A quadrant switching smooth control method, device and equipment for an electrostatic fluid system

Abstract

The present invention provides a quadrant switching smooth control method, device and equipment for an electro-hydraulic system, which relates to the field of electro-hydraulic composite drive control technology. The present invention obtains sensor state information, establishes a discretized state space equation, designs a cost function, calls an improved sequential quadratic programming to solve the optimal control quantity, smoothes processing instructions through a linear tracking differentiator, adopts a current distribution strategy and pressure feedforward compensation to calculate a reference value, and uses a PI controller and SVPWM to achieve collaborative anti-shock control. The present application can significantly improve the response speed and stability of the electro-hydraulic composite system during quadrant switching, effectively suppress impact and torque overshoot problems, and extend the service life of the equipment. It is suitable for high-performance demand scenarios under complex working conditions such as electric loaders, excavators and winches.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-hydraulic composite drive control, and in particular to a quadrant switching smooth control method, device and equipment for an electrostatic-hydraulic system. Background Art

[0002] Electro-hydraulic hybrid drive technology is a new type of drive method that has received widespread attention in the field of wheeled mobile engineering machinery in recent years. It combines the excellent control characteristics of electric motors with the high power density characteristics of hydraulic systems, and can meet the needs of heavy machinery for high power output and precise control. However, due to its low power density and weak carrying capacity, a single power source, such as an electric motor, performs insufficiently in direct driving scenarios with large inertia, large loads, and frequent acceleration and deceleration. In particular, when dealing with variable rotational inertia, speed overshoot and jitter are prone to occur, affecting handling performance and ride comfort. At the same time, although the hydraulic system has the advantage of high power output, its dynamic response speed is slow, making it difficult to meet the needs of fast switching working conditions. Therefore, how to coordinate the different characteristics of the motor and hydraulic device and give full play to the potential of both has become a key problem in the development of electro-hydraulic hybrid drive technology.

[0003] Existing electro-hydraulic hybrid drive systems typically employ a primary-secondary control logic, with the motor responsible for speed control and the hydraulic system responsible for torque control. This approach embeds hydraulic control within the motor's inner loop to reduce motor output torque, thereby improving system performance under conditions of short-term, high-power demands. However, this control strategy has significant drawbacks. On the one hand, the motor's current loop has a fast response speed, enabling it to quickly follow the reference signal during quadrant switching. On the other hand, the four-quadrant pump / motor is coaxially connected to the motor, and its displacement change time is determined by the mechanical characteristics of the variable mechanism, resulting in a much slower dynamic response of the hydraulic system than the motor. This mismatch in response speed significantly prolongs the overall system's quadrant switching time, preventing the full utilization of the respective performance advantages of the motor and hydraulic system. Furthermore, during quadrant switching, acceleration / deceleration, and loading / unloading, the motor and four-quadrant pump / motor may experience significant shock and torque overshoot, which not only affects ride comfort but also increases wear on the mechanical connection structure, shortening the system's service life.

[0004] To address the above issues, there is an urgent need for a method that can achieve coordinated control of the electro-hydraulic hybrid drive system to solve the impact and torque overshoot problems during quadrant switching, while taking into account the characteristics of rapid response of the motor and high power output of the hydraulic system.

[0005] In view of this, this application is hereby filed. Summary of the Invention

[0006] The present invention aims to provide a quadrant switching smooth control method, device and equipment for an electrostatic-hydraulic system to solve the technical problems of the existing electro-hydraulic hybrid drive system such as slow response speed, large impact and poor coordination during quadrant switching.

[0007] In order to solve the above technical problems, the present invention is implemented through the following technical solutions:

[0008] A quadrant switching smooth control method for an electrostatic fluid system, comprising:

[0009] S1, acquiring system status information, front-end working condition identification information, and vehicle status information collected by sensors; wherein the system status information includes the rotor position of the permanent magnet synchronous motor;

[0010] S2, obtaining the total required torque and load torque observation values ​​based on the front-end working condition identification information and the vehicle state information, establishing a discretized state space model by combining the kinematic equations of the permanent magnet synchronous motor and the four-quadrant pump / motor, and using the q-axis current, mechanical angular velocity, four-quadrant pump / motor displacement value, and current operating pressure difference as control variables, establishing a state space recursive prediction model within the prediction time interval and prediction interval for iterative processing to obtain a quadratic cost function of the control variable;

[0011] S3, iteratively solving the quadratic cost function using a sequential quadratic programming algorithm to obtain the optimal solution for the current command and the optimal solution for the pump displacement command at the current moment, that is, the optimal control variable;

[0012] S4, filtering and smoothing the optimal control quantity to generate a smoothed motor current command and a pump displacement command to the actuator drive layer;

[0013] S5, calculating the orthogonal axis reference current using a preset current distribution strategy according to the smoothed motor current command, and calculating the final pump displacement command based on the smoothed pump displacement command through pressure feedforward compensation;

[0014] S6, using a current loop PI controller to process the system state information and the orthogonal axis reference current to generate a dq axis reference voltage;

[0015] S7, after performing inverse Park transformation on the rotor position of the permanent magnet synchronous motor and the dq-axis reference voltage, generates a PWM signal to drive the permanent magnet synchronous motor through space vector pulse width modulation, and simultaneously outputs a proportional valve control signal to the hydraulic variable mechanism actuator to achieve smooth control of the electrostatic system during quadrant switching.

[0016] Preferably, the system status information also includes three-phase current signals, mechanical angular velocity of the permanent magnet synchronous motor, inlet pressure and outlet pressure of the four-quadrant pump / motor, and current displacement value;

[0017] The front-end working condition identification information includes the accelerator pedal opening, brake pedal travel and working mode selection signal, which is used to determine the driving mode required by the system;

[0018] The vehicle status information includes vehicle speed, acceleration, load condition, battery SOC value, hydraulic system pressure and temperature, which is used to assist in determining the current operating status of the system;

[0019] The three-phase current signal is converted into a rectangular axis current through Clack transformation and Park transformation; wherein the formula of Clack transformation is:

[0020] ;

[0021] in, is the static coordinate of the three-phase current; is the two-phase stationary coordinate after Clack transformation;

[0022] The formula for Park transformation is:

[0023] ;

[0024] in, is the DC current coordinate in the rotating coordinate system, is the rotor position angle of the permanent magnet synchronous motor.

[0025] Preferably, the discretized state space model includes the torque state prediction of the permanent magnet synchronous motor, the displacement state prediction of the four-quadrant pump / motor, the working pressure difference state prediction of the four-quadrant pump / motor, the torque state prediction of the four-quadrant pump / motor, and the angular velocity state prediction of the four-quadrant pump / motor, and its expression is as follows:

[0026] ;

[0027] ;

[0028] ;

[0029] ;

[0030] ;

[0031] ;

[0032] in, for The torque value of the permanent magnet synchronous motor at the moment; is the predicted torque value of the permanent magnet synchronous motor at the next moment; is the sampling time of the MPC controller; is the torque response time constant; is the motor torque coefficient; for Axis current command reference value;

[0033] for The displacement value of the four-quadrant pump / motor at any moment; The predicted displacement value of the four-quadrant pump / motor at the next moment; is the displacement response time constant; for Pump displacement command of the four-quadrant pump / motor at any moment;

[0034] for The working pressure difference of the four-quadrant pump / motor at all times; The working pressure difference of the four-quadrant pump / motor at the next moment; is the effective bulk modulus of hydraulic oil; is the total volume of the four-quadrant pump / motor; for The inlet flow of the four-quadrant pump / motor at any moment; for The outlet flow of the four-quadrant pump / motor at any moment; for Angular velocity of the four-quadrant pump / motor at the moment; is the angular velocity of the four-quadrant pump / motor at the next moment;

[0035] for Torque value of the four-quadrant pump / motor at the moment; is the torque value of the four-quadrant pump / motor at the next moment; is the pump / motor mechanical efficiency;

[0036] is the equivalent moment of inertia; for The load torque value of the electric / generator-pump / motor at the moment;

[0037] is the inlet pressure of the four-quadrant pump / motor; is the outlet pressure of the four-quadrant pump / motor.

[0038] Preferably, the state space recursive prediction model includes torque error prediction, impact degree prediction and quadrant switching time prediction, and is constructed based on the system state information with q-axis current, mechanical angular velocity, four-quadrant pump / motor displacement value and current working pressure difference as control variables, specifically:

[0039] Establishing a shock degree prediction model for electric / generator-pump / motor quadrant switching; wherein the shock degree prediction model for electric / generator-pump / motor quadrant switching includes: a shock degree prediction model for pump / motor and a shock degree prediction model for motor quadrant switching;

[0040] The pump / motor shock prediction model is divided into displacement change rate and pressure change rate;

[0041] The displacement change rate is established by the mathematical model of the variable mechanism - the swash plate, and is reflected by the change rate of the swash plate inclination angle;

[0042] Among them, the flow rate of the electromagnetic proportional valve of the variable mechanism is expressed as:

[0043] ;

[0044] Among them, C d is the orifice discharge coefficient; x v is the valve core displacement; A d is the gradient coefficient; p s is the valve inlet pressure; is the pressure of the variable cylinder a chamber; is the hydraulic oil density; is the pressure of the variable cylinder b chamber; 、 is the flow rate through the control valve;

[0045] ;

[0046] ;

[0047] ;

[0048] in, 、 They are the left and right chamber pressures of the variable cylinder of the four-quadrant pump / motor; 、 for unmodeled dynamics; is the effective working area of ​​the four-quadrant pump / motor variable cylinder; is the effective bulk modulus of hydraulic oil; is the flow rate of the four-quadrant pump / motor valve core; Variable cylinder piston displacement; is the cylinder leakage coefficient; is the total volume of the variable cylinder in the displacement conversion mechanism;

[0049] is the displacement value of the four-quadrant pump / motor at the current moment; is the distance the four-quadrant pump / motor variable cylinder acts on the swash plate torque; is the moment of inertia of the four-quadrant pump / motor swash plate; is the friction coefficient of the swash plate shaft; is the damping coefficient of the swash plate shaft; is the swash plate inclination angle; is the differential with respect to time t; is the swash plate interference torque;

[0050] The pressure change rate is reflected by the flow equation of the variable mechanism, which is expressed as:

[0051] ;

[0052] ;

[0053] in, 、 are the input flow and output flow of the variable mechanism respectively; is the angular velocity of the four-quadrant pump / motor at the current moment;

[0054] The impact degree of the four-quadrant pump / motor quadrant switching at the current moment; is the torque value of the four-quadrant pump / motor at the current moment; is the pump / motor mechanical efficiency; is the working pressure difference of the four-quadrant pump / motor at the current moment;

[0055] Use of permanent magnet synchronous motor Shaft current =0 control strategy, by controlling Shaft current The rate of change is used to reflect the impact of motor quadrant switching. The expression of the motor quadrant switching impact model is:

[0056] ;

[0057] in, The impact degree of the permanent magnet synchronous motor quadrant switching at the current moment; is the torque value of the permanent magnet synchronous motor at the current moment; is the effective area of ​​the four-quadrant pump / motor variable cylinder; is the total volume of the four-quadrant pump / motor; is the mechanical efficiency of the permanent magnet synchronous motor; is the permanent magnet flux; is the number of pole pairs of the permanent magnet synchronous motor; for Actual value of axis current command;

[0058] The displacement change time of the four-quadrant pump / motor is determined by the variable mechanism and external load. Since the bandwidth of the permanent magnet synchronous motor is much larger than that of the four-quadrant pump / motor, the quadrant switching time of the motor / generator-pump / motor quadrant switching is determined by the quadrant switching time of the four-quadrant pump / motor.

[0059] The four-quadrant pump / motor variable displacement mechanism includes an electromagnetic proportional valve and a variable displacement cylinder. The flow rate is controlled by controlling the opening of the proportional valve. The flow enters the variable displacement cylinder to overcome resistance and friction to generate thrust, pushing the swash plate to change the displacement.

[0060] Quadrant switching time for four-quadrant pumps / motors The expression is:

[0061] ;

[0062] in, is the swash plate inclination angle of the four-quadrant pump / motor; The changing angle of the swash plate during the quadrant switching process of the four-quadrant pump; is the plunger diameter of the four-quadrant pump / motor; is the number of plungers in a four-quadrant pump / motor; is the plunger distribution circle diameter of the four-quadrant pump / motor; is the displacement of the variable cylinder piston; 、 They are The first and second derivatives of ; is the damping coefficient; is the friction coefficient; The angle of the triangular groove of the distribution plate; J is the moment of inertia of the inclined plate.

[0063] Therefore, the cost function of the electric / generator-pump / motor quadrant switching model predicts the torque smoothing, that is, the cost function of the control quantity The expression is:

[0064] ;

[0065] in, 、 、 are the corresponding weight coefficients respectively; is the total number of MPC steps; for The torque value of the permanent magnet synchronous motor at the moment; for Torque value of the four-quadrant pump / motor at the moment; The impact degree of the four-quadrant pump / motor quadrant switching at the current moment; for Torque reference value of the four-quadrant pump / motor at any moment; The impact degree of the permanent magnet synchronous motor quadrant switching at the current moment; The quadrant switching time of the four-quadrant pump / motor; It means minimization;

[0066] Based on the discretized state space equation and the shock degree model, the cost function is linearized at the initial control sequence through Taylor expansion, and a quadratic approximate expression is constructed, that is, the expression of the quadratic cost function of the control quantity is:

[0067] ；

[0068] Among them, U is the control vector, which contains the q-axis current command reference value of the future step and pump displacement command ; T is the transpose sign; H is the symmetric positive definite Hessian matrix, which is composed of the second-order derivatives of each term in the cost function, that is, applying a small perturbation to each control variable , calculate the rate of change of the cost function, and its expression is:

[0069] ;

[0070] is the gradient vector, which is composed of the first-order derivatives of each term in the cost function. That is, the gradient of each control direction in the cost function is calculated by the first-order difference method. The expression is:

[0071] ;

[0072] in, 、 、 represents the control variable; 、 、 Represents the control variables 、 、 A small perturbation is applied.

[0073] Preferably, the process of iteratively solving the quadratic cost function by the sequential quadratic programming algorithm is specifically as follows:

[0074] Initialize the initial value of the control vector is the solution or zero vector of the previous control cycle;

[0075] Set the maximum number of iterations to , the gradient tolerance is , Armijo line search parameters are 、 ;

[0076] In each iterative solution process, the gradient of the current point is first calculated, and the formula is:

[0077] ;

[0078] in, Indicates the current iteration number gradient; The current iteration number The control vector of ; H is the symmetric positive definite Hessian matrix; is the gradient vector;

[0079] The formula for solving the quadratic programming subproblem is:

[0080] ;

[0081] And satisfy the control quantity constraint: ;

[0082] in, is the search direction; Indicates the current iteration number The approximate matrix of the Hessian matrix; 、 are the minimum and maximum values ​​of the control vector respectively;

[0083] The active set method is used to solve the quadratic programming subproblem, and the KKT system is solved by identifying the active constraint set to obtain the search direction. , the expression is:

[0084] ;

[0085] in, The current iteration number The effective set constraint matrix of Valid set The corresponding transposed constraint matrix; is the Lagrange multiplier vector, corresponding to the number of multipliers of the effective constraint;

[0086] Then perform an inexact line search to determine the step size, that is, from the initial search step size coefficient First, check the Armijo condition and curvature condition by backtracking. The Armijo condition is:

[0087] ;

[0088] The curvature condition is:

[0089] ;

[0090] If not satisfied, Reduce step size;

[0091] Update control variables After that, the BFGS formula is used to update the Hessian approximation matrix. The formula is:

[0092] ;

[0093] ;

[0094] ;

[0095] in, The current iteration number The search step coefficient of is the iterative difference vector of the control variables; is the iterative difference of the gradient difference; , is the current iteration number gradient;

[0096] The iteration termination condition is: when the gradient norm When the value is less than the set threshold or reaches the maximum number of iterations, the optimal control sequence is output. , and extract the first control quantity as the optimal control quantity at the current moment, that is, the optimal solution of the q-axis current instruction reference value at the current moment , the optimal solution for the pump displacement instruction at the current moment .

[0097] Preferably, filtering and smoothing the optimal control amount are specifically performed as follows:

[0098] For the motor current command, design a high-frequency critically damped LTD filter Perform filtering, the formula is:

[0099] ;

[0100] in, is the bandwidth parameter, which is determined by pole configuration; is the Laplace operator;

[0101] For the hydraulic displacement command, a low-frequency LTD filter is designed Perform filtering, the formula is:

[0102] ;

[0103] in, To obtain the bandwidth, we match the mechanical time constant of the variable mechanism and discretize the continuous transfer function by bilinear transformation method;

[0104] make , and obtain the discrete form of the motor current LTD:

[0105] ;

[0106] in, is the sampling period, is the complex frequency variable of the discrete system; is the filtered q-axis motor current command; 、 、 、 、 is the motor current LTD coefficient at the corresponding moment, which is obtained by the following formula:

[0107] ；

[0108] ；

[0109] ；

[0110] ；

[0111] ；

[0112] in, ;

[0113] Similarly, the hydraulic displacement LTD coefficient is derived;

[0114] After filtering is completed, dynamic limiting is performed and the motor current command constraint is:

[0115] ;

[0116] in, is the smoothed q-axis motor current command; 、 are the maximum and minimum values ​​of the q-axis motor current, respectively, which are determined by the inverter DC bus voltage and the motor thermal limit;

[0117] The pump displacement command constraint is:

[0118] ;

[0119] in, is the smoothed pump displacement instruction; is the pump displacement instruction after filtering; 、 are the maximum and minimum values ​​of the motor current respectively.

[0120] Preferably, the method further includes: using a clamping algorithm with anti-saturation compensation to limit the smoothed motor current command and pump displacement command, that is, when the output is saturated, freezing the integral term and calculating the residual between the unrestricted command and the actual output; after the saturation is released, injecting the compensation amount according to exponential decay, the formula is:

[0121] ;

[0122] in, is the compensation amount; is the compensation coefficient; is the saturation duration; Compensation time constant; is the saturated residual.

[0123] Preferably, the preset current distribution strategy of the permanent magnet synchronous motor adopts Control strategy:

[0124] , ;

[0125] in, is the d-axis current command; is the reference value of the q-axis motor current command; is the smoothed q-axis motor current command;

[0126] The formula for calculating the final pump displacement command through pressure feedforward compensation is:

[0127] ;

[0128] in, is the final pump displacement instruction; is the smoothed pump displacement instruction; is the total volume of the four-quadrant pump / motor; is the effective bulk modulus of hydraulic oil; is the load pressure; is the sampling time of the MPC controller; is the reference working pressure difference; is the actual working pressure difference.

[0129] The present invention also provides a quadrant switching smooth control device for an electrostatic hydraulic system, comprising:

[0130] a data acquisition unit, configured to acquire system status information, front-end operating condition identification information, and vehicle status information collected by sensors, and process the system status information through Clack transform and Park transform; wherein the system status information includes three-phase current signals, mechanical angular velocity and rotor position of the permanent magnet synchronous motor, and inlet pressure, outlet pressure, and current displacement value of the four-quadrant pump / motor;

[0131] a cost function construction unit for obtaining total required torque and load torque observation values ​​based on the front-end working condition identification information and the vehicle state information, establishing a discretized state space model in combination with the kinematic equations of the permanent magnet synchronous motor and the four-quadrant pump / motor, and establishing a state space recursive prediction model within a prediction time interval and a prediction interval for iterative processing to obtain a quadratic cost function of the control variable using the q-axis current, the mechanical angular velocity, the four-quadrant pump / motor displacement value, and the current working pressure difference as control variables;

[0132] an iterative solution unit, configured to iteratively solve the quadratic cost function by using a sequential quadratic programming algorithm to obtain an optimal solution for the current command and the pump displacement command at the current moment, i.e., an optimal control variable;

[0133] A filtering and smoothing unit, configured to filter and smooth the optimal control quantity, and generate a smoothed motor current instruction and a pump displacement instruction to the actuator drive layer;

[0134] a reference current calculation unit, configured to calculate a rectangular axis reference current using a preset current distribution strategy according to the smoothed motor current command, and calculate a final pump displacement command based on the smoothed pump displacement command through pressure feedforward compensation;

[0135] a reference voltage calculation unit, configured to process the system state information and the orthogonal axis reference current using a current loop PI controller to generate a dq axis reference voltage;

[0136] The modulation drive unit is used to perform inverse Park transformation on the rotor position of the permanent magnet synchronous motor and the dq-axis reference voltage, generate a PWM signal to drive the permanent magnet synchronous motor through space vector pulse width modulation, and simultaneously output a proportional valve control signal to the hydraulic variable mechanism actuator to achieve smooth control of the electrostatic system during quadrant switching.

[0137] The present invention also provides a quadrant switching smooth control device for an electrostatic hydraulic system, comprising a processor and a memory, wherein the memory stores a computer program, and the computer program can be executed by the processor to implement a quadrant switching smooth control method for an electrostatic hydraulic system as described above.

[0138] The present invention also provides a computer-readable storage medium having computer-readable instructions stored thereon. When the computer-readable instructions are executed by a processor of a device where the computer-readable storage medium is located, the quadrant switching smooth control method of an electrostatic system as described above is implemented.

[0139] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0140] The present invention combines the model predictive control method with an improved sequential quadratic programming algorithm to propose a model predictive torque smoothing control method for the electric / generator-pump / motor quadrant switching of an electrostatic-hydraulic system, so as to improve the shortcomings of the existing technology and realize efficient coordinated anti-shock control of the electro-hydraulic composite system during the quadrant switching process.

[0141] The improved sequential quadratic programming (SQP) algorithm introduces key technologies such as dynamic Hessian matrix update (BFGS formula), inexact line search (Armijo condition + curvature condition), and active set method to optimize the solution of QP subproblems, which significantly improves the convergence speed, robustness and engineering applicability of the traditional SQP algorithm.

[0142] This invention integrates model predictive control and an improved sequential quadratic programming algorithm to comprehensively optimize torque tracking error, jerkiness, and quadrant switching time, significantly improving the system's response speed and stability. By combining the rapid dynamic response of a permanent magnet synchronous motor with the high power output of a hydraulic system, this method fully leverages the potential of an electro-hydraulic hybrid drive system.

[0143] Furthermore, through pressure feedforward compensation and impact modeling, this method effectively suppresses the impact and torque overshoot that occur during quadrant switching, extending the service life of the equipment. This method can be widely applied to electric loader travel systems, electric excavator slewing systems, and winch slewing systems, meeting high-performance requirements under complex operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0144] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0145] Figure 1 This is a schematic diagram of the drive control flow of a quadrant switching smooth control method for an electrostatic hydraulic system provided in Example 1.

[0146] Figure 2This is a schematic diagram of a four-quadrant pump / motor variable mechanism provided in Example 1.

[0147] Figure 3 This is a flow chart of the algorithm for solving the improved sequential quadratic programming (SQP) provided in Example 1.

[0148] Figure 4 This is a schematic diagram of a quadrant switching smoothing control device for an electrostatic hydraulic system provided in Example 2.

[0149] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. DETAILED DESCRIPTION

[0150] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention for which protection is sought, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0151] Example 1

[0152] Embodiment 1 of the present invention provides a quadrant switching smooth control method for an electrostatic hydraulic system, which can be implemented by a quadrant switching smooth control device for an electrostatic hydraulic system (hereinafter referred to as a control device), and in particular, executed by one or more processors in the control device.

[0153] In this embodiment, the control device may be an electronic device equipped with a processor, which carries a computer program of the quadrant switching smooth control method of the electrostatic system and can be executed, such as a computer, a smart phone, a smart tablet, a workstation, etc., which is not limited here.

[0154] like Figure 1 As shown, a quadrant switching smooth control method for an electrostatic hydraulic system includes steps S1 to S7.

[0155] S1, obtains system status information, front-end operating condition identification information, and vehicle status information collected by sensors, and processes the system status information through Clack transform and Park transform; wherein, the system status information includes three-phase current signals, the mechanical angular velocity and rotor position of the permanent magnet synchronous motor, and the inlet pressure, outlet pressure, and current displacement value of the four-quadrant pump / motor.

[0156] In this embodiment, data is collected through preset sensors, and the collected information includes:

[0157] Electrostatic hydraulic system status information: including three-phase current signals, permanent magnet synchronous motor (PMSM) rotor position (for field-oriented control), four-quadrant pump / motor inlet and outlet pressures, speed, and current displacement value.

[0158] Front-end operating condition identification information: including accelerator pedal opening, brake pedal travel and operating mode selection signal (electric / generator-pump / motor-drive / combined drive), and the operating condition type (such as starting, acceleration, deceleration, climbing, etc.) provided by the vehicle control system, is used to determine the driving mode required by the system.

[0159] Vehicle status information: including vehicle speed, acceleration, load condition, battery SOC value, hydraulic system pressure and temperature, used to assist in determining the current operating status of the system.

[0160] The three-phase current signal can be converted into a rectangular axis current through Clack transformation and Park transformation; wherein the formula of Clack transformation is:

[0161] ;

[0162] in, is the static coordinate of the three-phase current; are the two-phase stationary coordinates after Clack transformation.

[0163] The formula for Park transformation is:

[0164] ;

[0165] in, is the DC current coordinate in the rotating coordinate system, is the rotor position angle of the permanent magnet synchronous motor.

[0166] S2, based on the front-end working condition identification information and vehicle status information, obtains the total required torque and load torque observation values, combines the permanent magnet synchronous motor and the four-quadrant pump / motor kinematic equations, establishes a discretized state space model, and uses the q-axis current, mechanical angular velocity, four-quadrant pump / motor displacement value and current working pressure difference as control quantities. Within the prediction time interval and prediction interval, establishes a state space recursive prediction model for iterative processing to obtain a quadratic cost function of the control quantity.

[0167] In this step, the total torque demand is calculated based on front-end operating condition identification information and the vehicle dynamics model. The total output torque required by the electro-hydraulic hybrid drive system is calculated. For example, the accelerator pedal position is filtered through a first-order lag filter and then input into the vehicle's torque demand mapping module to generate torque characteristic curves tailored to different operating conditions. This torque demand mapping module uses a built-in neural network generated through online training. Brake pedal travel is converted to regenerative braking torque demand using a piecewise linear function, whose slope is dynamically adjusted based on the SOC value (e.g., when SOC < 30%, the slope is reduced by 40% to protect the battery).

[0168] In quadrant-switching smooth control of electrostatic hydrostatic systems, accurate estimation of load torque observations is key to achieving interference rejection and dynamic compensation. Real-time load torque estimation using a state observer (such as a Kalman filter) effectively compensates for external disturbances (such as sudden load changes and friction variations) and improves system robustness. For example, existing Kalman filter-based load torque observers can generate real-time load torque estimates.

[0169] In this embodiment, the electric / generator-pump / motor quadrant means: in the electric mode, the pump or motor operates as an electric motor, consuming electrical energy and generating mechanical energy; in the generator mode, the pump or motor operates as a generator, converting mechanical energy into electrical energy.

[0170] Furthermore, the discretized state space model includes the torque state prediction of the permanent magnet synchronous motor, the displacement state prediction of the four-quadrant pump / motor, the working pressure difference state prediction of the four-quadrant pump / motor, the torque state prediction of the four-quadrant pump / motor, and the angular velocity state prediction of the four-quadrant pump / motor, and its expression is as follows:

[0171] ;

[0172] ;

[0173] ;

[0174] ;

[0175] ;

[0176] ;

[0177] in, for The torque value of the permanent magnet synchronous motor at the moment; is the predicted torque value of the permanent magnet synchronous motor at the next moment; is the sampling time of the MPC controller; is the torque response time constant; is the motor torque coefficient; for Axis current command reference value;

[0178] for The displacement value of the four-quadrant pump / motor at any moment; The predicted displacement value of the four-quadrant pump / motor at the next moment; is the displacement response time constant; for Displacement command of four-quadrant pump / motor at all times;

[0179] for The working pressure difference of the four-quadrant pump / motor at all times; is the effective bulk modulus of hydraulic oil; is the total volume of the four-quadrant pump / motor; for The inlet flow of the four-quadrant pump / motor at any moment; for The outlet flow of the four-quadrant pump / motor at any moment; for Angular velocity of the four-quadrant pump / motor at the moment;

[0180] for Torque value of the four-quadrant pump / motor at the moment; is the pump / motor mechanical efficiency;

[0181] is the equivalent moment of inertia; for The load torque value of the electric / generator-pump / motor at the moment;

[0182] is the inlet pressure of the four-quadrant pump / motor; is the outlet pressure of the four-quadrant pump / motor.

[0183] Then, the prediction time interval and prediction interval are set, and the q-axis current, mechanical angular velocity, four-quadrant pump / motor displacement value and current working pressure difference are used as control variables. The cost function is designed as a function of torque error prediction (obtained according to the discretized state space model), impact degree prediction (including motor current change rate and hydraulic displacement-pressure coupling impact) and quadrant switching time prediction. The cost weight coefficient is set, and a state space recursive prediction model is established to iteratively process state information within the prediction interval.

[0184] Specifically:

[0185] Establish an impact degree prediction model for electric / generator-pump / motor quadrant switching; wherein, the impact degree prediction model for electric / generator-pump / motor quadrant switching includes: a pump / motor impact degree prediction model and a motor quadrant switching impact degree model.

[0186] The pump / motor shock prediction model is divided into displacement change rate and pressure change rate;

[0187] like Figure 2 As shown, the displacement change rate is established by the mathematical model of the variable mechanism - the swash plate, and is reflected by the change rate of the swash plate inclination angle;

[0188] Among them, the flow rate of the electromagnetic proportional valve of the variable mechanism is expressed as:

[0189] ;

[0190] Among them, C d is the orifice discharge coefficient; x v is the valve core displacement; A d is the gradient coefficient; p s is the valve inlet pressure; is the pressure of the variable cylinder a chamber; is the hydraulic oil density; is the pressure of the variable cylinder b chamber; 、 is the flow rate through the control valve;

[0191] ;

[0192] ;

[0193] ;

[0194] in, 、 They are the left and right chamber pressures of the variable cylinder of the four-quadrant pump / motor; 、 for unmodeled dynamics; is the friction coefficient of the swash plate shaft; is the damping coefficient of the swash plate shaft; is the swash plate inclination angle; is the load of the variable mechanism; is the swash plate interference torque; is the total volume of the variable cylinder in the displacement conversion mechanism;

[0195] is the displacement value of the four-quadrant pump / motor at the current moment; is the distance the four-quadrant pump / motor variable cylinder acts on the swash plate torque; is the moment of inertia of the four-quadrant pump / motor swash plate; is the effective working area of ​​the four-quadrant pump / motor variable cylinder; is the effective bulk modulus of hydraulic oil; is the flow rate of the four-quadrant pump / motor valve core; is the displacement of the variable cylinder piston; is the cylinder leakage coefficient;

[0196] The pressure change rate is reflected by the flow equation of the variable mechanism, which is expressed as:

[0197] ;

[0198] ;

[0199] in, 、 are the input flow and output flow of the variable mechanism respectively; is the angular velocity of the four-quadrant pump / motor at the current moment;

[0200] The impact degree of the four-quadrant pump / motor quadrant switching at the current moment; is the torque value of the four-quadrant pump / motor at the current moment; is the pump / motor mechanical efficiency; is the working pressure difference of the four-quadrant pump / motor at the current moment;

[0201] Use of permanent magnet synchronous motor Shaft current =0 control strategy, by controlling Shaft current The rate of change is used to reflect the impact of motor quadrant switching. The expression of the motor quadrant switching impact model is:

[0202] ;

[0203] in, The impact degree of the permanent magnet synchronous motor quadrant switching at the current moment; is the torque value of the permanent magnet synchronous motor at the current moment; is the effective area of ​​the four-quadrant pump / motor variable cylinder; is the total volume of the four-quadrant pump / motor; is the mechanical efficiency of the permanent magnet synchronous motor; is the permanent magnet flux; is the number of pole pairs of the permanent magnet synchronous motor; for Actual value of axis current command;

[0204] The displacement change time of the four-quadrant pump / motor is determined by the variable mechanism and external load. Since the bandwidth of the permanent magnet synchronous motor is much larger than that of the four-quadrant pump / motor, the quadrant switching time of the motor / generator-pump / motor quadrant switching is determined by the quadrant switching time of the four-quadrant pump / motor.

[0205] Among them, the four-quadrant pump / motor variable mechanism includes an electromagnetic proportional valve and a variable cylinder. The flow rate is controlled by controlling the opening of the proportional valve. The flow enters the variable cylinder to overcome resistance and friction to generate thrust, pushing the swash plate to change the displacement.

[0206] The dynamic equation of the valve core is:

[0207] ;

[0208] Where, is the valve core quality; is the valve core damping coefficient; is the valve core displacement; is the spring stiffness coefficient; is the feedback force; is the first-order derivative of the valve core displacement; is the second-order derivative of the valve core displacement; is the electromagnet proportional coefficient; is the electromagnet current signal.

[0209] The Laplace change of the valve core displacement can be obtained:

[0210] ;

[0211] Where, is the spool damping ratio, ; is the natural oscillation frequency of the valve core, ;

[0212] s is a variable in the complex frequency domain, usually expressed as , is the real part, which represents the attenuation or growth factor of the system; is the imaginary part, is the imaginary unit, is the angular frequency.

[0213] Variable piston flow The equation is:

[0214] ;

[0215] Where A is the effective area of ​​the piston; is the piston movement speed.

[0216] Valve core cut-off flow The linearized equation is:

[0217] ;

[0218] in, is the flow gain coefficient; is the flow pressure coefficient; is the valve core displacement; is the load pressure.

[0219] The dynamic equation of the variable piston is:

[0220] ;

[0221] Where: M is the mass of the piston and load; C is the piston damping coefficient: is the return spring stiffness; is the piston displacement; is the load force.

[0222] Performing Laplace transformation yields:

[0223] ;

[0224] ;

[0225] Where, is the piston damping ratio, ; is the natural oscillation frequency of the piston, .

[0226] Therefore, the bandwidth of the four-quadrant pump is much smaller than that of the permanent magnet synchronous motor.

[0227] Among them, the quadrant switching time of the four-quadrant pump / motor is The expression is:

[0228] ;

[0229] in, is the swash plate inclination angle of the four-quadrant pump / motor; The changing angle of the swash plate during the quadrant switching process of the four-quadrant pump; is the plunger diameter of the four-quadrant pump / motor; is the number of plungers in a four-quadrant pump / motor; is the plunger distribution circle diameter of the four-quadrant pump / motor; is the displacement of the variable cylinder piston; 、 They are The first and second derivatives of ; is the damping coefficient; is the friction coefficient; Angle of triangular groove of distribution plate;

[0230] Therefore, the cost function of the electric / generator-pump / motor quadrant switching model predicts the torque smoothing, that is, the cost function of the control quantity The expression is:

[0231] ;

[0232] in, 、 、 are the corresponding weight coefficients respectively; is the total number of MPC steps; for The torque value of the permanent magnet synchronous motor at the moment; for Torque value of the four-quadrant pump / motor at the moment; The impact degree of the four-quadrant pump / motor quadrant switching at the current moment; for Torque reference value of the four-quadrant pump / motor at any moment; The impact degree of the permanent magnet synchronous motor quadrant switching at the current moment; The quadrant switching time of the four-quadrant pump / motor; It means minimization;

[0233] Based on the discretized state space equation and the shock degree model, the cost function is linearized at the initial control sequence through Taylor expansion, and a quadratic approximate expression is constructed, that is, the expression of the quadratic cost function of the control quantity is:

[0234] ；

[0235] Among them, U is the control vector, including the future q-axis current command reference value of step size and displacement command ,Right now:

[0236] ;

[0237] T is the transposition symbol; is the prediction step size; H is the symmetric positive definite Hessian matrix, which is composed of the second-order derivatives of each term in the cost function, that is, applying a small perturbation to each control variable , calculate the rate of change of the cost function, and its expression is:

[0238] ;

[0239] is the gradient vector, which is composed of the first-order derivatives of each term in the cost function. That is, the gradient of each control direction in the cost function is calculated by the first-order difference method. The expression is:

[0240] ;

[0241] in, 、 、 represents the control variable; 、 、 Represents the control variables 、 、 A small perturbation is applied.

[0242] S3, iteratively solving the quadratic cost function through a sequential quadratic programming algorithm to obtain the optimal solution of the current command and the optimal solution of the pump displacement command at the current moment, that is, the optimal control variable.

[0243] In this step, the Sequential Quadratic Programming (SQP) algorithm is an efficient iterative method for solving nonlinear constrained optimization problems. It gradually approaches the optimal solution by decomposing complex nonlinear optimization problems into a series of quadratic programming (QP) subproblems. The SQP algorithm transforms the original nonlinear optimization problem into a series of quadratic programming (QP) subproblems. In each iteration, the algorithm performs a quadratic approximation on the objective function at the current point and linearizes the constraints, thereby constructing a quadratic programming subproblem. Solving this quadratic programming subproblem yields a search direction, which is used to update the current solution. The algorithm then performs a line search along the search direction, determines an appropriate step size, and updates the solution. This process is repeated until convergence criteria are met, such as sufficient solution quality, the maximum number of iterations, or no significant improvement in the solution.

[0244] The sequential quadratic programming (SQP) algorithm is an improved SQP algorithm. The improved sequential quadratic programming (SQP) algorithm significantly improves the convergence speed, robustness, and engineering applicability of the traditional SQP algorithm by introducing key technologies such as dynamic Hessian matrix update (BFGS formula), inexact line search (Armijo condition + curvature condition), and active set method to optimize the solution of QP subproblems.

[0245] Dynamic Hessian Matrix Update (BFGS Formula): Traditional SQP typically uses a fixed Hessian matrix (such as the identity matrix or a constant approximation matrix) or calculates second-order derivatives through numerical differentiation, which is computationally intensive and susceptible to noise. This embodiment uses the BFGS quasi-Newton method to dynamically update the approximation of the Hessian matrix. This method indirectly approximates the Hessian matrix using gradient differential information, reducing computational complexity and being particularly suitable for high-dimensional problems. The dynamically updated approximation matrix better reflects the local curvature of the objective function, accelerating convergence. The BFGS formula ensures superlinear convergence under certain conditions, significantly faster than the linear convergence of traditional SQP.

[0246] Inexact Line Search (Armijo Condition + Curvature Condition): Traditional SQP typically uses a fixed step size or an exact line search (such as the golden section method), which is computationally intensive and can lead to divergence due to improper step size selection. This implementation introduces an inexact line search using Armijo and curvature conditions. This method uses a backtracking method to gradually reduce the step size, balancing computational efficiency and convergence. The Armijo condition ensures a monotonically decreasing objective function, while the curvature condition prevents excessively small step sizes, avoiding oscillation and divergence and improving algorithm stability. Inexact line search eliminates the need for a precise step size, significantly reducing the computational cost of each iteration.

[0247] Active set method optimizes QP subproblem solving: Traditional SQP typically uses the interior point method or simplex method to solve QP subproblems, which has high computational complexity and is particularly inefficient when there are many constraints. This embodiment uses the active set method to solve QP subproblems. The active set method only processes the currently active constraints, reducing computational dimensions and making it particularly suitable for sparsely constrained problems. By directly solving the KKT system, it avoids the iterative error of the interior point method and improves the accuracy of the search direction. In continuous optimization problems, the active set from the previous cycle can be used as the initial guess, accelerating convergence and facilitating hot starts.

[0248] like Figure 2 As shown, the process of iteratively solving the quadratic cost function by the sequential quadratic programming algorithm is specifically as follows:

[0249] Initialize the initial value of the control vector is the solution or zero vector of the previous control cycle;

[0250] Set the maximum number of iterations to (such as 100), the gradient tolerance is , Armijo line search parameters are 、 ,like , ;

[0251] In each iterative solution process, the gradient of the current point is first calculated, and the formula is:

[0252] ;

[0253] in, Indicates the current iteration number gradient; The current iteration number The control vector of ; H is the symmetric positive definite Hessian matrix; is the gradient vector;

[0254] The formula for solving the quadratic programming subproblem is:

[0255] ;

[0256] And satisfy the control quantity constraint: ;

[0257] in, is the search direction; Indicates the current iteration number The approximate matrix of the Hessian matrix; 、 are the minimum and maximum values ​​of the control vector respectively;

[0258] The active set method is used to solve the quadratic programming subproblem, and the KKT system is solved by identifying the active constraint set to obtain the search direction. , the expression is:

[0259] ;

[0260] in, The current iteration number The effective set constraint matrix of Valid set The corresponding transposed constraint matrix; is the Lagrange multiplier vector, corresponding to the number of multipliers of the effective constraint;

[0261] In this embodiment, the KKT system is an extension of the Lagrange multiplier method under inequality constraints, formally proposed by Harold W. Kuhn and Albert W. Tucker in 1951 (independently discovered by William Karush in 1939), and is applicable to the following optimization problems.

[0262] Then perform an inexact line search to determine the step size, that is, from the initial search step size coefficient First, check the Armijo condition and curvature condition by backtracking. The Armijo condition is:

[0263] ;

[0264] The curvature condition is:

[0265] ;

[0266] If not satisfied, Reduce step size;

[0267] Update control variables After that, the BFGS formula is used to update the Hessian approximation matrix. The formula is:

[0268] ;

[0269] ;

[0270] ;

[0271] in, The current iteration number The search step coefficient of is the iterative difference vector of the control variables; is the iterative difference of the gradient difference; , indicating the current number of iterations gradient.

[0272] In this embodiment, the iteration termination condition is set as: when the gradient norm When the value is less than the set threshold or reaches the maximum number of iterations, the optimal control sequence is output. , and extract the first control quantity as the optimal control quantity at the current moment, that is, the optimal solution of the q-axis current instruction reference value at the current moment , optimal solution for pump displacement command .

[0273] In this embodiment, the BFGS (Broyden-Fletcher-Goldfarb-Shanno) formula is a quasi-Newton method used to update the approximate matrix of the Hessian matrix. , to avoid directly calculating the second-order derivative. The core idea is to construct an approximation of the inverse of the Hessian matrix (or directly approximate the Hessian matrix) through the gradient difference information. ), thus maintaining superlinear convergence during iterations.

[0274] S4, filtering and smoothing the optimal control quantity, generating smoothed motor current instructions and pump displacement instructions to the actuator drive layer.

[0275] In this step, the optimal control quantity is transferred to the linear tracking differentiator for smooth transition processing. First, the first item of the optimal control quantity sequence output by the quadratic cost function solving module is received, that is, the current motor q-axis current command reference value and pump displacement command . For the fast dynamic response of the motor system (time constant ) and the hydraulic system responds slowly (time constant ) characteristics, a dual-channel linear tracking differentiator (LTD) is used for differential filtering.

[0276] For the motor current command, design a high-frequency critically damped LTD filter Perform filtering, the formula is:

[0277] ;

[0278] in, is the bandwidth parameter, which is determined by pole configuration; is the Laplace operator;

[0279] For the hydraulic displacement command, a low-frequency LTD filter is designed Perform filtering, the formula is:

[0280] ;

[0281] in, To obtain the bandwidth, we match the mechanical time constant of the variable mechanism and discretize the continuous transfer function by bilinear transformation method;

[0282] make , is the sampling period, and the discrete form of the motor current LTD is obtained:

[0283] ;

[0284] in, is the sampling period, is the complex frequency variable of the discrete system; is the filtered q-axis motor current command; 、 、 、 、 is the motor current LTD coefficient at the corresponding moment, which is obtained by the following formula:

[0285] ；

[0286] ；

[0287] ；

[0288] ；

[0289] ；

[0290] in, ;

[0291] Similarly, the hydraulic displacement LTD coefficient is derived.

[0292] In real-time processing, the historical data buffer is initialized to store the input and output values ​​at time k-1 and k-2. When a new instruction arrives:

[0293] 1) Update the input queue , displacement command ;

[0294] 2) Calculate the filter output according to the difference equation;

[0295] 3) Update the output queue;

[0296] 4) Shift historical data register.

[0297] After filtering is completed, dynamic limiting is performed and the motor current command constraint is:

[0298] ;

[0299] in, is the smoothed q-axis motor current command; 、 are the maximum and minimum values ​​of the q-axis motor current, respectively, which are determined by the inverter DC bus voltage and the motor thermal limit;

[0300] The displacement command constraint is:

[0301] ;

[0302] in, is the smoothed pump displacement instruction; is the pump displacement instruction after filtering; 、 are the maximum and minimum values ​​of the motor current respectively.

[0303] A clamping algorithm with anti-saturation compensation can also be used to limit the smoothed q-axis motor current command and pump displacement command. That is, when the output is saturated, the integral term is frozen and the residual between the unrestricted command and the actual output is calculated. After the saturation is released, the compensation amount is injected according to exponential decay. The formula is:

[0304] ;

[0305] in, is the compensation amount; is the compensation coefficient; saturation duration; Compensation time constant; is the saturated residual.

[0306] Finally, the smoothed instructions are output to the actuator drive layer.

[0307] S5, calculating the orthogonal axis reference current using a preset current distribution strategy according to the smoothed motor current command, and calculating the final pump displacement command based on the smoothed pump displacement command through pressure feedforward compensation.

[0308] In this step, the preset current distribution strategy of the permanent magnet synchronous motor adopts Control strategy:

[0309] , ;

[0310] in, is the d-axis current command; is the reference value of the q-axis motor current command; is the smoothed q-axis motor current command.

[0311] The four-quadrant pump / motor adopts a pressure feedforward compensation control strategy. The formula for calculating the final pump displacement command through pressure feedforward compensation is:

[0312] ;

[0313] in, is the final pump displacement instruction; is the smoothed pump displacement command; is the total volume of the four-quadrant pump / motor; Effective bulk modulus of hydraulic oil; is the load pressure; is the sampling time of the MPC controller; is the reference working pressure difference; is the actual working pressure difference.

[0314] S6 , using a current loop PI controller to process the system state information and the orthogonal axis reference current to generate a dq axis reference voltage.

[0315] The goal of this step is to make the actual current track the reference current instruction through the current loop PI regulator and output the dq axis reference voltage. Then implement position closed-loop control on the hydraulic pump variable mechanism to ensure that the final pump displacement instruction Precise tracking.

[0316] S7, performs inverse Park transformation on the rotor position of the permanent magnet synchronous motor and the dq-axis reference voltage, generates a PWM signal to drive the permanent magnet synchronous motor through space vector pulse width modulation, and simultaneously outputs a proportional valve control signal to the hydraulic variable mechanism actuator to achieve smooth control of the electrostatic system during quadrant switching.

[0317] In this step, the dq axis reference voltage is converted to the stationary coordinate system. Shaft two-phase static voltage.

[0318] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0319] The present invention combines the model predictive control method with an improved sequential quadratic programming algorithm to propose a model predictive torque smoothing control method for the electric / generator-pump / motor quadrant switching of an electrostatic-hydraulic system, so as to improve the shortcomings of the existing technology and realize efficient coordinated anti-shock control of the electro-hydraulic composite system during the quadrant switching process.

[0320] The present invention introduces model predictive control and an improved sequential quadratic programming algorithm to comprehensively optimize torque tracking error, impact degree, and quadrant switching time, thereby significantly improving the response speed and stability of the system. The method of the present invention combines the rapid dynamic response characteristics of the permanent magnet synchronous motor and the high power output characteristics of the hydraulic system to fully tap the potential of the electro-hydraulic composite drive system. In addition, the present invention effectively suppresses the impact and torque overshoot problems generated during the quadrant switching process through pressure feedforward compensation and impact degree modeling, thereby extending the service life of the equipment. The method can be widely used in the fields of electric loader travel systems, electric excavator slewing systems, and winch slewing systems to meet high performance requirements under complex working conditions.

[0321] Example 2

[0322] like Figure 4 As shown, the second embodiment of the present invention further provides a quadrant switching smooth control device for an electrostatic hydraulic system, comprising:

[0323] a data acquisition unit, configured to acquire system status information, front-end operating condition identification information, and vehicle status information collected by sensors, and process the system status information through Clack transform and Park transform; wherein the system status information includes three-phase current signals, mechanical angular velocity and rotor position of the permanent magnet synchronous motor, and inlet pressure, outlet pressure, and current displacement value of the four-quadrant pump / motor;

[0324] a cost function construction unit for obtaining total required torque and load torque observation values ​​based on the front-end working condition identification information and the vehicle state information, establishing a discretized state space model in combination with the kinematic equations of the permanent magnet synchronous motor and the four-quadrant pump / motor, and establishing a state space recursive prediction model within a prediction time interval and a prediction interval for iterative processing to obtain a quadratic cost function of the control variable using the q-axis current, the mechanical angular velocity, the four-quadrant pump / motor displacement value, and the current working pressure difference as control variables;

[0325] an iterative solution unit, configured to iteratively solve the quadratic cost function by using a sequential quadratic programming algorithm to obtain an optimal solution for the current command and the pump displacement command at the current moment, i.e., an optimal control variable;

[0326] A filtering and smoothing unit, configured to filter and smooth the optimal control quantity, and generate a smoothed motor current instruction and a pump displacement instruction to the actuator drive layer;

[0327] a reference current calculation unit, configured to calculate a rectangular axis reference current using a preset current distribution strategy according to the smoothed motor current command, and calculate a final pump displacement command based on the smoothed pump displacement command through pressure feedforward compensation;

[0328] a reference voltage calculation unit, configured to process the system state information and the orthogonal axis reference current using a current loop PI controller to generate a dq axis reference voltage;

[0329] The modulation drive unit is used to perform inverse Park transformation on the rotor position of the permanent magnet synchronous motor and the dq-axis reference voltage, generate a PWM signal to drive the permanent magnet synchronous motor through space vector pulse width modulation, and simultaneously output a proportional valve control signal to the hydraulic variable mechanism actuator to achieve smooth control of the electrostatic system during quadrant switching.

[0330] Example 3

[0331] The third embodiment of the present invention also provides a quadrant switching smooth control device for an electrostatic hydraulic system, which includes a memory and a processor. The memory stores a computer program, and the computer program can be executed by the processor to implement the quadrant switching smooth control method for the electrostatic hydraulic system as described above.

[0332] Example 4

[0333] The fourth embodiment of the present invention further provides a computer-readable storage medium, on which computer-readable instructions are stored. When the computer-readable instructions are executed by the processor of the device where the computer-readable storage medium is located, the quadrant switching smooth control method of the electrostatic system as described above is implemented.

[0334] In the several embodiments provided in the embodiments of the present invention, it should be understood that the disclosed devices and methods can also be implemented in other ways. The device and method embodiments described above are merely illustrative. For example, the flowcharts in the accompanying drawings show the possible architectures, functions, and operations of the devices, methods, and computer program products according to multiple embodiments of the present invention. In this regard, each box in the flowchart or block diagram can represent a module, program segment, or part of a code, which contains one or more executable instructions for implementing the specified logical functions. It should also be noted that in some alternative implementations, the functions marked in the boxes can also occur in an order different from that marked in the drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, as well as the combination of boxes in the block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified functions or actions, or can be implemented using a combination of dedicated hardware and computer instructions.

[0335] In addition, the functional modules in the various embodiments of the present invention may be integrated together to form an independent part, or each module may exist independently, or two or more modules may be integrated to form an independent part.

[0336] If the functions are implemented in the form of software modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, electronic device, or network device, etc.) to perform all or part of the steps of the methods described in various embodiments of the present invention. The aforementioned storage media include various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks. It should be noted that, in this document, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or device that includes a series of elements includes not only those elements but also other elements not explicitly listed, or also includes elements inherent to such process, method, article, or device. Without further constraints, an element defined by the phrase "comprises a..." does not preclude the existence of additional identical elements in the process, method, article or apparatus that includes the element.

[0337] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0338] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0339] The word "if," as used herein, may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to the determination" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)," depending on the context.

[0340] The "first" and "second" mentioned in the embodiments are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It is understood that the specific order or precedence of "first" and "second" can be interchanged where appropriate. It should be understood that the objects distinguished by "first" and "second" can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0341] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A quadrant switching smooth control method for an electrostatic fluid system, characterized in that: include: S1, acquiring system status information, front-end operating condition identification information, and vehicle status information collected by sensors, and processing the system status information through Clack transform and Park transform; wherein the system status information includes three-phase current signals, mechanical angular velocity and rotor position of the permanent magnet synchronous motor, and inlet pressure, outlet pressure, and current displacement value of the four-quadrant pump / motor; S2, obtaining the total required torque and load torque observation values ​​based on the front-end working condition identification information and the vehicle state information, establishing a discretized state space model by combining the kinematic equations of the permanent magnet synchronous motor and the four-quadrant pump / motor, and using the q-axis current, mechanical angular velocity, four-quadrant pump / motor displacement value, and current operating pressure difference as control variables, establishing a state space recursive prediction model within the prediction time interval and prediction interval for iterative processing to obtain a quadratic cost function of the control variable; S3, iteratively solving the quadratic cost function using a sequential quadratic programming algorithm to obtain the optimal solution for the current command and the optimal solution for the pump displacement command at the current moment, that is, the optimal control variable; the specific process of iteratively solving the quadratic cost function using the sequential quadratic programming algorithm is as follows: Initialize the initial value of the control vector is the solution or zero vector of the previous control cycle; Set the maximum number of iterations to , the gradient tolerance is , Armijo line search parameters are 、 ; In each iterative solution process, the gradient of the current point is first calculated, and the formula is: ； in, Indicates the current iteration number gradient; The current iteration number The control vector of ; H is the symmetric positive definite Hessian matrix; is the gradient vector; The formula for solving the quadratic programming subproblem is: ； And satisfy the control quantity constraint: ; in, is the search direction; Indicates the current iteration number The approximate matrix of the Hessian matrix; 、 are the minimum and maximum values ​​of the control vector respectively; The active set method is used to solve the quadratic programming subproblem, and the KKT system is solved by identifying the active constraint set to obtain the search direction. , the expression is: ； in, The current iteration number The effective set constraint matrix of Valid set The corresponding transposed matrix; is the Lagrange multiplier vector, corresponding to the number of multipliers of the effective constraint; Then perform an inexact line search to determine the step size, that is, from the initial search step size coefficient First, check the Armijo condition and curvature condition by backtracking. The Armijo condition is: ； The curvature condition is: ； If not satisfied, Reduce step size; S4, filtering and smoothing the optimal control quantity to generate a smoothed motor current command and a pump displacement command to the actuator drive layer; S5, calculating the orthogonal axis reference current using a preset current distribution strategy according to the smoothed motor current command, and calculating the final pump displacement command based on the smoothed pump displacement command through pressure feedforward compensation; S6, using a current loop PI controller to process the system state information and the orthogonal axis reference current to generate a dq axis reference voltage; S7, after performing inverse Park transformation on the rotor position of the permanent magnet synchronous motor and the dq-axis reference voltage, generates a PWM signal to drive the permanent magnet synchronous motor through space vector pulse width modulation, and simultaneously outputs a proportional valve control signal to the hydraulic variable mechanism actuator to achieve smooth control of the electrostatic system during quadrant switching.

2. A quadrant switching smooth control method for an electrostatic fluid system according to claim 1, characterized in that ,The front-end working condition identification information includes the accelerator pedal opening, the brake pedal travel and the working mode selection signal, which is used to determine the driving mode required by the system; The vehicle status information includes vehicle speed, acceleration, load condition, battery SOC value, hydraulic system pressure and temperature, which is used to assist in determining the current operating status of the system; The three-phase current signal is converted into a rectangular axis current through Clack transformation and Park transformation; wherein the formula of Clack transformation is: ； in, is the static coordinate of the three-phase current; is the two-phase stationary coordinate after Clack transformation; The formula for Park transformation is: ； in, is the DC current coordinate in the rotating coordinate system, is the rotor position angle of the permanent magnet synchronous motor.

3. The quadrant switching smooth control method of an electrostatic fluid system according to claim 2, characterized in that: The discretized state space model includes the torque state prediction of the permanent magnet synchronous motor, the displacement state prediction of the four-quadrant pump / motor, the working pressure difference state prediction of the four-quadrant pump / motor, the torque state prediction of the four-quadrant pump / motor, and the angular velocity state prediction of the four-quadrant pump / motor, and its expression is as follows: ； ； ； ； ； ； in, for The torque value of the permanent magnet synchronous motor at the moment; is the predicted torque value of the permanent magnet synchronous motor at the next moment; is the sampling time of the MPC controller; is the torque response time constant; is the motor torque coefficient; for Axis current command reference value; for The displacement value of the four-quadrant pump / motor at any moment; The predicted displacement value of the four-quadrant pump / motor at the next moment; is the displacement response time constant; for Pump displacement command of the four-quadrant pump / motor at any moment; for The working pressure difference of the four-quadrant pump / motor at all times; The working pressure difference of the four-quadrant pump / motor at the next moment; is the effective bulk modulus of hydraulic oil; is the total volume of the four-quadrant pump / motor; for The inlet flow of the four-quadrant pump / motor at any moment; for The outlet flow of the four-quadrant pump / motor at any moment; for Angular velocity of the four-quadrant pump / motor at the moment; is the angular velocity of the four-quadrant pump / motor at the next moment; for Torque value of the four-quadrant pump / motor at the moment; is the torque value of the four-quadrant pump / motor at the next moment; is the pump / motor mechanical efficiency; is the equivalent moment of inertia; for The load torque value of the electric / generator-pump / motor at the moment; is the inlet pressure of the four-quadrant pump / motor; is the outlet pressure of the four-quadrant pump / motor.

4. A quadrant switching smooth control method for an electrostatic fluid system according to claim 3, characterized in that The state space recursive prediction model includes torque error prediction, impact degree prediction and quadrant switching time prediction. It is constructed based on the system state information and takes q-axis current, mechanical angular velocity, four-quadrant pump / motor displacement value and current working pressure difference as control variables. Specifically: Establishing a shock degree prediction model for electric / generator-pump / motor quadrant switching; wherein the shock degree prediction model for electric / generator-pump / motor quadrant switching includes a shock degree prediction model for pump / motor and a shock degree prediction model for motor quadrant switching; The pump / motor shock prediction model is divided into displacement change rate and pressure change rate; The displacement change rate is established by the mathematical model of the variable mechanism - the swash plate, and is reflected by the change rate of the swash plate inclination angle; Among them, the flow rate of the electromagnetic proportional valve of the variable mechanism is expressed as: ； Among them, C d is the orifice discharge coefficient; x v is the valve core displacement; A d is the gradient coefficient; p s is the valve inlet pressure; is the pressure of the variable cylinder a chamber; is the hydraulic oil density; is the pressure of the variable cylinder b chamber; 、 is the flow rate through the control valve; ； ； ； in, 、 They are the left and right chamber pressures of the variable cylinder of the four-quadrant pump / motor; 、 for unmodeled dynamics; is the effective working area of ​​the four-quadrant pump / motor variable cylinder; is the effective bulk modulus of hydraulic oil; is the flow rate of the four-quadrant pump / motor valve core; is the displacement of the variable cylinder piston; is the cylinder leakage coefficient; is the total volume of the variable cylinder in the displacement conversion mechanism; is the displacement value of the four-quadrant pump / motor at the current moment; is the distance the four-quadrant pump / motor variable cylinder acts on the swash plate torque; is the moment of inertia of the four-quadrant pump / motor swash plate; is the friction coefficient of the swash plate shaft; is the damping coefficient of the swash plate shaft; is the swash plate inclination angle of the four-quadrant pump / motor; is the differential with respect to time t; is the swash plate interference torque; The pressure change rate is reflected by the flow equation of the variable mechanism, which is expressed as: ； ； in, 、 are the input flow and output flow of the variable mechanism respectively; is the angular velocity of the four-quadrant pump / motor at the current moment; The impact degree of the four-quadrant pump / motor quadrant switching at the current moment; is the torque value of the four-quadrant pump / motor at the current moment; is the pump / motor mechanical efficiency; is the working pressure difference of the four-quadrant pump / motor at the current moment; Use of permanent magnet synchronous motor Shaft current =0 control strategy, by controlling Shaft current The rate of change is used to reflect the impact of motor quadrant switching. The expression of the motor quadrant switching impact model is: ； in, The impact degree of the permanent magnet synchronous motor quadrant switching at the current moment; is the torque value of the permanent magnet synchronous motor at the current moment; is the effective area of ​​the four-quadrant pump / motor variable cylinder; is the total volume of the four-quadrant pump / motor; is the mechanical efficiency of the permanent magnet synchronous motor; is the permanent magnet flux; is the number of pole pairs of the permanent magnet synchronous motor; for Actual value of axis current command; The displacement change time of the four-quadrant pump / motor is determined by the variable mechanism and external load. Since the bandwidth of the permanent magnet synchronous motor is much larger than that of the four-quadrant pump / motor, the quadrant switching time of the motor / generator-pump / motor quadrant switching is determined by the quadrant switching time of the four-quadrant pump / motor. The four-quadrant pump / motor variable displacement mechanism includes an electromagnetic proportional valve and a variable displacement cylinder. The flow rate is controlled by controlling the opening of the proportional valve. The flow enters the variable displacement cylinder to overcome resistance and friction to generate thrust, pushing the swash plate to change the displacement. Quadrant switching time for four-quadrant pumps / motors The expression is: ； in, is the swash plate inclination angle of the four-quadrant pump / motor; The changing angle of the swash plate during the quadrant switching process of the four-quadrant pump; is the plunger diameter of the four-quadrant pump / motor; is the number of plungers in a four-quadrant pump / motor; is the plunger distribution circle diameter of the four-quadrant pump / motor; is the displacement of the variable cylinder piston; is the damping coefficient; is the friction coefficient; Angle of triangular groove of distribution plate; J is the moment of inertia of the swash plate; Therefore, the cost function of the electric / generator-pump / motor quadrant switching model predicting torque smoothing, that is, the cost function of the control quantity, is expressed as: ； in, 、 、 are the corresponding weight coefficients respectively; is the total number of MPC steps; for The torque value of the permanent magnet synchronous motor at the moment; for Torque value of the four-quadrant pump / motor at the moment; The impact degree of the four-quadrant pump / motor quadrant switching at the current moment; for Torque reference value of the four-quadrant pump / motor at any moment; The impact degree of the permanent magnet synchronous motor quadrant switching at the current moment; The quadrant switching time of the four-quadrant pump / motor; It means minimization; Based on the discretized state space equation and the shock degree model, the cost function is linearized at the initial control sequence through Taylor expansion, and a quadratic approximate expression is constructed, that is, the expression of the quadratic cost function of the control quantity is: ； Among them, U is the control vector, which contains the future step length Axis current command reference value and pump displacement command ; T is the transpose sign; H is the symmetric positive definite Hessian matrix, which is composed of the second-order derivatives of each term in the cost function, that is, applying a small perturbation to each control variable , calculate the rate of change of the cost function, and its expression is: ； is the gradient vector, which is composed of the first-order derivatives of each term in the cost function. That is, the gradient of each control direction in the cost function is calculated by the first-order difference method. The expression is: ； in, 、 、 represents the control variable; 、 、 Represents the control variables 、 、 A small perturbation is applied.

5. The quadrant switching smooth control method of an electrostatic fluid system according to claim 4, characterized in that The process of iteratively solving the quadratic cost function by the sequential quadratic programming algorithm also includes: Update control variables After that, the BFGS formula is used to update the Hessian approximation matrix. The formula is: ； ； ； in, The current iteration number The search step coefficient of is the iterative difference vector of the control variables; is the iterative difference of the gradient difference; , is the current iteration number gradient; The iteration termination condition is: when the gradient norm When the value is less than the set threshold or reaches the maximum number of iterations, the optimal control sequence is output. , and extract the first control quantity as the optimal control quantity at the current moment, that is, at the current moment Optimal solution for shaft current command reference value , the optimal solution for the pump displacement instruction at the current moment .

6. The quadrant switching smooth control method of an electrostatic fluid system according to claim 2, characterized in that , filtering and smoothing the optimal control quantity are specifically performed as follows: For the motor current command, design a high-frequency critically damped LTD filter Perform filtering, the formula is: ； in, is the bandwidth parameter, which is determined by pole configuration; is the Laplace operator; For the hydraulic displacement command, a low-frequency LTD filter is designed Perform filtering, the formula is: ； in, To obtain the bandwidth, we match the mechanical time constant of the variable mechanism and discretize the continuous transfer function by bilinear transformation method; make , and obtain the discrete form of the motor current LTD: ; in, is the sampling period, is the complex frequency variable of the discrete system; After filtering Axis motor current command reference value; 、 、 、 、 is the motor current LTD coefficient at the corresponding moment, which is obtained by the following formula: ； ； ； ； ； in, ; Similarly, the hydraulic displacement LTD coefficient is derived; After filtering is completed, dynamic limiting is performed and the motor current command constraint is: ； in, is the smoothed q-axis motor current command; 、 are the maximum and minimum values ​​of the q-axis motor current, respectively, which are determined by the inverter DC bus voltage and the motor thermal limit; The pump displacement command constraint is: ； in, is the smoothed pump displacement instruction; is the pump displacement instruction after filtering; 、 are the maximum and minimum values ​​of the motor current respectively.

7. A quadrant switching smooth control method for an electrostatic fluid system according to claim 6, characterized in that , also includes: using a clamping algorithm with anti-saturation compensation to limit the smoothed motor current command and pump displacement command. That is, when the output is saturated, the integral term is frozen and the residual between the unrestricted command and the actual output is calculated. After the saturation is released, the compensation amount is injected according to the exponential decay. The formula is: ； in, is the compensation amount; is the compensation coefficient; is the saturation duration; is the compensation time constant; is the saturated residual.

8. The quadrant switching smooth control method for an electrostatic fluid system according to claim 6, characterized in that ,The preset current distribution strategy of permanent magnet synchronous motor adopts Control strategy: ， ； in, is the d-axis current command; is the reference value of the q-axis motor current command; is the smoothed q-axis motor current command; The formula for calculating the final pump displacement command through pressure feedforward compensation is: ； in, is the final pump displacement instruction; is the smoothed pump displacement instruction; is the total volume of the four-quadrant pump / motor; is the effective bulk modulus of hydraulic oil; is the load pressure; is the sampling time of the MPC controller; is the reference working pressure difference; is the actual working pressure difference.

9. A quadrant switching smooth control device for an electrostatic fluid system, used to implement a quadrant switching smooth control method for an electrostatic fluid system according to any one of claims 1 to 8, characterized in that: include: a data acquisition unit, configured to acquire system status information, front-end operating condition identification information, and vehicle status information collected by sensors, and process the system status information through Clack transform and Park transform; wherein the system status information includes three-phase current signals, mechanical angular velocity and rotor position of the permanent magnet synchronous motor, and inlet pressure, outlet pressure, and current displacement value of the four-quadrant pump / motor; a cost function construction unit for obtaining total required torque and load torque observation values ​​based on the front-end working condition identification information and the vehicle state information, establishing a discretized state space model in combination with the kinematic equations of the permanent magnet synchronous motor and the four-quadrant pump / motor, and establishing a state space recursive prediction model within a prediction time interval and a prediction interval for iterative processing to obtain a quadratic cost function of the control variable using the q-axis current, the mechanical angular velocity, the four-quadrant pump / motor displacement value, and the current working pressure difference as control variables; an iterative solution unit, configured to iteratively solve the quadratic cost function by a sequential quadratic programming algorithm to obtain an optimal solution for the current command and the pump displacement command at the current moment, i.e., an optimal control variable; A filtering and smoothing unit, configured to filter and smooth the optimal control quantity, and generate a smoothed motor current instruction and a pump displacement instruction to the actuator drive layer; a reference current calculation unit, configured to calculate a rectangular axis reference current using a preset current distribution strategy according to the smoothed motor current command, and calculate a final pump displacement command based on the smoothed pump displacement command through pressure feedforward compensation; a reference voltage calculation unit, configured to process the system state information and the orthogonal axis reference current using a current loop PI controller to generate a dq axis reference voltage; The modulation drive unit is used to perform inverse Park transformation on the rotor position of the permanent magnet synchronous motor and the dq-axis reference voltage, generate a PWM signal to drive the permanent magnet synchronous motor through space vector pulse width modulation, and simultaneously output a proportional valve control signal to the hydraulic variable mechanism actuator to achieve smooth control of the electrostatic system during quadrant switching.

10. A quadrant switching smooth control device for an electrostatic hydraulic system, characterized in that: The invention comprises a processor and a memory, wherein the memory stores a computer program, and the computer program can be executed by the processor to implement a quadrant switching smooth control method of an electrostatic hydraulic system as claimed in any one of claims 1 to 8.

Images