JPS6156898B2 - - 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 filter circuit 5 enhances the low range,
The speed detection voltage signal, in which ripples in the high range have been reduced to a low level, 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 low-frequency feedback gain is inserted into the speed control loop has a small speed change in response to steady load torque changes, and a low response to disturbance torque. Speed fluctuation characteristics become better. 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 ripple signals of 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 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 ₂ ′, 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 ′, R ₆ ′ and capacitors C ₂ ′, C ₃ ′, and F ₂ ′ (s) = H ₂ ′・1/1+2K(S/ω _H )+(S/ _ωH ) ² ...
...(2) It has the following transfer function. Here, H ₂ ′=(R ₅ ′+R ₆ ′)/R ₆ ′, ω _H = 1/√
C ₂ ′C ₃ ′R ₃ ′R ₄ ′, K=ω _H /2・C ₃ ′・(R ₃ ′+R ₄ ′
- _C2'R3'R5 '/ _{C3'R6 '} ), and the corner angular frequency _ωH is selected _higher than _{ωL and ωN} . In addition, E _r1 ′, E _r2 ′
and _Vcc is the power supply. Therefore, the composite transfer function is becomes.

Each electric power 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, the side input terminals and output terminals of amplifiers 7 and 8 Since the terminal occupies five 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 be explained below based on illustrated embodiments.

FIG. 4 is a block diagram of one embodiment of the present invention. In the 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. The reference time width generator becomes the first level and becomes the second level after counting, the time width T _v corresponding to the speed obtained from the output AC signal of the frequency generator, and the reference time width T _r of the reference time width generator. and a time width comparator that compares the two and outputs a pulse-like signal with a time width corresponding to the difference between the two (T _v - _{T r} ). That is, when the speed is slow (T _v > T _r ), a current outflow signal with a time width of T _v - T _r is generated, and when the speed is fast (T _v < T _r ), a current outflow signal with a time width of T _r - T _v is generated. A current inflow signal with a time width is generated, and when the speed is equal to a reference value (T _v =T _r ), the output current remains 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. As a 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 V _cc are power supplies.

The compensation/filter circuit 9 connects a first resistor _R1 between input terminals a and b, and connects the b point to the amplifier 1.
A first capacitor C1 is connected between the output terminal c to which the output point of 0 is connected, and a first capacitor _C1 is connected between the point b and the amplifier
A second resistor R ₂ is connected between the side input point d, and between the side input point d and 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, and a third resistor R ₃ and a third capacitor C ₃ are connected in series between the side input point e and the output terminal c of the amplifier 10. It is constructed by connecting a fourth resistor R ₄ between the AC grounding point (power supply E _r in the figure), and 1/√ _{1 2 1 2} = ω _H (4) 1/C ₃ (R ₃ +R ₄ )=ω _L (5), it is set so that ω _L <ω _H /2 (6).

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

In DC and low range (low frequency range),
The impedance of capacitor C ₁ is large and is mainly fed back by capacitor C ₃ and resistors R ₃ and R ₄ . As a result, the amount of feedback decreases as the frequency component decreases, resulting in a low-frequency compensation characteristic that increases the gain in direct current and reduction.

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 resistors R ₃ and R ₄ 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=(R ₃ +R ₄ )/R ₄ .

On the other hand, in the high range (high frequency range), the third
The impedance of capacitor C ₃ becomes smaller than R ₃ + R ₄ , and capacitor C ₃ becomes equivalently short-circuited. As a result, the compensation/filter circuit 9
becomes a control source type low-pass filter that provides feedback through capacitor C ₁ and resistors R ₃ and R ₄ . 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 ₁ and R ₂ and capacitors C ₁ and C ₂ , and is calculated using equation (4) above. 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 ₄ )/R ₄ , K=
ω _H /2·C ₂ ·(R ₁ +R ₂ −C ₁ R ₁ R ₃ /C ₂ R ₄ ).

In addition, in the middle range (ω _L < ω < ω _H ), G(s)≒H=1+R ₃ /R ₄ (9), and by selecting the resistance ratio R ₃ /R ₄ , the necessary amplification can be achieved. gain can be obtained.

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

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 approximations (7), (8), and (9) no longer hold, so the frequency characteristics are quite different from those in Figure 5B. come. As a result, the configuration shown in FIG. 5A cannot 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 (10) is selected to improve the stability and controllability of speed control, and the fifth 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.

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 the motor speed detection is not limited to a frequency generator, and any type of motor can be used as long as it obtains an alternating current signal corresponding to the speed.

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

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional motor speed control device, Fig. 2 A and B are characteristic diagrams of the motor speed control device of Fig. 1, and Fig. 3 A and B are diagrams of the compensation circuit and filter in Fig. 1. Circuit configuration diagram and frequency characteristic diagram,
FIG. 4 is a block diagram of an embodiment of the present invention, and FIGS. 5A and 5B are diagrams showing an example of the configuration and frequency characteristics of a compensation/filter circuit used in the present invention. 1...Motor, 2...Frequency generator, 3...Speed detection circuit, 6...Motor drive circuit, 9...Compensation/filter circuit, 10...Amplifier, a...Input terminal, c...Output terminal , R ₁ , R ₂ , R ₃ , R ₄ ...resistor, C ₁ , C ₂ , C ₃ ... capacitor.

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; a motor drive circuit that amplifies and supplies drive power to the motor;
and the compensation/filter circuit has first and second resistors connected in series between the input terminal and the positive input point of the amplifier;
A first capacitor is connected between the connection point of the resistor and the output terminal connected to the output point of the amplifier, a second capacitor is connected between the positive input point of the amplifier and the AC ground point, and the second capacitor is connected between the positive input point of the amplifier and the AC ground point. A third capacitor and a third resistor are connected in series between the negative input point of the amplifier and the output terminal, a fourth resistor is connected between the negative input point of the amplifier and the AC grounding point, and the The values of the first, second, third, and fourth resistors are respectively R ₁ , R ₂ , R ₃ , and R ₄ , and the values of the first, second, and third capacitors are C ₁ , C ₂ , respectively. , C ₃ , and 1/√ _{1 2 1 2 =} ω _H 1 _/ C ₃ (R ₃ + R ₄ ) = ω _L. A motor speed control device characterized by: