JP2017188968A - Motor drive device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor drive device capable of enhancing a motor speed while suppressing a power loss as much as possible.SOLUTION: A motor drive device comprises: a converter that converts an AC voltage into a DC voltage, and that can perform a step-up operation; an inverter that converts an output voltage of the converter into an AC voltage having a predetermined frequency by switching, and outputs the AC voltage as drive power to a motor; and control means that controls the converter and the inverter. The control means controls the output voltage of the inverter so that a speed of the motor becomes a target speed, and in a case where the output voltage reaches an upper limit, executes field weakening control to the motor. In a case where a control amount of the field weakening control increases to a value equal to or more than a setting value, and a load of the inverter is equal to or more than a constant value, the control means subjects the converter to step-up operation and increases the output voltage of the converter.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a motor drive device that converts a voltage of an AC power source into a DC voltage, converts the DC voltage into an AC voltage having a predetermined frequency, and outputs the AC voltage as drive power to a motor.

  2. Description of the Related Art A motor drive device is known that converts the voltage of an AC power source into DC with a converter, converts the DC voltage into an AC voltage of a predetermined frequency with an inverter, and outputs the AC voltage as drive power to the motor.

  In this motor drive device, the rotor speed of the motor is estimated from the current flowing in the motor winding, and sensorless vector control is performed to control the on / off duty of the inverter switching so that the estimated rotor speed becomes the target speed. . In other words, it is on in the low speed operation range where the target speed is low, and the output voltage of the inverter is decreased by reducing the off duty, and it is on in the high speed operation range where the target speed is high (or from the medium speed operation range to the high speed operation range) Control to increase the output voltage of the inverter by increasing the off duty. When the on / off duty reaches the upper limit value, the motor speed is increased by field weakening control in which a negative field component current -Id is injected.

Japanese Patent Laid-Open No. 05-15193

  However, as the advance angle becomes larger due to the field weakening control, the operation of the motor eventually becomes unstable, and the risk that the motor will step out increases.

  On the other hand, it is possible to increase the motor speed by using a PWM converter capable of step-up operation by switching and increasing the output voltage of the PWM converter. However, the step-up operation of the PWM converter causes a large power loss. is there.

  The objective of embodiment of this invention is providing the motor drive device which can raise a motor speed, suppressing electric power loss as much as possible.

  The motor drive apparatus according to claim 1 includes a converter, an inverter, and control means. The converter can convert an AC voltage into a DC voltage and perform a boosting operation. The inverter converts the output voltage of the converter into an AC voltage having a predetermined frequency by switching, and outputs the AC voltage as drive power to the motor. The control means controls the output voltage of the inverter so that the speed of the motor becomes a target speed, and executes the field weakening control for the motor when the output voltage reaches the upper limit, and the control amount of the field weakening control Is higher than a set value and the load of the inverter is larger than a certain level, the converter is boosted to increase the output voltage of the converter.

The block diagram which shows the structure of one Embodiment. The flowchart which shows the control of the same embodiment. The figure which shows an example of the change of the output voltage in the same embodiment, a torque component current, and an advance angle. The figure which shows the raise and fall of the output voltage in the same embodiment with the change of a lead angle and target speed.

Hereinafter, an embodiment will be described with reference to the drawings.
As shown in FIG. 1, the input end of the PWM converter 2 is connected to the three-phase AC power source 1, and the input end of the inverter 3 is connected to the output end of the PWM converter 2. A phase winding Lu, Lm, Lw of a brushless DC motor (also referred to as a permanent magnet synchronous motor) 4 is connected to the output terminal of the inverter 3.

  The PWM converter 2 includes reactors 11, 12 and 13, bridge circuits of diodes 14 a to 19 a, switching elements such as IGBTs 14 to 19, and a smoothing capacitor 20, and has a function of direct current conversion (full wave rectification) by the diodes 14 a to 19 a. At the same time, the boosting operation, harmonic suppression, and power factor improvement by on / off switching of the IGBTs 14 to 19 are possible. By the boosting operation, for example, an AC voltage of 100V can be converted into a DC voltage of 300V.

  The bridge circuit of the diodes 14a to 19a includes a series circuit of the diodes 14a and 15a, a series circuit of the diodes 16a and 17a, and a series circuit of the diodes 18a and 19a. The interconnection points of the diodes 14a and 15a are connected to the R-phase power supply line of the three-phase AC power supply 1 through the reactor 11, and the interconnection points of the diodes 16a and 17a are connected to the S-phase of the three-phase AC power supply 1 through the reactor 12. The interconnection point of the diodes 18 a and 19 a is connected to the T-phase power supply line of the three-phase AC power supply 1 through the reactor 13. The diodes 14a to 19a are free-wheeling diodes built in the IGBTs 14 to 19. The smoothing capacitor 20 smoothes the output voltage of the PWM converter. The voltage of the smoothing capacitor 20 becomes the output voltage Vdc of the PWM converter 2.

  The inverter 3 connects IGBTs 31 and 32 in series, and a U-phase series circuit, IGBTs 33 and 34 in which an interconnection point of the IGBTs 31 and 32 is connected to the phase winding Lu of the brushless DC motor 4 is connected in series. Are connected to the phase winding Lv of the brushless DC motor 4. The IGBTs 35 and 36 are connected in series, and the connection point of the IGBTs 35 and 36 is connected to the phase winding Lw of the brushless DC motor 4. The output voltage Vdc of the PWM converter 2 is converted into a three-phase AC voltage having a predetermined frequency by on / off switching of each IGBT, and is output as drive power to the brushless DC motor 4. In addition, IGBT31-36 has the free-wheeling diodes 31a-36a. The element configuration and rating of the IGBTs 31 to 36 are the same as the element configuration and rating of the IGBTs 14 to 19 in the PWM converter 2.

  The brushless DC motor 4 includes a stator having three phase windings Lu, Lv, Lw connected in a star shape, and a rotor having a permanent magnet. The rotor rotates due to the interaction between the magnetic field generated by the current flowing through the phase windings Lu, Lv, and Lw and the magnetic field created by the permanent magnet. Current sensors 41, 42, and 43 for detecting a phase winding current (motor current) are arranged in a current path between the phase windings Lu, Lv, and Lw and the output terminal of the inverter 3.

  An inverter control unit 50 is connected to the inverter 3, and a converter control unit 70 is connected to the PWM converter 2. Then, main controller 80 is connected to inverter controller 50 and converter controller 70.

  The inverter control unit 50 is a so-called sensorless vector control unit that controls switching of the inverter 3 in accordance with the outputs of the current sensors 41, 42, 43 and a command from the main control unit 80. The current detection unit 51, speed estimation calculation unit 52, an integration unit 53, a subtraction unit 54, a speed control unit 55, an Id control unit 56, subtraction units 57 and 58, current control units 61 and 62, and a PWM signal generation unit 63.

  The current detector 51 captures currents (motor currents) flowing through the phase windings Lu, Lv, Lw of the brushless DC motor 4 from the outputs of the current sensors 41, 42, 43, and field components (d-axis components) of the captured currents. ) Id and torque component (q-axis component) Iq are detected. The field component current Id is a current converted into a field axis (d axis) coordinate on the rotor axis, and is also referred to as a d axis current or a reactive current. The torque component current Iq is a current converted into a torque axis (q-axis) coordinate on the rotor axis, and is also referred to as a q-axis current or an effective current. Data relating to the field component current Id and the torque component current Iq is supplied to the main controller 80.

  The speed estimation calculation unit 52 estimates the rotor speed ωest of the brushless DC motor 4 by calculation using the field component current Id and the torque component current Iq detected by the current detection unit 51. The integration unit 53 detects the rotor position θest of the brushless DC motor 4 by integrating the estimated rotor speed ωest of the speed estimation calculation unit 52. The detected rotor position θest is supplied to the current detection unit 51 and the PWM signal generation unit 63. The subtracting unit 54 obtains a deviation ωerr between the target speed ωref and the estimated rotor speed ωest by subtracting the estimated rotor speed ωest from the target speed ωref commanded from the main control unit 80.

  The speed control unit 55 calculates a target value Iqref of the torque component current Iq by calculating a proportional / integral control (PI control) on the deviation ωerr obtained by the subtracting unit 54. The Id control unit 56 obtains the target value Idref of the field component current Id from the target value Iqref of the torque component current Iq, and sets the “negative field component current” −Id commanded from the main control unit 80 to the target value Idref. Add to. The subtractor 57 obtains a deviation ΔId between the field component current Id and the target value Idref by subtracting the field component current Id detected by the current detector 51 from the target value Idref. The subtractor 58 obtains a deviation ΔIq between the torque component current Iq and the target value Iqref by subtracting the torque component current Iq detected by the current detector 51 from the target value Iqref.

  The current control unit 61 calculates a field component (d-axis component) Vd of the drive voltage to be applied to the brushless DC motor 4 by calculating a deviation ΔId in proportion / integral control (PI control). The field component Vd is a voltage converted into a field axis (d axis) coordinate on the rotor axis, and is also referred to as a d axis voltage or a reactive voltage. The current control unit 62 calculates the torque component (q-axis component) Vq of the drive voltage to be applied to the brushless DC motor 4 by calculating the deviation ΔIq in proportion / integral control (PI control). The torque component voltage Vq is a voltage converted into a torque axis (q-axis) coordinate on the rotor axis, and is also referred to as a q-axis voltage or an effective voltage.

  The PWM signal generation unit 63 generates a switching pulse width modulation signal (referred to as a PWM signal) for the inverter 3 according to the field component voltage Vd, the torque component voltage Vq, and the detected rotor position θest. By this PWM signal, each switching element of the inverter 3 is turned on and off. Data relating to the on / off duty D of the PWM signal is supplied to the main controller 80.

  Converter control unit 70 is a vector control unit that controls switching of PWM converter 2 in accordance with a command from main control unit 80 and output voltage Vdc of PWM converter 2.

  The main control unit 80 controls the output voltage of the inverter 3 so that the speed of the brushless DC motor 4 (estimated rotor speed ωest) becomes the target speed (ωref), and when the output voltage reaches the upper limit, the brushless DC motor 4 is executed, and when the control amount of the field weakening control is equal to or greater than a set value and the load of the inverter 3 is greater than a certain level, the PWM converter 2 is boosted to output the output voltage Vdc of the PWM converter 2. Raise.

  Specifically, the main control unit 80 controls the switching on / off duty D of the inverter 3 so that the estimated rotor speed ωest becomes the target speed ωref, and the on / off duty D reaches the upper limit value Ds. In this case, field weakening control is performed in which a “negative field component current” −Id is injected into the field component current Id, and the advance angle β, which is a control amount of the field weakening control, is greater than or equal to a set value β1 (for example, 40 °). When the torque component current Iq is greater than the set value Iq1, the PWM converter 2 is boosted to increase the output voltage Vdc of the PWM converter 2. The fact that the magnitude of the load of the inverter 3 is greater than a certain value is regarded as “the torque component current Iq is equal to or greater than the set value Iq1”. Further, the main control unit 80 sets a voltage change rate (Vdc / sec) when the output voltage Vdc of the PWM converter 2 is raised, and a voltage change rate (Vdc / sec) when the output voltage Vdc of the PWM converter 2 is lowered. Larger than.

Next, control executed by the inverter control unit 50, the converter control unit 70, and the main control unit 80 will be described with reference to the flowchart of FIG.
When the estimated rotor speed ωest is less than the target speed ωref (YES in step S1), the on / off duty D of switching in the inverter 3 is increased by an amount corresponding to the deviation ωerr between the estimated rotor speed ωest and the target speed ωref ( Step S2). As the on / off duty D increases, it is determined whether the on / off duty D has reached the upper limit value Ds (step S3). If the on / off duty D has not reached the upper limit value Ds (NO in step S3), the processing from step S1 is repeated.

  When the on / off duty D reaches the upper limit value Ds (YES in step S3), the speed of the brushless DC motor 4 cannot be increased as it is, so that the field component current Id has a predetermined amount of “negative field magnet”. Field weakening control for injecting the component current “−Id is executed (step S4). By this field weakening control, the speed of the brushless DC motor 4 increases.

  As the field weakening control is executed, it is determined whether or not the advance angle β, which is the control amount of the field weakening control, is equal to or larger than the set value β1 (step S5). If the advance angle β has not reached the set value β1 (NO in step S5), the processing from step S1 is repeated.

The advance angle β can be expressed as follows using the torque component current Iq, “negative field component current” −Id.
β = arctan (| −Id | / | Iq |) arctan: arc tangent function When the advance angle β is equal to or larger than the set value β1 (YES in step S5), the torque component current Iq corresponding to the magnitude of the load of the inverter 3 is It is determined whether or not it is greater than or equal to the set value Iq1 (step S6). When torque component current Iq has not reached set value Iq1 (NO in step S6), the processing from step S1 is repeated.

  When torque component current Iq is equal to or larger than set value Iq1 (YES in step S6), step-up operation (switching) of PWM converter 2 is started, and output voltage Vdc of PWM converter 2 is adjusted upward by a predetermined value (step). S7). When the output voltage Vdc increases, the on / off duty control functions effectively (the on / off duty D can be increased), and the speed of the brushless DC motor 4 further increases.

  Although it is possible to increase the speed of the brushless DC motor 4 by increasing the output voltage Vdc of the PWM converter 2, on the other hand, the step-up operation by switching of the PWM converter 2 causes a large power loss. Therefore, even when the advance angle β rises to the set value β1 or more, the PWM converter 2 is not immediately boosted and the torque component current Iq corresponding to the load of the inverter 3 becomes the set value Iq1 or more. Therefore, for the first time, the PWM converter 2 is boosted.

  In other words, when the torque component current Iq is less than the set value Iq1 (the load of the inverter 3 is less than a certain value), the operation of the brushless DC motor 4 does not become unstable immediately even if the advance angle β becomes equal to or greater than the set value β1. Therefore, the speed of the brushless DC motor 4 is increased by field weakening control in order to give priority to suppression of power loss. If the torque component current Iq becomes greater than or equal to the set value Iq1 (the load of the inverter 3 is greater than or equal to a certain value) with the advance angle β increased to the set value β1 or more, the operation of the brushless DC motor 4 becomes unstable and brushless. Since the risk of the DC motor 4 going out of step increases, the step-up operation of the PWM converter 2 is started in order to prioritize the resolution of the problem.

  As described above, by appropriately combining the field-weakening control and the step-up operation, the speed of the brushless DC motor 4 is increased while preventing unstable operation and step-out of the brushless DC motor 4 and suppressing power loss as much as possible. be able to. The speed control area of the brushless DC motor 4 extends to the high speed side.

  An example of changes in the advance angle β, the torque component current Iq, and the output voltage Vdc is shown in FIG. The step-up operation of the PWM converter 2 starts at a timing t1 when the advance angle β increases to the set value β1 or more and the torque component current Iq becomes the set value Iq1 or more. The output voltage Vdc of the PWM converter 2 maintains the level Vdc1 of only full-wave rectification until the timing t1.

  As the output voltage Vdc increases, it is determined whether or not the output voltage Vdc has reached the allowable maximum value Vdc2 (step S8). When the output voltage Vdc has not reached the allowable maximum value Vdc2 (NO in step S8), the processing from step S1 is repeated.

  When the output voltage Vdc reaches the allowable maximum value Vdc2 (YES in step S8), it is determined whether or not the advance angle β is a set value β2 (for example, 45 °) (step S9). If the advance angle β has not reached the set value β2 (NO in step S9), the processing from step S1 is repeated.

  When the advance angle β reaches the set value β2 despite the increase of the output voltage Vdc (YES in step S9), the “negative field component current” −Id injected so far is decreased by a predetermined amount. (Step S10). After this decrease, the processing from step S1 is repeated.

  In the high speed operation range where the advance angle β exceeds the set value β2, the operation of the brushless DC motor 4 becomes unstable regardless of the load, so when the advance angle β reaches the set value β2, the “negative field” The magnetic component current “−Id” is decreased.

  On the other hand, when the estimated rotor speed ωest is equal to or higher than the target speed ωref (NO in step S1), it is determined whether the estimated rotor speed ωest exceeds the target speed ωref (step S11). If the estimated rotor speed ωest is the same as the target speed ωref (NO in step S11), the processing from step S1 is repeated. If the estimated rotor speed ωest exceeds the target speed ωref (YES in step S11), it is determined whether the advance angle β is equal to or greater than the set value β1 (step S12).

  When the advance angle β is equal to or larger than the set value β1 (YES in step S12), if the PWM converter 2 is performing a boost operation (YES in step 13), the output voltage Vdc of the PWM converter 2 is decreased by a predetermined value (step) S14). After the descent, the processing from step S1 is repeated. When the PWM converter 2 is not performing step-up operation (NO in step 13), the “negative field component current” −Id is decreased by a predetermined amount (step S15). After this decrease, the processing from step S1 is repeated.

  If the advance angle β is less than the set value β1 (NO in step S12), “Negative field component current” −Id is decreased by a predetermined amount if field weakening control is being executed (YES in step S16). (Step S17). After this decrease, the processing from step S1 is repeated. When the field weakening control is not executed (NO in step S16), the switching ON / OFF duty D in the inverter 3 is decreased by an amount corresponding to the deviation ωerr between the estimated rotor speed ωest and the target speed ωref (step S16). S18). After this decrease, the processing from step S1 is repeated.

  The rise and fall of the output voltage Vdc is shown in FIG. 4 together with the changes in the advance angle β and the target speed ωref. In the period from when the PWM converter 2 starts boosting to when the output voltage Vdc reaches the allowable maximum value Vdc2, the advance angle β remains substantially constant at the set value β1 regardless of an increase in the target speed ωref or a sudden change in the load. In step S7, the output voltage Vdc is preferentially adjusted. Further, when adjusting the output voltage Vdc, the voltage change when the output voltage Vdc rises so that the advance angle β can be stably suppressed to less than the set value β2 and the adjustment control during the fall does not occur. The rate (Vdc / sec) is set larger than the voltage change rate (Vdc / sec) at the time of lowering.

[Modification]
In the above-described embodiment, the advance angle β is captured as the control amount of the field weakening control. However, instead of the advance angle β, the injection amount of “negative field component current” −Id may be captured as the control amount of the field weakening control. .

  In the above embodiment, the torque component current Iq is captured as the magnitude of the load of the inverter 3, but the load factor M of the brushless DC motor 4 with respect to the rated load of the inverter 3 may be captured as the magnitude of the load as it is. In this case, the main control unit 80 controls the switching ON / OFF duty D of the inverter 3 so that the estimated rotor speed ωest becomes the target speed ωref, and when the ON / OFF duty D reaches the upper limit value Ds. , Field weakening control is performed by injecting “negative field component current” −Id into the field component current Id, the advance angle β, which is the control amount of the field weakening control, rises to the set value β1 or more, and the rating of the inverter 3 When the load factor M of the brushless DC motor 4 with respect to the load is a set value M1 (for example, 76%) or more, the PWM converter 2 is boosted to increase the output voltage Vdc of the PWM converter 2.

  In addition, the said embodiment and modification are shown as an example and are not intending limiting the range of 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.

  DESCRIPTION OF SYMBOLS 1 ... Three-phase alternating current power supply, 2 ... PWM converter, 3 ... Inverter, 4 ... Brushless DC motor, 41, 42, 43 ... Current sensor, 50 ... Inverter control part, 70 ... Converter control part, 80 ... Main control part

Claims (4)

A converter that converts an AC voltage into a DC voltage and is capable of boosting operation;
An inverter that converts the output voltage of the converter into an alternating voltage of a predetermined frequency by switching, and outputs the alternating voltage as drive power to the motor;
The output voltage of the inverter is controlled so that the speed of the motor becomes the target speed, and when the output voltage reaches the upper limit, the field weakening control for the motor is executed, and the control amount of the field weakening control is greater than or equal to the set value. Control means for increasing the output voltage of the converter by boosting the converter when the load of the inverter rises above a certain level.
A motor drive device comprising: The control means estimates the rotor speed ωest of the motor from the field component current Id and torque component current Iq flowing through the motor, and switches on the inverter so that the estimated rotor speed ωest becomes the target speed ωref, The off-duty D is controlled, and when the on-off duty D reaches the upper limit value Ds, the field-weakening control is performed to inject the “negative field component current” −Id into the field component current Id. When the advance angle β, which is a control amount of field control, rises to a set value β1 or more and the torque component current Iq is a set value Iq1 or more, the converter is boosted to raise the output voltage of the converter;
The motor driving apparatus according to claim 1. The control means estimates the rotor speed ωest of the motor from the field component current Id and torque component current Iq flowing through the motor, and turns on switching in the inverter so that the estimated rotor speed ωest becomes the target speed ωref, The off-duty D is controlled, and when the on-off duty D reaches the upper limit value Ds, the field-weakening control is performed to inject the “negative field component current” −Id into the field component current Id. When the advance angle β, which is a control amount of field control, is equal to or greater than a set value β1 and the load factor M of the motor with respect to the rated load of the inverter is equal to or greater than a set value M1, the converter is boosted to increase the output voltage of the converter Let
The motor driving apparatus according to claim 1. The control means makes the voltage change rate when raising the output voltage of the converter larger than the voltage change rate when lowering the output voltage of the converter,
The motor driving device according to claim 1, wherein the motor driving device is a motor driving device.

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