JP2022147188A - Motor drive device - Google Patents

Abstract

To provide a motor drive device capable of achieving both of a high efficiency and robustness against a load fluctuation.SOLUTION: A motor drive device of a present embodiment, comprises: an electric conduction part that performs a power conduction to a stator winding of a motor; a current detection part that detects a current flowing in the stator winding; a peak current detection part that detects a peak value of the current; a phase difference detection part that detects a phase difference of an applied voltage to the motor and the current; a voltage calculation part that calculates the magnitude of the applied voltage on the basis of an input frequency command; a voltage correction part that corrects the applied voltage so as to reduce the peak current as possible; a lower limit setting part that sets a lower limit of the phase difference; and a control part that reduces the frequency command and increases the correction voltage by the voltage correction part when it is determined that the phase difference is smaller than the lower limit.SELECTED DRAWING: Figure 1

Description

Embodiments of the present invention relate to a drive device that controls a motor without using a rotational position sensor.

As power saving progresses in recent years, for example, a power conversion device for driving a three-phase brushless DC motor has a configuration in which half-bridge circuits for three phases are connected in parallel between positive and negative DC power lines. A half-bridge circuit is composed of a pair of semiconductor switching elements connected in series between DC power supply lines, and free wheel diodes connected in anti-parallel to each of the semiconductor switching elements.

In the power conversion device having the above configuration, the driving of each semiconductor switching element is PWM (Pulse Width Modulation) controlled. As a result, the DC power supplied from the DC power supply line is converted into three-phase AC power, and current is applied to the windings of the motor. As a circuit for driving a brushless DC motor, a sensor drive using a position sensor has been proposed especially for applications that require starting torque. However, in order to achieve cost reduction and miniaturization, there is a demand for a motor drive device that controls a motor without using a position sensor.

For example, instead of detecting the rotational position of the motor with a magnetic pole sensor such as a Hall element, there is a method of detecting the rotational position using the induced voltage generated in the motor windings and outputting the motor voltage based on this. In the 120° square wave drive that outputs a square wave voltage with a 120° energization electrical angle for one phase, the induced voltage can be detected in the 60° section where the output stops. However, the 120° rectangular wave drive has the problem that noise and vibration are greater than the 180° sinusoidal wave drive that outputs a sinusoidal voltage.

Generally, as a method of sinusoidal driving without using a position sensor, there is a method of calculating an induced voltage based on a motor voltage equation and estimating the rotational position using the induced voltage. However, this method requires a high calculation load, requires the use of an expensive microcomputer, and requires a motor constant.

On the other hand, there is a method called V/f control that makes the ratio (V/f) of the voltage (V) output from the inverter and the frequency (f) constant. No constants are required.

JP 2009-124812 A

However, in the V/f control, since the rotational position of the rotor is not grasped, if the load torque becomes too heavy, the rotation of the motor cannot follow the frequency command, resulting in an abnormal stop, that is, loss of synchronism. On the other hand, if the voltage command is set to a large value in order to avoid step-out, the efficiency will deteriorate.
Therefore, a motor drive device capable of achieving both high efficiency and robustness against load fluctuations is provided.

The motor driving device of this embodiment is
an energizing unit that energizes the stator windings of the motor;
a current detection unit that detects a current flowing through the stator winding;
a peak current detection unit that detects the peak value of the current;
a phase difference detection unit that detects a phase difference between the voltage applied to the motor and the current;
a voltage calculation unit that calculates the magnitude of the applied voltage based on an input frequency command;
a voltage correction unit that corrects the applied voltage so as to reduce the peak current as much as possible;
a lower limit value setting unit for setting a lower limit value of the phase difference;
and a control unit that reduces the frequency command and causes the voltage correction unit to increase the correction voltage when it is determined that the phase difference has fallen below the lower limit value.

1 is a functional block diagram showing a configuration of a motor drive device according to an embodiment; FIG. Vector diagram during V/f control Diagram showing FIG. 2 as a graph (part 1) Diagram showing FIG. 2 as a graph (Part 2) FIG. 4 is a diagram showing the relationship between the voltage-current phase difference and the torque when the duty is 90% and the motor rotation speed is 2900 rpm, 3000 rpm, and 3100 rpm. Diagram showing the control waveform when a load is applied without speed command adjustment Diagram showing control waveforms when load is applied with "with speed command adjustment" Diagram showing that the lower limit of the phase difference is changed according to the frequency command A diagram showing the effect of the output voltage correction amount calculation unit A diagram comparing the efficiency of V/f control and vector control of the present embodiment. Diagram showing a state in which output voltage correction is being performed stably A diagram showing a state in which the frequency command is halved from the state shown in FIG. FIG. 12 is a diagram showing a state in which the output voltage correction amount is proportional to the frequency command in the case shown in FIG. A diagram showing a state in which the acceleration and deceleration of the frequency command are repeated after the frequency command is adjusted and the output voltage drops. Diagram showing waveforms when "output voltage adjustment" is introduced in the case shown in FIG. FIG. 11 is a diagram showing step-out determination performed according to a change mode of voltage-current phase difference; Control main routine flow chart Flowchart of output adjustment processing

An embodiment will be described below with reference to the drawings. FIG. 1 is a functional block diagram showing the configuration of a motor drive device. For example, each phase winding of a motor 1, which is a permanent magnet motor, is connected to each phase output terminal of an inverter 2, which is a power converter. Although not specifically shown, the inverter 2 has a configuration in which half bridge circuits for three phases are connected in parallel between positive and negative DC power supply lines. A half-bridge circuit is composed of a pair of semiconductor switching elements connected in series between DC power supply lines, and free wheel diodes connected in anti-parallel to each of the semiconductor switching elements. A semiconductor switching element is, for example, an N-channel MOSFET or the like.

A frequency command ωref is input to the frequency command acceleration/deceleration limiting unit 3 from the outside. Output to the f/V converter 5 . For example, when the frequency command ωref suddenly changes stepwise, the acceleration/deceleration limiting unit 3 converts the command value so that it gradually increases in proportion to time. The f/V converter 5 outputs a voltage signal converted according to the input frequency command as a duty command in PWM control. Also, the frequency command is integrated by the integrator 6 to be converted into a position command.

A duty command and a position command via a subtractor 8 are input to the modulation control unit 7, and the modulation control unit 7 generates three-phase PWM signals (U, V, W±) to It is output as a gate signal to the semiconductor switching element.

The voltage-current phase difference detection processing unit 9 detects the motor current from the voltage from the one-shunt resistor arranged only on the negative power supply side of the inverter 2 or the three-shunt resistor arranged on the negative power supply side of each phase arm. to detect The voltage-current phase difference detection processor 9 calculates the difference between the voltage phase obtained from the modulation controller 7 and the motor current phase. In the case of the three-shunt method, the phase difference at the zero-cross point of the current is calculated, and in the case of the one-shunt method, the phase difference is calculated by obtaining the zero-cross point of the remaining one-phase current from the cross timing of the two-phase current.

A current peak detection processing unit 10 obtains the peak from the detected motor current, and an output voltage correction amount calculation unit 11 calculates a correction value for correcting the output voltage so that the current peak becomes as small as possible. output to When the phase difference detected by the voltage-current phase difference detection processing unit 9 becomes equal to or less than the lower limit value input by the lower limit value setting unit 14, the frequency command correction amount calculation unit 12 corresponding to the control unit lowers the frequency command. While outputting the correction value to the subtractor 4 , a command value for increasing the Duty command is output to the output voltage correction amount calculator 11 .

A step-out determination unit 13 corresponding to a rotational abnormality determination unit determines that the motor 1 has stepped out based on the change in the voltage-current phase difference detected by the voltage-current phase difference detection processing unit 9 . The correction timing determination unit 15 causes the output voltage correction amount calculation unit 11 to start voltage correction processing when the frequency command ωref matches the output of the frequency command acceleration/deceleration limiter 3 . The above constitutes the motor control device 16 .

FIG. 2 shows a vector diagram during V/f control. When the load torque is small, the current vector I approaches the d-axis, but when the load increases, it approaches the q-axis in order to increase the torque. If the load becomes too large, the field-weakening control is performed, and the current increases and the torque also increases.

3 and 4 are graphs of FIG. 2, showing the relationship between the phase difference between voltage and current, torque and current. When the PWM duty is constant, as the load increases, the magnetic pole delays, the d-axis current Id becomes negative, the voltage phase advances, and the phase difference decreases.

FIG. 5 shows the relationship between the voltage-current phase difference and the torque when the duty is fixed at 90% and the motor rotation speed is 2900 rpm, 3000 rpm, and 3100 rpm. Based on this relationship, in the present embodiment, when the phase difference becomes smaller and becomes 0 [deg] or less, control is added to increase the phase difference by decreasing the speed command, that is, the frequency speed command.

FIG. 6 shows control waveforms when a load is applied when "no speed command adjustment" and FIG. 7 "with speed command adjustment". Without speed command adjustment, the motor stepped out and stopped. It was possible to avoid stopping due to step-out. In addition, the lower limit value of the phase difference is changed by the lower limit setting unit 14 so as to be increased according to the frequency command ωref as shown in FIG. Robustness can be ensured.

FIG. 9 shows the effect of the output voltage correction amount calculator 11. FIG. A voltage command, that is, a duty command is automatically adjusted so that the peak value of the motor current is lowered. Details of the processing of the output voltage correction amount calculator 11 will be described later with reference to a control flowchart.

FIG. 10 compares the efficiency of the V/f control and vector control of this embodiment. The difference in efficiency from the vector control is less than 1 point, and the control of this embodiment achieves performance equivalent to that of the vector control.

It should be noted that the correction amount of the output voltage must be changed according to the frequency command. In FIGS. 11 to 13, in "execution of voltage correction", correction is executed at the timing when the waveform rises in an impulse shape. For example, when the frequency command is halved as shown in FIG. 12 from the state in which the output voltage is corrected stably as shown in FIG. 11, the control becomes unstable because the correction amount is too large. , it becomes difficult to suppress the current peak value. On the other hand, by making the correction amount of the output voltage proportional to the frequency command as shown in FIG. The current peak value can be stably suppressed appropriately.

Also, although the output voltage is reduced by performing the correction as described above, as shown in FIG. There is a problem that it becomes impossible to return to the frequency command, and acceleration/deceleration of the frequency command is repeated. Therefore, in this embodiment, by increasing the output voltage when the frequency command is lowered, "output voltage adjustment" that achieves high efficiency in V/f control and "frequency command adjustment" that responds to load fluctuations. ” is compatible with. FIG. 15 shows waveforms when the "output voltage adjustment" is introduced, and a state in which acceleration and deceleration of the frequency command are repeated can be avoided.

Here, if the correction voltage calculated by the output voltage correction amount calculator 11 is used as it is when the frequency command is lowered, the correction amount is too large and the output voltage becomes a negative value. There is a problem that it becomes impossible to drive. This problem can be solved by reducing the correction voltage calculated by the voltage correction unit in accordance with the ratio of the lowered frequency command to the original frequency command before the decrease. As a result, the overcorrection of the output voltage can be prevented, and the stop of the motor 1 can be avoided.

In addition, since the rotor rotation position of the motor 1 is not detected in the V/f control, it is required to appropriately detect a step-out caused by a sudden load change. In this embodiment, as shown in the portion surrounded by an ellipse in FIG. 16, when the voltage-current phase difference suddenly changes significantly to a positive value, step-out is detected by determining that it is out of step.

FIG. 17 shows a flow chart of the main control routine. This processing is executed, for example, in each PWM cycle whose frequency is approximately 20 kHz. First, the correction timing determination unit 15 determines whether or not the rotation frequency ω of the motor 1 matches the frequency command ωref (S01). If the rotational frequency ω does not match the frequency command ωref (NO), the rotational frequency is added or subtracted (S02). The addition/subtraction here is performed according to the frequency command addition/subtraction unit 3 .

When the rotation frequency ω matches the frequency command ωref (S01; YES), output voltage correction is started, and the voltage-current phase difference detection processing section 9 and the peak detection processing section 10 take in current values. If the current current value is greater than the held peak value, the peak detection processing unit 10 holds the updated current peak value (S1).

When the voltage-current phase difference detection processing unit 9 detects the zero-crossing point of the current (S2; YES), it executes processing for each cycle of the motor electrical angle. First, the voltage-current phase difference obtained last time is stored (S3), and then the current phase difference is calculated (S4). If the amount of change in the phase difference between the previous time and the current time is greater than the threshold value 1 (S5; YES), the step-out determination unit 13 determines that there is a step-out (S8). If the current phase difference is equal to or less than the threshold value 2 (S6; YES), the load on the motor 1 is increased, so the frequency command is reduced (S9) and the output voltage is increased (S10). If the current phase difference is greater than threshold 2 (S6; NO), output adjustment processing is performed (S7).

In the output adjustment process shown in FIG. 18, the index ε is calculated from the current peak value Ip or the current peak value Ip and the frequency ω, and the integrated value γa of the current peak value or the index ε is calculated (S11). A frequency command ωref is used for the frequency ω. Here, the integrated value γa is reset to zero every αref cycle of the current I by a process described later. αref is a natural number equal to or greater than "2". Therefore, the integrated value γa is also reset to zero every multiple cycles of the current I.

The integrated value γa(n) of the n-th period is given by the formula (1).
γa(n)=γa(n−1)+ε(n)=γa(n−1)+Ip/ω (1)
Ip: current peak value obtained in the n-th cycle
ω: frequency acquired in the n-th cycle
ε(n): n-th cycle index γa(n-1): integrated value of (n-1)th cycle

Next, the output voltage correction amount calculator 11 determines which stage (0 to 4) the output adjustment status of the driving voltage V is (S12). In the first determination, it is determined that Stage=0, for example.
<When Stage=0: Decrease the output voltage>
After decreasing the driving voltage V by a predetermined amount (S13), the output voltage correction amount calculator 11 sets Stage=1 (S14) and increments the count value α (S15). The count value α indicates how many cycles of the current I have elapsed since the previous comparison using the integrated value γa.

<When Stage=1: Hold the output voltage as it is>
The output voltage correction amount calculator 11 determines whether or not the count value α is greater than or equal to the reference value αref (S16). The reference value αref is a periodic value for resetting the integrated value γa to zero. If the count value α is smaller than the reference value αref (NO), the count value α is incremented (S22) and Stage=1 is maintained.

On the other hand, if the count value α is greater than or equal to the reference value αref (S16; YES), the output voltage correction amount calculator 11 calculates the integrated value γa from the previous comparison to the current comparison to It is compared with the integrated value γb (S17). If the integrated value γa is smaller than the integrated value γb (S18; YES), Stage=0 is set (S19). On the other hand, when the integrated value γa is greater than or equal to the integrated value γb, (NO) Stage is set to 2 (S21). Then, the count value α and the integrated value γa are reset to zero, and the integrated value γb is updated with the integrated value γa (S20).

<When Stage=2: Increase the output voltage>
After increasing the drive voltage V by a predetermined amount (S23), the output voltage correction amount calculator 11 sets Stage=3 (S24) and increments the count value α (S25).

<When Stage=3: Hold the output voltage as it is>
The output voltage correction amount calculator 11 determines whether or not the count value α is greater than or equal to the reference value αref (S26). If the count value α is smaller than the reference value αref (NO), the count value α is incremented (S32) and Stage=3 is maintained. On the other hand, when the count value α is equal to or greater than the reference value αref (YES), the integrated value γa and the integrated value γb are compared (S27). If the integrated value γa is smaller than the integrated value γb (YES), Stage=2 is set (S29). On the other hand, when the integrated value γa is greater than or equal to the integrated value γb, (NO) Stage is set to 0 (S31). Then, the same processing as in step S20 is performed (S30).

As described above, according to the present embodiment, in the motor drive device 16, the current peak detection processing unit 10 detects the peak value of the current supplied to the motor 1, and the voltage-current phase difference detection processing unit 9 detects the The phase difference between the output voltage to 1 and the current is detected. The f/V converter 5 calculates the output voltage Duty based on the input frequency command ωref, and the output voltage correction amount calculator 11 corrects the output voltage so as to reduce the current peak value as much as possible. Then, when determining that the phase difference has fallen below the lower limit value, the frequency command correction amount calculator 12 performs correction to lower the frequency command ωref and causes the output voltage correction amount calculator 11 to perform the correction.

With this configuration, it is possible to prevent step-out of the motor 1 by correcting the frequency command ωref, and to avoid a decrease in the output torque of the motor 1 by correcting the output voltage, thereby performing V/f control with high efficiency. It can be carried out.

Further, the correction timing determination unit 15 causes the output voltage correction amount calculation unit 11 to function when the frequency of the current applied to the motor 1 reaches the frequency command ωref, so that the correction of the output voltage can be started at an appropriate timing. . In this case, the output voltage correction amount calculator 11 changes the value by which the correction voltage is increased according to the energization frequency of the motor 1. Therefore, even if the frequency command suddenly drops, the output voltage is corrected satisfactorily. As a result, the control is stable and the current peak value can be suppressed appropriately.

Furthermore, since the output voltage correction amount calculator 11 adjusts the value of the correction voltage based on the frequency command ωref, it is possible to prevent overcorrection of the output voltage and stop the motor 1 . Further, since the lower limit value setting unit 14 changes the lower limit value of the phase difference according to the frequency command ωref, it is possible to ensure robustness against load fluctuations even if the frequency command ωref changes.

In addition, when the out-of-step determining unit 13 determines that the amount of change between the current phase difference and the previous phase difference exceeds the threshold value, it determines that the motor 1 is abnormal in rotation, that is, out of step. Even in V/f control in which detection is not performed, step-out of the motor 1 can be reliably determined.

(Other embodiments)
The control device 16 may be configured as a motor driver IC (integrated circuit).
The lower limit value of the phase difference does not necessarily have to be changed according to the frequency command ωref, and may be a constant value.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

In the drawing, 1 is a motor, 2 is an inverter, 5 is an f/V conversion unit, 9 is a voltage-current phase difference detection processing unit, 10 is a current peak detection processing unit, 11 is an output voltage correction amount calculation unit, and 12 is a frequency command. 13 is a step-out determination unit; 14 is a lower limit value setting unit; 15 is a correction timing determination unit; and 16 is a motor control device.

Claims (6)

an energizing unit that energizes the stator windings of the motor;
a current detection unit that detects a current flowing through the stator winding;
a peak current detection unit that detects the peak value of the current;
a phase difference detection unit that detects a phase difference between the voltage applied to the motor and the current;
a voltage calculation unit that calculates the magnitude of the applied voltage based on an input frequency command;
a voltage correction unit that corrects the applied voltage so as to reduce the peak current as much as possible;
a lower limit value setting unit for setting a lower limit value of the phase difference;
A motor driving device comprising: a control section that reduces the frequency command and causes the voltage correction section to increase the correction voltage when it is determined that the phase difference is below the lower limit value. 2. The motor drive device according to claim 1, further comprising a correction timing determination section that causes the voltage correction section to function when the frequency of the current applied to the motor reaches the frequency command. 3. The motor drive device according to claim 1, wherein the control unit changes the value by which the voltage correction unit increases the correction voltage according to the frequency of the current supplied to the motor. 4. The motor drive device according to any one of claims 1 to 3, wherein the control section adjusts the correction voltage value calculated by the voltage correction section based on the frequency command. The motor drive device according to any one of claims 1 to 4, wherein the lower limit value setting section changes the lower limit value according to the frequency command. 6. The motor according to any one of claims 1 to 5, comprising a rotation abnormality determination unit that determines that the motor rotation abnormality occurs when it is determined that the amount of change between the current phase difference and the previous phase difference exceeds a threshold. drive.

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