JP2002199785A - Motor controller, overheat detector for motor winding, motor control method, and overheat detecting method for the motor winding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve overload stopping function capable of stopping a motor by exactly detecting that the temperature of the entire windings is beyond rated temperature and responding to the detection, even if whatever operating condition the motor may be. SOLUTION: Based on current, running through the winding of the motor 3 and a phase difference θ in a slowly varying component, in voltage between terminals of the winding, overheat of the winding is detected to stop the motor 3. Namely, a comparator 7 detects that winding temperature rises and reaches its limit temperature tx from a phase signal (output of a phase detector 6) being lower than a preset value θx, so that modulation is stopped for a pulse width modulator 1. Thus, the winding is protected below the limit temperature, without causing heat generation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device, a motor winding over-temperature detecting device, and a motor control method and a motor winding over-temperature detecting method.

[0002]

2. Description of the Related Art Generally, when a DC motor is operated, the temperature of the winding rises due to the loss due to the DC resistance component of the winding or the loss of the magnetic material. In particular, when an abnormality such as an increase in friction occurs during full load operation, severe use conditions, load restraint, or friction, the heat generated by the winding may cause the insulation layer of the winding to melt, or may cause heating to the magnet. This has the effect of lowering the coercive force. As a result, the performance of the electric motor is reduced and the windings are deformed to increase the friction. In the worst case, a fire may occur due to abnormal heating.

In order to prevent these performance deteriorations and accidents,
Various winding temperature rise prevention devices are known. For example, there is a method in which a temperature sensor is attached to a winding, the temperature of the winding is measured by the sensor, and the operation of the motor is stopped when the measured value exceeds the rated temperature of the winding. Recently, a thermistor having a binary positive temperature coefficient and having a temperature at which the resistance value changes abruptly according to the rated temperature of the winding is mounted, and is used for overload protection.

[0004] However, these conventional techniques have the disadvantage that only the temperature of the part where the sensor or thermistor is attached can be measured. Also, it is necessary to prepare wiring to the sensor and the like independently of the wiring of the winding. Furthermore, when a high-output motor is used, the induced electromotive force increases, so that care must be taken to prevent the wiring to the sensor from being induced.

It is also known that a mechanism for detecting and shutting off an over-temperature is built in an electric motor. For example, the case where a thermal fuse or a thermostat is built in corresponds to this. When these elements are used, extra wires do not increase because they are inserted in series with the winding of the motor, but when a fuse is used, overtemperature detection and cutoff operation are limited to one time. There is a disadvantage that the operation test cannot be performed. On the other hand, when a thermostat is used, a space for installation is required, and thus there is a drawback that contact failure or the like due to a magnetic field or vibration is concerned.

In addition, by measuring the DC resistance value of the winding and calculating the temperature rise of the winding based on the measured resistance value and the comparison value, that is, the resistance value of the motor winding at normal temperature. , The winding temperature can be measured. However, this approach can only be used when the motor is stopped and is therefore unsuitable for monitoring the winding temperature during operation of the motor.

On the other hand, a so-called overload relay system, in which a heat wire is externally connected in series with the wiring to the winding of the electric motor and a thermoswitch is operated by a rise in the temperature, is widely known for the various methods described above. I have.

[0008]

However, the conventional overload relay system has a problem that it cannot be used in an environment where temperature conditions are severe because heat is required because a hot wire is required. In addition, since a DC resistance is present in principle, it is necessary to increase the voltage on the power supply side by that amount, which causes a problem of increasing the power supply cost. Further, since the heat capacity and the cooling characteristics of the externally attached heat wire do not always match with the winding, there is a disadvantage that the temperature does not always match with the temperature of the winding. In particular, when the motor winding is forcibly cooled by an external refrigerant, the difference becomes remarkable.

Accordingly, an object of the present invention is to provide
An electric motor capable of accurately detecting that the temperature of the entire winding has exceeded the rated temperature, regardless of the operating state of the electric motor, and achieving an overload stop function of quickly stopping the electric motor in response to the detection. It is an object of the present invention to provide a control device and a motor winding over-temperature detecting device, and a motor control method and a motor winding over-temperature detecting method.

[0010]

In order to achieve the above-mentioned object, the present invention according to claim 1 has a structure in which a winding of a motor is provided with a PWM.
An apparatus for controlling rotation by applying a drive voltage, wherein a phase detecting a phase difference between a constant frequency component of a current flowing through the winding and a constant frequency component of a voltage applied to the winding. And a modulation stopping means for stopping the application of the PWM drive voltage when the phase difference detected by the phase detecting means reaches a predetermined threshold value.

According to a second aspect of the present invention, in the control device according to the first aspect, the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding are controlled by the PWM motor. This is a frequency component corresponding to the constant frequency signal supplied to the pulse width modulator for driving.

According to a third aspect of the present invention, in the control device according to the first aspect, a current transformer (CT) connected in series with the motor winding is used as a means for detecting a constant frequency component of a current flowing through the winding. ) And a capacitor connected in parallel with the current transformer, wherein the first capacitor resonates at a fundamental constant frequency of pulse width modulation.
And a first binarizer for binarizing an output voltage of the first resonance circuit, and a constant frequency component of a voltage applied to the winding is provided. As means for detecting, a transformer connected in parallel to the motor winding, a transformer (PT) having an impedance sufficiently larger than that of the motor winding, and a capacitor connected in parallel to the transformer, A second capacitor that forms a second resonance circuit that resonates at a fundamental constant frequency of pulse width modulation, and a second binarizer that binarizes an output voltage of the second resonance circuit.

According to a fourth aspect of the present invention, the electric motor is a PWM motor.
An over-temperature detection device that detects that the winding of the electric motor has reached an over-temperature when driven by a system, comprising: a constant-frequency component of a current flowing through the winding; and a voltage applied to the winding. Phase detection means for detecting the phase difference between the constant frequency component of the
When the phase difference detected by the phase detecting means reaches a predetermined threshold value, a comparing means for judging that the temperature of the winding has reached an over-temperature is provided.

According to a fifth aspect of the present invention, in the over-temperature detecting device according to the fourth aspect, the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding are controlled by the electric motor. Is a frequency component corresponding to the constant frequency signal supplied to the pulse width modulator for driving the PWM in the PWM method.

According to a sixth aspect of the present invention, in the over-temperature detecting device according to the fourth aspect, as a means for detecting a constant frequency component of a current flowing through the winding, a current transformer connected in series with the motor winding. (CT), a first capacitor that is connected in parallel to the current transformer and forms a first resonance circuit that resonates at a fundamental constant frequency of pulse width modulation, and a first capacitor that forms a first resonance circuit. A transformer connected in parallel to the motor winding, as means for detecting a constant frequency component of the voltage applied to the winding, comprising: a first binarizer for binarizing the output voltage; Is a transformer (PT) that is sufficiently larger than the motor winding, and a capacitor connected in parallel with the transformer, and forms a second resonance circuit that resonates at the fundamental constant frequency of the pulse width modulation. 2 capacitor and the second resonance circuit Second binarizing the output voltage of the 2
And a digitizer.

According to a seventh aspect of the present invention, there is provided a method for controlling rotation by applying a PWM drive voltage to a winding of an electric motor, the method comprising: controlling a constant frequency component of a current flowing through the winding; A phase detecting step of detecting a phase difference between the applied frequency and a constant frequency component, and when the phase difference detected by the phase detecting step reaches a predetermined threshold, the application of the PWM drive voltage is stopped. And a modulation stop step.

According to an eighth aspect of the present invention, in the control method according to the seventh aspect, the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding are controlled by controlling the electric motor by PWM This is a frequency component corresponding to the constant frequency signal supplied to the pulse width modulator for driving.

According to a ninth aspect of the present invention, in the control method according to the seventh aspect, when detecting the constant frequency component of the current flowing through the winding, a current transformer ( CT), a capacitor connected in parallel with the current transformer, the first capacitor forming a first resonance circuit that resonates at a fundamental constant frequency of pulse width modulation, and an output of the first resonance circuit. When a constant frequency component of the current is detected using a first binarizer for binarizing the voltage, and a constant frequency component of the voltage applied to the winding is detected, A connected transformer, a transformer (PT) having an impedance sufficiently larger than that of the motor winding, and a capacitor connected in parallel to the transformer, which resonates at a fundamental constant frequency of the pulse width modulation. A second capacitor forming a second resonance circuit; The output voltage of the second resonance circuit for detecting a constant-frequency component of the voltage by using the second binarization unit for binarizing.

According to a tenth aspect of the present invention, the electric motor is a PW motor.
An over-temperature detection method for detecting that the winding of the electric motor has reached an over-temperature when driving in the M system, wherein the constant-frequency component of a current flowing in the winding and the voltage applied to the winding are A phase detection step of detecting a phase difference between the constant frequency component of the voltage and a phase difference detected by the phase detection step, wherein when the phase difference has reached a predetermined threshold, the temperature of the winding has reached an over-temperature. And a comparing step of determining

According to an eleventh aspect of the present invention, in the overtemperature detecting method according to the tenth aspect, the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding are controlled by the motor. Is a frequency component corresponding to the constant frequency signal supplied to the pulse width modulator for driving the PWM in the PWM method.

According to a twelfth aspect of the present invention, in the over-temperature detecting method according to the tenth aspect, when detecting the constant frequency component of the current flowing through the winding, a current transformer connected in series to the motor winding is used. And a capacitor connected in parallel with the current transformer, the first capacitor forming a first resonance circuit that resonates at a fundamental constant frequency of pulse width modulation, and the first resonance circuit When a constant frequency component of the current is detected using a first binarizer for binarizing the output voltage of the motor, and a constant frequency component of the voltage applied to the winding is detected, A transformer (PT) having an impedance sufficiently larger than that of the motor winding, and a capacitor connected in parallel with the transformer, the transformer having a basic constant frequency of the pulse width modulation. A second capacitor forming a resonating second resonance circuit; Detecting a constant frequency component of the voltage by using the support, and a second binarization unit for binarizing the output voltage of the resonant circuit of the second.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an example of a motor control device to which the present invention is applied. In the figure, reference numeral 1 denotes a pulse width modulator that determines an ON / OFF time width according to a modulation command value. 2a and 2b are drivers (totem drivers) that amplify ON / OFF pulses generated from the pulse width modulator 1. Reference numeral 3 denotes a DC motor driven by the drivers 2a and 2b.

Reference numeral 4a denotes a differentiator for detecting the winding voltage of the electric motor 3. 4b is a current detector for detecting a winding current of the electric motor 3. Reference numerals 5a and 5b denote band-pass filters that pass only constant frequency signal components. Reference numeral 6 denotes a phase detector for calculating a phase difference between the current signal and the voltage signal. 7
Is a comparator for comparing the phase signal output from the phase detector 6 with a predetermined value. 8 is PWM
This is a constant frequency oscillator (oscillator) that generates a periodic signal for modulation.

Next, the operation of the motor control device shown in FIG. 1 will be described. First, the pulse width modulator 1 generates a pulse for turning on the driver 2a and a pulse for turning on the driver 2b in accordance with the modulation command value in the cycle of the constant frequency oscillator 8. A square wave voltage modulated by the drivers 2a and 2b is applied to the windings of the electric motor 3, so-called PWM.
(Pulse Width Modulation) drive is performed.

Each voltage applied to both ends of the winding of the motor 3 is input to a differentiator 4a, and a voltage signal representing a potential difference between both ends of the winding is output. The current flowing through the winding is converted into a current signal by the current detector 4b. These voltage signal and current signal are input to the band-pass filters 5a and 5b, respectively, and only the passed constant frequency component is converted into a phase signal by the phase detector 6. The operating frequency band of the differentiator 4a and the current detector 4b must be able to detect the constant frequency component without distortion.

The impedance Z _m of the winding of the motor 3 is
It is represented by the following equation.

[0028]

[Number 1] _{Z m = L m + R m} ··· (1) where, L _m is the motor windings inductance, R _m is the DC resistance of the motor windings.

The relationship of the winding voltage V _m and the winding current I _m is represented by its own expression.

[0030]

(Equation 2) Assuming that the angular velocity of the constant frequency is ω, the above equation is expressed by the following equation.

[0031]

(Equation 3)

Assuming that the phase angle is θ, θ is expressed by the following equation.

[0033]

(Equation 4)

The DC resistance R _m varies with temperature. On the other hand, the inductance L _m is not affected by the temperature.

The change in the winding resistance R _m that occurs in accordance with the change in the winding temperature t ₁ is expressed by the following equation using the temperature coefficient α of R _{m at} a predetermined reference temperature t ₀ .

[0036]

R _m ′ = R _m (1 + α (t ₁ −t ₀ )) (5) The phase angle θ becomes smaller as the temperature rises.

The phase angle θ _{x at} the limit temperature t _x of the winding is:
From the above relationship, it is obtained by the following equation.

[0038]

(Equation 6)

The phase angle θ _x obtained by the equation (6) is set as a default value (reference value or threshold value) for the comparator 7. The comparator 7 detects the limit temperature t
_{The arrival} of _x is detected when the phase signal falls below a predetermined value, and the pulse width modulator 1 stops the modulation.
As a result, the motor 3 no longer generates heat and the windings are protected below the limit temperature.

[0040] When the inductance L _m direct current resistance R _m for the larger motor 3, the precision of the temperature set point is higher. If the control frequency of the electric motor 3 and the drive target associated therewith is close to the PWM carrier modulation frequency, there is a concern that the actual current component is mixed with the modulated carrier frequency components transmitted through the band-pass filters 5a and 5b, and an erroneous determination is made. Therefore, it is better to be sufficiently (10 times to several tens times) apart. Normally, a low-pass filter is provided for the modulation command value at a frequency sufficiently lower than the PWM modulation frequency, so that there is no problem.

At the time of starting the PWM modulation, since no carrier modulation frequency component is present in the winding voltage and the winding current, the result of the phase comparison is not determined. Therefore, the stop signal is temporarily suppressed at the start of the modulation. Although necessary, this can be achieved by passing the modulation start signal through a simple delay circuit.

The method of stopping the motor is not limited to the stop of the modulation, and the power supply to the drivers 2a and 2b may be cut off using a relay such as a magnet contactor.

In this embodiment, the voltage signal and the current signal are obtained by using the differentiator 4a and the current detector 4b. However, the voltage signal and the current signal are not necessarily required. I hope I can get it. Also, it is not necessary to be an analog signal,
A digital signal may be used as long as phase detection is possible.

For example, as another method for performing voltage detection, a bandpass filter is formed by providing a resonance circuit on the secondary side through a small transformer for a voltage divided by a transformer having a high winding ratio or a small capacitor. , May be binarized. As another method for detecting the current, a current transformer (CT: current transformer) may be used, a resonance circuit may be provided, a bandpass filter may be formed, and the signal may be binarized.

That is, when detecting the constant frequency component of the current flowing through the winding, a current transformer (CT) connected in series to the motor winding and a capacitor connected in parallel to the current transformer are used. A first capacitor that forms a first resonance circuit that resonates at a basic constant frequency of pulse width modulation, and a first binarizer that binarizes an output voltage of the first resonance circuit is used to supply a current. Can be detected. When detecting the constant frequency component of the voltage applied to the winding, a transformer (PT) connected in parallel with the motor winding and having a sufficiently large impedance compared to the motor winding.
A second capacitor that is connected in parallel with the transformer and forms a second resonance circuit that resonates at the fundamental constant frequency of the pulse width modulation; and that the output voltage of the second resonance circuit is 2 It is possible to detect the constant frequency component of the voltage using the second binarizer that converts the value.

When these methods are adopted, an offset occurs in the phase difference as compared with the case where the voltage and current are measured directly. However, the offset is calculated or measured in advance and reflected in the predetermined value (θ _x ). It should be left.

The predetermined value (θ _x ) can be uniquely obtained if the characteristics of the motor are known. However, the predetermined value (θ _x ) is not necessarily set by hardware, and a result calculated by software based on the characteristics of the motor may be used. Also, the phase detection and the comparison with the predetermined value can be realized by software using a high-speed microprocessor or digital signal processor.

It is not necessary to detect the temperature of the windings for all windings included in the motor, and it is sufficient to detect an over-temperature state for at least one winding.

[0049]

As described above, according to the present invention, the overheating of the winding is detected based on the phase difference between the current flowing through the winding of the motor and the constant frequency component of the voltage between the terminals of the winding, and the motor is stopped. By doing so, overload can be accurately and quickly prevented. In addition, a device for realizing these functions requires only a small cost in circuit technology, and it is also possible to equip each motor later. Thus, it is possible to maximize the performance of the electric motor.

Further, according to the present invention, it is possible to operate the apparatus many times without adding wires for temperature detection and without using unnecessary heating elements or power. In this case, since no mechanical parts are used, reliability can be improved.

Further, according to the present invention, it is possible to always detect the over-temperature of the winding while the power is supplied, regardless of the operating state of the motor, such as during operation or stoppage. No consideration is required.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a motor control device to which the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 pulse width modulator 2a, 2b driver (totem pole driver) 3 DC motor 4a difference device 4b current detector 5a, 5b bandpass filter 6 phase detector 7 phase detector (comparator) 8 constant frequency oscillator (oscillator)

Claims (12)

[Claims] 1. A device for controlling rotation by applying a PWM drive voltage to a winding of an electric motor, comprising: a constant frequency component of a current flowing through the winding; and a constant frequency of a voltage applied to the winding. A phase detection unit for detecting a phase difference between the component and a modulation stop unit for stopping the application of the PWM drive voltage when the phase difference detected by the phase detection unit reaches a predetermined threshold. A control device for an electric motor, characterized in that: 2. The control device according to claim 1, wherein a constant frequency component of a current flowing through the winding and a constant frequency component of a voltage applied to the winding have a pulse width for PWM driving the electric motor. A control device for a motor, wherein the control device has a frequency component corresponding to a constant frequency signal supplied to a modulator. 3. The control device according to claim 1, wherein: as means for detecting a constant frequency component of a current flowing through the winding, a current transformer (CT) connected in series to the motor winding; A first capacitor forming a first resonance circuit that resonates at a basic constant frequency of pulse width modulation, and a second capacitor that binarizes an output voltage of the first resonance circuit. A transformer connected in parallel to the motor winding, the impedance being lower than that of the motor winding as means for detecting a constant frequency component of the voltage applied to the winding. Transformer large enough (P
T) a second capacitor that is connected in parallel to the transformer and forms a second resonance circuit that resonates at the fundamental constant frequency of the pulse width modulation; and an output of the second resonance circuit. A motor control device, comprising: a second binarizer for binarizing a voltage. 4. An over-temperature detection device for detecting that a winding of an electric motor has reached an over-temperature when driving the electric motor by a PWM method, comprising: a constant-frequency component of a current flowing through the winding; Phase detection means for detecting a phase difference between a constant frequency component of a voltage applied to the winding, and a temperature of the winding when the phase difference detected by the phase detection means reaches a predetermined threshold. And a comparing means for determining that the temperature of the motor winding has reached an over-temperature. 5. The over-temperature detecting device according to claim 4, wherein the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding drive the electric motor in a PWM system. A temperature component corresponding to a constant frequency signal supplied to a pulse width modulator for detecting an overtemperature of a motor winding. 6. The over-temperature detecting device according to claim 4, wherein: as means for detecting a constant frequency component of a current flowing through the winding, a current transformer (CT) connected in series to a motor winding; A first capacitor that is connected in parallel to the current transformer and forms a first resonance circuit that resonates at a fundamental constant frequency of pulse width modulation; and binarizes an output voltage of the first resonance circuit. A transformer that is connected in parallel to the motor winding and has an impedance that is connected to the motor winding as means for detecting a constant frequency component of a voltage applied to the winding. A sufficiently large transformer (P
T) a second capacitor that is connected in parallel to the transformer and forms a second resonance circuit that resonates at the fundamental constant frequency of the pulse width modulation; and an output of the second resonance circuit. An over-temperature detecting device for a motor winding, comprising: a second binarizer for binarizing a voltage. 7. A method for controlling rotation by applying a PWM drive voltage to a winding of an electric motor, comprising: a constant frequency component of a current flowing through the winding; and a constant frequency component of a voltage applied to the winding. A phase detection step of detecting a phase difference between the components, and a modulation stop step of stopping the application of the PWM drive voltage when the phase difference detected by the phase detection step reaches a predetermined threshold. A method for controlling an electric motor, comprising: 8. The control method according to claim 7, wherein the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding have a pulse width for PWM driving the motor. A method for controlling a motor, wherein the frequency component is a frequency component corresponding to a constant frequency signal supplied to a modulator. 9. The control method according to claim 7, wherein when detecting a constant frequency component of the current flowing through the winding, a current transformer (CT) connected in series to the motor winding; A first capacitor forming a first resonance circuit that resonates at a basic constant frequency of pulse width modulation, the capacitor being connected in parallel with the current transformer, and binarizing an output voltage of the first resonance circuit When the constant frequency component of the current is detected using the first binarizer and the constant frequency component of the voltage applied to the winding is detected, a transformer connected in parallel to the motor winding is used. The transformer (P) whose impedance is sufficiently large compared to the motor winding.
T) a second capacitor that is connected in parallel to the transformer and forms a second resonance circuit that resonates at the fundamental constant frequency of the pulse width modulation; and an output of the second resonance circuit. A method for controlling a motor, comprising detecting a constant frequency component of a voltage using a second binarizer for binarizing the voltage. 10. When driving an electric motor by a PWM method,
An over-temperature detecting method for detecting that the winding of the electric motor has reached an over-temperature, wherein a constant frequency component of a current flowing through the winding and a constant frequency component of a voltage applied to the winding are detected. A phase detecting step of detecting a phase difference of the phase detection step, and, when the phase difference detected by the phase detecting step reaches a predetermined threshold value, a comparing step of determining that the temperature of the winding has reached an over-temperature. A method for detecting overheating of a motor winding. 11. The over-temperature detecting method according to claim 10, wherein the constant frequency component of the current flowing through the winding and the constant frequency component of the voltage applied to the winding drive the electric motor in a PWM system. A temperature component corresponding to a constant frequency signal supplied to a pulse width modulator for detecting an over-temperature of a motor winding. 12. The over-temperature detecting method according to claim 10, wherein when detecting a constant frequency component of a current flowing through the winding, a current transformer (CT) connected in series to the motor winding; A capacitor connected in parallel to the current transformer, the capacitor forming a first resonance circuit that resonates at a fundamental constant frequency of pulse width modulation; and a binary output voltage of the first resonance circuit. When detecting the constant frequency component of the current using the first binarizer to be converted and detecting the constant frequency component of the voltage applied to the winding, a transformer connected in parallel to the motor winding And a transformer (P) whose impedance is sufficiently large compared to the motor winding.
T) a second capacitor that is connected in parallel to the transformer and forms a second resonance circuit that resonates at the fundamental constant frequency of the pulse width modulation; and an output of the second resonance circuit. A method for detecting over-temperature of a motor winding, comprising detecting a constant frequency component of a voltage using a second binarizer for binarizing the voltage.