Power conversion device, motor drive device, and equipment for refrigeration cycle applications

Abstract

A power conversion device (1) comprises a converter (100), a capacitor (200), an inverter (300), and a control unit (500) that drives and controls the inverter (300). The control unit (500) comprises: a speed control unit (501) that outputs a first current command; a speed pulsation suppression control unit (502) that outputs a second current command; a capacitor current suppression control unit (503) that outputs a third current command; and an addition unit (504) that calculates the three outputted current commands, and outputs a fourth current command. The speed pulsation suppression control unit (502) and the capacitor current suppression control unit (503) adjust the pulsation amount of the current flowing through the motor (401) in a manner such that at least two values from among the loss that increases due to the current command of the speed pulsation suppression control unit (502) and the capacitor current suppression control unit (503), the capacitor current, and the speed pulsation of the motor (401) do not exceed an allowable upper-limit value.

Description

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

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

[0002] Conventionally, as disclosed in, for example, Patent Document 1, a power conversion device is known that converts AC power supplied from an AC power source into desired AC power and supplies it to a load, such as a motor used in a compressor of an air conditioner. In this type of power conversion device, the AC power supplied from the AC power source is rectified by a converter and smoothed by a capacitor. The power is then converted into the desired AC power by an inverter consisting of multiple switching elements and output to the load, i.e., the motor. For example, in a motor used in a compressor, load torque pulsation occurs as the compressor draws, compresses, and discharges a refrigerant. If this load torque pulsation is large, the compressor may experience large vibrations.

[0003] JP 2016-178814 A

[0004] In a power conversion device, when control is implemented to suppress motor speed pulsation to suppress compressor vibration, the speed pulsation decreases, but the capacitor current flowing in and out of the capacitor increases. Increased capacitor current can cause deterioration or failure due to heat generation. To suppress this, a large-capacity capacitor or multiple capacitors can be used, but this increases the cost of the capacitor and the size of the power conversion device circuit. On the other hand, control to suppress capacitor current flowing in and out of the capacitor increases compressor vibration. Furthermore, implementing these controls increases the current flowing in the motor, thereby increasing motor loss. Furthermore, increasing the current flowing in the converter and inverter also increases circuit loss. Therefore, these controls increase the overall loss of a motor drive device that includes a motor and a power conversion device. Thus, there is a trade-off relationship between the three variables of motor speed pulsation, capacitor current, and motor drive device loss. This trade-off relationship between these three variables was not previously recognized. Therefore, conventional motor drive devices, such as the technology disclosed in Patent Document 1, have been unable to properly balance this trade-off. Therefore, in conventional motor drive devices, excessive control to suppress motor speed pulsation and control to suppress capacitor current have been implemented, resulting in an increase in loss more than necessary, or conversely, insufficient control has been implemented, resulting in increased compressor vibration and an increase in capacitor current. As a result, it has been difficult for conventional motor drive devices to simultaneously achieve improved energy-saving performance and device miniaturization and cost reduction.

[0005] The present disclosure has been made in consideration of the above, and aims to provide a power conversion device that can achieve both improved energy-saving performance and reduced size and cost of the device.

[0006] In order to solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure is a power conversion device for driving a motor provided in a mechanical load, the power conversion device including: a converter for converting first AC power supplied from a commercial power source into DC power, a capacitor connected to an output terminal of the converter, an inverter connected across the capacitor for converting the DC power into second AC power and outputting the second AC power to the motor, and a control unit for driving and controlling the inverter. The control unit includes: a speed control unit for outputting a first current command for controlling the average speed of the motor, a speed pulsation suppression control unit for outputting a second current command for pulsating a current flowing through the motor in order to suppress speed pulsation of the motor caused by load torque pulsation of the mechanical load, a capacitor current suppression control unit for outputting a third current command for pulsating a current flowing through the motor in order to suppress the amount of capacitor current flowing in and out of the capacitor, and an adder unit for calculating the three output current commands and outputting a fourth current command. The speed pulsation suppression control unit and the capacitor current suppression control unit adjust the amount of pulsation in the current flowing through the motor so that at least two of the motor's speed pulsation, capacitor current, and losses increased by the current commands of the speed pulsation suppression control unit and the capacitor current suppression control unit do not exceed their allowable upper limit values.

[0007] The power conversion device according to the present disclosure has the effect of achieving both improved energy-saving performance and reduced size and cost of the device.

[0008] FIG. 1 is an explanatory diagram showing an example of the configuration of a power conversion device and a motor drive device according to a first embodiment. FIG. 2 is an explanatory diagram showing an example of the configuration of a control unit included in the power conversion device according to the first embodiment. FIG. 3 is an explanatory diagram showing an example of time-series waveforms of the motor speed, capacitor current, and motor current when the power conversion device according to the first embodiment does not perform speed pulsation suppression control and capacitor current suppression control. FIG. 4 is an explanatory diagram showing an example of time-series waveforms of the motor speed, capacitor current, and motor current when the power conversion device according to the first embodiment performs speed pulsation suppression control. FIG. 5 is an explanatory diagram showing an example of time-series waveforms of the motor speed, capacitor current, and motor current when the power conversion device according to the first embodiment performs capacitor current suppression control. FIG. 10 is an explanatory diagram showing an example of a hardware configuration to be realized. FIG. 11 is an explanatory diagram showing an example of a configuration of a power conversion device and a motor drive device according to a second embodiment. FIG. 12 is an explanatory diagram showing an example of a configuration of a control unit included in a power conversion device according to a third embodiment. FIG. 13 is an explanatory diagram showing an example of a configuration of a control unit included in a power conversion device according to a fourth embodiment. FIG. 14 is an explanatory diagram showing an example of a configuration of a control unit included in a power conversion device according to a fifth embodiment.

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

[0010] First Embodiment. Fig. 1 is an explanatory diagram showing an example configuration of a power conversion device and a motor drive device according to a first embodiment. The power conversion device 1 drives, for example, a motor 401 built into a compressor 400. Note that the power conversion device 1 can also be applied to motors provided in mechanical devices other than compressors. The compressor 400 includes a motor 401 and a mechanical load 402. The motor 401 is connected to the mechanical load 402 and performs mechanical work. As an example, the mechanical load 402 is a compression mechanism that compresses a refrigerant. The load torque of the compressor 400 changes when it draws, compresses, and discharges the refrigerant. When the speed of the motor 401 is approximately constant, the load torque has a periodic pulsating waveform.

[0011] There are no particular limitations on the mechanical structure for compressing the refrigerant in the compressor 400. The compressor 400 may be a rotary compressor, a reciprocating compressor, a scroll compressor, a screw compressor, or any other compressor.

[0012] The power conversion device 1 is connected to a commercial power supply 110 and a compressor 400. The commercial power supply 110 may be single-phase or three-phase. In the following description, a single-phase commercial power supply 110 will be described. The power conversion device 1 converts first AC power supplied from the commercial power supply 110 into second AC power having a desired amplitude and phase, and supplies the second AC power to the compressor 400. The power conversion device 1 includes a converter 100, a capacitor 200, an inverter 300, current detection units 301a and 301b, a DC bus voltage detection unit 201, and a control unit 500.

[0013] The motor drive device 2 includes the power conversion device 1 and a motor 401 provided in the compressor 400 .

[0014] Converter 100 is connected between commercial power supply 110 and capacitor 200, and rectifies and outputs first AC power supplied from commercial power supply 110. Capacitor 200, DC bus voltage detection unit 201, and inverter 300 are connected to the output terminal of converter 100. As shown in FIG. 1 , converter 100 is exemplified as a circuit using reactor 120 and diode rectifier 130, but other circuit configurations may also be used.

[0015] Capacitor 200 is, for example, an electrolytic capacitor or a film capacitor. Capacitor 200 has a capacity that can smooth the power rectified by converter 100 to a certain extent. The waveform of the voltage across capacitor 200 is not the same as the full-wave rectification of commercial power supply 110, but rather has a shape in which a voltage ripple corresponding to the frequency of commercial power supply 110 is superimposed on the DC component due to the smoothing effect of capacitor 200. The magnitude of this voltage ripple varies depending on the capacitor capacitance, but is generally not very large, being less than several tens of percent of the average value of the DC bus voltage.

[0016] Inverter 300 is connected to capacitor 200 and motor 401. Inverter 300 switches an internal power conversion element to convert the DC power stored in capacitor 200 into second AC power having a desired amplitude and phase, and outputs the second AC power to motor 401. Motor 401 rotates in accordance with the amplitude and phase of the second AC power supplied from inverter 300.

[0017] Each of the current detection units 301a and 301b detects the current value of one phase of the three-phase current output from the inverter 300 and outputs the detected current value to the control unit 500. When the motor 401 is a three-phase Y-connection, if the current values ​​of two phases of the three-phase current values ​​output from the inverter 300 are obtained, the current value of the remaining phase can be calculated using Kirchhoff's law. For this reason, currents for two phases are obtained here, but current detection units may be provided for all three phases. Alternatively, the three-phase current values ​​may be obtained using a known technique for reconstructing the three-phase current flowing through the motor from the current in the DC bus section of the inverter 300.

[0018] The control unit 500 determines whether the average rotation speed of the motor 401 is equal to the speed command ω ＊and determines the voltage and switching signals output from inverter 300. In this embodiment, this type of control by control unit 500 is referred to as "average speed control." When controlling an AC motor, control is generally performed on a dq rotating coordinate system synchronized with the rotor position of motor 401. To perform control on the dq rotating coordinate system, the rotor position of motor 401 is required. The rotor position of motor 401 may be detected by a position sensor (not shown), or a speed electromotive force may be calculated from the output voltage of inverter 300 and the current flowing through motor 401, and the rotor position may be estimated from the speed electromotive force. There are various methods for position sensorless control of AC motors, and one well-known example is sensorless vector control using an adaptive observer.

[0019] When the compressor 400 is driven, vibrations occur due to the refrigerant compression process. Low-cost compressors often have a simple mechanical structure and therefore large vibrations. A control method is known that pulsates the motor torque or the motor current flowing through the motor in synchronization with the load torque pulsation of the compressor 400 to prevent excessive force from being applied to the refrigerant piping and the installation floor surface due to the vibration of the compressor 400. Because this control method suppresses the pulsation of the motor speed, in this embodiment, this control method is referred to as "speed pulsation suppression control."

[0020] When the motor 401 is driven, a capacitor current Ic flows through the capacitor 200. The capacitor 200 has an internal resistance component. As a result, the capacitor 200 generates heat due to the capacitor current Ic. Generally, the capacitor 200 has a set upper limit for the allowable current, and if a current exceeding this limit continues to flow, the capacitor will heat up and deteriorate or fail. Generally, when the capacitor current Ic exceeds the upper limit, the upper limit itself is often increased by using a large-capacity capacitor or connecting multiple capacitors. However, these methods have problems such as increasing the cost of the capacitor 200 and increasing the size of the circuit of the motor drive device 2.

[0021] A control method is known that suppresses capacitor current Ic by pulsating the motor current in synchronization with the voltage ripple of capacitor 200. To reduce capacitor current Ic, the motor current is pulsated so as to reduce the difference between current Iin1 flowing from converter 100 and current Iin2 flowing into inverter 300. In this embodiment, this control is called "capacitor current suppression control." Utilizing capacitor current suppression control allows motor drive device 2 to be configured using inexpensive capacitors.

[0022] In addition to "average speed control," the control unit 500 can simultaneously execute "speed pulsation suppression control" and "capacitor current suppression control." However, when "speed pulsation suppression control" and "capacitor current suppression control" are executed, the peak value of the motor current increases, which increases motor loss and circuit loss in the motor drive device 2.

[0023] There is a trade-off relationship among the three variables of the speed pulsation of the motor 401, the capacitor current Ic, and the loss of the motor drive device 2. In conventional motor drive devices, it is difficult to adjust the balance of this trade-off, and excessive speed pulsation suppression control or capacitor current suppression control can increase losses more than necessary, or conversely, these controls can be under-executed, resulting in increased vibration of the compressor 400 or an increase in the capacitor current Ic. As a result, in conventional motor drive devices, it is difficult to simultaneously achieve improved energy-saving performance and reduced size and cost of the device.

[0024] To solve this problem, in the power conversion device 1 according to the first embodiment, the allowable upper limit of loss, the allowable upper limit of speed pulsation, and the allowable upper limit of capacitor current are input to the control unit 500. The control unit 500 then adjusts the amount of pulsation in the current of the motor 401 so that at least two of the speed pulsation of the motor 401, the capacitor current Ic, and the loss of the motor drive device 2 that increases due to the speed pulsation suppression control or the capacitor current suppression control do not exceed the allowable upper limits.

[0025] 2 is an explanatory diagram showing an example of the configuration of a control unit included in the power conversion apparatus according to the first embodiment. The control unit 500 includes a speed control unit 501, a speed pulsation suppression control unit 502, a capacitor current suppression control unit 503, an adder 504, a current control unit 505, a rotor position estimator 506, and a PWM (Pulse Width Modulation) signal generator 507. Here, a case where control is performed on a dq rotating coordinate system synchronized with the rotor position of the motor 401 will be described, but this is merely an example, and control may be performed in other coordinate systems. Note that, here, a dq rotating coordinate transformation is performed based on the estimated value θ of the rotor position of the motor 401 estimated by the rotor position estimator 506.

[0026] The speed control unit 501 calculates the average value of the estimated speed ω of the motor 401 estimated by the rotor position estimation unit 506 and the speed command ω ＊ and the first q-axis current command IqDC ＊ As a method of average speed control, PID (Proportional Integral Differential) control is well known. The rotor position estimator 506 outputs the three-phase voltage command Vuvw ＊ and the three-phase current detection value Iuvw, the estimated rotor position θest and estimated speed ωest of the motor 401 are estimated. When the motor speed is in a steady state, the first q-axis current command IqDC ＊ is roughly a constant value.

[0027] The speed pulsation suppression control unit 502 suppresses periodic speed pulsation of the motor speed by adjusting the second q-axis current command Iqrω ＊ In addition to the estimated speed ωest of the motor 401, the speed pulsation suppression control unit 502 also receives the allowable loss upper limit value Puav, the allowable speed pulsation upper limit value ωuav, and the allowable capacitor current upper limit value Icuav. The speed pulsation suppression control unit 502 calculates the second q-axis current command Iqrω in consideration of not only the estimated speed ωest of the motor 401 but also these allowable upper limits. ＊ When the motor speed is in a steady state, the second q-axis current command Iqrω is determined. ＊ is a sinusoidal waveform synchronized with the load torque pulsation.

[0028] The capacitor current suppression control unit 503 suppresses the amount of the capacitor current Ic by a third q-axis current command IqrC ＊ The capacitor current suppression control unit 503 may be input with the DC bus voltage Vdc detected by the DC bus voltage detection unit 201, or may be input with the detected value of the capacitor current Ic itself. Since the capacitor current Ic and the DC bus voltage Vdc have a differential and integral relationship, it is sufficient to input either one of them. In addition, the capacitor current suppression control unit 503 is input with the allowable loss upper limit value Puav, the allowable speed pulsation upper limit value ωuav, and the allowable capacitor current upper limit value Icuav. The capacitor current suppression control unit 503 calculates the third q-axis current command IqrC in consideration of not only the capacitor current Ic but also these allowable upper limits, similar to the speed pulsation suppression control unit 502. ＊ When the motor speed is in a steady state, the third q-axis current command IqrC ＊ has a sinusoidal waveform synchronized with the voltage ripple of the capacitor 200.

[0029] The adder 504 calculates a first q-axis current command IqDC ＊ and the second q-axis current command Iqrω ＊ and the third q-axis current command IqrC ＊ and are added together to obtain a fourth q-axis current command Iq ＊ Calculate the following.

[0030] The current control unit 505 outputs a fourth q-axis current command Iq ＊ and the three-phase current detection value Iuvw, and current control is performed based on the three-phase voltage command Vuvw. ＊ Output.

[0031] The PWM signal generator 507 generates a three-phase voltage command Vuvw ＊ Based on this, a switching signal is generated for the inverter 300. Carrier comparison modulation is a well-known method for generating a switching signal, but other methods may also be used.

[0032] Next, the operation of each control will be described with reference to FIGS. 3 to 5. FIG. 3 is an explanatory diagram showing an example of the motor speed, capacitor current, and time-series waveforms of the motor current when the power conversion device according to the first embodiment does not perform speed pulsation suppression control and capacitor current suppression control. However, the waveform of the capacitor current Ic is obtained by extracting only the frequency component identical to the motor speed and the frequency component twice the frequency of the commercial power supply 110. When speed pulsation suppression control and capacitor current suppression control are not performed, the motor current has a sinusoidal waveform. In this case, the motor drive device 2 has the highest energy efficiency because there is no increase in loss due to speed pulsation suppression control and capacitor current suppression control. However, the motor speed pulsates significantly due to periodic load torque pulsation. Furthermore, the capacitor 200 must absorb ripples in the power flowing in and out of the power conversion device 1. Therefore, the capacitor current Ic pulsates sinusoidally at a frequency twice the power supply frequency (hereinafter, this frequency will be referred to as power supply 2f).

[0033] FIG. 4 is an explanatory diagram showing an example of the motor speed, capacitor current, and time-series waveform of the motor current when the power conversion device according to the first embodiment performs speed pulsation suppression control. The waveform of the capacitor current Ic is obtained by extracting the same frequency component as the motor speed and a frequency component twice the frequency of the commercial power supply 110. The speed pulsation suppression control suppresses the speed pulsation of the motor 401 by pulsating the motor current. Therefore, in FIG. 4, the motor speed pulsation is suppressed compared to FIG. 3. However, the motor current is no longer a sine wave and contains two frequency components. Since the peak value of the motor current increases, the energy efficiency of the motor drive device 2 deteriorates. At this time, the ripple of the power flowing in and out of the power conversion device 1 also increases, and the capacitor current Ic also increases. Basically, the more one tries to suppress the speed pulsation of the motor 401 caused by the load torque, the worse the capacitor current Ic and the loss in the motor drive device 2 become.

[0034] FIG. 5 is an explanatory diagram illustrating an example of the motor speed, capacitor current, and time-series waveform of the motor current when the power conversion device according to the first embodiment performs capacitor current suppression control. The analyzed waveform of the capacitor current Ic is obtained by extracting a frequency component identical to the motor speed and a frequency component twice the frequency of the commercial power supply 110. The capacitor current suppression control suppresses the pulsation of the capacitor current Ic by pulsating the motor current. Therefore, in FIG. 5, the pulsation of the capacitor current Ic is suppressed compared to FIG. 3. However, the motor current is no longer a sine wave but contains two frequency components. The peak value of the motor current increases, deteriorating the energy efficiency of the motor drive device 2. At this time, the motor speed waveform is also no longer a sine wave but contains two frequency components. The motor speed waveform is such that it is caused by pulsating the motor current at a frequency different from the pulsation frequency of the load torque. Essentially, the smaller the capacitor current is, the worse the speed pulsation of the frequency component twice the commercial power supply 110 and the loss in the motor drive device 2 become.

[0035] Although not shown in the figures, the waveform when speed pulsation suppression control and capacitor current suppression control are implemented simultaneously is such that, basically, the more one tries to suppress the speed pulsation of motor 401 caused by load torque, the worse the capacitor current Ic and the loss in motor drive device 2 become, and the more one tries to reduce capacitor current Ic, the worse the speed pulsation of the frequency component twice that of commercial power supply 110 and the loss in motor drive device 2 become.

[0036] As described above, there is a trade-off relationship among the three variables of the speed pulsation of the motor 401, the capacitor current Ic, and the increase in loss of the motor drive device 2. This is a new fact that, to the best of the inventors' knowledge, has not been mentioned in any other literature.

[0037] The existence of a trade-off relationship among these three variables has not been recognized until now. Therefore, conventional motor drive devices have been unable to properly adjust the balance of this trade-off. As a result, excessive speed pulsation suppression control or capacitor current suppression control has resulted in an unnecessarily increased loss, or, conversely, insufficient control has resulted in increased vibration of the compressor 400 and an increase in the capacitor current Ic. As a result, conventional motor drive devices have had difficulty achieving both improved energy-saving performance and reduced size and cost.

[0038] Therefore, in the first embodiment, the trade-off relationship among the three variables of the speed pulsation of the motor 401, the pulsation of the capacitor current Ic, and the loss increase amount of the motor drive device 2 is taken into consideration, and the second q-axis current command Iqrω is calculated based on the allowable loss upper limit Puav, the allowable speed pulsation upper limit ωuav, and the allowable capacitor current upper limit Icuav. ＊ and the third q-axis current command IqrC ＊ Specifically, the second q-axis current command Iqrω is adjusted so that at least two of the speed pulsation of the motor 401, the pulsation of the capacitor current Ic, and the loss increase amount of the motor drive device 2 do not exceed the allowable upper limit values. ＊ and the third q-axis current command IqrC ＊ and adjust.

[0039] This control can perform a variety of operations depending on the purpose, achieving both improved energy-saving performance and reduced size and cost of the device.

[0040] Here, some examples of using the speed pulsation suppression control and the capacitor current suppression control are shown. If control is performed so that the capacitor current allowable upper limit value Icuav and the speed pulsation allowable upper limit value ωuav are not exceeded, the increase in loss in the motor drive device 2 due to the speed pulsation suppression control and the capacitor current suppression control can be kept to a necessary minimum.

[0041] When the motor speed is low and the load torque is large, the speed pulsation of the motor 401 is likely to become large. At this time, if the vibration frequency of the compressor 400 is close to the resonance point of the mechanical system, vibration is likely to become a problem. In such a case, since the speed pulsation allowable upper limit ωuav and the loss allowable upper limit Puav are likely to be exceeded, it is advisable to prioritize the speed pulsation suppression control over the capacitor current suppression control. In other words, the second q-axis current command Iqrω is set so that the speed pulsation of the motor 401 does not exceed the speed pulsation allowable upper limit ωuav and the loss increase amount of the motor drive device 2 does not exceed the loss allowable upper limit Puav. ＊ and the third q-axis current command IqrC ＊ Adjust.

[0042] When the motor speed is high and the load torque is large, the margin for the capacitor current allowable upper limit value Icuav tends to be small. When the motor 401 is operating at high speed, the speed pulsation is smaller than when the motor 401 is operating at low speed. Therefore, in such a case, it is advisable to prioritize the capacitor current suppression control over the speed pulsation suppression control. In this case, the second q-axis current command Iqrω is set so that the capacitor current Ic does not exceed the capacitor current allowable upper limit value Icuav and the loss increase amount of the motor drive device 2 does not exceed the loss allowable upper limit value Puav. ＊ and the third q-axis current command IqrC ＊ Adjust.

[0043] In the above case, control was performed so that at least two of the three allowable upper limits would not be exceeded, but it goes without saying that it is best not to exceed any of the allowable upper limits.

[0044] In this way, the power conversion device 1 and motor drive device 2 according to the first embodiment perform speed pulsation suppression control and capacitor current suppression control while taking into consideration the allowable loss upper limit value Puav, the allowable speed pulsation upper limit value ωuav, and the allowable capacitor current upper limit value Icuav, thereby making it possible to achieve both improved energy-saving performance and miniaturization and cost reduction of the device.

[0045] Next, a hardware configuration of the control unit 500 included in the power conversion device 1 according to the first embodiment will be described. Fig. 6 is an explanatory diagram showing an example of a hardware configuration that realizes the control unit included in the power conversion device 1 according to the first embodiment. As shown in Fig. 6, the control unit 500 includes, as an example, a processor 91 and a memory 92, which are connected via a system bus 93.

[0046] The processor 91 is a CPU (Central Processing Unit, also referred to as a central processing unit, processing unit, arithmetic unit, microprocessor, microcomputer, processor, or DSP (Digital Signal Processor)) or a system LSI (Large Scale Integration). Examples of the memory 92 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable Read Only Memory), and EEPROM (registered trademark) (Electrically Erasable Programmable Read Only Memory).

[0047] As described above, the power conversion device 1 and the motor drive device 2 according to the first embodiment control the operation of the inverter 300 using the control unit 500 based on the detection values ​​acquired from the respective detection units. Specifically, the control unit 500 generates a first q-axis current command IqDC ＊ and a second q-axis current command Iqrω that pulsates the current flowing through the motor 401 in order to suppress speed pulsation of the motor 401 that occurs due to load torque pulsation of the mechanical load 402. ＊ a speed pulsation suppression control unit 502 that outputs a third q-axis current command IqrC that pulsates the current flowing through the motor 401 in order to suppress the amount of the capacitor current Ic flowing in and out of the capacitor 200; ＊ and a capacitor current suppression control unit 503 that calculates the three output current commands and outputs a fourth current command Iq ＊and an adder 504 that outputs Ic. The speed pulsation suppression control unit 502 and the capacitor current suppression control unit 503 adjust the amount of pulsation in the current flowing through the motor 401 so that at least two of the speed pulsation of the motor 401, the capacitor current Ic, and the losses increased by the current commands of the speed pulsation suppression control unit 502 and the capacitor current suppression control unit 503 do not exceed their allowable upper limits. Therefore, the power conversion device 1 and the motor drive device 2 according to the first embodiment can achieve both improved energy-saving performance and reduced size and cost of the device.

[0048] Second Embodiment Fig. 7 is an explanatory diagram showing a configuration example of a power conversion device and a motor drive device according to a second embodiment. As shown in Fig. 7, a power conversion device 1a and a motor drive device 2a according to the second embodiment are configured by using a control unit 500a instead of the control unit 500 of the power conversion device 1 and the motor drive device 2 of the first embodiment shown in Fig. 1.

[0049] Fig. 8 is an explanatory diagram showing an example of the configuration of a control unit included in a power conversion device according to the second embodiment. As shown in Fig. 8, a control unit 500a has a configuration in which an allowable upper limit setting unit 508 is added to the control unit 500 of the first embodiment shown in Fig. 2. The allowable upper limit changes depending on the operating states of the motor 401 and the compressor 400. Therefore, by changing the allowable upper limit using the allowable upper limit setting unit 508 according to the operating states of the motor 401 and the compressor 400, it is possible to further improve energy-saving performance and achieve a smaller and less costly device.

[0050] 7, various sensors such as a condenser temperature sensor 202, a motor temperature sensor 403, and a motor acceleration sensor 404 may be used to determine the operating states of the motor 401 and the compressor 400. Note that these sensors are merely examples, and other types of sensors may be used to determine the operating states of the motor 401 and the compressor 400. For example, strain gauges may be used to measure stress in refrigerant piping (not shown) connected to the compressor 400, or the force with which the compressor 400 vibrates the installation floor. Furthermore, multiple motor acceleration sensors 404 may be used to calculate the acceleration of the center of gravity of the compressor 400.

[0051] The allowable upper limit setting unit 508 determines the allowable loss upper limit Puav, the allowable speed pulsation upper limit ωuav, and the allowable capacitor current upper limit Icuav based on the capacitor temperature Tc acquired by the capacitor temperature sensor 202, the motor temperature Tm acquired by the motor temperature sensor 403, and the housing acceleration Am acquired by the motor acceleration sensor 404. To determine these allowable upper limits, the allowable upper limit setting unit 508 may use a data table created by calculation in advance, may use some kind of evaluation function, or may use learning using artificial intelligence.

[0052] Similarly to the first embodiment, the speed pulsation suppression control unit 502 calculates the second q-axis current command Iqrω in consideration of the allowable loss upper limit Puav, the allowable speed pulsation upper limit ωuav, and the allowable capacitor current upper limit Icuav. ＊ The capacitor current suppression control unit 503 determines the third q-axis current command IqrC in consideration of the allowable loss upper limit Puav, the allowable speed pulsation upper limit ωuav, and the allowable capacitor current upper limit Icuav. ＊ Determine.

[0053] Here, several examples of operation patterns of the allowable upper limit setting unit 508 are shown. When the capacitor temperature Tc is high, it is necessary to reduce the capacitor current Ic. Therefore, the allowable upper limit setting unit 508 reduces the allowable capacitor current upper limit Icuav. At this time, the allowable loss upper limit Puav and the allowable speed pulsation upper limit ωuav may be increased at the same time. As a result, in the motor drive device 2a, capacitor current suppression control takes priority over speed pulsation suppression control and average speed control, and operation is performed to protect the capacitor 200.

[0054] Conversely, when the capacitor temperature Tc is low, the allowable capacitor current upper limit Icuav may be increased. At the same time, the allowable loss upper limit Puav and the allowable speed pulsation upper limit ωuav may be decreased. As a result, in the motor drive device 2a, average speed control and speed pulsation suppression control take priority over capacitor current suppression control, and operation is performed with an emphasis on energy saving performance and quietness of the compressor 400.

[0055] When the motor temperature Tm is high, the allowable upper limit setting unit 508 executes processing to lower the allowable loss upper limit Puav. In this way, the motor drive device 2a prioritizes average speed control over capacitor current suppression control and speed pulsation suppression control, enabling operation that emphasizes energy conservation performance. Furthermore, burnout of the motor 401 can be prevented.

[0056] Conversely, when the motor temperature Tm is low, the allowable upper limit setting unit 508 may perform processing to raise the allowable loss upper limit Puav. In this way, the motor drive device 2a can more actively perform capacitor current suppression control and speed pulsation suppression control, and can perform operation that prioritizes quietness of the compressor 400 and protection of the condenser 200.

[0057] Furthermore, the allowable upper limit setting unit 508 may perform frequency analysis processing, such as a Fourier transform, on the housing acceleration Am. If the frequency component of the load torque pulsation of the compressor 400 is large, the speed pulsation allowable upper limit value ωuav may be reduced. This allows the motor drive device 2a to more actively perform speed pulsation suppression control, enabling operation that prioritizes quietness of the compressor 400. Conversely, if the frequency component of the load torque pulsation is small, the speed pulsation allowable upper limit value ωuav may be increased. This weakens the effectiveness of the speed pulsation suppression control, reducing motor loss and capacitor current Ic.

[0058] When the power supply 2f component is large at the housing acceleration Am, the capacitor current allowable upper limit value Icuav may be set to a large value. This reduces the effectiveness of the capacitor current suppression control and reduces vibrations caused by the capacitor current suppression control. Conversely, when the power supply 2f component is small, the capacitor current allowable upper limit value Icuav may be set to a small value to increase the effectiveness of the capacitor current suppression control.

[0059] The allowable upper limit setting unit 508 may also change the allowable loss upper limit value Puav, the allowable speed pulsation upper limit value ωuav, and the allowable capacitor current upper limit value Icuav using other information, such as the rotation speed and load torque of the compressor 400. The optimal solution for the balance between these allowable upper limits varies depending on the purpose. Therefore, the allowable upper limit setting unit 508 may have a function for changing the allowable upper limits when an external command is received via a remote controller (not shown).

[0060] In this way, the power conversion device 1a and motor drive device 2a according to the second embodiment are provided with an allowable upper limit value setting unit 508 in the control unit 500a, so that the allowable upper limit value can be changed according to the operating state of the motor 401 and the compressor 400, thereby achieving further improvement in energy saving performance and miniaturization and cost reduction of the device.

[0061] Embodiment 3 In the first and second embodiments, the speed pulsation suppression control unit 502 and the capacitor current suppression control unit 503 take various allowable upper limits into consideration. However, when modifying an existing power conversion device or motor drive device to perform control similar to that of the first or second embodiment, there are cases in which software modifications are reduced by separating the calculation function for taking the allowable upper limits into consideration into a separate block. Therefore, in the third embodiment, as a modification of the first embodiment, a configuration example will be described in which the calculation function for taking the allowable upper limits into consideration into a separate block.

[0062] 9 is an explanatory diagram showing a configuration example of a control unit included in a power conversion device according to embodiment 3. A control unit 500b according to embodiment 3 includes an output upper limit value determining unit 509, a speed pulsation suppression control unit 502a, and a capacitor current suppression control unit 503a, instead of the speed pulsation suppression control unit 502 and the capacitor current suppression control unit 503 included in the control unit 500 according to embodiment 1.

[0063] The output upper limit value determiner 509 receives the allowable loss upper limit value Puav, the allowable speed pulsation upper limit value ωuav, and the allowable capacitor current upper limit value Icuav as inputs, and determines the output upper limit value IqLIM1 of the speed pulsation suppression control unit 502a and the output upper limit value IqLIM2 of the capacitor current suppression control unit 503a so that at least two of these allowable upper limits are not exceeded. The output upper limits IqLIM1 and IqLIM2 may be determined using a data table created by pre-calculation, an evaluation function, or learning using artificial intelligence. Alternatively, as described below, the output upper limits IqLIM1 and IqLIM2 may be determined using feedback control. The speed pulsation suppression control unit 502a operates based on the output upper limit value IqLIM1 and performs speed pulsation suppression control within the range of the output upper limit value IqLIM1. The capacitor current suppression control unit 503a operates based on the output upper limit value IqLIM2, and performs capacitor current suppression control within the range of the output upper limit value IqLIM2.

[0064] To prevent breakdowns in the motor drive device 2, maximum currents are specified for the motor 401 and the inverter 300. For this reason, current limiters (not shown) are provided inside the speed pulsation suppression control unit 502a and the capacitor current suppression control unit 503a. Therefore, the control unit 500b of the third embodiment can achieve control equivalent to that of the control unit 500 of the first embodiment by having the output upper limit value determination unit 509 appropriately determine the output upper limit values ​​IqLIM1 and IqLIM2 and using the current limiters (not shown) to change the operation of the speed pulsation suppression control unit 502a and the capacitor current suppression control unit 503a.

[0065] Next, a method for determining the output upper limit values ​​IqLIM1 and IqLIM2 will be described. If it is desired to operate the speed pulsation suppression control unit 502a aggressively, the output upper limit value IqLIM1 is increased. Conversely, if it is desired to limit the operation of the speed pulsation suppression control unit 502a, the output upper limit value IqLIM1 is decreased. Furthermore, if it is desired to operate the capacitor current suppression control unit 503a aggressively, the output upper limit value IqLIM2 is increased. Conversely, if it is desired to limit the operation of the capacitor current suppression control unit 503a, the output upper limit value IqLIM2 is decreased.

[0066] The advantages and disadvantages of the speed pulsation suppression control and the capacitor current suppression control are as described in the first and second embodiments. Which of the allowable loss upper limit value Puav, the allowable speed pulsation upper limit value ωuav, and the allowable capacitor current upper limit value Icuav should be prioritized depends on the intended use and operating conditions of the motor 401. The output upper limits IqLIM1 and IqLIM2 are determined so as not to exceed at least two of these allowable upper limits.

[0067] When modifying an existing power conversion device or motor drive device, the configuration of the control unit 500b according to the third embodiment can be utilized to reduce the number of parts of the software that need to be changed.

[0068] Fourth Embodiment Fig. 10 is an explanatory diagram showing an example of the configuration of a control unit included in a power conversion device according to a fourth embodiment. In the fourth embodiment, a mechanism for checking whether speed pulsation exceeds an allowable upper limit value is added to the configuration of the third embodiment. As shown in Fig. 10, a control unit 500c according to the fourth embodiment includes a speed pulsation detection unit 510 and an output upper limit value determination unit 509a instead of the output upper limit value determination unit 509 included in the control unit 500b according to the third embodiment.

[0069] The speed pulsation detection unit 510 detects or estimates the speed pulsation of the motor 401. For example, the speed pulsation detection unit 510 extracts a pulsation component ωr of an arbitrary frequency included in the estimated speed ωest of the motor 401. Then, the output upper limit value determination unit 509a performs feedback control so that the pulsation component ωr does not exceed the speed pulsation allowable upper limit value ωuav, and determines the output upper limit values ​​IqLIM1 and IqLIM2.

[0070] By performing the above-described feedback control, the control unit 500c can reliably control the speed pulsation to within the allowable upper limit. Furthermore, the speed pulsation suppression control unit 502a can perform the minimum speed pulsation suppression control necessary to keep the speed pulsation within the allowable upper limit. It is also preferable from the viewpoint of the capacitor current Ic that the speed pulsation suppression control not be performed excessively. This allows the motor drive device 2 to improve its energy-saving performance.

[0071] Fifth Embodiment Fig. 11 is an explanatory diagram showing a configuration example of a control unit included in a power conversion device according to a fifth embodiment. In the fifth embodiment, a mechanism for checking whether the capacitor current Ic exceeds an allowable upper limit value is added to the configuration of the third embodiment. As shown in Fig. 11, a control unit 500d according to the fifth embodiment includes a capacitor current detection unit 511 and an output upper limit value determination unit 509b instead of the output upper limit value determination unit 509 included in the control unit 500b according to the third embodiment.

[0072] The capacitor current detection unit 511 detects or estimates the amount of capacitor current Ic flowing in and out of the capacitor 200. For example, the capacitor current detection unit 511 estimates the capacitor current Ic flowing in the capacitor 200 from the DC bus voltage Vdc. Here, the estimated capacitor current value is represented by the symbol Icest, but any current detector may be used to directly measure the capacitor current Ic flowing in the capacitor 200. Then, the output upper limit value determination unit 509b performs feedback control so that the estimated current value Icest or the amount of the capacitor current Ic does not exceed the capacitor current allowable upper limit value Icuav, and determines the output upper limit values ​​IqLIM1 and IqLIM2.

[0073] By performing the above-described feedback control, the control unit 500d can reliably control the capacitor current Ic to within the allowable upper limit. Furthermore, the control unit 500d can perform the minimum necessary capacitor current suppression control to keep the capacitor current Ic within the allowable upper limit. It is also preferable to avoid excessive capacitor current suppression control in terms of speed pulsation. This allows the motor drive device 2 to achieve improved energy-saving performance.

[0074] Sixth Embodiment Fig. 12 is an explanatory diagram showing an example of the configuration of a control unit included in a power conversion device according to a sixth embodiment. In the sixth embodiment, a mechanism for checking whether the amount of loss increase exceeds an allowable upper limit value is added to the configuration of the third embodiment. As shown in Fig. 12, a control unit 500e according to the sixth embodiment includes a loss detection unit 512 and an output upper limit value determination unit 509c instead of the output upper limit value determination unit 509 included in the control unit 500b according to the third embodiment.

[0075] The loss detection unit 512 detects or estimates the loss of the motor drive device 2 that increases due to the speed pulsation suppression control and the capacitor current suppression control. The loss detection unit 512 detects or estimates the second q-axis current command Iqrω output by the speed pulsation suppression control unit 502a. ＊ and the third q-axis current command IqrC output by the capacitor current suppression control unit 503a. ＊and are fed back to calculate a loss increase amount ΔPest of the copper loss of the motor 401. At this time, the loss detection unit 512 may also simultaneously calculate increases in the iron loss of the motor 401, the mechanical loss of the motor 401, and the switching loss in the inverter 300. Then, the output upper limit value determination unit 509c performs feedback control so that the loss increase amount ΔPest calculated by the loss detection unit 512 does not exceed the allowable loss upper limit value Puav, and determines the output upper limit values ​​IqLIM1 and IqLIM2.

[0076] By performing the above-described feedback control, the control unit 500e can reliably control the loss increase ΔPest to be within the allowable upper limit, thereby improving the energy-saving performance of the motor drive device 2.

[0077] Seventh Embodiment In the seventh embodiment, a case where desired control cannot be achieved will be described. FIG. 13 is an explanatory diagram showing an example of the configuration of a control unit included in a power conversion device according to the seventh embodiment. As shown in FIG. 13, a control unit 500f according to the seventh embodiment includes a speed pulsation detection unit 510, a capacitor current detection unit 511, and an output upper limit value determination unit 509d, instead of the output upper limit value determination unit 509 included in the control unit 500b according to the third embodiment. The speed pulsation detection unit 510 is as described in the fourth embodiment. The capacitor current detection unit 511 is as described in the fifth embodiment.

[0078] The output upper limit value determiner 509d determines the output upper limits IqLIM1 and IqLIM2 so that at least two of the speed pulsation, capacitor current Ic, and loss increase do not exceed their respective allowable upper limits. However, if the allowable loss upper limit Puav, the allowable speed pulsation upper limit ωuav, and the allowable capacitor current upper limit Icuav are strictly set, any two or more of the speed pulsation, capacitor current Ic, and loss increase may exceed their allowable upper limits, regardless of how the output upper limits IqLIM1 and IqLIM2 are determined. Furthermore, if the output upper limits IqLIM1 and IqLIM2 cannot be determined appropriately for some reason, any two or more of the speed pulsation, capacitor current Ic, and loss increase may exceed their allowable upper limits. If the motor 401 is operated for a long time while this state continues, the motor 401 may burn out, the capacitor 200 may explode, the refrigerant pipe may break, or other damage or failure of the device may occur.

[0079] Therefore, the output upper limit value determiner 509d in the seventh embodiment has a function of issuing an alarm signal when any two of the speed pulsation of the motor 401, the capacitor current Ic, and the loss increase amount exceed the allowable upper limits for the determined output upper limit values ​​IqLIM1 and IqLIM2. That is, the output upper limit value determiner 509d has a mechanism for detecting that the desired control is not being achieved, and issues an alarm signal ALM when the desired control is not being achieved. The alarm signal ALM can notify the user that the desired control is not being achieved. This can prevent damage or malfunction of the device. The control unit 500f may also have a mechanism for automatically stopping the PWM signal if the alarm signal ALM is not canceled for a long period of time.

[0080] Eighth embodiment Fig. 14 is an explanatory diagram showing an example of the configuration of a control unit included in a power conversion device according to an eighth embodiment. A control unit 500g according to the eighth embodiment is configured to continue operation by reducing the motor speed when an output upper limit value determination unit 509d issues an alarm signal ALM. As shown in Fig. 14, the control unit 500g of the eighth embodiment is configured by adding a speed drooping unit 513 and a subtraction unit 514 to the configuration of the control unit 500f according to the seventh embodiment.

[0081] The speed drooping unit 513 normally outputs zero. When the output upper limit value determining unit 509d issues an alarm signal ALM, the speed drooping unit 513 outputs a signal Δω for reducing the speed of the motor 401. The subtracting unit 514 calculates the speed command ω ＊ The signal Δω is subtracted from the corrected speed command ω ＊＊ The speed control unit 501 outputs the corrected speed command ω ＊＊ and performs average speed control based on the first q-axis current command IqDC ＊ Output.

[0082] The reason why the motor speed is reduced when the alarm signal ALM is issued is that, in the case of the compressor 400, a reduction in motor speed increases the margin for the allowable loss upper limit Puav and the allowable capacitor current upper limit Icuav. A reduction in motor speed reduces the output power and the capacitor current Ic. Furthermore, when flux-weakening control is being performed, a reduction in motor speed reduces the d-axis current, thereby reducing the loss of the motor 401. For this reason, reducing the motor speed may enable control of at least two of the speed pulsation, capacitor current Ic, and loss increase within ranges that do not exceed their allowable upper limits.

[0083] As described above, in the power conversion device and motor drive device according to the eighth embodiment, since the control unit 500g has the speed drooping unit 513 and the subtraction unit 514, although the output power of the motor 401 decreases, the device can continue to operate within the allowable upper limit while preventing damage or failure of the device.

[0084] Ninth embodiment Fig. 15 is a refrigerant circuit diagram showing a configuration example of a refrigeration cycle applied device according to a ninth embodiment. A refrigeration cycle applied device 900 according to the ninth embodiment includes any one of the power conversion devices 1 and 1a described in the first to eighth embodiments. Note that Fig. 15 shows, as an example, a configuration including the power conversion device 1 described in the first embodiment.

[0085] The refrigeration cycle applied device 900 according to the ninth embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters.

[0086] The refrigeration cycle application equipment 900 includes a compressor 400 incorporating a motor 401, a flow path switching mechanism 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, which are connected via refrigerant piping 912.

[0087] Inside the compressor 400, a compression mechanism 904 that compresses the refrigerant and a motor 401 that operates the compression mechanism 904 are provided.

[0088] The refrigeration cycle device 900 can perform heating or cooling operation by switching the flow path of a flow path switching mechanism 902. The compression mechanism 904 is driven by a variable speed controlled motor 401. Note that although a four-way valve is shown as an example of the flow path switching mechanism 902, it may also be configured with a combination of two-way valves, for example.

[0089] During heating operation, the refrigerant is pressurized by the compression mechanism 904 and sent out, as shown by the solid arrow, and passes through the flow path switching mechanism 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910, and the flow path switching mechanism 902 in that order, before returning to the compression mechanism 904.

[0090] During cooling operation, the refrigerant is pressurized by the compression mechanism 904 and sent out, as shown by the dashed arrow, and passes through the flow path switching mechanism 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906, and the flow path switching mechanism 902 in that order, before returning to the compression mechanism 904.

[0091] During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant to expand it.

[0092] The power conversion device 1, 1a adjusts the amount of current pulsation so that at least two of the values ​​of the speed pulsation of the motor 401, the capacitor current Ic flowing in and out of the capacitor 200, and the losses increased by the speed pulsation suppression control and the capacitor current suppression control do not exceed their allowable upper limits. This makes it possible to realize a refrigeration cycle device 900 that has high energy-saving performance, is compact, and is low-cost.

[0093] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies or may be combined with other embodiments. Furthermore, it is also possible to omit or change part of the configuration without departing from the spirit of the invention.

[0094] 1, 1a Power conversion device, 2, 2a Motor drive device, 91 Processor, 92 Memory, 93 System bus, 100 Converter, 110 Commercial power supply, 120 Reactor, 130 Diode rectifier, 200 Capacitor, 201 DC bus voltage detection unit, 202 Capacitor temperature sensor, 300 Inverter, 301a, 301b Current detection unit, 400 Compressor, 401 Motor, 402 Mechanical load, 403 Motor temperature sensor, 404 Motor acceleration sensor, 500, 500a, 500b, 500c, 500d, 500e, 500f, 500g Control unit, 501 Speed ​​control unit, 502, 502a Speed ​​pulsation suppression control unit, 503, 503a Capacitor current suppression control unit, 504 Adder unit, 505 Current control unit, 506 Rotor position estimation unit, 507 PWM signal generation unit, 508 allowable upper limit value setting unit, 509, 509a, 509b, 509c, 509d output upper limit value determination unit, 510 speed pulsation detection unit, 511 capacitor current detection unit, 512 loss detection unit, 513 speed droop unit, 514 subtraction unit, 900 refrigeration cycle applied equipment, 902 flow path switching mechanism, 904 compression mechanism, 906 indoor heat exchanger, 908 expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping.

Claims

1. A power conversion device for driving a motor attached to a mechanical load, A converter that converts the first AC power supplied from the commercial power source into DC power, A capacitor connected to the output terminal of the converter, An inverter connected to both ends of the capacitor converts DC power into a second AC power and outputs it to the motor, The system comprises a control unit for driving and controlling the inverter, The control unit, A speed control unit that outputs a first current command for controlling the average speed of the motor, In order to suppress the speed pulsation of the motor caused by the load torque pulsation of the mechanical load, a speed pulsation suppression control unit outputs a second current command that causes the current flowing through the motor to pulsate, A capacitor current suppression control unit outputs a third current command that causes the current flowing to the motor to pulsate in order to suppress the amount of capacitor current flowing into and out of the capacitor, The system includes an adder that calculates the three output current commands and outputs a fourth current command, The speed pulsation suppression control unit and the capacitor current suppression control unit adjust the amount of current pulsation flowing to the motor so that at least two of the motor speed pulsation, the capacitor current, and losses including motor losses and circuit losses increased by the current commands of the speed pulsation suppression control unit and the capacitor current suppression control unit do not exceed preset tolerance limits, including the tolerance upper limit for speed pulsation, the tolerance upper limit for capacitor current, and the tolerance upper limit for losses. A power conversion device characterized by the following features.

2. The control unit further includes an allowable upper limit setting unit that sets the allowable upper limit according to the operating state of the motor and provides the set allowable upper limit to the speed pulsation suppression control unit and the capacitor current suppression control unit. The power conversion device according to feature 1.

3. The control unit prioritizes speed pulsation suppression control over capacitor current suppression control when the motor's rotational speed is below a predetermined value during low-speed operation, and prioritizes capacitor current suppression control over speed pulsation suppression control when the motor's rotational speed is above the predetermined value during high-speed operation. The power conversion device according to feature 1.

4. The system further includes an output limit determination unit that determines the output limit values ​​of the speed pulsation control unit and the capacitor current suppression control unit so that at least two of the losses increased by the motor speed pulsation, the capacitor current, and the current commands of the speed pulsation suppression control unit and the capacitor current suppression control unit do not exceed the allowable upper limit. The speed pulsation suppression control unit and the capacitor current suppression control unit adjust the amount of current pulsation flowing to the motor within the range of the upper output limit. The power conversion device according to feature 1.

5. The control unit further comprises a speed pulsation detection unit that detects or estimates the speed pulsation of the motor. The output upper limit determination unit performs feedback control so that the pulsation component of the velocity pulsation detected or estimated by the velocity pulsation detection unit does not exceed the allowable upper limit, and determines the output upper limit. The power conversion device according to feature 4.

6. The control unit further comprises a capacitor current detection unit that detects or estimates the amount of capacitor current flowing into and out of the capacitor, The output upper limit determination unit determines the output upper limit by performing feedback control so that the amount of current of the capacitor detected or estimated by the capacitor current detection unit does not exceed the allowable upper limit. The power conversion device according to feature 4 or 5.

7. The control unit further comprises a loss detection unit that detects or estimates the loss of the device that increases due to the current command of the velocity pulsation suppression control unit and the current command of the capacitor current suppression control unit. The output upper limit determination unit performs feedback control so that the loss detected or estimated by the loss detection unit does not exceed the allowable upper limit, and determines the output upper limit. The power conversion device according to feature 4 or 5.

8. The output limit determination unit has a function to issue an alarm signal if, at the determined output limit, any two of the following—the motor speed pulsation, the capacitor current, and the losses increased by the control of the speed pulsation suppression control unit and the capacitor current suppression control unit—exceed the allowable upper limit. The power conversion device according to feature 4 or 5.

9. The control unit further includes a speed control unit that outputs a signal to reduce the speed of the motor based on the alarm signal. The speed control unit outputs a first current command for controlling the average speed of the motor based on the signal output by the speed drop unit. The power conversion device according to feature 8.

10. A power conversion device according to any one of claims 1 to 5, A motor provided on a mechanical load and driven and controlled by the power conversion device, A motor drive device characterized by the following features.

11. A motor drive device according to claim 10, A refrigeration cycle application device characterized by the following features.