Air conditioner

Abstract

An air conditioner (200) comprises: a refrigerant circuit (100) having a compression element (31) that compresses a refrigerant; a compressor motor (30) serving as a drive source for the compression element (31); a power converter (2) equipped with a converter (21) for rectifying the AC voltage supplied from an AC power supply (1), a film capacitor (23) for smoothing the power rectified by the converter (21), and an inverter (22) that converts the power rectified by the converter (21) into AC power by means of a switching element and outputs the result to the compressor motor (30); and a control unit (4) that controls the refrigerant circuit (100) and the power converter (2). The control unit (4) controls switching operation by the switching element so that a carrier period in which the switching element performs switching and a carrier period in which the switching element does not perform switching are present in one cycle of a signal wave based on a voltage command.

Description

air conditioning equipment

[0001] The present disclosure relates to an air conditioner that performs temperature conditioning using a refrigeration cycle.

[0002] Conventionally, hydrofluorocarbon refrigerants and the like have been used in the refrigeration cycle of air conditioners. However, from the viewpoint of preventing global warming, there is a demand for the use of low global warming potential refrigerants, which have a low global warming potential and a small environmental impact. Low global warming potential refrigerants are, for example, hydrocarbon refrigerants. Hydrocarbon refrigerants are flammable refrigerants that include slightly flammable refrigerants other than non-flammable refrigerants.

[0003] Generally, the density of low-global-warming-potential (LGP) refrigerants is lower than that of hydrofluorocarbon refrigerants. Therefore, when a LGP ​​refrigerant is used in a refrigeration cycle, the refrigerant circulation rate must be increased to ensure the same heat exchange performance as when a hydrofluorocarbon refrigerant is used. To achieve this, the internal volume of the compressor that compresses the refrigerant must be increased, and the rotational speed of the compressor motor must be increased to increase the refrigerant circulation rate. Thus, when a LGP ​​refrigerant is used in a refrigeration cycle, the cost of maintaining performance increases, such as by enlarging the compressor to increase the internal volume. Therefore, the increase in the compressor cost must be offset by reducing the costs of other components.

[0004] For this reason, it has been proposed to reduce the size and cost of the air conditioner by reducing the capacitance of the main circuit capacitor of the inverter of the power converter that constitutes the air conditioner.

[0005] Reducing the capacitance of the main circuit capacitor increases the pulsation of the voltage across the main circuit capacitor. Patent Document 1 discloses a motor starter that detects the voltage between DC buses and determines the timing of start-up, thereby suppressing vibration and achieving stable start-up without loss of synchronism, even when the voltage between DC buses contains large pulsations.

[0006] JP 2007-318984 A

[0007] Reducing the capacity of the main circuit capacitor increases the pulsation of the voltage across the main circuit capacitor, reducing the voltage utilization rate. Because the magnitude of the compressor motor voltage is proportional to the motor's rotational speed, attempting to increase the maximum speed of the compressor motor to increase the amount of refrigerant circulating when the voltage utilization rate is low results in an insufficient inverter output voltage, resulting in unstable compressor motor control. The motor starter disclosed in Patent Document 1 can achieve stable startup without loss of synchronism during motor startup, but is unable to stabilize motor control outside of startup.

[0008] The present disclosure has been made in view of the above, and has an object to provide an air conditioner in which the compressor motor is stabilized even during periods other than startup.

[0009] In order to solve the above-mentioned problems and achieve the object, an air conditioning apparatus according to the present disclosure includes a refrigerant circuit having a compression element that compresses a refrigerant, a compressor motor that is a drive source for the compression element, a rectifier circuit that rectifies AC voltage supplied from an AC power source, a film capacitor that smoothes the power rectified by the rectifier circuit, and a power converter that includes an inverter that converts the power rectified by the rectifier circuit into AC power using switching elements and outputs the AC power to the compressor motor, and a control unit that controls the refrigerant circuit and the power converter. The control unit controls the switching operation of the switching elements so that, during one cycle of a signal wave based on a voltage command, there are carrier periods in which the switching elements perform switching and carrier periods in which the switching elements do not perform switching.

[0010] The air conditioning apparatus according to the present disclosure has the effect of being able to stabilize the compressor motor even when not in operation at startup.

[0011] FIG. 1 shows the configuration of an air conditioning apparatus according to embodiment 1. FIG. 2 shows the hardware configuration of a control unit of an air conditioning apparatus according to embodiment 1. FIG. 3 shows the output voltage waveform of an inverter of an air conditioning apparatus according to embodiment 1. FIG. 4 shows a comparative example of the output voltage waveform of an inverter in an air conditioning apparatus according to embodiment 1. FIG. 5 shows the bus voltage of a power converter in an air conditioning apparatus according to embodiment 1. FIG. 6 shows the configuration of an air conditioning apparatus according to a modified example of embodiment 1.

[0012] An air conditioning apparatus according to an embodiment will be described in detail below with reference to the drawings.

[0013] Embodiment 1. FIG. 1 is a diagram showing the configuration of an air conditioner according to Embodiment 1. The air conditioner 200 includes an outdoor unit 110 and an indoor unit 120. The outdoor unit 110 includes a compressor motor 30 and a compression element 31 constituting a compressor 3, a four-way valve 111, a heat-source-side heat exchanger 112, a power converter 2 for receiving power from an AC power source 1 and driving the compressor motor 30, and a control unit 4 for controlling the power converter 2 and the refrigerant circuit 100. The control unit 4 outputs a drive signal to the power converter 2 to control the inverter 22. The control unit 4 also outputs a refrigerant circuit control signal to the refrigerant circuit 100 to control the temperature conditioning of indoor air by the refrigerant. The indoor unit 120 includes an expansion device 121 and a load-side heat exchanger 122. The refrigerant circuit 100 is configured in the outdoor unit 110 and the indoor unit 120. The refrigerant circuit 100 is composed of a compression element 31 , a four-way valve 111 , a heat source side heat exchanger 112 , an expansion device 121 and a load side heat exchanger 122 .

[0014] The air conditioning device 200 also includes a fan for releasing heat from the refrigerant as it passes through the heat source-side heat exchanger 112, a fan motor that drives the fan, and other components, but these are not shown in Fig. 1. The configuration of the air conditioning device 200, including the refrigerant circuit 100, is not necessarily limited to the configuration illustrated in Fig. 1.

[0015] The power converter 2 includes a converter 21, which is a rectifier circuit that rectifies AC power supplied from the AC power source 1; a film capacitor 23 that functions as a main circuit capacitor and smoothes the power rectified by the converter 21; a reactor 24 provided between the converter 21 and the film capacitor 23; an inverter 22 that converts the power rectified by the converter 21 into AC power and outputs it to the compressor motor 30; and a bus voltage detection means 25 that detects the bus voltage of the power converter 2. The converter 21 may have a well-known structure that rectifies the AC power source voltage using, for example, a diode bridge. However, the converter 21 may also have a function to boost the rectified bus voltage in addition to the rectification function. While FIG. 1 shows an example in which the AC power source 1 is a three-phase power source, the AC power source 1 may also be a single-phase power source. Although not shown in FIG. 1 , the air conditioning apparatus 200 also includes a motor current detection means that detects the motor current required for control calculations in the control unit 4 to drive the compressor motor 30. The motor current detection means uses a well-known method for restoring the motor current, such as providing an ACCT (Alternating Current Transformer), a DCCT (Direct Current Transformer), or a shunt resistor in each phase of the motor, or providing a shunt resistor on the lower arm or bus of each phase of the inverter 22.

[0016] FIG. 2 is a diagram illustrating the hardware configuration of the control unit of the air conditioning apparatus according to the first embodiment. The control unit 4 is realized by a processor 91 that executes various processes, a memory 92 serving as a main memory, and a storage device 93 that stores information. The processor 91 may be a computing device such as an arithmetic unit, a microprocessor, a microcomputer, a central processing unit (CPU), or a digital signal processor (DSP). The memory 92 may be a non-volatile or volatile semiconductor memory such as a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM). The storage device 93 stores programs for executing various control processes. The processor 91 reads the programs stored in the storage device 93 into the memory 92 and executes them. The functions of the control unit 4 are realized by the processor 91 reading the programs stored in the storage device 93 into the memory 92 and executing them. The processing related to the motor control and the processing related to the refrigerant circuit control may be realized by the functions of a common processor 91, or may each be realized by the functions of separate processors 91. In accordance with the calculation processing of the control unit 4, a drive signal for driving the compressor motor 30 is output to each inverter 22.

[0017] In the air conditioner 200, a film capacitor 23 is used instead of a commonly used electrolytic capacitor as the main circuit capacitor of the inverter 22 of the power converter 2 that constitutes the air conditioner 200. By using the film capacitor 23, not only is the cost of the capacitor itself reduced, but the smaller main circuit capacitor also makes it possible to reduce the size of the electronic board on which the capacitor is mounted, and further to reduce the size of the power converter 2, thereby reducing the total cost. Furthermore, because the film capacitor 23 has a longer life than an electrolytic capacitor, using the film capacitor 23 as the main circuit capacitor also has the effect of reducing maintenance costs.

[0018] The inverter 22 converts the bus voltage of the power converter 2, which is the input voltage of the inverter 22, into an AC voltage by controlling the switching operation of the switching elements based on a drive signal from the control unit 4. The inverter 22 controls the output AC voltage and frequency by, for example, PWM (Pulse Width Modulation) control, which controls the on / off of the switching elements, based on the magnitude relationship between a signal wave based on a voltage command and a carrier wave. Here, the voltage command is a target value for the motor voltage of the compressor motor 30, i.e., a target value for the output voltage of the inverter 22.

[0019] FIG. 3 is a diagram showing the output voltage waveform of the inverter of the air conditioning apparatus according to embodiment 1. FIG. 4 is a diagram showing a comparative example of the output voltage waveform of the inverter in the air conditioning apparatus according to embodiment 1. The dotted lines in FIGS. 3 and 4 indicate the envelope of the carrier wave set based on the pulsation waveform of the bus voltage of the power converter 2. The thick solid lines in FIGS. 3 and 4 indicate the output voltage. The thin solid lines in FIGS. 3 and 4 indicate the signal wave based on the voltage command. Note that for simplicity of explanation, FIGS. 3 and 4 show waveforms for a single-phase inverter. The output voltage waveform of the inverter 22 of the air conditioning apparatus 200 according to embodiment 1 is an output voltage waveform obtained when control is performed to increase the output voltage by including carrier periods in which the switching elements perform switching and carrier periods in which the switching elements do not perform switching within one cycle of the signal wave based on the voltage command. In FIG. 3, periods T1 and T2 are carrier periods in which no switching occurs. The output voltage waveform of the comparative example shown in FIG. 4 is an output voltage waveform of the inverter when the switching elements are controlled to be turned on and off based on the magnitude relationship between the signal wave based on the voltage command and the carrier wave.

[0020] The upper limit of the inverter 22 output voltage is limited by the input voltage to the inverter 22, i.e., the bus voltage of the power converter 2. If the capacitance of the main circuit capacitor is large, switching occurs at every carrier cycle. However, the air conditioning apparatus 200 according to embodiment 1 uses a film capacitor 23 with a small capacitance as the main circuit capacitor of the inverter 22. Therefore, pulsation occurs in the output voltage of the inverter 22 when the on / off of the switching element is controlled simply based on the magnitude relationship between the signal wave based on the voltage command and the carrier wave. Figure 5 shows the bus voltage of the power converter in the air conditioning apparatus according to embodiment 1. In Figure 5, the thick solid line indicates the bus voltage when the main circuit capacitor has a large capacitance, and the thin solid line indicates the bus voltage when the main circuit capacitor has a small capacitance. As shown in Figure 5, using a film capacitor 23 with a small capacitance as the main circuit capacitor results in greater pulsation in the bus voltage than when an electrolytic capacitor with a large capacitance is used as the main circuit capacitor.

[0021] If the switching elements are controlled on and off simply based on the magnitude relationship between the signal wave based on the voltage command and the carrier wave, a voltage equivalent to that output from the inverter 22 when a main circuit capacitor with a large capacitance is used near the maximum point of the pulsation can be output. However, near the minimum point of the pulsation, the bus voltage, which is the upper limit of the output voltage, becomes smaller, and the output voltage also becomes smaller, so the average output voltage is lower than when a main circuit capacitor with a large capacitance is used.

[0022] 3 , the air conditioning apparatus 200 according to the first embodiment controls the switching operation of the switching elements so that, during one cycle of the signal wave based on the voltage command, there are carrier periods in which the switching elements perform switching and carrier periods in which the switching elements do not perform switching, by adjusting the amplitude of the carrier wave in the control unit 4, for example, based on the pulsating waveform of the bus voltage. Specifically, the air conditioning apparatus 200 according to the first embodiment controls the output voltage to increase by causing the signal wave to exceed the carrier wave even at times when the signal wave based on the voltage command would be smaller than the carrier wave without correction, thereby causing a carrier period in which no switching occurs.

[0023] Control to create a carrier cycle in which no switching occurs means applying, for one or more carrier cycles, a bus voltage, which is a voltage rectified by converter 21 that rectifies AC power supplied from AC power supply 1, between any output lines of inverter 22. For example, in a three-phase inverter, by applying, for one or more carrier cycles, a bus voltage, which is a voltage rectified by converter 21 that rectifies AC power supplied from AC power supply 1, between any two output lines of two phases, carrier cycles in which switching elements of two or more phases do not perform switching are created.

[0024] When the amplitude of the carrier wave is normalized to 1, the instantaneous amplitude of the carrier wave is Vdc / Vdc0. Here, Vdc is the instantaneous value of the bus voltage, and Vcd0 is the bus voltage value when the capacitance of the main circuit capacitor is sufficiently large. Ideally, in the case of a three-phase power supply, Vdc0 is √2 times, or 1.41 times, the effective line voltage of the power supply. In the case of a single-phase power supply, Vdc0 is 4 / π times, or 1.27 times, the effective line voltage of the power supply. Therefore, the control unit 4 sequentially calculates the value of Vdc / Vdc0 to generate a carrier wave by multiplying the original carrier wave by Vdc / Vdc0, and performs PWM control based on the corrected carrier wave multiplied by Vdc / Vdc0.

[0025] To obtain the instantaneous bus voltage Vdc, the power converter 2 incorporates the instantaneous bus voltage Vdc detected by the bus voltage detector 25 into the internal calculations of the control unit 4. The amplitude of the carrier wave can be set based on this incorporated instantaneous bus voltage Vdc. Furthermore, if calculations are performed simply without detecting the bus voltage, ideally, for a three-phase power supply, the minimum value of Vdc is √(3 / 2), i.e., 1.22, times the effective line voltage of the power supply. Therefore, Vdc can be set to a fixed value between 1.22 and 1.41 times the effective line voltage of the power supply. A carrier wave can then be generated by multiplying the original carrier wave by Vdc / Vdc0, and PWM control can be performed based on the corrected carrier wave by multiplying Vdc / Vdc0. In this case, although the output accuracy of the inverter voltage is lower than in the previously described method, the objective of improving the voltage utilization rate can still be achieved.

[0026] FIG. 6 is a diagram showing the configuration of an air conditioner according to a modification of the first embodiment. The air conditioner 200 according to the first embodiment does not include bus voltage detection means 25. Instead of performing PWM control based on a corrected carrier wave multiplied by Vdc / Vdc0, the air conditioner 200 maintains the amplitude of the carrier wave constant and multiplies the signal wave based on the voltage command by Vdc0 / Vdc to perform PWM control. When using the well-known space vector modulation method for PWM control, the air conditioner 200 according to the first embodiment reflects the pulsating bus voltage instantaneous value Vdc when calculating the modulation factor, thereby achieving the same effect as the air conditioner 200 according to the first embodiment. By controlling in this way to ensure the existence of a carrier period in which no switching occurs, the effective value of the output voltage increases, thereby improving the voltage utilization rate.

[0027] The air conditioning apparatus 200 according to embodiment 1 and the air conditioning apparatus 200 according to a modified example of embodiment 1 are able to stabilize the compressor motor 30 even at times other than startup by performing control to increase the output voltage by creating a carrier cycle in which no switching is performed.

[0028] Embodiment 2 The configuration of an air conditioning apparatus 200 according to Embodiment 2 is the same as that of the air conditioning apparatus 200 according to Embodiment 1. In the air conditioning apparatus 200 according to Embodiment 2, the control unit 4 controls the compressor motor 30 to operate while causing a carrier cycle in which no switching occurs, and when a power supply abnormality such as a drop in power supply voltage causes the detected bus voltage value to fall below a predetermined threshold, the control unit 4 performs control to reduce the rotation speed of the compressor motor 30. The method of controlling the rotation speed of the compressor motor 30 in the control unit 4 can be achieved by implementing a well-known motor speed control algorithm in the control unit 4, and is not limited to a specific control method.

[0029] In an operating state where control is performed to ensure that there is a carrier cycle in which no switching is performed, the voltage utilization rate is high and the power supplied to the compressor motor 30 is large. When power is regenerated from the compressor motor 30 to the power converter 2 from this state, it is easy to secure sufficient regenerative power.

[0030] In the control that reduces the rotation speed of the compressor motor 30 when the detected bus voltage value falls below a predetermined threshold, although the output to the compressor motor 30 is limited, the dropped bus voltage is increased by regenerating power in the film capacitor 23, thereby preventing the inverter 22 from stopping due to a low-voltage abnormality in the bus voltage. Generally, in air conditioners, once the inverter stops, a process is performed that prevents the inverter from restarting for a certain period of time, such as several minutes, to protect the compressor. For this reason, the air conditioner 200 according to the second embodiment allows the film capacitor 23 to regenerate power, thereby increasing the dropped bus voltage and preventing the inverter 22 from stopping due to a low-voltage abnormality in the bus voltage, thereby allowing the inverter 22 to continue operating as long as possible.

[0031] The control unit 4 presets a threshold value Vs1 for determining whether the bus voltage is low-voltage abnormality and a threshold value Vs2 for determining whether control to reduce the rotation speed of the compressor motor 30 is required, and detects a drop in the bus voltage based on the instantaneous bus voltage value Vdc and these threshold values. Note that the threshold value Vs2 is set to a value higher than the threshold value Vs1. In this embodiment, when a low-voltage abnormality occurs in the bus voltage, the inverter 22 is temporarily stopped.

[0032] When it is determined that the instantaneous value Vdc of the bus voltage falls below the threshold value Vs2, the output power to the compressor motor 30 is limited. The output power limit can be achieved by controlling the compressor motor 30 to reduce its rotational speed. Regenerative power is generated by the energy generated when the compressor motor 30 decelerates, and the reduction in the bus voltage stops, making it possible to maintain the minimum bus voltage necessary for the operation of the inverter 22.

[0033] When performing control to reduce the rotation speed of the compressor motor 30, the rotation speed command is reduced in a stepwise manner, triggered by determining that the bus voltage instantaneous value Vdc has fallen below the threshold value Vs2. Note that a proportional-integral control system may be configured to continuously change the rotation speed command in accordance with the difference between the bus voltage instantaneous value Vdc and the threshold value Vs2.

[0034] Furthermore, when the bus voltage recovers, the control to reduce the rotation speed of the compressor motor 30 may be stopped, and the speed of the compressor motor 30 may be controlled to return to the original rotation speed command. In this case, in order to suppress chattering in the operation, it is preferable to control the speed of the compressor motor 30 to return to the original rotation speed command when it is determined that the bus voltage instantaneous value Vdc has exceeded a threshold value Vs3 that is greater than the threshold value Vs2.

[0035] 7 is a flowchart of the processing of the air conditioner according to the second embodiment. The processing is started in an operating state in which the voltage utilization rate is high, that is, the power supplied to the compressor motor 30 is large and control is performed to ensure the existence of carrier periods in which no switching occurs. In step S1, the control unit 4 acquires the bus voltage instantaneous value Vdc detected by the bus voltage detection means 25. In step S2, the control unit 4 determines whether the bus voltage instantaneous value Vdc is less than the threshold value Vs1.

[0036] If the bus voltage instantaneous value Vdc is less than the threshold value Vs1, the result is Yes in step S2, and in step S3, the control unit 4 determines that the bus voltage is a low voltage abnormality and stops the inverter 22. If the bus voltage instantaneous value Vdc is equal to or greater than the threshold value Vs1, the result is No in step S2, and in step S4, the control unit 4 determines whether the bus voltage instantaneous value Vdc is less than the threshold value Vs2. If the bus voltage instantaneous value Vdc is less than the threshold value Vs2, the result is Yes in step S4, and in step S5, the control unit 4 starts control to reduce the rotation speed of the compressor motor 30. After step S5, the process returns to step S1, and the above-mentioned processes are repeated.

[0037] If the bus voltage instantaneous value Vdc is equal to or greater than the threshold value Vs2, the result of step S4 is No. In step S6, the control unit 4 determines whether the bus voltage instantaneous value Vdc is equal to or greater than the threshold value Vs3. If the bus voltage instantaneous value Vdc is equal to or greater than the threshold value Vs3, the result of step S6 is Yes. If control to reduce the rotation speed of the compressor motor 30 is being performed, the control to reduce the rotation speed of the compressor motor 30 is stopped in step S7, and control to return the rotation speed of the compressor motor 30 to the original rotation speed command is initiated. After step S7, the process returns to step S1, and the above-described process is repeated. Note that if the output power of the compressor motor 30 is not limited, nothing is done in step S7, and the process returns to step S1. If the bus voltage instantaneous value Vdc is less than the threshold value Vs3, the result of step S6 is No. In step S6, the process returns to step S1, and the above-described process is repeated.

[0038] In step S2, instead of determining whether the instantaneous bus voltage Vdc is less than the threshold value Vs1, a process of determining whether the instantaneous bus voltage Vdc is equal to or less than the threshold value Vs1 may be performed. Similarly, in step S4, instead of determining whether the instantaneous bus voltage Vdc is less than the threshold value Vs2, a process of determining whether the instantaneous bus voltage Vdc is equal to or less than the threshold value Vs2 may be performed. Furthermore, in step S6, instead of determining whether the instantaneous bus voltage Vdc is equal to or greater than the threshold value Vs3, a process of determining whether the instantaneous bus voltage Vdc is greater than the threshold value Vs3 may be performed.

[0039] By decelerating the motor and regenerating power to the film capacitor 23, which serves as the main circuit capacitor, the power converter 2 can increase the bus voltage. Furthermore, because the voltage utilization rate is higher than in air conditioners using electrolytic capacitors as the main circuit capacitors, the regenerated power is greater. In air conditioners using electrolytic capacitors as the main circuit capacitors, if an overvoltage is applied to the main circuit capacitor during regeneration, the internal resistance generates heat, causing the internal pressure to rise and the electrolytic capacitor's explosion-proof valve to operate. However, if a flammable refrigerant leaks for some reason, the operation of this explosion-proof valve can become an ignition source for the flammable refrigerant. In contrast, the air conditioner 200 according to embodiment 2, which uses the film capacitor 23 as the main circuit capacitor, experiences an open circuit failure when an overvoltage is applied to the main circuit capacitor during regeneration. This makes it less likely to become an ignition source during a failure, reducing the risk of ignition when using a flammable refrigerant.

[0040] Embodiment 3. Figure 8 is a diagram showing the configuration of an air conditioning apparatus according to embodiment 3. The air conditioning apparatus 200 according to embodiment 3 comprises an auxiliary capacitor 27 connected in parallel to the film capacitor 23, which is the main circuit capacitor, via a diode 26, and a resistor 28 connected in parallel to the auxiliary capacitor 27. Other than this, it is the same as the air conditioning apparatus 200 according to embodiment 1.

[0041] In an operating state in which the compressor motor 30 has a particularly high voltage utilization rate and is controlled to have a carrier cycle in which no switching occurs, if the compressor motor 30 suddenly decelerates or the inverter 22 is shut off due to a protective operation of the inverter 22 or other reasons, generating a large amount of regenerative power, the voltage will rise suddenly when the film capacitor 23, which is the main circuit capacitor, absorbs the regenerative power because the film capacitor 23 has a small capacity, and there is a risk of the overvoltage damaging each element of the power converter 2. The elements of the power converter 2 include the switching elements of the inverter 22 and the elements of the converter 21.

[0042] The auxiliary capacitor 27 absorbs the energy of regenerated power when it is generated by the compressor motor 30. The diode 26 rectifies the current so that it flows from the film capacitor 23 to the auxiliary capacitor 27. The resistor 28 consumes the energy of the regenerated power.

[0043] By connecting auxiliary capacitor 27 in parallel to film capacitor 23 via diode 26, the regenerative power can be absorbed not only by film capacitor 23 but also by auxiliary capacitor 27, so the voltage rise due to the energy of the regenerative power can be suppressed to below the withstand voltage of the capacitor. However, since energy is stored in auxiliary capacitor 27 in this state, dissipating this energy through resistor 28 can more effectively suppress overvoltage of the bus voltage.

[0044] By using a film capacitor 23 to reduce the capacity of the main circuit capacitor and by preventing the destruction of each element of the power converter 2 due to overvoltage caused by the regenerative power generated by the compressor motor 30, the air conditioning device 200 can reduce the risk of ignition of flammable refrigerant even if the flammable refrigerant leaks for some reason.

[0045] As in the second embodiment, the configuration of this embodiment is also effective when power is regenerated in the film capacitor 23 to increase the dropped bus voltage in order to avoid the inverter 22 stopping due to a low voltage abnormality in the bus voltage.

[0046] The configurations shown in the above embodiments are merely examples of the content, and may be combined with other known technologies, or parts of the configurations may be omitted or modified without departing from the spirit of the invention.

[0047] REFERENCE SIGNS LIST 1 AC power supply, 2 Power converter, 3 Compressor, 4 Control unit, 21 Converter, 22 Inverter, 23 Film capacitor, 24 Reactor, 25 Bus voltage detection means, 26 Diode, 27 Auxiliary capacitor, 28 Resistor, 30 Compressor motor, 31 Compression element, 91 Processor, 92 Memory, 93 Storage device, 100 Refrigerant circuit, 110 Outdoor unit, 111 Four-way valve, 112 Heat source side heat exchanger, 120 Indoor unit, 121 Expansion device, 122 Load side heat exchanger, 200 Air conditioning device.

Claims

1. a refrigerant circuit having a compression element that compresses a refrigerant; a compressor motor that is a drive source for the compression element; a power converter including a rectifier circuit that rectifies an AC voltage supplied from an AC power source, a film capacitor that smoothes the power rectified by the rectifier circuit, and an inverter that converts the power rectified by the rectifier circuit into AC power using a switching element and outputs the AC power to the compressor motor; a control unit that controls the refrigerant circuit and the power converter, the control unit controls the switching operation of the switching element so that, during one cycle of a signal wave based on a voltage command, there is a carrier period in which the switching element performs switching and a carrier period in which the switching element does not perform switching; An air conditioning apparatus that adjusts the amplitude of a carrier wave based on the pulsation waveform of the bus voltage of the power converter so that a signal wave exceeds the carrier wave, thereby creating a carrier period in which the switching element does not perform switching.

2. The air conditioning apparatus according to claim 1, wherein the control unit controls the switching operation of the switching elements so that there is a carrier period in which the switching elements do not perform switching during a period in which the signal wave is smaller than a carrier wave set based on a bus voltage of the power converter.

3. a bus voltage detection means for detecting a bus voltage of the power converter; The air conditioner according to claim 2 , wherein the carrier wave is set based on a detected value of the bus voltage.

4. a bus voltage detection means for detecting a bus voltage of the power converter; 3. The air conditioning apparatus according to claim 2, wherein the control unit controls the compressor motor to reduce its rotational speed when the detected value of the bus voltage falls below a predetermined first threshold during operation of the compressor motor to control the compressor motor so that a carrier period in which no switching occurs exists.

5. 5. The air conditioning apparatus according to claim 4, wherein the control unit stops the control to reduce the rotational speed of the compressor motor when the detected value of the bus voltage exceeds a second threshold value that is greater than the first threshold value during operation by controlling the rotational speed of the compressor motor.

6. The air conditioner according to any one of claims 1 to 5, further comprising: an auxiliary capacitor connected in parallel to the film capacitor via a diode; and a resistor connected in parallel to the auxiliary capacitor.