JP6381482B2 - Power converter and air conditioner - Google Patents

Description

  The present invention relates to a power converter for variable speed control of a rotating machine and an air conditioner using the power converter, and in particular, protects a rotating machine and power converting means based on an output current detection value of the power converter. It is related with the power converter device which was made to perform.

  A PWM (Pulse Width Modulation) signal is generated based on the comparison result after comparing a carrier wave of a predetermined frequency and a desired multiphase voltage command mainly by internal calculation of a microcomputer (hereinafter referred to as a microcomputer). There are known power conversion means such as an inverter that operates a switching element based on a PWM signal to output a multiphase AC voltage and drives a rotating machine.

  In such a power conversion means, the instantaneous value of the phase current of each phase at each positive and negative maximum amplitude of the carrier wave is converted to the current on the DC bus side or the three-phase (AC) output side of the power conversion means. A current is detected by a known current sensor (accurately, the detected value is converted into a voltage level), taken into a processor such as a microcomputer, and a known value is used on the processor using the detected instantaneous value of the phase current of each phase. The feedforward control calculation and the vector control calculation are executed to calculate the instantaneous value of each phase voltage command, and the PWM signal is generated based on the comparison between the instantaneous value of each phase voltage command and the carrier wave.

  Further, in such a power conversion means, each positive and negative maximum amplitude time point of the carrier wave corresponds to the half period of the carrier wave, in addition to the voltage zero section of the output of the power conversion means, Furthermore, since it corresponds to the midpoint vicinity of the zero voltage section, it is possible to detect the instantaneous value of the phase current of each phase without being affected by the pulsation included in the phase current, so the (half) period of the carrier wave, Alternatively, the control calculation described above is executed in such a manner that a cycle that is an integral multiple of the (half) cycle of the carrier wave is synchronized with the control calculation cycle.

Furthermore, when driving a rotating machine using a power conversion device having such power conversion means, the deterioration of the rotating machine, especially in the case of a synchronous machine having a permanent magnet as a field, prevents demagnetization of the permanent magnet, In general, an overcurrent protection function is provided in a power converter for the purpose of preventing destruction of a semiconductor element constituting the power converter.
As an existing method of overcurrent protection of a power converter, a current is detected (converted to a voltage level) by the above-described method, and a predetermined threshold value at which this detected (voltage) value operates as an overcurrent protection function is set. There is one that cuts off the output of the power conversion means when exceeding.

  Furthermore, as an example of a power conversion device that preferably performs these protections, based on the amount of change in the output current of the inverter detected by the output current detection means for each control calculation cycle and the predicted value of the output current in the next control calculation cycle There is a device that determines whether or not there is an abnormality and stops the PWM signal, that is, stops the output of the inverter if it is determined as abnormal. (For example, refer to Patent Document 1).

  As another example of a similar power conversion device, a drive current integrated value, which is a value obtained by integrating a drive current flowing in a drive circuit corresponding to a power conversion unit with a fastest calculation cycle capable of a predetermined calculation process, is a predetermined threshold. When the drive current flows beyond the normal operating range, the control mode of the AC motor is determined when the drive current exceeds the normal operating range, and the carrier of the determined control mode is detected. There is a device that adjusts to a suitable threshold according to the frequency and determines an abnormality in the drive current based on whether or not the current integrated value of the drive current exceeds a suitable threshold. (For example, refer to Patent Document 2).

  Further, as another example of a similar power conversion device, whether or not the maximum value of the drive current detected for each predetermined calculation cycle of the drive current flowing in the drive circuit corresponding to the power conversion means exceeds a suitable threshold value. And detecting an abnormality in the drive current by detecting that the maximum value of the drive current exceeds a suitable threshold value in each of the predetermined n (n is a natural number of 3 or more) consecutive calculation periods. Therefore, as in Patent Document 1, the threshold value is adjusted to a suitable threshold value according to the carrier frequency of the determined control mode, and the drive current abnormality is determined by whether or not the current integrated value of the drive current exceeds the suitable threshold value. There is a device for judging the above. (For example, refer to Patent Document 3).

Japanese Patent No. 5235390 Japanese Patent No. 4543781 Japanese Patent No. 4670413

  In the conventional apparatus shown in Patent Document 1, an abnormality is detected based on the amount of change in the output current of the inverter detected by the output current detection means for each control calculation cycle and the predicted value of the output current in the next control calculation cycle. In order to synchronize the carrier wave period and the control calculation period as described above, when the control calculation period changes according to the carrier frequency, the change amount and the If the current threshold that operates as desired is not changed as an overcurrent protection function compared with each predicted value, the amount of change in current per control operation cycle will change even if the current increase rate is the same, so the desired protection operation Is difficult to get. In particular, in the case of a synchronous PWM method in which the carrier frequency changes by an integer M times the inverter frequency (that is, the frequency of the three-phase voltage command), the control calculation cycle changes sequentially depending on the inverter frequency and the value of M, so that the influence becomes large. There was a problem.

In the conventional apparatus shown in Patent Document 2 or Patent Document 3, whether or not the integrated value of the drive current exceeds a predetermined threshold value, or n predetermined calculations in which the maximum value of the drive current continues. Although effective as protection against continuous load operation of the power conversion means, such as determining whether or not the threshold value has been exceeded in each cycle, there is a problem that it is difficult to cope with detection protection of current increase tendency In addition, the purpose of setting the threshold according to the carrier frequency is the viewpoint of the inverter load due to the change of the current waveform and the switching loss, and does not necessarily correspond to the influence caused by the calculation cycle.
Furthermore, as shown in the conventional apparatus, it is preferable to perform overcurrent protection detection at the fastest calculation cycle that can be processed, but in reality, it depends on the performance restrictions of the microcomputer that performs the calculation processing and the processing time of the control algorithm. There was a problem that there was a restriction on the shortest calculation cycle.

  The present invention has been made to solve the above-described problems, and realizes an overcurrent protection function for appropriate power conversion means regardless of the length of a control calculation period set based on a carrier frequency. An object of the present invention is to provide a power converter that can perform the above and an air conditioner using the power converter.

  A power conversion device according to the present invention includes a voltage command generation unit that generates a voltage command, a drive signal generation unit that generates a carrier wave and generates a drive signal based on the carrier wave and the voltage command, and a drive signal. A power conversion means for driving the rotating machine by outputting a voltage, a current detection means for detecting an output current of the power conversion means, a control calculation period setting unit for setting a control calculation period based on the frequency of the carrier wave, A power conversion means protection unit that performs a protection operation on the power conversion means when the amount of change in the output current per control calculation period exceeds a predetermined first current threshold, wherein the first current threshold is a control calculation period; The frequency is set based on at least one of the frequency of the carrier wave and the frequency of the voltage command.

  The power conversion device according to the present invention includes a voltage command generation unit that generates a voltage command, a drive signal generation unit that generates a carrier wave and generates a drive signal based on the carrier wave and the voltage command, and a drive signal. The power conversion means for driving the rotating machine by outputting a voltage based on the current, the current detection means for detecting the output current of the power conversion means, and the control calculation period setting unit for setting the control calculation period based on the frequency of the carrier wave And a power for performing a protection operation for the power conversion means when the predicted value of the output current in the next control calculation cycle predicted based on the amount of change in the output current per control calculation cycle exceeds a predetermined second current threshold value. A conversion means protection unit is provided, and the second current threshold is set based on at least one of the control calculation cycle, the frequency of the carrier wave, and the frequency of the voltage command.

  The air conditioner according to the present invention includes the above-described power conversion device and a compressor connected to the power conversion means of the power conversion device, and compresses the refrigerant in the refrigeration cycle by the rotation of the rotating machine constituting the compressor. It is what you do.

  According to this invention, since the overcurrent threshold for the power conversion means is set based on the control calculation cycle or a parameter related thereto, overcurrent protection for an appropriate power conversion means is realized regardless of the length of the control calculation cycle. In addition, the present invention has a remarkable effect that can prevent the destruction of the switching element of the power conversion means due to overcurrent and the deterioration and demagnetization of the rotating machine connected to the power conversion means.

It is a figure which shows the structure of the whole system provided with the power converter device which concerns on Embodiment 1 of this invention. It is a figure which shows the hardware constitutions of a system provided with the power converter device which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the relationship between the voltage phase of the voltage command which concerns on Embodiment 1 of this invention, and the carrier wave of synchronous PWM. In the power converter device which concerns on Embodiment 1 of this invention, it is a figure which shows an example of the relationship between the period of a carrier wave, and a control calculation period. It is the conceptual diagram which showed the relationship between the output current variation | change_quantity of the power conversion means which concerns on Embodiment 1 of this invention, and control calculation period (DELTA) t. It is the figure which showed the influence on the variation | change_quantity of an output current accompanying the difference (change) of control calculation period (DELTA) t which concerns on Embodiment 1 of this invention, and an output current estimated value. It is the conceptual diagram which showed an example of the suitable relationship between control calculation period (DELTA) t and electric current threshold value A, B which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the whole system provided with the power converter device which concerns on Embodiment 2 of this invention. It is a figure which shows an example of the relationship of the setting value of the frequency fc of the carrier wave with respect to the inverter frequency finv. It is a figure which shows the structure of the whole system provided with the power converter device which concerns on Embodiment 3 of this invention. It is a figure which shows the structure of the air conditioning apparatus to which the power converter device which concerns on Embodiment 5 of this invention is applied.

Embodiment 1 FIG.
Hereinafter, a power converter according to Embodiment 1 of the present invention will be described in detail with reference to FIGS. 1 to 7.
FIG. 1 is an overall view of a system including a power conversion device according to Embodiment 1, and includes a rotating machine 11, an AC power supply 12, and a power conversion device 100.
In this embodiment, a three-phase synchronous machine is assumed as the rotating machine 11, but the present invention is not limited to "three-phase" or "synchronous machine", and other phase numbers ( The present invention can be similarly applied to a rotating machine (for example, an induction machine) different from a synchronous machine or a two-phase rotating machine other than the three-phase machine.

In FIG. 1, the power conversion device 100 includes a voltage command generation unit 1, a drive signal generation unit 2, a power conversion unit 3, a current detection unit 4, a control calculation cycle setting unit 5, and a power conversion unit protection unit 6. .
FIG. 2 is a diagram showing a hardware configuration of a system including the power conversion device 100 according to Embodiment 1 of the present invention.

In the configuration of FIG. 1, the voltage command generation unit 1, the drive signal generation unit 2, the control calculation cycle setting unit 5, and the power conversion means protection unit 6 execute a program stored in the storage device 101 shown in FIG. 2. Implemented by the processor 102.
Although not shown, the storage device 101 includes a volatile storage device such as a random access memory and a nonvolatile auxiliary storage device such as a flash memory. Although not shown, the storage device 101 may include a volatile storage device such as a random access memory and an auxiliary storage device such as a hard disk instead of the nonvolatile auxiliary storage device.

The processor 102 executes a program input from the storage device 101. Since the storage device 101 includes an auxiliary storage device and a volatile storage device, a program is input to the processor 102 from the auxiliary storage device via the volatile storage device. Further, the processor 102 may output data such as a calculation result to the volatile storage device of the storage device 101, or may store the data in the auxiliary storage device via the volatile storage device.
In this embodiment, a plurality of processors 102 and a plurality of storage devices 101 may be linked. Furthermore, the storage device 101 and the processor 102 may be configured by, for example, a microcomputer or a DSP (Digital Signal Processor).

Next, the configuration and operation of the power conversion apparatus 100 will be described.
The voltage command generation unit 1 generates and outputs a three-phase AC voltage command necessary for driving the rotating machine 11 at a desired rotational speed. Specifically, by executing a well-known feedforward control calculation or vector control calculation every control calculation period (hereinafter referred to as a control calculation period Δt) set by a control calculation period setting unit 5 described later. The three-phase AC voltage commands Vu *, Vv *, and Vw * having a predetermined frequency (hereinafter referred to as the inverter frequency finv) are generated and output.
Although not shown, in these control calculations, a three-phase current detection value obtained by the current detection means 4 described later, or a position or speed sensor newly attached to the rotating machine 11 and a position detected by these sensors Alternatively, speed information may be used.

  The drive signal generation unit 2 generates a carrier wave having a predetermined frequency or a frequency (hereinafter referred to as a carrier wave frequency fc) calculated based on a three-phase AC voltage command frequency (inverter frequency finv). In addition, the three-phase AC voltage commands Vu *, Vv *, and Vw * are converted into modulated waves, and each phase that is a drive signal for the power conversion means 3 based on the magnitude comparison result between the carrier wave and the modulated wave. PWM signals PWMu, PWMv, and PWMw are generated and output to the power conversion means 3.

In the generation of the carrier wave, there are methods called an asynchronous PWM method and a synchronous PWM method. The former is a method for setting the carrier wave frequency fc regardless of the inverter frequency finv, and the latter is the inverter frequency finv (absolute value). ) This is a method of setting the carrier wave frequency fc to M times (M is a positive integer), and a positive integer M is often a multiple of 3.
Hereinafter, in the embodiment of the present invention, the case of the inverter frequency finv> 0 will be described. However, in the case of the inverter frequency finv <0, the present invention can be similarly applied by replacing the inverter frequency finv with the absolute value | finv |.

FIG. 3 is a diagram showing an example of the relationship between the voltage command voltage phase and the synchronous PWM carrier wave when M = 9, 6, 3, ie, synchronous 9 pulses, synchronous 6 pulses, and synchronous 3 pulses.
In the asynchronous PWM, in general, in order to maintain the symmetry of the waveform of the three-phase AC voltage output from the power conversion means 3, fc / finv, that is, the ratio between the frequency fc of the carrier wave and the inverter frequency finv. Is generally secured at fc / finv> 9 or more. In addition, since there is an upper limit of the frequency fc of the carrier wave due to restrictions such as loss and heat generation associated with the switching operation of the switching element of the power conversion means 3, in order to maintain the relationship of fc / finv> 9, the inverter frequency finv There is also an upper limit.

  In synchronous PWM, even if fc / finv is an integer M and fc / finv <9, the symmetry of the waveform of the three-phase AC voltage output from the power conversion means 3 is maintained, and the carrier wave Even under the restriction of the upper limit of the frequency fc, the maximum value of the inverter frequency finv can be set higher than in the asynchronous PWM method, and it is possible to drive even in a high speed region where it is difficult to drive with the asynchronous PWM.

  However, the frequency fc of the carrier wave always changes according to the inverter frequency finv and the set value of the integer M. Further, in order to stably output the three-phase AC voltage from the power conversion means 3, there is also a lower limit of the carrier wave frequency fc. Therefore, in the actual operation, the asynchronous PWM method and the synchronous PWM are selected according to the inverter frequency finv. The method is switched or the integer M, which is the ratio fc / finv of the asynchronous PWM method carrier wave or the synchronous PWM method, is set to an appropriate value. A PWM system and an integer M switching operation are assumed.

The power conversion means 3 converts the AC voltage supplied from the AC power source 12 into a DC voltage by a known rectifier circuit configured using a diode or the like, and the DC voltage is converted to PWM for each phase by a known three-phase inverter. Based on the signals PWMu, PWMv, and PWMw, the three-phase AC voltages Vu, Vv, and Vw of the frequency finv for driving the rotating machine 11 are output, and the three-phase AC voltage is supplied to the rotating machine 11.
In the three-phase inverter, two switching elements are connected in series to each phase (u, v, w phase), and a feedback diode is connected in antiparallel to each switching element. It is a well-known one that is switched based on phase PWM signals PWMu, PWMv, and PWMw. In general, switching elements and diodes are composed of elements composed of silicon Si, but silicon carbide SiC, gallium nitride GaN, diamond, etc., which are wide bandgap semiconductors capable of high withstand voltage and high temperature operation. You may use the element comprised by these.

  In the power conversion means 3, in addition to the power supply from the AC power source 12 as shown in FIG. 1, a power source or a battery that outputs a DC voltage may be connected for power supply. The rectifier circuit described above becomes unnecessary. Further, a configuration may be adopted in which a DC voltage is boosted by inserting a booster circuit such as a well-known DC-DC converter in a DC bus between the rectifier circuit and the three-phase inverter.

  The current detection unit 4 detects the output current of each phase of the power conversion unit 3, that is, the armature currents Iu, Iv, and Iw of the rotating machine 11 using a known ACCT sensor or DCCT sensor. Further, the detected output current (detected value) is converted into a voltage level by an amplifier and an A / D converter, and is taken into a processor 102 such as a microcomputer and used for a control calculation or the like.

When the rotating machine 11 is a three-phase rotating machine, the current detecting means 4 is configured to detect the output currents of all phases among the output currents Iu, Iv, Iw of each phase of the synchronous machine, or one phase The armature current Iw (for example, w phase) is obtained from the relationship of Iw = −Iu−Iv in a three-phase equilibrium state using the detected output currents Iu and Iv of the two phases. It may be configured to detect the output current.
In addition to the method of directly detecting the output current of each phase, a method of detecting the output current based on the current flowing through the DC bus between the rectifier circuit and the three-phase inverter, which is a well-known technique, may be used.

The control computation cycle setting unit 5 synchronizes the cycle of N / 2 times the carrier wave cycle (N is a positive integer), that is, a cycle of N times the half cycle of the carrier wave, and the control computation cycle Δt. In order to execute the control calculation, the control calculation period Δt is set to be Δt = N / (fc · 2) based on the carrier wave frequency fc set by the drive signal generation unit 2. To do.
That is, the control calculation cycle Δt is a function Δt = f (fc) of the carrier wave frequency fc.
As described above, this corresponds to the positive and negative maximum amplitude time points of the carrier wave corresponding to the half period of the carrier wave, in addition to the voltage zero interval of the output of the power conversion means 3, Since it corresponds to the middle point of the zero voltage section, it can detect the instantaneous value of the phase current of each phase without being affected by the pulsation contained in the phase current, so each positive and negative maximum amplitude of the carrier wave This is because it is desirable to set the control calculation cycle Δt based on the time point.

FIG. 4 is a diagram showing an example of the relationship between the carrier wave cycle and the control calculation cycle Δt, and shows the relationship when N = 1. N = 1 is not necessarily limited, and an integer (2, 3,...) Other than N = 1 may be selected.
In the setting of the integer N, if N = 1 when the frequency fc of the carrier wave is very high, the control calculation process performed by the processor 102 in the voltage command generation unit 1 or the like is set to the set control calculation cycle Δt. May not complete within 5 seconds and may cause overflow. If the value of N is increased when the frequency fc of the carrier wave is low, the control calculation cycle Δt becomes too long and a desired control response may not be obtained. For this reason, in setting the control calculation period Δt (that is, setting the integer N), based on the frequency fc of the carrier wave in consideration of the processing load of the control calculation, the performance of the processor 102, and the control response required for the system. Set.
The above is the configuration necessary for driving the rotating machine 11 in the first embodiment.

Next, the power conversion means protection unit 6 that is a feature of the present invention will be described.
The power conversion means protection unit 6 calculates the change amount ΔI of the output current per control calculation period Δt based on the output current I detected by the current detection means 4, and further outputs the output current detected by the current detection means 4. After calculating the output current predicted value I + ΔI in the next control calculation cycle based on I and the output current change ΔI, the output current change ΔI and the output current predicted value I + ΔI Based on at least one of them, it is determined whether or not the output current is abnormal, and an overcurrent protection operation for the power conversion means 3 is performed.

  In the overcurrent protection operation of the power conversion means 3, after calculating the output current variation ΔI and the predicted output current value I + ΔI for all phases, it is determined whether the output current is abnormal for each phase. Needless to say, it is desirable to perform an overcurrent protection operation on the power conversion means 3 when it is determined and determined to be abnormal in any phase, but in the following description, the operation in any one phase will be described. . (Same operation in other phases.)

FIG. 5 is a conceptual diagram showing the relationship between the change amount ΔI of the output current of the power conversion means 3 and the control calculation cycle Δt. The overcurrent protection operation for the power conversion means 3 in the first embodiment is shown in FIG. This will be described with reference to FIG.
In FIG. 1, the output current of each phase of the power conversion means 3 is synchronized with the positive and negative maximum amplitude points of the carrier wave for each control calculation period Δt set in the control calculation period setting unit 5. It is detected by the detection means 4. (The detection operation includes an operation in which the voltage level is converted by an amplifier and an A / D converter and is taken into a processor 102 such as a microcomputer.)

The detected output current I is stored once in the storage device 101 such as an accumulator register, for example, and the stored output current I is used as the previous value (hereinafter referred to as Iold) at the timing of the next control calculation. . In other words, the stored previous value Iold is updated every time the output current I is detected every calculation control period Δt.
From the previous value Iold and the output current detection value (current value) I, the output current change amount ΔI is calculated by the following equation (1), and further, the output current detection value (current value) I and the change in output current are calculated. The predicted value I + ΔI of the output current is calculated from the amount ΔI by the following equation (2).
・ Change in output current △ I = Current value I-Previous value Iold (1)
・ Predicted value of output current I + △ I = Present value I + Amount of change in output current △ I (2)

The output current change amount ΔI and the predicted output current value I + ΔI obtained above are compared with the current threshold value A and the current threshold value B (B> A) set by the method described later, respectively. When at least one of the conditions of the formulas (3) and (4) is satisfied, it is determined that there is an abnormality.
・ Absolute value of change in output current | ΔI |> Current threshold A (3)
・ Absolute value of predicted output current | I + ΔI |> Current threshold B (4)
As described above, a series of flow from the output current detection operation to the abnormality determination operation is performed for each phase, and when the abnormality is determined in any phase, the following protection operation for the power conversion unit 3 is performed.

As an example of the overcurrent protection operation for the power conversion means 3, the power conversion means protection unit 6 sends a PWM signal PWMu for each phase that is a drive signal for the power conversion means 3 to the drive signal generation unit 2 as shown in FIG. 1. , Outputs an OFF signal (OFF) for stopping all the outputs of PWMv and PWMw, and stops the output of the three-phase AC voltage from the power conversion means 3 to the rotating machine 11.
Alternatively, the power conversion means protection unit 6 may output a signal for stopping the switching operation of all the switching elements directly to the power conversion means 3 to stop the supply of the three-phase AC voltage.

Next, a method for setting the current thresholds A and B related to the overcurrent protection operation will be described.
In overcurrent protection, when a phenomenon occurs in which the output current of the power conversion means 3 increases stepwise due to factors such as load fluctuation (of the rotating machine 11) and control disturbance, the instantaneous value of the output current is the limit current. In order not to exceed the line, it is necessary to stop the supply of the three-phase AC voltage from the power conversion means 3 to the rotating machine 11 immediately before the line is exceeded.

The limit current line is caused by a deterioration phenomenon such as a dielectric breakdown due to heat generation when an excessive current flows through the rotating machine 11, or by a thermal demagnetization when the rotating machine 11 is a permanent magnet synchronous machine having a permanent magnet in the field. It is necessary to set the value so as to prevent all the phenomena caused by the overcurrent that may occur in the power conversion device 100 or the rotating machine 11 such as the degradation of the performance and the element destruction due to the excessive current of the switching element of the power conversion means 3. .
Normally, the limit current line is set to a value that does not cause the phenomenon that can occur with the smallest (absolute value) current among the above-mentioned phenomena caused by overcurrent, and a margin is considered for the limit current line. After that, the current threshold value in the overcurrent protection operation is set.

When the control calculation cycle Δt is set to a certain fixed value as in the conventional device disclosed in Patent Document 1, overcurrent protection operation is desired based on the limit current line and the maximum current during normal operation. The current thresholds A and B and the control calculation period Δt can be set in advance.
However, as in the present invention, the control calculation cycle Δt changes according to the frequency fc of the carrier wave, or according to the frequency of the three-phase AC voltage command (inverter frequency finv) as in the synchronous PWM method. In the case of changing, it is necessary to change the current thresholds A and B in accordance with the control calculation cycle Δt (in other words, the frequency fc of the carrier wave, the inverter frequency finv in the synchronous PWM method).
In short, the current thresholds A and B are set based on at least one of the control calculation cycle Δt, the frequency fc of the carrier wave, and the inverter frequency finv that is the frequency of the voltage command.

FIG. 6 is a diagram showing the influence on the change amount ΔI of the output current and the predicted output current value (I + ΔI) due to the difference (change) in the control calculation period Δt. The necessity of changing the current thresholds A and B according to the control calculation cycle Δt will be described.
In FIG. 6, the frequency fc of the carrier wave is lowered under the condition that the integer N that is a parameter for setting the control calculation period Δt is constant (in addition, in the synchronous PWM method, the inverter frequency finv is lowered). ) That is, as the carrier period becomes longer, the control calculation period Δt becomes longer from Δt1 to Δt2. (Δt1 <Δt2)

  When the output current I changes as shown by the thick solid line in FIG. 6, the output current change amount ΔI and the predicted output current value I + ΔI are obtained with reference to the time t0 (the current at this time is I0). The amount of change in the output current at the control calculation period Δt1 is ΔI1, the predicted value of the output current (predicted value 1) is the asterisk I1 + ΔI1 (= I0 + 2ΔI1) in FIG. The change amount of the output current at the period Δt2 is ΔI2, and the predicted value of the output current (predicted value 2) is the diamond mark I2 + ΔI2 (= I0 + 2ΔI2) in FIG.

Therefore, even when the current change is the same, there are differences in the current change amounts I1, ΔI2 and the predicted current values I1 + ΔI1, I2 + ΔI2 when the control calculation cycle is Δt1, Δt2, and therefore the same current thresholds A, B If the overcurrent protection operation is performed based on the above, there is a possibility that the desired protection operation is not achieved.
In FIG. 6, if the current threshold A is set to a fixed value such that “ΔI1 <current threshold A <ΔI2”, in the case where the control calculation cycle is Δt1 regardless of the same current change, In the case where the protective operation is not performed at t0 + Δt1 and the control calculation cycle is Δt2, the protective operation is performed at time t0 + Δt2.

From this, there is a possibility that it does not operate when protection for the power conversion means 3 is necessary, or on the contrary, it operates when protection for the power conversion means 3 is not necessary.
In the case of the current threshold B, in the example of FIG. 6, if the current threshold B is set to a fixed value slightly lower than I1 + ΔI1 (generally in the vicinity of the current I2 in FIG. 6), the control calculation cycle Is Δt1, at time t0 + Δt1, and since the predicted value 1 (I1 + ΔI1) at that time exceeds the current threshold B, a protection operation is performed. In the case where the control calculation cycle is Δt2, at time t0 + Δt2, Since the predicted value 2 (I2 + ΔI2) at the time exceeds the current threshold value B, the protection operation timing varies such that the protection operation is not performed until time t0 + Δt2.

Further, in an example different from the above in setting the current threshold B, in FIG. 6, when the current threshold B is set to a fixed value slightly lower than I2 + ΔI2, in the case where the control calculation cycle is Δt2, the time t0 + Δt2 In the case where the control operation cycle is Δt1, the predicted value 1 (I1 + ΔI1) at the time t0 + Δt1 does not exceed the current threshold value B, and at the time t0 + 2Δt1 when Δt1 has passed, The predicted value 1 ′ (I1 ′ + ΔI1 ′) at the time exceeds the current threshold B, and the protection operation is performed at time t0 + 2Δt1.
However, as described above, the control calculation cycle is shorter than Δt2, and in the example of FIG. 6, the time lag between time t0 + Δt2 and time t0 + Δ2t1 is small.

  Based on the above, it is desirable to set a value proportional to the length of the control calculation period Δt for the current threshold A, and the value for the current threshold B decreases as the control calculation period Δt increases. In other words, the margin for the limit current line may be set large.

FIG. 7 is a conceptual diagram showing an example of a preferable relationship between the control calculation cycle Δt and the current thresholds A and B. In practice, the relationship between the control calculation cycle Δt and the current thresholds A and B is stored in the storage device. 101 or the like is stored in the form of a table or a mathematical expression.
Also, instead of the control calculation period Δt, the carrier wave frequency fc, which is a parameter related to the setting of the control calculation period Δt, or the voltage command frequency (inverter frequency finv) in the synchronous PWM method (inverter frequency finv) A form in which a suitable relationship with the current thresholds A and B is stored may be used.

Therefore, regardless of the length of the control calculation cycle Δt, in order to make the protective operation for the power conversion means 3 operate as desired, the carrier wave which is a parameter related to the setting of the control calculation cycle Δt or the control calculation cycle Δt Current thresholds A and B need to be changed in accordance with the frequency fc or the frequency of the voltage command (inverter frequency finv) in the synchronous PWM method.
The above is the description of the system configured by the power conversion device 100 according to the first embodiment.

  In Embodiment 1 of the present invention, the output current change amount ΔI is calculated based on the output current I detected by the current detection means 4, and the output current I detected by the current detection means 4 and the output current are calculated. After calculating the predicted value I + ΔI of the output current in the next control calculation cycle based on the change amount ΔI, the output current is calculated based on the change amount ΔI of the output current or the predicted value I + ΔI of the output current. Although the system that determines whether or not it is abnormal and performs the overcurrent protection operation for the power conversion means 3 has been described, the output current change amount ΔI, the current threshold A, and the like, depending on the performance of the processor 102 and the calculation load processing capability The overcurrent protection operation may be performed only by comparing the current values, or the overcurrent protection operation may be performed only by comparing the predicted value I + ΔI of the output current with the current threshold value B. The method of It goes without saying that enables a more suitable overcurrent protection operation when.

  According to the first embodiment, the overcurrent threshold for the power conversion means is determined according to the control calculation cycle or a parameter related thereto, for example, the frequency of the carrier wave, or the voltage command frequency (inverter frequency) in the synchronous PWM method. Therefore, regardless of the length of the control calculation period set based on the carrier frequency, overcurrent protection for the appropriate power conversion means is realized, and the power conversion means is destroyed due to overcurrent and connected to the power conversion means. This has the effect of preventing deterioration and demagnetization of the rotating machine.

Further, the mode of setting the frequency of the carrier wave to M times the frequency of the voltage command (M is a positive integer), that is, by applying the synchronous PWM method, the inverter frequency finv is compared with the asynchronous PWM method. The maximum value can be set high, and it is possible to drive even in a high speed region where it is difficult to drive with asynchronous PWM, and there is an effect that it is possible to realize overcurrent protection for an appropriate power conversion means even in the high speed region.
Even when the carrier frequency does not change, that is, when the length of the control calculation period Δt does not change, the protective operation is performed as shown in FIG. 5 depending on the relationship between the timing of the control calculation period Δt and the current threshold A or B. The timing may vary. Therefore, by setting the current threshold based on the timing of the control calculation cycle Δt, there is an effect that the protection operation timing can be prevented from being delayed even if the control calculation cycle Δt is large.

Embodiment 2. FIG.
Next, a power converter according to Embodiment 2 of the present invention will be described with reference to FIG.
FIG. 8 shows an overall view of a system including a power conversion device 100A according to Embodiment 2 of the present invention, and is constituted by a rotating machine 11, an AC power source 12, and a power conversion device 100A.
The power conversion apparatus 100A includes a voltage command generation unit 1A, a drive signal generation unit 2, a power conversion unit 3, a current detection unit 4, a control calculation cycle setting unit 5, and a power conversion unit protection unit 6A.

In the first embodiment, as a protection operation for the power conversion unit 3, the power conversion unit protection unit 6 outputs to the drive signal generation unit 2 an output of a PWM signal of each phase that is a drive signal for the power conversion unit 3. All the signals for stopping were output, and the supply of the three-phase AC voltage from the power conversion means 3 to the rotating machine 11 was stopped.
In contrast, in power converter 100A according to the second embodiment of the present invention, power converter protection unit 6A provides a three-phase AC voltage output from voltage command generator 1A in order to continue the operation of rotating machine 11. By reducing the inverter frequency finv, which is the frequency of the voltage commands Vu *, Vv *, Vw *, the power output from the power conversion means 3 to the rotating machine 11 is reduced, and the power conversion means 3 is protected. It is a thing.

In the following, the configuration of the power conversion means protection unit 6A and the voltage command generation unit 1A, which are different from those in the first embodiment, will be mainly described in FIG. 8, and the same parts as those in FIG. To do.
The power conversion means protection unit 6A is the same as that of the first embodiment in that the output current abnormality determination is the same as in the first embodiment. Since it becomes a loose protection operation, it is determined as abnormal compared to the output current abnormality determination condition in the first embodiment, such as setting the current threshold A, B to a value smaller than the current threshold A, B in the first embodiment. It is desirable to make the conditions easy to do.
As a protection operation for the power conversion means 3, the power conversion means protection section 6A is configured such that the absolute value of the inverter frequency finv (the frequency of the three-phase AC voltage commands Vu *, Vv *, Vw * output from the voltage command generation section 1A ) Is output to the voltage command generator 1A.

That is, assuming that the inverter frequency before compensation based on the frequency compensation amount Δf set as the target value is finv0, finv = finv0 + Δf (however, | finv0 so that the signs of finv and finv0 do not invert before and after compensation) |> | Δf |), Δf <0 if the inverter frequency finv0> 0, and Δf> 0 if finv0 <0.
The frequency compensation amount Δf is an excess of the absolute value | ΔI | of the change amount of the output current with respect to the current threshold A to be compared in the output current abnormality determination, or the absolute value of the predicted output current value with respect to the current threshold B | It is obtained based on a proportional value corresponding to the excess of I + ΔI | and an integral value for each control calculation cycle Δt of these excesses. Further, the frequency compensation amount Δf may be obtained as a function of these excesses.

The voltage command generation unit 1A uses the frequency corrected by reducing the frequency compensation amount Δf by the frequency required for driving the rotating machine 11 at a desired rotational speed as an inverter frequency finv. Outputs phase AC voltage commands Vu *, Vv *, Vw *.
Therefore, although the speed deviation of the actual rotational speed with respect to the desired rotational speed occurs, unlike the case where the supply of the three-phase AC voltage from the power conversion means 3 to the rotating machine 11 is stopped, the operating state of the rotating machine 11 is continued. .
The above is the description of the system configured by the power conversion device 100A according to the second embodiment. According to the second embodiment, there is an effect that the protection of the power conversion means 3 can be realized while continuing the operation without stopping the rotating machine 11.

Embodiment 3 FIG.
Next, a power converter according to Embodiment 3 of the present invention will be described with reference to FIGS.
As described above, the protection operation for the power conversion means 3 in the present invention is a deterioration phenomenon such as dielectric breakdown due to heat generation when an excessive current flows through the rotating machine 11, and the rotating machine 11 has a permanent magnet in the field. This is performed in order to prevent the deterioration of performance due to thermal demagnetization in the case of a permanent magnet synchronous machine, and the phenomenon of element destruction due to excessive current of the switching element of the power conversion means 3, and the output current of the power conversion means 3 The purpose is to prevent the instantaneous value of the output current from exceeding the limit current line in the process of gradually increasing due to factors such as load fluctuation and control disturbance.

  However, in actual operation, the asynchronous PWM method and the synchronous PWM method are switched according to the inverter frequency finv, or an integer M which is the frequency fc of the asynchronous PWM method and the ratio of fc / finv of the synchronous PWM method is set. In this invention, the PWM method and the switching operation of the integer M are assumed in this invention, and the frequency fc of the carrier wave is discontinuous with respect to the inverter frequency finv. Sometimes.

FIG. 9 shows an example of the relationship of the set value of the carrier wave frequency fc to the inverter frequency finv. In FIG.
-Finv: 0Hz-333.3Hz ... Asynchronous PWM method fc: 3kHz
-Finv: 333.3Hz-500Hz ... Synchronous PWM system (M = 9)
fc: 9finv [Hz]
Finv: 500 Hz to 750 Hz ... Synchronous PWM method (M = 6)
fc: 6finv [Hz]
-Finv: 750 Hz--Synchronous PWM method (M = 3) fc: 3 finv [Hz]
Is assumed to be set.

In this case, as shown in FIG. 9, the frequency fc of the carrier wave switches discontinuously at finv: 500 Hz and 750 Hz. At this moment, the output current due to the shock caused by the discontinuous switching of the frequency fc of the carrier wave is different from the process in which the output current of the power conversion means 3 increases stepwise due to factors such as load fluctuation and control disturbance. The output current pulsation due to this switching usually converges in an instant.
In this third embodiment of the present invention, this instantaneous current pulsation may cause an overcurrent protection operation erroneously other than a phenomenon that should originally protect the power conversion means 3 such as load fluctuation or control disturbance. The overcurrent protection operation is not performed due to a shock caused by discontinuous switching of the carrier wave frequency fc, or the output current of the power conversion means 3 is stepwise due to factors such as load fluctuations and control disturbance described above. Due to the increasing phenomenon, the overcurrent protection operation is performed when the shock due to the discontinuous switching has a large influence on the power conversion means 3 and the rotating machine 11.

FIG. 10 shows an overall view of a system including a power conversion device 100B according to Embodiment 3 of the present invention, which is composed of a rotating machine 11, an AC power source 12, and a power conversion device 100B.
The power conversion device 100B includes a voltage command generation unit 1, a drive signal generation unit 2, a power conversion unit 3, a current detection unit 4, a control calculation cycle setting unit 5, and a power conversion unit protection unit 6B.
The power conversion device 100B according to the third embodiment of the present invention switches the carrier wave frequency fc discontinuously in order not to perform an overcurrent protection operation due to a shock caused by discontinuous switching of the carrier wave frequency fc. In this case, the protection operation of the power conversion means protection unit 6B is stopped during a predetermined period from the start of switching.

In the following, in FIG. 10, the configuration of the power conversion means protection unit 6 </ b> B different from that in Embodiment 1 will be mainly described, and the same parts as those in FIG.
In the power conversion means protection unit 6B, the point relating to the output current abnormality determination is the same as in the first embodiment, but the set value of the frequency fc of the carrier wave set by the drive signal generation unit 2 is used as the control calculation cycle Δt. Each time, it is determined whether or not the switching is discontinuous from the amount of change of the carrier wave frequency fc per control calculation period Δt. When it is determined that the switching is discontinuous, the switching is started (discontinuous switching). The protection operation for the power conversion means 3 is stopped for a predetermined period after the determination.

The protection operation stop period may be set based on the convergence time by obtaining the time until the output current pulsation due to switching converges based on prior measurement or prior analysis / simulation.
Alternatively, if the operation of switching the integer M, which is the ratio of fc / finv, is performed during the acceleration (decrease) speed at which the value of the inverter frequency finv increases or decreases, the inverter frequency to be switched (finv in the case of FIG. 9: In this case, the non-operation band may be set so that the protection operation is stopped until the value of finv changes by Δf ′. The value of the non-operating band Δf ′ may be set based on the convergence time and the acceleration / deceleration rate after the time until the output current pulsation converges is obtained by preliminary measurement, preliminary analysis / simulation.

In the period from switching to convergence, if the instantaneous maximum value of the pulsating current generated by switching exceeds the limit current line, a margin is set based on the instantaneous value of the output current of the power conversion means 3 and the limit current line. The protection operation of the power conversion means 3 may be performed based on a magnitude relationship with a predetermined threshold that is set.
The above is description of the system comprised by the power converter device 100B which concerns on Embodiment 3. FIG.

According to the third embodiment, when the frequency of the carrier wave is switched discontinuously, there is an effect that it is possible to prevent protection from being erroneously applied due to the output current pulsation due to the switching shock.
Further, when the influence of the switching shock on the power conversion means 3 and the rotating machine 11 is larger than the phenomenon in which the output current of the power conversion means 3 increases stepwise due to the above-described factors such as load fluctuation and control disturbance, the switching is performed. The overcurrent protection functions even against an output current pulsation due to a shock, and there is an effect that the overcurrent protection for the power conversion means 3 can be reliably performed.

Embodiment 4 FIG.
Next, a power conversion device according to Embodiment 4 of the present invention will be described. The configuration of power conversion device 100 in the fourth embodiment is the same as that in FIG.
The power conversion device according to the fourth embodiment has a configuration of an embodiment different from the abnormality determination of the output current of the power conversion means 3 described in the first to third embodiments. In the first embodiment described above, the output current of the power conversion means 3 for one time is stored in the storage device 101 as the previous value Iold, and the change amount ΔI of the output current is obtained from the current value I and the previous value Iold. However, if the change amount ΔI of the output current changes sharply and an overcurrent protection operation is urgently required, a plurality of past output current change amounts ΔI are stored and stored. By grasping the degree of change in the change amount I of the output current for each control calculation cycle Δt, the prediction accuracy until reaching the current threshold value B can be increased, and it becomes easy to cope in advance.

Based on this, the amount of change ΔI of the output current is stored in the storage device 101 for a plurality of times in the past, and the power conversion means protection unit 6 determines the abnormality of the output current based on these. good.
By storing at least one past change amount ΔI of the output current in the storage device 101, a finer determination can be made. As an example, abnormality determination is performed based on the amount of change ΔI of the output current for the past two times as in the following formulas (5) and (6).
・ Absolute value of change in output current | ΔI |> Threshold A (5)
・ Value of control calculation period Δt one minute before | ΔI |> Threshold A1 (6)
That is, it is determined that the output current is abnormal if both of the expressions (5) and (6) are satisfied. The operation at the time of abnormality determination is the same as that in the first embodiment.

Here, two values for storing the change amount ΔI of the past output current have been described, but it is not limited to two and may be three or more. In this case, noise resistance is further improved. To do.
Further, as an embodiment of output current abnormality determination different from the above, a plurality of output current variations ΔI calculated in the past every control calculation cycle Δt are stored in the storage device 101, and the stored L (L: an arbitrary positive integer representing the number of samples) output current change amount ΔI is taken, and as an example, the average of the output current change amounts ΔI for a plurality of past times as shown in the following equation (7) You may make it obtain | require absolute value (DELTA) Iave of a value.
ΔIave = | Σ (1, L) output current change amount ΔI / L | (7)

With respect to the average value Iave of the calculated change amount of the output current, the control calculation period Δt, or the carrier wave frequency fc that is a parameter related to the setting of the control calculation period Δt, or (three-phase AC in the synchronous PWM method) In comparison with the current threshold C set according to the voltage command frequency (inverter frequency finv), it may be determined that the output current is abnormal if the condition of equation (8) is satisfied. The operation at the time of abnormality determination is the same as that in the first embodiment.
.DELTA.Iave> threshold C (8)
In the above example, the average value of a plurality of past output current changes ΔI is targeted, but the weight is increased as the stored value is closer to the present, and the weight is decreased as the past is averaged. A weighted average may be used. In this case, since the weight is greater as it is closer to the present time, the value becomes closer to reality, and an abnormal current change can be detected more accurately.
The above is the description of the power conversion device according to the fourth embodiment.

  According to the fourth embodiment, since the abnormality determination of the output current of the power conversion unit 3 is performed using more information on the output current, the overcurrent protection for the power conversion unit is more reliably performed than in the previous embodiment. There is an effect that can be done.

Embodiment 5
Next, as an invention of Embodiment 5, an air conditioner using the power conversion device according to Embodiments 1 to 4 described above will be described with reference to FIG.
FIG. 11 is a configuration diagram of an air-conditioning apparatus according to Embodiment 5 of the present invention. Hereinafter, the case where the power converter device which concerns on Embodiment 1-4 is applied to a compressor and an air conditioning apparatus is demonstrated, referring FIG.

A power conversion device 100 shown in FIG. 11 is a power conversion device according to any one of Embodiments 1 to 4, and receives power supply from an AC power supply 12 and applies an AC voltage to the rotating machine 11 to rotate. To drive. The rotating machine 11 is connected to a compression element 51, and the rotating machine 11 and the compression element 51 constitute a compressor 50 that compresses the refrigerant.
The compressor 50, the four-way valve 52, the outdoor heat exchanger 53, the expansion device 54, the indoor heat exchanger 55, the four-way valve 52, and the compressor 50 are connected by refrigerant piping in this order to constitute a refrigeration cycle. Among these, the outdoor unit 61 includes a power conversion device 100, a compressor 50, a four-way valve 52, an outdoor heat exchanger 53, and an expansion device 54, and the indoor unit 62 includes an indoor heat exchanger 55. Has been.

Next, the operation of the air conditioner shown in FIG. 11 will be described taking cooling operation as an example.
When the cooling operation is performed, the four-way valve 52 causes the refrigerant discharged from the compressor 50 to go to the outdoor heat exchanger 53 in advance and the refrigerant flowing out from the indoor heat exchanger 55 to go to the compressor 50. It is assumed that the flow path is switched to.
When the rotating machine 11 of the compressor 50 is rotationally driven by the power conversion device 100, the compression element 51 of the compressor 50 connected to the rotating machine 11 compresses the refrigerant, and the compressor 50 discharges the high-temperature and high-pressure refrigerant. The high-temperature and high-pressure refrigerant discharged from the compressor 50 flows into the outdoor heat exchanger 53 via the four-way valve 52 and performs heat exchange with the outside air in the outdoor heat exchanger 53 to radiate heat.

The refrigerant flowing out of the outdoor heat exchanger 53 is expanded and depressurized by the expansion device 54, becomes a low-temperature and low-pressure gas-liquid two-phase refrigerant, flows into the indoor heat exchanger 55, and performs heat exchange with the air in the air-conditioning target space. The refrigerant evaporates into a low-temperature and low-pressure gas refrigerant and flows out of the indoor heat exchanger 55. The gas refrigerant flowing out from the indoor heat exchanger 55 is sucked into the compressor 50 via the four-way valve 52 and compressed again. The above operation is repeated.
In addition, in FIG. 11, although the example which applied the power converter device which concerns on Embodiment 1-4 to the compressor 50 of an air conditioning apparatus was shown, it is not limited to this, Other than an air conditioning apparatus The present invention may be applied to heat pump devices, refrigeration devices and other refrigeration cycle devices in general.
The above is the description of the air-conditioning apparatus according to Embodiment 5.

  According to the fifth embodiment, it is possible to detect a steep current change amount that occurs when the compressor is locked or stepped out during operation regardless of the length of the control calculation cycle set based on the carrier frequency, By realizing the overcurrent protection for the appropriate power conversion means, there is an effect of improving the reliability of the air conditioner using the power conversion device including the power conversion means.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments, and various design changes can be made. Within the scope of the present invention, each embodiment is described. These embodiments can be freely combined, and each embodiment can be modified or omitted as appropriate.

1, 1A: voltage command generation unit, 2: drive signal generation unit, 3: power conversion means,
4: current detection means, 5: control calculation cycle setting section, 6, 6A, 6B: power conversion means protection section,
11: rotating machine, 12: AC power supply, 50: compressor, 51: compression element, 61: outdoor unit,
62: Indoor unit, 100, 100A, 100B: Power conversion device, 101: Storage device,
102: Processor

Claims (11)

A voltage command generation unit that generates a voltage command; a drive signal generation unit that generates a carrier wave and generates a drive signal based on the carrier wave and the voltage command; and outputs a voltage based on the drive signal A power conversion means for driving a rotating machine; a current detection means for detecting an output current of the power conversion means; a control calculation period setting unit for setting a control calculation period based on the frequency of the carrier wave; and the control calculation period A power conversion means protection unit that performs a protection operation on the power conversion means when the amount of change in the output current per unit exceeds a predetermined first current threshold;
The first current threshold is set based on at least one of the control calculation period, the frequency of the carrier wave, and the frequency of the voltage command. A voltage command generation unit that generates a voltage command; a drive signal generation unit that generates a carrier wave and generates a drive signal based on the carrier wave and the voltage command; and outputs a voltage based on the drive signal A power conversion means for driving a rotating machine; a current detection means for detecting an output current of the power conversion means; a control calculation period setting unit for setting a control calculation period based on the frequency of the carrier wave; and the control calculation period The power conversion unit protection that performs a protection operation on the power conversion unit when the predicted value of the output current of the next control calculation cycle predicted based on the amount of change in the output current per unit exceeds a predetermined second current threshold value Part
The second current threshold is set based on at least one of the control calculation cycle, the frequency of the carrier wave, and the frequency of the voltage command.   The power conversion apparatus according to claim 1, wherein the control calculation cycle is set according to a change in the frequency of the carrier wave.   The control calculation cycle setting unit sets the control calculation cycle to N / 2 times the carrier wave cycle (N is a positive integer), according to any one of claims 1 to 3. The power converter described.   The drive signal generation unit has a mode in which the frequency of the carrier wave is set to M times the frequency of the voltage command (M is a positive integer). The power converter according to item.   The power conversion device according to any one of claims 1 to 5, wherein the power conversion unit protection unit performs a protection operation to stop voltage output from the power conversion unit.   The power conversion device according to any one of claims 1 to 5, wherein the power conversion means protection unit performs a protection operation for the power conversion means by reducing a frequency of the voltage command.   The power conversion means protection unit, when switching the frequency of the carrier wave discontinuously, stops the protection operation for the power conversion means during a predetermined period from the start of switching. The power conversion device according to any one of 7.   When the frequency of the carrier wave is switched discontinuously, the power conversion means protection unit performs power based on the magnitude relationship between the instantaneous value of the output current and a predetermined threshold during a predetermined period from the start of switching. The power converter according to any one of claims 1 to 7, wherein the converter performs a protection operation.   The power conversion means protection unit stores the change amount of the output current for a plurality of times in the past, and based on the stored degree of change of the output current change or the average value of the change amounts of the plurality of output currents. The power converter according to any one of claims 1 to 9, wherein a protection operation is performed on the power converter.   A refrigeration cycle comprising the power conversion device according to any one of claims 1 to 10 and a compressor connected to power conversion means of the power conversion device, and rotation of a rotating machine constituting the compressor. An air conditioner that compresses the refrigerant.

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