JP2005218275A - Motor coil temperature detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a coil temperature with high accuracy at low cost.
A current detection circuit 5 that performs current detection using a voltage across terminals of a shunt resistor 4 as an input, and an RC filter 61 that receives each phase output voltage of a three-phase inverter 2 and has a band lower than the maximum rotation frequency, The phase voltage detection circuit 6 including 62, the detected current value, and the detected phase voltage value are input to perform a predetermined calculation to calculate the coil resistance of the three-phase motor 3, and the calculated coil resistance and the coil held in advance And a coil temperature detecting unit 8 for detecting the coil temperature based on the temperature characteristic of the resistance.
[Selection] Figure 2

Description

  The present invention relates to an apparatus for detecting a coil temperature of a motor.

  In the motor, since the coil generates heat, the temperature becomes constant in a state balanced with the cooling effect at the motor installation location. However, if the cooling effect decreases or disappears due to some cause, the coil temperature rises. If the coil temperature becomes too high, the coil will burn and the motor will not operate.

  Therefore, when the coil temperature of the motor is detected and the coil temperature exceeds a predetermined temperature set in advance, coil burn can be prevented by stopping energization of the coil and stopping the motor.

  In order to detect the coil temperature in this way, it has been conventionally proposed to insert a thermistor or the like inside the motor casing.

  Conventionally, since an air conditioner has a compressor driven by a motor, it is necessary to prevent the occurrence of inconveniences such as oil diluting and causing seizure. For this reason, it is necessary to detect the internal temperature of the compressor as an index of how far the preheating operation is performed.

  In order to realize this requirement, measuring the internal temperature by inserting a thermocouple or the like inside the compressor causes a significant cost increase. Therefore, the discharge pipe temperature of the compressor is detected, and the compressor is detected from this temperature. It is proposed to estimate the internal temperature of and is put into practical use.

It has also been proposed to energize the compressor driving motor to such an extent that no driving force is generated, detect the coil resistance of the motor in the energized state, and detect the coil temperature from the temperature characteristics of the coil resistance (Patent Document 1). reference).
Specifically, as shown in FIG. 1, a voltage dividing resistor is connected between terminals of a DC part of an inverter that supplies AC output to a compressor drive motor, and a capacitor is connected in parallel with one of the voltage dividing resistors. Thus, a DC voltage detection circuit is configured, a shunt resistor is connected in series with one terminal of the DC section of the inverter, and a current detection circuit is provided for detecting the motor current from the voltage across the terminals of the shunt resistor.
JP 2000-243287 A

  When a configuration in which a thermistor or the like is inserted into the motor casing is employed, there is a disadvantage in that the cost increases.

  Further, when the method of estimating the internal temperature of the compressor from the discharge pipe temperature of the compressor is employed, there is a disadvantage that the temperature estimation error becomes large during the preheating operation at the time of stopping.

  In order to eliminate this inconvenience, it is conceivable to provide a thermistor and directly measure the fuselage temperature of the compressor. In this case, however, the cost increases.

  There are similar disadvantages in other devices driven by a motor.

  When the method of Patent Document 1 is adopted, the detection accuracy is degraded due to the influence of temperature characteristics of transistors, diodes, and the like included in the energization control unit that controls energization of the motor. In addition, since the motor voltage is significantly different between the normal operation state and the coil temperature detection, the motor voltage measurement at the coil temperature detection has a large variation, and consequently the detection accuracy is lowered. End up. Furthermore, when detecting the coil temperature, noise is generated due to switching in the energization control unit.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a motor coil temperature detection device that can detect a coil temperature with high accuracy at low cost.

A motor coil temperature detection device according to the present invention includes an inverter for controlling a motor, phase voltage detection means for detecting a phase voltage output from the inverter, phase current detection means, and detected phase voltage and phase current. And a coil temperature calculating means for calculating the coil temperature.
Here, the phase voltage detection means includes a filter having a band lower than the maximum rotation frequency, or a detection voltage range selected to be smaller than a voltage range that can be output during rotation control. Preferably there is.

  It is preferable to further include inverter control means for controlling the inverter so that a direct current flows during a period other than during rotation control of the motor, and the phase voltage is detected when the phase voltage is detected by the phase voltage detection means. It is preferable to further include inverter control means for controlling the inverter so as to adjust the PWM duty so that the average voltage of the phase is close to the potential of the signal line serving as a voltage reference.

  Furthermore, it is preferable to further include a coil temperature current detecting means used for detecting the coil temperature. As the coil temperature current detecting means, one for detecting an average current per carrier cycle, or an ON time. Alternatively, it is preferable that current detection is performed at the center of the OFF time.

  Furthermore, the coil temperature calculation means preferably calculates a coil resistance value from the detected phase voltage value and current value, and calculates the coil temperature from the temperature characteristic of the coil resistance. It is further preferable that correction by the above is further performed.

  Moreover, it is preferable to further include a pulse amplitude modulation circuit for controlling the output voltage of the inverter.

  Furthermore, the coil of the motor is preferably a coil of a compressor driving motor housed in a compressor casing.

  The motor coil temperature detection device according to the present invention has a specific effect that the coil temperature can be detected by detecting the phase voltage and phase current output from the inverter without using a thermocouple or the like.

  When the phase voltage detecting means including a filter having a band lower than the maximum rotation frequency is employed, the influence of noise can be eliminated and the motor phase voltage detection accuracy can be increased.

  When the phase voltage detection means is selected so that the detection voltage range is smaller than the voltage range that can be output during rotation control, the resolution can be increased and the detection accuracy of the motor phase voltage can be increased. be able to.

  When the inverter control means for controlling the inverter to flow a direct current during a period other than during the rotation control of the motor is further included, the coil temperature can be detected without rotating the motor.

  Inverter control means for controlling the inverter to adjust the PWM duty so that the average voltage of the phase for detecting the phase voltage is close to the potential of the signal line serving as the voltage reference when the phase voltage is detected by the phase voltage detection means In the case of further including the detection voltage, the detection voltage can be reduced.

In the case of further including coil temperature current detection means used for detecting the coil temperature, the resolution of current detection can be increased, and the current detection accuracy can be increased.
When the current detecting means for coil temperature is one that detects an average current per carrier cycle, it is possible to eliminate variations in current detection.
When the current detection means for coil temperature that uses current detection at the center of the ON time or OFF time is employed, it is possible to eliminate variations in current detection even in a state where no average current is detected.

  When the coil temperature calculation means is used that calculates the coil resistance value from the detected phase voltage value and current value and calculates the coil temperature from the temperature characteristic of the coil resistance, the coil temperature is calculated by simple calculation. can do.

  When the coil temperature calculation means that further corrects by the resistance value of the power supply line is adopted, the calculation accuracy of the coil resistance can be further increased and the detection accuracy of the coil temperature can be further increased.

  In the case of further including a pulse amplitude modulation circuit for controlling the output voltage of the inverter, the output voltage of the inverter can be controlled without switching the transistor of the inverter, and the occurrence of chopping sound due to switching can be prevented. it can.

  When the coil of the compressor drive motor accommodated in the casing of the compressor is adopted as the motor coil, the internal temperature of the compressor can be detected directly from the coil temperature.

  FIG. 2 is an electric circuit diagram showing an embodiment of a motor coil temperature detecting device of the present invention.

  This device is connected between a three-phase inverter 2 having a DC power source 1 as an input, a three-phase motor 3 to which a three-phase output of the three-phase inverter 2 is supplied, and the DC power source 1 and the three-phase inverter 2 A shunt resistor 4, a current detection circuit 5 that performs current detection using the voltage between the terminals of the shunt resistor 4 as input, and a filter in a band lower than the maximum rotational frequency (for example, the output voltage of each phase of the three-phase inverter 2) , RC filters 61 and 62), a detected current value (analog value) output from the current detection circuit 5, and a detected phase voltage value (analog value) output from the phase voltage detection circuit 6 The A / D converter 7 that performs analog / digital conversion processing with the input and outputs the detected current value (digital value) and the detected phase voltage value (digital value), and the digital value output from the A / D converter 7 A coil temperature detection unit 8 that performs a predetermined calculation as an input to calculate the coil resistance of the three-phase motor 3 and detects the coil temperature based on the calculated coil resistance and the temperature characteristics of the coil resistance held in advance; have.

  The three-phase inverter 2 has three pairs of transistors connected in series with each other between the + side terminal and the − side terminal of the DC power supply 1 and is connected in parallel so that each transistor has a reverse polarity. The connection point between each pair of transistors is used as the output terminal of the three-phase inverter 2. A transistor connected to the + side terminal is referred to as an upper arm transistor, and a transistor connected to the − side terminal is referred to as a lower arm transistor.

  The three-phase motor 3 is housed in the casing of the compressor 9 and acts as a drive source for the compressor.

  In FIG. 2, an inverter control unit that controls the three-phase inverter 2 in order to control the three-phase motor 3 to drive the compressor 9 is known in the art, and is not illustrated.

  The effect | action of the coil temperature detection apparatus of the motor of said structure is as follows.

  A duty is set so that the three-phase motor 3 does not rotate, and the transistor of the three-phase inverter 2 is switched. In this case, a rectangular voltage waveform with a low duty is output from the output terminal of the three-phase inverter. When this rectangular voltage waveform is supplied to the phase voltage detection circuit 6, an averaged DC voltage waveform is obtained by performing a filtering process in a band lower than the maximum rotation frequency.

  Further, a motor current is obtained by the current detection circuit 5 with the voltage across the terminals of the shunt resistor 4 as an input.

  Then, the obtained DC voltage and motor current are converted into digital values by the A / D converter 7 and supplied to the coil temperature detector 8.

  In the coil temperature detection unit 8, for example, the coil resistance of the three-phase motor 3 is calculated by dividing the DC voltage by the motor current, and the coil temperature is detected using the calculated coil resistance and the temperature characteristics of the coil resistance. To do.

  In this case, the voltage detection range of the phase voltage detection circuit 6 can be set to be smaller than the voltage range at the time of maximum voltage output (during compressor operation), so that the resolution can be increased, and consequently the detection accuracy of the coil temperature is increased. be able to.

However, when a and b are constants determined by calibration and R is a measured (calculated) coil resistance value, the coil temperature can also be calculated by calculating T = a × R + b. In this case, the temperature at the time of calibration is t ₀ , the resistance value measured at the time of calibration is R _t0 , the temperature coefficient that is different for each model is α, the resistance value of the power line (catalog value, measured value, etc. ) Is β,
a = {1 / (R _t0 −β)} {(1 / α) + (t ₀ −20)}
b = t ₀ −a × R _t0
Preferably, the detection accuracy of the coil temperature can be further improved by eliminating the influence of the resistance value of the power supply line.

In the above description, switching of the transistors of each phase of the three-phase inverter is not specifically described. However, as shown in FIG. 3, by selecting the voltage vectors τ ₀ , τ ₄ , τ ₆ , τ ₇ , a DC voltage can be applied to the three-phase motor 3 and a motor current can flow.

In this case, it is preferable to lengthen the time of τ ₀ and shorten the time of τ ₇ , and the detection voltage can be reduced (in other words, the average voltage of the phase for detecting the phase voltage becomes the voltage reference). The PWM duty can be adjusted to be close to the potential of the signal line).

Further, for example, among the voltage vectors τ ₀ , τ ₄ , τ ₆ , τ ₇ shown in FIG. 3, the time of τ ₀ is equal to the time of τ ₇ and the same switching pattern is repeated, thereby repeating the same switching pattern 3. A direct current can be passed through the coil, and the coil temperature can be detected without rotating the three-phase motor 3.

  Further, it is preferable to detect the current by the voltage across the shunt resistor 4 (voltage drop of the shunt resistor 4) and supply the detected current to an averaging processing circuit (not shown) for averaging. Regardless of the current fluctuation in the period, the variation in the detection current can be eliminated.

  Furthermore, since the current fluctuation in the ON period and the OFF period of the DC voltage is brought about as shown in FIG. 4, the current detection is performed at the center of the ON time or OFF time (one time of ON time or OFF time). This is preferably performed, and even when the average current is not detected, variation in the detected current can be eliminated.

  In the above, current detection is performed using the current detection circuit 5 that is also used during the operation period. However, it is preferable to separately provide a current detection circuit that operates only during the coil temperature detection operation, and the resolution of current detection can be increased.

  Furthermore, it is preferable to use a pulse amplitude modulation (PAM) circuit as shown in FIG. Specifically, a reactor 13 and a forward-connected diode 14 are connected in series between one output terminal of a full-wave rectifier circuit 12 that receives the AC power supply 11 and a corresponding input terminal of the three-phase inverter 2, A capacitor 15 is connected between the input terminals of the three-phase inverter 2, and a transistor 16 is connected between the connection point of the reactor 13 and the diode 14 and the other output terminal of the full-wave rectifier circuit 12.

  When this configuration is adopted, it is not necessary to switch the transistor of the three-phase inverter 2, so that chopping noise can be eliminated.

  In addition, a carrier signal is generally used for ON / OFF control of the transistor of the three-phase inverter 2 using a microcomputer or the like. In this case, it is preferable to raise the carrier frequency from the viewpoint of reducing noise in consideration of the relationship of the noise measurement value to the frequency of the carrier signal (carrier frequency). Specifically, it is preferable to set the carrier frequency to 1000 Hz or higher.

  However, as the carrier frequency is increased, the ON time of switching is inevitably shortened. Therefore, when current detection is performed using a shunt resistor, the ON time must be set to a predetermined time or more. The carrier frequency has an upper limit. In other words, there is a limit to noise reduction by increasing the carrier frequency.

  In consideration of such points, it is preferable to perform current detection using DCCT, and the carrier frequency can be increased by removing the above-described restrictions, and thus noise can be sufficiently reduced.

  If the coil temperature of the compressor drive motor is detected as described above, it can be used for detection of failures such as coil burning and abnormal heating. Further, the compressor internal temperature can be detected directly from the coil temperature.

  In the above embodiment, the compressor drive motor has been described as an example of the motor. However, the present invention is not limited to the compressor drive motor, and can be applied to various motors.

It is an electric circuit diagram which shows the structure of the conventional apparatus. 1 is an electric circuit diagram showing an embodiment of a motor coil temperature detection device of the present invention. It is a figure which shows an example of switching of the transistor of each phase of a three-phase inverter. It is a figure which shows an example of the electric current fluctuation in the ON period of a DC voltage, and an OFF period. It is an electric circuit diagram which shows the principal part of other embodiment of the coil temperature detection apparatus of the motor of this invention.

Explanation of symbols

2 Three-phase inverter 3 Three-phase motor 4 Shunt resistor 5 Current detection circuit 6 Phase voltage detection circuit 8 Coil temperature detection unit 13 Reactor 14 Diode 15 Capacitor 16 Transistor

Claims (12)

An inverter for controlling the motor, phase voltage detection means for detecting the phase voltage output from the inverter, phase current detection means, and coil temperature calculation means for calculating the coil temperature from the detected phase voltage and phase current. An apparatus for detecting a coil temperature of a motor, comprising: The coil temperature detection device according to claim 1, wherein the phase voltage detection means includes a filter having a band lower than a maximum rotation frequency. The coil temperature detection device according to claim 1 or 2, wherein the phase voltage detection means is selected so that a detection voltage range is smaller than a voltage range that can be output during rotation control. The coil temperature detection device according to any one of claims 1 to 3, further comprising inverter control means for controlling the inverter so that a direct current flows during a period other than during rotation control of the motor. Inverter control means for controlling the inverter to adjust the PWM duty so that the average voltage of the phase for detecting the phase voltage is close to the potential of the signal line serving as the voltage reference when the phase voltage is detected by the phase voltage detection means The coil temperature detection device according to claim 1, further comprising: The coil temperature detection device according to any one of claims 1 to 5, further comprising a coil temperature current detection means used for detecting the coil temperature. The coil temperature detecting device according to claim 6, wherein the coil temperature current detecting means detects an average current per carrier cycle. The coil temperature detection device according to claim 6, wherein the coil temperature current detection means detects current at the center of the ON time or OFF time. 9. The coil temperature calculation means according to claim 1, wherein the coil temperature calculation means calculates a coil resistance value from the detected phase voltage value and current value, and calculates a coil temperature from a temperature characteristic of the coil resistance. Coil temperature detection device. The motor coil temperature detection device according to any one of claims 1 to 9, wherein the coil temperature calculation means further performs correction based on a resistance value of a power supply line. The motor coil temperature detection device according to any one of claims 1 to 10, further comprising a pulse amplitude modulation circuit that controls an output voltage of the inverter. The motor coil temperature detection device according to any one of claims 1 to 11, wherein the coil of the motor is a coil of a compressor driving motor housed in a casing of the compressor.

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