JPH02131393A - Method of controlling single phase induction motor - Google Patents

Abstract

PURPOSE:To control the auxiliary winding current in each frequency and to stabilize the torque of a motor by changing the volume of current flowing to an auxiliary winding based on the frequency in the control system to control the rotating speed of the motor by changing the frequency of AC power. CONSTITUTION:In a single phase induction motor when its rotating speed is controlled by changing AC power supplied to this single phase induction motor having main and auxiliary windings, the volume of cur rent flowing to the auxiliary winding against the volume of current flowing to the main winding is caused to change based on the frequency of the AC power. The ratio of the current volume of the main winding to that of the auxiliary winding is adjusted so that always stabilized torque and high efficiency may be obtained based on the frequency of the AC power. Consequently, the torque reduction and drop in efficiency depending upon the frequency of the motor can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a control method for controlling the rotational speed of a single-phase induction motor, particularly when changing the frequency of alternating current power supplied to the motor.

(Example) Prior Art A conventional technology relating to a control method for a single-phase induction motor is described in Japanese Patent Application Laid-Open No. 63-73897. What is stated in this bulletin is
Using a variable voltage, variable frequency power supply, AC power of any frequency was supplied to the motor to control the rotation speed. In addition, a bypass circuit is installed to directly connect the commercial power supply to the motor, and when the motor is connected to a variable voltage or variable frequency power supply, the impedance element can be removed and widened. This enables constant torque operation in a wide frequency range.

(c) Problems to be Solved by the Invention In the conventional technology configured as described above, an impedance element (capacitor) is attached or removed.
At this time, the phase of the current flowing through the auxiliary winding changes, and around this cutting frequency, torque fluctuations occur in the motor, making it impossible to ensure constant torque operation.

In view of such problems, the present invention provides a control method that allows stable operating torque to be obtained at all times within a frequency variable range.

(2) Means for Solving the Problems The control method of the present invention is configured to control the rotational speed of a single-phase induction motor having a main winding and an auxiliary winding by changing the frequency of AC power supplied to the motor. In a single-phase induction stove machine, the ratio between the amount of current flowing in the main winding and the amount of current flowing in the auxiliary winding is changed based on the frequency of the AC power supplied. (*) Effect In this way, by changing the amount of current flowing through the auxiliary windings based on the frequency, the auxiliary winding currents at each frequency can be controlled to stabilize the motor torque and improve efficiency. .

(F) Example Hereinafter, an example using the control method of the present invention will be described based on the drawings. Figure 1 is a schematic diagram of the electrical circuit. In this figure, 1 is a single-phase induction motor, and a main winding 2 and an auxiliary winding 3 are arranged on a stator winding with an electrical angle shifted by 90 degrees. Reference numeral 4 denotes an operating (phase advance) capacitor connected to the auxiliary winding 3. Reference numeral 5 denotes a current limiting element (any device capable of controlling the flow rate, such as a triac) is connected to the auxiliary winding 3 so as to control the amount of current flowing therethrough. Note that 6 is a control terminal, and the amount of current flowing through the current limiting element 5 is adjusted by the voltage applied to this terminal. 7 and 8 are resistors and capacitors connected in series, which are connected in parallel with the current limiting element 5 to absorb transient changes that occur significantly when the current limiting element 5 operates.

Reference numeral 9 denotes a single-phase inverter circuit, in which a plurality of switching elements are periodically turned ON/OFF to convert DC power into desired AC power. 10 is a rectifying and smoothing circuit, which rectifies and smoothes the power supplied from the AC power supply 11 and outputs DC power to the single-phase inverter circuit 9.

No. 12 is an ON/OFF signal generating section, which controls ON/OFF of each switching element so that AC power having a frequency based on the frequency signal f is supplied to the electric motor 1. Reference numeral 13 denotes a current detector (such as a current transformer), which detects changes in the alternating current flowing through the motor 1. 1
4 is a buffer. Reference numeral 15 denotes a zero-crossing signal generating section, which determines the zero-crossing time from changes in the alternating current input via the buffer 14 and outputs a zero-crossing signal.

16 is an ignition signal generating section, and zero cross signal generating section 1
The amount of current flowing through the current limiting element 5 is controlled based on the signal from the current limiting element 5 and the frequency signal f. For example, if a triac (or phototriac) is used as the current limiting element 5, after T time (O≦T≦1
/2f (frequency)) for a time t, the current limiting element 5 starts energizing, thereby controlling the amount of current flowing through the auxiliary winding 3.

FIG. 2 is an explanatory diagram showing the conduction state of the current limiting element (trybook) 5 with respect to waveforms 17 and 18 showing changes in the alternating current voltage and alternating current applied to the motor 1. In this explanatory diagram, the left side is the current time, and the further to the right is the past time. Zero cross signal generator 1 for current waveform
After T time from the zero cross signal 19 outputted by TRIAC 6, current limiting element (TRIAC) 5 is kept open for t time.
The auxiliary winding 3 is energized. FIG. 3 is an explanatory diagram showing respective waveforms when AC power having a higher frequency than the AC power shown in FIG. 2 is supplied to the motor 1. Note that each range is the same as that shown in FIG.

In this way, the amount of current flowing through the auxiliary winding 3 is controlled by changing the energization time of the current limiting element 5 based on each frequency, so that the strength of the magnetic field generated from the main winding 2 and the strength of the magnetic field generated from the auxiliary winding 3 are always adjusted. This maintains an optimal balance with the strength of the magnetic field, stabilizing torque and improving efficiency.

Also, considering the change in internal impedance due to the frequency characteristics of the capacitor 4, 1! flows to the auxiliary winding 3! By setting the flow rate, it is possible to further achieve constant torque.

(G) Effects of the Invention The control method of the present invention is a single-phase induction motor having a main winding and an auxiliary winding. In electric motors, the amount of current flowing through the auxiliary windings relative to the amount of current flowing through the main windings is changed based on the frequency of the AC power, so stable torque and high efficiency can always be obtained based on the frequency of the AC power. It is possible to adjust the ratio between the amount of current in the main winding and the amount of current in the auxiliary winding. Therefore, by using the control method of the present invention, it is possible to suppress a decrease in torque and a decrease in efficiency depending on the frequency of the electric motor.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an electric circuit using an embodiment of the present invention, Figure 2 is an explanatory diagram showing the ON state of the triac corresponding to changes in the AC voltage and AC T current applied to the motor, and Figure 3. is an explanatory diagram when the frequencies are different, similar to FIG. 2. 1...Electric motor, 2...Main winding, 3...Auxiliary winding, 5...'\! t-flow limiting element.

Claims (1)

[Claims] (1) In a single-phase induction motor that controls the rotational speed of the motor by changing the frequency of AC power supplied to the single-phase induction motor that has a main winding and an auxiliary winding, the current that flows through the main winding. A control method for a single-phase induction motor, characterized in that the ratio between the amount of current flowing through the auxiliary winding and the amount of current flowing through the auxiliary winding is changed based on the frequency of supplied AC power.