JP2012082996A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air conditioner capable of preventing liquid compression without generating vibration and noise due to operation of a rotor, by heating a refrigerant.SOLUTION: The air conditioner includes the compressor 1 for compressing the refrigerant, a motor 8 for driving the compressor, an inverter 9 for impressing three-phase voltage to the motor 8, and an inverter control unit 11 for controlling the inverter 9. The inverter control unit 11 has a high-frequency AC voltage generation unit 13 for outputting a command of high-frequency AC voltage with higher frequency than that during compression operation of the motor 8, and a PWM signal forming unit 15 for forming a PWM signal based on the high-frequency AC voltage command and a carrier signal. The inverter 9 impresses AC voltage based on the PWM signal to heat the refrigerant in the compressor 1 by means of iron loss and copper loss without generating rotation torque in the motor.

Description

  In the air conditioner, the present invention prevents liquid compression of the compressor by heating the refrigerant.

As a conventional air conditioner for preventing liquid compression of the compressor by heating the refrigerant, “When the compressor 1 is stopped, the liquid refrigerant amount detection means 8 is the amount of liquid refrigerant that stays in the compressor 1. When the signal becomes equal to or greater than a predetermined value, the control device 7 outputs a signal, and when the signal is input, the weak winding frequency of the current is passed through the winding of the motor 5 to warm the motor winding and the liquid refrigerant stays at a low temperature. Prevents the compressor from being damaged and makes the air-conditioning operation start quickly (see, for example, Patent Document 1).
Further, “a switching control element is bridge-connected between a power source and a ground, and the energization control method in the motor preheating device is configured to energize the stator coil of the motor that drives the compressor, one end of which is Any one of the switching elements connected to the power supply side is turned on / off at a predetermined repetition period during a predetermined time, and at the same time, any two switching elements whose one ends are connected to the ground side are In the meantime, it is configured to repeatedly control the corresponding switching element in the same manner as described above so that the current flowing in the stator coil is in the reverse direction after that, and in particular, the switching element that is turned on and off. Is periodically changed so that the direction of the current of the stator coil is periodically reversed. Not only the heat generated by, the improvement of power efficiency is reduced as heat generation due to hysteresis loss occurs "while others (e.g., see Patent Document 2).

JP-A-8-226714 (Summary, FIGS. 1 and 2) Japanese Patent Laid-Open No. 11-159467 (page 3, FIGS. 1 and 4)

  However, in the prior art described in Patent Document 1, when the impedance of each phase in the motor winding is different, the current flows in all three phases due to the sneak current, so that the phase loss operation does not occur, and the rotor There is a problem that vibration and noise may be generated by the operation.

  In the prior art described in Patent Document 2, a magnetic field in the rotational direction is temporarily applied to the rotor by the on / off operation of the switch, and the rotor moves, thereby causing vibration and noise uncomfortable for the user. There is a problem that it may occur.

  The present invention has been made to solve the above-described problems, and is an air conditioner that prevents liquid compression of a compressor by heating a refrigerant without generating vibration and noise due to operation of a rotor. The purpose is to provide.

  An air conditioner according to the present invention includes a compressor that compresses refrigerant, a motor that drives the compressor, an inverter that applies a three-phase voltage to the motor, inverter control means that controls the inverter, and A bus voltage detecting means for detecting a bus voltage as a power source, wherein the inverter control means compresses the motor based on information on a predetermined amplitude and alternately inputted first phase and second phase. Based on the high-frequency AC voltage generating means for outputting a high-frequency AC voltage command having a higher frequency than the time, and the carrier signal determined according to the output of the high-frequency AC voltage generating means and the bus voltage, the PWM signal is generated. PWM signal generating means for outputting to the inverter, the inverter is an AC based on the PWM signal By applying pressure, without generating a rotational torque to the motor, it is to heat the refrigerant of the compressor of iron loss and copper loss.

  According to the present invention, an AC voltage is applied to the motor but no rotational torque is generated. Therefore, the compressor can be prevented from being compressed by heating the refrigerant without generating vibration and noise due to the operation of the rotor. An air conditioner can be obtained.

It is a figure which shows the structure of the air conditioner in embodiment of this invention. It is a figure which shows the PWM signal generation method in embodiment of this invention. It is the figure which carried out the vector display of the applied voltage to the motor from the inverter in embodiment of this invention. It is the figure which shows the schematic of the motor in embodiment of this invention, and the relationship between a rotor position and a phase current peak. It is the schematic which shows the change of the applied voltage in a certain rotor position of the motor in embodiment of this invention. It is a figure which shows another example of the PWM signal generation method in embodiment of this invention.

  Hereinafter, an example of an air conditioner according to the present invention will be described in detail with reference to the drawings.

Embodiment.
FIG. 1 is a diagram illustrating a configuration of an air conditioner according to an embodiment of the present invention.
As shown in FIG. 1, the air conditioner according to the embodiment of the present invention includes a refrigeration cycle 30, power calculation means 18, a converter 17, an inverter 9, a bus voltage detection means 10, and an inverter control means 11.
Further, the compressor 1, the four-way valve 2, the outdoor heat exchanger 3, the expansion valve 4 and the indoor heat exchanger 5 are connected via a refrigerant pipe 6 to constitute a refrigeration cycle 30. In the compressor 1, a compression mechanism 7 that compresses the refrigerant and a motor 8 that operates the compression mechanism 7 are provided. In addition, the compression mechanism 7 shall be a scroll mechanism, for example. The refrigeration cycle 30 is used in an air conditioner such as a separate air conditioner.

  The inverter 9 is connected to the motor 8 and the converter 17, and the general commercial power supply 22 is converted from alternating current to direct current by the converter 17. Then, a voltage is supplied from the inverter 9 to the motor 8 to drive the motor 8. The inverter 9 includes a bus voltage detecting means 10 that detects a bus voltage Vdc that is a power supply voltage of the inverter 9 and bridge-connected switching elements 16a to 16f.

  Further, in the power calculation means 18, a current detection means 20 for detecting a current supplied from the general commercial power supply 22 and a voltage detection means 21 for detecting a voltage are provided. In the power calculation means 18, a power calculation means 23 that calculates power from the current detected by the current detection means 20 and the voltage detected by the voltage detection means 21 is provided. The electric power supplied to the motor 8 is calculated by the power calculation means 18 and the calculation result is given to the inverter control means 11. The inverter control means 11 is connected to a control input terminal (not shown) of the inverter 9. In the inverter control means 11, a stagnation detection means 12, a high-frequency AC voltage generation means 13, a phase switching means 14 and a PWM signal generation means 15 are provided. Further, the high frequency AC voltage generating means 13 is provided with an adder 19.

The inverter control means 11 can be controlled by a microcomputer or DSP executing a control program on the memory.
Further, as described above, the power calculation means 18 performs power calculation on the supply side of the general commercial power supply 22 as shown in FIG. 1, but the same calculation is performed on the output side of the inverter 9 or the current in the inverter 9, You may calculate from a voltage.

Next, control of the inverter 9 by the inverter control means 11 will be described.
For example, when the temperature of the refrigeration cycle is equal to or lower than a predetermined value and a predetermined time has elapsed, the stagnation detection unit 12 determines that the refrigerant has stagnation.
In the inverter control unit 11, for example, when the stagnation detection unit 12 detects that the refrigerant has stagnate in the compressor 1, the command values Vu *, Vv * of the voltage applied to the motor 8 by the high-frequency AC voltage generation unit 13. Vw * is obtained, and the PWM signal generation means 15 generates a PWM signal based on the voltage command values Vu *, Vv *, Vw *.
Then, the inverter 9 receives switching signals corresponding to the PWM signals (UP, VP, WP, UN, VN, WN) sent from the inverter control means 11 (UP is 16a, VP is 16b, WP is 16c, UN drives 16d, VN drives 16e, and WN drives 16f).

FIG. 2 is a diagram illustrating a PWM signal generation method according to the embodiment of the present invention.
The voltage command signals Vu *, Vv *, Vw * in FIG. 2 are defined as follows, for example. Here, one of phase θ1 (corresponding to the first phase in the present invention) and θ2 (corresponding to the second phase in the present invention) set arbitrarily in advance is selected by the phase switching means 14, and Is θ. Then, the amplitude A is arbitrarily set in advance.

ここで、図２においては、θ１＝０［ｄｅｇ］、θ２＝１８０［ｄｅｇ］に設定した例を示している。これにより、Ｖｖ＊、Ｖｗ＊が同位相となり、Ｖｕ＊とＶｖ＊及びＶｗ＊とが異なる位相になる。
また、位相切換手段１４の位相切換タイミングについては、キャリア信号の、山及び谷のタイミングで行う。ここで、山とはキャリア信号の最大値の部分であり、谷とはキャリア信号の最小値の部分である。

Here, FIG. 2 shows an example in which θ1 = 0 [deg] and θ2 = 180 [deg] are set. As a result, Vv * and Vw * have the same phase, and Vu * and Vv * and Vw * have different phases.
The phase switching timing of the phase switching means 14 is performed at the peak and valley timings of the carrier signal. Here, the peak is the maximum value portion of the carrier signal, and the valley is the minimum value portion of the carrier signal.

  Then, the PWM signal generation means 15 has a voltage command signal obtained by the equations (1) to (3) and an amplitude Vdc / 2 at a predetermined frequency (Vdc is the bus of the inverter 9 detected by the bus voltage detection means 10). The carrier signal which is a triangular wave of (voltage) is compared. By generating the PWM signals UP, VP, WP, UN, VN, WN based on the mutual magnitude relationship, it is possible to output a PWM signal synchronized with the carrier.

  For example, in the UP of FIG. 2, when the voltage command signal Vu * (solid line) is larger than the carrier signal, 1 is set, and when the voltage command signal Vu * is less than the carrier signal, 0 is set. Then, the PWM signal is generated so that UN is 0 when UP is 1 and UN is 1 when UP is 0. In VP, 1 is set when the voltage command signal Vv * (broken line) is larger than the carrier signal, and 0 is set when the voltage command signal Vv * is less than the carrier signal. When VP is 1, VN is 0, and when VN is 0, VP is 1. For WP and WN, PWM signals are generated in the same manner as VP and VN.

In addition to the equations (1) to (3), there is no problem even if the voltage command signals Vu *, Vv *, Vw * are obtained by two-phase modulation, third harmonic superposition modulation, space vector modulation, or the like. Needless to say.
For example, when the two-phase modulation method is used, one of the phases is fixed to the positive or negative potential, and the other two phases are switched. As a result, the number of switching operations can be reduced as compared with the case where the three-phase modulation method is used.
For example, when the third harmonic superposition modulation method is used, the number of occurrences of the amplitude peak is increased by superimposing the third harmonic on the sine wave, so that modulation is performed compared to the case where the sine wave is used for the voltage command signal. The rate is improved.
For example, when the space vector modulation method is used, a PWM pattern having various characteristics can be generated by expressing the voltage command signal with a plurality of vectors and adjusting the output time of each vector.

  With the above method, the PWM signals for driving the switching elements 16a to 16f change as shown in the timing chart of UP, VP, and WP in FIG. The voltage vector is V0 (UP = VP = WP = 0) → V4 (UP = 1, VP = WP = 0) → V7 (UP = VP = WP = 1) → V3 (UP = 0, VP = WP) = 1) → V0 (UP = VP = WP = 0)...

FIG. 3 is a diagram in which the voltage applied from the inverter to the motor in the embodiment of the present invention is displayed as a vector.
As shown in FIG. 3, no current flows in the V0 vector, and + Iu current flows in the winding of the motor 8 when the V4 vector is applied. Further, no current flows in the V7 vector, and a current of −Iu flows in the winding of the motor 8 when the V3 vector is applied. As shown in FIG. 2, since the vector pattern of V4 and V3 appears in one carrier cycle (1 / fc), an alternating current synchronized with the carrier frequency fc can be generated. In this embodiment, U is the first phase in the present invention, and V and W are the other two phases in the present invention.

FIG. 4 is a schematic diagram of a motor in the embodiment of the present invention and a diagram showing a relationship between a rotor position and a phase current peak. FIG. 6 is a schematic diagram showing a change in applied voltage at a certain rotor position of the motor according to the embodiment of the present invention.
Here, in the compressor 1 of the present embodiment, for example, an IPM (Interior Permanent Magnet) motor is used as the motor 8. The IPM motor has a dependency on the rotational position of the winding inductance, and the impedance of the winding inductance is expressed by an electrical angular frequency ω × inductance value. Therefore, as shown in FIG. 4, when the inductance value changes depending on the rotor position, the impedance changes, and even when the same voltage is applied, the current flowing through the motor windings is different. As a result, the required power may not be obtained depending on the rotor position.

Therefore, as shown in FIG. 5, at a certain rotor position, the applied phase is shifted by θplus (corresponding to the third phase in the present invention) shown in FIG. At this time, the high-frequency AC voltage generating means 13 feedback-controls θplus so that the power calculated by the power calculating means 18 shown in FIG. 1 is always constant.
Specifically, the high frequency AC voltage generating means 13 adds the θplus from the adder 19 to the phases θ1 and θ2 selected by the phase switching means 14 to obtain the phase θ. Then, for example, by increasing the θplus at a predetermined period, the phase of the applied voltage can be shifted as shown in FIG. Note that θplus is a frequency lower than θ1 and θ2. Then, the PWM signal is obtained by the above-described method, and the switching elements 16 a to 16 f of the inverter 9 are driven to apply a voltage to the motor 8.

FIG. 6 is a diagram illustrating another example of the PWM signal generation method according to the embodiment of the present invention.
As shown in FIG. 6, when control is performed so as to switch between θ1 and θ2 only by the valley of the carrier signal, V0 → V4 → V7 → V7 → V3 → V0 → V0 → V3 → V7 → V7 → V4 → V0. As described above, since the voltage is applied in a two-carrier cycle, an AC voltage having a ½ carrier frequency can be applied to the winding of the motor 8. In the above description, θ1 and θ2 are switched only by the valley of the carrier signal, but may be switched only by the peak.
In the example in FIG. 6 as well, the phase of the applied voltage can be shifted as shown in FIG. 5 by adding θplus that increases in a predetermined cycle to θ1 and θ2 as shown in FIG.

  Further, by operating at a frequency higher than the operating frequency (˜1 kHz) at the time of the compression operation and applying a high frequency voltage to the motor 8, the rotor cannot follow the high frequency voltage, and thus rotational torque and vibration may occur. No. And it becomes possible to heat the motor 8 efficiently by utilizing the iron loss of the motor 8 due to the application of the high frequency voltage and the copper loss generated by the current flowing through the winding. Then, the liquid refrigerant staying in the compressor 1 is heated and vaporized by the heating of the motor 8 and leaks to the outside of the compressor 1. When the stagnation detecting means 12 determines that the refrigerant leakage has been performed for a predetermined amount or for a predetermined time, it determines that the refrigerant has returned to the normal state from the stagnation state, and ends the heating of the motor 8.

In addition, the frequency of the high-frequency AC voltage is equal to or lower than the switching frequency upper limit value of the switching elements 16 a to 16 f provided in the inverter 9. For example, in the inverter 9 in the present embodiment, the upper limit of the carrier frequency is about 20 kHz. Therefore, if the carrier frequency is set to 20 kHz, an AC voltage of 20 kHz can be applied to the motor 8 by switching the phase θ between the peak and valley of the carrier. Further, iron loss occurs due to higher frequency and heating can be performed efficiently, and current flowing to the inverter 9 can be reduced by increasing the winding impedance of the motor 8, and the inverter loss can be reduced, thereby suppressing CO ₂ emission. It is possible and effective for global warming countermeasures.

  Further, if the frequency of the high frequency voltage to be applied is 14 kHz or more, the vibration sound of the iron core of the motor 8 is almost outside the audible range of humans, which is effective in reducing noise. In addition, when the compressor 1 is an IPM (embedded magnet type) motor, the rotor surface where the high-frequency magnetic flux interlinks also becomes a heat generating portion, so that the refrigerant contact surface increases and the compression mechanism 7 is quickly heated. Since it is realized, it is possible to efficiently heat the refrigerant.

  Furthermore, in the case of a heating device having a frequency of 10 kHz and an output of 50 W, there are restrictions by the Radio Law. Therefore, by adjusting the amplitude of the voltage command so as not to exceed 50 W in advance and detecting the flowing current and performing feedback control, the compressor 1 in compliance with the Radio Law can be heated.

  The stator winding direction of the motor 8 starts winding on the phase terminal side of the motor 8 and ends winding on the neutral point side. When voltage is applied to the motor 8, heating is performed by two losses of copper loss and iron loss of the winding, but in the case of a concentrated winding motor with a small stator coil end and low winding resistance, the winding resistance is small and the copper is low. Less heat is generated due to damage. Therefore, in order to increase the amount of heat generated, it is necessary to flow a large amount of current through the windings, and the current flowing through the inverter 9 also increases, resulting in an excessive inverter loss.

  However, since the air conditioner according to the embodiment of the present invention is heated by applying a high frequency voltage, an inductance component due to a high frequency is increased, and a winding impedance is increased. Therefore, the current flowing through the winding is reduced and the copper loss is reduced, but the iron loss due to the application of the high frequency voltage is increased, so that the heating can be effectively performed. Furthermore, since the current flowing through the winding is small, the loss of the inverter 9 is also reduced, and heating with further reduced loss is possible.

  The material of the diode elements in the switching elements 16a to 16f and the converter 17 may be silicon, for example, but may be formed of a wide band gap semiconductor having a larger band gap than silicon. Examples of the wide band gap semiconductor include silicon carbide, a gallium nitride-based material, and diamond.

  Switching elements and diode elements formed by such wide band gap semiconductors have high voltage resistance and high allowable current density, so that switching elements and diode elements can be miniaturized. By using elements and diode elements, the inverter 9 and the converter 17 incorporating these elements can be miniaturized.

  Moreover, since heat resistance is also high, it is possible to reduce the size of the radiating fins of the heat sink and the air cooling of the water-cooled portion, so that the inverter 9 and the converter 17 can be further reduced in size.

  Furthermore, since the power loss is low, the switching elements 16a to 16f and the diode elements can be highly efficient, and further, the inverter 9 and the converter 17 can be highly efficient.

  As a result, the switching elements 16a to 16f can increase the frequency with a lower loss than when silicon or the like is used, and a carrier frequency of 20 kHz or higher can be used. In this case, it is possible to increase the impedance of the motor winding by increasing the frequency so that heating can be performed with higher efficiency. Of course, it is needless to say that a certain efficiency can be achieved from the above characteristics of the device without increasing the frequency.

  It is desirable that both the switching elements 16a to 16f and the diode element in the converter 17 be formed of a wide band gap semiconductor, but either one of the elements may be formed of a wide band gap semiconductor. The effect described in the form can be obtained.

As described above, the air conditioner according to the embodiment of the present invention can be effectively heated because the iron loss due to the application of the high frequency voltage increases.
Further, since the applied voltage is rotated to absorb the fluctuation of the current to the motor winding due to the rotor position, it does not depend on the rotor position of the motor.
Moreover, since the high frequency alternating voltage generation means 13 outputs a frequency component higher than the operating frequency during the compression operation of the motor, mechanical vibration from the compressor during heating is suppressed, and wear and noise of the bearing are suppressed.

  Further, when the compressor 1 is a scroll mechanism, it is difficult to perform high-pressure relief of the compression chamber, and therefore, when liquid refrigerant enters, the compression mechanism may be overstressed and damaged. However, according to the present embodiment, heat is effectively generated due to the iron loss of the motor 8 by applying a high-frequency voltage, so that efficient heating in the compressor 1 is possible. Thereby, since the liquid refrigerant in the compressor 1 evaporates and leaks to the outside, the amount of liquid refrigerant in the compressor 1 is greatly reduced, which is effective for preventing damage to the compressor 1.

  In addition, a highly efficient refrigerant heating method during standby, reduction of bearing vibration and noise in the compressor, and the European EuP Directive (Directive on Eco-Design of Energy-using Products), which are recent strict environmentally conscious design standards, and The possibility of adapting to Australia MEPS (Minimum Energy Performance Standards) can be increased.

  DESCRIPTION OF SYMBOLS 1 Compressor, 2 Four way valve, 3 Outdoor heat exchanger, 4 Expansion valve, 5 Indoor heat exchanger, 6 Refrigerant piping, 7 Compression mechanism, 8 Motor, 9 Inverter, 10 Bus-line voltage detection means, 11 Inverter control means, 12 Sleep detection means, 13 High frequency AC voltage generation means, 14 Phase switching means, 15 PWM signal generation means, 16a to 16f Switching element, 17 Converter, 18 Power calculation means, 19 Adder, 20 Current detection means, 21 Voltage detection means, 22 general commercial power supplies, 23 power calculation means, 30 refrigeration cycle.

Claims (14)

A compressor for compressing the refrigerant;
A motor for driving the compressor;
An inverter for applying a three-phase voltage to the motor;
Inverter control means for controlling the inverter;
A bus voltage detecting means for detecting a bus voltage which is a power source of the inverter;
With
The inverter control means includes
High-frequency AC voltage generating means for outputting a high-frequency AC voltage command having a higher frequency than that during the compression operation of the motor based on information on a predetermined amplitude and alternately inputted first phase and second phase, and the high-frequency AC voltage PWM signal generating means for generating a PWM signal based on the output of the generating means and a carrier signal determined according to the bus voltage and outputting the PWM signal to the inverter;
The inverter applies an AC voltage based on the PWM signal so as not to generate a rotational torque in the motor and heats the refrigerant in the compressor by iron loss and copper loss. . The inverter control means includes
Phase switching means for alternately selecting the first phase and a second phase that is approximately 180 degrees different from the first phase at a predetermined timing and inputting the phase to the high-frequency AC voltage generating means,
The said PWM signal generation means produces | generates the said PWM signal by comparing the said high frequency alternating voltage command output from the said high frequency alternating voltage generation means with the said carrier signal. Air conditioner.   3. The air conditioner according to claim 2, wherein the phase switching unit switches the first phase and the second phase at timings of peaks and troughs of the carrier signal.   The air conditioner according to claim 2, wherein the phase switching means switches the first phase and the second phase only to the peak timing of the carrier signal or only to the valley timing. . Power calculating means for calculating the power supplied to the inverter or the motor,
The high-frequency AC voltage generating means is configured to obtain information related to a third phase that increases at a predetermined period to information selected from among the information related to the first phase or the second phase based on the result of the power calculating means. The air conditioner according to any one of claims 1 to 4, wherein the phase of the three-phase voltage applied to the motor is changed by adding.   The air conditioner according to any one of claims 1 to 5, wherein a frequency of the high-frequency AC voltage command is equal to or lower than a switching frequency upper limit value of a switching element provided in the inverter.   The air conditioner according to any one of claims 1 to 6, wherein the rotor of the motor has an IPM structure.   The air conditioner according to any one of claims 1 to 7, wherein the stator winding of the motor is a concentrated winding.   The air conditioning according to any one of claims 1 to 8, wherein the stator winding of the motor starts to be wound from a phase terminal side of the motor and has been wound at a neutral point side. Machine. A stagnation detecting means for detecting a stagnation state of the refrigerant of the compressor;
The stagnation detection means determines that the refrigerant of the compressor is in a stagnation state when a temperature of the refrigeration cycle is equal to or lower than a predetermined value and a predetermined time has elapsed.
The air conditioner according to any one of claims 1 to 9, wherein the inverter heats the refrigerant in the compressor when it is determined that the refrigerant in the compressor is in a stagnation state. Machine.   The structure of the said compressor is a scroll type, The air conditioner as described in any one of Claims 1-10 characterized by the above-mentioned.   The air conditioner according to any one of claims 1 to 11, wherein when the frequency of the high-frequency AC voltage command exceeds 10 kHz, the input power of the motor is controlled to 50 W or less.   The air conditioner according to any one of claims 1 to 12, wherein a wide band gap semiconductor is used for a switching device used in the inverter. The air conditioner according to claim 13, wherein the wide band gap semiconductor is silicon carbide, a gallium nitride-based material, or diamond.

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