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

Abstract

A power conversion device (200) is provided with: a rectifying unit (3) that rectifies first AC power supplied from a commercial power source (1); a smoothing capacitor (5) connected to the output end of the rectifying unit (3); an inverter (30) that is connected to both ends of the smoothing capacitor (5), generates second AC power, and outputs the second AC power to a motor (7) that drives a load; and a control device (100) that controls the rotation speed of the motor (7) by controlling the operation of the inverter (30), and when the rotation speed of the motor (7) decreases, the control device (100) decreases a speed command value for controlling the rotation speed such that the difference between the rotation speed and the speed command value falls within a predetermined range.

Description

Technical Field

[0001] The present disclosure relates to a power conversion device, a motor drive device, and a refrigeration cycle application device that convert AC power into desired power. Background Art

[0002] In the past, in the conventional fan motor control, when the load torque becomes larger, the flowing current is increased in accordance with the load torque so as to follow the speed command. In the fan motor control of the power conversion device mounted on the air conditioner, etc., in order to prevent the speed from decreasing even when the load torque becomes unexpected due to frost, etc., that is, in order to follow the set speed command, the control is performed in a manner that a larger current flows in accordance with the load torque. However, in such fan motor control, when the load torque becomes larger than expected and the flowing current increases in accordance with the load torque to become an overcurrent, the operation of the fan motor stops, and the fan motor cannot be continuously operated. Therefore, it is not preferred in terms of comfort, energy saving, etc.

[0003] To address such a problem, Patent Document 1 discloses a technique for limiting input to speed control so that the q-axis current command value does not increase to a limit value when a torque command value that is too large compared to the maximum torque that a motor can output is requested.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2010-142031 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] However, according to the above-mentioned conventional technology, if control is performed by simply limiting the input of the speed command, there is a problem that the rotation speed of the fan motor may be reduced unnecessarily.

[0009] The present disclosure has been made in view of the above, and an object of the present disclosure is to obtain a power conversion device that can suppress a decrease in the rotation speed of a motor and continue the operation of the motor even when the load torque of a connected motor increases.

[0010] Means used to solve problems

[0011] In order to solve the above problems and achieve the purpose, the power conversion device disclosed in the present invention comprises: a rectifier, which rectifies the first AC power supplied from a commercial power supply; a capacitor, which is connected to the output end of the rectifier; an inverter, which is connected to both ends of the capacitor, generates a second AC power and outputs it to a motor driving a load; and a control device, which controls the operation of the inverter to control the rotation speed of the motor. When the rotation speed of the motor decreases, the control device reduces the speed command value so that the difference between the rotation speed and the speed command value used to control the rotation speed is within a specified range.

[0012] Effects of the Invention

[0013] The power conversion device of the present disclosure has an effect of being able to suppress a decrease in the rotation speed of the motor and to continue the operation of the motor even when the load torque of the connected motor increases. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram showing a configuration example of a power conversion device according to Embodiment 1.

[0015] Figure 2 This is a diagram showing a configuration example of an inverter included in the power conversion device according to the first embodiment.

[0016] Figure 3 This is a block diagram showing a configuration example of a control device included in the power conversion device according to the first embodiment.

[0017] Figure 4 This is a block diagram showing a configuration example of a voltage command value calculation unit included in the control device of the power conversion device according to the first embodiment.

[0018] Figure 5 This is a diagram showing characteristics of the rotation speed of a motor and the load torque of the motor when the power conversion device according to Embodiment 1 is mounted on refrigeration cycle application equipment.

[0019] Figure 6 This is a block diagram showing a configuration example of an operation continuation control unit included in the control device of the power conversion device according to the first embodiment.

[0020] Figure 7 This is a diagram showing the difference in characteristics depending on whether the operation continuation control unit of the control device included in the power conversion device according to the first embodiment performs the operation continuation control or not.

[0021] Figure 8 This is a flowchart showing the operation of the power conversion device according to the first embodiment.

[0022] Fig. 9 This is a diagram showing an example of a hardware configuration for realizing a control device included in the power conversion device according to the first embodiment.

[0023] Fig.10 This is a schematic diagram showing a calculation process in the power conversion device according to the third embodiment.

[0024] Fig.11 This is a diagram showing a configuration example of a refrigeration cycle application device according to a fourth embodiment. DETAILED DESCRIPTION

[0025] Hereinafter, a power conversion device, a motor drive device, and a refrigeration cycle application device according to an embodiment of the present disclosure will be described in detail based on the drawings.

[0026] Implementation method 1.

[0027] Figure 1 This is a diagram showing a configuration example of a power conversion device 200 according to the first embodiment. Figure 2 : This is a diagram showing a structural example of the inverter 30 provided in the power conversion device 200 of Embodiment 1. The power conversion device 200 is connected to a commercial power supply 1 and a motor 7. The power conversion device 200 converts the first AC power of the power supply voltage Vs supplied from the commercial power supply 1 into the second AC power having a desired amplitude and phase, and supplies it to the motor 7. The power conversion device 200 includes a reactor 2, a rectifier 3, a smoothing capacitor 5, an inverter 30, a bus voltage detection unit 10, a load current detection unit 40, and a control device 100. In addition, the motor drive device 400 is constituted by the power conversion device 200 and the motor 7. In addition, the refrigeration cycle application equipment 900 is constituted by the power conversion device 200, the motor 7, an outdoor fan 914, an outdoor heat exchanger 910, and a control unit 920. The outdoor heat exchanger 910 exchanges heat between the refrigerant flowing inside and the outside air. The outdoor fan 914 blows air to the outdoor heat exchanger 910. The motor 7 drives the outdoor fan 914 to rotate. In Figure 1 In the embodiment, only the structure necessary for explaining the power conversion device 200 in the refrigeration cycle application equipment 900 is shown. In the fourth embodiment, the detailed structure of the refrigeration cycle application equipment 900 is explained.

[0028] Reactor 2 is connected between commercial power source 1 and rectifier 3. Rectifier 3 includes a bridge circuit including rectifier elements 131 to 134, and rectifies and outputs first AC power of power source voltage Vs supplied from commercial power source 1. Rectifier 3 performs full-wave rectification.

[0029] The smoothing capacitor 5 is a smoothing element connected to the output end of the rectifier 3 and smoothing the power rectified by the rectifier 3. The smoothing capacitor 5 is, for example, a capacitor such as an electrolytic capacitor or a film capacitor. The smoothing capacitor 5 has a capacitance that smoothes the power rectified by the rectifier 3. The voltage generated in the smoothing capacitor 5 by smoothing is not a full-wave rectified waveform of the commercial power supply 1, but a waveform obtained by superimposing a voltage ripple corresponding to the frequency of the commercial power supply 1 on the DC component, and does not pulsate significantly. The frequency of this voltage ripple becomes a component twice the frequency of the power supply voltage Vs when the commercial power supply 1 is single-phase, and a component six times the frequency becomes the main component when the commercial power supply 1 is three-phase.

[0030] The bus voltage detection unit 10 detects the voltage across the smoothing capacitor 5, that is, the voltage between the DC buses 12a and 12b as the bus voltage Vdc, and outputs the detected voltage value to the control device 100. The load current detection unit 40 detects the load current Idc, which is the DC current flowing from the smoothing capacitor 5 into the inverter 30, and outputs the detected current value to the control device 100.

[0031] The inverter 30 is connected to both ends of the smoothing capacitor 5, and converts the power output from the rectifier 3 and the smoothing capacitor 5 into a second AC power having a desired amplitude and phase, that is, generates the second AC power, and outputs it to the motor 7 that drives the load. Specifically, the inverter 30 receives the bus voltage Vdc, generates a three-phase AC voltage with a variable frequency and voltage value, and supplies it to the motor 7 via the output lines 331 to 333. Figure 2 As shown, the inverter 30 includes an inverter main circuit 310 and a drive circuit 350. The input terminal of the inverter main circuit 310 is connected to the DC bus 12a, 12b. The inverter main circuit 310 includes switching elements 311 to 316. Rectifying elements 321 to 326 for return are connected in anti-parallel to the switching elements 311 to 316, respectively.

[0032] The drive circuit 350 generates drive signals Sr1 to Sr6 based on PWM (Pulse Width Modulation) signals Sm1 to Sm6 output from the control device 100. The drive circuit 350 controls the on and off of the switching elements 311 to 316 by the drive signals Sr1 to Sr6. Thus, the inverter 30 can supply a three-phase AC voltage with a variable frequency and a variable voltage to the motor 7 via the output lines 331 to 333.

[0033] The PWM signals Sm1 to Sm6 are signals having a signal level of a logic circuit, that is, a magnitude of 0V to 5V. The PWM signals Sm1 to Sm6 are signals whose reference potential is the ground potential of the control device 100. On the other hand, the drive signals Sr1 to Sr6 are signals having a voltage level required for controlling the switching elements 311 to 316, for example, a magnitude of -15V to +15V. The drive signals Sr1 to Sr6 are signals whose reference potential is the potential of the negative terminal, that is, the emitter terminal, of the corresponding switching elements 311 to 316.

[0034] The motor 7 rotates according to the amplitude and phase of the second AC power supplied from the inverter 30. The motor 7 is used, for example, for the compression operation of the compressor, the rotation operation of the fan, and the like. Figure 1 In the example of FIG. 7 , the motor 7 drives the outdoor fan 914 provided in the refrigeration cycle application device 900 as the load to rotate, and blows air to the outdoor heat exchanger 910 to cool the outdoor heat exchanger 910. Figure 1 The motor winding of the motor 7 may be a Δ connection, or may be a specification that allows switching between the Y connection and the Δ connection.

[0035] In addition, in the power conversion device 200, Figure 1 The configuration of each structure shown is an example, and the configuration of each structure is not limited to Figure 1 The example shown. For example, the reactor 2 may also be arranged at the rear stage of the rectifier 3. In addition, the power conversion device 200 may also include a boost unit, and the rectifier 3 may also have the function of a boost unit. In the following description, the bus voltage detection unit 10 and the load current detection unit 40 are sometimes collectively referred to as detection units. In addition, the voltage value detected by the bus voltage detection unit 10 and the current value detected by the load current detection unit 40 are sometimes referred to as detection values.

[0036] The control device 100 obtains the bus voltage Vdc from the bus voltage detection unit 10 and obtains the load current Idc from the load current detection unit 40. The control device 100 uses the detection values ​​detected by each detection unit to control the operation of the inverter main circuit 310, specifically, to control the on and off of the switching elements 311 to 316 of the inverter main circuit 310. The control device 100 controls the rotation speed of the motor 7 by controlling the on and off of the switching elements 311 to 316 of the inverter main circuit 310. In addition, the rotation speed of the motor 7 can also be expressed as the rotation speed of the motor 7. The same applies hereinafter. In addition, the control device 100 calculates the load torque of the motor 7. In addition, the control device 100 may not use all the detection values ​​obtained from each detection unit, but may use a part of the detection values ​​for control. In the present embodiment, the control device 100 performs control in a rotating coordinate system having a d-axis and a q-axis.

[0037] The detailed structure and operation of the control device 100 will be described. Figure 3 1 is a block diagram showing a configuration example of the control device 100 included in the power conversion device 200 according to Embodiment 1. The control device 100 includes an operation control unit 102 , an inverter control unit 110 , and an operation continuation control unit 121 .

[0038] The operation control unit 102 obtains the instruction information Qe from the control unit 920 of the refrigeration cycle application device 900. In the case where the refrigeration cycle application device 900 is an air conditioner, the instruction information Qe is, for example, information indicating the temperature detected by a temperature sensor (not shown), information indicating the set temperature indicated by a remote controller (not shown) as an operation unit, information on the selection of the operation mode, and information indicating the start and end of the operation. The operation mode refers to heating, cooling, dehumidification, etc. In addition, the operation control unit 102 obtains the speed instruction reduction amount Δω from the operation continuation control unit 121. * The operation control unit 102 calculates the speed command drop amount Δω based on the command information Qe and the speed command drop amount Δω. * , generate frequency command value ωe * , the frequency command value ωe * The voltage command value is a command value for generating a voltage to be applied to the motor 7. * The operation control unit 102 can obtain the rotational speed command value ωm from the rotational angular velocity command value ωm of the motor 7. * The value obtained by multiplying the number of pole pairs Pm of the motor 7 by the speed command reduction amount Δω * In addition, the operation control unit 102 generates a stop signal St, which is a signal for stopping the operation of the inverter 30, based on the command information Qe. The operation control unit 102 sets the frequency command value ωe *The voltage command value calculation unit 115 outputs the stop signal St to the PWM signal generation unit 118 of the inverter control unit 110 .

[0039] The inverter control unit 110 includes a current recovery unit 111 , a 3-phase to 2-phase conversion unit 112 , a d-axis current command value generation unit 113 , a voltage command value calculation unit 115 , an electric phase calculation unit 116 , a 2-phase to 3-phase conversion unit 117 , and a PWM signal generation unit 118 .

[0040] The current recovery unit 111 recovers the phase currents iu, iv, and iw flowing through the motor 7 based on the load current Idc detected by the load current detection unit 40. The current recovery unit 111 samples the load current Idc detected by the load current detection unit 40 at a timing determined based on the PWM signals Sm1 to Sm6 generated by the PWM signal generation unit 118, thereby recovering the phase currents iu, iv, and iw.

[0041] The 3-phase to 2-phase conversion unit 112 uses the electric phase θe generated by the electric phase calculation unit 116 described later to convert the phase currents iu, iv, iw recovered by the current recovery unit 111 into a d-axis current id as an excitation current and a q-axis current iq as a torque current, that is, current values ​​of the dq axes.

[0042] The d-axis current command value generating unit 113 generates the d-axis current command value Id in the aforementioned rotating coordinate system. * Specifically, the d-axis current command value generating unit 113 generates a d-axis current command value based on the q-axis current iq, the bus voltage Vdc, and the d-axis voltage command value Vd * , and q-axis voltage command value Vq * , find the most appropriate d-axis current command value Id with the best efficiency * , to drive the motor 7. The d-axis current command value generating unit 113 generates a d-axis current command value based on the q-axis current iq, the bus voltage Vdc, and the d-axis voltage command value Vd * And the q-axis voltage command value Vq * The output becomes the d-axis current command value Id with the current phase βm as follows * At this current phase βm, the output torque of the motor 7 becomes greater than or equal to a predetermined value or becomes the maximum, that is, the current value becomes less than or equal to a predetermined value or becomes the minimum. In addition, here, the d-axis current command value generating unit 113 obtains the d-axis current command value Id based on the q-axis current iq, etc. * , but this is an example and is not limited to this. The d-axis current command value generating unit 113 can generate the d-axis current command value based on the d-axis current id and the frequency command value ωe * The d-axis current command value Id is obtained *, the same effect can be obtained. In addition, the d-axis current command value generating unit 113 can also determine the d-axis current command value Id by using a weak magnetic flux control or the like. * .

[0043] The voltage command value calculation unit 115 calculates the frequency command value ωe obtained from the operation control unit 102 based on the frequency command value ωe. * , the d-axis current id and the q-axis current iq obtained from the 3-phase to 2-phase conversion unit 112, and the d-axis current command value Id obtained from the d-axis current command value generation unit 113 * , generate the d-axis voltage command value Vd * and q-axis voltage command value Vq * In addition, the voltage command value calculation unit 115 generates the d-axis voltage command value Vd * and q-axis voltage command value Vq * In the process, the q-axis current command value Iq is generated * Furthermore, the voltage command value calculation unit 115 calculates the voltage command value Vd based on the d-axis voltage command value Vd * , q-axis voltage command value Vq * , d-axis current id, and q-axis current iq to estimate the frequency estimation value ωest.

[0044] The electric phase calculation unit 116 calculates the electric phase θe by integrating the frequency estimated value ωest obtained from the voltage command value calculation unit 115 .

[0045] The 2-phase to 3-phase converter 117 uses the electric phase θe obtained from the electric phase calculator 116 to convert the d-axis voltage command value Vd obtained from the voltage command value calculator 115 into * and q-axis voltage command value Vq * That is, the voltage command value of the two-phase coordinate system is converted into the output voltage command value of the three-phase coordinate system, that is, the three-phase voltage command value Vu * 、Vv * 、Vw * .

[0046] The PWM signal generation unit 118 generates a 3-phase voltage command value Vu based on the 3-phase voltage command value Vu obtained from the 2-phase to 3-phase conversion unit 117. * 、Vv * 、Vw * The PWM signals Sm1 to Sm6 are generated based on the stop signal St obtained from the operation control unit 102. The PWM signal generation unit 118 stops outputting the PWM signals Sm1 to Sm6 based on the stop signal St, thereby also being able to stop the motor 7.

[0047] The configuration and operation of the voltage command value calculation unit 115 will be described in detail. Figure 41 is a block diagram showing a configuration example of a voltage command value calculation unit 115 included in the control device 100 of the power conversion device 200 according to Embodiment 1. The voltage command value calculation unit 115 includes a frequency estimation unit 501, addition and subtraction units 502, 504, 505, 509, and 513, a speed control unit 503, a d-axis current control unit 506, a q-axis current control unit 507, multiplication units 508, 510, and 512, and an addition unit 511.

[0048] The frequency estimation unit 501 calculates the frequency of the d-axis current id, the q-axis current iq, and the d-axis voltage command value Vd. * And the q-axis voltage command value Vq * , the frequency of the voltage supplied to the motor 7 is estimated and output as the frequency estimated value ωest. Figure 4 The frequency estimation value ωest output from the frequency estimation unit 501 to the outside of the voltage command value calculation unit 115 is Figure 3 The frequency estimated value ωest output from the voltage command value calculation unit 115 to the electric phase calculation unit 116. The adder and subtractor 502 calculates the frequency estimated value ωest from the frequency command value ωe * Subtract the frequency estimate ωest and output the frequency command value ωe * The frequency deviation del_ω from the frequency estimate ωest.

[0049] The speed control unit 503 calculates and outputs the q-axis current command value Iq based on the frequency deviation del_ω. * q-axis current command value Iq * is the command value of the q-axis current iq that makes the frequency deviation del_ω zero, that is, the frequency command value ωe * The speed control unit 503 is, for example, a proportional-integral (PI) controller, but is not limited thereto. The speed control unit 503 sets the q-axis current command value Iq to * The result is output to the subsequent adder-subtractor 505 and is also output to the operation continuation control unit 121 .

[0050] The adding and subtracting unit 504 calculates the d-axis current command value Id from * Subtract the d-axis current id and output the d-axis current command value Id * The d-axis current control unit 506 is constituted by, for example, a PI controller so that the d-axis current command value Id * The d-axis current control unit 506 operates so that the deviation from the d-axis current id converges to zero. The d-axis current control unit 506 outputs the first d-axis voltage command value Vdfb * .

[0051] The addition and subtraction unit 505 uses the q-axis current command value Iq* Subtract the q-axis current iq and output the q-axis current command value Iq * The q-axis current control unit 507 is constituted by, for example, a PI controller so that the q-axis current command value Iq * The q-axis current control unit 507 operates so that the deviation from the q-axis current iq converges to zero. The q-axis current control unit 507 outputs the first q-axis voltage command value Vqfb * .

[0052] The multiplication unit 508 performs a multiplication on the q-axis current command value Iq. * The q-axis inductance Lq of the motor 7 and the frequency estimation value ωest are multiplied to calculate and output the first d-axis voltage command value Vdfb * Compensation value Vdff * The addition and subtraction unit 509 calculates the first d-axis voltage command value Vdfb from * Subtract the compensation value Vdff * , the 1d-axis voltage command value Vdfb * and compensation value Vdff * Deviation (Vdfb * -Vdff * ) That is, the second d-axis voltage command value is the d-axis voltage command value Vd from the voltage command value calculation unit 115. * And output.

[0053] The multiplication unit 510 performs the calculation on the d-axis current command value Id. * The adding unit 511 multiplies the d-axis inductance Ld of the motor 7 and outputs the result. The output from the multiplication unit 510 is added. The multiplication unit 512 multiplies the output from the addition unit 511 by the frequency estimation value ωest, and calculates and outputs the first q-axis voltage command value Vqfb * Compensation value Vqff * The adder and subtractor 513 calculates the first q-axis voltage command value Vqfb from * Subtract the compensation value Vqff * , the 1q-axis voltage command value Vqfb * and compensation value Vqff * Deviation (Vqfb * -Vqff * ) That is, the second q-axis voltage command value is the q-axis voltage command value Vq from the voltage command value calculation unit 115. * And output.

[0054] Back to Figure 3In the control device 100, the operation continuation control unit 121 calculates the d-axis current id obtained from the 3-phase 2-phase conversion unit 112 and the q-axis current command value Iq obtained from the voltage command value calculation unit 115. * , to calculate the speed command decrease amount Δω * The operation continuation control unit 121 calculates the speed command decrease amount Δω * Output to the operation control unit 102.

[0055] In the present embodiment, the control device 100 performs control in the following manner: when the rotation speed of the motor 7 decreases, the speed command value is reduced so that the difference between the rotation speed and the speed command value for controlling the rotation speed is within a predetermined range. For example, when the outdoor heat exchanger 910 changes from a non-frost state where frost has not formed to a frosted state where frost has formed, the control device 100 increases the load torque of the motor 7 that drives the outdoor fan 914 in order to maintain the rotation speed of the motor 7, and the required current also increases, which may become an overcurrent state. Therefore, the control device 100 performs control in the following manner: the rotation speed is reduced in the frosted state by a load torque of the same degree as the load torque that can be output in the non-frost state, so that the motor 7 is rotated.

[0056] Here, the load torque is briefly described. The control device 100 can calculate the load torque, i.e., the estimated load torque Tm, based on the current value detected by the load current detection unit 40 and the parameters based on the specifications of the motor 7. Specifically, the control device 100 estimates the load torque of the motor 7 using the d-axis current id and the q-axis current iq output from the 3-phase 2-phase conversion unit 112, i.e., calculates the estimated load torque Tm of the motor 7. The control device 100 calculates the estimated load torque Tm of the motor 7 based on the following formula (1).

[0057]

[0058] In equation (1), Tm is the estimated load torque, Pm is the number of pole pairs of the motor 7, is the induced voltage constant of motor 7, Ld is the d-axis inductance of motor 7, Lq is the q-axis inductance of motor 7, id is the d-axis current, and iq is the q-axis current. When the rotational speed, i.e., the speed, of motor 7 follows the speed command value used to control the movement of motor 7 and motor 7 is running at a constant speed, the output torque of motor 7 and the load torque of motor 7 become the same size. Therefore, the output torque of formula (1) can be treated as the load torque. As described above, although the control device 100 obtains the d-axis current id and the q-axis current iq from the 3-phase 2-phase conversion unit 112, the pole pair number Pm of motor 7 and the induced voltage constant of motor 7 are maintained in advance. The d-axis inductance Ld of the motor 7 , and the q-axis inductance Lq of the motor 7 .

[0059] The relationship between the rotation speed of the motor 7 that drives the outdoor fan 914 and the load torque of the motor 7 will be described. Figure 5 1 is a diagram showing characteristics of the rotation speed of the motor 7 and the load torque of the motor 7 when the power conversion device 200 according to the first embodiment is mounted on the refrigeration cycle application equipment 900. Figure 5 In FIG. 1 , the horizontal axis represents the rotation speed of the motor 7, and the vertical axis represents the load torque of the motor 7. Figure 5 In FIG. 1 , the solid line with circles shows a polynomial representing the state when no frost occurs in the refrigeration cycle application device 900, and the dotted line with quadrilaterals shows a polynomial representing the state when frost occurs in the refrigeration cycle application device 900. The value shown by the solid line with circles is also called the reference setting value when no frost occurs. Figure 5 In the embodiment, the speed of the motor 7 on the horizontal axis can also be the speed of the outdoor fan 914. Figure 5 As shown, even when the rotation speed of the motor 7 is the same, the load torque becomes larger when frosting occurs in the refrigeration cycle application device 900 than when frosting does not occur in the refrigeration cycle application device 900. In addition, the higher the rotation speed of the motor 7, the greater the difference between the load torque when frosting occurs in the refrigeration cycle application device 900 and the load torque when frosting does not occur in the refrigeration cycle application device 900. Figure 5 In the example, when the rotation speed of motor 7 changes from a non-frost state to a frosted state at 2000 rpm, the control device 100 reduces the rotation speed of motor 7 to about 1400 rpm, thereby making the output load torque the same and allowing the rotation, i.e., the operation, of motor 7 to continue.

[0060] The detailed structure and operation of the operation continuation control unit 121 included in the control device 100 will be described. Figure 6 This is a block diagram showing a configuration example of the operation continuation control unit 121 included in the control device 100 of the power conversion device 200 according to Embodiment 1. The operation continuation control unit 121 includes a limit value calculation unit 141 , an addition and subtraction unit 142 , a deviation sign processing unit 143 , and an output unit 144 .

[0061] The limit value calculation unit 141 uses the d-axis current id obtained from the 3-phase to 2-phase conversion unit 112 to calculate the q-axis current command value iq used in the addition and subtraction unit 142. * The limit value calculation unit 141 calculates the limit value iq_lim based on the following equation (2).

[0062] iq_lim=√(3Ie 2 -id 2 )…(2)

[0063] In equation (2), iq_lim is a limit value, Ie is a limit value of the effective value of the phase current, and id is a d-axis current representing the current d-axis current value that can be obtained from the 3-phase to 2-phase converter 112. In addition, √(3Ie 2 -id 2 ) means (3Ie 2 -id 2 ). The limit value iq_lim indicates that, in order to give priority to the flow of the d-axis current id, the remainder after subtracting the d-axis current id from the limit value Ie of the effective value of the phase current can be used as the current magnitude of the q-axis current iq. The limit value calculation unit 141 outputs the limit value iq_lim obtained by calculation to the addition and subtraction unit 142.

[0064] The adder and subtractor 142 obtains the limit value iq_lim from the limit value calculator 141 and obtains the q-axis current command value iq_lim from the voltage command value calculator 115. * The addition and subtraction unit 142 subtracts the q-axis current command value iq from the limit value iq_lim. * , to calculate the limit value iq_lim and the q-axis current command value iq * The addition and subtraction unit 142 adds the limit value iq_lim obtained by calculation to the q-axis current command value iq * The deviation is output to the deviation sign processing unit 143.

[0065] The deviation sign processing unit 143 generates a deviation sign based on the limit value iq_lim calculated by the addition and subtraction unit 142 and the q-axis current command value iq * The deviation is used to control the speed command decrease amount Δω output from the output unit 144 to the operation control unit 102. * Specifically, the deviation sign processing unit 143 determines the difference between the limit value iq_lim and the q-axis current command value iq * When the deviation is greater than 0, that is, when the q-axis current command value iq * When the speed command decrease amount Δω is equal to or less than the limit value iq_lim, the output unit 144 is controlled to output the speed command decrease amount Δω. * = 0. The deviation sign processing unit 143 determines the difference between the limit value iq_lim and the q-axis current command value iq * When the deviation is less than 0, that is, when the q-axis current command value iq * When it is greater than the limit value iq_lim, the control is performed so that the output unit 144 outputs the difference between the limit value iq_lim and the q-axis current command value iq * The deviation is based on K Iac The value obtained by the integral control of / S is used as the speed command reduction amount Δω * In addition, KIac is the integral gain of the integral control, K Iac The S in the denominator of / S represents the Laplace operator.

[0066] The output unit 144 decreases the speed instruction by the amount Δω based on the control of the deviation sign processing unit 143. * =0 is output to the operation control unit 102, or the limit value iq_lim and the q-axis current command value iq * The deviation is based on K Iac The value obtained by the integral control of / S is taken as the speed command reduction amount Δω * Output to the operation control unit 102.

[0067] In this way, the control device 100 sets the q-axis current command value Iq as the speed command value. * Reduce the q-axis current command value Iq * The amount exceeds the limit value iq_lim, which is the q-axis current command value Iq * The control device 100 sets the q-axis current limit value, i.e., the limit value iq_lim, based on the limit value Ie of the effective value of the phase current, i.e., the current flowing from the power conversion device 200 to each phase of the motor 7, and the d-axis current id, which is the current d-axis current value. Figure 5 In the example, when the rotation speed of the motor 7 is 2000 rpm and changes from a non-frost state to a frosted state, the control device 100 makes the rotation speed of the motor 7 about 1400 rpm, thereby making it possible to make the output load torque the same and to continue the rotation, i.e., the operation of the motor 7. That is, even when the load torque of the motor 7 increases, the control device 100 controls the rotation speed of the motor 7 to decrease by more than the limit value iq_lim, thereby maintaining the maximum current in the power conversion device 200 and controlling the rotation of the motor 7.

[0068] In addition, the method by which the limit value calculation unit 141 calculates the limit value iq_lim is not limited to the example of formula (2). As long as the maximum current can be maintained in the power conversion device 200 and the rotation of the motor 7 can be controlled, the limit value iq_lim calculated by the limit value calculation unit 141 can also be calculated by other methods. For example, the limit value calculation unit 141 can also calculate the limit value iq_lim from the perspective of voltage saturation.

[0069] Figure 7 1 is a diagram showing the difference in characteristics caused by whether the operation continuation control unit 121 of the control device 100 provided in the power conversion device 200 according to the first embodiment performs the operation continuation control or not. Figure 7In FIG. 1 , the left side shows the case where the operation continuation control unit 121 does not perform the operation continuation control, and the right side shows the case where the operation continuation control unit 121 performs the operation continuation control. In addition, in both the case where there is no operation continuation control and the case where there is operation continuation control, Figure 7 The first segment represents the rotation speed of the motor 7, Figure 7 The second segment represents the torque of motor 7, Figure 7 The third section shows the phase currents iu, iv, iw of the motor 7. Figure 7 The fourth segment of represents the q-axis current iq of the motor 7. In addition, in all the graphs, the horizontal axis represents time. Figure 7 As shown, the graphs of the second, third, and fourth stages are the same in both the case where there is no operation continuation control and the case where there is operation continuation control.

[0070] In the absence of continuous control of operation, Figure 7 In the graph of the first section on the left side, the command value deviates from the estimated speed and the actual speed. This indicates the following state: although the power conversion device 200 wants to rotate the motor 7 with constant torque control or maximum torque, due to the influence of frost, etc., the torque required for the rotation of the motor 7 becomes large, and the desired speed, i.e., the speed indicated by the command value, cannot be achieved. When the state in which the command value deviates from the estimated speed and the actual speed continues, integral saturation (windup) phenomenon and the like occur, and the control easily becomes unstable. Therefore, it is not preferred in terms of the control of the control device 100. In contrast, in the case of continuous operation control, Figure 7 In the first section of the graph on the right side of , after a predetermined time has passed since the start of the continuous operation control, the command value decreases, thereby eliminating the state where the command value deviates from the estimated speed and the actual speed. As a result, the control device 100 can avoid the situation where the command value deviates from the estimated speed and the actual speed continuously, and achieve a stable control state.

[0071] The operation of the power conversion device 200 which is characteristic of the first embodiment will be described using a flowchart. Figure 8 1 is a flowchart showing the operation of the power conversion device 200 according to the first embodiment. In the power conversion device 200, the operation continuation control unit 121 of the control device 100 calculates the q-axis current command value Iq ＊ The operation continuation control unit 121 calculates the limit value iq_lim and the q-axis current command value iq obtained from the voltage command value calculation unit 115. * The operation continuation control unit 121 sets the limit value iq_lim and the q-axis current command value iq * When the deviation is greater than 0, that is, when the q-axis current command value iq *If the speed command is less than the limit value iq_lim (step S3: Yes), the speed command is decreased by the amount Δω * =0 is output to the operation control unit 102 (step S4). The operation continuation control unit 121 sets the limit value iq_lim and the q-axis current command value iq * When the deviation is less than 0, that is, when the q-axis current command value iq * If it is greater than the limit value iq_lim (step S3: No), the limit value iq_lim and the q-axis current command value iq * The deviation is based on K Iac The value obtained by the integral control of / S is taken as the speed command reduction amount Δω * The data is output to the operation control unit 102 (step S5).

[0072] As in the present embodiment, in the operation continuation control unit 121 of the control device 100, the q-axis current command value Iq * When the limit value iq_lim is used, as described above, the load torque of the motor 7 may simply increase, causing the q-axis current command value Iq * In the operation continuation control unit 121 of the control device 100, the q-axis current command value Iq * The case where the limit value iq_lim is limited includes, for example, the following case: after the control device 100 executes the flux weakening control to the limit, the speed decreases, causing the input of the speed control unit 503 to deviate, and the q-axis current command value Iq * Increases until it is limited by the limit value iq_lim.

[0073] Next, the hardware configuration of the control device 100 included in the power conversion device 200 will be described. Fig. 9 1 is a diagram showing an example of a hardware configuration for realizing the control device 100 included in the power conversion device 200 according to Embodiment 1. The control device 100 is realized by a processor 91 and a memory 92 .

[0074] The processor 91 is a CPU (also called a Central Processing Unit, a central processing device, a processing device, an arithmetic device, a microprocessor, a microcomputer, a processor, a DSP (Digital Signal Processor), or a system LSI (Large Scale Integration). The memory 92 can be exemplified by a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (registered trademark) (Electrically EPROM). In addition, the memory 92 is not limited thereto, and may be a magnetic disk, an optical disk, a high-density disk, a mini disk, or a DVD (Digital Versatile Disc).

[0075] As described above, according to the present embodiment, in the power conversion device 200, the operation continuation control unit 121 of the control device 100 sets the q-axis current command value Iq calculated by the voltage command value calculation unit 115 to * If the limit value iq_lim is greater than the limit value iq_lim calculated in consideration of maintaining the maximum current in the power conversion device 200, the limit value iq_lim and the q-axis current command value iq * The deviation is based on K Iac The value obtained by the integral control of / S is taken as the speed command reduction amount Δω * The frequency command value is output to the operation control unit 102. The operation control unit 102 decreases the frequency command value obtained by the calculation by the speed command decrease amount Δω. * The value obtained by the amount is taken as the frequency command value ωe * The control device 100 controls the rotation speed of the motor 7 to decrease by an amount exceeding the limit value iq_lim even when the load torque of the motor 7 increases, thereby maintaining the maximum current in the power conversion device 200 and continuing the rotation of the motor 7. The control device 100 can suppress the decrease in the rotation speed of the motor 7 and continue the operation of the motor 7 even when the load torque of the motor 7 connected to the power conversion device 200 increases.

[0076] In addition, in this embodiment, the case where the motor 7 targeted by the control device 100 is a fan motor that rotates the outdoor fan 914 is described, but the present invention is not limited thereto. As long as the same phenomenon of load torque increase occurs, the control device 100 can also perform the same control on motors 7 other than fan motors.

[0077] Implementation method 2.

[0078] In the first embodiment, the operation continuation control unit 121 calculates the q-axis current command value Iq obtained from the voltage command value calculation unit 115. * When it is larger than the limit value iq_lim, the operation continuation control is started. In the second embodiment, another timing at which the operation continuation control unit 121 starts the operation continuation control will be described.

[0079] The operation continuation control unit 121 may start the operation continuation control when the estimated speed of the motor 7 is smaller than the speed command value for the motor 7. When the estimated speed of the motor 7 is smaller than the speed command value for the motor 7, Figure 7 The operation continuation control unit 121 uses the estimated speed of the motor 7 and the speed command value for the motor 7 to determine whether the operation continuation control is performed, thereby achieving the same effect as the first embodiment.

[0080] In the case where the q-axis current command value Iq is used * When the condition that the motor 7 meets the limit value iq_lim as the first condition and the condition that the estimated speed of the motor 7 and the speed command value for the motor 7 are used as the second condition, the operation continuation control unit 121 may also start the operation continuation control when the first condition or the second condition continues for a predetermined period. Such a situation is set as the third condition. Usually, the motor 7 may temporarily become the state of the first condition or the second condition by accelerating or decelerating in the normal control based on the power conversion device 200. Therefore, in order to exclude the situation that the first condition or the second condition is temporarily reached due to the normal control based on the power conversion device 200, the operation continuation control unit 121 may also determine to start the operation continuation control when the period in which the first condition or the second condition is satisfied continues for a predetermined period, as in the third condition. That is, the operation continuation control unit 121 can reduce the speed command value when the first condition that the speed command value is limited by the predetermined limit value iq_lim is satisfied, when the second condition that the rotation speed of the motor 7 is smaller than the speed command value is satisfied, or when the third condition that the first condition or the second condition continues for a predetermined period is satisfied. It can be said that the operation continuation control unit 121 reduces the speed command value when it is impossible to perform control to make the rotation speed of the motor 7 follow the speed command value.

[0081] In addition, the timing when the operation continuation control unit 121 starts the operation continuation control has been described, but the operation continuation control unit 121 can stop the operation continuation control when any of the first condition, the second condition, or the third condition is no longer satisfied. However, the following situation is also considered: when the case of starting the operation continuation control and the case of stopping the operation continuation control are judged by the same value, the start and stop of the operation continuation control are repeated frequently depending on the situation. Therefore, the operation continuation control unit 121 can also consider the hysteresis phenomenon and use different values ​​as a reference for judgment when starting the operation continuation control and when stopping the operation continuation control.

[0082] Thus, the operation continuation control unit 121 can use some conditions to make a determination when starting the operation continuation control. In addition, the operation continuation control unit 121 can also use some conditions to make a determination when stopping the operation continuation control.

[0083] Implementation method 3.

[0084] In the third embodiment, a case where the calculation process in the speed control unit 503 of the voltage command value calculation unit 115 is changed by the operation continuation control of the operation continuation control unit 121 will be described.

[0085] Fig.10 This is a schematic diagram showing the calculation process in the power conversion device 200 according to the third embodiment. Fig.10 A part of the calculation process in the power conversion device 200 is extracted and the calculation flow of the extracted part is shown. Fig.10 In the example, the limit value indicates the limit value iq_lim calculated by the limit value calculation unit 141, the subsequent addition and subtraction processing indicates the processing of the addition and subtraction unit 142, and the subsequent speed reduction control indicates the processing based on K in the output unit 144. Iac The following addition process represents the internal process of the voltage command value calculation unit 115, and the following speed control represents the calculation process in the speed control unit 503. In the control device 100, when the operation continuation control unit 121 performs the operation continuation control, the q-axis current command value Iq output from the speed control unit 503 is * is limited to the limit value iq_lim. In this case, in the speed control unit 503, the integral control for the anti-integral windup processing is stopped. Therefore, when the operation continuation control unit 121 performs the operation continuation control, the speed control unit 503 Fig.10 As shown in the lower part of the figure, the q-axis current command value Iq can also be calculated only by proportional control. * , that is, the q-axis current command value Iq is calculated by proportional control * Speed ​​control when.

[0086] In such a case, the integral gain K of the integral control in the operation continuation control unit 121 described in the first embodiment is Iac It can also be expressed as formula (3).

[0087]

[0088] In equation (3), ωac is the control response in the speed control unit 503, ωsc is the control response in the operation continuation control unit 121, Pm is the number of pole pairs of the motor 7, is the induced voltage constant of the motor 7 , and J is the inertia of the motor 7 .

[0089] In this way, the control device 100 can also appropriately change the calculation expression and the like according to the control state.

[0090] Implementation method 4.

[0091] Fig.11 1 is a diagram showing a configuration example of a refrigeration cycle application device 900 according to a fourth embodiment. The refrigeration cycle application device 900 according to the fourth embodiment includes a power conversion device 200. The refrigeration cycle application device 900 according to the fourth embodiment can be applied to products having a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. Fig.11 In the present invention, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0092] As described above, the refrigeration cycle application device 900 includes the motor 7a similar to the motor 7 in Embodiment 1, and the outdoor fan 914. The motor 7a drives the outdoor fan 914 to rotate. The outdoor fan 914 blows air to the outdoor heat exchanger 910. The outdoor heat exchanger 910 exchanges heat between the refrigerant flowing inside and the air. In addition, the refrigeration cycle application device 900 is equipped with the compressor 8 having the motor 7b similar to the motor 7 in Embodiment 1 built therein, the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, and the outdoor heat exchanger 910 via the refrigerant piping 912.

[0093] A compression mechanism 904 for compressing the refrigerant and a motor 7b for operating the compression mechanism 904 are provided inside the compressor 8.

[0094] The refrigeration cycle application device 900 can perform heating operation or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by a motor 7b which is controlled by a variable speed.

[0095] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 904 and then sent out, and returns to the compression mechanism 904 through the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910 and the four-way valve 902.

[0096] During cooling operation, as shown by the dotted arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, and returns to the compression mechanism 904 through the four-way valve 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906 and the four-way valve 902.

[0097] During heating operation, the indoor heat exchanger 906 functions as a condenser to release heat, and the outdoor heat exchanger 910 functions as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 functions as a condenser to release heat, and the indoor heat exchanger 906 functions as an evaporator to absorb heat. The expansion valve 908 decompresses the refrigerant to expand it.

[0098] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, the embodiments may be combined with each other, and some configurations may be omitted or modified without departing from the spirit and scope of the invention.

[0099] Description of Reference Numerals

[0100] 1 Commercial power supply, 2 Reactor, 3 Rectification unit, 5 Smoothing capacitor, 7, 7a, 7b Motor, 8 Compressor, 10 Bus voltage detection unit, 12a, 12b DC bus, 30 Inverter, 40 Load current detection unit, 91 Processor, 92 Memory, 100 Control device, 102 Operation control unit, 110 Inverter control unit, 111 Current recovery unit, 112 3-phase 2-phase conversion unit, 113 d-axis current command value generation unit, 115 Voltage command value calculation unit, 116 Electric phase calculation unit, 117 2-phase 3-phase conversion unit, 118 PWM signal generation unit, 121 operation continuation control unit, 131-134, 321-326 rectification elements, 141 limit value calculation unit, 142, 502, 504, 505, 509, 513 addition and subtraction unit, 143 deviation sign processing unit, 144 output unit, 200 power conversion device, 310 inverter main circuit, 311-316 switching elements, 331-333 output lines, 350 drive dynamic circuit, 400 motor driving device, 501 frequency estimation unit, 503 speed control unit, 506 d-axis current control unit, 507 q-axis current control unit, 508, 510, 512 multiplication units, 511 addition unit, 900 refrigeration cycle application equipment, 902 four-way valve, 904 compression mechanism, 906 indoor heat exchanger, 908 expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping, 914 outdoor fan, 920 control unit.

Claims

1. A power conversion device comprising: a rectifier that rectifies the first AC power supplied from the commercial power supply; A capacitor connected to the output end of the rectifying unit; an inverter connected to both ends of the capacitor, generating a second AC power and outputting the second AC power to a motor driving a load; and a control device that controls the operation of the inverter to control the rotation speed of the motor, The control device reduces a speed command value for controlling the rotation speed so that a difference between the rotation speed and the speed command value falls within a predetermined range when the rotation speed of the motor decreases.

2. The power conversion device according to claim 1, wherein: The control device reduces the speed command value when control cannot be performed to make the rotation speed follow the speed command value.

3. The power conversion device according to claim 1 or 2, wherein: The control device reduces the speed command value when a first condition is satisfied that the speed command value is limited by a predetermined limit value, when a second condition is satisfied that the rotation speed is smaller than the speed command value, or when a third condition is satisfied that the first condition or the second condition continues for a predetermined period of time.

4. The power conversion device according to any one of claims 1 to 3, wherein: The control device reduces a q-axis current command value as the speed command value by an amount by which the q-axis current command value exceeds a q-axis current limit value of the q-axis current command value.

5. The power conversion device according to claim 4, wherein: The control device sets the q-axis current limit value based on a limit value of an effective value of a phase current, which is a current flowing from the power conversion device to each phase of the motor, and a current d-axis current value.

6. The power conversion device according to claim 4 or 5, wherein: The control device performs speed control when calculating the q-axis current command value by proportional control.

7. A motor drive device, wherein: The motor drive device includes the power conversion device according to any one of claims 1 to 6.

8. A refrigeration cycle application device, wherein: The refrigeration cycle application equipment includes the power conversion device according to any one of claims 1 to 6.

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