JPS6042714B2 - Motor control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor control method, and more particularly to a motor control method. The present invention relates to a method of controlling a motor that controls output.

Motors that drive compressors commonly used in refrigerators and air conditioners require a very large torque when starting up, so a large starting current flows through them.

Therefore, although motors with a certain capacity are used in such motors, once the motor starts and reaches a steady state, the load is not very large, and the motor is forced to operate inefficiently with its remaining power. It's summery. Therefore, if the voltage applied to the motor is appropriately reduced in such a steady state, more efficient operation can be achieved. First, what is shown in FIG. 1 is a conventional motor control method.

The motor 1 is a single-phase induction motor, for example, 50H2, I
An OOV commercial frequency power supply AC is applied, and a triax 2 is inserted between the power supply AC and the motor 1, and the output of the control circuit 3 is connected to the gate terminal of the triax 2. The control circuit 3 controls the ``ON'' and ``OFF'' states of the triax 2 using input from the power factor detector 4 of the motor 1. That is, when starting the motor 1, the triax 2 is completely turned on and the power supply AC is directly connected to the motor 1.
However, when the motor 1 reaches a steady state and the power factor falls below a predetermined value, the control circuit 3 applies a predetermined voltage to the gate terminal of the triax 2, and the power The motor 1 is driven with a waveform as shown in FIG. 2 by changing the flow angle of the motor. According to the waveform shown in Figure 2, the peak value does not change, but the effective voltage decreases, so the slippage of motor 1 increases and the rotational speed decreases, but at that time, the load on motor 1 in the steady state increases. The effective voltage is decreased until the rotational speed becomes such that the torque matches the maximum torque generated by the motor 1. This allows efficient operation in a steady state, but the disadvantage is that the drive waveform of the motor 1 is not a sine wave but a waveform as shown in Figure 2, which causes the motor 1 to beat and generate noise. However, it also had the disadvantage that the amount of power saved was smaller than when the voltage of the sine wave was lowered. The present invention has been made in view of the above-mentioned points, and provides a method of controlling a motor in which the motor is driven with a simulated sine wave and is always operated in a state of maximum efficiency.

The present invention will be described in detail below with reference to the drawings. FIG. 3 is a block diagram showing an embodiment of the present invention, in which 5 is a rectifier circuit for rectifying commercial frequency power supply AC, Cl and C2 are electrolytic capacitors, 6 is a switching means, Dl and D2 are diodes,
8 is a control circuit, 9 is a motor, L is a coil, C is a capacitor, 10 is a power factor detector, and 11 is a rotation speed detector. The commercial frequency power supply AC is rectified by the rectifier circuit 5 and has a voltage of 1 V and 1 V.
is converted into a DC power source and charged into electrolytic capacitors C1 and C2. Switching means 6 and 7 are connected to the DC power supplies +■ and -V, respectively, and the outputs of the switching means 6 and 7 are connected together and connected to the coil L. For the switching means 6 and 7, for example, a POWERMOSFET, a transistor, or a turn-off SCR is used. Coil L and capacitor C form a smoothing circuit, and apply a smoothed voltage to motor 9. The motor 9 is a single-phase induction motor, for example, a capacitor motor, and one end is connected to the connection point between the coil L and the capacitor C, and the other end is connected to the connection point between the electrolytic capacitors C1 and C2 via the power factor detector 10. wired. The control circuit 8 is formed of, for example, a microcomputer, and inputs the signal from the rotation speed detector 11 and the signal from the power factor detector 10, performs predetermined processing, and switches the switching means 6 and 7 depending on the terminals Sl and S2. It is controlled alternately. Diodes Dl and D2 connected between the input and output of the switching means 6 and 7 are the limits of ringing when the switching means 6 and 7 are at 0FF.
FIG. 4 shows pulse waveforms output to terminals S1 and S2 of the control circuit 8.

These pulses are used to form a simulated sine wave that is applied to the motor 9, and the pulse interval from the rise of each pulse to the rise of the next pulse is all time T, and the pulse width is the same as that of the first pulse. The pulses are Alt, a2t, a3t, . . . Ant in order from the pulse to the n-th pulse. Al,
a2, a3...A. is a predetermined constant,
It is determined that the pulse width is increased in order from the 1st pulse, with the sweetest pulse being the maximum, and the pulse width is further decreased in order from the 1st pulse to the nth pulse, AKaKaK...a÷〉A
n-1>An. Further, t is a variable time, and is varied depending on the power factor and rotational speed that are input to the control circuit 8 together with the pulse interval T. Next, we will explain how to create a pseudo sine wave. When the pulse shown in FIG. 4 is applied to the switching means 6 outputted to the terminal S1, the switching means 6 operates at 4"0N only during the period when the pulse is outputted.
Therefore, as shown in FIG. 5, a DC power supply +V having the same pulse interval and the same pulse width as the terminal S1 is generated at the output of the switching means 6. When Ant is output to terminal S1, T
After a period of time, Alt is output to the terminal S2. Therefore, when the pulse shown in FIG. 4 is outputted to the terminal S2, the output of the switching means 7 generates a DC power source 12 with the same pulse interval and the same pulse width. These DC power supplies +■ and -■
The pulse output is smoothed into a pseudo sine wave as shown in FIG. 5 by a smoothing circuit formed by a coil L and a capacitor C, and is applied to the motor 9. The period of this pseudo sine wave is 2r1T, and the frequency is 112nT. Therefore, the frequency can be varied by changing T, and even if the frequency, that is, the pulse interval T is changed while keeping t constant, the effective voltage value will also change. FIG. 6 is a characteristic diagram of the motor 9, which is a single-phase induction motor shown in FIG.
, the vertical axis is torque and power factor.

V1 to V5 is the motor 9 when the effective voltage is changed to V1 to ■5.
The broken line shows the torque curve applied to the motor 9, and the dashed line shows the power factor. The torque loaded on the motor 9 is large at the time of startup, and decreases when the motor 9 begins to rotate and reaches a steady state. When the motor 9 is driven with the operating voltage V1 at startup, the motor 9 rotates, and when the synchronous speed, that is, the suberi S, approaches O, it enters a steady state at the rotation speed where the torque curve 1 and the applied torque match. The power factor is very poor, about tin%. Therefore, when controlling this, the rotation speed detector 11 detects that the steady state has been reached, and the execution voltage applied to the motor 9 is changed from 1 to V5.
When the rotation speed is lowered to 1, the rotational speed decreases and the maximum torque of the torque curve V1 matches the applied torque. That is, since the power factor is about 80% near the maximum torque, the control circuit 8 may perform control by changing the time t so that the power factor becomes about 80% using the power factor detector 10. Another method is to apply the effective voltage V1 at startup, and then gradually reduce it as V1 → V2 → V3 → V4 → V5 once the motor 9 starts rotating, so that the power factor is 8.
There is a method of lowering the effective voltage until it reaches about 0%. Still another method is to drive by lowering the starting frequency. When the frequency of effective voltage V1 in Fig. 6 is 50H
z, if only the frequency is reduced without changing the pulse width time t for obtaining the effective voltage V1, the effective voltage will also be reduced at the same rate. However, since the current flowing through the motor 9 becomes easier to flow as the frequency is lowered, the current does not change, but the starting torque becomes larger since the motor starts at a lower frequency. At startup, the pulse interval T and frequency are 30Hz.
30Hz, which was determined so as to be created without changing the time t
When a similar sine wave of
Decrease 0%. At this time, the control circuit 8 shortens the time t, lowers the effective voltage value, and controls the rotational speed so that the power factor becomes about 80%, that is, the rotational speed becomes the maximum torque at that frequency.
Furthermore, as the time t is shortened, the pulse interval T is shortened and the frequency is increased. Then, the effective voltage value increases slightly and the rotational speed of the motor 9 increases, exceeding the maximum torque at the increased frequency and the power factor becoming 80% or less. The power factor detector 10 detects this, and the control circuit 8 works to lower the effective voltage value. By continuously repeating the above operation and gradually increasing the frequency, the motor 9 is always driven at the maximum torque, and the power factor becomes high. When the rotation speed detector 11 detects that the rotation speed of the motor 9 reaches a predetermined rotation speed by increasing the frequency, the control circuit 8 stops increasing the frequency and causes the motor 9 to operate steadily. Any of the methods described above can be performed by being stored in the microcomputer of the control circuit 8, but in either method, the rotation speed and power factor are input, and the pulse interval T and time t are determined based on these. , and outputs pulses as shown in FIG. 4 to terminals S1 and S2 to create an approximate sine wave. FIG. 7 is a flowchart showing the method by which the control circuit 8 outputs pulses to the terminals S1 and S2, and this will be explained. First, when the power is turned on and the microcomputer of the control circuit 8 operates, the microcomputer first performs initial settings.

For initial settings, one of the control methods described above is set. For example, when the frequency is gradually increased, the pulse interval T is set to 30 Hz, and the time t for determining the pulse width is also set to a predetermined effective value. The voltage value is set inside the microcomputer, the memory M of the microcomputer is cleared, and the output terminal S1 is specified to start operation. First, it is determined whether the memory M is 0 or not, and if it is 0, an initially set pulse interval T is set in a timer provided inside the microcomputer. Next, Alt is calculated based on the initially set time t, and after outputting a pulse to the predetermined output terminal, ie, S1, for the Alt time, 1 is added to the memory M, and the timer indicates that “゜0N゛, that is, time T has elapsed. Determine. When the timer is ゜゜0N゜, the pulse interval T and time t are reset according to the initially set control method based on the power factor and rotation speed. If the memory M is 1 instead of 0, M = 1. Based on the determination, the reset pulse interval T is set in the timer in the same way as described above, and the A2t time pulse calculated based on the reset time t is output, and after adding 1 to the memory, the timer is set. Determine "゜0N", and when it becomes "゛゜0N", reset the pulse interval T and time t. By repeating the above operation until M=n, the pulse shown in FIG. 4 is output to the output terminal S1. Also, when the memory M becomes n or more, the memory M is cleared, and it is determined whether S1 was specified until now, but S2 was specified, and if it is S1, then S2 is specified, and if S2, S1 is specified. Specify. By repeating the above operations, the pulses shown in FIG. 4 are alternately outputted to S1 and S2 based on the power factor and rotation speed. As described above, according to the present invention, the motor is driven by the simulated sine wave formed by the pulses output from the control circuit, so there is no beat, and the motor is driven by the simulated sine wave formed by the pulses output from the control circuit. is formed based on the power factor and rotational speed, so the motor is always driven in a state of maximum efficiency, which greatly reduces power consumption and downsizes the motor.

Furthermore, by using a microcomputer in the control circuit, the circuit can be simplified and its reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example, FIG. 2 is a drive waveform diagram of the conventional example shown in FIG. 1, FIG. 3 is a block diagram showing an embodiment of the present invention, FIGS. 4 and 5 3 is a waveform diagram of the embodiment shown in FIG. 3, FIG. 6 is a characteristic diagram of the motor shown in FIG. 3, and FIG. 7 is a flowchart showing the operation of the embodiment.

Claims (1)

[Claims] 1. A motor control method that detects the rotational speed, power factor, etc. of a motor and varies the effective voltage value applied to the motor, which includes switching means provided respectively at a positive terminal and a negative terminal of a DC voltage; It includes a smoothing circuit that smoothes the output of the switching means and supplies it to the motor, and a control circuit that controls the switching means. A pulse train consisting of a predetermined number is applied to the switching means by setting a certain pulse interval and pulse width and outputting a pulse having the set pulse width each time the set pulse interval is measured by a timer means. . A method for controlling a motor, characterized in that a positive voltage or a negative voltage outputted in a pulse form from the switching means is converted into an approximate sine wave by the smoothing circuit and applied to the motor.