JP6497307B2 - Air conditioner - Google Patents

Description

  The present invention relates to an air conditioner, and more particularly to a configuration for starting a compressor motor by an inverter.

Conventionally, the technique shown in Patent Document 1 is disclosed as a drive control device for a motor used in a refrigerator, an air conditioner, or the like. In Patent Document 1, a motor of a compressor used in a refrigerator is driven by an inverter, and the inverter is controlled using a switching signal generated by PWM control.
Further, in Patent Document 1, when starting the motor of this compressor, the frequency of the carrier signal used for generating the switching signal (PWM signal) is low when the rotational speed of the motor is lower than a predetermined threshold, Further, it is increased when the rotation speed becomes equal to or higher than the threshold value. As a result, the rotational position signal of the motor generated from the induced voltage generated in the motor winding by increasing the on-time of the switching signal by lowering the frequency of the carrier signal when the rotational speed of the motor is lower than a predetermined threshold. By detecting the rotational position by widening the pulse width, the step-out is prevented and the motor is reliably started.

FIG. 5 shows an air conditioner 90 using the technique disclosed in Patent Document 1. The air conditioner 90 includes an outdoor unit 80 and an indoor unit 50 that are communicatively connected to each other.
The outdoor unit 80 is connected to an input end 1 to which an AC power supply (not shown) is connected, a rectifier 4 connected to the input end 2, a converter 5 connected to the output side of the rectifier 4, and an output end of the converter 5. An inverter 6, a compressor motor 7 connected to the output terminal of the inverter 6, an outdoor unit controller 9 for controlling the entire outdoor unit 80 according to an instruction from the indoor unit 50, and a drive signal for driving the inverter 6 are output. The drive circuit 8 is provided. The motor 7 includes U-phase, V-phase, and W-phase windings (not shown).

  Further, the outdoor unit controller 9 detects a rotational position of the motor 7 based on the induced voltage generated in each winding of the motor 7 and outputs a rotational position signal, and an instruction from the outdoor unit controller 9. A switching signal for driving the motor 7 in accordance with the rotation speed command value generated is generated by PWM control and output to the drive circuit 8 to control the motor 7 by the 120-degree energization method, and the rotation speed of the motor 7 is set. A carrier frequency switching instructing unit 70 for outputting a frequency switching signal for switching between two types of carrier frequencies for generating a switching signal based on one of the two types of carrier frequencies according to the input frequency switching signal. A carrier signal generation unit 10 that generates a carrier signal and outputs the carrier signal to the inverter control unit 3 is provided.

The inverter control unit 3 receives the rotational speed command value from the outdoor unit control unit 9 and generates a switching signal that causes the motor 7 to rotate at the rotational speed specified by the rotational speed command value. The inverter control unit 3 performs control so that the energized phase of each winding of the motor 7 is switched every 60 degrees of electrical angle based on the input rotational position signal. Further, the inverter control unit 3 receives the carrier signal from the carrier signal generation unit 10, and determines and outputs the duty of the switching signal so as to generate a torque corresponding to the load of the motor 7 using this carrier signal. To do. In other words, the inverter control unit 3 increases the on-duty time of the switching signal (the time during which the switching element (not shown in the inverter 6 is turned on)) when the load of the motor 7 is large and does not reach the designated rotational speed, When the load of 7 is small and exceeds the instructed rotational speed, the on-duty time is shortened. In this way, the inverter control unit 3 determines the duty of the switching signal so that the instructed rotational speed can be maintained.
The carrier signal generation unit 10 receives a frequency switching signal output from the carrier frequency switching instruction unit 70, and outputs a carrier signal having a frequency of 4 kHz when the frequency switching signal is high level and 2 kHz when the frequency switching signal is low level.

  On the other hand, the carrier frequency switching instruction unit 70 includes a rotation speed detection unit 71 and a switching determination unit 72 therein. The carrier frequency switching instruction unit 70 receives a rotation position signal, and this rotation position signal is input to the rotation number detection unit 71. The rotation speed detection unit 71 measures the time for which the motor 7 rotates once, and calculates the rotation speed (unit: rps) for 1 second by dividing 1 second by this measured time.

  The calculated number of rotations per second is input to the switching determination unit 72. The switching determination unit 72 compares the input rotation number with a predetermined rotation speed threshold (10 rps), and inputs the input rotation. When the number is equal to or greater than the rotation speed threshold, the frequency switching signal is set to a high level, and when the number is less than the rotation speed threshold, the frequency switching signal is set to a low level and output. For this reason, the inverter control unit 3 executes PWM control using a carrier signal having a carrier frequency of 4 kHz when the rotational speed of the motor 7 is less than 10 rps, and when it is 2 kHz or 10 rps or more.

  As described above, the inverter control unit 3 widens the on-duty time of the switching signal by using a low carrier frequency when starting the motor 7 having a low rotation speed, so that the induced voltage of the winding of the motor 7 at the time of starting is increased. The pulse width of the waveform is widened so that the rotational position can be reliably detected by the rotational position detector 11. On the other hand, the inverter control unit 3 prevents the detection delay of the commutation timing for switching the energized phase by increasing the carrier frequency during normal operation of the motor 7 having a high rotational speed.

  FIG. 6 is an explanatory view for explaining conventional rotation control of the motor 7. The horizontal axis of FIG. 6 indicates time, the vertical axis of FIG. 6 (1) indicates the on-duty time (unit: μS (microseconds)) of the switching signal, and the solid line indicates an increase in the rotational speed of the motor 7. The broken line indicates the case where the speed is high (the load is light), and the broken line indicates the case where the rotation speed increase speed is low (the load is heavy). FIG. 6B shows the rotation speed (unit: rps) of the motor 7. The solid line shows a case where the rotation speed of the motor 7 is high (load is light), and the broken line shows a low rotation speed increase speed. Each case (heavy load) is shown. Note that t0 to t3 are times.

  In FIG. 6, when the rotational speed command value is input from the outdoor unit control unit 9, the inverter control unit 3 sets the on-duty time of the switching signal to 19 μS from t0 when the motor 7 is completely stopped, and the open loop method. As a result, the rotational speed of the motor is gradually increased. For example, when the rotational position of the motor 7 can be detected by the rotational position signal at t1, the control is switched from the open loop control to the closed loop control using the rotational position. However, after that, the number of revolutions is increased while increasing the on-duty time.

  On the other hand, when the rotation position signal is input to the carrier frequency switching instruction unit 71, the rotation number detection unit detects the current rotation number and outputs the rotation number to the switching determination unit 72. When the rotational speed increase speed of the motor 7 is fast, the rotational speed becomes 10 rps or more after t2. The switching determination unit 72 changes the frequency switching signal from the low level to the high level at t2 when the rotational speed becomes equal to or higher than the rotational speed threshold (10 rps). The carrier signal generation unit 10 outputs a carrier signal whose carrier frequency is changed from 2 kHz to 4 kHz to the inverter control unit 3 by the frequency switching signal. As a result, the on-duty time of the switching signal output from the inverter control unit 3 is reduced from 24 μS to 12 μS.

  Further, when the rotational speed increase rate of the motor 7 is slow, the rotational speed becomes 10 rps or more after t3. The switching determination unit 72 changes the frequency switching signal from the low level to the high level at t3 when the rotational speed becomes equal to or higher than the rotational speed threshold (10 rps). The carrier signal generation unit 10 outputs a carrier signal whose carrier frequency is changed from 2 kHz to 4 kHz to the inverter control unit 3 by the frequency switching signal. As a result, the on-duty time of the switching signal output from the inverter control unit 3 is reduced from 70 μS to 35 μS.

  In this way, the inverter control unit 3 has the rotation speed of the motor 7 equal to or greater than the rotation speed threshold, and the on-duty time of the switching signal output at this time is increased. As a result, the rotation position detection unit 11 reliably rotates. When the rotation speed is considered to be detectable, the motor 7 is controlled by switching the frequency of the carrier signal from a low frequency to a high frequency.

Incidentally, noise is generated inside the motor 7 due to changes in the current flowing in the winding of the motor 7, and the magnitude of this noise is larger when the carrier frequency of the switching signal is lower than when the carrier frequency of the switching signal is high. Tend to be.
FIG. 7 is an explanatory diagram for explaining a difference in noise due to a difference in carrier frequency. The horizontal axis in FIG. 7 is time. On the vertical axis, FIG. 7 (1) shows a switching signal when the carrier frequency is 4 kHz and the duty is 50%, and FIG. 7 (2) shows a switching signal when the carrier frequency is 2 kHz and the duty is 50%. . In FIG. 7, a broken line indicates a ripple current flowing in the winding of the motor 7.

When the inductance value of the motor winding and the voltage applied to the winding are the same, the period of the ripple current flowing through the winding becomes longer when the carrier frequency is lower than when the carrier frequency is higher. Therefore, in the current of the motor 7 that periodically changes as shown in FIG. 6B, the peak Ip2 of the ripple current value with the carrier frequency of 2 kHz is larger than the peak Ip4 of the current value with the carrier frequency of 4 kHz. .
If the change in the current flowing through the winding of the motor 7 is large, the vibration of the winding due to the change in current also increases, and noise is generated by the vibration of the winding.
Therefore, the vibration (noise) of the winding of the motor 7 due to the change in the ripple current is larger when the carrier frequency is 2 kHz than when it is 4 kHz. That is, in FIG. 6, when the rotational speed increase speed is fast, this noise is loud from t0 to t2 when the carrier frequency is low, and when the rotational speed is slow, the carrier frequency is low from start time t0 to t3. Noisy.

  The rotational speed threshold value for switching the carrier frequency is the minimum at which the rotational position detecting unit 11 can detect the rotational position even when the carrier frequency is 4 kHz in consideration of the load of the motor 7 and the input voltage of the inverter 6. The value is predetermined. Specifically, when the rotational speed increase speed of the motor 7 is fast, the carrier frequency at which the rotational position can be detected is 4 kHz, and is determined in advance to 10 rps, which is a rotational numerical value with an on-duty time of 12 μS. When the rotation speed is slow and the rotation speed is 10 rps, the on-duty time at the switched carrier frequency is 35 μS, which is more than necessary than the minimum on-duty time at which the rotation position can be detected, 12 μS. It is getting bigger.

Therefore, a method is conceivable in which the carrier frequency switching timing is not determined by the number of rotations but by the on-duty time of the switching signal. That is, for example, when the carrier frequency switching instruction unit 70 constantly monitors the on-duty time, and the on-duty time is a carrier frequency of 4 kHz, the rotation position detection unit 11 can detect the rotational position, for example, 12 μS. In this method, the carrier frequency is switched from 2 kHz to 4 kHz.
However, the on-duty time of the switching signal output from the inverter control unit 3 and the time width of the induced voltage at which the rotational position can be detected by the rotational position detecting unit 11 are not simply proportional, and the time width of the detectable induced voltage can be detected. Since it depends on the rotational speed as well as the on-duty time, the above-described method for monitoring the on-duty time cannot be adopted.

Next, the relationship between the time width of the induced voltage, the on-duty time, and the rotation speed will be described with reference to FIG.
FIG. 4A is a block diagram showing an internal circuit of the rotational position detector 11, and FIG. 2B is an explanatory diagram for explaining its operation.
Inside the rotational position detector 11, resistors 11a to 11d for detecting the voltage of a virtual neutral point of the induced voltage generated in each of the U-phase, V-phase, and W-phase windings of the motor 7, and a noise removing capacitor 11h, a comparator 11f, a reference voltage generation source 11e, and an integration circuit 11g.
One ends of the resistors 11a to 11c are connected to the U phase, V phase, and W phase of the winding of the motor 7, respectively, and the other ends of the resistors 11a to 11c are connected in common with one end of the resistor 11d, and the other end of the resistor 11d is Connected to ground. A capacitor 11h is connected in parallel with the resistor 11d.

On the other hand, one end of the resistor 11d is connected to the + input end of the comparator 11f, the reference voltage source 11e is connected to the − input end of the comparator 11f, and the output end of the comparator 11f is connected to the input end of the integrating circuit 11g. The rotation position signal is output from the output terminal of the integrating circuit 11g. An induced voltage appears at a virtual neutral point where the resistors are connected in common.

  FIG. 4 (2) is an explanatory diagram for explaining the operation of the rotational position detector 11. The horizontal axis indicates time, and in the vertical axis, FIGS. 4 (2) and (A) indicate switching signals, and FIG. ) (B) shows the voltage at the virtual neutral point when the rotational speed of the motor 7 is low, FIGS. 4 (2) and (C) show the output signal of the comparator 11f when the rotational speed is low, and FIG. D) shows the voltage at the virtual neutral point when the rotational speed of the motor 7 is high, and FIGS. 4 (2) and 4 (E) show the output signal of the comparator 11f when the rotational speed is high.

  As shown in FIGS. 4 (2) (B) and 4 (2) (D), the induced voltage appearing at the virtual neutral point has a pulse waveform, but the rise of the waveform is gentle due to the influence of the capacitor 11h. It is inclined to. For this reason, the pulse width of the output signal of the comparator 11f depends not only on the on-duty time of the switching signal but also on the magnitude of the induced voltage, that is, the rotation speed. As shown in FIGS. 4 (2) and (A), even if the on-duty time of the switching signal is the same, as shown in FIGS. 4 (2) (B) and 4 (2) (D), the reference voltage The pulse width of the output signal of the comparator 11f differs depending on the magnitude of the induced voltage compared with the reference voltage output from the generation source 11e, and the output signal of the comparator 11f is higher at a higher rotational speed than at a lower rotational speed. The pulse width becomes wider. That is, even when the on-duty time of the switching signal is short, the induced voltage becomes high when the rotational speed is high, and the output signal of the comparator 11f is a sufficient pulse that can pass through the integrating circuit 11g and output the rotational position signal. It becomes width.

  On the other hand, even if the rotational speed is low and the induced voltage is low, the comparator 11f can output an output signal having a wide waveform that can pass through the integrating circuit 11g when the on-duty time is long. A rotational position signal can be output.

  Thus, the pulse width of the output signal of the comparator 11f is not only related to the on-duty time of the switching signal, but also has a relationship corresponding to the number of rotations. For this reason, in order for the rotational position detector 11 to reliably detect the rotational position signal based on the induced voltage, it is necessary to satisfy both the on-duty time and the rotational speed conditions.

  As described above, the inverter control unit 3 outputs a switching signal with a longer on-duty time when the rotational speed increase speed is slow even when the rotational speed is the same, compared to when the rotational speed increase speed is fast. In other words, the inverter control unit 3 continues even if the carrier frequency is switched from 2 kHz to 4 kHz even if the number of rotations is low as long as the on-duty time is such that the rotational position detection unit 11 can detect the position. Position detection. For this reason, since this switching can be performed earlier than the conventional method of switching the carrier frequency only by the rotation speed threshold value, the noise generation time can be shortened as a result.

  However, for this purpose, there is a problem that the carrier frequency must be switched at a timing at which the rotational position signal by the induced voltage can be reliably detected by the rotational position detector 11 in consideration of both the rotational speed and the on-duty time.

Japanese Patent Laid-Open No. 11-318097 (page 7-8, FIG. 1)

  The present invention solves the above-described problems and prevents noise generated during control using a low carrier frequency while preventing a step-out when starting a motor driven by an inverter that is PWM controlled by switching the carrier frequency. The purpose is to make the occurrence period as short as possible.

In order to solve the above-described problems, the present invention according to claim 1 of the present invention includes an input terminal to which an AC power supply is connected, a DC power supply unit connected to the input terminal, and the DC power supply unit. An inverter connected to the output terminal, a motor connected to the output terminal of the inverter, a rotational position detection unit that detects the rotational position of the motor and outputs a rotational position signal, and an instructed rotational speed command value The control signal for generating and outputting the switching signal for driving the inverter by PWM control, and controlling the motor by a 120-degree energization method, and the carrier frequency of the carrier signal for generating the switching signal is the rotation speed of the motor. Carrier frequency switching instruction means for outputting a frequency switching signal to be switched based on the carrier, and the carrier having a carrier frequency corresponding to the input frequency switching signal An air conditioner having a carrier signal generating means for outputting to said control means to generate items,
The carrier frequency switching instruction means receives the rotational position signal and the switching signal, calculates a rotational speed from the input rotational position signal, and the rotational speed is greater than a predetermined rotational speed of the motor. And, when the on-duty time calculated from the input switching signal becomes larger than a predetermined on-duty time threshold, the carrier frequency higher than the carrier frequency of the carrier signal output by the carrier signal generating means The frequency switching signal for outputting a carrier signal is output.

  In the invention according to claim 2 of the present invention, the on-duty time threshold value is larger as the predetermined rotation speed of the motor is lower.

  By using the above means, the air conditioner according to the present invention uses a low carrier frequency while preventing a step-out while starting a motor driven by an inverter that is PWM controlled by switching the carrier frequency. The generation period of noise generated during control can be shortened as much as possible.

It is a block diagram which shows the Example of the air conditioner by this invention. It is a block diagram which shows the inside of the carrier frequency switching instruction | indication part by this invention. It is explanatory drawing explaining rotation control of the motor by this invention. It is explanatory drawing explaining operation | movement of a rotation position detection part. It is a block diagram which shows the conventional air conditioner. It is explanatory drawing explaining rotation control of the conventional motor. It is explanatory drawing explaining the difference in the noise by the difference in a carrier frequency.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail as examples based on the attached drawings. In addition, illustration and description of a heat exchanger, a refrigerant circuit, a fan motor, etc. that are not related to the present application are omitted. The same name and number are assigned to blocks having the same function in the blocks described in the background art.

FIG. 1 is a block diagram showing an air conditioner 20 using a technique according to the present invention. The air conditioner 20 includes an outdoor unit 40 and an indoor unit 50 that are communicatively connected to each other.
The outdoor unit 40 is connected to an input end 1 to which an AC power supply (not shown) is connected, a rectifier 4 connected to the input end 2, a converter 5 connected to the output side of the rectifier 4, and an output end of the converter 5. An inverter 6, a compressor motor 7 connected to the output terminal of the inverter 6, an outdoor unit controller 9 that controls the entire outdoor unit 40 according to an instruction from the indoor unit 50, and a drive signal that drives the inverter 6 are output. The drive circuit 8 is provided. The rectifier 4 and the converter 5 constitute a DC power supply unit 12. The motor 7 includes U-phase, V-phase, and W-phase windings (not shown).

  Further, the outdoor unit controller 9 detects a rotational position of the motor 7 based on the induced voltage generated in each winding of the motor 7 and outputs a rotational position signal, and an instruction from the outdoor unit controller 9. Inverter control unit 3 that generates a PWM signal that is a switching signal for driving motor 7 in accordance with the rotation speed command value that is generated and outputs the PWM signal to drive circuit 8 to control motor 7 by a 120-degree energization method, and a rotational position signal of motor 7 A switching signal is input, and a carrier frequency switching instruction unit 30 (carrier frequency switching instruction means) that outputs a frequency switching signal for switching between two types of carrier frequencies, and one of the two types of carrier frequencies according to the input frequency switching signal. A carrier signal generation unit 10 that generates a carrier signal having one frequency and outputs the carrier signal to the inverter control unit 3 is provided.

The inverter control unit 3 receives the rotational speed command value from the outdoor unit control unit 9 and generates a switching signal so as to rotate the motor 7 at the rotational speed specified by the rotational speed command value. The inverter control unit 3 performs control so that the energized phase of each winding of the motor 7 is switched every 60 degrees of electrical angle based on the input rotational position signal. Further, the inverter control unit 3 receives the carrier signal from the carrier signal generation unit 10 and determines the duty of the switching signal so that the rotation number of the motor 7 can be maintained using the carrier signal. And output.
The carrier signal generation unit 10 receives a frequency switching signal output from the carrier frequency switching instruction unit 30 and outputs a carrier signal having a frequency of 4 kHz when the frequency switching signal is high level and 2 kHz when the frequency switching signal is low level.
The duty of the switching signal means the ratio between the high level period and the low level period of the switching signal, and the on-duty time of the switching signal means the time of the high level period of the switching signal. Then, a switching element (not shown) in the inverter 6 is turned on during this high level period.

FIG. 2 is a block diagram showing the inside of the carrier frequency switching instruction unit 30.
The carrier frequency switching instruction unit 30 includes a rotation number detection unit 31 (rotation number detection unit), an on-duty time threshold extraction unit 32 (on-duty time threshold extraction unit), a comparison unit 33 (comparison unit), and an on-duty time. A calculation unit 34 (on-duty time calculation means) is provided. The carrier frequency switching instruction unit 30 is input with a rotational position signal, and this rotational position signal is input to the rotational speed detection unit 31. The rotation speed detector 31 measures the time for which the motor 7 rotates once, and calculates the rotation speed (unit: rps) for 1 second by dividing 1 second by this measured time.

  The calculated number of rotations per second is input to the on-duty time threshold value extraction unit 32. Even if the carrier frequency is switched from a low frequency to a high frequency at the input rotation number, the rotation position signal is detected by the rotation position detection unit 11. Is extracted from the threshold table stored in the on-duty time threshold value extraction unit 32, which is the shortest on-duty time that can be output. Note that the extracted on-duty time threshold value is input to the comparison unit 33.

Next, a threshold table storing an on-duty time threshold (unit: μS) that is a minimum on-duty time for generating an induced voltage that can be detected by the rotational position detection unit 11 will be described.
The contents of this threshold table correspond to, for example, the number of revolutions (unit: rps) 4, 5, 6, 7, 8, 9, 10, 11. .., 28, 26, 24, 22..., 28, 26, 24, 22..., 28, 26, 24, 22.

Next, a method for obtaining in advance an on-duty time threshold value in the threshold table used by the on-duty time threshold value extraction unit 32 will be described.
First, start-up of the motor 7 is started with the heaviest air-conditioning load. When the position of the motor 7 can be detected, the carrier is forcibly set in the start-up operation in which the on-duty time of the switching signal is gradually increased from 19 μS. By switching the frequency from 2 kHz to 4 kHz, the minimum on-duty time during which the position can be detected and the operation can be continued normally and the number of rotations at that time are recorded.

  Next, the start of the motor 7 is started in the state where the air conditioning load is lightest. When the position of the motor 7 can be detected, the carrier frequency is forcibly set in the start-up operation in which the on-duty time of the switching signal is gradually increased from 19 μS. By switching from 2 kHz to 4 kHz, the minimum on-duty time during which position detection is possible and operation can be continued normally and the number of rotations at that time are recorded.

  Then, starting the motor 7 with the air conditioning load at the center between the maximum and minimum, and when the position of the motor 7 can be detected, the start-up operation forcibly increases the on-duty time of the switching signal from 19 μS. By switching the carrier frequency from 2 kHz to 4 kHz, the minimum on-duty time during which position detection is possible and operation can be continued normally and the number of rotations at that time are recorded.

  In this way, the recorded rotational speed and on-duty time for each load size, that is, the recorded rotational speed and on-duty time threshold are tabulated. In order to further improve accuracy, the magnitude of the load may be subdivided, and the on-duty time threshold value and the number of rotations at that time may be obtained in detail and reflected in the table.

  As described above, the on-duty time threshold value extraction unit 32 uses a threshold table in which the on-duty time threshold value decreases as the rotational speed increases. This is because the higher the number of revolutions, the higher the induced voltage of the winding of the motor 7, and the rotational position detection unit 11 can reliably detect the rotational position even when the on-duty time of the switching signal is short. Conversely, the lower the rotation speed, the lower the induced voltage of the winding of the motor 7, and it becomes difficult to reliably detect the rotation position by the rotation position detection unit 11. Therefore, a long on-duty is required to ensure the detection. Corresponds to the need for time.

  On the other hand, the on-duty time calculation unit 34 receives one of the switching signals for switching on / off the switching elements in the inverter 6. The on-duty time calculation unit 34 detects the time from the rising edge to the falling edge of the input switching signal and outputs the detected time to the comparison unit 33 as the on-duty time.

  As described above, the on-duty time threshold value extraction unit 32 always extracts the on-duty time threshold value corresponding to the rotational speed that is input every moment and outputs it to the comparison unit 33. The comparison unit 33 receives the on-duty time output from the on-duty time calculation unit 34 and the calculated on-duty time threshold, and always compares the on-duty time with the on-duty time threshold. When the on-duty time threshold is exceeded, the frequency switching signal is set to high level. The comparison unit 33 sets the frequency switching signal to a low level when the on-duty time is less than the on-duty time threshold.

  However, since the on-duty time threshold value extraction unit 32 sets the frequency switching signal to a high level only once from the start of the start of the motor, the on-duty time becomes shorter by switching the carrier frequency and becomes less than the on-duty time threshold value. However, the frequency switching signal is not set to a low level. Then, the on-duty time threshold value extraction unit 32 first sets the frequency switching signal to the low level when the motor 7 is started next time, and starts the processing.

  Thus, the carrier frequency switching instruction unit 30 includes a plurality of combinations of the rotation speed and the corresponding on-duty time threshold value for each rotation speed, and the on-duty time is set to the on-duty time by any one of these combinations. When the threshold value is exceeded, the frequency switching signal is set to a high level. The carrier frequency switching instructing unit 30 can determine the optimum frequency switching with a plurality of combinations of the rotational speed and the corresponding on-duty time threshold value. One combination of corresponding on-duty time thresholds may be provided.

  In this way, the inverter control unit 3 generates a PWM signal using the carrier frequency of 2 kHz during a period when the rotational speed is low and it is difficult for the rotational position detection unit 11 to reliably detect the rotational position at the carrier frequency of 4 kHz. Then, when the period when the rotational position is high and the rotational position can be reliably detected by the rotational position detector 11 even at a carrier frequency of 4 kHz, the PWM signal is generated by switching the frequency and using the carrier frequency of 4 kHz. .

FIG. 3 is an explanatory diagram for explaining the rotation control for starting the motor 7 according to the present invention.
The horizontal axis of FIG. 3 represents time, FIG. 3 (1) of the vertical axis represents the on-duty time (unit: μS) of the switching signal, and FIG. 3 (2) represents the number of rotations of the motor 7 (unit: rps). 3 (3) shows the frequency switching signal, and FIG. 3 (4) shows the target period of the method for controlling the rotation of the motor 7. Note that t10 to t14 are times. The solid line in FIG. 3 shows the case where the speed of increase of the rotational speed of the motor 7 is fast (the load is light), and the broken line shows the case where the speed of increase of the rotational speed of the motor 7 is slow (the load is heavy). The dotted line is a graph of the on-duty time threshold value in the threshold value table.

  In FIG. 3, when the rotation speed command value is input from the outdoor unit control unit 9, the inverter control unit 3 turns on the duty of the switching signal from t10 when the motor 7 is completely stopped as shown in FIG. When the time is fixed at 19 μS and the rotational speed of the motor is gradually increased by the control of the open loop system as shown in FIG. 3 (2). For example, when the rotational position of the motor 7 can be detected by the rotational position signal at t11, Switch from open-loop control to closed-loop control using rotational position. However, after switching to this control, the inverter control unit 3 simultaneously increases the rotational speed while increasing the on-duty time of the switching signal.

  When the instructed rotation speed command value is input, the inverter control unit 3 controls the inverter 6 to reach this rotation speed as soon as possible. For this reason, when the on-duty time of the switching signal is short, the inverter control unit 3 does not become a lagging phase (the load is light), so that the rotation speed is increased in order to gradually advance the timing of switching the energization phase of each winding of the motor 7. Speed will also be faster. On the contrary, when the inverter control unit 3 has a lagging phase (a heavy load), the on-duty of the switching signal is increased, and the speed of increase in the rotational speed is increased in order to delay the timing for switching the energized phase of each winding of the motor 7. Become slow.

  As shown in FIG. 3 (3), the carrier frequency switching instruction unit 30 outputs the frequency switching signal at a low level (the carrier frequency is 2 kHz) at the time t10 when the start of the motor 7 is started. When the inverter control unit 3 switches to the closed loop control using the rotation position at t11, the inverter control unit 3 increases the rotation speed while increasing the on-duty time of the switching signal.

  When the speed of increase in the rotational speed is low, the on-duty time increases to 48 μS when the rotational speed is 5 rps at t12. The on-duty time threshold value extraction unit 32 of the carrier frequency switching instruction unit 30 extracts the 48 μS on-duty time threshold value with reference to the threshold value table because the rotation speed is 5 rps. The comparison unit 33 compares the on-duty time threshold value of 48 μS output from the on-duty time calculation unit 34 with the on-duty time threshold value of 48 μS, and the on-duty time is equal to or higher than the on-duty time threshold value. That is, the carrier frequency is instructed to 4 kHz.

  The high-level frequency switching signal is input from the carrier frequency switching instruction unit 30 to the carrier signal generation unit 10, and the carrier signal generation unit 10 switches from the 2 kHz carrier signal to the 4 kHz carrier signal and outputs it to the inverter control unit 3. Then, since the 4 kHz carrier signal is input, the inverter control unit 3 outputs a switching signal whose on-duty time is reduced from 48 μS to 24 μS, and further increases the rotation speed and the on-duty time.

  On the other hand, the inverter control unit 3 increases the on-duty time of the rotational speed and the switching signal from t11 even when the speed of increase in the rotational speed is fast. When the speed of increase in the rotational speed is high, the carrier frequency switching instruction unit 30 switches the frequency because the on-duty time is smaller than 36 μS, which is the on-duty time threshold at this time, even when the rotational speed is 7.5 rps at t13, for example. The signal remains low, i.e. the carrier frequency remains at 2 kHz.

  The carrier frequency switching instructing unit 30 compares the on-duty time threshold value of 24 μS output from the inverter control unit 3 with the 24 μS on-duty time threshold value output from the on-duty time calculating unit 34 when the rotation speed is 10 rps at t14. Since the on-duty time is equal to or greater than the on-duty time threshold, the frequency switching signal is instructed to a high level, that is, the carrier frequency is set to 4 kHz.

  The high-level frequency switching signal is input from the carrier frequency switching instruction unit 30 to the carrier signal generation unit 10, and the carrier signal generation unit 10 switches from the 2 kHz carrier signal to the 4 kHz carrier signal and outputs it to the inverter control unit 3. Then, since the 4 kHz carrier signal is input, the inverter control unit 3 outputs a switching signal that results in the on-duty time being reduced from 24 μS to 12 μS, and further increases the rotational speed and the on-duty time.

  As described above, the carrier frequency switching instruction unit 30 has a predetermined on-duty time threshold value whose rotational speed is larger than the predetermined rotational speed of the motor 7 and the on-duty time calculated from the input switching signal. When the frequency is larger than the output frequency, a frequency switching signal is output and an instruction to switch from a lower carrier signal to a higher frequency carrier signal out of two carrier frequencies of 2 kHz and 4 kHz is output. When the motor 7 driven by the inverter 6 is started, the generation period of noise generated when PWM control is performed by a carrier signal using a carrier frequency as low as 2 kHz can be made as short as possible while preventing step-out.

  In addition, since the threshold table is configured so that the on-duty time threshold value increases as the rotational speed of the predetermined motor decreases, the frequency switching signal can be output at an optimal timing to shorten the noise generation period. Can do.

  In the present embodiment, the carrier frequency switching instruction unit 30 is described as hardware. However, the present invention is not limited to this, and may be realized by software.

DESCRIPTION OF SYMBOLS 1 Input end 2 Input end 3 Inverter control part 4 Rectifier 5 Converter 6 Inverter 7 Inverter 7 Motor 8 Drive circuit 9 Outdoor unit control part 10 Carrier signal generation part 11 Rotation position detection part 11a, 11b, 11c, 11d Resistance 11e Reference voltage source 11f Comparator 11g Integration circuit 12 DC power supply unit 20 Air conditioner 30 Carrier frequency switching instruction unit (carrier frequency switching instruction unit)
31 Rotational speed detection unit (rotational speed detection means)
32 On-duty time threshold extraction unit (on-duty time threshold extraction means)
33 Comparison part (comparison means)
34 On-duty time calculation unit (on-duty time calculation means)
40 outdoor unit 50 indoor unit

Claims (2)

An input terminal to which an AC power supply is connected, a DC power supply unit connected to the input terminal, an inverter connected to an output terminal of the DC power supply unit, a motor connected to the output terminal of the inverter, and the motor A rotational position detector that detects the rotational position of the motor and outputs a rotational position signal; and generates and outputs a switching signal for driving the inverter according to the instructed rotational speed command value by PWM control, and the motor is energized 120 degrees. Control means for controlling in a system, carrier frequency switching instruction means for outputting a frequency switching signal for switching the carrier frequency of the carrier signal for generating the switching signal based on the number of rotations of the motor, and the input frequency switching Carrier signal generating means for generating the carrier signal having a carrier frequency corresponding to the signal and outputting the carrier signal to the control means is provided. A gas-conditioner,
The carrier frequency switching instruction means receives the rotational position signal and the switching signal, calculates a rotational speed from the input rotational position signal, and the rotational speed is greater than a predetermined rotational speed of the motor. And, when the on-duty time calculated from the input switching signal becomes larger than a predetermined on-duty time threshold, the carrier frequency higher than the carrier frequency of the carrier signal output by the carrier signal generating means An air conditioner that outputs the frequency switching signal for outputting a carrier signal.   2. The air conditioner according to claim 1, wherein the on-duty time threshold value is larger as the predetermined rotation speed of the motor is lower.

Images