JPS6143951B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stably controlling the speed of an electric motor over a long period of time in electric motor speed control.

Conventionally, the most common method for controlling the speed of an electric motor is to use an amplifier to amplify the deviation between the analog speed command signal and the analog speed detection signal of the tachogenerator directly connected to the motor shaft, as shown in Figure 1. It is used to amplify and control the motor speed.

In FIG. 1, 1 is a speed command setter, 2 is a mixer, 3 is a control amplifier, 4 is a power amplifier, 5 is an electric motor, 6 is a tachogenerator, and 7 is a rectifying filter.

In this method, the control performance is determined by long-term fluctuations (drift) in the motor command voltage and drift in the voltage generated by the tachometer generator of the speed detector.

That is, no matter how high the gain is added to the amplifier to improve speed stability, it is impossible to correct the drift of the command and speed detector.

As a speed command power supply, an IC power supply can handle long-term fluctuations of about 1% of temperature fluctuations and power supply fluctuations, but a power supply that requires accuracy of 0.1% or more cannot be achieved with an IC power supply and requires a high It requires multiple circuit configurations using precision Zener diodes, high precision operational amplifiers, transistors, etc.
Economic efficiency is also extremely disadvantageous.

On the other hand, the most popular speed detector at present is the single-phase AC tachometer generator.
This temperature drift of the output voltage is general-purpose,
High accuracy of 0.05%/℃ is about 0.01%/℃.

Therefore, if a general-purpose tachogenerator is used, a drift of about 1.25% will occur when the ambient temperature fluctuates by ±25°C.

In this analog command analog feedback method, the stability of speed control in steady state is ±25
Generally, the change in temperature is about 2%.

In order to eliminate the speed drift caused by the drift of the command voltage and speed detection, a digital control loop is provided outside the analog speed control loop to achieve a driftless system, which is shown in FIG.

In FIG. 2, 8 is a speed command oscillator, 9 is a waveform shaper, 10 is a mixer, 11 is a deviation counter,
12 is a digital to analog (D/A) converter.

In this method, control that requires a fast response such as sudden changes in load is performed using analog control, and steady drift is corrected using digital control.The deviation between the number of command pulses and the number of feedback pulses is measured using a digital counter. (up-down counter) 11, and the counter output is converted into an analog quantity by a D/A converter 12, which is added or subtracted as a correction amount to the analog speed command/analog speed detection signal loop.

Furthermore, FIG. 3 shows a conventional device.

13 is a frequency to voltage (F/V) converter, 14 is a mixer, and 15 is an integrator.

This method converts the feedback frequency into a frequency voltage (F/
V) It is converted into an analog voltage through the converter 13, and the deviation from the command analog voltage is integrated and added as a correction amount.

The present invention aims to solve the drawbacks of the conventional circuit system shown in FIG. 3 and to provide a low-cost, high-performance circuit system.

By the way, the defects of the conventional circuit system shown in FIGS. 2 and 3 are as follows.

○A In Figure 2, the oscillator for the speed command relative to the analog command is required to have high precision (driftless).

○Yes In Figure 2, the analog command itself must be highly accurate.

Although the deviation counter 11 can be realized with a low-cost IC, the D/A converter is still generally expensive, as IC technology has been actively developed in recent years.

Therefore, even today when IC technology has advanced, the method shown in FIG. 2 is still expensive.

FIG. 3 shows a method that has been put into practical use as a lower-cost version of the method shown in FIG. 2, but the method shown in FIG. 3 also has the following drawbacks.

○ Analog commands must be highly accurate (driftless).

○ Frequency-voltage converter 13 is required to be highly accurate (driftless), which is not economical.

(○) The integrator 15 is a general-purpose operational amplifier that is inexpensive, so it is more advantageous than the D/A converter 12, but it is still expensive.

Now, FIG. 4 shows a block diagram showing the configuration of one embodiment of the present invention.

16 is a deviation integrator, which is formed by S ₁ and S ₂ , switches, C and C ₁ , capacitors, and R, resistor.
OP ₂ is an operational amplifier (forms an integrator with capacitor C ₁ ), 17 and 19 are sign inverters, 18 is a pulse distributor, and 20 is a variable resistor.

As described above, the present invention has the following features regarding the drift correction circuit provided outside the analog control circuit.

○The frequency of the AC tachogenerator (TG) 6 used for analog feedback is used as the feedback signal of the correction circuit, and the frequency of the tachogenerator 6 is determined by the number of poles of the tachogenerator 6 and is completely proportional to the rotation speed of the motor 6. relationship, and does not include any drift factors due to temperature changes.

○ As a method of converting the frequency into an analog signal, the constant voltage accumulated in the capacitor C is
The circuit system is simplified by moving the integrator capacitor C _I once per cycle by switching switches S ₁ and S ₂ .

○S When switch _S1 is on, the amount of charge stored in capacitor C (Q= _-Vs・C, where _Vs is the reference voltage) is made proportional to the analog command voltage _KVs , and the analog command voltage KV This prevents the motor speed from drifting due to the drift of _s .

○Se In the circuit system of this example, the speed of the motor is not affected by the drift of the analog command voltage, so it is possible to use a general-purpose IC power source as the command power source, which leads to low costs. be able to.

○The constant charge switch method is used as the frequency-current conversion circuit.

Conventional frequency-to-current converters add pulses with a constant pulse width and pulse peak value to an integrator, but the circuit system that maintains a constant pulse width and pulse peak value has many factors that can cause drift. , which required high precision.

In this example, the only causes of drift are temperature changes in capacitor C and temperature changes in resistor R.
This is overcome at low cost by using mica capacitors and metal film resistors. Herein lies the advantage of simplification of this embodiment, and it also has great industrial merits.

FIG. 6 is a block diagram of another embodiment of the invention.

_R1 to _R19 are resistors, _C2 to _C4 are capacitors, _D1 to _D3
diodes, OP ₁ to _{OP 4} are operational amplifiers, NOR ₁
~NOR ₄ is a NOR logic element, T ₁ is a pulse transformer,
20 is an adjustment resistor.

Junction as a switch element for S ₁ and S ₂
FET, CMOS Quad NOR for pulse distributor 18
Quad OP AMP (see FIG. 7b) is applied to the gate (see FIG. 7a), sign inverter, deviation integrator, and waveform shaping circuit.

Further, although the transformer _T1 is provided in relation to the rectifier circuit 9 of the analog control system, it is not necessarily required, and the variable resistor 20 for gain adjustment is also used because of the limitation of the amount of correction by the deviation integration circuit. It is not something that is essential.

Note that junction FETs were used for analog switches S ₁ and S ₂ , but these are MOSFETs and CMOS
A switch or the like may also be used.

Further, the operational amplifier is not limited to a Quad operational amplifier, and although the frequency of the AC tachogenerator 6 for analog feedback is used as the frequency signal, a pulse generator may be provided separately.

Now, the configuration and operating principle of one embodiment of the present invention shown in FIG. 4 will be explained.

The output frequency of the AC tachogenerator 6 is given by the following equation.

=P/2・_Nrpn /60 (1 formula) where _Nrpn is the motor rotation speed per minute P is the number of poles of the AC tacho generator.

Therefore, the frequency of the tachogenerator 6 does not include any drift factors and is completely proportional to the rotation speed of the electric motor 5.

The operation of the pulse distributor 18 in FIG. 4 is as shown in FIG.

That is, in a half cycle of the tachogenerator 6, the switch _S1 is turned on, the switch _S2 is turned off, and the command voltage power source _-Vs is connected to the capacitor C.

Therefore, the charge Q stored in the capacitor C at this time is given by the following equation.

Q=-V _s・C ... (2 equations) In the next half cycle, switch S ₁ is turned off and switch S ₂ is turned on, and the charge stored in capacitor C is transferred through the thermal point of operational amplifier OP ₂ , It is transferred to the integrating capacitor C _I.

According to the operational principle of operational amplifiers, the summing point (-) input terminal is always fixed at the potential of OV, so the average current applied to the input of operational amplifier _OP2 through switch _S2 is given by the following equation.

=ΔQ/ΔT=−V _s ·C·ff f is the frequency of the tachogenerator 6. Therefore, the output V ₀₁ of the operational amplifier OP ₂ is given by the following equation (R is a resistance).

V ₀₁ =-1/C _I ∫(KV _s /R-V _s Cf) dt……(4
(Equation) Therefore, the output voltage V ₀₂ of the analog correction amount is V ₀₂ = 1/C _I ∫ (KV _s / R - V _s Cf) dt... (Equation 5) When (Equation 5) is converted to Laplace, it becomes the following equation. Become.

V ₀₂ (s)=V _s /C _I RS{K(S)-RCf(s)} =V _s /C _I RS{K(S)-RC・K _N1 N _rpn (S
)} =V _s /T _I S {K(S)-K _N・N _rpn (S)} However, K _N = RC・K _N1 K _N1 = P/2・1/60 T _I = C _I R The block diagram of the control system shown in FIG. 4 is expressed as shown in FIG.

In this block diagram, when the steady deviation E ₁ (s) when the command K(S) changes in a stepwise manner is considered, the following equation holds true.

E ₁ (s) = V _s K (S) - V _s K _N N rpm (S)
... (Formula 7) E ₂ (s) = V _s · K (S) - K _F N _rpn (s) + E ₁ (s) · 1/T _I S ... (Formula 8) N _rpn = E ₂ (S)・A・K ₁ /1 + T _n S ... (Formula 9) From (Formula 7), (Formula 8), and (Formula 9), N _rpn (s) = [V _s K (s) - K _F N _rpn (s) +E ₁ (s) 1/T _I S〕・A・K ₁ /1+T _n S therefore, However, K ₁ and K _F are proportional constants, and T _n is the electric motor 5.
is the time constant of

The Laplace transform when the command changes _K0 in a stepwise manner is K(s) = _K0 /S...(Equation 11) The steady-state deviation at this time is determined by control theory (final value theorem).
is given by the following equation.

Therefore, the steady-state deviation is theoretically zero.

In other words, it is controlled so that KV _s =V _s K _N ·N _rpn (Formula 13) K=K _N ·N _rpn (Formula 14).

As is clear from Equation (14), the rotation speed of the motor is controlled regardless of the reference (command) power source _Vs.

Therefore, a temperature drift in the power supply V _s does not cause a drift in the rotational speed.

From (Formula 6), K _N =R・C・P/2・1/60 (Formula 15), and since P is the number of poles of the motor, it is not a factor of drift.

Therefore, the cause of drift is due to capacitor C and resistor R, but if a mica capacitor is used, the drift will be around 20ppm/℃.
If a metal film resistor is used, a resistance of about 25 ppm/°C can be easily obtained, so in this example, the drift is 45 ppm/°C, 1125 ppm = 0.1125% for a temperature change of ±25°C, which is approximately It is possible to control the drift to 0.1%.

Thus, according to the present invention, it is possible to realize a motor speed control device with less drift and which is extremely economically advantageous, and it is believed that this invention will greatly contribute to the industrial field.

[Brief explanation of the drawing]

1 to 3 are schematic diagrams of a conventional device, FIG. 4 is a block diagram of an embodiment of the present invention, FIG. 5 is an explanatory diagram of its switching operation, and FIG. 6 is another embodiment of the present invention. 7a and 7b are schematic diagrams of the members to which the circuit is applied, and FIG. 8 is a control block diagram shown by the transfer function of the circuit of FIG. 4. 1... Speed command setter, 2, 10, 14... Mixer, 3... Control amplifier, 4... Power amplifier, 5
...Electric motor, 6...Tachogenerator, 7...Rectification filter, 8...Speed command oscillator, 9...Waveform shaper,
11... Deviation counter, 12... D/A converter,
13... F/V converter, 15... Integrator, 16...
... Deviation integrator, 17, 19 ... Sign inverter, 18
... Pulse distributor, 20 ... Variable resistor, C, C
_I , C ₂ to C ₄ ... Capacitor, D ₁ to _{D 3} ... Diode, NOR ₁ to _{NOR 4} ... NOR logic element, OP ₁ to OP ₄
...Operator amplifier, P ... Number of poles of motor, R
...Resistance, S ₁ , S ₂ ... Switch.

Claims (1)

[Scope of Claims] 1. A speed command setter that outputs an analog command voltage that commands the speed of a motor, which is a load, to which a voltage is applied from a constant voltage power supply; a mixer for supplying a differential voltage to a control amplifier; a control amplifier for outputting a voltage corresponding to the motor speed according to an input from the mixer; a means for driving the motor by using the output of the control amplifier via a power amplifier; A pulse generator that generates a pulse signal with a frequency proportional to the motor rotation speed; a means for converting the output of the pulse generator into a feedback voltage through a rectifying filter; a pulse distributor that outputs a first signal during a half cycle of the pulse signal and a second signal during the next half cycle of the pulse signal; and a pulse distributor that receives a constant voltage from a constant voltage wire and inverts the polarity of the voltage. a first sign inverter; a first switch that charges the capacitor with the output voltage of the first sign inverter with the first signal of the pulse divider; and a first switch that charges the capacitor with the output voltage of the first sign inverter with the first signal of the pulse divider; A deviation integrator consists of a second switch that discharges the charge and takes the deviation from the analog command voltage, and an integrator that integrates the deviation, and an analog correction voltage is sent to the mixer by reversing the polarity of the output voltage of the deviation integrator. An electric motor speed control device comprising: a second sign inverter that provides a second sign inverter;