JP7479560B2 - Refrigeration Cycle Equipment - Google Patents

Description

The present disclosure relates to a refrigeration cycle device.

In a refrigeration cycle device, in order to recover from the drop in refrigeration or air conditioning capacity that occurs when frost forms on the heat exchanger on the heat source side that functions as an evaporator, a defrosting operation is performed during operation to heat the heat exchanger on the heat source side and melt the frost. In the defrosting operation, the heat exchanger on the heat source side is heated, and thermal energy is consumed in the heat exchanger on the heat source side.

During defrosting operation, a large amount of liquid refrigerant is generated in the heat exchanger on the heat source side, consuming thermal energy and cooled. Some of the liquid refrigerant reaches the compressor via the accumulator. It is known that such a phenomenon called "liquid back" occurs, in which the liquid refrigerant returns to the compressor. Patent Document 1 discloses a method of heating the refrigerant with a power conversion device that supplies power to the compressor in order to prevent the liquid back phenomenon during defrosting operation.

International Publication No. 2020/008620

In defrosting operation, thermal energy is consumed to heat the heat exchanger on the heat source side, so the temperature of the heat exchanger on the user side drops. Originally, a refrigeration cycle device functions as a heat pump, for example during heating operation, in which the heat exchanger on the heat source side acts as an evaporator to lower the temperature, and the heat exchanger on the user side acts as a condenser to raise the temperature. Therefore, defrosting operation, which lowers the temperature of the heat exchanger on the user side, temporarily reduces the function as a heat pump, which is undesirable for users. For that reason, it is desirable for the defrosting operation to be as short as possible and for there to be as little change in temperature as possible.

Although many defrosting technologies have been studied to date, few have been linked to increasing the amount of heat applied to the refrigerant. For example, the method in Patent Document 1 is a method for heating a power conversion device to prevent a special environmental condition called liquid backflow during defrosting operation, and is not intended to improve the performance of a refrigeration cycle device under general defrosting conditions.

The present disclosure has been made to solve the above-mentioned problems, and aims to provide a refrigeration cycle device that can shorten the time during which heating capacity is reduced due to defrosting.

The present disclosure relates to a refrigeration cycle device. The refrigeration cycle device includes a refrigerant circuit including a compressor, an outdoor heat exchanger, a throttling device, an indoor heat exchanger, and a four-way valve, configured to circulate a refrigerant, an inverter that controls the compressor at a variable speed, and a temperature sensor that measures the temperature of the compressor. The refrigerant circuit is configured to be able to perform a defrosting operation in which the refrigerant discharged from the compressor is introduced into the outdoor heat exchanger by switching the direction of the four-way valve. The compressor includes a compression unit and a motor that drives the compression unit. The inverter has, as operation modes, a speed control mode in which the motor is controlled to approach a rotation speed corresponding to a command value, and an output control mode in which the current flowing through the motor is detected and the rotation speed of the motor is controlled to approach a target value.

The refrigeration cycle device according to the present disclosure makes it possible to selectively use the speed control mode and the output control mode. This makes it possible to shorten the time during which the heating capacity is reduced due to defrosting.

1 is a circuit configuration diagram of a refrigeration cycle device 100 according to a first embodiment. FIG. 4 is a diagram showing the flow direction of the refrigerant during defrosting. FIG. 2 is a cross-sectional view showing the structure of the compressor 1. FIG. 2 is a functional block diagram showing a configuration example of an inverter 20. FIG. 2 is a diagram showing the configuration of a control device 15. FIG. 4 is a diagram showing a configuration of a control circuit 41. FIG. 11 is a diagram for explaining an operation in an output control mode. 4 is a flowchart showing a method of controlling an operation mode during heating and defrosting operations in the control device 15. 4 is a time chart showing the operation of the refrigeration cycle apparatus 100 according to the first embodiment. FIG. 5 is a functional block diagram showing a modified example of the inverter in FIG. 4 . FIG. 1 is a cross-sectional view of an interior magnet motor for a compressor. FIG. 4 is a diagram showing stress applied to a thin-walled portion of the rotor core. FIG. 11 is a diagram showing the relationship between the rotation speed of a compressor motor and the stress of a bridge portion. FIG. 2 is a diagram showing the relationship between the frequency, voltage, and current output by an inverter. FIG. 13 is a diagram showing a configuration of a speed control unit 52 applied to the fourth embodiment.

The refrigeration cycle device according to this embodiment will be described below with reference to the drawings. Note that the size relationships between the components in the drawings may differ from the actual relationships. Also, in the drawings, the same reference numerals are used to denote the same or equivalent components, and this applies throughout the entire specification. Furthermore, the forms of the components shown in the entire specification are merely examples, and are not limited to these descriptions.

Embodiment 1.
<Configuration of refrigeration cycle device>
Fig. 1 is a circuit configuration diagram of a refrigeration cycle apparatus 100 according to embodiment 1. As shown in Fig. 1, the refrigeration cycle apparatus 100 includes an outdoor unit 103 and an indoor unit 104. The outdoor unit 103 and the indoor unit 104 are connected by extension pipes 101 and 102.

The refrigeration cycle device 100 comprises a refrigerant circuit 105, an inverter 20, a control device 15, and a temperature sensor 30.

The refrigerant circuit 105 includes a compressor 1, an outdoor heat exchanger 2, a throttling device 3, an indoor heat exchanger 4, a four-way valve 5, and an accumulator 6, which are connected by piping, and are configured to circulate the refrigerant.

The compressor 1 draws in refrigerant, compresses it, and discharges it at a high temperature and high pressure. The compressor 1 has a built-in compression mechanism 12 and a motor 11. The motor 11 generates power to drive the compression mechanism 12 of the compressor 1. The motor 11 is electrically connected to the inverter 20. The motor 11 is driven and controlled by the inverter 20.

Figure 3 is a cross-sectional view showing the structure of the compressor 1. The compressor 1 includes a housing 13, a motor 11, and a compression mechanism 12.

The compressor 1 draws in refrigerant through the suction pipe 1b, compresses it, and discharges it from the discharge pipe 1a at high temperature and pressure. The housing 13 of the compressor 1 houses the compression mechanism 12 and the motor 11.

The motor 11 has a winding 11a and an iron core 11b that are in contact with the refrigerant drawn in from the suction pipe 1b. The winding 11a and the iron core 11b are each configured to receive thermal energy from the refrigerant.

The explanation will be continued with reference to Fig. 1 again. The outdoor heat exchanger 2 and the indoor heat exchanger 4 are used to exchange heat between the refrigerant and a heat medium such as air. For example, a fin-tube type heat exchanger can be used as the outdoor heat exchanger 2 and the indoor heat exchanger 4.

When the refrigeration cycle device 100 is in cooling operation, the outdoor heat exchanger 2 functions as a condenser. When the refrigeration cycle device 100 is in heating operation, the outdoor heat exchanger 2 functions as an evaporator. Note that among refrigeration cycle devices, there are devices such as refrigerators in which the roles of the condenser/evaporator are reversed with the air conditioner, but the following explanation will be given using an air conditioner as a representative example.

The throttling device 3 expands and reduces the pressure of the refrigerant. The throttling device 3 is, for example, a device whose opening degree can be controlled as desired, such as an electronic expansion valve. The opening degree of the throttling device 3 is controlled, for example, by a control device 15. The throttling device 3 is connected between the outdoor heat exchanger 2 and the indoor heat exchanger 4.

The throttling device 3 allows the refrigerant flowing out of either the outdoor heat exchanger 2 or the indoor heat exchanger 4, whichever functions as a condenser, to flow into the other heat exchanger, which functions as an evaporator, at a low temperature and pressure. When the refrigeration cycle device 100 is in cooling operation, the refrigerant flowing out of the outdoor heat exchanger 2 flows into the throttling device 3, where it flows into the indoor heat exchanger 4 at a low temperature and pressure.

The four-way valve 5 has the function of switching the refrigerant flow direction during heating and cooling. The operation of the four-way valve 5 is controlled, for example, by the control device 15. The four-way valve 5 switches the refrigerant flow path so that the discharge side of the compressor 1 is connected to the heat exchanger that functions as a condenser, either the outdoor heat exchanger 2 or the indoor heat exchanger 4. The accumulator 6 stores surplus refrigerant.

The refrigerant flow direction shown in Figure 1 indicates the time of heating, when the high-temperature, high-pressure refrigerant discharged from the compressor 1 flows into the indoor heat exchanger 4. In addition, during defrosting, the flow direction of the refrigerant is reversed. Figure 2 is a diagram showing the refrigerant flow direction during defrosting. When the four-way valve 5 switches as shown in Figure 2, the high-pressure refrigerant discharged from the compressor 1 flows into the outdoor heat exchanger 2 and heats it.

The control device 15 has a mode determination unit 22 that determines whether the operation mode of the inverter 20 should be a speed control mode or an output control mode based on the current operating state (normal or defrosting), and a refrigeration cycle control unit 23 that generates a speed command value for the compressor 1 in normal operation. Note that the operating speed (rps) of the compressor 1 is often expressed in frequency (Hz), so the speed command value is also called a frequency command value.

The temperature sensor 30 detects the temperature of the refrigerant discharged from the compressor 1. The temperature sensor 30 is attached, for example, to the discharge pipe 1a of the compressor 1. Information on the temperature measured by the temperature sensor 30 is input to the mode determination unit 22 of the control device 15.

Next, the detailed configuration of the inverter 20 will be described with reference to Figure 4. Figure 4 is a functional block diagram showing an example configuration of the inverter 20.

The inverter 20 includes a control circuit 41 and a power conversion unit 40. The control circuit 41 receives a speed command value ω* ₁ from an external higher-level control device 15, and current detection signals Iu and Iw detected by current sensors 42a and 42b, and outputs a three-phase voltage command value Vuvw* to the power conversion unit 40.

The control circuit 41 includes an output control unit 21, a selector 61, a dq conversion unit 50, a speed estimation unit 51, a speed control unit 52, and a dq inverse conversion unit 55. In this embodiment, the inverter 20 is provided with an output control unit 21 that controls the output power to be approximately constant.

The dq conversion unit 50 generates the d-axis current value Id and the q-axis current value Iq based on the current detection signals Iu, Iw and the phase estimation value θ.

The speed estimator 51 generates a speed estimate ω _est based on the d-axis voltage command value Vd*, the q-axis voltage command value Vq*, the d-axis current value Id, and the q-axis current value Iq.

The speed control unit 52 generates a d-axis voltage command value Vd* and a q-axis voltage command value Vq* based on the speed command value ω*, the speed estimate value ω _est , the d-axis current value Id, and the q-axis current value Iq.

The dq inverse conversion unit 55 generates a three-phase voltage command value Vuvw* based on the d-axis voltage command value Vd* and the q-axis voltage command value Vq*, and outputs the three-phase voltage command value Vuvw* to the power conversion unit 40 to perform PWM control.

Figure 5 is a diagram showing the configuration of the control device 15. In Figures 1, 2 and 4, the control device 15 includes a mode determination unit 22 and a refrigeration cycle control unit 23 as functional blocks, but the actual hardware configuration includes, for example, a microcomputer.

Specifically, the control device 15 is composed of a CPU (Central Processing Unit) 151, memory (ROM (Read Only Memory) and RAM (Random Access Memory)) 152, and an input/output device (not shown) for inputting various signals. The CPU 151 deploys a program stored in the ROM into the RAM, etc. and executes it. The program stored in the ROM is a program in which the processing procedures of the control device 15 are written. The control device 15 executes control of the refrigeration cycle device in accordance with these programs. That is, the CPU 151 executes processing equivalent to the mode determination unit 22 and the refrigeration cycle control unit 23 in accordance with the program stored in the memory 152. This processing is not limited to processing by software, but can also be processed by dedicated hardware (electronic circuitry).

Figure 6 is a diagram showing the configuration of the control circuit 41. In Figure 4, the control circuit 41 includes, as functional blocks, an output control unit 21, a selector 61, a speed control unit 52, a speed estimation unit 51, a dq inverse transformation unit 55, and a dq transformation unit 50, but the actual hardware configuration includes, for example, a microcomputer.

Specifically, the control circuit 41 includes a CPU 411, a memory (ROM and RAM) 412, and an input/output device (not shown) for inputting various signals. The CPU 411 expands a program stored in the ROM into the RAM and executes it. The program stored in the ROM is a program in which the processing procedure of the control circuit 41 is written. The control circuit 41 executes PWM control of the inverter according to these programs. That is, the CPU 411 executes processing equivalent to the output control unit 21, the selector 61, the speed control unit 52, the speed estimation unit 51, the dq inverse conversion unit 55, and the dq conversion unit 50 according to the program stored in the memory 412. This processing is not limited to processing by software, and can also be processed by dedicated hardware (electronic circuitry).

Each functional block may be a single control unit controlled by the same CPU, or may be separate control units controlled by different CPUs.

The description will be continued with reference to Fig. 4 again. The inverter 20 operates based on the operation mode MODE determined by the control device 15. In the speed control mode, which is the normal operation mode, the selector 61 is set so that the speed command value ω* ₁ of the compressor 1 becomes the speed command value ω* given to the speed control unit 52. As a result, the inverter 20 controls the output frequency based on the speed command value ω* ₁ , and also controls the three-phase voltage command value Vuvw* so that losses in the inverter 20 and the motor 11 are substantially minimized. As a result, efficient operation is performed during normal operation.

On the other hand, in the output control mode, the output control unit 21 in the inverter 20 sequentially calculates the output (power) P of the motor 11 and the upper limit value P* of the output P, and controls the speed command value ω* ₂ so that the output P approaches P*. The selector 61 is set so that the speed command value ω* ₂ becomes the speed command value ω* given to the speed control unit 52.

Note that P* is the power command value, but here, an example will be described in which the maximum value Pmax is adopted to expand the operating range. The maximum value Pmax is the maximum value of the output power that is uniquely determined by the motor constants that represent the motor characteristics and the DC voltage Vdc. The output P and the speed command value ω* ₂ are calculated, for example, by the following formulas (1) and (2). Here, k is a constant, ω is the rotation speed, and Iq is the torque current.
P = k × ω × Iq ... (1)
ω* ₂ = P*/Iq/k ... (2)
Next, the difference in operation depending on the operation mode when the load torque changes will be described with reference to Fig. 7. Fig. 7 is a diagram for explaining the operation in the output control mode. In Fig. 7, Tmax [Nm] indicates the upper limit of the mechanical torque of the compressor 1, and fmax indicates the maximum frequency at the upper torque limit. The areas of the two hatched rectangles with points B and B' as their vertices indicate the magnitude of the motor output. In the heating and defrosting operations, a large motor output corresponds to a high heating capacity and a high defrosting capacity.

Consider the operating state at point A (fmax, Tmax) as the initial state. When the load torque is rapidly reduced due to defrosting operation, etc., in the speed control mode, the rotation speed remains constant regardless of the load torque, so the motor 11 is operated at the maximum frequency fmax corresponding to the torque Tmax. For this reason, in Figure 7, the operating point moves from point A to point B', and the motor output decreases in proportion to the reduction in the load torque.

On the other hand, in the output control mode, the motor 11 is controlled to increase its speed so as to maintain the output Pmax, so the operating point moves to point B and the output of the motor 11 does not change. In other words, the output control mode is an operation mode in which a decrease in the defrosting capacity or heating capacity due to changes such as a decrease in temperature, pressure, or dryness of the refrigerant sucked into the compressor 1 is unlikely to occur.

<Operation of the refrigeration cycle device>
Next, the operation during defrosting and heating operation, which is a feature of the present invention, will be described.

First, a method for setting the operation mode in the control device 15 will be described with reference to FIG. 8. FIG. 8 is a flowchart showing a method for controlling the operation mode during heating and defrosting operations in the control device 15. In the following, steps are abbreviated as S. If the current operation state is defrosting (YES in S1) and a certain amount of time has passed since the start of defrosting (YES in S2), the control device 15 sets the operation mode to the output control mode (S4).

Similarly, if the current operating state is heating (NO in S1) and the discharge temperature is below the judgment value (YES in S3), the operating mode is set to output control mode (S4).

If the current operating state is defrosting (YES in S1) and a certain period of time has not elapsed since the start of defrosting (NO in S2), the control device 15 sets the operating mode to the speed control mode (S5).

Similarly, if the current operating state is heating (NO in S1) and the discharge temperature is higher than the judgment value (NO in S3), the operating mode is set to the speed control mode (S5).

Next, the operation of the entire device will be described with reference to Figure 9. Figure 9 is a time chart showing the operation of the refrigeration cycle device 100 according to embodiment 1. The operation of this embodiment will be described with reference to the solid line waveforms T1 and F1.

When performing defrosting operation, the control device 15 switches the four-way valve 5 as shown at time tA so that the destination of the discharge gas from the compressor 1 is changed from the indoor heat exchanger 4 to the outdoor heat exchanger 2. As a result, the flow direction of the refrigerant is changed from the direction shown in Figure 1 to the direction shown in Figure 2. At the beginning of the switch, the discharge gas from the compressor 1 is at high temperature and high pressure. However, the high-temperature refrigerant flows into the frosted outdoor heat exchanger 2 and is cooled and decompressed. Therefore, if the defrosting operation is continued, the temperature and pressure of the refrigerant drawn into the compressor 1 also decrease as shown in waveform T1, and the discharge temperature decreases accordingly as shown at time tB.

At time tB, the control device 15 detects the decrease in discharge temperature shown in waveform T1 and switches the operation mode of the inverter 20 from the speed control mode to the output control mode.

In the output control mode, as shown by the waveform F1, the inverter 20 operates the compressor 1 at an operating frequency such that the output P is P=Pmax. At this time, the temperature and pressure of the refrigerant around the compressor 1 are relatively high, so the load torque of the compressor 1 is also high. For this reason, in the output control mode, the speed command value ω* ₂ is set to a relatively low value in the inverter 20. At this time, high-temperature refrigerant for defrosting flows into the outdoor heat exchanger 2, but the refrigerant temperature drops at the heat exchanger outlet because heat is taken away by the frost. On the other hand, during the defrosting operation, the indoor heat exchanger 4 is controlled not to exchange heat by stopping the blowing of air, etc., so that as a result, the thermal energy and pressure in the entire refrigerant circuit 105 connected by the refrigerant piping decrease, and the load torque for operating the compressor 1 also decreases accordingly.

The output control unit 21 detects the q-axis current, recognizes this decrease in the load torque, and increases the speed command value ω* ₂ based on equation (2). The increase in rotation speed increases the flow rate of the refrigerant in the refrigerant circuit 105 during defrosting operation, increasing the flow path pressure loss that increases according to the flow rate, and the thermal energy of the refrigerant, i.e., the temperature and pressure, increases according to the pressure loss, thereby increasing the defrosting capacity in the outdoor heat exchanger 2. By repeating the above operations, the defrosting can be quickly completed (time tC in FIG. 9).

When defrosting is completed at time tC, the control device 15 stops the inverter 20 and operates the four-way valve 5 to switch the refrigerant circulation direction to start heating operation and start the inverter 20 again. From time tC to tD, the output control mode continues even after heating starts, so output upper limit operation of P = Pmax is performed. At this time, the motor 11 operates at maximum output, so high heating capacity is obtained and the drop in refrigerant temperature during defrosting and the temperature drop on the indoor side are quickly recovered (time tD in Figure 9).

As a comparative example, the dashed waveforms T2 and F2 in Figure 9 show a time chart in the case of control only in the speed control mode. In the comparative example, unlike the case shown by the solid line, the operating frequency is not increased in accordance with the drop in discharge temperature during defrosting. As a result, the defrosting time (time tB to tC') is long, and the refrigerant temperature recovery after switching to heating is also slow, so the discharge temperature does not increase. Therefore, as shown in the waveform T2 from time tC' to tD', the drop in temperature in the room is not resolved for a long time. In other words, in the comparative example, the defrosting time of the refrigeration cycle device and the start-up time of heating are long, which indicates that user comfort is impaired.

Embodiment 2.
In the first embodiment, an example is shown in which the output control mode and the speed control mode are switched by the control device 15. In the second embodiment, an example is described in which the operation mode is switched inside the inverter. Fig. 10 is a functional block diagram showing a modified example of the inverter in Fig. 4.

The inverter 20A shown in Figure 10 includes a control circuit 41A and a power conversion unit 40. The control circuit 41A includes a minimum value selection unit 120 and a speed upper limit calculation unit 121 instead of the output control unit 21 and the selector 61 in the configuration of the control circuit 41 shown in Figure 4. The other configuration of the control circuit 41A is the same as that of the control circuit 41 shown in Figure 4, and the description will not be repeated.

Next, the operation will be described. The upper speed limit calculation unit 121 calculates the upper rotation speed limit value ω _max based on the following expressions (3) and (4).

It should be noted that Te indicates the output torque, and Pmax indicates the maximum output torque.
The minimum value selection unit 120 compares the command value ω* ₁ in the speed control mode with the rotation speed upper limit value _ωmax in the output control mode, and outputs the smaller one as the speed command value ω* for actual control. The minimum value selection unit 120 enables automatic switching between the output control mode and the speed control mode, and does not require an additional control signal from the control device 15. When the control device 15 requests the output control mode, it is sufficient to specify a rotation speed that is sufficiently higher than the rotation speed upper limit value _ωmax . Then, the speed command value ω* is set to the rotation speed upper limit value _ωmax , and the operation mode of the inverter 20A becomes the output control mode.

Embodiment 3.
In the following, preferred motor specifications for the acceleration operation during high-speed operation, which is the main operation in this embodiment, will be described with reference to Figures 11 and 12. Figure 11 is a cross-sectional view of an embedded magnet motor for a compressor. Figure 12 is a diagram showing the stress applied to the thin wall portion of the rotor core.

As shown in Figure 11, the motor 11 includes a rotor 66 and a stator 67. The rotor 66 of the motor 11 includes a plurality of permanent magnets 71 and an iron core (rotor core) 70. The stator 67 includes an iron core (stator core) 73 and a coil winding 74. As shown in Figure 12, the iron core 70 extends in the radial direction on the q-axis located between adjacent magnets 71A, 71B among the plurality of permanent magnets 71, and has a bridge portion 72A that holds the position of the adjacent magnets 71A, 71B.

Interior permanent magnet synchronous motors (IPMSMs) are widely used as a compressor motor configuration because it is easy to create a structure that prevents magnets from scattering.

In general, the maximum rotation speed of a compressor is specified by the operating frequency (fnom) corresponding to the rotation speed at which the maximum rated capacity is exerted. In the first embodiment, the control command value of the output control mode is described as a fixed value (Pmax), but under conditions where the load torque during defrosting is small, if the operating frequency is controlled to exceed the maximum frequency fnom, the defrosting performance can be improved.

In the IPMSM, by thinning the rotor core at the magnet end (bridge portion 72A in FIG. 12), leakage flux in the rotor is reduced, resulting in high output and high efficiency, but on the other hand, stress against centrifugal force is reduced. It should be noted that the control for light-load and high-speed operation described in the first and second embodiments is particularly effective in the IPMSM. The core must be made thinnest near the q-axis at the magnet end due to requirements in terms of efficiency. The mechanical strength of the rotor core of the IPMSM depends on the strength of this portion near the q-axis at the magnet end. The stress acting on the portion near the q-axis during rotation is shown below in Equations (5) to (7) and in FIG. 12.
^F2 = ^Fr2 + ^Ft2 ... (5)
Fr = ^Mω2 ... (6)
Ft = _k1 × T _L ... (7)
Here, Fr is centrifugal force, Ft is circumferential stress applied to the core, M is the moment of inertia of the outer periphery of the core, ω is angular velocity, _k1 is a proportionality coefficient, T _L is load torque, and F is stress applied to the bridge portion. Conventionally, the stress of the bridge portion has been designed to withstand centrifugal force, but the width of the bridge portion 72A in FIG. 12 is designed to be narrower in the circumferential direction in order to increase the output of the motor. As a result, it was found that the combined force F with the circumferential stress should be the design index. This is how the relationship in equation (5) was derived.

The stress F has a maximum value Fmax specific to the equipment based on the mechanical strength of the rotor. If we consider the condition of F = Fmax, it can be seen from the relational expressions (5) to (7) between the angular velocity ω and the load torque T _L that it is possible to make the angular velocity ω large when the load torque T _L is small. Therefore, the maximum rated torque is defined as T _L max, and the angular velocity under the condition of T _L = T _L max and stress F = Fmax, i.e., the angular velocity at the rated load, is defined as the maximum angular velocity ωnom. A diagram showing the relationship between the rotational speed of the compressor motor and the stress in the bridge section is shown in Figure 13.

On the other hand, in the compressor, the load torque T _L is a function of the refrigerant gas pressure, and the lower the pressure, the smaller the load torque. In this case, the load torque during defrosting is defined as T _L def, and the maximum angular velocity is defined as ωdef. First, T _L max > T _L def is established, and the circumferential stress Ft is reduced by the amount of torque reduction. From equations (5) to (7), it is possible to prevent the overall stress F from changing even if the centrifugal stress Fr is increased by the amount of stress Ft reduced.

That is, by utilizing the fact that the output torque during defrosting operation is smaller than the rated torque, the upper limit frequency can be expanded without increasing the torque rotor core strength. In the first and second embodiments, high-speed operation is performed during defrosting operation, which is an operating state in which the load torque is small, so it is clear that the stress on the rotor core does not increase excessively. That is, in the third embodiment, it is possible to provide a compressor that shortens the defrosting time by increasing the speed, while also reducing the burden on the strength side against destruction due to increased centrifugal force.

Embodiment 4.
During defrosting, there is a risk of a phenomenon (hereinafter referred to as liquid back) occurring in which the refrigerant that has been cooled and liquefied in the outdoor heat exchanger 2 reaches the compressor. Liquid backflow causes the lubricating oil inside the compressor to foam, resulting in poor lubrication. However, when high-speed operation is performed during defrosting as in the first to third embodiments, there is concern that liquid backflow may occur more easily. Below, a method for dealing with liquid backflow will be described with reference to FIG. 14.

Figure 14 shows the relationship between the frequency and the voltage and current output by the inverter. In Figure 14, the solid line indicates the output voltage, and the dashed line indicates the current. Here, the maximum rated frequency is represented by fmax, the maximum value of the output voltage is represented by Vmax, and the maximum frequency at which the motor can operate with maximum efficiency is represented by fnom. When operating a motor at a rotational speed equivalent to a frequency that exceeds the maximum frequency fnom, it is generally operated in weakened excitation mode, but since efficient operation is common from the perspective of energy conservation, the voltage is operated while maintaining the maximum value Vmax. In other words, the motor is operated with voltage and current at Va and Ia as shown in Figure 14.

Now, when considering operating the motor at a rotational speed equivalent to a higher frequency (fmax + Δf), it is customary to operate the motor with the voltage maintained at the maximum value Vmax unless there are particular problems. However, in defrosting operation, it is necessary to reduce the risk of mechanical damage due to liquid backflow, so in embodiment 4, a voltage (Vmax - ΔV) lower than the maximum value Vmax is deliberately output to the inverter. In this way, the current increases from Ib to Ic, and the motor generates heat as the current increases. This allows the refrigerant flowing into the compression mechanism of the compressor to be heated, making it possible to improve resistance to liquid backflow.

Figure 15 is a diagram showing the configuration of the speed control unit 52 applied to embodiment 4. In embodiment 3, the speed control unit 52 shown in Figure 15 is used as the speed control unit 52 in Figure 4 or Figure 10. The speed control unit 52 includes a q-axis current command calculation unit 110, a d-axis current command calculation unit 111, a voltage command calculation unit 112, a phase calculation unit 113, and subtractors 114 to 116. The control device 15 includes a heating determination unit 117 that controls ON/OFF of heating control based on the compressor discharge temperature Td and the operation mode MODE. HEAT indicates a heating control signal provided from the heating determination unit 117 in the control device 15.

The heating judgment unit 117 monitors the compressor discharge temperature Td and the operation mode MODE. If the operation mode is the output control mode and the discharge temperature Td is equal to or lower than the judgment temperature, it is determined that the compressor needs to be heated, and the heating judgment unit 117 sets the heating control signal to ON. In other cases, the heating judgment unit 117 sets the heating control signal to OFF.

When the external heating control signal HEAT is OFF, the d-axis current command calculation unit outputs the d-axis current command Id* according to normal d-axis current control. In this case, the d-axis current command Id* is determined by the following equations (8) and (9).
If V<Vmax, Id*=0 (8)
When V = Vmax

Here, R is the phase resistance, Ld is the d-axis inductance, Lq is the q-axis inductance, Φf is the induced voltage constant, ω is the electrical angular velocity, Id* is the d-axis current command, and Iq* is the q-axis current command.

On the other hand, when the heating control signal HEAT is ON, Id* is determined according to the following equation (10).

Here, Imax denotes the maximum current rating.
The maximum rated current value Imax is a value specific to the motor that is determined by the demagnetization current limit. In other words, the current is controlled at the maximum rated current value Imax, which is the maximum current value that the motor can tolerate. This increases the motor loss and can increase heat generation. In addition, Id* is a negative value in equation (10), but this is because it is considered that the d-axis current command cannot be increased at the inverter voltage upper limit. If the inverter voltage upper limit is sufficiently high, heating is possible even if a positive value is used.

In the above, the current limit is determined by the demagnetization current limit, but if the inverter current rating or motor detuning limit is lower than the demagnetization current limit, these may be set as upper limits to control the motor.

According to the refrigeration cycle device of the present disclosure, by controlling the compressor frequency to increase, the pressure loss in the refrigerant circuit and the mechanical loss, iron loss, and copper loss of the compressor increase, promoting an increase in the refrigerant temperature or refrigerant pressure. This allows the defrosting operation of the outdoor heat exchanger to be completed early, and the time during which the heating capacity of the indoor heat exchanger is reduced after the defrosting operation can be shortened.

In addition, shortening the defrosting time not only eliminates the feeling of cold air that users experience during heating operation, but also has the effect of improving the average heating capacity.

(summary)
Finally, the present embodiment will be summarized with reference to the drawings again. The refrigeration cycle device 100 of the present embodiment shown in FIG. 1 includes a refrigerant circuit 105 and an inverter 20. The refrigerant circuit 105 includes a compressor 1, an outdoor heat exchanger 2, a throttling device 3, an indoor heat exchanger 4, and a four-way valve 5, and is configured to circulate a refrigerant. The inverter 20 is configured to perform variable speed control of the compressor 1. The refrigerant circuit 105 is configured to perform a defrosting operation in which the refrigerant discharged from the compressor 1 is introduced into the outdoor heat exchanger 2 by switching the four-way valve 5 as shown in FIG. 2. The compressor 1 includes a compression mechanism 12 and a motor 11 that drives the compression mechanism 12. The inverter 20 has, as operation modes, a speed control mode in which the motor 11 is controlled to approach a rotation speed corresponding to a command value, and an output control mode in which the current flowing through the motor 11 is detected and the rotation speed of the motor 11 is controlled to approach a target value.

This configuration makes it possible to switch between the speed control mode and the output control mode of the inverter 20 in response to the refrigerant state that changes as a result of switching the four-way valve 5. This allows the rotation speed to automatically follow changes in the refrigerant state in a short period of time, providing a refrigeration cycle device that can improve capacity.

The inverter 20 is configured to operate using the output control mode during defrosting operation. This provides a refrigeration cycle device that can shorten the defrosting time, which is a weakness of heat pumps.

10, the output control mode is used when the value indicated by the command value ω* ₁ given from the outside becomes equal to or greater than the upper limit value _ωmax of the rotation speed determined by the DC voltage of the inverter 20, the characteristic value of the motor 11, and the current of the motor 11. Therefore, since the output control mode is applied only by the command value ω* ₁ given from the outside, a refrigeration cycle device with excellent feasibility and few changes to the interface can be provided.

As shown in FIG. 8, during defrosting operation (YES in S1), the operating mode is set to speed control mode when defrosting starts (S5), and after a certain time has elapsed since the start of defrosting (YES in S2), the operating mode is switched from speed control mode to output control mode (S4).

The refrigeration cycle device 100 shown in Fig. 1 further includes a temperature sensor 30 that measures the discharge temperature Td of the refrigerant discharged by the compressor 1. As shown in Fig. 8, the operation mode is set to the speed control mode (S5) when the discharge temperature Td of the compressor 1 is higher than the judgment value (NO in S3), and is set to the output control mode (S4) when the discharge temperature Td of the compressor 1 is lower than the judgment value (YES in S3).

As shown in Figure 11, the rotor 66 of the motor 11 includes a plurality of permanent magnets 71 and an iron core 70. As shown in Figure 12, the iron core 70 extends in the radial direction on the q-axis between adjacent magnets 71A, 71B among the plurality of permanent magnets 71, and has a bridge portion 72A that holds the position of the adjacent magnets 71A, 71B. This configuration makes it possible to provide a refrigeration cycle device that is a combination of a motor and an inverter that is highly feasible and has little effect on the motor rigidity due to high speed rotation.

As shown in Figure 15, the inverter 20 has a d-axis current command calculation unit 111 that controls the amplitude and phase of the current of the motor 11. During the output control mode, the d-axis current command calculation unit 111 controls the current command value Id* so that the current of the motor 11 becomes the maximum rated value Imax. With this configuration, the concern of liquid backflow due to high speed rotation is eliminated by increasing the heat generation of the motor, and a more reliable refrigeration cycle device can be provided.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims, not by the description of the embodiments above, and is intended to include all modifications within the meaning and scope of the claims.

1 Compressor, 1a Discharge pipe, 1b Suction pipe, 2 Outdoor heat exchanger, 4 Indoor heat exchanger, 3 Throttle device, 5 Four-way valve, 6 Accumulator, 11 Motor, 11a, 74 Winding, 11b, 70 Iron core, 12 Compression mechanism, 13 Housing, 15 Control device, 20, 20A Inverter, 21 Output control unit, 22 Mode determination unit, 23 Refrigeration cycle control unit, 30 Temperature sensor, 40 Power conversion unit, 41, 41A Control circuit, 42a, 42b Current sensor, 50 dq conversion unit, 51 Speed estimation unit, 52 Speed control unit, 55 dq inverse conversion unit, 61 Selector, 66 Rotor, 67 Stator, 71 Permanent magnet, 71A, 71B Magnet, 72A Bridge unit, 100 Refrigeration cycle device, 101, 102 Extension pipe, 103 Outdoor unit, 104 Indoor unit, 105 Refrigerant circuit, 110, 111 Axial current command calculation section, 112 Voltage command calculation section, 113 Phase calculation section, 120 Minimum value selection section, 121 Speed upper limit calculation section, 152, 412 Memory.

Claims (6)

a refrigerant circuit including a compressor, an outdoor heat exchanger, a throttling device, an indoor heat exchanger, and a four-way valve, the refrigerant being circulated;
an inverter that variably controls the speed of the compressor,
The refrigerant circuit is configured to be able to perform a defrosting operation in which the refrigerant discharged from the compressor is introduced into the outdoor heat exchanger by switching the four-way valve,
The compressor includes a compression mechanism and a motor that drives the compression mechanism.
the inverter has, as operation modes, a speed control mode in which the motor is controlled so as to approach a rotation speed corresponding to a command value, and an output control mode in which a current flowing through the motor is detected and the rotation speed of the motor is controlled so that an output of the motor approaches a target value;
The inverter is configured to be able to operate using the output control mode in the defrosting operation,
The output control mode is selected when an externally applied command value indicates a value equal to or greater than an upper rotation speed limit determined by a DC voltage of the inverter, a characteristic value of the motor, and a current of the motor. a refrigerant circuit including a compressor, an outdoor heat exchanger, a throttling device, an indoor heat exchanger, and a four-way valve, the refrigerant being circulated;
an inverter that variably controls the speed of the compressor,
The refrigerant circuit is configured to be able to perform a defrosting operation in which the refrigerant discharged from the compressor is introduced into the outdoor heat exchanger by switching the four-way valve,
The compressor includes a compression mechanism and a motor that drives the compression mechanism.
the inverter has, as operation modes, a speed control mode in which the motor is controlled so as to approach a rotation speed corresponding to a command value, and an output control mode in which a current flowing through the motor is detected and the rotation speed of the motor is controlled so that an output of the motor approaches a target value;
The inverter is configured to be able to operate using the output control mode in the defrosting operation,
In the defrosting operation, as the operation mode, the speed control mode is selected at the start of defrosting , and after a certain time has elapsed from the start of defrosting, the speed control mode is switched to the output control mode. a refrigerant circuit including a compressor, an outdoor heat exchanger, a throttling device, an indoor heat exchanger, and a four-way valve, the refrigerant being circulated;
an inverter that variably controls the speed of the compressor,
The refrigerant circuit is configured to be able to perform a defrosting operation in which the refrigerant discharged from the compressor is introduced into the outdoor heat exchanger by switching the four-way valve,
The compressor includes a compression mechanism and a motor that drives the compression mechanism.
the inverter has, as operation modes, a speed control mode in which the motor is controlled so as to approach a rotation speed corresponding to a command value, and an output control mode in which a current flowing through the motor is detected and the rotation speed of the motor is controlled so that an output of the motor approaches a target value;
The inverter is configured to be able to operate using the output control mode in the defrosting operation,
The compressor further includes a temperature sensor for measuring a discharge temperature of the refrigerant discharged from the compressor.
The refrigeration cycle apparatus, wherein, as the operation mode, the speed control mode is selected when the discharge temperature is higher than a judgment value, and the output control mode is selected when the discharge temperature is lower than the judgment value. a refrigerant circuit including a compressor, an outdoor heat exchanger, a throttling device, an indoor heat exchanger, and a four-way valve, the refrigerant being circulated;
an inverter that variably controls the speed of the compressor,
The refrigerant circuit is configured to be able to perform a defrosting operation in which the refrigerant discharged from the compressor is introduced into the outdoor heat exchanger by switching the four-way valve,
The compressor includes a compression mechanism and a motor that drives the compression mechanism.
the inverter has, as operation modes, a speed control mode in which the motor is controlled so as to approach a rotation speed corresponding to a command value, and an output control mode in which a current flowing through the motor is detected and the rotation speed of the motor is controlled so that an output of the motor approaches a target value;
The inverter is configured to be able to operate using the output control mode in the defrosting operation,
the inverter detects a q-axis current in the output control mode, recognizes a decrease in the load torque of the compressor , and increases a speed command value of the motor based on the following equation (2):
ω* ₂ = P*/Iq/k ... (2)
In the formula (2), ω* ₂ indicates a speed command value of the motor,
P* indicates the upper limit of the motor output,
Iq indicates the q-axis current,
k denotes a constant. The rotor of the motor includes a plurality of permanent magnets and an iron core.
The refrigeration cycle device according to any one of claims 1 to 4 , wherein the iron core has a bridge portion extending in a radial direction on the q axis located between adjacent magnets among the plurality of permanent magnets and holding the adjacent magnets in position. The inverter has a d-axis current command calculation unit that controls the amplitude and phase of a current of the motor,
The refrigeration cycle apparatus according to any one of claims 1 to 5, wherein the d-axis current command calculation unit controls a current command value during the output control mode so that a current of the motor becomes a maximum rated value.

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