Control device for AC motor and air conditioner

Abstract

In a compressor control device (310) used as an AC electric motor control device, a torque compensation unit (314) calculates a torque compensation value that is a compensation value for a basic torque and necessary for suppressing the rotational speed ripples of an AC electric motor (111), and outputs a torque compensation command representing the calculated torque compensation value. A compensation limiting unit (315) performs limiting processing for limiting the torque compensation value and outputs a post-limiting processing torque compensation command representing a post-limiting processing torque compensation value obtained by performing the limiting processing on the torque compensation value. In the limiting processing, the compensation limiting unit (315) limits the amplitude of the torque compensation value to a predetermined upper limit value or less. A first upper limit value that is an upper limit value when a target rotational speed value belongs to a first rotational speed interval is set to less than a second upper limit value that is an upper limit value when the target rotational speed value belongs to a second rotational speed interval representing a rotational speed smaller than the first rotational speed interval.

Description

Technical Field

[0001] The present disclosure relates to a control device for an alternating current motor and an air conditioner.

Background Art

[0002] As disclosed in Patent Document 1, a control device for an alternating current motor having a function of suppressing pulsation of the rotational speed of the alternating current motor is known. A periodically varying load torque acts on the alternating current motor. The control device for an alternating current motor includes a compensation unit that outputs a compensation signal for suppressing pulsation of the rotational speed to an inverter that drives the alternating current motor, and a limiter unit that limits the compensation amount represented by the compensation signal in order to suppress the power consumption of the alternating current motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Document 1 does not disclose any relationship between the degree of limiting the above compensation amount and the rotational speed of the alternating current motor. When the rotational speed of the alternating current motor is high, even if the compensation amount is limited by the limiter unit, the operation of the alternating current motor may become unstable.

[0005] An object of the present disclosure is to provide a control device for an alternating current motor that can suppress pulsation of the rotational speed of the alternating current motor and suppress destabilization of the operation of the alternating current motor when the rotational speed is high, and an air conditioner including this control device for an alternating current motor.

Means for Solving the Problems

[0006] The control device for an alternating current motor according to the present disclosure is An estimator that calculates an estimated rotational speed which is an estimated value of the rotational speed of an AC motor, and an estimated rotational acceleration which is an estimated value of the rotational acceleration of the AC motor; A rotational speed control unit that calculates a basic torque to be output to the AC motor, which is necessary to bring the rotational speed of the AC motor closer to a target rotational speed represented by a speed command, using the estimated rotational speed, and outputs a basic torque command representing the calculated basic torque; A torque compensation unit that calculates a torque compensation value, which is a compensation value for the basic torque, necessary to suppress pulsation of the rotational speed of the AC motor, using the estimated rotational acceleration, and outputs a torque compensation command representing the calculated torque compensation value; A compensation limiter that performs a limiting process for limiting the torque compensation value represented by the torque compensation command, and outputs a post-limiting torque compensation command representing a post-limiting torque compensation value obtained by subjecting the torque compensation value to the limiting process; An adder that adds the post-limiting torque compensation value represented by the post-limiting torque compensation command to the basic torque represented by the basic torque command, and outputs a combined torque command representing the combined torque obtained by the addition; A voltage command unit that outputs a voltage command representing a voltage necessary to output the combined torque represented by the combined torque command to the AC motor to an inverter that supplies power to the AC motor; comprising In the limiting process, the compensation limiter limits the amplitude of the torque compensation value that varies with time to be equal to or less than a predetermined upper limit value; The upper limit value depends on the value of the target rotational speed; A first upper limit value, which is the upper limit value when the value of the target rotational speed belongs to a first rotational speed range, is set to be smaller than a second upper limit value, which is the upper limit value when the value of the target rotational speed belongs to a second rotational speed range representing a rotational speed smaller than the first rotational speed range.

Advantages of the Invention

[0007] According to the above configuration, pulsation of the rotational speed of the AC motor can be suppressed, and destabilization of the operation of the AC motor when the rotational speed is high can be suppressed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0009] Hereinafter, with reference to the drawings, the air conditioner for railway vehicles according to the embodiment will be described. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[0010] [Embodiment 1] As shown in FIG. 1, the air conditioner 400 for railway vehicles according to the present embodiment includes an air conditioner 100 that air - conditions the passenger compartment of the railway vehicle using a refrigeration cycle, a power conversion device 200 that supplies the power required for air - conditioning to the air conditioner 100, and a control device 300 that controls the power conversion device 200. The air conditioner 100, the power conversion device 200, and the control device 300 are all mounted on the railway vehicle. The air conditioner 400 for railway vehicles is an example of the air conditioner according to the present disclosure.

[0011] The air conditioner 100 has a compressor 110 that compresses a refrigerant, and a group of cooperating devices 120 that, together with the compressor 110, constitute a refrigeration cycle through which the refrigerant circulates.

[0012] As shown in FIG. 2, the compressor 110 has a rotating shaft 112, an alternating current motor 111 that rotates the rotating shaft 112, a compression mechanism 113 that compresses the refrigerant by the rotation of the rotating shaft 112, and a housing 114 that houses the rotating shaft 112, the alternating current motor 111, and the compression mechanism 113.

[0013] Specifically, the alternating current motor 111 is a three-phase alternating current permanent magnet synchronous motor. Lubricating oil is stored at locations inside the housing 114 that can come into contact with the refrigerant. The compressor 110 is installed in a railway vehicle in a horizontally laid-down posture in which the rotating shaft 112 is inclined from the vertical direction.

[0014] Returning to FIG. 1 and continuing the explanation, the group of cooperating devices 120 includes an outdoor heat exchanger 121 that functions as a condenser for condensing the refrigerant compressed by the compressor 110, an expander 122 for expanding the condensed refrigerant, and an indoor heat exchanger 123 that functions as an evaporator for evaporating the expanded refrigerant. The gaseous refrigerant evaporated by the indoor heat exchanger 123 is compressed again by the compressor 110.

[0015] The air conditioner 100 also has an outdoor fan 131 that promotes heat exchange between the outdoor heat exchanger 121 and the outside air, and an indoor fan 132 that promotes heat exchange between the indoor heat exchanger 123 and the passenger compartment air.

[0016] The power conversion device 200 converts the power supplied from the overhead line to the railway vehicle and distributes the converted power to the alternating current motor 111 of the compressor 110, the outdoor fan 131, and the indoor fan 132. The control device 300 controls the power conversion device 200 to adjust the air conditioning capacity of the air conditioner 100.

[0017] The power conversion device 200 includes an inverter 210 for a compressor that supplies power to the AC motor 111 of the compressor 110. The inverter 210 for the compressor is an example of the inverter according to the present disclosure. Further, the control device 300 includes a control device 310 for the compressor that performs PWM (Pulse Width Modulation) control on the inverter 210 for the compressor. The control device 310 for the compressor is an example of the control device for an AC motor according to the present disclosure.

[0018] Hereinafter, the problems to be solved in the present embodiment will be described.

[0019] FIG. 3 shows the load torque acting on the AC motor 111 of the compressor 110. The vertical axis represents the load torque, and the horizontal axis represents the rotation angle of the rotor of the AC motor 111. As shown by the solid line in FIG. 3, the load torque acting on the AC motor 111 has one peak while the rotor makes one rotation.

[0020] The presence of this peak causes pulsations in the rotational speed of the rotor of the AC motor 111 (hereinafter referred to as the rotational speed of the AC motor 111) and the rotational acceleration (hereinafter referred to as the rotational acceleration of the AC motor 111). The frequency of the main component of the pulsation is equal to the number of rotations of the rotor per second. And the pulsations of the rotational speed and rotational acceleration of the AC motor 111 cause vibrations in the compressor 110.

[0021] FIG. 4 is a conceptual diagram showing the vibration level of the compressor 110. The vertical axis represents the vibration level, and the horizontal axis represents the angular frequency. As shown in FIG. 4, the vibration of the compressor 110 has an angular frequency component (hereinafter referred to as the fundamental wave component) that brings about the peak vibration level. In FIG. 4, the angular frequency of the fundamental wave component is denoted as ω. Also, in FIG. 3 referred to above, the fundamental wave component is shown by a dashed line.

[0022] The vibration of the compressor 110 caused by the pulsation of the AC motor 111 causes the generation of noise and the failure of the compressor 110. For this reason, it is desirable to suppress the peak vibration level below the target vibration level shown in FIG. 4.

[0023] Therefore, in order to reduce the pulsation that causes the vibration of the compressor 110, the control device 310 for the compressor shown in FIG. 1 performs torque compensation by adding a torque compensation value having a phase opposite to that of the fundamental wave component of the pulsation to the basic torque output to the AC motor 111.

[0024] However, simply performing torque compensation may cause the operation of the AC motor 111 to become unstable. This will be described below.

[0025] FIG. 5 shows the waveform of the output voltage that the compressor inverter 210 outputs to the AC motor 111 as a result of the above-described torque compensation. The vertical axis represents the output voltage, and the horizontal axis represents time. The higher the rotational speed of the AC motor 111, the higher the output voltage required to drive the AC motor 111.

[0026] For this reason, in a state where the rotational speed of the AC motor 111 is high, the instantaneous value of the output voltage may theoretically exceed the limit value of the output voltage of the compressor inverter 210. In particular, when torque compensation is performed, the amplitude of the output voltage is increased by the torque compensation, so that a situation where the instantaneous value of the output voltage theoretically exceeds the limit value is likely to occur. When the instantaneous value of the output voltage theoretically exceeds the limit value, the operation of the AC motor 111 becomes unstable.

[0027] In order to solve the problems described above, the control device 310 for the compressor according to the present embodiment includes a configuration for suppressing the destabilization of the operation of the AC motor 111. Hereinafter, the configuration of the control device 310 for the compressor will be specifically described.

[0028] As shown in FIG. 6, the control device 310 for the compressor includes a current detector 311 that detects the current output from the compressor inverter 210 to the AC motor 111, and an estimation unit 312 to which a current detection value that is the detection result of the current detector 311 is input.

[0029] Note that the current detection value includes the value of the current flowing through the U-phase coil of the AC motor 111, the value of the current flowing through the V-phase coil, and the value of the current flowing through the W-phase coil.

[0030] The estimation unit 312 calculates an estimated rotational speed, which is an estimated value of the rotational speed of the AC motor 111, and an estimated rotational acceleration, which is an estimated value of the rotational acceleration of the AC motor 111, using the detected current value. The estimation unit 312 includes a configuration in which a PI (Proportional Integral) controller and an integrator are connected in series.

[0031] Further, the compressor control device 310 includes a rotational speed control unit 313 to which a speed command representing the target rotational speed of the AC motor 111 and the above-described estimated rotational speed are input.

[0032] Note that the speed command is generated by the host controller 320 included in the controller 300 shown in FIG. 1. However, the compressor control device 310 may include a function of a speed command unit that generates the speed command. The speed command is generated based on the temperature of the passenger compartment that is the object of air conditioning and other physical quantities, a user operation for switching the air conditioning capacity of the air conditioning equipment 100, and the like.

[0033] The rotational speed control unit 313 calculates a basic torque to be output to the AC motor 111, which is necessary to bring the rotational speed of the AC motor 111 closer to the target rotational speed represented by the speed command, using the estimated rotational speed. Then, the rotational speed control unit 313 outputs a basic torque command representing the basic torque. The rotational speed control unit 313 includes a PI controller.

[0034] Further, the compressor control device 310 includes a torque compensation unit 314 to which the above-described estimated rotational acceleration is input. The torque compensation unit 314 calculates a torque compensation value, which is a compensation value for the above-described basic torque, necessary to suppress the pulsation of the rotational speed of the AC motor 111, using the estimated rotational acceleration. Then, the torque compensation unit 314 outputs a torque compensation command representing the torque compensation value.

[0035] Further, the compressor control device 310 includes a compensation limiting unit 315 to which the above-described torque compensation command is input. The compensation limiting unit 315 performs a limiting process for limiting the torque compensation value represented by the torque compensation command. Then, the compensation limiting unit 315 outputs a post-limitation torque compensation command representing the post-limitation torque compensation value obtained by subjecting the torque compensation value to the limiting process.

[0036] In addition, the compressor control device 310 includes an addition unit 316 that adds the post-limitation torque compensation value represented by the above-described post-limitation torque compensation command to the basic torque represented by the above-described basic torque command.

[0037] Note that the post-limitation torque compensation value is an AC signal and can alternately vary between positive and negative values. A value obtained by adding the post-limitation torque compensation value having a positive or negative sign to the basic torque is defined as the combined torque. The addition unit 316 outputs a combined torque command representing the combined torque.

[0038] Further, the compressor control device 310 includes a voltage command unit 317 that outputs a voltage command representing the voltage required to output the combined torque represented by the above-described combined torque command. The voltage command is output to the compressor inverter 210 that supplies power to the AC motor 111. The compressor inverter 210 outputs a voltage according to the voltage command to the AC motor 111.

[0039] Hereinafter, the operation of the compensation limiting unit 315 for preventing destabilization of the operation of the AC motor 111 will be described.

[0040] The torque compensation value represented by the torque compensation command is an AC value that varies over time. In the above-described limiting process, the compensation limiting unit 315 limits the amplitude of the torque compensation value to be equal to or less than a predetermined upper limit value while maintaining the average value of the torque compensation value.

[0041] FIG. 7 shows the waveform of the output voltage of the compressor inverter 210 when the amplitude of the torque compensation value is limited by the limiting process. Note that the AC waveform indicated by the dashed line in FIG. 7 shows the output voltage when the limiting process is not performed.

[0042] By limiting the amplitude of the torque compensation value to be equal to or less than the upper limit value in the limiting process, as shown in FIG. 7, the average value of the output voltage of the compressor inverter 210 is maintained while the amplitude of the output voltage is limited. As a result, it is possible to avoid a situation where the instantaneous value of the output voltage theoretically exceeds the above-described limit value. Therefore, the destabilization of the operation of the AC motor 111 is prevented.

[0043] However, as shown in FIG. 5, when the rotational speed of the AC motor 111 is low, the average value of the output voltage is lower than when the rotational speed of the AC motor 111 is high. That is, when the rotational speed of the AC motor 111 is low, the average value of the output voltage is farther from the above-described limit value than when the rotational speed of the AC motor 111 is high. Therefore, when the rotational speed of the AC motor 111 is low, it is sufficient even if the amount of limiting the amplitude of the torque compensation value in the limiting process is small.

[0044] Therefore, the compensation limiting unit 315 makes the upper limit value of the amplitude of the torque compensation value depend on the rotational speed of the AC motor 111, specifically, the value of the target rotational speed represented by the speed command shown in FIG. 6.

[0045] FIG. 8 specifically shows the dependence of the upper limit value on the value of the target rotational speed. The upper limit value when the value of the target rotational speed belongs to the first rotational speed range (hereinafter referred to as the first upper limit value) is set to be smaller than the upper limit value when the value of the target rotational speed belongs to the second rotational speed range representing a rotational speed smaller than the first rotational speed range (hereinafter referred to as the second upper limit value).

[0046] When the value of the target rotational speed belongs to the second rotational speed range, the average value of the output voltage is farther from the above-described limit value than when the value of the target rotational speed belongs to the first rotational speed range. Therefore, it is sufficient that the second upper limit value is larger than the first upper limit value.

[0047] On the one hand, when the value of the target rotational speed belongs to the first rotational speed range, the average value of the output voltage of the compressor inverter 210 approaches the aforementioned limit value more than when the value of the target rotational speed belongs to the second rotational speed range. Therefore, in order to greatly limit the amplitude of the output voltage of the compressor inverter 210, the first upper limit value is set smaller than the second upper limit value.

[0048] In this embodiment, the first upper limit value and the second upper limit value are constants that do not depend on the target rotational speed. Also, the first rotational speed range and the second rotational speed range are adjacent on the horizontal axis shown in FIG. 8, that is, the rotational speed axis representing the rotational speed.

[0049] The end point P1 of the first rotational speed range closer to the second rotational speed range represents the rotational speed when the output voltage of the compressor inverter 210 reaches a value of 60% or more and 90% or less, specifically 80%, of the aforementioned limit value.

[0050] First, the conditions that the second upper limit value should satisfy will be described from the perspective of the current supplied to the AC motor 111.

[0051] The torque T output by the AC motor 111 is expressed by the following formula (1) using the d-axis current Id which is the d-axis component of the current supplied to the AC motor 111 and the q-axis current Iq which is the q-axis component of the current supplied to the AC motor 111. T = Pm·φf·Iq ― Pm·(Lq - Ld)·Id·Iq …(1)

[0052] In formula (1), Pm is the number of pole pairs of the AC motor 111. φf is the induced voltage constant of the AC motor 111. Ld is the d-axis component of the inductance of the AC motor 111. Lq is the q-axis component of the inductance of the AC motor 111.

[0053] Ignoring the second term on the right side of formula (1) which represents the reluctance torque, the torque T can be regarded as proportional to the q-axis current Iq. Therefore, the limitation equivalent to the torque compensation value limitation performed by the compensation limitation unit 315 can be explained by the current limitation.

[0054] Therefore, using the current value $I_{lim}$ corresponding to the above-described limit value of the output voltage and the current $I_{drv}$ required for the output of the above-described combined torque, $I_{mar}$ represented by the following equation (2) is defined. The second upper limit value is determined under the condition that $I_{mar}>0$. $I_{mar}=\{(I_{lim}) 2 -(I_{drv}) 2 \} 0.5 …(2)

[0055] Next, regarding the conditions that the first upper limit value should satisfy, an explanation will be given from the viewpoints of the current and voltage supplied to the AC motor 111.

[0056] The output voltage of the compressor inverter 210 is represented by the following equation (3) using the d-axis voltage $V_d$ which is the d-axis component of the voltage supplied to the AC motor 111 and the q-axis voltage $V_q$ which is the q-axis component of the voltage supplied to the AC motor 111. Output voltage = $\{(V_d) 2 +(V_q) 2 \} 0.5 …(3)

[0057] Also, using the voltage equation, the d-axis voltage $V_d$ is represented by the following equation (4), and the q-axis voltage $V_q$ is represented by the following equation (5). $V_d = R\cdot I_d + s\cdot(L_d\cdot I_d)-\omega\cdot L_q\cdot I_q$ …(4) $V_q = R\cdot I_q + s\cdot(L_q\cdot I_q)+\omega\cdot(L_d\cdot I_d+\varphi_f)$ …(5)

[0058] In equations (4) and (5), $R$ is the winding resistance of the AC motor 111. $s$ is a differential operator represented by Laplace transform. $\omega$ is the angular frequency of the fundamental wave component of the load torque shown in FIG. 3 or an integer multiple thereof.

[0059] For simplicity, it is assumed that the d-axis current $I_d$ is sufficiently small. Also, for focusing on the steady state, in equations (4) and (5), the second term on the right side including the differential operator $s$ is ignored. Then, using equations (3), (4), and (5), the output voltage is represented by the following equation (6). Output voltage = {(ω·Lq·Iq) 2 +(R·Iq + ω·φf) 2} 0.5 …(6)

[0060] On the other hand, the fundamental wave component of the load torque shown in FIG. 3 is expressed by the following equation (7). Fundamental wave component = |TL_ac|cos(ωt) + TL_dc …(7)

[0061] The first term on the right side of equation (7) is canceled or reduced by the pulsation compensation performed by the torque compensation unit 314, the compensation limit unit 315, and the addition unit 316 working together. The output of the torque of the DC component corresponding to the second term on the right side of equation (7) is realized through the basic torque command.

[0062] The q-axis current Iq required to output the torque expressed by equation (7) to the AC motor 111 is expressed by the following equation (8) using equation (1). However, for simplicity, it is assumed that the d-axis current Id is sufficiently small. Iq = |TL_ac| / Pm / φf·cos(ωt) + TL_dc / Pm / φf …(8)

[0063] In the limiting process performed by the compensation limit unit 315, the amplitude of the torque compensation value is limited, so that the amplitude of the first term on the right side of equation (8) is limited while the average value represented by the second term on the right side of equation (8) is maintained.

[0064] Let the voltage value corresponding to the second term on the right side of equation (8) be Vdrv. Vdrv is expressed by the following equation (9) by substituting the second term on the right side of equation (8) into equation (6). Vdrv = {(ω·Lq·TL_dc / Pm / φf) 2 +(R·TL_dc / Pm / φf + ω·φf) 2} 0.5 …(9)

[0065] The first upper limit value is determined under the condition that the amplitude value of the voltage corresponding to the amplitude of the first term on the right side of equation (8) falls within the range of the difference between the limit value of the output voltage of the inverter 210 for the compressor and Vdrv expressed by equation (9).

[0066] Next, the acceleration level of the rotation of the AC motor 111 will be described.

[0067] Let the amplitude of the fundamental wave component of the load torque shown in FIG. 3 be |TL_ac|, and the amplitude of the synthetic torque represented by the synthetic torque command shown in FIG. 6 be |Tm_ac|. The acceleration level of the rotation of the AC motor 111 is represented by the following equation (10). Here, Jm represents the moment of inertia of the rotor of the AC motor 111. Acceleration level = 1 / Jm·(|Tm_ac|cos(ωt) - |TL_ac|cos(ωt) …(10)

[0068] In the above-described limiting process, when the amplitude of the torque compensation value is limited, the amplitude |Tm_ac| of the synthetic torque does not match the amplitude |TL_ac| of the fundamental wave component of the load torque. Therefore, the acceleration level represented by equation (10) does not become zero.

[0069] However, since the torque compensation value whose amplitude is limited by the limiting process is added to the basic torque, the amplitude |Tm_ac| of the synthetic torque is made closer to the amplitude |TL_ac| of the fundamental wave component of the load torque. As a result, the acceleration level represented by equation (10) is suppressed. For this reason, the pulsation of the rotational speed of the AC motor 111, and thus the vibration and noise of the compressor 110, are suppressed.

[0070] Note that there may be cases where the amplitude of the torque compensation value is originally less than the first upper limit value or the second upper limit value. In such cases, since the amplitude of the torque compensation value is not limited in the limiting process, theoretically, the amplitude |Tm_ac| of the synthetic torque can be made to match the amplitude |TL_ac| of the fundamental wave component of the load torque.

[0071] The concept of the torque compensation value after the limiting process represented by the torque compensation command shown in FIG. 6 includes not only the torque compensation value whose amplitude is reduced in the limiting process, but also the torque compensation value whose amplitude was originally less than the first upper limit value or the second upper limit value and thus was not reduced in the limiting process.

[0072] As described above, according to the present embodiment, since the torque compensation value after the restriction process is added to the basic torque represented by the basic torque command, the pulsation of the rotational speed of the AC motor 111 can be suppressed.

[0073] Also, as shown in FIG. 8, when the target rotational speed is large, the first upper limit value, which is the upper limit value for the amplitude of the torque compensation value, is set to be smaller than the second upper limit value, which is the upper limit value when the target rotational speed is small. For this reason, when the rotational speed of the AC motor 111 is large, a situation where the output voltage theoretically exceeds the limit value is less likely to occur. Therefore, it is possible to suppress the destabilization of the operation of the AC motor 111 when the rotational speed is high.

[0074] [Embodiment 2] FIG. 8 illustrates a configuration in which the upper limit value changes stepwise as the target rotational speed increases. The dependence of the upper limit value on the target rotational speed is not limited to the aspect shown in FIG. 8. Hereinafter, other aspects of the dependence of the upper limit value on the target rotational speed will be described.

[0075] As shown in FIG. 9, in the present embodiment, a third rotational speed interval intervenes between a first rotational speed interval in which the first upper limit value is defined and a second rotational speed interval in which the second upper limit value is defined.

[0076] In the third rotational speed interval, the upper limit value is a variable value having a linear variation characteristic that approaches the first upper limit value from the second upper limit value as it goes from the end point Q1 closer to the second rotational speed interval of the third rotational speed interval to the end point Q2 closer to the first rotational speed interval of the third rotational speed interval.

[0077] According to the present embodiment, when the target rotational speed of the AC motor 111 moves from one of the first rotational speed interval and the second rotational speed interval to the other, a large change is less likely to occur in the torque output of the AC motor 111. This contributes to the stabilization and long life of the operation of the AC motor 111.

[0078] The above has described Embodiments 1 and 2. FIG. 1 shows a compressor control device 310 as an example of a control device for an AC motor according to the present disclosure. The control target of the control device for an AC motor according to the present disclosure is not limited to the AC motor 111 of the compressor 110.

[0079] The control target of the control device for an AC motor according to the present disclosure may be the AC motor included in the outdoor fan 131, or may be the AC motor included in the indoor fan 132. Further, the control target of the control device for an AC motor according to the present disclosure may be the AC motor included in a device other than the air conditioner 100.

[0080] The present disclosure can be implemented in various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. The above-described embodiments are for explaining the present disclosure and do not limit the scope of the present disclosure. The scope of the present disclosure is indicated by the claims rather than the embodiments. Various modifications made within the scope of the claims and within the scope of the meaning of the disclosure equivalent thereto are considered to be within the scope of the present disclosure.

Description of Reference Numerals

[0081] 100 Air conditioner, 110 Compressor, 111 AC motor, 112 Rotating shaft, 113 Compression mechanism, 114 Housing, 120 Cooperative device group, 121 Outdoor heat exchanger, 122 Expander, 123 Indoor heat exchanger, 131 Outdoor fan, 132 Indoor fan, 200 Power conversion device, 210 Compressor inverter (inverter), 300 Control device, 310 Compressor control device (control device for an AC motor), 311 Current detector, 312 Estimation unit, 313 Rotational speed control unit, 314 Torque compensation unit, 315 Compensation limit unit, 316 Addition unit, 317 Voltage command unit, 320 Upper control device, 400 Railway vehicle air conditioner (air conditioner).

Claims

1. An estimator that calculates an estimated rotational speed that is an estimated value of the rotational speed of an AC motor, and an estimated rotational acceleration that is an estimated value of the rotational acceleration of the AC motor; Using the estimated rotational speed, a basic torque that is output to the AC motor and is necessary to bring the rotational speed of the AC motor closer to a target rotational speed represented by a speed command is calculated, and a basic torque command representing the calculated basic torque is output. A rotational speed control unit; Using the estimated rotational acceleration, a torque compensation value that is a compensation value for the basic torque and is necessary to suppress pulsation of the rotational speed of the AC motor is calculated, and a torque compensation command representing the calculated torque compensation value is output. A torque compensation unit; A compensation limiting unit that performs a limiting process for limiting the torque compensation value represented by the torque compensation command, and outputs a post-limitation torque compensation command representing a post-limitation torque compensation value obtained by subjecting the torque compensation value to the limiting process; An addition unit that adds the post-limitation torque compensation value represented by the post-limitation torque compensation command to the basic torque represented by the basic torque command, and outputs a combined torque command representing the combined torque obtained by the addition; A voltage command unit that outputs a voltage command representing a voltage necessary to output the combined torque represented by the combined torque command to an inverter that supplies power to the AC motor; comprising In the limiting process, the compensation limiting unit limits the amplitude of the torque compensation value that varies with time to be equal to or less than a predetermined upper limit value, The upper limit value depends on the value of the target rotational speed, A first upper limit value that is the upper limit value when the value of the target rotational speed belongs to a first rotational speed range is set to be smaller than a second upper limit value that is the upper limit value when the value of the target rotational speed belongs to a second rotational speed range that represents a rotational speed smaller than the first rotational speed range. A control device for an AC motor.

2. The first upper limit value and the second upper limit value are each a constant, A third rotational speed range is interposed between the first rotational speed range and the second rotational speed range, in the third rotational speed range, the upper limit value is a variable value having a variation characteristic of approaching the first upper limit value from the second upper limit value as it goes from the end point closer to the second rotational speed range of the third rotational speed range toward the end point closer to the first rotational speed range of the third rotational speed range. The control device for an alternating current motor according to claim 1.

3. The first upper limit value and the second upper limit value are each a constant, the first rotational speed range and the second rotational speed range are adjacent to each other. The control device for an alternating current motor according to claim 1.

4. The end point of the first rotational speed range closer to the second rotational speed range represents the rotational speed when the output voltage output from the inverter to the alternating current motor reaches a value of 60% or more and 90% or less of the limit value of the output voltage that can be output by the inverter. The control device for an alternating current motor according to any one of claims 1 to 3.

5. By limiting the amplitude of the torque compensation value to be equal to or less than the upper limit value in the limiting process, the amplitude of the output voltage is limited while the average value of the output voltage output from the inverter to the alternating current motor is maintained. The control device for an alternating current motor according to any one of claims 1 to 3.

6. The control device for an alternating current motor according to any one of claims 1 to 3, a compressor that has the alternating current motor and compresses a refrigerant by rotation of the alternating current motor, a cooperative device group that constitutes a refrigeration cycle in which the refrigerant circulates together with the compressor, An air conditioner comprising:

7. Mounted on a railway vehicle and air-conditioning a passenger compartment of the railway vehicle using the refrigeration cycle. The air conditioner according to claim 6.

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