JPH04344190A - Speed control method for single-phase capacitor motor - Google Patents

Abstract

PURPOSE:To provide a speed control method capable of conducting simply and at a low cost a wide and smooth speed control for a single-phase capacitor motor driving a fan, etc. CONSTITUTION:TRIAC connected in series between a single-phase capacitor motor 1 and its AC power supply is turned ON and OFF by the use of 1 cycle of power supply frequency as unit width, the ratio of ON and OFF intervals is controlled to a predetermined value, and the TRIAC is specified as photo- TRIAC 4 so as to conduct the potential insulation of a main power supply system and control system in a speed control system constitution. Further, a rectangular wave signal synchronized with the power supply frequency cycle is inputted to CPU 6 so that the CPU 6 is caused to conduct the preparation and operation of a required control signal for the TRIAC 4 by the use of the attribute of waveform edges of the rectangular wave signal and 1 cycle of the power supply frequency as unit width.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the speed of a single-phase condenser motor for driving a cooling fan of an air conditioner outdoor unit.

0002

[Prior Art] A conventional speed control method for a single-phase capacitor motor of this type involves providing a plurality of taps on the winding of the motor and using a relay circuit to select and switch the tap to which the power supply voltage is applied according to the required speed. How to change speed,
Alternatively, a continuous speed control method is known in which the voltage applied to the motor windings is adjusted by controlling the phase of the power supply voltage using a triac whose ignition is controlled by a trigger diode.

0003

[Problems to be Solved by the Invention] However, in the conventional speed control method as described above, for example, with respect to the above-mentioned winding tap changing method, the practical limit is to install three types of taps corresponding to three-stage speed switching. The speed adjustment must be rough, and the price increases due to the complicated structure of the motor.Furthermore, the relay circuit for switching the tap requires many parts and storage space within the device. Therefore, it was inevitable that the speed control device would become larger and more expensive. Furthermore, for example, regarding the method of controlling the phase of the power supply voltage using the triac, a complicated phase control circuit consisting of many analog circuit components is required, leading to an increase in the price of the speed control device. In view of the above, an object of the present invention is to provide a speed control method for a single-phase capacitor motor that enables continuous and wide-range speed adjustment and a simple and compact circuit configuration.

0004

[Means for Solving the Problems] In order to achieve the above object, the speed control method for a single-phase capacitor motor of the present invention includes the following steps:
A triac connected in series between a single-phase capacitor motor and its AC power source is turned ON and OFF with one cycle of the power frequency as a unit width, and the ratio between the ON and OFF widths is controlled to a predetermined value, and The triac is a phototriac to provide potential isolation between the main power supply system and the control system in the speed control system configuration, and a rectangular wave signal synchronized with the power frequency cycle is input to the CPU, and the CPU processes the rectangular wave signal. It is assumed that calculations are performed to count the waveform edges of the wave signal and to create a necessary control signal for the triac whose unit width is one cycle of the power supply frequency.

[0005]

[Operation] The output torque of a single-phase capacitor motor is proportional to the square of its applied voltage, and its speed is smaller than its synchronous speed, and is given as the speed at the point where the motor output torque and load torque coincide. Therefore, by appropriately changing the voltage applied to the motor to shift the point where both torques match, it is possible to change the speed of the motor to a predetermined value. Furthermore, instead of changing the amplitude of the alternating current voltage itself, the alternating current applied voltage is changed to such an extent that the speed pulsation does not pose a practical problem due to the inertia of the rotating part of the motor and the load. This can also be achieved by changing the ratio between the application (ON) period and the off-state (OFF) period of an AC voltage with a constant amplitude, within a range in which the AC voltage can be suppressed.

[0006] According to the above, the present invention changes and adjusts the ratio of ON and OFF periods of an AC applied voltage to a single-phase capacitor motor via a phototriac connected in series to its power supply path. Further, when determining the two periods, the two periods are determined using one cycle of the AC voltage as a unit width and a multiple thereof. In addition, as mentioned above, since the phototriac is used to isolate the potential between the main power supply circuit and the control circuit, the required control signal is TT.
Processing at L level becomes possible. Therefore, by performing edge counting of a rectangular wave input signal synchronized with the cycle of the power supply frequency and calculation of a predetermined period ratio in a CPU or the like, a predetermined value for both the ON and OFF periods with one cycle of the power supply frequency as a unit width can be determined. can be obtained easily and reliably. Furthermore, since the intermittent application of alternating current voltage to the motor according to the period ratio described above is repeated within an extremely short period of time compared to the inertia time constant of the rotating system including the motor and its load, the rotating system The velocity pulsation of is also extremely small.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to a circuit diagram of a single-phase capacitor motor speed control system shown in FIG. 1, and an operation waveform diagram of signals of various parts of the circuit shown in FIG. First, Figure 1
1 is a single-phase capacitor motor, which has a main winding and an auxiliary winding having a phase difference of 90 electrical degrees with respect to the main winding, and a capacitor 3 is connected in series with the auxiliary winding. It is something that is driven. Further, 2 is a fan, and 4 is a phototriac which is a bidirectional three-terminal thyristor to which the gate signal is optically transmitted. Furthermore, 5 is a power synchronization signal detection circuit, which includes a diode D, phototransistors P/TR,
It consists of resistors R2, R3, etc., and the single-phase power supply voltage Vac of the motor 1 (the example is AC100V, 50/60Hz
) and outputs a rectangular wave signal Sa only during the positive polarity period of the voltage. The signal Sa is input to the CPU 6, and the CPU calculates the ratio α of both ON and OFF command periods for the triac 4 with one cycle of the voltage Vac as a unit width [α=ON period width/(ON, OFF The sum of both period widths)] is calculated according to the speed command, and a control signal Sb according to the period ratio α is output. The signal Sb is applied to the light emitting element of the triac 4 via the buffer amplifier OA, and the triac is operated according to the period ratio α.
N, OFF to control intermittent power supply to the motor 1. Note that R1 is a current limiting resistor for the light emitting element circuit of the triac 4.

Next, the operating waveform diagram in FIG. 2 shows the power supply voltage Vac, the rectangular wave signal Sa, and the control signal Sb that changes the period ratio α to be specified according to the speed command. . In the case shown, the voltage Vac is 8
This shows the case where the ratio α is changed from 1/8 to 8/8 by taking the cycle as the period, that is, the sum of the above-mentioned ON and OFF period widths, and the frequency of the voltage Vac is set to 50Hz. Then, the power supply to the motor is 8/
This will be repeated every 50 seconds. This value is generally extremely small compared to the inertia time constant of the rotating system as a whole, and therefore the speed pulsation of the motor due to the intermittent power supply becomes extremely small.

[0009]

Effects of the Invention According to the present invention, a triac connected in series between a single-phase capacitor motor and its AC power source is turned ON and OFF using one cycle of the power frequency as a unit width, and The ratio is controlled to a predetermined value, and the triac is used as a phototriac to provide potential isolation between the main power supply system and the control system in the speed control system configuration, and a rectangular wave signal synchronized with the power frequency cycle is transmitted. The CPU calculates the waveform edges of the rectangular wave signal and generates a necessary control signal for the triac whose unit width is one cycle of the power supply frequency. Multi-stage, wide-range, and smooth speed control of a single-phase capacitor motor for driving can be performed with a simple and inexpensive control circuit configuration.

[Brief explanation of the drawing]

[Fig. 1] Circuit diagram showing an embodiment of the present invention

[Figure 2] Operation waveform diagram of signals of each part of the circuit in Figure 1

[Explanation of symbols]

1 Single phase capacitor motor 2
Fan 3 Capacitor 4 Phototriac 5
Power supply synchronization signal detection circuit 6
CPU OA Buffer amplifier P/TR Phototransistor R1 Resistor R2 Resistor R3 Resistor

Claims (3)

[Claims] Claim 1: A triac connected in series between a single-phase capacitor motor and its AC power supply is turned ON and OFF with one cycle of the power supply frequency as a unit width, and the ratio between the ON and OFF widths is controlled to a predetermined value. A speed control method for a single-phase capacitor motor, characterized in that: 2. The speed control method for a single-phase capacitor motor according to claim 1, wherein the triac is a phototriac, and potential isolation between the main power supply system and the control system in the speed control system configuration is performed. Speed control method for single-phase capacitor motor. 3. A speed control method for a single-phase capacitor motor according to claim 2, wherein a rectangular wave signal synchronized with a power supply frequency cycle is input to a CPU, and the CPU counts waveform edges of the rectangular wave signal and 1. A speed control method for a single-phase capacitor motor, characterized in that a calculation is performed to generate a necessary control signal for the triac whose unit width is one cycle of the power supply frequency.