Control method and control device of hydraulic system and engineering machinery

Abstract

The invention relates to the technical field of automatic control, and provides a control method and a control device of a hydraulic system and engineering machinery, vector control is used for directly regulating and controlling a hydraulic pump without depending on an intermediate link of the hydraulic system, the response is at a millisecond level, and when a load suddenly changes, the torque of a motor can be quickly limited, power overshoot is avoided, and the reliability of the hydraulic system is improved. The motor and battery system is protected, closed-loop control over the rotating speed is carried out, precision is higher, the torque upper limit is controlled by directly inputting the required power, the power is limited to be kept constant, the method is suitable for various complex scenes, high-speed and large-flow operation of the variable pump during light load can be achieved, the speed requirement is met, and the working efficiency is improved. And low-speed small-flow operation is achieved during heavy load, the safety requirement is met, a constant displacement pump and / or a variable displacement pump can be compatible at the same time, the problem that constant-power control cannot be achieved through the constant displacement pump is solved, and economy and environment friendliness are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of automatic control, and particularly relates to a control method for a hydraulic system, a control device for a hydraulic system, and a construction machine. Background Art

[0002] Constant power control is widely used in construction machines such as excavators and loaders. By adjusting the output of the engine and the hydraulic system, the power of the equipment is maintained constant under different working conditions. The core goal is to improve fuel efficiency, reduce energy consumption, and ensure the stable operation of the equipment under various load conditions. In working conditions with frequent load changes, this technology can significantly improve efficiency and energy-saving effects, while ensuring the stable operation of the equipment under different working conditions, reducing failures, avoiding overloading of the engine and the hydraulic system, and extending the service life of the equipment.

[0003] In related technologies, generally, the displacement of the hydraulic pump is adjusted to maintain a constant power, that is, when the load increases, the displacement is reduced; when the load decreases, the displacement is increased, or the engine (internal combustion engine) speed is adjusted to meet the power demand of the hydraulic pump.

[0004] However, in the above scheme of adjusting the displacement of the hydraulic pump to maintain a constant power, the dynamic response of hydraulic adjustment is a mechanical response, which depends on the dynamic characteristics of the hydraulic system, and there is a certain lag in adjustment. Especially when the load suddenly changes (such as when an excavator suddenly encounters hard rock), it will cause power overshoot and impact on the motor and battery system. At the same time, the pressure / flow control of the hydraulic system is affected by factors such as oil temperature and leakage, and the accuracy is low. In the scheme of achieving constant power by adjusting the engine (internal combustion engine) speed, the fuel injection amount is adjusted to maintain the speed stability. Limited by the fuel combustion process, the dynamic response is also slow. At the same time, the internal combustion engine uses fuel, which belongs to non-clean energy. Summary of the Invention

[0005] To solve the above technical problems, the first object of the present invention is to propose a control method for a hydraulic system.

[0006] The second object of the present invention is to propose a control device for a hydraulic system.

[0007] The third object of the present invention is to propose a construction machine.

[0008] The technical solution adopted by the present invention is as follows:

[0009] An embodiment of the first aspect of the present invention provides a control method for a hydraulic system, including the following steps: obtaining the required torque of the motor of the hydraulic system according to the load of the hydraulic pump of the hydraulic system, where the hydraulic pump includes a fixed-displacement pump and / or a variable-displacement pump; outputting a three-phase PWM (Pulse Width Modulation) signal to the motor according to the required torque; obtaining the actual speed of the motor, and judging whether the motor reaches the target speed according to the actual speed; when the motor reaches the target speed, judging whether the motor is in the constant power control mode; if the motor is in the constant power control mode, obtaining the required power, obtaining the torque upper limit according to the required power, and limiting the torque output by the motor according to the torque upper limit to limit the torque of the hydraulic pump.

[0010] The control method for the hydraulic system proposed above in the present invention may further have the following additional technical features:

[0011] According to an embodiment of the present invention, the above control method for the hydraulic system further includes: if the motor is not in the constant power control mode, obtaining the target speed; performing PI (Proportional-Integral) calculation according to the target speed and the actual speed of the motor to obtain the required torque of the motor.

[0012] According to an embodiment of the present invention, outputting a three-phase PWM signal to the motor according to the required torque specifically includes: obtaining the dq-axis current corresponding to the motor according to the required torque; obtaining the αβ-axis voltage according to the dq-axis current; generating a three-phase PWM signal by using SVPWM (Space Vector Pulse Width Modulation) according to the αβ-axis voltage and outputting it to the motor.

[0013] According to an embodiment of the present invention, the torque upper limit is specifically obtained according to the following formula: Tmax = 9549 * P / n; where Tmax is the torque upper limit, P is the required power, and n is the actual speed.

[0014] A second aspect embodiment of the present invention provides a control device for a hydraulic system, including: a first acquisition module, which is used to obtain the required torque of the motor of the hydraulic system according to the load of the hydraulic pump of the hydraulic system, and the hydraulic pump includes a fixed displacement pump and / or a variable displacement pump; a first output module, which is used to output a three-phase PWM signal to the motor according to the required torque; a first judgment module, which is used to obtain the actual speed of the motor and judge whether the motor reaches the target speed according to the actual speed; a second judgment module, which is used to judge whether the motor is in the constant power control mode when the motor reaches the target speed; a second output module, which is used to obtain the required power when the motor is in the constant power control mode, obtain the torque upper limit according to the required power, and limit the motor output torque according to the torque upper limit to limit the torque of the hydraulic pump.

[0015] The control device for the hydraulic system proposed above in the present invention may also have the following additional technical features:

[0016] According to an embodiment of the present invention, the above control device for the hydraulic system further includes: a PI module, which is used to obtain the target speed when the motor is not in the constant power control mode, perform PI calculation according to the target speed and the actual speed of the motor, and obtain the required torque of the motor.

[0017] According to an embodiment of the present invention, the first output module is specifically used for: obtaining the dq-axis current corresponding to the motor according to the required torque; obtaining the αβ-axis voltage according to the dq-axis current; generating a three-phase PWM signal by using SVPWM according to the αβ-axis voltage and outputting it to the motor.

[0018] According to an embodiment of the present invention, the second output module specifically obtains the torque upper limit according to the following formula: Tmax = 9549 * P / n; where Tmax is the torque upper limit, P is the required power, and n is the actual speed.

[0019] Advantages of the present invention:

[0020] The present invention uses vector control to directly regulate the hydraulic pump, without relying on the intermediate links of the hydraulic system, and the response is in milliseconds. When the load changes suddenly, it can quickly limit the motor torque, avoid power overshoot, and protect the motor and the battery system.

[0021] The speed control of the present invention adopts closed-loop control, with higher accuracy.

[0022] The present invention controls the torque upper limit by directly inputting power, restricts the power to remain constant and constant power, is applicable to various complex scenarios, can achieve high-speed and large-flow operation of a variable pump under light load to meet the speed requirements, and low-speed and small-flow operation under heavy load to meet the safety requirements. It can be compatible with fixed displacement pumps and / or variable displacement pumps at the same time, solves the problem that fixed displacement pumps cannot achieve constant power control, and is economical and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flowchart of a control method for a hydraulic system according to an embodiment of the present invention;

[0024] Figure 2 is a flowchart of a control method for a hydraulic system according to another embodiment of the present invention;

[0025] Figure 3 is a schematic block diagram of a control device for a hydraulic system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] Figure 1 is a flowchart of a control method for a hydraulic system according to an embodiment of the present invention, as Figure 1 shown, the method includes the following steps:

[0028] S1. Obtain the required torque of the motor of the hydraulic system according to the load of the hydraulic pump of the hydraulic system, and the hydraulic pump includes a fixed displacement pump and / or a variable displacement pump.

[0029] Specifically, the required torque of the motor is determined according to the load of the hydraulic pump. Generally, T = (V * ΔP) / 2π, where T is the required torque, V is the displacement of the hydraulic pump, and ΔP is the load.

[0030] S2. Output a three-phase PWM signal to the motor according to the required torque.

[0031] S3. Obtain the actual speed of the motor, and judge whether the motor reaches the target speed according to the actual speed.

[0032] S4. When the motor reaches the target speed, judge whether the motor is in the constant power control mode.

[0033] In the present invention, when the motor operating condition needs to enter the constant power control at a relatively stable speed, therefore, when the motor reaches the target speed, it is necessary to wait for the motor to reach the stable speed before proceeding with subsequent control. If the motor reaches the target speed and maintains for a certain period of time, it can be determined that the motor reaches the stable speed. The present invention can perform closed-loop control of the speed through a current sensor and an encoder, with an accuracy of up to ±1%, and the accuracy is high.

[0034] S5. If the motor is in the constant power control mode, obtain the required power, obtain the torque upper limit according to the required power, and limit the motor output torque according to the torque upper limit to limit the torque of the hydraulic pump.

[0035] Specifically, when the load of the hydraulic pump suddenly changes, the required torque of the motor in the hydraulic system will change accordingly. Obtain the required torque corresponding to the load, calculate the corresponding PWM signal and input it to the motor. After the motor is in a stable speed state, if it is in the constant power control mode, obtain the torque upper limit according to the required power, and limit the motor output torque according to the torque upper limit, so as to directly regulate the output torque of the hydraulic pump. Thus, the vector control is used to directly regulate the hydraulic pump, without relying on the intermediate links of the hydraulic system, and the response is in milliseconds. When the load suddenly changes, the motor torque can be quickly limited to avoid power overshoot and protect the motor and the battery system.

[0036] The required power is the magnitude of the target power to be controlled, and this power should not exceed the power external characteristic at the current speed, and this value is pre-stored through motor calibration. After entering the constant power control mode, the torque upper limit can be calculated by the formula T = 9549*P / n. Limit the motor output torque according to the torque upper limit to achieve constant power, which is applicable to various complex scenarios. It can realize high-speed and large-flow operation of the variable pump under light load to meet the speed requirements, and low-speed and small-flow operation under heavy load to meet the safety requirements. It can be compatible with fixed displacement pumps and / or variable displacement pumps at the same time, solve the problem that the fixed displacement pump cannot achieve constant power control, and is economical and environmentally friendly.

[0037] In a specific embodiment of the present invention, the torque upper limit is specifically obtained according to the following formula:

[0038] Tmax = 9549*P / n;

[0039] Wherein, Tmax is the torque upper limit, P is the required power, and n is the actual speed.

[0040] In an embodiment of the present invention, as Figure 2 shown, the above control method of the hydraulic system may further include:

[0041] S6. If the motor is not in the constant power control mode, obtain the target speed.

[0042] S7. Perform PI calculation based on the target speed and the actual motor speed to obtain the required torque of the motor.

[0043] Specifically, if the motor is not in the constant power control mode, perform PI calculation based on the slip between the target speed and the actual speed to obtain the corresponding torque.

[0044] In an embodiment of the present invention, as Figure 2 shown, output three-phase PWM signals to the motor according to the required torque, specifically including:

[0045] S21. Obtain the dq-axis currents corresponding to the motor according to the required torque.

[0046] Specifically, the dq-axis currents corresponding to the motor can be obtained by looking up a torque-dq-axis current table, and the torque-dq-axis current table is pre-stored in advance.

[0047] S22. Obtain the αβ-axis voltages according to the dq-axis currents.

[0048] S23. Generate three-phase PWM signals according to the αβ-axis voltages by using SVPWM and output them to the motor.

[0049] Specifically, the speed control is achieved by controlling the dq-axis currents through FOC (Field-Oriented Control). When the working condition is at a relatively stable speed, the constant power control can be entered. The current loop response of FOC is in the millisecond level, while the pressure / flow regulation of the hydraulic system requires dozens to hundreds of milliseconds. Especially when the load suddenly changes (such as when an excavator suddenly encounters hard rock), FOC can quickly limit the torque to avoid power overshoot and protect the motor and the battery system.

[0050] In summary, according to the control method of the hydraulic system in the embodiment of the present invention, vector control is used to directly regulate the hydraulic pump without relying on the intermediate links of the hydraulic system. The response is in the millisecond level. When the load suddenly changes, the motor torque can be quickly limited to avoid power overshoot and protect the motor and the battery system. Moreover, closed-loop speed control is performed with higher accuracy. The present invention also controls the torque upper limit by directly inputting the required power to limit the power and keep it constant at a constant power, which is applicable to various complex scenarios. It can enable the variable pump to operate at high speed and large flow under light load to meet the speed requirements, and operate at low speed and small flow under heavy load to meet the safety requirements. It can be compatible with fixed displacement pumps and / or variable displacement pumps at the same time, solving the problem that fixed displacement pumps cannot achieve constant power control, and is economical and environmentally friendly.

[0051] Corresponding to the above control method of the hydraulic system, the present invention also proposes a control device for the hydraulic system.

[0052] Figure 3It is a block diagram of a control device for a hydraulic system according to an embodiment of the present invention, as Figure 3 shown. The device includes: a first acquisition module, a first output module, a first judgment module, a second judgment module, and a second output module.

[0053] Among them, the first acquisition module is used to obtain the required torque of the motor of the hydraulic system according to the load of the hydraulic pump of the hydraulic system. The hydraulic pump includes a fixed-displacement pump and / or a variable-displacement pump; the first output module is used to output a three-phase PWM signal to the motor according to the required torque; the first judgment module is used to obtain the actual speed of the motor and judge whether the motor reaches the target speed according to the actual speed; the second judgment module is used to judge whether the motor is in the constant power control mode when the motor reaches the target speed; the second output module is used to obtain the required power when the motor is in the constant power control mode, obtain the torque upper limit according to the required power, and limit the motor output torque according to the torque upper limit to limit the torque of the hydraulic pump.

[0054] According to an embodiment of the present invention, the above control device for the hydraulic system further includes: a PI module. The PI module is used to obtain the target speed when the motor is not in the constant power control mode, perform PI calculation according to the target speed and the actual speed of the motor, and obtain the required torque of the motor.

[0055] According to an embodiment of the present invention, the first output module is specifically used to: obtain the dq-axis current corresponding to the motor according to the required torque; obtain the αβ-axis voltage according to the dq-axis current; generate a three-phase PWM signal by using SVPWM according to the αβ-axis voltage and output it to the motor.

[0056] According to an embodiment of the present invention, the second output module specifically obtains the torque upper limit according to the following formula: Tmax = 9549 * P / n; where Tmax is the torque upper limit, P is the required power, and n is the actual speed.

[0057] The control device for the hydraulic system according to the embodiment of the present invention directly regulates the hydraulic pump by using vector control, without relying on the intermediate links of the hydraulic system, and the response is in milliseconds. When the load changes suddenly, it can quickly limit the motor torque, avoid power overshoot, protect the motor and the battery system, and perform closed-loop control of the speed with higher precision. The present invention also controls the torque upper limit by directly inputting the required power, limits the power to keep it constant at a constant power, is applicable to various complex scenarios, can realize high-speed and large-flow operation of the variable-displacement pump under light load to meet the speed requirements, and low-speed and small-flow operation under heavy load to meet the safety requirements. It can be compatible with a fixed-displacement pump and / or a variable-displacement pump at the same time, solves the problem that the fixed-displacement pump cannot achieve constant power control, and is economical and environmentally friendly.

[0058] In addition, the present invention also proposes a construction machinery including the above control device for the hydraulic system.

[0059] For the construction machinery according to an embodiment of the present invention, vector control is used to directly regulate the hydraulic pump, without relying on the intermediate links of the hydraulic system, and the response is in the millisecond level. When the load suddenly changes, the motor torque can be quickly limited to avoid power overshoot, protect the motor and the battery system, and perform closed-loop control of the speed with higher precision. The present invention also controls the torque upper limit by directly inputting the required power, limits the power to maintain a constant constant power, is applicable to various complex scenarios, can realize high-speed and large-flow operation of the variable pump under light load to meet the speed requirements, and low-speed and small-flow operation under heavy load to meet the safety requirements. It can be compatible with fixed displacement pumps and / or variable displacement pumps at the same time, solves the problem that fixed displacement pumps cannot achieve constant power control, and is economical and environmentally friendly.

[0060] In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0061] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0062] Any process or method description shown in the flowchart or described in other ways herein can be understood as representing a module, segment, or part of the code including one or more executable instructions for implementing a customized logical function or process. The scope of the preferred embodiments of the present invention includes additional implementations, where the functions can be executed in a substantially simultaneous manner or in the reverse order according to the involved functions, rather than in the order shown or discussed, which should be understood by those skilled in the technical field to which the embodiments of the present invention belong.

[0063] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, which can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or in conjunction with these instruction execution systems, apparatus, or devices. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport a program for use by or in conjunction with an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium include the following: an electrical connection portion having one or more wirings (electronic device), a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable media on which the program can be printed, because the program can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpretation, or otherwise processing as appropriate, and then storing it in a computer memory.

[0064] It should be understood that various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), and the like.

[0065] Those of ordinary skill in the art of this technology can understand that all or part of the steps carried by the method of the above embodiments can be completed by instructing relevant hardware through a program, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiments.

[0066] In addition, each functional unit in various embodiments of the present invention may be integrated into a processing module, or each unit may exist physically alone, or two or more units may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of a software functional module. When the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it may also be stored in a computer-readable storage medium.

[0067] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A control method for a hydraulic system, characterized in that, It includes the following steps: Obtain the required torque of the motor of the hydraulic system according to the load of the hydraulic pump of the hydraulic system, where the hydraulic pump includes a fixed-displacement pump and / or a variable-displacement pump; Output a three-phase PWM signal to the motor according to the required torque; Obtain the actual speed of the motor, and judge whether the motor reaches the target speed according to the actual speed; When the motor reaches the target speed, judge whether the motor is in the constant power control mode; If the motor is in the constant power control mode, obtain the required power, obtain the torque upper limit according to the required power, and limit the motor output torque according to the torque upper limit to limit the torque of the hydraulic pump.

2. The control method of the hydraulic system according to claim 1, characterized in that, It also includes: If the motor is not in the constant power control mode, obtain the target speed; Perform PI calculation according to the target speed and the actual speed of the motor to obtain the required torque of the motor.

3. The control method of the hydraulic system according to claim 1, characterized in that, Outputting a three-phase PWM signal to the motor according to the required torque specifically includes: Obtain the dq-axis current corresponding to the motor according to the required torque; Obtain the αβ-axis voltage according to the dq-axis current; Generate a three-phase PWM signal by SVPWM according to the αβ-axis voltage and output it to the motor.

4. The control method of the hydraulic system according to claim 1, characterized in that, Specifically obtain the torque upper limit according to the following formula: Tmax = 9549 * P / n; Where, Tmax is the torque upper limit, P is the required power, and n is the actual speed.

5. A control device for a hydraulic system, characterized in that, It includes: A first acquisition module, which is used to obtain the required torque of the motor of the hydraulic system according to the load of the hydraulic pump of the hydraulic system, where the hydraulic pump includes a fixed-displacement pump and / or a variable-displacement pump; A first output module, which is used to output a three-phase PWM signal to the motor according to the required torque; A first judgment module, which is used to obtain the actual speed of the motor and judge whether the motor reaches the target speed according to the actual speed; A second judgment module, which is used to judge whether the motor is in the constant power control mode when the motor reaches the target speed; A second output module, which is used to obtain the required power when the motor is in the constant power control mode, obtain the torque upper limit according to the required power, and limit the motor output torque according to the torque upper limit to limit the torque of the hydraulic pump.

6. The control device of the hydraulic system according to claim 5, characterized in that It also includes: A PI module, which is used to obtain the target speed when the motor is not in the constant power control mode, perform PI calculation according to the target speed and the actual speed of the motor, and obtain the required torque of the motor.

7. The control device of the hydraulic system according to claim 5, characterized in that, The first output module is specifically used for: Obtain the dq-axis current corresponding to the motor according to the required torque; Obtain the αβ-axis voltage according to the dq-axis current; Generate a three-phase PWM signal by SVPWM according to the αβ-axis voltage and output it to the motor.

8. The control device of the hydraulic system according to claim 5, characterized in that, The second output module specifically obtains the torque upper limit according to the following formula: Tmax = 9549 * P / n; Where, Tmax is the torque upper limit, P is the required power, and n is the actual speed.

9. A construction machinery, including the control device of the hydraulic system according to any one of claims 5-8.

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