to be about 360V, considering the voltage drop of the AC voltage when the X-ray generator captures power. Therefore, the turn ratio should be about 490.
[0043]
In this case, for example, the stray capacitance of the secondary winding converted to the primary side obtained by Equation (1) is Cp of about 2.5 μF. At this time, the current flowing through the primary winding reaches 100 to 200 A even when the tube current flowing through the X-ray tube is small. Even when the tube current is large, the current of the secondary winding is always effective. The reactive current flowing in the stray capacitance is superimposed.
[0044]
This reactive current generates heat due to loss in the inverter and high-voltage transformer, so that not only the tube current necessary for the X-ray generator for high-speed scan X-ray CT can be output, but also for the dissipation of the generated heat. Measures such as providing cooling fins and cooling fans are required, and the apparatus becomes large.
[0045]
On the other hand, in the embodiment of the present invention shown in FIG. 1, since the step-up type high power factor AC / DC converter is provided on the DC input side of the soft switching inverter 5, this DC voltage is set to 600V to 800V, for example. Even if the turn ratio of the high voltage transformer 6 is small, a sufficient high voltage output can be obtained even when n = 180 to 200, for example.
[0046]
In this case, the primary winding current of the high voltage transformer 6 and the current flowing through the inverter are reduced to about 1/5 to 1/4 of the turns ratio compared to the conventional 490, and the high voltage transformer 6 primary winding is reduced. The copper loss and the conduction loss of the soft switching inverter 5, particularly when the tube current is small, can be greatly reduced. Using this converter having a boosting function as compared with the conventional diode type converter having no boosting function is very effective for reducing the loss of the X-ray generator as described above. There are several types of step-up AC / DC converters for single-phase AC power supplies and three-phase AC power supplies. The purpose of this example is to have a boost function and a high power factor. This is not limited to the circuit system and control system.
[0047]
Next, the soft switching 5 will be described. The conventional inverter generates a large switching loss because switching is performed in a state where a voltage is applied to the switching element of the inverter. However, the inverter used in this embodiment shown in FIG. This is a soft switching inverter that can reduce the power to almost zero.
[0048]
A soft switching inverter is one in which the loss caused by switching of switching elements constituting the inverter is reduced to almost zero by applying an inductor or a capacitor. Various soft switching inverters have been proposed, for example, one disclosed in Japanese Patent Application Laid-Open No. 6-25251. FIG. 2 is a diagram for explaining an example of the soft switching inverter disclosed in the above-mentioned public relations.
[0049]
In FIG. 2, 301 is a DC power supply, 311 to 314 are capacitors connected to the DC power supply 301, 311 and 312 and 313 and 314 are connected in series so that the connection point has an intermediate potential of the DC power supply 301. It has become. Reference numerals 321 to 324 are represented by IGBTs (insulated gate bipolar transistors), which are connected to a DC power source and configured in an H-type power semiconductor switching element, here an antiparallel diode auto. These four semiconductor switches 321 to 324 constitute one inverter. Reference numeral 302 denotes a load connected to the IGBTs 321 to 324 constituting the inverter. In the first embodiment shown in FIG. 1, the load corresponds to the primary winding and the subsequent windings (up to the X-ray tube) in the high voltage transformer. 341 and 342 are inductors connected between the connection point of IGBTs 321 and 322, the connection point of 323 and 324, the connection point of the capacitors 311 and 312 and the connection point of 313 and 314, respectively. Reference numerals 331 to 334 denote capacitors connected in parallel to the IGBTs 321 to 324, respectively.
[0050]
FIG. 3 is a time chart showing the operation of the soft switching inverter shown in FIG. The IGBTs 321 and 322 and the IGBTs 323 and 324 repeat ON / OFF operation alternately with a duty of 50% in accordance with the drive signals shown in FIGS. In addition, the IGBT 324 operates with a delay of the phase difference φ with respect to the IGBT 321 to control the time for outputting the voltage to the load 302 as shown in FIG. 3 (e). As a result, the X-ray shown in FIG. It is possible to control the DC high voltage supplied to the tube (hereinafter referred to as tube voltage).
[0051]
At the same time, a triangular wave current as shown in FIGS. 3F and 3G flows through the inductors 341 and 342 by the switching operation of the IGBTs 321 to 324. In the IGBTs 321 to 324, when the inductors 341 and 342 are not provided, the current indicated by the thin line in FIGS. 3 (h) to (k) flows. Become.
[0052]
The currents shown in FIGS. 3 (h) to 3 (k) are always in the negative direction, and the switch is turned on, and is turned off in the positive direction. When the current flows in the negative direction, it means that the anti-parallel die auto built in the IGBT is conducting, that is, the IGBT voltage is almost zero, and switching even if the IGBT is turned on in this state There is no loss. Further, when the IGBT is turned off, the IGBT current immediately becomes zero, but the voltage rise across the IGBT is delayed by the capacitors 311 to 314 connected in parallel to the IGBT, and no switching loss occurs.
[0053]
Thus, by providing the inductors 341 and 342 and the capacitors 331 to 334, it is possible to configure a soft switching inverter in which no switching loss occurs in the inverter.
[0054]
In the first embodiment of the present invention shown in FIG. 1, a soft switching inverter is realized by the inductor 21 and the capacitors 331 to 334 shown in FIG.
[0055]
In the soft switching inverter shown in FIG. 2, as shown in FIG. 3, the IGBTs 321 and 322 on the left side are originally turned on with current flowing in the diode. The inductor 341 can be omitted.
[0056]
Various circuit systems other than the circuit shown in FIG. 2 can be considered for the soft switching inverter. For example, in order to suppress the current flowing through the inductors 341 and 342 and reduce the loss caused by the current flowing through these inductors, a switch can be inserted in series with the inductor.
[0057]
The present invention is intended to reduce the switching loss that increases in the inverter part due to the higher voltage operation when the boost type high power factor AC / DC converter is operated at a high voltage. Since an inverter is used, the circuit system is not limited.
[0058]
In FIG. 1, a DC voltage increased by a step-up type high power factor AC / DC converter is connected to an anode drive circuit to drive the anode of the X-ray tube. This utilizes the fact that a sufficiently high voltage can be created as the voltage of the boost type starter, and this configuration also helps to reduce the size of the entire X-ray generator without the need for a separate high-voltage DC power supply. ing. Since the configuration and operation of this anode drive circuit are described in detail in Japanese Patent Application Laid-Open No. 2000-150193, detailed description thereof is omitted here.
[0059]
【Effect of the invention】
The effects according to the present invention are listed as follows.
[0060]
(1) By increasing the efficiency of the X-ray high-voltage device, the current flowing through the X-ray tube is increased by increasing the scanning time, and the high-output X-ray high voltage can be used for long-time spiral scanning with this large current. A device can be provided.
[0061]
(2) By improving the efficiency of the X-ray high-voltage device, the current flowing through the power transmission mechanism consisting of a slip ring and a brush that supplies power from the commercial power source to the X-ray high-voltage device is reduced. A reduction in maintenance man-hours, high reliability, and high image quality X-ray CT equipment can be provided.
[0062]
(3) The above X-ray high voltage device and X-ray tube anode rotation drive circuit have been reduced in size and weight so that they can be mounted on a scanner turntable, so a console with a built-in scanner, table and image processing unit. Thus, an X-ray CT apparatus having a small installation space can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing an example of a soft switching inverter.
FIG. 3 is a timing chart of a soft switching inverter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AC power supply, 111a, 111b, 111c, 111d ... Slip ring, 102a, 102b, 102c, 102d ... Brush, 31a, 31b, 31c, 22, 23, 311, 312, 313, 314, 331, 332, 333, 334: Capacitor, 21, 32a, 32b, 32c, 341, 342 ... Inductor, 4 ... Boost type high power factor AC / DC converter, 5 ... Soft switching inverter, 6 ... High voltage transformer, 7 ... High voltage rectifier, 8 DESCRIPTION OF SYMBOLS ... Smoothing capacitor, 10 ... X-ray tube, 11 ... Converter control circuit, 12 ... Inverter control circuit, 80 ... X-ray generator, 107 ... X-ray detection part, 108 ... Scanner rotation part, 109 ... Subject, 110 ... Image display device, 112 ... Image processing device, 116 ... Detector, 117 ... Amplifier, 301 ... DC power supply, 321, 322, 323, 324 ... Insulated gate type bipolar transistor (IGBT)

Claims (3)

A converter that converts AC voltage supplied from an AC power source to DC voltage, an inverter that is connected to the converter and converts DC voltage to AC, a high-voltage transformer that is connected to the inverter and boosts the output AC voltage, The rectifier is connected to the high voltage transformer and converts the output voltage of the high voltage transformer into a direct current, and an X-ray tube connected to the rectifier.
The converter includes a full-wave rectifier circuit configured by a switch capable of self-extinguishing, a first inductor connected between an AC input terminal of the full-wave rectifier circuit and the AC power source, and the AC power source. A converter control circuit for controlling the self-extinguishable switch so as to match the phase of the phase current and the phase voltage and match the output voltage of the full-wave rectifier circuit with the target voltage;
The inverter includes a semiconductor switching element, zero voltage switching means for turning on and off the switching element by setting the voltage of the semiconductor switching element to substantially zero, and the inverter for controlling the voltage applied to the X-ray tube. Means for controlling the timing of turning on and off the switching element ,
The zero voltage switching means comprises a second inductor and capacitor;
To reduce the loss current reactive current flowing to the stray capacitance of the high voltage transformer secondary winding is superposed is caused by flowing in the second inductor, the second inductor switch inserted in series An X-ray generating apparatus.   2. The X-ray generator according to claim 1, wherein an output voltage of the converter is converted into an alternating current by a second inverter, and an output of the second inverter is input to an anode driving means of the X-ray tube.   An X-ray detector that detects a transmitted X-ray dose distribution emitted from the X-ray tube and transmitted through the subject and amplifies the detection signal, and the X-ray tube and the X-ray detector are opposed to each other. A scanner rotation unit that rotates around, an image processing device that reconstructs a tomographic image of a diagnostic region by processing an output signal from an X-ray detection unit of the scanner rotation unit, and an output signal from the image processing device An X-ray CT apparatus comprising an image display apparatus for displaying a tomographic image, wherein the X-ray generator according to claim 1 is mounted on the scanner rotating unit.

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