JPS6042715B2 - Motor control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor control method, and particularly to a motor control method that detects the rotational speed or rate of rotation of the motor, and controls the output of the motor by varying the effective voltage value applied to the motor. Regarding the method.

The motors that drive the compressors typically used in refrigerators and air conditioners require very similar torque when starting up, and a very large starting current flows through them.

Therefore, a motor with a certain capacity is used for such a motor, but once the motor starts and reaches a steady state, the load is not very large, and the motor has surplus power to perform inefficient movements. I am doing it. Therefore, if the voltage applied to the motor is appropriately reduced in such a steady state, more efficient operation can be achieved. FIG. 1 shows a conventional motor control method.

The motor 1 is a single-phase induction motor, for example, 50H2, I
An OOV commercial frequency power supply 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 ``ON'' and ``OFF'' 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 AC is directly applied to the motor 1, and the power is sufficiently supplied to obtain a large torque.
When the motor 1 is in a steady state and the power factor is below a predetermined value, the control circuit 3 applies a predetermined voltage to the gate terminal of the triax 2, changes the flow angle of the power supply AC, and generates a waveform as shown in FIG. to drive motor 1. According to the waveform shown in Fig. 2, the peak value does not change, but the effective voltage decreases, so the slippage of the motor 1 increases and the rotation speed decreases.
At that time, the effective voltage is decreased until the rotational speed becomes such that the torque loaded on the motor 1 and the maximum torque generated by the motor 1 in a steady state match. This allows efficient operation in a steady state, but since the drive waveform of the motor 1 is not a sine wave but a waveform as shown in Figure 2, the motor 1 may beat and cause noise. There was also a drawback that the amount of power saved was smaller than when dropping the voltage of the sine wave. 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 book diagram showing an embodiment of the present invention, in which 5 is a rectifier circuit for rectifying a commercial frequency power supply AC, Cl and C2 are electrolytic capacitors, 6 and 7 are switching means, Dl and D2 are diodes, and 8 is a rectifier circuit for rectifying a commercial frequency power supply AC. The control circuit includes a motor, L a coil, C a capacitor, 10 a power factor detector, and 11 a rotation speed detector. The commercial frequency power supply AC is rectified by the rectifier circuit 5 to +■ and -■
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 sources +■ and 1, 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 linking limiters 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,a
2, a3...An is a predetermined constant, and the pulse width is increased in order from the first pulse, with the sweetest pulse being the maximum, and then the pulse width is increased in order from the ζth to the nth pulse. It was decided to make it smaller, a1 × A2 × A3 × ... a ■
〉a Kano 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 condensed 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 is at 60N only during the period when the pulse is outputted.
As shown in the figure, a DC power source +■ 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, after T time, terminal S
Alt is output to 2. Therefore, when the pulse shown in FIG. 4 is outputted to the terminal S2, a DC power source -V having the same pulse interval and the same pulse width is generated at the output of the switching means 7. The pulse outputs of these DC power supplies +V and 12 are smoothed into a similar sinusoidal wave as shown in FIG. 5 by a smoothing circuit formed by a coil L and a capacitor C, and are applied to the motor 9. The period of this approximate sine wave is 2r1t, and the frequency is 1/211T. Therefore, the frequency can be varied by changing T, the effective voltage value can be varied by changing the pulse width, or t, and even if the frequency, or pulse interval T, is changed while t is constant, the effective voltage value remains the same. changes. 6th
The figure shows motor 9, which is the single-phase induction motor shown in Figure 3.
, where the horizontal axis is the slip S of the motor 9, and the vertical axis is the torque and power factor.

■1~V5 is the effective electric power ■Motor 9 when changed from ■1~■5
The broken line shows the torque curve applied to the motor 9, and the dashed line shows the power factor. The torque applied to the motor 9 is large at startup and gradually decreases when the motor 9 begins to rotate. When the motor 9 is driven at the operating voltage V1 at startup, the motor 9 rotates, and when the synchronous speed, that is, the suberi S, approaches O, the motor 9 enters a steady state at a rotation speed where the torque curve V1 and the applied torque match. The power factor decreases to about 58%, resulting in poor efficiency. Therefore, if the effective voltage is lowered to V5 by applying it to the motor 9, the rotational speed decreases along the load torque curve, and a steady state is reached at the rotational speed of the maximum torque at (5). Near this maximum torque, the power factor is 8.
It is approximately 0%, and is operated at relatively high efficiency. Therefore, efficient operation is possible by controlling the effective voltage so that the rotational speed approaches the synchronous speed and the power factor becomes about 80%. Although this method applies to the steady state, it can also be applied after the motor 9 is started until the steady state is reached. That is, the frequency applied to the motor 9 is lowered and driven at startup, and the frequency is gradually increased until a predetermined number of rotations is reached, and the above-described control is performed for each frequency. For example, if the frequency of the effective voltage V1 in FIG. 6 is 50 Hz, if only the frequency is decreased without changing the pulse width time t for obtaining the effective voltage V1, the effective voltage will also decrease at the same rate. However, the current flowing through the motor 9 becomes easier to flow as the frequency is lowered, so the current does not change, but since the motor 9 is started at a lower frequency, the starting torque becomes larger. When the pulse interval T is determined to have a frequency of 30 Hz at startup, and a 30 Hz simulated sine wave created without changing the time t is applied to the motor 9, the motor 9 begins to rotate and generates the maximum torque at 30 Hz. If it exceeds that, the power factor will be 80%. decrease. At this time, the control circuit 8 short-circuits the time t to lower the effective voltage value and control the rotation 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 is. The rotation speed of the motor 9 increases slightly, exceeding the maximum torque at the higher frequency, and the power factor becomes 8.
It becomes 0% 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 operations and gradually increasing the frequency, the motor 9 is always driven at the maximum torque and the power factor becomes high. When the rotational speed detector 11 detects that the rotational speed of the motor 9 reaches a predetermined rotational 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 carried out 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 calculated based on these. is determined, and pulses as shown in FIG. 4 are output 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.

The initial settings are set to one of the control methods described above,
For example, when increasing the frequency gradually, set the pulse interval T to 30 Hz, set the time t for determining the pulse width to a predetermined effective voltage value, and then The computer's memory M is cleared and the output terminal S1 is specified to start the 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, that is, S1, for the Alt time, the memory M
1 is added to , and it is determined that the timer is ゜゛ON゛, that is, time T has elapsed. When the timer reaches "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.When the memory M is no longer 0, it is determined by M=1. In the same way as above, set the reset pulse interval T in the timer, output the A2t time pulse calculated based on the reset time t, add 1 to the memory, and then turn the timer on. When the pulse interval T and time t are determined and become ゜゜0N゛, the pulse interval T and time t are set again.By repeating the above operation until M=n, the pulse shown in Fig. 4 is outputted to the output terminal S1. .
Also, when memory M becomes n or more, memory M is cleared,
It is determined whether S1 has been specified until now, but S2 has been specified, and if S1 is specified, then S2 is specified, and if S2 is specified, S1 is specified. 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 approximate sine wave formed by the pulses output from the control circuit, so there is no beat, and the approximate sine wave that drives the motor is Since the motor is formed based on the power factor and rotation speed, the motor is always driven in a state of maximum efficiency, and the power consumption is greatly reduced and the motor is miniaturized. 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 this embodiment. 5... Rectifier circuit, 6,7... Switching means, 8... Control circuit, 9... Motor, 10... Power factor detection 11...Rotation speed detector.

Claims (1)

[Claims] 1. In a motor control method that detects the rotation speed, power factor, etc. of a motor and varies the effective voltage value applied to the motor, a switching means provided at a positive terminal and a negative terminal of a DC voltage; Set the pulse interval and pulse width, which are time variables, according to the motor rotation speed and power factor, etc.
a control circuit that alternately applies a pulse train consisting of a predetermined number to each of the switching means by outputting a pulse having the set pulse width every time a set pulse interval is measured by the timer means; The control circuit includes a smoothing circuit for smoothing a positive voltage or a negative voltage outputted in a pulse form from the means to create a condensed sine wave and applying it to the motor, and the control circuit generates a signal with a lower frequency and lower effective power than in a steady state when starting the motor. The pulse interval and pulse width are set to predetermined values in order to drive the motor with a voltage value, and when the motor is started, the frequency of the approximate sine wave gradually increases according to the rotation speed and power factor. A method for controlling a motor, characterized in that the pulse interval is set short so that the effective voltage value decreases, and the pulse width is set in a direction in which an effective voltage value decreases.