JPS6156897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor speed control device having low frequency compensation characteristics.

FIG. 1 shows a schematic configuration of a conventional motor speed control device. In the figure, a frequency generator 2 generates an AC signal corresponding to the rotational speed of a motor 1 whose speed is to be controlled (speed controlled) and inputs it to a speed detection circuit 3. The speed detection circuit 3 detects the speed of the motor 1 based on the alternating current signal of the frequency generator 2, and outputs an electric signal according to the speed. The compensation circuit 4 has a low frequency compensation characteristic that enhances low frequency components more than high frequency components, and greatly amplifies the direct current and low frequency components of the output signal of the speed detection circuit 3. The filter circuit 5 has low-pass filter characteristics and is designed to reduce ripples in high frequency components contained in the output signal of the compensation circuit 4. Compensation circuit 4
and the reduction is enhanced by the filter circuit 5,
The speed detection voltage signal with reduced high-frequency ripples is power amplified in the motor drive circuit 6 and supplies drive power to the motor 1.

In this way, a motor with low-frequency compensation characteristics in which a compensation circuit that increases the reduction feedback gain is inserted into the speed control loop has a small speed change in response to steady load torque changes, and a small speed change in response to disturbance torque. Fluctuation characteristics become good. Its characteristics are shown in Figures 2A and B. A in the same figure shows the frequency characteristic of the speed fluctuation with respect to the disturbance torque, which is approximated by a broken line.
The solid line X is the case with the compensation circuit 4, and the broken line Y
is the case where the compensation circuit 4 is not included. In addition,
ω _L is the corner angular frequency on the low band side, and ω _N is the corner angular frequency on the high band side. FIG. 2B shows the speed change with respect to steady load torque, where the solid line X shows the case with the compensation circuit 4, and the broken line Y shows the case with the compensation circuit 4.
This is the case when it does not have.

Also, the output signal of the speed detection circuit 3 is
In addition to fluctuations due to speed fluctuations, the ripple signal includes high frequency components such as ripples due to speed detection and ripples due to noise signals mixed in the AC signal of the frequency generator 2. As a result, in the absence of the filter circuit 5, the power supplied to the motor 1 by the motor drive circuit 6 varies according to the ripple signal, causing the motor 1 to vibrate at a high frequency. Furthermore, if the ripple signal is large, the stability of speed control of the motor 1 will be impaired. Therefore, it is desirable that the high-frequency cutoff characteristics of the filter circuit 5 be made steep.

For this purpose, conventionally, as shown in FIG. 3A, desired frequency characteristics have been obtained by using separate amplifiers 7 and 8 for the compensation circuit 4 and the filter circuit 5. In the same figure, the compensation circuit 4 includes an amplifier 7 and a resistor.
It is composed of R ₁ ′, R ₂ ′ and a capacitor C ₁ ′, and has a transfer function of F ₁ ′(s)=H ₁ ′·(1+ω _L /s) (1). Here, H ₁ ′=−
R ₂ ′/R ₁ ′, ω _L =1/C ₁ ′R ₂ ′.

The filter circuit 5 also includes an amplifier 8 and a resistor R ₃ ',
It is composed of R ₄ ′, R ₅ ′ and capacitors C ₂ ′, C ₃ ′, F ₂ ′ (s) = H ₂ ′・1/1+2K(s/ω _H )+(s/ω _H ) ² …
...(2) It has the following transfer function. Here, H ₂ ′=−R ₅ ′/R ₃ ′, ω _H = 1/√ ₂ ′ ₃ ′ ₄ ′ ₅
', K
= ω _H /2·C ₂ ′·(R ₄ ′+R ₅ ′), and the corner angular frequency ω _H is selected to be higher than ω _L and ω _N. Note that E _r1 ', E _r2 ' and Vcc are power supplies.

Therefore, the composite transfer function is becomes.

Each transfer function F ₁ ′(s), F ₂ ′(s) and
The frequency characteristic of the gain of F ₃ '(s) approximated by a polygonal line is shown in FIG. 3B. However, H ₁ ′=-1, H ₂ ′=-1
And so.

The broken line P in the figure is the transfer function of the compensation circuit 4.
F ₁ '(s), and the dashed line Q indicates the filter circuit 5.
is the transfer function F ₂ ′(s), and the solid line R is the composite transfer function F ₃ ′(s).

The composite transfer function F ₃ '(s) mentioned above is a very good one that amplifies the low-frequency components below ω _L and attenuates the high-frequency components above ω _H with a quadratic characteristic (-40 dB/dec). However, on the other hand, it has the following drawbacks.

(1) Since two amplifiers 7 and 8 are used,
The number of parts is large, the wiring is complicated, and the cost is also high.

(2) When the speed detection circuit 3, compensation circuit 4, filter circuit 5, and motor drive circuit 6 shown in Fig. 1 are configured with a monolithic IC and external components, Since the output terminal occupies four pins of a monolithic IC, it is not suitable for IC implementation.

Taking these points into consideration, the present invention combines low-frequency compensation characteristics (compensation circuit characteristics), high-frequency secondary attenuation characteristics (filter circuit characteristics), and mid-range gain settings into a single amplifier. The present invention provides a motor speed control device using the compensation/filter circuit thus realized. The present invention will also be explained below based on the illustrated embodiments.

FIG. 4 is a block diagram of one embodiment of the present invention. In the same figure, a frequency generator 2 generates an AC signal corresponding to the rotational speed of a motor 1, and a speed detection circuit 3 detects the speed of the motor 1 based on the AC signal of the frequency generator 2. Outputs an electrical signal. The speed detection circuit 3 uses a reference frequency generator that obtains stable clock pulses from a crystal oscillator, etc., and an AC signal from a frequency generator as a trigger signal, and starts counting from the time when the trigger is input. A reference time width generator that becomes the first level and becomes the second level after counting, a time width Tv corresponding to the speed obtained from the output AC signal of the frequency generator, and a reference time width Tr of the reference time width generator. The time width comparator compares the two and outputs a pulse-like signal with a time width corresponding to the difference (Tv-Tr) between the two. In other words, when the speed is slow (Tv>Tr),
A current outflow signal with a time width of Tv - Tr is generated, and when the speed is fast (Tv < Tr), a current inflow signal with a time width of Tr - Tv is generated, and when the speed is equal to the reference value (Tv = Tr). ), the output current is maintained at zero.

The output signal of the speed detection circuit 3 is input to the compensation/filter circuit 9, which enhances the low frequency component signal and sharply attenuates the high frequency component signal, smoothes the pulse signal of the speed detection circuit 3, and calculates the speed. The DC voltage is set accordingly. The output of the compensation/filter circuit 9 is power amplified by the motor drive circuit 6 and supplies drive power to the motor 1. the result,
The rotational speed of the motor 1 is controlled to be constant.

FIG. 5A shows a specific example of the configuration of the compensation/filter circuit 9. In the figure, 10 is an amplifier, and E _r and Vcc are power supplies.

The compensation/filter circuit 9 has a first resistor R ₁ between the input terminal a and the (inverting) input point b of the amplifier 10.
and the input point b on that side and the amplifier 10
Connect the first capacitor C ₁ between the output point c of
A second resistor R ₂ is connected between the output point c and the output terminal d of the amplifier 10, and the output terminal d is connected to the AC grounding point (a point that has the same AC potential as the grounding side of the power supply, and includes the power supply side). A second capacitor C ₂ is connected between the input terminal b and the output terminal d of the amplifier 10, and a third resistor R ₃ and a third capacitor C ₃ are connected in series between the side input point b and the output terminal d of the amplifier 10. 1/√ _{1 2 2 3} = ω _H ………(4) 1/C ₃ R ₃ = ω _L ………(5) When we set, ω _L <ω _H /2 ………(6) It is set as follows.

Here, first, the frequency characteristics of the compensation/filter circuit 9 will be explained.

The capacitance of the third capacitor C ₃ is made larger than the capacitance of the second capacitor C ₂ , and feedback is mainly provided by the capacitor C ₃ and the resistor R ₃ in direct current and low frequency range (low frequency range). the result,
The lower the frequency component, the smaller the amount of feedback, resulting in a low-frequency compensation characteristic that increases the gain in direct current and low frequencies.

FIG. 5B shows the frequency characteristics of the compensation/filter circuit 9 approximated by a broken line. According to the setting conditions of the above equation (6), the low-frequency corner angular frequency ω _L is approximately determined by the capacitor C ₃ and the resistor R ₃ , and is calculated by the equation (5). In the frequency range near and below ω _L , the transfer function can be approximately expressed as G(s)≈H·(1+ω _L /s) (7). Here, H= _-R3 / _R1 .

On the other hand, in the high range (high frequency range), the third
The impedance of capacitor C ₃ becomes smaller than resistor R ₃ , and capacitor C ₃ becomes equivalently shorted. As a result, the compensation/filter circuit 9
becomes a single feedback type low-pass filter fed back by capacitor _C1 and resistor _R3 . As shown in FIG. 5B, its characteristics become a low-pass filter with quadratic characteristics (-40 dB/dec). According to the setting conditions of equation (6), the high-frequency corner angular frequency ω _H is approximately determined by resistors R ₂ and R ₃ and capacitors C ₁ and C ₂ , and is calculated using equation (4).

In the frequency range near ω _H and above, the transfer function is approximately G(s)≒H・1/1+2K(s/ω _H )+(s/ω _H ) ² ...
…(8) Here, H=-R ₃ /R ₁ and K=ω _H /2·C ₁ ·(R ₂ +R ₃ ).

Furthermore, in the middle range (ω _L < ω < ω _H ), G(s)≒H=−R ₃ /R ₁ (9), and by arbitrarily selecting the resistance R ₁ , ω _L ,
The necessary gain can be obtained without changing ω _H and K. That is, the compensation/filter circuit 9
ω _L , ω _H , K, and H can be arbitrarily selected within the setting conditions of equation (6).

Therefore, the frequency characteristics of the compensation/filter circuit 9 as shown in FIG. 5A are good, having low-frequency compensation characteristics and high-frequency second-order attenuation characteristics as shown in FIG. 5B.

Next, the necessity of setting conditions for equation (6) will be explained. When the corner angular frequencies ω _L and ω _H are close to each other, the approximation equations (7), (8), and (9) no longer hold, so the frequency characteristic is quite different from that in Figure 5B. It's coming. As a result, the configuration shown in FIG. 5A does not provide desired characteristics. Furthermore, in motor speed control, if the corner angular frequency ω _L of low-pass compensation is close to the cut-off angular frequency ω _H of low-pass characteristics, the stability of motor speed control will be impaired. For these reasons, in order to obtain the desired gain and frequency characteristics with a single amplifier without impairing the stability of speed control, the setting condition of equation (6) is required.

In normal motor speed control, ω _H /50≦ω _L ≦ω _H /5 is selected within the range of (10) to improve the stability and controllability of speed control. It is desirable to reduce the mutual interference between the compensation characteristic and the secondary attenuation characteristic of the compensation/filter circuit 9 shown in FIG. A to improve the characteristic. There is also the advantage that selection of resistors R ₁ , R ₂ , R ₃ and capacitors C ₁ , C ₂ , C ₃ becomes easy.

In this way, if the compensation/filter circuit 9 shown in Fig. 5A is used, good frequency characteristics can be obtained with a single amplifier, so the number of components is small, and it is suitable for monolithic ICs. It has become a circuit with great industrial utility value.

Note that motor speed detection is not limited to a frequency generator, but any structure that can obtain an alternating current signal corresponding to the speed can be used.

Further, the speed detection circuit 3 described above may be constituted by, for example, a charge-hold-reset type frequency discriminator, which converts the AC signal of the frequency generator 2 into a DC voltage periodically corresponding to the frequency discriminator.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional motor speed control device, Figures 2A and B are characteristic diagrams of the motor speed control in Figure 1, and Figures 3A and B are the compensation circuit and filter circuit in Figure 1. Configuration diagram and frequency characteristic diagram, 4th
The figure is a block diagram of one embodiment of the present invention.
B is a configuration example diagram and a frequency characteristic diagram of a compensation/filter circuit used in the present invention. DESCRIPTION OF SYMBOLS 1... Motor, 2... Frequency generator, 3... Speed detection circuit, 6... Motor drive circuit, 9... Compensation/filter circuit, 10... Amplifier, a... Input terminal, d... Output terminal , R ₁ , R ₂ , R ₃ ...resistance,
C ₁ , C ₂ , C ₃ ... Capacitors.

Claims (1)

[Scope of Claims] 1. A speed-controlled motor, a speed detection means for obtaining an AC signal corresponding to the speed of the motor, and a speed detection means for detecting the speed of the motor based on the output AC signal of the speed detection means, and detecting the speed of the motor based on the output AC signal of the speed detection means. a speed detection circuit that outputs a corresponding electrical signal; a compensation/filter circuit that removes ripples from the output signal of the speed detection circuit and amplifies low frequency components including DC; comprising a motor drive circuit that amplifies and supplies drive power to the motor,
In the compensation/filter circuit, a first resistor is connected between the input terminal and the inverting input point of the amplifier, a second resistor is connected between the output point and the output terminal of the amplifier, and a first capacitor connected between the inverting input point and the output point of the amplifier;
A second capacitor is connected between the output terminal and the AC ground point, a third resistor and a third capacitor are connected in series between the inverting input point of the amplifier and the output terminal, and the The values of the first, second, and third resistors are respectively _R1 , _R2 , and _R3 , and the values of the first, second, and third capacitors are _C1 , _C2 , and _C3, respectively, When 1/√ _{1 2 2 3} = ω _H 1/C ₃ R ₃ = ω _L , the speed of the motor is characterized by including an active filter that satisfies ω _L <ω _H /2. Control device.