JPH0923685A - Air conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent breakdown of a switching element even during the normal rotation at the speed exceeding the control speed by turning off the switching element while the on-duty ratio of the chopping signal is minimized. SOLUTION: When strong wind works on an outdoor fan 7 during the speed control, the on-duty ratio of the PWM signal from a comparison circuit 17 is minimized. A minimum duty ratio detecting circuit 45 detects that the on- period of the chopping signal is equal to the predetermined minimum value and outputs the signal of level H. Thereby, an R-S flipflop 46 is set and the off-command in the level H is applied to a phase distribution circuit 19. In this case, the phase distribution circuit of the upper arm and lower arm forming the phase distribution circuit 19 turns off all switching elements 4 even when the off-command 47 is applied as in the case where the off-command 31 is applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air conditioner in which an outdoor fan is driven by a brushless motor and the speed (hereinafter, also referred to as rotation speed) is controlled.

[0002]

2. Description of the Related Art A three-phase brushless motor is a kind of DC motor which has U-, V-, and W-phase three-phase windings and is drive-controlled by a drive circuit composed of an electronic circuit. In particular, a variable speed is required. It is used for various purposes. An air conditioner in which an outdoor fan is driven by this three-phase brushless motor is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-130794.
The technique described in this publication is intended to suppress the voltage rise of the DC power supply unit due to the induced voltage when the motor is reversely rotated by wind to a certain value or less. Will be described with reference to.

As shown in FIG. 4, the DC power supply unit comprises a DC converter 2 connected to a commercial power supply 1 and a smoothing capacitor 3. The main circuit of the drive circuit has a configuration in which the arms formed by connecting the switching element 4 and the diode 5 in parallel so that the energization directions are opposite to each other are connected in parallel to the smoothing capacitor 3 by three-phase bridge connection. The brushless motor 6 is connected to the output end of the main circuit, and the outdoor fan 7 is connected to the brushless motor 6. The subscripts U, V, and W attached to the reference numerals of the switching elements 4 of the upper arm and the lower arm of each phase represent the phase, and the subscripts U and L represent the upper arm and the lower arm. Further, as the switching element, an IGBT, a transistor, a GTO thyristor,
A self-extinguishing element such as a MOS-FET is used.

The speed of the outdoor fan 7 is detected by the speed detection circuit 12 based on the rotational phase detection signal 11 output from the phase detector which is a Hall element built in the brushless motor 6. On the other hand, the speed command value of the outdoor fan 7 is given from the speed setter 13 as the speed command value of the brushless motor 6. The deviation between the speed command value and the speed detection value is obtained by the speed adjusting circuit 14, and the speed adjusting circuit 14 outputs the motor current command value 15 of a magnitude necessary for removing the speed deviation. The motor current command value 15 is compared with the triangular wave output from the carrier wave generation circuit 16 in the comparison circuit 17, where the signal is chopped and the PW of the on-duty ratio corresponding to the magnitude of the motor current command value 15 is obtained.
The control signal 18 consisting of M pulses is generated, and the phase distribution circuit 19
Is added to The phase distribution circuit 19 is composed of an upper arm phase distribution circuit 19a and a lower arm phase distribution circuit 19b as shown in FIG. The upper arm phase distribution circuit 19a uses the switching element 4 for each phase of the upper arm based on the rotation phase detection signal 11.
A control signal 20 for sequentially turning on and off is generated.
The lower arm phase distribution circuit 19b sequentially distributes the control signal 18 of each switching element related to the on-duty ratio control, and generates the control signal 21 that is the logical product of the rotation phase detection signal 11 and the control signal 18. And output. These control signals
Based on 20 and 21, the switching element drive circuits 22 and 23 of the upper arm and the lower arm control the gates of the switching elements to drive them on and off.

Here, the reverse rotation detection circuit 25 and the reference value setting device 2
6, the comparison circuit 27 and the AND gate 30 form a protection circuit for protecting the DC power supply unit. That is, based on the rotation phase detection signal 11, the reverse rotation detection circuit 25 causes the brushless motor 6 to operate.
While detecting the reverse rotation of, the reference value of the reference value setter 26 for setting the allowable reference value of the reverse rotation speed, and the speed detection value detected by the speed detection circuit 12 based on the rotation phase detection signal 11 comparison circuit When the speed detection value exceeds the reference value, a signal 28 is output, and this signal 28 and the reverse rotation detection signal 29 output from the reverse rotation detection circuit 25 are ANDed by an AND gate 30. The output of the AND gate 30 is added to the phase distribution circuit 19 as an OFF command 31 for all switching arms.

FIGS. 6A, 6B and 6C are waveform diagrams of the rotation phase detection signal 11, the upper arm ON / OFF control signal 20, and the lower arm ON / OFF control signal 21 in the normal state, respectively. Is shown. As illustrated, the switching elements of the lower arm paired with the upper arm are sequentially turned on and off by a so-called 120-degree conduction method. The on-duty ratio of the switching element of the lower arm is controlled according to the control signal 18. Here, the rotation phase detection signal 11 when the brushless motor 6 is rotating in the forward direction is shown in (a) of FIG. When is rotated in the reverse direction, the V phase advances by 120 degrees with respect to the U phase, as shown in FIG. As is clear from these relations, for example, it is possible to determine whether the U-phase level is H or L, based on the rise of the V-phase, whether the rotation is normal or reverse. The reverse rotation detection circuit 25 detects the reverse rotation of the brushless motor 6 according to this principle.

Here, when the brushless motor 6 is positively rotated by wind force, the voltage induced in the winding is generally lower than the terminal voltage of the smoothing capacitor 3, so that the problem of the rise in the DC voltage is unlikely to occur. However, the brushless motor 6
Is reversely rotated by the wind force, the on-phase of the switching element of the upper arm is switched, and at the moment of this switching, both switching elements are turned off and a winding short-circuit current flows through the smoothing capacitor 3. Therefore, when the reverse rotation speed is high, the frequency of charging also increases, and in addition to the rise in the induced voltage, the terminal voltage of the smoothing capacitor 3, that is, the DC portion voltage, sharply rises.

Therefore, in the drive circuit shown in FIG. 4, when the reverse rotation of the brushless motor 6 is detected and the rotation speed exceeds a preset reference value, an OFF command 31 is added to the phase distribution circuit 19. That is, an OFF command is applied to the upper arm phase distribution circuit 19a and the lower arm phase distribution circuit 19b to turn off the switching element to suppress the voltage rise of the smoothing capacitor 3.

[0009]

In the conventional air conditioner described above, the induced voltage of the winding when the outdoor fan is positively rotated by the wind force is lower than the terminal voltage of the smoothing capacitor 3, and it is It does not take measures against the voltage rise of the. This is presumed to be based on the premise that the rotation speed of the outdoor fan when the air conditioner is stopped does not exceed the rotation speed when the outdoor fan is actively driven.

However, if normal wind blows during speed control of the outdoor fan, the voltage induced in the winding may exceed the terminal voltage of the smoothing capacitor 3. That is, if a favorable wind blows during speed control of the outdoor fan, heat exchange in the outdoor heat exchanger is promoted, and the on-duty ratio of the control signal 28 output from the comparison circuit 27 is narrowed. Therefore, when the wind is strong, the outdoor fan may rotate at a speed exceeding the normal control speed with the on-duty ratio kept at a minimum.

As described above, when the outdoor fan rotates at a speed exceeding the normal control speed during speed control, the terminal voltage of the smoothing capacitor 3 rises due to the voltage induced in the winding of the brushless motor. However, this voltage may exceed the breakdown voltage of the switching element 4 and destroy the element.

The present invention has been made in order to solve the above problems, and even if the outdoor fan rotates forward beyond the control speed due to strong wind, the air conditioner can prevent the switching element from being destroyed. The purpose is to provide a machine.

[0013]

In order to achieve the above-mentioned object, the present invention has a main circuit in which three switching elements are provided in each of an upper arm and a lower arm which are connected in a three-phase bridge. The input side of is connected to the DC power supply, the brushless motor for driving the outdoor fan is connected to the output side,
The switching elements are sequentially turned on and off, and the on control signal of either one of the upper and lower arms is chopped at a predetermined frequency, and based on the deviation between the speed detection value of the brushless motor and the speed reference value. In an air conditioner that varies the on-duty ratio of a chopping signal, a minimum duty ratio detecting means for detecting that the on-duty ratio of the chopping signal is minimum, and a switching element while the minimum on-duty ratio is detected. And a speed control blocking means for turning off the switch.

In the present invention, while the on-duty ratio of the chopping signal is minimized, the switching element is turned off to prevent the speed control, so that only the normal wind rotates, so that the speed decreases. The induced voltage in the winding can be suppressed to a much lower level compared to the case where speed is increased by normal wind during speed control, thereby preventing the voltage rise of the DC power supply unit and the destruction of switching elements due to strong normal wind. You can

In addition to the above construction, the normal rotation detecting means for detecting the forward rotation of the brushless motor, the normal rotation of the brushless motor is detected, and the speed detection value is equal to or less than a preset value. At this time, a control block releasing means for releasing the block state of the speed control for the switching element is provided.

As described above, when the forward rotation of the brushless motor is detected and the speed detection value is equal to or less than the preset value, the blocking state of the speed control for the switching element is released so that the wind power is reduced. It is possible to quickly shift to speed control.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention. In the figure, the same elements as those in FIG. 4 showing the conventional apparatus are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, in addition to the elements shown in FIG. 4, a positive rotation detection circuit 41, a reference value setting device 42, a comparison circuit 43, an AND gate 44, and a minimum duty ratio detection circuit 45.
And an RS flip-flop 46 are added.

Of these, the forward rotation detection circuit 41 is, for example,
When the V-phase level is H based on the rising of the W-phase of the rotation phase detection signal 11, it is determined to be normal rotation and a signal of level H is output. The reference value of the reference value setter 42, which is set to a value slightly lower than the maximum control speed, is compared with the speed detection value of the brushless motor 6 detected by the speed detection circuit 12, and the speed detection value is the reference value. When it is below, it outputs a signal whose level is H. The AND gate 44 receives the output of the positive rotation detection circuit 41 as one input and the output of the comparison circuit 43 as the other input, and outputs the AND signal. The minimum duty ratio detection circuit 45 detects that the on-time of the chopping signal is a predetermined minimum width and outputs a signal of level H. For example, the time from the rise to the fall of the chopping signal. Can be determined by measuring The RS flip-flop 46 adds the output signal of the minimum duty ratio detection circuit 45 to the set terminal S,
The output signal of the AND gate 44 is added to the reset terminal R, and the H level signal output from the output terminal Q is added to the phase distribution circuit 19 as an OFF command. The reference value setter 42, the comparison circuit 43, the AND gate 44, and R- shown in FIG.
The one including the S flip-flop 46 corresponds to the control block releasing means of the present invention.

The operation of the present embodiment configured as described above will be described below, focusing on the part that is different in configuration from the conventional device. During speed control of the outdoor fan 7,
The forward rotation detection circuit 41 outputs an H signal. In this state, the speed of the outdoor fan 7 increases due to the normal wind, but the comparison circuit 43 until the reference value of the reference value setter 42 is reached.
Outputs an H signal. Therefore, the output signal of the AND gate 44 is H. This resets the RS flip-flop 46, so that its output signal is L. Therefore, the off command 47 to the phase distribution circuit 19 is not output. After that, the speed of the outdoor fan 7 is changed to the reference value setter 42.
When the reference value of is exceeded, the output signal of the comparison circuit 43 goes to L, A
The output signal of the ND gate 44 also changes to L, but the reset state of the RS flip-flop 46 does not change.

On the other hand, if the outdoor fan 7 receives normal wind during speed control, the on-duty ratio of the PWM signal output from the comparison circuit 17 is reduced. If strong winds act, the on-duty ratio of the PWM signal is minimized.
At this time, the minimum duty ratio detection circuit 45 outputs an H signal. As a result, the RS flip-flop 46 enters the set state, and the OFF command 47 whose level is H is transmitted to the phase distribution circuit 19
Is added to At this time, as shown in FIG. 2, the upper arm phase distribution circuit 19a and the lower arm phase distribution circuit 19b that form the phase distribution circuit 19 receive the OFF command 47 as in the case where the OFF command 31 is added. When added, all switching elements are turned off. Therefore, when the on-duty ratio cannot be made smaller during the speed control to suppress the speed increase, all the switching elements 4 are held in the off state.

Next, when all of the switching elements 4 are held in the off state, the influence of the strong wind on the outdoor fan 7 is mitigated, and its speed is set to the reference value set by the reference value setting device 42, that is, When the voltage falls below the maximum control speed of the brushless motor 6 or less, the output of the comparison circuit 43 changes to H, and the output of the AND gate 44 also changes to H, so that the RS flip-flop 46 operates. It is reset. As a result, the off command 47 is erased. As a result, the blocking state of the speed control by the PWM signal is released, and the original speed control state is restored.

Thus, according to this embodiment, even if the normal wind acts on the outdoor fan 7 to increase the rotation speed, the speed control is continued as long as the on-duty ratio can be reduced to cope with the on-duty ratio. When the ratio becomes the minimum and the speed control cannot be performed, all the switching elements 4 are kept in the OFF state to decrease the speed of the outdoor fan 7, and the speed falls below the maximum control speed to a set value or less. Then, since the speed control is restored, it is possible to prevent the voltage increase of the DC power supply unit and the destruction of the switching element due to the strong wind.

By the way, most functions of the speed control circuit described above, for example, the functions of the elements surrounded by the one-dot chain line 50 in FIG. 1 can be given to the microprocessor unit (MPU). Among these functions, a processing function for a part in which an element is newly added to the conventional device is shown in a flowchart in FIG. That is, in step 101, the rotation direction of the motor is detected based on the rotation phase detection signal, and in the next step 102, it is determined whether the rotation direction of the motor is the forward direction (normal wind). If it is in the opposite direction, the process (detailed description is omitted) corresponding to the downwind described with reference to FIG. 4 is executed, and only in the case of normal wind, the processes in and after step 104 are executed. Steps
At 104, the rotation speed of the motor is detected based on the rotation phase signal, and at step 105, the motor rotation speed control is executed by adjusting the duty ratio of the chopping signal. Then, in step 106, it is determined whether or not the duty ratio of the chopping signal is the minimum, and if it is not the minimum, the process is stopped in step 107. On the contrary, when the duty ratio of the chopping signal is the minimum, the speed control of the motor is stopped in step 108, and the rotation speed of the motor is detected in the next step 109. Next, in step 110, it is determined whether the motor rotation speed is lower than the set reference value lower than the maximum control speed.If it is the reference value or more, the subsequent processing is stopped and the value becomes the reference value or less. If it does, it returns to the motor speed control state. As described above, according to the processing procedure shown in the flowchart of FIG. 3, the speed control can be blocked and restored in the same manner as described with reference to FIGS. 1 and 2.

[0024]

As is apparent from the above description, according to the first aspect of the present invention, the switching element is turned off to control the speed while the on-duty ratio of the chopping signal is minimized. In order to prevent this, the speed is reduced because it is rotated only by normal wind, and the induced voltage in the winding can be suppressed to a much lower level than during speed control. Also, it is possible to prevent breakdown of the switching element.

Further, turning off the switching element is to cut off the power supply to the brushless motor in a state having sufficient heat exchange capacity, so that it is possible to suppress wasteful power consumption. There is also.

Further, in the second aspect of the present invention, when the forward rotation of the brushless motor is detected and the detected speed value is equal to or less than the preset value, the speed control block state for the switching element is released, It is possible to quickly shift to speed control when the wind power decreases.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of main elements according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a processing procedure when a microprocessor unit is provided with a main function of one embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an outdoor fan drive circuit of a conventional air conditioner.

FIG. 5 is a block diagram showing a detailed configuration of main elements of an outdoor fan drive circuit of a conventional air conditioner.

FIG. 6 is a time chart for explaining the operation of the outdoor fan drive circuit of the conventional air conditioner.

[Explanation of symbols]

 1 Commercial Power Supply 2 DC Converter 3 Smoothing Capacitor 4 Switching Element 5 Diode 6 Brushless Motor 7 Outdoor Fan 12 Speed Detection Circuit 13 Speed Setting Device 14 Speed Adjustment Circuit 14 16 Carrier Wave Generation Circuit 17, 43 Comparison Circuit 19 Phase Distribution Circuit 22, 23 Switching element drive circuit 26, 42 Reference value setter 30 AND gate 41 Forward rotation detection circuit 44 AND gate 45 Minimum duty ratio detection circuit 46 RS flip-flop

Claims (2)

[Claims] 1. A main circuit having a three-phase bridge connection and three switching elements provided on each of an upper arm and a lower arm, the input side of the main circuit is connected to a DC power source, and the output side is for driving an outdoor fan. Brushless motor is connected, the switching elements are sequentially turned on and off, and the ON control signal of either one of the upper and lower arms is chopped at a predetermined frequency, and the speed detection value of the brushless motor is detected. In an air conditioner that varies the on-duty ratio of the chopping signal based on the deviation between the on-duty ratio and the speed reference value, a minimum duty ratio detecting means for detecting that the on-duty ratio of the chopping signal is minimum, and the on-duty ratio. And a speed control blocking means for turning off the switching element while the minimum value is detected. Air conditioner, characterized in that. 2. A normal rotation detecting means for detecting that the brushless motor has normally rotated, and the switching when the normal rotation of the brushless motor is detected and a speed detection value is equal to or less than a preset value. The air conditioner according to claim 1, further comprising control blocking releasing means for releasing a blocking state of speed control for the element.