JP2008099507A - Inverter for air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter for air conditioner which aims at reduction of high frequency leakage current. <P>SOLUTION: The inverter for air conditioner comprises a converter 4 for converting the AC voltage of an AC power supply 3 into a DC voltage, a capacitor 5 for smoothing a DC voltage, a voltage type PWM system inverter 8 which controls a voltage applied to a motor for driving a compressor 1 by chopping the compressor voltage at the carrier frequency, a leakage current detector 6 provided between the AC power supply 3 and the converter 4 in order to detect a leakage current flowing through a stray capacitance 2, a first comparator 7 for comparing the difference between the output from the leakage current detector 6 and a first threshold, and a compressor regulator 9 for making the DC voltage variable and controlling the carrier frequency depending on the output from the first comparator 7 and a Duty signal from the inverter 8 wherein the high frequency leakage current can be reduced by stepping down the compressor voltage if the high frequency leakage current is larger than the first threshold, and fixing the compressor voltage when the Duty signal reaches a predetermined level and lowering the carrier frequency. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inverter device for an air conditioner intended to reduce high-frequency leakage current flowing from a winding of a compressor driving motor to ground via a stray capacitance.

  Conventionally, this type of inverter device for an air conditioner drives an inverter at a constant carrier frequency regardless of leakage current (see, for example, Patent Document 1). Therefore, with the chopping of the inverter, a high-frequency leakage current flows through the stray capacitance between the compressor and the ground. This leakage current is proportional to stray capacitance, carrier frequency, and power supply voltage.

  This high-frequency leakage current is dielectrically transmitted to the AC power source, which may adversely affect the air conditioner inverter device or cause malfunctions of other devices and breakers.

FIG. 4 shows a conventional inverter device for an air conditioner described in Patent Document 1. As shown in FIG. As shown in FIG. 4, a compressor 1 in which a motor having a three-phase winding is housed in a sealed case, a power supply 12, a converter 4, a smoothing capacitor 5, an inverter 6, a current sensor 13, and a control device. 14.
Japanese Patent Laid-Open No. 3-178595

  However, since the conventional configuration does not detect the leakage current, it cannot cope with the change in the dielectric constant of the stray capacitance due to the surrounding environment (temperature / humidity) or the increase in the leakage current due to aging. It had the subject of having a bad influence on the inverter apparatus for harmonic machines, or causing malfunction of other apparatuses, a breaker, etc.

  An object of the present invention is to solve the above-described conventional problems, and to provide an inverter device for an air conditioner that reduces high-frequency leakage current flowing from a winding of a compressor driving motor to ground via a stray capacitance. It is a thing.

  In order to solve the above-described conventional problems, an inverter device for an air conditioner according to the present invention includes a compressor in which a motor having a three-phase winding is housed in a hermetically sealed case and a stray capacitance is present between the ground and an AC power source. A converter that converts the voltage of the current into a DC voltage, a leakage current detector that is provided between the AC power supply and the converter and detects a leakage current flowing in the stray capacitance, and an output of the leakage current detector is preset. A first comparator that compares the difference between the first leakage current threshold and a compressor voltage that is a voltage applied to the compressor at a carrier frequency higher than the operating frequency of the compressor; A voltage-type PWM inverter that controls a voltage applied to a motor that drives the compressor; and a smoothing capacitor and an inverter, the output of the first comparator and the inverter A compressor controller that controls a compressor voltage and a carrier frequency of the inverter according to a duty signal output from the inverter, and if the leakage current is larger than the first leakage current threshold, the compressor voltage is If the duty signal becomes larger than the first duty threshold value preset in the compressor controller and the leakage current is still larger than the first leakage current threshold value, the compressor voltage is reduced. The step-down is maintained and the carrier frequency is lowered.

As a result, when the high frequency leakage current increases due to the surrounding environment, aging, etc., the compressor voltage is first stepped down. If the high frequency leakage current is equal to or higher than the set value even if the inverter duty is higher than a certain value, the compressor Since the rotation speed of the motor that drives the motor cannot be maintained, it is possible to reduce the high frequency leakage current by stopping the step-down of the compressor voltage and lowering the carrier frequency of the inverter. Can be solved.

  The inverter device for an air conditioner according to the present invention converts a voltage of an AC power source into a DC voltage and a compressor in which a motor having a three-phase winding is housed in a sealed case and has a stray capacitance between the motor and the ground. A leakage current detector that is provided between the converter, the AC power supply, and the converter and detects a leakage current flowing through the stray capacitance; an output of the leakage current detector; and a preset first leakage current threshold value; A first comparator for comparing a difference between the second leakage current threshold and a second comparator for comparing a difference between an output of the leakage current detector and a second leakage current threshold smaller than a preset first leakage current threshold. And a voltage type PWM that controls the voltage applied to the motor that drives the compressor by chopping the compressor voltage, which is the voltage applied to the compressor, at a carrier frequency higher than the operating frequency of the compressor. Provided between the inverter of the equation, the smoothing capacitor and the inverter, the compressor voltage and the output according to the output of the first comparator, the output of the second comparator and the duty signal output from the inverter A compressor controller for controlling the carrier frequency of the inverter, and if the leakage current is greater than the first leakage current threshold, the compressor voltage is reduced, but the Duty signal is the compressor If it becomes larger than the first duty threshold set in advance in the controller and the leakage current is still larger than the first leakage current threshold, the voltage drop of the compressor is maintained and the carrier frequency is lowered. On the contrary, if the leakage current is smaller than the second leakage current threshold, the carrier frequency is increased, and the carrier frequency is increased to an initial value. , Those still if the leakage current is less than the second leakage current, which was decided and features to boost the compressor voltage.

  As a result, when the high frequency leakage current increases due to the surrounding environment, aging, etc., the compressor voltage is first stepped down. Since the rotation speed of the motor that drives the motor cannot be maintained, the high frequency leakage current can be reduced by maintaining the compressor voltage and lowering the carrier frequency of the inverter. be able to. Conversely, if the high-frequency leakage current decreases, the carrier frequency is increased, and even if the carrier frequency reaches the initial value, if the high-frequency leakage current is still lower than the set value, the compressor voltage can be boosted. Therefore, it is possible to increase the rotation speed of the motor that drives the compressor, and as a result, it is possible to control the high-frequency leakage current to a certain width.

  In the inverter device for an air conditioner of the present invention, the compressor voltage is stepped down / boosted and the carrier frequency is raised / lowered according to a preset threshold value, and as a result, the high frequency leakage current is preset. It is possible to reduce the threshold value to less than the threshold value, and it is possible to ensure safety against electric shock due to leakage current.

According to a first aspect of the present invention, there is provided a compressor in which a motor having a three-phase winding is housed in a hermetically sealed case and a stray capacitance is present between the motor, a converter for converting a voltage of an AC power source into a DC voltage, and the AC power source A leakage current detector provided between the converter and configured to detect a leakage current flowing in the stray capacitance, and a first difference for comparing a difference between an output of the leakage current detector and a preset first leakage current threshold value. And a voltage for controlling the voltage applied to the motor driving the compressor by chopping the compressor voltage, which is the voltage applied to the compressor, at a carrier frequency higher than the operating frequency of the compressor Type PWM inverter, a smoothing capacitor, and an inverter. The compressor voltage and the inverter are set in accordance with the output of the first comparator and the duty signal output from the inverter. A compressor controller for controlling the carrier frequency of the compressor, and if the leakage current is greater than the first leakage current threshold, the compressor voltage is stepped down; however, the Duty signal is the compressor controller. If the leakage current is larger than the first preset duty threshold value set in advance and the leakage current is still larger than the first leakage current threshold value, the step-down of the compressor voltage is maintained and the carrier frequency is decreased. By using the inverter device for air conditioners as a feature, when the high-frequency leakage current increases due to the ambient environment or aging, the compressor voltage is first stepped down. If the leakage current is equal to or higher than the set value, the rotation speed of the motor that drives the compressor cannot be maintained. It is possible to reduce high-frequency leakage current by lowering the carrier frequency, safety for electric shock due to leakage current can be secured.

  According to a second aspect of the present invention, there is provided a compressor in which a motor having a three-phase winding is housed in a sealed case and has a stray capacitance between the ground, a converter for converting a voltage of an AC power source into a DC voltage, and the AC power source A leakage current detector provided between the converter and configured to detect a leakage current flowing in the stray capacitance, and a first difference for comparing a difference between an output of the leakage current detector and a preset first leakage current threshold value. Applied to the compressor, a second comparator for comparing a difference between an output of the leakage current detector and a second leakage current threshold value smaller than a first leakage current threshold value set in advance. A voltage-type PWM inverter that controls the voltage applied to the motor that drives the compressor by chopping the compressor voltage, which is a voltage generated by the compressor, at a carrier frequency higher than the operating frequency of the compressor; The compressor voltage and the carrier frequency of the inverter are controlled according to the output of the first comparator, the output of the second comparator, and the duty signal output from the inverter. A compressor controller configured to reduce the compressor voltage if the leakage current is greater than the first leakage current threshold, but the Duty signal is preset in the compressor controller. If the leakage current is still greater than the first leakage current threshold, the compressor voltage step-down is maintained, the carrier frequency is decreased, and conversely, the leakage current is decreased. If the current is smaller than the second leakage current threshold, the carrier frequency is increased, and even if the carrier frequency is increased to an initial value, the leakage current is still If the leakage current is smaller than the leakage current, the inverter voltage for the air conditioner is characterized by boosting the compressor voltage. However, if the high-frequency leakage current is equal to or higher than the set value even if the inverter duty is equal to or higher than a certain value, the rotational speed of the motor that drives the compressor cannot be maintained. By reducing the carrier frequency of the inverter, it is possible to reduce high-frequency leakage current, and safety against electric shock due to leakage current can be ensured. In addition, if the high-frequency leakage current decreases, the carrier frequency is increased, and if the high-frequency leakage current is still lower than the set value even if the carrier frequency reaches the initial value, the compressor voltage is increased. Therefore, it is possible to increase the number of rotations of the motor that drives the compressor, and as a result, it is possible to control the high-frequency leakage current to a certain width.

  In particular, the leakage current detector according to the first or second aspect of the present invention is provided between the smoothing capacitor and the compressor controller, so that the insulation between the AC side and the DC side becomes unnecessary, and the cost is reduced. Can be planned.

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

(Embodiment 1)
FIG. 1 shows a block diagram of an inverter device for an air conditioner according to a first embodiment of the present invention.

  In FIG. 1, 1 is a compressor in which a motor having a three-phase winding is housed in a sealed case, 2 is a stray capacitance floating between the compressor 1 and the ground, 3 is an AC power supply, 4 is an AC power supply 3 A converter that converts a voltage into a DC voltage, 5 is a smoothing capacitor that smoothes the DC voltage rectified by the converter 4, 6 is a leakage current detector that detects a high-frequency leakage current flowing through the stray capacitance 2, and 7 is a leakage current detector 6. The first comparator 8 compares the difference between the output of the output and the first leakage current threshold, and is applied to the motor that drives the compressor 1 by chopping the applied compressor voltage at the carrier frequency. A voltage type PWM inverter 9 for controlling the voltage is provided between the smoothing capacitor 5 and the inverter 8 and is applied to the compressor in accordance with the output of the first comparator 7 and the duty signal from the inverter 8. In A compressor controller for controlling the compressor voltage and the carrier frequency.

  About the inverter apparatus for air conditioners comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  After the voltage of the AC power source 3 is converted to a DC power source by the converter 4, it is smoothed by the smoothing capacitor 5 and rectified to a DC voltage with a small ripple. The DC voltage is increased or decreased according to the output of the first comparator 7 and the duty signal output from the inverter 8. The adjusted compressor voltage is chopped at the carrier frequency by the inverter 9, the voltage applied to the compressor driving motor is controlled, and the operating frequency of the compressor 1 is controlled.

  Here, when the high-frequency leakage current flowing through the stray capacitance 2 increases, the output of the leakage current detector 6 increases. When this output becomes larger than the first leakage current threshold, the output of the first comparator 7 is inverted. When the output of the first comparator 7 is inverted, the compressor controller 9 performs an operation for reducing the DC voltage. When the compressor voltage decreases, the high-frequency leakage current proportional to the voltage decreases. If the output of the leakage current detector 6 due to the reduced high-frequency leakage current is still larger than the first leakage current threshold, the voltage is further stepped down. Conversely, if the output is smaller than the first leakage current threshold, the compressor Fix with voltage. However, even if the duty signal from the inverter 8 exceeds a certain value, if the output of the first comparator 6 remains inverted, the rotational speed of the motor that drives the compressor cannot be maintained. The step-down of the compressor voltage is stopped, and the compressor controller 9 operates to lower the carrier frequency of the inverter 8. When the carrier frequency decreases, the high-frequency leakage current proportional to the frequency decreases. If the output of the leakage current detector 6 due to the reduced high-frequency leakage current is still larger than the first leakage current threshold, the carrier frequency is further lowered, and conversely if it is smaller than the first leakage current threshold, Fix at the carrier frequency.

  As described above, in the present embodiment, when the high-frequency leakage current increases, the high-frequency leakage current can be reduced by reducing the compressor voltage and lowering the carrier frequency.

(Embodiment 2)
FIG. 2 shows a block diagram of an inverter device for an air conditioner according to the second embodiment of the present invention.

In FIG. 2, 1 is a compressor in which a motor having a three-phase winding is housed in a sealed case, 2 is a floating capacity floating between the compressor 1 and the ground, 3 is an AC power source, 4 is an AC power source 3 A converter that converts a voltage into a DC voltage, 5 is a smoothing capacitor that smoothes the DC voltage rectified by the converter 4, 6 is a leakage current detector that detects a high-frequency leakage current flowing through the stray capacitance 2, and 7 is a leakage current detector 6. The first comparator 10 compares the difference between the output of the first leakage current threshold and the first leakage current threshold, and 10 indicates the difference between the output of the leakage current detector 6 and the second leakage current threshold smaller than the first leakage current threshold. A second comparator 8 for comparison, chopping the compressor voltage at the carrier frequency to control the voltage applied to the motor that drives the compressor 1, and a voltage type PWM inverter 9; smoothing capacitor 5 and inverter 8 Established between A compressor controller for controlling the compressor voltage and the carrier frequency is a voltage applied to the compressor in response to the Duty signal from the first comparator output 7 and the second comparator 10 and the inverter 8.

  About the inverter apparatus for air conditioners comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  After the voltage of the AC power source 3 is converted to a DC power source by the converter 4, it is smoothed by the smoothing capacitor 5 and rectified to a DC voltage with a small ripple. The DC voltage is increased or decreased according to the output of the first comparator 7 and the duty signal output from the inverter 8. The adjusted compressor voltage is chopped at the carrier frequency by the inverter 9, the voltage applied to the compressor driving motor is controlled, and the operating frequency of the compressor 1 is controlled.

  Here, when the high-frequency leakage current flowing through the stray capacitance 2 increases, the output of the leakage current detector 6 increases. When this output becomes larger than the first leakage current threshold, the output of the first comparator 7 is inverted. When the output of the first comparator 7 is inverted, the compressor controller 9 performs an operation for reducing the DC voltage. When the compressor voltage decreases, the high-frequency leakage current proportional to the voltage decreases. If the output of the leakage current detector 6 due to the reduced high-frequency leakage current is still larger than the first leakage current threshold, the voltage is further stepped down. Conversely, if the output is smaller than the first leakage current threshold, the compressor Fix with voltage. However, even if the duty signal from the inverter 8 exceeds a certain value, if the output of the first comparator 6 remains inverted, the rotational speed of the motor that drives the compressor cannot be maintained. The step-down of the compressor voltage is stopped, and the compressor controller 9 operates to lower the carrier frequency of the inverter 8. When the carrier frequency decreases, the high-frequency leakage current proportional to the frequency decreases. If the output of the leakage current detector 6 due to the reduced high-frequency leakage current is still larger than the first leakage current threshold, the carrier frequency is further lowered, and conversely if it is smaller than the first leakage current threshold, Fix at the carrier frequency.

  Further, when the output of the leakage current detector 6 becomes smaller than the second leakage current threshold, the output of the second comparator 10 is inverted. When the output of the second comparator 10 is inverted, the compressor controller 9 performs an operation of increasing the carrier frequency. As the carrier frequency increases, the high-frequency leakage current proportional to the frequency increases. If the output of the leakage current detector 6 due to the increased high-frequency leakage current is still smaller than the second leakage current threshold value, the carrier frequency is further increased. If the output is larger than the second leakage current threshold value, the carrier frequency is increased. To fix. However, even if the carrier frequency increases to the initial value, if the output of the leakage current detector 6 due to the high-frequency leakage current is still smaller than the second leakage current threshold, the compressor controller 9 increases the compressor voltage. To perform the operation. As the compressor voltage increases, the high-frequency leakage current proportional to the voltage increases. If the output of the leakage current detector 6 due to the increased high-frequency leakage current is still smaller than the second leakage current threshold, the compressor voltage is further boosted, and if it is larger than the second leakage current threshold, Fix with compressor voltage.

  As described above, in the present embodiment, when the high-frequency leakage current increases, the high-frequency leakage current can be reduced and the high-frequency leakage current can be reduced by lowering the compressor voltage and lowering the carrier frequency. When the current decreases, the high frequency leakage current can be controlled to a certain width by increasing the carrier frequency and boosting the compressor.

(Embodiment 3)
FIG. 3 shows a block diagram of an inverter device for an air conditioner according to a third embodiment of the present invention. The present embodiment is different from the first embodiment in that a leakage current detector 6 is provided between the smoothing capacitor 5 and the compressor voltage regulator 9.

  As for the inverter device for an air conditioner configured as described above, as in the first embodiment, when the high-frequency leakage current increases, the high-frequency leakage current is reduced by reducing the compressor voltage and lowering the carrier frequency. Can be reduced. In addition, since all can be configured on the direct current side, insulation between the alternating current side and the direct current side is not necessary, and the cost can be reduced.

  Although not shown, also in the second embodiment, the same effect can be obtained by providing the leakage current detector 6 between the smoothing capacitor 5 and the compressor controller 9.

  As described above, the inverter device for an air conditioner according to the present invention reduces the high-frequency leakage current by controlling the compressor voltage and the carrier frequency when the high-frequency leakage current exceeds a preset threshold value. Therefore, it can be applied to uses such as a refrigeration apparatus, a refrigerator, a heat pump type hot water heater, and a heat pump type washing and drying machine.

The block diagram of the inverter apparatus for air conditioners in Embodiment 1 of this invention The block diagram of the inverter apparatus for air conditioners in Embodiment 2 of this invention The block diagram of the inverter apparatus for air conditioners in Embodiment 3 of this invention Block diagram of conventional inverter device for air conditioner

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Floating capacity 3 AC power supply 4 Converter 5 Smoothing capacitor 6 Leakage current detector 7 1st comparator 8 Inverter 9 Compressor controller 10 2nd comparator 11 Three-phase power supply 12 Current sensor 13 Controller

Claims (3)

A compressor having a three-phase winding in a sealed case and having a floating capacity between the ground and a converter, a converter for converting the voltage of an AC power source into a DC voltage, and the AC power source and the converter are provided. A leakage current detector for detecting a leakage current flowing in the stray capacitance, a first comparator for comparing a difference between an output of the leakage current detector and a preset first leakage current threshold, and a compression A voltage type PWM inverter that chops a compressor voltage, which is a voltage applied to a compressor, at a carrier frequency higher than an operating frequency of the compressor, and controls a voltage applied to a motor that drives the compressor; , Provided between the smoothing capacitor and the inverter, according to the output of the first comparator and the duty signal output from the inverter, the compressor voltage and the carry of the inverter. A compressor controller for controlling the frequency, and if the leakage current is greater than the first leakage current threshold, the compressor voltage is reduced, but the Duty signal is preset in the compressor controller. If the leakage current is greater than the first leakage current threshold and the leakage current is still greater than the first leakage current threshold, the compressor voltage is held down and the carrier frequency is lowered. Inverter device for harmonic machine. A compressor having a three-phase winding in a sealed case and having a floating capacity between the ground and a converter, a converter for converting the voltage of an AC power source into a DC voltage, and the AC power source and the converter are provided. A leakage current detector for detecting a leakage current flowing in the stray capacitance, a first comparator for comparing a difference between an output of the leakage current detector and a preset first leakage current threshold, A second comparator that compares the difference between the output of the leakage current detector and a second leakage current threshold value that is smaller than a preset first leakage current threshold value, and a compressor that is a voltage applied to the compressor A voltage type PWM inverter that controls voltage applied to a motor that drives the compressor by chopping the voltage at a carrier frequency higher than the operating frequency of the compressor, a smoothing capacitor, and an inverter And a compressor for controlling a compressor voltage and a carrier frequency of the inverter according to a duty signal output from the output of the first comparator, the output of the second comparator, and the inverter A controller, and if the leakage current is greater than the first leakage current threshold, the compressor voltage is stepped down, but the Duty signal is preset in the compressor controller. If the leakage current is still greater than the first leakage current threshold, the voltage drop of the compressor voltage is maintained, the carrier frequency is decreased, and conversely, the leakage current is If it is smaller than the second leakage current threshold, the carrier frequency is increased, and even if the carrier frequency is increased to an initial value, the leakage current is still greater than the second leakage current. If smaller, thereby boosting the compressor voltage and wherein the air conditioner inverter device. The inverter device for an air conditioner according to any one of claims 1 and 2, wherein the leakage current detector is provided between a smoothing capacitor and a compressor regulator.

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