JPS6380794A - Electric motor control method - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling a motor, and in particular, when controlling the operation of a motor such as an electric washing machine using an electronic control circuit, it is possible to easily control the rotation speed and load amount. The present invention relates to an inexpensive electric motor control method suitable for detecting and controlling operation according to the detection result.

[Conventional technology]

Conventionally, in order to detect the rotational speed and load amount required for operation control of this type of motor, methods were used to measure the current flowing through the motor and the temporal changes in the current value, and calculate it from this measured value, or to detect the load amount. A separate detection device such as a magnet or a wire ring was installed around the shaft, and the signal obtained from this was used to determine the rotation speed of the load shaft and calculate the amount of load from the change in the rotation speed. . In addition, as a known technique, for example, Japanese Patent Application Laid-open No. 58
There is No.-195592.

[Problem that the invention seeks to solve]

With the above conventional technology, the current detection method is affected by voltage fluctuations and variations in motor characteristics, making it difficult to accurately measure rotation speed and load amount, and is also affected by ambient temperature and motor temperature rise. On the other hand, the method of installing a separate detection device has good measurement accuracy, but requires a separate detection device and wiring.

There were problems such as high cost and increased number of external noises entering the electronic control circuit due to the increase in wiring.

An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a method for detecting the rotation speed and load amount without separately installing a detection device, and controlling the operation of an electric motor using the detection results. It is about providing.

[Means for solving problems]

The above purpose is to detect the induced voltage generated in the stator winding due to the magnetism of the rotor after cutting off the current to the stator winding of the motor, and to determine the rotation speed from the waveform of this induced voltage. This is achieved by detecting the load amount from the state and controlling the operation of the electric motor based on the detected rotational speed and load amount.

While the motor is running, the rotor rotates due to the rotating magnetic field generated by passing current through the stator windings. However, after the current is cut off to the stator windings, the magnetic rotor rotates against the stator due to inertia. The motor acts as an alternating current generator by rotating against the motor, and the terminals of the stator winding have a frequency f (Hz ) is generated. By measuring the frequency of this voltage, the number of revolutions can be determined, and the amount of load on the motor can be determined from the state of change in the number of revolutions.

[Effect]

After cutting off the current to the stator windings, the magnetism possessed by the rotor is, in the case of a motor in which the rotor is composed of permanent magnets, the magnetism of this permanent magnet, and in the case of a motor in which the rotor is not a permanent magnet, This is the magnetism that remains in the laminated iron core that makes up the rotor. In the case of a permanent magnet rotor, the strength of its magnetic poles is constant, so the fltft pressure generated by the rotation of the rotor does not depend on its rotation speed.The voltage generated by the residual magnetism of the motor is:
As the residual magnetism decreases, it becomes small in a short time, and it is extremely unstable as it is greatly affected by the operating condition of the motor, so it is not recommended to try to obtain the rotational speed by detecting the voltage value. It is embarrassing and the detection error is large. On the other hand, if the frequency is determined by the formula f=1/T by measuring the period T of the generated voltage waveform and the rotation speed N is calculated from the frequency f, false detection will not occur.

〔Example〕

The present invention will be explained in detail below with reference to the drawings.

In an induction motor used in an electric washing machine or the like, a stator winding is wound around a groove in a stator core, and a rotor is disposed with a predetermined gap between the stator core and the stator core. This rotor has a structure in which electromagnetic steel plates are punched out and stacked, and aluminum conductors are cast into the grooves using a die-casting method.

By passing an alternating current through the stator windings, a rotating magnetic field is generated in the stator, and the rotor core is also magnetized and rotates. At this time, the relationship between the magnetizing force H and the magnetic flux B (fl! of the magnetic steel plate) generated by passing current through the stator winding is schematically expressed as shown in Figure 2, and when the current is alternating current, there is a hysteresis loop. Even if the current stops flowing and the magnetizing force H becomes zero, the magnetic flux B maintains a certain value. This is the residual magnetic flux, and the electromagnetic steel plate of the motor rotor in this example also
Even if the magnetizing force H disappears, there is residual magnetic flux, and the stator is magnetized to the same number of poles P, so the magnetic flux that cuts the winding changes as it rotates, causing the stator winding to rotate. An alternating voltage with a frequency f depending on the number is induced. The frequency j is expressed as f=P-N/120 and depends on the rotation speed N, and changes as shown in the first m when the rotation speed N changes due to the load.

The voltage generated at the terminals of the stator windings depends on the residual magnetism of the rotor, so the magnitude of the voltage is not constant, and as the magnetic flux becomes weaker, the generated voltage becomes extremely small. In order to know the load condition, it is not appropriate to measure the generated voltage or measure the voltage wave number at a stop.

In order to know the rotational speed and load amount from the voltage caused by such residual magnetism, it is best to measure the period T of the voltage wave generated and the temporal change in the period T. FIG. 1 shows a voltage wave generated in the stator winding and a waveform resulting from converting this voltage wave into a rectangular wave by a signal conversion circuit.

Now, the voltage generated in the stator winding due to residual magnetism is
Can be measured between the winding terminals of a motor. Figures 3 to 6 show various measurement methods. Figure 3 is a circuit diagram for measuring the voltage waves generated in the main winding of a motor M that rotates in one direction. The main winding of the motor that rotates the direction,
A circuit diagram in which the sum of the voltage waves generated in the auxiliary windings is measured between the terminals of the operating capacitor C. Figure 5 shows the voltage waves generated in the windings on one side of the motor during forward and reverse rotation. The circuit diagram for measuring , Figure 6 is for normal rotation.

FIG. 2 is a circuit diagram for measuring the sum of voltage waves generated in each winding of a motor that operates in reverse.

Next, an example will be described in which the operation of an electric washing machine is controlled using the period T and the number of rotations N measured by the above method.

FIG. 7 is a flowchart showing the procedure for detecting the amount of load driven by the electric motor. When the operation type signal from the operator is input to the control circuit from the key input circuit, the load is driven according to the selected operation type. When detecting the amount, as shown in the flowchart of FIG. 7, the power is turned on to supply current to the motor and drive the load for a predetermined period of time. As a result, both the load and the motor are operated at a predetermined rotation speed. When the current is cut off by turning off the power, the rotation speed of the motor decreases with a specific negative acceleration depending on the amount of load due to the balance between the inertia of the load and the motor, and the load and rotational resistance. Since the motor rotor has residual magnetism, an AC voltage waveform as shown in Figure 1 is generated in the stator windings, and after a short period of time specified by the current breaker, this induced AC voltage wave is By measuring the period, the number of rotations can be determined. From the rotational speed No at the time of current cutoff and the rotational speed N1 after Δ has elapsed, the rotational acceleration dω/dt of the motor can be approximately calculated as dω/dt=
Calculated as 2yc(No-N1)/60・Δt,
The load amount is estimated by making it correspond to the load amount that has been obtained through calculations and experiments in advance and is incorporated into the program. or,
After the current is cut off, the period of the induced voltage wave is measured at predetermined small time intervals Δt, To + Tt + Tz is taken in, and from this period, the acceleration of rotation of the motor dω/dt
The load amount can be estimated in the same way as above by calculating approximately P: the number of poles of the motor.

By repeating load amount detection using this method, the detection accuracy improves as the number of repetitions increases.

FIG. 8 is a diagram showing changes in the power generation waveform due to the residual magnetism of the motor, which changes depending on the load amount. In other words, when the load is light, inertial rotation does not stop easily, so (
a) As shown in the figure, the power generation waveform continues for a long time, and you can see many sinusoidal voltage waveforms, but if there is a lot of laundry, the rotational resistance will increase and the inertial rotation will not last long after the current is cut off. (c) As shown in the figure, the number of generated voltage waveforms is reduced. Similarly, at intermediate loads, (b)
As shown in the figure, a waveform between a small load and a large load is output. At this time, since the waveform interval Δt changes depending on the rotational resistance which is proportional to the load amount, the load amount can be measured by measuring the waveform interval immediately after the current is cut off or after a predetermined period of time has elapsed.

FIG. 9 is a flowchart showing a procedure for starting the load at a slow speed, a so-called soft start, or a slow acceleration start. When the operation type signal from the operator is input to the control circuit from the key input circuit, the load is driven according to the selected operation type. When performing acceleration starting, as shown in the flowchart of FIG. 9, when the power is turned on and current flows through the windings of the motor, the motor begins to drive the load. Let the shaft output torque of the electric motor be TR, the amount of inertia converted to the axis of the load system and the rotating part of the electric motor be J, the initial value of the rotation speed be NOrpm, and the elapsed time of driving the electric motor be t seconds.

The rotational speed Nrpm of the electric motor is approximately expressed as 2π. As this formula shows, since No=O at startup, the number of rotations N reached is proportional to the operating time t, and after operating for a short time of the initial operating time set according to the normal load, the Turn off the current to the winding. The rotational torque TR generated by the motor becomes zero, but due to the inertia J, the load system continues to rotate even though it has negative acceleration, and due to the residual magnetism of the rotor, the motor windings are An alternating voltage as shown is induced. By measuring the period T of the induced AC voltage wave immediately after the current is cut off, the rotation speed N (rpm) is calculated using the following equation.

N=120/ (P-T) By comparing this measured and calculated rotational speed with the rotational speed of the program that the control circuit has in advance, the next operating time is calculated, and the motor is controlled to ON-〇FF. do. By performing this method over at least the entire time of starting the electric motor, it becomes possible to slowly start up the load.

Conversely, if the above control is used when stopping load operation, the motor can be braked and stopped at any speed, if necessary, by flowing a reverse current through the motor.

Furthermore, by using the above control when driving a load, the load can be driven at any speed.

FIG. 10 is a flowchart showing a procedure for controlling the phase of the voltage applied to the electric motor and operating it at an arbitrary rotation speed. When the operation type signal from the operator is input to the control circuit from the key input circuit, the load is driven according to the selected operation type, but in this process, the motor to be controlled is programmed in advance. When the motor is operated by phase control at a rotational speed of 100 m, as shown in the flowchart of FIG. 10, when the m source is turned on and current flows through the windings of the motor, the motor begins to drive the load. The initially applied voltage has a voltage waveform whose phase is controlled by a program pre-installed in the control circuit for each type of operation selected by the operator. After operating in this state for a predetermined period of time, the current to the windings is cut off by turning off the power, and the period T of the AC voltage wave induced in the windings and generated by the rotation of the rotor having residual magnetism is measured. From this period T, the rotation speed N (rpm) can be calculated as N=120/(PT), so by comparing it with the predetermined rotation speed NIN incorporated in the control circuit program, the control phase can be calculated and the operation duration can be calculated. The calculated value is converted into a signal, and the motor is operated according to the one-phase control force formula to drive the load at an arbitrary rotation speed.

Such a means of detecting the rotation speed based on the residual magnetism of the electric motor itself can be used not only to control washing machines, but also to control the rotation speed of electric fans and ventilation fans, and control the rotation speed of balancers for checking the balance of wheels. It can be used as a rotation speed control device in a control system that controls the drive of an inertial load that continues to rotate inertia for some time even after the power to the motor is cut off.
Its range of applications is wide and covers all types of equipment that use electric motors, examples of which include the equipment mentioned above, as well as blowers.

Possible devices include compressors, conveyor motors, gear pumps, mold blocks, hoists, travel motors, clutch motors, and other devices that use electric motors as drive sources.

〔Effect of the invention〕

As explained above, according to the present invention, the rotation speed of the motor can be detected from the load wiring connected to the load drive switching circuit of the electronic control circuit, and the load amount can be detected from the state of change in this rotation speed. Since this method detects the rotation speed using the induced voltage waves generated in the stator windings due to the rotor's residual magnetism, there is no need to install a special detection device or special wiring for detection and control. Since it is possible to do this, it can be made cheaper than the conventional method.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the voltage waveform at the winding end due to rotor residual magnetism according to the present invention and the converted rectangular wave, Fig. 2 is a B-H hysteresis characteristic diagram of the magnetic material, and Figs. 3 to 6 The figures are respectively a voltage wave acquisition circuit diagram, Figure 7 is a flowchart of the load detection procedure, Figure 8 is a diagram showing that the output voltage waveform changes depending on the load, and Figure 9 is the control procedure for slow acceleration start. FIG. 10 is a flowchart of the rotation speed control procedure by phase control. B... Magnetic flux, H... Magnetizing force, Tlt Tx t T
a... Period of induced voltage wave.

Claims (1)

[Claims] 1. In a motor whose operation is controlled by an electronic control circuit, after cutting off the current to the stator winding of the motor, from the induced voltage waveform generated in the stator winding due to the magnetism of the rotor. An electric motor control method comprising: detecting the rotational speed of the electric motor; detecting a change in the rotational speed to detect a load amount driven by the electric motor; and controlling the electric motor according to the rotational speed or the load amount. 2. The magnetism possessed by the rotor is the magnetism possessed by the permanent magnet in the case of a motor in which the rotor is composed of a permanent magnet;
In the case of an electric motor in which the rotor is not a permanent magnet, the first claim is characterized in that the magnetism remains in the rotor core.
The electric motor control method described in . 3. The electric motor control method according to claim 1, wherein the rotation speed is detected by measuring the period of the induced voltage wave. 4. The load amount is detected by sequentially measuring the cycle of the induced voltage wave and detecting the degree of change in the measured cycle, as set forth in claim 1. electric motor control method. 5. The detection of the load amount is characterized in that the load amount is detected by measuring the period of the induced voltage wave after a predetermined time has elapsed after the current cutoff to the stator winding. The electric motor control method according to item 1. 6. The operation control of the motor after the current to the stator winding is interrupted is characterized by comparing the detected rotation speed and a set rotation speed, and performing phase control operation according to the comparison result. An electric motor control method according to claim 1. 7. Operation control of the motor after the current cutoff to the stator winding is performed by comparing the rotation speed detected at each elapsed time after the current cutoff with the set rotation speed at each elapsed time, and comparing these. The electric motor control method according to claim 1, characterized in that, depending on the result, phase control operation is performed so as to start or stop slowly. 8. A patent claim characterized in that the motor is a capacitor run induction motor, and the induced voltage waveform is detected using either the voltage across the terminals of the driving capacitor or the voltage between the terminals of the main winding. The electric motor control method according to item 1.