阅读说明：本技术 一种四象限工况下的变转速双泵控缸闭式系统速度闭环控制方法 (Speed closed-loop control method for variable-rotation-speed dual-pump cylinder control closed system under four-quadrant working condition ) 是由 张树忠 陈添益 李苏 唐一文 于 2019-12-29 设计创作，主要内容包括：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,计算变转速双泵控差动缸闭式系统液压缸所需流量、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。(According to the target speed, the flow, the elastic modulus and the viscosity of oil required by the hydraulic cylinder of the variable-speed double-pump-control differential cylinder closed system 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.)

1. A closed-loop control method for speed of a variable-speed dual-pump cylinder control closed system under a four-quadrant working condition is characterized by comprising the following steps of:

step one) according to the motion state of the servo motorDetermining the working condition of the system; the outlet pressure p of the energy accumulator is measured by a pressure sensor₁Hydraulic cylinder rodless cavity pressure p₂Pressure p against both ends of the rod chamber₃Determining the pressure difference delta p of the inlet and the outlet of the pump/motor;

the pump connected with the rodless cavity of the hydraulic cylinder is a pump 1, the pump connected with the rod cavity is a pump 2, and q is the same_P1、q_M1Respectively representing the flow of the working condition of the pump and the working condition of the motor connected with the rodless cavity of the hydraulic cylinder by q_P2、q_M2Respectively representing the flow of the working condition of a pump and the working condition of a motor which are connected with a rod cavity of the hydraulic cylinder; then there are:

pump/motor 1 the pressure differential of the large displacement pump/motor is:

Δp₁＝p₂-p₁

pump/motor 2 the pressure differential for the large displacement pump/motor is:

Δp₂＝p₃-p₁

step two) calculating the effective bulk modulus (B)_f) The calculation method is as follows:

in the formula p₀Is the initial pressure of the system; p is the pressure value p of two sides of the two pumps and the hydraulic cylinder respectively measured by the pressure sensor₂、p₃Where p is taken to be max (p)₂，p₃) (ii) a N is a gas polytropic index, and is more than or equal to 1 and less than or equal to 1.4; x₀The relative content of free air, B is the rated elastic modulus of the oil;

in order to make the modulus of elasticity more accurate, a minimum B is set_min：

B_f＝max(B_eff，B_min)

Step three), flow calculation:

under the working condition of the pump, the hydraulic cylinder controls the cavity input flow

q_P＝vA+K_LΔp

Under the working condition of the motor, the hydraulic cylinder controls the output flow of the cavity

q_M＝vA-K_LΔp

Wherein q is_P，q_MThe hydraulic cylinders control the actual input/output flow of the cavity under the working condition of the pump/motor respectively; v is the speed of the hydraulic cylinder; a is the effective working area A of the hydraulic cylinder, the effective working area of the hydraulic cylinder, the effective area of the rodless cavity under the pump working condition, the effective area of the rod cavity under the motor working condition, delta p is the pressure difference between two sides of the hydraulic cylinder, namely the pressure difference calculated by the pump/motor, K_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:

wherein n is the motor speed; ω is the angular velocity of the servo motor, and the pump operating conditions are:

wherein q is_aActual output flow of pump/motor under pump conditions, i.e. q_a＝q_P(ii) a 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: c_s，C_stLaminar flow and turbulent flow leakage coefficients respectively; b is_fThe effective elastic modulus of the oil liquid;

under the working condition of the motor

Wherein q is_aActual pump/motor input flow, i.e. q, under motor operating conditions_a＝q_M

Wherein:

wherein v is the viscosity of the oil, rho is the density of the oil, and omega is the angular velocity of the 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:

in the formula: t is the oil temperature, rho is the oil density, and the oil density is obtained through experimental measurement; p is a radical of₀Is at atmospheric pressure; p is the pressure of the hydraulic component, and p is max (p) measured by the pressure sensor₂，p₃)；C₁、C₂、C₃Is a coefficient and is obtained by experimental fitting;

and fifthly), after the rotating speed of the servo motor is calculated by the rotating speed calculation module of the servo motor and converted into a motor rotating speed signal, summing the motor rotating speed signal with the output obtained by self-adaptive control of speed negative feedback, and sending the summation result to a controller of the servo motor so as to control the output rotating speed of the servo motor.

Technical Field

The invention relates to the field of automatic control, in particular to a speed closed-loop control method of a variable-speed double-pump cylinder control closed system under a four-quadrant working condition.

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, the pump outlet pressure, the elastic modulus and the viscosity of the oil liquid required by the hydraulic cylinder of the variable-speed double-pump-control differential cylinder closed system are calculated by utilizing the rotating speed and the torque of the servo motor and the oil liquid 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 speed of a variable-speed dual-pump cylinder control closed system under a four-quadrant working condition is characterized by comprising the following steps of:

step one), determining the working condition of the system according to the motion state of the servo motor; the outlet pressure p of the energy accumulator is measured by a pressure sensor₁Hydraulic cylinder rodless cavity pressure p₂Pressure p against both ends of the rod chamber₃Determining the pressure difference △ p between the inlet and outlet of the pump/motor, and setting the pump connected to the rodless cavity of the hydraulic cylinder as pump 1 and the pump connected to the rod cavity as pump 2 to distinguish the flow rate of the two pumps/motors, i.e. using q as reference_P1、q_M1Respectively representing the flow of the working condition of the pump and the working condition of the motor connected with the rodless cavity of the hydraulic cylinder by q_P2、q_M2Respectively representing the flow of the working condition of a pump and the working condition of a motor which are connected with a rod cavity of the hydraulic cylinder; then there are:

pump/motor 1 the pressure differential of the large displacement pump/motor is:

Δp₁＝p₂-p₁

pump/motor 2 the pressure differential for the large displacement pump/motor is:

Δp₂＝p₃-p₁

step two) calculating the effective bulk modulus (B)_f) The calculation method is as follows:

in the formula p₀Is the initial pressure of the system; p is the system pressure; n is gas polytropic index (1 ≦ N ≦ 1.4), X₀The relative content of free air, B is the rated elastic modulus of the oil;

in order to make the modulus of elasticity more accurate, a minimum B is set_min：

B_f＝max(B_eff,B_min)

The volume elastic modulus of hydraulic oil is related to temperature, pressure and air in the oil, B in pure oil_f＝(1.2～2)×10³0.7 to 1.4 percent of (× 10) in the actual (oil-gas mixture) engineering under MPa³MPa；

Step three), flow calculation:

under the working condition of the pump, the hydraulic cylinder controls the cavity input flow

q_P＝vA+K_LΔp

Under the working condition of the motor, the hydraulic cylinder controls the output flow of the cavity

q_M＝vA-K_LΔp

Wherein q is_P,q_MThe actual input/output flow of a control cavity (namely a high-pressure cavity) of the hydraulic cylinder under the working condition of a pump/motor, v is the speed of the hydraulic cylinder, A is the effective working area A of the hydraulic cylinder, the effective working area of a hydraulic cylinder under the working condition of the pump, the effective area of a rodless cavity under the working condition of the pump and the effective area of a rod cavity under the working condition of the motor, △ p is the pressure difference of two sides of the hydraulic cylinder, namely the pressure difference calculated by the pump/motor, and K is the pressure difference calculated by the_LIs the leakage coefficient of the hydraulic cylinder.

Step four), calculating the rotating speed of the servo motor, wherein the calculating method comprises the following steps:

wherein n is the motor speed; ω is the angular velocity of the servo motor, and the pump operating conditions are:

wherein q is_aActual output flow of pump/motor under pump conditions, i.e. q_a＝q_P(ii) a 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); c_s,C_stLaminar flow, turbulent leakage coefficient; and B, effective elastic modulus of oil.

Under the working condition of the motor

Wherein q is_aActual pump/motor input flow, i.e. q, under motor operating conditions_a＝q_M

Wherein:

wherein v is the viscosity of the oil, rho is the density of the oil, and omega is the angular velocity of the 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:

in the formula: t is the oil temperature, rho is the oil density, and the oil density is obtained through experimental measurement; p is a radical of₀Is at atmospheric pressure; p is the pressure of the hydraulic element, and a pressure sensor is used for measuring; c₁、C₂、C₃Are coefficients, obtained by experimental fitting.

And step five), after the rotating speed of the motor is calculated and converted into a motor rotating speed signal by the servo motor rotating speed calculation module, summing the motor rotating speed signal with the output obtained by the speed negative feedback adaptive control.

Compared with the prior art, the invention has the following advantages:

1. 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.

2. The displacement of the hydraulic cylinder is calculated by considering the temperature, the compressibility of oil, pump/motor models with different rotating speeds and different pressure differences and leakage of the hydraulic cylinder, so that the robustness of the system is improved.

3. And identifying the four-quadrant working condition, and realizing high-performance speed closed-loop control and energy recovery under the four-quadrant working condition.

Description of the drawings:

fig. 1 is a flow chart of closed loop control.

Fig. 2 is a single pump closed hydraulic system circuit.

FIG. 3 is a four-state identification diagram.

Detailed description of the preferred embodiments

The technical scheme of the invention is as follows: according to the target speed, the pressure of an inlet and an outlet of a pump and the oil temperature are measured by using a pressure sensor and a temperature sensor, the flow, the pump pressure difference, the oil elastic modulus and the viscosity required by a hydraulic cylinder are calculated, and the rotating speed of a servo motor required at the moment is further calculated; and the model-based speed feedforward and speed negative feedback adaptive control are combined, and the overall structure diagram is shown as the following diagram:

the system mainly comprises a servo motor, two constant delivery pumps, a hydraulic cylinder, a working device, a low-pressure oil tank, a temperature sensor, a displacement or speed sensor, a pressure 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. Pressure is measured through pressure sensors at the outlet of the energy accumulator and the two sides of the hydraulic cylinder, the pressure difference between the inlet and the outlet of the pump is calculated, the temperature of the oil is obtained through the temperature sensors, and the measured pumping pressure and the measured temperature of the oil are input into a viscosity calculation module to obtain real-time viscosity; 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 pressure difference between the inlet and the outlet of the pump, 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.

And automatically identifying the operation condition of the pump/motor and automatically switching the algorithm. The motor speed, the pressure of a hydraulic circuit, the pressure of an inlet and an outlet of an energy accumulator and the pressure of two sides of a hydraulic cylinder are obtained through a motor driver, a temperature sensor and each pressure sensor, and meanwhile, the operation working condition of a pump/motor is automatically identified. Taking the left hydraulic pump/motor as an example, the hydraulic cylinder extends out, when the motor rotates forwards, if the pressure difference between the inlet and the outlet of the pump/motor is positive, the pump working condition is (I quadrant), otherwise, the motor working condition is (IV quadrant); when the hydraulic cylinder retracts, the motor rotates reversely, the pressure difference between the inlet and the outlet of the pump/motor is positive, the working condition of the motor is (II quadrant), and otherwise, the working condition of the pump is (III quadrant).

The hydraulic pump/motor on the right side is taken as an example, the hydraulic cylinder extends out, when the motor rotates forwards, if the pressure difference between the inlet and the outlet of the pump/motor is positive, the working condition of the motor is (I quadrant), otherwise, the working condition of the pump is (IV quadrant); when the hydraulic cylinder retracts, the motor rotates reversely, the pressure difference between the inlet and the outlet of the pump/motor is positive, the pump working condition is (II quadrant), and otherwise, the motor working condition is (III quadrant).

The pressure difference between the inlet and the outlet of the pump/motor is determined through 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 between the inlet and the outlet of the pump is measured through a pressure sensor to obtain the pressure p between the inlet and the outlet of the energy accumulator₁And pressure p of both ends of the hydraulic cylinder and the large and small displacement pumps₂、p₃。

The differential pressure of the large displacement pump/motor connected to the rodless chamber of the hydraulic cylinder is:

Δp₁＝p₂-p₁

the differential pressure of the large displacement pump/motor connected to the rodless chamber of the hydraulic cylinder is:

Δp₂＝p₃-p₁

since the pressure in the control chamber of the hydraulic cylinder is always greater than the pressure difference in the chambers other than the control chamber, the pressure difference in the pump connected to the control chamber is also greater, so the pressure difference used and calculated here takes the maximum value, namely: Δ p ═ max (Δ p)₁,Δp₂)。

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 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.

Mainly according to the formula (2) and the elastic modulus calculation formula, the elastic modulus of the system is calculated

As follows

In the formula p₀Is the initial pressure of the system; p is the pressure p measured by the pressure sensor at two sides of the two pumps and the hydraulic cylinder respectively₂、p₃，

Where p is max (p)₂,p₃) (ii) a N is a gas polytropic index,

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:

under the working condition of the pump, the hydraulic cylinder controls the cavity input flow

q_P＝vA+K_LΔp

Under the working condition of the motor, the hydraulic cylinder controls the output flow of the cavity

q_M＝vA-K_LΔp

Middle q_P,q_MThe actual input/output flow of a control cavity (namely a high-pressure cavity) of the hydraulic cylinder under the working condition of the pump/motor, v is the speed of the hydraulic cylinder, A is the effective working area of the hydraulic cylinder, △ p is the pressure difference of two sides of the hydraulic cylinder, namely the pressure difference calculated by the pump/motor, and K_LIs 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:

in the formula: p is a radical of₀-atmospheric pressure; p-the pressure of the hydraulic component in which it is located, measured by a pressure sensor, C₁、C₂、

C₃All are coefficients, obtained by fitting experimental data.

(1) 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:

wherein n is the motor speed; ω is the angular velocity of the servo motor, and the pump operating conditions are:

wherein q is_aThe actual output flow of the pump/motor under the pump condition, and also the actual input flow of the control chamber of the hydraulic cylinder under the pump condition, i.e. q_a＝q_P(ii) a 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); c_s,C_stLaminar flow, turbulent leakage coefficient; and B, effective elastic modulus of oil.

Under the working condition of the motor, the motor is

Wherein q is_aThe actual input flow of the pump/motor under the motor condition, and the actual output flow of the control cavity of the hydraulic cylinder under the motor condition, i.e. q_a＝q_M。

Wherein:

wherein v is the viscosity of the oil, rho is the density of the oil, and omega is the angular velocity of the motor;

(6) 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.