GB2617027A - Power conversion device and air-conditioning system - Google Patents

Abstract

This power conversion device comprises: a power converter (14) for converting DC voltage to AC voltage and applying the AC voltage to a motor (10); a control unit (1) for controlling the power converter (14); and a state estimation unit (51) for estimating the rotational speed of the motor and the phase of the motor. When an operation command is input from the outside when the motor (10) is in a free-running state, the control unit (1) causes the motor (10) to transit from the free-running state to an operation state on the basis of the estimated phase of the motor (10).

Description

DESCRIPTION

TITLE OF INVENTION:

Power Conversion Device and Air-Conditioning System

TECHNICAL FIELD

[0001] The present disclosure relates to a power conversion device and an air-conditioning system.

BACKGROUND ART

[0002] In recent years, in applications such as for driving a blower for an air-conditioner, sensorless motors having no means such as a Hall element for detecting a rotor position are widely used for the purposes of cost reduction, size reduction of device, and improvement in heat dissipation by reserving a space.

[0003] In an outdoor fan for air-conditioner, due to outside wind, for example, the fan may be brought into a rotating state (hereinafter, a free-running state) although a drive gear is stopped. Upon a forceful attempt to activate the blower in such a state, the blower may not be successfully activated due to step-out of the motor, for example. For this reason, the rotor position of a sensorless motor needs to be detected and reflected to the control of the motor prior to the activation of the blower.

[0004] For example, the power conversion device disclosed in PTL 1 infers, prior to the activation of a motor, the speed and location of a rotor while the motor is in the free-running state, based on a result of detection by an induced voltage sensing circuit. The power conversion device uses the speed and location of the rotor while the motor is in the free-running state as the initial values, and infers the speed and location of the rotor based on a q-axis voltage, a d-axis voltage, a q-axis current, and a d-axis current.

The power conversion device activates the motor based on the inferred speed and location of the rotor.

CITATION LIST

PA'l ENT LITERATURE [0005] PTL 1: Japanese Patent Laying-Open No. 2011-172382 -1 -SUMMARY OF INVENTION TECHNICAL PROBLEM [0006] However, the power conversion device disclosed in PTL 1 is unable to control the motor in a stable manner.

[0007] Therefore, an object of the present disclosure is to provide a power conversion device and an air-conditioning system that control the motor in a stable manner. SOLUTION TO PROBLEM [0008] A power conversion device includes: a power converter to convert a direct-current voltage into an alternating-current and apply the alternating-current to a motor; a control unit to control the power converter; and a state inference unit to infer a rotational speed and a phase of the motor. As an operation command is externally input to the control unit while the motor is in a free-running state, the control unit causes the motor to transition from the free-running state to an operating state based on the inferred phase of the motor.

ADVANTAGEOUS EFFECTS OF INVENTION

[0009] As an operation command is externally input to the power conversion device according to the present disclosure while the motor is in the free-running state, the power conversion device according to the present disclosure causes the motor to transition from the free-running state to the operating state, based on the inferred phase of the motor. According to the power conversion device of the present disclosure, this allows the motor to be controlled in a stable manner.

BRIEF DESCRIPTION OF DRAWINGS

[0010] Fig. 1 is a diagram depicting a configuration of a power conversion device according to Embodiment 1.

Fig. 2 is a diagram depicting a flow of controls when a motor 10 transitions from a free-running state to a steady-state operation.

Fig. 3 is a diagram for illustrating changes in a controlled phase Be.

Fig. 4 is a diagram depicting a flow of controls when an operation command is externally received while the motor 10 is free running with a low rotational speed, -2 -according to Embodiment 1.

Fig. 5 is a flowchart depicting a control procedure according to Embodiment 1. Fig. 6 is a diagram depicting a configuration of a power conversion device according to a variation of Embodiment 1.

Fig. 7 is a diagram depicting a flow of controls when an operation command is externally received while the motor 10 is free running with a low rotational speed, according to Embodiment 2 Fig. 8 is a flowchart depicting a control procedure according to Embodiment 2. Fig. 9 shows (a) and (b) each depicting an operation of the motor 10 which is activated while the motor 10 is free running in the reverse direction.

Fig. 10 is a flowchart depicting a control procedure according to Embodiment 3. Fig. 11 is a diagram depicting an operation of the motor 10 when an increase of a DC voltage Vdc exceeds a threshold TH upon implementation of a braking action. Fig. 12 is a flowchart depicting a control procedure according to Embodiment 4.

Fig. 13 is a flowchart depicting a control procedure according to Embodiment 5.

Fig. 14 is a diagram schematically depicting an air-conditioning system according to Embodiment 6.

DESCRIPTION OF EMBODIMENTS

[0011] Hereinafter, embodiments will be described, with reference to the accompanying drawings.

Embodiment 1 Fig. 1 is a diagram depicting a configuration of a power conversion device according to Embodiment 1.

[0012] The power conversion device includes a direct-current (DC) power supply 15, a power converter 14, a DC voltage detector 16, motor current detectors 11, 12, and 13, an UVW-to-dp conversion unit 9, a state inference unit 51, a control unit 1, subtractors 4 and 5, PI compensators 6 and 7, and a dq-to-UVW conversion unit 8. The state inference unit 51 includes a rotational-speed inference unit 2 and a phase inference unit 3. -3 -

[0013] A motor 10 is connected to the power converter 14 which converts direct current to any alternating current.

The power converter 14 is connected to the DC power supply 15. The power converter 14 converts a DC voltage Vds of the DC power supply 15 into three phase AC voltages Vu, Vv, and Vw. The power converter 14 applies the three phase voltages Vu, Vv, and Vw to the motor 10. This causes the motor 10 to drive. [0014] The DC voltage detector 16 detects a DC voltage Vdc of the DC power supply 15.

The motor current detectors 11, 12, and 13 detect the three phase currents Iu, Iv, and Iw flowing through the three phase lines connecting the power converter 14 and the motor 10, and send detection values to the UVW-to-dq conversion unit 9 and the rotational-speed inference unit 2. The three phase currents Iu, Iv, and Iw are motor currents.

[0015] The UVW-to-dp conversion unit 9 transforms a coordinate axis from a three-stationary reference frame to a d-q reference frame. The UVW-to-dp conversion unit 9 converts the three phase currents Iu, Iv, and Iw into a d-axis current Id and a q-axis current Iq, and outputs the d-axis current Id to the subtractor 5 and outputs the q-axis current Iq to the subtractor 4.

[0016] While the motor current detectors 11, 12, and 13 are connected to all the three phase lines in Fig. 1, other well-known approach may be used to detect the motor currents. For example, the relationship satisfying Iu + Iv + lw = 0 holds between the three phase currents, and, thus, two of the three phase lines may be connected to the motor current detectors 11 and 12 and the current value of the remaining one phase line may be derived by calculation. Moreover, a motor current detector 11 may be provided by adopting a single-shunt current sensing, which is a well-known approach in which the three phases are combined into one.

[0017] The rotational-speed inference unit 2 infers the rotational speed of the motor 10. For example, the rotational-speed inference unit 2 may infer the rotational speed of the motor 10, based on a motor constant of the motor 10, motor current values (a U-phase -4 -current Iu, a V-phase current Iv, and a W-phase current Iw) output from the motor current detectors 11, 12, and 13, and output voltages (a U-phase voltage Vu, a V-phase voltage Vv, and a W-phase voltage Vw) of the power converter 14. Alternatively, the rotational-speed inference unit 2 may infer the rotational speed of the motor 10, based on differences between: the output voltages (the U-phase voltage Vu, the V-phase voltage Vv, and the W-phase voltage Vw) of the power converter 14; and voltages (a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw*) output from the dq-to-UVW conversion unit 8. The method of inference of the rotational speed of the motor 10 by the rotational-speed inference unit 2 is not limited to the above method.

[0018] Based on the inferred rotational speed output from the rotational-speed inference unit 2, the phase inference unit 3 infers a phase of the motor 10, and outputs the inferred phase to the dq-to-UVW conversion unit 8 and the UVW-to-dq conversion unit 9. Specifically, the phase inference unit 3 integrates the inferred rotational speed, thereby calculating the inferred phase, which is a result of the integration. The dq-to-UVW conversion unit 8 and the UVW-to-dq conversion unit 9 use the inferred phase to transform the coordinate axis of the current.

[0019] The control unit 1 receives the inferred rotational speed output from the rotational-speed inference unit 2 as feedback input, and calculates a speed control command value for the motor 10. The control unit 1 outputs a d-axis current command value Id* and a q-axis current command value Iq*, based on the speed control command value. Upon externally receiving an operation command which includes, for example, a target rotational speed, the control unit 1 outputs the d-axis current command value Id* and the q-axis current command value Iq* based on the operation command. The control unit 1 adjusts the d-axis current command value Id* and the q-axis current command value Iq*, thereby performing a position sensorless control, a brake control, an activation control, and a synchronized current control. [0020] The subtractor 5 subtracts a d-axis current value Id, output from the UVW-to-dq conversion unit 9, from the d-axis current command value Id* output from the control -5 -unit 1, and outputs to a PI compensator 7 a current difference value Ids, which is a result of the subtraction. The subtractor 4 subtracts a q-axis current value Iq, output from the UVW-to-dq conversion unit 9, from the q-axis current command value Iq* output from the control unit 1, and outputs to a PI compensator 6 a current difference value Iqs, which is a result of the subtraction.

[0021] The PI compensator 7 outputs to the dq-to-UVW conversion unit 8 a d-axis voltage command value Vd* obtained by proportionally integrating the current difference value Ids. The PI compensator 6 outputs to the dq-to-UVW conversion unit 8 a q-axis voltage command value Vq* obtained by proportionally integrating the current difference value Iqs.

[0022] Using the DC voltage Vdc detected by the DC voltage detector 16 and an inferred phase Op output from the phase inference unit 3, the dq-to-UVW conversion unit 8 converts and outputs to the power converter 14 the d-axis voltage command value Vd* and the q-axis voltage command value Vq* into the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw*.

[0023] Based on the U-phase voltage command value Vu*, the V-phase voltage command value Vv*, and the W-phase voltage command value Vw*, the power converter 14 converts the DC voltage Vdc into the three phase AC voltages Vu, Vv, and Vw.

[0024] As the operation command is input to the control unit 1 while the motor 10 is in the free-running state, the control unit 1 causes the motor 10 to transition from the free-running state to the operating state, based on the inferred phase of the motor.

[0025] Fig. 2 is a diagram depicting a flow of controls when the motor 10 transitions from the free-running state to a steady-state operation.

[0026] In a time period Ti, the control unit 1 performs an inferential control for the free-running rotational speed. In a time period T3, the control unit 1 performs the position sensorless control thereby causing the motor 10 to perform the steady-state operation. In a time period T2, the control unit 1 switches the state of the motor 10 -6 -from the free-running state to the steady-state operation. The control unit 1 performs the position sensorless control in the time period T2 as well. In other words, the control unit 1 activates the position sensorless control at the end of the inferential control of the free-running rotational speed.

[0027] The inferential control for the free-running rotational speed performed in the time period Ti is now described.

Upon externally receiving the operation command, the control unit 1 infers the free-running rotational speed of the motor 10. If the motor 10 free runs while the power converter 14 is not in operation, an induced voltage is generated at the motor 10 which is based on the amplitude and phase in accordance with the free-running rotational speed of the motor 10. If the induced voltage has the same amplitude and the same phase as the three phase voltages Vu, Vv, and Vw output from the power converter 14, the potential difference therebetween is eliminated. As a result, three phase currents Iu, Iv, and Iw turn zero, which turns a d-axis current value Iq and q-axis current value Iq output from the UVW-to-dq conversion unit 9 zero. Accordingly, the control unit 1 outputs the d-axis current command value Id* and the q-axis current command value Iq* so that d-axis current value Id and q-axis current value Iq output from the UVW-to-dq conversion unit 9 are zero, thereby matching output voltages Vu, Vv, and Vw of the power converter 14 and the induced voltage generated at the motor 10. In this situation, the control unit 1 uses the inferred rotational speed output from the rotational-speed inference unit 2 as a free-running rotational speed Rf, and the inferred phase output from the phase inference unit 3 as a free-running phase Of. [0028] The switch control performed in the time period T2 is now described.

In order to cause the motor 10 to perform the steady-state operation by the position sensorless control, the phase of the motor 10 needs to be inferred. If the control is suddenly switched to the position sensorless control while the motor 10 is rotating, the control is disrupted. To counteract this, in the present embodiment, the control unit 1, in the time period T2, initially uses the free-running phase Of inferred in the time period Ti as a controlled phase Oc, and switches the controlled phase Oc so that -7 -the controlled phase Oc gradually approaches the inferred phase (a position sensorless phase) Op which is calculated and output in the position sensorless control. The controlled phase Oc is used for calculations at the dq-to-UVW conversion unit 8 and the UVW-to-dq conversion unit 9.

[0029] Fig. 3 is a diagram for illustrating changes in the controlled phase Oc.

The control unit 1 sets the controlled phase Oc in the time period T2 as follows: [0030] Oc = X x Of + (1 -X) x Op... (1) Provided that X changes from one to zero over time.

[0031] At the beginning of the time period T2, the inferred phase (the free-running phase) Of, calculated and output in the free-running rotational-speed inferential control, is used to control the motor 10. At the end of the time period T2, the inferred phase (the position sensorless phase) Op, calculated and output in the position sensorless control, is used to control the motor 10.

[0032] This causes the controlled phase Oc to switch, at the end of the time period T2, to the inferred phase (the position sensorless phase) Op calculated and output in the position sensorless control. As a result, a control of the motor 10 immediately after the position sensorless control is activated, can be prevented from being destabilized. The motor 10 is caused to operate in the steady-state operation by the position sensorless control at a time and after the controlled phase Oc is switched to the inferred phase (the position sensorless phase) Op calculated and output in the position sensorless control.

[0033] Here, a problem with the position sensorless control is that the motor 10 having a low rotational speed can deteriorate the accuracy of the rotational-speed inference unit 2, making the control unstable. This is because three phase current values (the U-phase current Iu, the V-phase current Iv, the W-phase current Iw) energizing the motor have very small values in a low rotational speed range for the motor 10, and therefore the accuracy of the calculation at the rotational-speed inference unit 2 deteriorates. In the present embodiment, such a problem is solved by a process as follows: -8 - [0034] Fig. 4 is a diagram depicting a flow of the controls when the operation command is externally received while the motor 10 is free running with a low rotational speed, according to Embodiment 1.

[0035] If the free-running rotational speed Rf is less than an activation permitting rotational speed Rm, which indicates the accuracy of the rotational-speed inference unit 2 being low, and the control unit 1 therefore performs the braking action. The braking action refers to an action of decelerating the motor 10. After the motor 10 is stopped by the braking action, the control unit 1 performs an activation action for the motor 10. The activation action refers to an action of increasing the rotational speed of the motor 10 from outside the operating range to within the operating range. This can prevent the phenomenon that the position sensorless control is destabilized. Subsequently, although not shown, the motor 10 transitions to the steady-state operation.

[0036] Accordingly, in Embodiment 1, if the rotational speed Rf of the motor 10 inferred while the motor 10 is in the free-running state is greater than or equal to the activation permitting rotational speed Rm (a first predetermined value), the control unit 1, in a switching period T2, performs the position sensorless control on the motor 10 and gradually switches the controlled phase Oc of the motor 10 from the phase Of inferred when the motor 10 is in the free-running state to the phase Op inferred by the position sensorless control, the switching period T2 being a time period in which the control unit 1 switches the motor 10 from the free-running state to the steady-state operation by the position sensorless control. If the rotational speed Rf of the motor 10 inferred while the motor 10 is in the free-running state is less than the activation permitting rotational speed (the first predetermined value) Rm, the control unit 1, in the switching period T2, controls the braking action of the motor 10 and, after the motor 10 is stopped, activates the motor 10.

[0037] Fig. 5 is a flowchart depicting a control procedure according to Embodiment 1. In step S100, the control unit 1 receives the operation command which includes the target rotational speed and so on.

[0038] In step S101, the control unit 1 begins an inferential control for the free-running -9 -rotational speed of the motor 10.

[0039] In step S102, the control unit 1 infers the free-running rotational speed Rf.

In step S103, if the inferred free-running rotational speed Rf is greater than or equal to the activation permitting rotational speed Rm, the process proceeds to step S104. If the inferred free-running rotational speed Rf is less than the activation permitting rotational speed Rm, the process proceeds to step 5105.

[0040] In step S104, the control unit 1 switches the controls by the position sensorless control. Subsequently, the process proceeds to step S107.

[0041] In step S105, the control unit 1 performs the braking action. After the motor 10 is stopped, the process proceeds to step S106.

[0042] In step S106, the control unit 1 performs the activation action. Subsequently, the process proceeds to step S107.

[0043] In step S107, the control unit 1 performs a steady-state operation control by the position sensorless control.

[0044] As described above, according to the present embodiment, a phase of the motor in the free-running state and a phase for the position sensorless control are inferred based on the detection values of the motor currents, and, using these phases, the state of the motor can be switched from the free-running state to the steady-state in a stable manner. According to the present embodiment, there is no need to provide a circuit for detecting the induced voltage. Therefore, size reduction and cost reduction of the power conversion device are achieved.

[0045] Variation of Embodiment 1 Fig. 6 is a diagram depicting a configuration of a power conversion device according to Variation of Embodiment 1.

[0046] The power conversion device according to Variation of Embodiment 1 is the same as the power conversion device according to Embodiment 1, except that the power conversion device according to Variation of Embodiment 1 includes a state inference unit 51A, instead of the state inference unit 51. The state inference unit 51A includes a rotational-speed inference unit 2A and a phase inference unit 3A. -10-

[0047] The rotational-speed inference unit 2A includes a first rotational-speed inference section 61 and a second rotational-speed inference section 62. The phase inference unit 3A includes a first phase inference section 63 and a second phase inference section 64. The first rotational-speed inference section 61 and the first phase inference section 63 form a first state inference unit 52. The second rotational-speed inference section 62 and the second phase inference section 64 form a second state inference unit 53.

[0048] In the position sensorless control of the motor 10, the first rotational-speed inference section 61 infers the rotational speed of the motor 10 based on motor currents, as described in Embodiment 1. While the motor 10 is free running, the second rotational-speed inference section 62 infers the rotational speed for the motor 10, based on motor currents, as described in Embodiment 1.

[0049] In the position sensorless control of the motor 10, the first phase inference section 63 infers the phase of the motor 10, based on the rotational speed of the motor 10 inferred by the first rotational-speed inference section 61, as described in Embodiment 1. While the motor 10 is free running, the second phase inference section 64 infers the phase of the motor 10, based on the rotational speed of the motor 10 inferred by the second rotational-speed inference section 62, as described in Embodiment 1.

[0050] The first rotational-speed inference section 61 and the second rotational-speed inference section 62 are switched by the control unit 1 for operation. The first phase inference section 63 and the second phase inference section 64 are switched by the control unit 1 for operation.

[0051] The second state inference unit 53 may include a detector for detecting the induced voltage or magnetic flux of the motor 10, as disclosed in well-known documents such as PTL 1, and infer the rotational speed of the motor 10 and the phase of the motor 10, based on the detection values of the detector.

[0052] Embodiment 2 In Embodiment 1, the motor 10 is suspended in a rotational speed range for the motor in which range the position sensorless control is destabilized. In this case, it is necessary that the motor 10 stops completely, and transitions to the activation action, and then transitions to a steady-state operation by the position sensorless control. As a result, it takes a longer time for the motor 10 to reach the externally commanded target rotational speed. In the present embodiment, the control unit 1 solves such a problem by adopting a synchronized current control.

[0053] In Embodiment 2, if a rotational speed Rf of a motor 10 inferred when the motor 10 is in the free-running state is greater than or equal to an activation permitting rotational speed Rm (a first predetermined value), the control unit 1, in a switching period T2, performs a position sensorless control on the motor 10 and gradually switches a controlled phase Oc of the motor 10 from a phase Of inferred when the motor 10 is in the free-running state to a phase Op inferred in the position sensorless control, the switching period T2 being a time period in which the motor 10 is switched from the free-running state to the steady-state operation by the position sensorless control. If the rotational speed Rf of the motor 10 inferred when the motor 10 is in the free-running state is less than the activation permitting rotational speed (the first predetermined value) Rm, the control unit 1 performs the synchronized current control on the motor 10 in the switching period T2, and, after the inferred rotational speed of the motor 10 reaches an end rotational speed (a second the predetermined value) Re, performs the position sensorless control on the motor 10.

[0054] Fig. 7 is a diagram depicting a flow of controls when an operation command is externally received while the motor 10 is free running with a low rotational speed, according to Embodiment 2.

[0055] If the free-running rotational speed Rf is less than the activation permitting rotational speed Rm, the accuracy of the rotational-speed inference unit 2 is low, and the control unit 1 thus performs the synchronized current control. After the rotational speed of the motor 10 reaches an end rotational speed Re by the synchronized current control, the control unit 1 switches controls. Subsequently, the control unit 1 performs the steady-state operation. -12-

[0056] Fig. 8 is a flowchart depicting a control procedure according to Embodiment 2. In step S200, the control unit 1 receives an operation command which includes a target rotational speed and so on.

[0057] In step S201, the control unit 1 begins an inferential control for the free-running rotational speed of the motor 10.

[0058] In step S202, the control unit 1 infers the free-running rotational speed Rf.

In step S203, if the inferred free-running rotational speed Rf is greater than or equal to the activation permitting rotational speed Rm, the process proceeds to step S204. If the inferred free-running rotational speed Rf is less than the activation permitting rotational speed Rm, the process proceeds to step 5205.

[0059] In step S204, the control unit 1 switches the controls by the position sensorless control. Subsequently, the process proceeds to step S207.

[0060] In step S205, the control unit 1 performs the synchronized current control. After the rotational speed of the motor 10 reaches an end rotational speed Re, the process proceeds to step S206.

[0061] In step 5206, the control unit 1 switches the controls by the position sensorless control. Subsequently, the process proceeds to step S207.

[0062] In step S207, the control unit 1 performs the steady-state operation control by the position sensorless control.

[0063] As described above, in the present embodiment, for activation of the motor 10 in a low inferred rotational speed range, use of the synchronized current control allows the motor 10 to more quickly reach the externally commanded target rotational speed, as compared to Embodiment 1.

[0064] Embodiment 3 A power conversion device according to Embodiment 3 switches controls in accordance with the direction of rotation of a motor in a free-running state.

[0065] The schemes described in Embodiments 1 and 2 are applicable, primarily, to the motor 10 that is free running in the forward direction. In the actual use environment of an air-conditioner, for example, the motor 10 may be affected by, for example, a -13 -natural wind, and free run in the reverse direction. If an operation command is externally received in such a situation, the motor 10 needs to be stopped free running and then driven in the forward direction. If the motor 10 has a large moment of inertia, however, re-generation energy may be produced upon an attempt to stop the motor 10. As a result, the re-generation energy may exceed the rating of a circuit included in the power conversion device.

[0066] A control unit 1 included in the power conversion device according to Embodiment 3 infers the direction of rotation of a motor 10 in the free-running state. If the inferred direction of rotation is the positive direction, the control unit 1 controls the motor 10 in a manner similar to Embodiment 2. If the inferred direction of rotation is the negative direction and the magnitude of an inferred rotational speed Rf is less than an activation permitting rotational speed (a first predetermined value) Rm, the control unit 1, in a switching period T2, controls the braking action of the motor 10, and, after the motor 10 stops, activates the motor 10.

[0067] Fig. 9 shows (a) and (b) each depicting an operation of the motor 10 which is activated while the motor 10 is free running in the reverse direction.

[0068] As shown in (a) of Fig. 9, if the direction of rotation of the motor 10 is the reverse direction and the absolute value of the inferred rotational speed Rf is less than the activation permitting rotational speed Rm, the control unit 1 performs the braking action thereby causing the motor 10 to stop the rotation. Subsequently, the control unit 1 performs the steady-state operation control.

[0069] As shown in (b) of Fig. 9, if the direction of rotation of the motor 10 is the reverse direction and the magnitude (the absolute value) of the inferred rotational speed Rf is greater than or equal to the activation permitting rotational speed Rm, the control unit 1 continues the inference of the free-running rotational speed, without performing the braking action, and places the power converter 14 on standby. During the standby state, none of the brake control, the activation control, and the normal operation is performed. Subsequently, if the magnitude (the absolute value) of the inferred rotational speed Rf is less than or equal to the activation permitting rotational speed -14-Rm, the control unit 1 performs the braking action thereby causing the motor 10 to stop the rotation. Subsequently, the control unit 1 performs the steady-state operation control.

[0070] Fig. 10 is a flowchart depicting a control procedure according to Embodiment 3.

In step 5300, the control unit 1 receives the operation command which includes a target rotational speed and so on.

[0071] In step 5301, the control unit 1 begins inferential controls for the free-running rotational speed and the direction of rotation of free run of the motor 10.

[0072] In step S302, if the direction of rotation of free run of the motor 10 is the positive direction, the process proceeds to step S303. If the direction of rotation of free run of the motor 10 is the reversed direction, the process proceeds to step S308.

[0073] In step 5303, the control unit 1 infers a free-running rotational speed Rf.

In step S304, if the inferred free-running rotational speed Rf is greater than or equal to the activation permitting rotational speed Pin, the process proceeds to step 5305. If the inferred free-running rotational speed Rf is less than the activation permitting rotational speed Rm, the process proceeds to step 5306.

[0074] In step S305, the control unit 1 switches the controls by a position sensorless control. Subsequently, the process proceeds to step S312.

[0075] In step S306, the control unit 1 performs a synchronized current control After the rotational speed of the motor 10 reaches the end rotational speed Re, the process proceeds to step S307.

[0076] In step S307, the control unit 1 switches the controls by the position sensorless control. Subsequently, the process proceeds to step S312.

[0077] In step 5308, the control unit 1 infers the free-running rotational speed Rf.

In step S309, if the absolute value of the inferred free-running rotational speed Rf is less than the activation permitting rotational speed Rm, the process proceeds to step S310. If the inferred free-running rotational speed Rf is greater than or equal to the activation permitting rotational speed Rm, the process returns to step 5302. [0078] In step 5310, the control unit 1 performs the braking action. After the motor -15 -stops, the process proceeds to step S311.

[0079] In step S311, the control unit 1 performs the activation action. Subsequently, the process proceeds to step S312.

[0080] In step 5312, the control unit 1 performs the steady-state operation control by the position sensorless control.

[0081] As described above, according to the present embodiment, while the motor 10 is free running in the reverse direction, the activation permitting rotational speed and the inferred rotational speed are compared with each other and the operations for controlling the motor 10 are switched. This can prevent re-generation energy, which is produced while the motor 10 is stopped free running, from exceeding the rating of a circuit included in the power conversion device.

[0082] Note that the activation permitting rotational speed Rm have different numeric values when the motor 10 is rotating in the forward rotation and when the motor 10 is rotating in the reverse rotation.

[0083] Embodiment 4 In addition to the functions according to Embodiment 3, a power conversion device according to Embodiment 4 stops the braking action upon a rapid increase of a DC voltage Vdc, such as upon application of an excessive external force during exercise of the braking action.

[0084] Fig. 11 is a diagram depicting an operation of a motor 10 when an increase of the DC voltage Vdc exceeds a threshold TH during the braking action.

[0085] Similarly to Embodiment 3, a control unit 1 performs the braking action if the absolute value of an inferred rotational speed Rf is less than an activation permitting rotational speed Rm. The control unit 1 stops the braking action, based on the DC voltage Vdc detected by a DC voltage detector 16 during the braking action.

[0086] The control unit 1 stops the braking action and places the power converter 14 on standby if an increase (slope) of the DC voltage Vdc per unit time is greater than or equal to the threshold TH, as shown in Fig. 11.

[0087] Fig. 12 is a flowchart depicting a control procedure according to Embodiment 4. -16-

The flowchart of Fig. 12 is the same as the flowchart of Fig. 10, except that the flowchart of Fig. 12 includes steps S401 and S402 between steps S309 and 5310. [0088] In step S401, if the increase (slope) of the DC voltage Vdc per unit time detected by the DC voltage detector 16 is greater than or equal to the threshold TH, the process proceeds to step 5402. If the increase (slope) of the DC voltage Vdc per unit time detected by the DC voltage detector 16 is less than threshold TH, the process proceeds to step S311.

[0089] In step S402, the control unit 1 stops the braking action. Subsequently, the process returns to step S302.

[0090] Note that, in step S401, it may be determined whether an instantaneous value of the DC voltage Vdc is greater than or equal to a threshold TH2, instead of determining whether the increase (slope) of the DC voltage Vdc per unit time is greater than or equal to the threshold TH.

[0091] As described above, in the present embodiment, the braking action is stopped based on the DC voltage Vdc during the braking action. This can more surely prevent re-generation energy, which is produced during the braking action, from exceeding the rating of a circuit included in the power conversion device.

[0092] Embodiment 5 A power conversion device according to Embodiment 5 performs a free-running rotational-speed inferential control for a reduced amount of time, and more quickly transitions to the operating state.

[0093] The free-running rotational speed and the direction of rotation are determined in the free-running rotational-speed inferential control, as described in Embodiments 3 and 4. Here, conditions under which free run occurs include occurrence of a momentary outage while the motor is in operation, and a case where an abnormality of a motor 10 is detected and the motor 10 is stopped. In the event of free run in these conditions, a re-activation action is carried out promptly, and the direction of free-running rotation is therefore the forward direction, as with the direction of rotation of the motor 10 in the operating state. -17-

[0094] Thus, in the present embodiment, a control unit 1 does not detect the direction of rotation of free run of the motor 10 if the motor 10 has recovered from a state that the motor 10 is stopped due to a momentary outage or from a state that the motor 10 is stopped due to occurrence of abnormality of the motor 10.

[0095] Fig. 13 is a flowchart depicting a control procedure according to Embodiment 5.

The flowchart of Fig. 13 is the same as the flowchart of Fig. 12, except that the flowchart of Fig. 13 includes steps S501 and S502.

[0096] In step S501, if the motor 10 has currently recovered from a state that the motor 10 is stopped due to a momentary outage, or the motor 10 has currently recovered from a state that the motor 10 is stopped due to occurrence of abnormality, the process proceeds to step S502. If the motor 10 is not currently recovered from a state that the motor 10 is stopped due to a momentary outage, or the motor 10 is not currently recovered from a state that the motor 10 is stopped due to occurrence of abnormality, the process proceeds to step S301.

[0097] In step S502, the control unit 1 begins an inferential control for the free-running rotational speed of the motor 10. Subsequently, the process proceeds to step S303. [0098] As described above, in the present embodiment, if the motor 10 has recovered from the event of a momentary outage while the motor 10 is in operation, or the motor 10 has recovered from a state that the motor 10 is stopped due to detection of abnormality, the rotational direction inferencing process is omitted from the free-running rotational-speed inferential control, thereby allowing the operation of the motor 10 to be resumed in a shorter time.

[0099] Embodiment 6 Fig. 14 is a diagram schematically depicting an air-conditioning system according to Embodiment 6. Fig. 14 omits the illustration of refrigerant pipes and power supply lines that are originally required for the air-conditioner to operate. The air-conditioning system includes a first air-conditioner 81, a second air-conditioner 82, and a central management device 22. The first air-conditioner 81 and the second air-conditioner 82 are installed at a factory, for example.

[0100] The first air-conditioner 81 includes a first indoor unit 17 and a first outdoor unit 21. The second air-conditioner 82 includes a second indoor unit 18 and a second outdoor unit. An air outlet of the first indoor unit 17 and an air outlet of the second indoor unit 18 are connected together by the duct 19. This allows an air to be blown to any location in the factory.

[0101] The first indoor unit 17 and the second indoor unit 18 each include a motor, and the power conversion device described in any of Embodiments 3 through 5.

[0102] The first indoor unit 17, the first outdoor unit 21, and the central management device 22 are connected together by a first communication line 91 The second indoor unit 18, the second outdoor unit 20, and the central management device 22 are connected together by a second communication line 92. The first indoor unit 17 transmits the state of a motor 10 and the state of the power conversion device, which are included in the first indoor unit 17, to the central management device 22 through the first communication line 91 The second indoor unit 18 transmits the state of a motor 10 and the state of the power conversion device, which are included in the second indoor unit 18, to the central management device 22 through the second communication line 92. The central management device 22 transmits a control signal to the first indoor unit 17 through the first communication line 91. The central management device 22 transmits a control signal to the second indoor unit 18 through the second communication line 92.

[0103] For example, if the first indoor unit 17 is in the operating state and the second indoor unit 18 is stopped, an air may be drawn into a fan of the second indoor unit 18 through the duct 19, depending on installation environment, and the motor of the second indoor unit 18 may be brought into a reverse free-running state. If the magnitude of a free-running rotational speed of the motor of the second indoor unit 18 is greater than or equal to an activation permitting rotational speed Itm, the motor 10 of the second indoor unit 18 may not operate even if the power conversion device of the second indoor unit 18 externally receives an operation command. The air-conditioning system according to the present embodiment can solve such a problem. -19-

[0104] If one of the first indoor unit 17 and the second indoor unit 18 is stopped and the other is in the operating state, the central management device 22 performs controls as follows. With the motor, included in the stopped indoor unit, being in the free-running state, if the inferred direction of rotation of the motor 10 is the negative direction and the magnitude of the inferred rotational speed of the motor 10 is greater than or equal to the activation permitting rotational speed (a first predetermined value) Rm, the central management device 22 reduces the operational frequency of the motor 10 included in the indoor unit in the operating state to control the magnitude of the inferred rotational speed of the motor 10 included in the stopped indoor unit to be less than the activation permitting rotational speed (the first predetermined value) Rm.

[0105] As described above, in the present embodiment, the rotational speed of the motor reversely free running is reduced by temporarily reducing the operational frequency of the motor included in another indoor unit connected by a duct to the indoor unit having the reversely free-running motor. This allows the magnitude of the rotational speed of the reversely free-running motor to be controlled to be less than the activation permitting rotational speed Rm. This can remedy the situation where the indoor unit is out of operation due to the occurrence of reverse free run caused by an air being drawn into the fan through the duct 19.

[0106] In the above description, the air-conditioning system includes two air conditioners. However, the present disclosure is not limited thereto. For example, the air-conditioning system may include three or more air conditioners. In the above description, the indoor units and the outdoor units are connected in one-to-one correspondence. However, the present disclosure is not limited thereto.

[0107] The presently disclosed embodiments above should be considered illustrative in all aspects and do not limit the present disclosure. The scope of the present disclosure is defined by the appended claims, rather than by the above description. All changes which come within the meaning and range of equivalency of the appended claims are intended to be embraced within their scope.

[0108] REFERENCE SIGNS LIST -20 - 1 control unit; 2, 2A rotational-speed inference unit; 3, 3A phase inference unit; 4, 5 subtractor; 6, 7 PI compensator; 8 dq-to-UVW conversion unit; 9 UVW-to-dq conversion unit; 10 motor; 11, 12, 13 motor current detector; 14 power converter; 15 DC power supply; 16 DC voltage detector; 17 first indoor unit; 18 second indoor unit; 19 duct; 20 second outdoor unit; 21 first outdoor unit; 22 central management device; 51, 51A state inference unit; 52 first state inference unit; 53 second state inference unit; 61 first rotational-speed inference section; 62 second rotational-speed inference section; 63 first phase inference section; 64 second phase inference section; 81 first air-conditioner; 82 second air-conditioner; 91 first communication line; and 92 second communication line. -21 -

Claims (10)

1. CLAIMS1. A power conversion device, comprising: a power converter to convert a direct-current voltage into an alternating-current voltage and apply the alternating-current voltage to a motor; a control unit to control the power converter; and a state inference unit to infer a rotational speed and a phase of the motor, wherein when an operation command is externally input to the control unit while the motor is in a free-running state, the control unit causes the motor to transition from the free-running state to an operating state based on the inferred phase of the motor.
2. 2. The power conversion device according to claim 1, wherein in a switching period in which the motor is switched from the free-running state to a steady-state operation by a position sensorless control, the control unit performs the position sensorless control of the motor and gradually switches a controlled phase of the motor from a phase inferred when the motor is in the free-running state to a phase inferred in the position sensorless control.
3. 3. The power conversion device according to claim 2, wherein the state inference unit includes: a first state inference unit which infers the rotational speed and the phase of the motor in the position sensorless control; and a second state inference unit which infers the rotational speed and the phase of the motor when the motor is in the free-running state.
4. 4. The power conversion device according to claim 3, wherein the second state inference unit: includes a detector which detects an induced voltage or a magnetic flux of the motor; and infers the rotational speed of the motor -22 -based on a detection value of the detector.
5. 5. The power conversion device according to any one of claims 1 to 4, wherein in a switching period in which the motor is switched from the free-running state to a steady-state operation by a position sensorless control, when the rotational speed inferred when the motor is in the free-running state is greater than or equal to a first predetermined value, the control unit performs the position sensorless control of the motor and gradually switches a controlled phase of the motor from a phase inferred when the motor is in the free-running state to a phase inferred in the position sensorless control, and in the switching period, when the rotational speed inferred when the motor is in the free-running state is less than the first predetermined value, the control unit controls a braking action of the motor, and, after the motor stops, activates the motor.
6. 6. The power conversion device according to any one of claims 1 to 4, wherein in a switching period in which the motor is switched from the free-running state to a steady-state operation by a position sensorless control, when the rotational speed inferred when the motor is in the free-running state is greater than or equal to a first predetermined value, the control unit performs the position sensorless control of the motor and gradually switches a controlled phase of the motor from a phase inferred when the motor is in the free-running state to a phase inferred in the position sensorless control, and in the switching period, when the rotational speed inferred when the motor is in the free-running state is less than the first predetermined value, the control unit performs a synchronized current control of the motor, and, after the inferred rotational speed of the motor reaches a second predetermined value, performs the position sensorless control of the motor.
7. -23 - 7. The power conversion device according to claim 6, wherein the control unit infers a direction of rotation of the motor in the free-running state, and, in the switching period, controls a braking action of the motor, and, after the motor stops, activates the motor when the inferred direction of rotation is a negative direction and a magnitude of the inferred rotational speed is less than the first predetermined value.
8. 8. The power conversion device according to claim 7, comprising a direct-current voltage detector to detect a direct-current voltage input to the power converter, wherein when the motor is in the braking action, the control unit stops the braking action of the motor, based on the detected direct-current voltage.
9. 9. The power conversion device according to claim 7 or 8, wherein the control unit does not detect a direction of rotation of free run of the motor when the motor recovers from a state that the motor is stopped due to outage or when the motor recovers from a state that the motor is stopped due to occurrence of abnormality.
10. 10. An air-conditioning system, comprising: a first air-conditioner; a second air-conditioner; and a central management device to monitor an operating state of the first air-conditioner and an operating state of the second air-conditioner, the first air-conditioner including a first indoor unit and a first outdoor unit, the second air-conditioner including a second indoor unit and a second outdoor unit, wherein an air outlet of the first indoor unit and an air outlet of the second indoor unit -24 -are connected together by a duct, the first indoor unit and the second indoor unit each include a motor and the power conversion device according to any one of claims 7 to 9, and where one of the first indoor unit and the second indoor unit is stopped and the other of the first indoor unit and the second indoor unit is in the operating state, when the motor included in the stopped indoor unit is in the free-running state, the inferred direction of rotation of the motor is the negative direction, and the magnitude of the inferred rotational speed of the motor is greater than or equal to the first predetermined value, the central management device reduces an operational frequency of the motor included in the indoor unit in the operating state to control the magnitude of the inferred rotational speed of the motor included in the stopped indoor unit to be less than the first predetermined value.-25 -