JP5851522B2 - Motor drive device - Google Patents

Description

  The embodiment relates to a motor drive device that drives a brushless DC motor used as a compressor motor, for example.

  For example, a brushless DC motor (also referred to as a permanent magnet synchronous motor) used as a compressor motor of a heat pump refrigerator has a stator with a plurality of phase windings and a rotor with a plurality of permanent magnets embedded therein, The refrigerant is sucked, compressed, and discharged, and the lubricating oil pump in the compressor is driven.

  The motor driving device for driving the brushless DC motor includes an inverter for supplying driving voltage to each phase winding, and performs so-called vector control. In vector control, the speed of the brushless DC motor (also referred to as the rotor speed) is estimated from the current flowing through each phase winding of the brushless DC motor, and the drive voltage to be supplied to the brushless DC motor is obtained from the estimated speed. A drive signal (PWM signal) necessary for obtaining the drive voltage from the inverter is generated.

  The brushless DC motor needs to be rotated at high speed, such as at the start of operation where a large amount of heat is required. However, when the brushless DC motor rotates at high speed, the value of the voltage induced in each phase winding becomes higher than the value of the drive voltage supplied to each phase winding. When this happens, it becomes impossible to pass a current through each phase winding, and as a result, speed control (also referred to as rotational speed control) of the brushless DC motor becomes impossible.

  As a countermeasure, so-called field weakening control in which a negative field component current is injected is performed in the high-speed rotation range of the brushless DC motor. When this field weakening control is performed, an increase in the induced voltage to each phase winding is suppressed, and the value of the induced voltage does not become higher than the value of the driving voltage supplied to each phase winding. That is, the speed control of the brushless DC motor can be continued without interruption.

  On the other hand, when a power failure of a voltage drop occurs in the commercial AC power supply, the value of the drive voltage supplied to each phase winding becomes lower than the value of the induced voltage to each phase winding. Also in this case, the speed control of the brushless DC motor becomes impossible. As a countermeasure, it is conceivable to continue the speed control of the brushless DC motor by monitoring the voltage of the commercial AC power source and performing field-weakening control when a power failure of a voltage drop occurs.

  As a countermeasure for the power supply voltage drop, an example is known in which the rotational energy of the motor is regenerated in the inverter at the time of a power failure, and this regeneration suppresses the voltage drop in the DC section in the inverter (Japanese Patent Laid-Open No. 2002-2002). No. 374700). In addition, there is known an example in which the weak field control is switched between execution and non-execution according to whether or not the voltage of the DC section in the inverter is equal to or higher than a certain value (Japanese Patent Laid-Open No. 2009-268304). Furthermore, an example is known in which the voltage control of the DC part in the inverter is increased by stopping speed control for the brushless DC motor at the time of an instantaneous power failure of the commercial AC power supply (Japanese Patent Laid-Open No. 2004-304965). .

  The negative field component current for field weakening control acts to cancel the magnetic flux generated from the phase winding. Therefore, when field-weakening control is performed, a loss corresponding to the product of the square of the negative field component current to be injected and the phase winding resistance occurs. This leads to an increase in power consumption.

  The objective of embodiment is providing the motor drive device which can continue appropriate speed control with respect to a motor, suppressing the increase in power consumption.

The motor drive device according to the embodiment includes an inverter, a smoothing capacitor, first control means, detection means, second detection means, and third control means . The inverter converts the voltage of the AC power source into DC, converts the DC voltage into AC, and outputs it as a drive voltage to the brushless DC motor. The smoothing capacitor smoothes the DC voltage in the inverter. The first control means estimates the speed of the brushless DC motor from the current flowing through the brushless DC motor, and drives and controls the inverter so that the estimated speed becomes a target speed. The detecting means detects the occurrence of a failure in the AC power supply. The second control means maintains the target speed within a range between an upper limit speed corresponding to a DC voltage in the inverter and a predetermined lower limit speed when occurrence of a fault is detected by the detection means. The third control means reduces the target speed to a reduction rate larger than the actual speed reduction rate of the brushless DC motor when the voltage of the smoothing capacitor drops below a set value after execution of the control by the second control means. And by correcting the rotational energy of the brushless DC motor as a regenerative voltage to the smoothing capacitor by correcting the lower limit speed as a limit, and the voltage of the smoothing capacitor increases to a value higher than the set value. Then, the control returns to the control of the second control means.

The block diagram which shows each embodiment. The flowchart which shows the control of one Embodiment. The time chart which shows the change of the direct-current voltage Vin and transition of various control in one Embodiment. The time chart which shows the other example of the change of the direct-current voltage Vin and the transition of various control in one Embodiment. The flowchart which shows the modification of control of one Embodiment.

Hereinafter, an embodiment will be described with reference to the drawings.
As shown in FIG. 1, an inverter 10 is connected to a commercial AC power supply 1 via a reactor 2, and a brushless DC motor (permanent magnet synchronous) used as a compressor motor of a heat pump refrigerator, for example, is connected to the output end of the inverter 10. 3) is also connected.

  The inverter 10 includes a rectifier circuit 11 that converts the AC voltage of the commercial AC power source 1 into a DC voltage, a smoothing capacitor 12 that smoothes the DC voltage output from the rectifier circuit 11, and the voltage of the smoothing capacitor 12 is turned on by switching elements. It has a switching circuit 13 that converts it into a three-phase AC voltage having a predetermined frequency when it is turned off. The output of the switching circuit 13 is supplied to the brushless DC motor 3 as a drive voltage.

  The brushless DC motor 3 has a stator on which a plurality of phase windings are mounted and a rotor in which a plurality of permanent magnets are embedded, and is housed in a compressor case to suck, compress, and discharge refrigerant in a heat pump refrigeration cycle. And the lubricating oil pump in the compressor case is driven. The lubricating oil pump supplies lubricating oil accumulated at the bottom of the compressor case to the sliding portion of the brushless DC motor 3. By this supply, an oil film is formed on the sliding portion of the brushless DC motor 3.

  A current sensor 4 for detecting a current (phase current) flowing in the U-phase winding of the brushless DC motor 3 is disposed in the U-phase energization path between the output terminal of the switching circuit 13 and the brushless DC motor 3. A current sensor 5 for detecting a current (phase current) flowing in the V-phase winding of the brushless DC motor 3 is disposed in a V-phase energization path between the output terminal of the switching circuit 13 and the brushless DC motor 3. Outputs of the current sensors 4 and 5 are supplied to the motor control unit 20. The current flowing through the W-phase winding of the brushless DC motor 3 can be calculated from the detection currents of the current sensors 4 and 5.

  The motor control unit 20 estimates the speed of the brushless DC motor 3 (also referred to as the rotor speed) from the detection currents of the current sensors 4 and 5, and determines the estimated speed ωm according to a speed command from an air conditioning control unit (not shown). The sensorless vector control (first control means) for turning on and off the switching element of the inverter 10 to output the driving voltage for reaching the target speed ωref from the inverter 10 is performed. A speed estimation unit 22, a speed control unit 23, a current control unit 24, a coordinate conversion unit 25, a voltage detection circuit 26, an output duty calculation unit 27, a PWM conversion unit 28, and a power failure detection unit 29 are included.

  The coordinate conversion unit 21 converts the detected currents of the current sensors 4 and 5 into field component currents converted into field axis (d-axis) coordinates and torque axis (q-axis) coordinates on the rotor axis in the brushless DC motor 3, respectively. Conversion into Id (also referred to as d-axis current) and torque component current (also referred to as q-axis current) Iq. The speed estimation unit 22 estimates the speed of the brushless DC motor 3 by calculation based on the field component current Id and torque component current Iq obtained by the coordinate conversion unit 21 and an equivalent equation of the brushless DC motor 3. The speed control unit 23 obtains a difference between the target speed ωref corresponding to the speed command and the estimated speed ωm. The current control unit 24 sets the target value for the torque component current Iq converted by the coordinate conversion unit 21 and the target value for the field component current Id to the difference (= ωref−ωm) obtained by the speed control unit 23. Set accordingly.

  The coordinate conversion unit 25 converts the target value for the torque component current Iq and the target value for the field component current Id set by the current control unit 24 into a d-axis coordinate on the rotor axis in the brushless DC motor 3. It converts into the component voltage Vd and the torque component voltage Vq converted into the q-axis coordinate. The voltage detection circuit 26 detects the voltage of the smoothing capacitor 12 as the DC voltage Vin of the DC part in the inverter 10. Based on the field component voltage Vd and torque component voltage Vq converted by the coordinate conversion unit 25 and the detection voltage Vin of the voltage detection circuit 26, the output duty calculation unit 27 turns on / off duty D for each switching element of the switching circuit 13. Is calculated. The PWM conversion unit 28 generates a drive signal (PWM signal) having a pulse width corresponding to the on / off duty D calculated by the output duty calculation unit 27. By this drive signal, each switching element of the switching circuit 13 is turned on and off. By this on / off operation, a three-phase AC voltage for driving the brushless DC motor 3 is output from the switching circuit 13.

  The speed control unit 23 also increases the negative field component current that increases as the on / off duty D approaches 100% so that the on / off duty D calculated by the output duty calculation unit 27 does not reach 100%. Field weakening control is performed to add −Id (also referred to as a negative d-axis current) to the target value of the field component current Id in the current control unit 24 (field weakening control means).

  When the detection voltage Vin of the voltage detection circuit 26 drops below the set value Vdip, the power failure detection unit 29 detects this as the occurrence of a failure (also referred to as an abnormality) in the commercial AC power supply 1. The occurrence of this failure is hereinafter referred to as a power failure. In addition, the power failure detection unit 29 detects the occurrence of a power failure when the decrease width Vr per unit time of the detection voltage Vin of the voltage detection circuit 26 is equal to or greater than a certain width Vdr. Further, after detecting the occurrence of the power failure, the power failure detection unit 29 supplies the power when the detection voltage Vin of the voltage detection circuit 26 exceeds the set value Vdip and the state continues for a predetermined time or more. Detect as failure recovery. The detection result of the power failure detection unit 29 is supplied to the speed control unit 23 and the current control unit 24.

  The voltage detection circuit 26 and the power failure detection unit 29 constitute a power monitoring system (power monitoring means) that detects the occurrence and recovery of a power failure.

  The speed controller 23 includes the following means (1) to (6) in addition to the first control means and the field weakening control means.

  (1) When the occurrence of a power failure is detected by the power failure detector 29, the upper limit speed ωh corresponding to the detected voltage Vin of the voltage detection circuit 26 is calculated from the detected voltage Vin, and the target speed ωref is calculated as the upper limit speed. Second control means for executing speed maintenance mode control for maintaining within a range of ωh and a predetermined lower limit speed ωl. The lower limit speed ωl is the minimum speed necessary for the brushless DC motor 3 to drive the lubricating oil pump in the compressor. The upper limit speed ωh corresponding to the detection voltage Vin is a value that decreases as the detection voltage Vin decreases.

  (2) After the speed maintaining mode control by the second control means, when the detection voltage Vin of the voltage detection circuit 26 drops below the set value Vreg (<Vdip), the target speed ωref is set to the actual speed of the brushless DC motor 3. A regenerative mode control is executed in which the smoothing capacitor 12 is charged with the rotational energy of the brushless DC motor 3 as a regenerative voltage, with a reduction rate larger than the speed reduction rate and with a lower limit speed ωl as a limit. When the voltage of the smoothing capacitor 12 rises due to the control and the detection voltage Vin of the voltage detection circuit 26 rises above the set value Vkp (> Vreg), the regeneration mode control is terminated and the speed maintenance mode control of the second control means is performed. 3rd control means to return to.

  (3) After the return to the speed maintenance mode control by the third control means, when the voltage recovery of the commercial AC power supply 1 occurs and the detection voltage Vin of the voltage detection circuit 26 rises to a place exceeding the set value Vreg, the target speed When the return mode control for increasing (returning) ωref at a predetermined normal speed increase rate is first executed, and after the voltage recovery of the commercial AC power supply 1 continues, the power failure detection unit 29 detects the recovery of the power failure. Fourth control means for executing a sudden increase mode control for rapidly increasing the target speed ωref to an original value corresponding to the speed command at an increase rate larger than the normal speed increase rate.

  (4) After the return to the speed maintenance mode control by the third control means, when the detection voltage Vin of the voltage detection circuit 26 falls below a predetermined value Voff (<Vreg) without causing voltage recovery of the commercial AC power supply 1 Based on the determination that the motor speed cannot be maintained at the lower limit speed ωl, the target speed ωref is corrected in the downward direction at a speed following the speed estimation process by the speed estimation unit 22 and the brushless DC motor 3 is stopped by the correction. Fifth control means for executing stop mode control.

  (5) After the brushless DC motor 3 is stopped by executing the stop mode control of the fifth control means, the voltage recovery of the commercial AC power supply 1 occurs and the detected voltage Vin of the voltage detection circuit 26 rises to a point where it exceeds the set value Vreg. In this case, restart mode control for restarting the brushless DC motor 3 and increasing the target speed ωref at the normal speed increase rate is first executed, and then the voltage recovery of the commercial AC power supply 1 continues, followed by the power failure detection unit 29. The sixth control means for executing the sudden increase mode control for rapidly increasing the target speed ωref to the original value according to the speed command at a rate higher than the normal speed increase rate when recovery from the power failure is detected .

  (6) Upon execution of the sudden rise mode control by the fourth control means and execution of the sudden rise mode control by the sixth control means, the detection voltage Vin at a certain time Trt after the power failure detection unit 29 detects recovery of the power failure. Seventh control means for executing motor current limit control for preventing step-out that may occur due to a response delay of drive signal generation control with respect to an increase in the motor. Specifically, the motor current limit control is a target of the field component current Id in the current control unit 24 so that the current flowing through the brushless DC motor 3 does not fall below a predetermined lower limit value. This is the control added to the value. The drive signal generation control includes on / off duty calculation processing of the output duty calculation unit 27 and drive signal generation processing of the PWM conversion unit 28.

  Next, the control of the motor control unit 20 will be described with reference to the flowchart of FIG. 2, the time chart of FIG. 3, and the time chart of FIG. FIG. 3 is an example of a change in the direct-current voltage Vin and various controls when the brushless DC motor 3 does not stop after a power failure occurs. FIG. 4 is an example of a change in the DC voltage Vin and a change in various controls when the brushless DC motor 3 is stopped after a power failure occurs.

  First, an example of FIG. 3 will be described. The voltage detection circuit 26 detects the DC voltage Vin of the DC portion in the inverter 10 and the decrease width Vr of the DC voltage Vin per unit time (step 101).

  When the detection voltage Vin of the voltage detection circuit 26 decreases, the field weakening control of the speed control unit 23 works along with the decrease. By this field weakening control, the motor current gradually increases.

  When the detection voltage Vin of the voltage detection circuit 26 falls below the set value Vdip, this is detected by the power failure detector 29 as the occurrence of a power failure (YES in step 102). At this time, if the failure detection flag f is “0” (YES in step 103), the speed control unit 23 sets “1” in the failure detection flag f (step 104), and the voltage detection circuit 26 An upper limit speed ωh corresponding to the detection voltage Vin is calculated from the detection voltage Vin (step 105). The upper limit speed ωh corresponding to the detection voltage Vin is a value that decreases as the detection voltage Vin decreases.

  When the target speed ωref is higher than the calculated upper limit speed ωh (YES in step 106), the speed control unit 23 corrects the target speed ωref to the upper limit speed ωh (step 107). Thus, the increase in the target speed ωref is limited to the upper limit speed ωh, so that the motor current decreases.

  When the target speed ωref is lower than the predetermined lower limit speed ωl (YES in step 108), the speed control unit 23 corrects the target speed ωref to the lower limit speed ωl (step 109).

  When the target speed ωref is equal to or lower than the upper limit speed ωh and equal to or higher than the lower limit speed ωl (NO in step 106, NO in step 108), the speed control unit 23 sets the target speed ωref to a value corresponding to the command speed as it is ( Step 110). In this way, the lowering of the target speed ωref is limited to the lower limit speed ω1, so that the power necessary for driving the lubricating oil pump in the compressor is secured.

  Through these steps 104 to 110, the speed maintenance mode control for maintaining the target speed ωref within the range of the upper limit speed ωh and the lower limit speed ωl is executed.

  After the occurrence of the power failure is detected by the power failure detection unit 29 (YES in step 102), the speed control unit 23 controls the speed maintenance mode if the failure detection flag f is “1” (NO in step 103). Is determined to be executed or not, it is determined whether or not the detected voltage Vin is equal to or lower than a predetermined value Voff (step 11). If the detected voltage Vin is not less than or equal to the predetermined value Voff (NO in step 111), the speed controller 23 determines whether or not the detected voltage Vin is less than or equal to the set value Vreg (step 113).

  As the detection voltage Vin decreases, the field weakening control of the speed control unit 23 works again, and the motor current gradually increases.

  When the detected voltage Vin drops below the set value Vreg (NO in step 111, YES in step 113), the speed control unit 23 executes the regeneration mode control (step 114). That is, the speed control unit 23 corrects the target speed ωref in the downward direction with a reduction rate larger than the actual speed reduction rate of the brushless DC motor 3 and with the lower limit speed ωl as a limit. Thereby, the rotational energy of the brushless DC motor 3 is charged to the smoothing capacitor 12 as a regenerative voltage.

  The speed control unit 23 determines whether or not the detection voltage Vin is equal to or higher than the set value Vkp during execution of the regeneration mode control (step 115). If the detected voltage Vin is less than the set value Vkp (NO in step 115), the speed control unit 23 continues to execute the regeneration mode control (step 114). When the detection voltage Vin becomes equal to or higher than the set value Vkp (YES in step 115), the speed control unit 23 resets the failure detection flag f to “0” in order to end the regeneration mode control and return to the speed maintenance mode control. (Step 116).

  If the failure detection flag f is “0” (YES in step 103), the speed control unit 23 repeats the execution of the speed maintenance mode control in steps 104 to 110. In the example of FIG. 3, the target speed ωref is limited to the lower limit speed ωl after the regeneration mode control is executed.

  Thereafter, when the voltage recovery of the commercial AC power supply 1 occurs and the detected voltage Vin rises to a point where it exceeds the set value Vreg (NO in step 111, NO in step 113), the speed control unit 23 in this case is a brushless DC motor. 3 is not stopped (NO in step 117), the return mode control is executed (step 118). That is, the speed control unit 23 increases (returns) the target speed ωref at a predetermined normal speed increase rate, and resets the failure detection flag f to “0” so as to return to the speed maintenance mode control.

  When the voltage recovery of the commercial AC power supply 1 continues and the detected voltage Vin exceeds the set value Vdip and the state continues for a predetermined time or longer, this is detected by the power failure detection unit 29 as a recovery from the power failure (step) 102 NO). At this time, if the failure detection flag f is “1” (YES in step 120), the speed control unit 23 executes the rapid increase mode control (step 121). That is, the speed control unit 23 rapidly increases the target speed ωref toward the original value according to the speed command at a rate higher than the normal speed increase rate, and sets the failure detection flag f to “return to the speed maintenance mode control”. Reset to 0 ”.

  When executing the rapid increase mode control, the speed control unit 23 executes the motor current limit control at a certain time Trt after the power failure detection unit 29 detects the recovery from the power failure. That is, the speed control unit 23 can be caused by a response delay of drive signal generation control (including on / off duty calculation processing of the output duty calculation unit 27 and drive signal generation processing of the PWM conversion unit 28) with respect to an increase in the detection voltage Vin. In order to prevent step-out, the positive field component current + Id is added to the target value of the field component current Id in the current control unit 24 so that the current flowing through the brushless DC motor 3 does not fall below a predetermined lower limit value. The fixed time Trt is longer than the control response delay with respect to the rise of the detection voltage Vin. Then, after the elapse of the fixed time Trt, the speed control unit 23 ends the rapid increase mode control and shifts to normal control (step 122).

  On the other hand, in the example of FIG. 4, when the decrease width Vr per unit time of the detection voltage Vin becomes equal to or greater than the constant width Vdr, this is detected by the power failure detection unit 29 as the occurrence of a power failure (step 102). YES) At this time, if the failure detection flag f is “0” (YES in step 103), the speed control unit 23 executes the above-described speed maintenance mode control (steps 104 to 110). By executing this speed maintenance mode control, the motor speed is maintained at the lower limit speed ωl. Thereby, the power required for driving the lubricating oil pump in the compressor is secured.

  After the occurrence of the power failure is detected by the power failure detection unit 29 (YES in step 102), the speed control unit 23 controls the speed maintenance mode if the failure detection flag f is “1” (NO in step 103). Is determined to be executed or not, it is determined whether or not the detected voltage Vin is equal to or lower than a predetermined value Voff (step 111).

  If the detected voltage Vin is equal to or lower than the predetermined value Voff (YES in step 111), the speed control unit 23 executes stop mode control based on the determination that the motor speed cannot be maintained at the lower limit speed ωl (step 112). . That is, the speed control unit 23 corrects the target speed ωref in a descending direction at a speed following the speed estimation process by the speed estimation unit 22 and stops the brushless DC motor 3 by the correction. In this case, since the brushless DC motor 3 is stopped while the target speed ωref is lowered at a speed following the speed estimation process, the rotor position at the time of the stop can be accurately grasped. As a result, a large starting torque can be secured and the time required for restarting the brushless DC motor 3 can be shortened.

  When the brushless DC motor 3 is stopped by executing the stop mode control, the speed control unit 23 recovers the voltage of the commercial AC power supply 1 and increases the detected voltage Vin to a value exceeding the set value Vreg (NO in Step 111). In this case, since the brushless DC motor 3 is stopped (YES in step 117), the restart mode control is executed (step 119). That is, the speed control unit 23 restarts the brushless DC motor 3 and increases the target speed ωref at the normal speed increase rate, and resets the failure detection flag f to “0” so as to return to the speed maintenance mode control. .

  When the voltage recovery of the commercial AC power supply 1 continues and the detected voltage Vin exceeds the set value Vdip and the state continues for a predetermined time or longer, this is detected by the power failure detection unit 29 as a recovery from the power failure (step) 102 NO). At this time, if the failure detection flag f is “1” (YES in step 120), the speed control unit 23 executes the rapid increase mode control (step 121). That is, the speed control unit 23 rapidly increases the target speed ωref toward the original value according to the speed command at a rate higher than the normal speed increase rate, and sets the failure detection flag f to “return to the speed maintenance mode control”. Reset to 0 ”.

  When executing the rapid increase mode control, the speed control unit 23 executes the motor current limit control at a certain time Trt after the power failure detection unit 29 detects the recovery from the power failure. That is, the speed control unit 23 is positive so that the current flowing through the brushless DC motor 3 does not fall below a predetermined lower limit value in order to prevent a step-out that may occur due to a response delay in the drive signal generation control with respect to the increase in the detection voltage Vin. The field component current + Id is added to the target value of the field component current Id in the current control unit 24. The fixed time Trt is longer than the control response delay with respect to the rise of the detection voltage Vin. Then, after the elapse of the fixed time Trt, the speed control unit 23 ends the rapid increase mode control and shifts to normal control (step 122).

  As described above, when the power failure occurs, the target speed ωref is maintained within the range between the upper limit speed ωh corresponding to the DC voltage Vin of the DC unit in the inverter 10 and the predetermined lower limit speed ωl, thereby reducing the negative speed. Execution of field weakening control for injecting field component current can be reduced.

  When field weakening control is executed, a loss corresponding to the product of the square of the negative field component current and the phase winding resistance occurs. Therefore, the increase in power consumption can be suppressed by reducing the execution of field weakening control. it can. Therefore, appropriate speed control for the brushless DC motor 3 can be continued while suppressing an increase in power consumption.

  Since the value corresponding to the voltage of the commercial AC power supply 1 is selected as the upper limit speed ωh, an operation that makes the best use of the energy supplied from the commercial AC power supply 1 is possible. Thereby, the operation of the heat pump refrigeration cycle driven by the brushless DC motor 3 can be stabilized as much as possible.

  Since the value corresponding to the voltage of the commercial AC power supply 1 is selected as the upper limit speed ωh, the speed of the brushless DC motor 3 is promptly followed by the recovery from the voltage drop of the commercial AC power supply 1 when the power supply is restored. Can do. Thereby, the shortage of capacity of the heat pump refrigeration cycle can be quickly compensated.

  Since the minimum speed required for the brushless DC motor 3 to drive the lubricating oil pump in the compressor is set as the lower limit speed ω1, the supply of the lubricating oil to the sliding portion of the brushless DC motor 3 is continued as much as possible. be able to. Therefore, the safety of the brushless DC motor 3 can be ensured.

  When the occurrence of a power failure is detected, the rotational energy of the brushless DC motor 3 is recovered as a regenerative voltage in the smoothing capacitor 12, and the charged voltage is used for driving the motor by speed maintenance mode control. The motor drive can be continued while enduring. Depending on the rating of the smoothing capacitor 12, the regenerative voltage can be limited to a value that does not exceed the rating of the smoothing capacitor 12 by changing the rate of decrease when the target speed ωref is corrected in the downward direction. Due to this limitation, failure of the smoothing capacitor 12 can be prevented.

  When the DC voltage Vin decreases to a value equal to or lower than the predetermined value Voff, the brushless DC motor 3 is stopped under the judgment that the motor speed cannot be maintained at the lower limit speed ωl. Remain in. Therefore, when the voltage of the smoothing capacitor 12 is used as the operating power of the motor control unit 20, the subsequent operation of the motor control unit 20 can be continued by the remaining voltage of the smoothing capacitor 12. If the voltage of the smoothing capacitor 12 becomes zero, the operation information in the motor control unit 20 is lost, or the brushless DC motor 3 cannot be restarted until the power failure is restored. Such a malfunction can be prevented. That is, the brushless DC motor 3 can be restarted promptly when recovery from the power failure is detected.

  When the brushless DC motor 3 is stopped, the brushless DC motor 3 is stopped while the target speed ωref is lowered at a speed that follows the speed estimation process, so that the rotor position at the time of the stop can be accurately grasped. A large starting torque can be secured and the time required for restarting the brushless DC motor 3 can be shortened.

  If the detected voltage Vin exceeds the set value Vdip, it is not immediately detected as a recovery from the power failure, but if the detected voltage Vin exceeds the set value Vdip and the state continues for a predetermined time or more. Since this is detected as restoration of the power failure, it is possible to prevent erroneous detection of restoration of the power failure caused by the increase of the voltage of the smoothing capacitor 12 due to regenerative energy. The specific value of the predetermined time is, for example, 1 second or more when the brushless DC motor 3 is continuously operated, and for example 1 second when the brushless DC motor 3 is stopped in order to quickly restart. Less than is set. If there is a false detection of power failure recovery due to a rise in the voltage of the smoothing capacitor 12 due to regenerative energy, the speed of the brushless DC motor 3 is stored in the smoothing capacitor 12 in an attempt to quickly return to the state before the power failure occurred. The extra energy is consumed, so the time to withstand a power failure is shortened. By preventing such erroneous detection, it is possible to suppress excessive consumption of energy stored in the smoothing capacitor 12. As a result, the time that can withstand a power failure increases.

  When recovering from a power failure such as an instantaneous power failure, the DC voltage Vin increases rapidly. At this time, the actual motor current becomes larger than the target value due to the response delay (time delay) of the drive signal generation control until the DC signal Vin is captured and the drive signal (PWM signal) is generated. The on / off duty D of the signal decreases rapidly. If this happens, the motor current decreases, the control becomes unstable, and step-out may occur. On the other hand, in the present embodiment, when recovering from a power failure, the motor current limit control is performed for a certain time Trt that is longer than the response delay of the drive signal generation control with respect to the rise in the detection voltage Vin, that is, the brushless DC motor Since the positive field component current + Id is added to the target value of the field component current Id in the current control unit 24 so that the current flowing in the current control section 24 does not fall below a predetermined lower limit value, the drive signal generation control for the increase in the detection voltage Vin is performed. It is possible to prevent the step-out that may occur from the response delay.

  In the above embodiment, the power failure detection unit 29 detects the occurrence of a power failure when the detection voltage Vin of the voltage detection circuit 26 drops below the set value Vdip, and detects the detection voltage Vin of the voltage detection circuit 26. Is detected as the occurrence of a power failure when the decrease width Vr per unit time is equal to or greater than a certain width Vdr. However, the present invention is not limited to this, and the drive signal ON / OFF duty for the inverter 10 (ON for the switching element of the inverter 10) The DC voltage Vin in the DC part of the inverter 10 is estimated from the magnitude of the off-duty D, and when the estimated voltage drops below the set value Vdip, it may be detected as the occurrence of a power failure. Alternatively, the power failure detector 29 may detect the occurrence of a power failure when the decrease width Vr per unit time of the estimated voltage is equal to or greater than a certain width Vdr. Alternatively, the power failure detection unit 29 may detect the occurrence of a power failure when the increase width per unit time of the on / off duty D is greater than or equal to a predetermined width.

  In the above embodiment, the power failure detection unit 29 detects the occurrence of the power failure, and then when the detected voltage Vin of the voltage detection circuit 26 exceeds the set value Vdip and the state continues for a predetermined time or more, This is detected as a power failure recovery. However, the present invention is not limited to this, and when the estimated voltage from the on / off duty D exceeds the set value Vdip and the state continues for a certain time or more, this is regarded as a power failure recovery. It may be detected.

  When the estimated voltage is used to detect the occurrence and recovery of a power failure, the voltage detection circuit 26 can be reduced, so that the circuit can be reduced in size and a signal line existing between the voltage detection circuit 26 and the motor control unit 20 is provided. Disappear. If the signal line is lost, the insulation of the motor control unit 20 is enhanced, and even if the motor control unit 20 is touched, there is no electric shock, and the risk during maintenance service is reduced.

  In Japan, the fluctuation range of the voltage of the commercial AC power source is 10V ± 6V when the standard voltage is 100V, and 202V ± 20V when the standard voltage is 200V. If the voltage drop at the wiring is 5%, the lower limit value is 91 V when the standard voltage is 100 V, and the lower limit value is 172 V when the standard voltage is 200 V. When no power failure has occurred, a voltage equal to or higher than this lower limit value is supplied. By determining that a power failure has occurred when a voltage less than the lower limit is detected, it is possible to reliably detect the occurrence of a power failure.

  The voltage range of the commercial AC power source is 101V ± 6V when the standard voltage is 100V, 202V ± 20V when the standard voltage is 200V, 12V when the standard voltage is 100V, and the standard voltage is 200V. The case has a width of 40V. The power consumption of the equipment connected to the system to which the commercial AC power supply voltage is supplied fluctuates and the voltage drop in the wiring changes, which is the cause of voltage fluctuations other than power supply failures. By determining that a power failure has occurred when a large voltage drop is detected, the power failure can be detected early when the supply voltage is higher than the standard. When the standard voltage is 100V and the upper limit is 107V by using the fluctuation more than the maximum voltage fluctuation assumed in the wiring from the power receiving end as reference, when the voltage reaches 102V, which is 5% lower than 107V, Is detected as a power failure. In this case, since the detection can be performed at a time earlier by 11V than 91V in the case of detection only by the voltage value, the motor rotation can be lowered quickly to reduce power consumption. As a result, the power failure can be tolerated for a longer time.

  In the above embodiment, the speed control unit 23 calculates the upper limit speed ωh corresponding to the detection voltage Vin of the voltage detection circuit 26 as the speed maintenance mode control (step 105), and the target speed ωref is the upper limit speed ωh. A process of determining whether or not the speed is higher (step 106), and a process of correcting the target speed ωref to the upper limit speed ωh when the target speed ωref is higher than the upper limit speed ωh (step 107) are executed. As shown in FIG. 5, the process of calculating the upper limit on / off duty Dh corresponding to the detection voltage Vin of the voltage detection circuit 26 (step 105), the on / off duty D calculated by the output duty calculator 27 is the upper limit on. , Processing for determining whether or not it is higher than the off-duty Dh (step 106), the on-off duty D is higher than the upper limit on-off duty Dh In this case, the target speed ωref is corrected to the value [= ωref− (Dh−D) · α] obtained by adding the coefficient α to the difference between the upper limit on, the off duty Dh and the on / off duty D (step 107) may be executed. Since the on / off duty D is calculated based on the field component voltage Vd and torque component voltage Vq converted by the coordinate conversion unit 25 and the detection voltage Vin of the voltage detection circuit 26, the change in the DC voltage Vin is used as a parameter. Contains.

  Other embodiments and modifications are presented as examples, and are not intended to limit the scope of the invention. The novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, and changes can be made without departing from the spirit of the invention. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalents thereof.

  The motor drive device of the embodiment can be used for driving a brushless DC motor used as a compressor motor of a heat pump refrigerator, for example.

Claims (8)

An inverter that converts the voltage of the alternating current power source into direct current, converts the direct current voltage into alternating current, and outputs the drive voltage to the brushless DC motor;
A smoothing capacitor for smoothing the DC voltage in the inverter;
A first control means for estimating a speed of the brushless DC motor from a current flowing in the brushless DC motor and driving the inverter so that the estimated speed becomes a target speed;
Detecting means for detecting occurrence of a fault in the AC power source;
Second control means for maintaining the target speed within a range between an upper limit speed corresponding to a DC voltage in the inverter and a predetermined lower limit speed when occurrence of a fault is detected by the detection means;
After execution of the control by the second control means, when the voltage of the smoothing capacitor drops below a set value, the target speed is set to a reduction rate larger than the actual speed reduction rate of the brushless DC motor and the lower limit speed is set. When the smoothing capacitor is charged as a regenerative voltage to the smoothing capacitor by correcting in the downward direction as a limit, the second control is performed when the voltage of the smoothing capacitor rises to a value higher than the set value. Third control means for returning to control of the means;
A motor drive device comprising: The detection means detects the occurrence and recovery of a fault in the AC power supply;
After the return to the control of the second control means by the third control means, when the voltage recovery of the AC power supply occurs and the voltage of the smoothing capacitor exceeds the set value, the target speed is set to A first speed increase rate, and then when the detection means detects a failure recovery, the target speed is increased to an original value at a speed higher than the normal speed increase rate. Control means,
The motor drive apparatus according to claim 1 , further comprising: After the return to the control of the second control means by the third control means, the brushless DC motor is stopped when the voltage of the smoothing capacitor drops below a predetermined value without causing the voltage recovery of the AC power supply. Fifth control means,
The motor drive device according to claim 2 , further comprising: When the voltage of the smoothing capacitor is reduced to a predetermined value or less without voltage recovery of the AC power supply after the return to the control of the second control means by the third control means, the fifth control means, Correcting the target speed in a descending direction at a speed following the estimation of the speed, and stopping the brushless DC motor by the correction;
The motor driving device according to claim 3 . After the brushless DC motor is stopped by the control of the fifth control means, when the voltage recovery of the AC power supply occurs and the voltage of the smoothing capacitor exceeds the set value, the brushless DC motor is restarted and The target speed is first increased at the normal speed increase rate, and then, when recovery from a fault is detected by the detection means, the target speed is increased to an original value and increased above the normal speed increase rate. Sixth control means for rapidly increasing at a rate;
The motor drive device according to claim 3 , further comprising: When the target speed suddenly rises by the fourth control means and the target speed suddenly rises by the sixth control means, a current flowing through the brushless DC motor is constant for a certain period of time after failure detection is detected by the detection means. Seventh control means for performing motor current limit control so as not to fall below a predetermined lower limit;
The motor drive device according to claim 5 , further comprising: The inverter converts the voltage of the AC power source to DC, converts the DC voltage to AC by turning on and off the switching element, and outputs it as a drive voltage to the brushless DC motor.
The first control means estimates the speed of the brushless DC motor from a current flowing through the brushless DC motor, and controls the switching element of the inverter to be turned on and off so that the estimated speed becomes a target speed.
The detecting means detects a DC voltage in the inverter, and when the detected voltage drops below a set value, or when a drop width per unit time of the detected voltage is a certain width or more, or for the switching element of the inverter When the DC voltage in the inverter is estimated from the size of the on / off duty and the estimated voltage drops below the set value, or when the reduced width per unit time of the estimated voltage is greater than or equal to the certain width, or the When the increase width per unit time of the on / off duty with respect to the switching element of the inverter is equal to or greater than a predetermined width, it is detected as a failure in the AC power supply
The motor driving apparatus according to claim 1. The detection means detects the occurrence of a fault in the AC power supply, and when the detected voltage or the estimated voltage exceeds the set value and the state continues for a certain period of time or more, it detects the fault in the AC power supply. Detect as recovery,
The motor driving apparatus according to claim 7 .

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