CN111258346A - Control Method to Overcome Motor Speed Overshoot - Google Patents

Abstract

The present invention relates to the technical field of electric motors, in particular to a control method for overcoming motor speed overshoot, which includes the following control process: a host computer sends a start command to a controller; the controller receives the start command of the host computer, and controls a frequency converter to drive the motor through a CAN bus The pressure sensor at the water outlet of the pump feeds back the water pressure value to the controller; the controller adopts the following algorithm to control the inverter to drive the motor and the water pump through the CAN bus according to the feedback signal of the pressure sensor, so as to adjust the pressure of the water pump; Its calculation formula is uout(t)=uout(t‑1)+Δu(t); Δu(t)=Kp(t)×[e(t)+e(t‑1)]+Ki(t)× e(t)+Kd(t)×[e(t)‑2×e(t‑2)+e(t‑1)]. The method provided by the invention overcomes the problem of pressure overshoot caused by rotational speed fluctuations, significantly improves the stability of the regulating pressure, and ensures the water supply with a stable flow of the water pump.

Description

Control Method to Overcome Motor Speed Overshoot

technical field

The invention relates to the technical field of electric motors, in particular to a control method for overcoming the overshoot of the motor speed.

Background technique

When the water pump is working, the controller controls the inverter to drive the motor and the water pump through the CAN bus according to the starting command and the pressure setting value of the host computer, and uses the feedback value of the high-pressure water pressure as the feedback signal to continuously adjust the frequency setting value on the CAN bus. , and then adjust the pressure value of high-pressure water. The PID algorithm selected by the controller is currently the most widely used control algorithm in the industrial field. It has the advantages of simple principle, easy implementation, wide application, independent control parameter pairs, and relatively simple parameter selection. PID control (ie proportional-integral-derivative control) uses the input parameter information and configuration information to carry out PID operation. According to the expected value (Expect), the current value (Current) and the proportional coefficient (Kp), integral coefficient (Ki), and differential coefficient (Kd) of the PID, carry out the latest N sampling operations and corrections, and finally output the results to the execution unit. The purpose is to make the results approach the expected value (Expect). It can be proved theoretically that PID algorithm is an effective method for dynamic quality correction of continuous system.

Usually, according to the corresponding relationship between the controller output and the actuator, the basic digital PID algorithm is divided into two types: positional PID and incremental PID. Incremental PID means that the output of the digital controller is only the increment Δu(t) of the control quantity. When the incremental algorithm is used, the control value Δu(t) output by the computer corresponds to the increment of the current actuator position, rather than the actual position of the corresponding actuator. Therefore, the actuator must have the control value increment. Accumulation function can complete the control operation on the controlled object. The cumulative function of the actuator can be calculated using the formula u _out (t)=u _out (t-1)+Δu(t); Δu(t)=Kp×[e(t)+e(t-1)]+Ki× e(t)+Kd×[e(t)-2×e(t-2)+e(t-1)] is programmed to complete, the controller according to the actual high pressure water pressure value and input set pressure value as The input variable e(t), the frequency set value of the inverter sent by the controller on the CAN bus is the output variable u _out (t), which is calculated according to the incremental PID algorithm to adjust the pressure of the high-pressure water to approach the set value. Pressure value. However, the use of the above-mentioned incremental PID algorithm has the following problems: under a fixed set pressure value, due to the hysteresis of the CAN bus and the influence of the motor's moment of inertia, the system is prone to overshoot.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a control method for overcoming the overshoot of the motor speed, so that the water pump can realize constant pressure water supply.

The present invention is achieved through the following technical solutions:

A control method for overcoming motor speed overshoot, comprising the following control procedures:

——The host computer sends a start command to the controller;

——The controller receives the start command of the host computer, and controls the inverter to drive the motor and the water pump to work through the CAN bus;

——The pressure sensor at the water outlet of the pump feeds back the water pressure value to the controller;

——The controller adopts the following algorithm to control the inverter to drive the motor and the water pump through the CAN bus according to the feedback signal of the pressure sensor, so as to adjust the pressure of the water pump;

Its calculation formula is uout(t)=uout(t-1)+Δu(t);

Δu(t)=Kp(t)×[e(t)+e(t-1)]+Ki(t)×e(t)+Kd(t)×[e(t)-2×e(t) -2)+e(t-1)].

uout(t) - the output of the controller;

Δu(t)——increment;

e(t)——the input of the controller, which is often the difference between the set value and the controlled quantity, that is, e(t)=r(t)-c(t)), which is actually between the set pressure and the actual pressure difference;

Kp(t)——the proportional coefficient of the controller;

Ki(t)——the integral coefficient of the controller;

Kd(t)——the differential coefficient of the controller;

a(t)=|u(t)-u(t-1)|;

b(t)=|speed(t)-speed(t-1)|, speed is the motor speed;

c(t)=a(t)/b(t)

Kp(t)=Kp, c(t)<a;

Kp(t)=0, c(t)≥a;

Ki(t)=Ki, c(t)<a;

Ki(t)=0, c(t)≥a;

Kd(t)=Kd, c(t)<a;

Kd(t)=0, c(t)≥a;

Kp, Ki, Kd, a are constants found by experiments.

The beneficial effects of the present invention

The control method for overcoming the motor speed overshoot provided by the present invention, after applying the optimized PID algorithm to the constant pressure regulation, can overcome the pressure overshoot problem caused by the speed fluctuation, the stability of the regulation pressure is significantly improved, and the realization of Constant pressure water supply from the pump.

Description of drawings

1 is a schematic diagram of the system structure of the present invention;

Fig. 2 is the control flow schematic diagram of the present invention;

Detailed ways

A control method for overcoming motor speed overshoot, comprising the following control procedures:

——The host computer sends a start command to the controller;

——The controller receives the start command of the host computer, and controls the inverter to drive the motor and the water pump to work through the CAN bus;

——The pressure sensor at the water outlet of the pump feeds back the water pressure value to the controller;

——The controller adopts the following algorithm to control the inverter to drive the motor and the water pump through the CAN bus according to the feedback signal of the pressure sensor, so as to adjust the pressure of the water pump;

Its calculation formula is uout(t)=uout(t-1)+Δu(t);

Δu(t)=Kp(t)×[e(t)+e(t-1)]+Ki(t)×e(t)+Kd(t)×[e(t)-2×e(t) -2)+e(t-1)].

uout(t) - the output of the controller;

Δu(t)——increment;

e(t)——the input of the controller, which is often the difference between the set value and the controlled quantity, that is, e(t)=r(t)-c(t)), which is actually between the set pressure and the actual pressure difference;

Kp(t)——the proportional coefficient of the controller;

Ki(t)——the integral coefficient of the controller;

Kd(t)——the differential coefficient of the controller;

a(t)=|u(t)-u(t-1)|;

b(t)=|speed(t)-speed(t-1)|, speed is the motor speed;

c(t)=a(t)/b(t)

Kp(t)=Kp, c(t)<a;

Kp(t)=0, c(t)≥a;

Ki(t)=Ki, c(t)<a;

Ki(t)=0, c(t)≥a;

Kd(t)=Kd, c(t)<a;

Kd(t)=0, c(t)≥a;

Kp, Ki, Kd, a are constants found by experiments.

The invention is a PID algorithm based on constant pressure water supply control developed to adapt to the stable adjustment of pressure based on the deficiency of the incremental PID algorithm. This new PID algorithm based on pressure regulation is an improvement based on the incremental algorithm.

When using the incremental calculation method, under the condition of the set pressure value, due to the hysteresis of the CAN bus and the influence of the rotational inertia of the motor, the controller increases the frequency value on the CAN bus, and the motor speed does not increase or decrease. When the amount of water increases to a certain level, the speed of the motor increases greatly, which will cause a sudden and substantial increase in the pressure of the high-pressure water, and the system will appear overshoot.

Aiming at the problem of overshoot, the solution adopted is to compare the change rate a(t) of the control output frequency with the change rate b(t) of the motor speed within a certain time t, that is, c(t)=a(t)/ b(t), when c(t)≥a (a is the constant found in the experiment), the PID operation result is maintained, that is, the PID coefficient is zero; when c(t)<a, the PID operates normally according to the coefficient.

This algorithm makes the motor start slowly, and the frequency value calculated by the incremental PID will gradually increase after the actual speed of the motor reaches a certain value. In other words, the principle of this PID algorithm is that when the actual speed does not reach the set speed, in different speed change intervals, the increase of the speed will not appear overshoot. When the motor speed rises slowly, the frequency value of the PID calculation result slowly rises; when the motor speed rises rapidly, the PID calculation result also rises rapidly.

PID is the abbreviation of English words Proportion, Integral and Differentialcoefficient. PID adjustment is actually composed of three adjustment methods: proportional, integral and differential. Their respective functions are as follows:

1. Proportional adjustment: It is to respond to the deviation of the system in proportion. Once the system has deviation, the proportional adjustment will immediately produce adjustment to reduce the deviation. The proportional effect is large, which can speed up the adjustment and reduce the error, but if the ratio is too large, the stability of the system will decrease, and even cause the instability of the system.

2. Integral adjustment function: It is to make the system eliminate the steady-state error and improve the indifference. Because there is an error, the integral adjustment is carried out until there is no difference, the integral adjustment stops, and the integral adjustment outputs a constant value. The strength of the integral action depends on the integral time constant Ti. The smaller the Ti, the stronger the integral action. Conversely, if Ti is large, the integral effect is weak, and adding integral adjustment can reduce the stability of the system and slow down the dynamic response. The integral action is often combined with the other two regulation laws to form a PI regulator or a PID regulator.

3. Differential adjustment effect: The differential effect reflects the change rate of the system deviation signal, has predictability, and can predict the trend of deviation change, so it can produce an advanced control effect. Before the deviation is formed, it has been eliminated by the differential adjustment effect. Therefore, the dynamic performance of the system can be improved. If the differential time is properly selected, the overshoot can be reduced and the adjustment time can be reduced. The differential action has a magnifying effect on the noise interference, so too strong differential adjustment is not good for the system anti-interference. The differential action cannot be used alone, and needs to be combined with the other two regulation laws to form a PD or PID controller.

Comprehensive analysis of the above process, when designing the incremental PID operation formula, the motor speed conversion frequency b(t) and the PID output result frequency conversion rate a(t)=u(t)-u(t-1) are introduced; (t)=a(t)/b(t) as a variable changes the coefficient of the PID operation. When c(t)≥a (a is the constant found by the experiment), the PID coefficient is zero; when c(t)<a, the PID operates according to the coefficient recovery constant.

Experiments show that this algorithm effectively solves the overshoot of the control output and realizes the constant pressure water supply of the pump.

To sum up, the control method for overcoming the motor speed overshoot protected by the present application overcomes the pressure overshoot problem caused by the speed fluctuation, the stability of the pressure regulation is significantly improved, and the water supply with the stable flow of the water pump is ensured.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (1)

1. The control method for overcoming the overshoot of the rotating speed of the motor is characterized by comprising the following control processes:

the upper computer sends a starting instruction to the controller;

the controller receives a starting instruction of the upper computer and controls the frequency converter to drive the motor and the water pump to work through the CAN bus;

the pressure sensor at the water outlet of the water pump feeds the water pressure value back to the controller;

the controller controls the frequency converter to drive the motor and the water pump to work through the CAN bus by adopting the following algorithm according to the feedback signal of the pressure sensor, so that the pressure of the water pump is regulated;

the formula is uout (t) ═ uout (t-1) + Δ u (t);

Δu(t)＝Kp(t)×[e(t)+e(t-1)]+Ki(t)×e(t)+Kd(t)×[e(t)-2×e(t-2)+e(t-1)]。

uout (t) -the output of the controller;

Δ u (t) -delta;

e (t) -the input to the controller, often the difference between the set and controlled quantities, i.e. e (t) -r (t) -c (t)), the actual difference between the set and actual pressures;

kp (t) -the proportional coefficient of the controller;

ki (t) -the integral coefficient of the controller;

kd (t) -the derivative coefficient of the controller;

a(t)＝|u(t)-u(t-1)|；

b, (t) | speed (t) |, speed is the motor speed;

c(t)＝a(t)/b(t)

Kp(t)＝Kp，c(t)＜a；

Kp(t)＝0，c(t)≥a；

Ki(t)＝Ki，c(t)＜a；

Ki(t)＝0，c(t)≥a；

Kd(t)＝Kd，c(t)＜a；

Kd(t)＝0，c(t)≥a；

kp, Ki, Kd, a are constants found in the experiment.

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