CN111075799B - Variable-speed pump control cylinder speed closed-loop control method - Google Patents

Variable-speed pump control cylinder speed closed-loop control method Download PDF

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CN111075799B
CN111075799B CN201911230372.2A CN201911230372A CN111075799B CN 111075799 B CN111075799 B CN 111075799B CN 201911230372 A CN201911230372 A CN 201911230372A CN 111075799 B CN111075799 B CN 111075799B
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pump
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pressure
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CN111075799A (en
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张树忠
吴安根
唐一文
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Fujian University of Technology
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
    • F15B21/02—Servomotor systems with programme control derived from a store or timing device; Control devices therefor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/665—Methods of control using electronic components
    • F15B2211/6656—Closed loop control, i.e. control using feedback
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/75—Control of speed of the output member

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Abstract

本发明根据目标速度，利用伺服电机转速和转矩、温度传感器所测得的油液温度，计算变转速单泵控差动缸闭式系统液压缸所需流量、泵出口压力、油液弹性模量、粘度，进而计算出该时刻所需要的伺服电机的转速；并将该基于模型的速度前馈与速度负反馈自适应控制相结合。

Figure 201911230372

According to the target speed, the invention uses the speed and torque of the servo motor and the temperature of the oil measured by the temperature sensor to calculate the required flow rate, pump outlet pressure and oil elasticity mode of the hydraulic cylinder of the variable speed single pump-controlled differential cylinder closed system. and viscosity, and then calculate the required speed of the servo motor at this moment; and combine the model-based speed feedforward with the speed negative feedback adaptive control.

Figure 201911230372

Description

Variable-speed pump control cylinder speed closed-loop control method
Technical Field
The invention relates to the field of automatic control, in particular to a closed-loop control method for controlling the speed of a cylinder of a variable-speed pump.
Background
Under the increasingly serious conditions of the rapid economic development and the problems of energy shortage, environmental pollution, labor cost rise and the like in China, a novel hydraulic energy-saving control technology capable of realizing low energy consumption, high efficiency and reliable operation is developed by combining the rapidly developed alternating current servo motor control technology, the hybrid power, the electromotion and the automation of mechanical equipment are promoted, and the hydraulic energy-saving control technology is one of the problems which need to be solved urgently in adapting to the social development of the manufacturing enterprises of the mechanical equipment in China and is also one of the research hotspots of the scientific research institutions and the manufacturing enterprises of the mechanical equipment all over the world.
Disclosure of Invention
According to the target speed, the flow required by the hydraulic cylinder, the pump outlet pressure, the elastic modulus and the viscosity of the oil are calculated by utilizing the rotating speed and the torque of the servo motor and the oil temperature measured by the temperature sensor, and the rotating speed of the servo motor required at the moment is further calculated; and combines this model-based velocity feedforward with velocity negative feedback adaptive control.
The invention is realized by adopting the following technical scheme:
a closed-loop control method for controlling the cylinder speed of a variable-speed pump comprises the following steps:
step one), determining the pressure difference of the inlet and the outlet of the pump through the output torque and the rotating speed of the servo motor, and calculating the pressure difference of the inlet and the outlet of the pump under the pump working condition through the following formula:
Ta=ΔpD+CvSΔpD+CfΔpD+Chσ2ΔpD
wherein T isaActually outputting torque for the servo motor; delta p is the pressure difference between the inlet and the outlet of the pump; d is the displacement of the pump; cv，Cf，ChSequentially comprises viscosity, friction and liquid dynamic loss coefficients of the oil liquid; s, sigma is a dimensionless number:
Figure GDA0003284275050000011
Figure GDA0003284275050000012
wherein v is the oil viscosity, p is the oil density, and omega is the angular velocity of the servo motor;
the viscosity of the oil changes along with the temperature, and the temperature of the oil is measured by a temperature sensor; the method for calculating the viscosity of the oil liquid comprises the following steps:
Figure GDA0003284275050000021
in the formula: t is oil temperature, rho is oil density, P0Is at atmospheric pressure; p is the pressure of the hydraulic component in which it is located, where the pressure P is measured by a pressure sensor between the tank and the pump/motor; c1、C2、C3Is a coefficient and is obtained by experimental fitting;
step two) calculating the effective bulk modulus BfThe calculation method is as follows:
Figure GDA0003284275050000022
in the formula p0Is the initial pressure of the system; p is the pump/motor output/input pressure calculated by the pressure calculation module; n is a gas polytropic index, the gas follows a certain rule in the compression process, and the gas polytropic index is a constant (1 is more than or equal to N is less than or equal to 1.4) describing the change process, and X is more than or equal to X0The relative content of free air, B is the rated elastic modulus of the oil; (note: the bulk modulus of elasticity of the hydraulic oil is related to the temperature, pressure and air in the oil, B in pure oilf=(1.2～2)×103MPa, trueIn the boundary (oil-gas mixture) engineering, (0.7-1.4) × 103MPa。
In order to make the modulus of elasticity more accurate, a minimum B is setmin：
Bf=max(Beff，Bmin)
Step three), flow calculation: the actual output flow of the hydraulic cylinder is obtained through the target speed and the inlet side pressure of the hydraulic cylinder, and the calculation formula is as follows:
q＝vA+KLΔp
wherein q is the actual output flow; v is the speed of the hydraulic cylinder; a is the effective working area of the hydraulic cylinder, the effective area of the rodless cavity under the working condition of the pump and the effective area of the rod cavity under the working condition of the motor; delta p is the pressure difference of two sides of the hydraulic cylinder, namely the pressure difference of the inlet and the outlet of the pump, K, calculated in the step one)LThe leakage coefficient of the hydraulic cylinder;
step four), calculating the rotating speed of the servo motor, wherein the calculating method comprises the following steps:
Figure GDA0003284275050000023
wherein n is the rotating speed of the servo motor; ω is the angular velocity of the servo motor, and its calculation formula is as follows:
Figure GDA0003284275050000031
wherein q is the actual output flow; x is pump displacement percentage; d is pump displacement; delta p is the pressure difference between the inlet and the outlet of the pump; s, sigma is a dimensionless number; cS，CStLaminar flow and turbulent flow leakage coefficients respectively; b isfThe effective elastic modulus of the oil liquid;
and step five), after the rotating speed of the servo motor is calculated by the rotating speed calculation module of the servo motor and is converted into a motor rotating speed signal, summing the output obtained by the speed negative feedback adaptive control, and sending the summation result to a controller of the servo motor so as to control the output rotating speed of the servo motor.
Compared with the prior art, the invention has the following advantages:
the model control and the adaptive control are combined, the speed of the hydraulic cylinder is close to the target speed through the feedforward control based on the model, the steady-state error is further eliminated through the adaptive control, the speed control precision of the hydraulic cylinder and the robustness of the system are improved, and the sensitivity of the system to the variation of the undetected and difficultly detected parameters is reduced, such as the increase of internal leakage after the abrasion of a pump or the reduction of the viscosity of oil is compensated through the adaptive control.
Drawings
Fig. 1 is a block flow diagram.
Detailed Description
The technical scheme of the invention is as follows: according to the target speed, calculating the flow required by the hydraulic cylinder, the pump outlet pressure, the elastic modulus and the viscosity of the oil by using the rotating speed and the torque of the servo motor and the oil temperature measured by the temperature sensor, and further calculating the rotating speed of the servo motor required at the moment; and the overall structure diagram of the model-based speed feedforward and speed negative feedback adaptive control is shown in fig. 1:
the system mainly comprises a servo motor, a constant delivery pump, a hydraulic cylinder, a working device, a temperature sensor, a displacement or speed sensor and the like. The connection mode is as follows: the servo motor drives the pump to control hydraulic oil in a hydraulic pump driving pipeline, and displacement control of the hydraulic cylinder is achieved. Acquiring the oil temperature through a temperature sensor, and inputting the measured oil temperature into a viscosity calculation module to obtain real-time viscosity; calculating the inlet-outlet pressure difference of the pump and the real-time outlet pressure of the pump by using the torque and rotating speed internal feedback signals of the servo motor and the calculated viscosity input pressure calculation model; the real-time elastic modulus is obtained by combining the outlet pressure of the pump with an elastic modulus calculation module; and calculating the required input flow of the hydraulic cylinder in real time by combining the target rotating speed and the system pressure, and inputting the flow, the elastic modulus, the viscosity and the pressure into a rotating speed calculation module to obtain a required motor rotating speed control signal for feedforward control. And speed negative feedback is carried out, the speed of the hydraulic cylinder is obtained through a differential or speed sensor of a displacement sensor of the hydraulic cylinder, and closed-loop control is carried out through self-adaptive control, such as fuzzy PID, neural network PID and other control methods, so that the speed control of the high-performance variable-speed pump cylinder control system is realized.
The pressure difference of the inlet and the outlet of the pump is determined by the output torque and the rotating speed of the servo motor, the system pressure is the pressure difference plus the pressure of the oil tank, and the pressure difference of the inlet and the outlet of the pump is mainly calculated by the following formula.
Ta＝ΔpD+CvSΔpD+CfΔpD+Chσ2ΔpD
Wherein T isaActually outputting torque for the servo motor; delta p is the pressure difference between the inlet and the outlet of the pump; d is the displacement of the pump; cv，Cf，ChThe viscosity, friction and liquid dynamic loss coefficient of the oil liquid are obtained; s and sigma are dimensionless numbers. The two dimensionless numbers in this formula are:
Figure GDA0003284275050000041
Figure GDA0003284275050000042
wherein v is the oil viscosity, p is the oil density, and ω is the motor angular velocity.
The elastic modulus is an effective bulk elastic modulus B (f) in consideration of the influence of the compression coefficients of the liquid, the gas and the container. The value of bulk modulus is influenced primarily by three factors: pressure, temperature and air content in the oil. Air exists in various forms: free air appears as pockets of air, entrained air (including air bubbles mixed with oil) and fully dissolved air.
The elastic modulus of the system is calculated mainly according to the formula (2) and an elastic modulus calculation formula, wherein the specific formula is as follows
Figure GDA0003284275050000043
In the formula p0Is the initial pressure of the system; p is the system pressure; n is gasThe number of the variable-body indexes,
X0the relative amount of free air and B is the nominal case modulus of elasticity of the oil.
The flow calculation module is mainly used for obtaining the flow of the hydraulic cylinder through the target speed and the inlet side pressure of the hydraulic cylinder, and the calculation formula is as follows:
q＝vA+KLΔp
wherein q is the hydraulic cylinder input flow (actual); v is the speed of the hydraulic cylinder; a is the effective working area of the hydraulic cylinder, and Deltap is the pressure difference between two sides of the hydraulic cylinder, i.e. the pump pressure difference, KLIs the leakage coefficient of the hydraulic cylinder.
The viscosity calculation module of the hydraulic system calculates the parameters influencing the output flow and the pressure of the constant delivery pump respectively to be the density rho of oil and the viscosity v of the oil, the density of the oil can be directly obtained through experimental measurement, and the viscosity of the oil changes along with the temperature change of the oil, so that a temperature sensor needs to be added into a hydraulic pipeline, and the temperature T of the oil in a hydraulic loop is monitored in real time. By carrying out polynomial fitting on experimental data, an expression of the relation between the oil viscosity and the temperature can be obtained:
Figure GDA0003284275050000051
in the formula: p is a radical of0-atmospheric pressure; p-is the pressure of the hydraulic component at which the pressure p is measured by the pressure sensor between the accumulator and the pump/motor; c1、C2、C3All are coefficients, obtained by fitting experimental data.
The servo motor rotating speed calculation module is used for calculating the rotating speed value of the servo motor by combining the flow value of the flow calculation module of the hydraulic cylinder, the pressure value of the pressure calculation module, the elastic modulus value calculated by the elastic module and the hydraulic oil viscosity of the viscosity calculation module, and converting the rotating speed value into a rotating speed signal. The specific rotating speed calculation formula is as follows:
Figure GDA0003284275050000052
wherein n is the motor speed; ω is the angular velocity of the servo motor, and its calculation formula is as follows:
Figure GDA0003284275050000053
wherein q isaOutput flow (actual); x pump displacement percentage; d, pump displacement; delta p pump inlet and outlet differential pressure; s, a dimensionless number of σ (same as 2 above); cS，CStLaminar flow, turbulent leakage coefficient; and B, effective elastic modulus of oil.
The servo motor rotating speed calculation module calculates the motor rotating speed and converts the motor rotating speed into a motor rotating speed signal, then the motor rotating speed signal and the output obtained by the speed negative feedback self-adaptive control are summed, and the summed result is sent to a controller of the servo motor, so that the output rotating speed of the servo motor is controlled, and the rapidity, the robustness and the like of the system are improved.

Claims (1)

1.一种变转速泵控缸速度闭环控制方法，其特征在于，包括如下步骤：1. a variable speed pump control cylinder speed closed-loop control method, is characterized in that, comprises the steps: 步骤一)通过伺服电机的输出转矩和转速确定泵进出口压差，泵工况的泵进出口压差通过下述公式计算：Step 1) Determine the pressure difference between the inlet and outlet of the pump through the output torque and rotational speed of the servo motor, and calculate the pressure difference between the inlet and outlet of the pump under the working condition of the pump by the following formula: Ta＝ΔpD+CvSΔpD+CfΔpD+Chσ2ΔpDT a =ΔpD+C v SΔpD+C f ΔpD+C h σ 2 ΔpD 其中Ta为伺服电机实际输出扭矩；Δp为泵进出口压差；D为泵的排量；Cv，Cf，Ch依次为油液的粘性、摩擦、液体动态损失系数；S，σ为无纲量数：Among them, T a is the actual output torque of the servo motor; Δp is the pressure difference between the inlet and outlet of the pump; D is the displacement of the pump; C v , C f , and C h are the viscosity, friction, and dynamic loss coefficient of the oil in turn; S, σ is a dimensionless quantity:
Figure FDA0003432260220000011
Figure FDA0003432260220000011
Figure FDA0003432260220000012
Figure FDA0003432260220000012
 其中v为油液粘度，ρ为油液密度，ω为伺服电机角速度；where v is the viscosity of the oil, ρ is the density of the oil, and ω is the angular velocity of the servo motor; 油液粘度随温度变化，油液温度由温度传感器测出；油液粘度的计算方法为：The oil viscosity changes with temperature, and the oil temperature is measured by the temperature sensor; the calculation method of oil viscosity is:
Figure FDA0003432260220000013
Figure FDA0003432260220000013
 式中：T为油液温度，ρ为油液密度，P0为大气压；P为所在液压元件的压力，此处压力P由油箱与泵/马达之间的压力传感器测量得到；C1、C2、C3为系数，通过实验拟合得到；In the formula: T is the temperature of the oil, ρ is the density of the oil, P 0 is the atmospheric pressure; P is the pressure of the hydraulic component, where the pressure P is measured by the pressure sensor between the oil tank and the pump/motor; C 1 , C 2. C 3 is a coefficient, obtained through experimental fitting; 步骤二)计算油液有效体积弹性模量Bf，计算方法如下：Step 2) Calculate the effective bulk elastic modulus B f of the oil, and the calculation method is as follows:
Figure FDA0003432260220000014
Figure FDA0003432260220000014
 式中p0为系统的初始压力；p为压力计算模块所计算出的泵/马达输出/输入压力；N为气体多变指数，气体在压缩过程中遵循一定的规律，气体多变指数即描述这一变化过程的常数(1≤N≤1.4)，X0为自由空气的相对含量，B为油液的额定弹性模量；where p 0 is the initial pressure of the system; p is the pump/motor output/input pressure calculated by the pressure calculation module; N is the gas variability index, the gas follows a certain law during the compression process, and the gas variability index is the description The constant of this change process (1≤N≤1.4), X 0 is the relative content of free air, and B is the rated elastic modulus of the oil; 为了使弹性模量更为准确，设定一个最小值Bmin：To make the elastic modulus more accurate, set a minimum value B min : Bf＝max(Beff，Bmin)B f =max(B eff , B min ) 步骤三)流量计算：通过液压缸的目标速度和进口侧压力获取液压缸实际输出流量的大小，计算公式如下：Step 3) Flow calculation: Obtain the actual output flow of the hydraulic cylinder through the target speed of the hydraulic cylinder and the pressure on the inlet side. The calculation formula is as follows: q＝VA+KLΔpq=VA+ KL Δp 其中q为实际输出流量；V为液压缸的速度；A为液压缸有效工作面积，在泵工况下为无杆腔有效面积，在马达工况下为有杆腔有效面积；Δp为液压缸两侧压差，即为步骤一)所计算出的泵进出口压差，KL为液压缸的泄漏系数；Among them, q is the actual output flow; V is the speed of the hydraulic cylinder; A is the effective working area of the hydraulic cylinder, which is the effective area of the rodless cavity under the pump condition and the effective area of the rod cavity under the motor condition; Δp is the hydraulic cylinder. The pressure difference on both sides is the pressure difference between the inlet and outlet of the pump calculated in step 1), and K L is the leakage coefficient of the hydraulic cylinder; 步骤四)计算伺服电机转速，计算方法如下：Step 4) Calculate the speed of the servo motor, and the calculation method is as follows:
Figure FDA0003432260220000021
Figure FDA0003432260220000021
 其中n为伺服电机转速；ω为伺服电机的角速度，其计算公式如下：Among them, n is the speed of the servo motor; ω is the angular speed of the servo motor, and its calculation formula is as follows:
Figure FDA0003432260220000022
Figure FDA0003432260220000022
 其中q为实际输出流量；x为泵排量百分比；D为泵排量；Δp为泵进出口压差；S，σ为无纲量数；Cs，Cst分别为层流，紊流泄漏系数；Bf为油液有效体积弹性模量；Among them, q is the actual output flow; x is the pump displacement percentage; D is the pump displacement; Δp is the pressure difference between the inlet and outlet of the pump; S and σ are dimensionless quantities; coefficient; B f is the effective bulk elastic modulus of oil; 步骤五)伺服电机转速计算模块计算出伺服电机转速并转化为伺服电机转速信号之后，和速度负反馈自适应控制得到的输出进行求和，并将求和结果送给伺服电机的控制器，从而控制伺服电机的输出转速。Step 5) After the servo motor speed calculation module calculates the servo motor speed and converts it into a servo motor speed signal, it sums up the output obtained by the speed negative feedback adaptive control, and sends the summation result to the controller of the servo motor, thereby Controls the output speed of the servo motor.
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