Control method of hydraulic dynamometer with segmentation and classification

Abstract

The control method of a hydraulic dynamometer with segmented and graded levels belongs to the technical field of prime mover calibration technology. In order to solve the problems of poor adjustment ability and high debugging risk of the existing hydraulic dynamometer control strategy, it includes: using the water inlet valve opening curve to perform closed-loop control on the water inlet valve, and using the "speed-torque" segmented curve with different segmented slopes to perform closed-loop control on the drain valve. The specific method of using the "speed-torque" segmented curve to perform closed-loop control on the drain valve includes: using the calibration key operating point of the prime mover as the segmentation point, dividing the operation process of the prime mover into several segments; performing "speed-torque" curve fitting on each segmented operation process, and obtaining several segments of curves with different slopes, namely the "speed-torque" segmented curve; according to the slopes of different segmented curves, obtaining the PID parameters of each segment, and performing graded position closed-loop PID control on the drain valve according to the PID parameters. The present invention is used for hydraulic dynamometers.

Description

Technical Field

[0001] The invention relates to a hydraulic dynamometer control method, belonging to the technical field of prime mover calibration. Background Art

[0002] Hydraulic dynamometer is a performance check and power consumption equipment for prime movers. The power, torque, speed and other parameters of prime movers (such as diesel engines, electric motors, gas turbines) are important performance indicators for equipment factory inspection. Large prime movers are often tested for performance and power consumption using high-power hydraulic dynamometers. Hydraulic dynamometers have the ability to adjust the load according to the working conditions of the prime mover, and rely on the water inlet valve and drain valve of the main body to adjust the load capacity.

[0003] The hydraulic dynamometer rotates synchronously with the rotor assembly on the main shaft of the prime mover through a coupling, stirring the water in the working chamber. Due to the centrifugal force generated by the rotation of the rotor and the effect of the rotor pits, a strong water vortex is generated between the shell and the rotor pits, which gives the shell a rotational torque, so that the torque of the power machine is transmitted to the shell by the rotor. The brake arm installed on the shell will rotate at an angle, so that the output force is measured by the tension and pressure sensor connected to the brake arm.

[0004] The hydraulic dynamometer adjusts the thickness of the water ring in the cavity by adjusting the opening of the inlet and outlet valves, thereby adjusting the power consumption. At present, the control strategy of the hydraulic dynamometer is: the inlet valve adjusts the valve opening of the inlet valve according to the preset speed-valve position linear curve; the outlet valve is used as the control and adjustment main control valve, and the control method is mainly based on the single-stage torque fitting curve closed-loop PID control. According to the continuous operating conditions of the prime mover, a "speed-torque fitting curve" is fitted. The curve is fitted in the form of T=a+b*n+c*n2+d*n3+e*n4, T is the target torque, and n is the speed of the prime mover; the hydraulic dynamometer measures the torque T*=F*L, F is the force value of the tension and pressure sensor detected, and L is the force arm of the hydraulic dynamometer; when T<T*, the outlet valve is closed, and when T>T*, the outlet valve is opened. The outlet valve performs closed-loop PID automatic adjustment according to the torque demand, and PID sets a set of parameters online. This control strategy has the following defects:

[0005] 1. During factory testing of prime movers, the operating conditions of several or dozens of specific operating points are often focused on, while there are generally no specific requirements for the operating process between the operating points. When a curve is fitted using known operating points in the current control strategy, either the curve has an unsmooth inflection point, increasing the control difficulty; or the fitted curve has a fitting deviation at the specific operating point that the prime mover focuses on;

[0006] 2. The current control strategy is that the prime mover fits a "speed-torque" curve based on continuous operating conditions, combined with a set of online PID parameters. This control strategy leads to poor regulation ability and cannot meet the requirements of full speed and full operating conditions of the hydraulic dynamometer. It cannot take into account the control requirements of low speed rapidity and high speed stability without overshoot.

[0007] 3. Once the load at a certain operating point changes during the prime mover test, it is necessary to refit the curve and re-adjust the PID parameters, which increases the workload of debugging and also increases the risk of debugging. Summary of the invention

[0008] The purpose of the present invention is to solve the problems of poor adjustment ability and high debugging risk of the existing hydraulic dynamometer control strategy, and to provide a segmented and graded hydraulic dynamometer control method.

[0009] The segmented and graded hydraulic dynamometer control method of the present invention comprises: using the water inlet valve opening curve to perform closed-loop control on the water inlet valve, and using a "speed-torque" segmented curve with different segmented slopes to perform closed-loop control on the drain valve.

[0010] Preferably, the specific method of using the water inlet valve opening curve to perform closed-loop control on the water inlet valve includes:

[0011] The water inlet valve is simulated by manual control mode to obtain the water inlet valve opening curve of the relationship between the unit speed and the water inlet valve opening;

[0012] The water inlet valve opening curve is used as the water inlet valve given instruction to perform closed-loop control on the water inlet valve.

[0013] Preferably, the water inlet control simulation of the water inlet valve is performed in manual control mode to obtain the water inlet valve opening curve of the relationship between the unit speed and the water inlet valve opening, which specifically includes:

[0014] Taking the unit speed as the reference point, the valve linearity, water inlet control, the interference of the water inlet valve adjustment on the drain valve and the corresponding opening of the drain valve are taken as coupling factors to obtain the relationship between the unit speed and the water inlet valve opening.

[0015] The water inlet valve opening curve is obtained by fitting the relationship between the unit speed and the water inlet valve opening.

[0016] Preferably, the specific method of using the "speed-torque" segmented curve to perform closed-loop control on the drain valve includes:

[0017] S1. Taking the key operating condition points of the prime mover as segmentation points, the operation process of the prime mover is divided into several segments;

[0018] S2, performing "speed-torque" curve fitting for each segmented operation process, and obtaining a number of curves with different slopes, namely, the "speed-torque" segmented curve;

[0019] S3. According to the slopes of different segmented curves, the PID parameters of each segment are obtained, and the graded position closed-loop PID control of the drain valve is performed according to the PID parameters.

[0020] Preferably, the specific method of performing "speed-torque" curve fitting for each segmented operation process described in S2 includes:

[0021] When the key operating points are densely packed, piecewise linear fitting is used to fit the "speed-torque" curve;

[0022] When the key operating points are discrete, a second-order curve or a third-order curve is used to fit the "speed-torque" curve.

[0023] Preferably, the specific method of obtaining the PID parameters of each segment according to the slopes of different segment curves in S3 includes:

[0024] When the slope of the segmented curve is small, set the PID parameters as follows: set P to a larger value and set I to a moderate value;

[0025] When the slope of the segmented curve is large, set the PID parameters as follows: reduce P and keep I unchanged;

[0026] When the slope of the segmented curve becomes significantly larger, set the PID parameters as follows: set P to a smaller value and add a D value.

[0027] Preferably, it also includes: firstly, manually controlling the water inlet valve and the drain valve according to the power characteristics of the prime mover, so that the opening of the water inlet valve and the drain valve in the full operating range is within the normal operating range, and the water inlet valve is opened to the valve position required for the full operating condition before the medium speed;

[0028] Then, the water inlet valve opening curve is used to perform closed-loop control on the water inlet valve, and a "speed-torque" segmented curve with different segmented slopes is used to perform closed-loop control on the drain valve.

[0029] Preferably, the openings of the water inlet valve and the drain valve in the full operating range are within the normal operating range, specifically including:

[0030] The working range of the water inlet valve and the drain valve are both adjusted within a linear range of 20%-80%.

[0031] Advantages of the present invention: The present invention proposes a segmented and graded hydraulic dynamometer control method, which obtains the optimal water inlet valve opening curve through a manual control mode according to the water supply pressure and flow conditions of the test bench. After the relationship between the water inlet valve opening and the speed is determined, the water inlet valve opening curve is input into the computer as a given instruction for the water inlet valve, and the water inlet valve performs position closed-loop control according to the speed of the prime mover and the opening curve.

[0032] The entire operation process of the prime mover is divided into several sections, and a series of working conditions that the prime mover is concerned about are used as the starting and ending points of the segmented torque curve. The torque curve is segmented and fitted. After fitting, the entire working condition is divided into several multi-segment "speed-torque" curves with different slopes. Different graded PID parameters are adjusted online for different slope curves. The drain valve performs graded position closed-loop PID control according to the multi-segment fitting curve of the prime mover's "speed-torque". Different PID parameter fittings meet the rapidity, stability, and small overshoot of the drain valve.

[0033] The present invention adjusts the control strategy of the hydraulic dynamometer, eliminates the fitting error of the working point of the prime mover calibration, and improves the control accuracy of each power curve by adjusting different PID parameter values ​​of the segmented curve, thereby improving the control accuracy of the hydraulic dynamometer, increasing the control stability, reducing the debugging workload, and reducing the debugging risk. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the multi-stage torque fitting curve diagram of hydraulic dynamometer;

[0035] Figure 2 It is the torque control block diagram of hydraulic dynamometer. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0038] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0039] Embodiment 1:

[0040] The segmented and graded hydraulic dynamometer control method described in this embodiment includes: using the water inlet valve opening curve to perform closed-loop control on the water inlet valve, and using a "speed-torque" segmented curve with different segmented slopes to perform closed-loop control on the drain valve.

[0041] Furthermore, the specific method of using the water inlet valve opening curve to perform closed-loop control on the water inlet valve includes:

[0042] The water inlet valve is simulated by manual control mode to obtain the water inlet valve opening curve of the relationship between the unit speed and the water inlet valve opening;

[0043] The water inlet valve opening curve is used as the water inlet valve given instruction to perform closed-loop control on the water inlet valve.

[0044] Furthermore, the water inlet control simulation of the water inlet valve is performed in manual control mode to obtain the water inlet valve opening curve of the relationship between the unit speed and the water inlet valve opening, which specifically includes:

[0045] Taking the unit speed as the reference point, the valve linearity, water inlet control, the interference of the water inlet valve adjustment on the drain valve and the corresponding opening of the drain valve are taken as coupling factors to obtain the relationship between the unit speed and the water inlet valve opening.

[0046] The water inlet valve opening curve is obtained by fitting the relationship between the unit speed and the water inlet valve opening.

[0047] Embodiment 2:

[0048] Combine the following Figure 1 To illustrate the present embodiment, the segmented and graded hydraulic dynamometer control method described in the present embodiment comprises: using an inlet valve opening curve to perform closed-loop control on the inlet valve, and using a "speed-torque" segmented curve with different segmented slopes to perform closed-loop control on the drain valve.

[0049] Furthermore, the specific method of using the "speed-torque" segmented curve to perform closed-loop control on the drain valve includes:

[0050] S1. Taking the key operating condition points of the prime mover as segmentation points, the operation process of the prime mover is divided into several segments;

[0051] S2, performing "speed-torque" curve fitting for each segmented operation process, and obtaining a number of curves with different slopes, namely, the "speed-torque" segmented curve;

[0052] S3. According to the slopes of different segmented curves, the PID parameters of each segment are obtained, and the graded position closed-loop PID control of the drain valve is performed according to the PID parameters.

[0053] Furthermore, the specific method of performing “speed-torque” curve fitting for each segmented operation process in S2 includes:

[0054] When the key operating points are densely packed, piecewise linear fitting is used to fit the "speed-torque" curve;

[0055] When the key operating points are discrete, a second-order curve or a third-order curve is used to fit the "speed-torque" curve.

[0056] Furthermore, the specific method of obtaining the PID parameters of each segment according to the slopes of different segment curves in S3 includes:

[0057] When the slope of the segmented curve is small, set the PID parameters as follows: set P to a larger value and set I to a moderate value;

[0058] When the slope of the segmented curve is large, set the PID parameters as follows: reduce P and keep I unchanged;

[0059] When the slope of the segmented curve becomes significantly larger, set the PID parameters as follows: set P to a smaller value and add a D value.

[0060] Furthermore, it also includes: firstly, manually controlling the water inlet valve and the drain valve according to the power characteristics of the prime mover, so that the openings of the water inlet valve and the drain valve in the full operating range are within the normal operating range, and the water inlet valve is opened to the valve position required for the full operating condition before the medium speed;

[0061] Then, the water inlet valve opening curve is used to perform closed-loop control on the water inlet valve, and a "speed-torque" segmented curve with different segmented slopes is used to perform closed-loop control on the drain valve.

[0062] Furthermore, the openings of the water inlet valve and the drain valve in the full operating range are within the normal operating range, specifically including:

[0063] The working range of the water inlet valve and the drain valve are both adjusted within a linear range of 20%-80%.

[0064] In the present invention, according to the water supply pressure and flow of the test bench, the optimal water inlet valve opening curve is explored through the manual control mode. The water inlet valve opening curve takes the speed of the unit as the reference point. The water inlet valve opening needs to consider multiple coupling factors such as valve linearity, water inlet control, the interference effect of water inlet valve regulation on the drain valve, and the corresponding opening of the drain valve. After the relationship between the water inlet valve opening and the speed is determined, the water inlet valve opening curve is input into the computer as the water inlet valve given instruction, and the water inlet valve performs position closed-loop control according to the speed of the prime mover and the opening curve.

[0065] According to the multi-stage hierarchical control method described in the present invention, the entire operation process of the prime mover is divided into several sections, and a series of operating points of concern to the prime mover are used as the segmented starting and ending points of the segmented torque curve. The torque curve is segmentedly fitted, and after fitting, the entire operating condition is divided into several sections of "speed-torque" curves with different slopes, and PID parameters with different grades are adjusted online for curves with different slopes.

[0066] How to use the hydraulic dynamometer: The power generated by the prime mover is transmitted to the rotor of the dynamometer through the transmission shaft. The rotor rotates in the water, and the water rotates with it due to the friction with the turntable. Under the action of centrifugal force, the water is thrown to the inner wall of the shell to form a water ring and increase its kinetic moment. At the same time, the shell will swing around the axis under the impact of water. When the water hits the shell wall, it is subject to friction resistance, and the kinetic energy is converted into heat energy. When the power generated by the prime mover is greater than the absorbed power of the hydraulic dynamometer, the speed of the unit increases; when the power generated by the prime mover is less than the absorbed power of the hydraulic dynamometer, the speed of the unit will decrease. Only when the output power of the prime mover is equal to the absorbed power of the hydraulic dynamometer can the prime mover be guaranteed to operate stably at the operating point. The working performance verification of the prime mover requires the hydraulic dynamometer to stably absorb the power at the current working point. When the power generated by the prime mover remains unchanged, the absorbed power of the hydraulic dynamometer is guaranteed to match the output power, so that the speed of the system remains stable and unchanged, ensuring that the prime mover operates stably at the assessment working point.

[0067] Control core of hydraulic dynamometer: Hydraulic dynamometer has two modes: manual control and automatic control. In manual control mode, the operator adjusts the valve position of the water inlet valve and the drain valve according to the power value to be consumed by the prime mover to ensure that the power consumption of the hydraulic dynamometer is equal to the power output of the prime mover and the unit operates stably at the operating point. Automatic control means no human intervention. The hydraulic dynamometer uses the speed value transmitted by the prime mover through the coupling as the operating condition information. The water inlet valve realizes closed-loop control according to the pre-set curve, and the drain valve realizes closed-loop control according to the pre-fitted torque curve.

[0068] Manual control mode and control method of hydraulic dynamometer: Manual control means that the operator takes power or torque as the operation target (power = torque * speed). At this time, the speed of the hydraulic dynamometer is controlled by the prime mover, and the speed of the prime mover fluctuates due to the power consumption of the hydraulic dynamometer. When the prime mover emits the specified working power, if the power consumption of the hydraulic dynamometer is equal to the power emitted by the prime mover, the prime mover will stably operate at the speed value corresponding to the specified power; when the power consumption of the hydraulic dynamometer is less than the power emitted by the prime mover, the system speed increases; when the power consumption of the hydraulic dynamometer is greater than the power emitted by the prime mover, the system speed decreases, which makes the system unable to operate at the target assessment working condition of the prime mover. The operator observes the difference between the current power consumption of the hydraulic dynamometer and the target power of the prime mover, and chooses to adjust the opening of the water inlet valve and the drain valve, thereby adjusting the thickness of the water ring in the hydraulic dynamometer to adjust the power consumption of the hydraulic dynamometer. When the power value measured by the hydraulic dynamometer is less than the target power value, open the water inlet valve and close the drain valve; when the power value measured by the hydraulic dynamometer is greater than the target power value, close the water inlet valve and open the drain valve; while the hydraulic dynamometer is adjusting the power, the prime mover will also adjust its output power value accordingly, ultimately making the unit stably operate at a specific operating point of the target speed and power.

[0069] Automatic control mode and control method of hydraulic dynamometer: The control principle of the automatic control mode of hydraulic dynamometer is similar to that of manual control. The automatic control mode of hydraulic dynamometer includes three control modes: speed control, torque control and power control.

[0070] The speed control mode is mainly used for automobile engine testing, factory testing of gas engines, diesel engines, steam turbines, motors, etc.

[0071] The torque control mode is based on the torque value as a constant target control quantity, combined with Figure 1 As shown, the actual measured torque value is compared with the target torque value, and the difference is used as the control instruction of the torque controller. The control instruction controls the actuator of the inlet and outlet valves to perform the switch valve action, changing the thickness of the water ring in the hydraulic dynamometer, thereby achieving the purpose of stabilizing the torque at a constant value.

[0072] The power control mode runs according to a pre-set power curve. The control principle is equivalent to the dynamic torque control mode. The given torque value changes according to the curve, and the control tracking target is still the torque value. The torque control and power control modes of hydraulic dynamometers are more commonly used.

[0073] In the automatic control mode, the water inlet valve implements closed-loop control according to the "speed-valve position" curve relationship. The control logic is simple and the control accuracy requirement is not high. The main purpose of the control is to ensure that sufficient water flow enters the hydraulic dynamometer to take away the heat after the dynamometer consumes power and avoid excessive water temperature rise; and to control the water volume not to be excessive, so as to avoid excessive water flow and impact on the hydraulic dynamometer bearings. The drain valve of the hydraulic dynamometer is used for the precise control of the hydraulic dynamometer. The control method of the present invention will be used in the control of the drain valve, thereby improving the control effect of the hydraulic dynamometer.

[0074] The control method of the drain valve of the present invention specifically includes: when the working point of the prime mover changes, that is, the speed and torque value of the prime mover change, the curve formed by fitting these change points is the prime mover power curve. In the process of curve fitting, it is impossible to ensure that all working points coincide with the fitting curve, resulting in deviations in the given control instructions of the prime mover verification key points. The present invention breaks through the conventional idea of ​​fitting a curve for all working points, takes the verification key points of the prime mover as the starting and ending points of the segmented fitting curve, and then considers the smoothness of the entire curve to perform segmented curve fitting, which not only ensures the accuracy of the power instruction of the verification key points, but also ensures the smoothness of the entire curve. Therefore, for the fitting curves of different segments, the PID parameters suitable for the segmented curve are adjusted online. When the prime mover is running at low speed and low power, the slope of the fitted curve is small, requiring the prime mover to move quickly from one operating point to the next operating point, and the overshoot limit of the adjustment is not strict. At this time, the P in the drain valve control PID parameter is large, and I takes an appropriate value to eliminate the steady-state error, which well meets the maneuverability requirements of the prime mover; when the prime mover is running at mid-speed and mid-power, the slope of the fitted curve becomes larger, requiring the prime mover to move quickly from one operating point to the next operating point, and the system overshoot is small. At this time, the P in the drain valve control PID parameter is slightly reduced, and I remains unchanged, which meets the maneuverability and stability requirements of the prime mover; when the prime mover is running at high speed and high power, the slope of the fitted power curve increases significantly, and the valve opening at this time has a very obvious impact on the power, requiring the system to take stability and no overshoot as the main control indicator. At this time, the P value is required to be small, and the D value is appropriately added to ensure smooth regulation of the system without overshoot.

[0075] When certain operating points need to be changed during the test, there is no need to change the entire prime mover power curve. Only the operating point to be changed needs to be changed, which will only affect the segmented power curve containing the operating point. Even if the control PID parameters need to be adjusted due to the change of the segmented power curve, the adjustment range is fine-tuning, which reduces the difficulty and risk of debugging and saves debugging time.

[0076] The specific implementation steps of the present invention include:

[0077] Manually control the inlet and drain valves according to the power characteristics of the prime mover to make the opening of the inlet and drain valves reasonable within the full operating range, and the working range of the inlet and drain valves can be adjusted within a good linear range of 20%-80%; before medium speed, open the inlet valve to the valve position required for the full operating condition to avoid interference of the inlet valve adjustment on the drain valve and increase the difficulty of adjusting the drain valve.

[0078] The opening curve of the water inlet valve is input into the control program so that the controller can complete the closed-loop position control of the water inlet valve.

[0079] Taking the example operating point data in Table 1 as an example, the prime mover torque curve fitting includes: determining several test operating points of the prime mover, using these operating points as segment endpoints of the multi-segment graded control curve. If the test points of the test operating condition are dense, piecewise linear fitting can be used for curve fitting; if the test operating points are discrete, second-order and third-order curves can be appropriately selected for segmented fitting to ensure that the entire curve is continuous and smooth, and the operating point fitting is accurate without fitting errors. Figure 2 The multi-segment torque fitting curve of the hydraulic dynamometer is shown in the figure. The multi-segment fitting curve of the drain valve is input into the control program.

[0080] Table 1

[0081] Working conditions Speed ​​(rpm) Torque(kNm) Power (kW) Condition 1 50 131 686 Condition 2 89 334 3113 Condition 3 121 676 8565 Condition 4 140 920 13487 Condition 5 171 1360 24352 Condition 6 184 1662 32022 Condition 7 200 1820 38115

[0082] The prime mover cooperates with the hydraulic dynamometer to do PID graded adjustment. In low working conditions, a larger P parameter is selected to improve the response speed of the system; in high working conditions, a smaller P is appropriately selected and the D parameter is appropriately added to reduce the system overshoot and improve the control accuracy of the system. The prime mover operates according to its assessment working point, and a series of working point torques are used as the control effect assessment value to obtain the ideal multi-stage graded PID value, thereby realizing the closed-loop control of the drain valve.

[0083] It has been verified through experiments that the multi-stage hydraulic dynamometer control method of the present invention can accurately control the hydraulic dynamometer to stably operate at the prime mover assessment operating point for a long time in practical applications, which greatly saves debugging time, improves control accuracy, and has good effects.

[0084] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A step-by-step hydraulic dynamometer control method, characterized in that: The method comprises: using the water inlet valve opening curve to perform closed-loop control on the water inlet valve, and using a "speed-torque" segmented curve with different segmented slopes to perform closed-loop control on the drain valve.

2. The control method of the segmented and graded hydraulic dynamometer according to claim 1, characterized in that: The specific method of using the water inlet valve opening curve to perform closed-loop control on the water inlet valve includes: The water inlet valve is simulated by manual control mode to obtain the water inlet valve opening curve of the relationship between the unit speed and the water inlet valve opening; The water inlet valve opening curve is used as the water inlet valve given instruction to perform closed-loop control on the water inlet valve.

3. The control method of the segmented and graded hydraulic dynamometer according to claim 2, characterized in that: The water inlet valve is simulated by the manual control mode to obtain the water inlet valve opening curve of the relationship between the unit speed and the water inlet valve opening, which specifically includes: Taking the unit speed as the reference point, the valve linearity, water inlet control, the interference of the water inlet valve adjustment on the drain valve and the corresponding opening of the drain valve are taken as coupling factors to obtain the relationship between the unit speed and the water inlet valve opening. The water inlet valve opening curve is obtained by fitting the relationship between the unit speed and the water inlet valve opening.

4. The control method of the segmented and graded hydraulic dynamometer according to claim 1, characterized in that: The specific methods of using the "speed-torque" segmented curve to perform closed-loop control on the drain valve include: S1. Taking the key operating condition points of the prime mover as segmentation points, the operation process of the prime mover is divided into several segments; S2. Perform "speed-torque" curve fitting for each segmented operation process to obtain several segments of curves with different slopes, namely, the "speed-torque" segmented curves; S3. According to the slopes of different segmented curves, the PID parameters of each segment are obtained, and the graded position closed-loop PID control of the drain valve is performed according to the PID parameters.

5. The control method of the segmented and graded hydraulic dynamometer according to claim 4, characterized in that: The specific method of performing "speed-torque" curve fitting for each segmented operation process described in S2 includes: When the key operating points are densely packed, piecewise linear fitting is used to fit the "speed-torque" curve; When the key operating points are discrete, a second-order curve or a third-order curve is used to fit the "speed-torque" curve.

6. The control method of the segmented and graded hydraulic dynamometer according to claim 4, characterized in that: The specific method of obtaining the PID parameters of each segment according to the slopes of different segment curves in S3 includes: When the slope of the segmented curve is small, set the PID parameters as follows: set P to a larger value and set I to a moderate value; When the slope of the segmented curve is large, set the PID parameters as follows: reduce P and keep I unchanged; When the slope of the segmented curve becomes significantly larger, set the PID parameters as follows: set P to a smaller value and add a D value.

7. The control method of the segmented and graded hydraulic dynamometer according to claim 1, characterized in that: It also includes: firstly, manually controlling the water inlet valve and the drain valve according to the power characteristics of the prime mover, so that the openings of the water inlet valve and the drain valve in the full working range are within the normal working range, and the water inlet valve is opened to the valve position required for the full working condition before the medium speed; Then, the water inlet valve opening curve is used to perform closed-loop control on the water inlet valve, and the "speed-torque" segmented curve with different segmented slopes is used to perform closed-loop control on the drain valve.

8. The control method of the segmented and graded hydraulic dynamometer according to claim 7, characterized in that: The openings of the water inlet valve and the drain valve in the full operating range are within the normal operating range, specifically including: The working range of the water inlet valve and the drain valve are both adjusted within a linear range of 20%-80%.

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