DE102022206540B3 - Method for controlling variable-speed fluid pumps - Google Patents

Abstract

The invention relates to a method for controlling a pump with a variable-speed drive, comprising: entering a target pressure value (pcmd) into a cascaded controller structure, the controller structure comprising a pressure control circuit (210, 212, 214, 216), the control system of the pressure control circuit a speed control circuit (220, 222, 224), into which a target speed is entered as a manipulated variable of a pressure regulator (210) of the pressure control circuit; wherein the controlled system of the speed control loop comprises a drive control loop (230, 232), into which a target drive torque is entered as a manipulated variable of a speed controller (220) of the speed control loop; forming (250) a pilot control value (Mffcmd) for the drive torque as a result of a time differential equation of the target pressure; and adding the pilot control value to the target drive torque, which is entered into the controlled system of the speed control loop.

Description

The present invention relates to a method for controlling variable-speed fluid pumps, as well as a computer program and a computing unit for carrying out the method.

In hydraulics, fluid pumps with a conveyor mechanism with a fixed delivery volume, which is driven by a drive with variable speed (so-called variable-speed constant pump), are often used. When operating such pumps, the volume flow and/or the delivery pressure are usually regulated by appropriately adjusting the speed. Such pumps are used, for example, for hydraulic units, pump drives or servo-hydraulic actuators, for example in machine tools or in plastics processing, such as in injection molding machines, blow molding machines, presses, etc., where high delivery pressures are required. Such pumps are mentioned in the publications DE10 2019 220 322 A1 , DE10 2012 009 136 A1 , DE 11 2018 003 927 B4 , DE 10 2015 221 684 A1 , DE 10 2014 224 337 A1 and DE 10 2005 039 758 A1 pointed out

The control of such variable-speed pumps can be implemented, for example, by a cascaded control structure in which a target pressure is specified and includes a pressure control loop, a speed control loop and a current control loop for the drive motor. However, the speed control loop is disturbed by the load torque M _L , which arises depending on the current pressure via the pump displacement volume. The pressure control circuit is also disturbed by the leakage volume flow from the pump. These disturbances worsen the control quality of the drive system.

It is therefore desirable to improve the control of variable-speed fluid pumps.

According to the invention, a method for controlling a pump with a variable-speed drive with the features of the independent patent claims is proposed. Advantageous refinements are the subject of the subclaims and the following description.

In particular, a method is proposed in which a target pressure value is first entered into a cascaded regulator structure, the regulator structure comprising a pressure control loop and the control system of the pressure control loop comprising a speed control loop, into which a target speed is entered as a manipulated variable of a pressure regulator of the pressure control loop . The controlled system of the speed control loop also includes a drive control loop, into which a target drive torque is entered as a manipulated variable of a speed controller of the speed control loop. In addition, a pilot control value for the drive torque is formed as a result of a time differential equation of the target pressure, and this pilot control value is added to the target drive torque, which is entered into the control system of the speed control loop.

In exemplary embodiments, the time differential equation of the target pressure can preferably comprise an inverse system model of the controlled system of the cascaded controller structure.

This inverse route model can be formed, for example, depending on a pressure dynamic in a load volume in which the pressure is regulated and a torque dynamic of the drive.

The precontrol value for the drive torque can be determined in exemplary embodiments by the following equation: $$M_{cmd}^{ff}=\frac{J_{eq}2\pi C_H}{v_G}{\ddot{p}}_L^d+\frac{2\pi }{v_G}\left(J_{eq}{C}_l+d_M{C}_H\right){\dot{p}}_L^d+\left(\frac{d_{M}2\pi C_l}{v_G}+\frac{v_G}{2\pi }\right)p_L^d$$

It is also possible to create a pre-control value for the speed, whereby the pre-control value for the speed is determined by: $${\text{n}}_{cmd}^{ff}=\frac{C_H}{v_G}{\dot{p}}_L^d+\frac{C_l}{v_G}\cdot p_L^d$$

This pilot control value can then be added to the target speed, which is output by the pressure controller as a manipulated variable. This can prevent the speed control loop from working against the torque precontrol.

Optionally, the target pressure value can be entered into a target value filter, which is set up to output a target trajectory for the target pressure value and the derivatives of the target pressure value, and this target trajectory can then be entered into the differential equation to form the pilot control value.

Such a setpoint filter can, for example, comprise a second-order state variable binomial filter.

Overall, the flatness-based pilot control proposed here dynamically compensates for load moments and disruptive volume flows. This improves the management behavior and the stability reserve of the system. The drive controller can be designed to be immune to interference, as the follow-up behavior is significantly improved by the feedforward control. This reduces the load on speed and pressure regulators. At the same time, the precontrol is insensitive to sensor noise.

A computing unit according to the invention, for example a control device of a hydraulic system, is set up, in particular in terms of programming, to carry out a method according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous because this causes particularly low costs, especially if an executing control device is used for additional tasks and is therefore present anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the accompanying drawing.

It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.

• 1 zeigt schematisch eine Fluidpumpe mit einem drehzahlvariablen Antrieb; und
• 2 zeigt eine beispielhafte Reglerstruktur gemäß einer möglichen Ausführungsform.

The invention is shown schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing.

• 1 shows schematically a fluid pump with a variable-speed drive; and
• 2 shows an exemplary controller structure according to a possible embodiment.

1 shows schematically components of a variable-speed fluid pump for which the methods described here can be used. In this example, the pump 10 has a conveyor mechanism 20, which can convey in two directions, a variable-speed drive 30 and a computing unit 40 for operating the pump.

The conveyor 20 can be designed, for example, as a constant pump that achieves a certain delivery volume per stroke or per revolution. The drive 30 is designed here as a standard motor that has an asynchronous motor 31 and a frequency converter 32. Alternatively, synchronous servo motors or other drive units can also be used. The speed n of the asynchronous motor 31 is variable, the speed being adjusted, for example, by the current applied to the drive motor 31.

The computing unit 40 can be used to control the pump 10, to which at least a target delivery pressure and optionally a target volume flow are supplied. The computing unit 40 can include a drive controller implemented in hardware or software technology, which determines the required manipulated variables and transmits them to the motor 30. It is optionally possible to determine the actual pressure using a sensor. The computing unit 40 can further determine, for example by monitoring the electrical current and the speed, which drive torque is currently being supplied by the drive, and can then For example, transmit a target speed to the drive unit 30 as a control signal. Alternatively, it is also possible for the drive unit 30 itself to include certain control or regulation elements and thus for example only a target torque for controlling the drive and thus the pump is specified by the computing unit 40 and is transmitted to the drive 30 as a control signal.

It is understood that this pump drive system is only described as an example and the controller variants described below are not limited to this system. In particular, the present invention can also be used with any other pumps and is not limited to fixed displacement pumps. It is also possible that certain parts of the cascaded controller structure are implemented in several separate computing units, that certain sensors are not present in other systems or that additional parameters are measured via sensors, or that the drive unit is designed differently than described here.

2 shows a controller structure for controlling a variable-speed fluid pump according to a possible embodiment.

A cascaded controller structure is provided, which nested within one another and includes a pressure control circuit, a speed control circuit and a drive control circuit such as a current control circuit. The current control circuit 230 for the pump drive is shown here only in a simplified manner and as an example and can be implemented in any way, for example as a PI controller; With a different drive variant, a different control circuit can also be used at this point, which regulates the drive torque of a pump drive. The current control circuit 230 receives a target drive torque M ^R _cmd as a reference variable and returns the actual value 232 of the drive torque M _act . A regulated drive torque M _M is thus obtained.

The target drive torque M ^R _cmd in turn is the manipulated variable of a speed control loop. The speed control loop receives a target speed n _cmd of the pump as a reference variable for a speed controller 220 and returns an actual speed n _act 222, the current control loop 230 together with the moment of inertia element 224, which consists of the drive torque M _M with the moment of inertia of the pump and motor outputs the controlled speed n, which forms the controlled system of the speed control loop.

The target speed n _cmd forms the manipulated variable of a pressure control circuit, the pressure controller 210 of which receives a target load pressure p _L ^d as a reference variable and returns an actual value p _L of the load pressure 212. The control system of the pressure control circuit thus includes the speed control circuit 220, 222, 224, the current control circuit 230, 232 and other control elements. The further control elements of the system include a proportional element 214 in order to convert the regulated speed n obtained from the speed control loop into a volume flow Q _p by taking into account the predetermined displacement V _g of the pump per revolution. The regulated load pressure p L is then obtained by means of a PI element 216 from the volume flow Q _p by taking into account the equivalent compression _module E ' _oil and the load volume V _L in which the pressure is regulated. The actual pressure p _act is in turn fed back via the pressure control circuit 212 to the input of the pressure regulator 210.

The speed control loop is disturbed by a load torque M _L , which can be mapped as a proportional element 240 from the existing load pressure p _L and the displacement volume V _g of the pump. The resulting load torque M _L counteracts the drive torque M _M.

In addition, the pressure control circuit is disturbed by the leakage volume flow Q _L of the pump, which results from the load pressure P _L and the leakage coefficient C _I and can be modeled as a proportional element 242. The leakage volume flow Q _L counteracts the volume flow Q _p of the pump.

In order to compensate for these disturbances, a pilot control 250 can now be provided according to the invention, which corrects the commanded drive torque M ^R _cmd for the pump drive, which is output by the speed controller 220 as a manipulated variable and enters the current control circuit 230 as a command variable, by a pilot control value M ^ff _cmd . The actual value that is entered into the current control loop or the controlled system of the speed control loop is the sum of the drive torque M ^R cmd and the pre-control value M ^ff cmd.

The pre-control value can be formed in particular via an inverse system model of the controlled system. This route model can be used according to the in 2 The controller structure shown can be derived as follows:

wobei C_h = V_L / E'_Öl die hydraulische Kapazität mit dem Ersatzkompressionsmodul E'_Öl und dem Lastvolumen V_L ist, V_g das Schluckvolumen der Pumpe ist, ω_M das Drehmoment des Antriebs ist, und C_l der druckabhängige Leckagebeiwert ist.The pressure dynamics in the load volume, ie the change ṗ _L in the load pressure, results in: $${\dot{p}}_L=\frac{1}{C_H}\cdot \left(\frac{v_G}{2\pi }\cdot {\omega }_M-C_l\cdot p_L\right)$$

where C _h = V _L / E' _oil is the hydraulic capacity with the equivalent compression module E' _oil and the load volume V _L , V _g is the displacement volume of the pump, ω _M is the torque of the drive, and C _l is the pressure-dependent leakage coefficient.

By deriving with respect to time one then obtains $${\ddot{p}}_L=\frac{1}{C_H}\cdot \left(\frac{v_G}{2\pi }\cdot {\dot{\omega }}_M-C_l\cdot {\dot{p}}_L\right)$$

wobei J_eq das äquivalente Trägheitsmoment ist, das sich aus den Trägheitsmomenten J_Pumpe der Pumpe und J_Motor des Antriebsmotors ergibt, J_eq= J_Pumpe + J_Motor;
wobei M_M das Antriebsmoment ist;
wobei V_g das Schluckvolumen der Pumpe ist, und
wobei d_M ein drehzahlbezogenes Reibmoment der Pumpe ist.The torque dynamics on the motor-pump shaft are: $${\dot{\omega }}_M=\frac{1}{J_{eq}}\left(M_M-\frac{v_G}{2\pi }{p}_L-d_M{\omega }_M\right)$$

where J _eq is the equivalent moment of inertia resulting from the moments of inertia J _pump of the pump and J _motor of the drive motor, J _eq = J _pump + J _motor ;
where M _M is the driving torque;
where V _g is the displacement volume of the pump, and
where d _M is a speed-related friction torque of the pump.

Substituting equation (3) into equation (2) results in: $${\ddot{p}}_L=\frac{1}{C_H}\cdot \left(\frac{v_G}{2\pi }\cdot \frac{1}{J_{eq}}\left(M_M-\frac{v_G}{2\pi }{p}_L-d_M{\mathrm{\omega }}_M\right)-C_l\cdot {\dot{p}}_L\right)$$

So you get a second-order differential equation that represents the route model. The inverse route model can now be used as a flatness-based pre-control 250 of an additive torque for the trajectory sequence of a required pressure dynamic [p _L , ṗ _L , p̈ _L ]. To do this, equation (4) can be converted according to the drive torque using equation (1), so that the pre-control law results as an inverse route model: $$M_{cmd}^{ff}=\frac{J_{eq}2\pi C_H}{v_G}{\ddot{p}}_L^d+\frac{2\pi }{v_G}\left(J_{eq}{C}_l+d_M{C}_H\right){\dot{p}}_L^d+\left(\frac{d_{M}2\pi C_l}{v_G}+\frac{v_G}{2\pi }\right)p_L^d$$

bzw. nach der Drehzahl aufgelöst wird: $${\text{n}}_{cmd}^{ff}=\frac{C_h}{V_g}{\dot{p}}_L^d+\frac{C_l}{V_g}\cdot p_L^d$$

Since it is a cascaded control loop, the pre-control signal from which the torque pre-control is derived can optionally also be supplied to the superimposed speed control loop. This can prevent the speed control loop from working against the torque precontrol. The corresponding pilot control signal can be calculated from equation (1) by dividing the equation according to the rotation frequency ${\mathrm{\omega }}_{cmd}^f$

or is resolved according to the speed: $${\text{n}}_{cmd}^{ff}=\frac{C_H}{v_G}{\dot{p}}_L^d+\frac{C_l}{v_G}\cdot p_L^d$$

This precontrol value can then also be added to the input of the speed control loop.

wobei τ die Zeitkonstante des Sollwertfilters ist. Grundsätzlich können die Solldruckwerte aber auch anders bestimmt werden. Dabei ist p_cmd der kommandierte Solldruckwert.To implement the precontrol 250, the time derivative variables of the setpoint pressure [p _L , ṗ̇ _L , p̈ _L ] can be determined by a setpoint filter 260. For example, a second-order state variable binomial filter can be used for this purpose. As an example, the target trajectory can be determined using the following differential equation: $${\ddot{p}}_L^d=\frac{1}{{\tau }^2}{p}_{cmd}-\frac{2}{\tau }{\dot{p}}_L^d-\frac{1}{{\tau }^2}{\ddot{p}}_L$$

where τ is the time constant of the setpoint filter. In principle, the target pressure values can also be determined differently. Where p _cmd is the commanded target pressure value.

The target trajectory obtained from equation (7) can now be inserted into the pre-control law, equation (5), and the pre-control torque M ^ff _cmd calculated with it can be calculated additively on the input of the current control circuit 230. The target trajectories can also be inserted into the pre-control law (6) for the speed.

A simpler alternative to pre-control for the drive controller is to only compensate for the load torque M _L , 240, so that the pre-control value for the drive torque in this variant results in M ^ff _cmd = (V _g /2 _π p _cmd from the commanded target pressure value. A setpoint filter is not required in this case. The precontrol value is then added to the output value of the speed controller 220 or the input value of the current control circuit 230, as in the previous embodiment.

By using the model-based pilot control according to the invention, the control behavior of the control improves, since the actuator (i.e. the drive motor of the pump) immediately reacts in a highly dynamic manner, even if no large control deviation occurs.

The follow-up behavior of the drive control (i.e. the current control loop) is also significantly improved by the pilot control. This reduces the load on speed and pressure regulators. At the same time, the precontrol is insensitive to sensor noise.

A control system as described here can be used for all variable-speed pumps, especially for pumps that control hydraulic units or hydraulic actuators. The described method with pilot control can also be used to control the force of servo-hydraulic actuators; In this case, a pressure is also regulated via a motor-pump unit, which can then be converted into a force value via the cylinder surfaces.

Claims (10)

Method for controlling a pump (10) with a variable-speed drive (30), comprising: entering a target pressure value (p _cmd ) into a cascaded controller structure, the controller structure comprising a pressure control circuit (210, 212, 214, 216), wherein the Control system of the pressure control circuit (210, 212, 214, 216) comprises a speed control circuit (220, 222, 224), in which a target speed n _cmd is entered as a manipulated variable of a pressure controller (210) of the pressure control circuit (210, 212, 214, 216). becomes; wherein the controlled system of the speed control loop (220, 222, 224) comprises a drive control loop (230, 232), into which a target drive torque M ^R _cmd is entered as a manipulated variable of a speed controller (220) of the speed control loop (220, 222, 224); Forming (250) a precontrol value (M ^ff _cmd ) for the drive torque M ^R _cmd , as a result of a time differential equation of the target pressure p _L ; and adding the pilot control value (M ^ff _cmd ) to the target drive torque M ^R _cmd, which is entered into the controlled system of the speed control loop (220, 222, 224). Procedure according to Claim 1 , where the time differential equation of the target pressure p _L comprises an inverse system model of the controlled system of the cascaded controller structure. Procedure according to Claim 2 , whereby the inverse route model is formed depending on a pressure dynamic ṗ _L in a load volume V _L in which the pressure is regulated, and a torque dynamic ω̇ _M of the drive (30). Method according to one of the preceding claims, wherein the pre-control value (M ^ff _cmd ) for the drive torque M ^R _cmd is determined by: $$M_{cmd}^{ff}=\frac{J_{eq}2\pi C_H}{v_G}{\ddot{p}}_L^d+\frac{2\pi }{v_G}\left(J_{eq}{C}_l+d_M{C}_H\right){\dot{p}}_L^d+\left(\frac{d_{M}2\pi C_l}{v_G}+\frac{v_G}{2\pi }\right)p_L^d$$

Method according to one of the preceding claims, further comprising: forming (250) a pre-control value ${\text{n}}_{cmd}^{ff}$

for the speed n, where the precontrol value ${\text{n}}_{cmd}^{ff}$

for the speed n is determined by: $${\text{n}}_{cmd}^{ff}=\frac{C_H}{v_G}{\dot{p}}_L^d+\frac{C_l}{v_G}\cdot p_L^d$$

and adding the input tax value ${\text{n}}_{cmd}^{ff}$

to the target speed n _cmd , which is output by the pressure controller (210) as a manipulated variable. Method according to one of the preceding claims, further comprising: entering the target pressure value (p _cmd ) into a target value filter (260), which is set up to produce a target trajectory for the target pressure value (p _cmd ) and the derivatives of the target pressure value ( p _cmd ) and input the target trajectory into the differential equation to form the feedforward control value. Procedure according to Claim 6 , wherein the setpoint filter (260) comprises a second-order state variable binomial filter. Computing unit comprising a processor configured to carry out the method according to any one of the preceding claims. Computer program comprising commands which, when the program is executed by a computer, cause it to follow the method Claim 1 until 7 to carry out. Computer-readable data carrier on which the computer program is written Claim 9 is stored.

Images