JPS586077B2 - How to operate loads such as fans driven by electric motors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a load such as a fan or pump driven by an electric motor in which the load factor varies widely depending on the rotation speed.

When operating a load such as a fan or pump using an electric motor, when the fan condition is constant (for example, damper, stator vane, etc. are fully open), the input power of the load driving electric motor is proportional to the cube of the rotation speed, and as shown in Figure 1. The characteristics shown in OCA curve A are shown.

On the other hand, when keeping the motor at the rated speed and adjusting the load output with a damper etc. on the machine side to obtain the same air volume as at a certain rotation speed when the damper is fully open, the input to the motor is
This is as shown by the OBA line entry in the figure.

(Here, the OBA line is point B, which is the motor input when the damper is adjusted at the rated rotation speed to obtain the same air volume as when the damper is fully open at 80% of the rated speed, although the motor speed does not change when the damper is adjusted. It is depicted as shown in .

) As is clear from the figure, when it is desired to widely adjust the air volume (load output), it is more advantageous to control the motor rotation speed than to adjust the damper because the input power is greatly reduced.

However, when a synchronous motor is used as a load driving motor, the only way to control the speed of the synchronous machine is to control the input frequency. Input frequency control is most suitable for speed control, and in either case it is necessary to drive with a variable voltage and variable frequency inverter.

On the other hand, when using a variable voltage and variable frequency inverter, such variable power supplies usually have losses before and after the IO, so the input characteristics in that case are as shown in OFD line C in Figure 1, and the rated speed is If the power source is located nearby, the loss will increase on the contrary, and since variable voltage and variable frequency power sources are expensive, the equipment cost will increase and become unbalanced.

This invention has been made in view of the above points, and provides an energy-saving operation method for a load such as a fan driven by an electric motor whose load factor varies widely depending on the rotation speed, which is relatively low cost and can reduce input loss. This is what we provide.

In other words, for a load such as a fan whose load factor is determined by the cube of the rotation speed, if you install a variable voltage and variable frequency power supply that can drive up to 80% of the rated speed, for example,
Its capacity is 0.83 = 0.5 1, which means that half of the rated capacity can be used, and when the load changes widely, the fan input can be reduced in the shaded area in Figure 1, leading to significant energy savings. be.

In this case, at 80% speed or higher, mechanical means such as a damper or a silent blade adjustment are used to adjust the output of the load during constant speed operation, and as a result, the input characteristics become as shown by thick line 2 in FIG.

In this way, it is possible to significantly improve loss with a small capacity variable voltage and variable frequency power supply.

FIG. 2 is an electrical circuit diagram of an embodiment of the present invention based on the principle described above.

In Fig. 2, 1 is a commercial AC power supply, 2 is a variable voltage and variable frequency power supply that can control a partial range up to the motor's rated speed (for example, from 0 to 80% speed), 3 and 4 are switches,
Reference numeral 5 designates a crusher or squirrel cage induction motor, 6 a load such as a fan, and 7 a rotation angle detector of the motor or a finger speed generator.

For example, suppose that a synchronous motor is used as the load driving motor, and the variable power supply 2 has a capacity that can cover the load up to 80% speed, and the switch 3 is opened and the switch 4 is turned off up to 80% speed. The synchronous machine 5 is driven by the variable voltage and variable frequency power supply 2.

When an air volume of 80% speed or more is required, the damper etc. are closed and the synchronous machine 5 is placed under a light load, and the frequency of the variable power source 2 is increased to a speed slightly higher than the speed of the commercial power source.

At this time, the synchronous machine armature voltage is kept constant by the field control of the synchronous machine.

When the synchronous machine frequency reaches a point slightly higher than the commercial power supply frequency, the switch 4 is opened and the synchronous machine field is strengthened to match the commercial power supply voltage, and the frequencies of the commercial power supply 1 and the synchronous machine output are adjusted to the allowable value ( Switch 3 is turned on when the phases match within 1-2% deviation).

In this way, the synchronous machine input can be switched from the variable power supply 2 to the commercial power supply 1 without a large transient phenomenon.

When the air volume is required to be less than 80% speed again, switch switch 3.
When the synchronous machine 5 is opened, the speed of the synchronous machine 5 decreases, but at this time, the frequency of the variable power supply 2 is changed in synchronization with the signal of the rotation angle detector 7 of the synchronous machine, and synchronized with the output frequency of the synchronous machine 5. By operating the machine and turning on the switch 4 when the speed drops below 80%, the variable power supply 2 can be smoothly connected to the synchronous machine without causing excessive transient phenomena.

Similarly, when using a squirrel cage induction motor as a load driving motor, the switch 3 is opened and the switch 4 is turned on until the speed reaches 80%, and the induction motor 5 is turned on by the variable power supply 2.
to drive.

When an air volume greater than 80% is required, the switch 4 is opened and the switch 3 is closed to operate the induction motor at the rated speed, and the air volume is adjusted using a damper.

When the air volume less than the air volume equivalent to the 80-chi speed is required again,
When the switch 3 is opened, the speed of the induction motor decreases, but at this time, the frequency of the variable power source 2 is changed by the finger speed generator 7 to follow the rotational speed of the induction motor 5, and the speed becomes 80% or less. By turning on the switch 4 and gradually raising the voltage of the variable power supply to a desired value when the power supply is turned on, the variable power supply can be smoothly connected to the induction motor without causing an excessive transient phenomenon.

As described above, in a load operation system where the load factor of a fan, pump, etc. changes widely depending on the rotational speed of the motor, the present invention provides a variable frequency power source that can be used as a power source for driving the motor from a commercial power source or a partial capacity variable voltage source. When driving the load at a speed below the rated speed of the motor and in a first speed range near the rated speed, the motor is directly driven by the commercial power source and the load factor of the load is adjusted by mechanical means. , when driving the load in a second speed range that descends from the speed range, the motor is driven by a variable voltage and variable frequency power source whose output capacity is adjusted to correspond to the power consumption of the motor in the second speed range. Therefore, the capacity of the variable voltage and variable frequency power supply can be significantly reduced compared to the rated capacity of the motor, making it possible to significantly reduce the cost of the variable voltage and variable frequency power supply, and significantly reducing input loss. It is possible to perform extremely energy-saving operation.

[Brief explanation of the drawing]

Figure 1 explains the principle of this invention, and shows the input characteristics of the load driving motor when various air volume adjustment methods are used.
FIG. 2 is a bronc diagram showing an embodiment of the present invention. In the figure, 1 is a commercial power supply, 2 is a variable voltage, variable frequency power supply,
3 and 4 are switches, 5 is an electric motor, 6 is a fan, and 7 is a rotation angle detector or a finger speed generator.

Claims (1)

[Scope of Claims] 1. In a method of operating a load that is driven by an electric motor and in which the load factor is changed depending on the rotational speed of the electric motor, the first speed.
Commercial use when driving the above loads in the temperature range. When the electric motor is directly driven by a power supply and the load factor of the load is adjusted by mechanical means, and the load is driven in a second speed range that descends from the speed range, the consumption of the electric motor in the second speed range is reduced. A method of operating a load such as a fan driven by an electric motor, characterized in that the electric motor is driven by a variable voltage and variable frequency power supply whose output capacity is adjusted according to the electric power. 2. A method of operating a load such as a fan driven by the motor according to claim 1, wherein a synchronous motor is used as the motor. 3. A method of operating a load such as a fan driven by the motor according to claim 1, wherein a squirrel cage induction motor is used as the motor.