Research on Constant Speed ​​Control System of DC Motor Phase-Locked Loop


Research on the constant-speed control system of phase-locked loop of DC motor in the first year of the knives of the knives and knives. Sun Guofu, Gu Qitai, Liu Xuebin, Tsinghua University, abstract, proposed the working principle of DC motor constant speed control similar to frequency synthesizer Phase-locked loop.
The working principle and design method of the basic structure of the phase-locked loop are introduced, and the experimental research is carried out.
Through the system, the DC torque motor with the open loop speed accuracy lower than) can be controlled, and the speed precision can be doubled. 0 Above Keyword Phase-Locked Loop DC Motor Constant Speed ​​Control Introduction Phase-locked loops are initially used in the electronics field to form high-precision frequency synthesizers to generate stable frequency signals. The basic structure is shown in the figure.
The main components include phase detector low-pass loop filter 助 (assist) and voltage-controlled oscillator gauss. The phase detector is used to compare the frequency and phase difference between the feedback signal and the reference frequency eight and output a deviation proportional to it. The voltage loop filter is used to suppress high frequency noise and to determine the dynamic characteristics of the system. The voltage controlled oscillator is used to generate the required high precision frequency signals.
The voltage controlled oscillator is replaced by a DC motor and its driving circuit, and the motor output speed is converted into a frequency signal and fed back to the phase detector by means of an encoder, thereby forming a phase-locked loop for the constant speed control of the DC motor. .
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The structure of the phase-locked loop is basically composed of the system structure and working principle. The system constitutes the phase detector and the loop filter. The system uses the Weigang-type digital phase detector.
It is a specially designed medium-scale trigger-type edge-triggered type digital frequency phase comparator whose output has no relationship with the harmonics and duty cycle of the input signal, and the phase difference between the reference signal and the feedback signal is two. In the range of two, there is a good linear relationship between the average output voltage and the signal phase difference.
The digital output of the day is converted to an analog voltage by a charge pump.
In addition, it also adds an op amp, which can easily form an active low-pass loop filter to filter out noise and high-frequency components in the error voltage, which is important for loop stability and system dynamics. effect.
Motor and its drive circuit The controlled object of this system is a split-type permanent magnet DC torque motor.
The motor has a fast response speed, good linearity, small torque fluctuation, and compact structure. It is a high-precision servo system actuator. Its rated voltage is the maximum no-load speed. The motor drive circuit is composed of a DC transistor amplifier circuit. The DC motor provides a drive current of sufficient power.
The photoelectric encoder type photoelectric encoder is used to convert the motor speed into a digital pulse sequence and feed it back to the phase detector.
It is mounted coaxially with the rotor of the motor and can output two square wave signals with X pulses per revolution. The phase difference between the two signals can be sent to the phase detector as a motor feedback pulse signal. It can also output a pulse per revolution. The signal is used as a reference for the starting position of the motor.
The principle of operation of the motor phase-locked loop system is to synchronize the feedback frequency signal with a given reference frequency signal.
The system adjusts the motor speed based on the frequency or phase difference between the two.
After the system enters the phase-locked state, the two frequencies are equal, and the phase is kept swinging back and forth within a small difference, so that the motor speed can be accurately synchronized to a given reference frequency.
Combined with the experimental principle circuit shown in the figure, fa several DC motor phase-locked loop constant speed control system research electrician technology magazine knife year second corpse two plants Meng k jade name A, 沂K apology sweat-like sighs charge pump spit hair The schematic circuit system principle circuit can describe its specific working process as follows: After the system is powered up, the motor starts to accelerate from the static state. Before the speed has not reached the given speed, the comparator output is high level. The output of the charge pump behaves as a high-resistance state to output some wide negative pulses, so that the terminal potential is reduced to the following. The power supply charges the integral capacitor, so that the voltage rises and the motor continues to accelerate.
If the motor speed has exceeded its given value, that is, when the comparator output is high, the high-resistance state outputs some wide negative pulses, and the base current is injected into the pin by the action of the charge pump. Discharge, causing the voltage to drop and the motor speed to slow down.
If the system is in the phase of phase identification, the system will phase-adjust the motor speed according to the phase difference between the feedback signal and the given signal. The specific adjustment process is as follows if the phase is delayed, it is high. The output string has a negative pulse whose falling edge and rising edge correspond to the falling edge of the sum, respectively, and the width of the low level is proportional to the phase difference between the sum.
The working process of the charge pump is similar to the case of several times, and the motor is accelerated to reduce the phase difference of the hysteresis.
If several phases lead, it is high, and the output string is negative pulse, and the width of the low level is proportional to the phase difference between the sum.
The working process of the charge pump is similar to that of the case, and the motor speed is slowed down to reduce the leading phase difference.
When several sums are in phase, and high level appears at the same time, and both show high impedance state, the filter integral capacitor is neither charged nor discharged, and remains constant, so that the motor speed is locked at the reference frequency fR and maintained with it. Synchronize.
System design and simulation According to the system block diagram shown in the figure, the open-loop transfer function of the system can be obtained as the potential constant of the motor, which is the electromechanical time constant of the motor.
The technical data provided by the manufacturer, combined with the system load, can be calculated as K. After the phase detector and motor are selected, the gain is determined.
Designers can only use the gain of the loop filter and motor drive circuit as design variables.
The influence of these two parameters on the system can be studied in many ways. We determine the specific values ​​of the two based on the filtering characteristics and the time domain indicators of the system control.
Compared with the general fixed filter, the phase-locked loop filter has its special feature that the phase-locked loop never has attenuating effect on the input frequency itself.
It only suppresses the white price of the input signal, so its design has independent prisoners.
In order to obtain better noise suppression effect, take the ruler, the knife price, ah, consider the feasibility of the actual system, take the drive circuit gain, the system open-loop frequency characteristics as shown in the curve.
The curve shows that the system is stable, but the phase margin is too small to meet the needs of practical applications.
For this purpose, a calibrating device is required.
For the sake of convenience, we introduce the active proportional differential link between the original system loop filter and the motor drive circuit. See the transfer function for the specific circuit. (In the formula, 3 is the price, thanks to its frequency characteristics as shown in the curve in the figure.
After the phase lead correction, the open-loop transfer function of the system becomes the angular rate. The open-loop frequency characteristic of the system is studied in the first phase of the DC motor phase-locked loop constant speed control system.
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The loop-opening frequency characteristics of the system after seven-pass correction are shown in the figure. After introducing the proportional differential correction device in the original system, the phase margin of the system is obviously improved, reaching the left and right.
The simulation curve of the unit step response of the closed-loop system is shown in the figure. The dotted line is the step response before correction, and the solid line is the corrected step response. The corrected transient response quality index of the system is obviously improved.
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Experimental study on the unit step response simulation curve of the time map system. In order to test the feasibility and actual control performance of the system, it is necessary to carry out experimental research.
According to the above circuit principle, we made the experimental circuit as shown in the figure and measured the motor speed in real time under the open-loop and closed-loop states of the phase-locked loop to compare the adjustment effect of the phase-locked loop control system on the motor speed. The measured number of revolutions is 5 degrees. The reference frequency given by the system is the corresponding motor speed. The figure shows the measured data of the motor speed, indicating the open loop condition, the closed loop of the image, the abscissa indicates the measured revolution, and the ordinate indicates Motor speed.
It can be calculated from the experimental data that in the open loop state, the motor speed accuracy is such that in the closed loop case, the speed accuracy can be increased by two orders of magnitude, reaching the field.
During the experiment, we found that the voltage amplification factor of the drive circuit should not be too large, otherwise the system will exhibit severe nonlinearity, which will reduce the control performance of the system. Secondly, a small capacitance in parallel with the loop filter resistor will make the phase-locked loop. The adjustment range tends to be stable, which is more conducive to the constant motor speed. In the experiment, the system is powered up to a constant speed (constant speed error is not more than 2)
Conclusion The phase-locked loop adjusts the motor speed according to the frequency or phase difference of the given signal and the feedback signal to ensure that the motor runs at an accurate speed without drifting due to temperature changes or component aging, thus making the motor long-term speed. The stability reaches the level of stability of the reference signal frequency.
The system uses the quartz crystal oscillator frequency division clock as the reference frequency, and its frequency accuracy and stability are very high, so the motor speed accuracy and stability are also very good. 0 It should be noted that the experimental results in this paper refer to the accuracy and stability of the motor operating cycle, and the instantaneous velocity in the week is not discussed in detail.
The DC motor phase-locked constant speed control system proposed in the paper has the advantages of low cost, simple structure, convenient adjustment and stable speed, which can meet the needs of high-precision applications.
If a programmable digital frequency counter is added to the feedback loop, the motor speed can be changed by changing its frequency division coefficient to form a high-precision DC motor stepped speed regulation system.
References Zhang Yusheng, Zhang Huining, Xing Jing.
Phase-locked loop frequency synthesizer.
Beijing Electronics Industry Press, touched the household account and the current division of the division, this division, Jia Tianji, as the intestines.
That is to say, the intestines praise this word down. Page 26 Electrotechnical magazine. The grounding and zero-connection protection system of the low-voltage power distribution system in the first phase of the knife can adopt the four-pole three-phase two-pole single-phase automatic switch to cut the phase line and cut the line at the same time.
The system is suitable for places where the environment is prone to single-phase grounding or fire and explosion. For example, the coal mine chemical plant textile factory can also be used in rural areas. In recent years, it has been gradually applied to important places such as emergency power supply hospital operating rooms in important buildings. And lighting system.
The above analysis of the advantages and disadvantages of various grounding forms and the applicable grounding method, the following analysis of how to use the leakage circuit breaker () D to select and configure the rated operating current.
The choice is to determine the safety margin of the shock energy (power time) selected at the end of the power distribution system.
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In the case of multi-level leakage protection, the upper rated operating current is the lower rated operating current, and the lower returnable time is the lower combined breaking time.
The normal leakage current of the system is less than the rated operating current. And a few.
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In the design and construction, the grounding method should be properly selected to prevent confusion, and the grounding should be mixed with zero to ensure the safety specification of electricity consumption.
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Beijing Machinery Industry Press, Zheng Zhengzhi.
Frequency synthesis.
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