Control method for overcoming overshoot of motor speed

Abstract

The present invention relates to the technical field of electric motors, and particularly to a control method for overcoming overshoot of the rotational speed of an electric motor. The control process thereof includes the following steps: The host computer issues a start command to the controller; the controller receives the start command from the host computer and controls the frequency converter to drive the electric motor and the water pump to work through the CAN bus; the pressure sensor at the water outlet of the water pump feeds back the water pressure value to the controller; the controller controls the frequency converter to drive the electric motor and the water pump to work through the CAN bus by using the following algorithm according to the feedback signal of the pressure sensor, so as to adjust the pressure of the water pump; the 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 present invention overcomes the overshoot problem of pressure caused by rotational speed fluctuations, significantly improves the stability of pressure adjustment, and ensures the water supply with a stable flow rate of the water pump.

Description

Technical Field

[0001] The present invention relates to the technical field of electric motors, and particularly to a control method for overcoming overshoot of the motor speed. Background Art

[0002] When the water pump is working, the controller controls the frequency converter to drive the electric motor and the water pump to work according to the start instruction of the upper computer and the pressure set value through the CAN bus, takes the high-pressure water pressure feedback value as the feedback signal, continuously adjusts the frequency set value on the CAN bus, and then adjusts the pressure value of the high-pressure water. The controller selects the PID algorithm, which is one of the most widely used control algorithms in the industrial field at present. It has the advantages of simple principle, easy to implement, wide application range, independent control parameter items, and simple parameter selection. PID control (i.e., proportional-integral-derivative control) uses the input parameter information and configuration information for PID operation. According to the expected value (Expect), the current value (Current), and the proportional coefficient (Kp), integral coefficient (Ki), and derivative coefficient (Kd) of PID, the nearest N sampling operations and corrections are performed, and finally the result is output to the execution component. The purpose is to make the result approach the expected value (Expect). It can be theoretically proved that the PID algorithm is an effective method for correcting the dynamic quality of continuous systems.

[0003] Generally, according to the corresponding relationship between the controller output and the actuator, the basic digital PID algorithm is divided into two types: position-type PID and incremental-type PID. The incremental-type PID means that the output of the digital controller is only the increment Δu(t) of the control quantity. When using the incremental algorithm, the control quantity Δu(t) output by the computer corresponds to the increment of the position of the actuator this time, rather than the actual position of the actuator. Therefore, it is required that the actuator must have the function of accumulating the control quantity increment to complete the control operation of the controlled object. The accumulation function of the actuator can be completed by 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)] programmed. The controller uses the actual high-pressure water pressure value and the input set pressure value as the input variable e(t), and the frequency set value of the frequency converter sent by the controller on the CAN bus is the output variable u out (t), and calculates according to the algorithm of the incremental-type PID to adjust the pressure of the high-pressure water to approach the set pressure value. However, when using the above-mentioned incremental-type PID algorithm, the following problems occur: under the fixed set pressure value, due to the hysteresis of the CAN bus and the influence of the inertia of the motor, the system is prone to overshoot. Summary of the Invention

[0004] 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 achieve constant pressure water supply.

[0005] The present invention is realized through the following technical solutions:

[0006] A control method for overcoming the overshoot of the motor speed, which includes the following control processes:

[0007] - The upper computer sends a start command to the controller;

[0008] - The controller receives the start command from the upper computer and controls the frequency converter to drive the motor and the water pump to work through the CAN bus;

[0009] - The pressure sensor at the water outlet of the water pump feeds back the water pressure value to the controller;

[0010] - The controller controls the frequency converter to drive the motor and the water pump to work through the CAN bus according to the feedback signal of the pressure sensor, and adopts the following algorithm to adjust the pressure of the water pump;

[0011] The calculation formula is uout(t) = uout(t - 1) + Δu(t);

[0012] Δu(t) = Kp(t) × [e(t) + e(t - 1)] + Ki(t) × e(t) + Kd(t) × [e(t) - 2 × e(t - 2) + e(t - 1)].

[0013] uout(t) - The output of the controller;

[0014] Δu(t) - Increment;

[0015] e(t) - The input of the controller, often the difference between the set value and the controlled quantity, that is, e(t) = r(t) - c(t)), actually the difference between the set pressure and the actual pressure;

[0016] Kp(t) - The proportional coefficient of the controller;

[0017] Ki(t) - The integral coefficient of the controller;

[0018] Kd(t) - The differential coefficient of the controller;

[0019] a(t) = |u(t) - u(t - 1)|;

[0020] b(t) = |speed(t) - speed(t - 1)|, speed is the motor speed;

[0021] c(t) = a(t) / b(t)

[0022] Kp(t) = Kp, when c(t) < a;

[0023] Kp(t) = 0, when c(t) ≥ a;

[0024] Ki(t) = Ki, when c(t) < a;

[0025] Ki(t) = 0, when c(t) ≥ a;

[0026] Kd(t) = Kd, when c(t) < a;

[0027] Kd(t) = 0, when c(t) ≥ a;

[0028] Kp, Ki, Kd, and a are constants obtained through experiments.

[0029] Advantages of the present invention

[0030] The control method for overcoming the overshoot of the motor speed provided by the present invention, after applying the optimized PID algorithm to the constant pressure regulation, can overcome the overshoot problem of the pressure caused by the speed fluctuation, significantly improve the stability of the pressure regulation, and achieve the constant pressure water supply of the water pump. Description of the drawings

[0031] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0032] Figure 2 It is a schematic diagram of the control flow of the present invention; Detailed implementation manners

[0033] The control method for overcoming the overshoot of the motor speed includes the following control processes:

[0034] - The host computer sends a start command to the controller;

[0035] - The controller receives the start command from the host computer and controls the frequency converter to drive the motor and the water pump to work through the CAN bus;

[0036] - The pressure sensor at the water outlet of the water pump feeds back the water pressure value to the controller;

[0037] - The controller, according to the feedback signal of the pressure sensor, controls the frequency converter to drive the motor and the water pump to work through the CAN bus by using the following algorithm, thereby adjusting the pressure of the water pump;

[0038] Its calculation formula is uout(t) = uout(t - 1) + Δu(t);

[0039] Δu(t) = Kp(t) × [e(t) + e(t - 1)] + Ki(t) × e(t) + Kd(t) × [e(t) - 2 × e(t - 2) + e(t - 1)].

[0040] uout(t) - Output of the controller;

[0041] Δu(t) - Increment;

[0042] e(t) - Input of the controller, often the difference between the set value and the controlled quantity, i.e., e(t) = r(t) - c(t)), actually the difference between the set pressure and the actual pressure;

[0043] Kp(t) - Proportional coefficient of the controller;

[0044] Ki(t) - Integral coefficient of the controller;

[0045] Kd(t) - Differential coefficient of the controller;

[0046] a(t) = |u(t) - u(t - 1)|;

[0047] b(t) = |speed(t) - speed(t - 1)|, where speed is the motor speed;

[0048] c(t) = a(t) / b(t)

[0049] Kp(t) = Kp, when c(t) < a;

[0050] Kp(t) = 0, when c(t) ≥ a;

[0051] Ki(t) = Ki, when c(t) < a;

[0052] Ki(t) = 0, when c(t) ≥ a;

[0053] Kd(t) = Kd, when c(t) < a;

[0054] Kd(t) = 0, when c(t) ≥ a;

[0055] Kp, Ki, Kd, and a are constants obtained through experiments.

[0056] Based on the deficiencies of the incremental PID algorithm, the present invention is a PID algorithm based on constant pressure water supply control developed to adapt to the stable regulation of pressure. This new PID algorithm based on pressure regulation is an improvement based on the incremental algorithm.

[0057] 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 motor inertia, when the controller increases the frequency value on the CAN bus, the motor speed does not increase or decrease. When the cumulative frequency increases to a certain extent, the motor speed increases significantly, which will cause a sudden large increase in the high-pressure water pressure, and the system will exhibit overshoot.

[0058] For the overshoot problem, the solution is as follows: within a certain time t, compare the change rate a(t) of the controlled output frequency with the change rate b(t) of the motor speed, that is, c(t) = a(t) / b(t). When c(t) ≥ a (a is a constant obtained through experiments), the PID operation result remains unchanged, that is, the PID coefficient is zero; when c(t) < a, the PID operates normally according to the coefficient.

[0059] This algorithm makes the frequency value calculated by the incremental PID wait until the actual speed of the motor reaches a certain value before gradually increasing when the motor starts slowly. In other words, the principle of this PID algorithm is that during the process when the actual speed has not reached the set speed, within different speed change intervals, the speed will not overshoot. When the motor speed rises slowly, the frequency value of the PID calculation result rises slowly; when the motor speed rises rapidly, the PID calculation result will also rise rapidly.

[0060] PID is an abbreviation of the English words Proportion, Integral, and Differential coefficient. PID regulation is actually composed of three regulation methods: proportion, integral, and differential. Their respective functions are as follows:

[0061] 1. Proportional regulation function: It responds to the deviation of the system proportionally. Once a deviation appears in the system, the proportional regulation immediately generates a regulation effect to reduce the deviation. A large proportional action can accelerate the regulation and reduce the error. However, an excessive proportion will reduce the stability of the system and even cause the system to become unstable.

[0062] 2. Integral regulation function: It enables the system to eliminate the steady-state error and improve the degree of no-error. Because there is an error, the integral regulation will proceed until there is no error, and then the integral regulation stops, and the integral regulation outputs a constant value. The strength of the integral action depends on the integral time constant Ti. The smaller Ti is, the stronger the integral action. Conversely, a large Ti means a weak integral action. Adding integral regulation 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.

[0063] 3. Differential regulation function: The differential action reflects the change rate of the system deviation signal and has predictability. It can predict the trend of the deviation change. Therefore, it can generate an anticipatory control action, and the deviation is eliminated by the differential regulation action before it is formed. Therefore, it can improve the dynamic performance of the system. When the differential time is selected appropriately, it can reduce overshoot and reduce the regulation time. The differential action has an amplifying effect on noise interference. Therefore, too strong differential regulation is not conducive to the anti-interference of the system. 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.

[0064] Through 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; c(t) = a(t) / b(t) is used as a variable to change the coefficient of the PID operation. When c(t) ≥ a (a is a constant obtained through experiments), the PID coefficient is zero; when c(t) < a, the PID operates according to the restored constant coefficient.

[0065] Experiments have proved that this algorithm effectively solves the overshoot of the control output quantity and realizes the constant-pressure water supply of the water pump.

[0066] In summary, the control method for overcoming the overshoot of the motor speed protected by this application overcomes the overshoot problem of pressure caused by speed fluctuations, significantly improves the stability of pressure regulation, and ensures the water supply with a stable flow rate of the water pump.

[0067] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. 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. Control method for overcoming overshoot of motor speed Characterized in that It includes the following control processes: - The host computer sends a start command to the controller; - The controller receives the start command from the host 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 back the water pressure value to the controller; - The controller controls the frequency converter to drive the motor and the water pump to work through the CAN bus by using the following algorithm according to the feedback signal of the pressure sensor, so as to adjust the pressure of the water pump; The calculation formula is: —— Output of the controller; ——Increment; —— The input of the controller is the difference between the set value and the controlled variable, , which is actually the difference between the set pressure and the actual pressure; —— proportional coefficient of the controller; Integral coefficient of the controller; —— Differential coefficient of the controller; ； , 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 obtained through experiments.

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