Compressor drive device and air-conditioning apparatus

Abstract

A compressor drive device (50) comprises: an inverter (4) that converts an AC voltage applied from an AC power supply (2) into a drive voltage for driving a compressor motor (14); a motor current detection unit (7) that detects a motor current flowing through the compressor motor (14); a bus voltage detection unit (5) that detects a bus voltage applied to the inverter (4); and a control unit (8) that controls the inverter (4). The control unit (8) has a first mode for heating a compressor (13) without rotating the compressor motor (14), and a second mode for driving the compressor motor (14) by PWM control. In the first mode, the control unit (8) PWM-controls a switching element (40) of the inverter (4) on the basis of a current detection value detected by the motor current detection unit (7), a current command that is a command value for the motor current, and a voltage detection value detected by the bus voltage detection unit (5), such that the current detection value follows the current command, and a direct current flows through the compressor motor (14).

Description

Compressor drive device and air conditioning device

[0001] The present disclosure relates to a compressor drive device for driving a compressor that includes a compression mechanism that compresses a refrigerant flowing in a refrigerant circuit of a refrigeration cycle device and a compressor motor that operates the compression mechanism, and to an air conditioner that includes the compressor drive device.

[0002] In air conditioners, when the outside air temperature is low, a phenomenon known as liquefied refrigerant accumulates in the compressor, which has a large heat capacity, while the unit is stopped. This phenomenon is called "refrigerant stagnation," or more simply, "stagnation." The liquid refrigerant accumulated in the compressor dissolves in the lubricating oil inside the compressor. This reduces the concentration of the lubricating oil and its viscosity. If the compressor is started in this state, low-viscosity lubricating oil will be supplied to the compressor's rotating shaft or compression mechanism, which may cause the sliding parts inside the compressor to seize due to poor lubrication.

[0003] Patent Document 1 below discloses a technique for applying an AC voltage to a compressor motor at a frequency higher than the operating frequency of the compressor motor during compression when refrigerant stagnation is detected. According to the technique of Patent Document 1, applying an AC voltage at a frequency higher than the operating frequency of the compressor motor during compression causes iron loss and copper loss due to high-frequency current in the compressor motor, and the heat generated by the iron loss and copper loss heats the compressor, preventing liquid refrigerant from accumulating in the compressor.

[0004] JP 2011-38689 A

[0005] As described above, in Patent Document 1, a high-frequency current is passed through the compressor motor to prevent liquid refrigerant from accumulating in the compressor. However, when performing feedback control using the method of Patent Document 1, a high-frequency current needs to be generated while being detected, which requires a current detection means and a processing device capable of high-speed processing, resulting in a problem of high cost.

[0006] The present disclosure has been made in view of the above, and an object of the present disclosure is to provide a compressor driving device that can perform feedback control for heating the compressor while suppressing an increase in cost.

[0007] To solve the above-mentioned problems and achieve the object, a compressor drive device according to the present disclosure drives a compressor including a compression mechanism that compresses a refrigerant flowing in a refrigerant circuit of a refrigeration cycle device and a compressor motor that operates the compression mechanism. The compressor drive device includes an inverter having a plurality of switching elements, a motor current detection unit that detects a motor current flowing through the compressor motor, a bus voltage detection unit that detects a bus voltage that is a DC voltage applied to the inverter, and a control unit that controls the operation of the inverter. The inverter converts an AC voltage applied from an AC power source into a drive voltage for driving the compressor motor and applies the drive voltage to the compressor motor. The control unit operates the inverter in two operating modes: a first mode in which the compressor is heated without rotating the compressor motor, and a second mode in which the compressor motor is driven by pulse width modulation control. In the first mode, the control unit performs pulse width modulation control of the switching elements based on the current detection value detected by the motor current detection unit, a current command which is a command value for the motor current, and the voltage detection value detected by the bus voltage detection unit, so that the current detection value follows the current command and a direct current flows through the compressor motor.

[0008] The compressor drive device according to the present disclosure has the advantage that feedback control for heating the compressor can be performed while suppressing increases in costs.

[0009] 2 is a diagram showing an example of the configuration of a heat pump device including a compressor driving device according to embodiment 1; FIG. 3 is a block diagram showing an example of the configuration of a controller related to the execution of a first mode in a control unit according to embodiment 1; FIG. 4 is a diagram showing an example of a control curve referred to by a d-axis current command generation unit shown in FIG. 2; FIG. 5 is a diagram for explaining the operation of a space vector modulation unit shown in FIG. 2;

[0010] A compressor drive device and an air conditioner according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. In the following description, multiple components of the same type will be designated by reference numerals with subscripts, but when these components are described collectively without distinguishing between them, the subscripts will be omitted as appropriate.

[0011] Embodiment 1 Fig. 1 is a diagram showing an example of the configuration of a heat pump apparatus 100 including a compressor driving device 50 according to embodiment 1. The heat pump apparatus 100 is composed of a refrigeration cycle apparatus 1 and a compressor driving device 50. The heat pump apparatus 100 having the configuration shown in Fig. 1 can be used in, for example, an air conditioner, a heat pump water heater, a refrigerator, a freezer, etc.

[0012] The refrigeration cycle apparatus 1 includes an outdoor heat exchanger 10, a four-way valve 11, an expansion valve 12, a compressor 13, and an indoor heat exchanger 16, which are connected via refrigerant piping 17 to form a refrigerant circuit. The compressor 13 includes a compression mechanism 15 for compressing the refrigerant flowing through the refrigerant circuit and a compressor motor 14 for operating the compression mechanism 15. The refrigeration cycle apparatus 1 can perform heating or cooling operation by switching the four-way valve 11. The refrigeration cycle apparatus 1 also includes a temperature detector 19 for detecting an ambient temperature T, which is the temperature of the location where the outdoor heat exchanger 10 or the compressor 13 is installed. The temperature detector 19 includes a temperature sensor (not shown). While FIG. 1 illustrates an example in which the temperature detector 19 is disposed near the outdoor heat exchanger 10, the present invention is not limited to this example. The temperature detector 19 may be disposed near the compressor 13 or at any location inside the housing that houses the outdoor heat exchanger 10 and the compressor 13.

[0013] The compressor driving device 50 includes a converter 3, an inverter 4, and a control unit 8 that controls the operation of the inverter 4. The inverter 4 is a three-phase inverter and has six switching elements 40a to 40f controlled by the control unit 8. The inverter 4 converts an AC voltage applied from an AC power source 2 into a drive voltage for driving a compressor motor 14 and applies the drive voltage to the compressor motor 14. The converter 3 is disposed between the AC power source 2 and the inverter 4, and converts the AC voltage applied from the AC power source 2 into a DC voltage and applies the DC voltage to the inverter 4.

[0014] The converter 3 includes a reactor 30, a diode bridge circuit 34 configured by connecting four diodes 31a to 31d in a single-phase bridge, and a capacitor 32 that smooths the voltage rectified by the diode bridge circuit 34. The electrical wiring connecting the converter 3 and the inverter 4 is sometimes called a DC bus, and in this document, the DC voltage output by the converter 3 is referred to as the "bus voltage." Note that the illustrated converter 3 is configured as a rectifier circuit without a boost function, but is not limited to this configuration. The converter 3 may also be a boost converter configured with at least one switching element. Furthermore, while the illustrated converter 3 is configured assuming that the AC power source 2 is single-phase AC, the AC power source 2 may also be three-phase AC. In this case, the converter 3 is configured with six diodes connected in a three-phase bridge.

[0015] The compressor driving device 50 also controls the bus voltage V ｄｃ and a bus voltage detector 5 for detecting a bus current I flowing between the converter 3 and the inverter 4. ｄｃ and a bus current detector 6 for detecting the motor current I of each of the three phases flowing through the compressor motor 14. ｕ , I ｖ , I ｗ The control unit 8 uses the voltage detection value detected by the bus voltage detection unit 5 and the current detection value detected by the motor current detection unit 7 to generate a PWM (Pulse Width Modulation) signal U for controlling each of the switching elements 40 a to 40 f of the inverter 4. ｐ , Vｐ , W ｐ , U ｎ , V ｎ , W ｎ The switching elements 40a to 40f generate the corresponding PWM signals (40a is U ｐ , 40b is V ｐ , 40c is W ｐ , 40d is U ｎ , 40e is V ｎ , 40f is W ｎ ), and the inverter 4 drives the compressor motor 14 at a desired rotation speed and torque. As the compressor motor 14 rotates, the compressor 13 repeats the operations of suction, compression, and discharge, and the refrigerant circulates in the refrigerant circuit, thereby performing heating or cooling operation.

[0016] The control unit 8 calculates the motor current I by using the current detection value detected by the bus current detection unit 6 instead of the current detection value by the motor current detection unit 7. ｕ , I ｖ , I ｗ is calculated, and the calculated value is used to generate the PWM signal U ｐ , V ｐ , W ｐ , U ｎ , V ｎ , W ｎ may be generated.

[0017] Next, the main points of the operation of the compressor driving device 50 according to the first embodiment will be described. First, the control unit 8 provided in the compressor driving device 50 according to the first embodiment has a first mode and a second mode as operation modes for operating the inverter 4. The first mode is an operation mode in which the compressor 13 is heated without rotating the compressor motor 14. The second mode is an operation mode in which the compressor motor 14 is driven by PWM modulation control.

[0018] Switching between the first mode and the second mode is performed based on the ambient temperature T detected by the temperature detector 19. The ambient temperature T detected by the temperature detector 19 is input to the control unit 8. The control unit 8 also stores a temperature threshold. The temperature threshold is a threshold for predicting the possibility of liquid refrigerant stagnation in the compressor 13. Before starting the compressor 13, the control unit 8 compares the ambient temperature T with the temperature threshold. If the ambient temperature T is less than or equal to the temperature threshold, the control unit 8 executes the first mode. If the temperature of the compressor 13 becomes equal to or greater than the temperature threshold after the first mode, or exceeds the temperature threshold, the control unit 8 transitions to the second mode and starts the compressor 13. Note that if the ambient temperature T is equal to or greater than the temperature threshold or exceeds the temperature threshold when determining before start-up, the control unit 8 executes the second mode without executing the first mode and starts the compressor 13.

[0019] 2 is a block diagram showing an example of the configuration of a controller 80 related to the execution of the first mode in the control unit 8 of the first embodiment. In FIG. 2, the controller 80 related to the execution of the first mode includes a d-axis current command generator 81, a current PI (Proportional Integral) control unit 82, a phase command generator 83, a space vector modulator 84, and a dq transformer 85. As shown in the figure, the controller 80 receives, as input signals, an environmental temperature T and a bus voltage V ｄｃ and the motor current I ｕ , I ｖ , I ｗ Based on these input signals, the controller 80 generates a PWM signal U that heats the compressor 13 without rotating the compressor motor 14. ｐ , V ｐ , W ｐ , U ｎ , V ｎ , W ｎ Generate.

[0020] In this paper, we will not explain the configuration of the control system related to the second mode in which the compressor motor 14 is driven by PWM modulation control. The second mode can be realized by well-known speed feedback control, but it may also be realized by a control system other than speed feedback control.

[0021] Next, the function and operation of each unit in the controller 80 shown in FIG. 2 will be described. First, the dq conversion unit 85 will be described. The dq conversion unit 85 converts the motor current I ｕ , I ｖ , I ｗ The detected value and the phase command θ ＊ and the d-axis current I ｄ and q-axis current I ｑ The output is the phase command θ ＊ is generated by the phase command generating unit 83. The dq transforming unit 85 performs "three-phase to dq axis coordinate transformation", which is achieved by implementing "three-phase to fixed coordinate axis transformation" and "fixed coordinate axis to rotating coordinate axis transformation", which are well-known techniques. Specifically, the "three-phase to fixed coordinate axis transformation" is performed by the following equation (1), and the "fixed coordinate axis to rotating coordinate axis transformation" is performed by the following equation (2). α , I β represents the fixed coordinate axis current.

[0022]

[0023] By performing the calculations of the above equations (1) and (2), the motor current I ｕ , I ｖ , I ｗ is the d-axis current I ｄ and q-axis current I ｑ The d-axis current I ｄ and q-axis current I ｑ The current that is the basis for the conversion to is the motor current I ｕ , I ｖ , I ｗ As mentioned above, the bus current I ｄｃ may also be used.

[0024] Next, the d-axis current command generating unit 81 will be described. The d-axis current command generating unit 81 generates a d-axis current command I ｄ ＊ The d-axis current command I generated by the d-axis current command generator 81 is generated. ｄ ＊On the other hand, as shown in FIG. 2, the d-axis current command I is determined in accordance with the ambient temperature T, using the ambient temperature T detected by the temperature detector 19 as an input signal. ｄ ＊ It is more preferable to determine the value of

[0025] 3 is a diagram showing an example of a control curve referred to by the d-axis current command generating unit 81 shown in FIG. 3. The horizontal axis of FIG. 3 represents the environmental temperature T, and the vertical axis represents the d-axis current command I ｄ ＊ As shown in FIG. 3, in the region where the ambient temperature T is low, the maximum current value I required to suppress the accumulation of the liquid refrigerant is ｄＭＡＸ The d-axis current command I ｄ ＊ The maximum current value I ｄＭＡＸ is determined so as to be equal to or less than the demagnetizing current of the compressor motor 14. As the ambient temperature T increases, the current value required to suppress the accumulation of liquid refrigerant decreases. Therefore, the current value is reduced in accordance with the ambient temperature T, and the minimum current value I ｄＭＩＮ The d-axis current command I ｄ ＊ Determine the minimum current value I ｄＭＩＮ is the minimum current value required to suppress the accumulation of liquid refrigerant. ｄ ＊ Once the d-axis current command I ｄ ＊ Since the current can be controlled to the minimum required to prevent the liquid refrigerant from accumulating, it is possible to prevent an increase in loss in the first mode due to an excessive current.

[0026] Next, the current PI control unit 82 will be described. The current PI control unit 82 controls the d-axis current I ｄ and q-axis current I ｑ and the d-axis current command I ｄ ＊ and q-axis current command I ｑ ＊ and are used as inputs, and the d-axis voltage command V ｄ ＊ and q-axis voltage command V ｑ ＊ As shown in Figure 2, the d-axis current Iｄ and q-axis current I ｑ is the output value of the dq conversion unit 85, and the d-axis current command I ｄ ＊ is the output value of the d-axis current command generator 81. Also, the q-axis current command I ｑ ＊ is fixed at 0.

[0027] The current PI control unit 82 controls the d-axis current I ｄ and d-axis current command I ｄ ＊ PI control is performed so that the deviation from the q-axis current I ｑ and q-axis current command I ｑ ＊ In this way, the current PI control unit 82 performs PI control so that the deviation between the dq-axis current command and the motor current I ｕ , I ｖ , I ｗ The d-axis voltage command V is calculated by using the detected values ​​of the d-axis current and the q-axis current, and the deviation from the calculated d-axis current is zero. When the d-axis voltage command V is calculated by using the detected values ​​of the d-axis current and the q-axis current, the d-axis voltage command V is calculated by using the detected values ​​of the d-axis current and the q-axis current. When the d-axis voltage command V is calculated by using the detected values ​​of the d-axis current and the q-axis current, the deviation from the calculated d-axis voltage command V is zero ... ｄ ＊ and q-axis voltage command V ｑ ＊ Generate.

[0028] Next, the phase command generator 83 will be described. The phase command generator 83 generates a phase command θ to be used by the dq transformer 85 and the space vector modulator 84. ＊ Generates a phase command θ ＊ The value of is any one of 30°, 90°, 150°, 210°, 270°, and 330°. The phase command generator 83 may keep one phase fixed while the first mode is being performed, or may switch and output the phase every time a certain time elapses.

[0029] Next, the space vector modulation unit 84 will be described. FIG. 4 is a diagram illustrating the operation of the space vector modulation unit 84 shown in FIG. 2. The inverter 4, which is a three-phase inverter, has six switching elements 40a to 40f. The switching elements 40a to 40c arranged on the high potential side are called upper arm switching elements, and the switching elements 40d to 40f arranged on the low potential side are called lower arm switching elements. Furthermore, a pair of an upper arm switching element 40 and a lower arm switching element 40 connected in series is called a leg.

[0030] When pairs of switching elements 40 in the upper and lower arms of the same leg are operated complementarily, the switching patterns representing the switching states of the six switching elements 40a to 40f can be expressed by combinations of the switching states of the three upper arm switching elements 40a to 40c or combinations of the switching states of the three lower arm switching elements 40d to 40f, for a total of eight patterns. Here, we consider combinations of the switching states of the three upper arm switching elements 40a to 40c.

[0031] The ON state of the switching elements 40a to 40c is represented by "1" and the OFF state by "0," and eight voltage vectors represented by combinations of the switching states of the switching elements 40a to 40c are represented by V0 to V7. Specifically, the voltage vectors V0 to V7 can be represented as combinations of the switching states of the upper arm switching elements 40a to 40c, as shown in FIG. 4, with V0 (000), V1 (100), V2 (110), V3 (010), V4 (011), V5 (001), V6 (101), and V7 (111). The state values ​​in parentheses represent the U phase, V phase, and W phase from left to right.

[0032] Of the voltage vectors V0 to V7, the voltage vectors V0 and V7 have an output voltage component of zero, and are therefore referred to as "zero vectors" as appropriate. Because the voltage vectors V0 and V7 have an output voltage component of zero, they are located at the origin, which is the center of the circle, on the vector diagram in FIG. 4. Furthermore, the voltage vectors V1 to V6 are real vectors whose output voltage components are not zero, and are therefore referred to as "fundamental vectors" as appropriate. In FIG. 4, they are represented as vectors with the same amplitude centered on the origin and a phase interval of 60°.

[0033] In space vector modulation, the output time of four voltage vectors, two basic vectors and two zero vectors, is distributed within one PWM control period, thereby generating an output voltage vector V with any magnitude and phase. ＊ As an example, in FIG. 4, an output voltage vector V with a phase angle α of 30° is obtained in an area surrounded by the zero vectors V0 and V7 and the basic vectors V1 and V2. ＊ When α=30°, the ratio of the output time of the fundamental vector V1 to the fundamental vector V2 is 1:1. If the ratio of the output time of the fundamental vector V1 to the fundamental vector V2 is changed, the phase angle α becomes other than 30°. If the ratio of the output time distribution of the zero vectors V0 and V7 is increased, the output voltage vector V ＊ The amplitude of the output voltage vector V becomes smaller, and if the distribution ratio of the output time of the zero vectors V0 and V7 is reduced, ＊ The amplitude of becomes larger.

[0034] In the space vector modulation implemented in the first mode, the output voltage vector V ＊ The magnitude of the d-axis voltage command V obtained from the current PI control unit 82 ｄ ＊ and q-axis voltage command V ｑ ＊ and the bus voltage V detected by the bus voltage detection unit 5. ｄｃ 4 is determined by the phase command θ generated by the phase command generating unit 83. ＊ The space vector modulation unit 84 performs space vector modulation to generate the PWM signal U ｐ , V ｐ, W ｐ , U ｎ , V ｎ , W ｎ The output voltage vector V ＊ When determining the dead time, the amount of voltage that compensates for the voltage error due to the dead time may be taken into consideration. The dead time is a time to prevent a leg short circuit, which is set to prevent the switching elements 40 of the upper and lower arms of the same leg from being turned on simultaneously.

[0035] 5A and 5B are diagrams showing examples of waveforms of PWM signals generated by the space vector modulation unit 84 shown in FIG. 2 when the first mode is implemented and when the second mode is implemented. The left side of FIG. 5 shows an example of the waveform of a PWM signal generated when the first mode is implemented, and the right side of FIG. 5 shows an example of the waveform of a PWM signal generated when the second mode is implemented. ＤＣ is the repetition frequency of PWM control when the first mode is implemented, and f Ｍ is the repetition frequency of the PWM control when the second mode is implemented.

[0036] In the first mode for heating the compressor 13, it is sufficient to continue to output a direct current, and a high response is not required compared to the second mode. Therefore, the repetition frequency f ＤＣ is the repetition frequency f when the second mode for rotating the compressor motor 14 is performed. Ｍ This allows the repetition frequency f ＤＣ and repetition frequency f Ｍ The magnitude relationship between ＤＣ <f Ｍ From this relationship, as shown in FIG. 5, the repetition period of PWM control when the first mode is performed is 1 / f ＤＣ is the repetition period 1 / f of PWM control when the second mode is implemented. Ｍ It will be longer than.

[0037] According to the controller 80 according to the first embodiment shown in FIG. 2, the space vector modulation unit 84 converts the PWM signal in the first mode for heating the compressor 13 into the bus voltage V detected by the bus voltage detection unit 5. ｄｃThis makes it possible to always obtain a constant DC current output even if the power supply voltage applied to the converter 3 from the AC power supply 2 fluctuates.

[0038] Furthermore, according to the controller 80 of the first embodiment, in the first mode for heating the compressor 13, the d-axis current command generation unit 81, the current PI control unit 82, and the space vector modulation unit 84 generate the d-axis current I based on the current detection value. ｄ is the d-axis current command I ｄ ＊ Feedback control is performed to follow the current. When feedback control is performed using the method of Patent Document 1 described above, it is necessary to generate a high-frequency current while detecting the high-frequency current, which requires a current detection means and a processing unit capable of high-speed processing, and an increase in cost is unavoidable. In contrast, the method of Embodiment 1 heats the compressor 13 by passing a DC current through the compressor motor 14, which does not require a current detection means and a processing unit capable of high-speed processing. Therefore, it is possible to perform feedback control to heat the compressor 13 while suppressing an increase in cost.

[0039] In addition, the heat generation amount P per phase of the motor winding of the compressor motor 14 ｃ can be expressed as the product of the winding resistance R per phase of the motor winding and the square of the phase current I flowing through the compressor motor 14, as shown in the following equation (3), which is a calculation equation for copper loss.

[0040]

[0041] As shown in the above formula (3), the heat generation amount P per phase of the motor winding of the compressor motor 14 is ｃ is proportional to the square of the phase current I, so the d-axis current command I ｄ ＊ In particular, under low temperature conditions where liquid refrigerant is likely to accumulate, it is effective to increase the d-axis current command I ｄ ＊ If the d-axis current command I is set to a high value, a high heating amount can be obtained to suppress the accumulation of liquid refrigerant. ｄ ＊If the control mode is set to determine the d-axis current command I ｄ ＊ By setting the value to a low value, it is possible to minimize the amount of heating and reduce power consumption during operation in the first mode.

[0042] In the first mode for heating the compressor 13, the phase command θ given to the space vector modulation unit 84 is ＊ By setting the phase command θ to 30°, 90°, 150°, 210°, 270°, or 330°, the number of phases through which the compressor motor 14 is energized can be limited to two phases. ＊ When the phase command θ is set to 30°, the current flows from the U phase to the W phase in the compressor motor 14, and almost no current flows in the V phase. ＊ When the angle is set to 90°, a current flows from the V phase to the W phase in the compressor motor 14, and almost no current flows in the U phase.

[0043] As mentioned above, the heat generation amount P per phase of the motor winding is ｃ Since is proportional to the square of the phase current I, by limiting the number of phases to which current flows to two, the motor windings can be heated effectively and efficiently. If the current value to be passed between two phases is to be given as a control command value, the d-axis current command I is the current value to be passed between two phases multiplied by √2. ｄ ＊ In addition, the phase command θ ＊ By switching the phases at regular intervals, the current flowing through the windings can be switched, and the compressor 13 can be heated while the amount of heat generated by the windings of each phase is made uniform.

[0044] Furthermore, in the first mode for heating the compressor 13, as shown in FIG. 5, the repetition frequency f ＤＣ The repetition frequency f of the PWM control when the second mode is implemented Ｍ If the switching loss of the switching element 40 of the inverter 4 is set lower than the first mode, it is possible to suppress the switching loss, and therefore it is possible to reduce the power consumption when the first mode is implemented.

[0045] Furthermore, when a refrigerant with a low GWP (Global Warming Potential), such as R290, is used as the refrigerant in the refrigeration cycle system 1, a larger stroke volume is required to ensure the same refrigeration capacity as conventional refrigerants with a high GWP, such as R32 or R410A. However, increasing the stroke volume also increases the size of the compressor 13, which tends to increase its heat capacity. Therefore, when a refrigerant with a low GWP is used in the refrigeration cycle system 1, fluctuations in the power supply voltage applied to the converter 3 or variations in the motor constant of the compressor motor 14 may cause the heating capacity of the compressor 13 to be insufficient. To address this issue, the method of the first embodiment can consistently obtain a constant DC current output, as described above. Therefore, the margin setting, which takes into account power supply voltage fluctuations and motor constant variations, can be kept to a minimum, enabling heating control of the compressor 13 while improving the operating efficiency of the refrigeration cycle system 1.

[0046] Next, a description will be given of a hardware configuration that realizes the functions of the control unit 8 according to embodiment 1. Fig. 6 is a block diagram showing an example of a hardware configuration that realizes the functions of the control unit 8 according to embodiment 1. To realize some or all of the functions of the control unit 8, as shown in Fig. 6, a configuration including a processor 91 that performs calculations and a memory 92 that stores programs read by the processor 91 can be used.

[0047] The processor 91 is an example of a computing means. The processor 91 may be a computing means called a microprocessor, a microcomputer, a central processing unit (CPU), or a digital signal processor (DSP). Examples of the memory 92 include non-volatile or volatile semiconductor memory such as random access memory (RAM), read-only memory (ROM), flash memory, erasable programmable read-only memory (EPROM), and electrically programmable programmable read-only memory (EEPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a minidisk, and a digital versatile disk (DVD).

[0048] The memory 92 holds a program that executes the functions of the control unit 8. The processor 91 receives and transmits necessary information and stores it in the memory 92, and the processor 91 executes the program held in the memory 92 and refers to the data and tables stored in the memory 92, thereby enabling the above-mentioned processing by the control unit 8 to be performed. The calculation results by the processor 91 can be stored in the memory 92.

[0049] As described above, the compressor drive device according to the first embodiment drives a compressor including a compression mechanism that compresses a refrigerant flowing in a refrigerant circuit of a refrigeration cycle device and a compressor motor that operates the compression mechanism. The compressor drive device includes an inverter having a plurality of switching elements, a motor current detection unit that detects a motor current flowing through the compressor motor, a bus voltage detection unit that detects a bus voltage that is a DC voltage applied to the inverter, and a control unit that controls the operation of the inverter. The inverter converts an AC voltage applied from an AC power source into a drive voltage for driving the compressor motor and applies the drive voltage to the compressor motor. The control unit has two operating modes for operating the inverter: a first mode in which the compressor is heated without rotating the compressor motor, and a second mode in which the compressor motor is driven by pulse width modulation control. In the first mode, the control unit performs pulse width modulation control of the switching elements based on the current detection value detected by the motor current detection unit, a current command that is a motor current command value, and a voltage detection value detected by the bus voltage detection unit so that the current detection value follows the current command and a DC current flows through the compressor motor. According to the compressor drive device of the first embodiment, heating is performed by passing a DC current through the compressor motor, so that a current detection means and a processing unit capable of high-speed processing are not required. This makes it possible to perform feedback control for heating the compressor while suppressing increases in costs.

[0050] In the above control, it is preferable to set the repetition frequency of PWM control to be lower when the first mode is implemented than when the second mode is implemented. By setting the repetition frequency of PWM control when the first mode is implemented lower than the repetition frequency of PWM control when the second mode is implemented, it is possible to suppress switching loss in the switching elements of the inverter and reduce power consumption when the first mode is implemented.

[0051] The refrigeration cycle apparatus may be provided with a temperature detector for detecting the ambient temperature of the location where the compressor is installed. The control unit can generate a current command based on the temperature detected by the temperature detector, thereby varying the current command used in the first mode according to the detected temperature. Although the accumulation of liquid refrigerant varies depending on temperature conditions, determining the current command based on the temperature detected by the temperature detector makes it possible to optimize the amount of heating for the compressor while suppressing power consumption during operation in the first mode.

[0052] In the first mode, the control unit can be configured to pulse-width-modulate the switching elements so that DC current flows through two of the three phases of the compressor motor. In this case, by switching the phase through which DC current flows, it is possible to heat the compressor while uniformly distributing heat from the windings of each phase.

[0053] The refrigerant used in the refrigerant circuit of the refrigeration cycle device may be a hydrocarbon refrigerant. Using a hydrocarbon refrigerant tends to increase the size of the compressor and its heat capacity. Therefore, compared to using a refrigerant with a higher GWP than a hydrocarbon refrigerant, this is less effective against fluctuations in power supply voltage and motor constants. On the other hand, the compressor drive device of embodiment 1 can always obtain a constant DC current output through the first mode by the control unit. This allows the margin setting, which takes into account fluctuations in power supply voltage and motor constants, to be kept to the minimum necessary value, thereby enabling compressor heating control to be performed while improving the operating efficiency of the refrigeration cycle device.

[0054] Second Embodiment When the compressor 13 is heated using the current as a command value as in the first embodiment, as can be understood from the above formula (3), the heat generation amount P ｃ The motor windings have characteristics that change depending on the ambient temperature, and as the ambient temperature T rises, the winding resistance R also increases. ｃWhen it is desired to accurately control the current command, it is preferable to determine the current command taking into consideration the winding resistance R during operation. In the second embodiment, a control method that takes this into consideration will be described.

[0055] 7 is a block diagram showing an example of the configuration of a controller 80A related to the execution of the first mode in the control unit 8 of the second embodiment. Comparing the configuration of the controller 80A shown in FIG. 7 with the configuration of the controller 80 shown in FIG. 2, the d-axis current command generating unit 81 is replaced with a d-axis current command generating unit 81A. While only the environmental temperature T was input as an input signal to the d-axis current command generating unit 81, the d-axis current command generating unit 81A further receives the d-axis current I in addition to the environmental temperature T. ｄ and q-axis current I ｑ and the d-axis voltage command V ｄ ＊ and q-axis voltage command V ｑ ＊ The major difference is that the input signal is the signal . In the following, the second embodiment will be described mainly with respect to the differences from the first embodiment, and the description of the commonalities between the first embodiment and the second embodiment will be omitted as appropriate.

[0056] Fig. 8 is a block diagram showing an example of the configuration of the d-axis current command generator 81A shown in Fig. 7. The d-axis current command generator 81A includes a power command generator 90, a resistance estimator 86, a divider 87, a square root calculator 88, and a coefficient multiplier 89.

[0057] 9 is a diagram showing an example of a control curve referred to by the power command generating unit 90 shown in FIG. 9. The horizontal axis of FIG. 9 represents the environmental temperature T, and the vertical axis represents the power command P ＊ As shown in FIG. 9, in the region where the environmental temperature T is low, the maximum power value P ＭＡＸ The power command P ＊ As the ambient temperature T increases, the power value required to prevent the liquid refrigerant from accumulating decreases. Therefore, the power value is reduced in accordance with the characteristics, and the minimum power value P ＭＩＮ The power command P ＊ Determine the minimum power value P ＭＩＮ is the minimum power value required to suppress the accumulation of liquid refrigerant. ＊ Once the power command P＊ Since the power consumption can be controlled to the minimum required to prevent the liquid refrigerant from accumulating, it is possible to prevent an increase in loss in the first mode due to excessive power consumption.

[0058] Next, the resistance estimation unit 86 will be described. The resistance estimation unit 86 estimates the d-axis current I ｄ and q-axis current I ｑ and the d-axis voltage command V ｄ ＊ and q-axis voltage command V ｑ ＊ and the resistance estimated value R^ is the estimated value of the winding resistance R of the compressor motor 14. As shown in FIG. 7, the d-axis current I ｄ and q-axis current I ｑ is the output value of the dq conversion unit 85, and the d-axis voltage command V ｄ ＊ and q-axis voltage command V ｑ ＊ is the output value of the current PI control unit 82.

[0059] The resistance estimation unit 86 estimates the d-axis voltage command V ｄ ＊ and q-axis voltage command V ｑ ＊ The composite vector V ＊ and the d-axis current I ｄ and q-axis current I ｑ The estimated resistance value R^ is calculated from the resultant vector Ia of the resultant vector V ＊ When calculating , a voltage amount that compensates for a voltage error due to dead time may be taken into consideration. If it is possible to actually measure the winding resistance R of the compressor motor 14 while the compressor motor 14 is operating, the actual measured value may be used as the resistance estimated value R. Alternatively, the resistance estimated value R may be the result of resistance estimation performed using another method.

[0060] The d-axis current command generating unit 81A generates a power command P ＊ and the resistance estimate R^, the d-axis current command I ｄ ＊ The heat generation amount P per phase of the motor winding of the compressor motor 14 is calculated. ｃ is expressed by the above formula (3), so when the current flow phase is limited to two phases, the heat generation amount Pｃ-ａｌｌ can be expressed by the following equation (4).

[0061]

[0062] In the above formula (4), the calorific value P ｃ-ａｌｌ Power Command P ＊ Substituting the estimated resistance value R^ for the winding resistance R and solving for the phase current I, we get the current command I ｐｅａｋ ＊ This calculation is performed by the divider 87 and the square root calculator 88 in FIG. 8. The current command I calculated at this time is ｐｅａｋ ＊ is a current value in the three-phase coordinate system, so it must be converted into the dq-axis coordinate system. ＊ is set to any of 30°, 90°, 150°, 210°, 270°, and 330°, so the current command I ｐｅａｋ ＊ The value obtained by multiplying by √2 is the d-axis current command I ｄ ＊ This calculation process is executed by the coefficient multiplier 89 in FIG. 8. By using the d-axis current command generating unit 81A configured as shown in FIG. 8, the current for heating the compressor 13 can be calculated as the current command I ｐｅａｋ ＊ It is possible to control it with

[0063] As described above, in the compressor drive device according to the second embodiment, the control unit includes a resistance estimator that estimates the winding resistance of the compressor motor, and the current command used in the first mode is calculated based on the power command determined in response to the temperature detected by the temperature detector and the resistance value of the winding resistance estimated by the resistance estimator. In the compressor drive device configured in this manner, in the first mode in which the compressor is heated, a current command that is a command value for the motor current is generated based on the power command generated in response to the ambient temperature, and the switching elements are pulse-width modulated so that the detected current follows the current command and DC current flows through the compressor motor. According to the compressor drive device according to the second embodiment, even if the resistance value of the winding resistance fluctuates during heating of the compressor motor, the flow of current can be automatically adjusted to maintain a constant heat generation amount of the motor winding.

[0064] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0065] REFRIGERATION CYCLE DEVICE, 2 AC POWER SUPPLY, 3 CONVERTER, 4 INVERTER, 5 BUS VOLTAGE DETECTION UNIT, 6 BUS CURRENT DETECTION UNIT, 7 MOTOR CURRENT DETECTION UNIT, 8 CONTROL UNIT, 10 OUTDOOR HEAT EXCHANGER, 11 FOUR-WAY VALVE, 12 EXPANSION VALVE, 13 COMPRESSOR, 14 COMPRESSOR MOTOR, 15 COMPRESSION MECHANISM, 16 INDOOR HEAT EXCHANGER, 17 REFRIGERANTIC PIPING, 19 TEMPERATURE DETECTOR, 30 REACTOR, 31a-31d DIODES, 32 CAPACITANT, 34 DIODE BRIDGE CIRCUIT, 40, 40a-40f SWITCHING ELEMENT, 50 COMPRESSOR DRIVE UNIT, 80, 80A CONTROLLER, 81, 81A d-AXIS CURRENT COMMAND GENERATION UNIT, 82 CURRENT PI CONTROL UNIT, 83 PHASE COMMAND GENERATION UNIT, 84 SPACE VECTOR MODULATOR, 85 dq CONVERSION UNIT, 86 RESISTANCE ESTIMATION UNIT, 87 DIVIDER, 88 SQUARE ROOT COMPUTER, 89 COEFFICIENT MULTIPLIER, 90 Power command generating unit, 91 processor, 92 memory, 100 heat pump device.

Claims

1. A compressor drive device for driving a compressor having a compression mechanism that compresses a refrigerant flowing in a refrigerant circuit of a refrigeration cycle device and a compressor motor that operates the compression mechanism, comprising: an inverter having a plurality of switching elements that converts an AC voltage applied from an AC power source into a drive voltage for driving the compressor motor and applies the drive voltage to the compressor motor; a motor current detection unit that detects a motor current flowing through the compressor motor; a bus voltage detection unit that detects a bus voltage that is a DC voltage applied to the inverter; and a control unit that controls the operation of the inverter, wherein the control unit has, as operation modes for operating the inverter, a first mode in which the compressor is heated without rotating the compressor motor, and a second mode in which the compressor motor is driven by pulse width modulation control, In the compressor drive device, in the first mode, the control unit performs pulse width modulation control of the switching element based on the current detection value detected by the motor current detection unit, a current command that is a command value for the motor current, and the voltage detection value detected by the bus voltage detection unit, so that the current detection value follows the current command and a direct current flows through the compressor motor.

2. The compressor drive device according to claim 1, further comprising a temperature detector for detecting the ambient temperature of the location where the compressor is installed, and wherein the control unit generates the current command based on the temperature detected by the temperature detector.

3. The compressor driving device according to claim 2, wherein the current command used in the first mode varies depending on the detected temperature.

4. The compressor drive device according to claim 2, wherein the temperature sensor of the temperature detector is disposed inside a housing that houses the compressor.

5. A compressor drive device as described in claim 2, wherein the control unit includes a resistance estimation unit that estimates the winding resistance of the compressor motor, and the current command used in the first mode is calculated based on a power command determined in accordance with the temperature detected by the temperature detector and the resistance value of the winding resistance estimated by the resistance estimation unit.

6. The compressor drive device according to claim 1, wherein the compressor motor is a three-phase motor, and the control unit, in the first mode, performs pulse width modulation control of the switching elements so that direct current flows through two of the three phases of the compressor motor.

7. The compressor driving device according to claim 1, wherein the repetition frequency of the pulse width modulation control is lower when the first mode is implemented than when the second mode is implemented.

8. The compressor drive device according to claim 7, wherein the refrigerant is a hydrocarbon refrigerant.

9. An air conditioner comprising a compressor driving device according to any one of claims 1 to 8.

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