JP7266439B2 - Motor controller and its control method - Google Patents

Description

The present invention relates to motor control.

A laser beam printer uses a brushless DC motor or the like to drive a photosensitive drum or a transfer belt. Generally, a brushless DC motor has a three-phase stator of U-phase, V-phase, and W-phase, and the motor is rotated by controlling the voltage applied to these. At this time, a stable rotation speed is realized by detecting the rotation speed that changes according to the load, etc. and feeding it back to the control.

Conventionally, the rotation speed was measured using a hall sensor, etc., but in recent years, a method of estimating the rotation speed from the three-phase current value without using a sensor and vector control (sensorless vector control) has become widely used. It is becoming (for example, patent document 1). However, in order to estimate the rotation speed without a sensor, it is necessary that the motor rotates at a relatively high rotation speed and that a sufficient induced current is generated. Therefore, a method (forced commutation mode) is used to force the motor to rotate by commutation (an operation that applies a voltage to each stator to create a rotating magnetic field) during the period from the start until the rotation speed increases to some extent. (For example, Patent Document 2). After the motor reaches a certain high rotational speed, the forced commutation mode is switched to vector control.

JP 2015-213398 A JP 2016-181945 A

However, since the forced commutation control is a method of applying a voltage to each phase of the motor by open-loop control, as a result, current consumption is large, and long-term use is not preferable from the viewpoint of power efficiency. Therefore, at startup, it is desirable to quickly switch from forced commutation control to SFOC with good power efficiency. However, immediately after switching from forced commutation control to SFOC, there is generally a large error in speed estimation, and there is a problem that it takes time for the motor speed to stably converge.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and it is an object of the present invention to provide a technique capable of shortening the start-up time while realizing stable motor control.

In order to solve the above problems, the motor control device according to the present invention has the following configuration. That is, a motor control device for controlling a motor is
detection means for detecting the current flowing through the motor;
estimating means for estimating the rotation speed of the motor from the current detected by the detecting means;
first driving means for driving the motor by forced commutation control;
second driving means for driving the motor by vector control based on the rotational speed of the motor estimated by the estimating means;
controlling the motor to be driven by the first driving means until a first period elapses from the start of control of the motor, and after the elapse of the first period, the second driving means; a first control means for controlling to drive the motor by
a second control means for controlling the execution frequency of the detection means and the estimation means;
has
The second control means controls the execution frequency of the detection by the detection means and the estimation by the estimation means during a second period after switching from driving by the first driving means to driving by the second driving means. is controlled to be higher than the second execution frequency in a third period subsequent to the second period within one control period in the second driving means .

ADVANTAGE OF THE INVENTION According to this invention, the technique which enables shortening of starting time can be provided, realizing stable motor control.

1 is a block diagram of a motor control device; FIG. 4 is a detailed block diagram of a motor speed estimator; FIG. FIG. 10 is a diagram exemplifying a change in the rotation speed of the motor when forced commutation is shifted to SFOC; FIG. 4 is a diagram showing processing timings in SFOC in a steady state; FIG. 10 is a diagram showing processing timing immediately after switching to SFOC; 4 is a flowchart of control mode switching processing; FIG. 7 is a diagram exemplifying the effects of control mode switching processing; FIG. 4 is a diagram showing processing timings of SFOC and engine control in a steady state; FIG. 4 is a diagram showing processing timings of SFOC and engine control immediately after switching to SFOC; 9 is a flowchart of control mode switching processing in the second embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. It should be noted that the following embodiments are not intended to limit the invention according to the scope of claims. Although multiple features are described in the embodiments, not all of these multiple features are essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
As a first embodiment of a motor control device according to the present invention, a motor control device for controlling a three-phase brushless motor will be described below as an example.

<Device configuration>
FIG. 1 is a block diagram of a motor control device according to the first embodiment. The motor control device includes a controller and an engine section.

The engine section includes a motor 100 , a motor driver 106 and a motor current detection section 101 . Here, motor 100 is a three-phase brushless motor. A motor driver 106 applies a pulse voltage to each coil end of the motor 100 to cause current to flow. A motor current detection unit 101 detects coil currents flowing in each phase (here, three phases (U, V, W)) of the motor 100 .

The controller includes an integrated control section 110 and an SFOC (Sensorless Field Oriented Control) section. The general control section 110 centrally manages the engine section and the SFOC section.

The SFOC section includes a motor speed estimation section 102 , a start control section 103 , a PI control section 104 and a PWM control section 105 . A motor speed estimating unit 102 calculates the electrical angle and rotational speed of the motor from two input values, the "three-phase current value" detected by the motor current detecting unit 101 and the "three-phase drive voltage value" applied to each coil end of the motor. to estimate The start control unit 103 instructs the motor current detection unit 101 to detect the motor current, and instructs the motor speed estimation unit 102 to perform estimation calculation. The PI control unit 104 performs proportional integral calculation processing based on the rotational speed of the motor estimated by the motor speed estimating unit 102 . PWM control unit 105 controls the pulse voltage applied to each coil end of motor 100 based on a command from PI control unit 104 .

Here, it is assumed that the processor (CPU) executes a program to implement the SFOC unit by software. However, part or all of it may be configured to be implemented by hardware such as FPGA or custom LSI.

FIG. 2 is a detailed block diagram of the motor speed estimator 102. As shown in FIG. Motor speed estimator 102 includes a three-phase to two-phase converter 120 , an induced voltage calculator 130 , a position calculator 140 , and a speed calculator 150 .

A three-phase to two-phase conversion unit 120 converts the three-phase current values (iu, iv, iw) detected by the motor current detection unit 101 and the three-phase drive voltage values (Vu, Vv, Vw) output by the PWM control unit 105 into It is used as an input, and each is converted into a two-phase component and output. The values converted into two-phase components are defined as two-phase drive voltages (Va, Vb) and two-phase current values (ia, ib), respectively.

The induced voltage calculator 130 calculates an A-phase induced voltage (Ea) and a B-phase induced voltage (Eb) from the two-phase drive voltages (Va, Vb) and the two-phase current values (ia, ib). When this is concretely represented by a formula, it is as follows.
Ea=Va−R×ia−L×dia/dt
Eb=Vb−R×ib−L×dib/dt

Here, R is the winding resistance and L is the winding inductance, each of which has a unique value. Also, dia/dt and dib/dt indicate the rate of current change in a certain time.

The position calculator 140 calculates the position (θ) by obtaining the arctangent of the ratio of the A-phase induced voltage (Ea) and the B-phase induced voltage (Eb). When this is concretely represented by a formula, it is as follows.
θ=tan ⁻¹ (−Eb/Ea)

The speed calculator 150 calculates the estimated speed value (ω) by obtaining the rate of change of the position (θ) in a certain time. When this is concretely represented by a formula, it is as follows.
ω=dθ/dt

FIG. 3 is a diagram exemplifying changes in the rotation speed of the motor when forced commutation is shifted to SFOC. Specifically, it shows the rotation speed of the motor 100 in the prior art in which the forced commutation mode control (forced commutation control) is simply switched to SFOC. The horizontal axis indicates time (t), and the vertical axis indicates motor rotation speed (rpm).

At startup, the motor is first driven in forced commutation mode 203 from speed 0 (zero) to a predetermined threshold speed. In FIG. 3, the predetermined threshold speed is control switching speed 202 . When the motor reaches a predetermined speed, control is switched from forced commutation control to SFOC. Furthermore, after that, when the speed of the motor reaches the target speed 201, the acceleration command is interrupted. After that, the motor continues to be driven at a constant speed until the target speed is changed.

A brief description will be given of control in the forced commutation mode referred to in Background Art. The forced commutation mode is a method of applying voltage to each phase of the motor by open loop control. Since the forced commutation mode consumes a large amount of current, it is not desirable to use it for a very long time. Therefore, it is preferable to switch from the forced commutation mode to the power efficient SFOC as early as possible at startup. However, immediately after switching from the forced commutation mode to the SFOC, the speed estimation error is generally large. Therefore, it takes time for the motor speed to converge to the target speed as indicated by the curve of the starting characteristic 210 .

Therefore, in the first embodiment, speed estimation (and current detection required for speed estimation) is performed more frequently immediately after switching to SFOC, thereby reducing the speed estimation error early.

FIG. 4 is a diagram showing processing timings in SFOC in a steady state. A steady state is, for example, a state in which the motor 100 is stably operating at the target speed 201 . Here, processing timings for two cycles of the PWM control cycle are shown.

In FIG. 4, "PWM" indicates a process of direct-to-current conversion for supplying current to the motor. "ADC" indicates analog-to-digital conversion processing for detecting motor current. "SFOC" refers to motor control. For example, control related to processing of coordinate transformation (three-phase two-phase transformation and rotating coordinate transformation) required for sensorless vector control, speed estimation, speed control, current control, and inverse coordinate transformation (stationary coordinate transformation and two-phase three-phase transformation) to run. "PWM data set" indicates PWM data output processing.

First, current detection processing 301 is performed by the motor current detection unit 101 . Next, motor speed estimation unit 102 performs motor speed estimation processing 302 for estimating the speed of the motor based on the detected current value. After that, the PI control unit 104 performs PI control processing 303 based on the estimated speed, and performs PWM data output processing 304 for outputting data based on the PI control result to the PWM control unit 105 .

FIG. 5 is a diagram showing processing timings in SFOC immediately after switching to SFOC. As mentioned above, the operations shown in FIG. 5 are specific to the first embodiment. In FIG. 4, the current detection process 301 and the motor speed estimation process 302 are each executed once within one control cycle. On the other hand, in FIG. 5, the current detection process 301 and the motor speed estimation process 302 are each executed twice within one control cycle.

First, current detection processing 510 is performed by the motor current detection unit 101 at time t1. Next, the motor speed estimation unit 102 performs motor speed estimation processing 511 for estimating the motor speed (ω1) based on the detected current value.

After that, at time t2, current detection processing 520 is performed by the motor current detection unit 101 . Next, the motor speed estimation unit 102 performs motor speed estimation processing 521 for estimating the motor speed (ω2) based on the detected current value. After that, PI control section 104 performs PI control processing 303 based on the estimated speed (ω2), and performs PWM data output processing 304 for outputting data based on the PI control result to PWM control section 105 .

In the above description, the frequency of current detection and speed estimation calculation is doubled. and the execution frequency of velocity estimation can be further increased.

FIG. 6 is a flowchart of control mode switching processing in the first embodiment. In S601, the integrated control unit 110 starts motor control in the forced commutation mode. Also, acquisition of the rotation speed of the motor 100 is started. Note that the rotation speed of the motor 100 may be obtained by operating the motor speed estimation unit 102 of the SFOC unit, or may be obtained using a separate encoder. In S602, the integrated control unit 110 determines whether or not the rotation speed of the motor 100 has reached the switching speed to SFOC (control switching speed 202), and proceeds to S603 if the switching speed has been reached.

In S603, the integrated control unit 110 switches to motor control by SFOC. In S604, the overall control unit 110 increases the frequency of current detection and speed estimation. For example, control is performed so that current detection and speed estimation are performed twice per control cycle.

In S605, the integrated control unit 110 determines whether or not the rotation speed of the motor 100 has reached the target speed 201. If the target speed 201 has been reached, the process proceeds to S606. In S606, the overall control unit 110 reduces the cycle of current detection and speed estimation. For example, control is performed so that current detection and speed estimation are performed once per control cycle.

FIG. 7 is a diagram exemplifying the effect of the control mode switching process. Specifically, FIG. 3 shows the rotation speed of the motor 100 when the control shown in FIG. 5 is performed after the start of control by SFOC (after reaching the control switching speed 202). As in FIG. 3, the horizontal axis indicates time (t) and the vertical axis indicates motor speed (rpm).

At startup, the motor 100 is first driven in the forced commutation mode 203 from speed 0 (zero) to a predetermined speed. When the motor reaches a control switching speed 202, which is a predetermined threshold speed, control is switched from forced commutation mode to SFOC. Immediately after the control is switched to SFOC, the frequency of current detection and speed estimation is increased as shown in FIG. As a result, the difference from the target speed is corrected at time intervals shorter than the control cycle. As a result, as indicated by the curve of the starting characteristic 710, speed followability with respect to the target speed 201 is improved. Furthermore, after that, when the speed of the motor reaches the target speed 201, the acceleration command is interrupted. Also, as shown in FIG. 4, the frequency of current detection and speed estimation is reduced. After that, the motor continues to be driven at a constant speed until the target speed is changed.

As described above, according to the first embodiment, in the motor control, the motor is driven by the forced commutation mode at the time of start-up and switched to the motor drive by SFOC. Also, immediately after switching to SFOC, the execution frequency of current detection and speed estimation is increased. As a result, it is possible to reduce the estimation error of the motor speed immediately after switching to SFOC, and it is possible to shorten the start-up time while realizing stable motor control.

(Modification)
In the above-described first embodiment, the control is switched to SFOC using the fact that the rotation speed of the motor reaches a predetermined threshold speed as a trigger, but the control may be switched to SFOC based on another trigger. For example, it may be configured to switch to SFOC after a first period (for example, a predetermined number of control cycles) has elapsed from the start of motor control.

In addition, in the above-described first embodiment, the frequency of execution of current detection and speed estimation is reduced when the rotational speed of the motor reaches the target speed as a trigger. Estimation may be performed less frequently. For example, the frequency of current detection and speed estimation may be reduced in a third period following a second period (for example, a predetermined number of control cycles) after transition to SFOC. It is sufficient to increase the frequency of current detection and speed estimation in at least one control cycle immediately after switching to SFOC.

Also, the example of performing current detection and speed estimation twice in one control cycle immediately after switching to SFOC has been described, but it may be performed N times (N is an integer equal to or greater than 2). In that case, the number of times in one control cycle may be gradually reduced. For example, it may be configured to perform three times immediately after shifting to SFOC control, reduce to two times after a predetermined time has elapsed, and reduce to one time after reaching the target speed.

(Second embodiment)
In the first embodiment, the execution frequency of current detection and speed estimation is increased immediately after switching to SFOC, and the execution frequency of current detection and speed estimation is restored after reaching the target speed. In the second embodiment, an example will be described in which the execution frequency of current detection and speed estimation immediately after switching to SFOC is controlled according to the status of other engine control processes.

Other engine control processing here may be, for example, processing for controlling various processes such as charging, exposure, development, transfer, and fixing in a laser beam printer. These engine control processes are executed asynchronously with the SFOC control cycle, and should be completed within a predetermined time from a certain trigger (for example, an interrupt notification indicating that the conveyed paper has reached a predetermined position). Control of nature.

Note that when the engine control process and the SFOC process are processed by one CPU, the time-sharing process is performed by switching at intervals of time. The engine control process is managed and executed by the integrated control unit 110 in the same manner as the SFOC.

FIG. 8 is a diagram showing processing timings of SFOC and engine control in a steady state. A steady state is, for example, a state in which the motor 100 is stably operating at the target speed 201 . Here, as in FIG. 4, processing timings for two PWM control cycles are shown.

Current detection processing 301, motor speed estimation processing 302, PI control processing 303, and PWM data output processing 304 are the same as in FIG. As described above, "engine control processing" indicates processing for controlling various processes in the laser beam printer, and the engine control processing 801 is executed within the control period 300. FIG.

The processing time and execution of the “engine control processing” are managed by the integrated control unit 110 and executed in parallel with the PWM data output processing 304 . The "engine control process" is managed and executed by the integrated control unit 110, but the "PWM data output process" is managed and executed by the PWM module (hardware), so that the processes can proceed in parallel. ing.

FIG. 9 is a diagram showing processing timings of SFOC and engine control immediately after switching to SFOC. In FIG. 8, the current detection process and the motor speed estimation process are each executed once within one control cycle. On the other hand, in FIG. 9, the current detection process and the motor speed estimation process are each executed twice within one control cycle.

First, at time t1, it is determined whether or not the frequency of current detection and speed estimation calculation within the control period 300 can be increased. As a criterion for determination, for example, it is first determined whether or not there is engine control to be performed within the control cycle 300 . In this case, the processing time of the engine control process to be controlled is predicted and divided, and whether or not it is possible to execute up to the divided engine control process 902 even if the frequency of the current detection process and the motor speed estimation process is increased within one control cycle. to decide. Further, when there is no engine control to be controlled within the control cycle 300, even if the frequency of the current detection processing and the motor speed estimation processing is increased within one control cycle as in the first embodiment, the PWM data output processing 304 is executed. Decide if it is possible.

When there is engine control to be performed within the control cycle 300, the determination as to whether the frequency of the current detection process and the motor speed estimation process can be increased can be expressed as follows, for example.
(t2-t1) > Ta (1)
(t3-t2)>Tb (2)

here,
Ta: Total estimated processing time of current detection 510, speed estimation 511, and divided engine control processing 901. do not have)
Tb: Total expected processing time of current detection 520, speed estimation 521, PI control 303, divided engine control processing 902 and PWM data output processing 304, whichever is longer Since it is predicted from the control cycle and the history of a certain period, it is not underestimated.)
is.

The simultaneous establishment of equations (1) and (2) is a condition for increasing the frequency of current detection and speed estimation calculation. If one of the formulas (1) and (2) does not hold, the division ratio between the engine control processing 901 and the engine control processing 902 is adjusted so that the formulas (1) and (2) hold. may (FIG. 9 shows an example in which it is determined that the frequency of current detection processing and motor speed estimation processing can be increased, and current detection and speed estimation calculation are performed twice in one control cycle.)

Processing after the above determination will be described in order. The motor current detection unit 101 performs current detection processing 510 . Next, the motor speed estimation unit 102 performs motor speed estimation processing 511 for estimating the motor speed (ω1) based on the detected current value. After the motor speed estimation process 511 ends, the divided engine control process 901 is executed.

After that, at time t2, the motor current detector 101 performs current detection processing 520 . Next, the motor speed estimation unit 102 performs motor speed estimation processing 521 for estimating the motor speed (ω2) based on the detected current value. After that, PI control section 104 performs PI control processing 303 based on the estimated speed (ω2), and performs PWM data output processing 304 for outputting data based on the PI control result to PWM control section 105 . Also, in parallel with the PWM data output processing 304, the other divided engine control processing 902 is executed. (As already explained, engine control processing and PWM data output processing can be performed in parallel.)

In the above description, the frequency of current detection and speed estimation calculation is doubled, but the frequency may be other than double. The execution frequency of current detection and speed estimation can be further increased as long as either the divided engine control process or the PWM data output process 304 can be completed before the next control cycle starts, whichever has the longer processing time.

FIG. 10 is a flowchart of control mode switching processing in the second embodiment. Since S601 to S603 are the same as those in FIG. 6, description thereof is omitted.

In S1000, at t1 in FIG. 9, the overall control unit 110 determines whether or not there is an engine control process to be controlled within the control cycle 300. FIG. If there is, proceed to S1001, otherwise proceed to S604.

In S1001, at t1 in FIG. 9, the overall control unit 110 predicts the processing time of the engine control process to be controlled within the control cycle 300. FIG. As a method of predicting the processing time, the processing time may be predicted based on the processing performed within the previous control cycle, or the processing time may be predicted based on the processing performed within a certain period of control cycle. may be used. Since the prediction is made from the previous control cycle or the history of a certain period of time, it is never underestimated.

At S1002, the overall control unit 110 divides the predicted engine control process. The method of dividing the engine control process may be equal division, or unequal division according to the priority of the process in the control cycle 300 . Also, it does not have to be divided.

Also, immediately after switching to SFOC, the priority of the engine control process may be lowered to intentionally shorten the processing time required for the engine control process. Also, as described above, if one of the equations (1) and (2) does not hold, the engine control processing 901 and the engine control processing 902 are executed so that the equations (1) and (2) hold. You may adjust a division ratio.

In S1003, the integrated control unit 110 determines whether or not the cycle of current detection and speed estimation calculation can be increased. Specifically, the simultaneous establishment of the above equations (1) and (2) is a condition for increasing the cycle of current detection and speed estimation calculation. If the conditions are satisfied, the process proceeds to S604, and if the conditions are not satisfied, the process proceeds to S605. Since steps S604 to S606 are the same as those in FIG. 6, description thereof will be omitted. Note that when it is determined at time t1 that the frequency of current detection and speed estimation calculation cannot be increased, the processing timing shown in FIG. 8 is adopted.

As described above, according to the second embodiment, in motor control, the motor is driven in the forced commutation mode at the time of start-up and switched to the motor drive in SFOC. In particular, the execution frequency of current detection and speed estimation immediately after switching to SFOC is determined according to the load status of other engine control processes (that is, processes other than vector control). As a result, even when the SFOC process and other engine control processes are performed by a single CPU, it is possible to efficiently change the execution frequency of current detection and speed estimation.

As a result, it is possible to reduce the estimation error of the motor speed immediately after switching to SFOC, and it is possible to shorten the start-up time while realizing stable motor control.

(Other examples)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the claims are appended to make public the scope of the invention.

100 motor; 101 motor current detection unit; 102 motor speed estimation unit; 103 start control unit; 104 PI control unit;

Claims (10)

A motor control device for controlling a motor,
detection means for detecting the current flowing through the motor;
estimating means for estimating the rotation speed of the motor from the current detected by the detecting means;
first driving means for driving the motor by forced commutation control;
second driving means for driving the motor by vector control based on the rotational speed of the motor estimated by the estimating means;
controlling the motor to be driven by the first driving means until a first period elapses from the start of control of the motor, and after the elapse of the first period, the second driving means; a first control means for controlling to drive the motor by
a second control means for controlling the execution frequency of the detection means and the estimation means;
has
The second control means controls the execution frequency of the detection by the detection means and the estimation by the estimation means during a second period after switching from driving by the first driving means to driving by the second driving means. is controlled to be higher than the second execution frequency in a third period following the second period within one control period in the second driving means. motor controller. 2. The motor control device according to claim 1, wherein the first period is a period from when control of the motor is started until the rotational speed of the motor reaches a predetermined threshold speed. 3. The motor control according to claim 1, wherein the second period is a period from switching to driving by the second driving means until the rotational speed of the motor reaches a target speed. Device. 4. The motor control device according to claim 1, wherein the third period is a period during which the motor is rotating at a target speed. 5. The apparatus according to any one of claims 1 to 4, wherein said second driving means performs said vector control in accordance with a difference between the rotational speed of said motor estimated by said estimating means and a target speed. motor controller. The first execution frequency is a frequency of N times (N is an integer equal to or greater than 2) in one control cycle of the second driving means,
6. The motor control device according to claim 1, wherein the second execution frequency is once in one control period of the second driving means. 2. The second control means, in the second period, determines whether or not to increase the first execution frequency based on the load status of processes other than the vector control. 7. The motor control device according to any one of items 1 to 6. 3. The second control means increases the first execution frequency by increasing the priority of the vector control over processes other than the vector control during the second period. 8. The motor control device according to any one of 1 to 7. A control method for a motor control device that controls a motor, comprising:
The motor control device
detection means for detecting the current flowing through the motor;
estimating means for estimating the rotation speed of the motor from the current detected by the detecting means;
first driving means for driving the motor by forced commutation control;
second driving means for driving the motor by vector control based on the rotational speed of the motor estimated by the estimating means;
has
The control method is
controlling the motor to be driven by the first driving means until a first period elapses from the start of control of the motor, and after the elapse of the first period, the second driving means; a first control step of controlling to drive the motor by
Regarding the execution frequency of the detection by the detection means and the estimation by the estimation means, the first execution frequency in a second period after switching from driving by the first driving means to driving by the second driving means is a second control step of controlling to be higher than a second execution frequency in a third period subsequent to the second period within one control period in the second driving means ;
A control method for a motor control device, comprising: A program for causing a computer to function as each means of the motor control device according to any one of claims 1 to 8.

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