JPH1014282A - Rotational state detector for motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the rotational state of an AC motor, even for an apparatus having no heat source, by comparing the zero-cross point of a commercial power supply voltage with the zero-cross point of a current flowing into the AC motor and then comparing the time difference of the zero-cross point with a predetermined time. SOLUTION: A rotational state-detecting means 7 is fed with zero-cross point detection signals from a voltage zero-cross point-detecting means 2 and a current zero-cross point-detecting means 6. The time difference between the zero-cross point of a voltage from a commercial power supply 1 and the zero- cross point (zero-cross point of the current) of a voltage across a resistor 5 is compared, at all times, with a predetermined time, and a decision is made that an AC motor 3 is locked when the time difference is equal to or shorter than the predetermined time. According to the arrangement, locked state of the AC motor can be detected, even for an apparatus having no heat source and the rotational state of the motor can be detected through a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting a rotational state of an AC motor used for an apparatus which needs to monitor the rotational state of a motor.

[0002]

2. Description of the Related Art Conventionally, as a method for detecting the rotational state of an AC motor driven by a commercial power supply, a rotational speed detecting means such as a pulse encoder is attached to the AC motor, and the rotational speed detected by the rotational speed detecting means is measured. There is known an apparatus that compares a predetermined rotation speed with a reference rotation speed.
However, this method has a disadvantage that an additional cost of expensive rotation speed detecting means is required and a space for mounting the rotation speed detecting means is required.

[0003] In an appliance having a heat source such as a fan heater, when the rotation speed of an AC motor for driving the fan decreases, the temperature in the appliance increases. Utilizing this, a method is known in which a temperature detecting element such as a thermistor is provided in an appliance, and the rotational state of the AC motor is detected by comparing the temperature detected by the temperature detecting element with a predetermined reference temperature. Have been. However, this method has a disadvantage that it cannot be used when there is no heat source or there is a heat source when the temperature inside the device is unstable.

When the load on the AC motor changes and the number of revolutions of the AC motor changes, the peak value of the current waveform flowing through the AC motor also changes. A method of detecting the rotation state of the AC motor by comparing the peak value of the current waveform flowing through the AC motor with a predetermined reference value utilizing this fact is known. However, in this method, an expensive A / D conversion element and its peripheral circuits are used to detect the peak value.
Since means for performing the arithmetic processing of the / D-converted peak value is required, the apparatus cost is increased, and the circuit configuration and the control program are disadvantageously complicated.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned disadvantages by providing a motor rotation state detection device which can detect the rotation state of an AC motor even in a device having no heat source and has a simple device configuration. The purpose is to provide it at low cost.

[0006]

The present inventors have conducted various studies to achieve the above object, and as a result, when the rotation speed of the AC motor changes due to a change in the load applied to the AC motor, the AC power is changed accordingly. It was found that the phase of the current flowing through the motor was shifted. The present invention takes advantage of this,
The rotation state of the AC motor is detected. That is, voltage zero-cross point detection means for detecting a zero-cross point of the voltage of a commercial power supply that is a drive source of an AC motor, voltage detection means for converting a current flowing through the AC motor into a voltage and detecting the voltage, and the voltage detection means A current zero-crossing point detecting means for detecting a zero-crossing point of the detected current, a zero-crossing point of the voltage of the commercial power supply detected by the voltage zero-crossing point detecting means, and an AC motor detected by the current zero-crossing point detecting means. A rotational state detecting means configured to detect a rotational state of the AC motor by comparing a time difference between the two with a zero-cross point of the current, and comparing the time difference with a predetermined time. Features.

In the present invention, the specified time is set to, for example, a time difference between a zero cross point of the voltage of the commercial power supply and a zero cross point of the current flowing through the AC motor when the AC motor is rotating at a steady speed. When the load on the AC motor changes and the number of revolutions of the AC motor changes, the phase of the current flowing through the AC motor shifts, so that the time difference between the zero-cross point of the voltage of the commercial power supply and the zero-cross point of the current flowing through the AC motor changes. Change. Therefore, the rotational state of the AC motor can be detected by comparing this time difference with the specified time.

[0008] The rotation state detecting means may include a time difference between a zero cross point of a commercial power supply detected by the voltage zero cross point detecting means and a zero cross point of a current flowing through the AC motor detected by the current zero cross point detecting means. However, when the time becomes equal to or less than a predetermined time, it is detected that the AC motor is in a locked state.

The present inventors have found that when the rotation speed of the AC motor decreases due to the locked state of the AC motor, the phase of the current flowing through the AC motor shifts forward. If the phase of the current flowing in the AC motor shifts forward, the time difference between the zero cross point of the commercial power supply and the zero cross of the current flowing in the AC motor decreases. Therefore, when the time difference becomes equal to or less than a predetermined time, it can be detected that the AC motor is in the locked state.

[0010]

FIG. 1 shows an example of an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a configuration diagram of a motor rotation state detection device according to the present embodiment, and FIG. 2 is a graph showing a relationship between a voltage waveform of a commercial power supply and a current waveform flowing through an AC motor.

Referring to FIG. 1, 1 is a commercial power supply, 2 is a voltage zero-cross point detecting means for detecting a zero-cross point of the voltage of the commercial power supply 1, 3 is an AC motor, 4 is a triac which is a voltage control element, Connected between AC motor 3 and commercial power supply 1. Reference numeral 5 denotes a resistor serving as a voltage detection element, which is connected in series with the triac 4. Reference numeral 6 denotes current zero-crossing point detecting means for detecting a current zero-crossing point.
Is input. Reference numeral 7 denotes a rotation state detecting means, which comprises a CPU 8, an I / O 9, a ROM 10, a RAM 11, and an external interface 12. Rotation state detection means 7
, Each of the zero-cross point detection signals output from the voltage zero-cross point detection means 2 and the current zero-cross point detection means 6 is input. Also, the rotation state detecting means 7 is a triac 4
To control the phase of the AC motor 3.

FIG. 2 shows a voltage waveform of the commercial power supply 1 and a current flowing through the AC motor 3 converted into a voltage by the resistor 5.
3 shows a relationship with a voltage waveform generated at both ends of the resistor 5.
In FIG. 2, A is the voltage waveform of the commercial power supply 1, and a is its zero-cross point (zero-cross point of the voltage). Also,
B is a voltage waveform generated at both ends of the resistor 5 when the AC motor 3 is rotating normally, and b is its zero-cross point (current zero-cross point). Then, when the load on the AC motor 3 increases due to, for example, adhesion of dust and the rotation speed of the AC motor 3 decreases, the inventors have previously determined that the phase of the voltage waveform generated at both ends of the resistor 5 is as shown by C. It was found that it shifted.

In FIG. 2, the zero cross point a of the voltage of the commercial power supply 1 and the resistance 5
The time difference between the zero-cross point b of the voltage generated at both ends of the resistor 5 is T _B = b−a. However, when the AC motor is locked, the zero-cross point of the voltage generated at both ends of the resistor 5 is shifted to the position c. time difference between the zero-cross point of the voltage of the commercial power supply 1 becomes _{T C = c-a (<} T B).

Therefore, the rotation state detecting means 7 uses this fact to set T _S = T _B ｒ r (r is a margin value in consideration of fluctuations of the commercial power supply 1) as a specified time, and The time difference ΔT between the zero-crossing point of the voltage of the commercial power supply 1 and the zero-crossing point of the voltage (zero-crossing point of the current) generated at both ends of the resistor 5 is constantly compared with the specified time T _S, and ΔT becomes T _S or less. Sometimes, it is determined that the AC motor 3 is in the locked state, and the locked state detection signal is output via the external interface 12.

According to this embodiment, only the inexpensive resistor 5 and the current zero-cross point detecting means 6 are necessary to detect the rotational state of the AC motor (the voltage zero-cross point detecting means 2 is an AC motor). (Necessary to perform the phase control described above), and expensive rotation speed detecting means such as a pulse encoder is not required. Further, since the temperature detecting means is not used, the object to be detected is not limited to a device having a heat source. Further, both outputs of the voltage zero-cross point detecting means 2 and the current zero-cross point detecting means 6 are digital pulses,
Since the data can be directly input to the CPU 8 via the I / O 9, an A / D conversion element and its peripheral circuits are not required.

The arithmetic processing in the rotation state detecting means 7 includes a subtraction processing for obtaining a time difference ΔT between a zero-cross point of the voltage of the commercial power supply 1 and a zero-cross point of the current flowing through the AC motor 3, and the time difference ΔT and the specified time. Since only the comparison process with T _S is performed, the peak value of the current flowing through the AC motor 3 is obtained to detect the rotation state of the AC motor 3 as in the case of detecting the rotation state of the AC motor 3
No complicated arithmetic processing is required for the / D-converted detection data.

Therefore, by using the present embodiment, it is possible to detect the locked state of the AC motor even in a device having no heat source, and it is possible to inexpensively configure a motor rotation state detection device having a simple device configuration. Becomes

In this embodiment, the time difference ΔT between the zero-cross point of the voltage of the commercial power supply 1 and the zero-cross point of the current flowing through the AC motor 3 is determined by a predetermined time T
_{Although the} AC motor is detected to be in the locked state when it becomes _S or less, other than this, for example, ΔT <T
_{When S} , the voltage application time to the AC motor 3 is increased, and when ΔT> T _S , the AC motor 3
By performing the phase control by the rotation state detecting means 7 so as to reduce the voltage application time to the AC motor 3, it is possible to perform the control to keep the rotation speed of the AC motor 3 constant even when the load of the AC motor 3 changes. It is possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a motor rotation state detection unit of the present embodiment.

FIG. 2 is a graph showing a relationship between a voltage waveform of a commercial power supply and a current waveform flowing in an AC motor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Commercial power supply, 2 ... Voltage zero cross point detection means, 3 ... AC motor, 4 ... Triac, 5 ... Resistance, 6 ... Current zero cross point detection means, 7 ... Rotation state detection means, 8 ... CP
U, 9 I / O, 10 ROM, 11 RAM, 12
External interface

Claims (2)

[Claims] 1. A voltage zero-cross point detecting means for detecting a zero-cross point of a voltage of a commercial power supply which is a driving source of an AC motor; a voltage detecting means for converting a current flowing through the AC motor into a voltage and detecting the voltage; Current zero-crossing point detecting means for detecting a zero-crossing point of the current detected by the detecting means; zero-crossing point of the voltage of the commercial power supply detected by the voltage zero-crossing point detecting means; and alternating current detected by the current zero-crossing point detecting means. The time difference between the two is determined by comparing the zero-cross point of the current flowing through the motor,
By comparing the time difference with a predetermined time,
A motor rotation state detection device comprising: a rotation state detection unit configured to detect a rotation state of an AC motor. 2. A time difference between a zero cross point of a commercial power supply detected by the voltage zero cross point detecting means and a zero cross point of a current flowing through the AC motor detected by the current zero cross point detecting means. The motor rotation state detection device according to claim 1, wherein when the predetermined time is equal to or shorter than a predetermined time, the AC motor is detected to be in a locked state.