JPH07322660A - Control method of motor - Google Patents

Abstract

PURPOSE:To damp the vibrations of load positively even at the time of a soft start and a soft stop by connecting switching elements in antiparallel with each phase of a power supply path and controlling the phase-control angles of each switching element. CONSTITUTION:When a current transformer 11 detecting currents flowing through a motor 5 is mounted and ACs generated on the secondary side are rectified by a rectifier circuit 12, an A-D converter B converts ACs into a digital signal, and transmits the signal over a microcomputer 9. The microcomputer 9 reads the current value, and uses the current value for arithmetically operating the phase-control angles of semiconductor switches 2, 3, 4. A detecting means 9a detecting the vibrations of the motor 5 from the read current value is provided, and the state of the control of the phase-control angles is changed in response to the generation of vibrations. The line voltage in v phase and V phase of a three-phase AC power 1 is stepped down by a transformer 7, and input to a rectifier circuit 8. The microcomputer 9 detects the rise of the rectangular wave signal of AC power-supply voltage, and controls the firing time, the phase-control angles, of the semiconductor switches 2, 3, 4.

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 antiparallel 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. Regarding control method.

[0002]

2. Description of the Related Art For example, in the case of driving a light load such as a fan, a pump or a plier, a switching element is provided in each phase of the power supply path as a method of soft starting and soft stopping the motor. There is a method of connecting in antiparallel and changing the control angle of each of these switching elements. FIG. 10 (a) shows the relationship between the control angle of each switching element corresponding to soft start and soft stop and time, and FIG. 10 (b) shows the relationship between the rotational speed and time of the corresponding pump. There is.

Here, at the time of start, the control angle is decreased from the magnitude for generating the starting torque to a minimum value according to a function curve in which the rate of change with time gradually increases, and at the time of stop, the control angle is changed with time. The value 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, the process of approaching the control angle to the minimum value, that is, before and after time t ₁ , and the process of gradually increasing the control angle from the minimum value, that is, time t _2. After and after, vibration is generated in the pump. It is considered that this is because the speed of the electric motor does not follow the control angle and repeats overshoot and undershoot.

As is well known, when the pump vibrates, noise is generated, and at the end, there is a problem that a water hammer phenomenon occurs and the life is affected. Also,
Other than a pump, for example, a fan, a blower, or the like, a motor for driving a light load, similar to the above, when the control angle of the switching element is changed to soft start and soft stop, the same vibration occurs and noise is generated. In addition, there is a problem that the life is affected.

The present invention has been made to solve the above problems, and soft-starts and / or soft-stops by changing the control angle of a switching element connected in antiparallel to each phase of a three-phase power supply path. In this case, it is an object of the present invention to provide a method for controlling an electric motor that can suppress load vibration.

[0007]

According to the present invention, a switching element is connected in antiparallel to each phase of a three-phase power supply path of an electric motor,
In the motor control method of changing the control angle of each of these switching elements to soft start and / or soft stop the motor, at the time of start, the start time according to the motor rating is set, and the current flowing in the motor and this current Based on a function curve with a substantially constant time change rate, the control angle is reduced from the maximum value until the detected current reaches a value at which the starting torque can be generated. The control angle is decreased according to a function curve in which the rate of change with time gradually increases until the occurrence of the vibration of the motor is detected after the value at which the torque is generated is detected, and it is set after the occurrence of the vibration of the motor is detected. The control angle is reduced to a minimum value according to a function curve in which the time change rate gradually decreases until the start time At the top, a stop time is set according to the motor rating, and two-phase control operation is performed by holding the switching elements for one phase in the fully conductive 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 with time gradually increases.

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

[0009]

In the process of repeating the soft start and soft stop experiments by changing the control angles of the switching elements connected in antiparallel to the respective phases of the three-phase power supply path, the inventor discovered the following items (1) to (3). If the control angle at the time of start is gradually decreased from the maximum value rather than being suddenly set to a value at which the starting torque is generated, a current corresponding to the load flows and the start can be accelerated. After the start, a smooth rotation increasing characteristic can be obtained by gradually increasing the rate of change of the control angle with time. Vibration occurs when approaching the rated speed, but the amplitude is small at the beginning of the vibrating 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. Vibration can be suppressed by switching to the two-phase control operation at the time of stop and increasing the control rate from the minimum value by gradually increasing the time change rate.

Therefore, in the present invention, at the time of start, the control angle is decreased from the maximum value according to a function curve having a substantially constant time change rate until the detected current reaches a value at which the starting torque can be generated. 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 then the control angle is decreased to a minimum value according to a function curve where the 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 fully conductive state, and the control angle is increased from the minimum value to the maximum value according to a function curve whose time change rate gradually increases. . As a result, vibration of the load can be suppressed, and a current corresponding to the load can be passed to accelerate the start.

Further, when the detected current of the electric motor reaches the peak value and the vibration width of the electric current within a predetermined time has exceeded the preset threshold value at least once after that, the vibration of the electric motor is detected. By determining that the vibration has occurred, the vibration can be easily and reliably detected by the microcomputer.

[0012]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram showing a configuration example of an apparatus for carrying out the present invention, showing a case where a pump is driven as a load. In the figure, semiconductor switches 2, 3 and 4 are respectively 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.
A pump 6 is connected to the electric motor 5. The primary side of the single-phase transformer 7 is connected between the U-phase and the V-phase of the three-phase AC power supply 1, and the rectifier circuit 8 is connected to the secondary side of the transformer 7.
Are connected. The rectifier circuit 8 supplies operating power to the microcomputer 9. In addition, on the secondary side of the transformer 7, a synchronization signal generation circuit 10 for generating a power supply synchronization signal is provided.
Are connected. The microcomputer 9 uses the sync signal from the sync signal generating circuit 10 to switch the semiconductor switches 2, 3,
The control angle of 4 is controlled. In this case, the current transformer 11 for detecting the current flowing through the electric motor 5 is provided, and when the rectifier circuit 12 rectifies the alternating current generated on the secondary side, the A / D converter 13 converts its output into a digital signal. It is added to the microcomputer 9. The microcomputer 9 reads the current value and uses it to calculate the control angles of the semiconductor switches 2, 3, 4. Further, the microcomputer 9 detects the vibration of the electric motor 5 from the read current value, and the vibration detecting means 9a.
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, in which a thyristor 21 and a thyristor 22 are connected in antiparallel so that the microcomputer 9 applies an ignition pulse to each gate of these thyristors. It has become.

Although not shown, the synchronizing signal generating circuit 10 applies a voltage obtained by half-wave rectifying with a diode to a resistor whose other end is grounded, and further applies it to one end of this resistor. The generated voltage is applied to an operational amplifier via an integrator, and the output of this operational amplifier is used as a synchronizing signal. Further, the microcomputer 9 is provided with a setting device (not shown) for setting a current that can generate a starting torque according to the weight of the load, and the setting device sets 0 to 200% of the rated current of the electric motor 5 by this setting device. The current value can be set. Further, although not shown, the microcomputer 9 sets a start time from the start to the rated speed and a stop time from the rated speed to the stop, and a control angle for the switching element. A setter for variably setting the minimum value and a setter for setting a threshold value of the vibration width for judging the occurrence of vibration from the current value are also attached.

The operation of this embodiment configured 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 full-wave rectifies the input voltage and applies it to the microcomputer 9 as operating power. On the other hand, the synchronization signal generation circuit 10 outputs a rectangular wave signal whose level is inverted from the half-wave rectified signal at each zero-cross point of the AC power supply voltage. The microcomputer 9 detects the rising edge of the rectangular wave signal and controls the firing time of the semiconductor switches 2, 3 and 4, that is, the control angle.

FIG. 3 (a) shows changes in the control angle α at the start and stop of the motor, and FIG. 3 (b) shows the current I of the motor and the revolutions per minute corresponding to the change in the control angle α. The change in N is shown.

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

Of the four curves in FIG. 3 (a), curve 1
Should be called a straight line because the rate of change over time is constant, but there is also a portion where the rate of change becomes almost constant when looking at some sections of the function curve, so the term curve is used here. I will use it.

Now, with a setting device (not shown), a current value I ₁ that can generate a starting torque according to the load is set, and a start time, a stop time, a vibration detection threshold value, and the like are set. The microcomputer 9 reads these set values and also the current detection values by the current transformer 11, the rectifier circuit 12 and the AD converter 13. Then, as shown in FIG. 3, the control angle α is decreased from α _max until the detected current value I reaches the set value I ₁ , for example, according to the curve 1 having a time change rate of 2 degrees / 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 the set value I ₁
Assuming that the time to arrive at t is t _A and the time when the start time set from this time t _A has elapsed is t _C , the curve 2 has point A (t _A , α ₁ ) and point C (t _C , α _min). ) And is a quadratic function that is concave upward through. Thus, when the control angle α is decreased according to the curve 2, the electric current I of the electric motor continues to increase, reaches a maximum at a certain point, and then decreases to settle to the rated current. On the other hand, the electric motor 5 is at time t _A.
The rotation starts immediately before, and approaches the rated rotation speed earlier than the time t _C.

Next, while the rotational speed N of the electric motor 5 approaches the rated rotational speed, the electric motor 5 and the pump 6 vibrate as described above. This vibration causes pulsation of the electric current I of the electric motor. The microcomputer 9 detects the occurrence of vibration from the pulsation of the current I. Then, it is assumed that this vibration is detected at the point B on the curve 2, the control angle at that time is α ₂ , and the time is t _B. After this point B, the microcomputer 9
Reduces the control angle α according to curve 3 from α ₂ to α _min . Here, the curve 3 is at point B (t _B , α ₂ ), and C
It is a function curve which is defined so as to pass through the point (t _C , α _min ) and whose time change rate is proportional to time t. By decreasing the control angle α according to the curve 3, when the occurrence of vibration is detected, a jumping 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 electric motor 5 is settled at the rated rotation speed in a short time.

Next, in order to stop the electric motor 5, D
When completely stopping at the point E when 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. The curve 4 is a quadratic function which is convex upward and passes through the point _D (t _D , α _min ) and the point E (t _E , α _max ).

During this stop period, that is,
From time t _D to time t _E , so-called two-phase control operation is performed in which the switching elements for one phase are held in a fully conductive state and the control angles of the switching elements for the other two phases are controlled. During this period, the current I once increases and then rapidly drops to zero. As a result, the large vibration at the time of stop described with reference to FIG. 10 can be suppressed.

FIG. 4 is an explanatory view for explaining a concrete example of the curves 2 and 3 described above. As shown in the figure, the time points A, B, and C are defined as t _A , t _B , and t _C ,
Let each control angle be α _A , α _B , and α _min . Also, point B and C
The control angle at time t _n assumed between the point and the point is α _n , at time t
the control angle of the _{n + 1} and α _{n + 1.}

Curve 2 is a function curve that satisfies the following relational expression.

[0026]

[Equation 1] Curve 3 is a function curve that satisfies the following relationship.

[0027]

[Equation 2] If the equation (2) is written separately, it is as follows.

[0028]

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

FIG. 5 is a flow chart showing the processing procedure of the microcomputer 9 which executes the above control. Here, first, after initializing the system, which is the normal initialization of the microcomputer, and enabling interrupts,
Judge whether the power supply frequency is 50Hz or 60Hz, and then
It is determined whether or not the power supply has an error such as a power failure (steps 101 to 104). If there is an error, the corresponding process is executed and the error is displayed (steps 105 and 106).
).

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

That is, the start time, the stop time,
It is checked whether or not parameters such as a threshold value of the vibration width have been input to detect the occurrence of vibration from the control angle α _min , the set current value I ₁ and the current. If they have not been input, these parameters are input (step 109,110). Then, it is checked whether or not 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-
114).

On the other hand, if it is a deceleration command, it is judged whether or not the curve has been calculated (step 116), and when not calculated, the process proceeds to the next step. Even when the process is completed, the next process is performed.

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

By the way, the contents of the process (step 118) for detecting the occurrence of vibration based on the detected current of the electric motor will be described with reference to FIG.
Further, a more detailed description will be given with reference to FIG. Curves 1 and 2
When the control angle is changed according to, as shown in FIG.
The motor current increases rapidly and then begins to decrease.
Pulsates in the process of settling to the rated current. Here, the point at which the current reaches the peak value is set as point M, and the difference between the peak and the valley of the pulsating current is set as the vibration width F _v . When vibration is not suppressed,
As shown in FIG. 6, the pulsation is repeated many times and the current value also repeats the same change, but FIG. 6 shows only the initial vibration, and the other shows the suppressed state. As is clear from this figure, after the vibration width F _v gradually increases,
It is getting smaller toward zero.

In this embodiment, the current I is sampled at a predetermined sampling period T, the current I reaches the point M, and thereafter, the oscillation width F _v of the current within a predetermined time is a preset threshold F. _When it exceeds _vo , it is judged that vibration has occurred.

That is, in the process of detecting the occurrence of vibration (step 118), as shown in FIG. 7, the initially set vibration width threshold F _vo is read (step 1181), and then the current I is sampled. Yes (step 1182). Next, it is confirmed that the point M has passed (step 1183), the vibration width F _v is calculated, and the calculated value is saved (step 11).
84). Next, the stored vibration width F _v and the vibration width threshold F _vo
And (step 1185), and when the condition of F _v > F _vo is satisfied, the vibration occurrence flag 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 _vo state continues for an appropriate number of times of two or more.

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

FIG. 8 is a measured value showing the current I and the number of revolutions N at the time of start employing the conventional control method for reference. As is clear from this figure, it is understood that the current I fluctuates greatly at the same time that the rotational speed fluctuates immediately before reaching the rated speed.

FIG. 9 is an actual measurement value showing the current I and the rotation speed N at the time of starting and at the time of stopping by the method of this embodiment using the same apparatus as described above. As is apparent from this figure, the fluctuations in the rotation speed N and the current I are small at both the start time and the stop time, so that it is understood that the vibration is suppressed to a low level.

Although the thyristors connected in anti-parallel are used as the semiconductor switches 2, 3 and 4 in the above embodiment, the same control as described above can be achieved by using a triac (bidirectional 3-terminal thyristor) instead. it can.

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

[0042]

As is apparent from the above description, according to the present invention, the switching element is connected in antiparallel to each phase of the power supply path and the control angle of each of these switching elements is controlled to be soft-started. Even in the case of soft stop, the vibration of the load can be surely suppressed. Further, by decreasing the control angle from the maximum value in accordance with a function curve having a substantially constant time change rate until the value at which the starting torque can be generated is reached, it is possible to accelerate the start even when the load is heavy.

Further, when the electric current of the electric motor reaches the peak value,
When the vibration width exceeds the threshold value at least once after that, it is possible to easily and surely detect the vibration by the microcomputer by determining that the vibration has occurred.

[Brief description of drawings]

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

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

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

FIG. 5 is a flowchart showing a processing procedure of a microcomputer for carrying out the present invention.

FIG. 6 is a diagram showing the relationship between current and time in order to explain the vibration detection principle of the present invention.

FIG. 7 is a flowchart showing a detailed processing procedure of a microcomputer according to an embodiment of the present invention.

FIG. 8 is an actual measurement value showing changes in current and rotation speed at the start according to the conventional control method.

FIG. 9 is an actual measurement value showing changes in the control angle, the current, and the rotation speed at the start and the stop according to the embodiment of the present invention.

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

[Explanation of symbols]

 2, 3, 4 Semiconductor switch 5 Electric 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

Front page continuation (72) Inventor Teruo Nodai 1-10-13 Iguchi, Mitaka City, Tokyo Kasuga Electric Machinery Co., Ltd. (72) Inventor Shionogi 1-10-13 Iguchi, Mitaka City, Tokyo Kasuga Electric Machine Co., Ltd.

Claims (4)

[Claims] 1. A method of controlling an electric motor, wherein switching elements are connected in antiparallel to respective phases of a three-phase power supply path of the electric motor, and a control angle of each switching element is changed to soft start the electric motor. The start time is set and the current flowing in the electric motor and the occurrence of vibration of the electric motor are detected based on this current, and the time change rate is set until the detected current reaches a value that can generate the starting torque. The control angle is decreased from the maximum value according to a substantially constant function curve, and the time rate of change gradually increases until the occurrence of vibration of the electric motor is detected after the detected current reaches a value capable of generating the starting torque. The control angle is decreased according to a function curve, and a time change is performed from when the occurrence of vibration of the electric motor is detected until a set start time elapses. A method of controlling a motor, characterized in that the control angle is reduced to a minimum value according to a function curve in which the rate gradually decreases. 2. A method of controlling an electric motor, wherein switching elements are connected in antiparallel to respective phases of a three-phase power supply path of the electric motor, and the control angles of these switching elements are changed to soft stop the electric motor. The stop time is set, and the two-phase control operation is performed by holding the switching elements for one phase in the fully conductive state until the set stop time elapses from the start of the stop, and the time change rate gradually increases. A control method for an electric motor, characterized in that the control angle is increased from a minimum value to a maximum value according to the following function curve. 3. A method of controlling a motor, wherein switching elements are connected in antiparallel to respective phases of a three-phase power supply path of the motor and the control angles of these switching elements are changed to soft start and soft stop the motor. The start time and stop time are set according to the rating, and the current flowing through the electric motor and the occurrence of vibration of the electric motor are detected based on this current, and the detected current reaches a value that can generate the starting torque. Until the occurrence of vibration of the electric motor is detected after the control current is decreased from the maximum value according to a function curve whose time change rate is substantially constant and the detected current reaches a value at which the starting torque can be generated. The control angle is decreased according to a function curve whose rate of change gradually increases, and the set angle is set after the occurrence of the vibration of the electric motor is detected. The control angle is reduced to the minimum value according to a function curve in which the time change rate gradually decreases until the start time elapses, and the switching element for one phase is fully conducted until the set stop time elapses from the start of the stop. A two-phase control operation is performed by maintaining the state, and a control angle is increased from a minimum value to a maximum value in accordance with a function curve whose time change rate gradually increases. 4. The detection of the occurrence of the vibration of the electric motor is carried out 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. The method for controlling an electric motor according to claim 1 or 3, wherein it is determined that the vibration of the electric motor occurs when the occurrence of the vibration occurs at least once.