CN109595223B - Control method of asymmetric electro-hydraulic proportional system based on precise modeling of proportional valve - Google Patents
Control method of asymmetric electro-hydraulic proportional system based on precise modeling of proportional valve Download PDFInfo
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Abstract
The invention discloses a control method of an asymmetric electro-hydraulic proportional system based on precise modeling of a proportional valve, which aims at solving the problem that the output flow characteristics of the proportional valve are asymmetric and the control of the whole system is influenced under the influence of asymmetric factors such as load, structure and the like of the asymmetric electro-hydraulic proportional system.
Description
Technical Field
The invention belongs to the technical field of machinery and electronics, and particularly relates to a control method of an asymmetric electro-hydraulic proportional system based on precise modeling of a proportional valve.
Background
The existing electro-hydraulic system positive and negative speed characteristic consistency research is improved through an asymmetric structure, or the problem of asymmetric response is solved through a complex modern control strategy, certain application problems exist, and some students utilize a load flow model of a proportional valve to perform compensation adjustment, but the model is established to neglect the influence of the flow state inside a servo valve, the adjustment range and precision are limited, when the opening of the proportional valve is small and the external load is overlarge, the adjustment deviation is large, and the high-precision response of the diminishing displacement tracking in the asymmetric electro-hydraulic proportional system is difficult to realize. According to the analysis, the existing asymmetric control strategy cannot meet the field practicability in the aspects of manufacturing cost, complex working conditions and stability. The invention provides a method for accurately modeling a proportional valve, converting the flow output characteristic of the proportional valve into a linear flow model through compensation, and finally realizing high-precision control of an asymmetric electro-hydraulic system through the conventional linear control strategy.
Disclosure of Invention
The invention provides a control method of an asymmetric electro-hydraulic proportional system based on precise modeling of a proportional valve, which aims to overcome the defect of realizing general asymmetric electro-hydraulic system control in the prior art, and compensates the asymmetry and nonlinearity of the flow output of the proportional valve into a symmetric and linear system model by using a compensation function, so that a unified linear controller is adopted to realize the high response precision of the asymmetric system, the design difficulty of the controller is reduced, and the debugging workload of control parameters is reduced.
In order to achieve the technical purpose, the technical scheme of the invention is as follows:
a control method of an asymmetric electro-hydraulic proportional system based on accurate modeling of a proportional valve solves a compensation function by utilizing a mathematical model of the proportional valve and based on an ideal linear proportional valve output flow model to obtain a compensation equation for realizing the symmetry of load flow;
wherein the compensation equation is:
wherein: when x isvWhen > 0,. DELTA.p ═ Ps-P1(ii) a When x isvWhen not more than 0, delta P ═ P1-PR，PSSupply pressure of oil to hydraulic pump, PRFor oil return tank pressure, P1Is the pressure of the rodless chamber; rho is the density of hydraulic oil and has the unit of kg/m3(ii) a V is the kinematic viscosity of the fluid in m2/s；xvThe unit of the opening amount of the valve port is m; cdtThe valve port flow coefficient is in a turbulent flow state; k is a radical ofcCoefficient related to critical Reynolds number, 0.1Rc≤kc≤0.2RcWherein R iscIs the critical Reynolds number; Δ p is the valve port pressure difference in Pa, and w is the valve port area gradient of the proportional valve in m.
According to the control method of the asymmetric electro-hydraulic proportional system based on the accurate modeling of the proportional valve, the compensation function is realized through the compensation of the input signal of the proportional valve:
setting an input signal u and an actual input signal u' by using a proportional valve, and controlling the actual input to be:
wherein
γ＝kcV, when xvWhen > 0,. DELTA.p ═ Ps-P1(ii) a When x isvWhen not more than 0, delta P ═ P1-PR；xvmaxIs the maximum value of spool displacement.
The control method of the asymmetric electro-hydraulic proportional system based on the accurate modeling of the proportional valve is characterized in that a mathematical model of the proportional valve is as follows:
the control method of the asymmetric electro-hydraulic proportional system based on the accurate modeling of the proportional valve is characterized in that an ideal linear proportional valve output flow model is as follows:
the ideal output flow of the proportional valve is in a linear relation with the displacement of the valve core and is not influenced by external loads.
For the asymmetric electro-hydraulic proportional system, the flow of the rodless cavity of the hydraulic cylinder is set as the load flow, and the forward and reverse movement of the hydraulic cylinder of the asymmetric electro-hydraulic proportional system can be realized without being influenced by factors such as load, structure and the like only by ensuring that the flow output of a valve port of the rodless cavity of the hydraulic cylinder connected with the proportional valve is ideal linear, so that the high performance of the response of the asymmetric electro-hydraulic proportional system is realized by adopting a unified linear controller, and the method is simple, feasible and effective to realize.
The invention has the technical effects that the control method of the asymmetric electro-hydraulic proportional system based on the accurate model of the proportional valve is provided, the nonlinear model of the proportional valve is compensated into the linear model by utilizing the compensation function, the load flow output of the proportional valve is linear, and the forward and reverse motion response of the asymmetric electro-hydraulic proportional system is not influenced by factors such as load, structure and the like when a unified linear controller is adopted, so that the unified controller realizes the high performance of the response of the asymmetric electro-hydraulic proportional system. The method is based on the compensation of a system model, and the response consistency of the electro-hydraulic proportional asymmetric system is simply and intelligently realized by acquiring the pressure value of the system, so that the on-site debugging workload is greatly reduced, and the problem of the response consistency of the asymmetric electro-hydraulic proportional system during load change is solved. The control method is simple and effective for solving the problem of asymmetric response, is suitable for industrial fields, and is low in cost and high in reliability.
Drawings
FIG. 1 is an internal block diagram of an asymmetric electro-hydraulic proportional system;
FIG. 2 is a schematic diagram of an asymmetric electro-hydraulic proportional system experiment table;
FIG. 3 is a PLC control schematic of the present invention;
FIG. 4 is a graph of the proportional valve flow output characteristics of the compensated system of the present invention at different load conditions;
FIG. 5 is a diagram of the variation of the pressure in the two chambers of the hydraulic cylinder without compensation control according to the present invention;
FIG. 6 is a graph of sinusoidal displacement tracking response under varying load without the compensation control of the present invention;
FIG. 7 is a graph of sinusoidal tracking error under varying load without the compensation control of the present invention;
FIG. 8 is a graph of the change in pressure in the two chambers of the hydraulic cylinder under the control of the compensation according to the present invention;
FIG. 9 is a graph of the sinusoidal displacement tracking response of an asymmetric electro-hydraulic system under varying loads after compensation control by the present invention;
FIG. 10 is a graph of sinusoidal displacement tracking error for an asymmetric electro-hydraulic system under varying load after compensation control by the present invention;
Detailed Description
The invention will be further described with reference to the following figures and examples.
The invention is implemented based on the following model:
1. accurate modeling of proportional valve
Wherein: rho is the density of hydraulic oil and has the unit of kg/m3(ii) a w is the area gradient of the valve port, and the unit is m; v is the kinematic viscosity of the fluid in m2/s；xvThe unit of the opening amount of the valve port is m; cdtThe valve port flow coefficient under the turbulent flow state is generally 0.7; k is a radical ofcCoefficient related to critical Reynolds number, 0.1Rc≤kc≤0.2RcWherein R iscIs the critical Reynolds number; Δ p is the valve port pressure differential in Pa.
2. Ideal flow rate
The ideal proportional valve output flow model is a linear model, as follows:
wherein: pSSupply pressure of oil to hydraulic pump, PRFor oil return tank pressure, xvmaxThe valve core displacement is the maximum value, the ideal proportional valve output flow is in a linear relation with the valve core displacement, and the valve is not influenced by external loads.
3. Compensation calculations
Given proportional valve input opening amount xvSetting the opening x of the proportional valve after compensation calculated by the controllerv'＝f(xv) So that the output load flow Q' is linearly output. The equations are listed below:
the compensation function is calculated as follows:
4. control compensation
In an actual system, a signal given to a proportional valve is a current value or a voltage value, and a signal proportional value u is set corresponding to the proportion of valve core displacement according to a proportional signal of a full-scale range of current or voltage, so that the relationship between the signal proportional value and the valve core displacement is as follows:
wherein: u is the ratio of the actual signal to the maximum signal of the proportional valve; x is the number ofvThe actual opening degree of the valve core of the proportional valve is obtained; x is the number ofvmaxThe maximum opening degree of the valve core of the proportional valve.
Setting the input signal as u, converting the calculated input signal as u', substituting the above formula into the compensation function, and simplifying to obtain:
wherein
Theoretically, after the proportional valve is compensated by the control of the formula, the output flow of the proportional valve can be ensured to be ideal and linear.
The invention is further illustrated below with reference to examples:
the internal structure of the asymmetric electro-hydraulic proportional system is shown in FIG. 1.
The load flow is the flow flowing into or out of the rodless cavity, the flow flowing into the rodless cavity is the load flow during forward motion, and the flow flowing out of the rodless cavity is the load flow during reverse motion. A control method of an asymmetric electro-hydraulic proportional system based on a proportional valve accurate model compensates nonlinear factors of output flow of a proportional valve, load and valve opening by using a compensation function, so that load flow output of the proportional valve is linear, and forward and reverse motion responses of the asymmetric electro-hydraulic proportional system are consistent when a unified controller is adopted.
Fig. 2 is a schematic diagram of an asymmetric electro-hydraulic system experiment table in an embodiment of the invention, wherein the experiment table comprises an asymmetric electro-hydraulic system hydraulic circuit, a load hydraulic circuit and a counter-top cylinder workbench. The hydraulic circuit of the asymmetric electro-hydraulic system is a control object of the invention, the hydraulic cylinder is an asymmetric cylinder, external load is provided through the load circuit, and the zero point of the proportional valve is tested at the position of 2% of the valve opening, so that the characteristic of the test system is tested by taking 2% as the zero point.
And related parameters can be known according to the model of the proportional valve, the model of the oil and the like of the experiment table.
(1) Regulating system pump oil pressure PS＝5MPa
(2) Structural parameters omega, x of proportional valvevmax
Gradient w of valve port area is 9.23 × 10-3m，xvmax＝0.5×10-3m；
(3)kcValue taking
The absolute viscosity mu of the oil is 51 cP; rho is 850kg/m3Kinematic viscosity of oil
kcCoefficient related to critical Reynolds number, take kcν＝0.014。
Fig. 3 shows a detection control system in an embodiment of the present invention, and the detection control system is composed of detection elements (pressure sensor, displacement sensor), a PLC control system, and a host computer. Pressure P of oil supply of parameter system of detection element detection systemSPressure P of return oilRPressure P of rodless and rodless chambers1，P2And the displacement response of the hydraulic cylinder.
FIG. 4 shows that the experimental bench of the embodiment of the invention gives different external loads through the load control loop, so that the valve port pressure difference is 0.1-0.6PSThe valve opening is changed from 2-15%, and the load flow characteristics of the system before and after the test control show that the compensation provided by the invention is usedAfter control, the load flow of different valve port pressure differences can be adjusted to the load flow when the approximate pressure difference is 2.5MPa, and the load flow curve is basically in a linear state, which shows that the flow output of the proportional valve is basically close to the load flow output of an ideal model under the control of the compensation function of the proportional valve.
FIGS. 6 and 7 show the displacement response curve with the tracking amplitude of 5mm and the frequency of 0.5Hz of the hydraulic cylinder when the asymmetric electro-hydraulic system does not adopt compensation control in the pressure state change process shown in FIG. 5, FIGS. 9 and 10 show the displacement response curve with the tracking amplitude of 5mm and the frequency of 0.5Hz of the hydraulic cylinder when the asymmetric electro-hydraulic system adopts the control method of the invention in the pressure state change process shown in FIG. 8, it can be known from the figure that the influence of the system motion control accuracy along with the pressure change of two cavities is large when the system does not use the control method, and when P is1When the pressure is 4MPa, the error reaches 0.8mm, while the displacement tracking response precision of the control method is almost irrelevant to the pressure change of two cavities of the hydraulic cylinder, and the errors are controlled within 0.5mm, namely after compensation control, the precision control of a system is almost not influenced by external loads, the motion response quality of the hydraulic cylinder can be better realized through a uniform control strategy, and the design difficulty of an asymmetric system controller is reduced.
Claims (1)
1. A control method of an asymmetric electro-hydraulic proportional system based on accurate modeling of a proportional valve is characterized in that a compensation function is solved by utilizing a mathematical model of the proportional valve and an ideal linear proportional valve output flow model to obtain a compensation equation for realizing symmetry of load flow;
wherein the compensation equation is:
wherein: when x isvWhen > 0,. DELTA.p ═ Ps-P1(ii) a When x isvWhen not more than 0, delta P ═ P1-PR，PSSupply pressure of oil to hydraulic pump, PRFor oil return tank pressure, P1Is made withoutThe pressure of the rod cavity; rho is the density of hydraulic oil and has the unit of kg/m3(ii) a V is the kinematic viscosity of the fluid in m2/s；xvThe unit of the opening amount of the valve port is m; cdtThe valve port flow coefficient is in a turbulent flow state; k is a radical ofcCoefficient related to critical Reynolds number, 0.1Rc≤kc≤0.2RcWherein R iscIs the critical Reynolds number; Δ p is valve port pressure difference with the unit of Pa, and w is valve port area gradient of the proportional valve with the unit of m;
the compensation function is realized by the input signal compensation of the proportional valve:
setting an input signal u and an actual input signal u' by using a proportional valve, and controlling the actual input to be:
wherein
γ＝kcV, when xvWhen > 0,. DELTA.p ═ Ps-P1(ii) a When x isvWhen not more than 0, delta P ═ P1-PR；xvmaxIs the maximum value of the displacement of the valve core;
the mathematical model of the proportional valve is as follows:
the output flow model of the ideal linear proportional valve is as follows:
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| CN109595223B (en) * | 2018-12-12 | 2020-09-04 | 长沙航空职业技术学院 | Control method of asymmetric electro-hydraulic proportional system based on precise modeling of proportional valve |
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| CN112096696B (en) * | 2020-09-30 | 2022-07-01 | 长沙航空职业技术学院 | Self-adaptive inversion control method for pump-controlled asymmetric hydraulic position system |
| CN112925355B (en) * | 2021-01-22 | 2022-04-19 | 浙江大学 | Nonlinear flow modeling and compensating method of load port independent hydraulic system |
| CN113431816B (en) * | 2021-07-14 | 2022-04-15 | 长沙航空职业技术学院 | Control method of asymmetric negative superposition proportional valve control asymmetric cylinder system |
| CN114370521B (en) * | 2022-01-13 | 2024-02-02 | 中国铁建重工集团股份有限公司 | Hysteresis compensation control method and system for electric proportional overflow valve |
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