JP2005224038A - Inverter controller and air conditioner equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct an error in the offset voltage of a current sensor due to temperature drift or the like and prevent degradation in control performance. <P>SOLUTION: An inverter controller comprises: an inverter 2 comprised of a plurality of switching elements; current detecting means 4a and 4b that detect the value of a current passed through a load motor 3; a zero cross detecting means 12 that detects the zero cross point of a current; a drive stopping means 13 that keeps off the switching elements of the inverter 2 for a predetermined time so that the current value is zeroed; an offset voltage detecting means 14 that stores the voltage values outputted from the current detecting means 4a and 4b during a period during which the current value is zero and updates the stored voltage values; and an actual current computing means that computes the value of a current passed through the load motor 3 from the voltage values outputted from the current detecting means 4a and 4b and the voltage values stored by the offset voltage detecting means 14. The switching elements of the inverter 2 are kept off at the zero cross point of a current detected by the zero cross detecting means 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inverter control device for controlling the operation of a motor, and more particularly to an inverter control device using a current detector and an air conditioner using the inverter control device.

  FIG. 8 shows an example of a conventional inverter control device. In FIG. 8, the control unit 110 controls the motor 103 winding current value detected by the current sensors 104a and 104b as a parameter in order to control the motor 103 to a predetermined speed based on the external speed command signal. A signal for driving the inverter 102 is generated and output as an inverter, and each switching element of the inverter 102 is driven.

  The current sensors 104a and 104b generally convert the detected current value into a voltage value and output it. Here, the sensor output voltage when the amount of current is zero is referred to as an offset voltage, and a value obtained by subtracting the offset voltage from the detected sensor output voltage is a detected current value.

  By the way, an error occurs in the offset voltage of the current sensors 104a and 104b due to temperature drift due to initial variations of products, changes in ambient temperature, and the like. This gives an error to the current value to be detected, causes distortion of the current waveform of the motor 103, lowers the efficiency or steps out, and lowers the control performance.

  As a method for correcting the error of the offset voltage of the current sensor, there is a method as shown in Patent Document 1. This is to detect the offset voltage of the current sensors 104a and 104b every time the motor 103 is turned off, and to sequentially correct the offset voltage with the updated offset voltage. Thereby, it is possible to correct an error of the offset voltage due to the initial variation of the product. Further, it is possible to correct an error in the offset voltage due to a temperature drift during operation after the operation of the motor 103 is turned off.

  Furthermore, as a method for correcting an error in the offset voltage of the current sensors 104a and 104b, there is a method as shown in Patent Document 2. In this method, the offset voltage is calculated by integrating one period of the output voltage of the current sensors 104a and 104b, and the error of the offset voltage is corrected using the calculated value.

  Further, the first time when the detected current value of the output voltage of the current sensors 104a and 104b in one cycle is positive and the second time when it is negative are measured, and the ratio between the first time and the second time is measured. Based on this, an offset voltage is calculated. The calculated value is used to correct the offset voltage error.

As a result, it is possible to correct the offset voltage error due to the initial variation of the product, and it is possible to correct the offset voltage error caused by the temperature drift or the like while the motor 103 is in the operating state.
JP 7-271445 A JP-A-5-252785

For example, an inverter control device for driving a compressor motor in an air conditioner is provided in an outdoor unit, and this outdoor unit is installed outdoors. Therefore, the temperature environment of the current sensor in the inverter control device varies greatly depending on the change in the outside air temperature and the operating state of the motor.

  However, in the configuration of the conventional inverter control device shown in Patent Document 1, it is possible to detect the offset voltage of the current sensors 104a and 104b while the motor 103 is off or after the operation is off, and correct the error. Although it is possible, the offset voltage that fluctuates due to a change in the outside air temperature or a temperature drift during the compressor motor operation cannot be corrected.

  As a result, an error occurs in the detected current value, and the control performance of the inverter control device is deteriorated.

  In recent years, in order to achieve further energy saving of the air conditioner, a one-piston rotary compressor with a small mechanical loss may be used. In this case, there is a characteristic that the sound and vibration of the compressor increase particularly in a low speed region. As a suppression method, torque control for keeping the torque during one rotation of the mechanism constant may be used. At this time, the current waveform of the compressor motor becomes a distorted current waveform as shown in FIG.

  However, in the configuration of the inverter control device shown in Patent Document 2, when the motor winding current waveform is a smooth sine wave, the change in the outside air temperature, the temperature drift, etc. during the compressor motor operation The offset voltage that fluctuates according to the above can be calculated and the error can be corrected. With this distorted current waveform, an accurate offset voltage cannot be calculated, and an offset voltage that fluctuates due to a change in the outside air temperature or a temperature drift during operation of the compressor motor cannot be corrected. In this case as well, there is a problem that an error occurs in the detected current value and the control performance of the inverter control device is deteriorated.

  The present invention solves such a conventional problem. Even if the current waveform is superimposed with the switching frequency of the inverter or the current waveform is distorted, the motor is not operated during operation. It is an object of the present invention to provide an inverter control device that can detect a change in an offset voltage due to a temperature change, a temperature drift, or the like, correct the error, and does not degrade the control performance.

  In order to solve the above problems, an inverter control device according to the present invention includes an inverter configured of a plurality of switching elements, which converts direct current into alternating current and supplies the load motor, and detects a current value flowing through the load motor to detect a voltage value. Current detecting means for converting to and outputting the current, zero cross detecting means for detecting the zero cross points of a plurality of phases of current flowing through the load motor, and the switching element of the inverter so that the current value flowing through the load motor becomes zero. A drive stop means for turning off at least one of them for a predetermined time, and a voltage value output by the current detection means during a period in which the current value flowing through the load motor becomes zero when the drive stop means turns off the switching element of the inverter. Offset voltage detection means for storing and updating, voltage value output by the current detection means and voltage stored by the offset voltage detection means And a actual current calculating means for calculating a value of the current flowing through the load motor from inverter in zero-crossing points of the current detected by the zero cross detection means - is intended for a predetermined time off the switching elements of the motor.

In the inverter control device of the present invention, the switching element of the inverter is superimposed on the current waveform of the load or the current waveform is turned off by turning off the switching element of the inverter for a predetermined time at the zero cross point of the current detected by the zero cross detecting means. Even if the distortion is large, a reliable inverter control device can be obtained without degrading the control performance by reliably correcting the fluctuation error of the offset voltage of the current detection means due to temperature drift during operation. Can be realized.

  The first invention includes an inverter configured of a plurality of switching elements, which converts direct current into alternating current and supplies the load motor, and current detection means that detects a current value flowing through the load motor, converts the current value into a voltage value, and outputs the voltage value And at least one of the inverter switching elements is turned off for a predetermined time so that the current value flowing through the load motor becomes zero. A drive stop means; and an offset voltage detection means for storing and updating a voltage value output by the current detection means during a period in which the current value flowing through the load motor becomes zero when the drive stop means turns off the switching element of the inverter. The current value flowing through the load motor is calculated from the voltage value output by the current detection means and the voltage value stored by the offset voltage detection means. Current calculation means, and by switching off the inverter switching element for a predetermined time at the zero cross point of the current detected by the zero cross detection means, the switching frequency component of the inverter is superimposed on the current waveform of the load or the current waveform Even if the distortion is large, the fluctuation error of the offset voltage of the current detection means due to temperature drift during operation can be reliably corrected, so that reliable inverter control without reducing the control performance An apparatus can be realized.

  Furthermore, since all control can be performed by software by using a microcomputer or the like, it is possible to realize an increase in the size of the apparatus and prevention of cost increase without requiring addition of a new circuit or the like.

  The second invention further includes stop interval measuring means for measuring an elapsed time after the drive stop means turns off at least one of the switching elements of the inverter for a predetermined time, and the drive stop means is measured by the stop interval measuring means. When the value exceeds a predetermined value, the switching element of the inverter is superimposed on the load current waveform by turning off the switching element of the inverter for a predetermined time at the zero cross point of the current detected by the zero cross detecting means. Even if the current waveform distortion is large, it is possible to reliably correct the fluctuation error of the offset voltage of the current detection means due to temperature drift during operation, so a highly reliable inverter without degrading the control performance. -A data control device can be realized.

  In addition, since the offset voltage is detected at predetermined time intervals at the zero crossing point of the current waveform of the load, distortion of the current waveform can be minimized.

  Furthermore, since all control can be performed by software by using a microcomputer or the like, it is possible to realize an increase in the size of the apparatus and prevention of cost increase without requiring addition of a new circuit or the like.

  According to a third aspect of the present invention, when the target speed of the load motor is below a predetermined value, the drive stop means turns off the inverter switching element for a predetermined time at the zero cross point of the current detected by the zero cross detection means. Even when the switching frequency component of the inverter is superimposed on the current waveform or the current waveform distortion is large, the fluctuation error of the offset voltage of the current detection means due to temperature drift during operation can be reliably corrected. Therefore, a highly reliable inverter control device can be realized without degrading the control performance.

  In addition, offset voltage detection is performed at the zero crossing point of the current waveform only when the target speed of the load motor is below the specified value, so that distortion of the current waveform can be minimized and the effect of current waveform distortion at high speeds can be suppressed. Can be eliminated.

  Furthermore, since all control can be performed by software by using a microcomputer or the like, it is possible to realize an increase in the size of the apparatus and prevention of cost increase without requiring addition of a new circuit or the like.

  The fourth invention further comprises an actual speed detecting means for detecting the actual speed of the load motor, and the driving stop means has a zero cross point of the current detected by the zero cross detecting means when the actual speed of the load motor is not more than a predetermined value. In this case, by switching off the switching element of the inverter for a predetermined time, even when the switching frequency component of the inverter is superimposed on the current waveform of the load or the current waveform distortion is large, current detection means due to temperature drift during operation, etc. Therefore, a highly reliable inverter control device can be realized without degrading the control performance.

  In addition, offset voltage detection is performed at the zero crossing point of the current waveform only when the actual rotation speed of the load motor is below the specified value, so that distortion of the current waveform can be minimized and high-speed range can be achieved even during transient response. The influence of the current waveform distortion at can be eliminated.

  Furthermore, since all control can be performed by software by using a microcomputer or the like, it is possible to realize an increase in the size of the apparatus and prevention of cost increase without requiring addition of a new circuit or the like.

  The fifth invention further comprises an ambient temperature detection means for detecting the ambient temperature of the current detection means, and when the change width of the ambient temperature is equal to or less than a predetermined value, the drive switching means turns off the switching element of the inverter. As a result, even if the inverter switching frequency component is superimposed on the current waveform of the load or the current waveform distortion is large, the fluctuation error of the offset voltage of the current detection means due to temperature drift during operation is ensured. Since it can correct | amend, a highly reliable inverter control apparatus is realizable, without reducing control performance.

  In addition, since the offset voltage is detected at the zero cross point of the current waveform only when the ambient temperature change of the current detection means is large, the distortion of the current waveform can be limited to a minimum.

  Furthermore, since all control can be performed by software by using a microcomputer or the like, it is possible to realize an increase in the size of the apparatus and prevention of cost increase without requiring addition of a new circuit or the like.

  The sixth aspect of the present invention is an air conditioner equipped with the inverter control device according to any one of the first to fifth aspects of the present invention, and is reliable without degradation in performance without increasing the size and cost of the device. High air conditioner can be realized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 is a control block diagram of an inverter control apparatus according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing a detailed configuration of the inverter in the block diagram of FIG.

  In FIG. 1, reference numeral 1 denotes a DC power source, 2 denotes an inverter which is composed of a plurality of switching elements and outputs a variable voltage / variable frequency AC voltage from the DC power source 1, and 3 is a motor whose speed is controlled by the inverter 2. For example, a brushless DC motor, an induction motor, a reluctance motor, or the like is used.

  Further, 4a and 4b are current sensors which are current detection means for detecting the current value flowing in each phase winding of the motor 3. Here, the current values Iv and Iw provided in the V phase and the W phase respectively flow. Is detected. The U-phase current value Iu is calculated from (Equation 1).

Iu = -Iv-Iw (1)
Reference numeral 12 denotes a zero-cross detection unit that detects a zero-cross point of a current waveform flowing in each phase of the motor 3. In this embodiment, the zero-cross detection unit 12 detects a current value calculated by an actual current calculation unit 15 described later.

  Further, 13 is a drive stop unit for turning off the drive signal of the inverter 2 for a predetermined time so that the current value flowing through each phase of the motor 3 becomes zero at the zero cross point of the current waveform detected by the zero cross detection unit 12. It is. 14 is an offset voltage detection unit for storing and updating the output voltage of the current sensors 4a and 4b as an offset voltage during the period when the drive stop unit 13 turns off the drive signal of the inverter 2 and the current value becomes zero. This is an actual current calculation unit that calculates an actual current value from the output voltages of the current sensors 4 a and 4 b during operation of the motor 3 and the offset voltage stored in the offset voltage detection unit 14.

  Reference numeral 10 denotes a control unit which includes a command current calculation unit 16, a current error calculation unit 17, and a drive signal creation unit 18.

  Based on an external speed command, the command current calculation unit 16 calculates a command current value for controlling the motor 3 to a predetermined speed. An error between the command current value calculated by the command current calculation unit 15 and the actual current value calculated by the actual current calculation unit 15 is obtained by the current error calculation unit 17, and the drive signal creation unit 18 uses this error value. A drive signal to be output to the inverter 2 is created and output, and the inverter 2 performs switching to control the speed of the motor 3.

  Here, the current sensors 4a and 4b convert the detected current value into a corresponding voltage value and output it. In particular, an output voltage value when the current is zero is referred to as an offset voltage, and a value obtained by subtracting the offset voltage from the detection voltage is a current value.

  The offset voltages of the current sensors 4a and 4b usually have characteristics that vary due to initial variations of products, temperature drifts during operation of the motor 3, and the like. As a result, an error occurs in the current value detected by the current sensors 4a and 4b, and control using this value causes a decrease in control performance.

  Hereinafter, a method of correcting the offset voltage error of the current sensor 4a in the inverter control apparatus of the present invention will be described in detail with reference to FIGS.

  The current sensor 4a is provided in the V phase of the motor 3, and detects a current value Iv flowing in the V phase. In the operation state of the motor 3, the zero cross detection unit 12 detects the zero cross point of the V-phase current waveform from the actual current calculation unit 15. The drive stop unit 13 turns off the switching elements 5b and 5e of the inverter 2 connected to the V-phase winding of the motor 3 shown in FIG.

  As a result, as shown in FIG. 3, the value of the current flowing in the V phase does not increase and maintains a zero state. The offset voltage detector 14 detects, updates, and stores the output voltage value of the current sensor 4a during this period as an offset voltage.

Further, the actual current calculation unit 15 calculates the actual current value using the updated offset voltage value and the voltage value obtained from the current sensor 4a.

  The offset voltage used for this calculation is always a value including fluctuation due to temperature drift during operation of the motor 3. Therefore, the actual current value obtained by the actual current calculation unit 15 can be obtained as a true value without being affected by the fluctuation error of the offset voltage.

  Thereafter, the method of creating a drive signal for the inverter 2 using this actual current value and the command current calculated by the command current calculation unit 16 to control the motor 3 is as described above.

  By performing the above control, it is possible to reliably correct the error of the offset voltage that fluctuates during operation, so that a highly reliable inverter control device can be realized without degrading the control performance.

  Further, in this inverter control device, in order to forcibly reduce the current flowing through the motor 3 to zero at the zero cross point, the influence of the switching frequency component of the inverter 2 superimposed on the current waveform and the current waveform distortion. I do not receive it.

  The offset voltage correction method for the current sensor 4b can be similarly performed.

  Therefore, according to the inverter control apparatus of the present invention, even if the switching frequency component of the inverter 2 is superimposed on the current waveform of the motor 3 or the current waveform distortion is large, the temperature drift during operation, etc. Therefore, it is possible to reliably correct the fluctuation error of the offset voltage of the current sensors 4a and 4b, thereby realizing a highly reliable inverter control device without degrading the control performance.

  Furthermore, since the control device of the present invention can be performed entirely by software by using a microcomputer or the like for the control unit 10, it is possible to prevent the increase in size and cost of the device without the need for adding a new circuit or the like. be able to.

(Embodiment 2)
FIG. 4 is a control block diagram of the inverter control apparatus according to the second embodiment of the present invention. 4, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  Reference numeral 20 denotes a stop interval measuring unit, which determines a time interval at which the drive stop unit 13 turns off the drive signal of the inverter 2. Hereinafter, a method of correcting the offset voltage error of the current sensor 4a in the inverter control apparatus of the present invention will be described with reference to FIGS.

  The current sensor 4a is provided in the V phase of the motor 3, and detects a current value Iv flowing in the V phase. In the operation state of the motor 3, the zero cross detection unit 12 detects the zero cross point of the V-phase current waveform from the actual current calculation unit 15. At this time, if the measured value at the stop interval measuring unit 20 is equal to or greater than a predetermined value, the drive stopping unit 13 is connected to the inverter connected to the V-phase winding of the motor 3 shown in FIG. -The switching elements 5b and 5e of the data 2 are turned off for a predetermined time. The subsequent description of the operation is the same as that of the first embodiment, and is omitted.

  With the above configuration and control, in addition to the effects of the first embodiment, offset voltage detection is performed at the zero crossing point of the current waveform of the motor 3, and correction is performed only at the minimum necessary interval. Waveform distortion can be minimized.

(Embodiment 3)
The configuration of the present embodiment is the same as that of the second embodiment, and a method for correcting the offset voltage error of the current sensors 4a and 4b will be described with reference to FIGS. Note that description of operations common to the description of the constituent elements is omitted, and only differences from the second embodiment will be described.

  The distortion of the current waveform in FIG. 3 may become undesirable in actual use because the ratio of the drive off period in one cycle of the current waveform increases as the rotational speed of the motor 3 increases.

  Therefore, in the present embodiment, when the target speed of the motor 3 becomes equal to or higher than a predetermined value in the control unit 10, control is performed so as to invalidate the off operation of the switching element of the inverter 2 by the drive stop unit 13.

  By performing the above control, it is possible to reliably correct the error of the offset voltage that fluctuates during the low / medium speed operation of the motor 3, so that the control performance is further reduced in addition to the effect of the first or second embodiment Therefore, a highly reliable inverter control device can be realized. In addition, since offset correction is not performed during high-speed operation, distortion of the current waveform that affects the motor 3 can be suppressed.

(Embodiment 4)
FIG. 5 is a control block diagram of the inverter control apparatus according to Embodiment 4 of the present invention. 5, the same components as those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 5, reference numeral 21 denotes an actual speed detection unit that detects the actual rotation speed of the motor 3, which is calculated from the current values of the V phase and W phase detected by the current sensors 4a and 4b in this embodiment. The detection of the actual rotational speed of the motor 3 by the actual speed detector 21 is not limited to this method, and may be calculated from the terminal voltage of the motor 3 or directly detected using a rotary encoder or the like. .

  Hereinafter, a method of correcting the offset voltage error of the current sensors 4a and 4b will be described in detail with reference to FIGS.

  The operation of the motor 3 is started by the inverter 2. At this time, the control unit 10 inputs a speed command from the outside, calculates a command current value by the command current calculation unit 16 so that the motor 3 is operated at the command speed, and drives the inverter 2 by the drive signal generation unit 18. Create a signal to

  The current sensors 4a and 4b are provided in the V phase and W phase of the motor 3, respectively, and detect the current value Iv flowing in the V phase and the current Iw flowing in the W phase. The U-phase current value Iu is calculated from (Equation 1) of the first embodiment.

  In the operation state of the motor 3, the zero cross detector 12 detects the zero cross points of the V-phase and W-phase current waveforms from the actual current calculator 15. At this time, if the measured value at the stop interval measuring unit 20 is equal to or greater than a predetermined value, the drive stopping unit 13 is connected to the inverter connected to the V-phase winding of the motor 3 shown in FIG. The switching elements 5b and 5e of the inverter 2 or the inverter 2 switching elements 5c and 5f connected to the W-phase winding of the motor 3 are turned off for a predetermined time.

  As a result, as shown in FIG. 3, the value of the current flowing in the V-phase or W-phase does not increase and maintains a zero state. The offset voltage detector 14 detects, updates and stores the output voltage value of the current sensors 4a and 4b during this period as an offset voltage.

  Here, the distortion of the current waveform in FIG. 3 may become undesirable in actual use because the ratio of the drive off period in one cycle of the current waveform increases as the rotation speed of the motor 3 increases.

  Therefore, in the present embodiment, the actual rotational speed of the motor 3 is detected by the actual speed detector 21 and the detected actual rotational speed is input to the command current calculator 16 of the controller 10. When the actual rotational speed of the motor 3 reaches a predetermined value or more, the control unit 10 performs control so as to invalidate the off operation of the switching element of the inverter 2 by the drive stop unit 13.

  By performing the above control, in addition to the effects in the first or second embodiment, the error of the offset voltage that fluctuates during the low and medium speed operation of the motor 3 can be reliably corrected. A highly reliable inverter control device can be realized without lowering. In addition, since offset correction is not performed during high-speed operation, distortion of the current waveform that affects the motor 3 can be suppressed. In particular, in this embodiment, since the actual rotation speed of the motor 3 is detected and the offset voltage correction control of the current sensors 4a and 4b is performed, the actual rotation speed of the motor 3 becomes equal to or higher than a predetermined speed even during a transient response. In this case, the offset voltage correction can be surely stopped.

(Embodiment 5)
FIG. 6 is a control block diagram of the inverter control apparatus according to Embodiment 5 of the present invention. 6, the same components as those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 5, reference numeral 22 denotes a temperature sensor of ambient temperature detecting means for detecting the ambient temperature of the current sensors 4a and 4b, and is constituted by a thermistor or the like.

  Hereinafter, a method of correcting the offset voltage error of the current sensors 4a and 4b will be described in detail with reference to FIGS.

  The operation of the motor 3 is started by the inverter 2. At this time, the control unit 10 inputs a speed command from the outside, calculates a command current value by the command current calculation unit 16 so that the motor 3 is operated at the command speed, and drives the inverter 2 by the drive signal generation unit 18. Create a signal to

  The current sensors 4a and 4b are provided in the V phase and W phase of the motor 3, respectively, and detect the current value Iv flowing in the V phase and the current Iw flowing in the W phase. The U-phase current value Iu is calculated from (Equation 1) of the first embodiment.

  In the operation state of the motor 3, the zero-cross detector 12 detects the zero-cross points of the V-phase and W-phase current waveforms from the actual current calculator 15. At this time, if the measured value at the stop interval measuring unit 20 is equal to or greater than a predetermined value, the drive stopping unit 13 is connected to the V-phase winding of the motor 3 shown in FIG. The switching elements 5b and 5e of the inverter 2 or the inverter 2 switching elements 5c and 5f connected to the W-phase winding of the motor 3 are turned off for a predetermined time.

  As a result, as shown in FIG. 3, the value of the current flowing in the V-phase or W-phase does not increase and maintains a zero state. The offset voltage detector 14 detects, updates and stores the output voltage value of the current sensors 4a and 4b during this period as an offset voltage.

  Here, the offset voltages of the current sensors 4a and 4b have characteristics that vary due to initial variations of components, temperature drifts during operation of the motor 3, and the like. Among these, regarding the expected variation of the components, the offset voltage values can be detected by detecting the output voltage values of the current sensors 4a and 4b when the motor 3 is off.

On the other hand, the fluctuation of the offset voltage due to the temperature drift is largely caused by the ambient temperature change of the current sensors 4a and 4b. Therefore, in this embodiment, the temperature sensor 22 periodically detects the ambient temperature of the current sensors 4a and 4b to detect these temperature changes. If this temperature change is not more than a predetermined value, it is considered that there is no temperature drift of the current sensors 4a and 4b, and the operation of turning off the switching element of the inverter 2 is stopped in order to detect the offset voltage during operation of the motor 3. .

  By performing the above control, in addition to the effects in the first to fourth embodiments, when the ambient temperature change of the current sensors 4a and 4b is large, the error of the offset voltage that fluctuates during operation can be reliably corrected. Therefore, a more reliable inverter control device can be realized without lowering the control performance. Further, since the offset correction is not performed when the ambient temperature change of the current sensors 4a and 4b is small, the distortion of the current waveform of the motor 3 can be further suppressed.

(Embodiment 6)
FIG. 7 shows an example of an air conditioner provided with an inverter control device according to Embodiment 6 of the present invention. 7, the same components as those in FIG. 4 are denoted by the same reference numerals, and detailed description thereof is omitted. Hereinafter, an air conditioner equipped with an inverter control device of the present invention will be described with reference to FIG.

  As shown in FIG. 7, the air conditioner includes an indoor unit 92, in addition to the inverter control device 81 shown in the second embodiment including the inverter 3 and the control unit 10, and the electric compressor 82 incorporating the motor 3. A refrigeration cycle comprising an outdoor unit 95 and a four-way valve 91 is provided.

  The indoor unit 92 includes an indoor heat exchanger 93 and an indoor fan 94, and the outdoor unit 95 includes an outdoor heat exchanger 96, an outdoor fan 97, and an expansion valve 98.

  A refrigerant as a heat medium circulates in the refrigeration cycle. The refrigerant is compressed by the electric compressor 82, and heat is exchanged with outdoor air by blowing from the outdoor blower 97 in the outdoor heat exchanger 96, and indoor air is blown from the indoor blower 94 in the indoor heat exchanger 93. And heat exchange. Indoor air conditioning is performed by the air after heat exchange in the indoor heat exchanger 93. Switching between cooling and heating is performed by reversing the direction of refrigerant circulation by a four-way valve 91.

  The refrigerant circulation in the refrigeration cycle as described above is performed by driving the electric compressor 82 by the inverter control device 81. The configuration and operation of the inverter control device 81 are as described in the second embodiment. Since there is, description is abbreviate | omitted.

  With the configuration described above, the inverter switching frequency component is superimposed on the load current waveform by detecting the offset voltage by turning off the inverter switching element at a predetermined interval for a predetermined time at the zero cross point of the load current waveform. Even if the current waveform distortion is large, the fluctuation error of the offset voltage of the current detection means due to temperature drift during operation can be reliably corrected, without increasing the size and cost of the device, A decrease in control performance such as a decrease in efficiency in the air conditioner can be suppressed.

  In this embodiment, the air conditioner using the inverter control device shown in the second embodiment as the compressor driving device has been described. However, the inverter of the other invention as shown in the first embodiment or the third to fifth embodiments is described. -Even if it uses an inverter control apparatus, the air conditioner which had the effect which the inverter control apparatus of each invention has similarly can be provided.

  In the inverter control device of the present invention, even if the electric compressor 82 is a one-piston rotary compressor, as shown in the fourth embodiment, an error in the offset voltage of the current sensor due to temperature drift during operation is corrected. Thus, it is possible to suppress a decrease in control performance.

Therefore, the inverter control device according to the present invention can be used to the maximum extent by using it for an air conditioner having a particularly severe operating temperature environment.

  Moreover, since the offset voltage correction control described above can be realized by software, it can be incorporated into a microcomputer in the control unit 10 and can be performed without adding parts or increasing costs. Have.

  In the first to fifth embodiments of the present invention, the constituent elements included in the control unit 10 are not limited to the combinations shown in the above-described embodiments, and other constituent elements 11 in FIGS. 1 and 4 to 6. To 21 may be included.

  In the first to fifth embodiments, the initial variation of the offset voltage of the current sensors 4a and 4b can be corrected by detecting the sensor output voltage as an offset voltage before the motor 3 is started. it can.

  The inverter control device of the present invention can be applied to applications such as a refrigerator and a freezer using a motor driven by an inverter because it can correct the offset error of the current sensor and suppress distortion of the current waveform.

Control block diagram of inverter control apparatus in embodiment 1 of the present invention The inverter circuit block diagram of the inverter control apparatus in Embodiment 1 of this invention Motor current waveform diagram of inverter control device of the present invention The control block diagram of the inverter control apparatus in Embodiment 2 and 3 of this invention Control block diagram of inverter control apparatus in embodiment 4 of the present invention. Control block diagram of inverter control apparatus in embodiment 5 of the present invention. The figure which shows the Example of the air conditioner provided with the inverter control apparatus of this invention Control block diagram of conventional inverter control device Motor current waveform diagram of 1-piston rotary compressor

Explanation of symbols

1 DC power supply 2 Inverter 3 Motor 4a, 4b Current sensor (current detection means)
5a, 5b, 5c, 5d, 5e, 5f Switching element 10 Control unit 12 Zero cross detection unit 13 Drive stop unit 14 Offset voltage detection unit 15 Actual current calculation unit 16 Command current calculation unit 17 Current error calculation unit 18 Drive signal generation unit 20 Stop interval measurement unit 21 Actual speed detection unit 22 Temperature sensor (Ambient temperature detection means)
DESCRIPTION OF SYMBOLS 81 Inverter control apparatus 82 Electric compressor 91 Four-way valve 92 Indoor unit 93 Indoor heat exchanger 94 Indoor fan 95 Outdoor unit 96 Outdoor heat exchanger 97 Outdoor fan 98 Expansion valve

Claims (6)

An inverter composed of a plurality of switching elements for converting direct current to alternating current and supplying the same to a load motor; current detection means for detecting a current value flowing through the load motor; converting the current value into a voltage value; A zero-cross detecting means for detecting zero-cross points of a plurality of phase currents flowing through the load motor, and a drive stop for turning off at least one of the switching elements of the inverter for a predetermined time so that the current value flowing through the load motor becomes zero Voltage detection means for storing and updating the voltage value output by the current detection means during a period when the current value flowing through the load motor becomes zero by turning off the switching element of the inverter. And the voltage value output from the current detection means and the voltage value stored in the offset voltage detection means And an actual current calculating means for calculating a current value flowing through the inverter, wherein the inverter switching element is turned off for a predetermined time at a zero cross point of the current detected by the zero cross detecting means. apparatus. The driving stop means further includes a stop interval measuring means for measuring an elapsed time after at least one of the switching elements of the inverter is turned off for a predetermined time, and the drive stopping means has a measured value of the stop interval measuring means as a predetermined value. 2. The inverter control device according to claim 1, wherein the inverter switching device is turned off for a predetermined time at a zero-cross point of a current detected by the zero-cross detection means in the case described above. 3. The drive stop means turns off the inverter switching element for a predetermined time at the zero cross point of the current detected by the zero cross detection means when the target speed of the load motor is below a predetermined value. An inverter control device according to claim 1. An actual speed detecting means for detecting the actual speed of the load motor is further provided, and the drive stopping means is a switching element of the inverter at the zero cross point of the current detected by the zero cross detecting means when the actual speed of the load motor is not more than a predetermined value. The inverter control device according to claim 1, wherein the inverter is turned off for a predetermined time. An ambient temperature detection means for detecting an ambient temperature of the current detection means is further provided, and when the change width of the ambient temperature is not more than a predetermined value, the switching element of the inverter is not turned off by the drive stop means. The inverter control device according to any one of claims 1 to 4. An air conditioner comprising the inverter control device according to any one of claims 1 to 5.

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