US20240053071A1 - Refrigeration cycle apparatus - Google Patents

Refrigeration cycle apparatus Download PDF

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Publication number
US20240053071A1
US20240053071A1 US18/259,097 US202118259097A US2024053071A1 US 20240053071 A1 US20240053071 A1 US 20240053071A1 US 202118259097 A US202118259097 A US 202118259097A US 2024053071 A1 US2024053071 A1 US 2024053071A1
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Prior art keywords
motor
control mode
compressor
speed
inverter
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US18/259,097
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English (en)
Inventor
Kazunori Sakanobe
Kengo Kakimori
Akane HONGYO
Akihiro TSUMURA
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Assigned to MITSUBISHI ELECTRIC CORPORATION reassignment MITSUBISHI ELECTRIC CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HONGYO, Akane, KAKIMORI, Kengo, SAKANOBE, KAZUNORI, TSUMURA, AKIHIRO
Publication of US20240053071A1 publication Critical patent/US20240053071A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B49/00—Arrangement or mounting of control or safety devices
    • F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
    • F25B49/025—Motor control arrangements
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B47/00—Arrangements for preventing or removing deposits or corrosion, not provided for in another subclass
    • F25B47/02—Defrosting cycles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B13/00—Compression machines, plants or systems, with reversible cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B41/00—Fluid-circulation arrangements
    • F25B41/20—Disposition of valves, e.g. of on-off valves or flow control valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B47/00—Arrangements for preventing or removing deposits or corrosion, not provided for in another subclass
    • F25B47/02—Defrosting cycles
    • F25B47/022—Defrosting cycles hot gas defrosting
    • F25B47/025—Defrosting cycles hot gas defrosting by reversing the cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2600/00—Control issues
    • F25B2600/02—Compressor control
    • F25B2600/021—Inverters therefor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/15—Power, e.g. by voltage or current
    • F25B2700/151—Power, e.g. by voltage or current of the compressor motor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
    • F25B2700/21—Temperatures
    • F25B2700/2115—Temperatures of a compressor or the drive means therefor
    • F25B2700/21152—Temperatures of a compressor or the drive means therefor at the discharge side of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B31/00—Compressor arrangements
    • F25B31/02—Compressor arrangements of motor-compressor units
    • F25B31/026—Compressor arrangements of motor-compressor units with compressor of rotary type

Definitions

  • the present disclosure relates to a refrigeration cycle apparatus.
  • a defrosting operation to heat the heat exchanger on the heat source side to thaw frost is performed during operations. Since the heat exchanger on the heat source side is heated in the defrosting operation, thermal energy is consumed in the heat exchanger on the heat source side.
  • PTL 1 discloses a method of heating refrigerant with an electric power conversion apparatus that supplies electric power to a compressor in order to prevent the liquid carry-over phenomenon during the defrosting operation.
  • the refrigeration cycle apparatus functions as a heat pump to lower a temperature of the heat exchanger on the heat source side with this heat exchanger serving as the evaporator and increases a temperature of the heat exchanger on the use side with this heat exchanger serving as a condenser during a heating operation. Therefore, the defrosting operation in which the temperature of the heat exchanger on the use side is lowered temporarily sets back the function as the heat pump, which is a state undesirable for a user. Therefore, the defrosting operation desirably lasts for a time period as short as possible and causes less variation in temperature.
  • the method in PTL 1 is a method of heating an electric power conversion apparatus for preventing such a special environmental condition as a liquid carry-over phenomenon during the defrosting operation, and it is not directed to improvement in performance of the refrigeration cycle apparatus under a general defrosting condition.
  • the present disclosure was made to solve the problem above, and an object thereof is to provide a refrigeration cycle apparatus capable of achieving decrease in time period during which heating capacity is lowered by defrosting.
  • the present disclosure relates to a refrigeration cycle apparatus.
  • the refrigeration cycle apparatus includes a refrigerant circuit including a compressor, an outdoor heat exchanger, a throttle device, an indoor heat exchanger, and a four-way valve, the refrigerant circuit being configured such that refrigerant circulates therethrough, an inverter to control the compressor as being variable in speed, and a temperature sensor that measures a temperature of the compressor.
  • the refrigerant circuit is configured to perform a defrosting operation in which refrigerant discharged from the compressor is introduced into the outdoor heat exchanger as a result of switching of the four-way valve.
  • the compressor includes a compression unit and a motor to drive the compression unit.
  • the inverter has, as an operating mode, a speed control mode in which the motor is controlled such that a rotation speed thereof is closer to a rotation speed corresponding to a command value and an output control mode in which a current that flows through the motor is detected and the rotation speed of the motor is controlled such that output from the motor is closer to a target value.
  • the speed control mode and the output control mode can selectively be used. Therefore, the time period during which heating capacity is lowered by defrosting can be decreased.
  • FIG. 1 is a circuit configuration diagram of a refrigeration cycle apparatus 100 according to a first embodiment.
  • FIG. 2 is a diagram showing a direction of a flow of refrigerant during defrosting.
  • FIG. 3 is a cross-sectional view showing a structure of a compressor 1 .
  • FIG. 4 is a functional block diagram showing an exemplary configuration of an inverter 20 .
  • FIG. 5 is a diagram showing a configuration of a control device 15 .
  • FIG. 6 is a diagram showing a configuration of a control circuit 41 .
  • FIG. 7 is a diagram for illustrating an operation in an output control mode.
  • FIG. 8 is a flowchart showing a method of controlling an operating mode in a heating operation and a defrosting operation in control device 15 .
  • FIG. 9 is a time chart showing an operation of refrigeration cycle apparatus 100 according to the first embodiment.
  • FIG. 10 is a functional block diagram showing a modification of the inverter in FIG. 4 .
  • FIG. 11 is a cross-sectional view of an interior magnet motor for a compressor.
  • FIG. 12 is a diagram showing stress applied to a rotor core small-thickness portion.
  • FIG. 13 is a diagram showing relation between a rotation speed of a motor of the compressor and stress in a bridge portion.
  • FIG. 14 is a diagram showing relation between a frequency, and a voltage and a current that are outputted from the inverter.
  • FIG. 15 is a diagram showing a configuration of a speed controller 52 applied to a fourth embodiment.
  • FIG. 1 is a circuit configuration diagram of a refrigeration cycle apparatus 100 according to a first embodiment.
  • refrigeration cycle apparatus 100 includes an outdoor unit 103 and an indoor unit 104 .
  • Outdoor unit 103 and indoor unit 104 are connected to each other through extension pipes 101 and 102 .
  • Refrigeration cycle apparatus 100 includes a refrigerant circuit 105 , an inverter 20 , a control device 15 , and a temperature sensor 30 .
  • Refrigerant circuit 105 includes a compressor 1 , an outdoor heat exchanger 2 , a throttle device 3 , an indoor heat exchanger 4 , a four-way valve 5 , and an accumulator 6 coupled through a pipe, and it is configured such that refrigerant circulates therethrough.
  • Compressor 1 suctions and compresses refrigerant to set refrigerant into a high-temperature and high-pressure state, and then discharges refrigerant.
  • Compressor 1 contains a compression mechanism portion 12 and a motor 11 .
  • Motor 11 generates motive power for driving compression mechanism portion 12 of compressor 1 .
  • Motor 11 is electrically connected to inverter 20 .
  • Drive of motor 11 is controlled by inverter 20 .
  • FIG. 3 is a cross-sectional view showing a structure of compressor 1 .
  • Compressor 1 includes a housing 13 , motor 11 , and compression mechanism portion 12 .
  • Compressor 1 suctions refrigerant through a suction pipe 1 b , compresses refrigerant to set refrigerant into the high-temperature and high-pressure state, and discharges refrigerant through a discharge pipe 1 a .
  • Compression mechanism portion 12 and motor 11 are accommodated in housing 13 of compressor 1 .
  • Motor 11 includes a winding 11 a and an iron core 11 b that are in contact with refrigerant suctioned through suction pipe 1 b .
  • Winding 11 a and iron core 11 b are each constructed to collect thermal energy from refrigerant.
  • Outdoor heat exchanger 2 and indoor heat exchanger 4 have heat exchanged between refrigerant and a heat medium such as air.
  • a fin tube heat exchanger can be used as outdoor heat exchanger 2 and indoor heat exchanger 4 .
  • outdoor heat exchanger 2 functions as a condenser.
  • outdoor heat exchanger 2 functions as an evaporator.
  • some refrigeration cycle apparatuses such as a refrigerator are reverse to an air-conditioner in roles of the condenser and the evaporator, an air-conditioner will be described below as a representative example.
  • Throttle device 3 serves to expand and decompress refrigerant. Throttle device 3 is an apparatus an opening of which is freely controllable, such as a solenoid expansion valve. The opening of throttle device 3 is controlled, for example, by control device 15 . Throttle device 3 is connected between outdoor heat exchanger 2 and indoor heat exchanger 4 .
  • Throttle device 3 sets refrigerant that flows out of one heat exchanger that functions as the condenser, of outdoor heat exchanger 2 and indoor heat exchanger 4 , into a low-temperature and low-pressure state, and has this refrigerant flow into the other heat exchanger that functions as the evaporator.
  • refrigerant that flows out of outdoor heat exchanger 2 flows into throttle device 3 to be set into the low-temperature and low-pressure state, and that refrigerant flows into indoor heat exchanger 4 .
  • Four-way valve 5 performs a function to make switching of a direction of flow of refrigerant between heating and cooling. An operation of four-way valve 5 is controlled, for example, by control device 15 .
  • Four-way valve 5 switches a flow channel of refrigerant such that a discharge side of compressor 1 is connected to a heat exchanger to function as the condenser, of outdoor heat exchanger 2 and indoor heat exchanger 4 .
  • Accumulator 6 serves as a storage where excessive refrigerant is stored.
  • FIG. 1 shows the direction of flow of refrigerant during heating, and the refrigerant at the high temperature and the high pressure discharged from compressor 1 flows into indoor heat exchanger 4 .
  • FIG. 2 is a diagram showing the direction of the flow of refrigerant during defrosting. As four-way valve 5 is switched as shown in FIG. 2 , the refrigerant at the high pressure discharged from compressor 1 flows into outdoor heat exchanger 2 and heats outdoor heat exchanger 2 .
  • Control device 15 includes a mode determination unit 22 to determine to which of the speed control mode and the output control mode the operating mode of inverter 20 is to be set based on a current operating state (during normal operations or during defrosting) and a refrigeration cycle controller 23 to generate a speed command value for compressor 1 during the normal operations. Since an operating speed (rps) of compressor 1 is often expressed by a frequency (Hz), the speed command value is also called a frequency command value.
  • Temperature sensor 30 detects a temperature of refrigerant discharged from compressor 1 . Temperature sensor 30 is attached, for example, to discharge pipe 1 a of compressor 1 . Information on the temperature measured by temperature sensor 30 is inputted to mode determination unit 22 of control device 15 .
  • FIG. 4 is a functional block diagram showing an exemplary configuration of inverter 20 .
  • Inverter 20 includes a control circuit 41 and an electric power converter 40 .
  • Control circuit 41 receives a speed command value ⁇ * 1 from external and higher-order control device 15 and current detection signals Iu and Iw detected by current sensors 42 a and 42 b , and outputs three-phase voltage command values Vuvw* to electric power converter 40 .
  • Control circuit 41 includes an output controller 21 , a selector 61 , a dq converter 50 , a speed estimator 51 , a speed controller 52 , and a dq reverse converter 55 .
  • inverter 20 is provided with output controller 21 to control outputted electric power to be substantially constant.
  • dq converter 50 generates a d-axis current value Id and a q-axis current value Iq based on current detection signals Iu and Iw and a phase estimation value ⁇ .
  • Speed estimator 51 generates a speed estimation value ⁇ est based on a d-axis voltage command value Vd*, a q-axis voltage command value Vq*, a d-axis current value Id, and a q-axis current value Iq.
  • Speed controller 52 generates d-axis voltage command value Vd* and q-axis voltage command value Vq* based on a speed command value ⁇ *, speed estimation value ⁇ est , d-axis current value Id, and q-axis current value Iq.
  • dq reverse converter 55 generates three-phase voltage command values Vuvw* based on d-axis voltage command value Vd* and q-axis voltage command value Vq*, and outputs three-phase voltage command values Vuvw* to electric power converter 40 for PWM control.
  • FIG. 5 is a diagram showing a configuration of control device 15 .
  • control device 15 includes mode determination unit 22 and refrigeration cycle controller 23 as the functional blocks in FIGS. 1 , 2 , and 4 , it includes, for example, a microcomputer as an actual hardware component.
  • control device 15 includes a central processing unit (CPU) 151 , a memory (a read only memory (ROM) and a random access memory (RAM)) 152 , and a not-shown input and output apparatus for input of various signals.
  • CPU 151 develops a program stored in the ROM on the RAM or the like and executes the same.
  • the program stored in the ROM is a program in which a procedure of processing in control device 15 is described.
  • Control device 15 controls the refrigeration cycle apparatus in accordance with the program.
  • CPU 151 performs processing corresponding to mode determination unit 22 and refrigeration cycle controller 23 in accordance with the program stored in memory 152 . This processing is not limited to processing by software, and processing by dedicated hardware (electronic circuitry) is also applicable.
  • FIG. 6 is a diagram showing a configuration of control circuit 41 .
  • control circuit 41 includes output controller 21 , selector 61 , speed controller 52 , speed estimator 51 , dq reverse converter 55 , and dq converter 50 as functional blocks in FIG. 4 , it includes, for example, a microcomputer as an actual hardware component.
  • control circuit 41 includes a CPU 411 , a memory (a ROM and a RAM) 412 , and a not-shown input and output apparatus for input of various signals.
  • CPU 411 develops a program stored in the ROM on the RAM or the like and executes the same.
  • the program stored in the ROM is a program in which a procedure of processing in control circuit 41 is described.
  • Control circuit 41 carries out PWM control of the inverter in accordance with the program.
  • CPU 411 performs processing corresponding to output controller 21 , selector 61 , speed controller 52 , speed estimator 51 , dq reverse converter 55 , and dq converter 50 in accordance with the program stored in memory 412 .
  • This processing is not limited to processing by software, and processing by dedicated hardware (electronic circuitry) is also applicable.
  • the functional blocks may be implemented by a single controller controlled by the same CPU or by different controllers controlled by respective different CPUs.
  • Inverter 20 performs an operation based on an operating mode MODE determined by control device 15 .
  • selector 61 is set such that speed command value ⁇ * 1 for compressor 1 attains to speed command value ⁇ * to be given to speed controller 52 .
  • Inverter 20 thus controls an output frequency based on speed command value ⁇ * 1 and controls three-phase voltage command values Vuvw* to substantially minimize loss in inverter 20 and motor 11 .
  • efficient operations are performed.
  • output controller 21 in inverter 20 successively calculates output (electric power) P from motor 11 and an upper limit value P* of output P, and controls a speed command value ⁇ * 2 such that output P becomes closer to P*.
  • Selector 61 is set such that speed command value ⁇ * 2 attains to speed command value ⁇ * to be given to speed controller 52 .
  • P* represents an electric power command value
  • Maximum value Pmax is a maximum value of output electric power uniquely determined by a motor constant which represents a characteristic of the motor and a direct-current (DC) voltage Vdc.
  • Output P and speed command value ⁇ * 2 are calculated, for example, in accordance with expressions (1) and (2) below, where k represents a constant, ⁇ represents a rotation speed, and Iq represents a torque current.
  • FIG. 7 is a diagram for illustrating an operation in the output control mode.
  • Tmax [Nm] represents an upper limit value of mechanical torque of compressor 1
  • f_max represents a maximum frequency at the upper limit of torque.
  • Areas of two hatched quadrangles having a point B and a point B′ as respective vertices thereof represent magnitude of output of the motor.
  • Great motor output in heating and defrosting operations corresponds to high heating capacity and defrosting capacity.
  • the output control mode is an operating mode in which lowering in defrosting capacity or heating capacity due to change such as lowering in temperature, lowering in pressure, or lowering in dryness of refrigerant suctioned by compressor 1 is less likely.
  • FIG. 8 is a flowchart showing a method of controlling the operating mode in the heating operation and the defrosting operation in control device 15 .
  • a step will be abbreviated as S below.
  • control device 15 sets the operating mode to the speed control mode (S 5 ).
  • the control device sets the operating mode to the speed control mode (S 5 ).
  • FIG. 9 is a time chart showing an operation of refrigeration cycle apparatus 100 according to the first embodiment. Operations in the present embodiment will be described with reference to waveforms T 1 and F 1 shown with solid lines.
  • control device 15 switches four-way valve 5 such that a destination of gas discharged from compressor 1 is changed from indoor heat exchanger 4 to outdoor heat exchanger 2 for performing the defrosting operation. Consequently, the direction of flow of refrigerant is changed from the direction shown in FIG. 1 to the direction shown in FIG. 2 .
  • gas discharged from compressor 1 is at the high temperature and the high pressure. Refrigerant at the high temperature, however, flows into frosted outdoor heat exchanger 2 and it is cooled and decompressed therein. Therefore, as the defrosting operation is continued, the temperature and the pressure of refrigerant suctioned into compressor 1 are also lowered as shown with waveform T 1 , and accordingly, the discharge temperature lowers as shown at time tB.
  • control device 15 detects lowering in discharge temperature shown with waveform T 1 and switches the operating mode of inverter 20 from the speed control mode to the output control mode.
  • speed command value ⁇ * 2 is set to a relatively small value.
  • refrigerant at the high temperature for defrosting flows into outdoor heat exchanger 2 . Since heat is carried away to frost, at an exit of the heat exchanger, the temperature of refrigerant lowers.
  • indoor heat exchanger 4 is controlled not to exchange heat by stop of air blow or the like. Consequently, thermal energy and the pressure in the entire refrigerant circuit 105 connected through a refrigerant pipe are lowered, and with this lowering, load torque for operation of compressor 1 is also lowered.
  • Output controller 21 detects a q-axis current to recognize this lowering in load torque, and increases speed command value ⁇ * 2 based on the expression (2).
  • a speed of flow of refrigerant in refrigerant circuit 105 during the defrosting operation increases.
  • a pressure loss in the flow channel that increases with the speed of the flow increases.
  • thermal energy that is, the temperature and the pressure, of refrigerant increases, and defrosting capacity of outdoor heat exchanger 2 increases. By repeating operations above, defrosting can quickly end (time tC in FIG. 9 ).
  • a time chart in the case of control only in the speed control mode is shown with waveforms T 2 and F 2 drawn with dashed lines in FIG. 9 as a comparative example.
  • the operation frequency is not increased with lowering in discharge temperature during defrosting. Therefore, a time period for defrosting (time tB to time tC′) is long. Furthermore, recovery of the temperature of refrigerant after switching to heating is also delayed, and hence the discharge temperature does not increase. Therefore, as shown with waveform T 2 from time tC′ to time tD′, a state in which an indoor temperature is low lasts for a long time.
  • the time period for defrosting of the refrigeration cycle apparatus is long and time required for start-up of heating is long. The comparative example shows that comfort of the user is compromised.
  • FIG. 10 is a functional block diagram showing a modification of the inverter in FIG. 4 .
  • An inverter 20 A shown in FIG. 10 includes a control circuit 41 A and electric power converter 40 .
  • Control circuit 41 A includes a minimum value selector 120 and a speed upper limit calculator 121 instead of output controller 21 and selector 61 in the configuration of control circuit 41 shown in FIG. 4 . Since control circuit 41 A is otherwise similar in configuration to control circuit 41 shown in FIG. 4 , description will not be repeated.
  • Speed upper limit calculator 121 calculates a rotation speed upper limit value ⁇ max in accordance with expressions (3) and (4) below.
  • Te represents output torque and Pmax represents maximum output torque.
  • Minimum value selector 120 compares command value ⁇ * 1 in the speed control mode and rotation speed upper limit value ⁇ max in the output control mode with each other, and outputs a smaller value as speed command value ⁇ * for actual control. Minimum value selector 120 allows automatic switching between the output control mode and the speed control mode, and addition of a control signal from control device 15 is not required. When control device 15 requests the output control mode, a rotation speed sufficiently higher than rotation speed upper limit value ⁇ max should only be designated. Since speed command value ⁇ * is thus set to rotation speed upper limit value ⁇ max , the operating mode of inverter 20 A is set to the output control mode.
  • FIG. 11 is a cross-sectional view of an interior magnet motor for a compressor.
  • FIG. 12 is a diagram showing stress applied to a rotor core small-thickness portion.
  • motor 11 includes a rotor 66 and a stator 67 .
  • Rotor 66 of motor 11 includes a plurality of permanent magnets 71 and an iron core (rotor core) 70 .
  • Stator 67 includes an iron core (stator core) 73 and a winding 74 of a coil.
  • iron core 70 includes a bridge portion 72 A that extends in a radial direction on the q axis located between adjacent magnets 71 A and 71 B of the plurality of permanent magnets 71 and holds positions of adjacent magnets 71 A and 71 B.
  • IPMSM interior permanent magnet synchronous motor
  • a maximum rotation speed of the compressor is defined by an operation frequency (f_nom) corresponding to a rotation speed at which maximum rated capacity is exhibited.
  • f_nom operation frequency
  • a control command value in the output control mode is described as a fixed value (Pmax). Under a condition where load torque during defrosting is low, however, when the operation frequency is controlled to exceed maximum frequency f_nom, defrosting performance is improved.
  • the IPMSM achieves less flux leakage in the rotor and high output and high efficiency, whereas stress against centrifugal force lowers. Control to achieve light-load and high-speed operations described in the first and second embodiments is described as particularly being effective in the IPMSM.
  • the core In the vicinity of the q axis at the end of the magnet, the core inevitably has to be smallest in thickness in order to meet requirements in terms of efficiency.
  • Mechanical strength of the rotor core of the IPMSM is dependent on strength in the vicinity of the q axis at the end of the magnet. Stress applied during rotation to a portion in the vicinity of the q axis is expressed in expressions (5) to (7) below and FIG. 12 .
  • Fr represents centrifugal force
  • Ft represents stress in a circumferential direction applied to the core
  • M represents inertial moment around an outer circumferential portion of the core
  • ⁇ represents an angular velocity
  • k 1 represents a proportionality factor
  • T L represents load torque
  • F represents stress applied to the bridge portion.
  • a width of bridge portion 72 A in FIG. 12 is designed such that a width in the circumferential direction is smaller in an attempt to achieve higher output of the motor. Consequently, it has been found that force F which is the resultant of stress in the circumferential direction and centrifugal force should be an indicator for design. This is the background of derivation of relation in the expression (5).
  • FIG. 13 shows a diagram of relation between a rotation speed of the motor of the compressor and stress in the bridge portion.
  • load torque T L is a function of a pressure of refrigerant gas; as the pressure is lower, load torque is lower.
  • load torque during defrosting is defined as T L def and a maximum angular velocity is defined as ⁇ def.
  • T L max>T L def is satisfied, and furthermore, stress Ft in the circumferential direction decreases by an amount comparable to decrease in torque.
  • the upper limit frequency can be increased without increase in rotor core strength against torque.
  • the high-speed operation is performed during the defrosting operation which is the operating state in which load torque is lowered, and therefore, stress applied to the rotor core clearly does not excessively increase.
  • the compressor on which less load is imposed in terms of strength against break due to increase in centrifugal force while a time period for defrosting is decreased by the high-speed operation can be provided.
  • FIG. 14 is a diagram showing relation between a frequency, and a voltage and a current that are outputted from the inverter.
  • a solid line represents an output voltage and a chain dotted line represents a current.
  • a maximum rated frequency is denoted as f_max
  • a maximum value of the output voltage is denoted as Vmax
  • a maximum frequency at which an operation at highest efficiency can be performed is denoted as f_nom.
  • the operation is performed with maximum value Vmax of the voltage being maintained, so long as there is no particular problem.
  • Possibility of a mechanical damage due to liquid carry-over should be lowered in the defrosting operation, and hence in a fourth embodiment, the inverter is intentionally controlled to output a voltage (Vmax ⁇ V) lower than maximum value Vmax.
  • Vmax ⁇ V voltage
  • the current increases from Ib to Ic, and with increase in current, the motor generates heat. Since refrigerant that flows into a compression mechanism of the compressor can thus be heated, resistance to liquid carry-over can be improved.
  • FIG. 15 is a diagram showing a configuration of speed controller 52 applied to the fourth embodiment.
  • speed controller 52 shown in FIG. 15 is used as speed controller 52 in FIG. 4 or 10 .
  • Speed controller 52 includes a q-axis current command calculator 110 , a d-axis current command calculator 111 , a voltage command calculator 112 , a phase calculator 113 , and subtractors 114 to 116 .
  • Control device 15 includes a heating determination unit 117 to control ON/OFF of heating control based on a compressor discharge temperature Td and operating mode MODE.
  • HEAT represents a heating control signal given from heating determination unit 117 in control device 15 .
  • Heating determination unit 117 monitors compressor discharge temperature Td and operating mode MODE. When the operating mode is set to the output control mode and discharge temperature Td is equal to or lower than a criterion temperature, it is determined that the compressor should be heated, and heating determination unit 117 sets the heating control signal to ON. Otherwise, heating determination unit 117 sets the heating control signal to OFF.
  • the d-axis current command calculator When externally given heating control signal HEAT is OFF, the d-axis current command calculator outputs d-axis current command Id* in accordance with normal d-axis current control. In this case, d-axis current command Id* is determined in accordance with expressions (8) and (9) below.
  • Id* is determined as
  • Vmax is determined as below.
  • V max ⁇ square root over (( RI d* ⁇ L q I q* ) 2 +( RI q* ⁇ L d I d* + ⁇ f ) 2 ) ⁇ (9)
  • R represents a phase resistance
  • Ld represents a d-axis inductance
  • Lq represents a q-axis inductance
  • ⁇ f represents an induced voltage constant
  • ⁇ represents an electrical angular velocity
  • Id* represents a d-axis current command
  • Iq* represents a q-axis current command.
  • Id* is determined in accordance with an expression (10) below.
  • I d* ⁇ square root over ( I max 2 ⁇ I q* 2 ) ⁇ (10)
  • Imax represents a maximum current rating
  • a maximum current rated value Imax is a value specific to the motor which is determined by a limit of a demagnetizing current. In other words, the current is controlled in accordance with maximum current rated value Imax which is a maximum current value allowable by the motor. Thus, a loss in the motor can increase and heat generation can increase.
  • Id* has a negative value in the expression (10), it is set as such in consideration of the fact that the d-axis current command cannot be increased at the voltage upper limit of the inverter, and when the voltage upper limit of the inverter is sufficiently high, heating can be done even when Id* is positive.
  • the current limit is determined by the limit of the demagnetizing current in the example above.
  • the motor may be controlled with the current rating or the limit of synchronization being set as the upper limit.
  • a pressure loss in the refrigerant circuit and a mechanical loss, an iron loss, and a copper loss in the compressor increase, which promotes increase in temperature or pressure of refrigerant. Therefore, the defrosting operation in the outdoor heat exchanger can be completed early, and a time period during which heating capacity is low in the indoor heat exchanger after the defrosting operation can be shorter.
  • Decrease in time period for defrosting is effective not only for elimination of feeling of cold by the user during the heating operation but also for improvement in average heating capacity.
  • Refrigeration cycle apparatus 100 in the present embodiment shown in FIG. 1 includes refrigerant circuit 105 and inverter 20 .
  • Refrigerant circuit 105 includes compressor 1 , outdoor heat exchanger 2 , throttle device 3 , indoor heat exchanger 4 , and four-way valve 5 , and it is configured such that refrigerant circulates therethrough.
  • Inverter 20 is configured to control compressor 1 as being variable in speed.
  • Refrigerant circuit 105 is configured to perform a defrosting operation in which refrigerant discharged from compressor 1 is introduced into outdoor heat exchanger 2 as a result of switching of four-way valve 5 as shown in FIG. 2 .
  • Compressor 1 includes compression mechanism portion 12 and motor 11 to drive compression mechanism portion 12 .
  • Inverter 20 has, as an operating mode, a speed control mode in which motor 11 is controlled such that a rotation speed of the motor is closer to a rotation speed corresponding to a command value and an output control mode in which a current that flows through motor 11 is detected and the rotation speed of motor 11 is controlled such that output from motor 11 is closer to a target value.
  • the speed control mode and the output control mode can selectively be used as the operating mode of inverter 20 in accordance with a state of refrigerant that changes with switching of four-way valve 5 . Therefore, a refrigeration cycle apparatus capable of achieving improvement in capacity, in which the rotation speed can automatically follow the state of refrigerant even when the state changes in a short period of time, can be provided.
  • Inverter 20 is configured to operate by using the output control mode in the defrosting operation.
  • a refrigeration cycle apparatus capable of achieving decrease in time period for defrosting, the time period being a shortcoming of a heat pump, can be provided.
  • the output control mode is used when a value indicated by externally given command value ⁇ * 1 becomes equal to or larger than rotation speed upper limit value ⁇ max determined by a DC voltage of inverter 20 , a characteristic value of motor 11 , and a current in motor 11 . Therefore, since the output control mode is applied only based on externally given command value ⁇ * 1 , a refrigeration cycle apparatus excellent in viability, with few points of change in interface, can be provided.
  • the operating mode is set to the speed control mode (S 5 ) at the time of start of defrosting, and after a certain time period has elapsed since start of defrosting (YES in S 2 ), switching from the speed control mode to the output control mode is made (S 4 ).
  • Refrigeration cycle apparatus 100 shown in FIG. 1 further includes temperature sensor 30 to measure discharge temperature Td of refrigerant discharged from compressor 1 .
  • temperature sensor 30 to measure discharge temperature Td of refrigerant discharged from compressor 1 .
  • the operating mode is set to the speed control mode (S 5 )
  • discharge temperature Td of compressor 1 is lower than the criterion value (YES in S 3 )
  • the operating mode is set to the output control mode (S 4 ).
  • rotor 66 of motor 11 includes a plurality of permanent magnets 71 and iron core 70 .
  • iron core 70 includes bridge portion 72 A that extends in a radial direction on the q axis located between adjacent magnets 71 A and 71 B of the plurality of permanent magnets 71 and holds positions of adjacent magnets 71 A and 71 B.
  • inverter 20 includes d-axis current command calculator 111 to control an amplitude and a phase of a current in motor 11 .
  • d-axis current command calculator 111 controls current command value Id* such that the current in motor 11 attains to maximum rated value Imax during the output control mode. According to such a configuration, concern about liquid carry-over involved with a higher speed of rotation can be eliminated by increase in amount of heat generation by the motor, and hence a more reliable refrigeration cycle apparatus can be provided.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Air Conditioning Control Device (AREA)
  • Control Of Ac Motors In General (AREA)
US18/259,097 2021-02-19 2021-02-19 Refrigeration cycle apparatus Pending US20240053071A1 (en)

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JPH06265244A (ja) * 1993-03-15 1994-09-20 Toshiba Corp 空気調和機
JP2001008003A (ja) * 1999-06-18 2001-01-12 Canon Inc 画像読取装置及び画像形成装置
JP4717446B2 (ja) 2005-01-07 2011-07-06 三菱電機株式会社 電動機装置
JP2010008003A (ja) * 2008-06-30 2010-01-14 Hitachi Appliances Inc 空気調和器
JP6265244B2 (ja) 2016-10-05 2018-01-24 カシオ計算機株式会社 端末装置、端末装置の制御方法及びそのプログラム
WO2020008620A1 (ja) * 2018-07-06 2020-01-09 三菱電機株式会社 冷凍サイクル装置および空気調和装置

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