JPH07294036A - Cryogenic refrigerator - Google Patents

Abstract

PURPOSE:To eliminate a phase conversion transformer which has been heretofore necessary to convert 3-phase AC currents to 3-phase AC currents and to simultaneously variably control not only a frequency but also a voltage in an inverter for controlling the synchronous motor of a cryogenic refrigerator. CONSTITUTION:An inverter steps up three-phase AC currents from a power source by a step-up transformer, then converts it to a DC current by a converter 5, and then converts it to 2-phase AC currents by a special purpose converter 7. In this case, the temperature of a cryogenic refrigerator is detected by a temperature sensor. When the temperature is high, a control circuit 11 sets the set frequency of the 2-phase AC currents to a high value. When the set frequency of the 2-phase AC currents is set to a high value, the set voltage is also similarly set to the high value to eliminate a decrease in the torque of a synchronous motor 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic refrigerator.

[0002]

2. Description of the Related Art A cryogenic refrigerator is, for example, a helium compressor and a cryogenic expander connected in a closed circuit.
It is known that when the cryogenic refrigeration system is started, the number of cycles of compression / expansion is increased by increasing the rotation speed of the electric motor to shorten the time until the low temperature is stabilized, that is, the cooling down time. The change of the rotation speed of the electric motor is performed by the inverter device. That is, the rotation speed of the electric motor is changed by changing the frequency of the alternating current from the power source.

However, when the electric motor is a synchronous motor, a two-phase alternating current with a 90-degree phase shift is required.

In order to obtain this two-phase alternating current, generally, a series oscillation circuit is formed by a single-phase alternating current power source, the constant of the coil of the Sycinnas motor, an external capacitor, and a resistor. , A two-phase alternating current with a phase difference of 90 degrees is generated and used. However, in order to change the frequency as described above, it is necessary to make the constant of the oscillation circuit variable. For this purpose, it is conceivable to make the capacity of the condenser variable, but since there is no variable condenser having a capacity withstand voltage used for this purpose, the rotational speed of the synchronous motor could not be changed.

Therefore, in Japanese Patent Laid-Open No. 261094/1990, the frequency of the three-phase alternating current from the power source is variable by using a general-purpose three-phase general-purpose inverter, and the three-phase alternating current is converted into two phases through a phase conversion transformer. It was connected to a synchronous motor.

[0006]

However, according to the conventional technique (JP-A-2-261094), the AC current output from the general-purpose three-phase inverter is input to the phase conversion transformer, and this AC current is Since harmonics are included, the loss in the phase conversion transformer becomes large. Further, since the loss becomes large, it is difficult to make the voltage variable in addition to making the frequency of the two-phase alternating current variable.

The present invention has been made in order to solve the above problems, and has a small power loss, and can easily perform not only frequency variable but also voltage variable control, and the rotational speed of a synchronous motor. It is an object of the present invention to provide a cryogenic refrigeration system that can be changed.

[0008]

In order to achieve the above object, the invention of claim 1 is a cryogenic refrigerator operated by a synchronous motor, wherein the temperature for detecting the temperature of the cryogenic refrigerator is used. The one-phase or three-phase alternating current from the sensor, the control circuit unit that increases the set frequency as the temperature detected by the temperature sensor is higher, and the two-phase alternating current with a 90-degree phase difference of the set frequency are converted. A cryogenic refrigeration system including an inverter device and a synchronous motor driven by a two-phase alternating current of the set frequency.

Further, in the second aspect of the present invention, the inverter device further comprises a step-up transformer for stepping up the voltage of the one-phase or three-phase alternating current from the power source, and the step-up transformer for converting the boosted one-phase or three-phase alternating current to the direct current. And a converter section for converting a direct current into a two-phase alternating current of a set frequency, and the control circuit section also increases a set voltage of the two-phase alternating current when the set frequency is increased. The cryogenic refrigerator according to Item 1.

[0010]

The temperature sensor detects the temperature of the cryogenic refrigerator, and if the detected temperature is high, the control circuit unit raises the set frequency. Based on this set frequency, the inverter device supplies the 1-phase or 3-phase alternating current from the power source with a 2-degree phase difference of 2 degrees.
Convert to phase alternating current. Therefore, the synchronous motor is driven by the two-phase alternating current having the set frequency.
In the invention of claim 2, the alternating current from the power source is stepped up by the step-up transformer, converted into the direct current in the converter section, and converted into the two-phase alternating current in the inverter section. Further, when the frequency of the two-phase alternating current is increased, the set voltage is also increased by the circuit unit that controls the inverter unit.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS.
Will be explained. That is, FIG. 1 is an overall schematic view, and the configuration of the inverter device of FIG. 1 is shown in FIG. A more specific circuit of FIG. 2 is shown in FIG.

In this embodiment, the alternating current of the power supply is 1
It is a three-phase alternating current with a phase difference of 20 degrees. This power source is first connected to the step-up transformer 3 in the inverter device 1. The step-up transformer 3 is connected to a converter unit 5 that converts a three-phase alternating current into a direct current. The converter unit 5 is connected to an inverter unit 7 that converts a direct current into a two-phase alternating current.

The converter section 3 comprises a plurality of diodes 9 for rectifying each phase. The inverter unit 7 is composed of a plurality of transistors 13 that are driven by the switching timing controlled by the control circuit unit 11. Control circuit unit 11
When the set frequency of the two-phase alternating current generated by controlling the switching timing of the transistor 13 is increased, the control is performed to increase the set voltage at the same time. Between the diode 9 and the transistor 13, there is provided a capacitor 15 for smoothing the DC current rectified by the diode 9 and having unevenness.

The inverter unit 7 includes the synchronous motor 1
Connected to 7. In the synchronous motor 17, two electromagnets 19 rotate a rotor 21 made of a permanent magnet.

The synchronous motor 17 drives a drive mechanism (not shown) of the cryopump unit 23 to operate the cryogenic refrigerator. For example, the cold panel 23 of the cryopump unit 23 that constitutes the cryogenic refrigerator.
A temperature sensor 25 is provided at P and sends a detection signal to the temperature detection device 27. The temperature detecting device 27 processes the detection signal and sends it to the control circuit unit 11 as a temperature signal.

The operation of this embodiment will be described below. First, a three-phase alternating current with a phase difference of 120 degrees is fed from the power source. Then, first, the voltage of each phase is boosted by the boosting transformer 3 (FIGS. 3A and 3B). After that, rectification is performed by the diode 9 of the converter unit 5 to generate a direct current (FIG. 3 (C)). The direct current immediately after leaving the diode 9 has irregularities, but is smoothed by the capacitor 15 (FIG. 3 (D)).

Then, the transistor 1 of the inverter unit 7
A pulsed voltage having an arbitrary pulse width and interval is generated by the three groups (FIG. 3 (E)), and a two-phase alternating current is generated as a whole (dotted line in FIG. 3 (E)). At this time, the switching of the transistor 13 is performed when the output two-phase alternating current is 9
The timing is controlled so as to have a 0 degree phase difference.

The frequency and voltage of this two-phase alternating current can be arbitrarily changed. That is, the control circuit unit 11 is the transistor 1
By changing the switching timing of No. 3, the frequency can be reduced (FIG. 3 (E)) or increased (FIG. 3 (F)) by changing the interval of each pulse. In addition, the voltage can be increased by changing the pulse width or the like and changing the pulse density (FIG. 3F).

The frequency or voltage is set by the control circuit unit 11 based on the temperature detected by the temperature sensor 25. That is, the temperature of the cryogenic refrigeration system is controlled by the temperature sensor 25.
Is detected and the set frequency is increased when the detected temperature is high. When the temperature is low, the set frequency is lowered.

For example, when the detected temperature is higher than the set temperature of 20K, a two-phase alternating current having a high frequency, for example 100 Hertz, is output. As a result, the rotational speed of the synchronous motor 17 is increased. When the temperature becomes lower than the set temperature, a two-phase alternating current having a steady frequency, for example, 60 hertz is output. As a result, the synchronous motor 17 has a steady rotation speed.

Further, when the set frequency is increased, the set voltage is also increased. The relationship between the frequency and the voltage is determined in advance so that the magnitude of the current supplied to the synchronous motor 17 is constant.

Electromagnet 19 excited by this two-phase current
Rotates the rotor 21, which is a permanent magnet.

As described above, according to this embodiment, the general-purpose three-phase inverter is not used to generate the two-phase AC current as in the conventional case, but the inverter device 1 for exclusive use is used.
As a result, a two-phase alternating current is generated, so that the alternating current output from the inverter device 1 is directly supplied to the synchronous motor 17 instead of via the phase conversion transformer as in the conventional case.
Can be supplied to. Therefore, the two-phase AC current including the harmonics does not have to pass through the phase conversion transformer as in the conventional case,
Power loss is small. Further, since it is not necessary to use a conventional phase conversion transformer, it is possible to easily control the voltage of the two-phase alternating current.

Further, since the alternating current from the power source is boosted in advance by the step-up transformer 3, an output voltage higher than the power source voltage can be supplied to the synchronous motor. In other words,
The setting width of the set voltage can be made sufficiently wide beyond the power supply voltage. Furthermore, since the step-up transformer 3 is provided in the front stage part of the inverter device 1, a two-phase alternating current including harmonics does not pass through the step-up transformer 3, and therefore power loss due to the step-up transformer 3 can be avoided. .

Since the set frequency and the set voltage of the two-phase alternating current are set by the temperature of the cryogenic refrigerator detected by the temperature sensor 25, the synchronous motor 17 can be reliably controlled up to the desired set temperature. . In this regard, conventionally, as described in, for example, Japanese Patent Application Laid-Open No. 60-171359, there is a technique in which the frequency of an alternating current to an electric motor is variable by an inverter device according to the pressure of helium gas flowing in a closed circuit. However, since this embodiment is controlled by temperature rather than pressure, control will be more direct.

Although the frequency is controlled stepwise by the set temperature in the above embodiments, it is possible to control the frequency continuously rather than stepwise in other embodiments. Further, in the above embodiments, the alternating current from the power source is a three-phase alternating current, but in other embodiments, it is 1
It may be a phase alternating current.

In the above embodiments, the inverter section 7 is explained as a so-called PWM inverter, but in other embodiments it may be a voltage control inverter or a current control inverter.

In addition, in the above embodiment, the inverter section 7 uses a BPT (bipolar power transistor) (FIG. 3), but in other embodiments, a thyristor or another transistor such as IGBT or MOSFET is used. It may be used.

[0029]

As described above, claim 1 or 2
According to the invention, since the two-phase alternating current whose frequency is converted by the inverter device and which contains harmonics is not input to the transformer such as the phase conversion transformer like the alternating current converted by the conventional inverter device. , Power loss is small. Further, since the frequency of the two-phase alternating current is changed depending on the temperature of the cryogenic refrigerator, the synchronous motor can be reliably controlled to the set temperature desired by the cryogenic refrigerator.

According to the second aspect of the present invention, the two-phase alternating current output from the inverter device can be directly supplied to the synchronous motor without using a phase conversion transformer as in the conventional case. It is possible to easily control the voltage in the device to be variable. Also, when the set frequency is increased, the set voltage is also increased,
It is possible to prevent the current to the synchronous motor from becoming small, and thus to prevent the torque from becoming small, so that it is possible to prevent inconvenience such as step-out even if the frequency is changed. In addition, the set voltage of the two-phase alternating current can be made sufficiently high by first boosting the alternating current from the power source with the boost transformer.

[Brief description of drawings]

FIG. 1 is an overall schematic block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a main part of FIG.

FIG. 3 is a circuit diagram more specifically showing FIG.

[Explanation of symbols]

 1 Inverter device 3 Booster transformer 5 Converter part 7 Inverter part 9 Diode 11 Control circuit part 13 Transistor 15 Condenser 17 Synchronous motor 19 Electromagnet 21 Rotor 23 Cryopump unit 25 Temperature sensor 27 Temperature detection device

Claims (2)

[Claims] 1. A cryogenic refrigerator operated by a synchronous motor, wherein a temperature sensor for detecting the temperature of the cryogenic refrigerator and a control circuit for increasing the set frequency as the temperature detected by the temperature sensor increases. Section, an inverter device for converting a one-phase or three-phase alternating current from a power source into a two-phase alternating current having a 90-degree phase difference of the set frequency, and a synchronous motor driven by the two-phase alternating current of the set frequency. , A cryogenic refrigerator. 2. The inverter device comprises a step-up transformer for stepping up the voltage of a one-phase or three-phase alternating current from a power source, a converter section for converting the stepped up one-phase or three-phase alternating current into a direct current, and a direct current. The cryogenic refrigeration system according to claim 1, further comprising: an inverter section for converting the two-phase alternating current into a two-phase alternating current having a set frequency, and the control circuit section also increases the set voltage of the two-phase alternating current when the set frequency is increased.