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

Abstract

A power conversion device (300) comprises: a converter (3) that rectifies power-supply voltage applied from an AC power supply (1); a capacitor (5) that is connected to the output end of the converter (3); an inverter (30) that is connected to both ends of the capacitor (5); and a control device (10) that controls the operation of the inverter (30). When a command modulation rate indicating the ratio of a voltage command amplitude in a voltage command applied to the inverter (30) to a DC voltage value applied to the inverter (30) exceeds 1, the power conversion device (300) corrects the voltage command so that the output voltage of the inverter (30) can be output linearly. When a voltage saturation amount occurs that is calculated from the voltage command and a voltage limit value determined by the DC voltage value, the power conversion device (300) performs flux-weakening control.

Description

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

[0001] The present disclosure relates to a power conversion device that performs power conversion, and an electric motor drive device and a refrigeration cycle application device that are provided with the power conversion device.

[0002] In power conversion devices, a control called "overmodulation control" is performed to increase the voltage utilization rate of the inverter. The overmodulation region, where overmodulation control is performed, is a region where the relationship between the voltage command and the inverter output voltage, which is the output voltage of the inverter, is nonlinear and not proportional. For this reason, overmodulation control performs a correction called a "modulation factor correction method" that corrects the command modulation factor, which indicates the ratio of the voltage command amplitude in the voltage command given to the inverter to the DC voltage value applied to the inverter, so that the inverter output voltage is output linearly.

[0003] By controlling the d-axis current so as to reduce the apparent magnetic flux even during overmodulation, a control called "flux-weakening control" is performed, which allows the motor to rotate even when the rotation speed or torque is high. Patent Document 1 listed below describes a general technique related to flux-weakening control.

[0004] Japanese Patent Application Laid-Open No. 2006-20411

[0005] However, when the modulation factor correction method and the flux-weakening control are simply combined, the voltage command value becomes excessive due to the modulation factor correction, which poses a problem that operation in the overmodulation region tends to become unstable. For this reason, some kind of ingenuity is required when combining the modulation factor correction method and the flux-weakening control.

[0006] The present disclosure has been made in consideration of the above, and aims to provide a power conversion device that can stabilize operation in the overmodulation region even when a modulation factor correction method and flux-weakening control are combined.

[0007] To solve the above-mentioned problems and achieve the object, a power conversion device according to the present disclosure is a power conversion device that supplies AC power to an electric motor that drives a load. The power conversion device includes a converter that rectifies a power supply voltage applied from an AC power supply, a capacitor connected to an output terminal of the converter, an inverter connected across the capacitor, and a control device that controls the operation of the inverter. When a command modulation factor indicating the ratio of a voltage command amplitude in a voltage command applied to the inverter to a DC voltage value applied to the inverter exceeds 1, the power conversion device corrects the voltage command so that the inverter output voltage can be output linearly, and performs flux-weakening control when a voltage saturation amount calculated from the voltage command and a voltage limit value determined by the DC voltage value occurs.

[0008] The power conversion device according to the present disclosure has the advantage that it is possible to stabilize operation in the overmodulation region even when the modulation factor correction method and the flux-weakening control are combined.

[0009] FIG. 1 is a diagram showing an example of the configuration of an inverter included in the power conversion device according to embodiment 1;

[0010] Hereinafter, a power conversion device, an electric 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 accompanying drawings.

[0011] First Embodiment. Fig. 1 is a diagram illustrating a configuration example of a power conversion device 300 according to a first embodiment. Fig. 2 is a diagram illustrating a configuration example of an inverter 30 included in the power conversion device 300 according to the first embodiment. The power conversion device 300 is connected to an AC power source 1 and a compressor 50. The compressor 50 is an example of a load having a characteristic in which the load torque fluctuates periodically when driven. The compressor 50 includes an electric motor 7. An example of the electric motor 7 is a three-phase permanent magnet synchronous motor. The power conversion device 300 converts a power supply voltage applied from the AC power source 1 into an AC voltage having a desired amplitude and phase and applies the AC voltage to the electric motor 7. The power conversion device 300 includes a reactor 2, a converter 3, a capacitor 5, a voltage detection unit 8, a control device 10, an inverter 30, and a current detection unit 40. The power conversion device 300 and the electric motor 7 included in the compressor 50 form an electric motor drive device 400.

[0012] Converter 3 includes four diodes D1, D2, D3, and D4. The four diodes D1 to D4 are bridge-connected to form a rectifier circuit. Converter 3 rectifies the power supply voltage applied from AC power supply 1 using the rectifier circuit formed by the four diodes D1 to D4. One end of the input side of converter 3 is connected to AC power supply 1 via reactor 2, and the other end of the input side is also connected to AC power supply 1. In addition, converter 3 has an output side connected to capacitor 5.

[0013] The converter 3 may have a boost function for boosting the rectified voltage in addition to the rectification function. A converter with a boost function may be configured with one or more transistor elements, or one or more switching elements in which a transistor element and a diode are connected in anti-parallel, in addition to or instead of a diode. The arrangement and connection of the transistor elements or switching elements in a converter with a boost function are well known, and therefore will not be described here.

[0014] The capacitor 5 is connected to the output terminal of the converter 3 via DC buses 9a and 9b. The DC bus 9a is a positive DC bus, and the DC bus 9b is a negative DC bus. The capacitor 5 smoothes the rectified voltage applied from the converter 3. Examples of the capacitor 5 include an electrolytic capacitor and a film capacitor.

[0015] The inverter 30 is connected to both ends of the capacitor 5 via the DC buses 9a and 9b. The inverter 30 converts the DC voltage smoothed by the capacitor 5 into an AC voltage for the compressor 50 and applies it to the motor 7 of the compressor 50. The voltage applied to the motor 7 is a three-phase AC voltage whose frequency and voltage value are variable.

[0016] 2, the inverter 30 includes an inverter main circuit 310 and a drive circuit 350. The inverter main circuit 310 includes switching elements 311 to 316. Freewheeling rectifying elements 321 to 326 are connected in anti-parallel to the switching elements 311 to 316, respectively.

[0017] In the inverter main circuit 310, the switching elements 311 to 316 are assumed to be IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), etc., but any elements capable of switching may be used. Note that if the switching elements 311 to 316 are MOSFETs, the same effect can be obtained without connecting the freewheeling rectifier elements 321 to 326 in anti-parallel because MOSFETs have parasitic diodes due to their structure.

[0018] Furthermore, the material forming the switching elements 311 to 316 is not limited to silicon (Si), and wide bandgap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), diamond, etc. Forming the switching elements 311 to 316 using wide bandgap semiconductors can further reduce loss.

[0019] 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 10. The drive circuit 350 controls the on / off of the switching elements 311 to 316 using the drive signals Sr1 to Sr6. This enables the inverter 30 to apply a variable frequency and variable voltage three-phase AC voltage to the electric motor 7 via the output lines 331 to 333.

[0020] The PWM signals Sm1 to Sm6 are signals having a signal level of a logic circuit, for example, a magnitude of 0 V to 5 V. The PWM signals Sm1 to Sm6 are signals with the ground potential of the control device 10 as a reference potential. 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 −15 V to +15 V. The drive signals Sr1 to Sr6 are signals with the potential of the negative terminal, i.e., the emitter terminal, of the corresponding switching element as a reference potential.

[0021] The voltage detection unit 8 detects the bus voltage Vdc by detecting the voltage across the capacitor 5. The bus voltage Vdc is the voltage between the DC buses 9a and 9b. The voltage detection unit 8 includes, for example, a voltage divider circuit that divides the voltage using resistors connected in series. The voltage detection unit 8 converts the detected bus voltage Vdc using the voltage divider circuit to a voltage suitable for processing in the control device 10, for example, a voltage of 5 V or less, and outputs the voltage detection signal, which is an analog signal, to the control device 10. The voltage detection signal output from the voltage detection unit 8 to the control device 10 is converted from an analog signal to a digital signal by an AD (Analog to Digital) converter (not shown) within the control device 10 and is used for internal processing in the control device 10.

[0022] The current detection unit 40 includes a shunt resistor inserted in the DC bus 9b. The current detection unit 40 detects the capacitor output current i.d.c. using the shunt resistor. The capacitor output current i.d.c. is the input current to the inverter 30, i.e., the current output from the capacitor 5 to the inverter 30. The current detection unit 40 outputs the detected capacitor output current i.d.c. to the control device 10 as a current detection signal, which is an analog signal. The current detection signal output from the current detection unit 40 to the control device 10 is converted from an analog signal to a digital signal by an AD conversion unit (not shown) within the control device 10 and is used for internal processing in the control device 10.

[0023] The control device 10 generates the above-mentioned PWM signals Sm1 to Sm6 to control the operation of the inverter 30. Specifically, the control device 10 changes the angular frequency ωe and voltage value of the inverter output voltage based on the PWM signals Sm1 to Sm6.

[0024] The angular frequency ωe of the inverter output voltage determines the rotational angular velocity of the electric motor 7 in terms of electrical angle. In this paper, this rotational angular velocity will also be represented by the same symbol ωe. The rotational angular velocity ωm of the electric motor 7 in terms of mechanical angle is equal to the rotational angular velocity ωe of the electric motor 7 divided by the number of pole pairs P. Therefore, there is a relationship expressed by the following equation (1) between the rotational angular velocity ωm of the electric motor 7 in terms of mechanical angle and the angular frequency ωe of the inverter output voltage. In this paper, the rotational angular velocity will sometimes be simply referred to as the "rotational speed" and the angular frequency will sometimes be simply referred to as the "frequency."

[0025] ωm=ωe / P…(1)

[0026] Next, a description will be given of the control device 10. Fig. 3 is a block diagram showing an example of the configuration of the control device 10 provided in the power conversion device 300 according to embodiment 1. The control device 10 includes an operation control unit 11 and an inverter control unit 12.

[0027] The operation control unit 11 receives command information Qe from the outside and generates a frequency command ωe* based on this command information Qe. The frequency command ωe* can be calculated by multiplying the rotation speed command ωm*, which is a command for the rotation speed of the electric motor 7, by the number of pole pairs P, as shown in the following equation (2).

[0028] ωe*=ωm*×P…(2)

[0029] When controlling an air conditioner as a refrigeration cycle-applied device, the control device 10 controls the operation of each part of the air conditioner based on command information Qe. The command information Qe is, for example, a temperature detected by a temperature sensor (not shown), information indicating a set temperature instructed from a remote control (not shown), which is an operation unit, information on the selection of an operation mode, and instruction information for starting and stopping operation. The operation mode is, for example, heating, cooling, dehumidification, etc. The operation control unit 11 may be located outside the control device 10. In other words, the control device 10 may be configured to obtain a frequency command ωe* from an external device.

[0030] The inverter control unit 12 includes a voltage command calculation unit 13, an electrical angle phase calculation unit 14, a space vector modulation unit 15, a PWM signal generation unit 16, a current restoration unit 17, a coordinate conversion unit 18, and an excitation current command control unit 19.

[0031] The current restoration unit 17 restores the phase currents iu, iv, and iw flowing through the motor 7 based on the capacitor output current idc detected by the current detection unit 40, and inputs the restored phase currents to the coordinate conversion unit 18. The current restoration unit 17 can restore the phase currents iu, iv, and iw by sampling the detected value of the capacitor output current idc detected by the current detection unit 40 at timing determined based on the PWM signals Sm1 to Sm6 generated by the PWM signal generation unit 16. Note that current detectors may be provided on the output lines 331 to 333 to directly detect the phase currents iu, iv, and iw and input them to the coordinate conversion unit 18. In this configuration, the current restoration unit 17 is not necessary.

[0032] The coordinate conversion unit 18 converts the phase currents iu, iv, iw restored by the current restoration unit 17 into a d-axis current id, which is an excitation current, and a q-axis current iq, which is a torque current, i.e., into current values ​​on the d- and q-axes, using the electrical angle phase θe generated by the electrical angle phase calculation unit 14, which will be described later.

[0033] The excitation current command control unit 19 generates a d-axis current command id*, which is an excitation current command, based on the q-axis current iq obtained from the coordinate conversion unit 18, the command modulation factor M obtained from the operation control unit 11, and the d-axis voltage command Vd** and q-axis voltage command Vq** calculated by the voltage command calculation unit 13 (described later). The excitation current command control unit 19 calculates a current phase angle at which the output torque of the electric motor 7 is equal to or greater than a set value or at its maximum value, and calculates the d-axis current command id* based on the calculated current phase angle. When calculating the d-axis current command id*, the excitation current command control unit 19 performs flux-weakening control and command modulation factor correction to determine the d-axis current command id*. The specific configuration and operation of the excitation current command control unit 19 will be described later. The excitation current command control unit 19 may calculate the d-axis current command id* using the motor current flowing through the electric motor 7 instead of the output torque of the electric motor 7. In this case, the d-axis current command id* is calculated based on the current phase angle at which the motor current flowing through the motor 7 is equal to or less than the set value or is at the minimum value.

[0034] The voltage command calculation unit 13 generates a d-axis voltage command Vd**, a q-axis voltage command Vq**, a frequency estimate ωest, a command modulation factor M*, and a voltage phase θv based on the frequency command ωe* acquired from the operation control unit 11, the d-axis current id and q-axis current iq acquired from the coordinate conversion unit 18, and the d-axis current command id* acquired from the excitation current command control unit 19. The command modulation factor M* and the voltage phase θv are used by the space vector modulation unit 15, the d-axis voltage command Vd** and the q-axis voltage command Vq** are used by the excitation current command control unit 19, and the frequency estimate ωest is used inside the electrical angle phase calculation unit 14 and the voltage command calculation unit 13. In this paper, when the command modulation factor M acquired from the operation control unit 11 and the command modulation factor M* calculated by the voltage command calculation unit 13 are distinguished without signs, the former will be referred to as a "first command modulation factor" and the latter will be referred to as a "second command modulation factor."

[0035] The electrical angle phase calculation unit 14 calculates the electrical angle phase θe by integrating the frequency estimate value ωest obtained from the voltage command calculation unit 13 .

[0036] The space vector modulation unit 15 generates three-phase voltage commands Vu*, Vv*, and Vw*, which are output voltage commands in a three-phase coordinate system, using the command modulation factor M* and voltage phase θv obtained from the voltage command calculation unit 13, and the electrical angle phase θe obtained from the electrical angle phase calculation unit 14.

[0037] The PWM signal generation unit 16 generates PWM signals Sm1 to Sm6 based on the three-phase voltage commands Vu*, Vv*, and Vw* obtained from the space vector modulation unit 15. Space vector modulation is a modulation method that combines six basic space vectors and two zero vectors to generate voltage vectors of any magnitude at any position in a hexagon and in a vector space within the hexagon. For each PWM modulation cycle, the PWM signal generation unit 16 uses the switching pattern of two adjacent space vectors during a specified period and the zero vector during the remaining period to generate PWM signals Sm1 to Sm6 whose switching patterns and pulse on times are controlled, and outputs the PWM signals to the inverter 30.

[0038] As described above, in a power conversion device, overmodulation control is performed to increase the voltage utilization rate of the inverter. FIG. 4 is a diagram showing the relationship between the command modulation rate and the actual modulation rate in a typical inverter. In FIG. 4, the region where the command modulation rate shown on the horizontal axis exceeds 1 is the overmodulation region. The command modulation rate is a value indicating the ratio of the voltage command amplitude in the voltage command given to the inverter 30 to the DC voltage value applied to the inverter 30. The actual modulation rate shown on the vertical axis is a value indicating the ratio of the inverter output voltage to the DC voltage value. As shown in FIG. 4, the relationship between the command modulation rate and the actual modulation rate is a nonlinear characteristic.

[0039] 5 is a diagram illustrating the modulation factor correction method described in the Background Art section. The overmodulation region is a region in which the relationship between the voltage command and the inverter output voltage is nonlinear and not proportional. Therefore, in this overmodulation region, as shown in FIG. 5, control is performed to obtain the intended inverter output voltage by multiplying the actual modulation factor by a nonlinear modulation factor correction coefficient according to the value of the actual modulation factor.

[0040] However, as shown in the characteristics of Figure 5, the value of the modulation factor correction coefficient in the modulation factor correction method exhibits a steep characteristic with respect to the actual modulation factor value. For this reason, as explained in the background art section, simply combining the modulation factor correction method and flux-weakening control can cause the voltage command to become excessively large due to the modulation factor correction, which can lead to a problem of unstable operation in the overmodulation region. Therefore, this paper proposes the following two methods to address this problem.

[0041] (1) First method: A method of performing flux-weakening control using a voltage command after modulation factor correction. (2) Second method: A method of performing flux-weakening control using a voltage command before modulation factor correction.

[0042] Hereinafter, the first method will be described in the first embodiment, and the second method will be described in the second embodiment.

[0043] 6 is a block diagram showing an example of the configuration of the voltage command calculation unit 13 included in the control device 10 of the power conversion device 300 according to Embodiment 1. The voltage command calculation unit 13 includes adders 130, 132, and 133, a speed controller 131, a d-axis current controller 134, a q-axis current controller 135, a frequency estimation unit 136, a voltage command amplitude calculation unit 137, a modulation factor correction coefficient calculation unit 138, and a command modulation factor and voltage phase calculation unit 140.

[0044] The frequency estimator 136 estimates the frequency of the voltage applied to the motor 7 based on the d-axis current id, the q-axis current iq, the d-axis voltage command Vd*, and the q-axis voltage command Vq*, and outputs the frequency estimated value ωest. Note that the frequency estimated value ωest output from the frequency estimator 136 to the outside of the voltage command calculator 13 in Fig. 6 is the frequency estimated value ωest output from the voltage command calculator 13 to the electrical angle phase calculator 14 in Fig. 3. The adder / subtractor 130 subtracts the frequency estimated value ωest from the frequency command ωe*, and outputs a frequency deviation del_ω between the frequency command ωe* and the frequency estimated value ωest.

[0045] The speed controller 131 calculates and outputs a q-axis current command iq*, which is a torque current command, based on the frequency deviation del_ω. The q-axis current command iq* is a command value of the q-axis current iq that makes the frequency deviation del_ω zero, that is, a command value of the q-axis current iq that makes the frequency command ωe* coincide with the frequency estimated value ωest. An example of the speed controller 131 is a proportional-integral (PI) controller, but is not limited to this example.

[0046] The adder-subtractor 132 subtracts the d-axis current id from the d-axis current command id* and outputs the deviation between the d-axis current command id* and the d-axis current id. The d-axis current controller 134 performs PI control to converge the deviation between the d-axis current command id* and the d-axis current id to zero. During this PI control, the d-axis current controller 134 may perform reduction control to reduce pulsating components generated due to the dead time of the switching elements 311 to 316 of the inverter 30 and the induced voltage distortion of the motor 7, or may perform decoupling control to suppress mutual interference with the d-axis due to the q-axis current command iq*. The d-axis current controller 134 outputs a d-axis voltage command Vd* using PI control.

[0047] The adder-subtractor 133 subtracts the q-axis current iq from the q-axis current command iq* and outputs the deviation between the q-axis current command iq* and the q-axis current iq. The q-axis current controller 135 performs PI control to converge the deviation between the q-axis current command iq* and the q-axis current iq to zero. During this PI control, the q-axis current controller 135 may perform reduction control to reduce pulsating components generated due to the dead time of the switching elements 311 to 316 of the inverter 30 and the induced voltage distortion of the motor 7, or may perform decoupling control to suppress mutual interference with the q-axis due to the d-axis current command id*. The q-axis current controller 135 outputs the q-axis voltage command Vq* using PI control.

[0048] The voltage command amplitude calculation unit 137 calculates a voltage command amplitude Vdq*_abs shown in the following equation (3) using the d-axis voltage command Vd* and the q-axis voltage command Vq*.

[0049] Vdq*_abs=√(Vd* ２ +Vq* ２ ) … (3)

[0050] The voltage command amplitude Vdq*_abs calculated by the voltage command amplitude calculation unit 137 is divided by a value obtained by multiplying the bus voltage Vdc by 1 / √2, and the result is input to the modulation factor correction coefficient calculation unit 138 .

[0051] The modulation factor correction coefficient calculation unit 138 calculates a modulation factor correction coefficient K using the voltage command amplitude Vdq*_abs. The modulation factor correction coefficient calculation unit 138 holds a table of characteristics such as those shown in FIG. 5 . The modulation factor correction coefficient calculation unit 138 recognizes an input value as a command modulation factor, and when the input value is 1 or less, sets the value of the modulation factor correction coefficient K by which the command modulation factor is multiplied to "1.0." When the voltage command amplitude Vdq*_abs exceeds 1, the modulation factor correction coefficient calculation unit 138 sets and outputs the corresponding value of the modulation factor correction coefficient K. Note that the means for realizing the modulation factor correction coefficient calculation unit 138 does not have to be a table. For example, the modulation factor correction coefficient calculation unit 138 may be configured to determine the value of the modulation factor correction coefficient K corresponding to the command modulation factor by calculation processing.

[0052] Inside the voltage command calculation unit 13, the d-axis voltage command Vd* is multiplied by the modulation factor correction coefficient K, and the multiplied value is output as the d-axis voltage command Vd**. Similarly, inside the voltage command calculation unit 13, the q-axis voltage command Vq* is multiplied by the modulation factor correction coefficient K, and the multiplied value is output as the q-axis voltage command Vq**. In this paper, when the d-axis voltage command Vd* before being multiplied by the modulation factor correction coefficient K and the d-axis voltage command Vd** after being multiplied by the modulation factor correction coefficient K are distinguished without signs, the former will be referred to as the "first d-axis voltage command" and the latter will be referred to as the "second d-axis voltage command." Similarly, when the q-axis voltage command Vq* before being multiplied by the modulation factor correction coefficient K and the q-axis voltage command Vq** after being multiplied by the modulation factor correction coefficient K are distinguished without signs, the former will be referred to as the "first q-axis voltage command" and the latter will be referred to as the "second q-axis voltage command."

[0053] The d-axis voltage command Vd** and the q-axis voltage command Vq** calculated by the voltage command calculation unit 13 are output to a command modulation factor and voltage phase calculation unit 140 inside the voltage command calculation unit 13. Furthermore, the d-axis voltage command Vd** and the q-axis voltage command Vq** calculated by the voltage command calculation unit 13 are output to an excitation current command control unit 19 shown in FIG.

[0054] 7 is a block diagram showing an example of the configuration of a command modulation factor and voltage phase calculation unit 140 included in the voltage command calculation unit 13 in the control device 10 of the power conversion device 300 according to Embodiment 1. The command modulation factor and voltage phase calculation unit 140 includes a command modulation factor calculation unit 141 and a voltage phase calculation unit 144. Furthermore, the command modulation factor calculation unit 141 includes a voltage command amplitude calculation unit 142.

[0055] A d-axis voltage command Vd**, a q-axis voltage command Vq**, and a bus voltage Vdc are input to the command modulation factor calculation unit 141. A voltage command amplitude calculation unit 142 uses the d-axis voltage command Vd** and the q-axis voltage command Vq** to calculate a voltage command amplitude Vdq**_abs shown in the following equation (4).

[0056] Vdq**_abs=√(Vd** ２ +Vq** ２ ) … (4)

[0057] The voltage command amplitude Vdq**_abs calculated by the voltage command amplitude calculation unit 142 is divided by a value obtained by multiplying the bus voltage Vdc by 1 / √2, and the result is output as a command modulation factor M*.

[0058] Furthermore, the voltage phase calculation unit 144 calculates the voltage phase θv shown in the following equation (5) using the d-axis voltage command Vd** and the q-axis voltage command Vq**.

[0059] θv = tan －１ (Vd** / Vq**)…(5)

[0060] As described above, the command modulation factor M* and voltage phase θv calculated by the command modulation factor and voltage phase calculation unit 140 are used in the space vector modulation unit 15 .

[0061] 8 is a block diagram showing an example configuration of the excitation current command control unit 19 included in the inverter control unit 12 in the control device 10 of the power conversion device 300 according to embodiment 1. The excitation current command control unit 19 includes a voltage command amplitude calculation unit 191, an adder / subtractor 192, an MTPA (Maximum Torque Per Ampere) control unit 193, an I (Integral) controller 194, and an id* comparison unit 195.

[0062] A d-axis voltage command Vd** and a q-axis voltage command Vq** are input to the voltage command amplitude calculation unit 191. The voltage command amplitude calculation unit 191 uses the d-axis voltage command Vd** and the q-axis voltage command Vq** to calculate the voltage command amplitude Vdq**_abs shown in the above equation (4).

[0063] The MTPA control unit 193 performs MTPA control on the q-axis current iq obtained from the coordinate conversion unit 18, and calculates one d-axis current command id* to be input to the id* comparison unit 195. The MTPA control is a control that adjusts the current phase of the current flowing through the electric motor 7 so as to maximize the torque generated by the electric motor 7. The MTPA control is well known, and since general MTPA control is used in this paper, a detailed description thereof will be omitted here.

[0064] Inside the excitation current command control unit 19, the command modulation factor M is divided by 1 / √2 times the bus voltage Vdc, and the divided value is input as a voltage limit value Vom*, which is a limit value of the d-axis and q-axis voltages, to an adder-subtractor 192. In addition, the adder-subtractor 192 also receives as input the voltage command amplitude Vdq**_abs calculated by the voltage command amplitude calculation unit 191.

[0065] The adder-subtractor 192 calculates the deviation between the voltage limit value Vom* and the voltage command amplitude Vdq**_abs, and inputs the calculated deviation as a voltage saturation amount ΔV to the I controller 194. The I controller 194 integrates the voltage saturation amount ΔV to calculate another d-axis current command id* to be input to the id* comparator 195. The id* comparator 195 selects the larger negative value from the d-axis current command id* output from the MTPA control unit 193 and the d-axis current command id* output from the I controller 194, and outputs the selected value as the d-axis current command id* to the voltage command calculation unit 13.

[0066] The integral gain Kfw of the flux-weakening control in the I controller 194 is set by the following equation (6).

[0067] Kfw=ωfw / (KωeLd)…(6)

[0068] In the above equation (6), ωfw is the cutoff angular frequency when the I controller 194 is viewed as a low-pass filter, Ld is the d-axis inductance, and ωe is the angular frequency of the inverter output voltage, as described above.

[0069] By using the excitation current command control unit 19 configured as described above, the voltage saturation amount is controlled so that the average value of the actual modulation factor, which is a value indicating the ratio of the inverter output voltage to the DC voltage value, becomes constant at a certain value. As a result, the voltage command fed back is controlled with good tracking relative to the voltage limit value, and the I controller 194 operates stably without windup or the like.

[0070] In general, the gain of integral control in flux-weakening control is ωfw / (ωeLd), but in the excitation current command control unit 19 in embodiment 1, the flux-weakening control is performed using a voltage command after modulation factor correction, and therefore, as in equation (6) above, the denominator of the integral gain Kfw needs to include the modulation factor correction coefficient K. By using the integral gain Kfw shown in equation (6) above, it is possible to stabilize operation in the overmodulation region even when the modulation factor correction method and flux-weakening control are combined.

[0071] As described above, the power conversion device according to the first embodiment includes a converter that rectifies a power supply voltage applied from an AC power supply, a capacitor connected to the output terminal of the converter, an inverter connected across the capacitor, and a control device that controls the operation of the inverter. When a command modulation factor indicating the ratio of a voltage command amplitude in a voltage command applied to the inverter to a DC voltage value applied to the inverter exceeds 1, the control device corrects the voltage command so that the inverter output voltage can be output linearly, and performs flux-weakening control when a voltage saturation amount calculated from the voltage command and a voltage limit value determined by the DC voltage value occurs. This flux-weakening control may be performed using the voltage command after modulation factor correction or the voltage command before modulation factor correction. The control device according to the first embodiment performs flux-weakening control using the voltage command after modulation factor correction. That is, the power conversion device according to the first embodiment performs flux-weakening control using the voltage command after modulation factor correction so that the inverter output voltage can be output linearly while stabilizing operation in the overmodulation region.

[0072] In the first embodiment, the control device calculates an excitation current command used in the flux-weakening control based on a voltage saturation amount calculated from a voltage command and a voltage limit value determined by a DC voltage value. With this control device configured in this manner, the voltage saturation amount is controlled so that the average value of the actual modulation factor, which is a value indicating the ratio of the inverter output voltage to the DC voltage value, becomes constant at a certain value during the flux-weakening control, thereby stabilizing the operation of the control device.

[0073] The gain of the flux-weakening control is an important parameter for stabilizing the operation of the control device. When the control device is configured to determine the excitation current command for the flux-weakening control from the voltage command after modulation factor correction, as in the first embodiment, it is desirable to set the gain of the flux-weakening control including the modulation factor correction coefficient. Configuring the control device in this way can contribute to stabilizing the operation of the control device.

[0074] Next, a description will be given of the hardware configuration of the control device 10 included in the power conversion device 300. Fig. 9 is a diagram showing an example of a hardware configuration realizing the control device 10 included in the power conversion device 300 according to embodiment 1. The control device 10 is realized by a processor 201 and a memory 202.

[0075] The processor 201 is a CPU (Central Processing Unit), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, a processor, a DSP (Digital Signal Processor), or a system LSI (Large Scale Integration). The memory 202 can be, for example, 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 Read Only Memory), or an EEPROM (Electrically Erasable Programmable Read-Only Memory). The memory 202 is not limited to these, and may also be a magnetic disk, an optical disk, a compact disk, a minidisc, or a DVD (Digital Versatile Disc).

[0076] Second Embodiment In a second embodiment, a control device configured using the second method described above, that is, a method of performing flux-weakening control using a voltage command before modulation factor correction will be described.

[0077] FIG. 10 is a block diagram showing an example configuration of a control device 10A included in a power conversion device 300 according to the second embodiment. The control device 10A includes an operation control unit 11 and an inverter control unit 12A. The inverter control unit 12A includes a voltage command calculation unit 13A, an electrical angle phase calculation unit 14, a space vector modulation unit 15, a PWM signal generation unit 16, a current restoration unit 17, a coordinate conversion unit 18, and an excitation current command control unit 19A. In FIG. 10, components having different functions from those of the control device 10 of the first embodiment shown in FIG. 3 are indicated by the subscript A. The same applies to FIGS. 11, 12, and 13. Hereinafter, the second embodiment will be described, focusing on the functions of the components that differ from those of the first embodiment.

[0078] The excitation current command control unit 19A generates a d-axis current command id*, which is an excitation current command, based on the q-axis current iq, the command modulation factor M acquired from the operation control unit 11, and the d-axis voltage command Vd* and q-axis voltage command Vq* calculated by the voltage command calculation unit 13A. The excitation current command control unit 19A calculates a current phase angle at which the output torque of the electric motor 7 is equal to or greater than a set value or at its maximum value, and calculates the d-axis current command id* based on the calculated current phase angle. When calculating the d-axis current command id*, the excitation current command control unit 19A performs flux-weakening control and command modulation factor correction to determine the d-axis current command id*. The specific configuration and operation of the excitation current command control unit 19A will be described later. The excitation current command control unit 19A may calculate the d-axis current command id* using the motor current flowing through the electric motor 7 instead of the output torque of the electric motor 7. In this case, the d-axis current command id* is calculated based on the current phase angle at which the motor current flowing through the motor 7 is equal to or less than the set value or is at the minimum value.

[0079] The voltage command calculation unit 13A generates a d-axis voltage command Vd*, a q-axis voltage command Vq*, a frequency estimate ωest, a command modulation factor M**, and a voltage phase θv based on the frequency command ωe* obtained from the operation control unit 11, the d-axis current id and q-axis current iq obtained from the coordinate conversion unit 18, and the d-axis current command id* obtained from the excitation current command control unit 19A. The command modulation factor M** and the voltage phase θv are used in the space vector modulation unit 15, the d-axis voltage command Vd* and the q-axis voltage command Vq* are used in the excitation current command control unit 19A, and the frequency estimate ωest is used inside the electrical angle phase calculation unit 14 and the voltage command calculation unit 13A.

[0080] 11 is a block diagram showing an example of the configuration of a voltage command calculation unit 13A included in a control device 10A of a power conversion device 300 according to embodiment 2. The voltage command calculation unit 13A includes adders 130, 132, and 133, a speed controller 131, a d-axis current controller 134, a q-axis current controller 135, a frequency estimation unit 136, and a command modulation factor and voltage phase calculation unit 140A.

[0081] Comparing voltage command calculation unit 13A shown in Fig. 11 with voltage command calculation unit 13 shown in Fig. 6, in Fig. 11, components such as voltage command amplitude calculation unit 137 and modulation factor correction coefficient calculation unit 138 are deleted from the configuration in Fig. 6. As described above, embodiment 2 employs a technique for performing flux-weakening control using a voltage command before modulation factor correction, and therefore components such as voltage command amplitude calculation unit 137 and modulation factor correction coefficient calculation unit 138 are unnecessary.

[0082] The d-axis voltage command Vd* and the q-axis voltage command Vq* calculated by the voltage command calculation unit 13A are output to a command modulation factor and voltage phase calculation unit 140A inside the voltage command calculation unit 13A. Moreover, the d-axis voltage command Vd* and the q-axis voltage command Vq* calculated by the voltage command calculation unit 13A are output to an excitation current command control unit 19A shown in FIG. 10 outside the voltage command calculation unit 13A.

[0083] 12 is a block diagram showing an example configuration of a command modulation factor and voltage phase calculation unit 140A included in a voltage command calculation unit 13A in a control device 10A of a power conversion device 300 according to Embodiment 2. The command modulation factor and voltage phase calculation unit 140A includes a command modulation factor calculation unit 141A and a voltage phase calculation unit 144A. Furthermore, the command modulation factor calculation unit 141A includes a voltage command amplitude calculation unit 142A and a command modulation factor correction unit 146A.

[0084] The d-axis voltage command Vd*, the q-axis voltage command Vq*, and the bus voltage Vdc are input to the command modulation factor calculation unit 141A. The voltage command amplitude calculation unit 142A uses the d-axis voltage command Vd* and the q-axis voltage command Vq* to calculate a voltage command amplitude Vdq*_abs shown in the following equation (7).

[0085] Vdq*_abs=√(Vd* ２ +Vq* ２ ) … (7)

[0086] The voltage command amplitude Vdq*_abs calculated by the voltage command amplitude calculation unit 142A is divided by a value obtained by multiplying the bus voltage Vdc by 1 / √2, and the result is input to the command modulation factor correction unit 146A as a command modulation factor M*.

[0087] The command modulation factor M* input to the command modulation factor correcting section 146A is calculated using the voltage command before modulation factor correction. Furthermore, the command modulation factor correcting section 146A has a table equivalent to that of the modulation factor correction coefficient calculating section 138. When the value of the input command modulation factor M* is 1 or less, the command modulation factor correcting section 146A outputs the value of the command modulation factor M* as is, and when the value of the command modulation factor M* exceeds 1, the command modulation factor correcting section 146A multiplies the command modulation factor M* by the corresponding modulation factor correction coefficient K and outputs the multiplied value as the command modulation factor M**.

[0088] Furthermore, the voltage phase calculation unit 144A calculates the voltage phase θv shown in the following equation (8) using the d-axis voltage command Vd* and the q-axis voltage command Vq*.

[0089] θv = tan －１ (Vd* / Vq*)…(8)

[0090] The command modulation factor M** and voltage phase θv calculated by the command modulation factor and voltage phase calculation unit 140A are used in the space vector modulation unit 15.

[0091] 13 is a block diagram showing an example of the configuration of an excitation current command control unit 19A included in an inverter control unit 12A in a control device 10A of a power conversion device 300 according to embodiment 2. The excitation current command control unit 19A includes a voltage command amplitude calculation unit 191A, an adder / subtractor 192, an MTPA control unit 193, an I controller 194A, an id* comparison unit 195, and a command modulation factor correction unit 196.

[0092] The d-axis voltage command Vd* and the q-axis voltage command Vq* are input to the voltage command amplitude calculation unit 191A, which uses the d-axis voltage command Vd* and the q-axis voltage command Vq* to calculate the voltage command amplitude Vdq*_abs shown in the above equation (7).

[0093] The MTPA control unit 193 performs MTPA control on the q-axis current iq acquired from the coordinate conversion unit 18 and calculates one d-axis current command id* to be input to the id* comparison unit 195 .

[0094] The command modulation factor correcting section 196 has a table equivalent to that of the command modulation factor correcting section 146A. When the value of the input command modulation factor M is 1 or less, the command modulation factor correcting section 196 outputs the value of the command modulation factor M as is. When the value of the command modulation factor M exceeds 1, the command modulation factor correcting section 196 multiplies the command modulation factor M by the reciprocal 1 / K of the corresponding modulation factor correction coefficient K and outputs the multiplied value. The command modulation factor M is multiplied by the reciprocal 1 / K in order to align the comparison level with the voltage command amplitude Vdq*_abs output from the voltage command amplitude calculating section 191A. In other words, because the voltage command amplitude Vdq*_abs is generated using a voltage command before modulation factor correction, the command modulation factor M is multiplied by the reciprocal 1 / K in relation to this processing.

[0095] Inside the excitation current command control unit 19A, the output of the command modulation factor corrector 196 is divided by 1 / √2 times the bus voltage Vdc, and the divided value is input as a voltage limit value Vom*, which is a limit value for the d-axis and q-axis voltages, to an adder-subtractor 192. In addition, the adder-subtractor 192 also receives as input a voltage command amplitude Vdq*_abs calculated by a voltage command amplitude calculation unit 191A.

[0096] The adder-subtractor 192 calculates the deviation between the voltage limit value Vom* and the voltage command amplitude Vdq*_abs, and inputs the calculated deviation as a voltage saturation amount ΔV' to the I controller 194A. The I controller 194A integrates the voltage saturation amount ΔV' to calculate another d-axis current command id* to be input to the id* comparison unit 195. The integral gain Kfw of the flux-weakening control in the I controller 194A is set by the following equation (9).

[0097] Kfw=ωfw / (ωeLd)…(9)

[0098] In the above equation (9), ωfw is the cutoff angular frequency when the I controller 194A is viewed as a low-pass filter, Ld is the d-axis inductance, and ωe is the angular frequency of the inverter output voltage, as described above.

[0099] By using the excitation current command control unit 19A configured as described above, the voltage saturation amount is controlled so that the average value of the actual modulation factor, which is a value indicating the ratio of the inverter output voltage to the DC voltage value, becomes constant at a certain value. As a result, the voltage command fed back is controlled with good tracking relative to the voltage limit value, and the I controller 194A operates stably without windup or the like.

[0100] Furthermore, in the excitation current command control unit 19 in the first embodiment, flux-weakening control is performed using a voltage command after modulation factor correction, and therefore, as in the above equation (6), the modulation factor correction coefficient K is required in the denominator of the integral gain Kfw. In contrast, in the excitation current command control unit 19A in the second embodiment, flux-weakening control is performed using a voltage command before modulation factor correction, and therefore, as in the above equation (9), the modulation factor correction coefficient K is not required. Conversely, if an integral gain using the modulation factor correction coefficient K is used, as in the excitation current command control unit 19 in the first embodiment, operation becomes unstable. Therefore, by using the integral gain Kfw shown in the above equation (9), it is possible to stabilize operation in the overmodulation region even when the modulation factor correction method and flux-weakening control are combined.

[0101] As described above, the power conversion device according to the second embodiment includes a converter that rectifies a power supply voltage applied from an AC power supply, a capacitor connected to the output terminals of the converter, an inverter connected across the capacitor, and a control device that controls the operation of the inverter. When a command modulation factor indicating the ratio of a voltage command amplitude in a voltage command applied to the inverter to a DC voltage value applied to the inverter exceeds 1, the control device corrects the voltage command so that the inverter output voltage can be output linearly, and performs flux-weakening control when a voltage saturation amount calculated from the voltage command and a voltage limit value determined by the DC voltage value occurs. That is, the power conversion device according to the second embodiment performs flux-weakening control using the voltage command before modulation factor correction so that the inverter output voltage can be output linearly while stabilizing operation in the overmodulation region.

[0102] In the second embodiment, the control device calculates an excitation current command used in the flux-weakening control based on a voltage saturation amount calculated from a voltage command and a voltage limit value determined by a DC voltage value and a modulation factor correction coefficient. With this control device configured in this way, the voltage saturation amount is controlled so that the average value of the actual modulation factor, which is a value indicating the ratio of the inverter output voltage to the DC voltage value, becomes constant at a certain value during the flux-weakening control, thereby stabilizing the operation of the control device.

[0103] The gain of the flux-weakening control is an important parameter for stabilizing the operation of the control device. When the control device is configured to determine the excitation current command for the flux-weakening control from the voltage command before modulation factor correction, as in embodiment 2, it is desirable to set the gain of the flux-weakening control without including the modulation factor correction coefficient. Configuring the control device in this way can contribute to stabilizing the operation of the control device.

[0104] Third Embodiment Fig. 14 is a diagram showing a configuration example of a refrigeration cycle-applied device 900 according to a third embodiment. The refrigeration cycle-applied device 900 according to the third embodiment includes the power conversion device 300 described in the first or second embodiment. The refrigeration cycle-applied device 900 according to the third embodiment can be applied to products equipped with a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 14, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0105] The refrigeration cycle application equipment 900 includes a compressor 50 incorporating the electric motor 7 in embodiment 1 or embodiment 2, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, which are attached via refrigerant piping 912.

[0106] The compressor 50 includes a compression mechanism 52 that compresses the refrigerant and an electric motor 7 that operates the compression mechanism 52 .

[0107] The refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902. The compression mechanism 52 is driven by an electric motor 7 that is variable speed controlled.

[0108] During heating operation, as shown by the solid arrow, the refrigerant is pressurized by the compression mechanism 52 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 52.

[0109] During cooling operation, as shown by the dashed arrow, the refrigerant is pressurized by the compression mechanism 52 and sent out, and returns to the compression mechanism 52 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.

[0110] During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant to expand it.

[0111] 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.

[0112] REFERENCE SIGNS LIST 1 AC power source, 2 Reactor, 3 Converter, 5 Capacitor, 7 Motor, 8 Voltage detection unit, 9a, 9b DC bus, 10, 10A Control device, 11 Operation control unit, 12, 12A Inverter control unit, 13, 13A Voltage command calculation unit, 14 Electrical angle phase calculation unit, 15 Space vector modulation unit, 16 PWM signal generation unit, 17 Current restoration unit, 18 Coordinate conversion unit, 19, 19A Excitation current command control unit, 30 Inverter, 40 Current detection unit, 50 Compressor, 52 Compression mechanism, 130, 132, 133, 192 Adder / subtractor, 131 Speed ​​controller, 134 d-axis current controller, 135 q-axis current controller, 136 Frequency estimation unit, 137, 142, 142A, 191, 191A Voltage command amplitude calculation unit, 138 Modulation factor correction coefficient calculation unit, 140, 140A command modulation factor and voltage phase calculation unit, 141, 141A command modulation factor calculation unit, 144, 144A voltage phase calculation unit, 146A, 196 command modulation factor correction unit, 193 MTPA control unit, 194, 194A I controller, 195 id* comparison unit, 201 processor, 202 memory, 300 power conversion device, 310 inverter main circuit, 311 to 316 switching elements, 321 to 326 rectifier elements, 331 to 333 output lines, 350 drive circuit, 400 electric motor drive device, 900 refrigeration cycle applied equipment, 902 four-way valve, 906 indoor heat exchanger, 908 expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping, D1 to D4 diodes.

Claims

1. A power conversion device that supplies AC power to an electric motor that drives a load, comprising: a converter that rectifies a power supply voltage applied from an AC power supply; a capacitor connected to an output end of the converter; an inverter connected to both ends of the capacitor; and a control device that controls the operation of the inverter, wherein when a command modulation factor indicating the ratio of a voltage command amplitude in a voltage command given to the inverter to a DC voltage value applied to the inverter exceeds 1, the power conversion device corrects the voltage command so that the output voltage of the inverter can be output linearly, and performs flux-weakening control when a voltage saturation amount calculated from a voltage limit value determined by the DC voltage value and the voltage command occurs.

2. The power conversion device according to claim 1, wherein the control device calculates an excitation current command used in flux-weakening control based on a voltage saturation amount calculated from the voltage command and a voltage limit value determined by the DC voltage value, and the flux-weakening control controls the voltage saturation amount so that an average value of an actual modulation factor, which is a value indicating the ratio of the inverter output voltage to the DC voltage value, becomes constant at a certain value.

3. The power conversion device according to claim 2, wherein the voltage limit value is calculated using a command modulation factor before modulation factor correction is performed.

4. A power conversion device according to any one of claims 1 to 3, wherein when the control device is configured to determine an excitation current command for flux-weakening control from a voltage command after modulation factor correction, a gain for the flux-weakening control is set including a modulation factor correction coefficient.

5. The power conversion device according to claim 1, wherein the control device calculates an excitation current command used in flux-weakening control based on a voltage saturation amount calculated from the voltage command and a voltage limit value determined by the DC voltage value and a modulation factor correction coefficient, and the flux-weakening control controls the voltage saturation amount so that an average value of an actual modulation factor, which is a value indicating a ratio of the inverter output voltage to the DC voltage value, becomes constant at a certain value.

6. The power conversion device according to claim 5, wherein the voltage limit value is calculated using a command modulation factor after modulation factor correction has been performed.

7. The power conversion device according to claim 1, 5 or 6, wherein when the control device is configured to determine an excitation current command for flux-weakening control from a voltage command before modulation factor correction, the gain for the flux-weakening control is set without including a modulation factor correction coefficient.

8. An electric motor drive device comprising a power conversion device according to any one of claims 1 to 7.

9. A refrigeration cycle device comprising the power conversion device according to any one of claims 1 to 7.

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