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

Abstract

A power conversion device (200) comprises: a rectifier unit (3) for rectifying a first AC power supplied from a commercial power supply (1); a smoothing capacitor (5) connected to an output end of the rectifier unit (3); an inverter (30) connected to both ends of the smoothing capacitor (5) and generating a second AC power to output the second AC power to a motor (7) for driving a load; and a control device (100) for controlling the operation of the inverter (30) to control the rotational speed of the motor (7). When the rotational speed of the motor (7) decreases, the control device (100) reduces a speed command value so that the difference between the rotational speed and the speed command value for controlling the rotational speed becomes within a specified range.

Description

[Technical Field]

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

[0002] Conventionally, typical fan motor control controls the fan motor by increasing the current flow in accordance with the load torque as the load torque increases, so as to follow a speed command. Fan motor control in power conversion devices installed in air conditioners and the like controls the fan motor by increasing the current flow in accordance with the load torque so as to prevent the speed from decreasing, even when the load torque becomes larger than expected due to frosting or the like. However, this type of fan motor control stops the fan motor operation when the load torque becomes larger than expected, causing an overcurrent due to the increased current flow in accordance with the load torque, making it impossible to continue operating the fan motor, which is undesirable in terms of comfort and energy conservation.

[0003] To address this problem, Patent Document 1 discloses a technique for limiting the input of speed control so that the q-axis current command value does not increase to the limiter value when a torque command value that is excessively greater than the maximum torque that the motor can output is requested. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-142031 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the above-described conventional technology, there is a problem in that simply limiting the input of a speed command may result in the rotation speed of the fan motor decreasing more than necessary.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a power conversion device that can continue operating a motor while suppressing a decrease in the rotational speed of the motor even when the load torque of the connected motor increases. [Means for solving the problem]

[0007] In order to solve the above problems and achieve the objectives, Show , A power conversion device, The power converter includes a rectifier that rectifies a first AC power supplied from a commercial power source, a capacitor connected to an output terminal of the rectifier, an inverter that is connected across the capacitor and generates a second AC power and outputs the second AC power to a motor that drives a load, and a control device that 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 a speed command value for controlling the rotation speed falls within a specified range. The q-axis current command value is reduced by the amount by which the q-axis current command value exceeds the q-axis current limiter value of the q-axis current command value, which is the speed command value, and the q-axis current limiter value is set based on the limiter value of the effective value of the phase current, which is the current of each phase flowing from the power conversion device to the motor, and the current d-axis current value. do. [Effects of the Invention]

[0008] The power conversion device according to the present disclosure has an advantage that, even when the load torque of the connected motor increases, it is possible to continue operating the motor while suppressing a decrease in the rotation speed of the motor. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a configuration example of a power conversion device according to a first embodiment; [Figure 2] FIG. 1 is a diagram showing a configuration example of an inverter included in a power conversion device according to a first embodiment; [Figure 3] FIG. 1 is a block diagram showing a configuration example of a control device provided in a power conversion device according to a first embodiment. [Figure 4]FIG. 1 is a block diagram showing a configuration example of a voltage command value calculation unit included in a control device for a power conversion device according to a first embodiment. [Figure 5] FIG. 10 is a diagram showing the characteristics of the motor rotation speed and the motor load torque when the power conversion device according to the first embodiment is mounted on a refrigeration cycle application device. [Figure 6] FIG. 1 is a block diagram showing a configuration example of an operation continuation control unit included in a control device for a power conversion device according to a first embodiment. [Figure 7] FIG. 10 is a diagram showing differences in characteristics depending on whether or not continuous operation control is performed by the continuous operation control unit of the control device provided in the power conversion device according to the first embodiment. [Figure 8] 1 is a flowchart showing the operation of the power conversion device according to the first embodiment. [Figure 9] FIG. 1 is a diagram showing an example of a hardware configuration for realizing a control device provided in a power conversion device according to a first embodiment. [Figure 10] FIG. 10 is a diagram showing an image of arithmetic processing in a power conversion device according to a third embodiment. [Figure 11] FIG. 10 is a diagram showing a configuration example of a refrigeration cycle application device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] Embodiment 1 FIG. 1 is a diagram illustrating a configuration example of a power conversion device 200 according to the first embodiment. FIG. 2 is a diagram illustrating a configuration example of an inverter 30 included in the power conversion device 200 according to the first embodiment. The power conversion device 200 is connected to a commercial power source 1 and a motor 7. The power conversion device 200 converts first AC power having a power supply voltage Vs supplied from the commercial power source 1 into second AC power having a desired amplitude and phase, and supplies the second AC power 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. The power conversion device 200 and the motor 7 form a motor drive device 400. The power conversion device 200, the motor 7, an outdoor fan 914, an outdoor heat exchanger 910, and a control unit 920 form a refrigeration cycle-applied device 900. The outdoor heat exchanger 910 exchanges heat between a refrigerant flowing therethrough and external air. The outdoor fan 914 sends air to the outdoor heat exchanger 910. The motor 7 drives and rotates the outdoor fan 914. Fig. 1 shows only the components of the refrigeration cycle device 900 that are necessary for explaining the power conversion device 200. The detailed configuration of the refrigeration cycle device 900 will be explained in the fourth embodiment.

[0012] The reactor 2 is connected between the commercial power supply 1 and the rectifier 3. The rectifier 3 has a bridge circuit formed by rectifier elements 131 to 134, and rectifies and outputs the first AC power of the power supply voltage Vs supplied from the commercial power supply 1. The rectifier 3 performs full-wave rectification.

[0013] Smoothing capacitor 5 is a smoothing element connected to the output terminal of rectifier 3 and smoothes the power rectified by rectifier 3. Smoothing capacitor 5 is, for example, an electrolytic capacitor, a film capacitor, or other capacitor. Smoothing capacitor 5 has a capacity that smooths the power rectified by rectifier 3, and the voltage generated across smoothing capacitor 5 due to smoothing is not a full-wave rectified waveform of commercial power source 1, but rather a waveform in which a DC component is superimposed with a voltage ripple corresponding to the frequency of commercial power source 1, and does not pulsate significantly. The frequency of this voltage ripple is twice the frequency of the power supply voltage Vs if commercial power source 1 is single-phase, and is mainly six times the frequency if commercial power source 1 is three-phase.

[0014] The bus voltage detection unit 10 is a detection unit that detects the voltage across the smoothing capacitor 5, i.e., 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 is a detection unit that detects the load current Idc, which is a DC current flowing from the smoothing capacitor 5 to the inverter 30, and outputs the detected current value to the control device 100.

[0015] The inverter 30 is connected across the smoothing capacitor 5 and converts the power output from the rectifier 3 and the smoothing capacitor 5 into second AC power having a desired amplitude and phase, i.e., generates the second AC power, and outputs it to the motor 7 that drives a load. Specifically, the inverter 30 receives the bus voltage Vdc and generates a three-phase AC voltage with a variable frequency and voltage value, which is supplied to the motor 7 via output lines 331 to 333. As shown in FIG. 2, the inverter 30 includes an inverter main circuit 310 and a drive circuit 350. Input terminals of the inverter main circuit 310 are connected to the DC buses 12a and 12b. The inverter main circuit 310 includes switching elements 311 to 316. Freewheeling rectifier elements 321 to 326 are connected in anti-parallel to the switching elements 311 to 316, respectively.

[0016] The drive circuit 350 generates drive signals Sr1-Sr6 based on PWM (Pulse Width Modulation) signals Sm1-Sm6 output from the control device 100. The drive circuit 350 controls the on / off of the switching elements 311-316 using the drive signals Sr1-Sr6. This enables the inverter 30 to supply a three-phase AC voltage with variable frequency and voltage to the motor 7 via the output lines 331-333.

[0017] The PWM signals Sm1 to Sm6 are signals having a signal level of a logic circuit, i.e., a magnitude of 0V to 5V. The PWM signals Sm1 to Sm6 are signals with a reference potential equal to 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 to control the switching elements 311 to 316, for example, a magnitude of -15V to +15V. The drive signals Sr1 to Sr6 are signals with a reference potential equal to the potential of the negative terminal, i.e., the emitter terminal, of the corresponding switching elements 311 to 316.

[0018] The motor 7 rotates in accordance with the amplitude and phase of the second AC power supplied from the inverter 30. The motor 7 is used, for example, for compressing the compressor and rotating the fan. In the example of FIG. 1, the motor 7 drives and rotates the outdoor fan 914 of the refrigeration cycle application device 900 as the load, and sends air to the outdoor heat exchanger 910 to cool the outdoor heat exchanger 910. Although FIG. 1 shows the motor 7 with its motor windings in a Y-connection, this is merely an example and is not limiting. The motor windings of the motor 7 may be in a Δ-connection, or may be switchable between a Y-connection and a Δ-connection.

[0019] Note that the arrangement of the components of the power conversion device 200 shown in Fig. 1 is an example, and the arrangement of the components is not limited to the example shown in Fig. 1. For example, the reactor 2 may be arranged after the rectifier 3. Furthermore, the power conversion device 200 may include a booster unit, or the rectifier 3 may be given the function of a booster unit. In the following description, the bus voltage detection unit 10 and the load current detection unit 40 may be collectively referred to as the detection unit. Furthermore, the voltage value detected by the bus voltage detection unit 10 and the current value detected by the load current detection unit 40 may be referred to as the detection value.

[0020] The control device 100 acquires the bus voltage Vdc from the bus voltage detection unit 10 and 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, the on / off of the switching elements 311 to 316 included in the inverter main circuit 310. The control device 100 controls the rotation speed of the motor 7 by controlling the on / off of the switching elements 311 to 316 included in the inverter main circuit 310. The rotation speed of the motor 7 may also be referred to as the rotation speed of the motor 7. This also applies hereinafter. The control device 100 also calculates the load torque of the motor 7. The control device 100 does not need to use all of the detection values ​​acquired from each detection unit, and may perform control using only some of the detection values. In this embodiment, the control device 100 performs control in a rotating coordinate system having a d-axis and a q-axis.

[0021] The following describes the detailed configuration and operation of the control device 100. Fig. 3 is a block diagram showing an example configuration of the control device 100 included in the power conversion device 200 according to the first embodiment. The control device 100 includes an operation control unit 102, an inverter control unit 110, and an operation continuation control unit 121.

[0022] The operation control unit 102 acquires command information Qe from the control unit 920 of the refrigeration cycle applied equipment 900. When the refrigeration cycle applied equipment 900 is an air conditioner, the command information Qe is information based on, for example, a temperature detected by a temperature sensor (not shown), information indicating a set temperature instructed from a remote controller (not shown) which is an operation unit, information on the selection of an operation mode, instruction information for starting and stopping operation, etc. The operation mode is, for example, heating, cooling, dehumidification, etc. The operation control unit 102 also acquires a speed command decrease amount Δω from the operation continuation control unit 121. * The operation control unit 102 acquires the command information Qe and the speed command decrease amount Δω * The frequency command value ωe is used to generate a voltage command value, which is a command value for the voltage to be applied to the motor 7, based on the * The operation control unit 102 generates the frequency command value ωe * Regarding the rotational speed command value ωm * The speed command decrease amount Δω is calculated by multiplying the value by the number of pole pairs Pm of the motor 7. * 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 generates a stop signal St, which is a signal for stopping the operation of the inverter 30, based on the command information Qe. * to the voltage command value calculation unit 115 of the inverter control unit 110, and outputs a stop signal St to the PWM signal generation unit 118 of the inverter control unit 110.

[0023] The inverter control unit 110 includes a current restoration unit 111, a three-phase to two-phase conversion unit 112, a d-axis current command value generation unit 113, a voltage command value calculation unit 115, an electrical phase calculation unit 116, a two-phase to three-phase conversion unit 117, and a PWM signal generation unit 118.

[0024] The current restoration unit 111 restores 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 restoration unit 111 samples the load current Idc detected by the load current detection unit 40 at timings determined based on the PWM signals Sm1 to Sm6 generated by the PWM signal generation unit 118, thereby restoring the phase currents iu, iv, and iw.

[0025] The 3-phase to 2-phase conversion unit 112 converts the phase currents iu, iv, and iw restored by the current restoration unit 111 into a d-axis current id, which is an excitation current, and a q-axis current iq, which is a torque current, i.e., current values ​​of the d- and q-axes, using an electrical phase θe generated by an electrical phase calculation unit 116 described later.

[0026] The d-axis current command value generating unit 113 generates the d-axis current command value Id * Specifically, the d-axis current command value generator 113 generates a q-axis current iq, a bus voltage Vdc, and a d-axis voltage command value Vd * and the q-axis voltage command value Vq * Based on this, the optimum d-axis current command value Id that will be most efficient for driving the motor 7 is calculated. * The d-axis current command value generator 113 calculates 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 * Based on this, the d-axis current command value Id becomes the current phase βm at which the output torque of the motor 7 becomes equal to or greater than the specified value or becomes the maximum, i.e., the current value becomes equal to or less than the specified value or becomes the minimum. * Here, the d-axis current command value generating unit 113 outputs the d-axis current command value Id based on the q-axis current iq, etc. * However, this is just an example and is not limiting. The d-axis current command value generating unit 113 calculates the d-axis current id, the frequency command value ωe * Based on the above, the d-axis current command value Id * The d-axis current command value generator 113 can obtain the d-axis current command value Id * may be determined.

[0027] The voltage command value calculation unit 115 calculates the frequency command value ωe obtained from the operation control unit 102. * the d-axis current id and the q-axis current iq acquired from the three-phase to two-phase conversion unit 112, and the d-axis current command value Id acquired from the d-axis current command value generation unit 113. * Based on this, the d-axis voltage command value Vd * and the q-axis voltage command value Vq * Furthermore, the voltage command value calculation unit 115 generates the d-axis voltage command value Vd * and the q-axis voltage command value Vq * In the process of generating the q-axis current command value Iq * Furthermore, the voltage command value calculation unit 115 generates the d-axis voltage command value Vd * and the q-axis voltage command value Vq * The frequency estimation value ωest is estimated based on the d-axis current id and the q-axis current iq.

[0028] The electrical phase calculation unit 116 calculates the electrical phase θe by integrating the frequency estimate value ωest obtained from the voltage command value calculation unit 115.

[0029] The two-phase to three-phase conversion unit 117 converts the d-axis voltage command value Vd * and the q-axis voltage command value Vq * , that is, the voltage command value in the two-phase coordinate system is calculated by using the electrical phase θe acquired from the electrical phase calculation unit 116 to calculate the three-phase voltage command value Vu * ,Vv * ,Vw * Convert to.

[0030] The PWM signal generation unit 118 converts the three-phase voltage command value Vu obtained from the two-phase to three-phase conversion unit 117 into a three-phase voltage command value Vu * ,Vv * ,Vw * and the stop signal St acquired from the operation control unit 102. The PWM signal generation unit 118 can also stop the motor 7 by not outputting the PWM signals Sm1 to Sm6 based on the stop signal St.

[0031] The configuration and operation of the voltage command value calculation unit 115 will be described in detail. Fig. 4 is a block diagram showing an example configuration of the voltage command value calculation unit 115 provided in the control device 100 of the power conversion device 200 according to the first embodiment. 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.

[0032] The frequency estimation unit 501 estimates 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 based on the frequency command value ωe and output as a frequency estimate value ωest. Note that the frequency estimate value ωest output from the frequency estimator 501 to the outside of the voltage command value calculator 115 in FIG. 4 is the frequency estimate value ωest output from the voltage command value calculator 115 to the electrical phase calculator 116 in FIG. 3. The adder / subtractor 502 estimates the frequency of the voltage supplied to the motor 7 based on the frequency command value ωe * The frequency command value ωe is calculated by subtracting the frequency estimate ωest from * and the frequency estimated value ωest, and outputs the frequency deviation del_ω.

[0033] The speed control unit 503 calculates the q-axis current command value Iq based on the frequency deviation del_ω. * Calculates and outputs the q-axis current command value Iq * is the command value of the q-axis current iq at which the frequency deviation del_ω becomes zero, that is, the frequency command value ωe * is a command value of the q-axis current iq for matching the frequency estimated value ωest. The speed control unit 503 is, for example, a proportional-integral (PI) controller, but is not limited to this. The speed control unit 503 controls the q-axis current command value Iq * is output to the subsequent adding / subtracting unit 505 and also to the operation continuation control unit 121.

[0034] The adder / subtractor 504 calculates the d-axis current command value Id *The d-axis current command value Id is calculated by subtracting the d-axis current id from * The d-axis current control unit 506 is configured, for example, by a PI controller, and outputs the deviation between the d-axis current command value Id * The d-axis current control unit 506 operates to converge the deviation between the first d-axis voltage command value Vdfb * Output.

[0035] The addition / subtraction unit 505 calculates the q-axis current command value Iq * The q-axis current command value Iq is calculated by subtracting the q-axis current iq from * and the q-axis current iq. The q-axis current control unit 507 is configured, for example, by a PI controller, and outputs the deviation between the q-axis current command value Iq * and the q-axis current iq to converge to zero. * Output.

[0036] The multiplication unit 508 calculates the q-axis current command value Iq * is multiplied by the q-axis inductance Lq of the motor 7 and the frequency estimation value ωest to obtain a first d-axis voltage command value Vdfb * Compensation value Vdff * The addition / subtraction unit 509 calculates and outputs the first d-axis voltage command value Vdfb * to compensation value Vdff * is subtracted to obtain the first d-axis voltage command value Vdfb * and compensation value Vdff * Deviation from (Vdfb * -Vdff * ) is converted into the d-axis voltage command value Vd * Output as

[0037] The multiplication unit 510 calculates the d-axis current command value Id * The adder 511 multiplies the output from the multiplier 510 by the d-axis inductance Ld of the motor 7 and outputs the result. The adder 511 adds the magnetic flux linkage vector φf of the motor 7 to the output from the multiplier 510. The multiplier 512 multiplies the output from the adder 511 by the frequency estimate value ωest to obtain a first q-axis voltage command value Vqfb * Compensation value Vqff* The addition / subtraction unit 513 calculates and outputs the first q-axis voltage command value Vqfb * to the compensation value Vqff * is subtracted to obtain the first q-axis voltage command value Vqfb * and compensation value Vqff * Deviation from (Vqfb * -Vqff * ) is converted into the q-axis voltage command value Vq * Output as

[0038] Returning to the description of the control device 100 in Fig. 3, in the control device 100, the operation continuation control unit 121 calculates the d-axis current id acquired from the three-phase to two-phase conversion unit 112 and the q-axis current command value Iq acquired from the voltage command value calculation unit 115. * Based on this, the speed command decrease amount Δω * The operation continuation control unit 121 calculates the speed command decrease amount Δω * is output to the operation control unit 102.

[0039] In this embodiment, when the rotation speed of motor 7 decreases, control device 100 controls the speed command value to decrease so that the difference between the rotation speed and a speed command value for controlling the rotation speed falls within a specified range. For example, when the outdoor heat exchanger 910 changes from a frost-free state (no frost) to a frosted state (frost), the load torque of motor 7 that drives outdoor fan 914 increases in order to maintain the rotation speed of motor 7, and the required current also increases, which may result in an overcurrent state. Therefore, control device 100 controls motor 7 to rotate at a reduced rotation speed in a frosted state using a load torque that is approximately the same as the load torque that can be output in a frost-free state.

[0040] Here, a brief explanation will be given of the load torque. The control device 100 can calculate the load torque, i.e., the estimated load torque Tm, using the current value detected by the load current detection unit 40 and parameters based on the specifications of the motor 7. Specifically, the control device 100 estimates the load torque of the motor 7, i.e., calculates the estimated load torque Tm of the motor 7, using the d-axis current id and q-axis current iq output from the three-phase to two-phase conversion unit 112. The control device 100 calculates the estimated load torque Tm of the motor 7 based on the following equation (1):

[0041] Tm=Pmφaiq+Pm(Ld-Lq)idiq…(1)

[0042] In equation (1), Tm is the estimated load torque, Pm is the number of pole pairs of motor 7, φa 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 rotation speed, i.e., speed, of motor 7 follows the speed command value for controlling the operation of motor 7 and motor 7 operates at a constant speed, the output torque of motor 7 and the load torque of motor 7 have the same magnitude. Therefore, the output torque of equation (1) can be treated as the load torque. As described above, control device 100 obtains the d-axis current id and the q-axis current iq from three-phase to two-phase conversion unit 112, but stores the number of pole pairs Pm of motor 7, the induced voltage constant φa of motor 7, the d-axis inductance Ld of motor 7, and the q-axis inductance Lq of motor 7 in advance.

[0043] 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. FIG. 5 is a diagram showing the 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 in the refrigeration cycle equipment 900. In FIG. 5, the horizontal axis represents the rotation speed of the motor 7, and the vertical axis represents the load torque of the motor 7. In FIG. 5, the solid line with circles plotted represents a polynomial that represents a state when no frost has formed in the refrigeration cycle equipment 900, and the dashed line with squares plotted represents a polynomial that represents a state when frost has formed in the refrigeration cycle equipment 900. The value represented by the solid line with circles plotted is also referred to as the reference set value when no frost has formed. In FIG. 5, the rotation speed of the motor 7 on the horizontal axis may be the rotation speed of the outdoor fan 914. As shown in FIG. 5, even when the rotation speed of the motor 7 is the same, the load torque is greater when frost has formed in the refrigeration cycle equipment 900 than when frost has not formed in the refrigeration cycle equipment 900. Furthermore, the higher the rotation speed of the motor 7, the larger the difference between the load torque when frost has formed in the refrigeration cycle apparatus 900 and the load torque when no frost has formed in the refrigeration cycle apparatus 900. In the example of Fig. 5, when the rotation speed of the motor 7 is 2000 rpm and the state changes from a non-frosted state to a frosted state, the control device 100 reduces the rotation speed of the motor 7 to about 1400 rpm, thereby keeping the output load torque at the same level while allowing the motor 7 to continue rotating, i.e., operating.

[0044] The following describes the detailed configuration and operation of the operation continuation control unit 121 included in the control device 100. Fig. 6 is a block diagram showing an example configuration 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 limiter value calculation unit 141, an addition / subtraction unit 142, a deviation sign processing unit 143, and an output unit 144.

[0045] The limiter value calculation unit 141 calculates the q-axis current command value iq in the addition / subtraction unit 142 using the d-axis current id acquired from the three-phase to two-phase conversion unit 112. *The limiter value calculation unit 141 calculates the limiter value iq_lim based on the following equation (2).

[0046] iq_lim=√(3Ie 2 -id 2 ) …(2)

[0047] In equation (2), iq_lim is a limiter value, Ie is a limiter value of the effective value of the phase current, and id is a d-axis current indicating the current d-axis current value that can be acquired from the three-phase to two-phase conversion unit 112. 2 -id 2 ) is (3Ie 2 -id 2 ) The limiter value iq_lim indicates the magnitude of the current that can be passed as the q-axis current iq, which is the remainder obtained by subtracting the d-axis current id from the limiter value Ie of the effective value of the phase current, in order to give priority to the d-axis current id. The limiter value calculation unit 141 outputs the limiter value iq_lim calculated by calculation to the addition / subtraction unit 142.

[0048] The adder / subtractor 142 obtains the limiter value iq_lim from the limiter value calculator 141 and calculates the q-axis current command value iq * The addition / subtraction unit 142 obtains the q-axis current command value iq from the limiter value iq_lim. * By subtracting the limiter value iq_lim and the q-axis current command value iq * The adder / subtractor 142 calculates the deviation between the limiter value iq_lim and the q-axis current command value iq * The deviation between the two is output to the deviation code processor 143.

[0049] The deviation sign processing unit 143 calculates the limiter value iq_lim calculated by the addition / subtraction unit 142 and the q-axis current command value iq * The speed command decrease amount Δω is output from the output unit 144 to the operation control unit 102 based on the deviation from the * Specifically, the deviation sign processor 143 controls the limiter value iq_lim and the q-axis current command value iq *When the deviation from the q-axis current command value iq is 0 or more, * is equal to or less than the limiter value iq_lim, the output unit 144 outputs the speed command decrease amount Δω * = 0. The deviation sign processor 143 controls the limiter value iq_lim and the q-axis current command value iq * When the deviation from the q-axis current command value iq is less than 0, * is greater than the limiter value iq_lim, the output unit 144 outputs the speed command decrease amount Δω * The limiter value iq_lim and the q-axis current command value iq * For deviations from K Iac The output is controlled so that the value obtained by integral control using / S is output. Iac is the integral gain of the integral control, and K Iac The S in the denominator of / S represents the Laplace operator.

[0050] The output unit 144 outputs the speed command decrease amount Δω based on the control of the deviation code processing unit 143. * =0, or speed command decrease amount Δω * The limiter value iq_lim and the q-axis current command value iq * For deviations from K Iac The value obtained by integral control using / S is output to the operation control unit 102.

[0051] In this way, the control device 100 determines the q-axis current command value Iq * The q-axis current command value Iq is the limiter value iq_lim of the q-axis current * The q-axis current command value Iq *The control device 100 sets a limiter value iq_lim, which is a q-axis current limiter value, based on a limiter value Ie of the effective value of the phase current, which is the current of each phase flowing from the power conversion device 200 to the motor 7, and a d-axis current id, which is the current d-axis current value. As a result, in the example of FIG. 5 , if the rotation speed of the motor 7 changes from a frost-free state to a frosted state when the rotation speed of the motor 7 is 2000 rpm, the control device 100 can continue the rotation, i.e., operation, of the motor 7 while maintaining the same output load torque by setting the rotation speed of the motor 7 to approximately 1400 rpm. In other words, even if an event occurs in which the load torque of the motor 7 increases, the control device 100 controls the rotation of the motor 7 while maintaining the maximum current in the power conversion device 200 by controlling the rotation speed of the motor 7 to decrease by the amount that exceeds the limiter value iq_lim.

[0052] The method by which the limiter value calculation unit 141 calculates the limiter value iq_lim is not limited to the example of equation (2). The limiter value iq_lim calculated by the limiter value calculation unit 141 may be calculated by another method as long as it is possible to control the rotation of the motor 7 while maintaining the maximum current in the power conversion device 200. For example, the limiter value calculation unit 141 may calculate the limiter value iq_lim from the perspective of voltage saturation.

[0053] FIG. 7 is a diagram showing differences in characteristics depending on whether or not continuous operation control is performed by the continuous operation control unit 121 of the control device 100 included in the power conversion device 200 according to the first embodiment. In FIG. 7, the left side shows a case where continuous operation control is not performed by the continuous operation control unit 121, and the right side shows a case where continuous operation control is performed by the continuous operation control unit 121. In addition, in both cases where continuous operation control is not performed and where continuous operation control is performed, the first row of FIG. 7 shows the rotation speed of the motor 7, the second row of FIG. 7 shows the torque of the motor 7, the third row of FIG. 7 shows the phase currents iu, iv, and iw of the motor 7, and the fourth row of FIG. 7 shows the q-axis current iq of the motor 7. In all graphs, the horizontal axis represents time. As shown in FIG. 7, the second, third, and fourth rows of graphs are similar in both cases where continuous operation control is not performed and where continuous operation control is performed.

[0054] Without continuous operation control, the first graph on the left side of FIG. 7 shows a state in which the command value diverges from the estimated speed and the actual speed. This indicates that the power conversion device 200 attempts to rotate the motor 7 using constant torque control or maximum torque, but the torque required to rotate the motor 7 increases due to factors such as frosting, making it impossible to achieve the desired rotation speed, i.e., the rotation speed indicated by the command value. If the command value diverges from the estimated speed and the actual speed continuously, control is likely to become unstable, such as through windup, which is undesirable for the control device 100. In contrast, with continuous operation control, the first graph on the right side of FIG. 7 shows that, after a specified time has elapsed since the start of continuous operation control, the command value decreases, eliminating the divergence between the command value and the estimated speed and the actual speed. This allows the control device 100 to avoid a situation in which the command value diverges from the estimated speed and the actual speed continuously and achieve a stable control state.

[0055] The operation of the power conversion device 200, which is a feature of the first embodiment, will be described using a flowchart. FIG. 8 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 a limiter value iq_lim for the q-axis current command value Iq* (step S1). The operation continuation control unit 121 calculates a limiter value iq_lim for the q-axis current command value Iq* obtained from the limiter value iq_lim and the voltage command value calculation unit 115. * The operation continuation control unit 121 calculates the deviation between the limiter value iq_lim and the q-axis current command value iq * When the deviation from the q-axis current command value iq is 0 or more, * is equal to or less than the limiter value iq_lim (step S3: Yes), the speed command decrease amount Δω * = 0 to the operation control unit 102 (step S4). * When the deviation from the q-axis current command value iq is less than 0, *is greater than the limiter value iq_lim (step S3: No), the speed command decrease amount Δω * The limiter value iq_lim and the q-axis current command value iq * For deviations from K Iac The value obtained by integral control using / S is output to the operation control unit 102 (step S5).

[0056] As in this embodiment, the q-axis current command value Iq * is limited by the limiter value iq_lim when, as described above, the load torque of the motor 7 simply increases and the q-axis current command value Iq * In some cases, the q-axis current command value Iq is limited by a limiter value iq_lim, but is not limited to this. * is limited by the limiter value iq_lim, for example, the speed may decrease after the control device 100 has performed the flux-weakening control to the limit, causing a deviation in the input of the speed control unit 503, and the q-axis current command value Iq * This includes cases where the value iq_lim is limited by the limiter value iq_lim.

[0057] Next, a description will be given of the hardware configuration of the control device 100 included in the power conversion device 200. Fig. 9 is a diagram illustrating an example of a hardware configuration that realizes the control device 100 included in the power conversion device 200 according to the first embodiment. The control device 100 is realized by a processor 91 and a memory 92.

[0058] 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 (Electrically Erasable Programmable Read Only Memory). However, the memory 92 is not limited to these, and may also be a magnetic disk, optical disk, compact disk, minidisc, or DVD (Digital Versatile Disc).

[0059] As described above, according to this embodiment, in the power conversion device 200, the operation continuation control unit 121 of the control device 100 controls the q-axis current command value Iq calculated by the voltage command value calculation unit 115. * is greater than the limiter value iq_lim calculated in consideration of maintaining the maximum current in the power conversion device 200, the limiter value iq_lim and the q-axis current command value iq * For deviations from K Iac / S is the value obtained by integral control, and the speed command decrease amount Δω * The operation control unit 102 outputs the speed command decrease amount Δω from the frequency command value obtained by calculation. * The frequency command value ωe is *to the voltage command value calculation unit 115. As a result, even if an event occurs in which the load torque of the motor 7 increases, the control device 100 controls the rotation speed of the motor 7 to decrease by the amount that exceeds the limiter value iq_lim, thereby enabling the motor 7 to continue rotating while maintaining the maximum current in the power conversion device 200. Even if the load torque of the motor 7 connected to the power conversion device 200 increases, the control device 100 can continue operating the motor 7 while suppressing a decrease in the rotation speed of the motor 7.

[0060] In this embodiment, the motor 7 targeted by the control device 100 is a fan motor that rotates the outdoor fan 914, but the present invention is not limited to this. The control device 100 can also perform similar control on motors 7 other than fan motors, as long as a similar event that increases the load torque occurs.

[0061] Embodiment 2 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. * becomes larger than the limiter value iq_lim, the continuous operation control is started. In the second embodiment, other timings at which the continuous operation control unit 121 starts the continuous operation control will be described.

[0062] The operation continuation control unit 121 may start the operation continuation control when the estimated speed of the motor 7 becomes smaller than the speed command value for the motor 7. The state when the estimated speed of the motor 7 becomes smaller than the speed command value for the motor 7 is as shown in the first graph on the left side of Fig. 7. The operation continuation control unit 121 can obtain the same effect as in the first embodiment by determining whether or not to perform the operation continuation control using the estimated speed of the motor 7 and the speed command value for the motor 7.

[0063] The operation continuation control unit 121 determines the q-axis current command value Iq *and limiter value iq_lim are defined as a first condition, and the aforementioned estimated speed of motor 7 and a speed command value for motor 7 are defined as a second condition. If the first condition or the second condition continues for a specified period, the continuous operation control may be initiated. This case is defined as a third condition. Generally, even during normal control by power conversion device 200, motor 7 may temporarily enter a state satisfying the first or second condition by accelerating or decelerating. Therefore, in order to eliminate cases where the first or second condition temporarily occurs due to normal control by power conversion device 200, the continuous operation control unit 121 may determine to initiate the continuous operation control when the period in which the first or second condition is satisfied continues for a specified period, as in the third condition. That is, the operation continuation control unit 121 can reduce the speed command value when a first condition is met in which the speed command value is limited by a specified limiter value iq_lim, or when a second condition is met in which the rotation speed of the motor 7 is smaller than the speed command value, or when a third condition is met in which the first condition or the second condition continues for a specified period. It can also be said that the operation continuation control unit 121 reduces the speed command value when it becomes impossible to control the rotation speed of the motor 7 to follow the speed command value.

[0064] Although the timing at which the continuous operation control unit 121 starts the continuous operation control has been described, the continuous operation control unit 121 can stop the continuous operation control when any of the requirements of the first condition, the second condition, or the third condition is no longer satisfied. However, if the same value is used to determine when to start the continuous operation control and when to stop the continuous operation control, it is possible that the start and stop of the continuous operation control will be repeated frequently in some cases. Therefore, taking hysteresis into consideration, the continuous operation control unit 121 may use different values ​​as criteria to determine when to start the continuous operation control and when to stop the continuous operation control.

[0065] In this way, the operation continuation control unit 121 can make a decision based on several conditions when starting the operation continuation control. The operation continuation control unit 121 can also make a decision based on several conditions when stopping the operation continuation control.

[0066] Embodiment 3 In the third embodiment, the operation continuation control of the operation continuation control unit 121 is Yo A case where the calculation process in the speed control section 503 of the voltage command value calculation section 115 is changed will be described below.

[0067] FIG. 10 is a diagram illustrating an image of the calculation process in the power conversion device 200 according to the third embodiment. FIG. 10 excerpts a part of the calculation process in the power conversion device 200 and shows the calculation flow of the excerpted part. In FIG. 10, the limiter value indicates the limiter value iq_lim calculated by the limiter value calculation unit 141, the next addition / subtraction process indicates the process of the addition / subtraction unit 142, and the next speed drooping control indicates the K Iac / S, the next addition processing indicates the internal processing of the voltage command value calculation unit 115, and the next speed control indicates the calculation processing in the speed control unit 503. In the control device 100, when the operation continuation control unit 121 is performing the operation continuation control, the q-axis current command value Iq * is limited to the limiter value iq_lim. In this case, the integral control for the anti-windup process is stopped in the speed control unit 503. Therefore, when the operation continuation control unit 121 is performing the operation continuation control, the speed control unit 503 controls the q-axis current command value Iq only by proportional control, as shown in the lower part of FIG. * is calculated, that is, the q-axis current command value Iq * The speed control when calculating may be performed by proportional control.

[0068] In such a case, the integral gain K Iac can be expressed as equation (3).

[0069] K Iac=(ωac / ωsc)×(Pm 2 ·φa / J) …(3)

[0070] 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, φa is the induced voltage constant of the motor 7, and J is the inertia of the motor 7.

[0071] In this way, the control device 100 can also change the calculation formula etc. as appropriate depending on the control state.

[0072] Embodiment 4 Fig. 11 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to the fourth embodiment. The refrigeration cycle-applied device 900 according to the fourth embodiment includes a power conversion device 200. The refrigeration cycle-applied device 900 according to the fourth embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 11, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0073] As described above, the refrigeration cycle device 900 includes a motor 7a similar to the motor 7 in the first embodiment, and an outdoor fan 914. The motor 7a drives and rotates the outdoor fan 914. The outdoor fan 914 sends air to an outdoor heat exchanger 910. The outdoor heat exchanger 910 exchanges heat between the refrigerant flowing therethrough and the air. The refrigeration cycle device 900 also includes a compressor 8 incorporating a motor 7b similar to the motor 7 in the first embodiment, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and the outdoor heat exchanger 910, all of which are attached via refrigerant piping 912.

[0074] Inside the compressor 8, a compression mechanism 904 that compresses the refrigerant and a motor 7b that operates the compression mechanism 904 are provided.

[0075] The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by a motor 7b that is variably controlled in speed.

[0076] During heating operation, as shown by the solid arrows, the refrigerant is pressurized by the compression mechanism 904 and sent out, passes 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, and returns to the compression mechanism 904.

[0077] During cooling operation, as indicated by the dashed arrow, the refrigerant is pressurized by the compression mechanism 904 and sent out, passes 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 and returns to the compression mechanism 904.

[0078] 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 decompresses and expands the refrigerant.

[0079] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention. [Explanation of symbols]

[0080] 1 Commercial power supply, 2 Reactor, 3 Rectifier, 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 restoration unit, 112 3-phase 2-phase conversion unit, 113 d-axis current command value generation unit, 115 Voltage command value calculation unit, 116 Electrical phase calculation unit, 117 2-phase 3-phase conversion unit, 118 PWM signal generation unit, 121 Operation continuation control unit, 131 to 134, 321 to 326 Rectifier element, 141 Limiter value calculation unit, 142, 502, 504, 505, 509, 513 Addition and subtraction unit, 143 Deviation code processing unit, 144 output unit, 200 power conversion device, 310 inverter main circuit, 311 to 316 switching elements, 331 to 333 output lines, 350 drive circuit, 400 motor drive 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 unit, 511 addition unit, 900 refrigeration cycle applied 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, a rectification unit that rectifies first AC power supplied from a commercial power source; a capacitor connected to an output terminal of the rectifier; an inverter connected to both ends of the capacitor to generate second AC power and output the second AC power to a motor that drives a load; a control device that controls the operation of the inverter to control the rotation speed of the motor; Equipped with the control device reduces the speed command value when the rotation speed of the motor decreases so that a difference between the rotation speed and a speed command value for controlling the rotation speed falls within a specified range; reducing the q-axis current command value by an amount corresponding to the q-axis current command value exceeding a q-axis current limiter value of the q-axis current command value, which is the speed command value; setting the q-axis current limiter value based on a limiter value of an effective value of a phase current, which is a current of each phase flowing from the power conversion device to the motor, and a current d-axis current value; Power conversion device.

2. the control device reduces the speed command value when it becomes impossible to control the rotation speed to follow the speed command value. The power conversion device according to claim 1 .

3. the control device reduces the speed command value when a first condition is satisfied that the speed command value is limited by a specified limiter value, or 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 specified period. The power conversion device according to claim 1 .

4. the control device performs speed control by proportional control when calculating the q-axis current command value. The power conversion device according to claim 1 .

5. A motor drive device comprising the power conversion device according to any one of claims 1 to 4.

6. A refrigeration cycle device comprising the power conversion device according to any one of claims 1 to 4.

Images