JP2718892B2 - Motor control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor in which switching elements are connected in anti-parallel to each phase of a three-phase power supply path, and the control angles of these switching elements are controlled to soft-start and / or soft-stop. It relates to a control method.

[0002]

2. Description of the Related Art For example, when driving a light load such as a fan, a pump or a probe, a switching element is provided in each phase of a power supply path as a method of soft-starting and soft-stopping an electric motor. There is a method of connecting in anti-parallel to change the control angle of each of these switching elements. FIG. 10A shows the relationship between the control angle and the time of each switching element corresponding to soft start and soft stop, and FIG. 10B shows the relationship between the rotation speed of the pump and time corresponding to this. I have.

Here, at the start, the control angle is reduced from the magnitude for generating the starting torque to a minimum value according to a function curve whose time change rate gradually increases, and at the stop, the control angle is changed over time. The rate was increased from a minimum value to a predetermined angle close to the maximum value according to a function curve in which the rate gradually increased.

When such control is executed, as is apparent from the figure, a process of approaching the control angle to the minimum value, that is, a process before and after time t ₁ and a process of sequentially increasing the control angle from the minimum value, ie, time t ₂ After that, vibrations are generated in the pumps. It is considered that this is because the overshoot and the undershoot are repeated without the speed of the motor following the control angle.

As is well known, when the pump vibrates, there is a problem that noise is generated, a water hammer phenomenon occurs at the end, and the life is affected. Also,
Other than the pump, for example, a fan, a motor that drives a light load such as a blower, as described above, the control angle of the switching element is changed, and soft start and soft stop are also generated. In addition, there is a problem that the life is affected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and performs a soft start and / or a soft stop by changing a control angle of a switching element connected in anti-parallel to each phase of a three-phase power supply path. In this case, an object of the present invention is to provide a control method of a motor that can suppress vibration of a load.

[0007]

According to the present invention, a switching element is connected in anti-parallel to each phase of a three-phase power supply path of an electric motor,
In a motor control method in which the motor is soft-started and / or soft-stopped by changing the control angle of each switching element, at the time of start, a start time according to the motor rating is set, and the current flowing through the motor and the current The control angle is reduced from the maximum value according to a substantially constant function curve until the detected current reaches a value at which the starting torque can be generated. From the time when the torque can be generated to the time when the occurrence of vibration of the electric motor is detected, the initial time change rate is remarkably compared with the time change rate before the start torque can be generated. The control angle is reduced according to a function curve that is small and the rate of change over time gradually increases, and the control angle is set after the occurrence of motor vibration is detected. It was until after the start time,
The control rate is reduced to a minimum value according to a function curve in which the initial time rate of change is significantly larger than the time rate of change immediately before the occurrence of the vibration of the electric motor is detected, and thereafter the time rate of change gradually decreases, At the time of a stop, a stop time according to the motor rating is set, and a two-phase control operation is performed by holding the switching elements for one phase in a fully conducting state until the set stop time elapses from the start of the stop, The control angle is increased from the minimum value to the maximum value according to a function curve in which the rate of change over time gradually increases.

The occurrence of vibration of the motor is detected at least once when the detected current of the motor reaches a peak value and thereafter, the vibration width of the current within a predetermined time exceeds a predetermined threshold value. When there is, it is good to judge that vibration has occurred.

[0009]

In the course of repeating the soft-start and soft-stop experiments by changing the control angles of the switching elements connected in anti-parallel to the respective phases of the three-phase power supply path, the inventor has discovered the following. If the control angle at the start is gradually reduced from the maximum value, rather than being set to a value at which the starting torque is suddenly generated, a current corresponding to the load flows and the start can be hastened. After the engine is started, a smooth rotation increasing characteristic can be obtained by gradually increasing the time change rate of the control angle. Vibration occurs when approaching the rated rotation speed, but the amplitude is small in the initial period of the vibration period, and the occurrence of vibration can be detected from this amplitude. Then, by rapidly changing the control angle to the minimum value after the occurrence of vibration is detected,
Vibration at the start can be substantially suppressed. When the operation is switched to the two-phase control operation at the time of stop and the control angle is increased from the minimum value by gradually increasing the time change rate, the vibration can be suppressed.

Therefore, in the present invention, at the start, the control angle is reduced from the maximum value according to a substantially constant function curve until the detected current reaches a value capable of generating the starting torque. From the occurrence until the occurrence of vibration is detected, the control angle is decreased according to a function curve whose time change rate gradually increases, and thereafter, the control angle is reduced to a minimum value according to a function curve whose time change rate gradually decreases, In addition, at the time of stop, the two-phase control operation is performed by holding the switching elements for one phase in the full conduction state, and the control angle is increased from the minimum value to the maximum value according to a function curve in which the rate of change with time gradually increases. . This makes it possible to suppress the vibration of the load and to speed up the start-up by supplying a current corresponding to the load.

In addition, when the detected current of the motor reaches a peak value and the oscillation width of the current within a predetermined time after that has at least once exceeded a preset threshold value, the oscillation of the By determining that vibration has occurred, the microcomputer can easily and reliably detect vibration.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram showing an example of the configuration of an apparatus embodying the present invention, in which a pump is driven as a load. In FIG. 1, semiconductor switches 2, 3, and 4 are connected to U, V, and W-phase power supply paths for supplying electric power from the three-phase AC power supply 1 to the electric motor 5, respectively.
A pump 6 is connected to the electric motor 5. A primary side of a single-phase transformer 7 is connected between the U-phase and the V-phase of the three-phase AC power supply 1, and a rectifier circuit 8 is connected to a secondary side of the transformer 7.
Is connected. The rectifier circuit 8 supplies operating power to the microcomputer 9. On the secondary side of the transformer 7, a synchronization signal generation circuit 10 for generating a power supply synchronization signal is provided.
Is connected. The microcomputer 9 uses the synchronization signal of the synchronization signal generation circuit 10 to switch the semiconductor switches 2, 3,
4 is controlled. In this case, a current transformer 11 for detecting a current flowing through the motor 5 is provided, and when the rectifier circuit 12 rectifies an alternating current generated on the secondary side, the A / D converter 13 converts the output to a digital signal. In addition to the microcomputer 9. The microcomputer 9 reads the current value and uses it for calculating the control angles of the semiconductor switches 2, 3, and 4. Further, the microcomputer 9 detects a vibration of the electric motor 5 from the read current value.
The control state of the control angle is changed according to the occurrence of vibration.

FIG. 2 shows an example of the configuration of the semiconductor switches 2, 3, and 4. Here, thyristors 21 and 22 are connected in anti-parallel, and the microcomputer 9 applies an ignition pulse to each gate of these thyristors. It has become.

Although not shown, the synchronization signal generating circuit 10 applies a voltage obtained by half-wave rectification by a diode to a resistor having the other end grounded, and further applies a voltage to one end of the resistor. The generated voltage is applied to an operational amplifier via an integrator, and the output of the operational amplifier is used as a synchronization signal. The microcomputer 9 has a setting device (not shown) for setting a current capable of generating a starting torque in accordance with the load of the load. The current value can be set. Further, although not shown, the microcomputer 9 is provided with a setting device for setting a start time from starting to reaching the rated speed and a stop time from the rated speed to stopping, and a control angle for the switching element. A setting device for variably setting the minimum value and a setting device for setting a threshold value of the vibration width for judging the occurrence of vibration from the current value are also provided.

The operation of the embodiment constructed as described above will be described below. The U-phase and V-phase line voltages of the three-phase AC power supply 1 are stepped down by the transformer 7 and input to the rectifier circuit 8. The rectifier circuit 8 performs full-wave rectification on the input voltage and applies it to the microcomputer 9 as operating power. On the other hand, the synchronization signal generating circuit 10 outputs a rectangular wave signal whose level is inverted at each zero cross point of the AC power supply voltage from the half-wave rectified signal. The microcomputer 9 detects the rise of the rectangular wave signal and controls the ignition time of the semiconductor switches 2, 3, and 4, that is, the control angle.

FIG. 3A shows a change in the control angle α when the motor starts and stops, and FIG. 3B shows a current I and the number of revolutions per minute of the motor corresponding to the change in the control angle α. The change of N is shown.

The microcomputer 9 decreases the control angle α from the maximum value α _max to the minimum value α _min at the start according to the function curves of the curve 1, the curve 2 and the curve 3, and at the stop, the control angle α according to the function curve of the curve 4. From the minimum value α _min to the maximum value α _max .

Of the four curves in FIG. 3A, curve 1
Should be called a straight line because the rate of change over time is constant, but there are also parts where the rate of change is approximately constant when looking at some sections of the function curve. I will use it.

Now, a setter (not shown) sets a current value I ₁ capable of generating a starting torque according to the load, and also sets a start time, a stop time, a threshold value for vibration detection, and the like. The microcomputer 9 reads these set values and also reads the current detection values obtained by the current transformer 11, the rectifier circuit 12, and the AD converter 13. Then, as shown in FIG. 3, until the current detection value I reaches the set value I _1, for example, reducing the control angle alpha from alpha _max according curve 1 having a time rate of change of 2 ° / cycle. This causes the current I to increase rapidly.

Next, when the current I reaches the set value I ₁ , A
Point, i.e., when the control angle is alpha _1, in turn reduces the control angle from the alpha ₁ in accordance with the curve 2 which varies in proportion to the square of the time to alpha _{mi n.} Here, the current I is equal to the set value I ₁
When the time at which the start time is reached is t _A , and the time at which the set start time elapses from this time t _A is t _C , the curve 2 has a point A (t _A , α ₁ ) and a point C (t _C , α _min). ) And an upwardly concave quadratic function. As described above, when the control angle α is decreased according to the curve 2, the electric current I of the motor continuously increases, but reaches a maximum at a certain point in time, and thereafter decreases and settles to the rated current. On the other hand, the electric motor 5 operates at time t _A.
Starts immediately before the time t, and approaches the rated rotational speed earlier than the time t _C is reached.

Next, while the rotation speed N of the electric motor 5 approaches the rated rotation speed, the electric motor 5 and the pump 6 vibrate as described above. This vibration causes a pulsation of the current I of the motor. The microcomputer 9 detects the occurrence of vibration from the pulsation of the current I. Then, the vibration at the point B on the curve 2 is detected, the control angle at that time time in alpha ₂ and was t _B. After this point B, the microcomputer 9
Reduces the control angle α from α ₂ to α _min according to curve 3. Here, curve 3 is obtained by comparing point B (t _B , α ₂ ) and C
This is a function curve that is determined so as to pass through the point (t _C , α _min ) and whose time change rate is proportional to the time t. By reducing the control angle α according to the curve 3, when the occurrence of vibration is detected, a jump operation for rapidly reducing the control angle to the minimum value α _min is performed. As a result, the large vibration at the start described with reference to FIG. 10 does not appear, and the motor 5 is settled to the rated speed in a short time.

Next, in order to stop the motor 5, D
When the vehicle is completely stopped at the point E at which the set stop time has elapsed from the point, the control angle α is increased from the minimum value α _min to the maximum value α _max according to the curve 4. Curve 4 is a quadratic function convex upward through point _D (t _D , α _min ) and point E (t _E , α _max ).

During this stop period, ie,
From time t _D to time t _E holds the switching element of one phase to full energization state to control the control angle of the other two phases of the switching elements, so called, has a two-phase control operation. During this period, the current I increases once and then rapidly drops to zero. As a result, the large vibration at the time of the stop described with reference to FIG. 10 can be suppressed.

FIG. 4 is an explanatory diagram for explaining a specific embodiment of the curves 2 and 3 described above. As shown, the times at points A, B, and C are denoted as t _A , t _B , and t _C , respectively.
Let each control angle be α _A , α _B , α _min . Also, point B and C
The control angle of the time t _n which were assumed between the point alpha _n, the time t
_Let the control angle of _{n + 1} be α _{n + 1} .

Curve 2 is a function curve satisfying the following relational expression.

[0026]

(Equation 1) Curve 3 is a function curve satisfying the following relationship.

[0027]

(Equation 2) (2) The following equation can be written separately.

[0028]

(Equation 3) Here, t _C -t _n is the remaining time, and y = 1 / x is a time compression function. Generally, y = c / x, where c is a constant,
The possible range of y is y = {0, 1}.

FIG. 5 is a flowchart showing a processing procedure of the microcomputer 9 for executing the above control. Here, first, after initializing the system, which is the normal initial setting of the microcomputer, and enabling interrupts,
Determine if the power frequency is 50Hz or 60Hz, then
It is determined whether there is an error such as a power failure in the power supply (steps 101 to 104). If there is an error, a process corresponding to the error is executed, and an error is displayed (steps 105 and 106).
).

Next, if there is no error, it is determined whether or not there is a command for a sudden stop, an acceleration command corresponding to a start, or a deceleration command corresponding to a stop (steps 107 and 108).
). If there is a sudden stop command, stop processing is executed (step 115), and if it is an acceleration command, the following processing is executed.

That is, start time, stop time,
It is checked whether or not parameters such as a threshold value of the vibration width have been input to detect the generation of vibration from the control angle α _min , the set current value I _1, and the current, and if not, these parameters are input (step 109,110). Then, it is checked whether the curves 1 and 2 have been calculated (step 111). Then, the entire system including the microcomputer is started, and the weight of the load, that is, the set current value I
₁ is read, and curves 1 and 2 are calculated (steps 112 to 112).
114).

On the other hand, if it is a deceleration command, it is determined whether or not the curve has been calculated (step 116). If not, the process proceeds to the next step. The process proceeds to the next process even at the end of the process.

That is, a rated current and a threshold value for detecting the occurrence of vibration are input, it is determined whether or not vibration has occurred, and if vibration has occurred, curve 3 is calculated (step 117).
~ 120). Then, whether the command is an acceleration command or a deceleration command is checked again. If the command is an acceleration command, the control angle α corresponding to the time is determined.
Are obtained from the calculated curves 1, 2, and 3, phase control is executed until the acceleration is completed, and the acceleration is displayed (steps 121 to 126). When the acceleration is completed, full voltage control is performed and the fact is displayed (steps 127 to 129).
If the command is a deceleration command, the control angle α corresponding to the time is obtained from the curve 4, the two-phase control operation is performed according to the control angle α, and the deceleration operation is displayed (steps 130 to 130).
133) Finally, the stop processing is executed (steps 134 to 13).
Five ).

The process of detecting the occurrence of vibration based on the detected current of the motor (step 118) is described in FIG.
This will be described in more detail with reference to FIG. Curves 1 and 2
When the control angle is changed according to the following equation, as shown in FIG.
After the motor current increases rapidly, it starts to decrease,
Pulsates in the process of setting to the rated current. Here, a point at which the current reaches the peak value is defined as a point M, and a difference between a peak and a valley of the pulsating current is defined as a vibration width _Fv . When vibration is not suppressed, FIG.
As shown in FIG. 6, the pulsation is repeated many times, and the current value repeats the same change. However, FIG. 6 shows only the initial vibration, and the other states are suppressed. As is clear from this figure, after the vibration width _Fv gradually increases,
It is getting smaller gradually toward zero.

[0035] The current I is in this embodiment are sampled at a predetermined sampling period T, the current I reaches the point M, and the threshold value F, the oscillation width F _v is preset current within a predetermined time thereafter _{When vo} is exceeded, it is determined that vibration has occurred.

That is, in the process for detecting the occurrence of vibration (step 118), as shown in FIG. 7, the threshold value _Fvo of the vibration width set first is read (step 1181), and then the current I is sampled. (Step 1182). Next, it is confirmed that the point M has passed (step 1183), the vibration width _Fv is calculated, and the calculated value is stored (step 11).
84). Next, the stored vibration width _Fv and the vibration width threshold value _Fvo
(Step 1185), and when the condition of F _v > F _vo is satisfied, a flag of occurrence of vibration is set (step 118).
6). In order to prevent erroneous detection due to disturbance, F _v > F
_The vibration generation flag may be set when the state of “ _vo” has been continued two or more appropriate times.

With the above processing, the above-described vibration suppression control at the start and the vibration suppression control at the stop can be executed.

FIG. 8 shows actually measured values of the current I and the rotational speed N at the start using the conventional control method for reference. As is apparent from this figure, the rotation speed fluctuates immediately before reaching the rated rotation, and at the same time, the current I fluctuates greatly.

FIG. 9 shows actually measured values of the current I and the number of revolutions N at the start and at the stop according to the method of the present embodiment using the same apparatus as described above. As is clear from this figure, at both the start time and the stop time, the fluctuation of the rotation speed N and the current I is small, so that the vibration is suppressed to be low.

In the above embodiment, thyristors connected in antiparallel are used as the semiconductor switches 2, 3, and 4. However, the same control as described above can be performed by using a triac (bidirectional three-terminal thyristor) instead. it can.

Further, in the above embodiment, the control of the motor for driving the pump has been described. However, the present invention is not limited to this, and can be applied to those for driving a light load such as a fan or a blower. Yes, and is also applicable to those that drive heavier loads.

[0042]

As is apparent from the above description, according to the present invention, a switching element is connected in anti-parallel to each phase of the power supply path, and the control angle of each of these switching elements is controlled to provide a soft start. In addition, even when a soft stop is performed, the vibration of the load can be reliably suppressed. In addition, by decreasing the control angle from the maximum value according to a function curve having a substantially constant time rate of change until reaching a value at which the starting torque can be generated, the starting can be accelerated even when the load is heavy.

Also, the current of the motor reaches the peak value,
When the vibration width exceeds the threshold value at least once thereafter, it is determined that the vibration has occurred, so that the microcomputer can easily and reliably detect the vibration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an apparatus for implementing the present invention.

FIG. 2 is a circuit diagram showing a detailed configuration of main elements of an apparatus for implementing the present invention.

FIG. 3 is a diagram showing a relationship between a control angle with respect to a switching element, a motor current and a motor rotation speed, and time in order to explain an operation of the device embodying the present invention.

FIG. 4 is a detailed explanatory diagram for determining a control angle for a switching element for implementing the present invention.

FIG. 5 is a flowchart illustrating a processing procedure of a microcomputer that implements the present invention.

FIG. 6 is a diagram showing a relationship between current and time for explaining the principle of vibration detection of the present invention.

FIG. 7 is a flowchart showing a detailed processing procedure of a microcomputer embodying the present invention.

FIG. 8 is an actually measured value showing a change in current and rotation speed at the time of start according to the conventional control method.

FIG. 9 is an actually measured value showing a change in a control angle, a current and a rotation speed at the time of start and at the time of stop according to the embodiment of the present invention.

FIG. 10 is a diagram showing a relationship between a control angle with respect to a switching element and a rotation speed and time according to a conventional control method.

[Explanation of symbols]

 2,3,4 Semiconductor switch 5 Motor 6 Pump 7 Transformer 8 Rectifier circuit 9 Microcomputer 10 Synchronous signal generation circuit 11 Current transformer 12 Rectifier circuit 13 A / D converter

Continued on the front page (72) Inventor Teruo Nonaga 1-10-13 Iguchi, Mitaka City, Tokyo Kasuga Electric Co., Ltd. JP-A-54-39824 (JP, A) JP-A-50-54821 (JP, A) JP-A-6-245560 (JP, A) JP-A-2-95186 (JP, A) ) Shokai Sho 59-141496 (JP, U)

Claims (4)

(57) [Claims] 1. A motor control method for connecting a switching element to each phase of a three-phase power supply path of an electric motor in an anti-parallel manner and changing the control angle of each switching element to soft-start the electric motor. The start time is set, and the current flowing through the motor and the occurrence of vibration of the motor are detected based on the current, and the rate of time change until the detected current reaches a value that can generate the starting torque is determined. The control angle is reduced from a maximum value according to a substantially constant function curve, and the start angle is reduced from when the detected current reaches a value capable of generating the start torque until the occurrence of vibration of the electric motor is detected .
Time change rate and ratio before reaching a value that can generate lux
In comparison, the control angle is reduced according to a function curve in which the initial time rate of change is remarkably small and the time rate of change thereafter gradually increases, and the set start time elapses after the occurrence of vibration of the electric motor is detected. Until the vibration of the motor
Initial time change compared to the time change rate immediately before detection
A control method for an electric motor, comprising: decreasing a control angle to a minimum value according to a function curve in which a rate is remarkably large and a time rate of change thereafter gradually decreases. 2. A method for controlling a motor in which a switching element is connected in anti-parallel to each phase of a three-phase power supply path of the motor and the control angle of each switching element is changed to soft-stop the motor. A two-phase control operation is performed by holding the switching elements for one phase in a fully-conductive state until the set stop time elapses from the start of the stop, and the time change rate gradually increases. A control angle increasing from a minimum value to a maximum value according to a function curve. 3. A method for controlling a motor in which a switching element is connected in anti-parallel to each phase of a three-phase power supply path of the motor and the control angle of each switching element is changed to soft-start and soft-stop the motor. A start time and a stop time according to the rating are set, and a current flowing through the motor and the occurrence of vibration of the motor are detected based on the current, and the detected current reaches a value that can generate a starting torque. up to the time rate of change substantially reduced from the maximum value of the control angle according to a certain function curve, generation of vibration of the motor from reaching the value detected current can generate starting torque is detected, the Starting
Time change rate and ratio before reaching a value that can generate lux
In comparison, the control angle is reduced according to a function curve in which the initial time rate of change is remarkably small and the time rate of change thereafter gradually increases, and the set start time elapses after the occurrence of vibration of the electric motor is detected. Until the vibration of the motor
Initial time change compared to the time change rate immediately before detection
The control angle is reduced to a minimum value according to a function curve in which the rate is extremely large and the time rate of change thereafter gradually decreases, and the switching elements for one phase are all switched until the set stop time elapses from the start of the stop. A two-phase control operation by maintaining a conduction state, and increasing a control angle from a minimum value to a maximum value according to a function curve in which a time change rate gradually increases. 4. The method according to claim 1, wherein the detection of the occurrence of the vibration of the electric motor is performed when the detected current of the electric motor reaches a peak value and thereafter, the vibration width of the electric current within a predetermined time exceeds a preset threshold value. 4. The method according to claim 1, wherein it is determined that vibration of the electric motor has occurred when at least once.