Power conversion device, motor drive device, and refrigeration cycle application equipment

Abstract

A power conversion device (1) comprises: an inverter (12) that applies a high-frequency voltage to a three-phase motor (4) that drives a compression mechanism (77) with which a compressor (71) is provided, said high-frequency voltage having a frequency that is greater than or equal to the operating frequency of the compressor (71); and a control unit (13) that controls the inverter (12). The control unit (13) controls the inverter (12) so that, of the three-phase outputs of the inverter (12), a first phase, the output voltage of which becomes maximum and a second phase, the output voltage of which becomes minimum are energized and the switching of a switching element for a third phase, which is the remaining one phase, is stopped.

Description

Power conversion devices, motor drive devices, and refrigeration cycle application equipment

[0001] The present disclosure relates to a power conversion device, a motor drive device, and a refrigeration cycle application device connected to a compressor.

[0002] Conventionally, in a power conversion device or the like that applies an AC voltage to a motor to drive the motor, a high-frequency AC voltage higher than the operating frequency range of the compressor motor during compression operation is applied from an inverter to the three-phase windings of the compressor motor to heat the compressor (hereinafter referred to as constrained energization). For example, Patent Document 1 discloses a technology in which a heat pump device applies to the motor a high-frequency voltage that prevents the motor from rotating, estimates a magnetic pole position indicating a rotor stop position of the motor based on an induced voltage of the motor, determines the amplitude and phase of a voltage command so that the amount of heat generated by the motor is the amount of heat required to vaporize the refrigerant remaining in the compressor, and generates a drive signal for the inverter to control the heating of the motor.

[0003] Patent No. 5795085

[0004] However, according to the above-mentioned conventional technology, the frequency of the carrier signal used to control the inverter is high, at about 14 kHz to 20 kHz, which causes a problem of large switching losses in the switching elements of the inverter.

[0005] The present disclosure has been made in consideration of the above, and aims to provide a power conversion device that can reduce switching loss in switching elements provided in an inverter when a high-frequency voltage that is equal to or higher than the operating frequency of the compressor is applied to the compressor to heat the compressor.

[0006] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure includes an inverter that applies a high-frequency voltage equal to or higher than the operating frequency of a compressor to a three-phase motor that drives a compression mechanism of the compressor, and a control unit that controls the inverter. The control unit controls the inverter so that, of the three-phase output of the inverter, a first phase having the maximum output voltage and a second phase having the minimum output voltage are energized, and so that switching of the switching elements for the remaining third phase is stopped.

[0007] The power conversion device according to the present disclosure has the advantage of being able to reduce switching losses in the switching elements of the inverter when a high-frequency voltage equal to or higher than the operating frequency of the compressor is applied to the compressor to heat the compressor.

[0008] FIG. 1 is a diagram showing an example of a configuration of a power conversion device according to a first embodiment; FIG. 2 is a flowchart showing the operation of a control unit included in the power conversion device according to the first embodiment; FIG. 3 is a diagram showing an example of a carrier signal used in a drive signal generation unit included in the control unit of the power conversion device according to the first embodiment; FIG. 4 is a flowchart showing an example of a first interrupt process for the flowchart shown in FIG. 2, in which a three-phase voltage command value generation unit of the drive signal generation unit included in the control unit of the power conversion device according to the first embodiment generates and outputs three-phase voltage command values ​​using a voltage phase command value θa at the peak timing of the carrier signal; FIG. 1 shows a relationship between a PWM signal generated by a PWM signal generating unit and a PWM modulation signal generating unit. FIG. 2 shows an example of an analytical waveform when constrained energization is performed in the power conversion device according to embodiment 1. FIG. 3 shows an example of an analytical waveform when constrained energization is performed by the heat pump device of Patent Document 1, which is described in the prior art document, as a comparative example. FIG. 4 shows an example of an analytical waveform during switching operation by the heat pump device of Patent Document 1, which is described in the prior art document, as a comparative example. FIG. 5 shows an example of an analytical waveform during switching operation of the power conversion device according to embodiment 1. FIG. 6 shows an example of a magnetic pole position of a three-phase motor connected to the power conversion device according to embodiment 1 and a change in winding inductance of the three-phase motor. FIG. 7 shows an example of a magnetic pole position of a three-phase motor connected to the power conversion device according to embodiment 1 and an average value of current effective value during constrained energization. FIG. 8 shows an example of an analytical waveform when constrained energization is performed by changing the voltage phase command value by 60 degrees in increments in the power conversion device according to embodiment 1. FIG. 9 shows an example of a hardware configuration for realizing a control unit provided in the power conversion device according to embodiment 1. FIG. 10 shows an example of a configuration of a refrigeration cycle application device according to embodiment 2.

[0009] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle applied device according to embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] First Embodiment. FIG. 1 is a diagram illustrating an example configuration of a power conversion device 1 according to a first embodiment. The power conversion device 1 is connected to a DC power supply 3 and a three-phase motor 4. The power conversion device 1 converts a bus voltage Vdc, which is a DC voltage supplied from the DC power supply 3, into an AC voltage having a desired amplitude and phase and supplies the AC voltage to the three-phase motor 4. The DC power supply 3 supplies the bus voltage Vdc to the power conversion device 1. In the example of FIG. 1 , the DC power supply 3 is in the form of a battery. However, the DC power supply 3 may be configured with an AC power supply such as a commercial power supply that supplies AC voltage, a rectifier circuit that rectifies the AC voltage supplied from the AC power supply, and a capacitor that smoothes the output from the rectifier circuit. The three-phase motor 4 is a motor having three-phase windings, i.e., U-phase, V-phase, and W-phase. The three-phase motor 4 is a compressor motor that operates a compression mechanism 77 inside a compressor 71. The power conversion device 1 and the three-phase motor 4 form a motor drive device 2.

[0011] The following describes the configuration and operation of the power conversion device 1. As shown in FIG.

[0012] The voltage detection unit 11 detects the bus voltage Vdc supplied from the DC power supply 3. The voltage detection unit 11 outputs the detected value of the bus voltage Vdc to the control unit 13.

[0013] The inverter 12 includes six switching elements 21a to 21f, and converts the bus voltage Vdc supplied from the DC power supply 3 into an AC voltage, which is output to the three-phase motor 4. Specifically, the inverter 12 converts the bus voltage Vdc into an AC voltage by turning on and off the switching elements 21a to 21f under the control of the control unit 13. The inverter 12 applies the converted AC voltages to the U-phase, V-phase, and W-phase windings of the three-phase motor 4 as voltages Vu, Vv, and Vw, respectively. Furthermore, during constrained current application, the inverter 12 applies a high-frequency voltage equal to or higher than the operating frequency of the compressor 71 to the three-phase motor 4, which drives a compression mechanism 77 included in the compressor 71.

[0014] Of the switching elements 21a to 21f, switching elements 21a and 21d are switching elements corresponding to the U phase, switching elements 21b and 21e are switching elements corresponding to the V phase, and switching elements 21c and 21f are switching elements corresponding to the W phase. Furthermore, of the switching elements 21a to 21f, switching elements 21a to 21c are upper arm switching elements, and switching elements 21d to 21f are lower arm switching elements. In the following description, the upper arm switching elements 21a to 21c may be simply referred to as upper arms, and the lower arm switching elements 21d to 21f may be simply referred to as lower arms.

[0015] The switching elements 21a to 21f are semiconductor switching elements such as, for example, IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors). The switching elements 21a to 21f may have a free-wheeling diode (not shown) connected in parallel to them in order to suppress surge voltages caused by switching. The free-wheeling diode may be a parasitic diode of the semiconductor switching element, but if the switching elements 21a to 21f are MOSFETs, it is also possible to realize a similar function by turning the diode on at the timing of free-wheeling. The switching elements 21a to 21f may be made of not only silicon (Si) but also wide bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), and gallium oxide (Ga). ２ O ３ By using materials such as diamond, it is possible to achieve low loss and high-speed switching.

[0016] The control unit 13 controls the operation of the inverter 12. Specifically, the control unit 13 controls the inverter 12 by generating and outputting PWM signals, which are drive signals for turning on and off the switching elements 21 a to 21 f included in the inverter 12.

[0017] The power conversion device 1 is capable of so-called constrained energization, in which a high-frequency voltage higher than the operating frequency of the compressor 71 is applied from the inverter 12 to the three-phase motor 4 that drives the compression mechanism 77 of the compressor 71 under the control of the control unit 13.

[0018] The configuration of the control unit 13 will be described. As shown in Fig. 1 , the control unit 13 includes a phase setting unit 14 and a drive signal generating unit 15. The drive signal generating unit 15 also includes a three-phase voltage command value generating unit 16 and a PWM signal generating unit 17.

[0019] The phase setting unit 14 sets voltage phase command values ​​θa and θb and outputs them to the drive signal generating unit 15. The voltage phase command value θb has a phase that differs by 180 degrees from the voltage phase command value θa. In the following description, the voltage phase command value θa may be referred to as a first phase, and the voltage phase command value θb may be referred to as a second phase.

[0020] The drive signal generation unit 15 acquires a voltage command value Va. For example, when the power conversion device 1 is installed in an air conditioner or the like, the voltage command value Va is a command value obtained based on an operation mode such as cooling operation or heating operation set by a user via a remote controller of the air conditioner, a set temperature set by the user, and the like. The drive signal generation unit 15 generates a high-frequency voltage command value Vk based on the acquired voltage command value Va and the bus voltage Vdc detected by the voltage detection unit 11. Specifically, the drive signal generation unit 15 generates the high-frequency voltage command value Vk using the following equation (1):

[0021] Vk=Va×√2 / Vdc…(1)

[0022] In the drive signal generating unit 15, the three-phase voltage command value generating unit 16 generates a three-phase voltage command value Vu based on the high-frequency voltage command value Vk and the voltage phase command values ​​θa and θb obtained from the phase setting unit 14. ＊ , Vv ＊ , Vw ＊ In the three-phase motor 4, the phases of the three phases, U, V, and W, generally differ from each other by 120 degrees (=2π / 3). Therefore, the three-phase voltage command value generating unit 16 generates the three-phase voltage command value Vu ＊ , Vv ＊ , Vw＊ For cosine waves whose phases differ by 2π / 3 as shown in the following equations (2) to (4), the voltage phase command value θa or the voltage phase command value θb is substituted for θ to generate a voltage command value for each phase.

[0023] Vu ＊ =Vk×cosθ…(2) Vv ＊ =Vk×cos(θ−(2π / 3))…(3) Vw ＊ =Vk×cos(θ+(2π / 3))…(4)

[0024] The three-phase voltage command value generator 16 generates the three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ When generating the phase command value θa, the voltage phase command value θb is used, but how to switch between the voltage phase command value θa and the voltage phase command value θb will be described later.

[0025] The PWM signal generator 17 generates a three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ Specifically, the PWM signal generator 17 generates the PWM signals UP, VP, WP, UN, VN, and WN based on the three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ is compared with a carrier signal, which is a reference signal having a specified frequency and an amplitude of Vdc / 2, to obtain a three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ and generates PWM signals UP, VP, WP, UN, VN, and WN based on the magnitude relationship of the carrier signal.

[0026] The drive signal generating unit 15 outputs the PWM signals UP, VP, WP, UN, VN, and WN to the corresponding switching elements 21 a, 21 b, 21 c, 21 d, 21 e, and 21 f to drive the inverter 12, thereby applying a voltage to the three-phase motor 4. As shown in Fig. 1 , the PWM signal UP is a drive signal that controls the on / off of the switching element 21 a, the PWM signal VP is a drive signal that controls the on / off of the switching element 21 b, the PWM signal WP is a drive signal that controls the on / off of the switching element 21 c, the PWM signal UN is a drive signal that controls the on / off of the switching element 21 d, the PWM signal VN is a drive signal that controls the on / off of the switching element 21 e, and the PWM signal WN is a drive signal that controls the on / off of the switching element 21 f. In addition, the drive signal generating unit 15 applies a high-frequency voltage from the inverter 12 to the three-phase motor 4 that will not rotate the rotor (not shown) of the three-phase motor 4, i.e., a high-frequency AC voltage that is outside the operating frequency range during compression operation of the three-phase motor 4, and the refrigerant in the compressor 71 can be heated by the iron loss and copper loss generated in the three-phase motor 4.

[0027] The operation of the control unit 13 will be described. Fig. 2 is a flowchart showing the operation of the control unit 13 included in the power conversion device 1 according to the first embodiment. In the control unit 13, the phase setting unit 14 sets initial values ​​of the voltage phase command values ​​θa and θb (step S101). As an example, the phase setting unit 14 sets the initial values ​​of the voltage phase command values ​​θa and θb as follows: the voltage phase command value θa = 90 degrees, and the voltage phase command value θb differs from the voltage phase command value θa by 180 degrees, so that the voltage phase command value θb = 90 + 180 = 270 degrees. The phase setting unit 14 outputs the set voltage phase command values ​​θa and θb to the three-phase voltage command value generation unit 16 of the drive signal generation unit 15.

[0028] The drive signal generating unit 15 acquires the bus voltage Vdc (step S102), acquires the voltage command value Va (step S103), and calculates the high-frequency voltage command value Vk by the above-mentioned equation (1) (step S104). In the drive signal generating unit 15, the three-phase voltage command value generating unit 16 adds 120 degrees to each of the voltage phase command values ​​θa and θb acquired from the phase setting unit 14 (step S105). The control unit 13 repeatedly performs the operations from step S102 to step S105 of the flowchart shown in FIG. 2 at regular intervals, for example, every 1 ms.

[0029] Here, in the drive signal generating unit 15, the three-phase voltage command value generating unit 16 switches between the voltage phase command values ​​θa and θb substituted for θ in equations (2) to (4) at the peak timings or valley timings of the carrier signal shown in Fig. 3. Fig. 3 is a diagram showing an example of a carrier signal used by the drive signal generating unit 15 included in the control unit 13 of the power conversion device 1 according to the first embodiment. Fig. 4 is a diagram showing an example of a carrier signal used by the three-phase voltage command value generating unit 16 of the drive signal generating unit 15 included in the control unit 13 of the power conversion device 1 according to the first embodiment, using the voltage phase command value θa at the peak timings of the carrier signal to generate the three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ 5 is a flowchart showing an example of a first interrupt process for the flowchart shown in Fig. 2, in which the three-phase voltage command value generating unit 16 of the drive signal generating unit 15 included in the control unit 13 of the power conversion device 1 according to the first embodiment generates and outputs the three-phase voltage command value Vu using the voltage phase command value θb at the valley timing of the carrier signal. ＊ , Vv ＊ , Vw ＊ 10 is a flowchart showing an example of a second interrupt process for the flowchart shown in FIG. 2, in which the interrupt process generates and outputs the

[0030] 3 is the same as the carrier signal used in the above-described PWM signal generating unit 17. The carrier signal has a carrier period of Tc, i.e., a carrier frequency of fc = 1 / Tc. In the drive signal generating unit 15, the three-phase voltage command value generating unit 16 and the PWM signal generating unit 17 may generate carrier signals independently, or the drive signal generating unit 15 may generate a common carrier signal for the three-phase voltage command value generating unit 16 and the PWM signal generating unit 17. Alternatively, the three-phase voltage command value generating unit 16 may generate a carrier signal and output it to the PWM signal generating unit 17, or the PWM signal generating unit 17 may generate a carrier signal and output it to the three-phase voltage command value generating unit 16.

[0031] As shown in FIG. 4, the three-phase voltage command value generator 16 waits if it is not a peak timing of the carrier signal (step S201: No), and if it is a peak timing of the carrier signal (step S201: Yes), it uses the voltage phase command value θa to generate the three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ 5, the three-phase voltage command value generator 16 waits if it is not a valley timing of the carrier signal (step S301: No), and if it is a valley timing of the carrier signal (step S301: Yes), it generates the three-phase voltage command value Vu using the voltage phase command value θb. ＊ , Vv ＊ , Vw ＊ 3 to 5, the three-phase voltage command value generator 16 generates the three-phase voltage command value Vu at the peak timings and valley timings of the carrier signal. ＊ , Vv ＊ , Vw ＊ The voltage phase command values ​​θa and θb used when generating the voltage phase command values ​​θa and θb are alternately switched.

[0032] The three-phase voltage command value generation unit 16 performs the first interrupt process shown in Fig. 4 for each carrier period Tc shown in Fig. 3, and performs the second interrupt process shown in Fig. 5 for each carrier period Tc shown in Fig. 3. Furthermore, the three-phase voltage command value generation unit 16 alternately performs the first interrupt process shown in Fig. 4 and the second interrupt process shown in Fig. 5 every half of the carrier period Tc, i.e., every Tc / 2. If the period of the first interrupt process and the second interrupt process, i.e., the carrier period Tc, is defined as a first calculation period, and the constant period in which the control unit 13 repeatedly performs calculations according to the flowchart shown in Fig. 2 is defined as a second calculation period, then the first calculation period is smaller than the second calculation period.

[0033] FIG. 6 is a diagram showing a three-phase voltage command value Vu generated by the three-phase voltage command value generating unit 16 of the drive signal generating unit 15 included in the control unit 13 of the power conversion device 1 according to the first embodiment. ＊ , Vv ＊ , Vw ＊ 7 is a diagram showing an image of the high-frequency voltage command value Vk and the voltage phase command values ​​θa and θb used when generating the three-phase voltage command value Vk. FIG. 7 is a diagram showing the relationship between the high-frequency voltage command value Vk generated by the three-phase voltage command value generator 16 of the drive signal generator 15 included in the control unit 13 of the power conversion device 1 according to the first embodiment and the PWM signals UP, VP, WP, UN, VN, and WN generated by the PWM signal generator 17. Since the relationship between the PWM signals UP, VP, WP, UN, VN, and WN and the corresponding switching elements 21a to 21f is as described above, FIG. 7 can also be said to be a diagram showing the switching patterns of the switching elements 21a to 21f of the inverter 12. Generally, when voltage command values ​​and the like are displayed as vectors, they are displayed in the V1 mode to V6 mode of the actual vectors of the three-phase current conduction shown in FIGS. 6 and 7 .

[0034] In contrast to this, in this embodiment, as described above, if the initial value of the voltage phase command value θa is set to 90 degrees and the initial value of the voltage phase command value θb is set to 270 degrees, the high-frequency voltage command value Vk when the voltage phase command value θa=90 degrees will be in the direction of the vector V2a, and the high-frequency voltage command value Vk when the voltage phase command value θb=270 degrees will be in the direction of the vector V5a, as shown in Fig. 6. That is, in this embodiment, when the high-frequency voltage command value Vk is displayed as a vector, it will be displayed as vectors V1a to V6a of the actual vectors of the two-phase current conduction shown in Figs.

[0035] In the example of FIG. 6 , the switching pattern of each of the switching elements 21a-21f of the inverter 12 alternates between the V2a vector and the V5a vector. As a result, as shown in FIG. 7 , the switching elements 21b, 21c, 21e, and 21f corresponding to the V and W phases are turned on and off, while the switching elements 21a and 21d corresponding to the U phase remain off, i.e., do not switch. Therefore, the control unit 13 can stop switching the switching elements 21a and 21d of the U phase, which is a phase in which the on / off states of the switching elements do not change. This allows the control unit 13 to stop switching two of the six switching elements 21a-21f included in the inverter 12, specifically the switching elements 21a and 21d, thereby reducing the switching loss caused by the switching elements in the inverter 12.

[0036] In this way, the control unit 13 controls the inverter 12 so that, of the three-phase output of the inverter 12, the first phase having the maximum output voltage and the second phase having the minimum output voltage are energized, and the remaining third phase, i.e., the switching of the switching elements, is stopped. The first phase having the maximum output voltage and the second phase having the minimum output voltage are the V phase and the W phase in the example of Fig. 6. The remaining third phase, i.e., the U phase, in the example of Fig. 6.

[0037] As described above, the three-phase voltage command value generator 16 adds 120 degrees to the voltage phase command values ​​θa and θb at regular intervals. Therefore, after a certain period, in FIG. 6 , when the voltage phase command value θa = 90 + 120 = 210 degrees, the high-frequency voltage command value Vk is in the direction of the V4a vector, and when the voltage phase command value θb = 270 + 120 - 360 = 30 degrees, the high-frequency voltage command value Vk is in the direction of the V1a vector. In this case, as shown in FIG. 7 , in the inverter 12, the switching elements 21b and 21e corresponding to the V phase do not perform switching. After the next regular period, in FIG. 6 , when the voltage phase command value θa = 210 + 120 = 330 degrees, the high-frequency voltage command value Vk is in the direction of the V6a vector, and when the voltage phase command value θb = 30 + 120 = 150 degrees, the high-frequency voltage command value Vk is in the direction of the V3a vector. In this case, as shown in Fig. 7, in inverter 12, switching elements 21c and 21f corresponding to the W phase do not perform switching. After the next fixed period, in Fig. 6, when the voltage phase command value θa = 330 + 120 - 360 = 90 degrees, the high-frequency voltage command value Vk is in the direction of the V2a vector, and when the voltage phase command value θb = 150 + 120 = 270 degrees, the high-frequency voltage command value Vk is in the direction of the V5a vector, and the voltage phase command values ​​θa and θb return to the state when they are at their initial values.

[0038] In this embodiment, the control unit 13 performs the repeated calculation of the flowchart shown in Fig. 2 at regular intervals, but the control unit 13 may perform the operation of the repeated calculation part of the flowchart shown in Fig. 2 by either one or both of the first interrupt processing shown in Fig. 4 and the second interrupt processing shown in Fig. 5. In particular, when the bus voltage Vdc supplied to the inverter 12 changes significantly, the control unit 13 may perform the operation of the repeated calculation part of the flowchart shown in Fig. 2 on the interrupt processing side, which allows the high-frequency voltage command value Vk to be adjusted in a short control period. ＊ , Vv ＊ , Vw ＊ The high frequency voltage command value Vk can be reflected in the generation of the voltage command value Vk in a short control period.

[0039] FIG. 8 is a diagram illustrating an example of an analytical waveform when constrained energization is performed in the power conversion device 1 according to the first embodiment. FIG. 9 is a diagram illustrating an example of an analytical waveform when constrained energization is performed in the heat pump device of Patent Document 1, a prior art document, as a comparative example. In FIGS. 8 and 9 , the first line from the top left indicates the carrier signal, the second line from the top left indicates the voltage phase command values ​​θa and θb, and the third line from the top left indicates the currents of each phase flowing from the inverter 12 to the three-phase motor 4. Also, in FIGS. 8 and 9 , the first line from the top right indicates the voltage V_Vp across the V-phase upper arm and the voltage V_Vn across the V-phase lower arm, the second line from the top right indicates the PWM signal for the U-phase upper arm, the third line from the top right indicates the PWM signal for the V-phase upper arm, and the fourth line from the top right indicates the PWM signal for the W-phase upper arm. In each graph, the horizontal axis represents time (seconds). Note that in FIG. 9 , the second line from the top left indicates the voltage phase command values ​​θa and θb, which are constant, with θa = 90 degrees and θb = 270 degrees. 8 and 9, the voltage command value Va has the same magnitude.

[0040] As can be seen by comparing Figures 8 and 9 , the power conversion device 1 of this embodiment has a section in which switching is stopped in one of the U, V, and W phases, as shown in the analysis waveform of Figure 8 . While Figure 8 shows the upper-arm PWM signals for each phase, the lower-arm PWM signals for each phase also have similar sections in which switching is stopped. This allows the power conversion device 1 to reduce switching loss due to the switching elements 21a to 21f of the inverter 12 during constrained conduction, compared to the constrained conduction of the heat pump device described in Patent Document 1. Taking the V-phase current around 0.097 seconds in the third graph from the top left of Figure 8 as an example, the voltage output when increasing the V-phase current corresponds to the V2a vector shown in Figures 6 and 7 , and the voltage output when decreasing the V-phase current corresponds to the V5a vector shown in Figures 6 and 7 . These voltage vectors are conduction patterns in which only one upper-arm phase is turned on. Therefore, the power conversion device 1 can reduce the common mode voltage compared to when two phases of the upper arm are turned on, and therefore can reduce switching noise.

[0041] 8 and 9, the current values ​​at the switching timings of the switching elements 21a to 21f of the inverter 12 are compared. In FIG. 9, a current of approximately 5 A flows in each phase at both switching timing #1 and switching timing #2. On the other hand, in FIG. 8, there is a large current section where approximately twice as much current flows as in FIG. 9, and a small current section where the current is close to zero. In FIG. 8, switching timing #2 occurs in the small current section, resulting in operation close to zero current switching, which makes it possible to reduce switching loss due to the switching elements 21a to 21f of the inverter 12.

[0042] Next, waveforms during switching operation of the power conversion device 1 of this embodiment are compared with waveforms during switching operation of a heat pump device described in Patent Document 1 as a comparative example. FIG. 10 is a diagram showing an example of analyzed waveforms during switching operation of the heat pump device described in Patent Document 1, a prior art document, as a comparative example. FIG. 11 is a diagram showing an example of analyzed waveforms during switching operation of the power conversion device 1 according to embodiment 1. In FIGS. 10 and 11 , the upper left side shows the voltage V_Vp across the V-phase upper arm and the voltage V_Vn across the V-phase lower arm at switching timing #1, and the lower left side shows the PWM signal for the V-phase lower arm and the PWM signal for the V-phase upper arm at switching timing #1. In FIGS. 10 and 11 , the upper right side shows the voltage V_Vp across the V-phase upper arm and the voltage V_Vn across the V-phase lower arm at switching timing #2, and the lower right side shows the PWM signal for the V-phase lower arm and the PWM signal for the V-phase upper arm at switching timing #2. 10 correspond to the switching timings #1 and #2 shown in FIG. 9, and the switching timings #1 and #2 shown in FIG. 11 correspond to the switching timings #1 and #2 shown in FIG.

[0043] At switching timings #1 and #2 of the switching operation of the heat pump apparatus of the comparative example shown in Figure 10, switching is performed while a current of approximately 5 A is flowing through inverter 12. At this time, as shown in Figure 10, for example, the V-phase upper arm voltage V_Vp and the V-phase lower arm voltage V_Vn undergo a steep voltage change because the inverter current is small. This occurs because the dead time ends before the charging and discharging of charge is completed in the parasitic capacitance (not shown) present in parallel with switching elements 21a to 21f. This results in a problem of increased switching noise in inverter 12.

[0044] On the other hand, switching timing #1 of the switching operation by the power conversion device 1 of this embodiment shown in FIG. 11 occurs during a high-current interval in which a large current flows through the inverter 12. Therefore, as shown in FIG. 11, sufficient charge is charged and discharged to the parasitic capacitances present in parallel with the switching elements during the dead time period. Therefore, in the power conversion device 1, abrupt voltage changes do not occur during the switching operation of the switching elements 21a to 21f of the inverter 12, and switching noise can be reduced compared to the comparative example shown in FIG. 10. Note that, as shown in FIG. 11, in the power conversion device 1 of this embodiment, switching timing #2 occurs during a low-current interval, and thus switching operation occurs when the inverter current is low, as in the comparative example shown in FIG. 10. However, the high-current interval and the low-current interval of the inverter 12 each occur for half a cycle of the carrier period Tc of the carrier signal. Therefore, the power conversion device 1 of this embodiment can reduce the average value of switching noise compared to the comparative example. Furthermore, the power conversion device 1 of this embodiment can reduce the frequency of switching noise to half of the frequency of switching noise generated in the comparative example, thereby reducing switching noise in the high frequency band.

[0045] In this way, the control unit 13 controls the inverter 12 to provide a first switching period in which the switching elements 21a to 21f provided in the inverter 12 perform switching operations when the charging and discharging of the parasitic capacitance of the switching elements is complete during the dead time period of the switching elements, and a second switching period in which the switching elements perform switching operations when the charging and discharging of the parasitic capacitance of the switching elements is not complete during the dead time period of the switching elements.

[0046] FIG. 12 is a diagram illustrating an example of changes in the magnetic pole position of the three-phase motor 4 connected to the power conversion device 1 according to the first embodiment and the winding inductance of the three-phase motor 4. FIG. 13 is a diagram illustrating an example of the magnetic pole position of the three-phase motor 4 connected to the power conversion device 1 according to the first embodiment and the average value of the effective current value during constrained energization. As shown in FIG. 12 , the magnitude of the inductance of the three-phase motor 4 changes twice per electrical angle cycle. Therefore, the effective current value during constrained energization, i.e., the heat generation amount due to constrained energization, also changes twice per electrical angle cycle. In this embodiment, the control unit 13 of the power conversion device 1 changes the voltage phase command values ​​θa and θb during constrained energization by 120 degrees each. Therefore, the power conversion device 1 can level out the influence of changes in inductance due to the magnetic pole position of the three-phase motor 4, thereby achieving an effect of keeping the average heat generation amount substantially constant regardless of the magnetic pole position of the three-phase motor 4. As a result, the power conversion device 1 can obtain a stable heat generation amount during constrained energization without performing complex magnetic pole position estimation processing or adding circuits.

[0047] In the present embodiment, the three-phase voltage command value generator 16 adds 120 degrees to the voltage phase command values ​​θa and θb at regular intervals. However, the present invention is not limited to this. The three-phase voltage command value generator 16 can also achieve the same effect when adding 60 degrees to the voltage phase command values ​​θa and θb at regular intervals. FIG. 14 is a diagram illustrating an example of an analyzed waveform when constrained current is performed by changing the voltage phase command values ​​θa and θb at 60 degrees increments in the power conversion device 1 according to the first embodiment. The types and arrangement of the analysis results shown in FIG. 14 are the same as those shown in FIG. 8 . As shown in FIG. 14 , the power conversion device 1 can provide a switching stop period and a large current period and a small current period even when adding 60 degrees to the voltage phase command values ​​θa and θb at regular intervals.

[0048] In this way, the control unit 13 changes the output voltage phase of the high-frequency voltage to a voltage phase command value θa, which is a first phase, or to a voltage phase command value θb, which is a second phase that is 180 degrees different from the first phase, for each first calculation period, and controls the inverter 12 to change the first phase and the second phase by 60 degrees or 120 degrees for each second calculation period, which is a calculation period longer than the first calculation period.

[0049] In the present embodiment, the three-phase voltage command value generator 16 switches between the voltage phase command values ​​θa and θb and adds 60 degrees or 120 degrees to the voltage phase command values ​​θa and θb, but this is not limiting. In the control unit 13, the phase setting unit 14 can also switch between the voltage phase command values ​​θa and θb and add 60 degrees or 120 degrees to the voltage phase command values ​​θa and θb. In this case, the phase setting unit 14 outputs the voltage phase command value θa or the voltage phase command value θb used by the three-phase voltage command value generator 16 each time.

[0050] Next, a description will be given of the hardware configuration of the control unit 13 included in the power conversion device 1. Fig. 15 is a diagram showing an example of a hardware configuration realizing the control unit 13 included in the power conversion device 1 according to embodiment 1. The control unit 13 is realized by a processor 91 and a memory 92.

[0051] The processor 91 is a CPU (Central Processing Unit, also called a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). Examples of memory 92 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (Electrically Erasable Programmable Read Only Memory). Furthermore, memory 92 is not limited to these, and may also be a magnetic disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0052] As described above, according to this embodiment, in the power conversion device 1, the control unit 13 controls the three-phase voltage command value Vu ＊ , Vv ＊ , Vw ＊ Regarding the voltage phase command values ​​θa, θb used when generating Vk, the voltage phase command value θb is set to have a phase that is 180 degrees different from the voltage phase command value θa, and further, 60 degrees or 120 degrees is added to each of the voltage phase command values ​​θa, θb for each constant calculation period in which the high-frequency voltage command value Vk is calculated. As a result, the power conversion device 1 does not need to perform switching of two switching elements in the inverter 12 including the switching elements 21a to 21f, and therefore the switching loss caused by the switching elements in the inverter 12 can be reduced.

[0053] Furthermore, as described above, the power conversion device 1 adds 60 degrees or 120 degrees to each of the voltage phase command values ​​θa and θb at each fixed calculation period for calculating the high-frequency voltage command value Vk, thereby enabling the power conversion device 1 to prevent uneven heating of the motor windings of the three-phase motor 4 during constrained energization.

[0054] Furthermore, the power conversion device 1 provides large current sections where large currents flow and small current sections where small currents flow in the U-phase current, V-phase current, and W-phase current flowing from the inverter 12 to the three-phase motor 4, and switches the switching elements 21 a to 21 f of the inverter 12 in the large current sections or the small current sections. This allows the power conversion device 1 to reduce switching noise generated in the switching elements 21 a to 21 f of the inverter 12.

[0055] Second Embodiment In a second embodiment, a case will be described in which the power conversion device 1 described in the first embodiment is mounted on a refrigeration cycle application device.

[0056] FIG. 16 is a diagram illustrating a configuration example of a refrigeration cycle-applied device 80 according to a second embodiment. As illustrated in FIG. 16 , the refrigeration cycle-applied device 80 includes a power conversion device 1. The refrigeration cycle-applied device 80 is, for example, the air conditioner described above. However, the device can also be applied to other products equipped with a refrigeration cycle, such as a refrigerator, a freezer, or a heat pump water heater. The refrigeration cycle-applied device 80 includes a compressor 71, a four-way valve 72, an internal heat exchanger 73, an expansion mechanism 74, and a heat exchanger 75, which are connected in sequence via a refrigerant pipe 76. The compressor 71 includes a compression mechanism 77 that compresses the refrigerant, and a three-phase motor 4 that serves as a compressor motor for operating the compression mechanism 77. The three-phase motor 4 is connected as a load to the inverter 12 of the power conversion device 1. That is, the refrigeration cycle-applied device 80 includes the power conversion device 1 described in the first embodiment.

[0057] 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.

[0058] 1 Power conversion device, 2 Motor drive device, 3 DC power supply, 4 Three-phase motor, 11 Voltage detection unit, 12 Inverter, 13 Control unit, 14 Phase setting unit, 15 Drive signal generation unit, 16 Three-phase voltage command value generation unit, 17 PWM signal generation unit, 21a to 21f Switching elements, 71 Compressor, 72 Four-way valve, 73 Internal heat exchanger, 74 Expansion mechanism, 75 Heat exchanger, 76 Refrigerant piping, 77 Compression mechanism, 80 Refrigeration cycle applied equipment, 91 Processor, 92 Memory.

Claims

1. An inverter that applies a high-frequency voltage exceeding the operating frequency of the compressor to a three-phase motor that drives the compression mechanism of the compressor, A control unit that controls the inverter, Equipped with, The control unit energizes the first phase, which has the maximum output voltage, and the second phase, which has the minimum output voltage, of the three phase outputs of the inverter, stops the switching of the switching element for the remaining third phase, and controls the inverter to periodically change the switching element corresponding to the third phase. Power converter.

2. The control unit controls the inverter such that it changes the output voltage phase of the high-frequency voltage to a first phase or a second phase that is 180 degrees different from the first phase for each first calculation cycle, and changes the first phase and the second phase by 60 degrees or 120 degrees for each second calculation cycle, which is a longer calculation cycle than the first calculation cycle. The power conversion device according to claim 1.

3. The control unit controls the inverter to provide a first switching period in which the switching element performs switching operations when the charging and discharging of the parasitic capacitance of the switching element is completed during the dead time period of the switching element, and a second switching period in which the switching element performs switching operations when the charging and discharging of the parasitic capacitance is not completed during the dead time period of the switching element. The power conversion device according to claim 1.

4. A motor drive device comprising a power conversion device according to any one of claims 1 to 3.

5. A refrigeration cycle application device comprising a power conversion device according to any one of claims 1 to 3.