Power control device, power control method, and air conditioner

Abstract

To automatically control an advance angle even when there is no large capacitor for smoothing a DC voltage.SOLUTION: A rectifier circuit 3 converts a first AC voltage into a DC voltage. The inverter circuit 4 includes a plurality of switching elements Q1 to Q6, converts the DC voltage into a second AC voltage, and supplies the second AC voltage to a three-phase motor 2. A control circuit 7 generates control signals S1 to S6 for the plurality of switching elements Q1 to Q6 so as to execute vector control of the three-phase motor 2 by using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage represented in a dq coordinate. The control circuit 7 increases or decreases an advance angle indicating a direction of a current vector composed of a d-axis current and a q-axis current with respect to a q-axis in accordance with a load applied to the three-phase motor 2, and generates a control signal based on the advance angle. The control circuit 7 calculates a modulation rate indicating a utilization rate of the DC voltage, and prohibits an increase in the advance angle when the modulation rate is equal to or less than a threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a power control device, a power control method, and an air conditioner. [Background technology]

[0002] A power control device for driving an AC motor such as a three-phase motor may include a rectifier circuit that converts AC voltage supplied from a commercial power grid or the like into DC voltage, and an inverter circuit that converts the DC voltage back into AC voltage. In this case, the power control device may further include a capacitor for smoothing the DC voltage. However, a large capacitor is required to sufficiently smooth the DC voltage, which may increase the size and cost of the device. Therefore, efforts are being made to reduce the capacitance of the capacitor for smoothing the DC voltage or to eliminate the capacitor.

[0003] For example, Patent Document 1 discloses a method for efficiently driving a motor at variable speed without requiring a large capacitor or choke coil in the rectifier circuit and without operating a regenerative brake even at the moment when the DC voltage drops significantly. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4065375 Summary of the Invention [Problem to be solved by the invention]

[0005] Vector control based on current and voltage expressed in dq coordinates may be used to drive an AC motor such as a three-phase motor. Vector control may include automatically controlling the advance angle, which represents the direction of a current vector in dq coordinates, so as to achieve a desired efficiency and / or a desired torque, depending on, for example, the rotational speed of the motor and the magnitude of the load (e.g., the current flowing through the motor).

[0006] Conventionally, automatic control of the lead angle is based on the premise that the DC voltage input to the inverter circuit is sufficiently smoothed and substantially constant. However, as in Patent Document 1, when the drive circuit does not have a large capacitor for smoothing the DC voltage, the DC voltage input to the inverter circuit is not sufficiently smoothed and has a voltage that fluctuates significantly depending on the waveform of the AC voltage input to the rectifier circuit. In this case, it is difficult to automatically control the lead angle to achieve the desired efficiency and / or desired torque. Therefore, there is a need for automatic control of the lead angle even when a large capacitor for smoothing the DC voltage is not provided.

[0007] An object of the present disclosure is to provide a power control device and a power control method that can drive a three-phase motor so as to automatically control the lead angle even when the motor does not have a large capacitor for smoothing the DC voltage, and an air conditioner equipped with such a power control device. [Means for solving the problem]

[0008] A power control device according to one aspect of the present disclosure includes: A power control device for driving a three-phase motor, a rectifier circuit that converts the first AC voltage into a DC voltage; an inverter circuit including a plurality of switching elements, which converts the DC voltage into a second AC voltage and supplies the second AC voltage to the three-phase motor; a control circuit that generates control signals for the plurality of switching elements so as to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; The control circuit increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; calculating a modulation factor indicating a utilization factor of the DC voltage; When the modulation rate is equal to or less than a first threshold value, the increase in the advance angle is prohibited. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, even if a large capacitor for smoothing a DC voltage is not provided, a three-phase motor can be driven so that the lead angle is automatically controlled. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing a configuration of a motor system according to a first embodiment. [Figure 2] 2 is a block diagram showing the configuration of a control circuit 7 in FIG. 1. FIG. [Figure 3] FIG. 2 is a diagram for explaining a first control method executed by the power control device 10 of FIG. [Figure 4] 1. FIG. 1 is a diagram for explaining a second control method executed by the power control device 10 of FIG. 1, showing a case where the current vector has an advance angle β3. [Figure 5] 1. FIG. 1 is a diagram for explaining a second control method executed by the power control device 10 of FIG. 1, showing a case where the current vector has an advance angle β4. [Figure 6] 2 is a timing chart for explaining the operation of the motor system of FIG. 1. [Figure 7] FIG. 10 is a diagram showing the configuration of an air conditioner 200 according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] [First embodiment] [Configuration of the first embodiment] Fig. 1 is a diagram showing the configuration of a motor system according to the first embodiment. The motor system in Fig. 1 includes an AC power supply 1, a three-phase motor 2, current sensors 5u, 5w, and 5w, a rotation sensor 8, and a power control device 10.

[0013] The AC power supply 1 supplies a single-phase AC voltage to the power control device 10. The AC power supply 1 may include, for example, a 100V or 200V commercial AC power supply.

[0014] The power control device 10 converts a single-phase AC voltage supplied from an AC power source 1 into a three-phase AC voltage having a variable voltage and a variable frequency, and supplies the three-phase AC voltage to a three-phase motor 2 to drive the three-phase motor 2 at a variable speed. The power control device 10 includes a rectifier circuit 3, an inverter circuit 4, a capacitor 6, and a control circuit 7.

[0015] The rectifier circuit 3 converts the single-phase AC voltage supplied from the AC power supply 1 into a DC voltage. The rectifier circuit 3 is, for example, a diode bridge including four diodes.

[0016] The inverter circuit 4 converts a DC voltage into a three-phase AC voltage and supplies the three-phase AC voltage to the three-phase motor 2. The inverter circuit 4 includes a full-bridge circuit including a plurality of, for example, six, switching elements Q1 to Q6. The switching elements Q1 to Q6 may be, for example, power transistors such as insulated gate bipolar transistors.

[0017] The capacitor 6 is connected to the DC bus between the rectifier circuit 3 and the inverter circuit 4, and reduces noise generated in the inverter circuit 4 and propagated to the rectifier circuit 3 and the AC power supply 1. The capacitor 6 may be small and have a small capacity, for example, a capacity of 10 to 20 μF.

[0018] The control circuit 7 generates control signals S1 to S6 that turn on / off the switching elements Q1 to Q6 of the inverter circuit 4, respectively, and applies the control signals S1 to S6 to the control terminals, for example, gates, of the switching elements Q1 to Q6, respectively.

[0019] The three-phase motor 2 is driven by a three-phase AC voltage supplied from the power control device 10. The three-phase motor 2 is, for example, a permanent magnet synchronous motor.

[0020] The current sensors 5u, 5w, 5w detect currents Iu, Iv, Iw flowing through the windings of each phase of the three-phase motor 2. The rotation sensor 8 detects the rotation speed ω and rotation phase θ of the rotor of the three-phase motor 2.

[0021] The currents Iu, Iv, and Iw of the respective phases detected by the current sensors 5u, 5w, and 5w are sent to the control circuit 7. The rotation speed ω and rotation phase θ detected by the rotation sensor 8 are also sent to the control circuit 7. The control circuit 7 also detects the voltage Vdc of the DC bus between the rectifier circuit 3 and the inverter circuit 4, and in the example of FIG. 1, the voltage across the capacitor 6. The control circuit 7 also receives a set value ω of the rotation speed of the three-phase motor 2 from outside the power control device 10. * The control circuit 7 receives the currents Iu, Iv, and Iw, the rotation speed ω, the rotation phase θ, the voltage Vdc, and the set value ω of the rotation speed. * Based on this, vector control of the three-phase motor 2 is performed using the d-axis current, q-axis current, d-axis voltage, and q-axis voltage expressed in dq coordinates. In addition, the control circuit 7 generates control signals S1 to S6 to turn on / off the switching elements Q1 to Q6 using pulse width modulation.

[0022] Fig. 2 is a block diagram showing the configuration of the control circuit 7 of Fig. 1. The control circuit 7 includes a torque control circuit 20, coordinate conversion circuits 21 and 22, a compensation circuit 23, comparison circuits 24 and 25, and a pulse width modulation (PWM) circuit 26.

[0023] The torque control circuit 20 controls the rotation speed ω and the set value ω of the rotation speed. * , voltage Vdc, q-axis voltage and d-axis voltage set value Vq expressed in dq coordinates * ,Vd * (described later) based on the d-axis current and q-axis current setting values ​​Id * ,Iq * Generate.

[0024] The coordinate conversion circuit 21 converts the currents Iu, Iv, Iw of the respective phases into a q-axis current Iq and a d-axis current Id expressed in dq coordinates based on the current rotation phase θ.

[0025] The comparison circuit 24 compares the q-axis current Id with the set value Iq of the q-axis current. * The comparator 25 generates an error between the d-axis current Iqn and the set value Id of the d-axis current. * Generate an error between

[0026] The compensation circuit 23 adjusts the set values ​​Vq of the q-axis voltage and the d-axis voltage expressed in the dq coordinate system so as to compensate for the errors in the q-axis current and the d-axis current. * ,Vd * Generate.

[0027] The coordinate conversion circuit 22 calculates the set values ​​Vq of the q-axis voltage and the d-axis voltage based on the current rotation phase θ. * ,Vd * is the set value Vu of the voltage applied between the windings of three-phase motor 2. * ,Vvw,Vw * Convert to.

[0028] The pulse width modulation circuit 26 uses pulse width modulation to adjust the voltage set point Vu * ,Vvw,Vw * The control signals S1 to S6 are generated from the signals.

[0029] [Operation of the first embodiment] As described above, the control circuit 7 performs vector control of the three-phase motor 2 using the d-axis current, q-axis current, d-axis voltage, and q-axis voltage represented in a dq coordinate system. The magnitude and direction of a current vector formed by the d-axis current and the q-axis current and a voltage vector formed by the d-axis voltage and the q-axis voltage represent the state of the three-phase motor 2. In particular, the efficiency and torque of the three-phase motor 2 are changed by changing the direction of the current vector, i.e., the lead angle representing the angle of the current vector relative to the q-axis. Therefore, the control circuit 7 increases or decreases the lead angle depending on the load on the three-phase motor 2. The load may represent, for example, the currents Iu, Iv, and Iw flowing through the three-phase motor 2. For example, the control circuit 7 may calculate the d-axis current and the q-axis current based on the currents Iu, Iv, and Iw, and calculate the torque of the three-phase motor 2 based on the d-axis current and the q-axis current. In this case, the control circuit 7 may increase or decrease the lead angle so as to bring the torque of the three-phase motor 2 closer to a target value. This allows the lead angle to be automatically controlled, for example, to maximize the torque of the three-phase motor 2.

[0030] If capacitor 6 has a small capacitance, the DC voltage input to inverter circuit 4 will not be sufficiently smoothed and may drop to near 0 V depending on the waveform of the single-phase AC voltage of AC power supply 1. If the input voltage of inverter circuit 4 is lower than the voltage applied between the windings of three-phase motor 2, the efficiency of driving three-phase motor 2 may decrease, or a brake current may be generated.

[0031] To address this issue, for example, Patent Document 1 discloses a technique for comparing a predicted value of the motor's terminal voltage with the input voltage of an inverter circuit and increasing or decreasing the set value of the d-axis current depending on the comparison result. Increasing or decreasing the d-axis current equivalently increases or decreases the lead angle. However, when a motor is used in an air conditioner compressor, for example, the input voltage and input current required by the motor fluctuate significantly due to fluctuations in ambient temperature or cycle load. Increasing or decreasing the set value of the d-axis current as in Patent Document 1 may result in an excessive increase in the lead angle, which may increase reactive power to the motor and reduce efficiency. Therefore, even in a motor without a large capacitor for smoothing the DC voltage, there is a need for a technique for automatically controlling the lead angle to achieve desired efficiency and / or torque without excessively increasing the lead angle.

[0032] Hereinafter, two control methods for automatically controlling the advance angle without excessively increasing the advance angle according to the embodiment will be described.

[0033] [First control method] When the utilization rate of the DC voltage Vdc, i.e., the voltage applied between the windings of the three-phase motor 2 relative to the DC voltage Vdc, is small, the lead angle increases excessively, which is likely to reduce the efficiency of the three-phase motor 2. Therefore, the control circuit 7 calculates the modulation rate M, which indicates the utilization rate of the DC voltage Vdc, using the following equation.

[0034]

number

[0035] The denominator of the right side of equation (1) may be the instantaneous value of the DC voltage Vdc, or may be the average value of the DC voltage Vdc over a predetermined time. * and the q-axis voltage setting value Vq * and shows the voltage applied between the windings of the three-phase motor 2.

[0036] FIG. 3 is a diagram illustrating a first control method executed by the power control device 10 of FIG. 1. Reference numeral 31 denotes a voltage limit ellipse when the modulation factor M=0.5 (i.e., 50%), and reference numeral 32 denotes a voltage limit ellipse when the modulation factor M=1 (i.e., 100%). Reference numeral 33 denotes a current vector that realizes a desired torque, i.e., a constant torque curve that indicates a combination of the d-axis current and the q-axis current. When the modulation factor M=0.5, the voltage limit ellipse intersects with the constant torque curve at point P1. The current vector Ia1=(Id1, Iq1) corresponding to point P1 has an advance angle β1. When the modulation factor M=1, the voltage limit ellipse intersects with the constant torque curve at point P2. The current vector Ia2=(Id2, Iq2) corresponding to point P2 has an advance angle β2. In the example of FIG. 3, |Ia1|>|Ia2|, β1>β2 hold.

[0037] 3, generally, when the modulation factor M decreases, the magnitude and advance angle of the current vector increase. When the modulation factor M decreases, the magnitude of the current vector required to achieve a desired torque increases, and the efficiency of the three-phase motor 2 decreases. Therefore, when the modulation factor M is equal to or less than a predetermined threshold, the control circuit 7 controls the set value Id of the d-axis current so as to prohibit an increase in the advance angle. * and the q-axis current setting value Iq * Generate these setting values ​​Id * and Iq * The control signals S1 to S6 corresponding to the modulation factor M are generated. "Prohibiting an increase in the advance angle" includes decreasing the advance angle or maintaining the current advance angle value. This makes it possible to prevent the efficiency of the three-phase motor 2 from decreasing further than the current value. The threshold value of the modulation factor M may be set to, for example, 0.9.

[0038] Furthermore, the control circuit 7 may increase the lead angle when the modulation factor M is sufficiently high.

[0039] [Second control method] The torque of the three-phase motor 2 varies depending on the q-axis voltage Vq. When the q-axis voltage Vq is negative, the torque also becomes negative, making it impossible to generate the desired torque.

[0040] Fig. 4 is a diagram for explaining the second control method executed by the power control device 10 of Fig. 1, showing a case where the current vector has an advance angle β3. The following variables are used in Fig. 4.

[0041] Id:d-axis current Iq:q-axis current Ia=(Id,Iq): current vector Vd: d-axis voltage Vq: q-axis voltage Va=(Vd,Vq): voltage vector Ld: d-axis inductance Lq: q-axis inductance Ψa: magnetic flux of the magnet Ψm: Flux linkage of three-phase motor 2 ω·Ψa: Induced voltage Ra: Resistance of three-phase motor 2

[0042] 4, the symbol "(β3)" added to a variable indicates that the variable changes depending on the advance angle. The q-axis voltage Vq satisfies the following equation.

[0043] Vq=ω·Ψa+ω·Ld·Id+Ra·Iq (2)

[0044] FIG. 5 is a diagram illustrating a second control method executed by the power control device 10 of FIG. 1, showing a case where the current vector has a lead angle β4. The lead angle β4 is greater than the lead angle β3. Comparing FIG. 4 and FIG. 5, it can be seen that increasing the lead angle reduces the q-axis voltage Vq. As mentioned above, if the q-axis voltage Vq becomes negative, the torque also becomes negative, making it impossible to generate the desired torque.

[0045] The control circuit 7 sets the q-axis voltage setting value Vq * is less than a predetermined threshold, the d-axis current setting value Id is set to prohibit the advance angle from increasing. * and the q-axis current setting value Iq * Generate these setting values ​​Id * and Iq *The control signals S1 to S6 corresponding to the values ​​of the thresholds may be generated. The thresholds may be set to 0. This prevents the lead angle from increasing excessively and the torque from becoming negative, enabling stable driving of the three-phase motor 2. Alternatively, the thresholds may be set to a small positive number close to 0, for example, 5% of the q-axis voltage Vq during normal operation of the three-phase motor 2. This prevents the lead angle from increasing excessively and the torque from becoming negative, enabling stable driving of the three-phase motor 2, while taking into account errors that occur in the motor system.

[0046] [Motor system operation] FIG. 6 is a timing chart illustrating the operation of the motor system of FIG. 1. FIG. 6 shows temporal changes in the modulation factor, the minimum value of the q-axis voltage Vq, the lead angle, and the load. The minimum value of the q-axis voltage Vq is monitored, for example, at time intervals equal to the period of the single-phase AC voltage of the AC power supply 1. If the single-phase AC voltage is 50 Hz, the minimum value of the q-axis voltage Vq is monitored at time intervals of 20 milliseconds, and if the single-phase AC voltage is 60 Hz, the minimum value of the q-axis voltage Vq is monitored at time intervals of 16.6 milliseconds. The load represents, for example, the current flowing through the three-phase motor 2.

[0047] In the period from time t0 to t1, immediately after starting the three-phase motor 2, the control circuit 7 executes initial control. In the initial control, the control circuit 7 increases or decreases the advance angle so as to maximize the torque of the three-phase motor 2, as in the prior art. As the load increases, the modulation factor gradually increases.

[0048] At time t1, the control circuit 7 starts the automatic control of the advance angle according to this embodiment. The control circuit 7 determines whether the modulation factor M is equal to or less than the threshold value Th1, i.e., whether the condition related to the first control method is satisfied, and also determines whether the set value Vq of the q-axis voltage is equal to or less than the threshold value Th1. * is less than 0 V, that is, whether the condition for the second control method is satisfied.

[0049] In the period from time t1 to t2, the modulation factor M is equal to or less than the threshold value Th1, in other words, the condition for the first control method is satisfied. Therefore, the control circuit 7 generates the control signals S1 to S6 to prohibit an increase in the lead angle. The control circuit 7 may maintain the current value of the lead angle.

[0050] In the period from time t2 to t3, the modulation factor M is higher than the threshold value Th1, and the set value Vq of the q-axis voltage * is equal to or greater than 0 V. In this case, the control circuit 7 executes normal control. In normal control, the control circuit 7 increases or decreases the lead angle so as to maximize the torque of the three-phase motor 2, as in the prior art. As the lead angle and load increase, the q-axis voltage gradually decreases.

[0051] In the period from time t3 to t4, the set value Vq of the q-axis voltage * is less than 0 V, in other words, the conditions for the second control method are met. Therefore, the control circuit 7 generates the control signals S1 to S6 so as to prohibit an increase in the lead angle. The control circuit 7 may decrease the lead angle or may maintain the current value of the lead angle.

[0052] In the period from time t4 to t5, the modulation factor M is higher than the threshold value Th1, and the set value Vq of the q-axis voltage * is equal to or greater than 0 V. In this case, the control circuit 7 performs normal control.

[0053] In the period after time t5, the control circuit 7 repeats the same processing as in the time period t3 to t5.

[0054] According to this embodiment, the control circuit 7 can drive the three-phase motor 2 so as to automatically control the lead angle even when the motor does not have a large capacitor for smoothing the DC voltage. In particular, when the load is light, the first control method can be executed to prevent the lead angle from increasing excessively, which would otherwise cause the efficiency of the three-phase motor 2 to decrease. Furthermore, when the load is heavy, the second control method can be executed to prevent the lead angle from increasing excessively, which would otherwise cause the torque to become negative, allowing the three-phase motor 2 to be driven stably.

[0055] [Advantages of the first embodiment] A power control device 10 according to a first embodiment drives a three-phase motor 2 and includes a rectifier circuit 3, an inverter circuit 4, and a control circuit 7. The rectifier circuit 3 converts a first AC voltage into a DC voltage. The inverter circuit 4 includes multiple switching elements Q1 to Q6, converts the DC voltage into a second AC voltage, and supplies the second AC voltage to the three-phase motor 2. The control circuit 7 generates control signals for the multiple switching elements Q1 to Q6 to perform vector control of the three-phase motor 2 using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in a dq coordinate system. The control circuit 7 increases or decreases a lead angle, which indicates the direction of a current vector formed by the d-axis current and the q-axis current relative to the q-axis, depending on the load on the three-phase motor 2, and generates a control signal based on the lead angle. The control circuit 7 calculates a modulation factor, which indicates the utilization rate of the DC voltage, and prohibits an increase in the lead angle if the modulation factor is equal to or less than a first threshold value.

[0056] With this configuration, even if a large capacitor for smoothing the DC voltage is not provided, it is possible to drive a three-phase motor so that the lead angle is automatically controlled.

[0057] According to the power control device 10 of the first embodiment, the control circuit 7 may calculate the modulation factor based on the d-axis voltage and the q-axis voltage.

[0058] This configuration allows the modulation rate to be calculated.

[0059] According to the power control device 10 of the first embodiment, the control circuit 7 may generate a control signal to prohibit an increase in the advance angle when the q-axis voltage is less than the second threshold value.

[0060] This configuration prevents the advance angle from increasing excessively, causing the torque to become negative, and enables the three-phase motor to be driven stably.

[0061] According to the power control device 10 of the first embodiment, the second threshold value may be zero.

[0062] This configuration prevents the advance angle from increasing excessively, causing the torque to become negative, and enables the three-phase motor to be driven stably.

[0063] According to a first embodiment of the present invention, the power control device 10 drives a three-phase motor 2 and includes a rectifier circuit 3, an inverter circuit 4, and a control circuit 7. The rectifier circuit 3 converts a first AC voltage into a DC voltage. The inverter circuit 4 includes multiple switching elements Q1 to Q6, converts the DC voltage into a second AC voltage, and supplies the second AC voltage to the three-phase motor 2. The control circuit 7 generates control signals for the multiple switching elements Q1 to Q6 to perform vector control of the three-phase motor 2 using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in a dq coordinate system. The control circuit 7 increases or decreases a lead angle, which indicates the direction of a current vector formed by the d-axis current and the q-axis current relative to the q-axis, depending on the load on the three-phase motor 2, and generates a control signal based on the lead angle. When the q-axis voltage is less than a second threshold, the control circuit 7 prohibits an increase in the lead angle.

[0064] With this configuration, even if a large capacitor for smoothing the DC voltage is not provided, it is possible to drive a three-phase motor so that the lead angle is automatically controlled.

[0065] A power control method according to a first embodiment is a power control method for a three-phase motor 2, and includes converting a first AC voltage to a DC voltage using a rectifier circuit 3, converting the DC voltage to a second AC voltage using an inverter circuit 4 including a plurality of switching elements Q1 to Q6, and supplying the second AC voltage to the three-phase motor 2, and generating control signals for the plurality of switching elements Q1 to Q6 so as to perform vector control of the three-phase motor 2 using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in a dq coordinate system. Generating the control signal includes increasing or decreasing a lead angle that indicates the direction of a current vector formed by the d-axis current and the q-axis current relative to the q-axis in accordance with a load on the three-phase motor, generating a control signal based on the lead angle, calculating a modulation factor that indicates a utilization rate of the DC voltage, and prohibiting an increase in the lead angle if the modulation factor is equal to or less than a first threshold value.

[0066] With this configuration, even if a large capacitor for smoothing the DC voltage is not provided, it is possible to drive a three-phase motor so that the lead angle is automatically controlled.

[0067] A power control method according to a first embodiment is a power control method for a three-phase motor 2, and includes converting a first AC voltage to a DC voltage using a rectifier circuit 3, converting the DC voltage to a second AC voltage using an inverter circuit 4 including a plurality of switching elements Q1 to Q6 and supplying the second AC voltage to the three-phase motor 2, and generating control signals for the plurality of switching elements Q1 to Q6 to perform vector control of the three-phase motor 2 using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in a dq coordinate system. Generating the control signal includes increasing or decreasing a lead angle that indicates the direction of a current vector formed by the d-axis current and the q-axis current relative to the q-axis in accordance with a load on the three-phase motor, generating a control signal based on the lead angle, and prohibiting an increase in the lead angle when the q-axis voltage is less than a second threshold value.

[0068] With this configuration, even if a large capacitor for smoothing the DC voltage is not provided, it is possible to drive a three-phase motor so that the lead angle is automatically controlled.

[0069] [Second embodiment] FIG. 7 is a diagram showing the configuration of an air conditioner 200 according to the second embodiment. The air conditioner 200 includes an indoor unit 210 and an outdoor unit 220. The indoor unit 210 includes an indoor motor 211, an indoor fan 212, an indoor heat exchanger 213, and a controller 214. The outdoor unit 220 includes an indoor motor 221, an outdoor fan 222, an outdoor heat exchanger 223, a compressor 224, a three-phase motor 224a, an expansion valve 225, a four-way valve 226, and a power control device 227. The indoor unit 210 and the outdoor unit 220 are connected via refrigerant piping 230. The compressor 224 includes a three-phase motor 224a. The power control device 227 drives the three-phase motor 224a in the same way as the power control device 10 according to the first embodiment. As a result, even if the power control device 227 does not have a large capacitor for smoothing the DC voltage, it is possible to drive the three-phase motor 224a so that the lead angle is automatically controlled.

[0070] [Advantages of the second embodiment] The air conditioner 200 according to the second embodiment includes a three-phase motor 224a and a power control device 227.

[0071] With this configuration, even if a large capacitor for smoothing the DC voltage is not provided, it is possible to drive a three-phase motor so that the lead angle is automatically controlled.

[0072] [Other embodiments] As described above, the embodiments have been described as examples of the technology disclosed in this application. For this purpose, the accompanying drawings and detailed description have been provided. However, the technology in this disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, the components described in the above embodiments can be combined to create new embodiments.

[0073] Therefore, the components shown in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to illustrate the above technology. Therefore, the fact that these non-essential components are shown in the accompanying drawings and / or detailed description should not be interpreted as immediately being essential.

[0074] Furthermore, since the above-described embodiments are intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0075] In the power control device 10, instead of providing a small-capacity capacitor 6 between the rectifier circuit 3 and the inverter circuit 4, the capacitor 6 may be omitted.

[0076] Instead of using three current sensors that respectively detect the current flowing through the windings of each phase of the three-phase motor 2, only two current sensors may be provided. Since the sum of the three current values ​​is always 0, if the currents of two phases are known, the current value of the remaining phase can be calculated.

[0077] [Summary of the embodiment] According to the power control device according to the first aspect of the present disclosure, A power control device for driving a three-phase motor, a rectifier circuit that converts the first AC voltage into a DC voltage; an inverter circuit including a plurality of switching elements, which converts the DC voltage into a second AC voltage and supplies the second AC voltage to the three-phase motor; a control circuit that generates control signals for the plurality of switching elements so as to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; The control circuit increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; calculating a modulation factor indicating a utilization factor of the DC voltage; When the modulation rate is equal to or less than a first threshold value, the increase in the advance angle is prohibited.

[0078] According to the power control device according to the second aspect of the present disclosure, in the power control device according to the first aspect, The control circuit calculates the modulation factor based on the d-axis voltage and the q-axis voltage.

[0079] According to a power control device according to a third aspect of the present disclosure, in the power control device according to the first or second aspect, The control circuit generates the control signal to prohibit the advance angle from increasing when the q-axis voltage is less than a second threshold value.

[0080] According to a power control device according to a fourth aspect of the present disclosure, in the power control device according to the third aspect, The second threshold is zero.

[0081] According to the power control device according to the fifth aspect of the present disclosure, A power control device for driving a three-phase motor, a rectifier circuit that converts the first AC voltage into a DC voltage; an inverter circuit including a plurality of switching elements, which converts the DC voltage into a second AC voltage and supplies the second AC voltage to the three-phase motor; a control circuit that generates control signals for the plurality of switching elements so as to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; The control circuit increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; When the q-axis voltage is less than a second threshold value, the increase in the advance angle is prohibited.

[0082] According to the air conditioner according to the sixth aspect of the present disclosure, A three-phase motor; and a power control device according to one of the first to fifth aspects.

[0083] According to a power control method according to a seventh aspect of the present disclosure, 1. A method for power control of a three-phase motor, comprising: converting the first AC voltage to a DC voltage using a rectifier circuit; converting the DC voltage into a second AC voltage using an inverter circuit including a plurality of switching elements, and supplying the second AC voltage to the three-phase motor; generating control signals for the plurality of switching elements to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; generating the control signal Increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; calculating a modulation factor indicative of a utilization factor of the DC voltage; If the modulation rate is equal to or less than a first threshold value, prohibiting the advance angle from increasing.

[0084] According to a power control method according to an eighth aspect of the present disclosure, 1. A method for power control of a three-phase motor, comprising: converting the first AC voltage to a DC voltage using a rectifier circuit; converting the DC voltage into a second AC voltage using an inverter circuit including a plurality of switching elements, and supplying the second AC voltage to the three-phase motor; generating control signals for the plurality of switching elements to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; generating the control signal Increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; and prohibiting the increase of the advance angle when the q-axis voltage is less than a second threshold value. [Industrial Applicability]

[0085] A power control device according to an aspect of the present disclosure is applicable to, for example, driving a motor of a compressor of an air conditioner. [Explanation of symbols]

[0086] 1 AC power supply 2 Three-phase motor 3 Rectifier circuit 4. Inverter circuit 5u, 5w, 5w current sensor 6 Capacitors 7 Control Circuit 8 Rotation Sensor 10 Power control device 20 Torque control circuit 21,22 Coordinate conversion circuit 23 Compensation circuit 24,25 Comparison circuit 26 Pulse Width Modulation (PWM) Circuit 200 Air conditioner 210 Indoor unit 211 Indoor motor 212 Indoor fan 213 Indoor heat exchanger 214 Controller 220 Outdoor unit 221 Indoor motor 222 Outdoor fan 223 Outdoor heat exchanger 224 Compressor 224a three-phase motor 225 Expansion valve 226 Four-way valve 227 Power Control Device 230 Refrigerant piping

Claims

1. A power control device for driving a three-phase motor, a rectifier circuit that converts the first AC voltage into a DC voltage; an inverter circuit including a plurality of switching elements, the inverter circuit converting the DC voltage into a second AC voltage and supplying the second AC voltage to the three-phase motor; a control circuit that generates control signals for the plurality of switching elements so as to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in a dq coordinate system; The control circuit increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load applied to the three-phase motor; generating the control signal based on the advance angle; calculating a modulation factor indicating a utilization factor of the DC voltage; prohibiting an increase in the advance angle when the modulation rate is equal to or less than a first threshold value; Power control device.

2. the control circuit calculates the modulation factor based on the d-axis voltage and the q-axis voltage. The power control device according to claim 1 .

3. the control circuit generates the control signal to prohibit the advance angle from increasing when the q-axis voltage is less than a second threshold value; The power control device according to claim 1 .

4. the second threshold is 0; The power control device according to claim 3.

5. A power control device for driving a three-phase motor, a rectifier circuit that converts the first AC voltage into a DC voltage; an inverter circuit including a plurality of switching elements, the inverter circuit converting the DC voltage into a second AC voltage and supplying the second AC voltage to the three-phase motor; a control circuit that generates control signals for the plurality of switching elements so as to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in a dq coordinate system; The control circuit increasing or decreasing a lead angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load applied to the three-phase motor; generating the control signal based on the advance angle; When the q-axis voltage is less than a second threshold value, the increase of the advance angle is prohibited. Power control device.

6. A three-phase motor; and a power control device according to any one of claims 1 to 5. Air conditioner.

7. 1. A method for power control of a three-phase motor, comprising: converting the first AC voltage to a DC voltage using a rectifier circuit; converting the DC voltage into a second AC voltage using an inverter circuit including a plurality of switching elements, and supplying the second AC voltage to the three-phase motor; generating control signals for the plurality of switching elements to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; generating the control signal increasing or decreasing an advance angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; calculating a modulation factor indicative of a utilization factor of the DC voltage; prohibiting an increase in the advance angle when the modulation rate is equal to or less than a first threshold value. A method for controlling power in a three-phase motor.

8. 1. A method for power control of a three-phase motor, comprising: converting the first AC voltage to a DC voltage using a rectifier circuit; converting the DC voltage into a second AC voltage using an inverter circuit including a plurality of switching elements, and supplying the second AC voltage to the three-phase motor; generating control signals for the plurality of switching elements to perform vector control of the three-phase motor using a d-axis current, a q-axis current, a d-axis voltage, and a q-axis voltage expressed in dq coordinates; generating the control signal increasing or decreasing an advance angle indicating a direction of a current vector formed by the d-axis current and the q-axis current relative to a q-axis according to a load on the three-phase motor; generating the control signal based on the advance angle; and prohibiting the increase of the advance angle when the q-axis voltage is less than a second threshold value. A method for controlling power in a three-phase motor.

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