Power conversion device, refrigeration cycle device, and motor system

Abstract

The power conversion device (100) supplies power to a three-phase motor (11) that drives a compressor (10) that compresses a refrigerant. The power conversion device (100) includes a three-phase inverter (102) having at least six semiconductor switches, and an inverter control unit (102a). The three-phase inverter (102) includes a U-phase leg (102U), a V-phase leg (102V), and a W-phase leg (102W). When preheating the refrigerant, the inverter control unit (102a) selects two legs from the U-phase leg (102U), the V-phase leg (102V), and the W-phase leg (102W). The inverter control unit (102a) controls the positive side semiconductor switch of the first leg and the negative side semiconductor switch of the second leg to be turned on and off at the same timing, controls the negative side semiconductor switch of the first leg and the positive side semiconductor switch of the second leg to be turned on and off at the same timing, and maintains the positive side semiconductor switch and the negative side semiconductor switch of the third leg off.

Description

[Technical field]

[0001] The present disclosure relates to a power conversion device, a refrigeration cycle device, and a motor system. [Background technology]

[0002] In order to prevent the refrigerant from liquefying inside the compressor in order to extend the life of the refrigeration cycle device, it is necessary to preheat the refrigerant. For this purpose, there is a method of preheating the refrigerant by wrapping an external heater around the compressor, but this leads to high costs and a large system. On the other hand, there is a method of preheating the refrigerant by winding copper loss or core iron loss by passing DC or AC current through the windings of the three-phase motor inside the compressor using the switching operation of the three-phase inverter used during normal operation. This realizes low cost and compactness of the system (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-297967 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the conventional technology has a problem in that common mode noise is large.

[0005] An object of the present disclosure is to reduce common mode noise. [Means for solving the problem]

[0006] A power conversion device according to one aspect of the present disclosure includes: A power conversion device that supplies power to a three-phase motor that drives a compressor that compresses a refrigerant, a three-phase inverter having at least six semiconductor switches electrically connected to the three-phase motor; an inverter control unit for controlling the at least six semiconductor switches; Equipped with The three-phase inverter includes: a U-phase leg including a positive U-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to a positive side of a DC power supply, and a negative U-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches which is connected in series with the positive U-phase switch and is connected to a negative side of the DC power supply, the U-phase leg corresponding to a U-phase of the three-phase motor; a V-phase leg including a positive V-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to the positive side of the DC power supply, and a negative V-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected in series to the positive V-phase switch and connected to the negative side of the DC power supply, the V-phase leg corresponding to a V-phase of the three-phase motor; a W-phase leg including a positive W-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to the positive side of the DC power supply, and a negative W-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected to the negative side of the DC power supply and is connected in series with the positive W-phase switch; and having When preheating the refrigerant, the inverter control unit selects two of the U-phase leg, the V-phase leg, and the W-phase leg, controls the positive side semiconductor switch of a first leg of the two selected legs and the negative side semiconductor switch of a second leg of the two selected legs to be turned on and off at the same timing, controls the negative side semiconductor switch of the first leg and the positive side semiconductor switch of the second leg to be turned on and off at the same timing, and maintains the positive side semiconductor switch and the negative side semiconductor switch of a third leg other than the two selected legs off. A refrigeration cycle device according to one aspect of the present disclosure includes: The power conversion device; Compressor and Equipped with. A motor system according to an embodiment of the present disclosure includes: The power conversion device; The three-phase motor; Equipped with. Effect of the Invention

[0007] According to the present disclosure, it is possible to provide a power conversion device capable of reducing common-mode noise. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing an example of a refrigeration cycle device 1 having a power conversion device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of a power supply unit and a three-phase inverter. [Diagram 3] FIG. 4 is a diagram illustrating an example of an inverter control unit during a refrigerant compressing operation. [Figure 4] FIG. 11 is a diagram illustrating an example of an operation of an inverter control unit during refrigerant preheating control. [Diagram 5] FIG. 4 is a diagram illustrating an example of an inverter control unit during refrigerant preheating control. [Figure 6] FIG. 11 is a diagram showing an example of the operation (waveform) of each component when current is applied to a U-phase and a V-phase among the three phases of a three-phase motor. [Figure 7] FIG. 11 is a diagram showing an example of the operation (waveform) of each component in the second embodiment. [Figure 8] FIG. 11 is a diagram showing an example of the operation (waveform) of each component in the third embodiment. [Figure 9] FIG. 13 is a diagram showing an example of the operation (waveform) of each component in the fourth embodiment. [Figure 10] FIG. 13 is a diagram showing an example of a current waveform when an AC component is superimposed on a triangular AC current. [Figure 11] FIG. 4 is a diagram showing an example of switching between two legs selected by an inverter control unit. [Figure 12]FIG. 4 is a diagram showing an example of a current pattern when burst heating is performed. [Figure 13] FIG. 4 is a diagram showing an example of a current waveform during burst heating. [Figure 14] 13 is a flowchart showing an example of the operation of an inverter control unit for preheating control in the power converter according to the eighth embodiment. [Figure 15] FIG. 4 is a diagram illustrating an example of a change in switching frequency in variable control of the switching frequency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same reference numerals indicate the same or corresponding parts. <Embodiment 1> Hereinafter, a power conversion device 100 according to a first embodiment will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a refrigeration cycle device 1 having a power conversion device 100 according to a first embodiment. The refrigeration cycle apparatus 1 includes a power conversion apparatus 100 and a compressor 10. The refrigeration cycle apparatus 1 is, for example, an air conditioner (Air To Air: ATA), a refrigeration / refrigeration apparatus, or an air conditioning / heating / hot water supply apparatus (Air To Water: ATW).

[0010] The power conversion device 100 in Fig. 1 includes a power supply unit 101 and a three-phase inverter 102. The power conversion device 100 is electrically connected to a compressor 10. In the example shown in Fig. 1, the three-phase inverter 102 is electrically connected to the compressor 10. The power conversion device 100 supplies electric power to a three-phase motor 11 provided inside the compressor 10.

[0011] The power conversion device 100 (specifically, a three-phase inverter 102) is electrically connected to a three-phase motor 11. The motor system 2 shown in FIG.

[0012] The compressor 10 has a three-phase motor 11 and a compression mechanism 12. The compressor 10 compresses the refrigerant used in the heat pump cycle. The three-phase motor 11 included in the compressor 10 drives the compression mechanism 12 of the compressor 10 during the refrigerant compression operation. The three-phase inverter 102 applies a voltage of a desired frequency and amplitude to the three-phase motor 11.

[0013] The power supply unit 101 and the three-phase inverter 102 are connected by a power line PL1, and the three-phase inverter 102 and the three-phase motor 11 are connected by a power line PL2. One end of the power supply unit 101 is connected to a ground line GL via a power supply ground line PGL. A parasitic capacitance SC to the ground exists between the three-phase inverter 102 and the ground line GL, and between the three-phase motor 11 and the ground line GL.

[0014] FIG. 2 is a diagram illustrating an example of the power supply unit 101 and the three-phase inverter 102. The power supply unit 101 includes a diode rectifier 101a and a smoothing capacitor 101b. The power supply unit 101 is electrically connected to a three-phase AC power supply system 103. In the example shown in FIG. 2, the diode rectifier 101a is electrically connected to the three-phase AC power supply system 103.

[0015] The AC voltage of the three-phase AC system power supply 103 is rectified by a diode rectifier and converted into a DC voltage. The smoothing capacitor 101b reduces the ripple component of the DC voltage. The DC voltage output by the power supply unit 101 is supplied to the three-phase inverter 102 via the power line PL1. The three-phase AC system power supply 103 may be, for example, a DC (storage battery, etc.), an AC (generator, converter, etc.), a single-phase (two-wire or three-wire), or a three-phase (three-wire or four-wire). The power supply unit 101 may include, for example, a power factor improvement circuit using a semiconductor switch, a step-up chopper circuit, a step-down chopper circuit, and an active filter circuit. Alternatively, it may be a combination of a plurality of these circuits. The DC voltage output by the power supply unit 101 may be highly pulsating.

[0016] The three-phase inverter 102 includes at least six semiconductor switches and an inverter control unit 102a. In the example shown in FIG. 2, the three-phase inverter 102 has semiconductor switches UP, VP, WP, UN, VN, and WN. Each of the semiconductor switches UP, VP, WP, UN, VN, and WN has an antiparallel diode. The semiconductor switches UP, VP, WP, UN, VN, and WN are electrically connected to the three-phase motor 11.

[0017] The semiconductor switches UP, VP, WP, UN, VN, and WN have a U-phase leg 102U, a V-phase leg 102V, and a W-phase leg 102W. The U-phase leg 102U corresponds to the U-phase of the three-phase motor 11. The V-phase leg 102V corresponds to the V-phase of the three-phase motor 11. The W-phase leg 102W corresponds to the W-phase of the three-phase motor 11. The U-phase may be referred to as the "first phase", the V-phase may be referred to as the "second phase", and the W-phase may be referred to as the "third phase". The U-phase leg 102U may be referred to as the "first leg", the V-phase leg 102V may be referred to as the "second leg", and the W-phase leg 102W may be referred to as the "third leg".

[0018] <U-phase leg 102U> The U-phase leg 102U has a semiconductor switch UP, which is a positive-side semiconductor switch connected to the positive side of a DC power supply (for example, the power supply unit 101), and a semiconductor switch UN, which is a negative-side semiconductor switch connected to the negative side of the DC power supply (for example, the power supply unit 101). The semiconductor switch UN is connected in series with the semiconductor switch UP. The semiconductor switch UP may also be referred to as the "positive-side U-phase switch UP". The semiconductor switch UN may also be referred to as the "negative-side U-phase switch UN". The positive-side semiconductor switch may also be referred to as the "positive-side switch", and the negative-side semiconductor switch may also be referred to as the "negative-side semiconductor switch".

[0019] <V-phase leg 102V> The V-phase leg 102V has a semiconductor switch VP which is a positive-side semiconductor switch connected to the positive side of a DC power supply (for example, the power supply unit 101), and a semiconductor switch VN which is a negative-side semiconductor switch connected to the negative side of the DC power supply (for example, the power supply unit 101). The semiconductor switch VN is connected in series with the semiconductor switch VP. The semiconductor switch VP is also referred to as the "positive-side V-phase switch VP". The semiconductor switch VN is also referred to as the "negative-side V-phase switch VN". The positive-side semiconductor switch is also referred to as the "positive-side switch", and the negative-side semiconductor switch is also referred to as the "negative-side semiconductor switch".

[0020] <W-phase leg 102W> The W-phase leg 102W has a semiconductor switch WP which is a positive-side semiconductor switch connected to the positive side of a DC power supply (for example, the power supply unit 101), and a semiconductor switch WN which is a negative-side semiconductor switch connected to the negative side of the DC power supply (for example, the power supply unit 101). The semiconductor switch WN is connected in series with the semiconductor switch WP. The semiconductor switch WP is also referred to as the "positive-side W-phase switch WP". The semiconductor switch WN is also referred to as the "negative-side W-phase switch WN". The positive-side semiconductor switch is also referred to as the "positive-side switch", and the negative-side semiconductor switch is also referred to as the "negative-side semiconductor switch".

[0021] The three legs (that is, the U-phase leg 102U, the V-phase leg 102V, and the W-phase leg 102W) are connected in parallel. Each leg is connected to output terminals U, V, W corresponding to the U-phase, V-phase, and W-phase respectively, and is connected to the power line PL2 via the output terminals U, V, W.

[0022] The semiconductor switches UP, VP, WP, UN, VN, WN use self-arc-extinguishing semiconductor elements such as MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and IGBT (Insulated Gate Bipolar Transistor). Also, the semiconductor switches UP, VP, WP, UN, VN, WN may be configured by connecting a plurality of semiconductor switches in parallel or in series.

[0023] The inverter control unit 102a is connected to the semiconductor switches UP, VP, WP, UN, VN, and WN. The inverter control unit 102a controls the semiconductor switches UP, VP, WP, UN, VN, and WN. The three-phase inverter 102 applies a desired voltage to the three-phase inverter 102 by switching the semiconductor switches UP, VP, WP, UN, VN, and WN on and off based on a control signal output by the inverter control unit 102a.

[0024] The three-phase inverter 102 has at least two operation modes. The operation modes include a refrigerant compression operation, which is a normal operation, and a refrigerant preheating control, which is an operation for preheating the refrigerant. The refrigerant preheating control is also called preheating control. The inverter control unit 102a can switch the operation mode of the three-phase inverter 102 according to a predetermined condition.

[0025] The three-phase inverter 102, in addition to controlling the rotational drive of the three-phase motor 11 associated with the refrigerant compression operation, can also control the preheating of the refrigerant by passing a DC or AC current through the windings of the three-phase motor 11 to suppress liquefaction of the refrigerant inside the compressor 10, using winding copper loss or core iron loss. By performing refrigerant preheating control, it is possible to eliminate the need for a heater that was previously attached externally to the compressor 10.

[0026] FIG. 3 is a diagram illustrating an example of the inverter control unit 102a during the refrigerant compressing operation. The inverter control unit 102a includes, for example, voltage commands Vu_ref, Vv_ref, and Vw_ref for each phase, a carrier 102b (for compression operation), a comparator 102c for judging whether the voltages are large or small, an AND circuit 102d, a NOR circuit 102e, and a Td delay unit 102f. The comparator 102c, the AND circuit 102d, the NOR circuit 102e, and the Td delay unit 102f constitute a circuit for providing a dead time during which both the positive and negative semiconductor switches of each leg are turned off so as not to cause a leg short circuit between the positive and negative semiconductor switches of each leg. The Td delay unit 102f delays the time Td of any dead time to be inserted.

[0027] In the refrigerant compression operation, for example, a comparator compares the sinusoidal voltage commands Vu_ref, Vv_ref, and Vw_ref, each phase shifted by 120 degrees, with a triangular carrier waveform to generate a base current for the on and off signals of the semiconductor switches. Then, the current is passed through an AND circuit 102d, a NOR circuit 102e, and a Td delay unit 102f to insert dead time and generate the final on and off signals for the semiconductor switches. In this way, a desired three-phase AC voltage is applied to the three-phase motor 11, which rotates and compresses the refrigerant.

[0028] The dead time can be set arbitrarily as long as it is equal to or longer than the minimum time required for preventing a leg short circuit. In order to reduce distortion of the output voltage or current, it is desirable to set the dead time short.

[0029] In refrigerant preheating control, the switching frequency of the semiconductor switches UP, VP, WP, UN, VN, and WN is often set higher from the viewpoint of heating performance or noise, compared to refrigerant compression operation control, and common mode noise in particular can be a problem. Therefore, this application discloses a control method for reducing common mode noise in the preheating control of the power conversion device 100. Common mode noise is defined as a current that flows in the ground line GL due to the switching operation of the semiconductor switch.

[0030] <Refrigerant preheating control> The refrigerant preheating control of the three-phase inverter 102 will be specifically described below. FIG. 4 is a diagram showing an example of the operation of inverter control unit 102a during refrigerant preheating control. The three-phase motor 11 is, for example, a Y-connection motor, and the motor winding impedances of each phase are Zu, Zv, and Zw. However, the three-phase motor 11 may be a delta-winding motor, and the multiple windings may be connected in series or in parallel, or a dual three-phase motor may be used. The number of poles may be any number.

[0031] In the preheat control, two of the three phases are selected, and the selected two phases are energized for a certain period of time. FIG. 4 shows an example in which the U phase and the V phase are selected. In this case, the current Iout for preheating the refrigerant flows only in the U phase and the V phase due to the line output voltage Vout, which is the difference between the U phase voltage Vu and the V phase voltage Vv of the power conversion device 100, and ideally does not flow in the W phase. In addition, the semiconductor switches of the power conversion device 100 only perform on-off switching operations of the U phase and the V phase semiconductor switches UP, UN, VP, and VN. The W phase semiconductor switches WP and WN are both off. In FIG. 4, the voltage of each phase is defined as positive when the voltage of each phase output terminal is seen from the negative side line of the DC voltage. In addition, the direction of the output current flowing from the U phase output terminal to the V phase output terminal via the impedance of the U phase and the V phase is defined as positive. The voltage of the DC power supply unit is Vdc.

[0032] In preheating control, the positive pole side semiconductor switch of the first phase and the negative pole side semiconductor switch of the second phase, and the negative pole side semiconductor switch of the first phase and the positive pole side semiconductor switch of the second phase are diagonally paired switches, and the on and off of the diagonal paired semiconductor switches of the selected two phases are switched in the same pattern. When current is passed through the U-phase and V-phase windings shown in Figure 3, the semiconductor switch UP and the semiconductor switch VN are a diagonal pair of switches, and the semiconductor switch UN and the semiconductor switch VP are a diagonal pair of switches, and the semiconductor switch UP and the semiconductor switch VN have the same switching pattern, and the semiconductor switch UN and the semiconductor switch VP have the same switching pattern.

[0033] That is, when preheating the refrigerant, the inverter control unit 102a selects two legs from the U-phase leg 102U, the V-phase leg 102V, and the W-phase leg 102W, controls the switching of the two selected legs, and turns off the positive side semiconductor switch and the negative side semiconductor switch of one leg other than the two selected legs.

[0034] Specifically, when preheating the refrigerant, the inverter control unit 102a selects two legs from the U-phase leg 102U, the V-phase leg 102V, and the W-phase leg 102W, controls the on / off of the positive side semiconductor switch of the first leg of the two selected legs and the negative side semiconductor switch of the second leg of the two selected legs at the same timing, controls the on / off of the negative side semiconductor switch of the first leg and the positive side semiconductor switch of the second leg at the same timing, and maintains the positive side semiconductor switch and the negative side semiconductor switch of a third leg other than the two selected legs off.

[0035] In this embodiment, the inverter control unit 102a selects, for example, the U-phase leg 102U and the V-phase leg 102V from the U-phase leg 102U, the V-phase leg 102V, and the W-phase leg 102W, and controls switching of the selected U-phase leg 102U and the V-phase leg 102V. Specifically, the inverter control unit 102a controls the positive U-phase switch UP and the negative V-phase switch VN to be turned on and off at the same timing, controls the negative U-phase switch UN and the positive V-phase switch VP to be turned on and off at the same timing, and keeps the positive W-phase switch WP and the negative W-phase switch WN of the W-phase leg 102W off.

[0036] The switching frequency of the two-phase semiconductor switches selected by the inverter control unit 102a is, for example, 9 kHz or higher. In this embodiment, the switching frequency of each of the semiconductor switches of the U-phase leg 102U and the V-phase leg 102V is 9 kHz or higher. That is, the switching frequencies of the positive U-phase switch UP, the negative U-phase switch UN, the positive V-phase switch VP, and the negative V-phase switch VN are each 9 kHz or higher. In this case, the heating efficiency is improved due to increased iron loss, and the heating time can be shortened.

[0037] FIG. 5 is a diagram illustrating an example of the inverter control unit 102a during refrigerant preheating control. The carriers 102b used to generate the switch pattern of each semiconductor switch are shown as two carriers 102b inverted by 180 degrees as an example. However, for example, there may be only one carrier 102b. In this case, it is sufficient if the signal logic or circuit generates the same switching pattern as in FIG. 4. Within the scope of the present application, one or more carriers 102b may be used to generate the switching pattern, and the signal logic of the switch may be appropriately switched for each switch.

[0038] DUTY is the ratio of the on-time of each semiconductor switch to one control period (e.g., from t1 to t7) during which the inverter output current Iout alternates between positive and negative in FIG. 6, which will be described later. In this embodiment, the DUTY of the positive U-phase switch UP and the negative V-phase switch VN is indicated as "DUTY1," and the DUTY of the positive V-phase switch VP and the negative U-phase switch UN is indicated as "DUTY2." Each semiconductor switch may be set to a DUTY of one or three or more. Alternatively, a mechanism for switching between multiple DUTYs may be used.

[0039] FIG. 6 is a diagram showing an example of the operation (waveform) of each component when current is applied to the U-phase and V-phase of the three phases of the three-phase motor 11. In Fig. 6, when the drive signal for each semiconductor switch output by the inverter control unit 102a is "1", the semiconductor switch is on, and when it is "0", the semiconductor switch is off. In Fig. 6, the positive U-phase switch UP and the negative V-phase switch VN, and the negative U-phase switch UN and the positive V-phase switch VP have the same on / off switching pattern. The positive W-phase switch WP and the negative W-phase switch WN are both off, so they are omitted in Fig. 6.

[0040] For example, the on-time of the semiconductor switch is set to prevent the refrigerant from liquefying, thereby providing a desired amount of heating depending on the impedance of various loads.

[0041] In this embodiment, the waveform of the current output from the three-phase inverter 102 (that is, the inverter output current Iout) is a discontinuous triangle, which makes it possible to obtain a desired amount of heating.

[0042] Figure 6 shows an example of a case where DUTY1 = DUTY2 = 0.15, which outputs a discontinuous AC current in a triangle. The definition of DUTY and the DUTY that can be specified are not limited to this. The actual current waveform is not a perfect triangle because the impedance of the three-phase motor winding is a compound of inductance, resistance, and capacitance components.

[0043] The operation of the output current Iout shown in FIG. 6 will be described below. Between time t1 and time t2, only the positive U-phase switch UP and the negative V-phase switch VN are turned on. This causes the output voltage Vout between the U-phase output terminals as viewed from the V-phase to become positive. Therefore, the output current Iout increases.

[0044] Between time t2 and time t3, all semiconductor switches are off. At this time, the inductance component of the motor windings causes the output current Iout to continue to flow. This causes the anti-parallel diodes VP and UN to conduct. Therefore, the output voltage Vout becomes negative and the output current Iout decreases.

[0045] Between time t3 and time t4, all the semiconductor switches continue to be off. When the output current Iout reaches zero at time t3, the anti-parallel diode becomes non-conductive and zero current continues.

[0046] These operations from time t1 to time t4 result in a positive current being output. On the other hand, for the negative current, the negative pole side U-phase switch UN and the positive pole side V-phase switch VP are switched. The current operation is the same as for the positive current.

[0047] Between time t4 and time t5, only the negative U-phase switch UN and the positive V-phase switch VP are turned on. This causes the output voltage Vout between the U-phase output terminals as viewed from the V-phase to become negative. Therefore, the output current Iout decreases.

[0048] Between time t5 and time t6, all semiconductor switches are off. At this time, the inductance component of the motor windings causes the output current Iout to continue to flow. This causes the anti-parallel diodes of the negative side V-phase switch VN and the positive side U-phase switch UP to conduct. As a result, the output voltage Vout becomes positive and the output current Iout increases.

[0049] Between time t6 and time t7, all the semiconductor switches continue to be off. When the output current Iout reaches 0 current at time t6, the anti-parallel diode becomes non-conductive and 0 current continues.

[0050] The specified duty is determined according to the winding impedance of each motor so as to achieve the desired heating power. In other words, the power is controlled by the ON time of the semiconductor switch.

[0051] In particular, when the motor winding impedance is low, the heating power tends to be excessive. In this case, it is effective to use a method in which all semiconductor switches are turned off within one control period as shown in FIG. 4, and a zero current section is provided to adjust the heating power. The time for which all semiconductor switches are turned off is a predetermined time that is longer than the dead time during the refrigerant compression operation, not preheating control. In other words, the time for which all semiconductor switches are turned off in one period of the output current Iout output from the three-phase inverter 102 is longer than the dead time during the refrigerant compression operation. This makes it possible to shorten the heating time or save energy by using an appropriate power to suppress liquefaction of the refrigerant.

[0052] On the other hand, the off time of the semiconductor switches determined from the desired power may be set to the dead time during normal refrigerant compression operation. Therefore, the time during which all the semiconductor switches are off in one period of the output current Iout output from the three-phase inverter 102 may be longer than the dead time during refrigerant compression operation. Even in this case, by setting the power appropriate for suppressing liquefaction of the refrigerant, it is possible to shorten the heating time or save energy.

[0053] Through the series of control operations described above, a current is passed from the power conversion device 100 to the windings of the three-phase motor 11 to preheat the refrigerant.

[0054] The desired heating power is determined, for example, from the amount of power and heating time required to suppress liquefaction of the refrigerant. Other examples include the maximum power that does not burn out the motor, and 50 W or less that does not require a high-frequency equipment application in Japan. In this embodiment, the power output from the three-phase inverter 102 is 50 W or less. In this case, there is an advantage that high-frequency equipment is not required.

[0055] The mechanism by which the preheating control of the power conversion device 100 reduces the common mode noise will be described below.

[0056] In the preheating control of the power conversion device 100, as shown in FIG. 6, two semiconductor switches constituting a diagonal pair are set to the same switching pattern. The two semiconductor switches of the diagonal pair are set to the same duty and compared with two carriers having a phase difference of 180 degrees, so that the output voltages of the respective phases are inverted to each other. Therefore, in the example of the waveform shown in FIG. 6, the output voltages Vu and Vv of the U phase and the V phase are inverted. As a result, a preheating current Iout flows in the U-phase and V-phase windings due to the line voltage Vout between the U phase and the V phase. Meanwhile, as the output voltages Vu and Vv of each phase are inverted, an inverted ground current also flows in the ground capacitance of each phase. As a result, the current flowing in the ground wire GL is cancelled out.

[0057] According to the first embodiment, it is possible to reduce common mode noise generated by the preheating control of the power conversion device 100. The control of the three-phase inverter 102 is not essentially limited to refrigerant preheating control. For example, it is applicable to the control of three-phase inverters or converters of induction heating devices, solar power generation, electric vehicles, battery storage systems, etc. In this case, it is also possible to reduce common mode noise.

[0058] <Embodiment 2> The power conversion device 100 according to the second embodiment will be described below with reference to the drawings. FIG. 7 is a diagram showing an example of the operation (waveform) of each component in the second embodiment. In this embodiment, the waveform of the current output from the three-phase inverter 102 (i.e., the inverter output current Iout) is a continuous triangle. The second embodiment differs from the first embodiment in that DUTY1=DUTY2=0.25. The output current waveform Iout has no section where 0 current continues, and is a continuous triangular AC current. The triangular AC current is also called a triangular waveform signal.

[0059] When the impedance of a three-phase motor is high, it is necessary to increase DUTY1 and DUTY2 and the current value to achieve the desired amount of heating. When DUTY1=DUTY2=0.25 or less, the triangular current is discontinuous, and when DUTY1=DUTY2=0.25 or more, the triangular current is continuous. When DUTY1=DUTY2=0.25, compared to when DUTY1=DUTY2=0.25 or less, there is a control feature in that the diagonal pair switches that output voltages of the opposite polarity are turned on at the same time that the anti-parallel diodes become non-conductive.

[0060] According to the second embodiment, by outputting a continuous triangular AC current, it is possible to increase the heating power compared to the first embodiment in which the AC current waveform is discontinuous and triangular.

[0061] <Embodiment 3> Hereinafter, a power conversion device 100 according to the third embodiment will be described with reference to the drawings. FIG. 8 is a diagram showing an example of the operation (waveform) of each component in the third embodiment. In the example shown in Fig. 8, an example of the waveform of each component that outputs a continuous AC current in a triangular shape different from that in the second embodiment is shown. In Figs. 6 and 7 of the first and second embodiments, this is the case where DUTY1 = DUTY2 = 0.5. When DUTY1 = DUTY2 = 0.5, it is necessary to insert a dead time in which all semiconductor switches are turned off to prevent short circuits between the upper and lower arms of the positive and negative semiconductor switches. Therefore, in practice, the time obtained by subtracting the dead time from the time of DUTY1 = DUTY2 = 0.5 is the actual on time of each semiconductor switch.

[0062] As with DUTY1=DUTY2=0.25 in Figure 7, the output current waveform Iout has no section where the current is 0, and is a continuous triangular AC current. Therefore, the heating power is approximately the same for DUTY1=DUTY2=0.25 in Figure 7 and 0.5 in Figure 8. The difference between these is the current state when the semiconductor switch is on. When DUTY1=DUTY2=0.25 or less, the output current is 0 when the semiconductor switch is on. On the other hand, when DUTY1=DUTY2=0.5, it is not 0. Also, when a MOSFET is used as the semiconductor switch, its own anti-parallel diode is conductive when the semiconductor switch is turned on, and when the switch is turned on, the reverse conduction path usually switches from the anti-parallel diode to the channel. When an IGBT is used as the semiconductor, the channel cannot be reverse-conductive even when the semiconductor switch is turned on, so its own anti-parallel diode is conductive. A feature of this type of switch is that the semiconductor switch that was on conducts forward when the polarity of the output current switches.

[0063] The DUTY can be selected from the range of more than 0.25 and less than 0.5. Within this DUTY range, the current is a continuous triangular AC current, and it operates in the same way as the DUTY = 0.5 described above.

[0064] According to the third embodiment, by outputting a continuous triangular AC current, it is possible to increase the heating power compared to the discontinuous triangular AC current waveform of the first embodiment.

[0065] <Fourth embodiment> A power conversion device 100 according to the fourth embodiment will be described below with reference to the drawings. FIG. 9 is a diagram showing an example of the operation (waveform) of each component in the fourth embodiment. 9 shows an example of waveforms of each part including a transient state when a DC current is superimposed on a triangular AC current. In the power conversion device 100 according to the fourth embodiment, a DC component is superimposed on the AC current output from the three-phase inverter 102.

[0066] Specifically, for DUTY1 of the positive side U-phase switch UP and the negative side V-phase switch VN, which correspond to a positive output voltage, and DUTY2 of the negative side U-phase switch UN and the positive side V-phase switch VP, which correspond to a negative output voltage, the positive voltage DUTY1 is made larger than the negative voltage DUTY2, thereby superimposing a positive DC current.

[0067] As shown in Fig. 9, in the steady state, DUTY1 and DUTY2 are 0.5. In reality, due to the resistance component of the motor windings, DUTY1 is slightly larger than 0.5 and DUTY2 is slightly smaller than 0.5.

[0068] The control means for superimposing the DC current includes feedback control, which senses the output current Iout and sets it to a predetermined DC current component. There is also open loop control, which does not sense the output current Iout but sets it to a predetermined DC current component with fixed DUTY1 and DUTY2. The above-mentioned predetermined DC component is determined from the predetermined heating power, as in the first embodiment.

[0069] For example, of two legs selected from the U-phase leg 102U, the V-phase leg 102V, and the W-phase leg 102W, the on-time of the positive pole side semiconductor switch of the first leg and the negative pole side semiconductor switch of the second leg are made different from the on-time of the negative pole side semiconductor switch of the first leg and the positive pole side semiconductor switch of the second leg, and a DC component is superimposed on the AC current output from the three-phase inverter 102 by feedback control or open loop control.

[0070] Although dead time is omitted in Fig. 9, in practice it is necessary to insert dead time. Although omitted in Fig. 9, by making the negative voltage DUTY2 larger than the positive voltage DUTY1, it is possible to superimpose a negative DC current, and the same effect can be obtained.

[0071] According to the fourth embodiment, the heating power by DC current can be added to the heating power by the triangular AC current in the first to third embodiments. This is effective as a means for increasing the heating power when the winding impedance of the motor is high. That is, in the fourth embodiment, the heating power can be increased.

[0072] <Embodiment 5> Hereinafter, a power conversion device 100 according to the fifth embodiment will be described with reference to the drawings. FIG. 10 is a diagram showing an example of a current waveform when an AC component is superimposed on a triangular AC current. In the power conversion device 100 according to the fifth embodiment, an AC component is superimposed on the AC current output from the three-phase inverter 102. In the fifth embodiment, a dead time is inserted similarly to the fourth embodiment (for example, FIG. 9).

[0073] Specifically, the ratio of the positive voltage DUTY1 and the negative voltage DUTY2 in the fourth embodiment is changed over time to superimpose an AC component on the triangular AC current. The frequency of the AC to be superimposed can be selected from a wide range of frequencies from low to high. For example, it may be a low frequency of 20 Hz or less, which is the lower limit of the audible frequency, or a high frequency of 10 kHz or more, which is close to the switching frequency. The selectable frequencies are not limited to the above examples.

[0074] As a means for superimposing an AC current component, there is a feedback control in which the output current Iout is sensed to obtain a predetermined AC current component. There is also an open loop control in which the output current Iout is not sensed but is set to fixed DUTY1 and DUTY2 to obtain a predetermined AC current component. As in the first embodiment, this predetermined AC current component is determined from a predetermined heating power.

[0075] For example, the on-time of the positive pole side semiconductor switch of the first leg and the negative pole side semiconductor switch of the second leg of two legs selected from the U-phase leg 102U, the V-phase leg 102V, and the W-phase leg 102W, and the on-time of the negative pole side semiconductor switch of the first leg and the positive pole side semiconductor switch of the second leg are changed over time, and an AC component is superimposed on the AC current output from the three-phase inverter 102 by feedback control or open loop control.

[0076] According to the fifth embodiment, the heating power can be increased by superimposing an AC component on the AC current.

[0077] <Sixth embodiment> The power conversion device according to the sixth embodiment will be described below with reference to the drawings. FIG. 11 is a diagram showing an example of switching between two legs selected by the inverter control unit 102a. In the sixth embodiment, the two phases to be energized are switched in sequence. That is, in the sixth embodiment, when the refrigerant is preheated, the two legs selected by the inverter control unit 102a are switched in sequence by the inverter control unit 102a.

[0078] 11, "UV" indicates the U-phase leg 102U and the V-phase leg 102V (i.e., the U-phase and the V-phase), "VW" indicates the V-phase leg 102V and the W-phase leg 102W (i.e., the V-phase and the W-phase), and "WU" indicates the W-phase leg 102W and the U-phase leg 102U (i.e., the W-phase and the U-phase). That is, in the example shown in FIG. 11, the two legs selected by the inverter control unit 102a are switched in the order of a set of the U-phase leg 102U and the V-phase leg 102V (also referred to as a first group), a set of the V-phase leg 102V and the W-phase leg 102W (also referred to as a second group), and a set of the W-phase leg 102W and the U-phase leg 102U (also referred to as a third group).

[0079] The order of the phases can be selected, for example, WU phase, VW phase, UV phase. It is also not necessary to heat all of the UV, VW, and WU phases, and for example, only the combination of UV and VW phases can be used. The energized phases at the start and end of the preheating operation can also be selected. The switching of each phase does not have to be continuous, and there may be a pause time for all phases. The energization time for each phase can be an extremely short time of one control cycle, or it can be in units of several milliseconds, several seconds, several minutes, or several hours.

[0080] According to the sixth embodiment, uneven heating of each phase can be reduced.

[0081] <Embodiment 7> The power conversion device according to the seventh embodiment will be described below with reference to the drawings. FIG. 12 is a diagram showing an example of a current pattern when burst heating is performed. In the seventh embodiment, a constant current-carrying time and a constant non-current-carrying time are provided for the two selected phases. For example, the sum of the switching operation time and the non-switching operation time of each semiconductor switch of the two legs selected by the inverter control unit 102a is longer than the time of one control period during which the output voltage of the current output from the three-phase inverter 102 alternates between positive and negative. Fig. 12 shows an example in which the UV phase is selected. The energized and non-energized times may be an extremely short time of one control cycle, or may be in units of several milliseconds, several seconds, several minutes, or several tens of minutes.

[0082] FIG. 13 is a diagram showing an example of a current waveform during burst heating. FIG. 13 shows a case where a continuous triangular AC current flows. The current waveform may be a discontinuous triangular current, a DC superimposed current, a low frequency current, or an AC superimposed current. There are various forms, such as a combination of these current waveforms. The energizing time and the non-energizing time do not have to be the same.

[0083] According to the seventh embodiment, a desired heating amount can be achieved by setting a current-on period and a current-off period, when averaged over time. Also, by using the burst method, the frequency of the current rising or falling from 0 current decreases, and noise in the high frequency band can be reduced.

[0084] <Embodiment 8> Hereinafter, a power conversion device 100 according to the eighth embodiment will be described with reference to the drawings. FIG. 14 is a flowchart showing an example of the operation of the inverter control unit 102a during preheating control in the power conversion device 100 according to the eighth embodiment. In the eighth embodiment, preheating is started or ended based on a detected amount that correlates with the amount of liquefaction of the refrigerant.

[0085] First, the inverter control unit 102a acquires a detection amount correlated with the amount of liquefaction of the refrigerant (step S1). The detection amount is, for example, the temperature of the refrigerant detected by a temperature sensor, or the stop time and operation time of the on / off control of the selected two legs.

[0086] The inverter control unit 102a judges whether the detected amount satisfies the criterion for starting preheating control (step S2). If the detected amount satisfies the criterion for starting preheating control, the inverter control unit 102a starts preheating control (step S3). If the detected amount does not satisfy the criterion for starting preheating control, the inverter control unit 102a acquires the detected amount again. The inverter control unit 102a continues to acquire the detected amount and waits until the criterion for starting preheating control is satisfied.

[0087] When preheating control is performed, a detection amount is obtained in the same manner as in step S1 (step S4). As in step S1, the detection amount is, for example, a temperature sensor, a stop time and an operation time of preheating control.

[0088] The inverter control unit 102a judges whether the detected amount satisfies the criterion for terminating preheating control (step S5). If the detected amount satisfies the criterion for terminating preheating control, the inverter control unit 102a terminates the preheating control. If the detected amount does not satisfy the criterion for terminating preheating control, the inverter control unit 102a performs preheating control again and acquires the detected amount. The inverter control unit 102a continues acquiring the detected amount and continues preheating until the criterion for terminating preheating control is satisfied.

[0089] According to the eighth embodiment, a predetermined heating amount can be achieved. Also, energy saving can be achieved by controlling preheating only at the timing when the refrigerant needs to be in a liquefied state.

[0090] <Embodiment 9> A power conversion device 100 according to the ninth embodiment will be described below with reference to the drawings. FIG. 15 is a diagram showing an example of a change in switching frequency in variable control of the switching frequency. In the first to eighth embodiments, an example in which the switching frequency is fixed has been shown, but in the ninth embodiment, the switching frequency is dynamically changed. That is, the inverter control unit 102a changes the switching frequency of each semiconductor switch of the two-phase legs selected by the inverter control unit 102a during operation of the three-phase inverter 102. For example, the inverter control unit 102a changes the switching frequency of each of the positive U-phase switch UP, the negative U-phase switch UN, the positive V-phase switch VP, and the negative V-phase switch VN during operation of the three-phase inverter 102.

[0091] Figure 15 shows an example where the switching frequency is changed in a triangular shape. Other examples include a sine wave shape and a rectangular shape with step changes. The upper limit, lower limit, and median value of the switching frequency are also dynamically changed.

[0092] According to the ninth embodiment, the noise spectrum can be spread by changing the switching frequency, and the quasi-peak or average noise can be reduced.

[0093] The features of each of the embodiments described above can be combined with each other.

[0094] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) A power conversion device that supplies power to a three-phase motor that drives a compressor that compresses a refrigerant, a three-phase inverter having at least six semiconductor switches electrically connected to the three-phase motor; an inverter control unit for controlling the at least six semiconductor switches; Equipped with The three-phase inverter includes: a U-phase leg including a positive U-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to a positive side of a DC power supply, and a negative U-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches which is connected in series with the positive U-phase switch and is connected to a negative side of the DC power supply, the U-phase leg corresponding to a U-phase of the three-phase motor; a V-phase leg including a positive V-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to the positive side of the DC power supply, and a negative V-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected in series to the positive V-phase switch and connected to the negative side of the DC power supply, the V-phase leg corresponding to a V-phase of the three-phase motor; a W-phase leg including a positive W-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to the positive side of the DC power supply, and a negative W-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected to the negative side of the DC power supply and is connected in series with the positive W-phase switch; and having When preheating the refrigerant, the inverter control unit selects two legs from the U-phase leg, the V-phase leg, and the W-phase leg, performs on / off control of the positive side semiconductor switch of a first leg of the two selected legs and the negative side semiconductor switch of a second leg of the two selected legs at the same timing, performs on / off control of the negative side semiconductor switch of the first leg and the positive side semiconductor switch of the second leg at the same timing, and maintains off the positive side semiconductor switch and the negative side semiconductor switch of a third leg other than the two selected legs. A power conversion device comprising: (Appendix 2) 2. The power conversion device according to claim 1, wherein an on-time of the semiconductor switch is set so as to suppress liquefaction of the refrigerant. (Appendix 3) 3. The power conversion device according to claim 1 or 2, wherein a waveform of a current output from the three-phase inverter is a discontinuous triangle. (Appendix 4) 3. The power conversion device according to claim 1 or 2, wherein a waveform of a current output from the three-phase inverter is a continuous triangle. (Appendix 5) 3. The power conversion device according to claim 1 or 2, wherein a DC component is superimposed on the AC current output from the three-phase inverter. (Appendix 6) 3. The power conversion device according to claim 1 or 2, wherein an AC component is superimposed on the AC current output from the three-phase inverter. (Appendix 7) 3. The power conversion device according to claim 1, wherein the time during which all of the semiconductor switches are off in one period of the current output from the three-phase inverter is equal to or longer than a dead time during a refrigerant compression operation. (Appendix 8) 3. The power conversion device according to claim 1, wherein the time during which all of the semiconductor switches are off in one period of the current output from the three-phase inverter is longer than a dead time during a refrigerant compression operation. (Appendix 9) 6. The power conversion device according to claim 5, wherein an on-time of the positive pole side semiconductor switch of the first leg and the negative pole side semiconductor switch of the second leg is made different from an on-time of the negative pole side semiconductor switch of the first leg and the positive pole side semiconductor switch of the second leg, and the DC component is superimposed on the AC current output from the three-phase inverter by feedback control or open loop control. (Appendix 10) 7. The power conversion device according to claim 6, wherein an on-time of the positive pole side semiconductor switch of the first leg and the negative pole side semiconductor switch of the second leg, and an on-time of the negative pole side semiconductor switch of the first leg and the positive pole side semiconductor switch of the second leg are changed over time, so that the AC component is superimposed on the AC current output from the three-phase inverter by feedback control or open loop control. (Appendix 11) 3. The power conversion device according to claim 1, wherein the two legs to be selected are switched sequentially by the inverter control unit. (Appendix 12) The power conversion device according to claim 1 or 2, wherein a sum of a switching operation time and a non-switching operation time of each of the semiconductor switches of the selected two legs is longer than a time of one control period during which an output voltage of a current output from the three-phase inverter alternates between positive and negative. (Appendix 13) 3. The power conversion device according to claim 1, wherein the switching frequencies of the positive side U-phase switch, the negative side U-phase switch, the positive side V-phase switch, and the negative side V-phase switch are 9 kHz or higher. (Appendix 14) 3. The power conversion device according to claim 1 or 2, wherein the power output from the three-phase inverter is 50 W or less. (Appendix 15) 3. The power conversion device according to claim 1, wherein the preheating is started or ended based on a detected amount correlated with an amount of liquefaction of the refrigerant. (Appendix 16) The power conversion device according to claim 15, wherein the detected quantity is a temperature of the refrigerant detected by a temperature sensor, or a stop time and an operation time of the on / off control of the selected two legs. (Appendix 17) 3. The power conversion device according to claim 1, wherein the inverter control unit changes switching frequencies of the positive side U-phase switch, the negative side U-phase switch, the positive side V-phase switch, and the negative side V-phase switch during operation of the three-phase inverter. (Appendix 18) The power conversion device according to claim 1 or 2; Compressor and A refrigeration cycle device comprising: (Appendix 19) The power conversion device according to claim 1 or 2; The three-phase motor; A motor system comprising: [Explanation of symbols]

[0095] 1 refrigeration cycle device, 2 motor system, 10 compressor, 11 three-phase motor, 100 power conversion device, 101 power supply unit, 102 three-phase inverter, 102a inverter control unit, 102U U-phase leg, 102V V-phase leg, 102W W-phase leg, UP, VP, WP, UN, VN, WN semiconductor switches.

Claims

1. A power conversion device that supplies power to a three-phase motor that drives a compressor that compresses a refrigerant, a three-phase inverter having at least six semiconductor switches electrically connected to the three-phase motor; an inverter control unit for controlling the at least six semiconductor switches; Equipped with The three-phase inverter includes: a U-phase leg including a positive U-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to a positive side of a DC power supply, and a negative U-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected in series with the positive U-phase switch and connected to a negative side of the DC power supply, the U-phase leg corresponding to a U-phase of the three-phase motor; a V-phase leg including a positive V-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to the positive side of the DC power supply, and a negative V-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected in series with the positive V-phase switch and connected to the negative side of the DC power supply, the V-phase leg corresponding to a V-phase of the three-phase motor; a W-phase leg including a positive W-phase switch which is a positive side semiconductor switch among the at least six semiconductor switches connected to the positive side of the DC power supply, and a negative W-phase switch which is a negative side semiconductor switch among the at least six semiconductor switches connected to the negative side of the DC power supply and is connected in series with the positive W-phase switch, the negative side semiconductor switch being one of the at least six semiconductor switches connected to the negative side of the DC power supply, the W-phase leg corresponding to a W-phase of the three-phase motor; having When the refrigerant is preheated, the inverter control unit selects two legs from the U-phase leg, the V-phase leg, and the W-phase leg, performs on / off control of the positive side semiconductor switch of a first leg of the two selected legs and the negative side semiconductor switch of a second leg of the two selected legs at the same timing, performs on / off control of the negative side semiconductor switch of the first leg and the positive side semiconductor switch of the second leg at the same timing, and maintains off the positive side semiconductor switch and the negative side semiconductor switch of a third leg other than the two selected legs. A power conversion device comprising:

2. 2. The power conversion device according to claim 1, wherein an on-time of the semiconductor switch is set so as to suppress liquefaction of the refrigerant.

3. 3. The power conversion device according to claim 1, wherein a waveform of a current output from the three-phase inverter is a discontinuous triangle.

4. 3. The power conversion device according to claim 1, wherein a waveform of a current output from the three-phase inverter is a continuous triangle.

5. 3. The power conversion device according to claim 1, wherein a DC component is superimposed on the AC current output from the three-phase inverter.

6. 3. The power conversion device according to claim 1, wherein an AC component is superimposed on the AC current output from the three-phase inverter.

7. 3. The power conversion device according to claim 1, wherein a time during which all of the semiconductor switches are off in one period of a current output from the three-phase inverter is equal to or longer than a dead time during a refrigerant compression operation.

8. 3. The power conversion device according to claim 1, wherein a time during which all of the semiconductor switches are off in one period of a current output from the three-phase inverter is longer than a dead time during a refrigerant compression operation.

9. 6. The power conversion device according to claim 5, wherein an on-time of the positive pole side semiconductor switch of the first leg and the negative pole side semiconductor switch of the second leg is made different from an on-time of the negative pole side semiconductor switch of the first leg and the positive pole side semiconductor switch of the second leg, and the DC component is superimposed on the AC current output from the three-phase inverter by feedback control or open loop control.

10. 7. The power conversion device according to claim 6, wherein an on-time of the positive pole side semiconductor switch of the first leg and the negative pole side semiconductor switch of the second leg, and an on-time of the negative pole side semiconductor switch of the first leg and the positive pole side semiconductor switch of the second leg are changed over time, so that the AC component is superimposed on the AC current output from the three-phase inverter by feedback control or open loop control.

11. 3. The power conversion device according to claim 1, wherein the selected two legs are switched in sequence by the inverter control unit.

12. 3. The power conversion device according to claim 1, wherein a sum of a switching operation time and a non-switching operation time of each of the semiconductor switches of the selected two legs is longer than a time of one control period during which an output voltage of a current output from the three-phase inverter alternates between positive and negative.

13. 3. The power conversion device according to claim 1, wherein the switching frequencies of the positive U-phase switch, the negative U-phase switch, the positive V-phase switch, and the negative V-phase switch are each 9 kHz or higher.

14. 3. The power conversion device according to claim 1, wherein the power output from the three-phase inverter is 50 W or less.

15. 3. The power conversion device according to claim 1, wherein the preheating is started or ended based on a detected amount that correlates with an amount of liquefaction of the refrigerant.

16. 16. The power conversion device according to claim 15, wherein the detected quantity is a temperature of the coolant detected by a temperature sensor, or a stop time and an operation time of the on / off control of the selected two legs.

17. 3. The power conversion device according to claim 1, wherein the inverter control unit changes the switching frequencies of the positive-side U-phase switch, the negative-side U-phase switch, the positive-side V-phase switch, and the negative-side V-phase switch during operation of the three-phase inverter.

18. The power conversion device according to claim 1 or 2; Compressor and A refrigeration cycle device comprising:

19. The power conversion device according to claim 1 or 2; The three-phase motor; A motor system comprising: