Fan control system and air conditioner that includes the same

A fan control system includes a first fan, a second fan that is adjacent to the first fan, a first motor that is configured to rotate the first fan, a second motor that is configured to rotate the second fan, and a control unit. The control unit is configured to control the rotational speeds of the first motor and the second motor, and to decrease the rotational speeds of both the first motor and the second motor when the rotational speed of the first motor must be decreased.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2007-135038, filed in Japan on May 22, 2007, the entire contents of which are hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a fan control system and more particularly relates to a fan control system that controls a plurality of fans and an air conditioner that comprises the same.

BACKGROUND ART

In recent years, the motors that drive the fans of outdoor units of air conditioners (hereinbelow, abbreviated as outdoor fans) have been controlled by inverters, wherein rotational speed is controlled in accordance with instructions regardless of the external load's size. Because outdoor fans are generally disposed outdoors, they are easily subject to loads in forward or reverse rotational direction caused by natural wind. As a result, motor current increases owing to loads in the reverse rotational direction, and the fan rotates at a speed that exceeds its target rotational speed owing to loads in the forward rotational direction; therefore, problems such as overcurrents, overvoltages, and loss of synchronization can sometimes arise and cause the fan to stop abnormally. One way of solving this problem is a method that has already been disclosed (e.g., refer to Japanese Patent Application Publication No. H8-303386), wherein a permissible rotational speed range, which is a speed range that is acceptable even when a motor is energized, is preset, and when the fan rotates at a speed outside of that permissible rotational speed, the motor is not energized.

SUMMARY OF THE INVENTION

Technical Problem

Nevertheless, while the method according to the Japanese Patent Application Publication No. H8-303386 principally avoids overloads when a single fan is driven, it does not disclose any method for dealing with the case wherein, as shown inFIG. 1, a plurality of outdoor fans are mounted in the same air passageway and, when all of the fans are operating, for example, just one of the fans becomes overloaded.

An object of the present invention is to provide a fan control system that controls a plurality of fans and, when a fan becomes overloaded during operation, eliminates that overload.

Solution to Problem

A fan control system according to a first aspect of the present invention comprises: a first fan; a second fan, which is adjacent to the first fan; a first motor, which rotates the first fan; a second motor, which rotates the second fan; and a control unit. The control unit controls the rotational speeds of the first motor and the second motor and, when the state has arisen wherein the operation of the first motor must be stopped, stops both the operation of the first motor and the operation of the second motor.

In this fan control system, the control unit stops the operation of the second motor when it stops the operation of the first motor; therefore, the situation wherein the first fan rotates in reverse or is subject to any load in the reverse rotational direction owing to dynamic pressure on the suction side of the second fan does not arise, which makes the first fan easy to restart.

A fan control system according to a second aspect of the present invention is a fan control system according to the first aspect of the present invention, wherein after the operation of the first motor and the second motor has been stopped, the control unit starts startup operations of the first motor and the second motor simultaneously.

In this fan control system, the first fan and the second fan start to rotate substantially simultaneously, which prevents situations wherein, for example, one fan rotates in reverse or one of the fans is subject to a load in the reverse rotational direction owing to dynamic pressure on the suction side of the other fan.

A fan control system according to a third aspect of the present invention is a fan control system according to the second aspect of the present invention, wherein the startup operations are started after the rotations of the first motor and the second motor have stopped.

In this fan control system, both the first motor and the second motor can be restarted from the stopped state, and therefore a load is not unnecessarily applied to either motor.

A fan control system according to a fourth aspect of the present invention is a fan control system according to the second aspect of the present invention, wherein the startup operations are started after the rotational speeds of the first motor and the second motor have fallen below a prescribed rotational speed.

In this fan control system, if the first motor and the second motor are rotating owing to inertial force after being stopped, or if the first motor and the second motor are rotating because the first fan and the second fan are subject to natural wind and cannot stop, then the system can stand by until the rotational speed of each of the motors reaches a rotational speed at which it can be started up, which decreases the load that is applied to each motor.

A fan control system according to a fifth aspect of the present invention is a fan control system according to the fourth aspect of the present invention, wherein the prescribed rotational speed is set to a rotational speed at which the first motor and the second motor do not stop abnormally when they are started up.

In this fan control system, the electrical currents that flow to the first motor and the second motor at startup or the DC voltages that increase owing to induced voltages generated by the first motor and the second motor at startup fall within permissible ranges, which decreases damage to each of the motors and its inverter circuit and rectification circuit.

A fan control system according to a sixth aspect of the present invention is a fan control system according to the second aspect of the present invention, wherein the startup operations are started after standing by for prescribed times since the operation of the first motor and of the second motor has been stopped.

In this fan control system, if each of the motors is rotating owing to inertial force even after the operation of the first motor and the second motor has been stopped, then the rotational speed of each of the motors can be decreased to a range at which it can be restarted by standing by for a prescribed time after the operation of each motor has stopped.

A fan control system according to a seventh aspect of the present invention is a fan control system according to the sixth aspect of the present invention, wherein the prescribed times are set to times at which the first motor and the second motor do not stop abnormally when they are started up.

In this fan control system, the electrical currents that flow to the first motor and the second motor at startup or the DC voltages that increase owing to induced voltages generated by the first motor and the second motor at startup fall within permissible ranges, which decreases damage to each of the motors and its inverter circuit and rectification circuit.

A fan control system according to an eighth aspect of the present invention comprises: a first fan; a second fan, which is adjacent to the first fan; a first motor, which rotates the first fan; a second motor, which rotates the second fan; and a control unit. The control unit controls the rotational speeds of the first motor and the second motor and, when the state has arisen wherein the rotational speed of the first motor must be decreased, decreases both the rotational speed of the first motor and the rotational speed of the second motor.

In this fan control system, if the rotational speed of the first motor decreases, then the first motor cannot oppose the load that works to rotate the first fan in reverse owing to dynamic pressure on the suction side of the second fan; therefore, the rotational speed of the second motor is decreased, which lightens the load that works to rotate the first fan in reverse.

A fan control system according to a ninth aspect of the present invention is a fan control system according to the eighth aspect of the present invention, wherein the range of decreases of the rotational speeds of the first motor and the second motor are determined based on the load state of the first fan.

In this fan control system, the range of decrease of the rotational speed is determined in accordance with the load state, and therefore the overload is eliminated early and an excessive decrease in airflow caused by decreasing the rotational speed more than necessary is prevented.

A fan control system according to a tenth aspect of the present invention is a fan control system according to the eighth or ninth aspects of the present invention, wherein the range of decrease of the rotational speed of the first motor and the range of decrease of the rotational speed of the second motor are different values.

In this fan control system, by making the ranges of decrease of the rotational speeds of the first motor and the second motor different, it is possible to reduce the range of decrease of the rotational speed of the motor that is not overloaded, and therefore excessive decrease in airflow is prevented.

A fan control system according to an eleventh aspect of the present invention comprises: a first fan; a second fan, which is adjacent to the first fan; a first motor, which rotates the first fan; a second motor, which rotates the second fan; and a control unit. The control unit controls the rotational speeds of the first motor and the second motor and, when the state has arisen wherein the rotational speed of the first motor must be decreased, decreases the rotational speed of the first motor and increases the rotational speed of the second motor.

In this fan control system, while the overload of the first motor is eliminated by a decrease in rotational speed of the first motor, the insufficient airflow of the first fan caused by the decrease in rotational speed of the first motor is supplemented by an increase in the rotational speed of the second motor.

A fan control system according to a twelfth aspect of the present invention is a fan control system according to the eleventh aspect of the present invention, wherein the range of decrease of the rotational speed of the first motor is determined based on the load state of the first fan.

In this fan control system, the range of decrease of the rotational speed is determined in accordance with the load state, and therefore the overload is eliminated early and an excessive decrease in airflow caused by decreasing the rotational speed more than necessary is prevented.

A fan control system according to a thirteenth aspect of the present invention is a fan control system according to the eleventh or twelfth aspects of the present invention, wherein the range of increase of the rotational speed of the second motor is determined based on the range of decrease of the rotational speed of the first motor and the sum of the airflows demanded of the first fan and the second fan.

In this fan control system, an excessive decrease in airflow is prevented.

A fan control system according to a fourteenth aspect of the present invention comprises: a first fan; a second fan, which is adjacent to the first fan; a first motor, which rotates the first fan; a second motor, which rotates the second fan; and a control unit. The control unit controls the rotational speeds of the first motor and the second motor and, when the state has arisen wherein the rotational speed of the first motor must be decreased, decreases the rotational speed of the first motor; when the rotational speed of the first motor, whose rotational speed has been decreased, is lower than a prescribed rotational speed, decreases the rotational speed of the second motor; and when the rotational speed of the first motor, whose rotational speed has been decreased, is higher than the prescribed rotational speed, increases the rotational speed of the second motor.

In this fan control system, if the rotational speed of the first motor falls below the prescribed rotational speed, then the first motor cannot oppose the dynamic pressure on the suction side of the second fan; therefore, the rotational speed of the second motor is decreased, which lowers the dynamic pressure on the suction side of the second fan. Moreover, when the rotational speed of the first motor is higher than the prescribed rotational speed, there is margin enough to oppose the dynamic pressure on the suction side of the second fan and therefore to rotate; therefore, the rotational speed of the second motor is increased, which makes it possible to supplement the decrease in airflow of the first fan owing to the decrease in rotational speed of the first motor.

A fan control system according to a fifteenth aspect of the present invention is a fan control system according to the fourteenth aspect of the present invention, wherein the range of decreases of the rotational speeds of the first motor and the second motor are determined based on the load state of the first fan.

In this fan control system, the range of decrease of the rotational speed is determined in accordance with the load state, and therefore the overload is eliminated early and an excessive decrease in airflow caused by decreasing the rotational speed more than necessary is prevented.

A fan control system according to a sixteenth aspect of the present invention is a fan control system according to the fourteenth or fifteenth aspects of the present invention, wherein the range of decrease of the rotational speed of the first motor and the range of decrease of the rotational speed of the second motor are different values.

In this fan control system, by making the ranges of decrease of the rotational speeds of the first motor and the second motor different, it is possible to reduce the range of decrease of the rotational speed of the motor that is not overloaded, and therefore excessive decrease in airflow is prevented.

A fan control system according to a seventeenth aspect of the present invention is a fan control system according to any one of the fourteenth through sixteenth aspects of the present invention, wherein the range of increase of the rotational speed of the second motor is determined based on the range of decrease of the rotational speed of the first motor and the sum of the airflows demanded of the first fan and the second fan.

In this fan control system, an excessive decrease in airflow can be prevented.

A fan control system according to a eighteenth aspect of the present invention is a fan control system according to any one of the first through seventeenth aspects of the present invention, wherein the first fan and the second fan are installed in the same air passageway.

In this fan control system, control is performed such that an unnecessary load does not act on the adjacent fan; therefore, it is unnecessary to partition the first fan and the second fan from one another even if they are installed in the same air passageway, which simplifies the structure.

An air conditioner according to a nineteenth aspect of the present invention comprises: a fan control system according to any one of the first through eighteenth aspects of the present invention.

In this air conditioner, the stoppage of the fans is suppressed, which prevents an excessive drop in the performance of the air conditioner.

Advantageous Effects of the Invention

In the fan control system according to the first aspect of the present invention, the control unit stops the operation of the second motor when it stops the operation of the first motor; therefore, the situation wherein the first fan rotates in reverse or is subject to any load in the reverse rotational direction owing to dynamic pressure on the suction side of the second fan does not arise, which makes the first fan easy to restart.

In the fan control system according to the second aspect of the present invention, the first fan and the second fan start to rotate substantially simultaneously, which prevents situations wherein for example, one fan rotates in reverse or one of the fans is subject to a load in the reverse rotational direction owing to dynamic pressure on the suction side of the other fan.

In the fan control system according to the third aspect of the present invention, both the first motor and the second motor can be restarted from the stopped state, and therefore a load is not unnecessarily applied to either motor.

In the fan control system according to the fourth aspect of the present invention, if the first motor and the second motor are rotating owing to inertial force after being stopped, or if the first motor and the second motor are rotating because the first fan and the second fan are subject to natural wind and cannot stop, then the system can stand by until the rotational speed of each of the motors reaches a rotational speed at which it can be started up, which decreases the load that is applied to each motor.

In the fan control system according to the fifth aspect of the present invention, the electrical currents that flow to the first motor and the second motor at startup or the DC voltages that increase owing to induced voltages generated by the first motor and the second motor at startup fall within permissible ranges, which decreases damage to each of the motors and its inverter circuit and rectification circuit.

In the fan control system according to the sixth aspect of the present invention, if each of the motors is rotating owing to inertial force even after the operation of the first motor and the second motor has been stopped, then the rotational speed of each of the motors can be decreased to a range at which it can be restarted by standing by for a prescribed time after the operation of the motor has stopped.

In the fan control system according to the seventh aspect of the present invention, the electrical currents that flow to the first motor and the second motor at startup or the DC voltages that increase owing to induced voltages generated by the first motor and the second motor at startup fall within permissible ranges, which decreases damage to each of the motors and its inverter circuit and rectification circuit.

In the fan control system according to the eighth aspect of the present invention, if the rotational speed of the first motor decreases, then the first motor cannot oppose the load that works to rotate the first fan in reverse owing to dynamic pressure on the suction side of the second fan; therefore, the rotational speed of the second motor is decreased, which lightens the load that works to rotate the first fan in reverse.

In the fan control system according to the ninth aspect of the present invention, the range of decrease of the rotational speed is determined in accordance with the load state, and therefore the overload is eliminated easily and an excessive decrease in airflow caused by decreasing the rotational speed more than necessary is prevented.

In the fan control system according to the tenth aspect of the present invention, by making the ranges of decrease of the rotational speeds of the first motor and the second motor different, it is possible to reduce the range of decrease of the rotational speed of the motor that is not overloaded, and therefore excessive decrease in airflow is prevented.

In the fan control system according to the eleventh aspect of the present invention, while the overload of the first motor is eliminated by a decrease in rotational speed of the first motor, the insufficient airflow of the first fan caused by the decrease in rotational speed of the first motor is supplemented by an increase in the rotational speed of the second motor.

In the fan control system according to the twelfth aspect of the present invention, the range of decrease of the rotational speed is determined in accordance with the load state, and therefore the overload is eliminated early and an excessive decrease in airflow caused by decreasing the rotational speed more than necessary is prevented.

In the fan control system according to the thirteenth aspect of the present invention, an excessive decrease in airflow is prevented.

In the fan control system according to the fourteenth aspect of the present invention, when the rotational speed of the first motor is higher than the prescribed rotational speed, there is margin enough to oppose the dynamic pressure on the suction side of the second fan and therefore to rotate; therefore, the rotational speed of the second motor is increased, which makes it possible to supplement the decrease in airflow of the first fan owing to the decrease in rotational speed of the first motor.

In the fan control system according to the fifteenth aspect of the present invention, the range of decrease of the rotational speed is determined in accordance with the load state, and therefore the overload is eliminated early and an excessive decrease in airflow caused by decreasing the rotational speed more than necessary is prevented.

In the fan control system according to the sixteenth aspect of the present invention, by making the ranges of decrease of the rotational speeds of the first motor and the second motor different, it is possible to reduce the range of decrease of the rotational speed of the motor that is not overloaded, and therefore excessive decrease in airflow can be prevented.

In the fan control system according to the seventeenth aspect of the present invention, an excessive decrease in airflow can be prevented.

In the fan control system according to the eighteenth aspect of the present invention, control is performed such that an unnecessary load does not act on the adjacent fan; therefore, it is unnecessary to partition the first fan and the second fan from one another even if they are installed in the same air passageway, which simplifies the structure.

In the fan control system according to the nineteenth aspect of the present invention, the stoppage of the fans is suppressed, which prevents an excessive drop in the performance of the air conditioner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will now be explained, referencing the drawings. Furthermore, the embodiments below are merely illustrative examples of the present invention and do not limit its technical scope.

First Embodiment

Fan Control System

FIG. 1is a configuration diagram of an air conditioner's outdoor unit that uses a fan control system according to an embodiment of the present invention. InFIG. 1, a first fan21and a second fan22, which are adjacent to one another, are disposed in an upper part of an air conditioner's outdoor unit2. The first fan21is directly coupled to a rotary shaft of a first motor31, and the second fan22is directly coupled to a rotary shaft of a second motor32. The rotational speeds of the first motor31and the second motor32are controlled by inverters, and their rotational speeds and acceleration can be easily changed.

A control unit4is housed in a prescribed electrical equipment box of the air conditioner's outdoor unit2and controls the rotational speeds of the first motor31and the second motor32. An outdoor heat exchanger13is disposed along sidewalls of the air conditioner's outdoor unit2. Suction ports20are formed in the sidewalls of the air conditioner's outdoor unit2; furthermore, by the rotation of the first fan21and the second fan22, the air is sucked in via the suction ports20, passes through the outdoor heat exchanger13, reaches the first fan21and the second fan22, and is blown out upward from the air conditioner's outdoor unit2.

FIG. 2is a circuit diagram of the fan control system. InFIG. 2, the control unit4comprises two rectification circuits41,42, two drive circuits51,52, and two inverter circuits61,62, all of which are for controlling the rotational speeds of the first motor31and the second motor32. The control unit4further comprises a microcomputer40, which controls the two drive circuits51,52. A CPU and memory are built into the microcomputer40. The first motor31and the second motor32are brushless DC motors; the first motor31comprises a stator, to which a voltage is supplied from the inverter circuit61, and a rotor, which comprises a magnet that opposes that stator; furthermore, the second motor32comprises a stator, to which a voltage is supplied from the inverter circuit62, and a rotor, which comprises a magnet that opposes that stator.

The rectification circuits41,42are bridge circuits that each comprise six diodes and supply DC voltages they generate from the AC voltage supplied by a power supply10to the inverter circuits61,62. The inverter circuits61,62are bridge circuits that each comprise six transistors and drive signals are input to the transistors from the drive circuits51,52.

A first rotational speed sensor71detects the rotational speed of the first motor31. A Hall element is incorporated in the stator of the first motor31, and the first rotational speed sensor71can detect the rotational speed of the rotor of the first motor31via that Hall element. Similarly, a second rotational speed sensor72detects the rotational speed of the second motor32. A Hall element is incorporated in the stator of the second motor32, and the second rotational speed sensor72can detect the rotational speed of the rotor of the second motor32via that Hall element.

In the present embodiment, the rotational speeds of the first motor31and the second motor32substitute for the rotational speeds of the first fan21and the second fan22. While monitoring the detection signals output from the first rotational speed sensor71and the second rotational speed sensor72, the microcomputer40inputs the drive signals to the transistors of the inverter circuits61,62such that the first fan21and the second fan22reach a prescribed rotational speed.

<Fan Stop and Restart Control>

In an air conditioner's outdoor unit wherein a plurality of fans is used in the same air passageway, if, when all of the fans are rotating, one of the fans becomes overloaded and stops, then the stopped fan either rotates in reverse or receives a load in the reverse rotational direction owing to dynamic pressure on the suction side of the rotating fan, making it difficult to restart. To avoid this problem, fan stop and restart control is performed in such a fan control system. Fan stop and restart control will now be explained, referencing the drawings.

FIG. 3is a flow chart of fan stop and restart control. In step S1inFIG. 3, the microcomputer40determines whether the first fan21or the second fan22has stopped abnormally owing to an overload. If either of these fans has abnormally stopped, then the method proceeds to step S2, wherein the operation of the fan that is not abnormally stopped is stopped and both the first fan21and the second fan22transition to a state wherein their operation is stopped.

In step S3, the method determines whether the rotations of the first fan21and the second fan22are stopped. Even if the operation of the first fan21and the second fan22is stopped, the fans sometimes either rotate owing to inertial force or rotate in the forward or reverse rotational directions owing to natural wind. If every motor is restarted in such a state, either the motor currents sometimes increase owing to the loads in the reverse rotational direction or the fans sometimes rotate at speeds that exceed their target rotational speeds owing to loads in the forward rotational direction, which causes problems such as overcurrents, overvoltages, and loss of synchronization, and the fans may stop abnormally. If the determination in step S3changes to YES, then the method proceeds to step S4, wherein restart operations of the first fan21and the second fan22are started.

In fan stop and restart control as described above, if even one of the fans of the plurality of fans used in the same air passageway stops abnormally, then the microcomputer40temporarily stops all of the fans and performs the restart operations.

The abovementioned fan stop and restart control is for the case wherein a fan stops abnormally owing to an overload; however, in actual operation, stopping a fan reduces the amount of heat exchanged by the outdoor heat exchanger13and decreases the operation performance of the air conditioner's outdoor unit2; therefore, it is preferable to avoid stopping a fan as much as possible. In this fan control system, when a fan becomes overloaded, fan overload avoidance control is performed, which eliminates the overload without immediately stopping the fan. Fan overload avoidance control will now be explained referencing the drawings.

FIG. 4is a flow chart of fan overload avoidance control. In step S11inFIG. 4, the microcomputer40determines whether the first fan21or the second fan22has become overloaded. If an overload is detected, then the method proceeds to step S12; if an overload is not detected, then the method continues to monitor for an overload.

In step S12, both the rotational speed N1of the first fan21and the rotational speed N2of the second fan22are decreased by prescribed numbers of rotations per minute. The control unit4both eliminates the overload by decreasing the rotational speed of the fan that has become overloaded and decreases the rotational speed of the adjacent fan, thereby suppressing the load that results from the dynamic pressure on the suction side of the adjacent fan.

The method determines the range within which the rotational speeds of the first motor31and the second motor32may be decreased based on the load state of the fan that has become overloaded; thereby, the overload is eliminated easily. In the present embodiment, to prevent an excessive decrease in airflow, the range of decrease of the rotational speed of the fan that is not overloaded is restricted as much as possible; as a result, the range of decrease of the rotational speed of the first motor31and the range of decrease of the rotational speed of the second motor32have different values.

In fan overload avoidance control of the present embodiment as described above, if even one fan of the plurality of fans used in the same air passageway becomes overloaded, then the microcomputer40decreases the rotational speeds of all of the fans.

First Modified Example of the First Embodiment

In fan stop and restart control according to the first embodiment, stopping the rotation of the first motor31and the second motor32is one condition for restarting the first motor31and the second motor32. However, if the first fan21and the second fan22are subject to natural wind, then their rotations are maintained and the method stands by until those rotations stop, which is inefficient. Accordingly, in the first modified example, control that permits restarting when rotational speed falls below a prescribed rotational speed is performed. This will now be explained, referencing the drawings.

<Fan Stop and Restart Control>

FIG. 5is a flow chart of fan stop and restart control according to a first modified example. In step S101inFIG. 5, the microcomputer40determines whether the first fan21or the second fan22has stopped abnormally owing to an overload. If either of these fans has abnormally stopped, then the method proceeds to step S102, wherein the operation of the fan that is not abnormally stopped is stopped and both the first fan21and the second fan22transition to a state wherein their operation is stopped.

In step S103, the method determines whether the rotational speeds of the first fan21and the second fan22have fallen below the prescribed rotational speed. Even if the operation of the first fan21and the second fan22is stopped, the motors sometimes either rotate owing to inertial force or rotate in the forward or reverse rotational directions owing to natural wind. If every motor is restarted in such a state, either the motor currents sometimes increase owing to the loads in the reverse rotational direction or the fans sometimes rotate at speeds that exceed their target rotational speeds owing to loads in the forward rotational direction, which causes problems such as overcurrents, overvoltages, and loss of synchronization, and the motors may stop abnormally.

However, if that rotational speed is less than the prescribed rotational speed at which it was empirically verified that the fan will not stop abnormally even if a restart operation is started, then the fan can be started up safely. If the determination in step S103changes to YES, then the method proceeds to step S104, wherein the restart operations of the first fan21and the second fan22are started.

Second Modified Example of the First Embodiment

In fan stop and restart control according to the first modified example, one condition for restarting the first motor31and the second motor32is the rotational speeds thereof falling below the prescribed rotational speed; furthermore, as a means of obtaining a similar effect, in the second modified example, control is performed wherein restarting is permitted after standing by for a prescribed time after the operation of the first motor31and the second motor32is stopped. This will now be explained, referencing the drawings.

<Fan Stop and Restart Control>

FIG. 6is a flow chart of fan stop and restart control according to a second modified example. In step S201inFIG. 6, the microcomputer40determines whether the first fan21or the second fan22has stopped abnormally owing to an overload. If either of these fans has abnormally stopped, then the method proceeds to step S202, wherein the operation of the fan that is not abnormally stopped is stopped and both the first fan21and the second fan22transition to a state wherein their operation is stopped.

In step S203, the method determines whether a prescribed time has elapsed since the operations of the first fan21and the second fan22were stopped. Even after the operation of the first fan21and the second fan22is stopped, the motors sometimes either rotate owing to inertial force or rotate in the forward or reverse rotational directions owing to natural wind. If every motor is restarted in the state wherein their rotational speeds have not fallen into a safe range, either the motor currents sometimes increase owing to the loads in the reverse rotational direction or the fans sometimes rotate at speeds that exceed their target rotational speeds owing to loads in the forward rotational direction, which causes problems such as overcurrents, overvoltages, and loss of synchronization, and the fans may stop abnormally.

However, if the prescribed time at which it was empirically verified that the fan will not stop abnormally even if a restart operation is started has elapsed, then the fan can be started up safely because its rotational speed has fallen into the safe range. If the determination in step S203changes to YES, then the method proceeds to step S204, wherein the restart operations of the first fan21and the second fan22are started.

<Features of the First Embodiment>

In this fan control system, when the control unit4stops the first motor31, it also stops the second motor32; therefore, the situation where the first fan21rotates in reverse owing to dynamic pressure on the suction side of the second fan22or is it subject to any load in the reverse rotational direction does not arise, which makes it easy for the first fan21to restart. Likewise, when the control unit4stops the second motor32, it also stops the first motor31; therefore, the situation where the second fan22rotates in reverse owing to dynamic pressure on the suction side of the first fan21or is it subject to any load in the reverse rotational direction does not arise, which makes it easy for the second fan22to restart. In addition, startup operations of the first motor31and the second motor32are started simultaneously; therefore, the first fan21and the second fan22start to rotate substantially simultaneously, and it is possible to prevent situations wherein, for example, the dynamic pressure on the suction side of one of the fans causes the other fan to rotate in reverse or a fan is subject to a load in the reverse rotational direction.

In this fan control system, if the system transitions to the state wherein the rotational speed of the first motor31must be decreased because of an overload, then the control unit4decreases the rotational speeds of both the first motor31and the second motor32and thereby lightens the load that works to rotate the first fan21in reverse. Likewise, if the system transitions to the state wherein the rotational speed of the second motor32must be decreased because of an overload, then the control unit4decreases the rotational speeds of both the second motor32and the first motor31and thereby lightens the load that works to rotate the second fan22in reverse.

Second Embodiment

In fan overload avoidance control according to the first embodiment, control that avoids overloads, wherein, when one of the fans overloads, the rotational speed of the other fan is decreased unconditionally, is adopted; however, to ensure sufficient airflow, control that increases the rotational speed—within a feasible range—of the fan that is not overloaded may be performed.

FIG. 7is a flow chart of fan overload avoidance control according to the second embodiment. In step S21inFIG. 7, the microcomputer40determines whether the first fan21is overloaded. If an overload is detected, then the method proceeds to step S22; if an overload is not detected, then the method proceeds to step S26.

In step S22, the rotational speed N1of the first fan21is decreased by a prescribed number of rotations, and the rotational speed N2of the second fan22is increased by a prescribed number of rotations. Here, decreasing the rotational speed of the first fan21eliminates the overload thereof and increases the rotational speed of the second fan22, which in turn supplements any decrease in airflow owing to the decrease in rotational speed of the first fan21.

The method determines the range of decrease of the rotational speed of the first motor31based on the load state of the first fan21; furthermore, determining the range of decrease of the rotational speed in accordance with the load state eliminates the overload early. In addition, to prevent an excessive decrease in airflow, the method determines the range of increase in the rotational speed of the second motor32based on both the range of decrease in the rotational speed of the first motor31and the sum of the airflows demanded of the first fan21and the second fan22.

However, even if the rotational speed of the first fan21is decreased in step S22, it is possible that the dynamic pressure on the suction side will increase owing to an increase in the rotational speed of the second fan22and that a load will work to rotate the first fan21in the reverse direction, thereby failing to eliminate the overload of the first fan21. Consequently, in step S23, the method determines whether the overload of the first fan21has been eliminated. If the overload has been eliminated, then the method proceeds to step S24; if the overload has not been eliminated, then the method returns to step S22.

In addition, even if the overload of the first fan21has been eliminated in step S22, it is also possible that the second fan22will overload owing to an increase in its rotational speed. Consequently, in step S24, the method determines whether the second fan22is overloaded. If an overload of the second fan22is detected, then the method proceeds to step S25, wherein the overload of the second fan22is eliminated by decreasing the rotational speed N2of the second fan22by a prescribed number of rotations. If an overload is not detected, then control terminates.

Furthermore, if an overload of the first fan21was not detected in step S21, then the method proceeds to step S26, wherein the method determines whether the second fan22is overloaded. Here, if an overload is detected, then the method proceeds to step S27; furthermore, if an overload is not detected, then the method returns to step S21.

In step S27, the rotational speed N2of the second fan22is decreased by a prescribed number of rotations, and the rotational speed N1of the first fan21is increased by a prescribed number of rotations. Here, decreasing the rotational speed of the second fan22eliminates the overload thereof and increases the rotational speed of the first fan21, which in turn supplements any decrease in airflow owing to the decrease in rotational speed of the second fan22.

The method determines the range of decrease of the rotational speed of the second motor32based on the load state of the second fan22; furthermore, determining the range of decrease of the rotational speed in accordance with the load state eliminates the overload early. In addition, to prevent an excessive decrease in airflow, the method determines the range of increase in the rotational speed of the first motor31based on both the range of decrease in the rotational speed of the second motor32and the sum of the airflows demanded of the first fan21and the second fan22.

However, even if the rotational speed of the second fan22is decreased in step S27, it is possible that the dynamic pressure on the suction side will increase owing to an increase in the rotational speed of the first fan21and that a load will work to rotate the second fan22in the reverse direction, thereby failing to eliminate the overload of the second fan22. Consequently, in step S28, the method determines whether the overload of the second fan22has been eliminated. If the overload has been eliminated, then the method proceeds to step S29; if the overload has not been eliminated, then the method returns to step S27.

In addition, even if the overload of the second fan22has been eliminated in step S27, it is also possible that the first fan21will overload owing to an increase in its rotational speed. Consequently, in step S29, the method determines whether the first fan21is overloaded. If an overload of the first fan21is detected, then the method proceeds to step S30, wherein the overload of the first fan21is eliminated by decreasing the rotational speed N1of the first fan21by a prescribed number of rotations. If an overload is not detected, then control terminates.

In fan overload avoidance control according to the second embodiment as described above, the microcomputer40avoids an overload by decreasing the rotational speed of the fan that has become overloaded and, while doing so, increases, as much as possible, the rotational speed of the adjacent fan, thereby supplementing the reduced airflow.

<Features of the Second Embodiment>

In this fan control system, if the system transitions to the state wherein the rotational speed of the first motor31must be decreased because of an overload, then the control unit4decreases the rotational speed of the first motor31and increases the rotational speed of the second motor32, thereby supplementing the insufficient airflow of the first fan21while eliminating the overload of the first motor31. Likewise, if the system transitions to the state wherein the rotational speed of the second motor32must be decreased because of an overload, then the control unit4decreases the rotational speed of the second motor32and increases the rotational speed of the first motor31, thereby supplementing the insufficient airflow of the second fan22while eliminating the overload of the second motor32.

Third Embodiment

As in the second embodiment, in fan overload avoidance control according to a third embodiment, to ensure sufficient airflow, control that increases the rotational speed—within a feasible range—of the fan that is not overloaded is performed.

FIG. 8is a flow chart of fan overload avoidance control according to the third embodiment. In step S31inFIG. 8, the microcomputer40determines whether the first fan21is overloaded. If an overload is detected, then the method proceeds to step S32; if an overload is not detected, then the method proceeds to step S36.

In step S32, the method decreases the rotational speed of the first fan21by the prescribed number of rotations and thereby eliminates the overload of the first fan21. In step S33, the method determines whether the rotational speed N1after the rotational speed of the first fan21has been decreased has fallen below a prescribed rotational speed Nc1. Here, the rotational speed that can oppose the dynamic pressure on the suction side of the adjacent second fan22is preset as the prescribed rotational speed Nc1; furthermore, if, after the reduction, the rotational speed falls below the prescribed rotational speed Nc1, then the overload of the first fan21will not be eliminated when the rotational speed of the second fan22is increased.

If the determination in step S33is YES, then the method proceeds to step S34, wherein the rotational speed of the second fan22is decreased by the prescribed number of rotations. The method determines the range of decrease of the rotational speeds of the first motor31and the second motor32based on the load state of the first fan21, and therefore the overload is eliminated early. Here, to prevent any excessive decrease in airflow, the range of decrease of the rotational speed of the second motor32, which is not overloaded, is restricted as much as possible, and therefore the range of decrease of the rotational speed of the first motor31and the range of decrease of the rotational speed of the second motor32are different values.

If the determination in step S33is NO, then the method proceeds to step S35, wherein the rotational speed of the second fan22is increased by the prescribed number of rotations, and thereby the reduced airflow is supplemented. The method determines the range of increase of the rotational speed of the second motor32based on the range of decrease of the rotational speed of the first motor31and the sum of the airflows demanded of the first fan21and the second fan22, which prevents any excessive decrease in airflow.

Furthermore, if an overload was not detected in step S31, then the method proceeds to step S36, wherein the method determines whether the second fan22is overloaded. If YES, then the method proceeds to step S37; if NO, then the method returns to START.

In step S37, the rotational speed of the second fan22is decreased by the prescribed number of rotations, which eliminates its overload. In step S38, the method determines whether the rotational speed N2after the rotational speed of the second fan22has been decreased has fallen below a prescribed rotational speed Nc2. Here, the rotational speed that can oppose the dynamic pressure on the suction side of the adjacent first fan21is preset as the prescribed rotational speed Nc2; furthermore, if, after the reduction, the rotational speed falls below the prescribed rotational speed Nc2, then the overload of the second fan22will not be eliminated when the rotational speed of the first fan21is increased.

If the determination in step S38is YES, then the method proceeds to step S39, wherein the rotational speed of the first fan21is decreased by the prescribed number of rotations. The method determines the range of decrease of the rotational speeds of the first motor31and the second motor32based on the load state of the first fan21, and therefore the overload is eliminated early. Here, to prevent any excessive decrease in airflow, the range of decrease of the rotational speed of the first motor31, which is not overloaded, is restricted as much as possible, and therefore the range of decrease of the rotational speed of the first motor31and the range of decrease of the rotational speed of the second motor32are different values.

If the determination in step S38is NO, then the method proceeds to step S40, wherein the rotational speed of the first fan21is increased by the prescribed number of rotations, which supplements the reduced airflow. The range of increase of the rotational speed of the first motor31is determined based on the range of decrease of the rotational speed of the second motor32and the sum of the airflows demanded of the first fan21and the second fan22, which prevents any excessive decrease in airflow.

In fan overload avoidance control according to the third embodiment as described above, the prescribed rotational speeds that can oppose the dynamic pressure on the suction side of the adjacent fan are preset; furthermore, to avoid an overload, the microcomputer40decreases the rotational speed of the fan that has become overloaded and, while doing so, increases the rotational speed of the adjacent fan if, even after decreasing its rotational speed, its rotational speed nevertheless exceeds the prescribed rotational speed; thereby, the reduced airflow is supplemented. Moreover, if the reduction in rotational speed causes the rotational speed to fall below the prescribed rotational speed, then the rotational speed of the adjacent fan is decreased.

<Features of the Third Embodiment

In this fan control system, if the system transitions to the state wherein the rotational speed of the first motor31must be decreased because of an overload, then the control unit4decreases the rotational speed of the first motor31; furthermore, when the rotational speed of the first motor31, whose rotational speed has been decreased, is lower than its prescribed rotational speed, the rotational speed of the second motor32is decreased; in addition, when the rotational speed of the first motor31, whose rotational speed has been decreased, is higher than its prescribed rotational speed, the rotational speed of the second motor32is increased. In other words, if the rotational speed of the first fan21is lower than its prescribed rotational speed, it is no longer possible to counter the dynamic pressure on the suction side of the second fan22, and therefore the rotational speed of the second fan22is decreased, which lowers the dynamic pressure on the suction side thereof. Moreover, if the rotational speed of the first fan21is higher than its prescribed rotational speed, then there is margin enough to rotate against the dynamic pressure on the suction side of the second fan22; therefore, the rotational speed of the second fan22is increased, which in turn supplements any decrease in airflow owing to the decrease in rotational speed of the first fan21.

Similarly, if the system transitions to the state wherein the rotational speed of the second motor32must be decreased because of an overload, then the control unit4decreases the rotational speed of the second motor32; furthermore, when the rotational speed of the second motor32, whose rotational speed has been decreased, is lower than its prescribed rotational speed, the rotational speed of the first motor31is decreased; in addition, when the rotational speed of the second motor32, whose rotational speed has been decreased, is higher than its prescribed rotational speed, the rotational speed of the first motor31is increased. In other words, if the rotational speed of the second fan22is lower than its prescribed rotational speed, it is no longer possible to counter the dynamic pressure on the suction side of the first fan21, and therefore the rotational speed of the first fan21is decreased, which lowers the dynamic pressure on the suction side thereof. Moreover, if the rotational speed of the second fan22is higher than its prescribed rotational speed, then there is margin enough to rotate against the dynamic pressure on the suction side of the first fan21; therefore, the rotational speed of the first fan21is increased, which in turn supplements any decrease in airflow owing to the decrease in rotational speed of the second fan22.

The first embodiment, the second embodiment, and the third embodiment explained exemplary cases wherein two fans are installed in the same air passageway, but the number of fans is not limited to two; rather, even in the case wherein there are numerous fans, all of the fans can be appropriately controlled by performing similar control.

INDUSTRIAL APPLICABILITY

According to the present invention as described above, when at least one fan of a plurality of adjacent fans becomes overloaded, it is possible to eliminate the overload without stopping that fan, which is useful in, for example, air conditioners and fan filter units that control a plurality of fans.