Patent Description:
There exists a conventional air-conditioning apparatus equipped with an inverter circuit that switches on and off at certain intervals a direct-current voltage output from a rectifying circuit and converts the direct-current voltage into an alternating-current voltage to variably control a speed of a motor in a compressor installed into an air-conditioning apparatus or other apparatuses. Because achieving high efficiency is considered important for a motor in a compressor that is incorporated into an air-conditioning apparatus, a motor having a rare earth permanent magnet disposed inside a rotor (hereinafter referred to as a permanent magnet synchronous motor) is commonly used as a motor in a compressor.

It has been proposed that a magnetic-pole position of a permanent magnet in a rotor is detected with a position sensor, for example, and a rotation speed of a permanent magnet synchronous motor is controlled on the basis of the magnetic-pole phase at which a current is detected. It has also been proposed that, for example, a rotation speed of a permanent magnet synchronous motor is controlled without using a magnetic-flux sensor (hereinafter referred to as position-sensorless control), (refer to Patent Literature <NUM>, for example). The position-sensorless control disclosed in Patent Literature <NUM> is used, for example, in a situation in which the interior of a compressor in an air-conditioning apparatus is under a high-temperature and high-pressure condition that is unsuitable for installing a magnetic-flux sensor into the compressor.

Patent Literature <NUM> discloses a motor protection system in conjunction with a controller monitoring the performance of redundant motor-driven prime movers having a lead prime mover and a lag prime mover. The controller uses motor protection measurements to determine if the lead motor-driven prime mover is in distress and activates operation of the lag motor-driven prime mover when lead prime mover is in distress.

In Patent Literature <NUM> a method for checking out-of-step of a synchronous motor is described in which electric degrees of the synchronous motor re detected and compared to each other to obtain a comparing result. It is determined that the synchronous motor is out of step when the comparing result satisfies a preset requirement.

In a conventional air-conditioning apparatus, however, when a compressor suctions liquefied refrigerant, load torque of a motor changes rapidly and exceeds a limit that the motor can provide. This leads to a phenomenon of losing synchronization (hereinafter referred to as "out of synchronization"), and the apparatus comes to an abnormal stop.

A motor that is controlled by the position-sensorless control disclosed in Patent Literature <NUM> is also likely to go out of synchronization because a magnetic-pole position of a rotor is not directly detected. Liquefied refrigerant is usually stored in an accumulator, and a compressor does not suction the liquefied refrigerant. However, in the event that an amount of the liquefied refrigerant delivered to the accumulator exceeds an allowable limit for the liquefied refrigerant to be stored in the accumulator during operation such as defrosting operation of a heat exchanger of an outdoor unit, the compressor may suction the liquefied refrigerant. As a result, the load torque may change rapidly, and the motor may go out of synchronization.

In view of the foregoing, the present invention provides a motor control device, a compressor, and an air-conditioning apparatus that enable operation to continue by avoiding an out-of-synchronization state of a motor in the case of increased load torque of the motor.

The problem is solved by the features of the independent claims.

A motor control device of an embodiment of the present invention is a motor control device controlling a motor, and the motor control device includes a load-torque detecting unit configured to detect load torque of the motor and a current correcting unit configured to control a current flowing through the motor in accordance with information detected by the load-torque detecting unit. The current correcting unit increases the current flowing through the motor in accordance with an increase in the load torque detected by the load-torque detecting unit.

A compressor of an embodiment of the present invention includes the motor controlled by the motor control device of the embodiment of the present invention.

An air-conditioning apparatus of an embodiment of the present invention includes the compressor of the embodiment of the present invention, a current detecting unit configured to detect a current of the motor, and an overcurrent protecting unit configured to stop the motor control device when the current detected by the current detecting unit is larger than or equal to a reference current.

According to the embodiments of the present invention, the current correcting unit enables the motor to continuously operate by avoiding going out of synchronization in the case of increased load torque of the motor because the current correcting unit increases the current flowing through the motor in accordance with an increase in the load torque detected by the load-torque detecting unit.

The same numerals or symbols refer to the same items or equivalents thereof in the following drawings including <FIG>, and the same numerals or symbols are used in the entire description of the embodiments below.

<FIG> is a schematic diagram illustrating a circuit configuration and a control block diagram of an air-conditioning apparatus <NUM> and a motor control device <NUM> of an Example useful to explain the present invention. <FIG> is a vector diagram of a configuration of magnetic-flux vector control by the motor control device <NUM> of the Example useful to explain the present invention.

Referring to <FIG>, the air-conditioning apparatus <NUM> includes a smoothing capacitor <NUM>, an inverter circuit <NUM>, a current detecting unit <NUM>, a gate driving circuit <NUM>, an overcurrent protecting unit <NUM>, a compressor <NUM> having a motor <NUM>, a condenser <NUM>, a pressure reducing unit <NUM>, and an evaporator <NUM>. The air-conditioning apparatus <NUM> obtains a direct-current voltage that is input to the inverter circuit <NUM> by performing AC-DC conversion on a voltage from an alternating-current power source. The alternating-current power is converted into direct-current power by a circuit such as a diode bridge circuit.

The smoothing capacitor <NUM> smooths ripples in the voltage after rectification. The inverter circuit <NUM> converts a direct-current voltage smoothed by the smoothing capacitor <NUM> into an alternating-current voltage and drives the motor <NUM>. The inverter circuit <NUM> includes six switching devices <NUM> and six return-current diodes, and a reverse current (return current) flows through each of the return-current diodes when a corresponding one of the switching devices <NUM> is turned off. Each of the switching devices <NUM> has a semiconductor device such as an IGBT (Insulated Gate Bipolar Transistor). The switching devices <NUM> of the inverter circuit <NUM> are each composed of a device made of silicon carbide, gallium nitride or related materials, or diamond, for example. An output line of the inverter <NUM> is connected to the motor <NUM> and the current detecting unit <NUM> is disposed on the output line of the inverter circuit <NUM>.

The current detecting unit <NUM>, for example, detects all phases of three-phase currents flowing through the motor <NUM> and outputs a voltage or current signal in accordance with a current flowing through the output line of the inverter circuit <NUM>. The current detecting unit <NUM> includes, for example, a current sensor that detects the current flowing through the motor <NUM>. An instantaneous current value of the motor <NUM> detected by the current detecting unit <NUM> is digitized and read into a microcomputer, for example.

The current detecting unit <NUM> may detect two-phase currents flowing through the motor <NUM> and derive a remaining one-phase current by summing the instantaneous values of the detected two-phase currents followed by multiplying the sum by -<NUM>. Alternatively, the current detecting unit <NUM> may generally be any of those that detect a magnetic flux in accordance with a current flow and convert the magnetic flux into a voltage, as long as a device such as a Hall element is incorporated therein.

The overcurrent protecting unit <NUM> has a function of protecting the inverter circuit <NUM> by causing the air-conditioning apparatus <NUM> to temporarily stop operating when the current detected by the current detecting unit <NUM> exceeds a predetermined reference current. For the motor <NUM> composed of a permanent magnet synchronous motor, when a current larger than or equal to a certain level flows through a stator winding, a phenomenon called demagnetization, which weakens a magnetic flux of a permanent magnet in a rotor, occurs. Further, for the motor <NUM> composed of a permanent magnet synchronous motor, when a current larger than or equal to a certain level flows through a stator winding, a loss increases in the IGBT in the inverter circuit <NUM>.

Thus, the reference current is determined, for example, in accordance with a demagnetization level of the motor <NUM> from the viewpoint of reducing or eliminating the aforementioned phenomenon called demagnetization. The reference current is also determined, for example, from the viewpoint of preventing the loss in the IGBT in the inverter circuit <NUM> from increasing. The overcurrent protecting unit <NUM> causes the air-conditioning apparatus <NUM> to temporarily stop operating, for example, when one of the aforementioned reference currents, whichever is smaller, is exceeded.

The overcurrent protecting unit <NUM> is constructed using hardware components such as an electronic circuit or configured to perform software protection in which a current detection signal is input to a microcomputer, for example, which performs a digital conversion process. If the overcurrent protecting unit <NUM> is configured to perform the software protection, the overcurrent protecting unit <NUM> allows greater design flexibility because the threshold can be changed freely and a variety of calculation processes can be performed.

The compressor <NUM> is a variable capacity compressor that compresses suctioned refrigerant and converts the refrigerant into high-temperature and high-pressure refrigerant, which is discharged from the compressor <NUM>. The compressor <NUM> includes the motor <NUM>. The motor <NUM> is constructed using a motor having a structure that incorporates a permanent magnet into a rotor (permanent magnet synchronous motor), which has a high energy-saving capacity, for example. The condenser <NUM> is a heat exchanger that condenses and liquefies the refrigerant discharged from the compressor <NUM>.

The refrigerant condensed and liquefied in the condenser <NUM> expands under a reduced pressure in the pressure reducing unit <NUM>. The evaporator <NUM> evaporates and gasifies the refrigerant flowing from the pressure reducing unit <NUM>. The compressor <NUM>, the condenser <NUM>, the pressure reducing unit <NUM>, and the evaporator <NUM> are connected in succession by using refrigerant pipes and constitute a refrigeration cycle apparatus.

Referring to <FIG>, the motor control device <NUM> includes a coordinate conversion unit <NUM>, a rotation speed command generating unit <NUM>, an integrating unit <NUM>, a γ-axis current command table <NUM>, a frequency compensating unit <NUM>, a voltage command calculating unit <NUM>, a load-torque detecting unit <NUM>, a current correcting unit <NUM>, and an inverse coordinate conversion unit <NUM>.

The motor control device <NUM> controls the gate driving circuit <NUM> so that the motor <NUM> is controlled to obtain a required rotation speed in response to a current detected by the current detecting unit <NUM>. When a voltage is applied between the gate and emitter terminals of the IGBT in response to a signal output from the gate driving circuit <NUM>, continuity between the collector and the emitter of the IGBT is established and a voltage is applied to the motor <NUM>.

In the case that the motor <NUM> is constructed using a permanent magnet synchronous motor, for example, the motor control device <NUM> detects a magnetic-pole phase of the permanent magnet by using a device such as a magnetic-flux sensor and controls the current on the basis of the magnetic-pole phase. However, installing a magnetic-flux sensor into a place that is under a high-temperature and high-pressure condition, such as the interior of the motor <NUM>, is not easy, and thus the air-conditioning apparatus <NUM> usually performs position-sensorless control without using a position sensor. In the Example , a magnetic-flux vector control method, in which an output voltage is controlled so that a primary magnetic flux generated in the motor is maintained at a constant value on a fixed axis, will be described in the following as an example of the position-sensorless control of the permanent magnet synchronous motor.

The coordinate conversion unit <NUM> converts three-phase alternating currents flowing through the motor <NUM> detected by the current detecting unit <NUM> into a direct current on the basis of a phase θ that synchronizes with a rotation speed of the motor. The coordinate conversion unit <NUM> outputs, on the basis of the phase θ, an excitation component current Iγ, which generates a magnetic flux that emerges in the motor <NUM>, and a torque component current Iδ, which is orthogonal to the excitation component current Iγ and contributes to a torque component of the motor <NUM>. As illustrated in <FIG>, the direction of the magnetic flux of the permanent magnet of the motor <NUM> is designated as the d-axis, and the axis orthogonal to the d-axis is designated as the q-axis. The γ- and δ-axes used for the present magnetic-flux vector control operate by generating control axes that differ from the d- and q-axes by an angle of Δθ.

The rotation speed command generating unit <NUM> performs a calculation of a command value for the rotation speed of the motor <NUM> so that the air-conditioning apparatus <NUM> obtains a required refrigeration capacity. The rotation speed command generating unit <NUM> also performs a calculation so that the rotation speed of the motor <NUM> increases in a situation such as requiring a larger refrigeration capacity, for example, cooling operation under a high-temperature outdoor-air condition. The rotation speed command generating unit <NUM> includes a microcomputer, for example. The rotation speed command generating unit <NUM> may control not only the rotation speed of the motor <NUM> but also a rotation speed of a motor of a fan and various actuators including an opening degree of an expansion valve in the pressure reducing unit <NUM>.

Hereinafter, a method to obtain the phase θ rotating with the γ- and δ-axes, which is used for the coordinate conversion, will be described.

As indicated by Expression (<NUM>), it is known that the rotation speed of the motor changes in proportion to a frequency f of a sinusoidal voltage applied to the motor. <NUM>] <MAT>.

Here, N represents the number of rotations of the motor per minute, expressed in [min-<NUM>]. f represents a frequency of the voltage applied to the motor, that is, the frequency [Hz] of the three-phase alternating-current voltage generated by the inverter circuit <NUM> in the case of the Example. p represents the number of magnetic poles of the motor <NUM> (hereinafter referred to as the number of poles).

As indicated by Expression (<NUM>), the rotation speed of the motor is proportional to the frequency of the inverter output voltage and inversely proportional to the number of poles. This indicates that the rotation speed of the motor can be controlled by controlling the frequency of the inverter output voltage. The motor control device <NUM> controls the inverter circuit <NUM> so as to generate a voltage having a frequency proportional to the command value for the rotation speed generated by the rotation speed command generating unit <NUM>.

Here, one characteristic of the magnetic-flux vector control is that the phase θ, which synchronizes with the rotation speed of the motor <NUM>, is obtained by integrating with respect to time an electric angular velocity that is derived from the aforementioned command value of the rotation speed command generating unit <NUM>. Then, in the Example, the final phase θ can be obtained by using the frequency compensating unit <NUM> described below so that the motor <NUM> rotates with further stability.

Next, detailed operation of the frequency compensating unit <NUM> will be described. The frequency compensating unit <NUM> has a role of compensating the angular velocity ω so that the motor <NUM> can follow the phase with stability with respect to the command value for the rotation speed described above even when load torque changes.

For example, in the case that a discharge pressure of the compressor <NUM> increases resulting in an increase in the load torque of the motor <NUM>, while the aforementioned torque component current Iδ also increases similarly, the instantaneous magnetic-pole phase of the motor <NUM> is actually delayed. Then, the frequency compensating unit <NUM> performs negative-feedback control using a value proportional to the torque component current Iδ to compensate the frequency so that the phase of the γ- and δ- axes, which are the control axes, is delayed to match the actual magnetic-pole position. In this way, the motor <NUM> can be operated with stable rotation without losing track of the magnetic-pole position and going out of synchronization.

Furthermore, for example, in the case that the discharge pressure of the compressor <NUM> decreases resulting in a decrease in the load torque of the motor <NUM>, the phase of the magnetic-pole position of the motor <NUM> advances. Then, because the amount of frequency compensation also decreases, the phase of the primary magnetic flux Φ of the motor <NUM>, which is controlled in accordance with the γ- and δ-axes, also advances, enabling the motor <NUM> to rotate with stability without losing track of the magnetic-pole position. Expression (<NUM>) is the equation used for the calculation performed in the frequency compensating unit <NUM>. <NUM>] <MAT>.

Here, the angular velocity ω represents the final angular velocity that has been compensated by the frequency compensating unit <NUM>. f is an inverter output frequency determined in accordance with the command for the compressor rotation speed. K is a proportional gain for the amount of frequency compensation with respect to the torque component current Iδ.

Although the angular velocity ω can follow a torque variation with an enhanced sensitivity as the frequency compensation gain K increases, too large a value for the frequency compensation gain K causes unstable control. Thus the most suitable value is determined in advance. Values of the frequency compensation gain K may be maintained in a table stored in a device such as a microcomputer so that the most suitable values are obtained for various operation patterns. In addition, although a value obtained using the coordinate conversion is used here for the torque component current lδ, a filtration process may be performed, so that only a component having a certain time constant is effective.

In the voltage command calculating unit <NUM>, a new term is added to the motor voltage equation for the feedback of an error Φerr in the magnetic flux that is a difference between a magnetic-flux command value Φ* and a calculated primary magnetic flux Φ so that a total magnetic flux generated in the motor <NUM> is equal to a predetermined reference value on the γ-axis. Then, voltage command values Vγ* and Vδ* that are to be generated on the γ- and δ- axes are obtained. The calculation is performed using the magnetic-flux command value Φ* for the primary magnetic flux generated in the motor <NUM>, Iγ and Iδ obtained by the aforementioned operation, resistance and inductance components and an induced voltage constant of the motor <NUM>, and the angular velocity ω. Here, the resistance and inductance components, the induced voltage constant, and other parameters of the motor <NUM> are intrinsic values that are measured in advance, and the measured values are maintained in a microcomputer, for example.

In the Example, the magnetic-flux vector control is performed so as to maintain the magnetic flux at a certain constant value on the γ-axis. The magnetic-flux command values Φ* that provide the most efficient operating condition of the motor <NUM> are measured in advance and maintained in a table, which enables efficient driving of the motor <NUM>.

For example, the torque component current Iδ is adopted as an input for tabulation, and the most suitable magnetic-flux command value Φ* for each torque component current Iδ is determined and maintained. The rotation speed of the motor <NUM> may be adopted as the input for tabulation, and the most suitable magnetic-flux command value Φ* for the motor <NUM> is determined and maintained. To further simplify the calculation, the magnetic-flux vector control may be configured by using Iγ as a command value to approximate the calculation based on the magnetic-flux command value Φ*.

In the Example, a configuration in which the most suitable values of the command values for ly are maintained in advance in the γ-axis current command table <NUM> will be described as an example (detailed operation of the current correcting unit <NUM>, which corrects the γ-axis current command value Iγ*, will be described below).

The inverse coordinate conversion unit <NUM> converts a direct-current value on the two axes into three-phase alternating-current values in accordance with the voltage command values on the γ- and δ-axes obtained by the voltage command calculating unit <NUM> and obtains voltage command values Vu*, Vv*, and Vw* of three-phase alternating current. The phase θ used in the inverse coordinate conversion unit <NUM> is the same phase θ as used in the coordinate conversion unit <NUM>. Because the voltage command values Vu*, Vv*, and Vw* are three-phase sinusoidal voltage signals, these values become PWM (Pulse Width Modulation) signals to switch on and off the IGBT devices of the inverter circuit <NUM>. The gate driving circuit <NUM> amplifies PWM signals generated in accordance with Vu*, Vv*, and Vw*, obtains signals of approximately ±<NUM> V, and applies each of the voltages between the gate and the emitter of a corresponding one of the IGBT devices to drive the gate of the corresponding IGBT device of the inverter circuit <NUM>.

In the Example, the primary magnetic flux of the motor <NUM> is controlled to be maintained at a predetermined constant value and on the γ-axis using the aforementioned configuration, so that the compressor <NUM> can be driven at a rotation speed such as to obtain a required refrigeration capacity. In this way, the rotation speed of the motor <NUM> can be controlled without using a magnetic-pole position sensor for the permanent magnet synchronous motor.

Next, operation of the load-torque detecting unit <NUM> will be described. As described above, with an increase in the load torque, the torque component current Iδ increases. This indicates that a state of the load torque can be detected by Iδ. In the case that Iδ exceeds a predetermined value, the motor <NUM> is controlled to avoid going out of synchronization by increasing the current from the command value determined by the γ-axis current command table <NUM> described above, that is, by increasing Iγ.

The threshold for Iδ is determined so that the current correcting unit <NUM> remains inactive in a normal operation range of the compressor <NUM> and is activated when load torque increases outside the operation range of the compressor <NUM>. The threshold for Iδ thus determined does not cause the command values in the γ-axis current command table <NUM> to be corrected while the compressor <NUM> remains in the normal operation range. Thus, the air-conditioning apparatus <NUM> maintains high-efficiency operation while the compressor <NUM> remains in the normal operation range, and avoids an out-of-synchronization state only in the case of operation under a high load-torque condition such as the case in which the refrigerant flows in the reverse direction. The air-conditioning apparatus <NUM> continues to operate in this way.

Overload operation in which the load torque of the motor <NUM> reaches a maximum, for example, is included in the normal operation range of the compressor <NUM>. Conditions outside the operation range of the compressor <NUM> include the case in which the refrigerant flows in the reverse direction and is suctioned by the compressor <NUM>, for example.

The threshold for Iδ may be variable and configured to be determined by the amount of variation in Iδ. In this way, early detection of a tendency toward an increase in the load torque can be performed in advance with noise or the like detected in error, and the compressor <NUM> can be operated in the normal operation range.

Hereinafter, a method of detecting an increase in the load torque on the basis of the amount of variation in Iδ will be described. The present control is performed by a device such as a microcomputer, for example, which determines the amount of variation in Iδ by calculating Iδ in every control cycle, storing in a memory the detected value of Iδ that is currently detected and the preceding value in every sampling period, and calculating a difference between the two as indicated by Expression (<NUM>). <NUM>] <MAT>.

<FIG> is a conceptual diagram illustrating an example of determination of a threshold for the load-torque detecting unit <NUM> in the motor control device <NUM> of the Example useful to explain the present invention. The horizontal axis of <FIG> represents time, and the vertical axis of <FIG> represents the torque component current Iδ.

During normal operation of the air-conditioning apparatus <NUM>, when the following two conditions (<NUM>) and (<NUM>) hold true simultaneously or either of the conditions is satisfied, the current correcting unit <NUM> is activated determining that the load torque outside the operation range of the compressor <NUM> is generated. <NUM>] <MAT>
[Math. <NUM>] <MAT>.

Threshold A is set at a value equal to or larger than a maximum value of Iδ in the normal operation range of the compressor <NUM>. Threshold B is set at a value equal to or larger than a maximum amount of variation in the torque component current Iδ generated by torque ripples of the motor <NUM> in the normal operation range. The values of threshold A and threshold B are predetermined, for example, by performing test operation in advance using an actual apparatus and measuring each value. The amount of variation in the torque component current Iδ is obtained by calculating a difference between detected values per sampling period, which are detected as described above by the microcomputer, for example. Threshold B for the amount of variation is set to a positive value because it is commonly known that the torque component current Iδ increases with an increase in the load torque of the motor <NUM>.

Next, the current correcting unit <NUM> will be described. The current correcting unit <NUM> increases the current flowing through the motor <NUM> with an increase in the load torque detected by the load-torque detecting unit <NUM>. The current correcting unit <NUM> operates so as to further increase the current command value from the current command value based on the γ-axis current command table <NUM> in the situation in which the load torque detected by the load-torque detecting unit <NUM> is outside the normal operation range of the compressor <NUM>. An increase in the current command value is achieved, for example, by adding a predetermined constant current command value in every control cycle. When the load torque of the motor <NUM> stops increasing and Iδ ceases to satisfy at least one of the conditions (<NUM>) and (<NUM>), for example, the current correcting unit <NUM> controls the current command value that has been increased to decrease to the previous Iγ current command value obtained from the γ-axis current command table <NUM>.

Even if the load torque increases rapidly because of an occurrence of reverse refrigerant flow in which the liquefied refrigerant is suctioned by the compressor <NUM> in a low outdoor-air condition, for example, the motor control device <NUM> of Embodiment <NUM> of the present invention can increase the γ-axis current command value, thereby increasing the current flowing through the motor <NUM>, which heats the motor <NUM>, and the liquefied refrigerant in the compressor <NUM> can be vaporized.

In the case of a locking failure occurrence in which the rotation shaft is locked because of malfunction of the motor <NUM> for some reason, an excessive current may flow through the motor <NUM>, resulting in a high temperature of the stator windings of the motor <NUM>. Particularly, if the motor <NUM> is subjected to the locking failure in a low rotation speed region of the compressor <NUM>, it is possible that the operation continues in a current range in which an inverter output voltage applied to the motor <NUM> is too small to activate the overcurrent protecting unit <NUM>. As a result, the temperature of the stator windings may be higher than or equal to an allowable limit because of prolonged continuous operation.

According to the Example, however, the motor control device <NUM> that controls the motor <NUM> includes the load-torque detecting unit <NUM> that detects the load torque of the motor <NUM> and the current correcting unit <NUM> that controls the current flowing through the motor <NUM> in accordance with the information detected by the load-torque detecting unit <NUM>, and the current correcting unit <NUM> increases the current flowing through the motor <NUM> in accordance with the increase in the load torque detected by the load-torque detecting unit <NUM>. Thus, in the case of the motor-locking failure in the low rotation speed region of the compressor <NUM>, the load-torque detecting unit <NUM> detects the locking state at an early stage, and the current correcting unit <NUM> is activated and increases the current flowing through the motor <NUM>, increasing the γ-axis current and activating the overcurrent protecting unit <NUM>. Thus, the air-conditioning apparatus <NUM> can be stopped safely before the temperature increase of the stator windings exceeds the allowable limit for the windings. Consequently, the motor <NUM> is capable of continuing operation by avoiding going out of synchronization in the case of the increase in the load torque of the motor <NUM>.

In the Example, although the magnetic-flux vector control has been described as an example of the position-sensorless control of the permanent magnet synchronous motor, other position-sensorless control may be adopted, and the command value for each current may be corrected when the load-torque detecting unit <NUM> detects the load torque outside the normal operation range of the compressor <NUM>. The motor <NUM> is also capable of continuing operation by avoiding going out of synchronization in the case of the increase in the load torque of the motor <NUM>.

In addition, in the case that the load torque increases rapidly due to the occurrence of the reverse refrigerant flow in which the liquefied refrigerant is suctioned by the compressor <NUM> in a low outdoor-air condition, for example, the increase in the γ-axis current command value causes an excessive current to flow through the motor <NUM>, and the motor <NUM> is heated. Thus, the reverse refrigerant flow can be suppressed, and the air-conditioning apparatus <NUM> can be stopped in the case of locking failure of the motor <NUM>.

In Embodiment , which differs from the Example, a load-torque detecting unit <NUM> employs a root-mean-square value calculating unit 26a, an unbalancing calculating unit 26b, and a power factor calculating unit 26c in place of Iδ obtained using the coordinate conversion. For an air-conditioning apparatus <NUM> of the Embodiment , configurations and operation that differ from those in the Example will be described, and the same components as those in the air-conditioning apparatus <NUM> of the Example will be denoted by the same numerals or symbols.

<FIG> is a schematic diagram illustrating a circuit configuration and a control block diagram of an air-conditioning apparatus <NUM> and a motor control device <NUM> of the Embodiment of the present invention. <FIG> is a vector diagram of a configuration of magnetic-flux vector control by the motor control device <NUM> of the Embodiment of the present invention. As illustrated in <FIG>, the motor control device <NUM> includes the root-mean-square value calculating unit 26a, the unbalancing calculating unit 26b, and the power factor calculating unit 26c.

The root-mean-square value calculating unit 26a calculates a root-mean-square (RMS) value of each phase current of the motor <NUM>. As is well known, the formula for calculating the root-mean-square value is given by averaging the square of an alternating current over one cycle followed by calculating the square root of the averaged value. When the average is calculated over one cycle of the alternating current, values sampled at every control cycle of the microcomputer can be used for approximate calculation. Alternatively, it is known that a root-mean-square value can be calculated by dividing an instantaneous peak value by √<NUM> for a sinusoidal-wave alternating current, and the root-mean-square value of current may be derived by using this formula from an instantaneous peak value obtained in one cycle, on which peak-hold operation is performed.

The unbalancing calculating unit 26b calculates an unbalanced value by calculating a difference in the root-mean-square value between individual phase currents that flow through the motor <NUM>. The root-mean-square values of phase currents are calculated by the root-mean-square value calculating unit 26a. An example of the calculation method is described as follows. <MAT> <MAT> <MAT>.

Because the root-mean-square values of three-phase currents are balanced during normal operation of the compressor <NUM> as illustrated in <FIG>, ΔU - V, ΔV - W, and ΔW - U are substantially <NUM> A. In the case that the motor <NUM> is locked, for example, the balance of inductance between the phases becomes disrupted, and the three-phase alternating currents of the motor <NUM> become unbalanced (<FIG>). In addition, the unbalanced values of the root-mean-square values of phase currents further increase during open-phase operation in which stator windings or wirings connecting the motor <NUM> and the inverter circuit <NUM>, for example, are disconnected (<FIG>).

The power factor calculating unit 26c calculates a power factor of the motor <NUM>. An increase in the load torque of the motor <NUM> and a state of the motor <NUM> when locked are detected based on an instantaneous current value of the motor <NUM>, unbalanced values of the root-mean-square values of phase currents, and a phase difference between the voltage and the current, that is, the power factor of the motor <NUM>.

When any one of the differences in the root-mean-square value ΔU - V, ΔV - W, and ΔW - U between the individual phase currents, which are calculated by the unbalancing calculating unit 26b, is larger than a predetermined first reference value, for example, the current correcting unit <NUM> determines that the motor <NUM> is malfunctioning with the load torque of the motor <NUM> increased and avoids an out-of-synchronization state of the motor <NUM> by controlling the motor <NUM> so as to increase the γ-axis current command value. Because the root-mean-square values of phase currents do not usually balance out among three phases owing to noise or a degree of current distortion, ΔU - V, ΔV - W, and ΔW - U sometimes deviate from zero even under the normal condition of the motor <NUM>. Thus, the first reference value is set to a value larger than the differences in the root-mean-square value between the individual phase currents in the normal operation range of the motor <NUM>, which are measured in advance, for example, in test operation using the actual apparatus. In addition, measuring at the same time unbalanced values of the root-mean-square values of phase currents in the case that the motor <NUM> is actually locked enables determination of the threshold for more certain detection of malfunctioning.

When the power factor calculated by the power factor calculating unit 26c is smaller than or equal to a second reference value, for example, the current correcting unit <NUM> determines that the motor <NUM> is malfunctioning with the load torque of the motor <NUM> increased and avoids an out-of-synchronization state of the motor <NUM> by controlling the motor <NUM> so as to increase the γ-axis current command value.

Here, the second reference value is smaller than or equal to a minimum power factor in the normal operation range of the motor <NUM>, which is measured in advance, for example, in test operation using the actual apparatus. It is known that the power factor degrades when the motor <NUM> is subjected to a locking failure, for example. Thus, the configuration such as in the Embodiment enables more certain detection of a rapid variation in the load torque of the compressor <NUM> or a failure state of the motor <NUM>.

Next, according to the Embodiment, a derivation of the power factor from Iγ, Iδ, Vy, and Vδ calculated by the motor control device <NUM> will be described. The power factor can be derived from a phase difference between the voltage applied to the motor <NUM> and the current.

Because the voltage applied to the motor <NUM> is a vector sum of Vγ and Vδ, a device such as a microcomputer can be used to calculate a phase difference θv of the vector sum of the voltages with respect to the γ- and δ-axes. In addition, in the magnetic-flux vector control of the Embodiment, because the γ-axis and the δ-axis are orthogonal to each other, the vector sum of Vγ and Vδ can be determined in accordance with the Pythagorean theorem, and the phase difference of the voltage vector can be obtained by Expression (<NUM>) (<FIG>). <NUM>] <MAT>.

The current flowing through the motor <NUM> can also be derived from a vector sum of the currents Iγ and Iδ. Thus, the phase difference of the current vector can be obtained by Expression (<NUM>) in a manner similar to the above description of the phase difference of the voltage vector. <NUM>] <MAT>.

Given θv-i as the phase difference between θv and θi, which are obtained by Expressions (<NUM>) and (<NUM>) above, the power factor is determined as COS(θv-i).

The current flowing through the motor <NUM> may be controlled using the unbalancing calculating unit 26b that calculates unbalancing between the root-mean-square values of phase currents of the compressor <NUM> and the power factor calculating unit 26c that calculates the power factor of the motor <NUM>. Specifically, for example, when the unbalanced value of the root-mean-square values of phase currents, which is calculated by the unbalancing calculating unit 26b, is larger than the predetermined first reference value, or when the power factor calculated by the power factor calculating unit 26c is smaller than or equal to the second reference value, the current correcting unit <NUM> may determine that the motor <NUM> is malfunctioning and avoid an out-of-synchronization state of the motor <NUM> by controlling the motor <NUM> so as to increase the γ-axis current command value.

When the condition for activating the current correcting unit <NUM> ceases to be satisfied, for example, the motor control device <NUM> determines that the motor <NUM> has returned to normal rotation. In the case of detecting with more certainty that the motor <NUM> has returned to normal rotation, the motor control device <NUM> determines that the motor <NUM> has returned to normal rotation, for example, when the value calculated by the root-mean-square value calculating unit 26a becomes smaller than or equal to a predetermined value. Then, when the motor <NUM> returns to normal rotation, the current correcting unit <NUM> decreases the increased γ-axis current command value to the normal current command value.

As described above, according to the Embodiment, the load-torque detecting unit <NUM> further includes the root-mean-square value calculating unit 26a that calculates the root-mean-square value of current of the motor <NUM> and the unbalancing calculating unit 26b that calculates the unbalanced value of the root-mean-square values of three-phase currents calculated by the root-mean-square value calculating unit 26a. Then, the current correcting unit <NUM> increases the current flowing through the motor <NUM>, determining that the load torque has increased when the unbalanced value calculated by the unbalancing calculating unit 26b is larger than the first reference value. Thus, the motor <NUM> can avoid going out of synchronization in the case of a rapid change in the load torque of the motor <NUM>, and even when the motor <NUM> is malfunctioning for some reason, increasing the γ-axis current enables early activation of the overcurrent protecting unit <NUM> and a safe halt of the air-conditioning apparatus <NUM>. In this way, reliability of the apparatus can be ensured.

According to the Embodiment, the load-torque detecting unit <NUM> further includes the power factor calculating unit 26c that calculates the power factor of the motor <NUM>, and the current correcting unit <NUM> increases the current flowing through the motor <NUM>, determining that the load torque has increased when the power factor of the motor <NUM> calculated by the power factor calculating unit 26c is smaller than or equal to the second reference value. Thus, the motor <NUM> can avoid going out of synchronization in the case of a rapid change in the load torque of the motor <NUM>, and even when the motor <NUM> is malfunctioning for some reason, increasing the γ-axis current enables early activation of the overcurrent protecting unit <NUM> and a safe halt of the air-conditioning apparatus <NUM>. In this way, reliability of the apparatus can be ensured.

According to the Embodiment, the load-torque detecting unit <NUM> further includes the root-mean-square value calculating unit 26a that calculates the root-mean-square value of current of the motor <NUM>, the unbalancing calculating unit 26b that calculates the unbalanced value of the root-mean-square values of three-phase currents calculated by the root-mean-square value calculating unit 26a, and the power factor calculating unit 26c that calculates the power factor of the motor <NUM>. Then, the current correcting unit <NUM> increases the current flowing through the motor <NUM>, determining that the load torque has increased when the unbalanced value calculated by the unbalancing calculating unit 26b is larger than the first reference value, or when the power factor of the motor <NUM> calculated by the power factor calculating unit 26c is smaller than or equal to the second reference value. Thus, the motor <NUM> can avoid going out of synchronization in the case of a rapid change in the load torque of the motor <NUM>, and even when the motor <NUM> is malfunctioning for some reason, increasing the γ-axis current enables early activation of the overcurrent protecting unit <NUM> and a safe halt of the air-conditioning apparatus. In this way, reliability of the apparatus can be ensured.

Claim 1:
A motor control device (<NUM>) controlling a motor (<NUM>), comprising:
a load-torque detecting unit (<NUM>) configured to detect load torque of the motor (<NUM>); and
a current correcting unit (<NUM>) configured to increase a current flowing through the motor (<NUM>) in accordance with an increase in the load torque detected by the load-torque detecting unit (<NUM>),
the load-torque detecting unit (<NUM>) including
a power factor calculating unit (26c) configured to calculate a power factor of the motor (<NUM>),
the current correcting unit (<NUM>) increasing the current flowing through the motor (<NUM>),
the motor control device (<NUM>) characterized by the current correcting unit (<NUM>) determining that the load torque has increased when the power factor of the motor (<NUM>) calculated by the power factor calculating unit (26c) is smaller than or equal to a reference value.