JP2006214650A - Stirling refrigerating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Stirling refrigerating system capable of exercising refrigerating performance in maximum when a piston does not have the maximum stroke in spite of a state for maximizing the stroke of piston. <P>SOLUTION: A control device implements the control of overmodulation, when it is determined that the piston is operated with the maximum stroke, modulation factor of PWM reaches maximum modulation factor, and a present stroke is smaller than the maximum stroke by more than a prescribed value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a Stirling refrigeration system having a Stirling refrigerator and a control device that controls the Stirling refrigerator.

Conventionally, the refrigerating capacity of a Stirling refrigerator is controlled by a control device. In the Stirling refrigerator, the refrigerating capacity is determined according to the size of the stroke of the piston. Therefore, the control device increases the stroke of the piston when a large refrigeration capacity is required. On the other hand, the control device reduces the stroke of the piston when a small refrigerating capacity is required.
JP 2003-314919 A

  However, in the above-described conventional Stirling refrigeration system, although the piston of the Stirling refrigerator needs to be driven with the maximum stroke, the piston may not be driven with the maximum stroke due to a large load. As a result, the Stirling refrigerator may not be able to exhibit the desired refrigeration capacity, and the object may not be rapidly frozen.

  The present invention has been made in view of the above-described problems, and the object thereof is the piston stroke when the piston stroke is not driven at the maximum stroke even though the piston is driven at the maximum stroke. Is to provide a Stirling refrigeration system that can bring the maximum stroke close to the maximum stroke and exhibit the desired refrigeration capacity.

  The Stirling refrigeration system of the present invention includes a Stirling refrigerator and a control device that controls the Stirling refrigerator by PWM (Pulse With Module). The control device is generated by PWM when the piston state determining means for determining whether or not the piston is driven at the maximum stroke and the piston state determining means determines that the piston is driven at the maximum stroke. The modulation rate determination means for determining whether or not the modulation rate of the amplitude of the alternating waveform has reached the maximum modulation rate (100%), and the modulation rate determination means determined that the modulation rate has reached the maximum modulation rate. The stroke determination means for determining whether or not the current stroke of the piston is smaller than the maximum stroke by a predetermined value or more, and the stroke determination means determines that the current stroke of the piston is smaller than the maximum stroke by a predetermined value or more. In some cases, modulation control means for executing overmodulation control is included.

  According to the above control, the stroke of the piston can be brought close to the maximum stroke by overmodulation control, and a desired refrigeration capacity can be obtained even when the load is large.

  In overmodulation control, it is desirable to execute PWM so that the virtual modulation rate becomes the maximum stroke / (maximum stroke−predetermined value).

  In the Stirling refrigerator, the stroke of the piston is detected in order to prevent the piston and the displacer from colliding with each other. However, since the stroke is detected on the assumption that the AC waveform generated by PWM is a sine curve, the stroke cannot be detected in overmodulation control.

  According to the above control, even during overmodulation control, the piston and the displacer are prevented from colliding due to the piston stroke becoming too large. Therefore, the risk of damage to the Stirling refrigerator is reduced.

  The above-described system includes a temperature detector that detects the temperature of the high-temperature part or the low-temperature part of the Stirling refrigerator and transmits temperature information of the high-temperature part or the low-temperature part to the control device. During the modulation control, the temperature of the high temperature part is lower than the temperature of the high temperature part immediately before the over modulation control is executed, or the temperature of the low temperature part is stored immediately before the over modulation control is executed. It is desirable to end the overmodulation control when the temperature is higher than the temperature of the low temperature part.

  According to the above control, it is possible to prevent the overmodulation control from being continued even though the load of the Stirling refrigerator is small, so that the piston can be driven with a stroke larger than the maximum stroke. Is prevented. This prevents the piston and the displacer from colliding with each other. Therefore, the risk of damage to the Stirling refrigerator is reduced.

  In addition, the system described above further includes a direct current generating unit that outputs a direct current voltage to the control device in order to generate an alternating current waveform by PWM, the control device includes a voltage detector that detects the direct current voltage, and the modulation control means includes During overmodulation control, when the DC voltage is higher than the DC voltage immediately before the overmodulation control is performed, it is desirable to end the overmodulation control.

  According to the above control, the piston is prevented from being driven with a stroke larger than the maximum stroke due to an unexpected increase in the DC voltage, and the piston and the displacer are prevented from colliding with each other. Therefore, the risk of damage to the Stirling refrigerator is reduced.

  In addition, the above-described system detects the temperature of the high-temperature part of the Stirling refrigerator and transmits the temperature information of the high-temperature part to the control device, and detects the temperature of the low-temperature part of the Stirling refrigerator and sends it to the control device. A low-temperature detector that transmits temperature information of the low-temperature part, and the control device includes a temperature-difference calculating means for calculating a temperature difference between the high-temperature part and the low-temperature part, and the modulation control means is controlling overmodulation Furthermore, it is desirable to end the overmodulation control when the temperature difference is smaller than the temperature difference immediately before the overmodulation control is executed.

  According to the above control, it is possible to prevent the overmodulation control from being continued even though the load of the Stirling refrigerator is small. This prevents the piston from being driven with a stroke larger than the maximum stroke, and prevents the piston and the displacer from colliding with each other. Therefore, the risk of damage to the Stirling refrigerator is reduced.

  According to the present invention, when the piston is not driven at the maximum stroke even though the piston is driven at the maximum stroke, the piston stroke is brought close to the maximum stroke and the desired refrigeration capacity is exhibited. A Stirling refrigeration system can be obtained.

  First, the Stirling refrigerator used for the refrigerator of the embodiment will be described.

  Drawing 1 is a sectional view showing Stirling refrigerator 40 of an embodiment. In the Stirling refrigerator 40, a cylindrical piston 1 and a displacer 2 are fitted in a cylindrical cylinder 3 composed of two parts. The piston 1 and the displacer 2 are provided via a compression space 9 and have an axis Y as a common drive shaft.

  An expansion space 10 is formed on the tip side of the displacer 2. The compression space 9 and the expansion space 10 communicate with each other via a medium flow passage 11 through which a working medium such as helium flows. A regenerator 12 is provided in the medium flow path 11. The regenerator 12 accumulates the heat of the working medium and supplies the accumulated heat to the working medium. A flange (flange) 3 a is provided in the middle of the cylinder 3. A bounce space (back pressure space) 8 is formed in the collar portion 3a by being sealed with a dome-shaped pressure vessel 4 attached thereto.

  The piston 1 is integrated with the support spring 5 on the rear end side. The displacer 2 is integrated with the support spring 6 through a rod 2 a that passes through the center hole 1 a of the piston 1. The support spring 5 and the support spring 6 are connected by a bolt and a nut 22. As will be described later, when the piston 1 reciprocates, the displacer 2 reciprocates with a predetermined phase difference with respect to the piston 1.

  An inner yoke 18 is fitted on the outer peripheral side of the cylinder 3 in the bounce space 8. The inner yoke 18 faces the outer yoke 17 through a gap 19. A driving coil 16 is fitted inside the outer yoke 17. An annular permanent magnet 15 is movably provided in the gap 19. The permanent magnet 15 is integrated with the piston 1 through a cup-shaped sleeve 14. The inner yoke 18, the outer yoke 17, the driving coil 16, and the permanent magnet 15 constitute a linear motor 13 that moves the piston 1 along the axis Y. Lead wires 20 and 21 are connected to the driving coil 16, and driving power is supplied to the linear motor 13 by the control device 30.

  In the Stirling refrigerator 40 having the above configuration, when the piston 1 reciprocates by the linear motor 13, the displacer 2 reciprocates with a predetermined phase difference with respect to the piston 1. As a result, the working medium moves between the compression space 9 and the expansion space 10. As a result, a reverse Stirling cycle is formed.

  In the Stirling refrigerator 40 of the above-described embodiment, when a drive voltage having a predetermined AC waveform is applied to the linear motor 13, the piston 1 reciprocates at a cycle and a stroke corresponding to the drive voltage having the predetermined AC waveform. Do. Therefore, by controlling the drive voltage applied to the linear motor 13, the cycle and stroke of the reciprocating motion of the piston 1 can be controlled.

  Next, the operating principle of the free piston type Stirling refrigerator of the above embodiment will be described in more detail. As the piston 1 moves so that the relationship between its position and time draws a sine wave, the working gas in the compression space 9 changes so that the relationship between its pressure and time draws a sine wave, and compression. Heat is released from the space 9 and flows into the expansion space 10 while being cooled by the regenerator 12 provided around the displacer 2.

The working gas in the expansion space 10 expands due to the movement of the displacer 2, and its temperature decreases. The working gas in the expansion space 10 changes so that the relationship between pressure and time draws a sine wave, and the displacer 2 is reciprocated with a predetermined phase difference with respect to the piston 1.
Further, a thermistor circuit (Tc thermistor) for measuring the temperature of the expansion space 10 as a low temperature part of the control device 30 (internally including a current sensor 33) shown in FIG. ) And a thermistor circuit (Th thermistor) for measuring the temperature of the compression space 9 as the high temperature portion. Note that PWM is used when converting a digital signal into an analog signal. That is, the plurality of pulses sequentially output from the control device 30 are configured such that the widths thereof change corresponding to the sine waveform, and an alternating current is generated.

  FIG. 2 is a diagram illustrating a state of electrical connection between the control device 30 and the Stirling refrigerator 40. A temperature sensor 34 for detecting the temperature Tc of the low temperature part and a temperature sensor 35 for detecting the temperature Th of the high temperature part are attached to the outer surface of the Stirling refrigerator 40.

  The control device 30 includes a TcA / D conversion unit 108 that converts output information of the temperature sensor 34 from analog information to digital information, and a ThA / D conversion unit 109 that converts output information of the temperature sensor 35 from analog information to digital information. Is provided. Further, an IPM (Intelligent Power Module) 200 that outputs driving power is connected to the linear motor 13 via the lead wires 20 and 21 and the hermetic seal terminal 37.

  Next, the IPM 200 and the microcomputer 1000 provided in the control device 30 according to the embodiment will be described with reference to FIGS. As shown in FIG. 3, an IPM 200 is used for controlling the drive voltage of the linear motor (M) of the present embodiment, that is, the linear motor 13 described above. The IPM 200 incorporates an inverter circuit 100. The inverter circuit 100 has four switching elements and is connected to a linear motor (M) housed in the Stirling refrigerator 40 in a manner as shown in FIG. The four switching elements are transistors Gu, Gx, Gv, and Gy, each of which has a flywheel diode connected between the source electrode and the drain electrode. As can be seen from FIG. 3, the transistor Gu and the transistor Gx are connected in series, and the transistor Gv and the transistor Gy are connected in series. The linear motor (M) has one terminal connected to a node between the transistors Gu and Gx, and the other terminal connected to a node between the transistors Gv and Gy.

  A series circuit of a capacitor C and a capacitor CC is connected in parallel to the inverter circuit 100. The series circuit is connected to the output side of the rectifier D, the AC power supply G is connected to the input side of the rectifier D, and a voltage doubler circuit including a capacitor C and a capacitor CC is configured. In addition, a resistor R1 and a resistor R2 are connected in parallel with the capacitors C and CC between the capacitor C and the capacitor CC and the inverter circuit 100, and a voltage divider that divides the voltage between the input terminals of the inverter circuit 100. A circuit is configured. A capacitor CCC for stabilizing the potential of the node between the resistor R1 and the resistor R2 is connected in parallel to the resistor R2, and the node between the resistor R1 and the resistor R2 is a microcomputer. Connected to 1000 voltage sensor ports. In the microcomputer 1000, a voltage signal that specifies the voltage of the DC power input to the inverter circuit 100 is input to the DC voltage sensor.

  Further, the input terminal of the circuit V functioning as a voltmeter is connected to the two terminals of the linear motor (M) in a one-to-one relationship, and the voltage value obtained by the circuit V is the U-phase voltage sensor of the microcomputer 1000. Sent to each of the support and V-phase voltage sensor ports. A circuit A that functions as an ammeter is provided between the DC power supply and the linear motor (M), and the current value obtained by the circuit A is transmitted to the current sensor port of the microcomputer 1000.

  The method for obtaining the voltage value and the current value is as follows. In obtaining the voltage value, the voltage applied to the linear motor (M) is divided by the circuit V, and the divided voltage value is input to the microcomputer 1000. The microcomputer 1000 performs A / D conversion on the voltage value to calculate an actual voltage value. The current value is acquired by amplifying the potential difference between both ends of the shunt resistor S by the circuit A including the operational amplifier, and inputting the amplified potential difference value to the microcomputer 1000. The microcomputer 1000 performs A / D conversion on the amplified potential difference value to calculate a current value.

FIG. 4 is a block diagram for explaining the configuration of a microcomputer 1000 for linear motor control in which one PWM inverter control timer (one channel) is built.
As shown in FIG. 4, the microcomputer 1000 according to the present embodiment includes a clock circuit as an oscillator, a CPU (Central Processing Unit) as arithmetic means, and a RAM (Random Access Memory) as rewritable storage means. And a read-only ROM (Read Only Memory). The ROM stores a program for controlling the transistors as the four switching elements. The RAM is a storage means for temporarily storing the result of the operation performed by the CPU according to the program stored in the ROM, and may include a temporary storage means such as a register. Further, the clock is used to form a clock pulse that is a basis for operating a timer to be described later, using a signal transmitted from the oscillator.

  Further, the microcomputer 1000 is provided with two registers corresponding to the two phases of the up / down timer 1, respectively. A set value to be described later is determined by this register. This set value determines the amplitude and frequency of a signal wave (sin wave) in PWM control. The setting value is set by the microcomputer 1000 when the duty ratio of the peak voltage pulse constituting the target AC waveform, that is, the maximum voltage value of the AC voltage and the frequency of the target AC waveform are input. Calculated automatically.

  The program in the ROM is set so that the phase angle difference between the U phase and the V phase is 180 degrees. The PWM control signal output from the U-phase control circuit is transmitted to the respective gate electrodes of the transistors Gu and Gx. The PWM control signal output from the V-phase control circuit is transmitted to the gate electrodes of the transistors Gv and Gy.

  In the present embodiment, the positive voltage is applied to the linear motor (M) at the timing when the U-phase voltage pulse is output, and the linear motor (M) is output at the timing when the V-phase voltage pulse is output. It is assumed that a negative voltage is applied to. Further, in the first half of one cycle, a waveform is formed only by the transistors Gu and Gy as shown in FIG. 5A, and in the second half of one cycle, as shown in FIG. A waveform is formed only by Gx, and in one cycle as a whole, as shown in FIG. 5C, the U-phase waveform and the V-phase waveform are alternately output with the phase shifted by 180 °.

  In the control of the Stirling refrigerator, the piston 1 and the displacer 2 do not resonate unless they are driven at a predetermined frequency. That is, if the frequency of the reciprocating motion of the piston 1 is significantly different from the resonance frequency of the piston 1 and the displacer 2, the Stirling refrigerator 40 cannot be driven. Therefore, the relationship between the above-described set value data string constituting the PWM signal wave and time must be set so as to draw a sine curve of a predetermined resonance frequency.

  However, in the overmodulation control described later, the PWM pulse width is the maximum value in each of the periods T1 and T2 shown in FIG. That is, a voltage having a magnitude of a DC voltage input to the inverter circuit 100 is applied to the linear motor (M). Further, in periods other than the periods T1 and T2, the PWM pulse width changes so that a part of the sine curve of the virtual modulation rate is drawn. The virtual modulation rate means a modulation rate of a virtual sine curve in overmodulation control, which will be described in detail later.

  Next, a method for detecting the stroke X of the piston 1 of the linear motor (M) will be described. In the Stirling refrigerator 40 of the present embodiment, the stroke X of the piston 1 is detected as follows.

  First, a steady driving state of the control device 30 will be described with reference to FIGS. 6 and 7. FIG. 6 shows a voltage V applied to the linear motor (M) in a steady state, a current I flowing through the coil 16 of the linear motor (M), an induced voltage E generated in the coil 16 of the linear motor (M), and a piston. It is the figure which showed the relationship of 1 displacement T. FIG. 7 is an equivalent circuit diagram of the linear motor (M). Further, as shown in FIG. 7, the direction of the current I generated by the induced voltage E is opposite to the direction of the current generated by the applied voltage V.

  As shown in FIG. 6, the phase of the current I is delayed by θ from the applied voltage V due to the influence of the inductance (L shown in FIG. 7) of the linear motor (M). Here, the magnitude of the thrust acting on the linear motor (M) is a value obtained by multiplying the value of the current I by the thrust constant α. Further, as can be seen from the equivalent circuit diagram shown in FIG. 9, the induced voltage E is represented by the following equation (1).

E = V−R × I × cos θ−L × sin θ × (dI / dt) (1)
Therefore, if the motor winding resistance R and the inductance L are known in advance, the induced voltage E is calculated using the voltage V acquired by the circuit V shown in FIG. 3 and the current I acquired by the circuit A shown in FIG. Can be calculated. The phase difference θ is obtained by calculating the difference between the phase value when the voltage V is peak and the phase value when the current I is peak. Further, the thrust constant α is calculated in advance by experiments, and the motor winding resistance R and the inductance L are values measured in advance.

  The piston stroke X is defined by the following equation (2).

X = 2 × [V−R × I × cos θ−L × sin θ × (dI / dt)] / (2 × π × f × α) (2)
Thus, if the phase difference θ, motor winding resistance R, voltage V, current I, applied frequency f, and thrust constant α are known, the stroke X can be calculated. The above-described method for calculating the stroke X is disclosed in detail in Japanese Patent Laid-Open Nos. 2003-314919 and 2003-65244.

  Next, the “current stroke X calculation process” will be described with reference to FIG.

  In the “current stroke X calculation process” shown in FIG. 8, first, in S81, a phase difference θ, which is the difference between the peak phase of the current waveform and the peak phase of the voltage waveform, is calculated. Next, in S82, the microcomputer 1000 calculates the current I flowing through the shunt resistor S using the signal transmitted from the circuit A shown in FIG. Thereafter, in S83, the microcomputer 1000 calculates the voltage V applied to the linear motor (M) using the signal transmitted from the circuit V shown in FIG. Next, in S84, the induced voltage E is calculated using the phase difference θ, the voltage V, the current I, the winding resistance value R, and the above-described equation (1). Thereafter, in S85, the stroke X is calculated using the above-described equation (2).

  Next, modulation rate and overmodulation control will be described with reference to FIG.

  The modulation rate means the maximum amplitude of the AC waveform, that is, the ratio of the amplitude of the actual AC waveform to the DC voltage input to the inverter circuit 100. Therefore, the maximum modulation rate is 100%. When the modulation factor is between 0% and 100%, the AC waveform becomes a sine curve. On the other hand, when the modulation rate exceeds 100%, that is, when overmodulation control is performed, the AC waveform has a shape in which the upper and lower portions of the virtual sine curve are cut.

  As shown in FIG. 9, the AC waveform changes from the AC waveform A to the AC waveform C as the modulation rate increases. When the modulation factor is 100%, the AC waveform C has an amplitude that matches the value of the DC voltage input to the inverter circuit 100. In the normal amplitude modulation control period until the modulation rate exceeds 100%, the AC waveform draws a sine curve. On the other hand, in the overmodulation control period, as shown by the AC waveform D. The AC waveform has a shape in which the upper and lower portions of the virtual sine curve are cut.

  Note that during overmodulation control, the AC waveform is not a sine curve, so the modulation rate cannot be specified, but depending on the modulation rate of the virtual sine curve that would have been drawn if the upper and lower parts were not cut. A modulation rate during overmodulation control is defined, and in the present embodiment, this modulation rate is hereinafter referred to as a virtual modulation rate.

  In addition, as the modulation rate increases, the area surrounded by the AC waveform increases, and the energy input to the linear motor (M) increases. Even when a sine curve is drawn with the upper and lower portions of the overmodulation control cut, the larger the virtual modulation rate, the larger the area surrounded by the AC waveform and the greater the energy applied to the piston 1.

  Therefore, in the present embodiment, when the piston 1 must be operated with the maximum stroke, if the stroke of the piston 1 does not reach the maximum value because the load of the Stirling refrigerator 40 is large, overmodulation control is performed. By executing this, control is performed to increase the stroke of the piston. Thereby, since the stroke of the piston 1 approaches the maximum stroke, the Stirling refrigerator approaches the desired refrigeration capacity.

  Further, when overmodulation control is being executed, the waveform of the AC voltage applied to the linear motor (M) is no longer a sine curve, so that the above-described stroke detection cannot be executed. This is because the stroke detection described above is control performed on the assumption that the voltage waveform is a sine curve.

  Therefore, in order to prevent a collision between the piston 1 and the displacer 2, it is necessary to limit the continuation of overmodulation control. This is because if the load on the Stirling refrigerator is reduced, the piston 1 reciprocates with a larger stroke even if the modulation rate is the same, and the piston 1 and the displacer 2 may collide. Therefore, during overmodulation control, it is desirable to end overmodulation control if the load on the Stirling refrigerator becomes smaller than immediately before overmodulation control is executed. The decrease in the load of the Stirling refrigerator is that the temperature Th of the high temperature part (compression space 9) is lower than that immediately before the overmodulation control, and the temperature Tc of the low temperature part (expansion space 10) is excessive. It can be determined by the fact that it has become higher than immediately before the modulation control, or because the difference between the temperature Th of the high temperature part and the temperature Tc of the low temperature part has become smaller than immediately before the control of overmodulation. Is possible. Further, when the DC voltage V (D) input to the inverter circuit 100 becomes larger than immediately before overmodulation, more energy is given to the piston 1 even if the virtual modulation rate is not changed. Therefore, it is desirable to end the overmodulation control.

  In general, as shown in FIG. 10, in the Stirling refrigerator, the difference between the temperature Th of the high temperature part and the temperature Tc of the low temperature part becomes large at the timing of the quick freezing operation. That is, the temperature Th of the high temperature part gradually increases, and the temperature Tc of the low temperature part gradually decreases. Therefore, when the state of temperature change shown in FIG. 10 collapses and the overmodulation control is terminated, it is possible to prevent the inconvenience that the displacer 2 and the piston 1 are in contact with each other.

  Next, a modulation control process performed by the control device for the Stirling refrigerator according to the present embodiment will be described with reference to FIGS. 11 and 12. First, in S1, it is determined whether or not a quick freezing operation is necessary. The quick freezing operation is required, for example, when the installation of the refrigerator equipped with the Stirling refrigerator is completed and the power is turned on, when the defrosting operation is completed, or when the stored food is rapidly frozen. Whether or not the quick freezing operation is necessary is determined by the condition in the control mode of the microcomputer 1000.

  If the quick freezing operation is not required in S1, the modulation control process is not executed. If the quick freezing operation is required, it is determined whether or not the maximum stroke command is issued in S2. That is, it is determined whether or not the piston 1 is driven at the maximum stroke. If the piston 1 is not driven at the maximum stroke, that is, if the maximum stroke command is not issued, the modulation rate control process is not executed, and the maximum stroke command is If so, it is determined in S3 whether or not the modulation rate is the maximum modulation rate (100%). Whether or not the modulation rate is the maximum modulation rate (100%) depends on whether the maximum value of the voltage pulse output from the circuit V of FIG. 3 to the microcomputer 1000 is the value of the DC voltage input to the inverter circuit 100. It is determined by whether or not.

  In S3, if the modulation rate of the AC voltage applied to the linear motor (M) is not the maximum modulation rate (100%), the modulation rate control process is not performed, but applied to the linear motor (M). If the modulation rate of the AC voltage is the maximum modulation rate, it is determined in S4 whether or not the current stroke of the piston 1 is a stroke equal to or less than “maximum stroke−predetermined value A”. This determination is performed using the actual stroke value of the piston 1 obtained by the stroke detection and the stored value of “maximum stroke−predetermined value A”. Note that the value of “maximum stroke—predetermined value A” is stored in the ROM in advance. Next, in S4, if the actual stroke value of the piston 1 is not a value equal to or less than “maximum stroke−predetermined value A”, the modulation rate control process is not performed, but the actual stroke value of the piston 1 is “ If the value is equal to or less than “maximum stroke−predetermined value A”, the process of S5 is executed.

  In S5, the current temperature Tc, the current temperature Th, the current temperature Th-temperature Tc, and the value of the DC voltage V (D) input to the current inverter circuit 100 are stored in the RAM, and overmodulation control processing is performed. Is executed. The temperature Tc is the temperature of the low temperature portion detected by the temperature sensor 34 shown in FIG. 2, the temperature Th is the temperature of the high temperature portion detected by the temperature sensor 35 shown in FIG. 2, and the DC voltage V (D) is 3 is a voltage acquired by the DC voltage sensor shown in FIG.

  Next, in S6, a virtual modulation rate defined by the equation of maximum stroke / (maximum stroke−predetermined value A) is calculated, and overmodulation using a part of the sine curve defined by this virtual modulation rate is used. The piston 1 reciprocates by the control. That is, overmodulation control is executed so that the piston 1 operates with a stroke that does not exceed the maximum stroke. The maximum stroke is a value that is predetermined and input to the ROM so that the piston 1 and the displacer 2 do not collide.

  While the overmodulation control is being executed, the stroke value cannot be calculated, and there is a possibility that the piston 1 and the displacer 2 may collide, but this is defined by the equation of maximum stroke / (maximum stroke−predetermined value A). If the piston 1 is operated at a virtual modulation rate, the piston 1 and the displacer 2 are prevented from colliding with each other, and a problem that quick freezing cannot be performed due to a large load is prevented.

  Next, in S10 of FIG. 12, it is determined whether or not the maximum stroke command is output. If the maximum stroke command is not output, the control device 30 ends the overmodulation control in S29. On the other hand, if the maximum stroke command is output in S10, it is determined in S11 whether or not the value of the temperature Th is lower than the stored value of the temperature Th in S5. It is determined whether or not the H flag is set. The H flag is a flag set in step S26 described later, and indicates that the stored value of the temperature Th is increasing. If the H flag is not set in S17, the control device 30 determines that the load of the Stirling refrigerator 40 has decreased, and controls overmodulation in S29 in order to prevent the piston 1 and the displacer 2 from colliding with each other. Exit. If the H flag is set in S17, the virtual modulation rate is reduced (down) by H% in S18, the H flag is reset, and the previous stored value −3 degrees as the stored value of the temperature Th. Is newly stored. Thereafter, the process of S10 is executed.

  On the other hand, if the temperature Th is not lower than the stored value in S11, it is determined in S12 whether or not the temperature Tc has risen above the stored value of the temperature Tc in S5. It is determined whether or not the C flag is set. The C flag is a flag that is set in S27 described later, and indicates that the stored value of the temperature Tc is decreasing. If the C flag is not set in S19, the control device 30 determines that the load on the Stirling refrigerator 40 has decreased, and ends the overmodulation control in S29. On the other hand, if the C flag is set in S19, the virtual modulation rate is reduced (down) by C% in S20, the C flag is reset, and the stored value of the temperature Tc is the previous stored value + 3 degrees. Is newly stored. Thereafter, the process of S10 is executed.

  In S12, if the temperature Tc is not higher than the stored value of the temperature Tc in S5, the process of S13 is executed. In S13, it is determined whether or not the value of the DC voltage V (D) input to the inverter circuit 100 is higher than the stored value of the DC voltage V (D) in S5. In S21, it is determined whether or not the B flag is set. The B flag is a flag that is set in S28, which will be described later, and indicates that the value of the DC voltage V (D) is decreasing.

  If the B flag is not set in S21, the control device 30 determines that the load of the Stirling refrigerator 40 has decreased, and ends the overmodulation control in S29. On the other hand, if the B flag is set in S21, the virtual modulation rate is decreased (down) by B% in S22, the B flag is deleted, and the previous stored value is stored as the stored value of the DC voltage V (D). + 3V is newly stored. Thereafter, the process of S10 is executed. If the value of DC voltage V (D) is not higher than the stored value of DC voltage V (D) in S5 in S13, the process of S14 is executed.

  In S14, it is determined whether or not the temperature Th has increased 3 degrees or more from the stored value. If the temperature Th has increased 3 degrees or more from the stored value, it is determined in S23 whether or not the H flag has been set. Is done. If the H flag is not set, the virtual modulation rate is further increased (increased) by H% in S26, the stored value of the temperature Th is changed to the value of the temperature Th of S5 + 3 ° C., and the H flag is set. The Thereafter, the process of S10 is executed. If the H flag is set in S23, the process of S15 is executed.

  Further, the process of S15 is also executed when the temperature Th has not risen by 3 degrees or more from the stored value in S14. In S15, it is determined whether or not the temperature Tc has decreased by 3 degrees or more from the stored value. If it has decreased by 3 or more degrees, it is determined in S24 whether or not the C flag is set. If the C flag is not set in S24, the virtual modulation rate is further increased (increased) by C% in S27, the stored value of the temperature Tc is changed to the stored value −3 ° C. of S5, and the C flag is set. Is done. Thereafter, the process of S10 is executed. If the C flag is set in S24, the process of S16 is executed. Further, if the temperature Tc is not lowered by 3 degrees or more from the stored value in S15, the process of S16 is executed.

  In S16, it is determined whether or not the value of the DC voltage V (D) is 3V or more lower than the stored value. If it is 3V or more, it is determined whether or not the B flag is set in S25. Is done. If the B flag is not set in S25, the virtual modulation rate is further increased (increased) by B% in S28, the stored value of the DC voltage V (D) is changed to the stored value −3 ° C. of S5, and The B flag is set. Thereafter, the process of S10 is executed. If the B flag is set in S25, the process of S1 is executed.

  Note that the value for changing the stored value of the RAM in each of the above-described S18, S20, and S22 is not limited to +3 or -3, and is appropriately determined according to the characteristics of the Stirling refrigerator 40. In addition, the value of the virtual modulation factor that is changed in each of the above-described S18, S20, and S22 is a value obtained by experiment, and is a value determined so that the piston 1 and the displacer 2 do not collide. is there.

  In short, in the continuous control 1 shown in FIG. 12, the temperature Th is lower than the temperature Th immediately before the overmodulation control stored in S5 of FIG. 11, or the temperature Tc is stored in S5 of FIG. When the temperature is higher than the temperature Tc immediately before the overmodulation control or when the value of the DC voltage is larger than the value of the DC voltage immediately before the overmodulation control stored in S5 of FIG. The control device 30 determines that the load on the Stirling refrigerator 40 has decreased, and ends the overmodulation control. Therefore, the piston 1 and the displacer 2 are prevented from colliding.

  Further, instead of the continuation control 1 shown in FIG. 12, the continuation control 2 as shown in FIG. 13 may be executed. In the continuation control 2 shown in FIG. 13, it is first determined whether or not the maximum stroke command is output in S30. If the maximum stroke command is not output, the control device 30 ends this process. If the maximum stroke command is output in S30, it is determined in S31 whether or not the temperature difference Th-Tc is lower than the stored value of the temperature difference Th-Tc in S5. The process of S30 and the process of S31 are repeated. On the other hand, if the temperature difference Th−Tc is lower than the stored value, the control device 30 determines that the load on the Stirling refrigerator 40 has decreased, and ends the overmodulation control.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is sectional drawing which shows the structure of the Stirling refrigerator of embodiment. It is a figure for demonstrating the relationship between the linear motor of the Stirling refrigerator of embodiment, and a control apparatus. It is a figure for demonstrating the structure of the alternating current power generation apparatus of embodiment. It is a block diagram of the microcomputer used in the alternating current power generation device of an embodiment. It is a figure for demonstrating the voltage pulse of a U phase and the voltage pulse of a V phase. It is a reference figure for demonstrating the relationship of the phase of the electric current of a linear motor, the phase of a voltage, and the phase of a piston. It is an equivalent circuit diagram of a linear motor at a constant time. It is a flowchart for demonstrating the present stroke calculation process of the refrigerator of embodiment. It is a figure for demonstrating the voltage waveform in overmodulation control. It is a figure which shows the temperature change of the high temperature part and low temperature part in overmodulation control. It is a flowchart for demonstrating an overmodulation control process. It is a flowchart for demonstrating an overmodulation control process. 12 is a flowchart for explaining another example of overmodulation control processing.

Explanation of symbols

  1 piston, 13 linear motor, 30 control device, 40 Stirling refrigerator.

Claims (5)

Stirling refrigerator,
A control device for controlling the Stirling refrigerator by PWM (Pulse With Module),
The controller is
Piston state determining means for determining whether or not the piston is driven at a maximum stroke;
Whether or not the modulation rate of the amplitude of the AC waveform generated by the PWM reaches the maximum modulation rate (100%) when it is determined by the piston state determination means that the piston is driven at the maximum stroke Modulation rate determination means for determining whether or not
Stroke determining means for determining whether or not the current stroke of the piston is smaller than the maximum stroke by a predetermined value or more when it is determined by the modulation rate determining means that the modulation rate has reached the maximum modulation rate;
A Stirling refrigeration system including modulation control means for performing overmodulation control when the stroke determination means determines that the current stroke of the piston is smaller than a maximum stroke by a predetermined value or more.   2. The Stirling refrigeration system according to claim 1, wherein in the overmodulation control, the PWM is executed such that a virtual modulation rate becomes the maximum stroke / (the maximum stroke−the predetermined value). A temperature detector for detecting a temperature of a high temperature part or a low temperature part of the Stirling refrigerator and transmitting temperature information of the high temperature part or the low temperature part to the control device;
The modulation control means, during the overmodulation control, the temperature of the high temperature part is lower than the temperature of the high temperature part immediately before executing the overmodulation control, or the overmodulation control 2. The Stirling refrigeration system according to claim 1, wherein the control of the overmodulation is terminated when the temperature of the low temperature portion is higher than the temperature of the low temperature portion stored immediately before execution. A DC power supply generating unit that outputs a DC voltage to the control device to generate the AC waveform by the PWM;
The control device includes a voltage detector that detects the DC voltage,
The modulation control means ends the overmodulation control when the DC voltage is larger than the DC voltage immediately before executing the overmodulation control during the overmodulation control. Item 4. A Stirling refrigeration system according to item 1. A high-temperature detector that detects the temperature of the high-temperature part of the Stirling refrigerator and transmits temperature information of the high-temperature part to the control device;
A low temperature detector that detects the temperature of the low temperature part of the Stirling refrigerator and transmits temperature information of the low temperature part to the control device;
The control device includes a temperature difference calculating means for calculating a temperature difference between the high temperature part and the low temperature part,
The modulation control means ends the overmodulation control when the temperature difference during the overmodulation control is smaller than the temperature difference immediately before the overmodulation control is performed; The Stirling refrigeration system according to claim 1.

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